Copper in the sediment and sea surface microlayer near a fallowed, open-net fish farm

Sediment and sea surface microlayer samples near an open-net salmon farm in Nova Scotia, were analysed for copper. Copper is a constituent of the feed and is an active ingredient of anti-foulants. The salmon farm was placed in fallow after 15years of production. Sampling was pursued over 27months. Elevated copper concentrations in the sediments indicated the farm site as a source. Bubble flotation due to gas-emitting sediments from eutrophication is a likely process for accumulating copper in the sea surface microlayer at enriched concentrations. Elevated and enriched concentrations in the sea surface microlayer over distance from the farm site led, as a result of wind-drift, to an enlarged farm footprint. The levels of copper in both sediments and sea surface microlayer exceeded guidelines for protection of marine life. Over the 27months period, copper levels persisted in the sediments and decreased gradually in the sea surface microlayer.     

Carbon isotopic fractionation in lipids from methanotrophic bacteria: relevance for interpretation of the geochemical record of biomarkers

Experiments with cultured aerobic methane oxidising bacteria confirm that their biomarker lipids will be significantly depleted in 13C compared to the substrate. The methanotrophic bacteria Methylococcus capsulatus and Methylomonas methanica, grown on methane and using the RuMP cycle for carbon assimilation, show maximum 13C fractionation of approximately 30% in the resultant biomass. In M. capsulatus, the maximum fractionation is observed in the earliest part of the exponential growth stage and decreases to approximately 16% as cells approach stationary phase. This change may be associated with a shift from the particulate form to the soluble form of the methane monooxygenase enzyme. Less than maximum fractionation is observed when cells are grown with reduced methane availability. Biomass of M. capsulatus grown on methanol was depleted by 9% compared to the substrate. Additional strong 13C fractionation takes place during polyisoprenoid biosynthesis in methanotrophs. The delta 13C values of individual hopanoid and steroid biomarkers produced by these organisms were as much as l0% more negative than total biomass. In individual cultures, squalene was 13C-enriched by as much as 14% compared to the triterpane skeleton of bacteriohopaneaminopentol. Much of the isotopic dispersion in lipid metabolites could be attributed to shifts in their relative abundances, combined with an overall reduction in fractionation during the growth cycle. In cells grown on methanol, where there was no apparent effect of growth stage on overall fractionation there were still significant isotopic differences between closely related lipids including a 5.3% difference between the hopane and 3 beta-methylhopane skeletons. Hopane and sterane polyisoprenoids were also 13C-depleted compared to fatty acids. These observations have significant implications for the interpretation of specific compound isotopic signatures now being measured for hydrocarbons and other lipids present in sediments and petroleum. In particular, biomarker lipids produced by a single organism do not necessarily have the same carbon isotopic composition.     

泌阳凹陷第三系湖相泥质白云岩中特殊甾烷化合物分布特征及地球化…

在研究羊毛甾烷的基础上，又从泌阳凹陷第三系湖相泥质白云岩地层中检测出了其他系列的特殊甾烷化合物，如３β－乙基甾烷（Ｃ２９－Ｃ３１），３β－正丙基甾烷（Ｃ３０－Ｃ３２）和３β－丁基甾烷（Ｃ３１－Ｃ３３）和甲藻甾烷等。这些特殊甾烷集中出现的情况曾未报道过。除母源输入具有特殊组合外，水体较高盐度和强还原环境可能是这些化合物得以保存的重要原因。     

Balancing urban and peri-urban exchange: water geography of rural livelihoods in Mexico

The peri-urban area is the region where there is a more dynamic interaction between the urban and rural. The peri-urban area supplies natural resources, such as land for urban expansion and agricultural products to feed the urban population. In arid and semi-arid lands, such as northern Mexico, these areas may also be the source of water for the city's domestic demand. In addition, scholars argue that peri-urban residents may have a more advantageous geographical position for selling their labour and agricultural products in cities and, by doing so, sustaining their livelihoods. A considerable number of studies have examined the peri-urban to urban natural resources transfer in terms of land annexation, housing construction, and infrastructure issues; however, the study of the effects of the reallocation of peri-urban water resources to serve urban needs is critical as well because the livelihoods of peri-urban residents, such as those based on agriculture and livestock, depend on water availability. In the case of Hermosillo there is a tremendous pressure on the water resources of peri-urban small farm communities or ejidos because of urban demand. Based on interviews and structured surveys with producers and water managers, this paper examines how peri-urban livelihoods have been reshaped by the reallocation of the city's natural resources in many cases caused some ejido members or ejidatarios to lose livelihoods.     

Induction of DNA strand breaks in the mussel (Mytilus trossulus) and clam (Protothaca staminea) following chronic field exposure to polycyclic aromatic hydrocarbons from the Exxon Valdez spill

In 2002, 13 years after the Exxon Valdez spill, mussels and clams were examined for lingering oil exposure and damage. Known oil patches were sampled at four locations, and compared to nearby reference areas (same bay), and were also compared to "hot reference" sites to verify the methods used (Cordova harbor and fresh diesel spill at Port Chalmers). Passive samplers deployed for a month at the sites, along with tissue samples, confirmed that the oiled sites were oiled (fingerprinting back to Exxon Valdez oil) and that reference sites were clean. The highest PAH loads were detected in sub-surface interstitial waters at oiled sites. Exposure at the surface was generally low level, and probably intermittent. DNA damage was assessed in blood cells using sensitive comet analyses. DNA strand breakage was detected in both mussels and clams, with the highest level of damage detected at "hot reference" sites of Cordova harbor and Port Chalmers. Bioavailability and DNA damage at the oiled sties was low, indicating there has been substantial progress in recovery from the spill 13 years before, yet low level bioavailability and damage were still detectable.     

Predicting summer hypoxia in the northern Gulf of Mexico: riverine N, P, and Si loading

We conducted a statistical analysis to discern the relative strengths of the loading of various forms of nitrogen, phosphorus, dissolved silicate and their molar ratios on the variance in the size of the summertime low oxygen zone found off the Mississippi River, northern Gulf of Mexico. A stable statistical model that included Year and riverine nitrate+nitrite loading for the 2 months prior to the measurement of hypoxic zone size described 82% of its variation in size from 1978 to 2004. The usefulness of the term Year is consistent with the documented increase in carbon stored in sediments after the 1970s, which is when the hypoxic zone is predicted to have become a regular feature on the shelf and to have expanded westward. The increased carbon storage is anticipated to cause a sedimentary respiratory demand influencing the size of the zone, and whose temporal influence is cumulative and transcends the annual variations in nitrogen loading. The variable Year is negatively correlated with the TN:TP ratio in a way that suggests N, not P, has become more important as a factor limiting phytoplankton growth in the last 20 years. Nitrogen, in particular nitrate+nitrite, and not phosphorus, dissolved silicate, or their molar ratios, appears to be the major driving factor influencing the size of the hypoxic zone on this shelf. This conclusion is consistent with cross-system analyses that conclude that the TN:TP ratio in the Mississippi River, currently fluctuating around 20:1, is indicative of nitrogen, not phosphorus, limitation of phytoplankton growth. Nutrient management that places stronger emphasis on reducing nitrogen loading as compared to phosphorus loading, is justified.