Use of voltammetric solid-state (micro)electrodes for studying biogeochemical processes: Laboratory measurements to real time measurements with an in situ electrochemical analyzer (ISEA)

Solid-state voltammetric (micro)electrodes have been used in a variety of environments to study biogeochemical processes. Here we show the wealth of information that has been obtained in the study of sediments, microbial mats, cultures and the water column including hydrothermal vents. Voltammetric analyzers have been developed to function with operator guidance and in unattended mode for temporal studies with an in situ electrochemical analyzer (ISEA). The electrodes can detect the presence (or absence) of a host of redox species and trace metals simultaneously. The multi-species capacity of the voltammetric electrode can be used to examine complex heterogeneous environments such as the root zone of salt marsh sediments. The data obtained with these systems clearly show that O₂ and Mn²⁺ profiles in marine sedimentary porewaters and in microbial biofilms on metal surfaces rarely overlap indicating that O₂ is not a direct oxidant for Mn²⁺. This lack of overlap was suggested originally by Joris Gieskes' group. In waters emanating from hydrothermal vents, Fe²⁺, H₂S and soluble molecular FeS clusters (FeS_aq) are detected indicating that the reactants for the pyrite formation reaction are H₂S and soluble molecular FeS clusters. Using the ISEA with electrodes at fixed positions, data collected continuously over three days near a Riftia pachyptila tubeworm field generally show that O₂ and H₂S anti-correlate and that H₂S and temperature generally correlate. Unlike sedimentary environments, the data clearly show that Riftia live in areas where both O₂ and H₂S co-exist so that its endosymbiont bacteria can perform chemosynthesis. However, physical mixing of diffuse flow vent waters with oceanic bottom waters above or to the side of the tubeworm field can dampen these correlations or even reverse them. Voltammetry is a powerful technique because it provides chemical speciation data (e.g.; oxidation state and different elemental compounds/ions) as well as quantitative data. Because (micro)organisms occupy environmental niches due to the system's chemistry, it is necessary to know chemical speciation. Voltammetric methods allow us to study how chemistry drives biology and how biology can affect chemistry for its own benefit.     

Dissolved inorganic and organic iodine in the Chesapeake Bay and adjacent Atlantic waters: Speciation changes through an estuarine system

The distributions of iodate, iodide and dissolved organic iodine (DOI) were determined in two deep sub-basins in the Chesapeake Bay, the shallow waters at the mouth of the Bay and the adjacent North Atlantic between the late spring and the early fall along the net flow-path of the water entering and exiting the Chesapeake Bay by using an improved analytical scheme designed for the quantitative recovery of DOI. The concentration of R-DOI found in the surface mixed layer in the upper Bay was about twice of those found at the same location in previous studies. (R-X was the concentration of a dissolved iodine species X that had been normalized to a constant salinity of 35.) Thus, DOI in estuarine waters might have been underestimated significantly in the earlier studies. Following the water along its net flow-path, iodate initially constituted more than 60% of total iodine (TI) in the source water in the Middle Atlantic Bight off the Delmarva Peninsula. As this water entered the Chesapeake Bay through the northern part of its mouth, the concentration of R-iodate decreased while that of R-iodide increased progressively until the former became undetectable in the surface mixed layer while the latter reached a maximum of 0.42 μM in the deep water in the upper Bay. Then, the concentration of R-iodate rebounded while that of R-iodide decreased in the outflowing water that exited through the southern part of the mouth of the Bay and was later entrained by the Gulf Stream. The concentration of R-DOI in the surface waters followed the same pattern as R-iodide and reached a maximum of 0.20 μM in the upper Bay. However, R-DOI was depleted in the deep water in the sub-basins. Its concentration dropped to around the detection limit in the suboxic waters in the upper Bay. R-TI in the Bay far exceeded that in the incoming Middle Atlantic Bight water and reached 0.55 μM in the upper Bay. These distributions of the iodine species suggest that, as water from the Middle Atlantic Bight intruded into the Chesapeake Bay, in the well oxygenated surface mixed layer, iodate was reduced to iodide, and the inorganic iodine species could also be converted to DOI. In the deep water, iodate and DOI were converted to iodide. Superimposed on these inter-conversions among the iodine species, dissolved iodine, possibly in the form of iodide, was also added to the water column from the underlying sediments and the process was especially significant in the suboxic deep water in the upper Bay. Mixing between the surface mixed layer and the deep water could also have increased the concentrations of iodide and total iodine in the former.     

Local and regional species diversity of benthic Isopoda (Crustacea) in the deep Gulf of Mexico

Recent studies of deep-sea faunas considered the influence of mid-domain models in the distribution of species diversity and richness with depth. In this paper, I show that separating local diversity from regional species richness in benthic isopods clarifies mid-domain effects in the distribution of isopods in the Gulf of Mexico. Deviations from the randomised implied species ranges can be informative to understanding general patterns within the Gulf of Mexico. The isopods from the GoMB study contained 135 species, with a total of 156 species including those from an earlier study. More than 60 species may be new to science. Most families of deep-sea isopods (suborder Asellota) were present, although some were extremely rare. The isopod family Desmosomatidae dominated the samples, and one species of Macrostylis (Macrostylidae) was found in many samples. Species richness for samples pooled within sites ranged from 1 to 52 species. Because species in pooled samples were highly correlated with individuals, species diversity was compared across sites using the expected species estimator (n=15 individuals, ES₁₅). Six depth transects had idiosyncratic patterns of ES₁₅, and transects with the greatest short-range variation in topography, such as basins and canyons, had the greatest short-range disparity. Basins on the deep slope did not have a consistent influence (i.e., relatively higher or lower than surrounding areas) on the comparative species diversity. ES₁₅ of all transects together showed a weak mid-domain effect, peaking around 1200–1500 m, with low values at the shallowest and deepest samples (Sigsbee Abyssal Plain); no longitudinal (east–west) pattern was found. The regional species pool was analyzed by summing the implied ranges of all species. The species ranges in aggregate did not have significant patterns across longitudes, and many species had broad depth ranges, suggesting that the isopod fauna of the Gulf of Mexico is well dispersed. The summed ranges, as expected, had strong mid-domain patterns, contrasting with the local species richness estimates. The longitudinal ranges closely matched a randomized pattern (species ranges placed randomly, 1000 iterations), with significant deviations in the east attributable to lower sampling effort. The depth pattern, however, deviated from the mid-domain model, with a bimodal peak displaced nearly 500 m shallower than the mode of the randomized distribution. The deviations from random expectation were significantly positive above 1600 m and negative below 2000 m, with the result that regional species richness peaked between 800 and 1200 m, and decreased rapidly at deeper depths. The highest species richness intervals corresponded to the number of individuals collected. Residuals from a regression of the deviations on individual numbers, however, still deviated from the randomized pattern. In this declining depth-diversity pattern, the Gulf of Mexico resembles other partially enclosed basins, such as the Norwegian Sea, known to have suffered geologically recent extinction events. This displaced diversity pattern and broad depth ranges implicate ongoing re-colonization of the deeper parts of the Gulf of Mexico. The Sigsbee Abyssal Plain sites could be depauperate for historical reasons (e.g., one or more extinction events) rather than ongoing ecological reasons (e.g., low food supply).     

Ecosystem responses to recent oceanographic variability in high-latitude Northern Hemisphere ecosystems

As part of the international MENU collaboration, we compared and contrasted ecosystem responses to climate-forced oceanographic variability across several high latitude regions of the North Pacific (Eastern Bering Sea (EBS) and Gulf of Alaska (GOA)) and North Atlantic Oceans (Gulf of Maine/Georges Bank (GOM/GB) and the Norwegian/Barents Seas (NOR/BAR)). Differences in the nitrate content of deep source waters and incoming solar radiation largely explain differences in average primary productivity among these ecosystems. We compared trends in productivity and abundance at various trophic levels and their relationships with sea-surface temperature. Annual net primary production generally increases with annual mean sea-surface temperature between systems and within the EBS, BAR, and GOM/GB. Zooplankton biomass appears to be controlled by both top-down (predation by fish) and bottom-up forcing (advection, SST) in the BAR and NOR regions. In contrast, zooplankton in the GOM/GB region showed no evidence of top-down forcing but appeared to control production of major fish populations through bottom-up processes that are independent of temperature variability. Recruitment of several fish stocks is significantly and positively correlated with temperature in the EBS and BAR, but cod and pollock recruitment in the EBS has been negatively correlated with temperature since the 1977 shift to generally warmer conditions. In each of the ecosystems, fish species showed a general poleward movement in response to warming. In addition, the distribution of groundfish in the EBS has shown a more complex, non-linear response to warming resulting from internal community dynamics. Responses to recent warming differ across systems and appear to be more direct and more pronounced in the higher latitude systems where food webs and trophic interactions are simpler and where both zooplankton and fish species are often limited by cold temperatures.     

PCB resistance within phytoplankton populations in polluted and unpolluted marine environments

A comparison between clones of two species of diatoms, Asterionella japonica and Ditylum brightwellii, isolated from Sandy Hook, New Jersey (polluted site) and Montauk, New York (unpolluted site) indicated that some of the clones from Sandy Hook were more resistant to polychlorinated biphenyls (PCB). A japonica was less sensitive to PCB than D. brightwellii since seven clones of A. japonica from both sites were tolerant of 25 μg litre^?1 PCB whereas no clones from either site of D. brightwellii showed such resistance. Growth under high light intensity increased the sensitivity to PCB in all clones except one super-resistant clone from Sandy Hook which was not affected even by additions of 50 μg litre^?1 to the growth medium. This interactive effect of light on PCB sensitivity may relate to the photo-adaptive characteristics of each clone.     

Selected chemical contaminants in surface sediments of Commencement Bay and the Tacoma Waterways, Washington, USA

Eight metals, 21 organic priority pollutants, and 11 other contaminants and contaminant-related sediment characteristics were measured in surface sediments (upper 2 cm) at 21 locations in Commencement Bay and the Tacoma Waterways, Washington. Summary statistics were calculated and statistical approaches (analysis of variance, multiple comparisons tests, cluster analysis and principal component analysis) were applied to subsets of the data to classify sediment contamination. Overall sediment contamination was highest in the Sitcum, City and Hylebos Waterways, intermediate in Commencement Bay, at the entrances to the Tacoma Waterways and in the outer reaches of the Blair and Hylebos Waterways, and lowest at the Blair Waterway turning basin, the mouth of the Puyallup River and at a reference site near Browns Point. High concentrations of some contaminants appeared to be related to proximity to sources of contaminants. Depositional vectors, and chemical adsorption processes may also influence the spatial distribution of sediment contamination in the study area.Results of simple and partial correlation analyses indicate that arsenic, iron and manganese may be more closely associated with the clay fraction, while cadmium, copper and polynuclear aromatic hydrocarbons may be more closely associated with the total organic carbon content of sediments. We were unable to discriminate statistically between the affinity of chromium, lead, zinc and phthalates with the % clay or the total organic carbon content of sediments.     

Dispersion of bauxitic red mud in the Gulf of Corinth, Greece

Bauxitic red-mud slurry, discharged by an aluminium processing factory on the shelf of the Gulf of Corinth, Greece, is used as a tracer to examine sediment transport and dispersion processes in a tectonically active deep basin.

The Gulf of Corinth is a silled elongate basin with a maximum depth of 860 m; it is characterised by high seismicity. The red mud is discharged through a pipeline at a depth of 100 m, where it forms an extensive deposit.

Grab sampling has shown that the red mud extends over the slope and the abyssal plain up to a distance of 17 km from the mouth of the pipeline. It forms small scattered sheet-like deposits of up to 3 cm in thickness. The structures observed in the scattered patches of the red mud, which in some places are overlain by a thin veneer of grey/olive green (natural) sediments, suggest that the red mud is transported from the shelf to the abyssal plain by gravitative sediment flows. The flows are triggered by earthquakes.

Granulometric and geochemical analyses of the red-mud samples show that the red mud, during its transport from the shelf to the abyssal plain, is subjected to mixing with the surrounding sediments. A different mixing ratio is determined, however, by reference to the various trace metals (Fe, Ni, Co, Pb).     

Biochemical and ultrastructural observations of long-term silver accumulation in the mussel, Mytilus edulis

The cellular distribution and chemical forms of Ag were determined in mussels after accumulation of the metal from sea water. The major accumulations were either in the vacuoles of connective tissue macrophages, where it was associated with S, or in deposits in the fibrillar layer of the basement membranes of the digestive diverticulum and kidney epithelia, where it was bound to the sulphydryl and sulphate groups of glycoproteins and proteoglycans. In acutely exposed animals, about 10 % of the accumulated Ag was found in a (Ag, Cu)-binding protein with characteristics indicating that it may be a metallothionein. There was a concomitant increase in the body Cu levels after Ag exposure and 40 % of this was bound to this low molecular weight metal-binding protein.     

The US freedom of navigation program preserving the law of the sea

The 1982 United Nations Convention on the Law of the Sea prescribed extensive rules of behavior for the international community in the oceanic regime. Some of the most important provisions of the Convention are those regarding the freedom of navigation and overflight in various maritime zones, i.e. territorial seas, international straits, archipelagos, exclusive economic zones and the high seas.While most coastal nations are complying with the navigation and overflight provisos of the Convention, some are not. Where excessive maritime claims exist, the US has evolved an ambitious Freedom of Navigation (FON) Program which challenges these excessive claims. This Program was initiated under the Carter Administration in 1979 and has continued, unabated, ever since.As the international community prepares for the day when the 1982 Convention becomes universally-recognized international law, there are likely to be periodic excessive maritime claims. In cases where the Convention's dispute settlement provisos fail to resolve excessive claims, the community of nations may find it useful to use the US FON Program as an example for the enforcement of maritime rules.