Nutrient Cycling Processes Along the Sierran Front to the Cascades

Abstract

<bold>ABSTRACT</bold>Previous research has identified a corresponding relationship between O horizon accumulation and high concentrations of N and P in overland/litter interflow leachate. This nutrient rich leachate can discharge directly into surrounding tributaries in the form of surface runoff or infiltrate into the soil matrix via preferential flow paths. The presence of seasonal preferential infiltration in forested Sierran soils is now well documented, but less known is whether or not the preferential infiltration of nutrient laden percolate results in the development of isolated nutrient "hot spots" in the underlying mineral soil. The purpose of this investigation was to assess the spatio-temporal dynamics of nutrient cycling in sub-alpine forest soils along the Sierran front northward to the Cascades. Large quantities of nutrients were found to reside in the O horizon, leaching at mostly unknown locations into the soil matrix; varying with total water flux and retention time. Nutrient rich "hot spots" were also found under natural conditions, but rarely occurred at the same sampling point for two consecutive years, fluctuating seasonally and annually. Only four of the 256 resin capsule grid points (1.5%), one of 96 first fall precipitation capsule grid points (0.01%) and one of the 128 resin lysimeter grid points (0.78%) exhibited similar trends over both years. Nutrient infiltration variability and sporadic distribution of "hot spots" may facilitate excessive nutrient loading into hydrologic systems and the opportunistic advancement of invasive plant species to out-compete natives. The proper understanding of nutrient cycling dynamics in forested ecosystems is essential for sustaining historical landscape attributes. Key Words: <italic>nutrient cycling, sub-alpine forests, hydrologic, water quality</italic>