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San Francisco Estuary Project

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San Francisco Estuary Project

Nancy Vera

BIO/315 - Ecology and Evolution

May 2, 2016

Dr. Ilse Silva-Krott

San Francisco Estuary Project

An estuary is a partially enclose body of water where fresh river water meets the salty ocean water (Cohen, 2000). Estuaries have always been important for humans because of its economic and cultural benefits. However, they provide important ecosystems services for many organisms that depend on them. Among the most valuable ecosystem services they provide is habitat protection (NOAA Ocean Service Education, 2008). Habitat protection is critical because the primary cause of the extinction of species is habitat destruction (Smith & Smith, 2012). Habitat destruction causes habitat fragmentation. Habitat fragmentation is the alteration of habitat that results in a spatial separation of habitat units from a previous state of greater continuity. This fragmentation has caused a reduction in biodiversity as it was seen in the previous discussion and reduces the efficacy of the ecosystem. Habitat fragmentation is the result of the increase in human population and activities (Hogan, 2015).

The San Francisco area has seen an increase in human population that was initially triggered by the gold rush. During this era, the population of the region increased from 400 to 25,000 people within two years. Human population in the area has been increasing gradually after this period until it reached 8.5 million people nowadays. Over this same period, nearly half of the San Francisco Estuary's watershed has been turned into farms and rangeland, and about one-fifth of the watershed irrigated for crops. About four percent is urbanized, and one tenth of that has been industrialized (Cohen, 2000).

The San Francisco Estuary is the largest estuary in western North America, and it is a critical biological resource since it provides a nursery for young fish and crabs, winter feeding for migratory birds and is the home of many organisms.  It is made up of two areas: the Bay and the Delta. The Bay is made up of four smaller bays, and the Delta is a swampland. The estuary drains 40% of the state of California, and the surface water it receives is from rain and snow. Half of this water is diverted to be used by farms, factories and households. To divert the water, dams were built, and they have blocked the way to salmon spawning grounds. Pumps used have destroyed plankton, eggs, and young fishes. And the destruction of 80% of the marshes has reduced the carrying capacity as feeding ground for birds and nursery for fish and shellfish (Cohen, 2000).

While human population and activity growth have damage estuaries, efforts are being made to conserve them. Restoration efforts for the San Francisco Estuary started as early as the 1970s, but it has been growing throughout time. In the 1980s and 1990s, much of the restoration efforts were focused on individual projects that tried to mitigate the habitat fragmentation in the estuary. The first effort was to restore the salty marsh ecosystems and then the freshwater tidal wetlands. The next effort was in planting even though it was not widespread because of the belief that with the proper conditions plants will grow on their own. But for them to grow they need to be at the correct elevation because of the tidal inundation rates that affect the anaerobiosis and salinity of the soil (Callaway, Parker, Vasey, Schile,  & Herbert, 2011).

These systems lacked complexity and the restoration effort then have incorporated additional approaches. Using the approach of "over-excavating or leaving them at lower elevations, they are trying to develop channels that will help suspend and move sediment. The mentality of mitigation was changed to a mentality of restoration in which detail maps of priorities helped identified the needs. Small projects have given way to larger projects that will have landscape level effects (Callaway, Parker, Vasey, Schile,  & Herbert, 2011).

Regardless of all the efforts, there are issues that need to be addressed. One of the issues is the promotion of biodiversity and ecosystem functions in restored habitats. Much of the effort to restore biodiversity has been focused on plant diversity in tidal wetlands. But invasive plants are a threat to biodiversity since they are widely distributed, and they reproduce fast. But not only invasive plants are the problem, but there are invasive animals that affect native species and ecosystem functions. Another issue is contamination, and elevated levels of mercury have been found in the estuary, and the research about it is part of restoration projects. Water extraction of underlying aquifers is also a challenge for the restoration sites because it makes the site to loose elevation (Callaway, Parker, Vasey, Schile,  & Herbert, 2011).



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