Nutrient Dynamics of the Delta: Effects on Primary Producers

Abstract

Increasing clarity of Delta waters, the emergence of harmful algal blooms, the proliferation of aquatic water weeds, and the altered food web of the Delta have brought nutrient dynamics to the forefront. This paper focuses on the sources of nutrients, the transformation and uptake of nutrients, and the links of nutrients to primary producers. The largest loads of nutrients to the Delta come from the Sacramento River with the San Joaquin River seasonally important, especially in the summer. Nutrient concentrations reflect riverine inputs in winter and internal biological processes during periods of lower flow with internal nitrogen losses within the Delta estimated at approximately 30% annually. Light regime, grazing pressure, and nutrient availability influence rates of primary production at different times and locations within the Delta. The roles of the chemical form of dissolved inorganic nitrogen in growth rates of primary producers in the Delta and the structure of the open-water algal community are currently topics of much interest and considerable debate. Harmful algal blooms have been noted since the late 1990s, and the extent of invasive aquatic macrophytes (both submerged and free-floating forms) has increased especially during years of drought. Elevated nutrient loads must be considered in terms of their ability to support this excess biomass. Modern sensor technology and networks are now deployed that make high-frequency measurements of nitrate, ammonium, and phosphate. Data from such instruments allow a much more detailed assessment of the spatial and temporal dynamics of nutrients. Four fruitful directions for future research include utilizing continuous sensor data to estimate rates of primary production and ecosystem respiration, linking hydrodynamic models of the Delta with the transport and fate of dissolved nutrients, studying nutrient dynamics in various habitat types, and exploring the use of stable isotopes to trace the movement and fate of effluent-derived nutrients.

Is Extinction Inevitable for Delta Smelt and Longfin Smelt? An Opinion and Recommendations for Recovery

“…Recent studies suggest increased ammonium concentrations in the Delta and stochiometric ratios of nitrogen and other nutrients may be limiting phytoplankton production in the Delta, a phenomenon referred to as the "Ammonium Paradox" (Dugdale et al 2007;Glibert et al 2011Glibert et al , 2014Glibert et al , 2016Dahm et al 2016;Wilkerson and Dugdale 2016). Decreased ammonium concentrations during high flow periods have coincided with beneficial phytoplankton blooms in the North Delta, suggesting lowered ammonium concentrations may have a positive at least locally (Parker et al 2012a(Parker et al , 2012bDugdale et al 2013;Glibert et al 2014).…”

“…However, it is uncertain whether ammonium is having such a pervasive impact throughout the estuary and given the body of research on the effect of the invasive clam population on phytoplankton in Suisun Bay, this phenomenon has received considerable scrutiny and stimulated debate among researchers in the estuary. For review of the topic we suggest Dahm et al (2016).…”

“…High ammonium concentrations from wastewater have also been strongly implicated in the increased prevalence of Microcystis blooms in the Delta since 1999 (Dahm et al 2016). However, Microcystis blooms in the Delta have also been associated with high irradiance, increased water clarity, warm waters, and low flows (Lehman et al 2008(Lehman et al , 2013.…”

Perspectives on Bay–Delta Science and Policy

“…That is to say, there seemed to be little need to worry about nutrient levels in the Delta. As turbidity is declining in the Delta, however, this view is giving way to a more complex narrative that considers the various forms of nitrogen as well as nutrient ratios, fluid dynamics, and the role of invasive species in productivity at the base of the food web (Dahm et al 2016;Schoellhamer et al 2016). Of particular interest now are the nutrient conditions that promote development of blooms of cyanobacteria, especially Microcystis, and expansion of the waterweeds Egeria densa and Eichhornia crassipes.…”

“…Now, however, increasing water clarity ) may allow phytoplankton to grow fast enough to escape the inhibitory effect of ammonium, and to develop blooms fueled by the abundant nitrate. But phytoplankton in the Delta will now be competing with Microcystis, Egeria, and Eichhornia, which can absorb ammonium preferentially and outcompete phytoplankton for the nutrient pool (Dahm et al 2016). How these invading species will affect the food web is, as yet, uncertain.…”