Journal Journalof ofCoastal CoastalResearch Research
pg -- pg 1385 1389
ICS2011 ICS2011 (Proceedings)
ISSN 0749-0208 0749-0208
Natural and anthropogenic impacts on a macrotidal sandy beach of the Brazilian Amazon (Ajuruteua, Pará): guidelines for coastal management S. M. O. de Oliveira†, L. C. C. Pereira†*, A. Vila-Concejo‡, A. Gorayeb∞, R. C. de Sousa†, P. W. M. Souza-Filho§ and R. M. da Costa† †Instituto de Estudos Costeiros, Universidade Federal do Pará, Bragança, 68600-000, Brazil *Email: firstname.lastname@example.org
‡School of Geosciences, The University of Sydney, Sydney, 2006, Australia Email: email@example.com
∞Departamento de Geografia, Universidade Federal do Ceará, Fortaleza, 60833-500, Brazil Email: firstname.lastname@example.org
§Centro de Geociências, Universidade Federal do Pará, Belém, 66075-110, Brazil Email: email@example.com
ABSTRACT Oliveira, S.M.O. de, Pereira, L.C.C., Vila-Concejo, A., Gorayeb, A., Sousa. R.C. de, Souza-Filho, P.W.M. and Costa, R.M. da, 2011. Natural and anthropogenic impacts on a macrotidal sandy beach of the Brazilian Amazon (Ajuruteua): guidelines for coastal management. Journal of Coastal Research, SI 64 (Proceedings of the 11th International Coastal Symposium), 1385 – 1389. Szczecin, Poland, ISBN ISSN 0749-0208 The Amazon coast presents a diversified landscape, varying from established urban areas with high rates of population growth to vast, well-preserved natural systems with low population density. In the Brazilian state of Pará, both human activities and natural impacts affect coastal resources and the local economy, which is based on tourism and fishing. The aim of the present study was to evaluate the influence of these two processes on the characteristics of a macrotidal beach (Ajuruteua) in northeastern Pará and provide local authorities with guidelines for the implementation of effective coastal management programs. Social and natural variables were assessed between April 2008, and September 2009. The Ajuruteua waterfront is characterized by the presence of precarious wooden structures built on mangroves, dunes and the intertidal zone, with limited infrastructure. Unregulated urban expansion, associated with natural conditions, is the main factor responsible for the erosive processes observed in the northwestern sector of the beach. River discharge and circulation processes are the main factors responsible for the high levels of water turbidity and dissolved nutrients observed in the study. Bacterial contamination is caused by the discharge of untreated domestic sewage, although the rapid turnover of the water in this high-energy environment dissipates the pollution rapidly. Priorities for local environment planning should include: (i) the prohibition of new buildings in risk areas; (ii) the improvement of recreational facilities and the provision of adequate services (public sanitation system and water supply); and (iii) the establishment of a permanent and appropriate water quality monitoring program. ADDITIONAL INDEX WORDS: Sewage, Erosion processes, Unregulated occupation, Amazon beach.
INTRODUCTION The growing demographic pressures on the natural environment constitute one of the challenges of the twenty-first century. Coastal zones are especially vulnerable, due to the combined pressures of activities such as industries, shipping, fisheries, agriculture, and tourism. This scenario requires the development of effective management plans that not only protect impacted areas, but also uphold their productivity and guarantee standards of public health in local communities (Belfiore, 2003; Lau, 2005; Lozano et al., 2005; Pereira et al., 2007a). The 480 km of coastline that stretches between the mouth of the Amazon, in the Brazilian state of Pará, and São Marcos Bay in Maranhão is characterized by an irregular outline with many islands, bays and estuaries, and one of the World’s largest continuous tracts of mangrove forest. This region presents considerable contrasts between intensively developed sites with high rates of population growth, and vast areas with low population density and well-preserved ecosystems (Szlafsztein and Sterr, 2007). In the Brazilian state of Pará, both human activities and natural impacts affect coastal resources and the local economy, which is based on tourism and fishing. These problems are
accentuated due to the lack of interest on the part of local authorities with regard to the development or implementation of management programs for the protection of the coastline and its infrastructure from natural or anthropogenic impacts. This study was developed at Ajuruteua, a macrotidal beach within the Amazon coastal zone in northern Brazil, and the third most popular among tourists in the state of Pará. The local residents depend on traditional fisheries and tourism. Previous studies have identified a number of social and environmental problems related primarily to the unregulated occupation of the area and the lack of interest on the part of local authorities with regard to providing infrastructure and services (Souza-Filho et al., 2003; Krause and Glaser, 2003; Pereira et al., 2006, 2007b). The present study aimed to evaluate the impacts of natural events and human activities, and provide the local government bodies with effective guidelines for the implementation of coastal management programs.
STUDY AREA The study area was Ajuruteua Beach (Figure 1) located in the northeastern corner of the Brazilian state of Pará, around 36
Journal of Coastal Research, Special Issue 64, 2011 1385
Natural and anthropogenic impacts on a macrotidal sandy beach
km from the town of Bragança. It is 2.5 km long, and forms an arc along NW-SE direction presenting two different sectors: Northwestern (erosion sector) and Southeastern (accretion sector). Ajuruteua is a macrotidal dissipative sandy beach which is 200 to 300 m wide during low spring tides (Alves and El-Robrini, 2006; Monteiro et al., 2009). It is bordered by the Atlantic Ocean, the Chavascal and Barca channels, dunes, cheniers, sandy ridges and mangrove vegetation (Souza-Filho et al., 2006).
were collected every 3 hours for measuring hydrological variables dissolved oxygen, pH, turbidity, dissolved nutrients, chlorophyll-a and thermotolerant coliforms) using Niskin oceanographic bottles. In the laboratory, the turbidity was determined by a turbidity meter and the pH by a pH meter. Dissolved oxygen concentrations were measured according to the Winkler method (see Strickland and Parsons, 1968), and nutrients according to Strickland and Parsons (1972) and Grasshoff et al. (1983). Chlorophyll-a content and thermotolerant coliform abundance were determined by the methods of Strickland and Parsons (1972) and APHA (2005), respectively.
RESULTS AND DISCUSSION NW
ct se or SE sec tor
Ca et é
es tu ar y
Figure 1. Geographic location of Ajuruteua beach in northern Brazil. Local tides are semidiurnal and asymmetric, maximum tidal elevations between5.0 and 5.5 m occur during the equinoctial spring tides March and September. Circulation patterns are dominated by tidal currents, which flow to the northwest during the ebb tide and to the southeast during the flood tide (Monteiro et al., 2009; Cavalcante et al., 2010). The climate is equatorial humid with a mean annual temperature of around 27°C and precipitation of 2,500 mm, which is concentrated in the period between January and June (wet season) (Martorano et al., 1993; INMET, 2009). The waterfront is occupied by numerous wooden buildings, with about 300 permanent inhabitants. Ajuruteua is one of the state’s most popular beaches, receiving more than 90,000 visitors each July (Pereira et al., 2007b).
METHODS A series of social and natural variables were evaluated between April 2008, and September 2009. All buildings and other installations on the beach were identified and counted. Data on wind speeds and precipitation were obtained from the National Meteorological Institute. Ten campaigns of over 25 hours each were conducted during periods of spring tide. A mini-current meter, CTD, and wave and tide data loggers were bottom mounted and deployed at a depth of 1.7 m in the subtidal zone; average data were recorded every 10 minutes. Samples of sub-surface water
The precipitation pattern recorded during the study period was typical of the region with annual precipitation over 2,500 mm, when 85% of which fell during the wet season. The strongest winds, mainly from the northeast, were recorded during the dry season (maximal speeds up to 6.7 m/s), while moderate winds from the northeast and southeast were common during the wet season (maximal speeds up to 4.0 m/s). At low latitudes, coastal processes are controlled by natural phenomena distinct from those observed in temperate and polar areas. In this region of the Amazon, the low latitude and climatic conditions, such as high solar radiation and precipitation rates, associated with presence of a large fluvial system (including the Amazon and dozens of other estuaries) are together responsible for a unique set of hydrodynamic and hydrological conditions e.g. Coriolis acceleration is weak, coastal circulation is affected by factors such as river discharge and semi-diurnal macrotidal conditions, etc. (Marengo et al. 1995; Beardsley et al., 1995; Nittrouer and DeMaster, 1986; Geyer et al., 1996). In the studied area, the maximal recorded range was 5.5 m during equinoctial spring tides. The local coastal circulation is dominated by tidal currents that run to the northwest at speeds of up to 0.5 m/s, and to the southeast at up to 0.6 m/s. The tidal currents at Ajuruteua are strongly influenced by the discharge of the Caeté estuary, which runs mainly to the southeast during the flood tide and to the northeast during the ebb tide. Similar results are registered by Monteiro et al. (2009); Pereira et al. (2009) and Cavalcante et al. (2010). The local tides are asymmetric, with longer ebb tide periods (6.5 to 7.5 h) and with higher current speeds being recorded during the shorter flood tide. The Amazon Coast presents normally a strong tidal asymmetry pattern as a consequence of the great breadth and shallow depth of its shelf, as well as its sand banks, mangrove systems, creeks and estuaries (Mazda et al., 1995; Lam-Hoia et al., 2006). In Ajuruteua, the presence of sandbanks and bars around Caeté Bay is also one of the factors responsible for the asymmetry of local tides (Pereira et al., 2009; Monteiro et al., 2009; Cavalcante et al., 2010). Significant wave heights can exceed 1.0 m at high tide and spilling waves break on two or more bars situated in the intertidal zone, some distance from the maximum spring tide level. But tidal currents are stronger than wave generated currents and thus equinoctial spring tide events (October, 2008 and March, 2009) caused the periods of highest hydrodynamic energy. Wave energy was modulated by the low tide due to wave attenuation on sand banks; this coincides with results by Monteiro et al. (2009). The beach presented erosive characteristics in its northwest sector and depositional features in the southeast sector. Previous studies made by Pereira et al. (2007b) showed that the northwest sector was eroding at a rate of almost 4.0 m3/m/year of fine
Journal of Coastal Research, Special Issue 64, 2011 1386
Oliveira et al.
sediment (fine and very fine sand). The opposite pattern was found in the southeast sector. This sector had accreting characteristics with a bar system, frontal vegetated dunes; it also has better territorial occupation in terms of planning when compared with the nothwest sector. Wind and precipitation, and equinoctial spring tide events associated with the shape of the beach, local currents, and unregulated building in the dune zone, are the main factors responsible for these erosive and depositional processes (Souza-Filho et al., 2006; Monteiro et al., 2009).
Hydrological Features Marked seasonal patterns were also observed in the hydrological and microbiological variables. The lowest salinity (as low as 5.8 psu), temperature (27.5°C), and pH (6.94) were all recorded in the wet season, as were the highest turbidity (up to 305 NTU), and concentrations of dissolved oxygen (> 8.0 mg/l), dissolved nutrients (nitrite: 3.31 µmol/l; nitrate: 11.70 µmol/l; phosphate: 3.00 µmol/l; silicate: 343.05 µmol/l), and chlorophyll-a (39.35 mg/m³). Conversely, the highest salinity (up to 36.7 psu), temperatures (30.8°C), and pH (up to 8.99) were recorded in the dry season, as well as the lowest turbidity (as low as 10 NUT), and concentrations of (up to 6.6 mg/l) dissolved nutrients (nitrite: 0.064 µmol/l; nitrate: 0.02 µmol/l; phosphate: 0.119 µmol/l; silicate: 12.88 µmol/l), and chlorophyll-a (1.06 mg/m³). Thermotolerant coliforms were recorded in both seasons. In general, Amazon coastal waters are eutrophic, alkaline, turbid, well-oxygenated and highly productive (Sousa et al., 2008; Silva et al., 2009; Santos et al., 2008; Costa et al., 2009; Guimarães et al., 2009; Magalhães et al., 2009; Monteiro et al., 2009 and Pereira et al., 2010). Climatic conditions on this coast, associated with the presence of large fluvial and mangrove systems, and its unique hydrodynamic conditions, are the main factors responsible for the seasonal fluctuations in hydrological variables (Meade et al., 1985; Figueroa and Nobre, 1990; Marengo et al., 1995; Geyer et al., 1996). The present study indicated that some aspects of the quality of the water e.g. turbidity, pH, dissolved oxygen and nitrate at Ajuruteua beach were inadequate according to the National Council for the Environment (CONAMA) criteria for coastal waters that require absent visually for turbidity, and up to 6.0 mg/l for dissolved oxygen, 8.5 for pH, and 0.4 mg/l for nitrate. The sum of the evidence indicates that these standards should be re-evaluated carefully before they can be applied reliably to the evaluation of the water quality at Amazon beaches. The lack of a public sanitation system at Ajuruteua, combined with the discharge of domestic sewage directly onto the beach and the presence of cesspits in the intertidal zone are the primary factors determining the inadequate bacteriological quality of the local water. Contamination was nevertheless mitigated by the high tide current speeds that contribute to the efficient renovation of the local marine waters. Similar conditions were recorded by Silva et al. (2009) at other urban beaches on the Amazon littoral. According to CONAMA standards (Resolution nº 357 of 2005), the water was inappropriate for use (more than 20% of samples with over 1,000 fecal coliforms per 100 ml) during only 10% of the study period. These conditions were recorded in some samples during equinoctial spring tides, when the water level reached the cesspits in the intertidal zone, and in the vacation period, when the number of beachgoers was at its peak.
Social Variables Bragança has a prominent role in the tourism industry of Pará, not only for the natural beauty of its beaches and other landscapes, but also its cultural and historical heritage. While the
town, and in particular Ajuruteua, receive thousands of tourists each year, the beach has limited services and infrastructure. These conditions, together with the relative isolation of the region and the prolonged wet season, combine to limit the potential for the development of the tourist industry. The difference in the number of visitors between the vacation period (Figure 2A) and low season (Figure 2B), when the beach is frequented only by local residents or sporadic tourists (Pereira et al., 2006), is quite striking. The waterfront of Ajuruteua beach is composed of a number of precarious wooden structures (109 houses, 30 guesthouses and 6 bars) built on mangroves, dunes and the intertidal zone (Figure 2B, 2D and 2E). There are only 13 street lights for the whole area, and there is no public water supply or sanitation system, public telephones or garbage collection, and only intermittent street cleaning. Police and lifeguards patrol the beach only in July. During this month, the increase in the discharge of sewage and the disposal of solid waste directly onto the beach has a negative effect on the quality of the water. Toilets are only available in the bars, and are restricted to customers. Vehicles are driven onto the beach and parked in the intertidal zone (Figure 2C), mainly during the peak season. This has caused traffic jams and accidents, as well as the degradation of dunes (Pereira et al., 2007b). Some of the buildings and infrastructure, primarily in the northwestern sector, have been partially or completely destroyed by erosive processes. This process occurred during the equinoctial spring tides in March and September, which provoked the loss of lamp posts, bars, restaurants and hotels (Krause and Glaser, 2003 and Pereira et al., 2007b).
FINAL CONSIDERATIONS River discharge and circulation processes are the main factors responsible for the high levels of water turbidity, chlorophyll-a, and dissolved oxygen and nutrients recorded during the present study. While the water was often inadequate for public use according to CONAMA criteria, revised criteria may be needed for the reliable evaluation of Amazon coastal beaches. Bacterial contamination is caused by the discharge of untreated domestic sewage directly onto the beach, although the rapid turnover of the water in this high-energy hydrodynamic system limits the level of contamination; large equinoctial tides have the additional problem of reaching more ceespits and other contamination sources thus bringing more contaminants into the surf zone. The development of an effective coastal management plan for this region is of the utmost importance. Priorities for local planning should include: (i) the prohibition of new building in risk areas (intertidal zone, dunes and mangroves); (ii) the improvement of recreational facilities (restaurants, hotels, sports areas) and provision of adequate infrastructure (public sanitation system and water supply, parking areas), and (iii) the establishment of a permanent and appropriate water quality monitoring program.
LITERATURE CITED Alves, M.M.S. and El-Robrini, M., 2006. Morphodynamics of a Macrotidal Beach: Ajuruteua. Bragança North Brazil. Journal of Coastal Research, SI39, 949-951. APHA (American Public Health Association); AWWA (American Water Works Association), and WEF (Water Environment Federation), 2005. Standard methods for the examination of water and wastewater. Virginia: Water Environment Federation, 1368p. Beardslay, R.C.; Candela, J.; Limeburner, R.; Geyer, W.R.; Lentz, S.J.; Castro, B.M.; Cacchione, D., and Carneiro, N., 1995. The
Journal of Coastal Research, Special Issue 64, 2011 1387
Natural and anthropogenic impacts on a macrotidal sandy beach
Figure 2. General conditions recorded in Ajuruteua beach. M2 tide on the Amazon shelf. Journal of Geophysical Research, 100 (C2), 2283-2319. Belfiore, S., 2003. The growth of integrated coastal management and the role of indicators in integrated coastal management: introduction to the special issue (Editorial). Ocean and Coastal Management, 46, 225-234. Cavalcante, G. H.; Kjerfve, B.; Knoppers, B., and Feary, D. A. 2010. Coastal currents adjacent to the Caeté Estuary, Pará
Region, North Brazil. Estuarine, Coastal and Shelf Science, 88(1), 84-90. CONAMA (Conselho Nacional do Meio Ambiente), 2005. Resolução nº. 357, de 17 de março de 2005. Disponível em: <http://mma.gov.br>. Acesso em: março de 2005. Costa, R.M. da; Leite, N.R., and Pereira, L.C.C., 2009. Mesozooplankton of the Curuçá Estuary (Amazon Coast, Brazil). Journal of Coastal Research, SI56, 400-404.
Journal of Coastal Research, Special Issue 64, 2011 1388
Oliveira et al.
Figueroa, S.N. and Nobre, C.A., 1990. Precipitations distribution over Central and Western Tropical South América. Climanálise – Boletim de Monitoramento e Análise Climática, 5(6), 36-45. Geyer, W.R.; Beardsley, R.C.; Lentz, S.J.; Candela, J.; Limeburner, R.; Johns, W.E.; Castro, B.M., and Soares, I.D., 1996. Physical oceanography of the Amazon shelf. Continental Shelf Research, 16, 575-616. Grasshoff, K.; Emrhardt, M., and Kremling, K., 1983. Methods of Seawater Analysis. New York: Verlag Chemie, 419p. Guimarães, D. de O.; Pereira, L.C.C.; Monteiro, M.C.; Gorayeb, A., and Costa, R.M., 2009. Effects of the influence on the Cereja River and Caeté Estuary (Amazon littoral, Brazil). Journal of Coastal Research, SI56, 1219-1223. INMET (Instituto Nacional de Meteorologia), 2009. Estação Automática de Bragança. Disponível em <WWW. inmet.gov.br/sonabra>. Acesso em: setembro de 2008 e novembro de 2009. Krause, G. and Glaser, M., 2003. Co-evolving geomorphological and socio-economic dynamics in a coastal fishing village of the Bragança Region (Pará, North Brazil). Ocean & Coastal Management, 46, 859-874. Lam-Hoia, T.; Guiral, D., and Rougier, C., 2006. Seasonal change of community structure and size spectra of zooplankton in the Kaw River Estuary (French Guiana). Estuarine, Coastal Shelf, 68 (1-2), 47-61. Lau, M., 2005. Integrated coastal zone management in the People’s Republic of China. An assessment of structural impacts on decision-making processes. Ocean and Coast Management, 48, 115–159. Lozano, L.O.; Barba, G.A; Weiss, S.V., and Salgado, G.M.A., 2005. Environmental evaluation and development problems of the Mexican Coastal zone. Ocean and Coastal Management, 48, 161-176. Magalhães, A.; Leite, N.R.; Silva, J.G.S.; Pereira, L.C.C., and Costa, R.M. da, 2009. Seasonal variation in the copepod community structure from a tropical Amazon estuary, Northern Brazil. Annals of the Brazilian Academy of Sciences, 81(2), 187-197. Marengo, J., 1995. Interannual variability of deep convection in the tropical South American sector as deduced from ISCCP C2 data. International Journal Climatology, 15(9), 995-1010. Martorano, L.G.; Pereira, L.C.; Cezar, E.G.M., and Pereira, I.C.B., 1993. Estudos climatológicos do Estado do Pará, classificação climática (Köppen) e deficiência hídrica (Thornthwhite, Mather). Belém, SUDAM/EMBRPA, SNLCS, 53 p. Mazda Y.; Kanazawa, N., and Wolanski, E., 1995. Tidal asymmetry in mangrove creeks. Hydrobiology, 295, 51-58. Meade, R.H.; Dune, T., and Richey, J.E., 1985. Storage and remobilization of suspended sediment in the lower Amazon River of Brazil. Science, 228, 488-490. Monteiro, M.C.; Pereira, L.C.C., and Oliveira, S.O., 2009. Morphodynamic changes of a macrotidal sand beach in the Brazilian Amazon coast (Ajuruteua-Pará). Journal of Coastal Research, SI56, 103-107. Nittrouer, C.A. and Demaster, D.J., 1986. Sedimentary Process on the Amazon Continental Shelf: Past, Present and Future Research. Continental Shelf Research, 6, 5-32. Pereira, L.C.C.; Guimarães, D.O.; Costa, R.M. da, and SouzaFilho, P.W.M., 2007b. Use and Occupation in Bragança Littoral, Brazilian Amazon. Journal of Coastal Research, SI50, 1116-1120. Pereira, L.C.C.; Medeiros, C.; Jiménez, J.A., and Costa, R.M. da., 2007a. Use and Occupation in the Olinda littoral (NE, Brazil):
Guidelines for an Integrated Coastal Management. Environmental Management, 40, 210-218. Pereira, L.C.C.; Mendes, C.M.; Monteiro, M. da C., and Asp N.E., 2009. Morphological and sedimentological changes in a macrotidal sand beach in the Amazon littoral (Vila dos Pescadores, Pará, Brazil). Journal of Coastal Research, SI56, 113-117. Pereira, L.C.C.; Monteiro, M.C.; Guimarães, D.O.; Matos, J. B., and Costa, R.M. da, 2010. Seasonal effects of wastewater to the water quality of the Caeté river estuary, Brazilian Amazon. Annals of the Brazilian Academy of Sciences, 82(2), 1-12. Pereira, L.C.C.; Ribeiro, M.J.S.; Guimarães, D.O., Souza-Filho, P.W.M., and Costa, R.M., 2006. Formas de uso e ocupação na Praia de Ajuruteua-Pará (Brasil). Desenvolvimento e Meio Ambiente, 13, 19-30. Santos, M.L.S.; Medeiros, C.; Muniz, M.; Feitosa, M.L.S.; Schwamborn, R., and Macedo, S.J., 2008. Influence of the Amazon and Pará' Rivers on water composition and phytoplankton biomass on the adjacent shelf. Journal of Coastal Research, 24(3), 585-593. Silva, I. R. da; Pereira, L.C.C., Guimarães, D. de O.; Trindade , W.N., Asp, N.E., and Costa, R.M. da, 2009. Environmental status of urban beaches in São Luís (Amazon Coast, Brazil). Journal of Coastal Research, 56, 1301-1305. Sousa, E.B de; Costa, V.B. da; Pereira, L.C.C., and Costa, R.M. da, 2008. Microfitoplâncton de águas costeiras amazônicas: Ilha de Canela (Bragança, PA, Brasil). Acta Botânica Brasílica, 22(3), 626-636. Souza-Filho, P.W.M.; Martins, E.S.F., and Costa, F.R., 2006. Using mangroves as a geological indicator of coastal changes in the Bragança macrotidal flat, Brazilian Amazon: A remote sensing data approach. Ocean & Coastal Management, 49, 462-475. Souza-Filho, P.W.M.; Tozzi, H.A.M., and El-Robrini, M., 2003. Geomorphology, land use and environmental hazards in Ajuruteua macrodital sandy beach, northern Brazil. Journal of Coastal Research, SI35, 580-589. Strickland, J.D. and Parsons, T.R.A., 1972. Manual of sea water analysis. Bulletin Fisheries Research Board of Canada, 125, 1-205. Strickland, J.D.H. and Parsons, T.R.A., 1968. A practical handbook of sea water analysis. Bulletin Fisheries Research Board of Canada, 167, 1-311. Szlafsztein, C. and Sterr, H., 2007. A GIS-based vulnerability assessment of coastal natural hazard, state of Pará, Brazil. Journal of Coastal Conservation, 11, 53-66.
ACKNOWLEDGEMENTS This study was financed by FAPESPA (Fundação de Amparo à Pesquisa do Estado do Pará) through universal project no. 115/2008. The authors would also like to thank CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnologia), CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) and FAPESPA for individual research grants. We are also indebted to Stephen Ferrari for his careful correction of the English.
Journal of Coastal Research, Special Issue 64, 2011 1389