The long-term results of the Agricultural Runoff Monitoring programme in Latvia

The Agricultural Runoff Monitoring Programme has been implemented in Latvia since 1995 until present. Water quality monitoring activities along with hydrological measurements are carried out at subsequent spatial scales including groundwater (20 wells), experimental plots (1 site with 16 plots), subsurface drainage fields (6 sites), small catchments (10 sites), small and medium size rivers (23 sites). The main objective of the programme is to document and assess the current status and long-term changes in nitrogen concentrations and losses as affected by natural and anthropogenic factors.

Water samples are collected on a monthly basis using a grab sampling approach or composite flow proportional sampling where discharge measurement structures and data loggers are installed. Water samples are analyzed for nitrogen and phosphorus compounds according to the national standards.

The study results show a large variation in NO3-N concentrations among the spatial scales of monitoring with the lowest mean annual concentrations in groundwater (below 1.0 mg l-1) and the highest in the discharge from subsurface drainage fields and experimental plots (over 7.0 mg l-1). Overall, NO3-N concentrations follow the patterns of discharge having the highest concentrations during high flow conditions in winter and spring, while the lowest concentrations during low or no flow conditions in summer and autumn. These patterns highlights the great importance of subsurface and surface drainage systems, which act as pathways for transport of excess water and soluble forms of nitrogen from agricultural fields to surface waters.

It is essential to continue activities within the Agricultural Runoff Monitoring Programme also in the future, especially in the light of need to quantify changes in water quality as related to implementation of the Farm to Fork strategy aiming to reduce the use of fertilisers by at least 20% and nutrient losses by at least 50% by 2030.