Chesapeake Bay Sediments Research Articles

Organic compounds in Chesapeake Bay sediments

The concentrations of organic compounds in bottom sediments from the main stem of the Chesapeake Bay are reviewed. In all stations listed in this paper, a few distinct polynuclear aromatic hydrocarbons (PAH) are present at much higher concentrations than other organic compounds. There is a general trend in concentrations of these PAH decreasing from north to south. This likely reflects the higher human population density in the northern region. Over the time period of 1979 to 1986, the levels of polynuclear aromatic hydrocarbons have remained relatively constant at the stations considered in this manuscript.

Dose-Related Toxicity of Copper and Cadmium in Striped Bass Larvae from the Chesapeake Bay: Field Considerations

Copper and cadmium monitoring in Chesapeake Bay sediments indicates that metal contamination exists in nursery areas for striped bass (Moronesaxatilis), which has been in serious decline over the last 17 years. Whole water metal concentrations in one spawning river were within an order of magnitude of published acutely toxic concentrations. Larval striped bass were exposed in the laboratory to copper and cadmium concentrations which were acutely toxic over a 96h period (24 and 19 µg L−1, respectively), and to sub-lethal concentrations of these metals over a three week period. Larvae from acutely toxic metal treatments, sub-lethal metal concentrations and control tanks were analyzed for cadmium and copper and the frequency distribution of metal body burdens was compared with field data. The distribution of copper concentrations in laboratory-exposed larvae was completely within the range of field specimens, and there was considerable overlap in cadmium frequency distributions from laboratory and field larvae. These results together with other published data suggest that environmental metal concentrations in some spawning tributaries of the Chesapeake Bay may pose a threat to striped bass, and the suggestion is made that greater efforts should be made to link laboratory and field toxicological data.

Origin of Dolomite Cement in Chesapeake Group (Miocene) Siliciclastic Sediments: An Alternative Model to Burial Dolomitization

ABSTRACT Ferroan dolomite and calcite cement fossiliferous sandstone unite in the Choptank and Calvert Formations (Miocene) of western Maryland and northern Virginia. The average composition of the dolomite is Ca.55Mg.43Fe.02CO3, though nonferroan dolomite is also present. The dolomite is generally euhedral and zoned, and it may have fluid-inclusion-rich cores. Calcite cements are dominantly composed of equant spar, though a fine, acicular, isopachous rim cement may be present. Calvert Formation dolomite is chemically similar to Choptank Formation dolomite, though the former contains both calcite inclusions and hollow centers. A relatively simple burial history for ferroan dolomite and calcite cement, coupled with petrographic and isotopic evidence, indicates that some of the dolomite has a marine origin, possibly under the influence of sulfate-reducing organisms. Later recrystallization may have occurred under the influence of alternating marine and meteoric-phreatic conditions. Zoned dolomite rhombs, dolomite with calcite cores, and clear dolomite rims indicate episodic crystallization, possibly due to multiple periods of phreatic conditions. Most of the calcite cement is demonstrably meteoric in origin. Dolomite cement is generally confined to permeable sandy intervals bounded on the top and bottom by clays of low permeability. When buried, this sequence would be similar to dolomite sequences inferred to be of deep burial in origin. The timing of dolomite formation in Chesapeake Bay sediments is significant in that most of the dolomite has derived its magnesium from sources other than the clays, as has been suggested in deep-burial dolomitization models.

C/S method for distinguishing freshwater from marine sedimentary rocks

In organic-rich sediments laid down in fresh water, much less diagenetic pyrite is formed than in analogous marine sediments because of the much lower concentrations of dissolved sulfate found in most fresh waters as compared to seawater. As a result, modern organic-rich freshwater sediments exhibit a much higher organic carbon-to-pyrite sulfur ratio (C/S) than marine sediments with similar organic contents. On this basis, C/S ratios can be used to distinguish ancient marine from freshwater (or slightly brackish) sedimentary rocks. This is demonstrated here for several Carboniferous shales and siltstones. The C/S technique cannot distinguish brackish-water sediments deposited under salinities greater than half that of seawater from marine sediments, as demonstrated by analyses of modern Chesapeake Bay sediments. Also, the method is not applicable to nearly pure limestones or to rocks low in organic matter (less than about 1% organic carbon). Saline (high sulfate) phases of ancient lakes can be distinguished from nonsaline phases using the C/S method.

Methylation of Tin by Estuarine Microorganisms

Mixed inoculums of microorganisms from Chesapeake Bay sediments transformed inorganic tin (SnCl(4) . 5H(2)O) to organotin compounds. Dimethyltin and trimethyltin species were identified as products by gas chromatography-mass spectrometry. Methylated tin species were not observed in sterile controls or in poisoned controls. Thus, estuarine microorganisms have the potential for transforming tin to toxic organotins and for mobilizing tin in the ecosystem.

Regional geochemistry of trace elements in Chesapeake Bay sediments

The concentrations of Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb in 177 surface sediment samples from throughout Chesapeake Bay are reported. Analyses were made of both unfractionated samples and the <63 μm fractions. Analytical uncertainty, always less than ±10%, controlled reproducibility in analyses of the <63 μm fractions, but sampling variance controlled reproducibility in the unfractionated samples, especially when coarse-grained sediments were being analyzed. Sediments in the northernmost part of the bay are enriched relative to average continental crust in all elements except Cr. This reflects the composition of dissolved and suspended material being delivered to that region by the Susquehanna River. The enriched sediments appear not to be transported south of Baltimore in significant quantily. Zinc, cadmium, and lead are enriched relative to average crust throughout the bay and in most other estuaries in the eastern United States.

Time dependent transport in Chesapeake Bay sediments; Part 1, Temperature and chloride

Time dependent transport in Chesapeake Bay sediments; Part 1, Temperature and chloride

Organic material of recent Chesapeake Bay sediments.

Organic material of recent Chesapeake Bay sediments.

The cause of the acoustically impenetrable, or turbid, character of Chesapeake Bay sediments

Many shallow water, fine-grained sediments are almost acoustically impenetrable to the energy from high resolution, low energy continuous seismic profilers. It has been alleged that this anomalous acoustic behavior is the result of interstitial gas bubbles that produce reverberation within the sediment, but no analyses were made until recently to test this hypothesis. Determinations of the compressibility of sediments from acoustically impenetrable, or turbid, zones and from contiguous zones of good penetration in Chesapeake Bay showed that the acoustically turbid sediments are several orders of magnitude more compressible than acoustically clear sediments of very similar grain size. The increased compressibility is a result of the presence of interstitial gas bubbles. Other acoustically turbid zones are produced by buried shell beds, and do not show an increase in compressibility.

OBSERVATIONS OF GASES IN CHESAPEAKE BAY SEDIMENTS1

Summer and winter depth distributions of Ar, N2, CH4, and total CO2 in Chesapeake Bay sediments are reported. Methane increased with depth in the sediment from undetectable quantities at the surface to concentrations of 150 and 85 ml/liter in water depths of 30.4 and 15.2 m. The observed maximum concentrations agree well with values calculated assuming that the CH4 is controlled by ebullition from the sediment. Argon and N2 in the surface sediments were present in concentrations near that of the overlying water and decreased with depth to values of 0.1 and 2 ml/liter. Depth variations of the N2 : Ar ratio indicate selective removal of N2. Stripping by bubbles of CH4 accounts for the selective removal of N2 and the decrease with depth of both Ar and N2. Total CO2 increased with depth to concentrations of 1,500 ml/liter and pH remained uniform with depth at about 7. Low values of total H2S and an abundance of acid‐labile sulfides in the sediments indicate that sulfide species are removed by mineral formation. All depth variations showed a break at about 25‐cm depth, indicating that mixing takes place to this depth.

Chemistry of Southern Chesapeake Bay Sediments

The depositional and early diagenetic environments in southern Chesapeake Bay are interpreted in terms of horizontal and vertical variations of percent content by weight of sediment of (1) organic and inorganic arbon, (2) total phosphorus, (3) total iron, (4) calcium and magnesium, (5) sodium and potassium, and (6) Kjeldahl nitrogen. Sediment reworking activities by benthic invertebrates are shown by non-laminated structure of the sediment and homogeneous vertical distribution of the major cations. Organic carbon and total iron contents are highest in the fine, deepest water sediments. The existence of organoiron complexes in the sediment is supported by a positive correlation between organic carbon and total iron. An aerobic hydrosol condition of the surface sediments is indicated by high phosphorus contents. Organic carbon: Kjeldahl nitrogen ratios suggest that the organic matter of subsurface sediments is largely refractory.

Frequencies of infaunal invertebrates related to water content of Chesapeake Bay sediments : Harrison W. and Marvin L. Wass, 1965. Southeast Geol., 6 (4): 177–187

Frequencies of infaunal invertebrates related to water content of Chesapeake Bay sediments : Harrison W. and Marvin L. Wass, 1965. Southeast Geol., 6 (4): 177–187