Factors affecting seasonality of lithogenic and biogenic particle flux in a large estuarine ecosystem

Seasonal patterns of vertical flux over two years (2001-2003) at two stations in the Bras d'Or Lakes, a large estuary in Cape Breton Island, Nova Scotia, were determined using aluminum and organic carbon in settled particles collected in moored traps to calculate lithogenic (terrigenous) and marine biogenic fractions. On an annual basis, lithogenic material comprised 53% and 81% of dry weight and 48% and 66% of organic carbon in settled particles at the deep- (128 m) and shallow-water (41 m) locations, respectively. Peaks in runoff, inferred from rain and snowfall precipitation, ice cover and possible horizontal transport of resuspended sediment coincided with maximum sedimentation rates of lithogenic material during unstratified periods between October and March. Biological factors correlated with phytoplankton and ice algal primary production and seasonal changes in zooplankton grazing inferred from phaeopigments controlled biogenic particle fluxes under stratified conditions between June and September and during winter. Year-to-year variations in deposition of lithogenic and marine biogenic material depended on seasonal differences in stratification, precipitation, freeze/melt conditions and the extent of ice cover.