Nutrient dynamics in a subalpine wetland of California

Many wetlands in the Lake Tahoe Basin have been lost to development. The disturbed watershed has resulted in increased quantities of nutrients in the surface runoff that feeds Lake Tahoe, and has been directly linked to declining water quality in the lake. This study was conducted in the remnant wetlands of the Upper Truckee Marsh in the southern portion of the Lake Tahoe Basin in the Sierra Nevada Mountains of California. The region is characterized by cold winters and warm summers.; The main objective of the study was to determine the spatial and temporal behavior of nutrient concentrations in the surface and interstitial waters at Pope and Cove East which were once part of the contiguous Upper Truckee wetland system, and the relative influence that dominant plant species and varying water levels have on these concentrations. It also examined nutrient dynamics in a simulated subalpine wetland mesocosm. The measured nutrients, considered the most important to the eutrophication of Lake Tahoe, were nitrogen (N), phosphorus (P), and iron (Fe). The dominant wetland plants were Carex rostrata, Scirpus acutus, Nuphar polysepalum, and Juncus balticus.; Three transects were sampled running across the marsh towards the lake. The sampling sites corresponded to different dominant vegetation types. Interstitial water samples were collected by hand pump from perforated PVC pipes which acted as wells. Samples were obtained at different levels of the interstitial water.; Water level was the factor that most influenced nutrient behavior in the natural wetland, as well as in the wetland mesocosm. Aerobic and anaerobic conditions at the soil-water interface in both systems dictated the dynamics of almost every nutrient. Concentrations varied greatly between vegetation zones. The lowest concentrations for the most part implied seasonal removal. Iron behavior was influenced more by the local site-topography and sediment type than by the dominant plant species.; A mesocosm experiment was conducted to test the effect of flooding on redox potential and N, P and Fe behavior in a simulated subalpine wetland. Redox potential at {dollar}-{dollar}40 cm depth stayed low ({dollar}-{dollar}183 mV) during the whole period while at {dollar}-{dollar}10 cm and {dollar}-{dollar}20 cm it increased as the water level receded.; Natural and controlled wetlands are effective in reducing nitrogen, phosphorus, and iron in the Lake Tahoe Basin. The remnants of the Upper Truckee Marsh continues to play an important role in decreasing the amount of eutrophicating nutrients flowing into the lake's oligotrophic waters.