Examination of the Dissolved Inorganic Nitrogen Budget in Three Experimental Microbasins with Contrasting Land Cover-A Mass Balance Approach

摘要

A long-term hydrological and water chemistry research was conducted in three experimental microbasins differing in land cover: (1) a purely agricultural fertilized microbasin, (2) a forested microbasin dominated by Carpinus betulus (European hornbeam), and (3) a forested microbasin dominated by Picea abies (L.) (Norway spruce). The dissolved inorganic nitrogen (DIN: NH_4~+, NO_2~-, NO_3~-) budget was examined for a period of 3 years (1991-1993). Mean annual loads of DIN along with sulfate SO_4~(2-) and base cations Ca~(2+), Mg~(2+), Na~+, K~+, and HCO_3~-were calculated from ion concentrations measured in stream water, open-area rainfall, throughfall (under tree canopy), and streamwater at the outlets from the microbasins. Comparison of the net imported/ exported loads showed that the amount of NO_3~-leached from the agricultural microbasin is ～3.7 times higher (43.57 kg ha~(-1) a~(-1)) than that from the spruce dominated microbasin (11.86 kg ha~(-1) a~(-1)), which is a markedly higher export of NO_3~- compared to the hornbeam dominated site. Our analyses showed that land cover (tree species) and land use practices (fertilization in agriculture) may actively affect the retention and export of nutrients from the microbasins, and have a pronounce impact on the quality of streamwater. Sulfate export exceeded atmospheric rainfall inputs (measured as wet deposition) in all three microbasins, suggesting an additional dry depositions of SO_4~(2-) and geologic weathering.