Recent Advances in Understanding Flow Dynamics and Transport of Water-Quality Constituents in the Sacramento–San Joaquin River Delta

Abstract

This paper, part of the collection of research comprising the State of Bay-Delta Science 2016, describes advances during the past decade in understanding flow dynamics and how water-quality constituents move within California's Sacramento-San Joaquin River Delta (Delta). Water-quality constituents include salinity, heat, oxygen, nutrients, contaminants, organic particles, and inorganic particles. These constituents are affected by water diversions and other human manipulations of flow, and they greatly affect the quantity and quality of benthic, pelagic, and intertidal habitat in the Delta. The Pacific Ocean, the Central Valley watershed, human intervention, the atmosphere, and internal biogeochemical processes are all drivers of flow and transport in the Delta. These drivers provide a conceptual framework for presenting recent findings. The tremendous expansion of acoustic and optical instruments deployed in the Delta over the past decade has greatly improved our understanding of how tidal variability affects flow and transport. Sediment is increasingly viewed as a diminishing resource needed to sustain pelagic habitat and tidal marsh, especially as sea level rises. Connections among the watershed, Delta, and San Francisco Bay that have been quantified recently highlight that a landscape view of this system is needed, rather than consideration of each region in isolation. We discuss interactions of multiple drivers and information gaps.

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.…”

“…As monitoring data accumulate, new multi-dimensional models of hydrodynamics and distribution of water constituents should become feasible (MacWilliams et al 2016;Schoellhamer et al 2016), allowing dispersal and concentrations of contaminants moving through the Delta to be predicted. Coupled with data on lethal and sublethal toxicities, species distributions, and food webs Fong et al 2016;Perry et al 2016), these tools should facilitate assessments of the species-specific and ecosystem consequences of contaminant loadings in the Delta.…”

“…Work on the components of CASCaDE continues, and this strategy could be elaborated further through inclusion of even more detailed hydrodynamic and water-quality monitoring, and by building in the essential food web dynamics in a landscape ecology context Dahm et al 2016;Fong et al 2016;Grossman 2016;MacWilliams et al 2016;Schoellhamer et al 2016;Weins et al 2016).…”

“…The Delta Plan is to be updated on a regular basis. It is possible that within a few years advances in multidimensional fluid dynamics modeling coupled with physical, chemical, and ecological process modeling (MacWilliams et al 2016;Perry et al 2016;Schoellhamer et al 2016) will allow specific endpoints to be identified that will constitute positive environmental and water supply outcomes. At the very least, development and testing of such models can become a priority in the Science Action Agenda (DSP 2013 …”

Nutrient Dynamics of the Delta: Effects on Primary Producers

“…The proliferation of invasive aquatic macrophytes within the Delta, especially Egeria densa (Brazilian waterweed) and Eichhornia crassipes (water hyacinth), has also raised questions about the sources of nutrients that support summertime coverage of up to 15% of the Delta's waterways by submerged and floating aquatic vegetation (Santos et al 2009). The growing water clarity in the Delta Hestir et al 2013) contributes to the increasing role for primary producers in Delta food webs, and the interactions among primary producers, light, nutrients, and hydrodynamics are emerging as critical Delta research topics (Schoellhamer et al 2016). The chemical forms and concentrations of inorganic nitrogen (i.e., ammonium and nitrate) and the stoichiometry of nitrogen and phosphorus (N : P ratios) are also hypothesized to affect rates of primary production, the composition of the primary producer communities, and the structure of the aquatic food web (Dugdale et al 2007;Parker et al 2012a;Glibert et al 2016).…”