Water Quality in the River Test at Leckford

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1 Summary Water Quality in the River Test at Leckford Site of Special Scientific Interest A serious decline in freshwater invertebrates at Leckford is investigated. Recent Invertebrate surveys have shown a serious decline in Riverflies and Gammarus species which appears to be connected to elevated levels of phosphates and suspended solids (silt) in the river. A decline in the Blue Winged Olive population at Leckford, plus a recent paper on the egg survival rates of this species supports this. Levels of these two determinants are reviewed from a number of monitoring sites at Leckford between 2000 and 2017 using Environment Agency water quality data from the Water Quality Archive (Beta). This includes two private sewage treatment works where levels of phosphates and suspended solids remained high long after they were closed. After what appears to be a major upgrade at the Chilbolton Sewage Treatment Works, very high phosphate levels were drastically reduced; whilst this initially reduced the high levels of phosphates recorded in the river at the Mayfly Inn, these have risen again. In contrast, phosphate levels in the River Anton have remained well within the standard guide for a chalk stream, however the Fullerton Sewage Treatment Works (on the River Anton) discharges into the River Test upstream of the Mayfly Inn (Fig 3). The high phosphate levels in the River Test are diluted by water entering from the River Anton, but the lower levels below the confluence still mostly remain above the standard guideline for phosphates expected for a chalk stream. This local study needs to be extended to other sites on the River Test because whilst elevated levels of phosphates and suspended solids remain (and probably increase), there seems to be little chance of restoring this world famous river to its former glory. Introduction A reduction in Riverflies on the River Test has been evident for over 20 years. The Angler s Monitoring Initiative (AMI) courses run at the Leckford Field Centre observed this decline over many years and prompted detailed studies of the Blue Winged Olive (Serratella ignita) and the Mayfly (Ephemera danica). It is now well established that high levels of phosphates and fine sediments can seriously deplete freshwater invertebrate populations. The Environment Agency has monitored these (and many other determinants) at a number of sites in the Leckford area over a long period. This report compares invertebrate Benchmark data recorded at Leckford over a three year period with water quality measurements collected by the Environment Agency at five sites since

2 Decline in the Blue Winged Olive (Serratella ignita) The Blue Winged Olive (Serratella ignita) is one of the commonest Mayflies in the UK and with large populations on most rivers; Bass et al (1976) recorded 1500 nymphs per square meter in the Bere stream in Dorset. However, in common with many other rivers, populations on the River Test at Leckford have seriously declined (Bennett & Gilchrist 2010). Eggs of this species mostly overwinter in the egg stage and Everall et al (2017) has shown that prolonged exposure to orthophosphates and suspended solids (silt) leads to high mortalities. Even relatively modest levels of suspended solids and orthophosphate had significant effects on egg survival but there was a greater effect when orthophosphate levels were used in combination with a 10 mg/l background of suspended solids, which is probably more in keeping with river conditions. 2

3 There is a standard guideline level of 0.04 mg/l (Max 0.05 mg/l) for phosphate for designated wildlife sites to protect the natural ecology of Chalk Rivers (JNCC 2014); S&TC/EA are working to a 0.02 mg/l standard on the River Itchen. Salmon & Trout Conservation invertebrate benchmark surveys (S&TC Riverfly Census) taken just above the Mayfly Inn at Fullerton over a three year period ( ) show low numbers of Riverfly and Gammarus species; these appear to be consistent with elevated levels of phosphates (TRPI) and siltation (PSI). Phosphate and suspended solids are therefore reviewed from five Environment Agency monitoring sites at Leckford. River Test: 1. Chilbolton Sewage Treatment Works. 2. The Mayfly Inn - just upstream of the confluence with the Anton. 3. Longstock (Downstream of the confluence). River Anton: 4. Fullerton Sewage Treatment Works. 5. Fullerton - just upstream of the confluence with the Test. 3

4 Fig. 4 Invertebrate Benchmark Monitoring at the Mayfly Inn Spring & Autumn Invertebrate benchmark surveys recorded at The Mayfly Inn between 2015 & 2017 show that numbers of Riverflies and Gammarus were well below those expected for a chalk stream and indicate levels of sediments above the level of concern and under pressure from both sedimentation and phosphorus enrichment. 4

5 Leckford - Phosphate Levels Phosphate levels at Chilbolton STW (upstream of the Mayfly Inn) were extremely high until 2007 when, presumeably, the site was upgraded with phosphate stripping to bring it down to concentual levels. This resulted in a significant downward trend in the high phosphate levels in the river at the Mayfly Inn over a six year period (Fig. 6), but this did not reach the standard guideline of 0.04mg/l (blue line) before sharply rising again. Phosphate levels in the River Anton have remained well within the standard guideline for a chalk stream but it needs to be noted that these are measured upstream of the Fullerton STW outflow, which discharges into 5

6 the River Test upstream of the Mayfly Inn (Fig 3). This means that the monitoring site at the Mayfly Inn will be recording phosphate levels from both Chilbolton and Fullerton STW s. Monthly mean levels of phosphates over the S&TC study period on the River Anton (Black Line) have remained mostly within the standard guideline of 0.04mg/l, but levels on the Test at the Mayfly Inn (above the confluence with the Anton) are well above it, and with a seasonal peak in July, but as stated above, this will be from both Chilbolton & Fullerton STW s. Although phosphate levels recorded at Longstock (downstream of the confluence) are lower than those at the Mayfly Inn, they mostly exceeded the standard guideline. 6

7 Two private STW s at the Leckford Estate and the Mayfly Inn were closed before 2000, but EA monitoring continued until This shows high phosphate levels at the Mayfly Inn, and increasing levels at the Leckford Estate. Leckford Suspended Solids Suspended solid levels increased at Fullerton STW to peak in 2008 and then quickly reduced and remained at similar levels to those at Chilbolton STW. 7

8 Suspended solids on the River Anton at Fullerton were mostly lower than those on the River Test at Longstock. The peak winter consecutive levels at Longstock (shown in brackets) are not seen in the suspended solids levels recorded at either of the STW s. There is no river data for suspended solids on the River Test above the confluence at the Mayfly Inn site but high levels were still being recorded at the two closed private sewage treatments (with some very high peaks) up until monitoring ceased in

9 Monthly data over the S&TC study period shows seasonal changes with high levels in the early part of the year and reducing during the summer and autumn. Levels at Longstock generally follow those on the River Anton, but with higher peaks in the early part of 2016 and Conclusions There seems little doubt that the decline of Riverflies at Leckford is connected to the elevated levels of phosphates and suspended solids over a long period. Blue Winged Olive eggs are exposed to high levels of phosphates and various levels of suspended solids both before and after the upgrade of the Chilbolton STW (Figs. 5 & 6). BWO eggs have a long incubation period, but the eggs of the Mayfly Ephemera danica hatch in about 24 days (Bennett 2007) and should therefore be less affected. Whilst Everall et al (2017) used constant amounts of orthophosphates and suspended solids delivered over the long incubation period, it could well be that shorter exposure to high levels of these determinants could also lead to mortalities. 9

10 Whilst levels of phosphates in the River Anton have remained well within the standard guidelines for a chalk stream, phosphate levels in the River Test, above the confluence (Mayfly Inn), have remained well in excess of the guidelines both before and after the upgrade at Chilbolton STC and it needs to be noted that the Fullerton STW also discharges into the River Test upstream of the Mayfly Inn. Whilst dilution from the River Anton results in lower phosphate levels at Longstock, these mostly exceed the standard guidelines for a chalk stream. High levels of phosphates and suspended solids were still being recorded (up to 2005) at the two private STW s at the Leckford Estate and the Mayfly Inn long after these were closed (pre 2000). It s not known what impact these may have had whilst they were operating or since their closure, but high levels of phosphates remain in the river at the Mayfly Inn. This study highlights problems on the River Test at Leckford, and this needs to be carried out at other sites on the river to highlight other local problems; similar studies have been carried out on the Upper Hampshire Avon and the River Wey in Surrey. A nutrient management plan for phosphorus is also in place for the Hampshire Avon (Chapman 2015). Whilst these elevated levels of phosphates and suspended solids remain (and probably increase) there seems little chance of restoring this world famous river to its former glory. References: Bass J.A.B., Studies on Ephemerella ignita (Poda) in a chalk stream in Southern England. Hydrobiologia Bennett, C.J., The ecology of a seven year study of the life cycle of the mayfly Ephemera danica. Freshwater Forum 27, 3-14 Bennett. C., Gilchrist, W., Chapter 22. Riverflies. In: Maclean, N. (Ed.) Silent Summer. The State of Wildlife in Britain and Ireland. Cambridge University Press, Cambridge, UK. Chapman C River Avon - Special Area of Conservation Nutrient Management Plan for Phosphorus. David Tyldesley and Associates. Everall, N.C., et al Sensitivity of the early life stages of a mayfly to fine sediments and orthophosphate levels. Environmental Pollution. Joint Nature Conservation Committee Common standards monitoring guidance for rivers. ISSN Dr Cyril Bennett MBE March 2018 (Updated July 2018) 10