Distribution of phosphorus along the Delaware,an urbanized coastal plain estuary

The Delaware Estuary is heavily urbanized with elevated concentrations of phosphorus from industrial and municipal inputs. For 24 research cruises during 1986–1988, total phosphorus (TP) concentration was highest near maximum inputs in the tidal river and at low salinity where turbidity was maximal. In these contiguous regions, average TP concentration over the study period was 5.3–6.1 μM. Downstream of the TP peak in the high turbidity zone of the estuary, TP decreased to minimum concentrations (1.3–1.5 μM) near the mouth of Delaware Bay. Distributions of dissolved reactive (DRP), dissolved organic (DOP), and particulate (PP) phosphorus along the estuary reflected spatial and temporal patterns in phosphorus inputs, turbidity, river flow, and biological production. In the river, DRP was 2–4 μM (51–65% of TP) and inversely related to river flow. PP, although enriched in the river (1–3 μM), was highest (>4 μM) in the turbidity maximum at low salinity. In the bay, distributions of DRP, PP, and DOP were all linked, in different ways, to biological production. The dependence of DOP on production was, however, complex and affected by DRP concentrations. During the past 30 yr, there has been a fourfold decrease in TP concentrations in the tidal river of the Delaware Estuary. This dramatic decrease in TP, however, is contrasted by an apparent increase in DRP concentration over the past 12 yr. This apparent increase in DRP may be linked to improved water quality (e.g., higher pH) in the river over the past decade.