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Surface Water and Groundwater Nitrogen Dynamics in a Well Drained Riparian Forest within a Poorly Drained Agricultural Landscape
Citation:
Davis, J. H., S. M. Griffith, AND P. J. WIGINGTON JR. Surface Water and Groundwater Nitrogen Dynamics in a Well Drained Riparian Forest within a Poorly Drained Agricultural Landscape. JOURNAL OF ENVIRONMENTAL QUALITY. American Society of Agronomy, MADISON, WI, 40:505-516, (2011).
Impact/Purpose:
The effectiveness of riparian zones in mitigating nutrients in ground and surface water depends on the climate, management and hydrogeomorphology of a site.
Description:
The effectiveness of riparian zones in mitigating nutrients in ground and surface water depends on the climate, management and hydrogeomorphology of a site. The purpose of this study was to determine the efficacy of a well-drained, mixed-deciduous riparian forest to buffer a river from N and P originating from a poorly-drained grass seed cropping system. The study site was adjacent to the Calapooia River in the Willamette Valley, Oregon, USA. Water was found to move from the cropping system to the river through the slow movement of groundwater and also through the rapid drainage of surface water through an intermittent stream in a swale that cuts through the site. Low groundwater NO3- concentrations (0.2-0.4 mg NO3- -N L-1) in the surface piezometers of the cropping system were associated with low rates of mineralization and nitrification (0.10 kg N ha-1 d-1) and high amounts of plant uptake of N (155 kg N ha-1 y-1). The cropping system surface soil and sandy, well-drained riparian forest soil profile were predominantly aerobic, reducing the potential for removal of NO3- through denitrification while increasing the removal of soluble PO4- from groundwater through precipitation reactions. The riparian forest had higher rates of mineralization (0.32 kg N ha-1 d-1) that produced quantities of soil N that were within range of plant uptake estimates, leading to relatively low concentrations of groundwater nitrate (0.6-1.8 mg NO3- -N L-1). During winter hydrological events, the riparian forest receives river water, giving this system the potential to not only influence nutrient concentrations in groundwater from conterminous agricultural landscapes but also from river water that contains nutrients from agricultural lands higher in the basin. The swale was found to have the highest rates of denitrification on site and to contribute total phosphorus and dissolved organic carbon to the river. Given the dynamic nature of the hydrology of our Calapooia River site, our data suggest the riparian forest plays a role not only in reducing export of nitrate and phosphorus from the CS to the river, but also in processing nutrients from river water.