Surface Water Discharge Research Articles

Constraining the annual groundwater contribution to the water balance of an agricultural floodplain using radon: The importance of floods

AbstractThe water balance of drained floodplains is highly dynamic with complex groundwater–surface water interactions operating over varying spatial and temporal scales. Here we hypothesize that the majority of groundwater discharge will follow flood events in a modified wetland. To test this hypothesis, we developed a detailed water balance that quantifies the contribution of groundwater discharge to the annual water budget of an extensively drained agricultural floodplain. A clear relationship between surface water radon measurements and groundwater level indicated alternating connection–disconnection dynamics between the drains and shallow groundwater. This relationship was used to develop a radon mass balance to quantitatively model groundwater discharge continuously throughout the year. Groundwater discharge varied by four orders of magnitude over the study period, with daily average rates ranging from 0 to 27,200 m3 d−1, peaking just a few hours after floods receded. Flood events occurred only 12% of the time yet contributed 72–76% of the total groundwater discharge. During flood recession periods, aerial groundwater discharge rates reached up to 325 cm d−1 which were some of the highest rates ever estimated. We proposed that the high drainage density of this site (12.4 km constructed drains km−2 catchment area) enhanced groundwater discharge during wet periods due to increased connectivity with the soil. Overall, groundwater discharge contributed 30–80% to the total surface water discharge. This study offers insight into the dynamic behavior of groundwater within an extensively drained floodplain, and the importance of capturing flood events to quantify total groundwater contribution to floodplain water balances.

Hydrology and phosphorus transport simulation in a lowland polder by a coupled modeling system

Modeling the rain-runoff processes and phosphorus transport processes in lowland polders is critical in finding reasonable measures to alleviate the eutrophication problem of downstream rivers and lakes. This study develops a lowland Polder Hydrology and Phosphorus modeling System (PHPS) by coupling the WALRUS-paddy model and an improved phosphorus module of a Phosphorus Dynamic model for lowland Polder systems (PDP). It considers some important hydrological characteristics, such as groundwater–unsaturated zone coupling, groundwater–surface water feedback, human-controlled irrigation and discharge, and detailed physical and biochemical cycles of phosphorus in surface water. The application of the model in the Jianwei polder shows that the simulated phosphorus matches well with the measured values. The high precision of this model combined with its low input data requirement and efficient computation make it practical and easy to the water resources management of Chinese polders. Parameter sensitivity analysis demonstrates that Kuptake, cQ2, cW1, and cQ1 exert a significant effect on the modeled results, whereas KresuspensionMax, Ksettling, and Kmineralization have little effect on the modeled total phosphorus. Among the three types of uncertainties (i.e., parameter, initial condition, and forcing uncertainties), forcing uncertainty produces the strongest effect on the simulated phosphorus. Based on the analysis result of annual phosphorus balance when considering the high import from irrigation and fertilization, lowland polder is capable of retaining phosphorus and reducing phosphorus export to surrounding aquatic ecosystems because of their special hydrological regulation regime.

Performance Analysis of Vertical Flow Constructed Wetland to Treat Domestic Wastewater using Two Different Filter Media and Canna as a Plant

Objectives: Investigation for low cost, small scale, decentralized waste water treatment system for small communities and suburbs was done in this study. Total passive system, artificially engineered to treat domestic wastewater by mimicking the natural water purifying processes of river, swamp and wetlands, gives us what is known as constructed wetland. Methods: In this paper, we carried out the design and installation of two laboratory scale vertical flow constructed wetland within the premises of Lovely Professional University sewage treatment Plant. Two separate systems of height 45 cm and average diameter 15 cm was created, one with gravel and sand as a media and other with gravel, sand and soil as a media. Both the wetland was planted with Canna sp as an excellent phytoremediating plant and was available easily in locality. This plant shows very high growth rate and has a large rhizome. The waste water was fed through the 1.5cm diameter pipe. Eight liter of pretreated wastewater from the university Sewage treatment plant was fed with a retention period of 2 days, feeding was done in such a way that the gravitation does all the work, as the feeding tank was placed higher above both the wetland. Feeding was control by the valve. Findings: Initial analysis of wastewater subjected to wetland shows dramatic reduction in the visible suspended solids and color. Dissolve oxygen was improved from 3.6±0.4mg/L to 5±.2mg/L in both the wetland system. pH in effluent from both the CW was in between 6.5-8.5, pH of influent was in between 9±0.4. BOD5 at 20oC of both the effluent form vertical flow CW was found to be below 30mg/L as against the 180-190mg/L of influent given to wetland, which was well within the range as per as Environment (protection) rules, 1986 of GOI for inland surface water discharge. Application/Improvement: Potable water is already a scare resource; even the water for irrigation is becoming scarce and not to forget the depleting ground water table. The findings of this study shows us a potential cheap method to treat wastewater generated, which can be used to met our agricultural water demand and can even be used to recharge ground water.

CFD investigations of OXYFLUX device, an innovative wave pump technology for artificial downwelling of surface water

No other environmental variable of such ecological importance to estuarine and coastal marine ecosystems around the world has changed so drastically, in such a short period of time, as dissolved oxygen in coastal waters. The prevalent methods for counteracting anoxic sea events are indirect measures which aim to cut-down anthropic loads introduced in river and marine environments. To date, no direct approaches, like artificial devices have been investigated except the WEBAP and OXYFLUX devices. The present paper adopts a numerical approach to the analysis of the pumped surface water as well as the analysis of the dynamic response of the OXYFLUX device. By means of a CFD-RANS code and through the application of overset grid method, the 1/16 OXYFLUX model’s dynamic response and pumping performance are evaluated. The appropriate grid is selected after an extensive sensitivity analysis carried out on 9 different grids. The CFD model is validated by comparing numerical and physical results of heave decay test, heave response, and surface water discharge under the action of regular waves. The extensive comparison with experimental results shows consistently accurate predictions. The main findings of the study show that nonlinear effects remarkable reduce the dynamic behaviour of the OXYFLUX and generate an unexpected second harmonic for pitch response intensifying the overtopping discharge also for small waves caused by the summer's low intensity winds.

Seasonal exports and drivers of dissolved inorganic and organic carbon, carbon dioxide, methane and δ13C signatures in a subtropical river network

Riverine systems act as important aquatic conduits for carbon transportation between atmospheric, terrestrial and oceanic pools, yet the magnitude of these exports remain poorly constrained. Interconnected creek and river sites (n=28) were sampled on a quarterly basis in three subcatchments of the subtropical Richmond River Catchment (Australia) to investigate spatial and temporal dynamics of dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), carbon dioxide (CO2), methane (CH4), and carbon stable isotope ratios (δ13C). The study site is an area of high interest due to potential unconventional gas (coal seam gas or coal bed methane) development. DIC exports were driven by groundwater discharge with a small contribution by in situ DOC remineralization. The DIC exports showed seasonal differences ranging from 0.10 to 0.27mmolm−2catchmentd−1 (annual average 0.17mmolm−2catchmentd−1) and peaked during winter when surface water discharge was highest. DOC exports (sourced from terrestrial organic matter) had an annual average 0.07mmolm−2catchmentd−1 and were 1 to 2 orders of magnitude higher during winter compared to spring and summer. CO2 evasion rates (annual average of 347mmolm−2water aread−1) were ~2.5 fold higher during winter compared to spring. Methane was always supersaturated (0.19 to 62.13μM), resulting from groundwater discharge and stream-bed methanogenesis. Methane evasion was highly variable across the seasons with an annual average of 3.05mmolm−2water aread−1. During drier conditions, stable isotopes implied enhanced CH4 oxidation. Overall, carbon losses from the catchment were dominated by CO2 evasion (60%) followed by DIC exports (30%), DOC exports (9%) and CH4 evasion (<1%). Our results demonstrated broad catchment scale spatial and temporal variability in carbon dynamics, and that groundwater discharge and rain events controlled carbon exports.

Self-Assembly of Single-Sized and Binary Colloidal Particles at Air/Water Interface by Surface Confinement and Water Discharge

We present an innovative apparatus allowing self-assembly at air/water interface in a smooth and reproducible way. The combination of water discharge and surface confinement of the area over which self-assembly takes place allows transfer of the assembled monolayer without any risk of damage to the colloidal crystal. As we demonstrate, the designed approach offers remarkable advantages in terms of cost and robustness compared to state-of-the art methods and is suitable for the fabrication of highly ordered monolayers even for more challenging assembly experiments such as transfer on rough substrates or assembly of binary colloids. Hence, our apparatus represents a significant headway toward high scale production of large area colloidal crystals. For the binary colloid assembly experiments, we also report the first experimental demonstration of a morphology based on the alternation of three and four small particles in the interstices between large particles.

Characterization of Chyulu Hills Watershed Ecosystem Services in South-Eastern Kenya

&lt;p class="1Body"&gt;Water is an important good provided by watersheds and is critical in sustaining life and socio-economic development. This study evaluated water provision in the Chyulu Hills watershed which is one of the important dry land water catchments in Kenya. Surface water discharge was mainly through rivers and springs with the latter being more prevalent than the former while ground water provision was primarily through boreholes and shallow wells. Springs discharged the highest water volume annually estimated at 128.14million m&lt;sup&gt;3&lt;/sup&gt; or 85.14% of all the water discharged in the watershed, with shallow wells and boreholes discharging the least water. For all the springs found in the watershed, Mzima springs discharged the highest water volume estimated at nearly 113.15 million m&lt;sup&gt;3&lt;/sup&gt; annually or 88.30% of the water produced by all the springs; and about 75.19% of the water in the entire watershed. Rivers which were active had a total water discharge of about 20.66million m&lt;sup&gt;3&lt;/sup&gt; per year, with Kibwezi River discharging 17.59 million m&lt;sup&gt;3&lt;/sup&gt; annually or 85.14% of all the water from rivers. Shallow wells were mainly prevalent at Nthongoni and the Makindu, and their annual water discharge was about 16.96million m&lt;sup&gt;3&lt;/sup&gt; per year with boreholes contributing 98.87% (approximately 16.76 million m&lt;sup&gt;3&lt;/sup&gt;/yr.) of the ground water, and the rest (19,169.92m&lt;sup&gt;3&lt;/sup&gt;/yr.) being contributed by shallow wells. The total amount of water discharged in the watershed by the combined water source types was about 150.49 million m3/yr.&lt;/p&gt;

Assessing of landscape potential for water management regarding its surface water (using the example of the micro-region Minčol)

Abstract The presence of water is one of the decisive factors of landscape’s natural potential. Water affects landscape’s predisposition for agricultural production, water supply available to the wide population and industry (the most important is the yield of water resources). Ponds, lakes and other water areas are zones of recreation and relaxation. Near sources mineral water, several world-famous spas were build. Waterways are also used to generate electricity. Geothermal underground water represents a very significant landscape potential. Determining hydrological potential of the area is important for the regional development. This paper assesses the landscape potential for water management regarding its surface waters in the micro-region Minčol. The micro-region was divided by a square grid, and for each square, we determined the appropriateness of this potential based on score points. The determining evaluation criteria were static reserves of surface water, waterway ranking and annual average discharge. First, we determined the significance (value) of individual criteria (classification characteristics), and then we calculated the values of individual classifiers, which were then multiplied by the value of the individual classifier intervals. The summary of points in each square belongs to a particular degree of suitability for water management based on surface waters. The potential was divided into five degrees (intervals): very unfavourable potential, unfavourable potential, moderately favourable potential, favourable potential and very favourable potential.

Qualitative Assessment of Mine Water of the Western Jharia Coalfield Area, Jharkhand, India

A geochemical study of mine water in the Western Jharia coalfield area was undertaken to assess its quality and suitability for drinking and domestic purposes. To assess mine water quality of the study area, a systematic sampling was carried out during the monsoon season, 2013. Eighteen representatives mine water sample were collected from both underground (underground sump and surface water discharge) and opencast mines, and analyzed for pH, electrical conductivity (EC), total dissolved solids (TDS) , major cations (Ca2+, Mg2+, Na+ and K+) and major anions (HCO3- F-, Cl-, NO3-, SO42-). The pH of the analyzed mine waters ranged from 6.8 o 8.3 and electrical conductivity (EC) values ranged from 608 uS cm-1 to 1350 uS cm-1. TDS ranged from 432 to 1080 mg L-1 and the spatial differences in TDS reflect the geological formations, hydrological processes and prevailing mining conditions of the region. The anion and cation chemistry indicate the general ionic abundance as: HCO3-&gt; SO42-&gt; Cl-&gt; NO3-&gt;F- and Mg2+&gt;Ca2+&gt; Na+&gt; K+ in the mine water of the study area. The water quality assessment indicated that total dissolved solids (TDS), total hardness (TH), magnesium and sulphate are the major parameters of concern in the study area and make it unsuitable for drinking and domestic purposes.

A new numerical framework for simulating the control of weather and climate on the evolution of soil-mantled hillslopes

We present a new numerical framework for simulating short to long-term hillslope evolution. This modeling framework, to which we have given the name CLICHE (CLImate Control on Hillslope Evolution), aims to better capture the control of climate on soil dynamics. It allows the use of realistic forcing that involves, through a specific time discretization scheme, the variability of both the temperature and precipitation at time scales ranging from the daily rainfall events to the climatic oscillations of the Quaternary, also including seasonal variability. Two simple models of soil temperature and soil water balance permit the link between the climatic inputs and derived quantities that take part in the computation of the soil flux, such as the surface water discharge and the depth of the non-frozen soil layer. Using this framework together with a multi-process parameterization of soil transport, we apply an original method to calculate hillslope effective diffusivity as a function of climate. This allows us to demonstrate the ability of the model to simulate observed rates of hillslope erosion under different climates (cold and temperate) with a single set of parameter values. Numerical experiments furthermore suggest a potential high peak of sediment transport on hillslopes during the glacial-interglacial transitions of the Quaternary. We finally discuss the need to improve the parameterization of the soil production and transport processes in order to explicitly account for other key controlling factors that are also climate-sensitive, such as biological activity.

Removal of Six Estrogenic Endocrine-Disrupting Compounds (EDCs) from Municipal Wastewater Using Aluminum Electrocoagulation

Conventional wastewater treatment plant (WWTP) processes are primarily designed to reduce the amount of organic matter, pathogens, and nutrients from the incoming influent. However, these processes are not as effective in reducing the concentrations of micropollutants, including endocrine-disrupting compounds (EDCs), which notoriously evade traditional wastewater treatment technologies and are found even in tertiary-treated effluent. For WWTPs practicing deep-well injection or surface-water discharge, EDCs in the treated effluent are discharged into groundwater or the aquatic environment where humans and wildlife may potentially suffer the effects of chemical exposure. In the current laboratory-scale study, we tested a bench-top electrocoagulation (EC) unit utilizing aluminum blades for the removal of six estrogenic EDCs [estrone (E1), 17β-estradiol (E2), estriol (E3), 17α-ethinylestradiol (EE2), bisphenol-A (BPA), and nonylphenol (NP)]. Samples of municipal wastewater influent and tertiary-treated effluent were spiked with the six EDCs in order to test the removal efficiency of the EC unit. The mean concentration of each EDC component was statistically lower after EC treatment (removal range = 42%–98%). To our knowledge, this is the first study to investigate aluminum electrocoagulation for removal of these specific EDCs, including nonylphenol (without the ethoxylate chain), as well as natural and synthetic estrogens.

Natural pollution (As, F) and eutrofication (N, P) in the basin of El Divisorio stream, Argentina

The interrelation between hydrochemistry and hydrodinamicswas analyzed in the basin of El Divisorio stream. Thiswas to gain undestanding in the magnitude, distribution of toxicions (As, F) and behaviour in the discharge of main nutrients (P,N) contributing to the eutrofication of Paso de las Piedras Dam.During two years, 47 sites were sampled determining several parameters:geographical position for each sampling point, phreaticlevel depth, and As, F, PO4 and N-NO3 concentrations. Repeatedmeasures, Fisher test, correlation and regression analysis were appliedto all variables. Highly significant space and time differences(P<0.01) with increments of 0.3 m were detected for isohypses. Atevery site, differences with a variable degree of significance wererecognized for chemical parameters (As, F, PO4 and N-NO3). Hydrodinamicsbehaves mainly in accord with the seasonal rainfallcontribution; run off affects some of the hydrochemical parametersgiving rise to a variability that influences water quality. N-NO3 andPO4 concentrations are the main factors that cause eutroficationexpressed through algae bloom episodes and deterioration of storedwater quality. P is the critical element and in the dry periods thehighest contribution is through groundwater flux and to a lesserextent by the continuous discharge of surface water. In the periodof greater runoff, these elements incorporated to the sedimentarycharge as a result of soil erosion, and coming by fertilizers and pesticidesare transported in suspension towards the reservoir.

Modeling for Inter-Basin Groundwater Transfer Identification: The Case of Upper Rift Valley Lakes and Awash River Basins of Ethiopia

Groundwater movement beneath watershed divide is one component of the hydrological cycle that is typically ignored due to difficulty in analysis. Numerical ground-water models, like TAGSAC, have been used extensively for predicting aquifer responses to external stresses. In this paper TAGSAC code was developed to identify the inter-basin groundwater transfer (IBGWT) between upper Awash River basin (UARB) and upper rift valley lakes basin (URVLB) of Ethiopia. For the identification three steady state groundwater models (for UARB, URVLB and for the two combined basins) were first created and calibrated for the 926 inventoried wells. The first two models are conceptualized by considering the watershed divide between the two basins as no-flow. The third model avoids the surface water divide which justifies IBGWT. The calibration of these three models was made by changing the recharge and hydrogeologic parameters of the basins. The goodness of fit indicators (GoFIs) obtained was better for the combined model than the model that describes the URVLB. Furthermore, the hydraulic head distribution obtained from the combined model clearly indicates that there is a groundwater flow that doesn’t respect the surface water divide. The most obvious effect of IBGWT observed in these two basins is that it diminishes surface water discharge from URVLB, and enhances discharge in the UARB. Moreover, the result of this study indicates potential for internal and cross contamination of the two adjacent groundwater.

Infiltration vs. Surface Water Discharge: Development of Guidance for Stormwater Managers

Stormwater managers are increasingly faced with the need to address many potentially-conflicting issues as part of their activities, ranging from flood prevention to protection of downstream habitat. New philosophies, such as a post-development goal of mimicking pre-development hydrology, have been promoted as addressing both the goals of water quality and water quantity control. These new management plans incorporate both infiltration and surface treatment/discharge into the development. A flowchart was developed to aid stormwater managers in stepping through the process of selecting an appropriate management/treatment technology. This title belongs to This title belongs to WERF Research Report Series ISBN: 9781843397649 (eBook)

Annual sulfate budgets for Dutch lowland peat polders: The soil is a major sulfate source through peat and pyrite oxidation

Summary Annual sulfate mass balances have been constructed for four low-lying peat polders in the Netherlands, to resolve the origin of high sulfate concentrations in surface water, which is considered a water quality problem, as indicated amongst others by the absence of sensitive water plant species. Potential limitation of these plants to areas with low sulfate was analyzed with a spatial match-up of two large databases. The peat polders are generally used for dairy farming or nature conservation, and have considerable areas of shallow surface water (mean 16%, range 6–43%). As a consequence of continuous drainage, the peat in these polders mineralizes causing subsidence rates generally ranging between 2 and 10 mm y−1. Together with pyrite oxidation, this peat mineralization the most important internal source of sulfate, providing an estimated 96 kg SO4 ha−1 mm−1 subsidence y−1. External sources are precipitation and water supplied during summer to compensate for water shortage, but these were found to be minor compared to internal release. The most important output flux is discharge of excess surface water during autumn and winter. If only external fluxes in and out of a polder are evaluated, inputs average 37 ± 9 and exports 169 ± 17 kg S ha−1 y−1. During summer, when evapotranspiration exceeds rainfall, sulfate accumulates in the unsaturated zone, to be flushed away and drained off during the wet autumn and winter. In some polders, upward seepage from early Holocene, brackish sediments can be a source of sulfate. Peat polders export sulfate to the regional water system and the sea during winter drainage. The available sulfate probably only plays a minor role in the oxidation of peat: we estimate that this is less than 10% whereas aerobic mineralization is the most important. Most surface waters in these polders have high sulfate concentrations, which generally decline during the growing season when aquatic sediments are a sink. In the sediment, this sulfur is reduced and binds iron more strongly than phosphorus, which can be released to the overlying water and potentially fuels eutrophication. About 76% of the sampled vegetation-sites exceeded a threshold of 50 mg l−1 SO4, above which sensitive species, such as Stratiotes aloides, and several species of Potamogeton were significantly less abundant. Thus high sulfate concentrations, mainly due to land drainage and consequent mineralization, appear to affect aquatic plant community composition.

Higher species richness and abundance of fish and benthic invertebrates around submarine groundwater discharge in Obama Bay, Japan

Study focusThere have been far more studies on how the variability in surface water discharge affects production of animal communities in aquatic ecosystems while less information has been accumulated on the mechanisms of how the groundwater supply works. Study regionPhysical and biological surveys were conducted to test the hypothesis that high level of submarine ground water discharge enhances species richness, abundance and biomass of fishes and invertebrates in coastal waters of Obama Bay, Japan, where a high contribution of nutrients (ca. 65% of phosphorus) to total provided through all freshwater has been reported. Survey for horizontal distribution of radon-222 (222Rn) concentration showed high levels of submarine groundwater discharge in the west part of survey area. Fish and invertebrate communities were compared within a relatively small spatial scale (ca. 100m) in relation to level of submarine groundwater discharge. New hydrological insightsSpecies richness, abundance and biomass of fishes and abundance and biomass of turban snail and hermit crab were significantly higher in the area with high 222Rn concentration. Abundance of gammarids, the most major prey item of the fishes, was 18 times higher in the area with high 222Rn concentration. Since the turban snail, hermit crab and gammarids feed on producers (phytoplankton and benthic microalgae), submarine groundwater are concluded to increase species richness and production of fishes and invertebrates through providing nutrients and enhancing primary production.

Pharmaceutical occurrence in groundwater and surface waters in forests land-applied with municipal wastewater.

The occurrence and fate of pharmaceutical and personal care products in the environment are of increasing public importance because of their ubiquitous nature and documented effects on wildlife, ecosystems, and potentially humans. One potential, yet undefined, source of entry of pharmaceuticals into the environment is via the land application of municipal wastewater onto permitted lands. The objective of the present study is to determine the extent to which pharmaceuticals are mitigated by or exported from managed tree plantations irrigated with municipal wastewater. A specific focus of the present study is the presence of pharmaceutical compounds in groundwater and surface water discharge. The study site is a municipality that land-applies secondary treated wastewater onto 930 hectares of a 2000-hectare managed hardwood and pine plantation. A suite of 33 pharmaceuticals and steroid hormones was targeted in the analysis, which consisted of monthly grab sampling of groundwater, surface water, and wastewater, followed by concentration and cleanup via solid phase extraction and separation, detection, and quantification via liquid chromatography coupled with tandem mass spectrometry. More than one-half of all compounds detected in irrigated wastewater were not present in groundwater and subsequent surface water. However, antibiotics, nonsteroidal anti-inflammatory drugs, caffeine, and other prescription and over-the-counter drugs remained in groundwater and were transported into surface water at concentrations up to 10 ng/L. These results provide important documentation for pharmaceutical fate and transport in forest systems irrigated with municipal wastewater, a previously undocumented source of environmental entry.

Assessment of Industrial Effluents Quality and their Possible Impact on Surface Water

The printing, textile, wood and plastics industries have an important environmental impact, since they consume large amounts of water and produce highly polluted waste waters (Sostar-Turk et al. 2005). The current study aimed to investigate several effluents generated by different industries based on their physicochemical parameters and to evaluate their possible impact on the water body. Effluents from two printings, a textile, a wood and a plastics industry from Cluj County were analysed for various physicochemical parameters such as temperature, pH, biochemical and chemical oxygen demand, total dissolved solids, total suspended solids, total nitrogen, total phosphorus, ammonium, chloride, sulphate, petroleum ether extractible substances and detergents. The samples were analysed using the corresponding standard procedures SR ISO 105523-97, SR ISO 1899/1-03, SR ISO 6060-96, STAS 9187-84, STAS 6953-81, Merck 14543, Merck 14537, SR ISO 7150/1-01, EPA 375.4/05, SR IS 9297-01, SR ISO 7150/1-01, SR EN 903-03. The temperature, total dissolved solids, chloride, sulphate and detergents content of the effluents were within the permissible limits for surface water discharge, while the other parameters exceeded the limit set by legislation. The data of the present study showed that the analysed physicochemical parameters significantly varied with the effluent source. The study indicated a seasonal variation for several parameters, dictated by the production regime of the manufacture. In many cases the quality of the studied effluents was below the limits set by Romanian and UE legislation.

Mixing effects on nitrogen and oxygen concentrations and the relationship to mean residence time in a hyporheic zone of a riffle-pool sequence

Flow paths and residence times in the hyporheic zone are known to influence biogeochemical processes such as nitrification and denitrification. The exchange across the sediment-water interface may involve mixing of surface water and groundwater through complex hyporheic flow paths that contribute to highly variable biogeochemically active zones. Despite the recognition of these patterns in the literature, conceptualization and analysis of flow paths and nitrogen transformations beneath riffle-pool sequences often neglect to consider bed form driven exchange along the entire reach. In this study, the spatial and temporal distribution of dissolved oxygen (DO), nitrate ( NO3−) and ammonium ( NH4+) were monitored in the hyporheic zone beneath a riffle-pool sequence on a losing section of the Truckee River, NV. Spatially varying hyporheic exchange and the occurrence of multi-scale hyporheic mixing cells are shown to influence concentrations of DO and NO3− and the mean residence time (MRT) of riffle and pool areas. Distinct patterns observed in piezometers are shown to be influenced by the first large flow event following a steady 8 month period of low flow conditions. Increases in surface water discharge resulted in reversed hydraulic gradients and production of nitrate through nitrification at small vertical spatial scales (0.10–0.25 m) beneath the sediment-water interface. In areas with high downward flow rates and low MRT, denitrification may be limited. The use of a longitudinal two-dimensional flow model helped identify important mechanisms such as multi-scale hyporheic mixing cells and spatially varying MRT, an important driver for nitrogen transformation in the riverbed. Our observations of DO and NO3− concentrations and model simulations highlight the role of multi-scale hyporheic mixing cells on MRT and nitrogen transformations in the hyporheic zone of riffle-pool sequences.

Evaluation of drought impact on groundwater recharge rate using SWAT and Hydrus models on an agricultural island in western Japan

Abstract. Clarifying the variations of groundwater recharge response to a changing non-stationary hydrological process is important for efficiently managing groundwater resources, particularly in regions with limited precipitation that face the risk of water shortage. However, the rate of aquifer recharge is difficult to evaluate in terms of large annual-variations and frequency of flood events. In our research, we attempt to simulate related groundwater recharge processes under variable climate conditions using the SWAT Model, and validate the groundwater recharge using the Hydrus Model. The results show that annual average groundwater recharge comprised approximately 33% of total precipitation, however, larger variation was found for groundwater recharge and surface runoff compared to evapotranspiration, which fluctuated with annual precipitation variations. The annual variation of groundwater resources is shown to be related to precipitation. In spatial variations, the upstream is the main surface water discharge area; the middle and downstream areas are the main groundwater recharge areas. Validation by the Hydrus Model shows that the estimated and simulated groundwater levels are consistent in our research area. The groundwater level shows a quick response to the groundwater recharge rate. The rainfall intensity had a great impact on the changes of the groundwater level. Consequently, it was estimated that large spatial and temporal variation of the groundwater recharge rate would be affected by precipitation uncertainty in future.