Stream Groundwater Research Articles

Coupled transport and reaction kinetics control the nitrate source‐sink function of hyporheic zones

The fate of biologically available nitrogen (N) and carbon (C) in stream ecosystems is controlled by the coupling of physical transport and biogeochemical reaction kinetics. However, determining the relative role of physical and biogeochemical controls at different temporal and spatial scales is difficult. The hyporheic zone (HZ), where groundwater–stream water mix, can be an important location controlling N and C transformations because it creates strong gradients in both the physical and biogeochemical conditions that control redox biogeochemistry. We evaluated the coupling of physical transport and biogeochemical redox reactions by linking an advection, dispersion, and residence time model with a multiple Monod kinetics model simulating the concentrations of oxygen (O2), ammonium (NH4), nitrate (NO3), and dissolved organic carbon (DOC). We used global Monte Carlo sensitivity analyses with a nondimensional form of the model to examine coupled nitrification‐denitrification dynamics across many scales of transport and reaction conditions. Results demonstrated that the residence time of water in the HZ and the uptake rate of O2 from either respiration and/or nitrification determined whether the HZ was a source or a sink of NO3 to the stream. We further show that whether the HZ is a net NO3 source or net NO3 sink is determined by the ratio of the characteristic transport time to the characteristic reaction time of O2 (i.e., the Damköhler number, DaO2), where HZs with DaO2 < 1 will be net nitrification environments and HZs with DaO2 ≪ 1 will be net denitrification environments. Our coupling of the hydrologic and biogeochemical limitations of N transformations across different temporal and spatial scales within the HZ allows us to explain the widely contrasting results of previous investigations of HZ N dynamics which variously identify the HZ as either a net source or sink of NO3. Our model results suggest that only estimates of residence times and O2uptake rates are necessary to predict this nitrification‐denitrification threshold and, ultimately, whether a HZ will be either a net source or sink of NO3.

Stochastic analysis of stream–groundwater interaction subject to temporally correlated recharge

summary In this article, the coupled equations describing the transient groundwater flow and stream flow fluctuations are solved based on the Fourier–Stieltjes integral representation, where the lateral inflow term in the stream flow perturbation equation connects the process of groundwater flow to that of stream flow. The closed-form solutions describing the variability in groundwater flow specific discharge and stream flow discharge are developed to quantify the influence of the variability in temporally correlated recharge in an unconfined aquifer on the stream flow discharge. We found from the closed-form solutions that the temporal correlation scale and the variance of recharge fields influence the variability in groundwater flow specific discharge and the stream flow discharge positively. In addition, the hydraulic diffusivity coefficient takes the role of reducing the variability in stream flow discharge.

Is 222Rn a suitable tracer of stream–groundwater interactions? A case study in central Italy

River water infiltration into an unconfined porous aquifer (∼73% gravels, ∼12% sands, ∼15% silts and clays) in the Petrignano d’Assisi plain, central Italy, was traced combining isotopic techniques (222Rn) with hydrochemical and hydrogeologic techniques in order to characterize the system under study. The 222Rn gave information about the river water residence times within the aquifer and hydrochemical data, in a two-component mixing model, which allowed estimating the extent of mixing between surface waters and groundwater in wells at increasing distances from the river. The mixing measured in the well closer to the riverbank indicated a higher contribution of river water (up to 99%) during the groundwater recession phase and a moderate contribution (up to 64%) during the recharge phase. A model describing 222Rn concentrations in groundwater as the result of both parent/daughter nuclide equilibrium and mixing process (222Rn mixing/saturation model) was used to describe observed Rn concentrations and mixing index trends with the aim of evaluating water mean infiltration velocities along the transect. The stream bank infiltration velocities obtained by the model ranged from 1mday−1 during groundwater recharge periods, when river water infiltration is lower, to 39mday−1 during recession phases, when river water infiltration is larger.

The effect of precipitation events on inorganic carbon in soil and shallow groundwater, Konza Prairie LTER Site, NE Kansas, USA

Abstract Monthly sampling for 1 year at the Konza Prairie LTER (Long-Term Ecological Research) Site in northeastern Kansas shows a connection between the annual cycles of CO2 in soil air and shallow groundwater DIC (dissolved inorganic C). Soil air CO2 reached 6–7% in July to mid-August, when moisture was not limiting to soil respiration. Following the annual maximum there was a sequential decrease in CO2 in three soil horizons to less than 0.5% because of moisture deficiency in the late summer and temperature decline in the fall and winter. Groundwater pCO2 reached its maximum of 5% in October; the lag-time of 2–3 months may correspond to the travel time of soil-generated CO2 to the water table. The time-variable CO2 caused an annual carbonate-mineral saturation cycle, intensifying limestone dissolution and DIC production when CO2 was high. The C flux depended on respiration and rainfall regimes, and had two main pathways. Transport of soil CO2 in the dissolved form with diffuse flow of recharge water was the most effective during the growing season so long as soil moisture was present. Downward movement of gaseous CO2 and equilibration with groundwater at the water table was favorable in July to August. Storm rainfall events recharged the aquifer within a few hours through preferential flow and stream–groundwater interaction, resulting in dilution of groundwater rather than forcing entrapped CO2 downward. Calculated C flux from the unsaturated zone to the unconfined aquifer in the monitoring period was 0.26 ± 0.03 M/m2/a of C, which is less than 1% of the CO2 that is released by soil to the atmosphere via efflux. However, meteoric precipitation was only 72% of average annual precipitation during the study period, so this study represents dry-condition flux. In addition, increased respiration rates due to warming of the atmosphere have the potential to cause a higher C flux to the saturated zone, intensifying weathering and groundwater acidification, so that further study is suggested.

Water quality and benthic macroinvertebrate communities in karst landscapes of North Island, New Zealand: influences of water sources, habitat type and anthropogenic disturbances

In karst landscapes, aquatic habitats differ in terms of the relative contributions of different water sources (allogenic surface stream vs autogenic karst groundwater) and their geomorphology. Benthic macroinvertebrate community structure in these habitats is likely to vary in response to this heterogeneity, as well as to the physicochemical differences between water flowing through pasture vs native forest dominated catchments. Surveys were conducted to examine the influences of water source, habitat type (main stream-ways and side passages in caves, and epigean springs) and surrounding land use (native forest or pasture) on the water quality and benthic community structure in the Maniapoto Karst, North Island, New Zealand. Generally, springs and cave side passages received more autogenic water, indicated by lower temperatures and higher conductivities, than the main stream-ways of caves. However, in terms of community structure, the epigean springs and cave side passages were most distinct from each other, whilst the main stream-ways of caves were intermediate between the other two habitats. Temperature and nitrate concentrations were higher in sites surrounded by pasture than those in native forest, but surrounding land use exerted less influence on macroinvertebrate community structure than habitat type. A comparison of community structure in caves with high and low tourist traffic failed to identify any significant effects.

Internal catchment process simulation in a snow‐dominated basin: performance evaluation with spatiotemporally variable runoff generation and groundwater dynamics

AbstractHydrologic models have increasingly been used in forest hydrology to overcome the limitations of paired watershed experiments, where vegetative recovery and natural variability obscure the inferences and conclusions that can be drawn from such studies. Models are also plagued by uncertainty, however, and parameter equifinality is a common concern. Physically‐based, spatially‐distributed hydrologic models must therefore be tested with high‐quality experimental data describing a multitude of concurrent internal catchment processes under a range of hydrologic regimes. This study takes a novel approach by not only examining the ability of a pre‐calibrated model to realistically simulate watershed outlet flows over a four year period, but a multitude of spatially‐extensive, internal catchment process observations not previously evaluated, including: continuous groundwater dynamics, instantaneous stream and road network flows, and accumulation and melt period spatial snow distributions. Many hydrologic model evaluations are only on the comparison of predicted and observed discharge at a catchment outlet and remain in the ‘infant stage’ in terms of model testing. This study, on the other hand, tests the internal spatial predictions of a distributed model with a range of field observations over a wide range of hydroclimatic conditions. Nash‐Sutcliffe model efficiency was improved over prior evaluations due to continuing efforts in improving the quality of meteorological data collection. Road and stream network flows were generally well simulated for a range of hydrologic conditions, and snowpack spatial distributions were well simulated for one of two years examined. The spatial variability of groundwater dynamics was effectively simulated, except at locations where strong stream–groundwater interactions exist. Model simulations overall were quite successful in realistically simulating the spatiotemporal variability of internal catchment processes in the watershed, but the premature onset of simulated snowmelt for one of the simulation years has prompted further work in model development. Copyright © 2011 John Wiley & Sons, Ltd.

Subsurface Mobilization of Phosphorus in an Agricultural Riparian Zone in Response to Flooding from an Upstream Reservoir

Riparian wetlands can act as both phosphorus (P) sources and sinks depending upon a range of factors that affect hydrological and biogeochemical processes that govern P mobilization. Stream flow, groundwater levels and water chemistry (total P (TP), soluble reactive P (SRP)) were measured in a series of nested piezometers along three transects located in a riparian zone prior to and throughout a flood event resulting from the release of water from an upstream reservoir. Results of the study show that the stream was influent on all sampling dates, and groundwater flow through the riparian zone was longitudinal to the channel, rather than transverse to the stream. This drainage pattern affected riparian zone biogeochemistry. The riparian zone was a source of TP and SRP to the shallow groundwater system under both pre-flood and flood conditions, as P levels were higher in piezometers at the downstream end of the riparian zone (p <0.001). Flooding induced a brief increase in TP concentrations in shallow groundwater due to mixing with surface runoff following overbank flooding; however, these concentrations quickly returned to pre-event levels. In contrast, SRP concentrations in shallow groundwater decreased during flooding, likely resulting from mixing with oxygen-rich stream water. A large pulse of TP (12,000 g L1) was observed in the creek on the peak flood date. This P did not originate from the reservoir and was more likely due to the mobilization of P from the riparian zone surface when overbank flooding occurred. The results indicate that autumn flooding of riparian zones downstream from impoundments may mobilize phosphorus if overbank flooding occurs, thereby reducing the nutrient retention potential of riparian zones in some settings.

Preliminary evaluation of a radioactive waste repository safety performance by a Monte Carlo simulation-based reliability model

Abstract Disposal facilities are designed to provide long-term isolation of the wastes from the human environment by means of a system of barriers, both engineered and natural. In this regard, it is required that the containment function of the multi-barrier system be evaluated by a quantitative risk analysis procedure, also called performance assessment. This entails the implementation of a Probabilistic Safety Assessment model for representing the stochastic failure behavior of the repository barriers, estimating the release rates of radionuclides into the groundwater stream and the doses from subsequent ingestion of drinking water. To this aim, a Monte Carlo simulation scheme is provided within a reliability modelling approach for the safety performance analysis of a repository, accounting also for barrier degradation processes. An application to a case study of the literature is presented to validate the approach and demonstrate its simplicity and flexibility.

Contributions of the International Atomic Energy Agency to the development and practice of isotope hydrology

The International Atomic Energy Agency (IAEA) has played a crucial role in promoting and expanding the use of isotopes in hydrology over the last five decades to gain unique insights into the functioning of terrestrial and atmospheric water cycles. In this essay, an historical perspective of IAEA activities is provided, along with some of the achievements and recent initiatives. When the IAEA was formally established in 1957, radioactive fallout from atmospheric thermonuclear testing, particularly tritium, and its impact on human health and the environment posed serious societal concerns. This led the IAEA to initiate a global project to measure tritium concentrations in precipitation. Brian Payne, first Head of the Isotope Hydrology Section of IAEA, convened a scientific advisory committee in 1959 to define the scope of hydrological aspects of tritium monitoring in precipitation. The committee of three eminent scientists — Fritz Begemann, Erik Eriksson and Hans E. Suess — emphasized that, based on contemporary publications, tritium and stable isotopes of oxygen and hydrogen in precipitation would be useful for studying many watercycle processes, including water-residence time and evaporation losses from lakes and reservoirs, groundwater age and aquifer dynamics, continental water balance, age of hot spring water, and mixing time of the oceans (e.g. Friedman 1953; Epstein and Mayeda 1953; Dansgaard 1953; Urey et al. 1951; Libby 1953). The IAEA’s precipitation monitoring efforts began in 1960, and were later expanded to a global scale in 1961 by collaboration with the World Meteorological Organisation (WMO). This expanded network became known as the IAEA-WMO Global Network for Isotopes in Precipitation (GNIP). The number of operational GNIP stations has varied over the years. Originally 161 stations were in operation. By 1963–1964 there was a maximum of about 220 stations, and currently 185 stations in 53 countries contribute samples. In its 50 years of existence, the GNIP database has gained about 120,000 monthly records of stable oxygen and hydrogen isotopes and tritium from more than 900 meteorological stations worldwide. Dansgaard (1964) conducted a comprehensive analysis of stable isotope data from the GNIP and proposed key relationships between precipitation isotopes and climate. In particular, isotope correlations between surface air temperature and amount of precipitation were crucial to interpreting palaeoclimate records preserved in proxy archives such as ice cores, lake sediments, groundwater, tree rings and speleothems. Stable isotope data from the GNIP continue to be extensively utilized in climate research. Most general circulation models currently in use have been expanded to simulate precipitation isotopes (Joussaume et al. 1984; Jouzel et al. 1997; Hoffmann et al. 2000) and GNIP data provide a means to validate these models. A number of IAEA publications have reported on the statistical evaluations of precipitation isotope distributions (e.g., Yurtsever and Gat 1981; Rozanski et al. 1991, 1993; Aggarwal et al. 2010). Figure 1 shows all GNIP stations past and present, and a global map of interpolated stable oxygen isotope data (1961–2004) using active and inactive stations. The continuous operation of GNIP has also been critical for the use of tritium in hydrology, hydrogeology, and hydrometeorology. In addition to tritium in precipitation, tritium in rivers, lakes and groundwater has yielded invaluable information on the dynamic aspects of the water cycle such as the residence time of water in the different hydrologic reservoirs and hydrograph separation in stream flow. Similarly, stable isotope data in precipitation, surface water and groundwater were invaluable for characterizing the role of groundwater in streams, rivers and lakes, the geographic and temporal origin of groundwater recharge and its effect on the water balance of hydrologic systems, especially in wetlands and evaporation prone areas. Due to the very nature of the methodology, isotope hydrology’s emphasis has been Received: 4 March 2010 /Accepted: 28 August 2010 Published online: 24 September 2010

A multi-scale method for identifying groundwater exchanges sustaining critical thermal regimes in streams

A holistic understanding of heterogeneous groundwater-induced thermal regimes was developed for a Southern Ontario creek using a multi-scale field approach. To better understand the habitat characteristics sustained by the groundwater and surface water exchanges, the relationship between groundwater inputs and stream temperatures were investigated at stream, segment, geomorphic-unit and micro-habitat levels. Continuous point temperature measurements at various locations along the main channel were used to determine seasonal and spatial stream temperature trends and to identify areas of possible groundwater contributions. Methods effective for quantifying and locating groundwater inputs were evaluated, including the velocity-area method, stream temperature surveys and sediment temperature measurements. Sediment temperature mapping of riffle-pool and plane-bed geomorphic units illustrated highly varied substrate temperatures in the plan-view of the creek. The potential application of thermal imaging was also explored and thermal images successfully illustrated a groundwater-sustained micro-habitat. The results demonstrated that these multi-scale field techniques allow for different groundwater–surface water exchange processes to be observed and more effectively capture the complexity of these exchanges than single-level field approaches.

Ecology and management of the hyporheic zone: stream–groundwater interactions of running waters and their floodplains

AbstractOver the last 25 y, stream ecosystem theory has expanded to include explicitly the vertical dimension of surface–groundwater linkages via the hyporheic zone and below alluvial floodplains. Hydrological exchange between the stream and hyporheic zone mediates transport of products from the biogeochemical activities within the sediments. Hot-spots of primary productivity in the surface stream often result from upwelling nutrient-rich water. Conversely, downwelling surface water supplies organic matter and dissolved O2 to hyporheic invertebrates and microbes, enhancing hyporheic productivity. Many of the papers seminal to conceptual and empirical advances in hyporheic research have been published in J-NABS, reflecting stream benthologists’ awareness of the relevance of processes and biota in the hyporheic zone. However, major research gaps remain. One is the need for further empirical data to test the predictions of several current conceptual frameworks that hypothesize conditions under which the hypo...

Optimal design of a hybrid air stripping/pervapouration system for removal of multicomponent VOCs from groundwater

Groundwater streams contaminated with volatile organic compounds (VOCs) require proper treatment to comply with drinking requirement restrictions. Air stripping and pervapouration are two common treatment technologies for groundwater contaminated with VOCs. An attractive alternative for VOC treatment may be to combine these two technologies together within the same circuit since this offers potential advantages over the operation of either of these systems alone. The current study focuses on the important issue of determining in an objective and systematic manner how to combine these two technologies to meet the drinking water requirements in the most cost-effective manner. Superstructure optimisation is the framework for hybridisation investigated in this study to determine the optimal treatment network and operating conditions for the treatment units to achieve desired water qualities. Two case studies illustrating the proposed approach are presented and the sensitivity of their optimal solutions to perturbations in certain operating conditions is discussed.

Treating causes not symptoms: restoration of surface - groundwater interactions in rivers

Many river restoration projects seek to address issues associated with impaired hydrological and ecological connectivity in longitudinal (e.g. effects of dams, weirs) or lateral (e.g. alienated floodplain) dimensions. Efforts to restore the vertical dimension of impaired stream–groundwater exchange are rare, hampered by limited understanding of the factors controlling this linkage in natural alluvial rivers. We propose a simplified two-axis model of the ‘primary drivers’ (sediment structure and vertical hydraulic gradient) of stream–groundwater exchange that acknowledges their interaction and provides a practical template to help researchers and river managers pose hypothesis-driven solutions to restoration of damaged or lost vertical connectivity. Many human activities impact on one or both of these drivers, and we review some of the tools available for treating the causes (rather than symptoms) in impacted stream reaches. For example, creating riffle-pool sequences along stream reaches will enhance vertical hydraulic gradient, whereas flushing flows can remove clogging layers and sustain sediment permeability. Our model is a first step to specifying mechanisms for recovery of lost vertical connectivity. Assessing results of river restoration using this approach at reach to catchment scales will provide scientific insights into the interplay of hydrology, fluvial geomorphology and river ecosystem function at appropriately broad scales.

Seasonal biogeochemical hotspots in the streambed around restoration structures

Rapid exchange of stream water and groundwater in streambeds creates hotspots of biogeochemical cycling of redox-sensitive solutes. Although stream–groundwater interaction can be increased through stream restoration, there are few detailed studies of the increased heterogeneity of water and solute fluxes through the streambed and associated patterns of biogeochemical processes around stream restoration structures. In this study, we examined the seasonal patterns of water and solute fluxes through the streambed around a stream restoration structure to relate patterns of water flux through the streambed to morphology of the channel and biogeochemical processes occurring in the bed. We characterized different biogeochemical zones in the streambed using principal component analysis (PCA) and examined the change in spatial patterns of these zones during different seasons. The PCA results show that two principal components summarized 83% of the variance in the original data set. Streambed pore water was characterized as oxic (indicating production of nitrate), anoxic (indicating sulfate, iron and manganese reduction), or stream-like (indicating there was minimal change in the stream water chemistry in the bed). Regardless of season of the year, anoxic zones were predominantly located upstream of the structure, in a low-velocity pool, and oxic zones were predominantly located downstream of the structure, in a turbulent riffle. We expect structures that span the full channel, are impermeable, and permanent, such as those installed in natural channel design restoration will similarly impact biogeochemical processing in the streambed. The installation of these types of restoration structures may be a way to increase the degree of biogeochemical cycling in stream ecosystems.

Short-term colonization patterns of macroinvertebrates in alpine streams

We examined the short-term colonization of habitat patches by larval macroinvertebrates in 6 different types of alpine streams, including permanent kryal (glacier-melt), rhithral (rain and snow-melt), and krenal (groundwater) streams, kryal and rhithral lake outlets, and temporary rhithral streams. Abundant macroinvertebrates found in the different streams were common alpine species, although taxon richness, invertebrate density, and Simpson's diversity were highest in krenal and rhithral streams and lowest in kryal lake outlets. Cages filled with natural substrata were placed in riffle/run habitats in each stream and replicate cages were subsequently collected after 3, 8 and 30 days during early summer. Benthic and drifting invertebrates also were collected to compare with cage assemblages at each stream. Colonization of cages was rapid at most sites with high total densities and biomass occurring within 3 days. Simpson's diversity was highest on day 3, and decreased and stabilized by day 8 in all stream types. Chironomids, simuliids, and the mayfly Baetis alpinus were common early colonizers of cages at most streams. The turbellarian Crenobia alpina was a common colonizer of cages in temporary rhithral streams, and heptageniids were most common in rhithral stream cages. Chloroperlids were common colonizers of cages in krenal and kryal streams, and trichopterans were most common in cages of permanent krenal and temporary rhithral streams. Less common and rare taxa were late colonists of cages, having highest densities by day 30. The similar colonization patterns observed among alpine stream types may reflect altitudinal constraints on the regional species pool.

Spatial heterogeneity of water temperature across an alpine river basin

AbstractRiver temperature remains a subject of major worldwide research, yet understanding of multi‐scale thermal variability across river systems is limited. Such studies are necessary to elucidate the relative importance of site‐specific (reach‐scale) versus landscape controls. This article addresses this research need by identifying water temperature variability across an alpine river basin, using high‐resolution (15 min) water column temperature data at 29 sites in the Taillon–Gabiétous basin, French Pyrénées. Thermal patterns were examined in relation to a suite of meteorological (incoming shortwave radiation, air temperature, and precipitation) and basin characteristics (altitude, azimuth, stream length, and stream order). Mean water temperature for the monitoring period varied markedly across the river basin, ranging from 0·4 °C at the Taillon Glacier to 14·6 °C in a south‐facing hillslope groundwater stream. Basin‐scale water temperature patterns were strongly influenced by stream water source. Stream temperature was also significantly associated with basin characteristics, most notably altitude, azimuth, and stream length. Thermal heterogeneity across the basin was higher than that along the Taillon Glacier stream, despite rapid longitudinal warming rates with distance from the glacier snout. The timing of thermal extremes (maximum/minimum) during two contrasting hydrometeorological events (hot summer day vs intense hail/rain storm) revealed a clear synchronicity of thermal response among sites, although notable exceptions included karstic groundwater streams that were weakly influenced by concurrent meteorological conditions. Overall, the study demonstrates high thermal heterogeneity at the basin scale (being equal to, or greater than, that found in previous investigations), and the major effect of water source and landscape factors such as altitude, azimuth, and stream length on alpine stream temperature. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Modeling the effects of lowland stream restoration projects on stream–subsurface water exchange

The relative effect of individual elements of restoration projects on stream–subsurface water exchange was studied by identifying elements that were most effective in increasing downwelling stream water (DSW) into subsurface environments using groundwater flow modeling. Several restoration projects studied in lowland streams involved riffle-pool construction, lateral gravel bar construction and channel re-meandering. Simulations using a homogeneous field of mean hydraulic conductivity that removed heterogeneity showed a large decline in DSW in the four restoration projects studied, suggesting that use of coarse sediments in construction initially increases stream–subsurface water exchange, but the effects may not persist in streams where fine sediments clog streambeds. In two riffle-pool construction projects studied, modification of the channel gradient showed a greater effect on DSW than the alteration of substrate texture. In the gravel bar construction site, modeling results indicated that the construction of a riffle-pool sequence along the bar had a greater effect than the construction of the gravel bar itself. In contrast in the channel re-meandering site, the combination of a greater sinuosity and a lower hydraulic head along the small riffles resulted in re-meandering having a greater effect than the associated riffle-pool construction. A simulation in which the floodplain sediments of low saturated hydraulic conductivity at the re-meandered site were replaced with sandy gravels increased DSW by 10 times. This modeling suggests that the addition of coarse sediments in combination with re-meandering would be required to significantly enhance stream–subsurface water exchange in reaches with fine-grained floodplain sediments. Designing the size and type of morphologic features constructed in restoration projects is somewhat flexible, and the use of modeling to simulate stream–groundwater interactions may help to enhance the hydrologic link with a stream and the subsurface environment in restored stream reaches.

Assessment by multivariate analysis of groundwater–surface water interactions in urbanized Mediterranean streams

Streams in Mediterranean areas are characterized by a variable discharge regime with annual floods and droughts. Natural flow perturbations result in permanent and temporary rivers and, as a consequence, unique ecosystems. Human pressures such as treated and non-treated waste water discharge impact severely on these streams, since waste water dilution depends on river flow dynamics. Furthermore, their hydrological status worsens with the capture of stream discharge by surface or groundwater exploitation. Multivariate analysis has been widely used to analyze large sets of variables in environmental studies. In the present work, a hydrological study reinforced by principal component analysis (PCA), followed by cluster analysis of the PCA results, has been used to determine surface water origin and its interactions with groundwater in Mediterranean streams. The results show that hydrological observations are supported by PCA and cluster analysis. Additionally, this joint analysis makes it possible to observe the significance of the interaction between streams and aquifers in anthropized Mediterranean Basins. Groundwater exploitation can seriously impact on permanent streams, reducing their dilution capacity, and can even cause the capture of the whole stream discharge. Furthermore, good quality water contributions allow continuous stream flows and better waste water dilutions all year long. Finally, the results show that the presence and quality of surface water in temporary reaches during dry periods directly depends on groundwater contributions.

Isotopic characteristics of meteoric waters in the Belgrade region

The stable isotope composition of hydrogen (δ2H) and oxygen (δ18O) in monthly precipitation and river water (Sava River and Danube) samples in the Belgrade area gathered between 1992 and 2005 are determined. The local meteoric water line δ2H=7.8 (±0.2) δ18O+7.3(±1.6) (r 2=0.98, n=60, σ=0.52) for the whole period of observation is close to the global meteoric water line. The amount-weighted mean δ2H and δ18O values of precipitation were−65±27 ‰ and−9.4±3.4 ‰, respectively. Good correlation between δ18O values (r>rsim0.67) and ambient temperature and relative humidity was obtained. Stream-water data ranged from−94 to−60 ‰ for δ2H and from−11.0 to ∼5.7 ‰ for δ18O with highly statistically significant difference (p>0.01) between the Sava River and the Danube. In addition, the isotopic compositions of local precipitation and adjacent river water at monitoring sites were compared. Obtained data will give an opportunity to improve the knowledge of mixing stream water and local groundwater, and assessment of potential groundwater risks and pressures in the Belgrade basin.

A Numerical Modeling System of the Hydrological Cycle for Estimation of Water Fluxes in the Huaihe River Plain Region, China

Abstract To analyze the water budget under human influences in the Huaihe River plain region in China, the authors have developed a numerical modeling system that integrates water flux algorithms into a platform created by coupling a soil moisture model with the modular three-dimensional finite-difference groundwater flow model (MODFLOW). The modeling system is largely based on physical laws and employs a numerical method of the finite difference to simulate water movement and fluxes in a horizontally discretized watershed or field. The majority of model parameters carry physical significance and can be determined by field and laboratory measurements or derived from watershed characteristics contained in GIS and remote sensing data. Several other empirical parameters need to be estimated by model calibration. The numerical modeling system is calibrated in the Linhuanji catchment (2 560 km2) to estimate surface runoff, groundwater recharge, and groundwater loss for evapotranspiration and stream baseflow. Model validation is conducted at a small runoff experimental field (1.36 km2) in the Wuduogou Hydrological Experimental Station to test the model’s capability to simulate hydrological components and estimate water fluxes using observed stream stage and groundwater data, as well as lysimeter-measured precipitation recharge and groundwater loss. As proven by the promising results of model testing, this physically based and distributed-parameter model is a valuable contribution to the ever-advancing technology of hydrological modeling and water resources assessment.