Pick Our Brain - July 2011

Why are nutrients that we usually think of as ‘good’ sometimes considered ‘bad’?

When Good Nutrients Go Bad

Although nutrients-nitrogen and phosphorus-are essential for all life and important for plant and animal growth, nutrients in high concentrations can adversely affect human health and aquatic life. Nutrient pollution, especially from nitrogen and phosphorus, has for decades consistently ranked as one of the top causes of degradation in U.S. waters. One example is the presence of excessive amounts of nitrate in surface water and groundwater used for drinking water. This can result in “blue-baby syndrome,” a condition that occurs when oxygen levels in the blood of infants is low and can sometimes be fatal. In addition, elevated nutrient concentrations can trigger a process called eutrophication in which loading of excess nutrients results in extreme, often unsightly, growth of algae and other nuisance aquatic plants. These organisms clog water intake screens and filters and can interfere with recreational activities, such as fishing, swimming, and boating. Subsequent decay of these organisms result in foul odors, bad taste, and low dissolved oxygen in water (hypoxia) that can harm fish and shellfish that are economically and ecologically important. High nutrient concentrations also cause blooms of harmful algae, which can be toxic to fish and other organisms, including humans.

Increasing input of nutrients into the Delta is a scientific topic of much current interest. Harmful algae and aquatic weeds are growing concerns in the Delta, and the role of increased nutrients is being investigated. Harmful algal blooms, aquatic weeds, and increased inputs of nutrients suggest that eutrophication is a growing problem in the Delta.

1906 San Francisco Earthquake
Microcystis in the San Joaquin River
(Photo courtesy of Scott Waller, Department of Water Resources)