Robert B. Biggs

Chesapeake Bay Anoxia: Origin, Development, and Significance

Anoxia occurs annually in deeper waters of the central portion of the Chesapeake Bay and presently extends from Baltimore to the mouth of the Potomac estuary. This condition, which encompasses some 5 billion cubic meters of water and lasts from May to September, is the result of increased stratification of the water column in early spring, with consequent curtailment of reoxygenation of the bottom waters across the halocline, and benthic decay of organic detritus accumulated from plankton blooms of the previous summer and fall. The Chesapeake Bay anoxia appears to have had significant ecological effects on many marine species, including several of economic importance.

THE ESTUARY AS A SEDIMENT TRAP: ALTERNATE APPROACHES TO ESTIMATING ITS FILTERING EFFICIENCY

Abstract: The trapping efficiency of estuaries for particulate matter is reviewed using box models, evaluation of historical changes in bathymetry, geochronologic data, and the capacity-inflow ratio. Most of the open water estuaries of the world are more or less efficient sediment “filters”. Those which are not have evolved to estuarine deltaic environments. For estuarine systems that we have evaluated, it appears that biologically mediated sedimentation processes have the capability to overwhelm all others in the deposition of fine sediments. For example, the major filter-feeding species in Delaware Bay are capable of depositing 200 times the annual fluvial input of suspended sediment.

Phosphorus Distribution in Sediments of the Delaware River Estuary

In order to determine the primary factors related to the accumulation of phosphorus in estuarine sediments, a study of phosphorus fractions in sediments of the Delaware River Estuary was undertaken. A correlation matrix between the phosphorus fractions, determined by serial extraction, and 14 sediment variables was computed. Total phosphorus and total inorganic phosphorus in the sediment-phosphorus reservoir decreases with increasing salinity. This variation is correlated with decreasing iron oxyhydroxide content in the sediment. Neither clay content nor calcium carbonate content appear to be significantly correlated with variation in total inorganic phosphorus content in the fine-grained sediments of this estuary. Although calcium phosphate is concluded to be a major constituent of the sediment-phosphorus reservoir, there was no evidence found that it is authigenic in this environment.

Metals in Estuarine Sediments: Factor Analysis and Its Environmental Significance

Q-mode factor analysis has been used to partition the variability of environmentally active metals in Delaware Bay sediments. Three factors, identified as a natural background source, an oceanic or seawater source, and an estuarine source, account for 96 percent of the metal variability.

Special Characteristics of Estuaries

Estuaries are characterized by the gradient of salinity in a semi-enclosed coastal system. A working classification for drowned river estuaries has been developed and is based on the dominance of certain terms in the salt balance equation. Tidal and wind energy, as well as freshwater flow and density gradients, are responsible for mixing. Suspended and bottom sediment distribution may be characterized for each estuarine type. These sediments are of exceptional importance to the routes and fates of nutrients and other chemical materials. Although particular estuaries are transient in geological or evolutionary time spans, the estuarine environment has been common through a long geologic time, resulting in the evolution of a group of organisms uniquely capable of using the salinity gradient to a competitive advantage. These species, well adapted to the rigorous estuarine environment, frequently produce high standing crops and biomass from a small number of species. The range of nutrient inputs to the estuarine system is reviewed, along with the major nutrient processes and pathways which operate internally. Particularly successful models of nutrient movement are discussed.

Effect of spoil disposal on benthic invertebrates

Abstract Hydraulic dredging and spoil disposal behind the inner breakwater in Delaware Bay has an impact over several kilometres from the site of operations. While dissolved oxygen and the density of animals fell in the areas immediately affected, the total impact of this operation appears to have been small. There may even have been some recruitment of animals to the spoil areas after the operations.