Assessing hyporheic exchange and associated travel times by hydraulic, chemical, and isotopic monitoring at the Steinlach Test Site, Germany

First results of a multi-disciplinary hyporheic monitoring study are presented from the newly established Steinlach Test Site in Southern Germany. The site is located in a bend of the River Steinlach (mean discharge of 1.8 m³/s) underlain by an alluvial sandy gravel aquifer connected to the stream. The overall objective is a better understanding of hyporheic exchange processes at the site and their interrelations with microbial community dynamics and biochemical reactions at the stream–groundwater interface. The present paper focuses on the distribution of lateral hyporheic exchange fluxes and their associated travel times at the Steinlach Test Site. Water level dynamics in various piezometers correspond to the different domains of hydraulic conductivity in the shallow aquifer and confirms hyporheic exchange of infiltrated stream water across the test site. Hydrochemical compositions as well as increased damping of continuous time series of electrical conductivity (EC) and temperature at the respective piezometers confirmed the inferred distribution of hyporheic flowpaths. Mean travel times ranging from 0.5 days close to the stream to more than 8 days in the upstream part of the test site could be estimated from deconvolution of EC and δ¹⁸O–H₂O data. The travel times agree well with the presumed flowpaths. Mg/Ca ratios as well as model fits to the EC and δ¹⁸O data indicate the presence of an additional water component in the western part of the test site which most likely consists of hillslope water or groundwater. Based on the mean travel times, the total lateral hyporheic exchange flux at the site was estimated to be of the order of 1–2 L/s.     

A large-scale study of hyporheic nitrate dynamics in a semi-arid catchment,the Tafna River,in Northwest Algeria

Very few studies have evaluated the role of the hyporheic zone (HZ) in aquatic ecosystem functioning or the factors driving hyporheic exchange flows on a large scale, especially in a semi-arid environment such as the Tafna watershed in Algeria. To understand this role through time and space, hydrogeochemical parameters, particularly nitrate concentrations (NO₃–N), were measured monthly between February 2013 and April 2014 in surface water (SW), interstitial water (IW) and groundwater (GW) along a 170-km stretch from the river’s source to the outlet into the main stream of the Tafna River and its Isser and Chouly tributaries. The significant longitudinal evolution of NO₃–N in the HZ was related to stream order and distance from the source. Moreover, the study indicated a significant difference between nitrate concentrations in the riffles (R) and pools (P) of the Tafna wadi. Principal component analysis (PCA) revealed the considerable impact of agriculture on nitrate concentrations. This study indicated on a large scale that nitrate-rich HZ contributed to increasing surface nitrate concentrations in upwelling sites and could be an important nitrate source for downstream SW, particularly during low-water (LW) periods when the Tafna can run dry on the surface. Thus, these results underline the importance of hyporheic zones functioning to the water quality of the watershed (process of enrichment and retention of nitrogen).     

Characterization of channel planform features and sinuosity indices in parts of Yamuna River flood plain using remote sensing and GIS techniques

River planform features and sinuosity are widely acknowledged as important geomorphological indices that control the channel hydraulics and stream power which determines the flow velocity and sediment supply to downstream reaches. Despite their significance, there has been little study about these indices in mighty Yamuna River for understanding the topographic control and hydraulic regime. This paper investigates the channel planform features and sinuosity by employing topographic map, digital elevation model (DEM), and satellite imageries to elucidate the morphological, sedimentological, and hydrological characteristics of the channel. Based on sinuosity index (varies between 1.02 and 1.41), the river segments are categorized into straight (segments 1, 3, 4, 5, 6), sinuous (segments 2, 7, 8, 9, and 11), and meandering (segment 10). The parameters analyzed to find out the influencing factors on sinuosity indicate geomorphological and anthropologic control in their development. Tectonic control of sinuosity in the studied stretch is ruled out as it is flowing through an alluvial plain with low rate of discharge.     

Stream chloride concentrations as a function of land use: a comparison of an agricultural watershed to an urban agricultural watershed

The concentration of chloride (Cl^?) in streams in northern regions has increased as a result of applications of deicers. This study focused on quantifying the relationship between land use and stream Cl^? concentrations. The study area comprises two adjacent watersheds in central Illinois, with similar geology and climate but different land uses (agricultural and urban). GIS analysis delineated watershed land use and calculated road surface areas. Stream water samples were collected and analyzed for anionic composition. During the winter months, streams dominated with urban land use experienced a 20-fold increase in Cl^? concentrations (range between 36 and 1350 mg L^?1); Cl^? concentrations in agricultural dominated streams also increased, but the increase was smaller (3X) and concentrations remained low (between 11 and 58 mg L^?1). As road salts are not the sole source of Cl^? in a stream, Cl^? and bromide (Br^?) mass ratios (Cl/Br) and Cl^? and sodium (Na) molar ratios ([Cl]/[Na]) were used to identify potential sources of Cl^?. The ratios indicate urbanized watersheds were impacted by road salts; agricultural watersheds ratios indicate other anthropogenic sources. A nonlinear relationship between urban land use and stream Cl^? concentrations indicates urban land use as low as 23% results in elevated Cl^? concentrations (greater than 150 mg L^?1) in stream waters.     

Heat tracing to determine spatial patterns of hyporheic exchange across a river transect

Significant spatial variability of water fluxes may exist at the water-sediment interface in river channels and has great influence on a variety of water issues. Understanding the complicated flow systems controlling the flux exchanges along an entire river is often limited due to averaging of parameters or the small number of discrete point measurements usually used. This study investigated the spatial pattern of the hyporheic flux exchange across a river transect in China, using the heat tracing approach. This was done with measurements of temperature at high spatial resolution during a 64-h monitoring period and using the data to identify the spatial pattern of the hyporheic exchange flux with the aid of a one-dimensional conduction-advection-dispersion model (VFLUX). The threshold of neutral exchange was considered as 126 L m^?2 d^?1 in this study and the heat tracing results showed that the change patterns of vertical hyporheic flux varied with buried depth along the river transect; however, the hyporheic flux was not simply controlled by the streambed hydraulic conductivity and water depth in the river transect. Also, lateral flow dominated the hyporheic process within the shallow high-permeability streambed, while the vertical flow was dominant in the deep low-permeability streambed. The spatial pattern of hyporheic exchange across the river transect was naturally controlled by the heterogeneity of the streambed and the bedform of the stream cross-section. Consequently, a two-dimensional conceptual illustration of the hyporheic process across the river transect is proposed, which could be applicable to river transects of similar conditions.     

水位变化影响下的河水-地下水侧向交互带地球化学动态

为了解不同水位变化影响下的河水与地下水侧向交互带地球化学特征动态,以重庆市马鞍溪为研究对象,选取丰水期向枯水期过渡的10-12月为研究期,对河水、地下水及交互带的水位、水温、溶解氧（DO）、pH值、电导率（EC）进行监测,结合对水体主要离子浓度的分析。结果表明,随枯水期到来,侧向交互带水位发生较大变化,交互带与河水间的水位梯度缩小,河水入渗动力逐渐减弱。水位的变化及入渗水温的降低,使交互带微生物活动减弱,pH值上升且变幅减小,DO上升。在其影响下,交互带EC下降,变幅减小,交互带对NO₃-、SO₄2-的净化能力降低,对Mn、Zn等重金属固定能力增强。通过分析交互带地球化学特征的变化,可推断出随马鞍溪枯水期的到来,侧向交互带边界由距河岸30~50 cm移动至距河岸30 cm以内。     

Heat tracing to examine seasonal groundwater flow beneath a low-gradient stream in rural central Illinois,USA

The thermal profile of a streambed is affected by a number of factors including: temperatures of stream water and groundwater, hydraulic conductivity, thermal conductivity, heat capacity of the streambed, and the geometry of hyporheic flow paths. Changes in these parameters over time cause changes in thermal profiles. In this study, temperature data were collected at depths of 30, 60, 90 and 150 cm at six streambed wells 5 m apart along the thalweg of Little Kickapoo Creek, in rural central Illinois, USA. This is a third-order low-gradient baseflow-fed stream. A positive temperature gradient with inflection at 90-cm depth was observed during the summer period. A negative temperature gradient with inflection at 30 cm was observed during the winter period, which suggests greater influence of stream-water temperatures in the substrate during the summer. Thermal models of the streambed were built using VS2DHI to simulate the thermal profiles observed in the field. Comparison of the parameters along with analysis of temperature envelopes and Peclet numbers suggested greater upwelling and stability in temperatures during the winter than during the summer. Upwelling was more pronounced in the downstream reach of the pool in the riffle and pool sequence.     

Relationship between electrical conductivity, <Superscript>18</Superscript>O of water and NO<Subscript>3</Subscript> content in different streamflow stages

The Ballenera Creek has 160 km² being a small catchment in the Pampa Plain in Argentina. This area has been deeply modified by human action through agricultural activities. From 2013 to 2017, electrical conductivity, stable isotopes of water and nitrate concentration monitoring program were conducted. The sampling included weekly and bimonthly samples in two sites along the stream, several groundwater wells and monthly precipitation. Chemical and isotopic tracers are used to discriminate the streamflow components and to evaluate their incidence in the nitrate concentration. The easiest conceptual model for gaining streams contemplates two main elements: direct runoff and groundwater (baseflow and pre-event water). The direct runoff has the lowest electrical conductivity and ¹⁸O_w variable content. The baseflow component is characterized by the highest electrical conductivity and isotope composition quite constant. Finally, pre-event water has an intermediate electrical conductivity and isotopic content close to the rainfall-weighted average composition. The nitrate concentration obtained was in general related to the different stream stages and was a useful indicator to evaluate the fertilization in agricultural zones.     

Fluvial response to active extension: evidence from 3D seismic data from the Frio Formation (Oligo-Miocene) of the Texas Gulf of Mexico Coast, USA

Tectonic deformation of the land surface is known to influence the gradient, water and sediment discharge and the grain-size of modern fluvial systems. Any change in these variables alters the equilibrium of a fluvial system, potentially causing a change in channel morphology. 3D seismic data from the Tertiary (Miocene) age, Upper Frio Formation, Kelsey Field, South Texas, in the US are used to examine changing fluvial channel morphology through time during a period of active growth of a rollover anticline in the hangingwall of a normal fault (the Vicksburg Fault). The studied interval varies between 22 and 47 m thick, and spans several hundred thousand years. It consists of an alternation of fluvial sandstones, overbank mudstones and coal. Seismic extractions show the evolution of sinuous fluvial channels during a phase of growth fault activity. Prior to growth, a single sinuous channel is imaged. During growth, the fluvial system became decapitated by a developing rollover anticline, and a highly sinuous drainage network formed, with frequent avulsion events, headward propagation of streams and related stream capture. Increased channel sinuosity was spatially associated with increased avulsion frequency in the area down dip to the east of the rollover anticline, more than 10 km from the active fault. More than 25 m of relative accommodation developed on the flank of the growing rollover anticline compared with on the crest. The increased channel sinuosity is interpreted as reflecting an increase in longitudinal valley slope analogous to observations made in flume experiments and modern river systems. The increase in avulsion frequency is attributed to increased aggradation as the rivers adjusted back to equilibrium grade following the increase in slope.     

Interpretative matrices approach to ranking lake sub-basin pollution potential: an applied study in Brazil

In 2005 a Cylindrospermopsis raciborskii bloom occurred in the Rio Verde Lake Basin (Brazil). To address this concern, a field analysis was performed to measure physicochemical variables and flows in 14 sub-basins, between 2008 and 2009. Measurements of mean total P (0.039 mg/L ± 0.018 mean SD), mean total Kjeldahl N (0.260 mg/L ± 0.226 mean SD), and mean BOD (1.2 mg/L ± 0.4 mean SD) concentrations were low in most streams, while COD reached a high of 27.1 mg/L (±4.9 mean SD). One tributary was responsible for 85 % of TP load, 77.1 % of TKN load, 78 % of t-BOD load, and 79 % of t-COD load. These concentrations and loads were used to develop the pollution potential assessment matrix (2PAM), which considered three different perspectives: stream water quality, reservoir ecosystem equilibrium, and sub-basin management. Each factor (TP, TKN, BOD and COD) was weighted based on concentration, total load and unit-area load. Pollution potential differed depending on which perspective was considered. The matrix developed, 2PAM, provides a new way to analyze concentrations and loads, enabling basin managers to prioritize action plans according to desired use within the basin.     

微弯河岸沿线扰动压强分布特性试验

河岸沿线的压强梯度是河岸侧向潜流交换及河岸带物质和能量传递的主要驱动力。为揭示微弯河岸边界的扰动压强分布规律和主要影响因素,利用室内变坡水槽系统,制作不同体形的正弦形河道模型,实测一个周期波长的河岸表面压强水头,研究河岸不同分层、不同弯曲程度和不同水流条件下的沿线压强分布特性,并进行影响因素的敏感性分析。试验结果表明,在缓流条件下正弦形微弯河岸的沿线扰动压强分布呈曲线形波动,不同分层的压强分布规律大体相同。在河岸弯曲程度较小时,压强波动的峰值与谷值分别出现于凹岸和凸岸的曲率最大位置。河岸沿线扰动压强的变化主要受河岸振幅与波长比a/λ和来流弗劳德数Fr的影响,敏感性分析表明a/λ比Fr的影响更为显著。     

Shallow groundwater systems in a polar desert, McMurdo Dry Valleys, Antarctica

The McMurdo Dry Valleys (MDVs), Antarctica, exist in a hyperarid polar desert, underlain by deep permafrost. With an annual mean air temperature of ?18 °C, the MDVs receive <10 cm snow-water equivalent each year, collecting in leeward patches across the landscape. The landscape is dominated by expansive ice-free areas of exposed soils, mountain glaciers, permanently ice-covered lakes, and stream channels. An active layer of seasonally thawed soil and sediment extends to less than 1 m from the surface. Despite the cold and low precipitation, liquid water is generated on glaciers and in snow patches during the austral summer, infiltrating the active layer. Across the MDVs, groundwater is generally confined to shallow depths and often in unsaturated conditions. The current understanding and the biogeochemical/ecological significance of four types of shallow groundwater features in the MDVs are reviewed: local soil-moisture patches that result from snow-patch melt, water tracks, wetted margins of streams and lakes, and hyporheic zones of streams. In general, each of these features enhances the movement of solutes across the landscape and generates soil conditions suitable for microbial and invertebrate communities.     

Delineation of spatial-temporal patterns of groundwater/surface-water interaction along a river reach (Aa River,Belgium) with transient thermal modeling

Among the advances made in analytical and numerical analysis methods to quantify groundwater/surface-water interaction, one methodology that stands out is the use of heat as an environmental tracer. A large data set of river and riverbed temperature profiles from the Aa River in Belgium has been used to examine the spatial-temporal variations of groundwater/surface-water interaction. Exchange fluxes were calculated with the numerical heat-transport code STRIVE. The code was applied in transient mode to overcome previous limitations of steady-state analysis, and allowed for the calculation of model quality. In autumn and winter the mean exchange fluxes reached ?90 mm d^?1, while in spring and early summer fluxes were ?42 mm d^?1. Predominantly gaining conditions occurred along the river reach; however, in a few areas the direction of flow changed in time. The river banks showed elevated fluxes up to a factor of 3 compared to the center of the river. Higher fluxes were detected in the upstream section of the reach. Due to the influence of exchange fluxes along the river banks, larger temporal variations were found in the downstream section. The exchange fluxes at the river banks seemed more driven by variable local exchange flows, while the center of the river was dominated by deep and steady regional groundwater flows. These spatial and temporal differences in groundwater/surface-water exchange show the importance of long-term investigations on the driving forces of hyporheic processes across different scales.     

Changes in irrigation management and quantity and quality of drainage water in a traditional irrigated land

Irrigated agriculture allows for the increase of agrarian yields and stability in food supply and raw materials, being, at the same time, responsible for the reduction of water resources availability and for the pollution by salts and nitrate. This work aims to analyze the impact of changes in irrigation management (establishment of an on-demand flood irrigated system, assignment of irrigation allowances and water payment for surface and irrigation water consumption) in a traditional irrigated land on drainage flow, electrical conductivity and nitrate concentration in irrigation return flows between the year 2001 and the period 2005–2008. Changes in water management significantly modified quantity (lower drainage) and quality (electrical conductivity and nitrate) of irrigation return flows, keeping similar evolution paths during the year with water ameliorants in summer due to the use of good irrigation water quality. Salinity in irrigation return flows is not a current problem in the area as electrical conductivity values in water did not exceed the limit established for water used in irrigation or intended for human consumption. Despite the fact that changes in irrigation management and crop distribution have reduced nitrate concentrations in irrigation return flows by 43 %, the water still presents nitrate values exceeding the 50 mg NO₃ ^?/l. Thus, nitrate remains as the main agro-environmental problem in this irrigation area. However, the nitrate concentration trends detected in this work mark the possibility of reaching nitrate values below 50 mg NO₃ ^?/l in the case of maintenance of the conditions in this agricultural system.     

Factors affecting the movement and persistence of nitrate and pesticides in the surficial and upper Floridan aquifers in two agricultural areas in the southeastern United States

Differences in the degree of confinement, redox conditions, and dissolved organic carbon (DOC) are the main factors that control the persistence of nitrate and pesticides in the Upper Floridan aquifer (UFA) and overlying surficial aquifer beneath two agricultural areas in the southeastern US. Groundwater samples were collected multiple times from 66 wells during 1993–2007 in a study area in southwestern Georgia (ACFB) and from 48 wells in 1997–98 and 2007–08 in a study area in South Carolina (SANT) as part of the US Geological Survey National Water-Quality Assessment Program. In the ACFB study area, where karst features are prevalent, elevated nitrate-N concentrations in the oxic unconfined UFA (median 2.5 mg/L) were significantly (p = 0.03) higher than those in the overlying oxic surficial aquifer (median 1.5 mg/L). Concentrations of atrazine and deethylatrazine (DEA; the most frequently detected pesticide and degradate) were higher in more recent groundwater samples from the ACFB study area than in samples collected prior to 2000. Conversely, in the SANT study area, nitrate-N concentrations in the UFA were mostly <0.06 mg/L, resulting from anoxic conditions and elevated DOC concentrations that favored denitrification. Although most parts of the partially confined UFA in the SANT study area were anoxic or had mixed redox conditions, water from 28 % of the sampled wells was oxic and had low DOC concentrations. Based on the groundwater age information, nitrate concentrations reflect historic fertilizer N usage in both the study areas, but with a lag time of about 15–20 years. Simulated responses to future management scenarios of fertilizer N inputs indicated that elevated nitrate-N concentrations would likely persist in oxic parts of the surficial aquifer and UFA for decades even with substantial decreases in fertilizer N inputs over the next 40 years.     

Active channel systems in the West Basin,Andaman Fore Arc: results from high-resolution bathymetry surveys and GIS analysis

Using multibeam swath bathymetric survey, a moderate sinuosity meandering channel was identified in the West Basin which is extending up to the northwestern corner of the Alcock Rise. Detailed morphometric analysis indicates that this channel is a mature sinuous channel which acts as a major conduit for the sediments into the West Basin. The straight length of the channel is ～70 km with an axial length of ～85 km. Furthermore, the maximum width is 1.5 km and minimum width is 0.4 km with an average sinuosity value of ～1.16, indicating its moderate meandering nature. It is interesting to note that this channel lacks the physical connection with the continental slope of the Andaman and Nicobar Islands. From multibeam data, the channels seem to emerge from Andaman Island; by using GIS techniques, a derived channel network system is obtained to identify the source, which reveals that its exact source is the Irrawaddy Delta system. Furthermore, this study even suggests that the major contribution of modern sediments to the Andaman Fore Arc basin is from Irrawaddy Delta, and sediment supply from Andaman continental slope also played an important role.     

On-line fluorometry of multiple reactive and conservative tracers in streams

Performing tracer tests using artificial tracer compounds is a common practice to characterize natural streams regarding their (reactive) transport properties. Recently, the fluorescent compound resazurin was introduced as a reactive stream tracer to quantify hyporheic exchange and metabolic activity of streams. This tracer, together with its reaction product resorufin and a conservative tracer (in our case fluorescein), provides additional information about transport properties of the stream and its hyporheic zone and can therefore overcome restrictions that are commonly affiliated with the use of conservative tracers alone. However, all previously published studies using this tracer system were based on manual sampling of the water. This usually limits the number of measurements and thus the achievable temporal resolution, and potentially endangers data quality due to inadequate handling of samples. In this paper, a modified version of the GGUN-FL30 on-line fluorometer is presented in which the optics have been modified to allow measuring the concentrations of all three tracers simultaneously at intervals of 10 s. Experiments under controlled and natural conditions showed that the performance of the on-line fluorometer regarding tracer separation efficiency and practical detection limits is comparable to a high-performance laboratory spectrofluorometer. Furthermore, suggestions are given on how to correct tracer signal fluctuations caused by temporal changes in temperature and pH that might occur during a field tracer test.     

Spectrophotometric determination of hydroxylamine in biological wastewater treatment processes

Hydroxylamine, a very important intermediate in nitrification, has a direct relationship with the production of nitrous oxide in biological wastewater treatment processes. The spectrophotometric method taking ferric ammonium sulfate and 1, 10-phenanthroline as the oxidant and the chromogenic agent, respectively, was used to determine the concentration of hydroxylamine in biological wastewater treatment processes. The impacts of nitrite, nitrate, orthophosphate, calcium ion and trace elements on the method were examined. The results indicated that the spectrophotometric method can be used for the determination of hydroxylamine in biological wastewater treatment processes. The correlation was significant in the range of 0.02–1.00 mg N/L (y = 1.5078x ? 0.0132, R ² = 0.9991), and the range varied to 0.05–1.00 mg N/L when nitrite and orthophosphate presented. Nitrate, calcium ion and trace elements did not interfere with the determination of hydroxylamine nitrogen. When the concentrations of nitrite nitrogen in the samples were lower than 15.00 mg/L, nitrite had a minor interference on the method. The impacts of orthophosphate on the method were complex. When the concentrations of hydroxylamine nitrogen were higher than 0.10 mg/L, the interference of orthophosphate on the method can be ignored. However, when the concentrations of hydroxylamine nitrogen in the samples were lower than 0.10 mg/L, orthophosphate had significant impacts on the determination, and a numerical method proposed can eliminate the interference of orthophosphate. The spectrophotometric method can determine the concentration of hydroxylamine in biological wastewater treatment processes quickly and conveniently and was helpful to understand the function of NH₂OH in N₂O production in biological wastewater treatment processes.     

A new method for analyzing the effects of joints and stratigraphy on spring locations: a case study from the Sacramento Mountains, south central New Mexico, USA

A novel method for analyzing the effects that stratigraphic layers and joints have on spring locations is presented, with specific relevance for the southern Sacramento Mountains, south central New Mexico, USA. Bedrock in this heavily vegetated mountain block is mostly covered by alluvium and soil, making direct field observations difficult, and necessitating alternative methods. Elevations of a mapped geologic contact are used to produce a three-dimensional stratigraphic surface. A histogram of spring stratigraphic positions, calculated from this surface, indicates zones of preferential groundwater flow. Field measurements are combined with GIS analyses to quantify joint control on spring locations within stream valleys, and these results are compared to traditional lineament analysis. Stream valleys are parallel to joints observed in the field, and joint-parallel segments selected from digital elevation model (DEM)-mapped streams are up to 900 m in length. The abundance of springs throughout the study area decreases logarithmically with distance from these joint-parallel stream segments. Springs are more than twice as abundant within 25 m of joint-parallel stream segments compared with manually mapped lineaments from air-photos. Higher correlation with spring locations and significant time reduction by using GIS to select joint-parallel streams for lineament interpretation indicate that the method provides a good alternative to manual lineament analysis.     

南海北部莺歌海盆地东方区上新统侧积复合体沉积特征及成因

基于三维地震数据的剖面、切片和属性解释,在南海北部莺歌海盆地东方1-1地区发现一种特殊类型的沉积体。按照侧积复合体弯曲度大小可分为高弯度型和低弯度型两类,在地震剖面上均以叠瓦状强振幅反射为主要识别标志,不同之处是前者在平面上通常呈一组同心半环,后者则表现为带状展布。侧积复合体可能为重力流水道多期“下切-充填”并发生连续横向迁移而成,其下部由互相切叠的水道底部沉积组成,一般粒度较粗且横向连续性好,可作为良好的油气储集层;而向上变为砂泥间互的岩性组合,连通性减弱、储集性能降低。侧积复合体的发现对深水重力流沉积体系研究具有重要意义,且可为研究区的油气勘探提供新的远景目标。