[1] The finite-element model WWTM is applied to a system of lagoons at the Virginia Coast Reserve, USA. The model solves the shallow water equations to compute tidal fluxes, and is equipped with a wave propagation module to calculate wave height during local wind events. The model is validated using measured water elevations, wave heights, and periods at five locations within the lagoon system. Scenarios with different wind conditions, storm surges, and relative sea level are simulated. Results are analyzed in terms of bottom shear stresses on the tidal flats, a measure of sediment resuspension potential, and total wave energy impacting the marsh boundaries, which is the chief process driving lateral marsh erosion. Results indicate that wave energy at the marsh boundaries is more sensitive to wind direction than are bottom shear stresses. Wave energy on marsh boundaries and bottom shear stresses on the tidal flats increase with sea level elevation, with the former increasing almost ten times more than the latter. Both positive and negative feedbacks between wave energy at the boundaries and bottom shear stresses are predicted, depending on the fate of the sediments eroded from the salt marsh boundaries.

In shallow coastal ecosystems where most of the seafloor typically lies within the photic zone, benthic autotrophs dominate primary production and mediate nutrient cycling and sediment stability. Because of their different structure and metabolic rates, the 2 functional groups of benthic macrophytes (seagrasses, macroalgae) have distinct influences on benthic−pelagic coupling. Most research to date in these soft-bottomed systems has focused on mature seagrass meadows where shoot densities are high and on dense macroalgal mats that accumulate in response to eutrophication. Relatively little is known about the influence of low-biomass stands of seagrass and macroalgae on nutrient fluxes and sediment suspension. Using an erosion microcosm with controlled forcing conditions, we tested the effects of the eelgrass Zostera marina L. and the invasive macroalga Gracilaria vermiculophylla on sediment suspension and nutrient fluxes under high-flow conditions. At low densities, G. vermiculophylla increased sediment suspension and increased the nutrient flux from the sediment to the water column. For macroalgae, increased sedi ment suspension is likely due to dislodgement of sediment particles by bedload transport of the algae. In this case, the increase in sediment transport was reflected in an increase in nutrient flux from the sediment, showing that modification of physical forcing by benthic primary producers can also affect nutrient flux. The presence or absence of Z. marina did not have a significant effect on nutrient flux. However, the results suggest that there may be a range of low shoot densities for which storm-like flows increase sediment suspension to values higher than those expected for a bare sediment bed.

Seagrass meadows accumulate carbon in sediments as a result of in situ production and sedimentation of particulate organic matter (OM). We quantified the contribution of OM sources to the sediment carbon pool in restored seagrass meadows of different ages (unvegetated and 4 and 10 yr since restoration) in the Virginia coastal bays. Using carbon (C) and nitrogen (N) stable isotopes, we estimated the contribution of seagrass (Zostera marina), benthic diatoms and sestonic particles (BD/S), and macroalgae (MA) to the sediment OM pool influenced by restoration (top 10 cm) with a Bayesian mixing model. Marsh grass was not a likely source based on C:N ratios of the sediment OM. The 4 and 10 yr seagrass meadows had similar OM source contributions to the top 10 cm of sediment, which were distinct from those of unvegetated sites. Seagrass, BD/S, and MA contributed 41, 56, and 3%, respectively, in the 10 yr age treatments and 50, 46, and 4%, respectively, in the 4 yr age treatments. Diagenesis of OM sources had little impact on the source contribution estimates. In combination with carbon accumulation rates at these sites (37 g C m . This study demonstrates how seagrass restoration contributes to the sequestration of 'blue carbon' and quantifies the impact restored seagrass meadow age has on stored sediment carbon.

The smooth cordgrass Spartina alterniflora is the foundation species in intertidal salt marshes of the North American Atlantic coast. Depending on its elevation within the marsh, S. alterniflora may be submerged for several hours per day. Previous ecosystem-level studies have demonstrated that S. alterniflora marshes are a net sink for nitrogen (N), and that removal of N from flooding tidal water can provide enough N to support the aboveground biomass. However, studies have not specifically investigated whether S. alterniflora plants assimilate nutrients through their aboveground tissue. We determined in situ foliar and stem N uptake kinetics for

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