A Biogeochemical View of Estuarine Eutrophication: Seasonal and Spatial Trends and Correlations in the Delaware Estuary

Abstract

The Delaware River and Bay Estuary is one of the major urbanized estuaries of the world. The 100-km long tidal river portion of the estuary suffered from major summer hypoxia in the past due to municipal and industrial inputs in the urban region; the estuary has seen remarkable water quality improvements from recent municipal sewage treatment upgrades. However, the estuary still has extremely high nutrient loading, which appears to not have much adverse impact. Since the biogeochemistry of the estuary has been relatively similar for the past two decades, our multiple year research database is used in this review paper to address broad spatial and seasonal patterns of conditions in the tidal river and 120 km long saline bay. Dissolved oxygen concentrations show impact from allochthonous urban inputs and meteorological forcing as well as biological influences. Nutrient concentrations, although high, do not stimulate excessive algal biomass due to light and multiple nutrient element limitations. Since the bay does not have strong persistent summer stratification, there is little potential for bottom water hypoxia. Elevated chlorophyll concentrations do not exert much influence on light attenuation since resuspended bottom inorganic sediments dominate the turbidity. Dissolved inorganic carbon and dissolved and particulate organic carbon distributions show significant variability from watershed inputs and lesser impact from urban inputs and biological processes. Ratios of dissolved and particulate carbon, nitrogen, and phosphorus help to understand watershed and urban inputs as well Electronic supplementary material The online version of this article (as autochthonous biological influences. Owing to the relatively simple geometry of the system and localized anthropogenic inputs as well as a broad spatial and seasonal database, it is possible to develop these biogeochemical trends and correlations for the Delaware Estuary. We suggest that this biogeochemical perspective allows a revised evaluation of estuarine eutrophication that should have generic value for understanding other estuarine and coastal waters.

Elevated ammonium concentrations from wastewater discharge depress primary productivity in the Sacramento River and the Northern San Francisco Estuary

“…20-ml dissolved inorganic carbon (DIC) samples were collected in glass scintillation vials, preserved according to Sharp et al (2009) with 200 lL 5% w/v HgCl 2 and stored in the dark. These data were used for calculating 13 C uptake rates.…”

“…However, study of estuarine eutrophication globally for more than three decades has revealed a range of ecosystem responses to nutrient enrichment (Sharp, 2001). Increased nutrients may lead to eutrophication with undesirable consequences, but not in all cases (Cloern, 2001;Sharp et al, 2009). Rather than stimulating algal processes, negative effects on phytoplankton physiology have been observed (MacIsaac et al, 1979;Wilkerson et al, 2006).…”

Seasonal variability of the inorganic carbon system in a large coastal plain estuary

“…Depending on river discharge conditions, DIC concentrations typically range from about 300 to 1200 µmol kg at the head of the estuary at Trenton (Sharp et al, 2009). During the spring and summer surveys when discharge was high, DIC and TA concentrations were about 300 µmol kg −1 lower than concentrations in the fall when river discharge was low (Fig.…”

The effect of inorganic nitrogen speciation on primary production in the San Francisco Estuary

“…After collection, water was held for 48-h at 50% PAR to allow phytoplankton to reduce the ambient N concentration prior to studying phytoplankton N uptake with increasing NH 4 (Sharp et al, 2009). Samples for inorganic nutrients were passed through a GF/F filter to remove particulate matter before nutrient analysis .…”