Macroinvertebrate Survey of Drayton watercress farm outflow, Alresford , Hants
Report prepared by Robert Aquilina MSc MCIEEM
August 2018
Macroinvertebrate survey of Drayton watercress farm outflow, Alresford, Hants
Robert Aquilina MSc MCIEEM
August 2018
Robert Aquilina MSc MCIEEM is an independent consulting ecologist specialising in protected species and freshwater ecology. He is a Full member of the Institute of Ecology and Environmental Management and abides by their Code of Professional Conduct. For further details see www.cieem.net www.aquilina-environmental.co.uk
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Table of contents Summary .............................................................................................................. 4 Introduction .......................................................................................................... 5 Methods ............................................................................................................... 5 BMWP ............................................................................................................................................. 6 WHPT .............................................................................................................................................. 6 Locations ......................................................................................................................................... 7
Results .................................................................................................................. 8 Conclusions ........................................................................................................... 8 Photographs of some typical members of the community ...................................... 9 References ........................................................................................................... 10 Appendix 1 Species recorded. ............................................................................... 11
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Summary
A macroinvertebrate survey of the outflow from the Drayton watercress beds at Alresford, Hampshire were carried out using standard sampling techniques. The purpose was to examine the conditions in the outflow as high up the farm as possible prior to its passage through the settling ponds. The species present indicated good diversity and water quality scores for a small headwater stream but did indicate moderate impact from fine sediments. A complete list of species is presented together with abundance and diversity (WHPT and BMWP) scores.
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Introduction
The purpose of this survey was to assess the discharge from the watercress beds at Drayton as high up the water course as possible. The watercress beds are situated at a borehole at the head of a small chalk stream. After passage through the watercress beds, the water is discharged and forms the head of the stream which receives further discharges as it proceeds through the farm. Before it leaves the farm, the water passes through an extensive network of settlement ponds which remove sediment to levels below the EA discharge consent limit. This unnamed stream joins the River Alre via Old Alresford Pond, which in turn joins the River Itchen, an important chalk stream for salmon and trout fishing and conservation. The site was visited by Robert Aquilina on Wednesday 22nd August 2018 and samples were collected for analysis in the laboratory using standard techniques. The weather conditions were dry and suitable for the survey with normal water flow levels. Industry standard survey and extraction techniques for the stream (Environment Agency 2012) were used to assess the species present. Methods The methodology followed is the standard Environment Agency survey and extraction protocol which results in a species list with abundance data. This forms the basis for calculating a number of indices designed to assess the impacts of various factors (depending on the index selected) but in this case is used to calculate the standard BMWP and its more sophisticated modification WHPT. Aquatic macroinvertebrates were collected using a standard size FBA D-frame pond net from the major habitats along the stream (stands of different wetland plants, distinctive substrates, tree roots etc.). All the different habitats present were allocated a proportion of the overall sampling time (3 minutes) and different areas of the same mesohabitat were subsampled to ensure that as great a range as possible was sampled. Each location was also searched for an additional minute looking for surface dwelling animals such as water skaters and whirligig beetles and inspecting submerged habitats such as logs and larger stones for attached animals.
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The samples were preserved in 70% IMS and sorted in the laboratory, where all the invertebrates were extracted. The standard BMWP invertebrate groups were recorded : Tricladida (flatworms), Gastropoda (snails and bivalves), Crustacea (slaters, shrimps and crayfish), Hirudinea (leeches), Megaloptera (alderflies), Plecoptera (stoneflies), Ephemeroptera (mayflies), Odonata (dragonflies and damselflies), Hemiptera (water bugs), Coleoptera (water beetles), Trichoptera (caddisflies) and Diptera (true flies). Voucher specimens were retained in order to check their identity. Dead mollusc shells, and empty caddis cases were discarded and only whole animals were included in the counts.
BMWP Condition assessment of running waters is based on the BMWP (Biological Monitoring Working Party) score. These BMWP family scores (1-10) are industry standard and reflect the sensitivity of the families to pollution. The higher the family score, the more sensitive to oxygen depletion the family is and therefore their presence indicates a cleaner or less impacted site. The effects of pollution generally are to impose a Biological Oxygen Demand upon the receiving waters and so sensitive families are progressively excluded as the BOD increases. The score for each family present is totalled to give a site score. Because these site BMWP scores are influenced by sample size (a high score can be achieved through a large number of low scoring families as well as a small number of high scoring families) an Average Score Per Taxa (ASPT) is also calculated from the resulting BMWP scores and allows further interpretation of the results. The higher the ASPT, the greater the proportion of more sensitive families in the sample and therefore the better the site condition.
WHPT WHPT better reflects the quality of the invertebrate community because it is based on a wider range of taxa (mostly families), in particular, WHPT includes more families of Diptera and some families that were grouped together in BMWP (known as BMWP composite taxa) are considered separately in WHPT. So 106 taxa are included in WHPT as opposed to the 82 in BMWP. Additionally the abundance of each taxa is taken into account through the use of abundance classes, the WHPT score for each taxa present depending on its abundance. 6
Abundance category Numerical abundance AB1 AB2 AB3 AB4
1-9 10 -99 100 - 999 >1000 Table 1: WHPT abundance classes
Apart from accounting for abundance, the calculation of scores is the same as for BMWP and results in equivalent but more accurate reflection of water quality. The scores derived are WHPT overall score (equivalent to BMWP), N taxa and ASPT.
Locations
Photograph 1: Drayton Farm outflow. The channel is approximately 1 - 1.5 metres wide and 0.2 – 0.3 metres deep. Water flow is maintained by discharge from the borehole. The habitats present consisted of gravel, coarse and fine sands, Ranunculus beds and marginal Glyceria maxima with 7
small amounts of other marginal plants. This represents the head of the stream as upstream are the watercress beds and borehole supply.
Results
The full species lists and abundance are presented as an appendix. The results are summarised here.
Date
22.8.2018
BMWP WHPT N-taxa (BMWP) 106
149.4
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N-taxa (WHPT)
ASPT (BMWP)
ASPT (WHPT)
32
4.61
4.67
Table 2. Summary of results
The results show good but not high scores.
Conclusions The results are somewhat lower than might be expected for a stream of this size (albeit small) and diversity of habitat which suggests that there is some detectable impact from sediments discharged in the water column. As the purpose of this report is to determine results upstream of the settlement ponds, this is to be expected. Inspection of the species list show a predominance of the species favouring the marginal vegetation as opposed to gravel bed species. This has the effect of lowering the index scores and again is a reflection of the relatively small amounts of gravel bed at this point in the channel. The absence of a number of cased caddis species normally associated with gravel beds supports this (e.g. Sericostoma personatum or Silo nigricornis ). The presence of large trout as well as many small Bullhead and 3spine Stickleback suggest that sediment discharge is of an intermittent nature.
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Photographs of some typical members of the community
Rhyacophila dorsalis (20mm)
Anisus leucostoma (4-5mm) Oxythera sp. (4-5mm)
Gyraulus crista (3mm) Drusus annulatus (12mm)
Valvata piscinalis (5mm)
Baetis vernus (11mm)
Simulium (blackfly) cocoons (5mm)
Oreodytes sanmarkii (3mm)
References
Environment Agency. (2012). Freshwater macro-invertebrate sampling in rivers. Operational instruction 018_08. Environment Agency. Environment Agency. (2012). Freshwater macro-invertebrate analysis of riverine samples. Operational instruction 024_08. Environment Agency. Environment Agency. (2014). Walley Hawkes Paisley Trigg (WHPT) index of river invertebrate quality and its use in assesing ecological status. Brief Guide version 5. Paisley,M.F., Trigg,D.J. and Walley,W.J. (2013). Revision of the Biological Monitoring Working Party (BMWP) score system: derivation of present-only and abundancerelated scores from field data. River Research and Appications. 30: 887-904.
Appendix 1 Species recorded. Group
BMWP family
Species
Common name
Tricladida
Dugesiidae
Dugesia polychroa gr.
Flatworm
Tricladida
Planariidae
Polycelis nigra
Flatworm
Tricladida
Planariidae
Polycelis tenuis
Flatworm
Mollusca
Lymnaeidae
Lymnaea palustris
Marsh pond snail
Mollusca
Lymnaeidae
Radix balthica
Wandering snail
Mollusca
Planorbidae
Anisus leucostoma
Button ramshorn
Mollusca
Planorbidae
Gyraulis crista
Nautilus ramshorn
Mollusca
Valvatidae
Valvata piscinalis
Common valve snail
Mollusca
Ancylidae
Ancylus fluviatilis
River limpet
Mollusca
Sphaeridae
Pisidium sp.
Pea mussel
Crustacea
Asellidae
Asellus aquaticus
Water slater
Crustacea
Gammaridae
Gammarus pulex
Freshwater shrimp
Hirudinea
Erpobdellidae
Erpobdella octoculata
Leech
Hirudinea
Glossiphonidae
Glossiphonia complanata
Leech
Hirudinea
Glossiphonidae
Helobdella stagnalis
Leech
Hirudinea
Glossiphonidae
Theromyzon tessulatum
Hirudinea
Piscicolidae
Piscicola geometra
Fish leech
Ephemeroptera
Ephemerellidae
Serratella ignita
Blue-winged Olive
Ephemeroptera
Baetidae
Baetis vernus
Medium Olive
Ephemeroptera
Baetidae
Cloeon dipterum
Pond olive
Plecoptera
Nemouridae
Nemoura cinerea
Stonefly
Status
=Lymnaea peregra
Abundance
3 3 9 23 258 7 26 1 6 1 7 223 11 17 6 1 2 9 320 1 2
Group
BMWP family
Species
Common name
Coleoptera
Dytiscidae
Oreodytes sanmarkii
Diving beetle
Coleoptera
Dytiscidae
Coleoptera
Dytiscidae
Agabus didymus
Diving beetle
Coleoptera
Dytiscidae
Agabus paludosus
Diving beetle
Coleoptera
Elmidae
Elmis aenea
Riffle beetle
larva and adults
Coleoptera
Elmidae
Riolus subviolaceus
Riffle beetle
larva and adults
Trichoptera
Rhyacophilidae
Rhyacophila dorsalis
Caseless caddis
Trichoptera
Glossosomatidae
Agapetus fuscipes
Saddle-case caddis
Trichoptera
Hydroptilidae
Hydroptila sp.
Cased caddis
Trichoptera
Hydroptilidae
Oxyethira sp.
Cased caddis
Trichoptera
Limnephilidae
Drusus annulatus
Cased caddis
Trichoptera
Limnephilidae
Limnephilus lunatus
Cased caddis
Diptera
Ceratopogonidae
Biting midge
larvae
Diptera
Chironomidae
Non-biting midge
larvae
Diptera
Culicidae
Mosquito
larvae
Diptera
Dixidae
Meniscus midge
larvae
Diptera
Ephydridae
Diptera
Psychodidae
Diptera
Sciomyzidae
Diptera
Simulidae
Diptera Diptera
Diving beetle
Dixa + Dixella
Status
larvae
larvae not identifiable to species larvae not identifiable to species
larvae Pericoma sp.
Moth fly
larvae
Snail-killing flies Blackflies
larvae early instars not identifiable to species
Stratiomyidae
Soldier fly
larvae
Tipulidae
cranefly
larvae
Simulium sp.
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Abundance
30 9 1 1 2 1 8 20 133 147 27 4 8 243 50 7 18 19 1 88 1 12
Group
BMWP family
Species
Common name
Status
Abundance
Diptera
Tipulidae(Pediciidae)
Dicranota sp.
cranefly
larvae
Others
Hydracarina
Water mite
Others
Oligochaeta
True worms
20 22 158
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