Trends in microfluidic systems for in situ chemical analysis of natural waters

Spatially and temporally detailed measurement of ocean, river and lake chemistry is key to fully understanding the biogeochemical processes at work within them. To obtain these valuable data, miniaturised in situ chemical analysers have recently become an attractive alternative to traditional manual sampling, with microfluidic technology at the forefront of recent advances. In this short critical review we discuss the role, operation and application of in situ microfluidic analysers to measure biogeochemical parameters in natural waters. We describe recent technical developments, most notably how pumping technology has evolved to allow long-term deployments, and describe how they have been deployed in real-world situations to yield detailed, scientifically useful data. Finally, we discuss the technical challenges that still remain and the key obstacles that must be negotiated if these promising systems are to be widely adopted and used, for example, in large environmental sensor networks and on low-power underwater vehicles

Longitudinal transformation of nitrogen and carbon in the hyporheic zone of an N-rich stream: A combined modelling and field study

A combined modelling and field study approach was used to examine biogeochemical functioning of the hyporheic zone in two gravel bars in an N-rich fourth-order stream (River Hers, south-west France). Surfacewater and interstitial water were sampledmonthly (August 1994–January 1995), the latter in a network of 29 piezometers in the first gravel bar and 17 in the second. In both gravel bars, the hyporheic zone was created only by advected channelwater without any connectionwith groundwater. Longitudinal chemical profiles of Dissolved Organic Carbon (DOC), nitrate (NO3–N), ammonium (NH4–N) and Dissolved Oxygen (DO) were established for both gravel bars. Ambient and potential denitrification weremeasured in the laboratory during the same period using the acetylene inhibition technique. Factors limiting denitrification were also examined by testing the separate effects of nitrate or nitrate + carbon additions. A 1D reactive-transport model was used to simulate longitudinal transformation of nitrogen in the hyporheic zone, and to estimate the role of organic matter (DOC and POC) in the biogeochemical functioning of the hyporheic zone. Denitrification measurements with nitrate and nitrate + carbon additions both showed increased denitrification, suggesting that denitrification might not be C-limited at this site. Observations and model results showed the hyporheic zone to be a sink of DOC and nitrate, but DOC consumption appeared insufficient to explain nitrate depletion measured in the two gravel bars. Field data were better modelled when an additional DOC source from the POC fraction degraded by anaerobic respiration was included in the model

Microbiological and molecular evaluation of an alluvial water well field and fouling-related phenomena

An important source of water for the city of North Battleford, Saskatchewan is groundwater extracted from wells installed adjacent to the North Saskatchewan River. Unfortunately, these wells undergo fairly rapid deterioration (3-4 years) leading to reduced well capacity and water quality. The reasons for this deterioration are poorly understood. The studies in this thesis have tried to quantify the prevalence, activity and diversity of microbial populations in the aquifer and to explain the possible outcomes of microbial interaction with the environment which might lead to biofouling of the wells. A panel of conventional cultural, microscopic, metabolic and molecular techniques were utilized to analyze water, sediment and biofilm samples collected from various locations in the aquifer. The studies indicated that the aquifer was anoxic and harboured abundant concentrations of iron and manganese very close to the well and also presence of diverse groups of organisms including Fe-, Mn-, S-oxidizing bacteria as well as Fe-, Mn-, nitrite- and sulphate-reducing bacteria. A two year spatio-temporal study indicated that the biofilm growth significantly increased within the 1-2 m zone from the well and were also associated with a rapid reduction in specific capacity of the well. PCR, qPCR, and DGGE analyses indicated that the microbial community composition and diversity varied with space and time with greatest changes detected within the zone proximal to the well. Sequence data indicated that the major bacterial species prevalent in the aquifer belonged to Sulfuricurvum spp., Rhodobacter spp., Methylobacter spp., Acidovorax spp., and Geobacter spp. The studies demonstrated that water extraction influenced microbial community diversity, activity and composition, the effect of which did not extend beyond 1-2 m well radius. The application of impressed current did not demonstrate any anti-fouling effect, but rather favoured the growth of biofilm around the well and the accumulation of insoluble precipitates leading to accelerated deterioration of the well. Overall, the microbial community diversity, activity and composition in the study aquifer changed with respect to time and space, and water extraction. These changes altered the biogeochemical processes in the aquifer, especially within the zone closest to the wells leading to clogging and well deterioration

Coupling bioturbation activity to metal (Fe and Mn) profiles in situ

This work was supported by a University of Aberdeen 6th century scholarship (awarded to L. T.), CEFAS Lowestoft (DP204), NERC NFSD support (08/02) and a SAMS research bursary (awarded to L. T)Peer reviewedPublisher PD

In situ capping of contaminated sediments: spatial and temporal characterization of biogeochemical and contaminant biotransformation processes

Contaminated aquatic sediments pose health risks to fish, wildlife, and humans and can limit recreational and economic uses of surface waters. Technical and cost effective in situ approaches for sediment management and remediation have been identified as a research need. Subaqueous in situ capping is a promising remedial approach; however, little is known regarding its impact on underlying sedimentary processes and the feasibility of bioaugmented caps at sites subject to contaminated groundwater seepage. This work specifically addresses (1) the impact of capping on biogeochemical processes at the sediment-water interface, (2) the ability and degree to which indigenous sediment microorganisms colonize an overlying cap, (3) the effect of advective flow direction on redox conditions within a cap, (4) natural contaminant bioattenuation processes within capped sediment, and (5) limitations toward a functional bioreactive in situ cap. Laboratory-scale experiments with capped sediment columns demonstrated that emplacement of a sand-based in situ cap induced an upward, vertical shift of terminal electron accepting processes into the overlying cap while simultaneously conserving redox stratification. Upflow conditions simulating a groundwater seep compressed anaerobic processes towards the cap-water interface. Microorganisms indigenous to the underlying sediment colonized cap material and spatial population differences generally reflected redox stratification. Downflow of oxic surface water through the cap, simulating tidally-induced recharge, created fully oxic conditions within the cap, demonstrating that flow direction strongly contributes to redox conditions. Experiments simulating capped sediment subject to contaminated groundwater seepage revealed a reduction of natural bioattenuation processes with time, stemming from the elimination of labile organic matter deposition to the sediment and a subsequent lack of electron donor. Thus, parent contaminants within groundwater seeps will be subject to minimal biotransformations within the sediment before entering a reducing cap. A bioreactive cap, inoculated with microorganisms capable of reductive dehalogenation, was established to reductively dechlorinate tetrachloroethene present in the groundwater; however electron donor amendments to sediment effluent were required to achieve complete dechlorination of tetrachloroethene to non-toxic ethene. Results from this work improve understanding of biogeochemical and bioattenuation processes within capped aquatic sediments and should aid in the development of active capping technologies.Ph.D.Committee Co-Chair: Joseph B. Hughes; Committee Co-Chair: Kurt D. Pennell; Committee Member: Danny D. Reible; Committee Member: Frank E. Loeffler; Committee Member: Jim C. Spain; Committee Member: Martial Taillefert; Committee Member: Terry W. Stur

Toward a Balanced Strategy to Address Contaminated Groundwater Plumes at the Massachusetts Military Reservation

This document contains the findings and recommendations of the Technical Review and Evaluation Team (TRET) for the plume containment project at the Massachusetts Military Reservation (MMR). The findings and recommendations are in response to the 60 Percent Plume Containment Design, submitted by Operational Technologies (OpTech) in January 1996. In short, the TRET recommends the MMR depart substantially from the strategy of simultaneous, 100 percent containment and treatment that was assigned to OpTech for design in accordance with the Record of Decision (ROD) for Interim Action. This strategy guided the course of the plume containment project over the past two year

Mustard catch crop enhances denitrification in shallow groundwater beneath a spring barley field

The study was funded by Department of Agriculture and Food through the Research Stimulus Fund Programme (Grant RSF 06383) in collaboration with the Department of Civil, Structural & Environmental Engineering, Trinity College Dublin, Ireland.peer-reviewedOver-winter green cover crops have been reported to increase dissolved organic carbon (DOC) concentrations in groundwater, which can be used as an energy source for denitrifiers. This study investigates the impact of a mustard catch crop on in situ denitrification and nitrous oxide (N2O) emissions from an aquifer overlain by arable land. Denitrification rates and N2O-N/(N2O-N + N2-N) mole fractions were measured in situ with a push–pull method in shallow groundwater under a spring barley system in experimental plots with and without a mustard cover crop. The results suggest that a mustard cover crop could substantially enhance reduction of groundwater nitrate NO3--N via denitrification without significantly increasing N2O emissions. Mean total denitrification (TDN) rates below mustard cover crop and no cover crop were 7.61 and 0.002 μg kg−1 d−1, respectively. Estimated N2O-N/(N2O-N + N2-N) ratios, being 0.001 and 1.0 below mustard cover crop and no cover crop respectively, indicate that denitrification below mustard cover crop reduces N2O to N2, unlike the plot with no cover crop. The observed enhanced denitrification under the mustard cover crop may result from the higher groundwater DOC under mustard cover crop (1.53 mg L−1) than no cover crop (0.90 mg L−1) being added by the root exudates and root masses of mustard. This study gives insights into the missing piece in agricultural nitrogen (N) balance and groundwater derived N2O emissions under arable land and thus helps minimise the uncertainty in agricultural N and N2O-N balances

Non-Conservative Behavior of Select Naturally-Occurring Radionuclides and Metals in Coastal Waters.

Water column samples from three vastly contrasting coastal regimes (Framvaren Fjord, Norway, the Amazon and Mississippi River outflow regions) were analyzed to study the estuarine transport and scavenging processes of \sp{210}Pb, \sp{210}Po, \sp{234}U and \sp{238}U. The Amazon and Mississippi River outflow regions are two of the world\u27s largest river-ocean mixing systems that contrast each other sharply in many physiographical and geochemical features. The Amazon is a tropical, high energy, shelf environment where estuarine physico-chemical processes are strongly influenced by sediment-water interactions. The Mississippi system on the other hand discharges much of its load close to the shelf-break where estuarine geochemical processes are largely separated from benthic processes. The distribution of uranium in these two systems reflects the vastly contrasting environments. In the Amazon, U is consistently non-conservative--showing removal at all river discharge stages. Removal of U from this water column onto particulates involves scavenging by colloidal-sized metal oxides, flocculation and subsequent aggregation up the particle size spectrum. In the Mississippi River outflow region, U is conservative at all normal river discharge stages. However, during flood/drought conditions uranium does exhibit non-conservative estuarine behavior and U removal is thought to be a function of the reactivity of the carrier phase. Framvaren Fjord represents a unique environment in which to investigate estuarine chemistry. At about a salinity of 21 and a depth of 20 meters (well within the photic zone), a very sharp O\sb2/H\sb2S boundary controls the vertical distribution of a suite of trace metals and radionuclides. The uptake and release of such elements by dense communities of anoxygenic phototrophic bacteria (e.g., Chlorobium and Chromatium spp.) create very sharp concentration peaks at the redoxcline. Such bio-concentration at the O\sb2/H\sb2S boundary has been observed in the vertical profiles of \sp{210}Po, \sp{210}Pb, Fe, Mn, U, Ba and Sr. Mechanisms or processes to create such distributions must be biogenic and are most likely microbially mediated. Results from this study indicate that even elements once thought to be quite non-reactive in natural waters, such as uranium, can in fact be susceptible to both biotic and abiotic enrichment/depletion processes