Monday, 7 November 2005
7

Dynamics of Soil Nitrogen Cycling Affected by Moisture Levels in Wetlands of the New Jersey Pinelands (Usa): a Laboratory Incubation Experiment.

Shen Yu1, Jean-Christophe Clement2, and Joan Ehrenfeld1. (1) Rutgers University, 14 College Farm Road, New Brunswick, NJ 08901, (2) West Virginia University, 53 Campus Drive, Morgantown, WV 26506

Water withdrawals for human use can alter soil moisture conditions in wetlands, with potential effects on nitrogen cycling processes. Wetlands in the New Jersey Pinelands are maintained by a groundwater aquifer, and thus may be sensitive to such changes. A 30-week microlysimeter laboratory incubation was conducted on soils from four stands (an upland pine stand, a pine wetland, a pine-hardwood wetland, and a cedar swamp). Replicate microcosms of mineral soils (pine-upland, pine-wetland and pine-hardwood) and organic soils (cedar swamp) were maintained at three moisture levels (saturated, 60% and 30% water-holding capacity). Surprisingly, only the organic soil differed significantly in N cycling at different moisture levels. Net mineralization and nitrification rates increased with decreasing moisture, and the soil accumulated more ammonium and nitrate. Mineral soils from the pine-upland and pine-hardwood wetland had similar net mineralization rates (409±30 and 403±6 mg N m-3 DM day-1, respectively), which were significantly higher than the rates in the organic soil (316±134 mg N m-3 DM day-1) and the mineral soil from the pine wetland (226±28 mg N m-3 DM day-1). Net nitrification rates were highest in the organic soils held at 30% and 60% water-holding capacity (83 and 114 mg N m-3 DM day-1, respectively) compared with the mineral soils. But the saturate organic soil had a very low net nitrification rate (9 mg N m-3 DM day-1), which is similar to all mineral soils with net nitrification rates below 10 mg N m-3 DM day-1 regardless of moisture levels. Principle component analysis showed a similar pattern for both N fractions and N cycling processes. The results suggest that changes in soil moisture in cedar swamps due to water withdrawals could result in elevated production of nitrate and nitrate leaching to surface waters.

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