Ecosystem Structure, Function and Change

Ecosystem Structure, Function and Change

In the area that I live in we have the San Luis National Wildlife Refuge. The refuge is over 26,800 acres of wetlands, riparian forests, native grasslands, and vernal pools (U.S. Fish & Wildlife Service, 2012). In 1966 was when the first piece of land was purchased, and since then it has grown to comprise of six refuge units. The units are called: San Luis, East Bear Creek, West Bear Creek, Freitas, Blue Goose, and Kesterson. If it were not for the refuge many animals would have lost their homes and there would actually be a few extinct species of animals as well.
In the San Luis National Wildlife Refuge there are four different types of ecosystems. The first type of ecosystem that can be found in the refuge is riparian woodlands. The riparian woodlands are found along rivers and sloughs, and they consist of willows, cottonwoods and oaks ( U.S. Fish & Wildlife Service, 2012). The second type of ecosystem that can be found is wetlands. Wetlands include permanent marshes which contain water year-round. However depending on how much rain the refuge gets in the winter depends on the level of water in the wetlands. Grasslands are the third type of ecosystem in the San Luis National Wildlife Refuge and that type of ecosystem is actually the most common one in the refuge. The grasslands are dominated by annual and perennial grass species. The last of the ecosystems that is found in the refuge is vernal pools. These ecosystems are seasonally-flooded during the rainy season until late spring when the water is evaporated and the ground turns into a dry mud bowl. The refuge has so many different types of ecosystems and in the past they have all been affected by humans, however not in a good way.
When it comes to how humans have affected the biogeochemical cycles in the San Luis National Wildlife Refuge it is not good at all. The biggest cycle that has been affected by humans is the biogeochemical cycling of selenium. Since California is the leading agricultural state in the United States most of the farming is done in the Central Valley and this requires an extensive amount of irrigation to keep up with the production of food. Unfortunately with all this irrigation it created soil salinization problems (Presser, T.S. & Ohlendorf, H.M., 1987). There has been solutions to save the threatened agricultural lands for the salinization however this then caused problems for the San Luis National Wildlife Refuge. In 1985 the San Luis National Wildlife Refuge was closed due to selenium poisoning in the water fowl, fish, and mammals. There was also high concentrations of boron, chromium, and molybdenum which disrupted the natural ionic balance of the aquatic system. Farms around the refuge were the ones to blame for the contamination because they were discharging their waste water in the wetlands cannels. In 1996 a proposal was made to reopen the San Luis Drain, so that farmers could dispose of their waste water with the drain instead of releasing the waste water into the Mud Slough. The Mud Slough was also extended in the refuge to help fix the toxic levels, and restore the refuge back to normal.
Since the Drain was reopened for the farmers and no longer was waste water being drained into the wetlands through the Mud Sloughs the selenium levels have dropped. To this day samples are taken every year to monitor the toxic levels. Although the toxic levels are not where they used to be they are a lot lower and are no longer at a dangerous level. In one year the selenium levels went from 10,000 lbs in 1996 to 7,300 lbs in 1997 (Beckon, Henderson, Mauner, & Schwarzbach, 1997). Since the selenium levels were lowered it allowed researchers to go in and study the wildlife of each ecosystem. By studying each ecosystem many animals have returned by natural or have been reintroduced back into the refuge that had once been there before the toxic levels of selenium. One such animal that has been recently reintroduced into the refuge is the black-tailed deer (U.S. Fish & Wildlife Service, 2012). Nest boxes, and raised dirt mounds have also been made by humans to help restore the natural wildlife habitats in the refuge. In the grasslands controlled burns, grazing, mowing and disking is also done to help preserve the ecosystem because it helps prepare the ground for seeding.
Thanks to the dedication of the men and women who have been studying each of the ecosystems in the San Luis National Wildlife Refuge there have been a few animals who were on the endangered species list removed because their habitat has been restored. Interactions between humans and ecosystems usually do not have a happy ending for the ecosystem because the humans usually just destroy it, however it's nice to see that the ecosystems in the San Luis National Wildlife Refuge are surviving even though they went through a rough time in the past. If it were not for humans though and stepping in to restore these ecosystems in the past they probably would not be here today. It's important that humans learn to take care of the world around them because it will not always be there.

References U.S. Fish and Wildlife Service. (2012). San Luis. Retrieved from http://www.fws.gov/refuge/San_Luis/what_we_do/resource_management.html Presser, T. S. & Ohlendorf, H. M. (1987). Biogeochemical Cycling of Selenium in the San Joaquin Valley, California, USA. Retrieved from http://wwwrcamnl.wr.usgs.gov/Selenium/Library_articles/EnvMan11.pdf Beckon, W.N. , Henderson,J.D. , Maurer,T.C. , and Schwarzbach, S.E. (1997). What are the Biological Effects of Reopening the San Luis Drain?. Retrieved from http://www.fws.gov/pacific/ecoservices/envicon/pim/reports/Sacramento/San%20Luis.html