Extent and ecosystem impacts of Biological Soil Crust in the Colorado River Basin

Abstract: On the Colorado Plateau, the main watershed for the Colorado River, mat-forming associations of mosses, lichens, fungi and cyanobacteria known as Biological Soil Crusts (BSC) cover an extensive amount of soil surface. BSC are known to provide critical services for this ecosystem, such as stabilization of soil surfaces against wind and water erosion, addition of biologically fixed N and C to low-fertility soils, and provision of microsites for vascular plant establishment. However BSC are particularly vulnerable to mechanical disturbance by humans, for which recovery times may be slow. This paper examines the ways that global change in the form of altered climate and increased human presence in the region affect BSC, and how these impacts may lead to changes in water supply and quality in the Colorado River. It is suggested that direct disturbance of BSC by increased human visitation to the region is the primary threat to BSC, followed by losses due to climate change related to alterations in precipitation timing and frequency. There is reason to believe that heightened erosion due to loss of BSC has resulted in changes of alpine snowpack albedo and runoff to the Colorado River, as well as changes in sediment and nutrient loading to lower tributaries. However, more information is needed to establish the magnitude to which BSC disturbance is responsible for these effects.