Dynamics of nitrogen and phosphorus budgets in riparian buffer zones.
ABSTRACT- Our studies on changes of N and P budgets in experimental riparian grey alder forest plots in Estonia since early 1990s consider main inputs and outputs of N (atmospheric deposition, lateral surface and subsurface flow, N2 fixation, N2O and N2 emission) as well as accumulation in plant biomass, litter and soil. Due to the stopping of agricultural activities in the upslope agricultural fields in 1992, the lateral inflow of N by groundwater and overland flow has been decreased from >50 to 25.6 kg N ha-1 yr-1. Recent investigations suggest that the decrease continues. However, the outflow has not been changing significantly, being about 10-13 kg N/(ha*yr). The N2 emission has increased from 51.2 in 1995 to >300 kg N/(ha*yr) in 2003. This change that results in decrease in soil N pool can be explained with forest succession and relevant change in bacterial communities. Further studies on relationship of CH4, CO2, N2 and N2O emissions will provide with more information on potential of greenhouse gas fluxes in riparian ecosystems. Considering all inputs and outputs, the N and P removal efficiency in grey alder stands seems to slow down with increasing stand/tree age. In the same time, immobilization of N in soil is increasing. This suggests that grey alder buffer communities should be managed by regeneration cutting. It removes part of nutrients and helps to keep N and P removal rate high.
Key words: denitrification, grey alder, nutrients, riparian forest
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