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It’s not just the sewage

Ongoing efforts to tie Delta water quality problems to urban discharges continued at the NAS committee briefings last week.

Fortunately, there were public comments to supplement the scheduled briefings. Deirdre Des Jardins (see brief bio at the end of this newsletter) gave the committee a bibliography of major studies on the effect of other stressors besides urban discharges.

For example, research by the original Pelagic Organism Decline (POD) team shows that both the Corbula clam invasion and toxic algal blooms are associated with low Delta flows.

(Corbula amurensis, introduced into the estuary in ships from Asia, filters nutrients out of the water, reducing the food supply for native organisms. An algal bloom is a rapid increase in the population of algae. Some algal blooms contain toxins that damage other organisms.)

According to Des Jardins, a 2010 paper by Heather Peterson shows that the invasive Corbula clam shifts up-estuary and down-estuary following Delta outflows that influence the salinity of the water (the salinity gradient, X2).

The toxic algal blooms started in September 1999 in the Southern and Central Delta with low Delta flows and high temperatures, and have continued since then in the summer and early fall. Des Jardins cites a 2010 paper by Peggy Lehman, based on extensive testing by the POD team in 2005. This testing showed that the blooms were correlated with total nitrogen inputs, but NOT ammonia (which is associated with urban wastewater). The two main locations for blooms in 2005 were the San Joaquin River at Antioch, and Old River.

Pyrethroid pesticides from the San Joaquin Valley may also be killing some of the key zooplankton species. That means nothing to eat at the bottom of the food chain. Des Jardins notes that the top dischargers of pyrethroids are San Joaquin Valley agricultural users. The pyrethroids are attached to sediments, so it is important to control runoff of sediments – for example, with riparian vegetation.

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