32 research outputs found
Ambient groundwater flow diminishes nitrate processing in the hyporheic zone of streams
No full textModeling and experimental studies demonstrate that ambient groundwater reduces hyporheic exchange, but the implications of this observation for stream N-cycling is not yet clear. Here we utilize a simple process-based model (the Pumping and Streamline Segregation or PASS model) to evaluate N-cycling over two scales of hyporheic exchange (fluvial ripples and riffle-pool sequences), ten ambient groundwater and stream flow scenarios (five gaining and losing conditions and two stream discharges), and three biogeochemical settings (identified based on a principal component analysis of previously published measurements in streams throughout the United States). Model-data comparisons indicate that our model provides realistic estimates for direct denitrification of stream nitrate, but overpredicts nitrification and coupled nitrification-denitrification. Riffle-pool sequences are responsible for most of the N-processing, despite the fact that fluvial ripples generate 3-11 times more hyporheic exchange flux. Across all scenarios, hyporheic exchange flux and the Damköhler Number emerge as primary controls on stream N-cycling; the former regulates trafficking of nutrients and oxygen across the sediment-water interface, while the latter quantifies the relative rates of organic carbon mineralization and advective transport in streambed sediments. Vertical groundwater flux modulates both of these master variables in ways that tend to diminish stream N-cycling. Thus, anthropogenic perturbations of ambient groundwater flows (e.g., by urbanization, agricultural activities, groundwater mining, and/or climate change) may compromise some of the key ecosystem services provided by streams
Root effects on the spatial and temporal dynamics of oxygen in sand-based laboratory-scale constructed biofilters
No full textIt is now well known that roots introduce oxygen into the soil environment through radial oxygen loss. The oxygen dynamics surrounding roots in periodically flushed environments, however, remains unstudied. We investigated the impact of roots of the macrophyte Carex appressa (Cyperaceae), on the small (rhizosphere) scale spatiotemporal dynamics of sediment oxygen consumption in a periodically flushed soil mimicking natural percolation events. Oxygen dynamics around the roots of C. appressa were studied using a planar optode installed in a rhizobox containing sand. A sand-based culture medium was used to simulate conditions in constructed biofiltration wetlands. The use of planar optodes allowed the generation of two dimensional images of sediment oxygen dynamics, that were used to quantify the patterns and kinetics of oxygen consumption. In addition to greatly increasing the spatial heterogeneity of oxygen in the substrate, the area immediately surrounding the roots became sites of both enhanced oxygen consumption, likely due to increased microbial activity associated with the input of carbon-rich rhizodeposits, and radial oxygen loss. This study highlights the profound impact of roots upon sub-surface oxygen dynamics in the rhizosphere. © 2013 Elsevier B.V.David A. Minett, Perran L.M. Cook, Adam J. Kessler, Timothy R. Cavagnar
Testing assumptions of the eukaryotic inhibitor method for investigating interactions between aquatic protozoa and bacteria, applied to marine sediment
No full textEffects of changes in nutrient loading and composition on hypoxia dynamics and internal nutrient cycling of a stratified coastal lagoon
No full textAbstract. The effects of changes in catchment nutrient loading and composition on the phytoplankton dynamics, development of hypoxia and internal nutrient dynamics in a stratified coastal lagoon system (the Gippsland Lakes) was investigated using a 3D coupled hydrodynamic biogeochemical water quality model. The study showed that primary productivity was equally sensitive to changed dissolved inorganic and particulate organic nitrogen loads, highlighting the need for a better understanding of particulate organic matter bioavailability. Stratification and sediment carbon enrichment are the main drivers for the hypoxia and subsequent sediment phosphorus release in the Lake King. High primary production stimulated by large nitrogen loading brought by winter flood contributed almost all the sediment carbon deposition (as opposed to catchment loads) which was ultimately responsible for summer bottom-water hypoxia. Interestingly, internal recycling of phosphorus was more sensitive to changed nitrogen loads than total phosphorus loads, highlighting the potential importance of nitrogen loads exerting a control over systems that become phosphorus limited (such as during summer nitrogen-fixing blooms of cyanobacteria). Therefore, the current study highlighted the need to reduce both TN and TP for water quality improvement in estuarine systems.
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Constraining denitrification in permeable wave-influenced marine sediment using linked hydrodynamic and biogeochemical modeling
No full textCatchment land use predicts benthic vegetation in small estuaries
No full textMany estuaries are becoming increasingly eutrophic from human activities within their catchments. Nutrient loads often are used to assess risk of eutrophication to estuaries, but such data are expensive and time consuming to obtain. We compared the percent of fertilized land within a catchment, dissolved inorganic nitrogen loads, catchment to estuary area ratio and flushing time as predictors of the proportion of macroalgae to total vegetation within 14 estuaries in south-eastern Australia. The percent of fertilized land within the catchment was the best predictor of the proportion of macroalgae within the estuaries studied. There was a transition to a dominance of macroalgae once the proportion of fertilized land in the catchment exceeded 24%, highlighting the sensitivity of estuaries to catchment land use
Efficient long-range conduction in cable bacteria through nickel protein wires
No full textFilamentous cable bacteria display long-range electron transport, generating electrical currents over centimeter distances through a highly ordered network of fibers embedded in their cell envelope. The conductivity of these periplasmic wires is exceptionally high for a biological material, but their chemical structure and underlying electron transport mechanism remain unresolved. Here, we combine high-resolution microscopy, spectroscopy, and chemical imaging on individual cable bacterium filaments to demonstrate that the periplasmic wires consist of a conductive protein core surrounded by an insulating protein shell layer. The core proteins contain a sulfur-ligated nickel cofactor, and conductivity decreases when nickel is oxidized or selectively removed. The involvement of nickel as the active metal in biological conduction is remarkable, and suggests a hitherto unknown form of electron transport that enables efficient conduction in centimeter-long protein structures.</p
Interactions between design, plant growth and the treatment performance of stormwater biofilters
No full textDevelopment of a gas diffusion probe for the rapid measurement of pCO2 in aquatic samples
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