The influence of floodplain habitat on the quantity and quality of riverine phytoplankton carbon produced during the flood season in San Francisco Estuary

Abstract

Primary productivity, community respiration, chlorophyll a concentration, phytoplankton species composition, and environmental factors were compared in the Yolo Bypass floodplain and adjacent Sacramento River in order to determine if passage of Sacramento River through floodplain habitat enhanced the quantity and quality of phytoplankton carbon available to the aquatic food web and how primary productivity and phytoplankton species composition in these habitats were affected by environmental conditions during the flood season. Greater net primary productivity of Sacramento River water in the floodplain than the main river channel was associated with more frequent autotrophy and a higher P:R ratio, chlorophyll a concentration, and phytoplankton growth efficiency (a B ). Total irradiance and water temperature in the euphotic zone were positively correlated with net primary productivity in winter and early spring but negatively correlated with net primary productivity in the late spring and early summer in the floodplain. In contrast, net primary productivity was correlated with chlorophyll a concentration and streamflow in the Sacramento River. The flood pulse cycle was important for floodplain production because it facilitated the accumulation of chlorophyll a and wide diameter diatom and green algal cells during the drain phase. High chlorophyll a concentration and diatom and green algal biomass enabled the floodplain to export 14-37% of the combined floodplain plus river load of total, diatom and green algal biomass and wide diameter cells to the estuary downstream, even though it had only 3% of the river streamflow. The study suggested the quantity and quality of riverine phytoplankton biomass available to the aquatic food web could be enhanced by passing river water through a floodplain during the flood season.

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

“…However the data reported here, similar to the limited primary production estimates for the main channel provided by Lehman et al (2008), indicate that primary production and phytoplankton biomass in the Sacramento River in spring are actually lower than rates and stocks found in the Northern SFE (including in the well-described low productivity region of Suisun Bay, e.g. Kimmerer, 2005;Wilkerson et al, 2006).…”

A Conceptual Model of the Aquatic Food Web of the Upper San Francisco Estuary

“…Ponds can create low dissolved oxygen conditions in adjacent sloughs, or export food subsidies (O'Rear and Moyle 2010;O'Rear 2012). Floodplains (such as the Yolo Bypass or Cosumnes River) may provide large seasonal food subsidies to the Delta in the form of detritus (derived from aquatic and terrestrial vegetation), phytoplankton and zooplankton (Sommer et al 2001;Lehman et al 2007). The Sacramento River, as the largest single input into the upper estuary, has large regional influence, and is likely a major source of detrital subsidies to the region (Jassby 2008) (Linkage 1.41).…”

“…Phytoplankton in the upper estuary are dominated by diatoms and microflagellates (Lehman and Smith 1991;Müeller-Solger et al 2002). Linkage 2.11 shows the important, well understood, and predictable effect of silica on diatoms and the small reciprocal effect of diatoms on silica.…”

“…Flows also structure interactions, as when overland flows deliver trophic subsidies (Sommer et al 2001;Lehman et al 2007). Periods of low flow may support phytoplankton blooms in regions of high residence time (Glibert et al 2014).…”

“…A few examples have been cited of broad-scale system response to flow changes. The Yolo Bypass, an off-channel causeway used for diverting Sacramento River flows across a floodplain, may contribute to phytoplankton blooms at times (Lehman et al 2007), but there remain uncertainties as to how these inputs affect downstream food web dynamics and higher trophic levels.…”