Results

Photograph 4: Manor Farm outflow.

Results

The full species lists are presented as an appendix. Note that the significance of blank counts against species in each site means that that species has been recorded in previous seasons but not this one. The results summarised here consist of number of species, abundance and WHPT, N-taxa and ASPT for current and previous years. These are presented by site as well as by index for comparative purposes.

The significant measure of water quality is the ASPT score. This is because gross scores such as abundance or WHPT are heavily influenced by sampling bias and would be expected to vary on every occasion to some extent. To overcome such bias the Average Score Per Taxon (ASPT) is calculated which reflects more accurately the water quality with higher scores representing less impact.

Site Date # species Abundance N-taxa WHPT ASPT

Bishop’s Sutton 22.5.2018 49 1237 35 194.6 5.56 28.5.2019 31 1478 27 139.3 5.16 14.5.2020 51 1660 36 196.5 5.46 19.5.2021 38 1182 33 166.5 5.05 Below Drayton Farm 22.5.2018 47 813 34 174.8 5.14 28.5.2019 40 1165 31 154.3 4.98 6.5.2020 52 1331 38 204.4 5.38 5.5.2021 44 1004 32 176.1 5.50 Above Drayton Farm 22.5.2018 46 1966 32 149.4 4.67 28.5.2019 39 1809 29 146.9 5.07 6.5.2020 47 1835 37 197.2 5.33 5.5.2021 46 1425 35 184.9 5.28 Manor Farm 22.5.2018 53 1675 38 204.8 5.39 28.5.2019 39 2515 34 186.5 5.49 14.5.2020 47 2032 38 215.2 5.66 19.5.2021 53 1596 40 228.7 5.72

Table 2. Results summary

The results show a mixed picture with Manor Farm showing an increase, above Drayton Farm being almost exactly the same and slight declines (not significant) at Bishops Sutton and below Drayton Farm. Improvements in scores are highlighted in blue and equivalent scores in orange in Table 2.

All indices show improvements since 2019. Table 3 gives the means of the reported values in comparison with this years results. Increases in values are highlighted in blue, but the differences between 2021 results and the mean are very small and certainly insignificant.

Site Date # species Abundance N-taxa WHPT ASPT

Bishop’s Sutton 19.5.2021 38 1182 33 166.5 5.05 mean 40.0 1440.0 32.0 167.2 5.2 Below Drayton Farm 5.5.2021 44 1004 32 176.1 5.50 mean 45.3 1166.7 33.7 178.1 5.3 Above Drayton Farm 5.5.2021 46 1425 35 184.9 5.28 mean 44.0 1689.7 33.7 176.3 5.2 Manor Farm 19.5.2021 53 1596 40 228.7 5.72 mean 46.3 2047.7 37.3 210.1 5.6

Table 3. Comparison with three year running mean.

Gammarus counts are summarised below but also show an increase at both Drayton sites.

Site 2018 2019 2020 2021

Bishop’s Sutton 323 405 530 286 Below Drayton 91 243 386 470 Above Drayton 223 115 261 284 Manor Farm 638 272 805 293

Table 4. Gammarus counts

240

220

200

180

160

140

120

WHPT scores

01/05/2018 01/07/2018 01/09/2018 01/11/2018 01/01/2019

01/03/2019 01/05/2019 01/07/2019 01/09/2019 01/11/2019 01/01/2020 01/03/2020 01/05/2020 01/07/2020 01/09/2020 01/11/2020 01/01/2021 01/03/2021 01/05/2021

Manor Farm Above Drayton Below Drayton Bishops Sutton

Graph 1. WHPT scores 2018 - 2021

Graph 1 shows the WHPT scores across the four years for which May data has been collected. No significant trend is apparent with the data oscillating around the mean as would be expected in a stable system that was neither in recovery nor decline.

The results are consistent with good water quality and high biodiversity, as would be expected in chalk streams showing little impact from the watercress operations.

Variations in biodiversity which are reflected in these indices are due to a number of factors which will vary from year to year :-

 Weather o The particularly cold spring has noticeably affected the marginal vegetation which is considerably reduced. The weather will have little effect on the stream itself as it is fed from a borehole with water at a more or less constant temperature. However significant rainfall events will increase sediment entering the stream which has a negative effect.  Stream vegetation management o Manor Farm is cleared of in-channel vegetation by the landowner which would be expected to have a depressing effect on biodiversity as there are less habitats available. This is at odds with the results which may be due to recovery after previous disturbance or just natural variation. Below Drayton Farm, the channel is too shaded for any in-channel vegetation to develop. The other two sites can be expected to undergo annual variations in the amount of vegetation present which is reported each year in the location descriptions.  Sampling efficacy o As previously discussed these samples are representative of the community present but vary slightly year on year which will contribute to some of the variation in results.

It is interesting to note that two new species never previously recorded have been found this year. These are a mayfly Paraleptophlebia submarginata at the below Drayton Farm site. This is a large mayfly typically found in stony streams and rivers. The second is the Nationally Scarce moss beetle Ochthebius exsculptus found at both below Drayton Farm and at Manor Farm. This is an unusual record as the beetle is more often found in the north of England and Scotland and has not been recorded in Hampshire before. It is typically found in running water or on the edge of streams.