PHYSICAL AND MINERALOGICAL PROPERTIES OF COASTAL SANDS AND THEIR IMPACT ON BIOGEOCHEMICAL ACTIVITY AND THE MODIFICATION OF LAND-DERIVED SUBSTANCES

Beach sand is not a biogeochemical desert as was once believed, but rather dynamic and productive. In addition to providing many ecological services, a sandy beach is a focus of important economic activity. As a result, coastal managers must balance preserving the ecosystem services it provides while cultivating a booming beach economy. Engineering interventions such as beach nourishment strike a delicate balance between these two goals. The aim of this research study is to examine relationships between sedimentary geophysical characteristics and biogeochemical reactivity, as they vary across natural and nourished beaches of Long Bay, South Carolina.

Sand from the swash zone of four sites along Long Bay is analyzed for its permeability, porosity, grain size distribution statistics, organic matter content, and carbonate content. The four sites show statistically significantly different values for these properties, that largely determine the role of sand grains as a microbiological habitat. Preliminary nutrient addition experiments confirm significant uptake rates and, in the case of phosphate, a positive relationship between sand grain size and uptake rate. Based on these preliminary results, flow-through chamber experiments are designed to measure fluxes of oxygen, inorganic nitrogen, phosphate, iron, and other redox-sensitive species. Fluxes of these chemical species are indicative of microbially-mediated reactivity. The data are used to test for relationships between geophysical properties and biogeochemical fluxes. Finally, sampling and experimentation with sand from an active nourishment project pre- and post-nourishment reveal the impact, if any, of a rapid anthropogenic disturbance on the biogeochemical function on the beach as a result of significant changes in geophysical and mineralogical properties of the sand.

This study helps gain insight into the biogeochemical functioning of beaches of Long Bay, South Carolina, the predictive power of geophysical and mineralogical properties as to the reactivity of sand, and potentially important considerations around sand selection for beach nourishment. We expect that our findings will add to the growing body of knowledge of the ecological services provided by beach sands.