The effects of simulated rain on the erosion threshold and biogeochemical properties of intertidal sediments

The effects of simulated rain on the erosion threshold and biogeochemical properties of cores of muddy intertidal sediments were measured. Rain was simulated with a trailer-mounted device that produced rain with an intensity and drop size similar to that of natural rain. Erosion thresholds were measured with a cohesive strength meter (CSM) and sediment samples for analysis of the biogeochemical properties of the sediment were collected using the cryogenic contact-core technique. Rain caused significant disruption of the sediment surface, often resulting in significantly lower erosion thresholds and increased relative erosion rates. The removal of unconsolidated surface sediments and the revealing of deeper more consolidated sediments, however, caused an increase in the measured erosion threshold and a reduction in erosion rate in some treatments. The biogeochemical properties of the sediment were significantly altered by even a short duration of rain (5 min). Bio-dependent properties such as the amount of chlorophyll a and carbohydrates were generally decreased by rain. The presence of a visible biofilm did not significantly mediate the effects of rain on erosion thresholds, in contrast to their ability to significantly reduce erosion by tidal flows.