Soils and the city: man shaping the Ghent urban landscape, hydrology and soils - excursion

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Excursion Guide

Soils and the city: man shaping the Ghent urban landscape, hydrology and soils Soil Science Society of Belgium national excursion 24th May 2019

Organisers: Nele Delbecque, Frank Gelaude and Ann Verdoodt

ACKNOWLEDGEMENTS Our sincere acknowledgements go to the following staff members of Ghent Municipality that enthusiastically agreed to share their visions, challenges and pending questions and that willingly contributed to contribute to our excursion: Geert Heyneman, urban ecologist Karen De Boeck, urban ecohydrologist Groendienst, Departement Publieke Ruimte, Stad Gent Renaat De Coene, engineer Pieter Van den Dorpe, project coordinator Dienst Wegen, Bruggen & Waterlopen, Departement Stedelijke Ontwikkeling, Stad Gent Marc Pinte, spatial planner Dienst Stedenbouw en ruimtelijke planning, Departement Stedelijke Ontwikkeling, Stad Gent

TABLE OF CONTENTS PROGRAMME ........................................................................................................................... 1 INTRODUCTION ........................................................................................................................ 2 SITE 1: PLAGGIC CAMBISOL AT ‘DE SMET-DE NAEYERPARK’ ....................................... 13 SITE 2: VALUABLE URBAN SOILS AT ‘CITADELPARK’ ...................................................... 18 SITE 3: TERTIARY OUTLIER ‘BLANDIJNBERG’ ................................................................... 21 SITE 4: ‘SINT-PIETERSABDIJ’, URBAN VITICULTURE ....................................................... 23 SITE 5: URBIC TECHNOSOL AT ‘MUINKPARK’ ................................................................... 25 SITE 6: ‘HERTSTRAAT’, GREENING OF RESIDENTIAL NEIGHBOURHOODS ................. 30 SITE 7: SPOLIC TECHNOSOL AT ‘KONING ALBERTPARK’ ............................................... 32 SITE 8: LAURENTPLEIN, BUILDING A DAM AND WEIR ON THE SCHELDT..................... 38 SITE 9: REEP, BISDOMPLEIN................................................................................................ 41 SITE 10: ZANDBERG, NEDERPOLDER-HOOGPOORT ....................................................... 42 REFERENCES ......................................................................................................................... 44 NOTES ..................................................................................................................................... 46

PROGRAMME 9h00: Appointment at Gent-Sint-Pieters railway station 9h20-10h00: Site 1: De Smet de Naeyerpark, Onafhankelijkheidslaan Introduction to geomorphology and hydrology of Ghent area Soil description, analysis and classification of a Stagnic Umbrisol 10h25-11h05: Site 2: Citadelpark, commando bunker Mapping valuable urban soils in Ghent Soil augering of a “very valuable anthropogenic soil” 11h15-11h30: Site 3: Blandijnberg – Kattenberg, Victor Hortastraat Geomorphology and geology of the ‘Blandijnberg’ 11h40-11h50: Site 4: Sint-Pietersabdij, Sint-Pietersplein History of ‘Sint-Pietersabdij’ and ‘Sint-Pietersdorp’ 12h00 -13h00: Lunchbreak with sandwiches and soup at Pietersbar 13h10- 13h30: Site 5: Muinkpark Land use and geomorphology of the ‘Muinkmeersen’ Soil description, analysis and classification of an Urbic Technosol 13h35-13h55: Site 6: Hertstraat Unsealing and greening of residential neighborhoods 14h10-14h50: Site 7: Koning Albertpark Soil description, analysis & classification of a Pretic Anthrosol ‘Harmonisch Parkbeheer’ and vision on soil-related aspects of public urban green management in Ghent 15h05-15h25: Site 8: François Laurentplein Role and control of water in historical Ghent 15h30-16h05: Site 9: Reep – Bisdomplein History of the Scheldt portus Role and control of water in contemporary Ghent 16h15-16h25: Site 10: Zandberg, Nederpolder – Hoogpoort Geomorphology and geology of the Zandberg Transport, agriculture and drinking water supply within the former inner city 16h30: Closing

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INTRODUCTION Geomorphology, geology and hydrology of Ghent Contemporary land- and soilscape The city of Ghent is found at an altitude ranging from about 7m to 24m a.s.l (Belgian national reference for altitude measurements determined during the ‘Tweede Algemene Waterpassing’ or ‘Deuxième Nivellement Général’). The most prominent topographic feature when consulting the Digital Terrain Model (Figure 0.1) is the ‘Blandijnberg’, a large “mountain” (Dutch: berg) which dominated the surrounding landscape of the meandering Lys (Leie) and Scheldt (Schelde) rivers. Another “mountain” called ‘Zandberg’ leans against its north-northeastern slope. Both host the most prominent buildings of the Ghent scenery: the university library (Boekentoren) at the Blandijnberg, and the three towers of Saint Nicholas’ church, the belfry and the Saint Bavo’s cathedral at the Zandberg.

The soil map of Ghent clearly illustrates the lack of survey and analytical data inside the city center, which has been mapped as “anthropogenic” (Figure 0.2, Sys and Vandenhoudt, 1963).

Yet, the soil map does show how Ghent is practically surrounded by marshlands or “watermeadows” (Dutch: meersen), corresponding to Late-Glacial paleo-meanders of the Lys and Scheldt rivers. Imperfectly to poorly drained sand, loamy sand and sandy loam (Lep, Pdp, Sep) soil types are found on the levees and strongly gleyic clayey (Eep and Ufp) soil types dominate the basin deposits. In wet winters, the latter depressions are flooded. The de Ferraris (1778) map provides one of the best views on these impressive water meadows west (BourgoyenOssemeersen, Blaarmeersen, Assels), north (Wondelgemmeersen, current harbour area), and east (Gentbrugse meersen, Damvallei, Heirnis and current cloverleaf R4-E17) of Ghent.

While both Lys and Scheldt rivers have a similar discharge, the Lys meanders slowly within her rather wide, alluvial valley, while the Scheldt river valley is much narrower. Thus, two very different rivers meet in Ghent. The confluence of two rivers Lys and Scheldt, the water meadows, and hills have largely determined the structure of the city. The town of Ghent thus originated in the flat river landscape of the Flemish Valley, near the confluence of the rivers Lys and Scheldt ànd close to a Tertiary outlier, the Blandijnberg.

However, in the currently built-up environment, much (more) of the original topography and hydrography, has been obscured – not only by tall buildings – but also by raising grounds, dumping meanders and digging new canals.

The panoramic view of the city, made by an anonymous painter around 1543 (Figure 0.3), portrays several small hills, often occupied by windmills, as well as water meadows inside the current city center. Many current street names, some being about 800 years old, refer to “mountains”. By consequence, the original geomorphology of the city was more complex than described above.

We guide you along some of these diverse geomorphological features and illustrate how Ghent converted from a river landscape into the socio-natural city environment we experience today.

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Figure 0.1. Topographic map (5 m resolution) of the Ghent area (source: DHMV2, Informatie Vlaanderen). Numbered dots indicate the approximate location of our excursion stops: (1) De Smet-De Naeyerpark, (2) Citadelpark, (3) Kattenberg, (4) Sint-Pietersabdij, (5) Muinkpark, (6) Herstraat, (7) Koning Albertpark, (8) Laurentplein, (9) Reep, and (10) Zandberg

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Figure 0.2. Soil map (scale 1:20000) in the Ghent area (source: Databank Ondergrond Vlaanderen, Digital Soil Map of Flanders, map sheets 22-1 Gent and 22-2 Melle) showing the unsurveyed built-up zone superimposed on a pedoscape dominated by sandy to loamy sandy soils (blue colours) and sandy loam soils (yellowish colours). Note the patches of wet and moist, clayey soils in former river meanders of the Lys (Bourgoyen-Ossemeersen, Blaarmeersen and Assels) west of Ghent, the Scheldt (Gentbrugse meersen) south and east of Ghent, and the Kale Durme (Wondelgemse meersen) north of Ghent. Numbered dots indicate the approximate location of our excursion stops: (1) De Smet-De Naeyerpark, (2) Citadelpark, (3) Kattenberg, (4) Sint-Pietersabdij, (5) Muinkpark, (6) Herstraat, (7) Koning Albertpark, (8) Laurentplein, (9) Reep, and (10) Zandberg

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Figure 0.3. Panoramic view on Ghent, anonymous, year 1534 (STAM – Ghent City Museum) – Ghent seen from the east - northeast

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Geological and geomorphological genesis of the Ghent area During the early periods of the Cenozoic (previously referred to as Tertiary), the Ghent area was flooded by the sea, albeit being close to the shoreline. Relatively limited sea level fluctuations of few meters up to about ten meter, resulted in significant differences in sedimentation with alternating series of clayey (deep water) and sandy (shallow water) marine sediments (Figure 0.4).

Figure 0.4. Tertiary lithostratigraphy (1:50,000) of the Ghent area (source: Databank Ondergrond Vlaanderen). Numbered dots indicate the approximate location of our excursion stops: (1) De Smet-De Naeyerpark, (2) Citadelpark, (3) Kattenberg, (4) Sint-Pietersabdij, (5) Muinkpark, (6) Herstraat, (7) Koning Albertpark, (8) Laurentplein, (9) Reep, and (10) Zandberg

The river landscape developed in the Pleistocene epoch of the Quaternary period, which was characterized by alternation of glacials and interglacials. Upon a drastic lowering of the sea level (glacial), thick layers of the marine Cenozoic sediments were eroded and the Flemish valley developed (Figure 0.5). As the sea retreated in northern direction, a number of rivers cut deeply into the tertiary marine sediments. The center of the Flemish valley was found just north of Gent, 6

while its southern extensions approximately corresponded to the current valleys of the Lys and Upper-Scheldt. The remnant Cenozoic sediments of this valley became covered with quaternary fluvio-periglacial sedimentary materials of variable composition, deposited by rain or meltwater in cold, wet periods (Figure 0.6).

Figure 0.5. Geomorphological map of the microrelief in the surroundings of Ghent, showing the presence of cover sand ridges (n° 5, 6, 7 & 8) and shifting (land) dunes (n° 11) and river dunes (n° 12) within the fluvioperiglacial plain, intersected by the river flood zones (winter time) (source: Denis, 1992 after De Moor & Heyse, 1989, adapted by Antrop, 2016).

During the Late-Weichselian at the end of the Pleistocene, a very cold but dry period with very little vegetation, wind erosion further modified the river landscape. Formation of a large cover sand ridge named Maldegem and Stekene (with a west – east orientation) blocked the flowing down of Lys and Scheldt, turning their direction to the east, to Antwerp. The finest soil particles were blown (far) away and sand surfaces covered the landscape, constituting cover sands (dekzanden) that filled the Flemish Valley. Such aeolian deposits accumulated to cover sand ridges, perpendicular to the dominant north to northwestern winds. They consist of well sorted, fine to moderately fine sands. They typically cover a grind layer, the deflation surface. Shifting sands on these cover sand surfaces locally resulted in the formation of land dunes. While also within the dried sandy riverbeds, drifting sand could accumulate to form river dunes.

The alternation of glacials and interglacials in the Pleistocene had also affected the character of the river networks, giving rise to braided rivers affecting large areas during the glacials, and meandering rivers during the interglacials.

Finally, the permafrost disappeared and meandering rivers cut into the Weichselian sediments.

The Holocene valleys however got filled with alluvial sediments following the rise of the sea level, groundwater table and change in climate.

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Figure 0.6. Quaternary geological map of Ghent (scale 1:50,000, source: Databank Ondergrond Vlaanderen, Quartairgeologische kaart - Kaartblad 22 Gent, by S. Vermeire, J. Roder, S. Sammier i.s.m. G. De Moor (Haecon nv.), 1999)

Reconstructing the urban landscape, hydrography, geology and soilscape The unique location of Ghent in the Flemish Valley implies that these diverse geomorphological features – the prominent tertiary outlier, the slightly elevated cover sands, and the low-lying water meadows, are and/or were also found within its territory.

Multidisciplinary data sources (old maps, paintings, accounts, toponyms, augerings, geological maps), yet of variable age and reliability, can be integrated into spatially continuous representations of this partly visible, partly hidden urban environment. Reconstructions of the original “natural” urban landscape, hydrography, geology and soilscape however remains a challenge. Figure 0.7 shows the location of the cover sands and marshlands in and around Ghent (Gelaude, 2018).

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Figure 0.7. Cover sands (yellow) and water meadows (green) and Tertiary outlier ‘Blandijnberg (orange) in and around Ghent (map by F. Gelaude)

Urban soil sampling and analysis campaign in Ghent Fifteen undisturbed soil cores were collected within the city of Ghent in the frame of a doctoral research. Sampling locations were selected by random stratified sampling based on land use and time since urbanization, using a GIS (Figure 0.8, Table 0.1). Three different land uses were considered: parks, residential zones and the aggregated land use class ‘institutional / commercial / industrial’. In addition, three city quarters were selected as proxy for time since development: ‘Wondelgem’ was developed only after 1969. ‘Station South’ was mainly urbanized in the beginning of the 20th century. Lastly, ‘Inner City’ was urbanized prior to 1884.

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Figure 0.8. A) Location of Ghent in Belgium; B) Sampling locations in three city quarters (Wondelgem, Station South and Inner City) of Ghent.

Undisturbed soil cores were collected using a soil column cylinder auger (diam. 10 cm, 100 cm) mounted on gasoline driven mechanical hammer (Figure 0.9). Where possible, profiles were sampled up to a minimal depth of 125 cm (in two runs, namely 0-100 cm, 100-125 cm). The soil columns were transferred to plastic liners for transport and stored in the freezer (-20°C). Next, the frozen cores were split using a benchtop mounted diamond saw blade. Cutting planes were carefully cleaned by removing a fine layer of material, and air-dried. One soil core half was used for scanning, whereas the other soil core half was used for soil description and physico-chemical characterization.

Detailed profile descriptions were carried out on the undisturbed soil cores according to the Guidelines for Soil Description (FAO, 2006).

Soil cores were analyzed on horizon basis for a range of physical and chemical properties. Organic debris was removed and samples were hand-sieved to separate the coarse (> 2mm) from the fine (≤ 2 mm) fraction. pH was measured in 1 mol·l-1 KCl (1:5 soil:extract) using a combined glass electrode (ISO 10523:2008). Electrical conductivity was measured in a 1:5 soil:water ratio (Van Ranst et al., 1999). Soil particle size distribution (clay: 0-2 µm, loam: 2-50 µm, sand: 50-2000 µm) was determined using the Robinson-Köhn pipette method after removal of organic carbon and 10

carbonates. Total carbon (TC) and total inorganic carbon (TIC) was analyzed by catalytic oxidation and infrared spectrometry after acid digestion (H 3PO4), respectively, using the SSM-5000A Shimadzu. Total organic carbon (TOC) equaled the difference between the measured TC and TIC concentrations. For some samples, significant amounts of technic organic carbon (OCtech) from soots, ashes or coal were expected. For these samples, OCtech was calculated by TC – TIC – OChum, the latter being humus content estimated after carbon analysis with (to destroy the humus) and without application of water peroxide (H2O2).

Table 0.1: Site characteristics for soil profiles collected in the quarters Wondelgem (C1-C5), Station South (C6-C10) and Inner City (C11-C15). Profile E1 has been collected at an archeological excavation at the former ‘Wintercircus’, located in Inner City.

Profile no.

C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 E1

Land use Park Industrial Industrial Residential Residential Institutional Park Residential Residential Institutional Park Residential Residential Park Park Commercial

Land cover Grass Grass Grass Grass Grass Grass Grass Wood chips Grass Grass Grass Gravel Grass Grass Grass Concrete

Adress Park Buffer R4 Pantserschipstraat Industrieweg Langeveld Marcastraat Schoonmeersen Park de Smet de Naeyer Achilles Musschestraat Flamingostraat Campus De Sterre Park Baudelohof Onderstraat Willem Tellstraat Koning Albertpark Muinkpark Sint-Pietersnieuwstraat

Coordinates 51.096°N; 3.704°E 51.094°N; 3.724°E 51.092°N; 3.690°E 51.091°N, 3.699°E 51.085°N; 3.709°E 51.033°N; 3.703°E 51.033°N; 3.713°E 51.033°N; 3.720°E 51.031°N; 3.707°E 51.025°N; 3.709°E 51.059°N; 3.728°E 51.056°N; 3.724°E 51.047°N; 3.722°E 51.045°N; 3.731°E 51.042°N; 3.731°E 51.048°N; 3.728°E

Figure 0.9. A) Sampling using soil column cylinder auger mounted on a mechanical hammer; B) Undisturbed soil core after sampling.

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In addition, undisturbed soil cores were scanned using the Multi-Sensor Core Logger (Geotek Ltd.) to provide high-resolution photographs, and determine magnetic susceptibility and gamma density. The collected soil profiles strongly differ in morphological and soil physico-chemical characteristics (Figure 0.10). During the excursion, we will shed light on some of these collected soil profiles to uncover the diversity of urban soils in the city of Ghent.

Figure 0.10. Overview of soil profiles collected in the quarters Wondelgem (C1-C5), Station South (C6-C10) and Inner City (C11-C15). Profile E1 has been collected at an archeological excavation at the former ‘Wintercircus’, located in Inner City. Information on site characteristics is provided in Table 0.1.

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SITE

1:

PLAGGIC CAMBISOL NAEYERPARK’

AT

‘DE

SMET-DE

Aim At this first excursion site, we will:  Introduce you to (see Introduction): • the general geomorphology and hydrology of Ghent, • some challenges and approaches to inventorying natural resources in an urban context, • our urban soil sampling and analysis strategy, • Discuss the features of a Plaggic Cambisol developed in sandy fluvio-periglacial quaternary deposits, and • Present the future unsealing project of the ‘de Smet de Naeyerpark’.

General information Location

Elevation Profile description authors Approach

De Smet de Naeyerpark Nearby address: Onafhankelijkheidslaan 18, 9000 Gent Coordinates : 51° 01’ 58.38’’ N, 3° 42’ 54.34’’ (WGS1984) 104155 m X; 191628 m Y (Lambert72) 9.6 m a.s.l.(Digitaal Hoogtemodel Vlaanderen II, 1m resolution, altitudinal reference: TAW/DNG) Nele Delbecque, Stefaan Dondeyne 10 cm diameter soil column cylinder auger mounted on gasoline driven mechanical hammer

Soil formation factors Geomorphology and geology Located in the gently undulating mesorelief south of Ghent, the site is found about 3 to 4 meters higher than the surrounding Lys and Scheldt valleys (about 7 m a.s.l.) and water-meadows (about 6 m a.s.l.). Microrelief consisting of a depressional center surrounded by raised borders reflects the park landscaping design. According to the Quaternary geological map, map sheet n° 22 Ghent (1:50 000; Figure 0.6), the parent material consists of colluvium overlying Weichselian fluvioperiglacial sediments.

Land use and vegetation The site is covered by grass of the contemporary lawn of the ‘de Smet de Naeyerpark’. This park is located south of the historical city center, in the quarter previously known as ‘Sint-Pieters-Aalst’.

It belonged to the outer walls domain of Saint Peters’ Village until 1795 (see Site 4). Although the quarter had a rural character until deep in the 20th century, the neighborhood around the park drastically transformed with the organization of the World Fair of 1913 and the associated building of the ‘Gent-Sint-Pieters’ Railway Station (Stad Gent, 2018). The fair, taking place from April to November 1913 covered an impressive area of 115 ha. Figure 1.1 shows the main entrance to the fair, corresponding to the contemporary location of the de Smet de Naeyerpark. In 1926, the grounds were parceled out for the construction of the bourgeoisie neighborhood known as

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‘Miljoenenkwartier’ (EN: quarter of millions) (Stad Gent, 2018a). The allotment plan dating from 1926 (Figure 1.2) features the park largely as we still know it today.

Figure 1.1. Main entrance of World Fair in 1913, now part of de Smet de Naeyerpark at Kortrijksesteenweg (SAG)

Figure 1.2. Allotment plan of the earl ‘de Smet de Naeyer’ quarter in 1926 (SAG)

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Soil description, analysis and classification Figure 1.3 and Table 1.1 provide the soil description and analytical data, respectively. The soil profile (Figure 1.3) classifies as a Orthoeutric Plaggic Cambisol (Pantoarenic, Densic, Humic) (IUSS Working Group WRB, 2015).

Table 1.1. Physico-chemical properties by horizon of the soil profile at ‘de Smet de Naeyerpark’. (EC = electrical conductivity; SOC = soil organic carbon; IC = inorganic carbon; CF = coarse fraction (> 2mm).

Hor. Ahp Ap E/B E1 Bt E2 2Btd

Depth (cm) 0-11 11-34 34-55 55-70 70-73 73-80 80-105

pH-KCl EC (-) (µS·cm-1) 3.9 114.6 3.9 43.3 4.2 34.7 4.7 36.8 4.4 39.9 4.4 31.4 4.9 40.0

SOC (%) 3.0 0.8 0.1 0.0 0.0 0.0 0.0

IC (%) 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Sand (%) 84.4 80.6 87.2 90.5 84.6 88.5 89.4

Silt (%) 10.0 14.7 8.7 5.6 8.1 7.4 3.2

Clay (%) 5.6 4.7 4.1 3.9 7.3 4.1 7.3

CF (%) 1.3 3.7 0.3 0.0 0.0 0.0 0.0

Soil texture ranges from loamy sand to sand (Pantoarenic). The surface horizon consists of a 34cm thick ploughed horizon (Ap) enriched in organic matter. As we cannot reconstruct all past human interventions, it remains uncertain to which extent the Ap horizon results from park layout or still witnesses to the use as agricultural land prior to development. The Ap horizon qualifies as an umbric horizon, having likely a low base saturation as indicated by its very low pH-KCl (3.9).

The artefact content (gravel, charcoal and brick fragments) is very low and limited to the Ap horizon. Beyond 34 cm, the profile lacks clear evidence of human disturbance. The E/B horizon is likely the result of bioturbation. At 55 cm, a weakly developed soil with alternating eluvial and a thin illuvial horizons is found in the fluvio-periglacial parent material. The E1, Bt and E2 horizons consist of well-sorted sand, likely of aeolian origin. They overly a 2Btd horizon with slightly higher clay content and stratification, possibly reflecting its fluviatile origin. Distinct mottling prevails from 34 cm onwards (oxido-reduction features indicating stagnic conditions) and likely results from limited permeability of the dense, layered 2Btd horizon. Manganese concentrations are found from 34 cm onwards, but mainly in 2Btd.

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Figure 1.3. Morphological description of profile at ‘de Smet de Naeyerpark’.

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Unsealing to restore soil-mediated ecosystem services The ‘de Smet de Naeyerpark’ constitutes a green oasis of about 3.60 ha, but is cut into three parts separated by parking lots.

Soil sealing – the covering of soil with (near) impervious materials (concrete, asphalt) – strongly affects the delivery of soil-mediated ecosystem services. The high thermal admittance of the pavement materials contributes to the urban heat island effect. Another major issue is its impact on urban water regulation. Especially during extreme rainfall events, significant amounts of rainfall running off the impervious surfaces can overload drainage/sewage systems. Pollutants originating from the urban traffic and other activities tend to concentrate in the runoff and reduce water quality when discharged into watercourses, requiring costly treatment. Runoff also implies a loss of water to our underground water systems.

Climate and water sensitive urban designs promote the development of blue and green infrastructure at the expense of sealed surfaces within the inner city center. As such, with the financial support of the Flemish government, about 1500 m² of sealed surface (parking zones 1 and 2, Figure 1.4) will be removed in the near future (Stad Gent, 2019) creating one single park having the shape of … a glass of Champaign.

Figure 1.4. Unsealing project (zones 1 and 2) connecting the three parts of the ‘De Smet de Naeyerpark’ (start indicating the profile site location)

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SITE 2: VALUABLE URBAN SOILS AT ‘CITADELPARK’ Aim At this excursion site, we will:  Touch upon mapping valuable soils in Ghent  Discover characteristics of a “very valuable” urban soil in Citadelpark by augering

General site information Location

Elevation

Citadelpark Nearby address: Koning Leopold II-laan 45, 9000 Gent Coordinates : 51° 02’ 23.28’’ N, 3° 43’ 11.28’’ (WGS1984) 104485 m X; 192377 m Y (Lambert72) 29.1 m a.s.l.(Digitaal Hoogtemodel Vlaanderen II, 1m resolution, altitudinal reference: TAW/DNG)

Soil formation factors Geomorphology and geology The ‘Citadelpark’ is located in the middle of the watershed divide of the rivers Lys and Scheldt.

Within the park, the altitude varies from 14 to 29 m, because of its strongly varied landscape design. According to the Quaternary geological map, map sheet n° 22 Ghent (Figure 0.6), the parent material consists of colluvium. The intensive anthropogenic impact (wee land use and vegetation) potentially exposed Tertiary sediments, more specifically the Lede (1 m thickness) and Aalter Formation (3 m thickness).

The virtual augering app (https://virtueleboring.dov.vlaanderen.be/virtueleboring/model/g3dv2) yields: 

Lede Formation: marine unit consisting of calcareous and glauconiferous, fine sand. Some layers of sandy limestone or calcareous sandstone occur (normally three). A pebble layer with reworked elements (fossil and rock fragments) from older deposits forms the base. The stone layers are frequently associated with coarse sediment layers (with the coarse base too).

Nummulites variolarius is abundantly present (Mourlon, 1873, Fobe, 1988).



Aalter Formation: marine unit consisting of a grey green, glauconiferous, clayey sand with fine sandy clay layers and many thin sandstone layers. It is followed upwards by grey, fine sand, being very fossiliferous at the top. The whole is covered by brown green to dark green glauconiferous, very fine, locally silty sand, with many fossil fragments (Dewalque, 1868).

Land use and vegetation This most vulnerable south flank of the Blandijnberg (see site 3) offered good sight onto the surrounding landscape, and proved ideal for building military fortifications of the city. On the 1543 panoramic view, the two former gates Heuvelpoort and Kortrijksepoort are recognized. In the 17 th century, the Fort de Monterey was built. It was destroyed one century later. The current park owns its name to the citadel. Built under the Dutch rule, between 1819 and 1831, the citadel was intended to protect the region of Ghent against the French (Figure 2.1).

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The brick fortress was partly hidden from its enemies by a glacis, an earthen bank, and was covered with soil to protect it from bombing. With the Belgian independence in 1830, the citadel partly lost its utility and was used as infantry and artillery casern of the Belgian army until 1870.

Figure 2.1. Plan of the citadel superimposed on the current street map (Capiteyn, 2007)

Starting from 1875, most of the citadel was demolished and the site was redeveloped as municipal park. It was designed in English style, as a landscape garden using the original hilly character and some of the former constructions. The resulting hilly part of the park along the Leopold-II-laan and Normaalschoolstraat dates back from this period (1880) and houses one of the few remnants of the old citadel (casemates) in the underground. In 1938, a commando bunker of the anti-aircraft defense was added to the site.

Soil development at Citadel Park We choose to auger the soil on top of the constructed hill, below the oldest plane trees. This soil is expected to be at least 100 years old and “constructed” using material from the surroundings in order to cover/protect the citadel in the subsoil.

Valuable urban soils Justification Within the city, pressure on the subsurface is large. Nevertheless, some soils have an intrinsic or archive value and can be considered cultural heritage or patrimony. Regardless of their performance for specific land uses, they represent scientific or societal value as they inform about the anthropogenic or natural history. The Green Infrastructure Management Service (‘Groendienst’) of Ghent municipality aims at developing a strategy – inspired on the project “Valuable soils in Flanders” (Ampe et al., 2006) - that allows identifying, mapping and protecting the valuable soils found within the city. The ultimate goal is to develop a reference to be consulted by planners, decision makers and contractors when designing and executing spatial development plans or environmental impact assessments. In case valuable soils are found within the project area, further research to ensure maximum protection is recommended.

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Approach The approach aims at classifying the soils into three categories: 

Very valuable soils, meeting the criteria set for valuable soils (Ampe et al., 2006) of distinctiveness, rarity, exceptional age and/or integrity. If the soil is very valuable, its protection from sealing or destruction will be advised. This includes natural soils of river valleys (e.g. levees), unique cover sand zones (e.g. heathland soils), “old” forest or grassland soils, and special historico-cultural (e.g. plaggen) or anthropogenic soils (e.g. parks) with an undisturbed genesis of about 100 years.



Valuable soils, specific to the Ghent case are natural soils on cover sands as well as anthropogenic soils featuring at least 30 years of undisturbed development and/or found in (castle) parks



Less valuable soils, being sealed, raised, grubbed, and/or levelled

Additional criteria related to the contribution of soils to water cycling and water quality will be envisaged.

This implies that three maps are key to their identification: the biological valuation map (Dutch: biologische waarderingskaart), the physical landscape valuation map (Dutch: fysische landschapskaart, UGent, 1995), and the soil map. The latter two maps essentially focus on the urban periphery, while the biological valuation map includes urban municipal parks. Within the non-surveyed inner city, extra observations are needed (Custers et al., 2019).

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SITE 3: TERTIARY OUTLIER ‘BLANDIJNBERG’ Aim At this excursion site we’ll:  Study the geomorphology and geology of the Kattenberg and Blandijnberg  Discuss human interest in this characteristic feature

Geomorphology and geology The ‘Blandijnberg’ is an elongated, flattened hill, its longitudinal axis having a NNE-SSW orientation. We reach the Blandijnberg from the smoothly sloping south. In contrast, the east and west facing slopes, respectively leading towards the borders of the Scheldt and Lys, are steeply sloping. The north-facing hill slope merges with the cover sand ridge of the Zandberg (sand mountain, excursion stop 10), and has been modified by the digging of the Ketelvaart canal.

With an elevation of 29.12 m at its highest point, the hill rises about 20 to 23 m above the alluvial plane of the Lys and Scheldt. It must have been a prominent feature in the otherwise rather flat landscape of the Flemish Valley. At times of flooding, the hill was completely surrounded by water.

The Blandinium hill is an outlier, testifying of a former erosion surface. The predecessors of the current Lys and Scheldt thus must have been eroding and transporting massive amounts of sediments towards the sea. Only the site of the Blandijnberg escaped this very intense river action.

The Cenozoic substrate of Ghent found below the Blandijnberg as well as below the more recent fluvial deposits of the Lys and Scheldt covering the rest of Ghent (Figure 0.4 and 3.1, Table 3.1) consists of the greyish green glauconite-containing fine sands of Vlierzele (Formation of Gentbrugge). Greyish green, very fine sands of the formation of Aalter, containing glauconite and mica, carbonates, clay, and rich in fossils, cover these deposits up to an altitude of 18 m. A fossilrich “base grind“ separates these sediments from the formation of Lede. The latter is found between 18 and 25.5 m and is characterized by pale yellow, carbonate-rich, glauconite-containing, fine sands and sandstone banks. The formation of Maldegem, with its two sections “Lid van Asse” and “Lid van Ursel” constitutes the upper sediments. A dark green almost black layer dominated by glauconite, and covered by greenish gray clay, which is also rich in glauconite, characterizes the Lid van Asse. This clay-rich layer protects the hill from erosion. A 1 m thick layer of greyishblue clay characterizes the lid van Ursel. The formation of Maldegem is found only in the neighborhood of the Kattenberg and the Rozier, where the university library is located. The marine sediments date from the Eocene and are 51 to 39 million years old (Gelaude, 2018).

At some places on the flat hilltop, deposits that are more recent have been conserved. At these places, the Cenozoic sediments are covered by a “base grind” of rounded gravel (27 m), possibly indicating the presence of a terrace of the Scheldt river, and covered by mid-Pleistocene sediments.

Exploitation and use Since the 15th century, but possibly earlier, the clay at the Blandijnberg was exploited by both potters for pottery and by fullers to scour wool (scouring action of smectite).

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Figure 3.1. Geological profile of the ‘Blandijnberg’, indicating the various tertiary sediments (Dumont 1951 in Gelaude 2018).

Table 3.1. Lithostratigraphy of the ‘Blandijnberg’ (Gelaude, 2018)

Abbreviations on current geological map old geological map & fig. 3.1 MaUr, MaAs A Ld Le AaOe P2 GeVl P1 GePi GeMe Tt Yd

Name of the formation F. of Maldegem, L. of Asse-Ursel F. of Lede F. of Aalter, L. of Oedelem F. of Gentbrugge, L. of Vlierzele F. of Gentbrugge, L. of Pittem F. of Gentbrugge, L. of Merelbeke F. of Tielt

Despite the fact that the hill is not a prominent feature anymore in the urban landscape, it is still taking an important place in the city life. The hill hosts three water towers, located at the Kattenberg, providing the Ghent citizens of drinking water. The two, bricked water towers (18801882) are the oldest of Flanders. The circular massive brick walls (1.5 – 2.5 m thickness) carry a large cast iron tub, which is coated with a wooden wall (Deseyn and Linters). Architect Dirk Bontinck (1977) built the new water tower at Kattenberg in Gent. With the UGent library – the book tower – the Blandijnberg has become a university outlier as well.

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SITE 4: ‘SINT-PIETERSABDIJ’, URBAN VITICULTURE Aim At this excursion site, we will:  touch upon the history of Sint-Pietersabdij and Sint-Pietersdorp  situate the early settlement nuclei in the natural landscape of Ghent

History of Sint-Pietersabdij The Sint-Pietersabdij (English: abbey of Saint Peter), founded in the 7th century, stands as one of the early settlement nuclei of Ghent and is situated on the southeast flank of the outlier ‘Blandinium’ at the river bank of the Scheldt. The Sint-Baafsabdij (English: abbey of Saint Bavo), also founded in the 7th century, was established at the west end of a cover sand ridge, situated in the east of Ghent (Figure 4.1).

Figure 4.1. Site of Ghent in the year 1000 with indication of early settlement nuclei and geomorphological features (cover sand ridges (yellow); Tertiary outlier ‘Blandinus hill’ (orange); marshes (Dutch: meersen; green); water (blue) (Gelaude, 2018).

Similar to the Sint-Baafsabdij, the Sint-Pietersabdij was raised on behalf of Amandus in his effort to Christianize the region. At first relatively poor, the abbey grew into one of the richest of the 23

County of Flanders by the 10th century. By the 15th century, the abbey territory, referred to as SintPietersdorp (English: Sint-Pieters village), equaled 2.5 ha and included farms, storehouses, gardens, houses as well as farmland, all surrounded by a fence wall (Figure 4.2 and 4.3). Across its borders, the abbey exploited large domains and even entire villages as agricultural and pasture land (Historische Huizen Gent, 2018a).

Figure 4.2. Sint-Pietersdorp in 1534 as depicted on ‘Panoramisch Gezicht van Gent’ (STAM).

Figure 4.3. Sint-Pietersdorp in 17th century (Sanderus, Flandria Illustrata, 1641 uit Capiteyn A. et al. 2007)

Much of Sint-Pietersdorp did not stand the test of time. For example, the former church was destroyed during the iconoclasm (Dutch: Beeldenstorm) in 1566 and 1578. The destroyed church was replaced by the current baroque church, which was built in the 17-18th century only (Inventaris Onroerend Erfgoed, 2018a).

Urban viticulture A small vineyard is found on the eastern slope of the Blandijnberg, in the garden of SintPietersabdij. The first records of a vineyard at the abbey date back from the 9th century. In 1983, a vineyard was re-established. The vineyard hosts four grape varieties (Muller Thurgau, Joahnitter, Phoenix and Sirius) and disease management is restricted to agents allowed in organic viticulture (f.e sulphur and copper derivates) (Historische Huizen Gent, 2018b).

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SITE 5: URBIC TECHNOSOL AT ‘MUINKPARK’ Aim At this excursion site, we will:  Introduce the geomorphology and history of the former ‘Muinkmeersen’  Touch upon ‘cultural layers’ in urban environments  Discuss the features of an ‘old’ Urbic Technosol developed in human-transported and humanmade material

General information Location

Elevation Profile description authors Approach

Muinkpark Nearby address: Hertstraat 62, 9000 Gent Coordinates : 51° 02’ 31.92’’ N, 3° 43’ 49.80’’ (WGS1984) 105236 m X; 192637 m Y (Lambert72) 7.2 m a.s.l.(Digitaal Hoogtemodel Vlaanderen II, 1m resolution, altitudinal reference: TAW/DNG) Nele Delbecque, Stefaan Dondeyne 10 cm diameter soil column cylinder auger mounted on gasoline driven mechanical hammer

Soil formation factors Geomorphology and geology The Muinkpark is located in the former Muinkmeersen (marshes of the monks), which refers to the lower area of marshes and meadows besides the Sint-Pietersabdij, in the floodplain of the river Scheldt (Figure 0.1). Holocene alluvium covers the Pleistocene fluvio-periglacial sediments (Figure 0.6).

Land use and vegetation In the 12th century a watermill, known as the Clapschiete, was built on a straightened canal, the Muinkscheldt. The watermill was property of Sint-Pietersabdij. The navigation used the old branch of the Scheldt: the Old Scheldt. In 1297, the city constructed a big watermill a few hundred meters downstream, which announced the end of the watermill of the abbey. From that moment onwards, the Muinkscheldt could be used as channel for ships. The Old Scheldt river remained to cross the Muinkmeersen for centuries. Due to annual flooding, the Muinkmeersen remained unurbanized until the 19th century and were used as pasture and meadows to feed livestock. In addition, the proximity of water made it the ideal location for the bleaching of textile, as nicely illustrated by the painting of Wynantz (19th century; Figure 5.1) (Gelaude, 2018).

In 1837, Ghent welcomed the first train (line Ghent-Mechelen), which entered the city through the - until then - unexploited Muinkmeersen. The first large train station ‘Ghent South’, was built in what is now the ‘Koning Albertpark’, also known as ‘Zuidpark’. In 1851, following the success of the zoo of Antwerp, a part of the Muinkmeersen became home of the ‘Gentse Diergaerde’ or ‘Den Biestehof’, which hosted a collection of exotic animals (Fig. 5). Unfortunately, the zoo was bankrupted in 1904 and was bought and parceled out by the city of Ghent. The current ‘Muinkpark’ (1,3 ha) is the only remain of the once 5.5 ha large zoo (Stad Gent, 2016a; Muinkparkwijk, 2018a, 2018b).

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Figure 5.1. View on the ‘Muinkmeersen’ (in front) and the Sint-Pietersabdij (in the back) (Wynantz 18201823, SAG)

Figure 5.2. Litho by Van Loo, F. on the 5.5 ha large zoo ‘Gentse Diergaerde’, end 19th century

The Muinkmeersen is an illustrative example of human impact on the landscape, soils and hydrology in Ghent. Surrounded by wetlands, the development and expansion of Ghent implied that the natural hydrographic system had to be altered. Human interventions included the straightening of rivers, construction of weirs, bridges and dikes and reinforcing of riverbanks (Gelaude, 2010). Other solutions included the elevation of lower areas with anthropogenic fill. Note that the presence of these ‘cultural layers’ is not isolated to locations with (former) lower elevation, as cities were often built on their own ‘garbage’. Consequently, these so-called anthropogenic fills tend to have high contents of artefacts like construction debris or household waste. In Moscow (Russia) for example, cultural layers of up to 20 m depth have been reported (Alexandrovskaya and Alexandrovskaykiy, 2000; Alexandrovskaya and Panova 2003).

Also in Ghent, evidence of anthropogenic fill is plentiful. The ‘Grondmechanische Kaart Gent’ (1:5 000) (De Beer et al., 1976) maps the geological and ground-mechanical state of the subsurface and provides an indication of the thickness of by human-transported material (Figure 5.3).

According to the map, the former Muinkmeersen were raised with 0-2 m of anthropogenic fill.

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Figure 5.3. Thickness of raised and reworked ground with which the former relief was elevated / levelled as given by De Beer et al. (1976). The Muinkpark is indicated by a red dash line.

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Figure 5.4. View on the raised Muinkmeersen (SAG)

Soil description, analysis and classification The descriptive and lab analytical data for the soil profile collected in Muinkpark are given in Figure 5.5 and Table 5.1, respectively. The soil classifies (IUSS Working Group WRB, 2015) as Urbic Technosol (Calcaric, Humic, Mollic, Loamic, Pantotransportic). The soil profile entirely consists of human-transported and artifactic material (Pantotransportic). Especially horizons dUA2-1 and dUA2-2 have abundant artefacts, which mainly consist of construction debris (bricks, plaster) (Urbic qualifier). Yet, this anthropogenic soil profile shows evidence of pedogenesis: the upper horizons (Ahu1, Ahu2, Ahu3) show well-developed soil structure with high amounts of humified organic matter, which together qualify as mollic horizon.

Apart from the upper horizon Ahu1 (pH-KCl = 6.0), the entire soil profile shows an alkaline soil reaction (pH-KCl ≥ 7.2). The presence of carbonates was indeed quantified through a HCl (10%) test, indicating that the soil matrix is moderately to strongly calcareous. Nonetheless, analytical results generally indicate low amounts of inorganic carbon, as most of the carbonate containing artefacts is pertained as coarse fraction (>2mm).

The entire profile has a high total organic carbon content (TOC). Although a significant part of the TOC corresponds to technic carbon (ashes, hard coal), the profile is likely Humic (>1% of OC hum in upper 50 cm). Note that whereas Technosols tend to be perceived as infertile, this soil profile resembles a fertile soil with a mollic horizon with sufficient nutrients, and having a high organic matter content throughout, thereby functioning as a carbon sink.

Table 5.1. Physico-chemical properties by horizon of the soil profile at ‘Muinkpark’. (EC = electrical conductivity; TOC = total organic carbon; OChum = soil organic carbon; OCtech = technic organic carbon; TIC = total inorganic carbon; CF = coarse fraction (> 2mm). Prefix ‘^’ in horizon name refers to dumped material, their codes can be looked up in Guidelines for Soil Description (FAO, 2006).

Horizon ^Ah ^Auh1 ^Auh2 ^Cuk ^Cu1 ^Cu2 ^Cu3 ^Cu4

Depth (cm) 0-10 10-18 18-23 23-50 50-65 65-80 80-95 95-120

pH-KCl EC (-) (µS·cm-1) 6.0 317 7.3 140 7.2 128 7.2 141 7.2 168 7.4 182 7.4 146 7.4 148

TOC (%) 6.9 3.6 4.1 1.2 1.4 1.1 2.0 1.1

OChum (%) 5.1 1.3 2.3 1.0 1.1 1.1 1.3 1.0

OCtech (%) 1.8 2.3 1.7 0.2 0.3 0.0 0.6 0.1

TIC (%) 0.0 0.1 0.1 0.1 0.2 0.9 0.8 0.4

Sand (%) 80.7 81.1 61.8 38.5 67.3 63.3 60.4 72.3

Silt (%) 6.4 9.8 22.6 32.4 15.5 28.7 33.4 23.5

Clay (%) 12.9 9.1 15.6 29.1 17.2 8.0 6.2 4.2

CF (%) 7 24 14 10 74 51 41 23

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Figure 5.5. Morphological description of soil profile at ‘Muinkpark’.

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SITE 6: ‘HERTSTRAAT’, GREENING OF RESIDENTIAL NEIGHBOURHOODS Aim At this excursion site, we will:  present the urban greening project of Hertstraat  discuss benefits of and challenges to urban green projects

Site history The area of the urban greening project of Hertstraat and surroundings includes streets with names referring to the former zoo (e.g. Zebrastraat, Alpacastraat, Hertstraat, …). The neighborhood partly consists of the so-called ‘beluiken’ (inner courts), dead end streets with many, small houses without private gardens, as a reponse to the urgent need for housing in the 19th century.

Urban greening project By 2050, cities will be home to more than 70% of the world’s population. Increasing urbanisation poses many challenges to human well-being and the environment, in the form of climate change; air quality; water availability and quality; land use; and waste management. At the same time, cities are key to address global environmental challenges, as choices made in cities today about long-lived urban infrastructure shape the city of tomorrow (OECD and Bloomberg Philantropies, 2014).

Urban green plays a key role in the shift towards low-carbon, climate-resilient urban infrastructure (OECD and Bloomberg Philantropies, 2014). Not only does it contribute to carbon sequestration (in soil and vegetation), it also offers co-benefits to the wellbeing of citizens, e.g. through tempering of the urban heat island effect. In Ghent, the city administration (Dienst Wegen, Bruggen en Waterlopen, Departement Stedelijke Ontwikkeling) has recently commissioned the greening of residential neighborhoods in the Hertstraat and surroundings. The project area covers six streets (Hertstraat, Buffelstraat, Alpacastraat, Keviestraat, Takkebosstraat. Langhalsstraat; see Figure 6.1). The plans are designed with the aim to increase quality of life of its inhabitants, with space for urban green and social activities. To reduce traffic pressure, the project area will be designated as ‘woonerf’, with a speed limit of 20 km/h and priority for pedestrians. The Keviestraat, Takkebosstraat and Langhalsstraat will be transformed into car-free streets, where entrance is exceptionally allowed to cars with an access permit. The implantation of urban green includes large façade gardens, trees as well as green infiltration strips and wadi’s to maximize water infiltration (Figure 6.2).

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Figure 6.1. Urban greening project area covering Hertstraat, Buffelstraat, Alpacastraat, Takkebosstraat, Keviestraat and Langhalsstraat.

Figure 6.2. Impression of the future neighbourhood of Hertstraat and surroundings (Stad Gent, 2018b).

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SITE 7: SPOLIC ALBERTPARK’

TECHNOSOL

AT

‘KONING

Aim At this site, we will:  Discuss the features of a ‘young’ Spolic Technosol developed in human-transported and human-made material  Introduce you to magnetic susceptibility as an indicator of human disturbance.  Discuss soil-related opportunities and challenges of public urban green design and management

General information Location

Elevation Profile description authors Approach

Koning Albertpark Nearby address: Franklin Rooseveltlaan, 9000 Gent Coordinates : 51° 02’ 43.08’’ N, 3° 43’ 55.56’’ (WGS1984) 105352 m X; 192986 m Y (Lambert72) 8.0 m a.s.l.(Digitaal Hoogtemodel Vlaanderen II, 1m resolution, altitudinal reference: TAW/DNG) Nele Delbecque, Stefaan Dondeyne 10 cm diameter soil column cylinder auger mounted on gasoline driven mechanical hammer

Soil formation factors Geomorphology and lithology Similar to the previous stop (Muinkpark), Koning Albertpark is located in the middle of the former Muinkmeersen, in the annual flooded floodplain of the Muinkscheldt and the Old Scheldt rivers.

Similar to Muinkpark, the soil develops in human-transported and human-made materials.

Land use and vegetation Until the 19th century, the area was unurbanized and used as pastureland and meadows to feed livestock, as well as for bleaching of textile. The park hosted the South Railway Station, Ghent’s first large train station built in 1837. It was a terminal station. After the occupation of station GentSint-Pieters, the South Station was broken down in 1928 and converted to park area in the 1930s.

The last relicts of the Old Scheldt were filled up or overarched. The park has been redeveloped in 2006 and a drainage system has been installed to overcome water stagnation problems.

Soil description, analysis and classification Soil profile description, laboratory and proximal analytical data are presented in Figure 7.1 and Table 7.2, respectively. The soil classifies (IUSS Working Group WRB, 2015) as Spolic Technosol (Drainic, Humic, Loamic, Technic, Pantotransportic).

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Figure 7.1. Morphological description of profile at park ‘King Albert

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Texture ranges from loamy sand to sandy loam (Loamic). Artefacts are common (Technic) and apart from construction rubble, comprise coal, ashes and slag, bearing witness to the former railway station. Remarkably, the soil profile has several dark horizons with visible remnants of coal and slag. Total organic carbon content is very high throughout the soil profile (4.6-23.7%), and mainly results from the addition of technic organic carbon (coal, ashes – industrial waste materials, hence spolic), rather than soil organic carbon.

In strong contrast with the nearby site of Muinkpark, topsoil formation is limited to the upper 5 cm.

The site has been redeveloped some 10 years ago, which can explain limited evidence of pedogenesis. Also note the presence of mussel shells which have been dumped as human waste, and do not easily weather in this highly alkaline soil.

Table 7.1: Physico-chemical properties by horizon of the soil profile at ‘Koning Albertpark’ (EC = electrical conductivity; TOC = total organic carbon; OChum = soil organic carbon; OCtech = technic organic carbon; TIC = inorganic carbon; CF = coarse fraction (> 2mm)).

Horizon ^Ahuh ^Ahu 2^Cu1 2^Cu2 2^Cu3 2^Cu4 2^Cu5 2^Cu6 3^Cu7 3^Cu8 3^Cu9

Depth (cm) 0-5 5-14 14-26 26-53 53-57 57-63 63-75 75-95 95-107 107-120 120->140

pH-KCl EC (-) (µS·cm-1) 6.6 534 7.4 247 7.4 139 7.4 286 7.0 675 7.3 380 6.6 376 7.2 280 7.3 170 7.3 258 7.3 158

TOC (%) 11.2 9.5 9.0 4.8 20.7 4.6 5.3 5.9 17.2 7.1 23.7

OChum (%) 8.4 2.3 2.1 1.6 2.4 1.7 3.2 1.9 3.8 2.7 5.7

OCtech (%) 2.8 7.2 6.9 3.1 18.3 2.9 2.0 4.0 13.4 4.4 18.0

TIC (%) 0.1 0.1 0.3 0.3 0.0 0.5 0.0 0.1 0.0 0.1 0.1

Sand (%) 74.0 79.7 74.6 71.5 78.1 74.4 55.5 47.3 74.4 70.9 74.5

Silt (%) 16.3 13.4 22.3 19.0 14.7 17.3 29.3 38.1 21.2 20.3 18.5

Clay (%) 9.7 6.9 2.8 9.5 7.3 8.3 15.2 14.6 4.4 8.8 7.0

CF (%) 20 39 29 10 20 18 1 4 7 23 30

Total elemental concentrations of heavy metals (among others) were determined by proximal sensing using a bench-top mode operated portable X-ray fluorescence analyser (Oxford XMET8000 Expert with a Rh X-ray tube (4W, max. 50kV, max. 200 μA) and integrated large area silicon drift detector (165 eV)). Figure 7.2 compares the observed depth profile in Koning Albertpark with those of four other urban soils.

Magnetic susceptibility as an indicator of human disturbance Besides conventional lab analysis, proximal sensing techniques can provide useful soil information in a time-efficient, non-destructive way. Magnetic susceptibility is a measure of the degree of magnetization of soil material upon applying an external magnetic field. The magnetic signal originates from the presence of magnetic materials in the soil, which can be both of natural or anthropogenic origin. For example, under natural conditions, dehydration and subsequent oxidation of ferrihydrite in the soil leads to the formation of magnetite, a highly magnetic mineral.

As this process requires the presence of organic material, magnetite is especially found in the humus-rich upper horizons. Magnetic particles can also migrate and accumulate at lower depth, for example through illuviation of iron oxides in the B horizon. Certain parent materials, like igneous rocks, have high contents of magnetic minerals, whereas the magnetic signal of sedimentary deposits is limited. The main source of magnetic materials remains however anthropogenic. Ironcontaining particles are oxidized to magnetic particles by burning of fossil fuels and can as such be an indicator of the degree of human disturbance (based on Declercq, 2016).

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Figure 7.2. Portable XRF measured concentrations of heavy metals with increasing depth in the soil profiles at Park de Smet de Naeyer, Muinkpark, Koning Albertpark and Willem Tellstraat

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In the light of the doctoral research of Nele Delbecque, magnetic susceptibility (MS) was measured by means of an MS2E sensor mounted on the Geotek MultiSensor Core Logger, providing 1dimensional, continuous MS measurements of the entire soil profile, at a resolution of 2mm. MS profiles for four contrasting soil cores are presented in Figure 7.2. The first three soil profiles originate from sites visited during this excursion, namely Park de Smet de Naeyer (Site 1), Muinkpark (Site 5) and Koning Albertpark (Site 7). The last profile was collected in a residential garden in Willem Tellstraat, located in the historical city center.

MS of the soil profile in Park De Smet de Naeyer is generally low, but highest for the Ap horizon (Figure 7.3), where the natural MS is likely elevated through human activities. Contrastingly, MS in the C horizons is close to 0, indicating that human disturbance is limited. The peak in MS at around 30cm depth originates from the presence of a coal fragment.

For the soil profile in Muinkpark, MS is high throughout as a result of anthropogenic input of magnetic materials. Also note the higher magnetic susceptibility for horizon dUA2-1 (50-65 cm) that contains many bricks. During the process of brick making (baking at high temperatures and subsequent cooling), clay particles align according to the earth magnetic field, explaining their magnetic signal.

Whereas the soil profile at Muinkpark mainly constitutes of construction rubble, the soil profile of Koning Albertpark has a high proportion of coal, slag and ashes, resulting in higher MS values with peaks exceeding 1000 SI¡10 -5. On average, MS is highest for the greyish-blackish horizons (Munsell chroma = 1).

Lastly, the soil profile collected at Willem Tellstraat shows high MS values in the upper horizons, but drops to near-zero values below 92 cm depth. Below 92 cm, an artefact-free horizon is found.

Seen the low MS values for this horizon, we hypothesize that it concerns the original (nondisturbed?) parent material of the Formation of Lede (calcareous and glauconiferous, fine sand, Nummulites variolarius is abundantly present (Mourlon, 1873, Fobe, 1988).

Figure 7.3: Magnetic susceptibility measured by MS2E mounted on Geotek MSCL on undisturbed soil core collected at (A) Park de Smet de Naeyer; (B) Muinkpark; (C) Koning Albertpark and (D) Willem Tellstraat

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Opportunities and challenges of soil management in public urban green For the layout of new public green, preference goes to working with the in situ soil rather than bringing in new soil material, even if the in situ soil is of lower quality. If soil comprises many coarse materials, experience is that planting of new vegetation is not successful. Yet, sieving to remove the coarse fragments inevitably leads to loss of soil structure and is therefore avoided where possible. The experience is that even shallow soils with many coarse fragments can evolve to healthy green vegetation and eventually to forests by means of spontaneous soil formation and natural succession of vegetation. Such forest vegetation constitutes the climax vegetation and has the largest climate buffering potential.

Where necessary, the process of soil formation and revegetation can be accelerated by a single application of organic material (e.g. compost), which benefits soil aggregate formation and increases the water storage capacity. The application of organic material is especially used in case of more demanding green, like playing fields or soils holding many coarse fragments. For example, a layer of hay and compost was applied onto a compacted rubble-containing soil in the Gentbrugse Meersen to facilitate the tree planting and growth.

Where soil reconstruction is needed, it is important that soils resemble where possible natural soil profiles, and have a climate robust design. This is nicely illustrated by the Arbedpark (Figure 7.4).

Here, a park was lain out on a former industrial site with a reclaimed, sealed subsoil. Soil reconstruction involved the use of different soil textures (1) for profile reconstruction; and (2) to intend spatial variation in vegetation. A sandy substrate was put on top of a clayey base layer.

Well-vegetated hills on permeable sandy textures are intertwined with wadis, and a marsh with shrubs on sand and a recycled peat layer (Heyneman, personal communication).

Figure 7.4: Views on Arbedpark (left) and flower garden at railway station Gent-Sint-Pieters (right), both laid out on ‘reconstructed’ soil

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SITE 8: LAURENTPLEIN, BUILDING A DAM AND WEIR ON THE SCHELDT Aim At this excursion site, we will:  Discuss how human interventions altered the natural hydrographic system, e.g. by dams, weirs, canalizations and damping of watercourses.  Highlight the importance of water (drinking water, transport, industry) in the historical city of Ghent

Historical river management Controlling the hydrographic system End 13th century, circa 1270, citizens of Ghent constructed a dam (Brabant dam), a weir (Braamgaten) and a watermill (Stadswatermolen) to block the water of the Scheldt river (Figures 8.1, 8.2 and 8.3), forcing the water to flow to the Lys via the canal ‘Ketelvaart’. As a result, the water level upstream rose with more than 3 feet (almost 1 m).

These major interventions were intended to benefit the navigation of goods, but came with an additional advantage: the city was able to control the river for several purposes. It was used for military inundations of the water meadows to protect the city, for navigation, to drive the watermill, for flushing dirty water, and as ‘clean’ water for households. Note that until the 19th century, Ghent did not have a sewer system and counted few public draw-wells. All the water was provided by both rivers Lys and Scheldt. In order to drain dirty water, all weirs of the city were opened two days a week. In the evening, the weirs were closed again, providing citizens with fresh water (Gelaude, 2018).

Industrial revolution and declining water quality During the Middle Ages, the Scheldt and Lys river still formed an extensive network of river branches that meandered through the landscape (De Clercq, 2005). With the advent of the Industrial Revolution, the cities’ view drastically changed. At the end of the 19th century, large textile factories and metal construction plants were raised in and outside the historical center, transforming Ghent in an industrial city (Boussauw, 2014). In absence of adequate environmental legislation, waste (water) from industry and households was simply dumped into the rivers. Given their strong economic importance, citizens were merely convicted to live in the midst of these open ditches, with frequent outburst of cholera that killed thousands of people (Devrieze, 2013a; Devrieze, 2013b).

Overaching and filling of waterways Subsequent sanitation projects often went hand in hand with the replacement of neglected neighborhoods by stately homes and broad lanes and the damping or overarching of many waterways (Figure 8.3) (De Clercq, 2005). The same fate was suffered by Nederscheldt. The weir and mill at the Brabantpoort were broken down in 1884, when the Nederscheldt (or Reep) was overarched over a distance of 142 m to lay out the Francois Laurent square (Figure 8.4) (Hespel, 1972; Devriese, 2013a).

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Figure 8.1: Braampoort as depicted on Panoramisch Gezicht op Gent (1534), STAM Ghent City Museum.

Figure 8.2: Braamgaten and watermill (left) in 1584 on painting by Lieven van der Schelden (STAM); and (right) on painting of Wijnantz (1820-1823) (SAG)

Figure 8.3: Comparison of hydrography of Ghent in 1530 and 1926 (SAG, 1926)

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Figure 8.4: Overarching of Nederscheldt (or Reep) around 1884, nowadays corresponding to Laurentplein (Beeldbank, SAG)

During the 1960’s, the search for extra car parking spaces led to a new episode of overarching or filling up several waterways. The remaining part of the Nederschelde between the Reep and the Bisdomkaai was not overarched, but the waterway was filled with tons of sand from the digging of the Ringvaart (Figure 8.5) (Devriese, 2013b), a canal outside the city that connected the most important waterways surrounding Ghent. This allowed ships to travel around instead of through the city, eradicating the economic importance of the waterways located in the city center.

Figure 8.5: (left) Parking space on top of the damped Reep (Beeldbank Gent; s.d.; a), and (right) Filling up the Reep with sand from the Ringvaart (Beeldbank Gent, s.d.; b).

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SITE 9: REEP, BISDOMPLEIN Aim At this excursion site, we will:  Illustrate how water is re-introduced in contemporary Ghent, using the Reep as case study.

Re-appreciation of the Ghent blue infrastructure Opening of some overached or filled waterways From the 60s and 70s, heavy industry moved to the port area in the North of the city. Nonetheless, water quality remained unsatisfying in the 70s, 80s and 90s of last century. Only in the 90s, investments in better sewer and water purification systems significantly improved the water quality of Ghent’s waterways. Moreover, attempts were launched to reduce car traffic and parking lots in the city, adopting the ‘Mobiliteitsplan met P(arkeer)-route (1997) and the recent circulation plan (2016).

Soon, plans to re-open the filled waterways were made and water regained its right of existence in the city. The ‘Ajuinlei’ was reopened in 1999 (Gelaude, 2018). Only in the end of 2018, the Reep was finally reopened, making it possible to navigate again around the city center (Gelaude, 2018).

Towards a climate-smart Ghent These actions fit within the climate adaptation plan (2016 – 2019) of Ghent. In order to make Ghent climate change resilient, the city aims to:      

Avoid any further soil sealing Greening of the city Promote development of the green-blue infrastructure Create space for water Maximise the water buffering capacity of the city Provide (blue-green) infrastructure that has a cooling effect

Space-efficient, heat- and water-robust design and development of not only the public but also the private domain will be promoted (Stad Gent, 2016b).

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SITE 10: ZANDBERG, NEDERPOLDER-HOOGPOORT Aim At this excursion site, we will:  Visit the quaternary cover sand ridge – river dune  View the central axis that connected the portus of the Scheldt river to the portus of the Lys

Geomorphology and geology The Zandberg (English: ‘Sandy hill’) is part of the Quaternary cover sand ridge (or river dune) extending from the Kouter to the Kalandeberg, to the Zandberg, where it reaches its highest point (13.84 TAW), to the Hoogpoort (Figure 10.1). It forms the watershed divide between the Scheldt and Lys rivers. Its toponym refers to its textural composition as well as its use for sand excavation (Gelaude, 2010). Many sand excavations, mainly from medieval origin, have indeed been identified on the flanks of the Zandberg (Laleman and Vermeiren, 2010).

Figure 10.1. Map showing the rather parabolic dune comprising the Zandberg, the Hoogpoort-Nederpolder axis connecting the portus of the Lys with the Scheldt, as well as the confluence of Lys and Scheldt (based on Open Street Map and Digital Elevation Model Flanders II)

Origin of the city The Zandberg is historically important as, most likely during the 7 th century, an agrarian settlement was established which operated independently from the abbeys of Saint Peter and Saint Bavo.

The city thus originated on the bank of the Scheldt near the confluence of the Scheldt and Lys rivers. In the 9th century, the settlement had become the oldest ‘portus’ or medieval trade center of Ghent, known as ‘Gandavum’ (Inventaris Onroerend Erfgoed, 2018). The relatively steep riverbank made it the ideal location for the loading and unloading of ships. The sand ridge itself provided enough space for houses and other infrastructure, safe from flooding. Lastly, also the proximity of fertile soils (Kouter) contributed to the suitability of this location. Nowadays, the name ‘Zandberg’ corresponds to a small square, located on the northeast flank towards the Scheldt river (Laleman and Vermeiren, 2010).

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The portus held important access roads that still exist today. The Nederpolder and Hoogpoort formed the central axis of the settlement and connected the portus of the Scheldt with that of the Lys. Urban archeologists have inventoried more than 200 stone houses from the 12 th and 13nd century, which are referred to as ‘Stenen’ (English: Stones), many of which are located along the axis Nederpolder-Hoogpoort (Figure 3.2; Laleman & Raveschot, 1999). In the Hoogpoort, almost every stone house had a private deep well (Gelaude, 2018).

Figure 10.2: (left) Map indicating the location of ‘Stenen’ (highlighted in dark grey) in the center of Ghent (SAG) and (right) Example of a ‘Steen’: the Korenstapelhuis at Graslei (Belgiumview).

The oldest settlers were mainly engaged in livestock and agriculture (f.e. Veldstraat, Nederkouter, Korenmarkt). The ‘kouters’ with fine sandy to sandy loam soils were fertile soils for agriculture, whereas marshes were used for grazing of cattle. Many street names in the historical city center still resemble agrarian relicts: Veldstraat (English: field street), Kouter, Ganzendries (English: village green or the common of the goose), Koestraat (English: cow street), Lange Meer (English: long marsh), Korte Meer (English: short marsh) (Gelaude, 2018).

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