High salinity may be cause of Delta woes

Editorial
Sunday, April 30, 2006

WE HAVE FOUND the problem, and it is us. That bit of paraphrased wisdom from Walt Kelly's "Pogo" may well apply to the deteriorating Delta ecosystem. For the past several years there has been a sharp and unexplained collapse of the populations of open-water fish, including the Delta smelt, longfin smelt, threadfin shad and young striped bass. Recently, engineers from the Contra Costa Water District have discovered a strong correlation between Delta salinity in the fall and populations of smelt the following summer. The greater the salinity the smaller the smelt population. The relationship between autumn salinity and the smelt has been consistent since the late 1980s. That is when the overbite clam population, which was introduced to the Bay Area from Asia, began to multiply and spread. Also, about a decade ago, water shipments to the San Joaquin Valley and Southern California were shifted from the spring to other times of the year. The idea behind the shift was to protect fish that spawned near the intake of water pumps at Tracy. Unfortunately, the time shift appears to have made the Delta saltier in the fall. The Asian overbite clam, which flourishes in brackish water, began to spread more rapidly from San Francisco Bay into Suisun Bay and into the Delta as salinity levels rose. The clams eat the same phytoplankton and other tiny organisms that the smelt and other fish rely on, forcing fish farther up the Delta and depleting much of their population. The numbers of smelt are so low that extinction is a possibility. What is dismaying is that the data obtained by the water district could have and should have been gathered years earlier. Had that been the case, perhaps something could have been done by now to better protect the Delta ecosystem. One would have thought that with all the money CalFed, a coalition of various water users, spent on Delta studies, the correlation among higher salinity levels, the spread of the overbite clam and the diminution of open-water, or pelagic, fish would have been discovered. Unfortunately, the relationship was not properly examined. As a result, a decision to shift pumping times may have caused major harm to the Delta environment that will be difficult to reverse. The CCWD study is not conclusive, and further, more exacting research is being done by the pelagic organism decline (POD) team of scientists. But the work done by the water district strongly indicates that salinity is the key element in the ecological problems in the Delta. However, it is not the salinity alone that seems to be the cause. There is a strong correlation between fall salinity levels and summer smelt populations in the years since the overbite clam arrived. But, there was no correlation before that time. That has caused researchers to theorize that it is the spread of the overbite clam, that is a likely suspect in causing declines of fish numbers. But without higher salinity levels, the clam may not have spread so far into Suisun Bay and the Delta. What is needed now is continued thorough research to establish causal as well as correlative factors regarding salinity levels, clam expansion and fish populations. The next step is to determine if and when more fresh water may have to be diverted into the Delta. The current situation is unacceptable. High salinity levels diminish the quality of drinking water as well as upset the delicate ecological balance of the Delta. It may well be that we have reached the limit in the volume of water we can pump southward. The sooner we know for sure the better we can address the problem.