Infiltration Of River Water Research Articles

Natural attenuation of naphthalene along the river-bank infiltration zone of the Liao River, Shenyang, China

In this study, the natural attenuation of naphthalene during riverbank infiltration was examined using batch experiments. The results indicated that, as the grain size and the permeability coefficient decreased, the natural attenuation rate of naphthalene increased, and it was highest in loam (62%) and lowest in coarse sand (20%). The half-life of naphthalene was longest in coarse sand (700 d) and shortest in mild clay (250 d). Facultative anaerobes such as Methylophilaceae accounted for about 70% of the total bacteria and played a major role in naphthalene degradation. A high total organic carbon concentration and large specific surface area can promote natural attenuation of naphthalene. Moreover, the adsorption to riverbank sediment in the hyporheic zone and bioremediation by indigenous microorganisms can effectively eliminate naphthalene during river water infiltration to the riverbank aquifer.

Evaluation of groundwater recharge sources based on environmental tracers in an arid alluvial fan, NW China

Environmental tracers include stable isotopes and chloride in natural water were used to recognize the recharge sources of groundwater in Nalenggele alluvial fan, NW China. There is little effective recharge from local precipitation, the original resources of groundwater are glacier melting water and precipitation in high Kunlun mountain, groundwater is directly recharged by river infiltration along the river stretch and lateral groundwater flow from the high mountain area. In this study the effects of the depth infiltrated of river water on the mixing ratio was investigated. Results show that the mixing ratio decreases with the infiltrated river water depth.

Hydroclimatic drivers of the growth of riparian cottonwoods at the prairie margin: River flows, river regulation and the Pacific Decadal Oscillation

Cottonwoods, riparian poplars, are facultative phreatophytes and can obtain water from shallow soil moisture originating from rainfall, or from the deeper capillary fringe above the alluvial water table that is recharged by river water infiltration. The correspondence between cottonwood growth and river flows should reveal the dependency upon alluvial groundwater and subsequently, the vulnerability to reduced river flows. To explore this association, we analyzed historic growth patterns of plains cottonwoods (Populus deltoides) along the Red Deer River (RDR), which is at the northwestern limit of the North American Great Plains. We developed chronologies of yearly radial increments (RI) and basal area increments (BAI) and explored correspondences with the environmental records from the past century. In this semi-arid region, the RI or BAI were not correlated with local precipitation while negative correlation with growth season temperature (T) (r = −0.37, p < 0.01) could reflect reduced growth with hot summers. There was correlation between growth and annual river discharge (Q, and particularly log Q that approximates river stage) and this increased with two year averaging (r = 0.51, p < 0.01), reflecting carry-over in the watershed hydrology and in the ecophysiological response. There was correspondence with the Pacific Decadal Oscillation index (PDO, r = −0.45, p < 0.01), which provides multi-decade transitions that influence Rocky Mountain headwater precipitation and other weather characteristics, and river flows. The combination of Q, PDO and T provided the strongest multiple regression model, accounting for 44% of the historic growth variation (52% correspondence for 1953–2013). The RDR was dammed in 1983, enabling winter flow augmentation, but summer flows were sustained and cottonwood growth and the streamflow correspondence persisted. This indicates that it is the pattern of dam operation and not damming per se that determines the fate of established riparian cottonwoods downstream. This study revealed that these cottonwoods are phreatophytic and dependent upon alluvial groundwater that is recharged from the river. This provides a research strategy to determine whether riparian woodlands along other regulated rivers are similarly groundwater-dependent and could be vulnerable to river flow reductions from excessive water withdrawal for irrigation or other uses, or with climate change.

Dynamic processes of hyporheic exchange and temperature distribution in the riparian zone in response to dam-induced water fluctuations

We examined the dynamic processes of hyporheic exchange and temperature distribution in a riparian zone in response to low-temperature water fluctuations downstream of the Xin’an River Dam, China, using analytical and mainly hydrodynamic methods. For this purpose, we installed six HM21 piezometers (R, P1–P5) between the river water and the groundwater at an interval of approximately 2 m perpendicular to the flow path. We also installed 20 PT100 thermistors (T1–T20) along the transect at depths of 1.19 m to 3.58 m and monitored the temperatures of river and air. Water levels and temperatures were automatically logged every 5 min by the real-time system from November to December 2014 and sent to the remote platform through the remote terminal unit. Results revealed that the intensity and direction of the hyporheic exchange (Q) between the river water and the groundwater varied periodically (t = 1 d) with the water level of the river. In each cycle, the Q was in a counterclockwise loop curve with the water level of the river and with the non-uniform distribution along the transect perpendicular to the river, which showed that the farther the lateral exchange was away from the river, the lower its intensity and the more hysteretic the alteration of its direction. The daily exchange width and residence time had no necessary connection with the average river stage, but mainly depended on the amplitude of the fluctuating river stage and the duration of river infiltration and established a strong linear relationship with their product. The temperature distribution of the riparian aquifer was mainly affected by the surface radiation and river water infiltration. It was characterized as “cool on the surface and warm at the bottom” in the vertical direction and could be divided into low-, medium-, and high-temperature zones along the horizontal direction. The horizontal infiltration distance (L) increased by power functions with the increase in infiltration rate (v) and decrease in river temperature (T).

A Bayesian approach to infer nitrogen loading rates from crop and land-use types surrounding private wells in the Central Valley, California

Abstract. This study is focused on nitrogen loading from a wide variety of crop and land-use types in the Central Valley, California, USA, an intensively farmed region with high agricultural crop diversity. Nitrogen loading rates for several crop types have been measured based on field-scale experiments, and recent research has calculated nitrogen loading rates for crops throughout the Central Valley based on a mass balance approach. However, research is lacking to infer nitrogen loading rates for the broad diversity of crop and land-use types directly from groundwater nitrate measurements. Relating groundwater nitrate measurements to specific crops must account for the uncertainty about and multiplicity in contributing crops (and other land uses) to individual well measurements, and for the variability of nitrogen loading within farms and from farm to farm for the same crop type. In this study, we developed a Bayesian regression model that allowed us to estimate land-use-specific groundwater nitrogen loading rate probability distributions for 15 crop and land-use groups based on a database of recent nitrate measurements from 2149 private wells in the Central Valley. The water and natural, rice, and alfalfa and pasture groups had the lowest median estimated nitrogen loading rates, each with a median estimate below 5 kg N ha−1 yr−1. Confined animal feeding operations (dairies) and citrus and subtropical crops had the greatest median estimated nitrogen loading rates at approximately 269 and 65 kg N ha−1 yr−1, respectively. In general, our probability-based estimates compare favorably with previous direct measurements and with mass-balance-based estimates of nitrogen loading. Nitrogen mass-balance-based estimates are larger than our groundwater nitrate derived estimates for manured and nonmanured forage, nuts, cotton, tree fruit, and rice crops. These discrepancies are thought to be due to groundwater age mixing, dilution from infiltrating river water, or denitrification between the time when nitrogen leaves the root zone (point of reference for mass-balance-derived loading) and the time and location of groundwater measurement.

Spatiotemporal Responses of Groundwater Flow and Aquifer‐River Exchanges to Flood Events

AbstractRapidly rising river stages induced by flood events lead to considerable river water infiltration into aquifers and carry surface‐borne solutes into hyporheic zones which are widely recognized as an important place for the biogeochemical activity. Existing studies for surface‐groundwater exchanges induced by flood events usually limit to a river‐aquifer cross section that is perpendicular to river channels, and neglect groundwater flow in parallel with river channels. In this study, surface‐groundwater exchanges to a flood event are investigated with specific considerations of unconfined flow in direction that is in parallel with river channels. The groundwater flow is described by a two‐dimensional Boussinesq equation and the flood event is described by a diffusive‐type flood wave. Analytical solutions are derived and tested using the numerical solution. The results indicate that river water infiltrates into aquifers quickly during flood events, and mostly returns to the river within a short period of time after the flood event. However, the rest river water will stay in aquifers for a long period of time. The residual river water not only flows back to rivers but also flows to downstream aquifers. The one‐dimensional model of neglecting flow in the direction parallel with river channels will overestimate heads and discharge in upstream aquifers. The return flow induced by the flood event has a power law form with time and has a significant impact on the base flow recession at early times. The solution can match the observed hydraulic heads in riparian zone wells of Iowa during flood events.

Hot Spots and Hot Moments of Nitrogen in a Riparian Corridor

AbstractWe use 3‐D high‐resolution reactive transport modeling to investigate whether the spatial distribution of organic‐carbon‐rich and chemically reduced sediments located in the riparian zone and temporal variability in groundwater flow direction impact the formation and distribution of nitrogen hot spots (regions that exhibit higher reaction rates when compared to other locations nearby) and hot moments (times that exhibit high reaction rates as compared to longer intervening time periods) within the Rifle floodplain in Colorado. Groundwater flows primarily toward the Colorado River from the floodplain but changes direction at times of high river stage. The result is that oxic river water infiltrates the Rifle floodplain during these relatively short‐term events. Simulation results indicate that episodic rainfall in the summer season leads to the formation of nitrogen hot moments associated with Colorado River rise and resulting river infiltration into the floodplain. The results further demonstrate that the naturally reduced zones (NRZs) present in sediments of the Rifle floodplain have a higher potential for nitrate removal, approximately 70% greater than non‐NRZs for typical hydrological conditions. During river water infiltration, nitrate reduction capacity remains the same within the NRZs, however, these conditions impact non‐NRZs to a greater extent (approximately 95% less nitrate removal). Model simulations indicate chemolithoautotrophs are primarily responsible for the removal of nitrate in the Rifle floodplain. These nitrogen hot spots and hot moments are sustained by microbial respiration and the chemolithoautotrophic oxidation of reduced minerals in the riparian zone.

Hydrogeological investigations of river bed clogging at a river bank filtration site along the River Warta, Poland

Abstract River bank filtration (RBF) is a system that enriches groundwater resources by induced infiltration of river water to an aquifer. Problematic during operation of RBF systems is the deterioration of infiltration effectiveness caused by river bed clogging. This situation was observed in the Krajkowo well field which supplies fresh water to the city of Poznań (Poland) during and after the long hydrological drought between the years 1989 and 1992. The present note discusses results of specific hydrogeological research which included drilling of a net of boreholes to a depth of 10 m below river bottom (for sediment sampling as well as for hydrogeological measurements), analyses of grain size distribution and relative density studies. The results obtained have allowed the recognition of the origin of the clogging processes, as well as the documentation of the clogged parts of the river bottom designated for unclogging activities.

River water infiltration enhances denitrification efficiency in riparian groundwater

Nitrate contamination in ground- and surface water is a persistent problem in countries with intense agriculture. The transition zone between rivers and their riparian aquifers, where river water and groundwater interact, may play an important role in mediating nitrate exports, as it can facilitate intensive denitrification, which permanently removes nitrate from the aquatic system. However, the in-situ factors controlling riparian denitrification are not fully understood, as they are often strongly linked and their effects superimpose each other. In this study, we present the evaluation of hydrochemical and isotopic data from a 2-year sampling period of river water and groundwater in the riparian zone along a 3rd order river in Central Germany. Based on bi- and multivariate statistics (Spearman's rank correlation and partial least squares regression) we can show, that highest rates for oxygen consumption and denitrification in the riparian aquifer occur where the fraction of infiltrated river water and at the same time groundwater temperature, are high. River discharge and depth to groundwater are additional explanatory variables for those reaction rates, but of minor importance. Our data and analyses suggest that at locations in the riparian aquifer, which show significant river water infiltration, heterotrophic microbial reactions in the riparian zone may be fueled by bioavailable organic carbon derived from the river water. We conclude that interactions between rivers and riparian groundwater are likely to be a key control of nitrate removal and should be considered as a measure to mitigate high nitrate exports from agricultural catchments.

Sustainable drinking water quality improvement by managed aquifer recharge in Tuusula region, Finland

Managed aquifer recharge (MAR) is used for drinking water quality improvement in Finland. Finnish lakes are typically humic-containing natural organic matter (NOM). A typical MAR plant includes infiltration of lake or river water into an unconfined esker aquifer and withdrawal of water from wells, a few hundred meters downstream. The infiltrated water should have a residence time of at least around 1 month before withdrawal to provide time for processes needed to break down or remove NOM. Since 1979, Tuusula Region Water Utility (TRWU) has produced drinking water from lake water using managed aquifer recharge. TRWU operates two MAR plants which do not use precipitation and disinfection chemicals. Raw water is infiltrated without any pretreatment. TRWU has experience from basin, sprinkling, and well infiltration. NOM is reduced from 7.7 to 2.1–2.6 mgTOC/l before abstraction of the water from wells. Abstracted water is post-treated by limestone filtration and disinfected by ultra-violet radiation before pumping for distribution. A specific feature of the MAR process is the delayed influence of the raw water temperature on the abstracted water temperature. Design and operational experiences of the MAR plants are presented and discussed. Special emphasis is given for NOM reduction, temperature effects, comparison of infiltration techniques, and costs.

Mapping the fresh-saltwater interface in the coastal zone using high-resolution airborne electromagnetics

A major part of the drinking water in the Netherlands is derived from groundwater stored in coastal and inland aquifers. The water occurs through natural processes, but in some areas artificial infiltration of lake and river water in the coastal sand dunes is necessary to support the demand for clean drinking water in the densely populated country. In fact, artificial infiltration along the Dutch coast has been common practice for decades and is an essential part of the drinking water supply. The sustainability of this approach demands detailed knowledge of the fresh–saltwater balance to avoid salinization of the aquifers. The availability and quality of the groundwater are typically estimated using groundwater models, which can be used to forecast the behaviour of groundwater systems to external stresses, such as climate change. The reliability of groundwater models hinges on measurements such as hydraulic heads, stream flow rates, permeability of the subsurface and in coastal regions the boundary conditions for the coastal edge of the model. Here, a limiting factor is often the lack of offshore data since it is logistically difficult and costly to drill in the seabed. Airborne electromagnetics are increasingly being used to support groundwater management through high-resolution largescale mapping of aquifer properties. The method provides strong sensitivity to important hydrogeological units such as the fresh-saltwater interface and clay layers (which often constitute the base of the aquifers). Hence, AEM has been widely used to address issues such as mapping saltwater intrusion (Gunnink etal., 2012; Jørgensen et al., 2012) and aquifer delineation (Chandra et al., 2016; Schamper et al., 2013). One of the key advantages of the method is that it is airborne, allowing areas, which would otherwise be difficult to access, to be mapped in a cost-effective manner. As demonstrated in the present study, the fresh-saltwater interface and coastal boundary conditions of the groundwater model can be determined by combining onshore and offshore airborne electromagnetics.

Sewage-Borne Ammonium at a River Bank Filtration Site in Central Delhi, India: Simplified Flow and Reactive Transport Modeling to Support Decision-Making about Water Management Strategies

In the Indian metropolis of Delhi, the Yamuna River is highly influenced by sewage water, which has led to elevated ammonium (NH4+) concentrations up to 20 mg/L in the river water during 2012–2013. Large drinking water production wells located in the alluvial aquifer draw high shares of bank filtrate. Due to the infiltrating river water, the raw water NH4+ concentrations in some wells exceed the threshold value of 0.5 mg/L ammonia-N of the Indian drinking water specifications, making the water unfit for human consumption without prior treatment. However, to meet the city’s growing water demand, it might be advantageous to consider the long-term use of the well field. This requires the development of an adapted post-treatment unit in concert with an adjusted well field management. To better understand the groundwater dynamics and contamination and decontamination times at the well field, a theoretical modeling study has been conducted. The results of 2D numerical modeling reveal that the groundwater flux beneath the river is negligible because of the aquifer and river geometry, indicating that infiltrating river water is not diluted by the ambient groundwater. Increasing the water abstraction in the wells closest to the river would result in a larger share of bank filtrate and a decreasing groundwater table decline. Simplified 1D reactive transport models set up for a distance of 500 m (transect from the riverbank to the first production well) showed that the NH4+ contamination will prevail for the coming decades. Different lithological units of the aquifer (sand and kankar—a sediment containing calcareous nodules) have a strong influence on the respective contamination and decontamination periods, as the retardation of NH4+ is higher in the kankar than in the sand layer. Although this simplified approach does not allow for a quantification of processes, it can support decision-making about a possible future use of the well field and point to associated research needs.

The impact of sewage-contaminated river water on groundwater ammonium and arsenic concentrations at a riverbank filtration site in central Delhi, India

The groundwater abstracted at a well field near the Yamuna River in Central Delhi, India, has elevated ammonium (NH4 +) concentrations up to 35 mg/L and arsenic (As) concentrations up to 0.146 mg/L, constituting a problem with the provision of safe drinking and irrigation water. Infiltrating sewage-contaminated river water is the primary source of the NH4 + contamination in the aquifer, leading to reducing conditions which probably trigger the release of geogenic As. These conclusions are based on the evaluation of six 8–27-m deep drillings, and 13 surface-water and 69 groundwater samples collected during seven field campaigns (2012–2013). Results indicate that losing stream conditions prevail and the river water infiltrates into the shallow floodplain aquifer (up to 16 m thickness), which consists of a 1–2-m thick layer of calcareous nodules (locally known as kankar) overlain by medium sand. Because of its higher hydraulic conductivity (3.7 × 10−3 m/s, as opposed to 3.5 × 10−4 m/s in the sand), the kankar layer serves as the main pathway for the infiltrating water. However, the NH4 + plume front advances more rapidly in the sand layer because of its significantly lower cation exchange capacity. Elevated As concentrations were only observed within the NH4 + plume indicating a causal connection with the infiltrating reducing river water.

Influence of Decolmatation of Channel Deposits of the Ufa River on the Change of Water Quality from the Wells of Infiltration Water Abstraction

There was investigated the influence of the process decolmatation (removal) of channel sediments along the coastal zone of the Ufa River on the change in the component composition of the limited-volatile organic components (LVOC) and the content of salts of total hardness in water from wells of infiltration water abstraction located on the river bank. There was demonstrated that colmated benthic deposits, on the one hand, are a natural barrier preventing the penetration of LVOC technogenic origin from the river water into the well water, but on the other hand, they are reason of anaerobic conditions in the filler beds, which leads to intensification of biochemical destruction processes of organic compounds in them with accumulation of biodegradation products. In addition, as a result of a decrease in the proportion of infiltrated river water in the ground formations, the total hardness of the well water increases, which impairs its organoleptic properties. After the work on the decolmatation of benthic deposits, an increase of in the infiltration of river water into underground layers was noted, which led to a decrease of the concentration of biodegradation products of organic compounds in them (carboxylic acids, esters, ketones, aldehydes, iso-. cyclo-, unsaturated hydrocarbons, nitrogen compounds, squalene), the concentration of phtaleic acid esters.

Tidal controls on riverbed denitrification along a tidal freshwater zone

AbstractIn coastal rivers, tidal pumping enhances the exchange of oxygen‐rich river water across the sediment‐water interface, controlling nitrogen cycling in riverbed sediment. We developed a one‐dimensional, fluid flow and solute transport model that quantifies the influence of tidal pumping on nitrate removal and applied it to the tidal freshwater zone (TFZ) of White Clay Creek (Delaware, USA). In field observations and models, both oxygenated river water and anoxic groundwater deliver nitrate to carbon‐rich riverbed sediment. A zone of nitrate removal forms beneath the aerobic interval, which expands and contracts over daily timescales due to tidal pumping. At high tide when oxygen‐rich river water infiltrates into the bed, denitrification rates decrease by 25% relative to low tide. In the absence of tidal pumping, our model predicts that the aerobic zone would be thinner, and denitrification rates would increase by 10%. As tidal amplitude increases toward the coast, nitrate removal rates should decrease due to enhanced oxygen exchange across the sediment‐water interface, based on sensitivity analysis. Denitrification hot spots in TFZs are more likely to occur in less permeable sediment under lower tidal ranges and higher rates of ambient groundwater discharge. Our models suggest that tidal pumping is not efficient at removing surface water nitrate but can remove up to 81% of nitrate from discharging groundwater in the TFZ of White Clay Creek. Given the high population densities of coastal watersheds, the reactive riverbeds of TFZs play a critical role in mitigating new nitrogen loads to coasts.

Fate of Arsenic during Red River Water Infiltration into Aquifers beneath Hanoi, Vietnam.

Recharge of Red River water into arsenic-contaminated aquifers below Hanoi was investigated. The groundwater age at 40 m depth in the aquifer underlying the river was 1.3 ± 0.8 years, determined by tritium–helium dating. This corresponds to a vertical flow rate into the aquifer of 19 m/year. Electrical conductivity and partial pressure of CO2 (PCO2) indicate that water recharged from the river is present in both the sandy Holocene and gravelly Pleistocene aquifers and is also abstracted by the pumping station. Infiltrating river water becomes anoxic in the uppermost aquifer due to the oxidation of dissolved organic carbon. Further downward, sedimentary carbon oxidation causes the reduction of As-containing Fe-oxides. Because the release of arsenic by reduction of Fe-oxides is controlled by the reaction rate, arsenic entering the solution becomes highly diluted in the high water flux and contributes little to the groundwater arsenic concentration. Instead, the As concentration in the groundwater of up to 1 μM is due to equilibrium-controlled desorption of arsenic, adsorbed to the sediment before river water started to infiltrate due to municipal pumping. Calculations indicate that it will take several decades of river water infiltration to leach arsenic from the Holocene aquifer to below the World Health Organization limit of 10 μg/L.

First report on organochlorine pesticides in water in a highly productive agro-industrial basin of the Central Valley, Chile

The Ñuble River flows through an agricultural area in the central zone of Chile in which different types of fruits are grown. The objective of this study was to identify the levels and source of organochlorine pesticides (OCPs) in the surface waters of the Ñuble River. Surface water samples were collected at 10 sampling points and analyzed for 19 organochlorine pesticides during the dry (spring-summer) and wet (autumn-winter) periods of 2013 and 2014. The results revealed that concentrations of total OCPs in surface waters ranged from 0.12 to 26.28 ng/l. Endosulfan and lindane were the main OCPs in the water. The maximum OCP levels were found in the dry period, while significantly lower concentrations were recorded in the wet period. This indicates that patterns of OCPs have varied in the last 10 years as this study found low concentrations of DDT and metabolites but significantly increased concentrations of α-endosulfan. Given the fact that OCPs were withdrawn from agricultural used many years ago, their presence indicates that they may be still in use clandestinely. Findings of significant concentrations of endosulfan and lindane in this study lead to the conclusion that the chemical fallow practices contribute to runoff into the river and surface water infiltration into groundwater. Because no studies have previously measured OCP levels in agricultural basins in Chile, this study is an important contribution to the knowledge of organochlorine contaminants present in surface water in Chile.

The Effect of Artificial Recharge on Hydrochemistry: A Comparison of Two Fluvial Gravel Pit Lakes with Different Post-Excavation Uses in The Netherlands

Gravel pit lakes form when gravel deposits are excavated below the water table. We studied two fluvial gravel pit lakes called De Lange Vlieter (DLV Lake) and the Boschmolen Plas (BP Lake), in the Meuse River valley (The Netherlands). Water from the Meuse River is pumped only into the DLV Lake that is used for drinking water production. The mean values, the linear trends and seasonal patterns of time series data (2003–2014), of temperature, pH, nitrate, phosphate and sulphate were compared using one-way tests of variance and tests of differences. The effects of river water infiltration on DLV Lake are (1) a change in lake water temperature; (2) an increase in nitrate concentration (3) an increase in phosphate concentration and (4) a decrease in sulphate concentration. The effects of the air blowers in DLV Lake are (1) mixing of lake water; (2) decreasing pH in spring and summer (3) water oxygenation. Linear regression analysis shows an initially increasing nitrate concentration in DLV Lake that can be explained by the input of nitrate rich Meuse river water. Instead decreasing nitrate and phosphate concentrations in BP Lake and Meuse River reflect a diminished use of fertilizers. The gravel pit lake water temperature does not reflect climatic changes but the use of DLV Lake for artificial recharge has an impact on the seasonal and long-term trends in hydrochemistry. This poses a challenge to lake managers to find the right balance between reduction of eutrophication and accumulation of nutrients and sulphate.

Observations and analytical modeling of freshwater and rainwater lenses in coastal dune systems

Observations are reported on (i) groundwater recharge rates under various types of vegetation as measured with megalysimeters in the dunes, (ii) freshwater lenses along the Dutch North Sea coast in the early 1900s, and (iii) rainwater lenses that develop on top of laterally migrating, artificially recharged riverwater. Subsequently analytical methods are presented to estimate annual natural groundwater recharge as function of rainfall and vegetation, and to calculate the size, shape and transition zone of freshwater lenses on saline groundwater and rainwater lenses on infiltrated riverwater. An empirical correction factor, based on the hydraulic resistance of an aquitard within the freshwater lens, is proposed to account for the frequently observed reduction of the Ghyben-Herzberg ratio of 40. This factor raises the groundwater table, reduces the depth of the fresh/salt interface and increases the lens formation time. The suite of methods offers a tool box for knowledge based water management of dune systems, by rapidly predicting: (i) more or less autonomous changes due to sealevel rise, climate change and vegetation development; and (ii) the potential (side) effects of interventions. Knowing what happened or will happen to the fresh water lens or a rainwater lens is important, because changes impact on important natural habitat parameters such as salinity, depth to groundwater table, decalcification rate (and thus on pH, Ca/Al, PO4, NH4) and nutrient availability, and on drinking water supply. The analytical models are applied to predict effects of sealevel rise, coastal progradation, vegetation changes, and increased temperature of coastal air and river water to be infiltrated.

Geochemical Characteristics of Lateral Hyporheic Zone Between the River Water and Groundwater, a Case Study of Maanxi in Chongqing

The hyporheic zone is a place where river water and groundwater mutually exchange and mix. It plays an important role in protecting the ecology and water quality of river water and groundwater. In order to study the geochemical characteristics of lateral hyporheic zone in river and ground water, water temperature, dissolved oxygen, pH, electrical conductivity were measured automatically at the hyporheic zone of Maanxi in Chongqing. The concentrations of ions in water and elements in sediment within the hyporheic zone were also analyzed. The results showed that the hydrochemical species of lateral hyporheic zone in Maanxi was HCO3-Ca·Mg. Affected by the infiltration of river water, the coefficient variations of water temperature, dissolved oxygen, pH and electrical conductivity in the hyporheic zone were lower than those observed in the river under the buffer action. Along with the farther distance from the riverbank, an anoxia redox environment was formed in the hyporheic zone due to a physical, chemical and biological interactions. An acid and alkali environment was also formed with a decreasing pH trend near the riverbank and hyporheic zone. Under its influence, concentrations of K+, NH4+-N, NO3- and SO42- decreased. Mn, electrical conductivity, and the concentrations of Ca2+, Mg2+, Ba2+ and Sr2+ firstly increased and then decreased, while the concentrations of Fe, Al3+ were elevated. Affected by the long-time interaction of river water and groundwater, the elementary concentrations in the sediment were relatively high at the place of about 30 cm away from the riverbank. This consequently formed a hydrogeochemical gradient in the hyporheic zone. The boundary of the hyporheic zone was inferred at 30 to 50 cm away from the riverbank, whereas the boundary of shallow hyporheic zone was located at 10 cm away from the riverbank. In the process of river water recharging groudnwater, hyporheic zone of river and groundwater played an important role in the purification of water quality.