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TECHNICAL REPORTS

Landscape and Watershed Processes

Inorganic Nitrogen and Phosphorus in Sierran Forest O Horizon Leachate

^a Hydrologic Sciences Program, College of Agriculture, Biotechnology, and Natural Resources, Univ. of Nevada, Reno, NV 89512
^b Dep. of Natural Resources and Environmental Science, College of Agriculture, Biotechnology, and Natural Resources, Univ. of Nevada, Reno, NV 89512
^c Dep. of Natural Resources and Environmental Science, College of Agriculture, Biotechnology, and Natural Resources, Univ. of Nevada, Reno, NV 89512

^* Corresponding author (wilymalr{at}cabnr.unr.edu)

Received for publication December 19, 2005. High in situ concentrations of inorganic N and P have been reported in overland/litter interflow from Sierran forests, indicating that these nutrients are derived from the forest floor O horizons. To test this hypothesis, forest floor monoliths consisting of the combined O_e and O_i horizons were collected near the South Shore of Lake Tahoe, Nevada, for leaching experiments. Three monoliths were left intact, and three were hand-separated according to horizon for a total of three treatments (combined O_e+O_i, O_e only, and O_i only) by three replications. Samples were randomized and placed into lined leaching bins. Initial leaching consisted of misting to simulate typical early fall precipitation. This was followed by daily snow applications and a final misting to simulate spring precipitation. Leachate was collected, analyzed for NH₄⁺–N, NO₃^––N, and PO₄^3––P, and a nutrient balance was computed. There was a net retention of NH₄⁺–N, but a net release of both NO₃^––N and PO₄^3––P, and a net release of inorganic N and P overall. Total contributions (mg) of N and P were highest from the O_e and O_e+O_i combined treatments, but when expressed as per unit mass, significantly (p < 0.05) higher amounts of NO₃^––N and PO₄^3––P were derived from the O_i materials. The nutrients in forest floor leachate are a potential source of biologically available N and P to adjacent surface waters. Transport of these nutrients from the terrestrial to the aquatic system in the Lake Tahoe basin may therefore play a part in the already deteriorating clarity of the lake.