Examination of the Relative Influence of Vegetation, Distance from Inflow, and Elevation on Sedimentation in a Coastal Californian Wetland

Ryan M. Bassett, California State University, Monterey Bay


Wetlands and floodplains can act as areas of sediment deposition and storage. Therefore, they have the capability to improve downstream water quality and physical habitat. However, sedimentation rates may vary greatly within even a single wetland or floodplain. Much of the knowledge on wetland sedimentation rates is based on studies in controlled wetlands, where the setting and inflow may be carefully manipulated. While wetland systems receiving unregulated inflows are far more abundant, they are not as well studied. Determining which environmental factors drive deposition patterns may allow land managers to optimize sedimentation in managed wetlands. Additionally, quantified rates of sedimentation and land accretion have become important for managers considering the likelihood of habitat conversion, such as from freshwater wetlands to brackish or salt marsh, given climate change and subsequent sea level rise.

We evaluated the influence of vegetation type and density, elevation, and proximity to the point of inflow on sedimentation in a natural Californian wetland receiving unregulated inflows through model comparison and evidence ratios based on Akaike information criterion weights. In addition to generating an interpolated surface generated from 59 artificial grass mat sediment traps, we conducted a mass-balance sediment budget to act as an independent check of the total sedimentation in the wetland basin. Sedimentation values over the eight month study period ranged from 254.0 to 2875.2 g/m2, with an average of 1054.6 g/m2.We found strong evidence that distance from the point of inflow was the driving factor in depositional patterns, with vegetation also potentially playing a role. However, some of these postulated influences may have been confounded with each other; vegetation type and density were determined to be moderately correlated with distance from the point of inflow (R = 0.273 and R = 0.325, respectively). This limited our ability to conclude if vegetation was a driving influence on observed sedimentation patterns.