Upstream Thinking in Action: the River Cober
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UPSTREAM THINKING IN ACTION: THE RIVER COBER Figure 3 Top 5 interventions About the catchment § The water quality issues in the Cober catchment have been identified as (quantified in Farmscoper) ammonium levels (over 2 mg L-1) and pesticides (MCPA and Mecoprop in used in the Cober catchment. Background site information particular); he River Cober catchment § Ammonium levels were elevated for ca. 1.88% of the time, but the (Figure 1 and Figure 2) lies threshold of 2 mg L-1 was exceeded in 0.85% of time, adding up to within the Cober and Lizard around 74 hours per year (on average across the study period); TEA Operational catchment which falls within the wider Cornwall West § Overall, a positive contribution of Upstream Thinking in the catchment Figure 2 illustrates the level of farm Water quality in the and Fal EA Management Catchment. is likely to have reduced the frequency of ammonium detections in the engagement in UsT2 within the It drains a 53.75 km2 area of West catchment since 2015, as seen in the continuous ammonia signal; Cober catchment. Whilst the area Cober catchment Cornwall. The River Cober (Upper § Use of the Chemcatcher passive sampling devices has shown high of catchment engaged appears small and Lower) itself rises at Nine numbers of pesticide detections throughout the monitoring period; (8% of the total UsT focus area), Ammonium in river water Maidens Down, winding across the regulatory limit of 100 ng L-1 per compound and per detection was this is mainly because only a small Porkellis Moor and passing alongside exceeded on four occasions in the River Cober; number of farms could be targeted n the River Cober, the mean Helston to reach Cornwall’s largest for very specific interventions concentration of ammonium from § natural lake, the Loe Pool. MCPA and Mecoprop remain present throughout the catchment; following identification of key samples analysed over the last 15 metaldehyde has not been detected in the Releath Stream. opportunities to reduce ammonium, Iyears is 0.23 mg L-1; in the Releath Agricultural activity within the based on farm type (dairy), Stream the mean concentration is catchment is centred around proximity to watercourse and land 0.094 mg L-1. For the period 2015 to intensive dairy farming, with rough slope. 2018 this drops to 0.044 mg L-1 and grazing taking place on marginal 0.064 mg L-1 for the Cober and the Physical interventions completed via land. Interventions in the catchments Releath, respectively. Concentrations UsT, which were quantifiable within were led by Cornwall Wildlife in the blended raw water at the Figure 2 Map of engagement by the CWT as part the Farmscoper software, amounted Trust (CWT). SWW water treatment works were of UsT in the Cober catchment. to a cumulative total of 1,026 ha. The typically lower, with an average of Catchment Challenges most commonly used interventions 0.032 mg L-1 over the last 15 years, are shown in Figure 3. They are increasing to 0.047 mg L-1 more The River Cober was identified as mostly aimed at targeting nutrients, recently. The median values for at-risk for pesticides and ammonium. although farm track management sampling points are at or below the Ammonium has been problematic is also thought to have an impact limits of detection, showing a positive in the past and can have significant on sediment losses to streams and contribution of Upstream Thinking impacts on the water treatment rivers. in the catchment to reducing the and its cost. The primary source of Figure 4 Timeseries for rainfall, this pollutant is manure and slurry flow and ammonium samples and frequency of ammonium detections from agriculture. Concentrations continuous measurements alongside in the catchment. of ammonium can increase rapidly a threshold (orange dotted line) of under spate or flood conditions 0.2 mg L-1. when the sources of ammonium are directly connected to the surface streams and rivers. To deal with this issue, the water treatment works has auto-shutdown facilities in place, which prevent the works from abstracting and treating water Figure1 The River when its quality deteriorates beyond Cober; picture by Emilie Grand- certain thresholds. As the security Clement of the water supply is compromised during these periods, it is important that they do not persist for too long. Catchment Activities to work with farmers to identify Activities in the Cober catchment opportunities to improve dirty started in 2015, i.e. later than some water management and prevent other Upstream Thinking catchments. ammonium runoff. In addition, work Ammonium can originate from was undertaken to improve land diffuse and point source pollution management to reduce erosion, and therefore a focus of CWT buffer run-off and reduce nutrient activity in the Cober catchment was inputs to the soil and streams. 56 Upstream Thinking Evaluating the impact of farm interventions on water quality at the catchment scale 57 UPSTREAM THINKING IN ACTION: THE RIVER COBER UPSTREAM THINKING IN ACTION: THE RIVER COBER High-frequency signals from sensors Values for ammonium are elevated months. Sensor levels for ammonium Similarly, the catchment is experiencing very high single in the river also play an important over this threshold for a small are, in general, lowest in the summer contaminant detections, with values going beyond the regulatory role in understanding the behaviour proportion of the time (0.85%). Each (July, August and September). limit of 100 ng L-1 on four occasions in the River Cober (e.g. -1 Figure 5 Relative abundance of compounds detected at of ammonium. Figure 4 shows the year these exceedances occur on between 110 and 197 ng L ), one of which was at SWW’s SWW water treatment works, with water originating seasonal patterns in flow, ammonium multiple occasions for short periods Pesticide detection in the water treatment works. Although the Releath Stream has a high from the Releath Stream (left) and the River Cober signal, and ammonium samples, of time, adding up to around 74 Cober catchment number of detections, they never exceed 31 ng L-1. (right). with a threshold value of 0.2 mg L-1 hours per year (on average across displayed. Above this level, the works the study period). The signal is Since 2016, the Cober catchment are temporarily shut down to protect elevated for a greater proportion of has experienced a high number of the drinking water supply, as such time (1.88%) over winter in January, pesticide detections (i.e. between levels are difficult to remove from February and March (Table 1) and 3 and 16) in all streams monitored drinking water. more peaks are seen during these (Table 2). This number of detections appears to be slightly lower in the second half of the monitoring period Time threshold (i.e. between Autumn 2017 and exceeded Time Period Autumn 2018), with the number of Percentage detections in Autumn 2017 being Hours of time the lowest across all sites. Table 1 Average time Winter (OND) 10.6 hr 0.48% per season where the signal exceeds the Table 2 Total number of detections, exceedances -1 Winter (JFM) 41.3 hr 1.88% shutdown threshold of above 100 ng L , maximum concentrations 0.2 mg L-1. detected and total number of compounds Summer (AMJ) 19.6 hr 0.89% detected in the river Cober and the Releath stream between spring 2016 and autumn 2018. Summer (JAS) 3.1 hr 0.14% The blue shading indicates a severity scale separately applied to each parameter, from light Hydrological year 74.2 hr 0.85% blue (low) to dark blue (high). Spring Autumn Spring Autumn Spring Autumn 16 16 17 17 18 18 Between two and seven different high concentrations; the usage of been detected in the River Cober chemicals were found at each Mecoprop is also consistent across (Autumn 2017 and 2018), but never R. Cober (Burras bridge) N/A N/A 15 5 8 11 location. Figure 5 shows a sites and deployment periods but in the Releath. This compound is R. Cober (Porkellis comparison between the Releath at lower concentrations. All of typically used on edible crops, and 15 11 16 3 10 9 Total number bridge) Stream and the River Cober. these compounds can be used in may therefore have been used on of detections The same chemicals are found grasslands, which represents one the 22% of the catchment in arable SWW asset - R. Cober 14 12 15 5 12 14 in both streams, highlighting of the main land use types in the land. Overall, this data is invaluable SWW asset - Releath their usage throughout the catchment. Metaldehyde (the active information for the Cornwall Wildlife 15 13 14 10 9 8 stream catchment. MCPA and Fluroxypyr ingredient found in slug pellets) Trust to target pesticide usage in the in particular are found in very is the only compound that has catchment. R. Cober (Burras bridge) N/A N/A 1 0 1 0 R. Cober (Porkellis 0 1 0 0 0 0 Exceedances bridge) over Spring hedge in Cornwall; 100 ng L-1 SWW asset - R. Cober 0 1 0 0 0 0 photo by Sue Hocking (CWT). SWW asset - Releath 0 0 0 0 0 0 stream R. Cober (Burras bridge) N/A N/A 132 1 197 3 Max R. Cober (Porkellis 92 153 29 1 57 2 concentration bridge) of individual pesticide SWW asset - R. Cober 40 110 4 11 9 2 (ng L-1) SWW asset - Releath 7 31 27 13 29 3 stream R. Cober (Burras bridge) N/A N/A 7 3 4 5 R. Cober (Porkellis 5 5 6 2 5 5 Total number bridge) of compounds SWW asset - R.