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 µM), and a measurable depletion of surface water dissolved oxygen (equivalent to an apparent oxygen utilization of 100–250 µg‐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.