Research Program Area: Ecosystem & Multimedia Effects
The objectives of the Soils Processes research at Emerald Lake Watershed were to assess physical, chemical and biological processes contributing to the production or consumption of acidity in soils and to assess the net effect of soil processes on surface water quality in an alpine watershed. The ELW consists of a high elevation lake in a subalpine to alpine Sierra Nevada landscape. The soils found in ELW are typical of those found throughout the Sierra Nevada and are shallow and rocky. However, these soils do support subalpine to alpine vegetation.
Most of the N and S in ELW soils is stored in organic forms. Most of the soil P is present in nearly insoluble mineral forms. The ELW soils can adsorb only small quantities of sulfate thus, their capacity for buffering acid additions by sulfate adsorption is also fairly low. Concentrations of Al, Ca, Mg, K, and Na in both soil solution and stream samples reflected patterns of mineral weathering in the watershed. Calculations showed that bicarbonate alkalinity resulted from mineral weathering in that the major basic cations (Ca2+, Mg2+, K+, Na+) were primarily in their free ionic form. Rainfall and throughfall collected during four precipitation events in 1985 showed that evergreens (pine and chinquapin) tended to contribute many substances to throughfall including Al while willows apparently removed N compounds. Organic acids were a very important part of throughfall solution chemistry. Organic acids in water extracts of leaf litter from pine, chinquapin and willow were characterized and the results were used in the analysis of throughfall solution chemistry. Litter from three vegetative types was collected and returned to ELW for incubation to monitor decomposition. Most of the weight loss from decomposition during the initial year of the study occurred during the winter. Mineralization was very slow during the summer due to very dry soil conditions. Mineralization is very sensitive to acid additions. Summer CO2 concentrations in the soils were high enough to increase soil solution acidity and influence the speciation of dissolved elements. Lysimeters were installed at four sites in the watershed to extract soil water. Concentrations of N compounds found in surface waters appear to be directly related to concentrations found in soil solutions. Three small streams were sampled in the watershed to observe differences in water quality along their Iengths. Aluminum concentrations appeared to be related to the solubility of an aluminum hydroxide mineral. Nitrate was highest during the spring and fall, but NH4+ was highest during the summer. This could be due to plant and microbial assimilation of NO3- in mid-summer. Sulfate concentrations declined downstream apparently due to adsorption by soils. The overall chemistry of stream waters reflects the mineral composition of soils and rocks at ELW. Mineral weathering exerts a major influence on Ca, Na, Mg and K concentrations in surface waters at ELW.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
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