Mark E. Hines

Anaerobic metabolism: linkages to trace gases and aerobic processes

This review of anaerobic metabolism emphasizes aerobic oxidation, because the two processes cannot be separated in a complete treatment of the topic. It is process oriented and highlights the fascinating microorganisms that mediate anaerobic biogeochemistry. We begin this review with a brief discussion of CO 2 assimilation by autotrophs, the source of most of the reducing power on Earth, and then consider the biological processes that harness this potential energy. Energy liberation begins with the decomposition of organic macromolecules to relatively simple compounds, which are simplified further by fermentation. Methanogenesis is considered next because CH 4 is a product of acetate fermentation, and thus completes the catabolism of organic matter, particularly in the absence of inorganic electron acceptors. Finally, the organisms that use nitrogen, manganese, iron, and sulfur for terminal electron acceptors are considered in order of decreasing free-energy yield of the reactions.

Carbon flow to acetate and C1 compounds in northern wetlands

High latitude wetlands are significant sources of atmospheric methane, with emission rates that are susceptible to effects of climate change. Our data demonstrate that unlike mid-latitude wetlands, methane in northern peatlands is not derived from acetate or C1 compounds. These latter compounds accumulate to high levels with acetate as the primary organic end product of anaerobic decomposition. Acetate is ultimately degraded aerobically to carbon dioxide after diffusion into oxic regions of peat. Therefore, organic precursors destined for methane in mid-latitude wetlands are degraded to carbon dioxide in northern wetlands. A warming-induced initiation of acetoclastic methanogenesis could substantially increase methane production.

Formation of alunite, jarosite and hydrous iron oxides in a hypersaline system: Lake Tyrrell, Victoria, Australia

Abstract Alunite (KAl 3 (SO 4 ) 2 (OH) 6 ) and jarosite (KFe 3 (SO 4 ) 2 (OH) 6 ) are common weathering products of aluminosilicates and pyrite. Long-range transport of the constituents forming these minerals and the subsequent deposition of alunite and jarosite in an evaporite setting have not been previously documented. Such conditions for the occurrence of alunite and jarosite were investigated in a hypersaline system where acid groundwater enriched in K, Al, Fe(III) and SO 4 enter a saltplaya lake. Sediment cores were studied by thin section, XRD and SEM-EDS. Groundwater and pore-water chemistries were also analyzed. The results show that alunite and jarosite occur together or as individual layers and cements within the top 20 cm of the sediments, where the groundwater is most concentrated due to evaporation. Hydrous Fe-oxides also occur as cements or vein fillings with the alunite and jarosite, but are distributed throughout the 70-cm sediment column studied. The results are consistent with a model in which alunite and jarosite precipitate as a result of the evaporation of water. Thermodynamic modeling indicates that the pore water in the playa sediments maybe in equilibrium with alunite, jarosite and hydrous Fe-oxides.

Application of static and dynamic enclosures for determining dimethyl sulfide and carbonyl sulfide exchange in Sphagnum peatlands: Implications for the magnitude and direction of flux

A static enclosure method was applied to determine the exchange of dimethyl sulfide (DMS) and carbonyl sulfide (OCS) between the surface of Sphagnum peatlands and the atmosphere. Measurements were performed concurrently with dynamic (flow through) enclosure measurements with sulfur-free air used as sweep gas. This latter technique has been used to acquire the majority of available data on the exchange of S gases between the atmosphere and the continental surfaces and has been criticized because it is thought to overestimate the true flux of gases by disrupting natural S gas gradients. DMS emission rates determined by both methods were not statistically different between 4 and >400 nmol m−2 h−1, indicating that previous data on emissions of at least DMS are probably valid. However, the increase in DMS in static enclosures was not linear, indicating the potential for a negative feedback of enclosure DMS concentrations on efflux. The dynamic enclosure method measured positive OCS flux rates (emission) at all sites, while data using static enclosures indicated that OCS was consumed from the atmosphere at these same sites at rates of 3.7 to 55 nmol m−2 h−1. Measurements using both enclosure techniques at a site devoid of vegetation showed that peat was a source of both DMS and OCS. However, the rate of OCS efflux from decomposing peat was more than counterbalanced by OCS consumption by vegetation, including Sphagnum mosses, and net OCS uptake occurred at all sites. We propose that all wetlands are net sinks for OCS.

Calcification of cyanobacterial mats in Solar Lake, Sinai

Pore-water samples were obtained from the shallow-water part of Solar Lake (Sinai) where luxurious cyanobacterial mats grow. These samples were analyzed for Ca/sup 2 +/, Mg/sup 2 +/, Sr/sup 2 +/, Cl/sup -/, SO/sub 4//sup 2 -/, and titration alkalinity (TA) to determine the role of cyanobacterial growth and degradation on the calcification of the mats. The data are modeled thermodynamically to predict mineral-pore-water equilibria. The data support earlier bacterial and sedimentological studies suggesting that the degradation of the cyanobacterial mat via sulfate reduction is of major importance in the calcification process. 34 references, 1 figure, 2 tables.

Mercury distribution in water, sediment and soil in the Idrijca and SoĉAhca river systems

Although the production of mercury (Hg) at the Idrija mercury mine, Slovenia, stopped in 1994, the tailings and contaminated soils in the mining region are continuously eroded and serve as a permanent source of Hg to the downstream rivers, flood plains and the Gulf of Trieste. The present article describes measurements of total Hg and monomethylmercury (MeHg) in various environmental compartments in the rivers Idrijca and So|

Mercury Methylation by the Methanogen Methanospirillum hungatei

|Ahca and the Gulf of Trieste during the period 1998–2000. Total Hg in the Idrijca river water upstream of the mercury mine varied between 2.8 and 6.9 ng l−1 and increased to 197 ng l−1 downstream of the mercury mine and remained elevated further downstream along the rivers Idrijca and So|

Geochemistry of acid brines : Lake Tyrrell, Victoria, Australia

|Ahca (from c. 10 to 59 ng l−1), with lowest concentrations found in marine waters (from 0.2 to 2.0 ng l−1). The concentrations of total Hg were higher after the rain, which caused erosion and transport of particles enriched with Hg. Concentrations of MeHg were quite variable and did not follow the same trend as total Hg. The concentrations of MeHg in August 1999 were significantly higher than in June 1998, indicating the importance of seasonal effects, as well as hydrological conditions, on the production of MeHg. Above the mercury mine, MeHg was 0.1–0.2 ng l−1 and doubled below the mercury mine. Downstream, in the rivers Idrijca and So|