Ecohydrological research of lake-watershed relations in diversified landscape (Masurian Lakeland, Poland)

The postglacial, hilly-moraine, lowland landscape that dominates in the lak eland region of northeastern Poland (Masurian Lakeland) is highly diversifi ed in terms of land forms (hills, ridges, outwash plains, land depressions, steep slopes), land use and cover (mosaic pattern of different sites, vege tation patches, and arable land), and geological substrate (surface deposit s of different permeability in respect to precipitation infiltration). The stream network and wetland patches dispersed among the fields and wetland z ones close to lake shores play a crucial role in transport and transformati on of nutrient compounds before they eventually reach the lake ecosystems. The river Jorka watershed (area about 65 km(2), length of river about 15 km , discharge between 0.1 and 1.5 m(3) s(-1)) contains a typical fragment of lakeland area, with a highly mosaic structure. Precipitation, discharge in 11-17 small streams, nitrate-nitrogen and total phosphorus loading transpor ted in streams, and changes in their concentration while passing through la keshore wetland zones were studied over several years and seasons (vernal f reshet, summer drought). There was no trend in seasonal and year-to-year ch anges of TP and N-NO3 concentration while transported with stream waters an d no direct relation to discharge. The most frequent range of values of con centration for TP and N-NO3 were 0.08-0.5 and 0.1-0.8 mg l(-1), respectivel y. The export rates for both nutrients were higher in spring than in summer . The vernal freshet was found to be the most important hydrological event that stimulated the transport of phosphorus and nitrate-nitrogen in surface waters and sustained an adequate moisture condition in wetland zones to re move both nutrients transported with groundwaters. It was found that the co ncentration of both nutrients in that period significantly decreased toward s the lakeshore, particularly in the case of nitrate-nitrogen. In the summe r (drought period) there was a significant decrease of dissolved phosphorus but no change in the case of nitrate-nitrogen. The consequences of these p henomena for lake protection zones are emphasised. (C) 2000 Elsevier Scienc e B.V. All rights reserved.