WHAT ROLE DOES BIOLOGICAL DIVERSITY PLAY IN A WATERSHED?

Commonly, species diversity is interpreted as biological diversity, and since few marine groups, except marine mammals, have had very much genetic work done, and community functions are only well known from a few systems, it is the taxonomic interpretation of diversity that is most commonly discussed (e.g., species or higher taxonomic levels such as families and classes, orders and phyla). Of all the species that we know, roughly 16% are from the seas. General diversity patterns in the sea are similar to those on land, there are more smaller than larger species, and there are more tropical species than temperate or polar species. There are centers of diversity for specific taxa, and the structure of communities and ecosystems is based on particular patterns of energy availability.

For example, estuary systems are productive due to importation of nitrogen from the land, coral reefs are also productive, but use scarce nutrients efficiently by specially adapted filter feeding mechanisms. Abyssal communities, on the other hand, depend on their entire energy supply from detritus fall from upper levels in the ocean. Perhaps the most specifically adapted of all life forms are the hydrothermal vent communities that employ chemosynthesis rather than photosynthesis for primary production. Water temperature, salinity, and pressure create differing ecosystems in ways that are distinctly different from terrestrial systems.

In addition, the boundaries between systems may be dynamic, and are certainly more difficult to detect than on land. Freshwater ecosystems are aquatic systems which contain drinkable water or water of almost no salt content. Freshwater resources include lakes and ponds, rivers and streams, reservoirs, wetlands, and groundwater. The United States derives many benefits from these freshwater resources. They provide the majority of our nation's drinking water resources, water resources for agriculture, industry, sanitation, as well as food including fish and shellfish. They also provide recreational opportunities and a means of transportation. In addition, freshwater ecosystems are home to numerous organisms (e.g., fish, amphibians, aquatic plants, and invertebrates). It has been estimated that 40% of all known fish species on Earth come from freshwater ecosystems.

The World Resources Institute on Biodiversity has also reported that almost 50 percent of freshwater snails in the Southeastern United States are now endangered or extinct due to channelization and impoundment of rivers. There are seven major groups of organisms known to inhabit freshwater ecosystems. These groups include vertebrates (e.g., fish, amphibians, reptiles, birds, and mammals), invertebrates (e.g., protozoan, myxozoans, rotifers, worms, mollusks), plants, algae, fungi, bacteria, and viruses. As in marine environments, phytoplankton and zooplankton form the base of the food chain. Periphyton, macrophytes (aquatic plants), insects, fish, and amphibians are also found in freshwater environments. Various bird species like osprey, ducks, and raptors also frequent freshwater systems. Despite all of their value and importance, many freshwater ecosystems are being severely damaged by human activities.

The major threats to freshwater biodiversity include runoff from agricultural and urban areas, the invasion of exotic species, and the creation of dams and water diversion. Overexploitation and pollution also threaten groundwater supplies. These kinds of threats and others have already significantly impacted the biodiversity within these ecosystems. Worldwide, most types of freshwater ecosystems generally are in grave condition and are declining at a much faster rate than terrestrial systems. Consider some of the evidence: More than 20 percent of the world's known 10,000 freshwater fish species have become extinct or imperiled in recent decades. In the United States, 303 fish species, or 37 percent of the freshwater fish fauna, are at risk of extinction; 17 species have already gone extinct, mostly in this century.

More than two-thirds of U.S. freshwater mussel species are vulnerable to extinction or are already extinct. Imperilment rates are disproportionately higher than those for terrestrial plants and animals. Half of the world's wetlands are estimated to have been lost during the 20th century, with more than half having already been destroyed in the United States. Historical trends in commercial fisheries data for major rivers of the world show dramatic declines during the 20th century. Biodiversity is the variety and variability of life on Earth. This includes all of the plants and animals that live and grow on the Earth, all of the habitats that they call home, and all of the natural processes of which they are a part. The earth supports an incredible array of biodiversity-from Thailand's tiny bumblebee bat to the ocean's great blue whale-with plants and animals of all shapes and sizes in between.

Biodiversity is essential to every aspect of the way that humans live around the world. Plants and animals provide people with food and medicine, trees play an important role in absorbing greenhouse gases and cleaning the air we breathe, and rivers and watersheds provide the clean water that we drink. Unfortunately, the earth's biodiversity is disappearing, with an estimated 1,000 species per year becoming extinct. Conserving biodiversity is especially crucial in developing countries where people's livelihoods are directly dependent on natural resources such as forests, fisheries and wildlife. Why Conserve Biodiversity? Biodiversity is the very foundation for all the Earth's essential goods and services. The air we breathe, water we drink, and the food we eat all depend on the Earth's rich biodiversity. USAID's biodiversity conservation activities not only protect the environment in developing countries but also have significant economic value to the United States.

Plants and animals provide people with food and medicine. Forty percent of all prescriptions written today are composed from the natural compounds found in different species. An estimated 80,000 edible plants are found in the world, and one in every three mouthfuls of the food you swallow is prepared from plants pollinated by wild insects and animals. The extinction of each additional species results in the irreversible loss of unique genetic materials, each of which has potential for development of medicines and foods and associated enterprises that create jobs. While plants and animals keep you well fed and healthy, trees play an important role in absorbing greenhouse gases. Through photosynthesis, trees absorb and store atmospheric carbon, helping to combat global warming and purifying the air we breathe.

Forests also control soil erosion and purify water. As natural systems breakdown, people around the world are forced to find alternative and often more costly ways to maintain adequate supplies of clean water or to deal with increasingly polluted air. The net economic benefits of biodiversity are estimated to be at least $3 trillion per year, or 11 percent of the annual world economic output. These are reasons enough alone to begin to monitor and preserve the biodiversity of watershed areas.