ASSESSMENT

* A Past View of Resources in the Lahontan Region

* Deer Creek Watershed Conservancy

* Watershed Risk Assessment

* Mercury Contamination

Strategies for Improving Watersheds and Aquatic Biodiversity

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Although few changes other than extinction are irreversible in an absolute sense, many environmental modifications can be considered to be effectively irreversible. Most structures, such as large dams, canals, residential developments, and highways, are permanent for practical purposes. However, impacts from permanent structures can often be reduced by changes in use of the structures or by creative mitigation. Other persistent impacts, such as unsurfaced forest roads and agricultural fields, can be removed or mitigated, and ecological functions of the site can be restored with sufficient investment. Cessation of chronic disturbances, such as grazing or trampling in riparian areas, seasonal water diversions, and stocking of nonreproducing fish, will allow natural recovery of different aspects of an ecosystem at varying rates. For example, wet meadows converted to dry terraces above an incised stream as a result of overgrazing may not recover even over a century without active restoration work. Riparian vegetation tends to become reestablished within a few years after chronic disturbance is eliminated, but readjustment of channel morphology to a natural shape may require decades. Although disturbances such as a single timber harvest or a fire can have severe short-term effects, natural recovery from them generally occurs at a much faster rate than recovery from chronic disturbances.

Knowledge Base

The knowledge base for improving water allocation and implementing sound watershed management in the Sierra Nevada is notably weak. Economic values of water in different uses are not well established. Information about water demand and historic water rights is not easily accessible. Records of water quality and sediment yield are available at very few sites throughout the mountain range. Rates of natural and accelerated erosion have not been measured at many locations in the Sierra Nevada. The impacts of various water and land-management practices are not quantified or even known in some cases. In the few cases where long-term, rangewide surveys exist, such as grazing transects in wet meadows on the national forests, data have not been summarized until now. The effectiveness of best management practices and restoration techniques are largely untested. In general, the basic data for sound decision making about improving water and watershed management are lacking. Specific habitat requirements of most riparian-dependent terrestrial vertebrate species are poorly documented, and general surveys of species distribution for most aquatic invertebrate species are missing. Adequate monitoring of natural processes, impacts, mitigation, and restoration could provide a much better basis for water resources planning and administration. Inadequate information is currently a major constraint on improvements in water and land management.
In summary, the aquatic/riparian systems are the most altered and impaired habitats of the Sierra. Species losses and changes in species assemblages have been accelerated in aquatic and aquatic-connected habitats. Frogs, in particular, have been declining at an alarming rate in recent years. Native fish and other assemblages have been fragmented by water projects. Many aquatic species are either listed as threatened or endangered or will be candidates for listing if present trends continue. The declines were especially severe during the first hundred years of water development, starting with hydraulic mining. Although declines have subsequently slowed in most cases, many continue and there is little evidence of long-term improvement in the status of aquatic organisms.
Restoration, better management, and research are needed to recover lost habitat, prevent further loss, and monitor efficacy of management. Suggested solutions are outlined in the strategies and in the individual assessments of volume II.