Spatial and temporal variation in the hydrodynamic landscape in intertidal salt marsh systems

Abstract

Despite the well-accepted role of water flow in mediating ecological processes, the spatial and temporal variation of hydrodynamic conditions experienced by organisms is largely unknown in intertidal estuarine habitats. Current ecological and hydrodynamic sampling approaches may prevent adequate assessment of these impacts by confounding spatial and temporal variation, failing to encompass adequate spatial and temporal variation in measurement and interpretation, and/or not clearly identifying appropriate turbulent flow parameters. We examined spatial and temporal variation in turbulent flow parameters using six acoustic Doppler velocimeters within and among four sites in Wassaw Sound, Georgia, USA. We also collected data across and within sites at time periods corresponding to different tidal types (i.e., neap, mean, and spring). Variation in water flow within sites was similar and highly correlated at locations up to 20 m. In contrast, spatial and temporal variation in water flow among distant sites was highly variable, had lower correlation than within-site comparisons, and exhibited high site specificity for some flow parameters. Flow parameters did not correlate with each other, suggesting that specific parameters need to be identified to correctly interpret the effect of water flow on ecological interactions. Our results suggest that ecological and hydrodynamic measurements need to occur at similar spatial and temporal scales to minimize the confounding impact of spatial and temporal variability in water flow. Further, consideration of these issues should provide a better framework in which to assess the interaction between water flow and ecological processes and help generate testable hypotheses that incorporate how these interactions vary spatially and temporally.