Physical Controls on the Distribution of the Submersed Aquatic Weed Egeria densa in the Sacramento-San Joaquin Delta, California and Implications for Habitat Restoration

Abstract

The invasive aquatic plant Egeria densa (Brazilian waterweed) is a submersed aquatic plant that has expanded its distribution in both its native and introduced range. Because the plant grows so densely, it can become a problem for management of waterways and habitat restoration projects. It is difficult to remove once established and mechanical and chemical controls have shown limited effectiveness. Here we analyze the distribution of E. densa in the Sacramento-San Joaquin Delta (the Delta) of California, USA, using environmental variables that include mean water velocity, mean water turbidity, and water column depth. We found that increasing water column depth strongly limited E. densa occurrence, especially when depth at mean lower low water (MLLW) exceeds 2 m. The highest probability of occurrence occurred at locations with a water column depth of-1 to 2 m at MLLW. Turbidity had a reliably negative effect on E. densa occurrence; as water clarity has increased in the Delta, it has likely favored the spread of the plant. Neither mean water velocity nor maximum water velocity had a reliable effect on E. densa probability, in spite of scientific and observational evidence that it is sensitive to flows. These results suggest potentially serious problems with restoration projects that emphasize shallow water habitat in the range favored by E. densa. Without some way to manage spread of the plant-through spraying, sediment loading, or gating-channels in such projects are at risk of being taken over by E. densa. However, these results should be interpreted in light of the fact that water outflow in water year 2008 was very low, and that E. densa abundance may be partially controlled by higher water flows than those considered here.

Fish-Habitat Relationships Along the Estuarine Gradient of the Sacramento-San Joaquin Delta, California: Implications for Habitat Restoration

“…2). The center of the lake is too deep for SAV colonization (~4-5 m; Durand et al 2016), with just a narrow strip of shallow, littoral habitat fringing the perimeter densely colonized by SAV.…”

“…The San Francisco Estuary (SFE) in California, USA, is a large, highly altered estuary where heavy anthropogenic modifications have moderated estuarine variability (Conomos et al 1985;Monismith et al 2002;Monsen et al 2007). Hydrodynamic variability is constrained by year-round dam releases designed to maintain a consistent salinity gradient (Knowles 2002;Lund et al 2008), which dampens variability in several other hydrodynamic variables including turbidity (Durand et al 2016) and temperature (Moyle et al 2012). In addition to a Fig.…”

Modeling the Influence of Outflow and Community Structure on an Endangered Fish Population in the Upper San Francisco Estuary

“…The temporal and spatial coverage of these field surveys has enabled to evaluate the role of hydrodynamic forcing on the distribution and relative abundance of planktonic, pelagic, and benthic species (e.g., [24,38,[55][56][57]). Additional monitoring of aquatic macrophytes by the University of California at Davis, has been conducted extensively using a combination of field sampling and remote sensing in the upper SF Estuary (e.g., [58,59]).…”

Evaluating the Aquatic Habitat Potential of Flooded Polders in the Sacramento–San Joaquin River Delta

“…The alien clams Potamocorbula amurensis (Nichols et al 1990;Kimmerer 2004;Winder and Jassby 2010;Winder et al 2011) and Corbicula fluminea (Hymanson et al 1994) spread throughout the Delta and Suisun Bay, causing chronic phytoplankton depletion. The submersed aquatic weed Egeria densa expanded its range, altering the structure and function of open-water tracts and slow-moving sloughs Toft 2000;Brown 2003;Durand et al 2016). By 2000, pelagic organisms had greatly declined in the upper estuary ).…”

“…However, not all regions of the Delta have responded in the same way. Suisun Marsh has been largely unaffected by the pelagic organism decline (O'Rear and Moyle 2010;personal data 2007-2016. In addition, Suisun Marsh, the CLC, and Liberty Island have had much more limited invasions of submersed aquatic vegetation (SAV) and clams (personal observations 2007-2016Baumsteiger et al 2017).…”