Upstream Thinking in Action: the River Fowey
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UPSTREAM THINKING IN ACTION: THE RIVER FOWEY About the catchment § The River Fowey is at risk for pesticides, namely MCPA, mecoprop and Figure 2 Variations in flow (top), colour (middle) metaldehyde. and turbidity (bottom) per hydrological year in Background site information Water quality in the the River Fowey between 2012-2013 and 2017- § Water quality monitoring has also shown a slight decrease in turbidity 2018, all flow values considered. he Fowey catchment falls throughout the 2012-2013 to 2017-2018 period, all flow conditions within the Colliford Strategic Fowey catchment considered; at low flow the decrease is noticeable for both turbidity and Supply Area, south-west of colour, which may be attributable to UsT interventions. As such change TBodmin Moor, in Cornwall (Figure Long-term changes in water is not yet visible at high flows, it is hoped that it will be noticeable after 3). SWW abstracts water from continued engagement and further interventions are implemented in the colour and suspended the Lower River Fowey for potable catchment. supply, with water being fed directly sediment pollution to the water treatment works. § Although a number of pesticides are detected along the River Fowey and hen all flow is considered Additionally, another abstraction is at SWW assets, the he maximum concentration measured in river water (Figure 2), continuous being used in the catchment (Figure (as time weighted average) are consistently below 100 ng L-1, and the measurements at the 1). Catchment intervention measures total concentration of all pesticides is below 500 ng L-1, thereby fulfilling waterW treatment works in the River are being delivered by West Country the Upstream Thinking objectives. Fowey show no significant decrease Rivers Trust. § The frequency of pesticide detections in the raw water in the lower in colour between hydrological Catchment Challenges River Fowey has not decreased significantly with time; however, the work years. However, a slight decrease in carried out has highlighted the most problematic compounds that occur turbidity (representing suspended The River Fowey is at risk for in the river water, enabling project partners to target their actions in the sediment concentrations in water) pesticides, in particular MCPA and catchment. is observed. More precisely, mean Mecoprop, both used for broadleaf turbidity has been reduced from weeds control, and for metaldehyde, 7.5 NTU in 2012-2013 to 3.8 NTU a common pesticide against slugs and Figure 1 Map of engagement in 2017-2018, although maximum snails. by WRT as part of UsT in the Fowey catchment. values remain the same, with peaks reaching 150 NTU on occasion. Catchment Activities Reduction of both colour and Catchment activities delivered through turbidity in water is important to Upstream Thinking 2 have mostly reduce primary water treatment focused on capital grants, such as yard costs in drinking water. infrastructure to support livestock or When only low flow is considered dairy enterprises. There have also been (Figure 3), both colour and turbidity pesticide amnesties and support for show a significant decrease between field trials of alternative methods. 2012-2013 and 2017-2018: mean As of May 2019, 33% of the Fowey colour values change from 15 to catchment has been engaged in 12.9 Hazen, whilst mean turbidity Figure 3 Low flow (≤Q70) variations (top) and Upstream Thinking 2 by Westcountry values decrease from 5.4 to corresponding values in colour (middle) and turbidity Rivers Trust (WRT) (Figure 1), 1.4 NTU over the same period. (bottom) per hydrological year in the river Fowey between with physical activities focussing on As low flow periods often coincide 2012-2013 and 2017-2018. The red arrow shows the such things as fencing off rivers to with high water demand, such observed trend between 2012-2013 and 2017-2018. prevent livestock access, minimising results are encouraging, as cleaner the volumes of dirty water produced water abstracted in the summer and management of manure. These months may be less costly to treat. interventions are known to reduce Amongst the interventions used nitrogen and phosphorus levels in in the catchment, only fencing off water1. watercourses from livestock is likely to have an impact on sediment losses and turbidity, which might explain the small decrease, but also highlights the potential to address these problems more significantly if further measures are adopted across the catchment. The River Fowey at SWW’s WTW; photo by Emilie Grand-Clement. 60 Upstream Thinking Evaluating the impact of farm interventions on water quality at the catchment scale 61 UPSTREAM THINKING IN ACTION: THE RIVER FOWEY UPSTREAM THINKING IN ACTION: THE RIVER FOWEY However, such change is not observed at high flow (Figure 4), with the difference between years Figure 5 likely due to inter-annual variability. Maximum Moreover, high flow conditions are detections per likely to be the most problematic pesticides as time weighted periods for WTWs due to higher average diffuse pollution and contaminant between Spring concentrations delivered by rainfall 16 and Autumn events. This lack of change at high 18 in the river flow might indicate that a more Fowey at Trekeive steps extensive range of measures is (left) and at needed to affect the catchment at Restormel WTW large scale. (right) during chemcatcher Pesticide detections within deployment the Fowey catchment campaigns. Detections in the Fowey catchment were generally low (Figure 5), with a maximum detection of -1 35 ng L for 2,4-D at the Trekeive Figure 6 Relative steps abstraction point (autumn abundance 2018), and never reached either of pesticides -1 found in the the 100 ng L per compound or River Fowey at the cumulated concentration of Trekeive steps -1 500 ng L regulatory limits. Higher (left) and at concentrations experienced Restormel WTW upstream indicate a source of certain (right) during Chemcatcher compounds higher in the catchment, deployment and a dilution downstream closer to campaigns. the WTW. Figure 4 High flow (≥Q5) variations (top) and corresponding values in colour (middle) and turbidity There is, however, no significant (bottom) per hydrological year in the River Fowey change between seasons throughout between 2012-2013 and 2017-2018. the project. In fact, the highest detections occurred in autumn The Fowey catchment: a patchwork of woodland, 2018, highlighting the need for intensive grassland and arable land use; photo by Most pesticides in the Fowey Emilie Grand-Clement. continued catchment interventions catchment are present consistently and pesticide amnesties in the Fowey across most deployment periods catchment. and on both locations, such as for In the Fowey catchment; photo by Hazel Kendall (WRT). example 2,4-D or metaldehyde (in autumn deployments only) as shown on Figure 6. This is a useful assessment of the range of compounds to target in the catchment. For example, MCPA, which had been identified as a particularly problematic compound by the EA between 2009 and 2013, is still detected regularly at the water treatment works, but at low concentrations, whilst Mecoprop (identified as another problematic compound) is being detected during all spring deployments. REFERENCES Most of the pesticides detected at Bromoxynil is solely found at the Restormel WTW are also found WTW, albeit in low concentrations, 1. Cuttle, S.P., et al. (2016). A method- upstream at Trekeive steps, however indicating an intermediate source centric ‘User Manual’ for the mitigation between Trekeive steps and of diffuse water pollution from their respective proportions vary agriculture. Soil Use and Management, 32, Stone bridge on the River Fowey; Restormel WTW. between deployment periods. Only 162-171. photo by Hazel Kendall (WRT). 62 Upstream Thinking Evaluating the impact of farm interventions on water quality at the catchment scale 63.