How do Urban Lots Help Protect the Environment in the Lake Tahoe Basin?

Water Quality

Lake Tahoe watersheds are the natural drainage systems that supply the lake with water. Precipitation that falls within the Lake Tahoe Basin (both rain and snow) flows into the ground to creeks and streams, then into the lake. Water that travels through an undisturbed watershed is usually very pure due to the soil, plants, and organisms that act as a natural water purification system. In fact, in an undisturbed forest, more than ninety-five percent of rain and snowmelt percolates into the ground, where it is filtered on its way to the nearest stream.

In 1968 scientists began testing the clarity of the lake with a device known as a Secchi disk. The secchi disk measures the depth of visibility in the lake. Since the 1960’s, the readings have shown a decline in water clarity.

The deterioration in water quality has occurred primarily because the watersheds of Lake Tahoe have been disturbed by the building of roads and urban areas. Pavement, rooftops, and other impervious surfaces found in developed areas repel over ninety percent of all precipitation. Instead of being filtered by soil, water rapidly runs off these impervious surfaces creating surface runoff. Surface runoff typically concentrates in ditches and gullies, causing soil erosion. These increased run-off flows also cause increased erosion when they reach streams and transport sediments such as nitrogen and phosphorus into streams and eventually into Lake Tahoe.

Acquiring undeveloped urban intermix parcels that are environmentally sensitive (meadows, streams, highly erosive soils, and steep topography) has helped to mitigate the negative impacts of development on Lake Tahoe's watersheds. These acquired undeveloped parcels have prevented the increase of impervious surfaces within Lake Tahoe's watersheds and continue to provide the natural hydrologic function of undisturbed forest areas. In addition, these parcels can slow the flow of water in between developed areas and provide opportunities for construction of erosion control structures.

[Photo]:  This photo shows Lake Tahoe from above Emerald Bay.  There are sillhouettes of trees on t
View of the clear blue waters of Lake Tahoe from Emerald Bay (West shore)

 

[Photo]:  This is taken from an aerial view and shows the coastline along the east shore by Secret
Aerial view of the amazing clarity of Lake Tahoe's waters at Secret Harbor (East shore)

 

In 1968 scientists began testing the clarity of the lake with a device known as a secchi disk.  The secchi disk measures the depth of visibility in the lake.  Throughout the years the readings have shown a decline in water clarity. 

 

 

[Graphic]:  This is a line graph of secchi disk results from 1968-2002.  The x-axis is year of study and the y-axis is depth of clarity in feet.  In 1968 the depth of visibility in Lake Tahoe was just over 100 feet and by 2002 it declined to about 80 feet.  The graph depicts an underwater scene with fish swimming and a large boat at the surface lowering a secchi disk.

 

This graphic representation of secchi test results from 1968-2002 shows the declining clarity of the lake. Data were provided by the UC Davis Tahoe Research Group and the graphic was provided by the League to Save Lake Tahoe.

 

 

 

Wildlife Habitat

 

The Lake Tahoe Basin contains significant habitat for wildlife. Most critical habitats in the Lake Tahoe basin occur in the lower montane forests (below 7000 feet) where the majority of development is also concentrated. As a result of this urbanization habitat has been reduced, fragmented, and degraded. Even in areas of less intensive development, the natural landscape has been significantly modified by recreational activities, roads and trails. An urban biodiversity study, which began in 2002, was conducted by the University of Nevada-Reno and the University of California-Davis in conjunction with the Forest Service. The study looks at the contributions of urban intermix parcels in supporting biological diversity in the Lake Tahoe Basin. The study determined that the presence of undeveloped urban parcels helps retain important habitat characteristics that otherwise may not exist in similarly developed landscapes. The results of the study also provide management agencies in the Basin with information and adaptive management tools to achieve biodiversity restoration goals and objectives.

[Photo]: There is a large dead tree in the center of the photo.  Photo shows urban intermix parcel
Dead tree on an urban lot retained for wildlife habitat.



 

Urban Biodiversity Study

An urban biodiversity study, which began in 2002, was conducted by the University of Nevada-Reno and the University of California-Davis in conjunction with the Forest Service. The study looks at the contributions of urban intermix parcels in supporting biological diversity in the Lake Tahoe Basin. The study determined that the presence of undeveloped urban parcels helps retain important habitat characteristics that otherwise may not exist in similarly developed landscapes. The results of the study also provide management agencies in the Basin with information and adaptive management tools to achieve biodiversity restoration goals and objectives. For more information, read the Biodiversity Paper.

 

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