Abstract
In the Lake Tahoe Basin in California and Nevada (USA), managing nutrient export from watersheds into streams and the lake is a significant challenge that needs to be addressed to improve water quality. Leaching and runoff of phosphorus (P) from soils is a major nutrient source to the lake, and P loading potential from different watersheds varies as a function of landscape and ecosystem properties, and how the watershed is managed. In this research, P availability and speciation in forest and meadow soils in the Lake Tahoe Basin were measured at two watersheds with different parent material types. Soils developed on andesitic parent materials had approximately twice as much total P compared to those developed on granitic parent materials. Regardless of parent material, organic P was 79–92% of the total P in the meadow soils, and only 13–47% in the forest soils. Most of the soil organic P consisted of monoester P compounds, but a significant amount, especially in meadow soils, was diester P compounds (up to 30% of total extracted P). Water extractable P (WEP) concentrations were ~10 times greater in the granitic forest soils compared to the andesitic forest soils, which had more poorly crystalline aluminosilicates and iron oxides that retain P and thus restrict WEP export. In the meadow soils, microbial biomass P was approximately seven times greater than the forest soils, which may be an important sink for P leached from upland forests. Results show that ecosystem and parent material are important attributes that control P speciation and availability in the Lake Tahoe Basin, and that organic P compounds are a major component of the soil P and are available for leaching from the soils. These factors can be used to develop accurate predictions of P availability and more precise forest management practices to reduce P export into Lake Tahoe.
Highlights
Lake Tahoe, located in the Sierra Nevada Mountain range in California and Nevada, is the sixth largest lake by volume in the United States
We investigated the influence of parent material and ecosystem type on soil P species and solubility in the Lake Tahoe Basin
Total P concentrations in Tahoe soils developed in andesitic parent materials were over two times greater than in soils developed in the granitic parent materials (Figure 2), which is consistent with expected differences based on parent material
Summary
Lake Tahoe, located in the Sierra Nevada Mountain range in California and Nevada, is the sixth largest lake by volume in the United States. It is classified as an ultra-oligotrophic lake, meaning that it has naturally low nutrient concentrations and low primary production, and it is renowned for the clarity of its water (Hatch et al, 2001; Goldberg et al, 2015). A recent lake-clarity model demonstrated that a return to the historical Secchi depth reading in Lake Tahoe would be possible within 20 years if P loading were reduced by at least 2.75% per year (Sahoo et al, 2010). To control P sources and subsequent loading into surface waters, a full understanding of P cycling and species in soils in the Lake Tahoe Basin is required
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