River Yealm Water Quality Group
1. Historic analyses of water quality
Historic analyses of water quality data archived by the Environment Agency (EA) and the Centre for Environment, Fisheries and Aquaculture Science (CEFAS) have been undertaken by the RYWQG including in collaboration with the University of Plymouth to better understand how pollutants as have included tributyl tin from antifouling paints, suspended sediments from quarrying and other activities, bacterial markers of faeces (i.e. Escherichia coli) from land run off and sewage, phosphate, nitrate, metals and hydrocarbons have each varied throughout our catchment over the past 20 years.
Tributyl tin
Data show how concentrations of tributyl tin (TBT) sampled in water at the bottom of estuary off Warren Point from 1999 to 2019 remained high (> 0.01 μg/l) for at least 12 years after exceptionally toxic effects on marine life had been identified in the early 1980’s; but which concentrations, in response to the prohibition of TBT paints, have since fallen well below recommended environmental quality standards (< 0.002μg/l).
Suspended solids
Concentrations of suspended solids sampled in water at Puslinch Bridge from 2007 to 2021 averaged (± 95% confidence interval) 23.00 ± 4.00 mg/l. This long-term average is statistically (p < 0.05) similar to the EU Freshwater Fish Directive’s Guideline Standard of 25 mg/l used by the Environment Agency to help set controls on discharges of inorganic material from quarries, open caste coal sites, and mines.
Bacterial markers of faeces
Average values for bacterial markers of faeces (i.e. Escherichia coli) in the lower reaches of the river at Puslinch Gauging Station from 2007 to 2021 were consistently and very significantly (p<0.05) above “sufficient” Environment Agency water quality environmental thresholds for inland bathing waters, associated classifications being “Poor”, with no improvement over the past two decades, and with established detriment to local shellfish industry, produce requiring significant treatment before being marketed.
Nitrates and phosphates
Further analyses were undertaken during 2024 in collaboration with University of Plymouth, studying historical data extracted from the Environment Agency archive for nine stations throughout the Yealm catchment. Findings suggest how the EUs 1991 Nitrate Directive, followed by Water Framework Directive, acted to reduce nitrate pollution by limiting agricultural practices as include applications of manure and inorganic fertiliser, following which, we can see a clear decrease at most sites over the past 20 years. Phosphate, on the other hand, has certainly not decreased over the same 20 years, when it has regularly exceeded the consensual USL of 1 mg/l (as defined by the U.S. Environmental Protection Agency 1986).
See reports on historic perspective:
EA Water Quality Archive results downloaded to show concentrations of Escherichia coli from 2007 to 2024, at three sites: Hele Cross towards the top of River Yealm and Puslinch Gauging Station towards the bottom of River Yealm, plus Kitley Lake outflow from Silverbridge tributary that feeds the estuary further below. The horizontal red line denotes the Environment Agency water quality environmental threshold for inland bathing waters of 900 cfu/100ml, above which threshold the associated classification is “Poor” (Hawkins 2021).
2. "Yealm Dippers” Westcountry Rivers Trust Citizen Science Investigation
To date, analyses of findings from Yealm Dippers measures as part of the WRT CSI, taking monthly water quality measures at key sites that include each significant tributary, thereby monitoring background water quality throughout the Yealm catchment, suggest the following:
a) Throughout the River Yealm catchment, phosphate represents a general benchmark upon which to improve.
b) Widespread concentration of phosphate and total dissolved solids at times of low water level, in the absence of rainfall and associated land runoff, places a priority on reducing relatively continuous inputs such as from industry and/or sewage.
c) To aid the conservation of the Atlantic Salmon in known historic spawning and rearing habitats, there is a need to reduce inputs from industry, sewage and/or surface runoff to (i) the River Piall; (ii) Lee Mill Stream, compromising lower reaches in the main channel of River Yealm; and (iii) the main channel of River Yealm between The Borough and Puslinch Bridge, spanning Yealmpton sewage works.
d) There is an urgent need to identify and act upon sources contributing to exceptional levels of phosphate and total dissolved solids in Newton Stream.
e) There is a need to identify and act upon sources or activities contributing to high levels of phosphate in the upper reaches of Silverbridge Lake Stream, including for high temperature in the middle reaches and high total dissolved solids in the lower reaches.
f) There is widespread potential to reduce inputs that appear most likely to be associated with surface runoff in Coffin Stream, Wembury Stream, Long Brook Stream, Ridgecott Lake Stream, Noss Mayo Stream, Brook Lake Stream and Cofflete Stream.
See report of data analyses identifying pollution hotspots and required actions:
3. Continuous Water Monitoring
Purchased by the RYWQG in January 2023, the “Yealm Sonde” is an In-Situ AquaTROLL 600 which, combined with an In-Situ VuLink CI cellular unit, automatically transmits data defining river water quality measured every 15 minutes for remote storage and viewing, informing upon the river’s chemistry and physics, also sending immediate SMS alerts of pollution events that enable citizen scientists to undertake event sampling, towards identifying sources.
Data from the “Yealm sonde” has provided an excellent baseline of the response of the Yealm catchment to changes in hydrology, recording seasonal variations in measured water quality parameters that are generally in line with expected concentrations and levels for the catchment’s geology and location.
Events observed are varied – some driven by natural processes and some by anthropogenic influences. Events included relatively short-lived (4 to 5 hour duration) spikes in concentration (e.g. dissolved solids); as well as prolonged deviations from baseline values (e.g. pH), regular, more rhythmical trends (e.g. the diurnal oxygen cycles) through to sporadic increases that appear uncoupled from depth/rainfall (e.g. turbidity). Such observations suggest a complex catchment with many factors contributing to the overall water quality signal with time.
Future work to expand knowledge of the catchment response could include additional automated monitoring units placed on main tributaries further upstream, to pinpoint more accurately where the sources of pollution are, and how these are diluted with time and distance from the source. CSI measures are already being undertaken at strategic locations upstream and for the collection of further data that are not possible to capture using the sonde (e.g. phosphate, photographs and other contextual information).
See the report of first years findings from the “Yealm Sonde”:
Live data recorded by the "Yealm Sonde" every 15 minutes are shared online every 4 hours with the EA and other organisations, as may be seen with interactive options to view separate measured parameters and timelines here.
Alternatively, a summary of recordings by the "Yealm Sonde" over the past 7 days is illustrated below:
Summary of recordings undertaken every 15 minutes by the "Yealm Sonde" over the past 7 days, updated here every 4 hours. DO = dissolved oxygen (mg/l).
4. Riverfly survey
Aquatic insects known as riverflies are at the base of the food chains for many river species. To provide a recognised measure of ecological health, in partnership with WildFish’s SmartRivers Riverfly Census, “Yealm Dippers” are surveying riverfly diversity and abundance throughout our catchment.
Findings are being mapped against our coincident WRT CSI measures of river water quality to establish associated ecological impact, thus informing the selection of priority sites to protect and restore. Our data also contribute to WildFish’s national SmartRivers programme, whilst providing a baseline with potential to establish ecological benefits of remediative actions through our catchment.
To date, this project has sampled 6 strategic sites starting in Autumn 2023, with plans to repeat annually in both spring and autumn at those same sites for a minimum of 3 years.
See the first riverfly monitoring report:
