The influence of catchment land cover on phosphorus balance for large freshwater systems

A load assessment method applicable to catchments with multiple land cover types was studied using a mathematical model of phosphorus balance for the Lake Ladoga and the Neva Bay freshwater systems (an area of about 280,000 km²). The calculation of phosphorus load included both point and nonpoint sources of loading, as well as phosphorus retention in receiving waters. The decreasing agricultural land use area for the Russian part of the studied area was documented and its effects on water quality demonstrated. The importance of Lake Ladoga in retaining total phosphorus (P _tot ) from upstream reaches and preventing phosphorus export into the already anthropogenically eutrophied Neva Bay was demonstrated. For the largest urban area in the studied region (St. Petersburg), municipal wastewater inputs in the Neva Bay were assessed using historic data and planned future wastewater treatment facilities.

Keywords: Phosphorus balance; point and nonpoint sources; phosphorus retention; wastewater treatment