The word nutrients sounds like a good thing—they make our food healthy, for example. But in our rivers, lakes, and bays, nutrients can pose water quality challenges. In the right amounts, nutrients such as nitrogen and phosphorus support plant and animal growth in key waterways such as the San Francisco Bay and the Sacramento-San Joaquin Delta. Excess amounts can cause toxic algae blooms and reduced oxygen in the water. Consequences can include die-offs of fish, mammals and birds, and human illness.
The main sources of nutrients in the Bay-Delta are sewage plant discharge and agricultural runoff. Jim Cloern, a USGS scientist and member of PPIC’s water policy research network, has been studying water quality in the Bay-Delta since the late 1970s.
“San Francisco Bay has historically shown resistance to the harmful consequences of nutrient pollution, but in recent decades there are signs this resistance is weakening,” Cloern says. Algae levels in the bay have increased, oxygen levels have declined, and algal toxins and toxin-producing species are sometimes present at levels to cause concern, he notes.
In the Delta, nutrient pollution has contributed to the spread of invasive aquatic plants such as water hyacinth and recurrent blooms of the toxic blue-green alga Microcystis. The role of nutrients in the collapse of many fish species in the Delta has prompted lively debates, but one thing is clear: they are a significant source of stress on California’s struggling native species. Conditions are worsening with the drought, which has reduced freshwater flows into the Bay-Delta and increased temperatures.
There is a growing understanding among wastewater managers and regulators that a new round of investments is needed.
“The Bay Area’s wastewater treatment plants will need to continually adapt to growing water quality challenges, either voluntarily or through regulations,” Cloern says.
One option on the table is increasing levels of treatment, which can be costly. For example, Sacramento’s wastewater treatment plant is undergoing a $2 billion upgrade to reduce the volume of nutrients entering the Delta. Other options can complement or substitute for treatment plant upgrades. For instance, restoring wetlands can filter out nutrients and other pollutants, while also providing valuable habitat and protection from floods.
Another tough question is how to manage agricultural runoff from animal production and fertilizer use in the Central Valley, the main source of nutrients in the Delta. These sources are dispersed, which makes treatment difficult and expensive. Controlling farm pollutants at the source is likely the most cost-effective solution. This will require working with farmers to adjust their practices.
Thankfully, the days when untreated sewage and industrial waste poured directly into the Bay-Delta are long gone. But the next water quality challenge is on the horizon. Climate change will intensify our current challenges, as invasive plants and toxic algae thrive in warmer temperatures. Cloern suggests that we need a nutrient management strategy for the Bay-Delta that “anticipates these future changes so that investments are designed in a thoughtful and scientifically grounded way.”
Read California’s Water Quality Challenges (PPIC Water Policy Center fact sheet, October 2015)
Visit the PPIC Water Policy Center water quality resource page