The effect of artificially restricted tidal exchange in a California salt marsh

The hydrology of coastal marshes is being increasingly manipulated by human activities.  The effects of these hydrological alterations have been widely investigated in east coast marshes, but few studies have thoroughly examined the effects in west coast salt marshes, especially while taking into account the variation associated with site, season and tidal elevation.  The objective of my study was to examine in a central California salt marsh (1) how tidal restriction affects salt marsh sediments, (2) how sediment quality affects the tissue quality of the dominant vegetation (Salicornia virginica), and (3) how the response of sediments and vegetation to tidal restriction varies with marsh elevation and time.  I found a significant effect of tidal exchange*time*elevation and of site*time on sediment salinity, moisture and NH₄-N, as well as an effect of elevation and of site*time on S. virginica tissue salinity, C:N, and sediment NO₃-N.  I also found more depleted δ¹³C values of S. virginica tissue at higher elevations compared to middle and lower elevations, and a trend towards more depleted δ¹⁵N values of S. virginica tissue at tidally restricted sites.  Overall, my results suggest that the effects of alterations in tidal exchange cannot be fully examined without taking into account spatial and temporal variability.  Understanding how this system is responding to increasing alterations in hydrology is essential for directing management efforts to conserve the few remaining west coast salt marshes.