Influence of catchment characteristics,forestry activities and deposition on nitrogen export from small forested catchments |
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| Authors: | Ahti Lepistö Lotta Andersson Berit Arheimer Karin Sundblad |
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| Institution: | 1. Finnish Environment Agency, P.O. Box 140, FIN-00251, Helsinki, Finland
2. Department of Water and Environmental Studies, Link?ping University, S-58183, Link?ping, Sweden
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| Abstract: | The ability to predict nitrogen export from forested catchments is essential in order to evaluate the effects of anthropogenic activities on the trophic status of lakes and sea areas, and to extrapolate the results to catchments from which no measurements are available. Data from 20 forested catchments (0.3–42 km2) in Finland and Sweden during the 10-year period 1979–88 were used to develop empirical multivariate regression models of average NO3-N, NH4-N and organic N export fluxes as a function of geomorphological, meteorological, hydrological, deposition and forest management variables. A combination of high inorganic N deposition or air temperature and a low extent of organic soils was related to (R2 = 0.64) high losses of NO3-N. A strong correlation between N deposition and air temperature makes it difficult to distinguish the effects of one variable from the other. Retention of deposited nitrogen is still high in most of the catchments. High losses of NH4-N had the strongest correlation with forestry activities and stream density. A combination of drainage percentage and temperature was related to (R2 = 0.53) losses of NH4-N. The most important factors explaining spatial variability of organic N losses were clearly forestry activities. A combination of high percentage of drainage and clear-cutting was related to (R2 = 0.81) high organic N losses. However, within the catchments, large-scale forest management practices were needed before any clear effect on spatial variability was detected. All the equations obtained were influenced by the choice of a limited number of catchments. No causal relationships between losses and the explaining variables can be inferred from this type of study. |
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