Hydrological Approach Research Articles

Rain simulation in patchy landscapes: Insights from a case study in the Central Alps

Simulating heavy rain events to analyze potential surface runoff and related soil erosion is a well-established approach in alpine ecology and hydrology. In steep and inaccessible terrain with highly variable relief and vegetation, as occurs in mountainous regions, the rain simulators used to date are often not adapted to the abovementioned characteristics. This study reviews heavy rainfall simulators and presents a consequentially developed rain simulator that covers an area of 10m2. The results of simulated heavy rainfall events (100mmh−1) demonstrated the sprinkling equipment used here to be a useful tool, delivering robust results when studying surface runoff at small scales in a heterogeneous terrain. A comparison to rainfall simulation on a 50m2 plot revealed no significant differences, which demonstrates the equipment used at the scale of 10m2 to be above a “minimum area” for rainfall simulation. Finally, the impacts of plot size on runoff behavior are discussed to provide useful information using a rainfall simulator in the field. The presented rainfall simulator turned out to be a valuable tool for obtaining more detailed information on the surface runoff of small patterned landscapes (i.e., in both natural and managed grass and dwarf-shrublands) by delivering results comparable to those of larger-scale rain simulators (covering 50 or 100m2).

Correcting for systematic biases in multiple raw GCM variables across a range of timescales

Summary Many hydro-climatological applications require use of General Circulation Models (GCMs) outputs. However, the raw information as available from GCMs often contains significant systematic biases when compared with observations. This necessitates some kind of statistical adjustment to be carried out on the GCM fields before their use in any application. It is common to correct the GCM simulations by removing the systematic biases at the time scale of interest, usually individually for each GCM variable that is needed. The outcome is a set of bias corrected variables that are not assessed for bias in their joint dependence structure, nor biases in all attributes at other time scales (such as daily and monthly and annual) except the one under consideration. In this paper, we present a bias correction approach that simultaneously adjusts for the biases in multiple variables across multiple time scales. The proposed Multivariate Recursive Nesting Bias Correction (MRNBC) approach simultaneously corrects many GCM variables and repeats the procedure across different levels of temporal aggregation to impart observed distributional and persistence properties at multiple time scales. The bias corrected series exhibits improvements across all variables and over all the time scales considered. The use of the approach in hydrology and water resources related downscaling applications is expected to deliver better results.

High latitude hydrological changes during the Eocene Thermal Maximum 2

The Eocene hyperthermals, including the Paleocene–Eocene Thermal Maximum (PETM) and Eocene Thermal Maximum 2 (ETM2), represent extreme global warming events ∼56 and 54 million years ago associated with rapid increases in atmospheric greenhouse gas concentrations. An initial study on PETM characteristics in the Arctic region argued for intensification of the hydrological cycle and a substantial increase in poleward moisture transport during global warming based on compound-specific carbon and hydrogen isotopic (2H/1H) records from sedimentary leaf-wax lipids. In this study, we apply this isotopic and hydrological approach on sediments deposited during ETM2 from the Lomonosov Ridge (Integrated Ocean Drilling Program Expedition 302). Our results show similar 2H/1H changes during ETM2 as during the PETM, with a period of 2H-enrichment (∼20‰) relative to “pre-event” values just prior to the negative carbon isotope shift (CIE) that is often taken as the onset of the hyperthermal, and more negative lipid δ2H values (∼−15‰) during peak warming. Notably, lipid 2H-enrichment at the base of the event is coeval with colder TEX86H temperatures.If 2H/1H values of leaf waxes primarily reflect the hydrogen isotopic composition of precipitation, the observed local relationship between temperature and 2H/1H values for the body of ETM2 is precisely the opposite of what would be predicted using a simple Rayleigh isotope distillation model, assuming a meridional vapor trajectory and a reduction in equator-pole temperature gradients. Overall, a negative correlation exists between the average chain length of n-alkanes and 2H/1H suggesting that local changes in ecology could have impacted the hydrogen isotopic compositions of leaf waxes. The negative correlation falls across three separate intervals — the base of the event, the initial CIE, and during the H2 hyperthermal (of which the assignment is not fully certain). Three possible mechanisms potentially explain 2H-enriched signals at the base of the event, including (1) intense local drying and cooling leading to evaporative 2H-enrichment; (2) changes in frequency/intensity of storm events and its impact on high latitude amount effects; and (3) changes in low-latitude temperatures. Evidence for hydrological shifts at the base of both hyperthermals suggests that hydrological change or the factors promoting hydrological change played a role in triggering the release of greenhouse gases. Generation of similar high-resolution isotopic- and temperature records at other latitudes is crucial for understanding the causal links between temperature and hydrological changes and may help constrain the source and mechanism of carbon release that triggered the early Eocene hyperthermals.

Identifying dominant controls on hydrologic parameter transfer from gauged to ungauged catchments – A comparative hydrology approach

Summary Daily streamflow information is critical for solving various hydrologic problems, though observations of continuous streamflow for model calibration are available at only a small fraction of the world’s rivers. One approach to estimate daily streamflow at an ungauged location is to transfer rainfall–runoff model parameters calibrated at a gauged (donor) catchment to an ungauged (receiver) catchment of interest. Central to this approach is the selection of a hydrologically similar donor. No single metric or set of metrics of hydrologic similarity have been demonstrated to consistently select a suitable donor catchment. We design an experiment to diagnose the dominant controls on successful hydrologic model parameter transfer. We calibrate a lumped rainfall–runoff model to 83 stream gauges across the United States. All locations are USGS reference gauges with minimal human influence. Parameter sets from the calibrated models are then transferred to each of the other catchments and the performance of the transferred parameters is assessed. This transfer experiment is carried out both at the scale of the entire US and then for six geographic regions. We use classification and regression tree (CART) analysis to determine the relationship between catchment similarity and performance of transferred parameters. Similarity is defined using physical/climatic catchment characteristics, as well as streamflow response characteristics (signatures such as baseflow index and runoff ratio). Across the entire US, successful parameter transfer is governed by similarity in elevation and climate, and high similarity in streamflow signatures. Controls vary for different geographic regions though. Geology followed by drainage, topography and climate constitute the dominant similarity metrics in forested eastern mountains and plateaus, whereas agricultural land use relates most strongly with successful parameter transfer in the humid plains.

Inverse determination of groundwater inflow using water balance simulations

The IWAS project Ukraine deals among others with the water balance in the headwaters of the river Western Bug. During investigations in the sub-catchment Sasiv, a gap in the water balance was detected by Pluntke et al. (Environ Earth Sci, this issue, 2014). The runoff of this sub-catchment is significantly higher than that of any other catchment in the region. Unexpectedly, in 2011 the runoff was observed to be higher than precipitation. We hypothesize additional subsurface flow in the Sasiv catchment from adjacent aquifers. The hydrological model BROOK90 was used to model water flows. In addition to publicly available meteorological input data from the NOAA and ECA&C databases, own precipitation measurements in Sasiv were used. The mean seasonal leaf area index (LAI)—cycle of forest, grass, and agricultural land was determined using satellite data. To improve the output quality, the model was adapted for the superior catchment Kamianka-Buzka/Western Bug (2,500 km2). It was calibrated for the period 2001–2006 and validated for 2007–2011. Infiltration and drainage parameters were unknown, and were therefore calibrated applying Monte Carlo simulations. It was not possible to calibrate the sub-catchment Sasiv (107 km2) due to high deviations of the natural water balance. Thus, the model was calibrated for the superior catchment and afterwards applied to the Sasiv catchment. The monthly estimated inflow was calculated based on, first, a constant term, which is a fixed monthly inflow with its minimum in October (22 mm) and its maximum in May (41 mm). Secondly, a dynamic term was added. Here, different dependencies were tested, e.g., precipitation, soil moisture, groundwater level, and modelled runoff. The best coefficient of determination was achieved using a monthly modelled runoff from the 4 months before the current time. The model showed a good performance in the validation period (R2 = 0.88). On average, the runoff observed in Sasiv consists of 60 percent groundwater inflow. At the gauge Kamianka-Buzka, this fraction is still about 5 %. The determined LAI cycles and the usage of an additional precipitation station near Sasiv significantly improved the quality of the water balance modelling in the Sasiv sub-catchment. The presented hydrological model approach was extended by hydrogeological simulations to enhance the understanding of processes in groundwater and surface water interactions. Therefore, it was a special challenge to model with scarce data the heterogeneous hydrogeological character of the catchment. The multi-level calibration enables a comprehensible estimation of annual groundwater recharge rates (30–700 mm) of the shallow quaternary aquifer, which is drained by the river Bug system.

The Influence of Accurate Lag Time Estimation on the Performance of Stream Flow Data-driven Based Models

The timing of variables for stream flow prediction models remains a common problem, particularly with regards to stream flow data-driven based models. Accurate estimation of lag time (Lt), which is representative of time interval, is a potential solution to this problem. The main objective of this paper is to explore possibilities of improving the performance of stream flow data-driven based models by developing a new and simple hydrological approach to accurately estimate Lt between upstream and downstream stations in the Selangor River Basin. The Lt was estimated by means of several empirical formulas along with the new proposed approach that is based on observed hourly stream flow records and water level data. The estimated Lt was used to select the input and output variables for two Multiple Linear Regression models (MLR)—as examples of data-driven based models—to explore the capacity to enhance stream flow data-driven based model performance. An assessment of the two models’ result performance indicates that the MLR model, which is dependent on the proposed method, produced roughly 5 % overall improvement in root mean squared error (RMSE), mean absolute error (MAE) and mean absolute percentage error (MAPE). Not only do the results highlight how effective the proposed approach is in estimating Lt to improve the stream flow MLR model’s performance, but they also serve as a starting point to further study potential improvements from other types of data-driven based models.

A new method for deriving glacier centerlines applied to glaciers in Alaska and northwest Canada

Abstract. This study presents a new method to derive centerlines for the main branches and major tributaries of a set of glaciers, requiring glacier outlines and a digital elevation model (DEM) as input. The method relies on a "cost grid–least-cost route approach" that comprises three main steps. First, termini and heads are identified for every glacier. Second, centerlines are derived by calculating the least-cost route on a previously established cost grid. Third, the centerlines are split into branches and a branch order is allocated. Application to 21 720 glaciers in Alaska and northwest Canada (Yukon, British Columbia) yields 41 860 centerlines. The algorithm performs robustly, requiring no manual adjustments for 87.8% of the glaciers. Manual adjustments are required primarily to correct the locations of glacier heads (7.0% corrected) and termini (3.5% corrected). With corrected heads and termini, only 1.4% of the derived centerlines need edits. A comparison of the lengths from a hydrological approach to the lengths from our longest centerlines reveals considerable variation. Although the average length ratio is close to unity, only ~ 50% of the 21 720 glaciers have the two lengths within 10% of each other. A second comparison shows that our centerline lengths between lowest and highest glacier elevations compare well to our longest centerline lengths. For > 70% of the 4350 glaciers with two or more branches, the two lengths are within 5% of each other. Our final product can be used for calculating glacier length, conducting length change analyses, topological analyses, or flowline modeling.

Application of distributed KIneMatic wave STOrm Runoff Model (KIMSTORM) for flood simulation considering dam release in the NamHan river basin of Korea

This study describes the application of distributed hydrologic model, KIneMatic wave STOrm Runoff Model (grid-based KIMSTORM) to simulate the flood discharge considering dam releases during storm event. The model adopts single flowpath algorithm, and simulates surface and subsurface water depth by routing the water balance of hydrologic components at each cell. For the 12,373 km2 watershed having four dams (two multipurpose, one hydroelectric, and one flood regulation) of NamHan river in Korea, the model was calibrated and verified at five stream locations (two on main and three on tributary) for six flood events with the average Nash–Sutcliffe model efficiency of 0.77. The release amount from dam cell was successfully delivered to the next down cell as an inflow and propagated to the downstream because the model solves the flow routing with hydrologic approach. From the spatiotemporal model results, we could trace the growth of overland flow discharge, the flood flow progress, and the regulation effect by the dams.

Identifying conservation priorities for aquatic refugia in an arid zone, ephemeral catchment: a hydrological approach

ABSTRACTThe conservation priorities for protecting aquatic habitat of arid zone rivers requires an understanding of the drivers of distribution, characteristics and persistence of aquatic refugia in ephemeral to intermittent arid zone rivers. We describe and analyse the aquatic refugia that persist during drought periods in a large, arid, ephemeral river, the Neales River of central Australia, concentrating on refugia for fish and the hydrological processes that influence their location, characteristics and persistence. Field data were collected on flow events, water‐level fluctuations in waterbodies during periods of no flow, waterbody dimensions and salinity. Modelling of open‐water evaporation rates, analysis of salinity changes and frequency of flow events were used to investigate the main processes determining the persistence of waterbodies. The catchment contained both fluvial waterholes and artesian springs providing aquatic refugia. In addition, anthropogenic refugia, in the form of small dams situated on the floodplain and uncontrolled flow from artesian bores, also provided potential refuge. The catchment only contained one waterhole that had a cease‐to‐flow depth sufficient to persist over a no‐flow period of 24 months, but this would also dry within 24–30 months. The capacity of the artesian springs to act as refugia is limited by their shallow depths and limited connectivity with the main river system. These data illustrate the vulnerability of the fluvial ecology of ephemeral, arid zone rivers to long‐term droughts and water resource use and assist in identifying specific refugia that require conservation management. Copyright © 2014 John Wiley & Sons, Ltd.

A physically based distributed hydrological model of wadi system to simulate flash floods in arid regions

Many hydrological approaches have been developed for humid areas; however, we still have many challenges regarding flash floods simulation in arid regions. Thus, the main purpose of this study is to develop a physically based hydrological model for flash floods simulation, to understand the hydrological processes, and to overcome the water relating problems, as water scarcity, data deficiency. In this study, Hydrological River Basin Environmental Assessment Model incorporating wadi system (Hydro-BEAM-WaS) integrated with both Geographic Information System (GIS) and remote sensing data is proposed. To overcome the lack of observational data, Global Satellite Mapping of Precipitation (GSMaP) data has been compared with the Global Precipitation Climatology Center (GPCC) data. We found that the GSMaP has an overestimated or underestimated systematic seasonal bias. Wadi El-Khoud in Oman was chosen for model calibration, while the River Nile basin in Egypt was chosen for flash flood simulations. The simulation has been successfully carried out where it exhibits a reasonable fit between both the simulated and observed results, in spite of the deficiency of high quality observations. This approach can be used to evaluate and simulate the wadi runoff behaviors, such as discontinuous surface flow. It also can help in estimating the initial and transmission losses. Flash flood water has been assessed and evaluated as new water resources, which would be properly utilized to overcome the problem of water shortage in such regions. The proposed model has been proven to provide reliable simulations of flash floods referring to ungauged wadi systems.

Determination of water requirements of the Gavkhuni wetland, Iran: A hydrological approach

This study compared three hydrological methods – low flow frequency analysis, flow duration curve (FDC), and concentration-discharge (C-D) modeling – to determine the water requirement of the Gavkhuni wetland located in an arid region of Iran. Due to the effects of water impounding upstream on the hydrological regime of the Gavkhuni's inflow after construction of the Zayandehrud dam, none of the methods produced satisfactory results.Consequent modification of the hydrological regime of the wetland's inflow using a scaling process allowed all the methods except low flow frequency analysis to dependably estimate the base flow for the wetland. The results of the C–D method revealed that this method can provide a minimum health condition from the water quality point of view, while the results of the FDC demonstrated that not only the inflow estimated using this method can supply minimum conditions in terms of water quality parameters, but it also covers most areas of the wetland, based on the results of hydraulic modeling.The results reveal that the hydrological methods implemented in this study can dependably estimate environmental water allocation for wetlands in arid and semi-arid regions when there is no detailed knowledge about the biological requirements of the wetlands' biota.

Hydrological behaviour of a drained agricultural peat catchment in the tropics. 1: Rainfall, runoff and water table relationships

Hydrological data of a drained tropical peat catchment have been analysed through conventional quantitative hydrological approaches to characterize its hydrological behaviours and changes due to continuous drainage for a long period. The results show that the hydrology of the catchment is extremely dynamic and the catchment is flashy in nature. A decreasing trend in peak flow amount and an increasing trend in baseflow amount was observed in the catchment, indicating that continuous drainage has reduced the risk of both flooding and water scarcity in the catchment. Correlation analysis among rainfall, runoff and groundwater table reveals that saturation excess-near surface flow is the dominant mechanism responsible for rapid runoff generation in the catchment. Therefore, any physical alterations or disturbances to the upper part of the peat profile would definitely affect the overall hydrological behaviour of the peat catchment.Editor Z.W. Kundzewicz; Associate editor D. HughesCitation Katimon, A., Shahid, S., Abd Wahab, A.K., and Ali, M.H., 2013. Hydrological behaviour of a drained agricultural peat catchment in the tropics. Part 1: Rainfall, runoff and water table relationships. Hydrological Sciences Journal, 58 (6), 1297–1309.

A combined geochemical and hydrological approach for understanding macronutrient sources

This study employed complementary geochemical techniques and distributed hydrological modelling to investigate multiple sources of catchment macronutrients and characterise their changes in contrasting storm and baseflow conditions. This approach was demonstrated for the Beult catchment in the county of Kent (England), a designated Site of Special Scientific Interest (SSSI) indentified as failing to meet water quality standards for key nutrients under the Water Framework Directive. Significant changes in nutrient stoichiometry and bioavailability are observed for surface waters under contrasting flow regimes. Soluble reactive phosphorus (SRP) concentrations are approximately twice as high during baseflow compared to high flow, while the inverse is true for particulate, colloidal and dissolved hydrolysable phosphorus, dissolved organic carbon and nitrate. Nitrogen (N):phosphorus (P) ratios are lower during baseflow for most surface waters impacted by diffuse sources of pollution. Fluorescence indices of dissolved organic matter (DOM) show that waste water inputs may be locally important sources of more complex low molecular weight DOM, particularly during baseflow. Nitrate N and O isotope signatures, combined with other dissolved chemical tracers, confirm the dominance of wastewater N inputs at sites downsteam of sewerage treatment works during baseflow, with a shift towards the soil N pool in surface waters across the catchment during high flow. Distributed hydrological modelling using the Grid-to-Grid model reveal areas with the greatest runoff also export higher N and P concentrations, and hence deliver a greater flux of macronutrients, while forested areas with low nutrient concentrations reduce runoff and nutrient fluxes. During periods of high runoff, nested sampling indicates that nutrient fluxes scale with catchment area. This combined approach enables a more thorough assessment of the macronutrient sources and dynamics, better informing management options in nutrient impacted catchments.

Characterization of process-oriented hydrologic model behavior with temporal sensitivity analysis for flash floods in Mediterranean catchments

Abstract. This paper presents a detailed analysis of 10 flash flood events in the Mediterranean region using the distributed hydrological model MARINE. Characterizing catchment response during flash flood events may provide new and valuable insight into the dynamics involved for extreme catchment response and their dependency on physiographic properties and flood severity. The main objective of this study is to analyze flash-flood-dedicated hydrologic model sensitivity with a new approach in hydrology, allowing model outputs variance decomposition for temporal patterns of parameter sensitivity analysis. Such approaches enable ranking of uncertainty sources for nonlinear and nonmonotonic mappings with a low computational cost. Hydrologic model and sensitivity analysis are used as learning tools on a large flash flood dataset. With Nash performances above 0.73 on average for this extended set of 10 validation events, the five sensitive parameters of MARINE process-oriented distributed model are analyzed. This contribution shows that soil depth explains more than 80% of model output variance when most hydrographs are peaking. Moreover, the lateral subsurface transfer is responsible for 80% of model variance for some catchment-flood events' hydrographs during slow-declining limbs. The unexplained variance of model output representing interactions between parameters reveals to be very low during modeled flood peaks and informs that model-parsimonious parameterization is appropriate to tackle the problem of flash floods. Interactions observed after model initialization or rainfall intensity peaks incite to improve water partition representation between flow components and initialization itself. This paper gives a practical framework for application of this method to other models, landscapes and climatic conditions, potentially helping to improve processes understanding and representation.

Groundwater and surface water interactions in an alluvial plain, Tuul River Basin, Ulaanbaatar, Mongolia

Drinking water supplies in Ulaanbaatar, the capital of Mongolia, are completely dependent on groundwater sourced from pumping wells located in an alluvial plain of the Tuul River which flows through Ulaanbaatar. The interaction between groundwater in the alluvial plain and river surface water was investigated using a hydrological and multi-tracers approach. The observed groundwater contour map clearly shows that the Tuul River recharges the floodplain groundwater and groundwater flows from east to west. The similarity of chemical and stable isotopic compositions suggests that groundwater is mainly recharged by Tuul River water in the vicinity of the river. In addition, considering groundwater contours and chemical composition, groundwater in the northern and southern mountain sides contribute to floodplain groundwater. Stable isotopic information suggests that winter season precipitation also contributes to the groundwater, because groundwater in a specific region has a considerably lower isotopic ratio. Using the End Member Mixing Analysis applying oxygen-18, SiO 2 and HCO 3 as tracers, the contribution ratios of the Tuul River, groundwater in the northern and southern mountain regions, and winter season precipitation to floodplain groundwater are estimated to be 58% to 85%, 1% to 54%, 0% to 16%, and 0% to 12%, respectively.

Going Back to the Roots: The Need to Link Plant Functional Biology with Vadose Zone Processes

Soil plant atmosphere continuum concepts used in vadose zone hydrology approach plants as physical entities. This approach has proven very valuable in the past decades. The need to upscale such concepts provokes the question if plant functional biology should be considered, as larger scales also imply variation in (micro)climate and soil composition. Habitat manifestation is an expression of its evolutionary history and although the spatial distribution of habitats is largely driven by current climates, a soil's water holding capacity and hence its formation over time may have played a role.Separate mechanisms involved in the soil plant atmosphere continuum are often understood and incorporated in numerical models for predictive purposes, yet interrelationships pose challenges, especially when such relationships cross traditional scientific disciplinary boundaries. In fact, the exact driver for root water uptake is itself subject of scientific debate, as there is no consensus on whether the driver for root water uptake is soil moisture content (e.g. [1]) or soil water potential (e.g. [2]). To evaluate soil water availability in relation to crop yield prognoses and the stability of natural vegetation, integrated concepts are sorely needed, especially in the perspective of climate change [3] and global water scarcity [4]. We present considerations and possible approaches for linking plant functional biology and vadose zone processes.

EVALUASI RENCANA KINERJA KOLAM RETENSI (RETARDING BASIN) DALAM UPAYA PENGENDALIAN BANJIR TUKAD MATI DI KOTA DENPASAR

Tukad Mati is one of the rivers in the province of Bali that unfolds and flows in Badung regency and Denpasar. Inundation due to flooding is a problem that often occurs in this region during the rainy season. In an effort to overcome problems of flooding have been many studies carried out so as to produce flood control alternatives such as normalization, diversion channels and retarding basins. Retarding basin is one of flood control alternative that has not been much studied. In this study conducted a simulation of flood prevention alternative with retarding basin at Tukad Mati, by the hydrology approach method and hydraulics using HEC-RAS 4.0 program applications. Simulations performed on the current river flow conditions (existing condition) and to the existing conditions with the retarding basin, according to the detail design of retarding basin in the city of Denpasar and evaluate the effectiveness of the retarding basin in the river basin flood control of Tukad Mati. Flood control by retarding basin based on simulations with the 2 (two) years flood return period, resulting in a reduction of water level by an average of 0.42 meters or an average of 12% of the maximum water level in the conditions without retarding basin, which occurred in along the grooves on the lower reaches of the retarding basin and inundation waters still occur in some places, particularly in the downstream of Umadui Dam. Economic analysis of both the analysis of Benefits/Cost produces a parameter of BCR, NPV and IRR are not meet the feasibility requirements. The effective retention of retarding basin based on simulation results are 282,630.00 m3 with the ability to flood accommodate for 3-4 hours. In terms of economic development retarding basin is not feasible in terms of comparative costs and benefits

For improvement in understanding eco-hydrological processes in mire

Various anthropogenic stressors have caused mire degradation in subarctic northern Japan, such as drying and the invasion of an alder-dominant shrub forest. The Japanese government recently started a nature conservation project to restore a formerly meandering river in order to prevent invasive forest species and to rehabilitate the original mire ecosystem. In this study, the process-based National Integrated Catchment-based Eco-hydrology (NICE) model is further developed to improve accuracy in evaluation of nonlinear interactions and feedback of hydro-geomorphology and vegetation dynamics in the ecosystem. The simulated results clarify the impact of groundwater level change, sediment deposition, and nutrient availability on the complex alder invasion after refining the model to include newly-developed down-scaling and feedback processes. The model also shows the interaction between groundwater and inundated flow and its effect on vegetation change, which sheds light on two conflicting conceptualizations of peatland hydrology. This integrated system links the hydrological approach to the ecological one implicitly in the model, and throws some light on the refinement of tipping-point early warning systems for sustainable development and the improvement in boundless biogeochemical cycles along terrestrial-aquatic continuum for global environmental change.

Microbial and hydrological influences on nitrate isotopic composition in an agricultural lowland catchment

Summary The interaction between microbially-mediated nitrogen cycling and catchment hydrology affects the amount and isotopic composition of nitrate exported from catchments in drainage waters. Dominant microbial and hydrological influences were investigated using δ 15 N NO3 and δ 18 O NO3 of nitrate from the Wensum catchment in East Anglia, eastern England; a 570 km 2 lowland agricultural catchment. Samples were collected from catchment waters, precipitation, dry deposition, agricultural fertiliser and sewage effluent. Catchment water nitrate concentration and isotopic composition can be explained by microbially-mediated cycling of nitrogen inputs through nitrification to denitrification, resulting in a reduced nitrate load exported from the Wensum catchment. Seasonal, transient and through-year constant isotopic signals from nitrogen cycling processes reflect the influence of dynamic and stable hydrological factors. A three-member mass-balance mixing model demonstrates an increasing influence from Chalk groundwater downstream in the Wensum headwaters, and the displacement of shallow groundwater into the river by runoff explains the isotopic and hydrochemical stability seen in the river Wensum under varying flow conditions. Together this demonstrates a powerful application of a dual isotope and hydrological approach in the understanding of an agricultural catchment’s response to nitrogen loading.

Hydrochemical and Isotope Evidence of Groundwater Contamination of Cultivated Fields of Semi-Arid Environments in Tunisia

This present study, which uses geochemical and isotope hydrological approaches, attempts to provide appropriate scientific information about the dominant geochemical processes that influence groundwater chemical composition in a semi-arid region of cultivated field. Therefore, particular emphasis has been placed on (1) the evolution of solute concentrations within the hydrological system as well as in the vadose zone, (2) the contribution of anthropogenic processes to the groundwater contamination, and (3) the estimation of groundwater recharge deriving from return flow of irrigation water. It has been demonstrated that the excess of irrigation waters has significantly influenced the rate of groundwater recharge. The annual amount of groundwater recharge related to the irrigation practices is approximately 100 mm. Modification of the geochemical characteristics of the Zeroud aquifer groundwater is caused by water-rock interaction, including both the dissolution of evaporate and the cation exchange process. However, anthropogenic processes related to the return flow of irrigation waters have led to extremely high nitrate concentrations and flushing of solutes, such as chloride, sulfate, sodium, and calcium. The isotopic signature provides evidence of groundwater contamination. Indeed, the relatively enriched stable isotope concentrations and low tritium concentrations highlight the important contribution of irrigation waters to the local groundwater recharge, particularly in the Menzel Mhiri agricultural area.