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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Californias economy derives enormous benefits from water diverted from the streams, rivers, and lakes of the Sierra Nevada. A major cost associated with these benefits has been deterioration of the biotic integrity and sustainability of the aquatic systems, as reflected in declines in the distribution and abundance of native aquatic and riparian organisms. Water determines the distribution and abundance of many plants and animals throughout the Sierra Nevada by shaping and providing habitat. Lakes and streams support rich communities of native organisms both in the water and in adjoining riparian areas. These water bodies also support cities, farms, and industries within and distant from the mountains. Water was critical for development of the mining economy that dominated California for years after the gold rush. The Sierra Nevada has provided high-quality water for natural communities for millennia and for modern society for more than half a century. But in less than twenty years the risk of Giardia has spread to such an extent that virtually everywhere in the mountains one can no longer casually drink from a stream or lake, and concern for other microorganisms, such as Microsporidium , in water supplies is growing. Development of streams and other resources of the Sierra Nevada over the past 150 years has met the downstream demands of society throughout California but has impaired the quality and availability of water for both ecological and social needs in many parts of the mountain range.

Aquatic Ecosystems

Aquatic and riparian habitats are linked in direct and complex ways and are fundamentally dependent on natural flows of water. Natural supplies of water and its constituents (mineral particles, solutes, organic matter, biota) are highly variable over time, changing markedly between seasons and between years and over space. The native biota is well adapted to these seasonal patterns and extremes, but Californians have not been satisfied with the natural distribution of water and have engineered extensive control over the waters of the Sierra Nevada. Hydrologic processes have been further modified by side effects of the development of other natural resources of the Sierra Nevada. As human activities have altered characteristics of streams (such as volume of water, flood peaks, duration of low flows, seasonal timing, sediment supply, amounts of nutrients and organic matter, and water temperature) aquatic and riparian ecosystems have been forced to change. Other ecological changes have been deliberate, such as introduction of exotic species (e.g., brook trout, bullfrog), conversion of streams to lakes, and conversion of riparian zones to roads and structures.
In many respects aquatic systems have shown remarkable resilience. Vegetation along many streams gutted by mining has returned. Agencies are beginning to recognize the special nature of riparian areas, and some are developing practices intended to protect in-stream and associated resources. Present-day water projects at least recognize that the aquatic system requires some flows to exist. And some fisheries agencies personnel are becoming attuned to the needs of all organisms rather than the special management of a few. Nevertheless, the net results of a century and a half of these disturbances to the Sierra Nevada are greatly simplified and impaired aquatic ecosystems. Aquatic and riparian habitats have been severely altered and continue to deteriorate, leading to the loss of native species, ecosystem functions, and services to human society.

Invertebrates

The best indicators of the health of the aquatic system of the Sierra Nevada may be the group of organisms we know the least aboutinvertebrates. These small creatures are rarely seen or considered by most people, but they are central to aquatic ecosystems because they consume algae and organic matter and become food for fish, birds, mammals, amphibians, and reptiles. These organisms represent a great diversity of species. Species restricted to the Sierra Nevada (endemic) in two major groups of aquatic insects, the caddisflies and the stoneflies, were estimated for this report to be 19% (of 199 species) and 25% (of 122 species), respectively. A wealth of evolutionary, ecological, and biogeographical information is contained in Sierra aquatic invertebrates. Some species are highly specialized and are found only in a few wetlands, springs, or small streams. When these limited habitats are altered, their dependent invertebrates are likely to disappear.
Shifts in composition of invertebrate communities suggest changes in aquatic habitat or water quality, and invertebrates have been used to assess changes for many years. The great diversity of aquatic invertebrates makes them an especially valuable tool for monitoring almost any kind of aquatic habitat. The invertebrate fauna of the Sierra Nevada has probably changed dramatically since the 1850s because of major changes in habitat, and some species have become extinct. However, few species-level inventories of aquatic invertebrates exist for the Sierra, and the distribution of most species is poorly known.