This practical session was led by Jeremy Biggs (CEO, Freshwater Habitats Trust; Visiting Professor, Oxford Brookes University) and Dr Matthew Bulbert (Senior Lecturer, Oxford Brookes University). The session introduced the standard plant and macroinvertebrate survey method for ponds, for PSYM. The location of this practical was at Rivermead Nature Park, Oxford.

PSYM

Pond PSYM (Predictive SYstem for Multimetrics) practical

15 April 2024

The Freshwater Habitats Trust developed the PSYM method that is now recognised as the standard method for assessing pond ecological quality in the UK. This method predicts what the expected freshwater plant and invertebrate community would be if the pond was undegraded (by using reference sites), then compares this to the results of the survey allowing the ecological quality of the pond to be assessed (Freshwater Habitats Trust, 2019).

The method follows the steps:

1. Environmental data are taken for the pond

2. Surveys of the plant and animal communities

3. PSYM uses the environmental data to predict what plants/animals should be present if the pond was undegraded

4. PSYM calculates metrics based on the observed plant and animal lists

PSYM Overview

Both plant and animal communities are surveyed as together they respond to a wide range of factors indicating degradation e.g. plants are sensitive to nutrient status and animals are more sensitive to oxygen levels. For ponds, macroinvertebrates and macrophytes are used as the taxa most practical and effective for this assessment.

Along with location and survey details e.g. Grid reference, date, surveyor etc. the following variables are recorded:

• Altitude (m): taken from map.

• pH: from test.

• Shade % pond overhung: estimate how much of the pond is overhung by imagining the pond in plan-view and estimating what overhangs it. For this I walked around the perimeter of the pond, wading in where necessary.

• % emergent plant cover: Essentially estimating the cover of plants sticking out of the water. This needs to be estimated as if they were densely packed together.

• Inflow: present/absent (1/0), note this can be natural or man-made.

• Pond area (m2): Find the max winter water level to determine where the edge of the pond is. You can look for where the water plants e.g. rushes are, some ponds have pipes/dams to control the level. Can pace out 2 sides of the pond to calculate this but you need to know your pace size!

• % pond margin grazed: from livestock only, NOT wild animals.

• Pond base: pick up and feel from a few places. Can use the handle of a net to dig some up and check. Categorise as either 0-32%, 33-66% or 67-100% for: Clay/silt, Sand/gravel/cobbles, bed rock, peat or other.

Environmental data

A sketch of the pond is also required to show the shape and main features.

For the pond in this exercise the data are:

• Ph = alkaline (no test taken in this session)

• 10% shade

• 35-40% emergent plant cover

• inflow = 0

• area = 330 square metres

• % grazed = 0%

• Pond base: Clay/Silt = 3, Sand = 1

Me surveying in the pond

The pond at Rivermead Nature Park

For the plant survey a complete list of all wetland plants that are within the outer edge of the pond is to be made. There is a list of all those that are viewed as ‘wetland’ that are to be recorded, which can then be used to calculate 3 metrics:

1. · Number of submerged and emergent plant species

2. · Trophic Ranking Score (TRS) (where applicable scores are assigned to species in the list)

3. · Number of uncommon plant species (where the rarity score is greater than 2)

(Freshwater Habitats Trust, 2019)

The % cover is typically recorded as well, although this is not used for PSYM. The edges of the pond are usually the most biodiverse area. In this practical session, although we did not go around the whole pond we saw:

Bullrushes, club rushes and yellow irises being common. Other species found include rigid hornwort, water soldier (which looks a bit like a pineapple, not native to this part of England, shown in the photo below), common stonewort (not included in the PSYM list), creeping bent (common at pond margins), water cress, water horsetail, water figwort, creeping buttercup (a terrestrial plant so ignored for PSYM assessment), meadowsweet, great willowherb and bittersweet.

Plant survey

Water soldiers

The method used for invertebrate surveying is a standard 3-minute hand-net sampling. This isn’t 3 minutes continuous, it is possible to stop and walk to another part of the pond – it is 3 minutes of total sampling time, so short bursts e.g. 5 seconds can be done. It is important to select different meso-habitats e.g. at the edges, by different vegetation etc. to sample the diversity of the pond. Ideally not too many so that it isn’t too complex, e.g. 6 meso-habitats of 30 seconds at each seems sensible. Invertebrates are tipped into a bucket to be taken away and sorted/identified to family level off-site. Note that any fish or amphibians caught are to be noted on the sheet and then returned to the pond (Freshwater Habitats Trust, 2019). In our case we saw plenty of toad tadpoles, as well as some smooth newts.

The following 3 metrics can then be calculated from the results:

1. Average score per taxon (ASPT)

2. Number of dragonfly (Odonata) and alderfly (Megaloptera) families

3. Number of beetle (Coleoptera) families

(Freshwater Habitats Trust, 2019)

Invertebrate survey

In the session we recorded 21 families. Note how the list in the PSYM fieldsheet is ordered so that it starts with Group 1 taxa which are those that are most sensitive to a lack of oxygen and pollution (this list was originally based on rivers).

The families found:

• Aeshnidae: Hawkers (Dragonflies)

• Caenidae: Mayflies

• Limnephilidaae: Caddisflies, case constructing

• Gammaridae (Crangonyctidae): shrimps

• Coenagriidae: Damselfies

• Gerridae: Pond skaters

• Nepidae: water scorpion

• Naucoridae: saucerbugs

• Pleidae: back swimmer

• Corixidae: water boatmen (we saw lesser water boatman)

• Dytiscidae (Noteridae): diving beetles

• Hydrophilidae (Hydraenidae): water scavenger beetles

• Baetidae: small mayflies

• Hydrobiidae (Bithyniidae): Snail (with pointy shell)

• Lymnaeidae: Pond snail

• Planorbidae: Ramshorn snail

• Sphaeriidae: fingernail clam?

• Erpobdellidae: Leeches

• Asellidae: Waterlice i.e. a pond slater or water hoglouse

• Chironomidae: Midges

• Oligochaete: Worms

Unusually, we might have expected to find the following families but did not sample any:

• Phryganeidae: Caddisflies

• Leptoceridae: Long-horned caddisflies

• Polycentropodidae: Caddisflies

• Ancylidae (Acroloxidae): Limpets

• Gyrinidae: Whirligig beetles

We also saw some mites, but these are not included in the PSYM assessment.

In this session I performed some hand-net sampling, and samples were tipped into trays (as shown in the photo below) for us to attempt to identify in the field to give an overview, rather than following the full PSYM process.

Photos show (clockwise from top left): Water scorpion Nepidae, Damselfly larva Coenagriidae, Dragonfly larva Odonata, Smooth newt and Caddisfly larvae Limnephilidaae, Toad tadpoles

Net used for sampling, along with a sorting tray.

Reflection

This session provided valuable insight into the process of performing a PSYM survey of a pond. I enjoyed wading in, and seeing what was found! I can see how a complete PSYM survey can be time consuming, and expertise is required to identify everything on the lists. I would be interested in understanding how the ‘reference’ sites of undegraded ponds have been selected as these are the baseline that others are being compared to.

References

Freshwater Habitats Trust (2019) Predictive System for Multimetrics (PSYM). Available at: https://freshwaterhabitats.org.uk/advice-resources/survey-methods-hub/psym/ (Accessed: 04 June 2024).