Life Histories, Salinity Zones, and Sublethal Contributions of Contaminants to Pelagic Fish Declines Illustrated with a Case Study of San Francisco Estuary, California, USA

Abstract

Human effects on estuaries are often associated with major decreases in abundance of aquatic species. However, remediation priorities are difficult to identify when declines result from multiple stressors with interacting sublethal effects. The San Francisco Estuary offers a useful case study of the potential role of contaminants in declines of organisms because the waters of its delta chronically violate legal water quality standards; however, direct effects of contaminants on fish species are rarely observed. Lack of direct lethality in the field has prevented consensus that contaminants may be one of the major drivers of coincident but unexplained declines of fishes with differing life histories and habitats (anadromous, brackish, and freshwater). Estuaries and Coasts (2012) 35:603-621 DOI 10.1007/s12237-011-9459-6 indicates that examining the effects of contaminants and other stressors on specific life stages in different seasons and salinity zones of the estuary is critical to identifying how several interacting stressors could contribute to a general syndrome of declines. Moreover, warming water temperatures of the magnitude projected by climate models increase metabolic rates of ectotherms, and can hasten elimination of some contaminants. However, for other pollutants, concurrent increases in respiratory rate or food intake result in higher doses per unit time without changes in the contaminant concentrations in the water. Food limitation and energetic costs of osmoregulating under altered salinities further limit the amount of energy available to fish; this energy must be redirected from growth and reproduction toward pollutant avoidance, enzymatic detoxification, or elimination. Because all of these processes require energy, bioenergetics methods are promising for evaluating effects of sublethal contaminants in the presence of other stressors, and for informing remediation. Predictive models that evaluate the direct and indirect effects of contaminants will be possible when data become available on energetic costs of exposure to contaminants given simultaneous exposure to non-contaminant stressors.

Reevaluating the Generality of an Empirical Model for Light-Limited Primary Production in the San Francisco Estuary

“…They attributed summer diatom blooms in Suisun Bay prior to 1987 to accumulation of phytoplankton biomass rather than a high growth rate (Cloern 1979;Cole and Cloern 1984 reported by Cole and Cloern (1984); the slight seasonal increase that we observed for P B M(24) occurred in parallel with the movement of the sampling area from Central Bay to Suisun Bay and the western Delta Cole and Cloern (1984) for spring. It has been hypothesized that growth rates of phytoplankton in the northern SFE have potentially decreased as a result of increased NH 4 loading (Dugdale et al 2007;, contaminants (Brooks et al 2012), and shifts in phytoplankton community composition (Lehman 2000;Glibert et al 2011). The decline in both P (24) reported by Alpine and Cloern (1992) was much higher than other estimates of P B M(24) reported for the SFE (Table 1) but similar to values reported for some other estuaries (e.g., Pennock and Sharp 1986).…”

“…Like many other urbanized estuaries around the world, the SFE has experienced perturbations in key ecosystem drivers, including sediment and nutrient loads (Schoellhamer 2011;Jassby 2008), quantity and diversity of toxic pollutants (Brooks et al 2012), decreased phytoplankton biomass, and a loss of diatoms (e.g., Alpine and Cloern 1992;Kimmerer 2004;Dugdale et al 2007), and changes in zooplankton and fish (Mueller-Solger et al 2002;Kimmerer 2005). Although the original authors of the light-utilization model for the SFE (Cole and Cloern 1984) predicted that the empirical efficiency factor y would likely respond to such changes, this parameter has been previously recalculated for the northern estuary only twice (Alpine and Cloern 1992;Jassby et al 2002).…”

“…Smaller autotrophs including flagellates and cyanobacteria now appear to dominate the autotrophic community (Lehman 2000;Glibert et al 2011). Phytoplankton community structure was likely altered via size-selective grazing by the clams (Werner and Hollibaugh 1993) although additional drivers, including pesticides (Brooks et al 2012), changing nitrogen-to-phosphorus ratio (Glibert et al 2011), and increased ammonium loads (Dugdale et al 2007;Glibert et al 2011;) have also been implicated. At the same time, reduced sediment loads to the northern SFE, a consequence of damming upstream tributaries (Jassby 2008;Schoellhamer 2011) has resulted in increased water transparency and more favorable conditions for phytoplankton growth.…”

Elevated ammonium concentrations from wastewater discharge depress primary productivity in the Sacramento River and the Northern San Francisco Estuary

“…With the exception of Stockton, major cities in the Northern SFE and Delta do not carry out advanced secondary treatment and discharge N primarily in the form of NH 4 rather than NO 3 . As of 2006, 75% of the effluent released by Delta treatment plants was processed only to the secondary level (Brooks et al, 2011). Approximately 90% of the total N in the Northern SFE originates from a single point source, at the Sacramento Regional WTP (SRWTP), which discharges approximately 15 metric tons of N per day, largely as NH 4 , to the Sacramento River (Jassby, 2008).…”

Perspectives on Bay–Delta Science and Policy

“…Targeted research in the Delta and adjacent waters has shown that Delta water is often acutely or sublethally toxic to a range of aquatic organisms, particularly near sources of urban or agricultural discharge (Brooks et al 2012;Biales et al 2015).…”