Stream denitrification is thought to be enhanced by hyporheic transport but there is little direct evidence from the field. To investigate at a field site, we injected 15NO3−, Br (conservative ...tracer), and SF6 (gas exchange tracer) and compared measured whole‐stream denitrification with in situ hyporheic denitrification in shallow and deeper flow paths of contrasting geomorphic units. Hyporheic denitrification accounted for between 1 and 200% of whole‐stream denitrification. The reaction rate constant was positively related to hyporheic exchange rate (greater substrate delivery), concentrations of substrates DOC and nitrate, microbial denitrifier abundance (nirS), and measures of granular surface area and presence of anoxic microzones. The dimensionless product of the reaction rate constant and hyporheic residence time, λhzτhz define a Damköhler number, Daden‐hz that was optimal in the subset of hyporheic flow paths where Daden‐hz ≈ 1. Optimal conditions exclude inefficient deep pathways where substrates are used up and also exclude inefficient shallow pathways that require repeated hyporheic entries and exits to complete the reaction. The whole‐stream reaction significance, Rs (dimensionless), was quantified by multiplying Daden‐hz by the proportion of stream discharge passing through the hyporheic zone. Together these two dimensionless metrics, one flow‐path scale and the other reach‐scale, quantify the whole‐stream significance of hyporheic denitrification. One consequence is that the effective zone of significant denitrification often differs from the full depth of the hyporheic zone, which is one reason why whole‐stream denitrification rates have not previously been explained based on total hyporheic‐zone metrics such as hyporheic‐zone size or residence time.
Key Points
1)Tracers show hyporheic‐zone denitrification is significant for stream N budget
2)Active volume for denitrification differs from full hyporheic zone
3)Damköhler ratio and hyporheic flux to discharge ratio control significance
Comprehensive understanding of surface water and groundwater interaction is essential for effective water resources management. Groundwater and surface water are closely connected components that ...constantly interact with each other within the Earth’s hydrologic cycle. Many studies utilized observations to explain the surface water and groundwater interactions by carefully analyzing the behavior of surface water features (streams, lakes, reservoirs, wetlands, and estuaries) and the related aquifer environments. However, unlike visible surface water, groundwater, an invisible water resource, is not easy to measure or quantify directly. Nevertheless, demand for groundwater that is highly resilient to climate change is growing rapidly. Furthermore, groundwater is the prime source for drinking water supply and irrigation, and hence critical to global food security. Groundwater needs to be managed wisely, protected, and especially sustainably used. However, this task has become a challenge to many hydrologic systems in arid to even humid regions because of added stress caused by changing environment, climate, land use, population growth, etc. In this issue, the editors present contributions on various research areas such as the integrated surface water and groundwater analysis, sustainable management of groundwater, and the interaction between surface water and groundwater. Methodologies, strategies, case studies as well as quantitative techniques for dealing with combined surface water and groundwater management are of interest for this issue.
Previously regarded as the passive drains of watersheds, over the past 50 years, rivers have progressively been recognized as being actively connected with off‐channel environments. These connections ...prolong physical storage and enhance reactive processing to alter water chemistry and downstream transport of materials and energy. Here we propose river corridor science as a concept that integrates downstream transport with lateral and vertical exchange across interfaces. Thus, the river corridor, rather than the wetted river channel itself, is an increasingly common unit of study. Main channel exchange with recirculating marginal waters, hyporheic exchange, bank storage, and overbank flow onto floodplains are all included under a broad continuum of interactions known as “hydrologic exchange flows.” Hydrologists, geomorphologists, geochemists, and aquatic and terrestrial ecologists are cooperating in studies that reveal the dynamic interactions among hydrologic exchange flows and consequences for water quality improvement, modulation of river metabolism, habitat provision for vegetation, fish, and wildlife, and other valued ecosystem services. The need for better integration of science and management is keenly felt, from testing effectiveness of stream restoration and riparian buffers all the way to reevaluating the definition of the waters of the United States to clarify the regulatory authority under the Clean Water Act. A major challenge for scientists is linking the small‐scale physical drivers with their larger‐scale fluvial and geomorphic context and ecological consequences. Although the fine scales of field and laboratory studies are best suited to identifying the fundamental physical and biological processes, that understanding must be successfully linked to cumulative effects at watershed to regional and continental scales.
Key Points:
Hydrologic exchange prolongs physical storage and reactive processing in river corridors
Consequences for water quality, ecological metabolism, and wildlife habitat provision
Challenge linking small‐scale physical drivers with larger‐scale ecological consequences
Improved monitoring of inundation area variations in lakes and reservoirs is crucial for assessing surface water resources in a growing population and a changing climate. Although long-record optical ...satellites, such as Landsat missions, provide sub-monthly observations at fairly fine spatial resolution, cloud contamination often poses a major challenge for producing temporally continuous time series. We here proposed a novel method to improve the temporal frequency of usable Landsat observations for mapping lakes and reservoirs, by effectively recovering inundation areas from contaminated images. This method automated three primary steps on the cloud-based platform Google Earth Engine. It first leveraged multiple spectral indices to optimize water mapping from archival Landsat images acquired since 1992. Errors induced by minor contaminations were next corrected by the topology of isobaths extracted from nearly cloud-free images. The isobaths were then used to recover water areas under major contaminations through an efficient vector-based interpolation. We validated this method on 428 lakes/reservoirs worldwide that range from ~2 km2 to ~82,000 km2 with time-variable levels measured by satellite altimeters. The recovered water areas show a relative root-mean-squared error of 2.2%, and the errors for over 95% of the lakes/reservoirs below 6.0%. The produced area time series, combining those from cloud-free images and recovered from contaminated images, exhibit strong correlations with altimetry levels (Spearman's rho mostly ~0.8 or larger) and extended the hypsometric (area-level) ranges revealed by cloud-free images alone. The combined time series also improved the monthly coverage by an average of 43%, resulting in a bi-monthly water area record during the satellite altimetry era thus far (1992–2018). The robustness of this method was further verified under five challenging mapping scenarios, including fluvial lakes in humid basins, reservoirs with complex shape geometries, saline lakes with high mineral concentrations, lakes/reservoirs in mountainous regions, and pan-Arctic lakes with frequent snow/ice covers. Given such performance and a generic nature of this method, we foresee its potential applications to assisting water area recovery for other optical and SAR sensors (e.g., Sentinel-2 and SWOT), and to estimating lake/reservoir storage variations in conjunction with altimetry sensors.
•A novel method is proposed to recover missing lake areas under cloud contamination.•This method was validated on 428 lakes and reservoirs worldwide over 26 years.•The recovery errors for over 95% of the 428 lakes/reservoirs are below ~6%.•The produced water area time series show strong correlations with altimetry levels.•This method results in water area time series at an average bi-monthly frequency
The impact of climate change on surface water resources is reasonably well studied. However, the impact on groundwater resources has only been considered by a few studies worldwide. Here we present ...an analysis of climate change impacts on groundwater resources in a well‐instrumented 6,800‐km2 watershed in the Laurentian Great Lakes Basin. We employ a physics‐based modeling pipeline consisting of an ensemble of high‐resolution regional climate model projections based on the Weather Research and Forecasting model and the fully integrated three‐dimensional hydrologic model HydroGeoSphere. The Weather Research and Forecasting model is run at a resolution as fine as 10 km using two different physics configurations, while HydroGeoSphere simulates the terrestrial hydrosphere at subkilometer scale, from deep groundwater to surface water, including surface water‐groundwater interactions. The two Weather Research and Forecasting model physics configurations exhibit opposite climate change responses in summer precipitation. The hydrologic simulations follow the climate forcing, but due to the memory of the subsurface, differences in summer affect the entire seasonal cycle. In the drier climate scenario groundwater levels and recharge decline, while in the wetter scenario groundwater levels rise (recharge remains unchanged). Soil moisture changes accordingly, but primarily in late summer. It is also shown that the magnitude of climate change impacts on groundwater is strongly modulated by local physiographic features. In particular, regions where the groundwater table is deep (below 2 m; 15% of the area) show a high sensitivity to changes in climate forcing. Furthermore, changes in groundwater levels, recharge, and soil moisture typically occur in the same regions, suggesting potentially compounding impacts.
Plain Language Summary
In many watersheds groundwater maintains minimum flows and soil moisture during dry periods. In this study we investigate the possible impacts of different climate change scenarios on groundwater and soil moisture in a major watershed in southern Ontario, Canada. We use a state‐of‐the‐art hydrologic model that simulates groundwater and surface water, together with climate scenarios that are derived from an ensemble of high‐resolution regional climate projections. The main result is that changes in groundwater and soil moisture generally follow the direction of changes seen in net precipitation from the climate models, but the spatial pattern and magnitude of changes are strongly modulated by local topography and geology. In general, regions that have a deeper groundwater table today are more sensitive and may experience larger changes in the future. As expected, our simulations do not match observations perfectly, but we believe that we are able to identify uncertainties that are likely to affect the conclusions. The primary uncertainty here lies in the change in summer precipitation, which dominates the climate change response: it is large enough to either cause a drier or a wetter future, and the interaction between surface water and groundwater appears to spread changes in summer across the entire year.
Key Points
Climate change impact modeling using a regional climate model and a fully integrated surface water‐groundwater model
Primary uncertainty in summer precipitation controls soil moisture and has delayed influence over seasonal groundwater fluctuations
Magnitude of climate change impacts on soil moisture and groundwater are strongly modulated by local physiography
Fiber optics opens window on stream dynamics Selker, John; van de Giesen, Nick; Westhoff, Martijn ...
Geophysical research letters,
December 2006, Letnik:
33, Številka:
24
Journal Article, Web Resource
Recenzirano
Odprti dostop
A new approach to monitoring surface waters using distributed fiber optic temperature sensing is presented, allowing resolutions of temperature of 0.01°C every meter along a fiber optic cable of up ...to 10,000 m in length. We illustrate the potential of this approach by quantifying both stream temperature dynamics and groundwater inflows to the Maisbich, a first‐order stream in Luxembourg (49°47′N, 6°02′E). The technique provides a very rich dataset, which may be of interest to many types of environmental research, notably that of stream ecosystems.
•Fully integrated groundwater model was used to simulate esker aquifer hydrology.•Locations of simulated GW–lake interaction agreed with airborne thermal image data.•Magnitude of simulated GW influx ...to lakes resembled stable isotope flux estimates.•Transient GW–lake interaction was revealed with fully integrated simulation method.
Water resources management is moving towards integration, where groundwater (GW), surface water (SW) and related aquatic ecosystems are considered one management unit. Because of this paradigm shift, more information and new tools are needed to understand the ecologically relevant fluxes (water, heat, solutes) at the GW–SW interface. This study estimated the magnitude, temporal variability and spatial distribution of water fluxes at the GW–SW interface using a fully integrated hydrological modelling code (HydroGeoSphere). The model domain comprised a hydrologically complex esker aquifer in Northern Finland with interconnected lakes, streams and wetlands. The model was calibrated in steady state for soil hydraulic conductivity and anisotropy and it reproduced the hydraulic head and stream baseflow distribution throughout the aquifer in both transient and steady state modes.
In a novel analysis, model outputs were compared with the locations and magnitude of GW discharge to lakes estimated using field techniques. Spatial occurrence of GW–lake interaction was interpreted from airborne thermal infrared imaging. The observed GW inflow locations coincided well with model nodes showing positive exchange flux between surface and subsurface domains. Order of magnitude of simulated GW inflow to lakes showed good agreement with flux values calculated with a stable water isotope technique. Finally, time series of GW inflow, extracted as model output, showed moderate annual variability and demonstrated different interannual inflow changes in seepage and drainage lakes of the aquifer.
Overall, this study demonstrated the ability of a fully integrated numerical model to reproduce observed GW–SW exchange processes in a complex unconfined aquifer system. The model-based estimates obtained for GW influx magnitude and spatial distribution, along with information on GW quality can be used to estimate ecologically relevant fluxes in future water resources management.
Following extreme flooding in eastern Australia in 2011, the Australian Government established a programme to improve access to flood information across Australia. As part of this, a project was ...undertaken to map the extent of surface water across Australia using the multi-decadal archive of Landsat satellite imagery. A water detection algorithm was used based on a decision tree classifier, and a comparison methodology using a logistic regression. This approach provided an understanding of the confidence in the water observations. The results were used to map the presence of surface water across the entire continent from every observation of 27years of satellite imagery. The Water Observation from Space (WOfS) product provides insight into the behaviour of surface water across Australia through time, demonstrating where water is persistent, such as in reservoirs, and where it is ephemeral, such as on floodplains during a flood. In addition the WOfS product is useful for studies of wetland extent, aquatic species behaviour, hydrological models, land surface process modelling and groundwater recharge. This paper describes the WOfS methodology and shows how similar time-series analyses of nationally significant environmental variables might be conducted at the continental scale.
•Demonstrates a system for continental, multi-temporal analysis of satellite imagery•Analysis of Australian Landsat data from 1987 to 2014 for surface water•Details an operational, continental-scale surface water product suite•Provides a confidence assessment method for very large classifications
Monitoring the spatiotemporal dynamics of surface water from remote sensing imagery is essential for understanding water's impact on the global ecosystem and climate change. There is often a tradeoff ...between the spatial and temporal resolutions of imagery acquired from current satellite sensors and as such various spatiotemporal image fusion methods have been explored to circumvent the challenges this situation presents (e.g., STARFM). However, some challenges persist in mapping surface water at the desired fine spatial and temporal resolution. Principally, the spatiotemporal changes of water bodies are often abrupt and controlled by topographic conditions, which are usually unaddressed in current spatiotemporal image fusion methods. This paper proposes the SpatioTemporal Surface Water Mapping (STSWM) method, which aims to predict Landsat-like, 30 m, surface water maps at an 8-day time step (same as the MODIS 8-day composite product) by integrating topographic information into the analysis. In addition to MODIS imagery acquired on the date of map prediction and a pair of MODIS and Landsat images acquired temporally close to the date of prediction, STSWM also uses the surface water occurrence (SWO, which represents the frequency with which water is present in a pixel) and DEM data to provide, respectively, topographic information below and above the water surface. These data are used to translate the coarse spatial resolution water distribution representation observed by MODIS into a 30 m spatial resolution water distribution map. The STSWM was used to generate an 8-day time series surface water maps of 30 m resolution in six inundation regions globally, and was compared with several other state-of-the-art spatiotemporal methods. The stratified random sampling design was used, and unbiased estimators of the accuracies were provided. The results show that STSWM generated the most accurate surface water map in which the spatial details of surface water were well-represented.
•STSWM is a new spatiotemporal fusion method applied to surface water mapping•Water occurrence data and DEM indicated bathymetry and above-water topography•STSWM generates 30 m surface water map at an 8-day time step•STSWM outperformed other methods in heterogeneous landscapes
As one of main directions of green mining, short-wall block backfill mining (SBBM) could provide active control of water-conducting fractures development and strata movement. Furthermore, it could ...solve the problem of gangue accumulation on surface. According to the physical similarity criterion and the characteristics of SBBM technology, the protection effect for surface water resources of SBBM was studied by physical similarity simulation tests. The results of tests had shown that SBBM decreased the water-conducting fractures development caused by strata movement after coal mining, and it has a significant effect in protecting surface water resources above the working face. Therefore, based on movement characteristics of overlying strata using SBBM, a mechanical analysis model was established under SBBM for a superimposed beams in elastic foundation with extended water-conducting fractures in overlying strata, furthermore, a method to calculate the height of water-conducting fractured zone (HWFZ) in SBBM was given, and the mechanical mechanism of water-conducting fractures development in overlying strata was revealed. The calculated HWFZ after SBM was only 2.0 m according to the mechanical model, whereas the measured HWFZ of the washing fluid loss and drilling TV imaging was 6.3 m in experimental SBBM working face. The field-measured data was closely consistent with the results of the tests (7.9 m) and the mechanical calculation (2.0 m), which verified the accuracy of physical similarity simulation tests and the mechanical model. The results of the study will enhance the recovery rate of coal resources, and they have a significant for protection of the ecological environment.
Display omitted
•SBBM was proposed to recover coal seam under surface water.•Surface water resources protection effect using SBBM was analyzed by physical tests.•Mechanical mechanism of water-conducting fractures development was explained.•A method was proposed to calculate HWFZ in SBBM.
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