Geochemistry of biogenic pyrite and ferromanganese coatings from a small watershed: A bacterial connection?

Present‐day groundwater in an alluvial aquifer in Holocene floodplain deposits in east‐central Alabama contains 0.1–4 mg/L Fe, 0.1–0.7 mg/L Mn, ～1–10 μg/L each of Co, Ni, As, Zn, La, and Ce, and 40–175 μ/L Ba. There is a distinct correspondence between trace elements present in groundwater and those concentrated on ferromanganese coatings on present‐day stream alluvium in the study area. This indicates that the reduction and dissolution of such coatings in the alluvial aquifer, probably mediated by Fe‐ and Mn‐reducing bacteria, has been a major control on groundwater chemistry. Authigenic euhedral pyrite crystals up to 1.5 cm in diameter replace lig‐nitic macro wood fragments near the base of the alluvial aquifer, and sulfur isotope data (δ³⁴S values from +3 to ‐40‰_CDT) indicate that pyrite precipitated as a consequence of bacterial sulfate reduction in and adjacent to the irregularly distributed wood fragments. The authigenic pyrite contains several hundred parts per million of As, Co, and Ni, indicating that these trace elements were coprecipitated in pyrite during bacterial sulfate reduction. Results suggest a strong geomicrobiological control on trace element cycling in the study area.     

Stability of interstitial crustacean communities in an isolated alluvial aquifer

The temporal stability of interstitial crustacean communities was investigated in relation to environmental variability in a perched aquifer, characterized by limited connection with surface waters. The author hypothesized that strong physico-chemical stability would enhance persistence and affect dominance patterns for groundwater fauna. Fifteen wells were sampled four times over a two-year period in order to assess the global stability of ground waters and to evaluate temporal changes in species assemblages. For each station, environmental patterns displayed only minor changes, while between-site differences were much larger. At the scale of the aquifer, strong temporal stability was found for groundwater physical and chemical variables. Interstitial crustaceans displayed diverse assemblages dominated by cyclopoid taxa. High persistence characterized community composition and structure (species relative abundance patterns, species richness, Shannon's diversity index) over the study period. Most well faunas were dominated numerically by a single species, whether micro- or macrocrustacean assemblages were considered. Faunal persistence observed in the aquifer was greater than that reported in many surface waters and was probably related to the strong environmental stability.     

环境质量评价中的生物指示与生物监测

通过比较生物指示与生物监测技术和仪器分析技术的分析过程及原理,结合北京市土壤中土壤脲酶与土壤重金属含量之间的相关关系的案例,及生物指示与生物监测技术在水生生态系统及大气污染研究中的应用状况,系统阐述了生物指示与生物监测技术研究的发展历程、研究前沿及发展方向.指出定量校正及不同学科与地区的科学团队的合作是生物指示与生物监测技术研究中需要克服的关键问题,并提出生物指示与生物监测技术研究的目标是整合不同学科的研究方向,为人类健康与环境安全的保护与预测提供技术支持.     

Temporal water stress effects on nodulation,nitrogen accumulation and growth of soybean

The objective of this study, carried out over 2 years, was to evaluate the effect of soil properties on the response of maize (Zea mays L.) to zinc applications and relate these properties to soil test Zn for predicting the Zn status of soils considering the effect of environmental conditions. The relative yield, expressed as an index of crop response, was related through multiple regression to CEC (or clay), electrical conductivity (or exchangeable Na), and bulk density consistently throughout the two year period that included one relatively wet, cool and cloudy growing season when variations in relative yield were explained also by 0.5M NaHCO₃-extractable-P and organic C. A procedure is presented to establish limits for the soil propeties and soil-test-extractable-Zn and to meaningfully combine them into a model to predict soil Zn status. A model that combined soil test Zn, texture and electrical conductivity was satisfactory for the purpose of prediction and for adoption for soil testing on a routine basis. The suggested approach may be suitable for designing models with soil properties associated with crop responses to micronutrients in other situations. Deceased 22 September 1988     

Oxygen supply and the adaptations of animals in groundwater

1. The first part of this review focuses on the oxygen status of natural groundwater systems (mainly porous aquifers) and hyporheic zones of streams. The second part examines the sensitivity of groundwater organisms, especially crustaceans, to low oxygen concentrations (< 3.0 mg L^?1 O₂). 2. Dissolved oxygen (DO) in groundwater is spatially heterogeneous at macro- (km), meso- (m) and micro- (cm) scales. This heterogeneity, an essential feature of the groundwater environment, reflects changes in sediment composition and structure, groundwater flow velocity, organic matter content, and the abundance and activity of micro-organisms. Dissolved oxygen also exhibits strong temporal changes in the hyporheic zone of streams as well as in the recharge area of aquifers, but these fluctuations should be strongly attenuated with increasing distance from the stream and the recharge zone. 3. Dissolved oxygen gradients along flow paths in groundwater systems and hyporheic zones vary over several orders of magnitude (e.g. declines of 9 × 10^?5 to 1.5 ×10^?2 mg L^?1 O₂ m^?1 in confined aquifers and 2 × 10^?2 to 1 mg L^?1 O₂ m^?1 in parafluvial water). Several factors explain this strong variation. Where the water table is close to the surface, oxygen is likely to be consumed rapidly in the first few metres below the water table because of incomplete degradation of soil-generated labile dissolved organic carbon (DOC) in the vadose zone. Where the water table is far from the surface, strong oxygen depletion in the vicinity of the water table does not occur, DO being then gradually consumed as groundwater flows down the hydraulic gradient. In unconfined groundwater systems, oxygen consumption along flow paths may be compensated by down-gradient replenishment of DO, resulting either from the ingress of atmospheric oxygen or water recharge through the vadose zone. In confined groundwater systems, where replenishment of oxygen is impossible, the removal time of DO varies from a few years to more than 10 000 years, depending mainly on the organic carbon content of the sediment. Comparison of the hyporheic zones between systems also revealed strong differences in the removal time and length of underground pathways for DO. This strong variability among systems seems related to differences in contact time of water with sediment. 4. Although groundwater macro-crustaceans are much more resistant to hypoxia than epigean species, they cannot survive severe hypoxia (DO < 0.01 mg L^?1 O₂) for very long (lethal time for 50% of the population ranged from 46.7 to 61.7 h). In severe hypoxia, none of the hypogean crustaceans examined utilized a high-ATP yielding metabolic pathway. High survival times are mainly a result of the combination of three mechanisms: a high storage of fermentable fuels (glycogen and phosphagen), a low metabolic rate in normoxia, and a further reduction in metabolic rate by reducing locomotion and ventilation. It is suggested here that the low metabolic rate of many hypogean species may be an adaptation to low oxygen and not necessarily result from an impoverished food supply. 5. An interesting physiological feature of hypogean crustaceans is their ability to recover from anaerobic stress and, more specifically, rapidly to resynthesize glycogen stores during post-hypoxic recovery. A high storage and rapid restoration of fermentable fuels (without feeding) allows groundwater crustaceans to exploit a moving mosaic of suboxic (< 0.3 mg L?1 O₂), dysoxic (0.3–3.0 mg L^?1 O₂) and oxic (> 3 mg L^?1 O₂) patches. 6. It is concluded that although hypogean animals are probably unsuited for life in extensively or permanently suboxic groundwater, they can be found in small or temporarily suboxic patches. Indeed, their adaptations to hypoxia are clearly suited for life in groundwater characterized by spatially heterogeneous or highly dynamic DO concentrations. Their capacity to survive severe hypoxia for a few days and to recover rapidly would explain partly why ecological field studies often reveal the occurrence of interstitial taxa in groundwater with a wide range of DO.     

Metazoans from a sandy aquifer: dynamics across a physically and chemically heterogeneous groundwater system

We investigated the relationship between groundwater metazoans and their physical and chemical environment in a shallow Atlantic Coastal Plain aquifer adjacent to the Chesapeake Bay, Maryland, USA. Average abundance of the groundwater organisms over a 1 % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaSGaaeaaca% aIXaaabaGaaGOmaaaaaaa!3776!\[{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace}\!\lower0.7ex\hbox{$2$}}\] year period were large (% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaaca% WG4baaaaaa!36FB!\[\overline x \] = 471⁻¹; range = 0–10001⁻¹) and included a wide range of taxa (nematodes, rotifers, copepods, oligochaetes, and others). Highest meiofaunal abundances occurred in the summer and fall with considerable variation across a study site that spanned hundreds of meters. We found that over 70% of the variability in the abundance of total meiofauna at Wye Island could be explained by date, sampling location, and conductivity. Additional physical and chemical factors (e.g., dissolved oxygen, nitrate, dissolved organic carbon) which were significantly related to faunal abundances, differed among taxa. Nematode abundances were negatively related to nitrate concentrations. Copepod and oligochaete abundances were highest at intermediate pH values (4–6). Copepods also occurred in higher abundances at higher conductivity (> 0.25 dS m ⁻¹). Rotifers were most abundant at higher oxygen values (> 6 mg l⁻¹). The high faunal abundances found in this sandy aquifer, and the degree to which such habitats are understudied (especially in North America), suggest a great need for additional research to elucidate factors that control faunal dynamics.     

Effects of thermal energy discharge on shallow groundwater ecosystems

The use of groundwater as a carrier of thermal energy is an important source of sustainable heating and cooling. However, the effects of thermal use on geochemical and biological aquifer characteristics are poorly understood. Here, we have assessed the impacts of heat discharge on an uncontaminated, shallow aquifer by monitoring the hydrogeochemical, bacterial and faunal parameters at an active thermal discharge facility. The observed variability between wells was considerable. Yet, no significant temperature impacts on bacterial or faunal abundance and on bacterial productivity were observed. Also, we did not observe an improved survival or growth of coliforms with temperature. In contrast, the diversity of bacterial terminal restriction fragment (T-RF) length polymorphism fingerprints and faunal populations was either positively or negatively affected by temperature, respectively, and the abundance of selected T-RFs was clearly temperature dependent. Canonical correspondence analysis indicated that both the impact of temperature and of surface water from a nearby river, were important drivers of aquifer biotic variability. These results demonstrate that aquifer thermal energy discharge can affect aquifer bacteria and fauna, while at the same time controlling only a minor part of the total seasonal and spatial variability and therefore posing no likely threat to ecosystem functioning and drinking water protection in uncontaminated, shallow aquifers.     

大陈岛礁海域甲壳类生物多样性特征

以大陈岛礁海域甲壳类为研究对象,多维度分析其多样性时空格局,探索指数间关系,并检验不同层面多样性对局地尺度环境因素的响应。旨在全面多尺度探究大陈岛礁海域甲壳动物群落生态现状,从物种多样性、谱系多样性和功能多样性等不同视角展示该海域生物多样性特征。结果显示:甲壳类群落多样性具有季节异质性,Shannon-Wiener指数(H'')、分类多样性指数(Delta)和分类差异指数(Delta*)在秋、春季显著较高,而功能丰富度指数(FRic)在夏、冬季显著较高,功能分异指数(FDiv)和功能分散指数(FDis)在夏季明显低于其它季节。同一维度内,指数间表现出不同程度相关性,物种多样性指数间相关性相对较强。不同维度间,物种丰富度指数(S)与功能丰富度指数(FRic)中度正相关,分类多样性指数(Delta)和分类差异指数(Delta*)与功能分散指数(FDis)中到高度相关。对于局地尺度环境因子变化的响应,功能多样性最为强烈,谱系多样性次之,而物种多样性的关键生态驱动可能为较大尺度的空间因素。研究表明,不同层面多样性的形成受到不同尺度生态因子驱动,因此综合各维度多样性特征及对应受控因子分析,在生物多样性评估中可揭示指数背后更为全面和完整的生态过程。     

Influence of geographic database scale on prediction of groundwater vulnerability to pesticides

Selection of optimal locations for sampling of groundwater is an important aspect of determining the fate of pesticides in the environment. For large land areas such as states and counties, the interaction of physical and chemical properties of soil, geologic strata, and pesticide molecule are quite complicated and highly variable. This article presents information that shows that the scale of the database influences not only the prediction of the vulnerability of ground‐water to pesticides, but also the areal coverage. In this study, the statewide agricultural pesticide in groundwater model was modified to evaluate the vulnerability of the uppermost aquifer in Woodruff County, AR, to pesticides. The state scale model used soil, geological, and topological databases on a 1:500,000 scale. In contrast, the county‐scale model used databases that were specific to the data layer rather than inferred and used soils at a 1:24,000 scale. A land use component was added to both models to reflect where pesticides are possibly applied in the county. The predictive ability of the two models was compared for nine wells previously sampled for pesticides. On the average, the county‐scale model had higher indices for the wells, indicating a greater vulnerability of groundwater to pesticides at these locations. At the well site where the highest concentration of a pesticide was found, the county‐scale model had a considerably higher vulnerability index.