The objective of this study was to evaluate the nitrogen (N) biogeochemistry of an 18-22 year old forested watershed in western Maryland. We hypothesized that this watershed should not exhibit symptoms of N saturation. This watershed was a strong source of nitrate (NO 3 À ) to the stream in all years, with a mean annual export of 9.5 kg N ha À1 year À1 and a range of 4.4-18.4 kg N ha À1 year À1 . During the 2001 and 2002 water years, wet deposition of inorganic N was 9.0 kg N ha À1 year À1 and 6.3 kg N ha À1 year À1 , respectively. Watershed N export rates in 2001 and 2002 water years were 4.2 kg N ha À1 year À1 and 5.3 kg N ha À1 year À1 , respectively. During the wetter water years of 2003 and 2004, the watershed exported 15.0 kg N ha À1 year À1 and 18.4 kg N ha À1 year À1 , rates that exceeded annual wet deposition of N by a factor of two (7.5 kg N ha À1 year À1 in 2003) and three (5.5 kg N ha À1 year À1 in 2004). Consistent with the high rates of N export, were high concentrations (2.1-3.3%) of N in foliage, wood (0.3%) and fine roots, low C:N ratios in the forest floor (17-24) and mineral soil (14), high percentages (83-96%) of the amount of mineralized N that was nitrified and elevated N concentrations (up to 3 mg N l À1 ) in soil solution. Although this watershed contained a young aggrading forest, it exhibited several symptoms of N saturation commonly observed in more mature forests.
Abstract. Land cover and land use changes can substantially alter hydrologic ecosystem services.Water availability and quality can change with modifications to the type or amount of surface vegetation, the permeability of soil and other surfaces, and the introduction of contaminants through human activities. Efforts to understand and predict the effects of land use decisions on hydrologic services-and to use this information in decision making-are challenged by the complexities of ecosystem functioning and by the need to translate scientific information into a form that decision makers can use. Hydrologic modeling coupled with scenario analysis can (1) elucidate hydrologic responses to anticipated changes in land use and (2) improve the utility of scientific information for decision making in a manner that facilitates stakeholder involvement. Using a combination of general concepts and concrete examples, this paper summarizes hydrologic consequences of land use changes and describes the use of modeling and scenario analysis to inform decision making. Two case studies integrate the concepts raised in the paper and illustrate how an approach employing modeling and scenario analysis offers a potentially powerful way to link research on hydrologic services with decision making.
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