WaterProtect team in the Irish Action Lab has developed a new multi-dimensional approach for monitoring the fate of agricultural herbicides and applied it in two river catchments in County Wexford – Ballycanew and Castledockerell.
Following application and beyond their action on weed plants, herbicide degradation and transport to surface and ground water is controlled by a variety of factors including the physical and chemical characteristics of soil-subsoil-bedrock, land use, management practices, timing of herbicide application and prevailing environmental conditions. The monitoring for herbicides only a few times per year in rivers or groundwater may not provide enough data to assess environmental or human health risks.
Under the lead of the two new members of the Irish Action Lab, Majid Khan and Fabiola Barros Costa, the team have looked into a monitoring approach that addressed all these factors. A suite of herbicides were monitoring in rivers using passive samplers that captured all flow conditions over a 1-year period, and 95 private drinking water wells of groundwater source were sampled. This was undertaken in grassland and arable land use settings in two river catchments in County Wexford. The passive samplers were first installed in streams at outlets of the two catchments at the start of November 2018 and the monitoring is on-going to date. These samplers are deployed and removed on a fortnightly basis and provide time-weighted average of herbicide concentration over the deployment period.
The dataset on seasonal and temporal variability of herbicides in water provide information on how herbicide inputs in water are controlled by physical and hydrological conditions within the two catchments. This type of information is needed to understand the dynamics of water quality and to design multi-actor and collaborative mitigation measures to reduce herbicide losses to water. Future strategies need to consider risky areas and risky times for the application of herbicides (and all pesticides) to minimise both incidental losses and build-up of stores in soils. This multi-dimensional and whole catchment approach provides a detailed assessment of herbicide fate on agricultural land. The method can be used wherever pesticides are an unintended pollution problem and the datasets can be used as important knowledge exchange resources.
Launching a new monitoring campaign
Using this whole catchment approach, the Irish Action Lab will lead a new monitoring campaign in the two catchments. Small sub-catchments and sampling locations have been identified along the streams. In those sites passive samplers will be installed in early June, the peak time of herbicide application and when concentrations of herbicides in the streams are at its highest. The results will provide a better understanding of the temporal and spatial variability of drivers and controls for loss of pesticides to water.