Spatial Variations in Nutrient and Particulate Matter Concentrations in Pyramid Lake, Nevada, USA, during a Dry Period

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Abstract
Spatial heterogeneity of nutrients, particulate matter, and chlorophyll were examined in Pyramid Lake during a dry period. In May 1991, variations in constituent concentrations were associat ed with shallow regions (chlorophyll), upwelling regions (nitrate), and river inflow (silicate and total P). However, only the spatial pattern of elevated silicate concentration near the mouth of the Truckee River was consistent throughout the year. Late-spring chlorophyll enrichment in shallow regions like the south basin appeared to be part of seasonal variations between the deep, central region of the lake and shallows possibly associated with light availability. During the study period, processes associated with strong winds appeared to be an important source of spatial heterogeneity. Profiles and spatial distributions of temperature and nitrate concentration during May 1991 indicated upwelling along the northwest and southwest margins of the lake. Examination of wind data for the region revealed that winds favorable for upwelling were common at Pyramid Lake, and temperature profiles along the north-south axis of the lake indicated additional upwelling events in June and September 1990. Strong winds also transport a large quantity of dust over the lake surface, which may be a major source of particle-bound P.