Consolidation and volumetric soil-water content of salt marsh soils following habitat modification for mosquito control

The runnelling form of habitat modification for mosquito control in saltmarsh increases tidal frequency, and may affect soil properties such as volumetric soil-water content and consolidation. The effects of habitat modification on soil properties are in turn likely to affect ecological processes. Runnels constructed mechanically to a depth of no more than 0.3 m with smooth, spoon shaped edges linked isolated mosquito-breeding pools in the high marsh to the tidal source at the saltmarsh/mangrove interface. The physical design of runnels may result in a significant increase in the frequency of flooding tidal events that flush isolated mosquito-breeding pools. Impacts of the runnelling technique were determined at three marshes using two sampling protocols: (a) comparisons between modified and unmodified shores and (b) comparisons with lateral distance from a runnel. At one marsh, volumetric water content was significantly higher at runnelled than at unrunnelled sites after tides that only partly inundated the marsh, but this pattern was not found at the other marshes. Soil consolidation was greater further from the shore, but was not different between runnelled and unrunnelled shores. Measurements at different lateral distances from runnels demonstrated higher water content levels and lower consolidation up to 5 m from runnels and no effect further away. The varied responses to runnelling at different marshes may reflect specific site characteristics such as slope and hydraulic tidal forces. Remedial strategies for similar mosquito control techniques, based on habitat modification, should include dynamic classifications of saltmarshes.