Stream Surface Research Articles

Enrichment of arsenic in surface water, stream sediments and soils in Tibet

Groundwater in sedimentary deposits in China, Southern, and Southeast Asia down gradient from the Tibetan plateau contains elevated As concentrations on a regional scale. To ascertain the possibility of source region As enrichment, samples of water (n=86), stream sediment (n=77) and soil (n=73) were collected from the Singe Tsangpo (upstream of the Indus River), Yarlung Tsangpo (upstream of the Brahmaputra River) and other drainage basins in Tibet in June of 2008. The average arsenic concentration in stream waters, sediments and soils was 58±70μg/L (n=39, range 2–252μg/L), 42±40mg/kg (n=37, range 12–227mg/kg), and 44±27mg/kg (n=28, range 12–84mg/kg) respectively for the Singe Tsangpo and was 11±17μg/L (n=30, range 2–83μg/L), 28±11mg/kg (n=28, range 2–61mg/kg), and 30±34mg/kg (n=21, range 6–173mg/kg) respectively for the Yarlung Tsangpo. A dug well contained 195μg/L of As. In addition to elevated As levels in surface and shallow groundwater of Tibet, hot spring and alkaline salt lake waters displayed very high As levels, reaching a maximum value of 5,985μg/L and 10,626μg/L As, respectively. The positive correlation between [As] and [Na]+[K] in stream waters indicates that these surface water arsenic enrichments are linked to the hot springs and/or salt lakes. Further, 24% of As in stream sediment is reductively leachable, with bulk As displaying a positive correlation with stream water As, suggesting sorption from stream water. In contrast, the fraction of reductively leachable As is negligible for soils and several rock samples, suggesting that As in them is associated with un-weathered minerals. Whether the pronounced As anomaly found in Tibet affects the sedimentary As content in deltas downstream or not requires further study.

Carbon Dioxide in Boreal Surface Waters: A Comparison of Lakes and Streams

The quantity of carbon dioxide (CO2) emissions from inland waters into the atmosphere varies, depending on spatial and temporal variations in the partial pressure of CO2 (pCO2) in waters. Using 22,664 water samples from 851 boreal lakes and 64 boreal streams, taken from different water depths and during different months we found large spatial and temporal variations in pCO2, ranging from below atmospheric equilibrium to values greater than 20,000 μatm with a median value of 1048 μatm for lakes (n = 11,538 samples) and 1176 μatm for streams (n = 11,126). During the spring water mixing period in April/May, distributions of pCO2 were not significantly different between stream and lake ecosystems (P > 0.05), suggesting that pCO2 in spring is determined by processes that are common to lakes and streams. During other seasons of the year, however, pCO2 differed significantly between lake and stream ecosystems (P < 0.0001). The variable that best explained the differences in seasonal pCO2 variations between lakes and streams was the temperature difference between bottom and surface waters. Even small temperature differences resulted in a decline of pCO2 in lake surface waters. Minimum pCO2 values in lake surface waters were reached in July. Towards autumn pCO2 strongly increased again in lake surface waters reaching values close to the ones found in stream surface waters. Although pCO2 strongly increased in the upper water column towards autumn, pCO2 in lake bottom waters still exceeded the pCO2 in surface waters of lakes and streams. We conclude that throughout the year CO2 is concentrated in bottom waters of boreal lakes, although these lakes are typically shallow with short water retention times. Highly varying amounts of this CO2 reaches surface waters and evades to the atmosphere. Our findings have important implications for up-scaling CO2 fluxes from single lake and stream measurements to regional and global annual fluxes.

Stream Surface Parametrization by Flow‐Orthogonal Front Lines

AbstractThe generation of discrete stream surfaces is an important and challenging task in scientific visualization, which can be considered a particular instance of geometric modeling. The quality of numerically integrated stream surfaces depends on a number of parameters that can be controlled locally, such as time step or distance of adjacent vertices on the front line. In addition there is a parameter that cannot be controlled locally: stream surface meshes tend to show high quality, well‐shaped elements only if the current front line is “globally” approximately perpendicular to the flow direction. We analyze the impact of this geometric property and present a novel solution – a stream surface integrator that forces the front line to be perpendicular to the flow and that generates quad‐dominant meshes with well‐shaped and well‐aligned elements. It is based on the integration of a scaled version of the flow field, and requires repeated minimization of an error functional along the current front line. We show that this leads to computing the 1‐dimensional kernel of a bidiagonal matrix: a linear problem that can be solved efficiently. We compare our method with existing stream surface integrators and apply it to a number of synthetic and real world data sets.

Characterization of the Deltaproteobacteria in contaminated and uncontaminated stream sediments and identification of potential mercury methylators

Microbial communities were examined in surface stream sediments at 5 conta - minated sites and 1 control site near Oak Ridge, TN, USA, to identify bacteria that could be con- tributing to mercury (Hg) methylation. The phylogenetic composition of the sediment bacterial community was examined over 3 quarterly sampling periods (36 samples) using 16S rRNA gene pyro sequencing. Only 3064 sequences (0.85% of the total community) were identified as Delta - proteobacteria, the only group known to methylate Hg, using the Ribosomal Database Project classifier at the 99% confidence threshold. Constrained ordination techniques indicated statisti- cally significant positive linear correlations between Desulfobulbus spp., Desulfonema spp. and Desulfobacca spp. and methyl-Hg concentrations at the Hg-contaminated sites. In contrast, the distribution of organisms related to Byssovorax spp. was significantly correlated to inorganic car- bon, nitrate and uranium concentrations but not to Hg or methyl-Hg. Overall, the abundance and richness of Deltaproteobacteria sequences were higher in uncontaminated sediments, while the majority of the members present at the contaminated sites were either known potential metal- reducers/methylators or metal tolerant species. Given the abundance relative to other known Hg methylators and the association with methyl-Hg, Desulfobulbus spp. is considered a prime candi- date for involvement in Hg methylation in these streams.

Chemical weathering fluxes from volcanic islands and the importance of groundwater: The Hawaiian example

We investigated the products and rates of chemical weathering on the Hawaiian Islands, sampling streams on Kaua’i and both streams and groundwater wells on the island of Hawai’i. Dissolved silica was used to investigate the flowpaths of water drained into streams. We found that flowpaths exert a major control on the observed chemical weathering rates. A strong link exists between the degree of landscape dissection and flowpaths of water through the landscape, with streams in undissected landscapes receiving water mainly from surface runoff and streams in highly dissected landscapes receiving a considerable fraction of their water from groundwater (springs and/or seepage). Total alkalinity in Hawaiian streams and groundwater is produced exclusively by silicate chemical weathering. We find that fluxes of total alkalinity (often called “CO2 consumption rate” in the geochemical literature), from the islands are lower than those observed in basaltic regions elsewhere. Groundwater is, overall, the major transport vector for products of chemical weathering from the Hawaiian Islands. On the youngest and largest island, submarine groundwater discharge (SGD) transports more than an order of magnitude more solutes to the ocean than surface water and on the youngest part of the youngest island, SGD is the only link between the terrestrial weathering system and the ocean. These results suggest that groundwater, and particularly SGD, needs to be included in geochemical weathering budgets of volcanic islands.

Lattice Boltzmann simulation of liquid water transport in turning regions of serpentine gas channels in proton exchange membrane fuel cells

A two-phase lattice Boltzmann model is employed for direct numerical simulation of liquid water transport in the turning regions of serpentine gas channels in proton exchange membrane (PEM) fuel cells. Two different types of serpentine gas channels with either a smooth U-shaped or a sharp right-angled turning region are examined. Numerical results indicate that a smooth U-shaped turning region is beneficial to liquid water removal in a serpentine gas channel. An increased gas stream velocity or channel surface contact angle can further assist the process. Liquid water tends to accumulate in the sharp right-angled turning region because of the acting direction of the gas shear force. Increased gas stream velocity and surface contact angle are not very helpful for liquid water removal in the right-angled turning region under all the tested conditions. This numerical study is intended to provide improved fundamental understandings of liquid water transport mechanisms in serpentine gas channels of PEM fuel cells.

Riparian microclimate and evaporation from a coastal headwater stream, and their response to partial-retention forest harvesting

This study focused on a headwater forest stream in coastal British Columbia, Canada. Air temperature, humidity and wind speed were measured at a height of 1.5m above the stream and at a control site within a clearcut located approximately 1km from the study stream, both before and after partial-retention forest harvesting along the stream. A specially designed evaporimeter was used to measure evaporation. Laboratory trials confirmed the reliability of evaporimeter measurements. Prior to harvesting, wind speeds were low and vapour pressure gradients above the stream were weak, leading to low rates of evaporation. Following harvesting, the decreased shading and increased ventilation over the stream led to higher wind speeds, lower vapour pressures, higher daily maximum air temperatures, higher stream temperatures and surface vapour pressures, and higher rates of evaporation. A wind function that has been used to estimate stream evaporation in a number of previous studies, but which had not been compared to measured stream evaporation, was found to overestimate evaporation. An empirical wind function fitted to the evaporimeter data differed from three others that have been derived for predicting stream evaporation in that our data did not support the inclusion of an intercept. It is hypothesized that the lack of an intercept for our data reflects the strongly stable conditions over the stream. Further research should measure stream evaporation over a broad range of streamflow and meteorological conditions, with particular attention to the role of atmospheric stability.

Automatic Stream Surface Seeding: A Feature Centered Approach

AbstractThe ability to capture and visualize information within the flow poses challenges for visualizing 3D flow fields. Stream surfaces are one of many useful integration based techniques for visualizing 3D flow. However seeding integral surfaces can be challenging. Previous research generally focuses on manual placement of stream surfaces. Little attention has been given to the problem of automatic stream surface seeding. This paper introduces a novel automatic stream surface seeding strategy based on vector field clustering. It is important that the user can define and target particular characteristics of the flow. Our framework provides this ability. The user is able to specify different vector clustering parameters enabling a range of abstraction for the density and placement of seeding curves and their associated stream surfaces. We demonstrate the effectiveness of this automatic stream surface approach on a range of flow simulations and incorporate illustrative visualization techniques. Domain expert evaluation of the results provides valuable insight into the users requirements and effectiveness of our approach.

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

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

Prediction method of impeller performance and analysis of loss mechanism for mixed-flow pump

A loss model for the mixed-flow pump impellers was developed by summarizing a variety of loss calculation formulas systematically. The internal flow field of the impeller was obtained by employing the iterative calculation for S1 and S2 stream surfaces to solve the continuity and motion equations of fluid. Based on the calculation method of the flow field and the loss model, it is achieved to predict the impeller performance of the mixed-flow pump and the performance curves of a mixed-flow pump model with adjustable blades. Compared with the test data, the loss model of the mixed-flow pump based on the iterative calculation can predict the impeller performance quickly and accurately, which has a high value on the engineering applications. Based on the test verification, curves of various kinds of losses varied for the flow rate were analyzed under different blade angles. In addition, the mechanisms of various kinds of losses inside the mixed-flow pump impeller were discussed in-depth.

Distribution and Accumulation of Metals in Tadpoles Inhabiting the Metalliferous Streams of Eastern Chalkidiki, Northeast Greece

The present study investigates the accumulation of heavy metals [copper (Cu), lead (Pb), zinc (Zn), magnesium (Mn), cadmium (Cd), nickel (Ni), and chromium (Cr)] in tadpoles inhabiting the metalliferous streams flowing within the Asprolakkas River basin (northeast Chalkidiki peninsula, Greece) and the effect of potentially harmful elements in stream water and sediment on the corresponding levels in their tissue. Animals were collected from six sampling sites influenced by a wide range of surface water and stream sediment trace element concentrations. The results of the chemical analyses showed that tadpoles accumulated significant levels of all of the examined metals. The range of whole-body mean measured concentrations were (in dry mass) as follows: Cu (46-182 mg/kg), Pb (103-4,490 mg/kg), Zn (494-11,460 mg/kg), Mn (1,620-13,310 mg/kg), Cd (1.2-82 mg/kg), Ni (57-163 mg/kg), and Cr (38-272 mg/kg). The mean concentrations of Pb, Zn, Mn, Ni, Cr, and Cd in Kokkinolakkas stream, which drains a currently active mining area, were the highest ever reported in tadpoles. Our results indicate that whole-body levels of Pb, Zn, Cu, and Cd increase with stream sediment concentrations and that these organisms tend to accumulate metals bound to Fe and Mn oxides. In addition, high dissolved concentrations and significant concentrations associated with more labile geochemical phases of sediments for specific metals were contributing factors determining whole-body levels. Given the observed bioconcentration factors, as well as the correlation with sediment concentrations, it is proposed that these organisms could be considered as bioindicators of environmental contamination and may be used for monitoring purposes within this metal-rich zone and, perhaps, within other rivers affected by metal mining.

Conical gas flows with shock waves and turbulent boundary layer separation

The results of a theoretical and experimental investigation of nonsymmetric flow around a V-wing with supersonic leading edges are presented. The range of the angles of attack and yaw, on which additional singular lines are formed on the windward cantilever of the wing, are experimentally determined using different techniques of flow diagnostics. These are one convergence line and two divergence lines in the transverse flow which were not previously observable in the calculations of ideal-gas flow around wings. It is established that the appearance of the three new alternating singular lines located between the central chord of the wing and a convergence line, exterior to them and occurring within the framework of the ideal gas model, is associated with the relation between the intensities of two contact discontinuities. One of these proceeds from the branching point of the bow shock above the leeward cantilever, while the second issues out of the triple point of a λ-shaped shock configuration accompanying developed turbulent-boundary-layer separation generated by an internal shock incident on the leeward cantilever surface. If the intensity of the contact discontinuity proceeding from the branching point of the bow shock is large as compared with that of the contact discontinuity of the λ-configuration, then the flow pattern realized on the windward cantilever is analogous to that obtained within the framework of the ideal gas model, that is, it includes one convergence line on the wing surface. Under these conditions, the results of the calculations within the framework of the ideal gas model are applicable for understanding the phenomena occurring in the wing shock layer in a considerable part of the control parameter range, including the regimes with intense internal shocks generating turbulent boundary layer separation from the leeward cantilever. Corrections should be made only for a carachteristic pressure distribution in the separation zone and, as a consequence of separation, for an elevated pressure level in the vicinity of the central chord which is the stagnation line of the transverse flow that has passed across the oblique and terminating shocks of the λ-configuration and possesses a higher stagnation pressure than the flow that has passed in an ideal gas across the internal shock incident normally on the leeward cantilever. This is possible only when the divergence line, at which the stream surface enclosing the turbulent boundary layer separation zone enters, does not go over from the leeward onto the windward cantilever.

Using periodic analytic elements to analyze aquifer tests near surface waters

In riverbank filtration (RBF), the objective is to indirectly pump water from a river into wells near the river, by inducing recharge through the river sediments. Design models must quantify the rate of induced infiltration from surface waters, which is often controlled by the hydraulic resistance between the surface water body and the aquifer. Traditional tools for aquifer-test analysis near surface streams have limited utility for directly estimating the resistance of a streambed or riverbed. The authors have developed software tools for aquifer test analysis using an analytic element model for periodically varying flow called Wigaem. The Wigaem code can explicitly represent the plan-view geometry of surface streams and the aquifer perimeter, including tributary streams when necessary. All boundary conditions in the model may vary periodically, including water levels in surface waters and pumping rates of wells in the simulation. A constant-discharge pumping test may be simulated by extending the pumping regime in time such that it becomes periodic and the total discharge during the period of simulation equals zero. Problems caused by the Gibbs phenomenon are reduced through application of a moving average filter, which makes Wigaem suitable for very general aquifer test problems. By calibrating the model to match observed water-level data, the model is used to estimate the transmissivity, storativity, and the entry resistance of surface waters, which are crucial for the design of RBF systems. This approach is applied to a site in central Illinois, United States.

Process length scales and longitudinal damping in karst conduits

Simple mathematical models often allow an intuitive grasp of the function of physical systems. We develop a mathematical framework to investigate reactive or dissipative transport processes within karst conduits. Specifically, we note that for processes that occur within a characteristic timescale, advection along the conduit produces a characteristic process length scale. We calculate characteristic length scales for the propagation of thermal and electrical conductivity signals along karst conduits. These process lengths provide a quantitative connection between karst conduit geometry and the signals observed at a karst spring. We show that water input from the porous/fractured matrix is also characterized by a length scale and derive an approximation that accounts for the influence of matrix flow on the transmission of signals through the aquifer. The single conduit model is then extended to account for conduits with changing geometries and conduit flow networks, demonstrating how these concepts can be applied in more realistic conduit geometries. We introduce a recharge density function, ϕR, which determines the capability of an aquifer to damp a given signal, and cast previous explanations of spring variability within this framework. Process lengths are a general feature of karst conduits and surface streams, and we conclude with a discussion of other potential applications of this conceptual and mathematical framework.

Conceptual Models for Carbonate Aquifers

The very diverse types of ground‐water behavior in carbonate terrains can be classified by relating the flow type to a particular hydrogeologic environment each exhibiting a characteristic cave morphology. The ground water may move by diffuse flow, by retarded flow, or by free flow. Diffuse flow occurs in less soluble rocks such as extremely shaley limestones or crystalline dolomites. Integrated conduits are rare. Caves tend to be small, irregular, and often little more than solutionally widened joints. Retarded flows occur in artesian environments and in situations where unfavorable stratigraphy forces ground water to be confined to relatively thin beds. Network cave patterns are characteristic since hydrodynamic forces are damped by the external controls. Solution occurs along many available joints. Free flowing aquifers are those in which solution has developed a subsurface drainage system logically regarded as an underground extension of surface streams. These streams may have fully developed surface tributaries as well as recharge from sinkholes and general infiltration. Characteristic cave patterns are those of integrated conduit systems which are often truncated into linear, angulate, and branchwork caves. Free Flow aquifers may be further subdivided into Open aquifers lying beneath karst plains and Capped aquifers in which significant parts of the drainage net lie beneath an insoluble cap rock. Other geologic factors such as structure, detailed lithology, relief, and locations of major streams, control the details of cave morphology and orientation of the drainage network.

Análise do dimorfismo e morfometria em Enhydrus sulcatus

Enhydrus sulcatus (Wiedeman, 1821) (Coleoptera: Gyrinidae) were found swimming in circles on the surface of streams shaded by forests in preserved sites. The sexual dimorphism was evaluated in that species through the quantification of differences occurring among the length of the first pair of legs, width of the mesonotum, total lengthand body mass of 112 individuals, 71 being females and 41 males. There was significant difference among the width of the mesonotum (KW-H(1.112) = 32.80; p &lt; 0.05), total length (KW-H (1.112) = 38.00; p &lt; 0.05), length of the first leg (KW-H(1.112) = 47.58; p &lt;0.05) and body weight (KW-H (1.82) = 23.86; p &lt; 0.05) of male and female E. sulcatus.The length of the first leg relates positively and significantly with the width of the mesonotum (r2 = 0.40; p &lt; 0.05), with the total weight (r2 = 0.36; p &lt; 0.05) and with the total body length of individuals E. sulcatus (r2 = 0.33; p &lt; 0.05). The total length of individuals of E.sulcatus relates positively and significantly with width of the mesonotum (r2 = 0.65; p &lt;0.05). In this study a clear sexual dimorphism was shown in Enhydrus sulcatus and was present in various other body structures besides the tarsal dilations.Key words: sexual dimorphism, Gyrinidae, Enhydrus sulcatus, measured morphometrics.

Geochemical signature of surface water and stream sediments of a mineralized drainage basin at NE Chalkidiki, Greece: A pre-mining survey

The geochemical characteristics of surface water and stream sediments in Asprolakkas drainage basin, an area of Tertiary mineralization within amphibolite, located at NE Chalkidiki peninsula, Greece, were investigated in order to establish the geochemical baseline conditions prior to any type of new mining activities. The area represents the only example of active mining and processing of base metal sulfide ore in Greece and also includes an unmined porphyry Cu–Au ore deposit at Skouries. In a wider context, this research represents a pre-mining baseline geochemical study that can be used as an analog for similar metallogenetic provinces in areas with a Mediterranean type climate.Concentrations of dissolved major ions and trace metals displayed wide variability within the study area. Kokkinolakkas stream, draining the exploited Pb–Zn (±Ag) ore bodies, is strongly influenced by chemical weathering of sulfide minerals and presents elevated levels of SO4 (429–857mgl−1), Pb (4–64μgl−1), Zn (290–1350μgl−1), Mn (1680–7899μgl−1), Ni (12–50μgl−1), Cd (2–8μgl−1), As (8–45μgl−1) and Sb (9–16μgl−1). Stream water of unmined areas demonstrated a different chemical composition with elevated values mainly for Pb (up to 45μgl−1) and As (up to 141μgl−1). Hydrological conditions highly influence the behavior of major elements and metals. Stream bed sediments from Kokkinolakkas and Tsarkia Lakkos, located at the head waters of Asprolakkas basin, have anomalous values in Pb (1165–3439mgkg−1), Zn (1368–4538mgkg−1), As (964–2714mgkg−1), Sb (30–70mgkg−1), Cd (3.8–21.6mgkg−1) and Mn (6811 up to >10,000mgkg−1). Mobility of selected trace metals was investigated through the application of a 5-step sequential extraction procedure. Results show that, despite the high total metal content, the majority of analyzed elements are mainly bound to relatively immobile operationally defined geochemical phases of amorphous to poorly crystalline Fe and Mn oxides and the residual fraction. Considering the planned mining developments in the area, the results of this study may assist mine planners to set realistic goals for monitoring and remediation programs.

The hyporheic zone as an invertebrate refuge: a review of variability in space, time, taxa and behaviour

The hyporheic zone is a potential refuge that can promote persistence of benthic invertebrates during adverse conditions in surface streams. For decades, changes in invertebrate depth distribution have been investigated in relation to flood, low flow and drying events, but evidence for use of the hyporheic refuge remains equivocal. This review examines the evidence for the hyporheic zone’s refugial role during adverse hydrological conditions. Refuge potential is influenced by determinants in four categories. First, refuge use varies spatially in relation to physical habitat parameters, including sediment porosity and hydrologic exchange. Second, refuge use is temporally variable and reflects disturbance characteristics including rate of onset. Third, refuge use is taxon-specific, depending on a range of morphological, behavioural and physiological traits. Fourth, the behaviours governing refuge use vary, with both active migrations and passive habitat use playing important roles in community persistence. These four determinants interact to influence refuge use; for example, the physical habitat providing an adequate refuge will vary between taxa. Despite this variability, the hyporheic zone is an important component in the suite of refuges that facilitate community resilience to disturbance events. As such, its ecological integrity should be safeguarded through sensitive management and effective rehabilitation schemes.

Floodplain restoration enhances denitrification and reach‐scale nitrogen removal in an agricultural stream

Streams of the agricultural Midwest, USA, export large quantities of nitrogen, which impairs downstream water quality, most notably in the Gulf of Mexico. The two-stage ditch is a novel restoration practice, in which floodplains are constructed alongside channelized ditches. During high flows, water flows across the floodplains, increasing benthic surface area and stream water residence time, as well as the potential for nitrogen removal via denitrification. To determine two-stage ditch nitrogen removal efficacy, we measured denitrification rates in the channel and on the floodplains of a two-stage ditch in north-central Indiana for one year before and two years after restoration. We found that instream rates were similar before and after the restoration, and they were influenced by surface water NO3- concentration and sediment organic matter content. Denitrification rates were lower on the constructed floodplains and were predicted by soil exchangeable NO3- concentration. Using storm flow simulations, we found that two-stage ditch restoration contributed significantly to NO3- removal during storm events, but because of the high NO3- loads at our study site, < 10% of the NO3- load was removed under all storm flow scenarios. The highest percentage of NO3- removal occurred at the lowest loads; therefore, the two-stage ditch's effectiveness at reducing downstream N loading will be maximized when the practice is coupled with efforts to reduce N inputs from adjacent fields.

Hydraulic conductivity of the High Plains Aquifer re‐evaluated using surface drainage patterns

The High Plains Aquifer (HPA), underlying parts of 8 states from South Dakota to Texas, is one of the largest fresh water aquifers in the world and accounts for 30% of the groundwater used for irrigation in the US. Determining the distribution of HPA's hydraulic conductivity (K) is critical for water management and addressing water quality issues. K is traditionally estimated from well pumping data coupled with computer modeling and is known to be highly variable, spanning several orders of magnitude for the same type of rock. Here we show that applying our innovative method of determining effective horizontal K to HPA (based on surface drainage patterns and a dynamic equilibrium assumption) produced results generally consistent with those from traditional methods but reveals much more detailed spatial variation. With the exception of a few places such as the Sand Hills area, our results also show for the first time (to the best of our knowledge) a distinct relationship between surface stream drainage density and subsurface aquifer K in a major aquifer system on a regional scale. Because aquifer particle size strongly controls K, our results can be used to study patterns of past sediment movement and deposition.