Factors which shape the load of water ecosystems with mineral nitrogen runoffs in rural areas

The present study of factors which affect the load of water ecosystems with mineral nitrogen compounds (N-NH₄ and N-NO₃) was conducted in the Olsztyn Lake District and covered the time period from 1992 to 1999. Three capture basins were investigated: agricultural drained with a drain network, agricultural drained with a drainage ditch, and agricultural-forested drained with scattered drains and ditches. It was found that the concentration and load of mineral forms of nitrogen in waters running off from rural areas were closely dependent on meteorological conditions, the kind of artificial drainage system in use, and the type of land use in the catchment area. In waters carried away through the drainage systems, average annual concentrations of N-NH₄ ranged from 0.16 mg dm^-3 (the agricultural capture basin drained with ditches) to 1.09 mg dm^-3 (the agricultural catchment drained with a network of drains); the amounts of N-NO³ ranged from 0.29 mg dm^-3 (the agricultural-forested catchment) to 8.06 mg dm^-3 (the agricultural catchment drained with a network of drains). It was also observed that a larger share of arable lands in the land use structure in a given catchment caused an increase in the load of N-NO₃ determined in drained waters. In addition, it was confirmed that the amounts of mineral nitrogen carried away with drained waters annually varied from 12.78 kg N (6.7 kg N on average) per 1 ha of an agriculturally used catchment, of which N-NO₃ was a dominant form (12.23 kg).