The Sacramento-San Joaquin Delta and the San Francisco Bay Estuary ecosystem has been drastically altered by human activity since at least the mid-1800s, leading to numerous physical, chemical and biological changes [e.g., see Healey (2008) and Healey et al. (2008) for overviews]. Recent concerns include (1) the precipitous decline of four fish species that inhabit the Delta (collectively referred to as the pelagic organism decline, or POD) and (2) apparent major shifts in community composition of algae and higher trophic levels in the Delta and downstream in Suisun Bay. The four POD species of concern are delta smelt (longfin smelt), threadfin shad and striped bass. One of the potential causes of the POD and the community changes is the discharge of increasing concentrations of a combination of ammonia (NH3) and ammonium (NH4+) into the Delta ecosystem and eventually into Suisun Bay. For brevity, we hereafter abbreviate the ammonia/ammonium combination as ammonia/um.
To address the potential for adverse effects of ammonia/um on the Bay-Delta ecosystem, a ammonia/um workshop was convened by the CALFED Science Program on 10 and 11 March 2009 in Sacramento, California. We participated as an expert panel and were charged with preparing a framework for research that will address the role of ammonia/um in the Bay-Delta ecosystem.
In this report, we present our perception and interpretation of the major concerns related to ammonia/um in the Bay-Delta ecosystem; a conceptual framework of the major physical, chemical and biological drivers controlling the ecosystem (including POD populations); our assessment of the major research needs; and concluding remarks. For some research needs, we recommend specific types of research and provide literature citations; however, for other research needs we recommend general approaches for which targeted research will be determined later. In many ways, Bay-Delta research is breaking new ground by tackling a large-scale, complex freshwater-estuarine ecosystem affected by multiple, interactive stressors. Consequently, the Bay-Delta research program will establish a template for future research and management decisions in other hydrologically, biogeochemically, and trophically-similar systems, rather than relying on paths trodden by others.