Habitat use,temporal abundance variability,and diet of blue crabs from a New Jersey estuarine system

In a long-term, spatially comprehensive beam trawl survey of the Navesink River-Sandy Hook Bay estuary, the blue crabCallinectes sapidus was one of the most abundant species. Seasonal changes in abundance were evident, with low abundances in summer followed by peak abundances in the fall, after juveniles recruited to the estuary. We saw no long-term trends in abundance during the 5 yr study. Location in the navesink River or Sandy Hook Bay explained most of the variance in abundance within any one survey. In diet analyses, we found evidence of cannibalism in all seasons, but in the size range of crabs caught in this study (10–180 mm), we did not find a relationship between cannibalism and juvenile crab abundance. Within surveys, crabs divided into 20 mm size categories showed no sizerelated differences in location within the estuary or among 7 habitat types examined (algae bed, amphipod bed, beach, channel, marsh edge, mid-depth, and sandbar). Channels and sandbars tended to exhibit lower crab abundance than other habitats. Shallow habitats with and without cover were equally preferred by juvenile blue crabs, implying that the presence of structure was not critical. Spatial models of crab abundance (<- 80 mm carapace width) to environmental data were fit from several seasons of intensive sampling in the Navesink River-Sandy Hook Bay estuary between summer 1996 and spring 1998. These models indicated that fine-grained sediments, tmmperature, depth, and salinity were good indicators of crab abundance in spring, summer, and fall. Using these spatial models and environmental data collected in subsequent seasons (summer 1998−fall 1999), we were able to predict blue crab abundance in the river as evidenced by significant correlations between predicted and observed abundances. For the size range of crabs examined here, physical conditions may be as important as structural habitat types or cannibalism in determining habitat use in northerly estuaries.     

The Lissajous transformation IV. Delaunay and Lissajous variables

Relations are established between the Delaunay variables defined over a phase space E in four dimensions and the Lissajous variables defined over a four-dimensional phase space F when the latter is mapped onto E by a parabolic canonical transformation.     

陆地生态系统模拟研究中IBIS模型开发应用的回顾和展望

全球动态植被模型(DGVM)是研究生态系统复杂过程和全球变化的强有力工具。本文基于过去20多年全球已发表的文献,对得到广泛关注和应用的DGVM之一——集成生物圈模拟器(Integrated Biosphere Simulator,IBIS)的开发、改进、发展及应用进行了总结。IBIS是一个在全球变化等多领域中有着广泛应用的模型。自1996年诞生以来,IBIS在陆地生态系统的碳、氮、水循环,植被动态、陆气耦合、水域系统耦合和气候变化影响等多个方面取得了验证和应用。本文较为系统地阐述了IBIS模型在V2.5版本后的不同发展方向,主要针对IBIS模型在水文过程(蒸散、土壤水分、地下水、径流)、植被动态(植被功能型、土地覆盖变化)、植被生理过程(植被物候、光合作用、植被生长、碳分配)、土壤生物地球化学过程(土壤碳氮循环及反馈、温室气体排放等)以及包括土地利用变化、干扰与管理等人类活动过程等方面的改进与发展进行了全面的综述;在此基础上,对模型在生态系统生产力、碳水收支、水分利用效率、温室气体排放、自然干扰(干旱、火灾、虫害)和人类活动(土地利用变化、农业经营)等方面的应用,以及模型的技术性改进方面进行了回顾;最后对模型的前景和进一步发展提出了一些见解。     

Ionic exchange in groundwater hydrochemical evolution. Study case: the drainage basin of El Pescado creek (Buenos Aires province,Argentina)

The phreatic aquifer beneath the Pampean plain, in eastern central Argentina, constitutes a relevant source of water supply in the area. The objective of this work was to assess the significance of the cation exchange processes in the hydrochemical evolution of this aquifer, based on a study case located in the middle and upper basin of the El Pescado creek. Results indicate that Ca²⁺/Na⁺ exchange is the main process determining the evolution of groundwater from the recharge areas (Ca–HCO₃) towards the local discharge areas (Na–HCO₃), as well as representing a source of Na⁺ contribution to the water in the aquifer. This hydrochemical characteristic is central to the identification of local discharge areas within a plain environment which extends regionally. The ion exchange capacity of these discharge areas has environmental importance, due to its influence on groundwater quality and potential groundwater uses. These results may be applied to any aquifer sharing similar hydrogeological characteristics.     

Eco-hydrological role of deep aquifers in the Salado sedimentary basin in the Province of Buenos Aires,Argentina

Although not well known, the eco-hydrological functions of deep aquifers (those having no contact with surface hydrological events) play an important role in the hydrological regime because they can affect the type of habitats, the availability of water and nutrients and the salinity of the medium, among other environmental features. This work aims at characterizing the deep Tertiary hydrogeological units of the Salado sedimentary basin in the Province of Buenos Aires, Argentina, at a regional scale, and to determine their environmental importance in the hydrological cycle. The geological characterization of the study area is based on the drilling profiles from oil exploration wells bored by different oil companies between 1948 and 1994, and also from the existing literature. The conclusion is that water exchange between quaternary surface aquifers in contact with atmospheric events and deep tertiary aquifers is one of the main processes that keep the hydrologic balance of the region. Not only is this crucial for the conservation of the numerous and well-developed ecosystems in the basin wetlands, but also significant for the agricultural and cattle-raising activities of the region.     

Response of Nebraska Sand Hills Natural Vegetation to Drought, Fire, Grazing, and Plant Functional Type Shifts as Simulated by the Century Model

The Nebraska Sand Hills exist in a semi-arid climatic environment and the land surface is grassland growing on sandy soils. These soils have been periodically active throughout the Holocene, but are currently stabilized by the vegetation. However, a shift in climate could cause grassland death and eventual sand dune remobilization. Our studies used the CENTURY nutrient cycling and ecosystem model to investigate the impacts of drought, plant functional type, fire, grazing, and erosion on Nebraska Sand Hills vegetation and dune stability. Fire and grazing alone had little impact on the vegetation, but when combined with mild drought, biomass decreased. Overall biomass increased if one plant functional type was allowed to dominate the ecosystem. Addition of as little as 1 mm of erosion per year under current climate conditions decreases vegetation as much as a drought 20 percent drier than the worst of the 1930s drought years in Nebraska.     

The influence of interpolation and station network density on the distributions and trends of climate variables in gridded daily data

We study the influence of station network density on the distributions and trends in indices of area-average daily precipitation and temperature in the E-OBS high resolution gridded dataset of daily climate over Europe, which was produced with the primary purpose of Regional Climate Model evaluation. Area averages can only be determined with reasonable accuracy from a sufficiently large number of stations within a grid-box. However, the station network on which E-OBS is based comprises only 2,316 stations, spread unevenly across approximately 18,000 0.22° grid-boxes. Consequently, grid-box data in E-OBS are derived through interpolation of stations up to 500 km distant, with the distance of stations that contribute significantly to any grid-box value increasing in areas with lower station density. Since more dispersed stations have less shared variance, the resultant interpolated values are likely to be over-smoothed, and extreme daily values even more so. We perform an experiment over five E-OBS grid boxes for precipitation and temperature that have a sufficiently dense local station network to enable a reasonable estimate of the area-average. We then create a series of randomly selected station sub-networks ranging in size from four to all stations within the E-OBS interpolation search radii. For each sub-network realisation, we estimate the grid-box average applying the same interpolation methodology as used for E-OBS, and then evaluate the effect of network density on the distribution of daily values, as well as trends in extremes indices. The results show that when fewer stations have been used for the interpolation, both precipitation and temperature are over-smoothed, leading to a strong tendency for interpolated daily values to be reduced relative to the “true” area-average. The smoothing is greatest for higher percentiles, and therefore has a disproportionate effect on extremes and any derived extremes indices. For many regions of the E-OBS dataset, the station density is sufficiently low to expect this smoothing effect to be significant and this should be borne in mind by any users of the E-OBS dataset.     

Measurement of methanotroph and methanogen signature phosopholipids for use in assessment of biomass and community structure in model systems

Methanotrophic biomass and community structure were assessed for a soil column enriched with natural gas. An increase in microbial biomass, based on phospholipid ester-linked fatty acids (PLFA), was apparent for the natural gas-enriched column relative to a control column and untreated surface soil. Following GC-MS analyses of the derivatized monounsaturated fatty acids, the major component (22% of the PLFA) of the natural gas-enriched column was identified as 18·1Δ 10c. This relatively novel fatty acid has only been previously reported as a major component in methanotrophs. Its presence in the soil, together with other supportive evidence, implies that this microbial metabolic group makes a large contribution to the column flora. Other microbial groups were also recognized and differences compared between the soils analysed. A recently developed HPLC method for the separation and characterisation of archaebacterial phospholipid-derived signature di- and tetra-ether lipids was used to examine methane-producing digesters. With this technique, methanogenic biomasses of approximately 10¹¹ bacteria per g dry weight of digestor material were determined. Differences between ratios of diether to tetraether phospholipids were apparent for the digestors analysed, though the causes are at this stage unknown. Taken together, these two methods can be used to estimate methanotrophic and methanogenic contributions in both model systems and environmental samples.     

Acid neutralization mechanisms and metal release in mine tailings: a laboratory column experiment

Mining and milling of base metal ore deposits can result in the release of metals to the environment. When sulfide minerals contained in mine tailings are exposed to oxygen and water, they oxidize and dissolve. Two principal antagonistic geochemical processes affect the migration of dissolved metals in tailings impoundments: sulfide oxidation and acid neutralization. This study focuses on acid neutralization reactions occurring in the saturated zone of tailings impoundments. To simulate conditions prevailing in many tailings impoundments, 0.1 mol/L sulfuric acid was passed continuously through columns containing fresh, unoxidized tailings, collected at Kidd Creek metallurgical site. The results of this column experiment represent a detailed temporal observation of pH, Eh, and metal concentrations. The results are consistent with previous field observations, which suggest that a series of mineral dissolution-precipitation reactions control pH and metal mobility. Typically, the series consists of carbonate minerals, Al and Fe(III) hydroxides, and aluminosilicates. In the case of Kidd Creek tailings, the dissolution series consists of ankerite-dolomite, siderite, gibbsite, and aluminosilicates. In the column experiment, three distinct pH plateaus were observed: 5.7, 4.0, and 1.3. The releases of trace elements such as Cd, Co, Cr, Cu, Li, Ni, Pb, V, and Zn were observed to be related to the pH buffering zones. High concentrations of Zn, Ni, and Co were observed at the first pH plateau (pH 5.7), whereas Cd, Cr, Pb, As, V, and Al were released as the pH of the pore water decreased to 4.0 or less.