NEARSHORE SEDIMENTATION IN CHESAPEAKE BAY: POTENTIAL EFFECTS ON SAV DISTRIBUTIONS AND ANTHROPOGENIC MODIFICATIONS

Sediment characteristics in nearshore (<~2m) Chesapeake Bay environments show significant spatial and temporal variability that can impact benthic organisms, particularly submerged aquatic vegetation (SAV). To examine these variations, 3-m long vibracores have been collected in a variety of nearshore environments. At each site, a geochronology is established with ²¹⁰Pb (half-life 22.3 y), verified with ¹³⁷Cs (half-life 30.7 y), and down-core profiles of grain size and organic content are compared with historical SAV distributions evident in aerial photographs. Two themes emerge from this research: 1) sedimentary characteristics (i.e., grain size and accumulation rate) likely influence SAV distributions, and 2) anthropogenic activities, such as shoreline hardening and breakwater construction, modify the type of sediment that accumulates in the nearshore. The former is consistent with the hypothesis that SAV presence/absence is related to changes in sedimentary characteristics – areas with stable beds have relatively stable sediment composition, while areas with declining beds have either finer sediments when SAV is absent or a reduced accumulation rate that leaves seeds vulnerable to erosion/predation before germination. Overprinted on these trends are anthropogenic modifications. In particular, shoreline hardening appears to result in more fine and organic material supplied to the nearshore that could ultimately prove detrimental to SAV. The effect of breakwaters is more site-specific, depending on sediment supply. However, in general, sediment behind breakwaters tends to be finer and more organic, with an increase in sedimentation rate post-construction, relative to an adjacent control site.