FROM WATERSHED CLEARANCE TO INDUSTRIALIZATION – THE SEDIMENT RECORD OF ESTUARINE PALEOPRODUCTIVITY

We compare the sediment records of micro-fossil and chemical indicators of estuarine primary production over the history of New Bedford Harbor, Massachusetts. New Bedford Harbor was permanently settled by Europeans around 1676. The primary activity in the watershed was subsistence farming, until the mid eighteenth century when the small estuary began to grow into what would become the world’s largest whaling port. With the subsequent decline of the whaling industry came textile mills and, later, factories producing electrical capacitors and releasing PCBs into the city’s Harbor. Although the Harbor was placed on the EPA’s National Priority List for cleanup (i.e., a Superfund site) because of high concentration of PCBs in its sediments, it is also highly contaminated with metals and other organic chemicals. Population growth paralleled industrial growth and introduced high levels of nutrients in waters, as well.

Our indicators of paleo-primary production (pigments, biogenic silica, diatoms and cysts of autotrophic dinoflagellates) show four major changes in the aquatic ecosystem. Early forest clearance increased nutrient loading to the estuary temporarily stimulating production. A second pulse in production was stimulated by introduction of nutrients with discharge of urban sewage. Later declines in “production” are probably due to improvements in municipal sewage disposal practices, but impacts of the introduction of toxic substances from local industries cannot be discounted. Over this time our diatom record suggests that the base of production also shifted from one that was benthic-dominated to one that was pelagic-dominated. A final increase in production is reflected solely by increased pigment flux in our last years of record, but preceded by a dinoflagellate bloom. We assume this is due to a major shift in the phytoplankton community to one presently dominated by nanoplankton.