Impact of Surfactant on Configuration of Petroleum Hydrocarbon Lens

A laboratory-scale physical model was constructed for visual observation of the basic 2-D flow characteristics of a gasoline spill through an unconfined aquifer and the subsequent treatment with a surfactant. The model consists of a parallel-plate glass tank (1?m×1?m×5?cm) packed with Ottawa sand. Gasoline was released from a point source in the vadose zone. As the specific gravity of gasoline is less than one (LNAPL), it pooled above the water saturated pores of the tension saturated region of water. Beyond the lens of gasoline, the height of the capillary fringe was reduced due to capillary pollution. The gasoline lens was then treated with an aqueous phase surfactant solution of 2% dodecyl benzene sulfonate (anionic) and 2% polyethoxylate nonyl phenol (nonionic). This surfactant solution reduced the interfacial tension between the gasoline and the aqueous phase by an order of magnitude. The surfactant solution was released from the same point source in the vadose zone as the gasoline. As a result, the location and geometry of the gasoline lens and the polluted capillary fringe were significantly altered. These changes were investigated using vertical equilibrium models, the capillary number, the buoyancy number and the total trapping number to evaluate the approach of pretreatment as a potential remediation strategy.     

The effect of anthropogenic disturbance on the hydrochemical characteristics of riparian wetlands at the Middle Ebro River (NE Spain)

In natural systems, the chemistry of floodplain waters is a function of the source of the water, which is influenced by geomorphic features of riparian wetlands. However, anthropogenic disturbances may alter both geomorphic features and the natural balance of water mixing in the floodplain. The aim of this study was to classify riparian wetlands and characterize their water characteristics in one reach of the Middle Ebro River to assess the hydrochemical functioning of the system. In order to accomplish that goal, water samples were collected at 40 sampling sites during low-water conditions and two floods of different magnitude. Moreover, geomorphic characteristics of riparian wetlands were also analyzed to interpret the results at broader spatio-temporal scales. Three group of wetlands were identified using multivariate ordination: (1) major and secondary channels highly connected to the river by surface water, containing weakly ionized water with high nitrate levels during floods; (2) secondary channels and artificial ponds located in riparian forests near the river, most of which were affected by river seepage during the examined events. This type of sites had high major ions concentrations and elevated spatial variability with respect to nutrient concentrations during floods; (3) Siltated oxbow lakes, whose hydrogeochemical features seemed to be unaffected by factors related to river fluctuations. Total dissolved solids, major ion (sulfate, chloride, sodium, calcium, magnesium, and potassium) and nutrient (nitrate, ammonium and organic nitrogen, and phosphate) depended upon the relationships between surface and subsurface water flows. Seasonal changes and geomorphic characterization indicated that a strong functional dependence of floodplain wetlands close to the main river channel is established, whereas most of the floodplain area remains disconnected from river dynamics. Moreover, the effect of nitrate-enriched agricultural runoff seems to affect water quality and hydrochemical gradients of the system. Based on our results, we propose different types of actions for the management of the Ebro River flow to ensure a more natural ecological functioning of its floodplains. Handling editor: P. Viaroli     

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.     

A methodological approach to the use of terrestrial invertebrates for the assessment of alluvial wetlands

We review progress toward developing a data-analysis system using invertebrate species lists in wetland evaluation procedures. Species lists for Mollusca, Carabidae (Coleoptera), Empidoidea and Syrphidae (Diptera), derived from samples collected at six stations along a transect established at a site on the floodplain of the River Loire (France) provide the raw data. An initial analysis using a traditional ordination method (Correspondence Analysis) is carried out. A data base was established for the 118 mollusc, carabid and syrphid species recorded, and each species was then treated not as a simple integer, but as an amalgam of digitised attributes deemed responsive to wetland conditions, in a correspondence analysis on instrumental variables. Despite the generalized nature of the attributes as defined for this example, the approach demonstrates a marked increase in interpretability of the output of analysis, in respect of the relation between the species and the floodplain environment. It also highlights the value of use of data pertaining to more than one taxonomic group and of selecting these taxonomic groups on the basis of complementarity of their bioindicator potential.Corresponding Editor: J.T.A. Verhoeven     

Diffuse atrazine pollution in German aquifers

Until its prohibition in Germany in 1991, atrazine was the mostfrequently applied herbicide in maize cultivation. Moreover, it was used in orchards andvineyards and as a total herbicide on non-cultivated grounds (railways, factory grounds).Later on, atrazine was substituted mainly by terbutylazine. Terbutylazine and terbutrynare the only s-triazines presently permitted in Germany. Nevertheless, atrazine and itsmetabolite desethylatrazine are by far the most abundant herbicides detected in near surfacegroundwater. This might be due to wash-outs from the pools of atrazine and its metabolitesfrom the soil into the groundwater or continuing illegal applications. Samples takenfrom maize fields in 1994 showed that 6.2% of 471 fields tested were treated with atrazinedespite the prohibition of its use. Nevertheless, the overall trend is in fact a slow decreasein atrazine concentrations where it is detected in groundwater and, simultaneously often aslight increase in desethylatrazine concentrations. But this is not the case forall sampling points, and increasing concentrations in several aquifers are observedas well. Factors governing the adsorption, degradation, persistence and the possible transferinto the aquifer and the current situation concerning atrazine occurrence in German aquiferswill be discussed.     

Microbial Diversity and Biogeochemistry of a Shallow Pristine Canadian Shield Groundwater System

An investigation was conducted to assess the microbial diversity and biogeochemistry of a pristine shallow glaciofluvial groundwater system on the Canadian Shield. Vadose zone sands were very fine-grained, consisting mostly of iron oxide-coated quartz. Below the water table in the saturated zone, iron oxide-coating on quartz grains were absent, owing presumably to reductive dissolution by Fe(III)-reducing bacteria and chemical weathering, respectively. Groundwater pH was circumneutral at 6.4 + 0.1, and Eh was slightly reducing at 349 ± 15 mV compared to local surface waters at 417 ± 21 mV; the total dissolved solids concentration in groundwater was 45.2 ± 6.9 mg/L. A total of 269 clones were sequenced and compiled into a 16S rRNA gene library, and representative operational taxonomic units (OTU) were retrieved from basic local alignment search tool (BLAST) analyses at the species-level across 7 phyla, including Acidobacteria, Actinobacteria, Bacteroidetes, Chlorobi, Firmicutes, Planctomycetes, and Proteobacteria. Aerobic, anaerobic, and facultative anaerobic heterotrophs were predominant among the OTU. Lithoautotrophic ammonium- and nitrite-oxidizers were especially prominent, as were diazotrophs, nitrate- and nitrite-reducers. Representative OTU also included Fe(II)-oxidizers and Fe(III)-reducers, whereas those associated with sulfur cycling were rare. These observations suggest that there is considerable potential for biogeochemical cycling of nitrogen and iron within shallow glaciofluvial groundwater systems on the Canadian Shield.     

Microbiological Comparison of Core and Groundwater Samples Collected from a Fractured Basalt Aquifer with that of Dialysis Chambers Incubated In Situ

Microorganisms associated with basalt core were compared to those suspended in groundwater pumped from the same well in the eastern Snake River Plain Aquifer (Idaho, USA). Two wells located at different distances from the source of a mixed-waste plume in the fractured basalt aquifer were examined. In the well more distal from the plume source, an array of dialysis chambers filled with either deionized water or crushed basalt was equilibrated to compare the microorganisms collected in this fashion with those from core and groundwater samples collected in a traditional manner from the same well. The samples were characterized to determine the total amount of biomass, presence of specific populations or physiological groups, and potential community functions. Microorganisms and their activities were nearly undetectable in core and groundwater collected from the well farthest from the plume source and substantially enriched in both core and groundwater from the well closest to the plume source. In both wells, differences (statistically significant for some measures) were found between bacteria associated with the cores and those suspended in the groundwater. Significantly higher populations were found in the basalt- and water-filled dialysis chambers incubated in the open well compared with core and groundwater samples, respectively. For a given parameter, the variation among dialysis chambers incubated at different depths was much less than the high variation observed among core samples. Analyses on selected basalt- and water-filled dialysis chamber samples suggested that these two communities were compositionally similar but exhibited different potential functions. Documented knowledge of cell physiological changes associated with attachment and potential differences between attached and unattached communities in aquifers indicate that careful consideration should be given to the type of sample media (i.e., core, groundwater, substrata incubated in a well) used to represent a subsurface environment.