The chemistry of the Delaware estuary. General considerations1

Abstract

Many properties were measured in the Delaware estuary from freshwater to its mouth (30 ‰ salinity). Distinctive mixing patterns in property‐salinity plots illustrate predictable behavior for different parameters. For example, alkalinity always shows an expected positive linear relationship and dissolved organic carbon a negative linear relationship (indicative of conservative mixing). In contrast, phosphate shows a nonlinear plot suggestive of an estuarine source, nitrate a nonlinear plot suggestive of biochemical reactivity, and dissolved iron a nonlinear plot indicative of geochemical reactivity. The upper estuary has very high levels of nutrients, especially nitrate (near 200 µ M), and a measurable depletion of surface water dissolved oxygen (equivalent to an apparent oxygen utilization of 100–250 µ g‐atoms O·liter −1 in winter and summer). However, oxygen levels appear to be consistently above 35% saturation in the upper estuary and are near saturation throughout most of the estuary. The high nutrients do not cause algal blooms in the upper estuary; instead primary productivity appears maximal in the lower estuary. It is postulated that high suspended sediment in the upper estuary causes severe light limitation and as a result moderate utilization of nutrients sustains moderate productivity throughout the estuary and throughout the year.