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 sedimen t grain-size distribution. Benthic microalgal biomass was sampled in sedime nts collected from two sets of North Carolina estuaries, Massachusetts and Cape Cod bays, and Manukau Harbour in New-Zealand. Comparisons of benthic m icro:algal biomass and sediment grain-size distributions in these coastal a nd estuarine ecosystems frequently showed a negative relationship between t he proportion of fine-grained sediments and benthic microalgal biomass meas ured as chlorophyll a. The highest sedimentary chlorophyll a levels general ly occurred in sediments with lower percentages of fine particles (diameter < 125 mm). A negative relationship between the proportion of fine sediment s and benthic microalgal biomass suggests anthropogenic loadings of fine se diment may reduce the biological productivity of shallow-water ecosystems.