Landscape modification and land use over the past 150 years have impacted the Region’s soil resources. These impacts are especially prevalent in and around developed areas, and in areas influenced by Comstock era logging. Urban development in particular has physically altered the landscape, resulting in soil removal, grading, compaction, and higher erosion risk. These impacts have altered the ability of soils and vegetation communities to cycle nutrients and absorb and store water.
Soils provide a variety of key functions including sustaining vegetation, water filtration and storage, providing habitat for a wide variety of organisms, and providing a platform for development. The soil conservation threshold standards protect the Region’s soil resources and provide their continued ability to filter and retain nutrients for a variety of purposes.
These goals are directly reflected in the policies of the Regional Plan, which serve to:
· Prevent soil erosion from the Region’s watersheds by focusing development on more suitable soil types and ensuring development activities occur when soils are less susceptible to erosion.
Stream environment zone (SEZ) is a term unique to the Tahoe Region, that the TRPA Code of Ordinances defines as “Generally an area that owes its biological and physical characteristics to the presence of surface or ground water” (TRPA, 2012a). This definition includes perennial, intermittent, and ephemeral streams; wet meadows, marshes, and other wetlands; and riparian areas or other areas expressing the presence of surface and ground water.
These policies also play a critical role in contributing to the water quality, vegetation, and wildlife goals of the region.
The soil conservation thresholds are grouped into two reporting categories, impervious cover and SEZ. Impervious cover is a primary indicator of land disturbance. Excessive impervious surface contributes to sediment and nutrient inputs to Lake Tahoe and its tributaries, alters surface hydrology and modifies groundwater recharge regimes. The results are often negative impacts on soil health, fisheries, wildlife habitat and vegetation growth(Lahontan & NDEP, 2010; Raumann and Cablk, 2008). SEZs provide a variety of critical services in the basin, including water quality maintenance through nutrient cycling and sediment retention, flood attenuation, infiltration and groundwater recharge, open space, scenic and recreational enjoyment, wildlife habitat, and wildfire abatement, among many other functions and values (Roby et al., 2015).
This section provides an evaluation of the status of indicators relative to the 10 soil conservation targets related to impervious cover and one indicator related to SEZs (Table 5-1).