The Effects of Meteorological and Hydrological Conditions on Nutrient Losses from Agricultural Areas in Latvia

Abstract Water quality in any stream is affected by complex interactions between natural and anthropogenic factors in a given catchment area. Agriculture has been identified as a major contributor of nitrogen and phosphorus inputs to surface waters in the Baltic Sea region. Although decisions regarding agricultural management practices, e.g. crop rotation, tillage, fertilization, have a direct impact on likelihood and magnitude of nitrogen and phosphorus losses from agricultural areas to surface waters, natural factors such as meteorological and hydrological conditions have a triggering role in processes determining transformations, storage, uptake and losses of nutrients. In order to investigate the effects of meteorological (precipitation and air temperature) and hydrological (runoff) conditions on water quality (losses of total nitrogen (TN) and total phosphorus (TP)) the results of the Agricultural Runoff Monitoring Programme collected at three monitoring sites (Berze, Mellupite, and Vienziemite) during the time period of 1995–2020 were summarized and analysed. The pronounced differences in mean annual air temperature and annual precipitation were observed when the meteorological information representing the periods of twenty years was compared indicating for evidences of climate change. In addition, the relationships between seasonal precipitation and runoff was detected. As affected by the hydrological behaviour the losses of TN and TP in agricultural catchments had large variations depending on the intensity of agricultural production and site location. The changes in seasonal and annual patterns of precipitation, air temperature and runoff may increase the risks of nutrient losses from agricultural catchments in the future.