George W. Luther

Inorganic and organic sulfur cycling in salt-marsh pore waters.

Sulfur species in pore waters of the Great Marsh, Delaware, were analyzed seasonally by polarographic methods. The species determined (and their concentrations in micromoles per liter) included inorganic sulfides (≤3360), polysulfides (≤326), thiosulfate (≤104), tetrathionate (≤302), organic thiols (≤2411), and organic disulfides (≤139). Anticipated were bisulfide increases with depth due to sulfate reduction and subsurface sulfate excesses and pH minima, the result of a seasonal redox cycle. Unanticipated was the pervasive presence of thiols (for example, glutathione), particularly during periods of biological production. Salt marshes appear to be unique among marine systems in producing high concentrations of thiols. Polysulfides, thiosulfate, and tetrathionate also exhibited seasonal subsurface maxima. These results suggest a dynamic seasonal cycling of sulfur in salt marshes involving abiological and biological reactions and dissolved and solid sulfur species. The chemosynthetic turnover of pyrite to organic sulfur is a likely pathway for this sulfur cycling. Thus, material, chemical, and energy cycles in wetlands appear to be optimally synergistic.

Pyrite and oxidized iron mineral phases formed from pyrite oxidation in salt marsh and estuarine sediments

Abstract We used scanning electron microscopy and energy dispersive X-ray analysis to examine sediments from vegetated portions of three salt marshes, the Great Sippewissett Marsh (Cape Cod, MA), Sapelo Island (Georgia), and the Hackensack Meadowlands (N.J.), and from the sediments of an estuary, Newark Bay (N.J.). Pyrite particles were abundant in sediments from all sites. Both fine grained pyrite crystals and framboids were found. Single, fine grained crystals (diameter = 0.2 to 2.0 micrometers) predominated in all samples, strong evidence for rapid formation of pyrite. We also found both microcrystalline and framboidal iron-oxyhydroxide phases in many of the sediment samples. This is evidence of pyrite oxidation within the sediments and suggests that iron is conserved in salt marshes even as pyrite is oxidized. The thermodynamic stability of iron phases in marsh sediments, and recent pyrite oxidation studies in coal, suggest goethite as the crystalline iron-oxyhydroxide phase present. In addition, we sometimes found a red amorphous coating on grass roots from the Great Sippewissett and Sapelo Island marshes. This coating is likely a form of hydrated iron (III) oxide.

Trace metal solubility in salt marsh sediments contaminated with sewage sludge

As part of a study to investigate the effect of nutrient and metal pollution on salt marshes, a sewage sludge fertilizer has been applied to experimental plots in Great Sippewissett Marsh, MA, since 1974. The concentration of nutrients, soluble sulfides, and metals were measured in porewater from these plots every 4–6 weeks from April to December in 1980. Metal and nutrient concentrations in these plots were consistently greater than in corresponding control plots. Nutrients stimulated growth of Spartina alterniflora, the dominant vegetation on these plots, and higher grass production increased sediment oxidation. Concentrations of soluble sulfide in fertilized plots were an order of magnitude lower than in surrounding areas. For much of the year sulfides could not be detected in porewater from surface sediments of fertilized plots. The solubility of metals in sediments in fertilized plots was greatly increased by the decrease in sulfide concentrations. For much of the year, the top 4 cm of the sediments in fertilized plots were undersaturated with respect to all metal sulfide minerals. This undersaturation may account for the large loss of metals observed on these plots. It appears that in the surface sediments of these plots the retention of metals may be governed in part by adsorption onto iron oxyhydroxides. Precipitation of metal sulfides may be important in limiting the penetration of metals deeper into the sediment. At 6 cm, Zn and Cd were always close to the solubility of their respective sulfide minerals. Below 4 cm, iron was undersaturated with respect to all iron monosulfide minerals but supersaturated with respect to pyrite. Copper was supersaturated with respect to CuS and Cu2S in all samples where sulfide was above the detection limit. Gel filtration experiments indicated that significant amounts of iron and copper were organically complexed in the porewater and may have been partially responsible for the large supersaturations.

Heavy metal distribution in Newark Bay sediments

Abstract Bottom sediments have been analysed from Newark Bay, New Jersey, for zinc, lead, cadmium, and mercury. The bottom sediment analyses show that the bay sediments are enriched over background levels up to 65 times for zinc, 128 times for lead, 180 times for cadmium, and 155 times for mercury. Analyses of the metal distribution and of available tidal hydraulic data indicate the metal concentrations are due to a combination of source and tidal hydraulics. Dye tracer experiments gathering Lagrangiantype data appear to yield the best result in the investigation of metal trasport phenomena.

On the speciation of metals in the water column of a polluted estuary

Abstract The dissolved ( ;0.40 μm) contains metals in the form of sulphides (Fe, Zn, Cu, Mn), oxides and oxyhydroxides (Si, Al, Fe, Cu, Ni, Sn), phosphate (Ca, Ce, La), clay minerals (Fe, Zn, Cu, Ti) and carbonaceous material (Fe, Cu, Zn) as demonstrated by X-ray microanalysis. The solid phases are likely present in colloidal form in the dissolved fraction of the water column as well. The forms of the metals in the water column are partially due to the resuspension of bottom sediments by dredging and natural processes, to sewage outfall and to natural geochemical processes.

Partial recovery of Newark Bay, NJ, following pollution abatement

Abstract For the seven months terminating on 17 August 1980, primary sewage effluent was discharged into Newark Bay. From 22 July to 6 October 1980, we collected physical, chemical and biological data in the Newark Bay estuary from the lower Passaic River to New York Harbor. During the period of maximum discharge, the Passaic River and much of Newark Bay were anoxic or nearly so. Recovery of the Newark Bay water following sewage abatement took approximately 30 days. During most of the study period, a bloom of blue-green algae characterized the ‘Passaic River water’. This water was also characterized by chlorophyll-a values as high as 73 mg m −3 . Chlorophyll concentration almost always increased up the bay, along with decreasing salinity, increasing temperature, increasing phosphate-P and decreasing nitrate-N. The decrease in nitrate, however, was associated with an increase in ammonia-N and total N during the period of sewage discharge.

Tidal and seasonal variations of sulfate ion in a New Jersey marsh system

Sulfate variations during a tidal cycle were investigated at three sites in a highly polluted tidal marsh. Sulfate- chlorinity relationships were determined in the light of fluctuations in temperature, dissolved oxygen and pH. The relationships were found to be seasonal in nature, being affected by temperature and rainfall effects on biologic productivity. Both reduction of sulfate ion to a sulfide species and oxidation of sulfide species to the sulfate ion were found to occur. Consideration of the sulfide oxidation process suggests the possibility that metals precipitated as sulfides may be mobilized and redistributed in the marsh system.

Voltammetric methods of sulfate ion analysis in natural waters

Abstract Sulfate anion can be measured in waters of widely varying salinity by polarography and amperometry. Polarography is the preferred method because it allows for measurement of sulfate in the 50-ppm range. The polarographic method is rapid, precise, and can be adapted for smaller sample volumes by simple modification of the sample preparation. We report a precision of 0.17% on I.A.P.S.O. standard seawater and 0.90% on 50-ppm samples. Amperometry requires more time overall for analyses because it is a titrimetric method, but it also is a precise technique (0.28% on I.A.P.S.O. standard seawater). Both techniques do not require any unusual sample preparation and are easily performed in most laboratories.