科研之友
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摘要
Water connectivity in the hillslopes of the upland-riparian zone has environmental implications for stream nitrate-N (NO3 (-)-N) export during rain events. This study was conducted to measure the shallow groundwater table over a hillslope with upland, interface, and riparian forest components and measure the stream NO3 (-)-N concentrations in a 36.6 km(2) agricultural and forested watershed (AFW) in the Shibetsu area of northern Japan from July to November 2009. The groundwater and stream hydrographs at seasonal and rain event scales indicated that the hillslope water connectivity was first established from the riparian forest, and then expanded to the upland after several rain events. The hillslope water connectivity has important implications for NO3 (-)-N export in the watershed since the NO3 (-)-N export may primarily be explained by a flushing mechanism. The NO3 (-)-N export only flushed from riparian forest during the early water connection stage. While in the well water connection stage, the flush of NO3 (-)-N occurred with the subsurface flow from the upland which had a high shallow groundwater table and displayed higher stream NO3 (-)-N concentrations. However, lower stream NO3 (-)-N concentrations occurred during the late water connection stage and indicated that the N source in the upland might be limited due to denitrification and NO3 (-)-N leaching processes. Nevertheless, it was decided that the hydrology and biogeochemical reactions occurring in the upland controlled the stream NO3 (-)-N export. A conceptual model was formulated that explained the impacts of the hillslope water connectivity on the watershed stream NO3 (-)-N export during rain events in early, well, and late water connection stages within the AFW.
