Effect of treated-sewage contamination upon bacterial energy charge, adenine nucleotides, and DNA content in a sandy aquifer on Cape Cod.

Changes in adenylate energy charge (ECA) and in total adenine nucleotides (A(T) and DNA content (both normalized to the abundance of free-living, groundwater bacteria) in response to carbon loading were determined for a laboratory-grown culture and for a contaminated aquifer. The latter study involved a 3-km-long transect through a contaminant plume resulting from continued on-land discharge of secondary sewage to a shallow, sandy aquifer on Cape Cod, Mass. With the exception of the most contaminated groundwater immediately downgradient from the contaminant source, DNA and adenylate levels correlated strongly with bacterial abundance and decreased exponentially with increasing distance downgradient. ECAS (0.53 to 0.60) and the ratios of ATP to DNA (0.001 to 0.003) were consistently low, suggesting that the unattached bacteria in this groundwater study are metabolically stressed, despite any eutrophication that might have occurred. Elevated ECAS (up to 0.74) were observed in glucose-amended groundwater, confirming that the metabolic state of this microbial community could be altered. In general, per-bacterium DNA and ATP contents were approximately twofold higher in the plume than in surrounding groundwater, although ECA and per-bacterium levels of A(T) differed little in the plume and the surrounding uncontaminated groundwater. However, per-bacterium levels of DNA and A(T) varied six- and threefold, respectively, during a 6-h period of decreasing growth rate for an unidentified pseudomonad isolated from contaminated groundwater and grown in batch culture.(ABSTRACT TRUNCATED AT 250 WORDS)     

The ecology of a subterranean isopod, Caecidotea tridentata

1. The blind isopod Caecidotea tridentata is the dominant invertebrate in a simple community of subterranean organisms inhabiting the local, shallow aquifer under Konza Prairie, Kansas, U.S.A.
2. The ecology of this karst aquifer was explored by sieving water from a spring, collecting water samples for analysis, and manipulating sediments and invertebrates in the laboratory. The size frequency distribution was stable and gravid females were present throughout the year, suggesting continuous reproduction.
3. The number of isopods collected per litre was negatively correlated with discharge and the abundance of bacteria, but positively related to the numbers of an amphipod ( Bactrurus hubrichti ). This may be explained if both the isopods and the amphipods track the saturated zone below the top of the water table; at lower discharge, the top of the water table is closer to the spring outlet. The suspended bacteria wash out in greater numbers with high discharge.
4. When isopods and carbon were added in a pairwise experimental design to sediments collected from the aquifer, the isopods significantly stimulated numbers and activity of planktonic and sedimentary bacteria, while carbon had no effect. This suggests that invertebrates can affect the microbes locally in an aquifer.     

The ecology of a subterranean isopod, Caecidotea tridentata

1. The blind isopod Caecidotea tridentata is the dominant invertebrate in a simple community of subterranean organisms inhabiting the local, shallow aquifer under Konza Prairie, Kansas, U.S.A.
2. The ecology of this karst aquifer was explored by sieving water from a spring, collecting water samples for analysis, and manipulating sediments and invertebrates in the laboratory. The size frequency distribution was stable and gravid females were present throughout the year, suggesting continuous reproduction.
3. The number of isopods collected per litre was negatively correlated with discharge and the abundance of bacteria, but positively related to the numbers of an amphipod ( Bactrurus hubrichti ). This may be explained if both the isopods and the amphipods track the saturated zone below the top of the water table; at lower discharge, the top of the water table is closer to the spring outlet. The suspended bacteria wash out in greater numbers with high discharge.
4. When isopods and carbon were added in a pairwise experimental design to sediments collected from the aquifer, the isopods significantly stimulated numbers and activity of planktonic and sedimentary bacteria, while carbon had no effect. This suggests that invertebrates can affect the microbes locally in an aquifer.     

Dynamics of an oligotrophic bacterial aquifer community during contact with a groundwater plume contaminated with benzene, toluene, ethylbenzene, and xylenes: an in situ mesocosm study

An in situ mesocosm system was designed to monitor the in situ dynamics of the microbial community in polluted aquifers. The mesocosm system consists of a permeable membrane pocket filled with aquifer material and placed within a polypropylene holder, which is inserted below groundwater level in a monitoring well. After a specific time period, the microcosm is recovered from the well and its bacterial community is analyzed. Using this system, we examined the effect of benzene, toluene, ethylbenzene, and xylene (BTEX) contamination on the response of an aquifer bacterial community by denaturing gradient gel electrophoresis analysis of PCR-amplified 16S rRNA genes and PCR detection of BTEX degradation genes. Mesocosms were filled with nonsterile or sterile aquifer material derived from an uncontaminated area and positioned in a well located in either the uncontaminated area or a nearby contaminated area. In the contaminated area, the bacterial community in the microcosms rapidly evolved into a stable community identical to that in the adjacent aquifer but different from that in the uncontaminated area. At the contaminated location, bacteria with tmoA- and xylM/xylE1-like BTEX catabolic genotypes colonized the aquifer, while at the uncontaminated location only tmoA-like genotypes were detected. The communities in the mesocosms and in the aquifer adjacent to the wells in the contaminated area consisted mainly of Proteobacteria. At the uncontaminated location, Actinobacteria and Proteobacteria were found. Our results indicate that communities with long-term stability in their structures follow the contamination plume and rapidly colonize downstream areas upon contamination.     

Protozoa in Subsurface Sediments from Sites Contaminated with Aviation Gasoline or Jet Fuel

Numbers of protozoa in the subsurface of aviation gasoline and jet fuel spill areas at a Coast Guard base at Traverse City, Mich., were determined. Boreholes were drilled in an uncontaminated location, in contaminated but untreated parts of the fuel plumes, and in the aviation gasoline source area undergoing H₂O₂ biotreatment. Samples were taken from the unsaturated zone to depths slightly below the floating free product in the saturated zone. Protozoa were found to occur in elevated numbers in the unsaturated zone, where fuel vapors mixed with atmospheric oxygen, and below the layer of floating fuel, where uncontaminated groundwater came into contact with fuel. The same trends were noted in the biotreatment area, except that numbers of protozoa were higher. Numbers of protozoa in some contaminated areas equalled or exceeded those found in surface soil. The abundance of protozoa in the biotreatment area was high enough that it would be expected to significantly reduce the bacterial community that was degrading the fuel. Little reduction in hydraulic conductivity was observed, and no bacterial fouling of the aquifer was observed during biotreatment.     

The thermal regime of rivers: a review

1. The thermal regime of rivers plays an important role in the overall health of aquatic ecosystems, including water quality issues and the distribution of aquatic species within the river environment. Consequently, for conducting environmental impact assessments as well as for effective fisheries management, it is important to understand the thermal behaviour of rivers and related heat exchange processes. 2. This study reviews the different river thermal processes responsible for water temperature variability on both the temporal (e.g. diel, daily, seasonal) and spatial scales, as well as providing information related to different water temperature models currently found in the literature. 3. Water temperature models are generally classified into three groups: regression, stochastic and deterministic models. Deterministic models employ an energy budget approach to predict river water temperature, whereas regression and stochastic models generally rely on air to water temperature relationships. 4. Water temperature variability can occur naturally or as a result of anthropogenic perturbations, such as thermal pollution, deforestation, flow modification and climate change. Literature information is provided on the thermal regime of rivers in relation to anthropogenic impacts and such information will contribute to the better protection of fish habitat and more efficient fisheries management.     

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.     

Spatial and temporal changes in microbial community structure associated with recharge-influenced chemical gradients in a contaminated aquifer

In a contaminated water-table aquifer, we related microbial community structure on aquifer sediments to gradients in 24 geochemical and contaminant variables at five depths, under three recharge conditions. Community amplified ribsosomal DNA restriction analysis (ARDRA) using universal 16S rDNA primers and denaturing gradient gel electrophoresis (DGGE) using bacterial 16S rDNA primers indicated: (i). communities in the anoxic, contaminated central zone were similar regardless of recharge; (ii). after recharge, communities at greatest depth were similar to those in uncontaminated zones; and (iii). after extended lack of recharge, communities at upper and lower aquifer margins differed from communities at the same depths on other dates. General aquifer geochemistry was as important as contaminant or terminal electron accepting process (TEAP) chemistry in discriminant analysis of community groups. The Shannon index of diversity (H) and the evenness index (E), based on DGGE operational taxonomic units (OTUs), were statistically different across community groups and aquifer depths. Archaea or sulphate-reducing bacteria 16S rRNA abundance was not clearly correlated with TEAP chemistry indicative of methanogenesis or sulphate reduction. Eukarya rRNA abundance varied by depth and date from 0 to 13% of the microbial community. This contaminated aquifer is a dynamic ecosystem, with complex interactions between physical, chemical and biotic components, which should be considered in the interpretation of aquifer geochemistry and in the development of conceptual or predictive models for natural attenuation or remediation.     

Using Boreholes as Windows into Groundwater Ecosystems

Groundwater ecosystems remain poorly understood yet may provide ecosystem services, make a unique contribution to biodiversity and contain useful bio-indicators of water quality. Little is known about ecosystem variability, the distribution of invertebrates within aquifers, or how representative boreholes are of aquifers. We addressed these issues using borehole imaging and single borehole dilution tests to identify three potential aquifer habitats (fractures, fissures or conduits) intercepted by two Chalk boreholes at different depths beneath the surface (34 to 98 m). These habitats were characterised by sampling the invertebrates, microbiology and hydrochemistry using a packer system to isolate them. Samples were taken with progressively increasing pumped volume to assess differences between borehole and aquifer communities. The study provides a new conceptual framework to infer the origin of water, invertebrates and microbes sampled from boreholes. It demonstrates that pumping 5 m³ at 0.4–1.8 l/sec was sufficient to entrain invertebrates from five to tens of metres into the aquifer during these packer tests. Invertebrates and bacteria were more abundant in the boreholes than in the aquifer, with associated water chemistry variations indicating that boreholes act as sites of enhanced biogeochemical cycling. There was some variability in invertebrate abundance and bacterial community structure between habitats, indicating ecological heterogeneity within the aquifer. However, invertebrates were captured in all aquifer samples, and bacterial abundance, major ion chemistry and dissolved oxygen remained similar. Therefore the study demonstrates that in the Chalk, ecosystems comprising bacteria and invertebrates extend from around the water table to 70 m below it. Hydrogeological techniques provide excellent scope for tackling outstanding questions in groundwater ecology, provided an appropriate conceptual hydrogeological understanding is applied.     

Dynamics of an Oligotrophic Bacterial Aquifer Community during Contact with a Groundwater Plume Contaminated with Benzene, Toluene, Ethylbenzene, and Xylenes: an In Situ Mesocosm Study

An in situ mesocosm system was designed to monitor the in situ dynamics of the microbial community in polluted aquifers. The mesocosm system consists of a permeable membrane pocket filled with aquifer material and placed within a polypropylene holder, which is inserted below groundwater level in a monitoring well. After a specific time period, the microcosm is recovered from the well and its bacterial community is analyzed. Using this system, we examined the effect of benzene, toluene, ethylbenzene, and xylene (BTEX) contamination on the response of an aquifer bacterial community by denaturing gradient gel electrophoresis analysis of PCR-amplified 16S rRNA genes and PCR detection of BTEX degradation genes. Mesocosms were filled with nonsterile or sterile aquifer material derived from an uncontaminated area and positioned in a well located in either the uncontaminated area or a nearby contaminated area. In the contaminated area, the bacterial community in the microcosms rapidly evolved into a stable community identical to that in the adjacent aquifer but different from that in the uncontaminated area. At the contaminated location, bacteria with tmoA- and xylM/xylE1-like BTEX catabolic genotypes colonized the aquifer, while at the uncontaminated location only tmoA-like genotypes were detected. The communities in the mesocosms and in the aquifer adjacent to the wells in the contaminated area consisted mainly of Proteobacteria. At the uncontaminated location, Actinobacteria and Proteobacteria were found. Our results indicate that communities with long-term stability in their structures follow the contamination plume and rapidly colonize downstream areas upon contamination.     

Distribution of Methanotrophs in Trichloroethylene-Contaminated Aquifers in a Natural Gas Field

The distribution of methanotrophs was examined in shallow aquifers contaminated with trichloroethylene in the southern Kanto gas field, Chiba, Japan. The total populations of methanotrophs and the numbers of methanotrophs producing soluble methane monooxygenase (sMMO) were determined separately. Hydrostratigraphic units of a Pleistocene to Holocene stratum consisted of three aquifers separated by nontransmissive silt layers. Dissolved methane concentrations increased with depth and were highest in the third aquifer. The number of methanotrophs was higher in the second aquifer than in the first aquifer. A clear relationship was observed between microbial populations and lithofacies. The greatest abundance of methanotrophs was observed in the coarse sand layers of the second aquifer, with the lowest abundance observed in silt layers. The high abundance of methanotrophs in the coarse sand in the second aquifer implied that this part of the stratum plays an important role in in situ bioremediation.     

Seasonal and vertical distribution of planktonic bacteria and heterotrophic nanoflagellates in the middle Adriatic Sea

Temporal and spatial patterns of bacteria and heterotrophic nanoflagellates (HNF) were studied monthly from January 1997 to December 1998 in the middle Adriatic Sea. Bacterial and HNF relationships with phytoplankton biomass and temperature were analyzed to examine how the relative importance of bottom-up and top-down factors may shift over seasons and locations. For the coastal area, an inconsistent relationship between bacterial abundance and chlorophyll a and a stronger relationship between bacterial abundance and bacterial production suggest that other substrates than those of phytoplankton origin are important for bacteria. The analysis of simultaneous effects of temperature and bacterial production on bacterial abundance showed that the effect of temperature obscured the effects of bacterial production, suggesting that bacterial growth itself is highly temperature-dependent. The relationship between HNF abundance and bacterial abundance was slightly improved by the inclusion of in situ temperature, bacterial production or both parameters, as additional independent variables. About 60% of the variability in HNF abundance can be explained by bacterial abundance, bacterial production and temperature. In the open sea, tight coupling of bacterial abundance with chlorophyll a concentrations implied that phytoplankton-derived substrates have a dominant role in controlling bacterial abundance. During the colder months, bacterial abundance was high enough to support higher HNF abundance than observed, suggesting that predation exerted a minor depressing influence on bacterial abundance during that period. During the spring-summer period, HNF controlled bacterial standing stocks by direct cropping of bacterial production.Communicated by: H.-D. Franke     

象山港电厂温排水增温对浮游细菌群落空间分布的影响

沿海电厂产生的温排水已造成了较严重的环境问题,如生物病害和赤潮暴发频率增加。现有研究多关注温排水增温对浮游动、植物多样性的影响,而缺乏在物质能量循环过程起核心纽带作用的微生物对增温的响应和反馈。考虑到生态系统对增温的反馈取决于浮游植物的初级生产力和微生物异养呼吸之间的平衡,利用Illumina测序技术结合水体理化性质研究了象山港电厂温排水增温梯度下浮游细菌的空间分布特征。温排水预期的海水增温显著地增加了水体中硝氮(P=0.041,单因素方差分析)、化学需氧量(P0.001)、油污(P=0.004)和余氯(P=0.003)的浓度;但降低了溶解氧(P=0.034)和叶绿素a(P=0.045)的含量。此外,相似性分析发现温排水增温显著地(r=0.338;P=0.042)改变了浮游细菌群落结构,空间分布遵循空间距离-群落相似性衰减(r=-0.582;P=0.026)模型,周转速率为0.0013。细菌多样性主要受水体溶解氧、化学需要量和叶绿素a的影响,分别控制了34.6%、20.1%和10.0%的多样性变异。冗余分析(RDA)群落变异主要受环境因子(包括温度、油污、溶解氧和叶绿素a)的影响,一共解释了55.6%的群落变异;增温仅解释了4.8%的群落变异。因此,浮游细菌群落结构主要受环境因子的影响,这种各因子对群落变异相对贡献比例的特征与增温主要通过改变水质和浮游植物特征,以间接作用影响细菌群落组成的观念一致。此外,细菌多样性和群落组成受不同环境因子的驱动。相比而言,空间距离只控制了较小比例的群落变异(7.1%)。此外,筛选到11个细菌科,这些科的相对丰度与增温幅度显著相关,变化特征与各科已知的生态功能相吻合,如海洋螺菌科(Oceanospirillaceae)中有些菌株能够降解石油污染物,其相对丰度在高油污浓度站点增加(油污浓度与增温幅度正相关,r=0.558;P=0.030);嗜温的弧菌科相对丰度与增温幅度正相关。综上,研究结果初步明确了浮游细菌群落对电厂温排水增温的响应特征,并筛选到敏感的细菌科来指示和预测增温对生态功能的潜在影响。     

Bacteria and viruses in the water column of tropical freshwater reservoirs

In tropical freshwater reservoirs of Sri Lanka, which are linked in an aquatic network, bacterial abundance and production as well as virus abundance, frequency of viral infection and virus production were investigated together with a set of nutrient species (Kjeldahl-N, NO3-N, total P, soluble P, PO4-P). At two characteristic seasons (wet season, dry season), samples were taken from two types of reservoirs (new upland impoundment and ancient, shallow lowland reservoir), each during 4 days at various depths of the entire water columns. Kjeldahl-N and total P were greatly elevated in the wind-mixed water body of the shallow impoundment during the dry season, whereas the deeper reservoir type exhibited no obvious seasonality. In SYBR green trade mark -stained samples, bacterial abundance showed no seasonal pattern in either reservoir type. Bacterial secondary production, however, was significantly elevated in the entire water column of the shallow impoundment under wind-mixed conditions in the dry season. Highest abundance of virus particles and elevated frequency of bacteria containing mature phages were also observed in the shallow reservoir during the dry season indicating favourable conditions for virus propagation. Data from this aquatic network show that most virus parameters, such as abundance or frequency of visibly infected cells, were positively linked to bacterial abundance and production, but also to organic nitrogen or some phosphorus species. We calculated that between 13.2% and 46.1% of the bacterial standing stocks would be subjected to virus-mediated mortality. Estimates of bacteriophage production revealed that from 10 x 10(9) up to 98 x 10(9) phages were produced per litre and day. Bacteria and viruses in the studied tropical freshwater system appear to be linked to various environmental conditions and may affect processes at the ecosystem scale.     

Subsurface Dwelling Crustaceans as Indicators of Hydrological Conditions,Oxygen Concentrations,and Sediment Structure in an Alluvial Aquifer

The relation between environmental conditions and the species composition and individual abundance of crustaceans was investigated in a shallow alluvial aquifer, located in the Danube wetlands (Lobau, Austria). Samples, consisting of groundwater, sediment, and fauna, were taken from permanent installed wells by means of a piston pump five times in a year cycle. The results show that the spatial and temporal distribution, individual abundance, and species richness of crustacean fauna is related to hydrological conditions, oxygen concentrations, and geologic structures in the alluvial aquifer. Therefore, crustaceans, divided in stygoxene, stygophile, and stygobite species, can be used as bioindicators of these environmental conditions in an aquifer. It is suggested that beside physicochemical analyses also the crustacean fauna should be considered to characterise a groundwater ecosystem.     

Robustness to thermal variability differs along a latitudinal gradient in zooplankton communities

Determining how thermal variability will affect the structure, stability, and function of ecological communities is becoming increasingly important as global warming is predicted to affect not only average temperatures but also increase the frequency of long runs of high temperatures. Latitudinal differences in the responses of ecological communities to changes in their thermal regimes have also been predicted based on adaptations over evolutionary time to different thermal environments. We conducted an experiment to determine whether variability in temperature leads to consistent changes in community structure, temporal dynamics, and ecosystem functioning in laboratory analogues of natural freshwater supralittoral rock pool communities inhabited by meiofauna and zooplankton collected from sub‐Arctic, temperate, and tropical regions. Thermal variability of +4 °C around mean temperature led to increased extinction frequency, decreases in consumer abundance, increases in temporal variability of consumer abundance, and shifts from predominately negative interactions observed under constant temperature to positive interactions in the temperate and tropical communities but not in the sub‐Arctic communities. That sub‐Arctic zooplankton communities may be more robust to thermal variability than temperate or tropical communities’ supports recent studies on macrophysiological adaptations of species along latitudinal gradients and suggests that increasing thermal variability may have the greatest effects on community structure and function in tropical and temperate regions.     

Long-term changes within the invertebrate and fish communities of the Upper Rhône River: effects of climatic factors

There is increasing evidence that the global climate change is already having measurable biological impacts. However, no study (based on actual data) has assessed the influence of the global warming on communities in rivers. We analyzed long‐term series of fish (1979–1999) and invertebrate (1980–1999) data from the Upper Rhône River at Bugey to test the influence of climatic warming on both communities. Between the periods of 1979–1981 and 1997–1999, the average water temperature of the Upper Rhône River at Bugey has increased by about 1.5°C due to atmospheric warming. In the same period, several dams have been built from 12.5 to 85 km upstream of our study segment and a nuclear power plant has been built on it. Changes in the community structure were summarized using multivariate analysis. The variability of fish abundance was correlated with discharge and temperature during the reproduction period (April–June): low flows and high temperatures coincided with high fish abundance. Beyond abundance patterns, southern, thermophilic fish species (e.g. chub, and barbel) as well as downstream, thermophilic invertebrate taxa (e.g. Athricops, Potamopyrgus) progressively replaced northern, cold‐water fish species (e.g. dace) and upstream, cold‐water invertebrate taxa (e.g. Chloroperla, Protoneumura). These patterns were significantly correlated with thermal variables, suggesting that shifts were the consequences of climatic warming. All analyses were carried out using statistics appropriate for autocorrelated time series. Our results were consistent with previous studies dealing with relationships between fish or invertebrates and water temperature, and with predictions of the impact of climatic change on freshwater communities. The potential confounding factors (i.e. dams and the nuclear power plant) did not seem to influence the observed trends.     

Impact of groundwater abstraction on a Banksia woodland, Swan Coastal Plain, Western Australia

Summary The Gnangara Groundwater Mound, centred 38 km north of Perth, Western Australia, is a large, shallow unconfined aquifer that is currently under abstraction as part of the public metropolitan water supply. To investigate the impact of lowering groundwater levels on a Banksia woodland on the Mound, vegetation monitoring near a groundwater abstraction bore (known as P50) began 1 year before becoming operational. In February 1991, 2 years after abstraction commenced, extensive death of the Banksia overstorey was observed within close proximity of the bore, following a short period of high summer temperatures. The site was subsequently revisited and the understorey floristic composition, abundance and vigour of overstorey species resurveyed, and compared with data collected from a site under long‐term monitoring and not currently influenced by abstraction. A lowering of groundwater level by 2.2 m at P50 between the summers of 1990 and 1991, resulting from the cumulative effects of abstraction and below average annual rainfall (low groundwater recharge), coincided with a loss of between 20 and 80% of adults of overstorey species and up to 64% of adults of understorey species within 200 m of the bore. Over a similar time period no significant decreases in the abundance of overstorey or understorey species were recorded in the monitored site not influenced by groundwater abstraction. Of the overstorey species, Holly‐leaf Banksia (Banksia ilicifolia) displayed the greatest susceptibility and lowest net recovery following the abstraction event at P50. The negative impact of groundwater drawdown on Holly‐leaf Banksia populations makes this overstorey species an important indicator of decreasing groundwater levels on the Gnangara Groundwater Mound. Water stress may have been the primary cause of vegetation death in close proximity to the P50 bore, although this would have been exacerbated by extreme summer temperatures (> 45°C) recorded during February 1991. The P50 scenario represents a localized response to an acute drawdown event, in association with other environmental factors, and provides invaluable information on the assessment of groundwater abstraction and poor groundwater recharge events on a Banksia woodland community. However, there are limitations in using the community response at P50 to manage the impact of drawdown events on other plant communities occurring on sandy, shallow aquifers.     

Bacterially mediated iron cycling and associated biogeochemical processes in a subtropical shallow coastal aquifer: implications for groundwater quality

Bacterially mediated iron redox cycling exerts a strong influence on groundwater geochemistry, but few studies have investigated iron biogeochemical processes in coastal alluvial aquifers from a microbiological viewpoint. The shallow alluvial aquifer located adjacent to Poona estuary on the subtropical Southeast Queensland coast represents a redox-stratified system where iron biogeochemical cycling potentially affects water quality. Using a 300 m transect of monitoring wells perpendicular to the estuary, we examined groundwater physico-chemical conditions and the occurrence of cultivable bacterial populations involved in iron (and manganese, sulfur) redox reactions in this aquifer. Results showed slightly acidic and near-neutral pH, suboxic conditions and an abundance of dissolved iron consisting primarily of iron(II) in the majority of wells. The highest level of dissolved iron(III) was found in a well proximal to the estuary most likely a result of iron curtain effects due to tidal intrusion. A number of cultivable, (an)aerobic bacterial populations capable of diverse carbon, iron, or sulfur metabolism coexisted in groundwater redox transition zones. Our findings indicated aerobic, heterotrophic respiration and bacterially mediated iron/sulfur redox reactions were integral to carbon cycling in the aquifer. High abundances of dissolved iron and cultivable iron and sulfur bacterial populations in estuary-adjacent aquifers have implications for iron transport to marine waters. This study demonstrated bacterially mediated iron redox cycling and associated biogeochemical processes in subtropical coastal groundwaters using culture-based methods.     

The phreatic aquifer of the ‘Plana de Castellón’ (Spain):relationships between animal assemblages and groundwater pollution

An applied groundwater study of the Plana de Castellón was performed to investigate possible impacts of pollutants on ecological characteristics of the aquifer. The area is illustrative for a western mediterranean coastal plain, densely populated, industrialized, and with intensive agricultural land-use. During one year, six wells in a subsection of the plain were monitored, simultaneously sampled for zoological and physicochemical analysis. Heavy metals and pesticides were not (or at very low levels) detected in the wells. Low correlations were found between physicochemical and biological data, but there were indications that organic pollution affects the abundance of the fauna. A logarithmic relationship between abundance and COD/BOD₅-ratio is postulated. Salinization, an important threat to the groundwater of the area, was clearly reflected in the chemistry of one of the wells. Probably, this process has important consequences for abundance and diversity of the fauna.