One of the most important indicators of the health of a body of water is its ability to support life. All too often, U.S. waters fail this fundamental test -- water harms rather than sustains life.
The Bay-Delta estuary is one of the country's richest ecosystems, but it is under constant threat from pollution. How has it fared in the face of this danger? This question is hard to answer accurately, because surprisingly little regular monitoring of the estuary's water quality is performed. What tests have been conducted suggest that pollution levels are cause for concern.
Those tests revealed episodes of acute toxicity, strong enough to kill juvenile fish and shrimp. The contamination -- thought to come largely from pesticides from agricultural discharges and from urban runoff -- has effects throughout the estuary's food chain.
Effects on Estuary Life
Shrimp and small fish are vital sources of food for larger fish and mammals in the estuary. So, when water pollution kills shrimp or small fish, the effects can travel up the food chain.
In addition, the timing of toxic episodes makes a difference. Even brief episodes can have long-term effects if they occur when animals are young and vulnerable. Many of the toxic episodes revealed by the testing occurred at such periods, coinciding with the early life stages of larger fish that are in decline, including delta smelt, chinook salmon, longfin smelt, splittail, steelhead trout, and green sturgeon. Scientists also suspect that if toxicity is high enough to kill shrimp and small fish, it could harm larger fish and mammals in more ways than decreasing their supply of food.
The Need for Research
In 1999 and 2000, toxic episodes in the estuary were less frequent than in the two previous years. The many possible explanations include use of less toxic substances, more responsible use of pesticides, and weather patterns that minimized the impact of periodic discharges to the estuary.
Several more years of monitoring data are needed to determine if this is a short- or long-term change. Scientists also need additional data on how widespread toxicity is in the estuary. So far, monitoring has mostly occurred at relatively few sites around the bay, with other portions of the estuary receiving little -- if any -- testing.
Until this testing is done, scientists won't have the information they need to fully understand the condition of the Bay-Delta's water. They can only speculate on the extent of contamination, how much progress the Bay Area has made in reducing it, and how much remains to be done.