Organic Matter Sources in the Water Column and Sediments of the Hudson River Estuary: the Use of Plant Pigments as Tracers

The purpose of this study was to document inputs of organic matter into the Hudson River Estuary using plant pigments as tracers. Plant pigments (carotenoids and chloropigments) were determined using high pressure liquid chromatography (HPLC). Water column and sediment samples were collected in 1988 and 1989, from stations along a 165 km transect in the Hudson River Estuary. In the water column, high concentrations of lutein were found at stations adjacent to wetland areas indicating inputs of vascular plant detritus, particularly during late fall. Chlorophyll b/lutein ratios at these stations were 2-4 which are similar to that found in fresh vascular plant material collected from the Hudson. Low chlorophyll b/lutein ratios at Haverstraw Bay, a shallow and turbid area of the estuary, indicate high levels of sediment resuspension. Cyanophyte blooms, as indicated by high concentrations of myxoxanthophyll, reach their peak in late summer at the Hudson and Kingston stations. The chlorophyll a from these algae may comprise as much as 78% of the total chlorophyll a pool during these periods. Concentrations of total phaeophorbide, an indicator of grazing activity, were not correlated with chlorophyll a but were correlated with fucoxanthin and/or fucoxanthinol. This correlation suggests that much of the zooplankton grazing activity is associated with high quality food resources such as diatoms and not with cyanophytes. Surface sediments from a coarse-grained sandy habitat had significantly lower amounts of total organic matter than muddy habitats. However, the sandy sediment had higher grazing activity per gram organic matter, as indicated by total phaeophorbides. Higher concentrations of chlorophyll a and fucoxanthin at the sandy habitat indicate the presence of benthic diatoms which are high quality (low C/N ratio) living resources in contrast to the detrital sources (high C/N, mostly vascular plant) at the muddy stations. High concentrations of chlorophyllide a at some muddy stations, near macrophyte beds, suggest inputs of epiphytic diatom detritus. Overall, sediment pigments of the Hudson estuary are derived from vascular plant material that does not reflect the pigment signature of the water column.