Soil Phosphorus Speciation and Availability in Meadows and Forests in Alpine Lake Watersheds With Different Parent Materials

Citation

Heron, T., Strawn, D.G., Dobre, M., Cade-Menun, B.J., Deval, C., Brooks, E.S., Piaskowski, J., Gasch, C., Crump, A. (2021). Soil Phosphorus Speciation and Availability in Meadows and Forests in Alpine Lake Watersheds With Different Parent Materials. Frontiers in Forests and Global Change, [online] 3 http://dx.doi.org/10.3389/ffgc.2020.604200

Plain language summary

Lake Tahoe, in the Sierra Nevada Mountain range in California and Nevada, has naturally low nutrient concentrations and is renowned for its water clarity. Phosphorus (P) entering the lake will trigger algal blooms and reduce water quality, so it is important to carefully manage P in the soil surrounding the lake. Loss of P from soil to water occurs via leaching and runoff, and will depend on properties such as soil parent material and land use or ecosystem type. This study determined P forms, availability and potential transport in forest and meadow soils in the Lake Tahoe Basin 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 to 92% of the total P in the meadow soils, and only 13 to 47% in the forest soils. Water-extractable P concentrations were approximately ten times greater in the granitic forest soils compared to the andesitic forest soils, which indicates that potential P loss is greater from granitic than andesitic soils. These factors can be used to develop accurate predictions of P availability and more precise forest management practices to reduce P loss into Lake Tahoe from soils in the surrounding meadows and forests.

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.

Publication date

2021-02-23

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