Constraints on hydraulic parameters and implications for groundwater flux across the upland–estuary interface

Analyses of independent laboratory- and field-scale measurements from two sites on Sapelo Island, Georgia reveal heterogeneity in hydraulic parameters across the upland–estuary interface. Regardless of the method used (short-duration pumping tests, amplitude attenuation of tidal pumping data, sediment grain size distributions, and falling head permeameter tests), we obtain hydraulic conductivity of 10⁻⁴ m s⁻¹ for the fine-grained, well-sorted, clean sands that make up the upland areas. Proximal to the upland–estuary boundary, the tidal pumping analyses and permeameter tests suggest that hydraulic conductivities decrease by more than two orders of magnitude, a result consistent with the presence of a clogging layer. Such a clogging layer may arise due to a variety of physical, chemical, or biological processes. The extent and orientation of the layers of reduced hydraulic conductivity near the upland–estuary boundary influence the nature of the aquifer's response to tidal forcing. Where the lower conductivity layer forms a relatively flat creek bank, tidal pumping produces a primarily mechanical response in the adjacent aquifer. Where the creek bank is nearly vertical, there is a more direct hydraulic connection between the tidal creek and the adjacent aquifer. The clogging layer likely contributes to the development of complicated flow pathways across the upland–estuary boundary. Effective flow paths calculated from tidal pumping data terminate within the marsh, beyond the boundary of the upland aquifer, suggesting a diffuse regime of groundwater discharge in the marsh. We postulate that, in many settings, submarsh flow may be as important as seepage faces for groundwater discharge into the marsh–estuary complex.     

A comparison of congeneric PCB patterns in American eels and striped bass from the Hudson and Delaware River estuaries

The Hudson River estuary has enormous spatial variation in polychlorinated biphenyl (PCB) contamination due in large part to historical point source discharges above Troy Dam. The Delaware River estuary has accumulated significant levels of PCBs through decades of industrial, municipal, and non-point source inputs. The overall goal of this research was to use existing data sets to compare and contrast the patterns of accumulated PCB congeners in sub-populations of American eels and striped bass inhabiting these two estuaries and surrounding coastal waters. Using principal component analysis and analysis of covariance (ANCOVA), inter- and intra-estuarine differences in accumulated congeneric patterns were denoted for both species. Results from our study support the idea that migratory behaviors of striped bass hamper the use of accumulated congener-specific PCB patterns in providing information on localized contamination, although major regional differences were seen between upriver Hudson River fish, downriver Hudson River fish and fish from other areas within this study. This study provides additional evidence for the use of the American eel as a biomonitoring tool, since its limited home range provides finer resolution of regional contamination.     

Polychlorinated biphenyl contamination in selected estuarine and coastal marine finfish and shellfish of New Jersey

Analysis of polychlorinated biphenyls (PCBs) in selected finfish and shellfish from the estuarine and coastal marine waters of New Jersey reveals variable levels of contamination in different regions of the state. Monitoring surveys conducted by the New Jersey Department of Environmental Protection during the last two decades indicate that biota from the northeast region are the most severely contaminated with PCBs. Early monitoring in the 1970s showed that as much as 75% of the finfish and 50% of the shellfish analyzed for Aroclor 1254—the most persistent and toxic mixture of PCBs—contained detectable levels of PCB in their edible flesh. The American eel (Anguilla rostrata), bluefish (Pomatomus saltatrix), striped bass (Morone saxatilis), white catfish (Ictalurus catus), white perch (M. americana), and blue crab (Callinectes sapidus) exhibited high PCB levels in 1981–1982, generally approaching or exceeding the United States Food and Drug Administration action level of 2 ppm fresh weight for these organisms. PCB contamination in finfish and shellfish collected during survey periods of 1986–1987 and 1988–1991 was consistent with the previous years' data showing the northeast region of the state to be the most severely contaminated. Despite decreases in contaminant levels in some species (e.g., striped bass) and regions, results of the most recent survey confirm widespread occurrences of PCBs above background levels in the edible portions of various species from many areas of New Jersey.     

Rifting of oceanic crust at Endeavor Deep on the Juan Fernandez microplate

The development of an anomalously deep rift appears to be a common characteristic of the evolution of microplates along the East Pacific Rise, including the Galapagos, Easter, and Juan Fernandez microplates. We investigate crustal rifting at Endeavor Deep on the Juan Fernandez microplate using bathymetry, gravity and side scan sonar data. An initial phase of lithospheric extension accompanied by extensive subsidence results in the formation of a very deep rift valley (up to 4 km of relief, 70 km long and 20 km wide). Morphological observations and gravity data derived from GEOSAT satellite altimetry show the subsequent initiation of crustal accretion and development of a mature spreading center. Recent models of the kinematics of microplate rotation allow the amount of opening across Endeavor Deep over the past 1 m.y. to be quantified. We develop a simple mechanical model of rifting involving block faulting and flexural response to explain the gravity signature over the rift valley. The Bouguer gravity anomaly is asymmetric with respect to the surface topography and requires that a shallow-dipping fault on the western wall of the valley dominate the extension at Endeavor Deep. Consideration of three similar microplate rift valleys leads us to suggest that asymmetric rifting is the characteristic process forming microplate deeps.