Sediment grain size effect on benthic microalgal biomass in shallow aquatic ecosystems

Benthic microalgal biomass is an important fraction of the primary producer community in shallow water ecosystems, and the factors controlling benthic microalgal biomass are complex. One possible controlling factor is sediment grain-size distribution. Benthic microalgal biomass was sampled in sediments collected from two sets of North Carolina estuaries, Massachusetts and Cape Cod bays, and Manukau Harbour in New-Zealand. Comparisons of benthic micro:algal biomass and sediment grain-size distributions in these coastal and estuarine ecosystems frequently showed a negative relationship between the proportion of fine-grained sediments and benthic microalgal biomass measured as chlorophyll a. The highest sedimentary chlorophyll a levels generally occurred in sediments with lower percentages of fine particles (diameter < 125 mm). A negative relationship between the proportion of fine sediments and benthic microalgal biomass suggests anthropogenic loadings of fine sediment may reduce the biological productivity of shallow-water ecosystems.