Our monitoring of the water quality in the Water Friendly Farming project study catchments is now providing an insight into some important issues. Phosphorus is the main nutrient limiting plant growth in water, and the reason for the failure of many watercourses to meet water quality targets. It can come from farmland, where it is associated with eroded soils, or from domestic sources such as sewage treatment works or septic tanks. Pesticides are mainly of concern for drinking water supply, the most problematic being Metaldehyde (from slug pellets) as this cannot be removed by currently available water treatment methods. We are monitoring both phosphate and Metaldehyde as part of the Water Friendly Farming project.
Phosphorus
In each of the three catchments, our periodic sampling of water from tributaries over the past year reveals that the highest phosphorus concentrations are associated with the tributary containing a sewage treatment works. This is most prominently the case for the Eye Brook (graph below), but in each of the other two catchments the phosphorus concentration in the tributary with the sewage treatment works is at least twice that of the other tributaries, making a substantial impact on the quality of water at the base of the catchment.
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| Total phosphorus concentrations in the upper Eye Brook, the end of the catchment, and three tributaries, includig one with a sewage treatment works (Means of 18 samples taken over 12 months). |
This is a reminder that, even in agricultural catchments, all residents are having an impact on water quality. We are drawing up plans for a local campaign to reduce the use of phosphate-based washing products, an action that can reduce phosphate discharge by up to about 20%.
Farming remains an important contributor of sediment and associated phosphorus, mainly through the loss of soil to water, and the farming community across the upper Eye Brook and Stonton Brook catchments is active in taking steps to reduce both loss of soil and nutrients to water.
Metaldehyde
Regulation of drinking water supply sets an arbitrary limit of 0.1 micrograms of pesticide per litre of water, regardless of any risk to the environment or human health. As well as monitoring Metaldehyde at the base of two of the project catchments, when it rained we also collected samples from field drains, potentially an important pathway by which pesticides move from arable land to watercourses. Our sampling was carried out during the autumn when slug pellets are widely used on crops.
Metaldehyde concentrations at the base of each catchment exceeded the limits set for drinking water supply. As it was such a wet autumn across the country, this is much the same as for many other streams nationally. In field drains, the concentration was much lower, with the exception of one drain which was very variable and reached much higher concentrations (graph below).
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| Autumn Metaldehyde concentrations at the base of two catchments, and in field drains during rain. |
This suggests that perhaps field drains are not routinely the main pathway by which Metaldehyde reaches water. The one occurrence of high concentrations may have resulted from inaccurate placement or spillage and numerous small incidents such as this, whether involving surface runoff or drains, may be what is causing the drinking water limits to be exceeded. Alternative products to Metaldehyde are either much more expensive or have proven negative impacts on wildlife, including beneficial invertebrates such as earthworms and pest predators. Responsible use of Metaldehyde provides the best option for farm businesses, for food production and for the environment.
