Factors affecting short-term variability in sediment pH as a function of marsh elevation in a Virginia mesohaline marsh

An analysis of 5 days of nearly continuously recorded sediment temperature, pH, and radiation measurements along a transect in a mesohaline marsh in Virginia suggests there was a shift in control over short-term pH variability from tidal inundation to radiation with height of the marsh surface at least in the surficial sediments. There was little evidence for tidal control of pH variability at depth in the sediment column. However, biological control of subsurface pH variability was evident both near the tidal creek and in the high marsh. Sediment pH means were generally highest toward the tidal creek and lower in the high marsh. The latter zone had the highest pH variability with diurnal pH excursions up to two units being observed during the experimental period. It is hypothesized that macrophyte transpiration or a series of interlocking mechanisms associated with photosynthesis and microbial activity were responsible for the pH excursions observed at depth in the marsh, since the rapid changes in pH were triggered at sunrise and sunset. The large excursions in sediment pH in the high marsh rhizosphere suggest that geochemical activity may be dynamic over the diurnal cycle.