SURVEY OF NONPOINT SOURCE AGRICULTURAL AND URBAN RUNOFF POLLUTION INFLOW ONTO THE SALTON SEA FROM MAJOR TRIBUTARIES

The U.S. Environmental Protection Agency (EPA) has identified nonpoint source pollution as the main reason why 40% of all American rivers, lakes, and estuaries are not suitable for human uses. The main contributor of point and nonpoint water pollution in the United States is agricultural activity. In the Salton Sea cultural eutrophication is caused by agricultural and urban runoff from its three main tributaries: the New, Alamo, and Whitewater Rivers.

Water samples from the three inputs were collected at four locations throughout the course of the rivers. Data collected included: nitrate ion concentration, turbidity, salinity, dissolved oxygen, pH, and temperature.

At every river the amount of nitrate is greater at the point of discharge than at the source. The average nitrate concentration at the source for all three rivers is 7.5 ml/L. The average nitrate concentration at the point of discharge into the sea for all three rivers is 18.8 ml/L (2.5 times the starting amount and almost twice the maximum allowable amount for drinking water set by the EPA). Average nitrate concentration at the source of the Alamo is 8.8 ml/L and 14.3 at the mouth. Average nitrate concentration at the source of the New is 8.7 ml/L and 22.3 at the mouth. Average nitrate concentration at the source of the Whitewater is 5.2 ml/L and 24.6 at the mouth. The Alamo showed a slight decrease in nitrate at one site before levels increased again at the following downriver site. The New and Whitewater Rivers showed an upward trend in nitrate concentrations at each downriver test site.

The Alamo and the New Rivers have their sources across the border in Mexico. Mexicali on the other side of the border is an urban area, which might explain the low levels of nitrate of the two rivers on entry to the U.S. The Alamo and New river run through over 400 agricultural fields and cattle ranches in Imperial Valley. The Whitewater River’s source is in the San Bernardino Mountains. On its course through the Coachella Valley it runs adjacent to about ten golf courses and four major urban centers before it reaches the sea.

This research illustrates how the Salton Sea tributaries contribute to cultural eutrophication of the lake system at specific geographic points. Research like this can be used as a tool for targeted runoff prevention and monitoring in the future.