DIFFUSE NUTRIENT LOADING FROM AGRICULTURAL LANDS ALONG THE LUGA RIVER, LENINGRAD REGION

The study aimed to compare the calculated and directly measured total nitrogen input from farm fields into the water bodies exposed to crop-growing practices and livestock facilities in place. The study applied an IEEP-designed model for diffuse loading calculation. The study area was a dairy farm with 2100 head of animals and 2000 ha of fields, located in the Luga River catchment, the Leningrad Region. 40 ha were selected for elementary plots. The geoinformation systems served to identify the watercourses from the fields into the river and the water sampling points for measuring the concentration of total nitrogen and nitrate nitrogen. The calculations by the model showed the average specific nitrogen runoff from the fields was 44.96 kg ha(-1). The monitoring data analysis revealed the Kjeldahl total nitrogen content in the water varying from 1.4 to 3.1 mg (dm(3))(-1), and the nitrate nitrogen content-from 2.28 to 9.1 mg (dm(3))(-1) depending on the season and precipitation. The calculation of the monitoring data demonstrated the inputs of total nitrogen from farm fields into watercourses ranging from 35.24 to 36.84 kg ha(-1). Comparing the nitrogen runoff data, calculated by the model and directly measured by the nitrogen concentrations in watercourses, disclosed a discrepancy in the study territories from 17 to 21% explained by several factors. In general, the study demonstrated sufficient convergence, with certain assumptions, of two methods for identifying the nitrogen inputs into water bodies. The direct measurements method is hard to apply to large catchments. The method of IEEP is designed mostly for analysing the nutrient inputs from vast territories to form a comprehensive overview of current and forecast situations without taking into account specific places with possible violations. This method focuses on the elaboration and introduction of strategic measures for environmentally sustainable rural development.