Influence Of Surface Water Research Articles

Shaping pre-modern digital terrain models: The former topography at Charlemagne's canal construction site.

The use of remote sensing techniques to identify (geo)archaeological features is wide spread. For archaeological prospection and geomorphological mapping, Digital Terrain Models (DTMs) on based LiDAR (Light Detection And Ranging) are mainly used to detect surface and subsurface features. LiDAR is a remote sensing tool that scans the surface with high spatial resolution and allows for the removal of vegetation cover with special data filters. Archaeological publications with LiDAR data in issues have been rising exponentially since the mid-2000s. The methodology of DTM analyses within geoarchaeological contexts is usually based on “bare-earth” LiDAR data, although the terrain is often significantly affected by human activities. However, “bare-earth” LiDAR data analyses are very restricted in the case of historic hydro-engineering such as irrigation systems, mills, or canals because modern roads, railway tracks, buildings, and earth lynchets influence surface water flows and may dissect the terrain. Consequently, a "natural" pre-modern DTM with high depth accuracy is required for palaeohydrological analyses. In this study, we present a GIS-based modelling approach to generate a pre-modern and topographically purged DTM. The case study focuses on the landscape around the Early Medieval Fossa Carolina, a canal constructed by Charlemagne and one of the major medieval engineering projects in Europe. Our aim is to reconstruct the pre-modern relief around the Fossa Carolina for a better understanding and interpretation of the alignment of the Carolingian canal. Our input data are LiDAR-derived DTMs and a comprehensive vector layer of anthropogenic structures that affect the modern relief. We interpolated the residual points with a spline algorithm and smoothed the result with a low pass filter. The purged DTM reflects the pre-modern shape of the landscape. To validate and ground-truth the model, we used the levels of recovered pre-modern soils and surfaces that have been buried by floodplain deposits, colluvial layers, or dam material of the Carolingian canal. We compared pre-modern soil and surface levels with the modelled pre-modern terrain levels and calculated the overall error. The modelled pre-modern surface fits with the levels of the buried soils and surfaces. Furthermore, the pre-modern DTM allows us to model the most favourable course of the canal with minimal earth volume to dig out. This modelled pathway corresponds significantly with the alignment of the Carolingian canal. Our method offers various new opportunities for geoarchaeological terrain analysis, for which an undisturbed high-precision pre-modern surface is crucial.

Interannual changes in summer phytoplankton community composition in relation to water mass variability in the East China Sea

The surface distribution of the phytoplankton community was investigated in July 2009, 2010, 2011, and 2013 on the mid-shelf of the East China Sea (ECS), which is under the influence of Changjiang River Diluted Water (CDW) and the Kuroshio Current. This study, based on a CHEMTAX analysis of phytoplankton pigments, revealed a predominance of cyanobacteria and prochlorophytes in the eastern ECS, which is perennially under the influence of oligotrophic Kuroshio Surface Water. Towards the west, on the mid-shelf of the ECS, the composition of the phytoplankton community varied from year to year. Diatoms dominated in 2009 and 2013, when dissolved inorganic phosphate (DIP) concentrations were higher than during 2010 and 2011. During the latter two years, characterized as high-nitrate years, a mixed population of cyanobacteria, chlorophytes, and other groups was observed. Cluster analysis based on the phytoplankton community composition together with a PCA of shipboard hydrographic and nutrient data for all four years helped to confirm that the summer phytoplankton community structure of the ECS was regulated by the mixing of water masses and the variability of nutrient ratios within the CDW as it moved offshore. Our results show that elevated DIP concentrations in the CDW favor the growth of diatoms and dinoflagellates. The primary pathway for DIP inputs appears to be the upwelling of high-phosphate subsurface waters along the coast of China.

Assessing the Distribution Characteristics of Surface Water Geochemistry and Pollution of Heavy Metals within Soil in the Changjiang River Delta, China

Li, J.; Song, Y.; Mao, C., and Li, T., 2018. Assessing the distribution characteristics of surface water geochemistry and pollution of heavy metals within soil in the Changjiang River Delta, China. In: Wang, D. and Guido-Aldana, P.A. (eds.), Select Proceedings from the 3rd International Conference on Water Resource and Environment (WRE2017). Journal of Coastal Research, Special Issue No. 84, pp. 109–113. Coconut Creek (Florida), ISSN 0749-0208.This study aimed to understand the spatial distribution and geochemical characteristics of heavy metals in soil in Changjiang River Delta, and also the impact of surface water geochemistry on the mobility of heavy metals in soil. The levels of Ca2+ and Na+ in surface water reached 80% of total cation level, ranging 33.00–97.50 mg/L and 9.00–334.90 mg/L, respectively. HCO3− was more than 50% of total anion concentration, making the type of surface water as Ca-HCO3 or Ca-Na-HCO3. The concentration of cations and anions followed the order: coastal > middle > inland. The soils were strongly polluted with Cd in this study. More than 50% of Cd concentration exceeded the standard. Spatial changes in As, Cd, and Pb levels followed the order: middle > coastal > inland, same as that for soil pH. Speciation results of heavy metals showed that more than 50% of Cd was exchangeable. Principal component analysis results showed that the change in exchangeable fraction of As, Hg, and Pb followed the same order: middle > coastal > inland. Exchangeable Cd followed a trend different from that of Cr. Three areas were characterized by the mobility of As, Hg, and Pb. Scores of samples from different areas implied the influence of surface water on the mobility of heavy metals in soil. Geochemical variation in surface water indicated the mobility of heavy metals through correlation and spatial analysis of geochemistry of surface water and speciation of heavy metals in soil.

Wetlands inform how climate extremes influence surface water expansion and contraction

Effective monitoring and prediction of flood and drought events requires an improved understanding of how and why surface-water expansion and contraction in response to climate varies across space. This paper sought to (1) quantify how interannual patterns of surface-water expansion and contraction vary spatially across the Prairie Pothole Region (PPR) and adjacent Northern Prairie (NP) in the United States, and (2) explore how landscape characteristics influence the relationship between climate inputs and surface-water dynamics. Due to differences in glacial history, the PPR and NP show distinct patterns in regards to drainage development and wetland density, together providing a diversity of conditions to examine surface-water dynamics. We mapped surface-water extent across eleven Landsat path/rows representing the PPR and NP (images spanning 1985-2015). The PPR not only experienced a 2.6-fold increase of surface-water extent under median conditions relative to the NP, but also showed a 3.4-fold greater difference in surface-water extent between drought and deluge conditions. The relationship between surface-water extent and accumulated water availability (precipitation minus potential evapotranspiration) was quantified per watershed and statistically related to variables representing hydrology-related landscape characteristics (e.g., infiltration capacity, surface storage capacity, stream density). To investigate the influence stream-connectivity has on the rate at which surface water leaves a given location, we modeled stream-connected and stream-disconnected surface water separately. Stream-connected surface water showed a greater expansion with wetter climatic conditions in landscapes with greater total wetland area. Disconnected surface water showed a greater expansion with wetter climatic conditions in landscapes with higher wetland density, lower infiltration and less anthropogenic drainage. From these findings, we can expect that shifts in precipitation and evaporative demand will have uneven effects on surface-water quantity. Accurate predictions regarding the effect of climate change on surface-water quantity will require consideration of hydrology-related landscape characteristics including wetlands.

Influential factors detection for surface water quality with geographical detectors in China

Surface water quality is a matter of serious concern in China. This study quantitatively analyzes the spatial–temporal characteristics of surface water quality among 100 monitoring stations in China during 2015. A geographical detector was used to detect the influential annual and seasonal factors. Surface water quality is primarily controlled by the content of nutrient pollutants and organic pollutants. Natural factors (precipitation, temperature, soil erosion, and terrain) and anthropogenic factors [land use type, population density, and per capita gross domestic product (GDP-per-capita)] were selected as geographical proxies to be tested for their explanatory power for surface water quality. Results indicated that the top three factors influencing the annual mean of nutrient pollutants were the population density, terrain, and precipitation, the explanatory power of which was 0.82, 0.35, and 0.24, respectively. The interactive explanatory power for population density and terrain was 0.88 and for population density and precipitation was 0.87, both exhibiting enhanced interaction relationships. The top three factors influencing the annual mean of organic pollutants were population density, temperature, and basin, the explanatory power of which was 0.46, 0.29, and 0.27, respectively. The interactive explanatory power for population density and basin was 0.80 and for terrain and precipitation was 0.82, both demonstrating a nonlinear enhanced interaction relationship. For seasonal changes, the nutrient pollutants and organic pollutants were both affected by agricultural runoff due to seasonal farming. This study revealed that anthropogenic factors influenced surface water quality two to three times more than natural factors.

Process-based monitoring and modeling of Karst springs – Linking intrinsic to specific vulnerability

The presented work illustrates to what extent field investigations as well as monitoring and modeling approaches are necessary to understand the high discharge dynamics and vulnerability of Karst springs. In complex settings the application of 3D geological models is essential for evaluating the vulnerability of Karst systems. They allow deriving information on catchment characteristics, as the geometry of aquifers and aquitards as well as their displacements along faults.A series of Karst springs in northwestern Switzerland were compared and Karst system dynamics with respect to qualitative and quantitative issues were evaluated. The main objective of the studies was to combine information of catchment characteristics and data from novel monitoring systems (physicochemical and microbiological parameters) to assess the intrinsic vulnerability of Karst springs to microbiological contamination with simulated spring discharges derived from numerical modeling (linear storage models). The numerically derived relation of fast and slow groundwater flow components enabled us to relate different sources of groundwater recharge and to characterize the dynamics of the Karst springs.Our study illustrates that comparably simple model-setups were able to reproduce the overall dynamic intrinsic vulnerability of several Karst systems and that one of the most important processes involved was the temporal variation of groundwater recharge (precipitation, evapotranspiration and snow melt). Furthermore, we make a first attempt on how to link intrinsic to specific vulnerability of Karst springs, which involves activities within the catchment area as human impacts from agriculture and settlements. Likewise, by a more detailed representation of system dynamics the influence of surface water, which is impacted by release events from storm sewers, infiltrating into the Karst system, could be considered.Overall, we demonstrate that our approach can be the basis for a more flexible and differentiated management and monitoring of raw-water quality of Karst springs.

Potential use of low-cost data loggers for groundwater temperature in a regulatory program for public water supply: impact of measurement frequency at a karst spring

A simple low-cost procedure for data collection and evaluation was developed to investigate the utility of continuous data loggers and the impact of measurement frequency on a water-quality monitoring method for use in a regulatory program for public water supply and groundwater under the direct influence of surface water (GWUDI). Data loggers were utilized to continuously measure groundwater temperature, descriptive statistics and the coefficient of variation to demonstrate rapid and significant variations. Temperature data were collected from a karst spring located in the Great Valley section of Pennsylvania and reported on daily and 15-min measurement frequencies. In response to five summer rain events, thermographs constructed with the 15-min measurements indicated rapid large-magnitude temperature variations. The average magnitude of change across the five events was 5.3 °C, but the shifts operated on quick timescales; thus, variations were not captured when data were reported on the daily frequency. This resulted in a distorted evaluation on how significant the groundwater temperature variations were, because results were dependent on measurement frequency. The average coefficient of variation percentage for the 15-min datasets was 12%, compared to 3% for the dataset of daily measurements. These findings could have important implications to a public water-supply regulatory program, because the regulatory definition for GWUDI includes those groundwater sources that display rapid and significant variations in water quality. Without high-frequency measurements, one alarming result could be that GWUDI sources, particularly those located in fast-acting hydrogeologic settings, are misevaluated when maximum or minimum water-quality variations are not included in the evaluation. Advancement in science and technology has resulted in data loggers for groundwater temperature that are economical, robust, and easy to install. Thus, their application in regulatory programs should no longer be underutilized, especially in karst spring settings where source construction deficiencies and focused recharge features can result in rain-induced rapid infiltration and water-quality variations on the minute-to-hour timescale.

Impact of hydroclimatic variability on regional-scale landscape connectivity across a dynamic dryland region

In dynamic dryland regions, accounting for spatiotemporal landscape dynamics is essential to understanding how ecological habitat networks are affected by hydroclimatic variability at regional or sub-continental scales. Here we assess how changes in the distribution and availability of surface water influence potential landscape connectivity for water-dependent organisms by combining graph theory network analysis with a Landsat-derived, seasonally continuous 25-year surface-water time-series. We focused on Australia’s Murray Darling Basin (MDB), a globally significant and ecologically stressed 1millionkm2 semi-arid region recently affected by two unprecedented hydroclimatic extremes: the 1997–2010 Millennium Drought and 2010–2012 La Niña floods. We constructed potential habitat networks for two dispersal abilities using circuit theory resistance distances, and used ‘habitat availability’ graph theory metrics as indicators of regional-scale connectivity. We analysed 792 unique potential habitat networks containing over 6.6 million nodes, making our study one of the largest spatially explicit ecological network analyses yet conducted. Our indicators of connectivity revealed consistently positive but spatially heterogeneous relationships between flooded habitat area and landscape connectivity. Connectivity increased by over two orders of magnitude along the spectrum from severe drought to flood, associated with a transition from connectivity driven by intra-habitat or short-distance dispersal during drought to long-distance dispersal during wet conditions. Reductions in connectivity during drought were lower than expected given equivalent decreases in surface water habitat area, suggesting habitat network structure provides a degree of resistance to dry conditions. By providing insights into the processes driving connectivity during different phases along the drought-flood spectrum, our approach may assist in guiding conservation management aimed at maintaining or improving landscape connectivity within dynamic environments faced with increasing hydroclimatic variability.

Study on the weight coefficient influence of surface water on the stability of open-pit dump. Comparative analysis of 6 degree seismic simulation

Taking Baorixile open-pit coal mine as an example, the regional hydrogeological conditions and the mining area hydrogeological conditions are briefly introduced. Analyzing the factors influencing the stability of open pit dump, discussing the classification and proportion of influencing factors, the numerical simulation of the influence of surface water and seismic vibrations on the stability of open-pit dump is carried out. Results show: Surface water is an important factor affecting the stability of open-pit dump, extremely sensitive to the safety factor, the influence of slope instability is similar to that of intensity 6 earthquake. The weight coefficient of surface water to slope stability is in the range of 0.4 to 0.9.

The land morphology approach to flood risk mapping: An application to Portugal

In the last decades, the increasing vulnerability of floodplains is linked to societal changes such as population density growth, land use changes, water use patterns, among other factors. Land morphology directly influences surface water flow, transport of sediments, soil genesis, local climate and vegetation distribution. Therefore, the land morphology, the land used and management directly influences flood risks genesis. However, attention is not always given to the underlying geomorphological and ecological processes that influence the dynamic of rivers and their floodplains.Floodplains are considered a part of a larger system called Wet System (WS). The WS includes permanent and temporary streams, water bodies, wetlands and valley bottoms. Valley bottom is a broad concept which comprehends not only floodplains but also flat and concave areas, contiguous to streams, in which slope is less than 5%. This will be addressed through a consistent method based on a land morphology approach that classifies landforms according to their hydrological position in the watershed. This method is based on flat areas (slopes less than 5%), surface curvature and hydrological features.The comparison between WS and flood risk data from the Portuguese Environmental Agency for the main rivers of mainland Portugal showed that in downstream areas of watersheds, valley bottoms are coincident with floodplains modelled by hydrological methods. Mapping WS has a particular interest in analysing river ecosystems position and function in the landscape, from upstream to downstream areas in the watershed. This morphological approach is less demanding data and time-consuming than hydrological methods and can be used as the preliminary delimitation of floodplains and potential flood risk areas in situations where there is no hydrological data available.The results were also compared with the land use/cover map at a national level and detailed in Trancão river basin, located in Lisbon metropolitan area, an urbanized basin that suffered heavy flooding in the last decades. This study also contributes to a better understanding of the basin morphology at a local-scale and the effects of soil sealing in downstream flood risks.This work will contribute to the understanding of the morphology, ecology and land use of watersheds that could be used to reduce runoff and downstream flood risk. This can be accomplished by using natural water retention and infiltration methods or higher-level based planning instead of a reaction to local decisions on flood hazards. This morphological approach to map landforms, including wet system, is a valuable tool to assist policy makers and planners in flood risk and land use management, floodplain restoration, agricultural land management practices, and location of human activities according to ecological suitability.

Symbiosis revisited: phosphorus and acid buffering stimulate N<sub>2</sub> fixation but not <i>Sphagnum</i> growth

Abstract. In pristine Sphagnum-dominated peatlands, (di)nitrogen (N2) fixing (diazotrophic) microbial communities associated with Sphagnum mosses contribute substantially to the total nitrogen input, increasing carbon sequestration. The rates of symbiotic nitrogen fixation reported for Sphagnum peatlands, are, however, highly variable, and experimental work on regulating factors that can mechanistically explain this variation is largely lacking. For two common fen species (Sphagnum palustre and S. squarrosum) from a high nitrogen deposition area (25 kg N ha−1 yr−1), we found that diazotrophic activity (as measured by 15 − 15N2 labeling) was still present at a rate of 40 nmol N gDW−1 h−1. This was surprising, given that nitrogen fixation is a costly process. We tested the effects of phosphorus availability and buffering capacity by bicarbonate-rich water, mimicking a field situation in fens with stronger groundwater or surface water influence, as potential regulators of nitrogen fixation rates and Sphagnum performance. We expected that the addition of phosphorus, being a limiting nutrient, would stimulate both diazotrophic activity and Sphagnum growth. We indeed found that nitrogen fixation rates were doubled. Plant performance, in contrast, did not increase. Raised bicarbonate levels also enhanced nitrogen fixation, but had a strong negative impact on Sphagnum performance. These results explain the higher nitrogen fixation rates reported for minerotrophic and more nutrient-rich peatlands. In addition, nitrogen fixation was found to strongly depend on light, with rates 10 times higher in light conditions suggesting high reliance on phototrophic organisms for carbon. The contrasting effects of phosphorus and bicarbonate on Sphagnum spp. and their diazotrophic communities reveal strong differences in the optimal niche for both partners with respect to conditions and resources. This suggests a trade-off for the symbiosis of nitrogen fixing microorganisms with their Sphagnum hosts, in which a sheltered environment apparently outweighs the less favorable environmental conditions. We conclude that microbial activity is still nitrogen limited under eutrophic conditions because dissolved nitrogen is being monopolized by Sphagnum. Moreover, the fact that diazotrophic activity can significantly be upregulated by increased phosphorus addition and acid buffering, while Sphagnum spp. do not benefit, reveals remarkable differences in optimal conditions for both symbiotic partners and calls into question the regulation of nitrogen fixation by Sphagnum under these eutrophic conditions. The high nitrogen fixation rates result in high additional nitrogen loading of 6 kg ha−1 yr−1 on top of the high nitrogen deposition in these ecosystems.

Contrasting patterns of phytoplankton pigments and chemotaxonomic groups along 30°S in the subtropical South Atlantic Ocean

This work describes the spatial distribution of pigments and main taxonomic groups of phytoplankton in the biogeochemical provinces of the subtropical South Atlantic Ocean, along 30°S latitude. Seawater samples (surface to 200m depth) were collected along 120 oceanographic stations occupied in the early austral spring of 2011, during a CLIVAR Repeat Hydrography cruise. The pigments were identified and quantified by high performance liquid chromatography (HPLC), and CHEMTAX software was used to determine the relative contributions of the main taxonomic groups to total chlorophyll a (phytoplankton biomass index). Sampling stations were grouped into three provinces: Africa, Gyre, and Brazil, corresponding to the eastern, central, and western sectors of the transect, respectively. Our results showed that both vertical and horizontal distribution patterns of pigments and taxonomic groups were mainly determined by the availability of light and/or nutrients. Photosynthetic carotenoids (PSCs), associated with small flagellates (mainly haptophytes), dominated the light-limited and nutrient-enhanced deep chlorophyll maximum (DCM) layers of both the Brazil and Gyre provinces, as well as the upwelling influenced surface waters of the Africa province. The latter showed the highest chlorophyll a values ​​(>1mgm–3) and abundance of dinoflagellates in the coastal region. Photoprotective carotenoids (PPCs) were predominant in the nutrient-poor and well-lit surface layers of the Brazil and Gyre provinces, associated with a low content of chlorophyll a (~0.1mgm–3) and dominance of prokaryotes (Synechoccocus and Prochloroccocus). This study demonstrates that pigment analysis can provide a useful approach to better understand the distribution of phytoplankton communities along physical-chemical gradients in a still undersampled region of the South Atlantic Ocean.

Factors controlling groundwater salinization and hydrogeochemical processes in coastal aquifers from southern Spain.

In detrital coastal aquifers, seawater and surface water may interact with groundwater in multiple ways. Understanding the interference of water fluxes in this type of environment is essential to effectively manage the groundwater resources in water-stressed regions, such as the Mediterranean coastal fringe. In this research, the characterization of the main hydrogeochemical processes and the interaction between surface water and groundwater in the Marbella-Estepona coastal aquifers (southern Spain) have been carried out by means of the combined use of different hydrogeochemical indicators along with isotope data. The results show that the diversity of source lithologies (peridotite, carbonate and/or metapelitic) substantially conditions the groundwater geochemistry. The analysis of ionic deltas made it possible a preliminary screening of the geochemical reactions that occur in the Marbella-Estepona aquifers, while the Discriminant Analysis allowed for a consistent classification of sampled groundwater types. The dissolution of calcite and dolomite determines the chemical composition of the groundwater from the eastern sector that are more conditioned by the rainwater infiltration. The dissolution of magnesium-bearing minerals (predominantly forming peridotite rocks) is observed in groundwater samples from the western and central sectors, whose chemical composition showed a greater influence of surface water. The spatial analysis of rCl-/Br- in groundwater has permitted to corroborate that saline intrusion is negligible, hardly affecting to its original water quality. The irregularly distributed recharge by precipitation (seasonal effect) and the atmospheric circulation of cloud fronts (coastal/continental effect) explains why most of groundwater sampled is isotopically impoverished with respect to the rainfall signature. The isotope approach also suggests the hydraulic relationship between surface water and groundwater in the study site. A deeper knowledge of spatial hydrogeochemical variations in coastal groundwater and the influence of water sources over them are crucial for a sustainable groundwater management and global change adaptation in equivalent Mediterranean water-stressed regions.

Minor effect of beaver dams on stream dissolved organic carbon in the catchment of a German drinking water reservoir

Rising concentrations of dissolved organic carbon (DOC) are negatively affecting the water quality in several drinking water reservoirs. The presence of beaver dams can influence surface water quality on a catchment scale. In recent years, beavers have been re-introduced in numerous locations in Central Europe. We investigated whether the presence of beaver dams in the catchment of a German drinking water reservoir impacts DOC quantity and quality in the streams entering the Wehebach reservoir in Germany. By comparing water quality upstream and downstream of beaver dams during three low discharge situations we did not find a significant effect of dams both on DOC quantity and quality. The analysis of long term monitoring data at the gauges showed that beaver dams had a negligible effect on the DOC load to the reservoir. DOC quantity was closely linked to iron concentration in the streams. Co-precipitation with iron minerals was an effective process removing DOC from the stream-water. By analyzing fluorescence excitation emission indices we show that beaver dams did not have a clear effect on DOC quality. We conclude that the presence of beaver dams has only small effects on water quality and is not a problem for water quality in the downstream drinking water reservoir.

Groundwater under strong influence of surface water – case study from Črneče (Northern Slovenia)

Groundwater under strong influence of surface water – case study from Črneče (Northern Slovenia)

Phosphate treatment by onsite wastewater systems in nutrient-sensitive watersheds of North Carolina's Piedmont.

The goal of this study was to gain a better understanding of the PO4-P treatment efficiency of onsite wastewater systems (OWS) installed in nutrient-sensitive watersheds of the North Carolina Piedmont. Four OWS including two conventional and two single-pass sand filter (SF) systems were evaluated at sites with clay-rich soils. Piezometers were installed near all of the OWS, and down-gradient from the conventional OWS for groundwater collection and characterization. Septic tanks, groundwater, SF effluent, and surface waters were sampled each season during 2015 (five times) and analyzed for PO4-P and Cl concentrations and for various environmental parameters. The conventional and SF OWS reduced PO4-P concentrations by an average of 99% and 90%, respectively, before discharge to surface waters. Mass-load reductions of PO4-P were also greater for the conventional OWS (mean 95%), relative to SF (83%) systems. The effluents discharged by SF OWS were influencing surface water quality. Additional treatment of the effluent from single-pass SF with reactive media is suggested, along with monitoring of the final effluent for PO4-P concentrations. This research provides important information that is absent from the published literature concerning PO4-P contributions to water resources from OWS in clay soils.

Assessment of the denitrification process in alluvial wetlands at floodplain scale using the SWAT model

As alluvial plains support intensive agricultural activities, they often suffer from groundwater nitrate pollution. Denitrification is recognised as an important process in nitrate pollution control in riparian zones. In shallow aquifer zones influenced by recharged surface water, denitrification efficiently attenuates nitrate in groundwater as well, and the exchange between surface water and groundwater has a significant impact on the occurrence of denitrification. Denitrification is simulated in numerous models, however most models do not take into account the denitrification occurring in shallow aquifers or the influence of recharge surface water in the alluvial aquifer with organic carbon and bacteria to activate denitrification. In this study, a new module was developed that represents the occurrence of denitrification in the shallow aquifer of alluvial floodplains. Nitrate inputs in the shallow aquifer caused by the recharged river water through both lateral (river bank) and vertical (surface) infiltration and the influence of flooding on nitrate leaching were added to the Soil and Water Assessment Tool – Landscape Unit Darcy (SWAT-LUD) model. The influences of both dissolved organic carbon (DOC) and particulate organic carbon (POC) on denitrification were evaluated. The modified model was applied on an experimental site located in the floodplain of the Garonne River (southwest France). Results showed that the modified SWAT-LUD model was able to simulate the aquifer nitrate concentration in the near-bank zone (riparian zone) satisfactorily. The near-bank zone in the floodplain played the most important role in attenuating nitrate through denitrification with an annual denitrification rate of around 130kg N-NO3−ha−1y−1, representing about 40% of the nitrate input in this area. POC was more important than DOC in the denitrification process, especially in the near-bank zone where 98% of the nitrate was attenuated through POC consumption. Relationships between denitrification rates, groundwater levels and total input nitrate masses in the near-bank zone were determined. The results illustrated that groundwater levels were positively related to the denitrification rates in the near-bank zone. The absolute denitrification rate increased as the nitrate content increased, but the relative consumption rate by denitrification decreased.

Quantifying the influence of surface water–groundwater interaction on nutrient flux in a lowland karst catchment

Abstract. Nutrient contamination of surface waters and groundwaters is an issue of growing importance as the risks associated with agricultural run-off escalate due to increasing demands on global food production. In this study, the influence of surface water–groundwater interaction on the nutrient flux in a lowland karst catchment was investigated with the aid of alkalinity sampling and a hydrological model. The objective of the study was to determine the impact of ephemeral karst lakes (turloughs) on the surface water–groundwater nutrient flux, and whether these lakes act as sources or sinks of nutrients within the groundwater flow system. Water samples were tested from a variety of rivers, turloughs, boreholes and springs at monthly intervals over 3 years. Alkalinity sampling was used to elucidate the contrasting hydrological functioning between different turloughs. Such disparate hydrological functioning was further investigated with the aid of a hydrological model which allowed for an estimate of allogenically and autogenically derived nutrient loading into the karst system. The model also allowed for an investigation of mixing within the turloughs, comparing observed behaviours with the hypothetical conservative behaviour allowed for by the model. Within the turloughs, recorded nutrient concentrations were found to reduce over the flooded period, even though the turloughs hydrological functioning (and the hydrological model) suggested this would not occur under conservative conditions. As such, it was determined that nutrient loss processes were occurring within the system. Denitrification during stable flooded periods (typically 3–4 months per year) was deemed to be the main process reducing nitrogen concentrations within the turloughs, whereas phosphorus loss is thought to occur mostly via sedimentation and subsequent soil deposition. The results from this study suggest that, in stable conditions, ephemeral lakes can impart considerable nutrient losses on a karst groundwater system.

The precarious freshwater resources of Sable Island, Nova Scotia, Canada: Occurrence and management considerations

This paper presents an overview of the hydrogeology and the freshwater resources of Sable Island, Nova Scotia. The role of the sand deposits, morphology and dynamics of the dune structures and systems, precipitation, and tidal influences are discussed. The distribution, quality, and importance of both surface water and groundwater resources of the island are also presented. Fresh groundwater on the Island occurs in an unconfined sand lens aquifer. Studies to date on the hydrogeology of the island have shown highly variable rates of precipitation, both seasonally and annually, which in combination with the influence of shifting dune structures contribute to a dynamic freshwater /saltwater balance. Infiltration rates into the permeable aquifer system are greater than precipitation rates, precluding surface water flow.The chemical quality of water in the freshwater lens aquifer is generally good and meets the Guidelines for Canadian Drinking Water Quality. The aquifer is vulnerable to surface contamination, however, due to its shallow, unconfined nature, and any water supply wells are highly likely to be classified as being ‘under the direct influence of surface water’ (GUDI). Under these conditions a multi-barrier source water protection plan is considered essential for managing future public drinking water supplies on the Island. Recommendations for future studies, including long-term monitoring of water level trends, are provided to support the sustainable use of groundwater on the Sable Island.

Intercomparison of dissolved iron isotope profiles from reoccupation of three GEOTRACES stations in the Atlantic Ocean

Intercomparison of trace metal data is a key aspect of the International GEOTRACES program, allowing data from multiple laboratories and countries to be combined to produce high-resolution datasets for the oceans. The use of crossover stations by the GEOTRACES program provides the opportunity both for comparison of analytical techniques and assessment of temporal variability in the cycling of trace metals such as iron (Fe). Here, we present the first comparison of dissolved Fe stable isotope ratio (δ56Fe; relative to IRMM-014) profiles in the oceans, from reoccupations of three locations in the Atlantic Ocean; (1) the Bermuda Atlantic Time Series station (31.75°N 64.17°W) during the US GEOTRACES IC1 cruise (June 2008) and the US GEOTRACES GA03 cruise (Nov. 2011); (2) the Tenatso Time Series station near Cape Verde (17.4°N 24.5°W) during the U.S GEOTRACES GA03 cruises (2010; 2011), and (3) a station in the Cape Basin close to South West Africa (31.1–31.4°S 36.5°W) during the French GEOTRACES GIPY4 Bonus Good Hope Cruise (Feb. 2008) and the UK GEOTRACES GA10 D357 cruise (Oct. 2010). These datasets provided us with the opportunity not only to compare sampling and analysis techniques by two different laboratories (USC and LEGOS), but also the temporal variability of δ56Fe at these locations on a 1–3year timescale. We found that a good agreement between data and profiles generated by different laboratories does allow assessment of temporal variation of δ56Fe in the water column, as well as spatial variability and synthesis of datasets from different regions of the ocean. In fact, comparison of δ56Fe at the three locations in this study demonstrates a remarkable consistency between the shapes of ocean δ56Fe profiles measured 1–3years apart, pointing to the overall stability of Fe cycling at all three locations on these timescales, despite the expected dynamic nature of the Fe cycle. This consistency is highlighted by strong agreement in δ56Fe throughout the whole water-column at Bermuda, and in waters deeper than 500m in the Cape Basin, which suggests that different water masses may carry distinct δ56Fe signatures. In contrast to these stable δ56Fe, we did observe apparent temporal variability in δ56Fe between cruises at other locations and in surface waters, both throughout the water column at Cape Verde, and in Agulhas-leakage influenced surface waters in the Cape Basin. Such temporal variability may thus provide information about changes in internal Fe cycling or external Fe sources on these timescales. Overall, this study highlights the usefulness of repeat δ56Fe measurements to provide information on the variability of Fe cycling throughout the oceans.