Abundance and Taxonomic Diversity of Bacteria Inhabiting the Sediment-Water Interface in a Marine Harbor Channel

Ocean Science Journal - The abundance of bacteria inhabiting the sediment-water interface and their taxonomic composition were determined with the fluorescence in situ hybridization (FISH) method...     

Assessment of elemental contamination in estuarine and coastal environments based on geochemical and statistical modeling of sediments

Sediment of variable mineralogical, textural and metal contaminant composition was collected from 38 estuaries along the Atlantic and Gulf of Mexico coasts of the United States and analyzed for total Al, Ag, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Si, Sn, Tl and Zn concentrations. Based on observed covariation of elements at 15 estuaries remote from contaminant inputs, linear regressions of metals on Al were used to model the metal content in baseline sediments. A geochemical model for the covariation was developed, verified and used to guide the statistical modelling approach. Comparison of metal concentrations predicted by the models with those occurring in uncontaminated geological materials suggests that baseline relationships are valid for the entire region sampled. Using these baseline relationships, sediment metal concentrations can be partitioned into natural and anthropogenic fractions. Models improve the comparability of metal levels in sediments by correcting for variable background concentrations that, if left uncorrected, only serve to increase total data variability and reduce detection of spatial and temporal differences.Examples of the application of baseline models to pollution studies are provided. A continuing decline in Pb concentrations in Mississippi River delta sediments is observed consistent with the declining use of Pb additives in gasoline since 1970. Major spatial trends in contaminant metals in sediments along the Atlantic and Gulf of Mexico coasts are noted.     

Asian dustfall in the St. Elias Mountains, Yukon, Canada

In April 2001, a major atmospheric dustfall event occurred in the St. Elias Mountains, Yukon Territory, Canada. Field samples were collected and analyzed for particle size, mineralogy, chemical composition and Sr, Nd and Pb isotopes. Dusts found above ∼3000 m had their source in the Gobi desert region of northern China and Inner Mongolia, and were transported to the Yukon following a series of major dust storms that took place in early April. Dusts found below 3000 m had local (Yukon) or mixed source(s). The Asian dusts had a modal volume diameter of ∼4 μm typical of far-traveled mineral aerosols. However larger (>10 μm) particles were also found at ∼5000 m, suggesting a very rapid trans-Pacific transport in the mid-troposphere. We estimate that the April 2001 event deposited from 5500 to 6335 tons of dust over an area of 21,000 km² in the southwestern Yukon, most of which probably fell within a week. Our findings are consistent with instrumental observations and model simulations of the April 2001 event. While the dust cloud was reportedly mixed with volatile pollutants from Asia, we found no evidence of metal pollution associated with the dustfall in the Yukon. Our findings contribute to clarify the dynamics and the geochemical impact of Asian dust long-range transport events, and to better estimate eolian fluxes of dustborne elements (e.g., Fe) to the Ocean associated with such events. They may also assist in identifying past Asian dust events in ice cores drilled from the St. Elias Mountains icefields, to develop a long-term record of their frequency, magnitude and source(s).