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1.
While restoring hyporheic flowpaths has been cited as a benefit to stream restoration structures, little documentation exists confirming that constructed restoration structures induce comparable hyporheic exchange to natural stream features. This study compares a stream restoration structure (cross‐vane) to a natural feature (riffle) concurrently in the same stream reach using time‐lapsed electrical resistivity (ER) tomography. Using this hydrogeophysical approach, we were able to quantify hyporheic extent and transport beneath the cross‐vane structure and the riffle. We interpret from the geophysical data that the cross‐vane and the natural riffle induced spatially and temporally unique hyporheic extent and transport, and the cross‐vane created both spatially larger and temporally longer hyporheic flowpaths than the natural riffle. Tracer from the 4.67‐h injection was detected along flowpaths for 4.6 h at the cross‐vane and 4.2 h at the riffle. The spatial extent of the hyporheic zone at the cross‐vane was 12% larger than that at the riffle. We compare ER results of this study to vertical fluxes calculated from temperature profiles and conclude significant differences in the interpretation of hyporheic transport from these different field techniques. Results of this study demonstrate a high degree of heterogeneity in transport metrics at both the cross‐vane and the riffle and differences between the hyporheic flowpath networks at the two different features. Our results suggest that restoration structures may be capable of creating sufficient exchange flux and timescales of transport to achieve the same ecological functions as natural features, but engineering of the physical and biogeochemical environment may be necessary to realize these benefits.  相似文献   

2.
Ground water discharge is often a significant factor in the quality of fish spawning and rearing habitat and for highly biologically productive streams. In the present study, water temperatures (stream and hyporheic) and seepage fluxes were used to characterize shallow ground water discharge and recharge within thestreambed of Catamaran Brook, a small Atlantic salmon (Salmo salar) stream in central New Brunswick, Canada. Three study sites were instrumented using a total of 10 temperature sensors and 18 seepage meters. Highly variable mean seepage fluxes, ranging from 1.7 x 10(-4) to 2.5 cm3 m(-2) sec(-1), and mean hyporheic water temperatures, ranging from 10.5 degrees to 18.0 degrees C, at depths of 20 to 30 cm in the streambed were dependent on streambed location (left versus right stream bank and site location) and time during the summer sampling season. Temperature data were usefulfor determining if an area of the streambed was under discharge (positive flux), recharge (negative flux), or parallel flow (no flux) conditions and seepage meters were used to directly measure the quantity of water flux. Hyporheic water temperature measurements and specific conductance measurements of the seepage meter sample water, mean values ranging from 68.8 to 157.9 microS/cm, provided additional data for determining flux sources. Three stream banks were consistently under discharge conditions, while the other three stream banks showed reversal from discharge to recharge conditions over the sampling season. Results indicate that the majority of the water collected in the seepage meters was composed of surface water. The data obtained suggests that even though a positive seepage flux is often interpreted as ground water discharge, this discharging water may be of stream water origin that has recently entered the hyporheic zone.The measurement of seepage flux in conjunction with hyporheic water temperature or other indicators of water origin should be considered when attempting to quantify the magnitude of exchange and the source of hyporheic water.  相似文献   

3.
Stream temperature is a critical water quality parameter that is not fully understood, particularly in urban areas. This study explores drivers contributing to stream temperature variability within an urban system, at 21 sites within the Philadelphia region, Pennsylvania, USA. A comprehensive set of temperature metrics were evaluated, including temperature sensitivity, daily maximum temperatures, time >20°C, and temperature surges during storms. Wastewater treatment plants (WWTPs) were the strongest driver of downstream temperature variability along 32 km in Wissahickon Creek. WWTP effluent temperature controlled local (1–3 km downstream) temperatures year-round, but the impacts varied seasonally: during winter, local warming of 2–7°C was consistently observed, while local cooling up to 1°C occurred during summer. Summer cooling and winter warming were detected up to 12 km downstream of a WWTP. Comparing effects from different WWTPs provided guidelines for mitigating their thermal impact; WWTPs that discharged into larger streams, had cooler effluent, or had lower discharge had less effect on stream temperatures. Comparing thermal regimes in four urban headwater streams, sites with more local riparian canopy had cooler maximum temperatures by up to 1.5°C, had lower temperature sensitivity, and spent less time at high temperatures, although mean temperatures were unaffected. Watershed-scale impervious area was associated with increased surge frequency and magnitude at headwater sites, but most storms did not result in a surge and most surges had a low magnitude. These results suggest that maintaining or restoring riparian canopy in urban settings will have a larger impact on stream temperatures than stormwater management that treats impervious area. Mitigation efforts may be most impactful at urban headwater sites, which are particularly vulnerable to stream temperature disruptions. It is vital that stream temperature impacts are considered when planning stormwater management or stream restoration projects, and the appropriate metrics need to be considered when assessing impacts.  相似文献   

4.
This study compared summer stream temperature between two years in the Star Creek catchment, Alberta, a headwater basin on the eastern slopes of the Canadian Rocky Mountains. Star Creek is a subsurface water dominated stream, which represents important habitat for native salmonid species. Hydrometeorological data from May to September of 2010 and 2011 accompanied by stream energy budget calculations were used to describe the drivers of stream temperature in this small forested stream. Mean, maximum, and minimum weekly stream temperatures were lower from May to August and higher in September 2011 compared to 2010. Weekly range in stream temperature was also different between years with a higher range in 2010. Inter‐annual stream temperature variation was attributed discharge differences between years, shown to be primarily governed by catchment‐scale moisture conditions. This study demonstrates that both meteorological and hydrological processes must be considered in order to understand stream temperature response to changing environmental conditions in mountainous regions. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

5.
Urbanization threatens headwater stream ecosystems globally. Watershed restoration practices, such as infiltration‐based stormwater management, are implemented to mitigate the detrimental effects of urbanization on aquatic ecosystems. However, their effectiveness for restoring hydrologic processes and watershed storage remains poorly understood. Our study used a comparative hydrology approach to quantify the effects of urban watershed restoration on watershed hydrologic function in headwater streams within the Coastal Plain of Maryland, USA. We selected 11 headwater streams that spanned an urbanization–restoration gradient (4 forested, 4 urban‐degraded, and 3 urban‐degraded) to evaluate changes in watershed hydrologic function from both urbanization and watershed restoration. Discrete discharge and continuous, high‐frequency rainfall‐stage monitoring were conducted in each watershed. These datasets were used to develop 6 hydrologic metrics describing changes in watershed storage, flowpath connectivity, or the resultant stream flow regime. The hydrological effects of urbanization were clearly observed in all metrics, but only 1 of the 3 restored watersheds exhibited partially restored hydrologic function. At this site, a larger minimum runoff threshold was observed relative to the urban‐degraded watersheds, suggesting enhanced infiltration of stormwater runoff within the restoration structure. However, baseflow in the stream draining this watershed remained low compared to the forested reference streams, suggesting that enhanced infiltration of stormwater runoff did not recharge subsurface storage zones contributing to stream baseflow. The highly variable responses among the 3 restored watersheds were likely due to the spatial heterogeneity of urban development, including the level of impervious cover and extent of the storm sewer network. This study yielded important knowledge on how restoration strategies, such as infiltration‐based stormwater management, modulated—or failed to modulate—hydrological processes affected by urbanization, which will help improve the design of future urban watershed management strategies. More broadly, we highlighted a multimetric approach that can be used to monitor the restoration of headwater stream ecosystems in disturbed landscapes.  相似文献   

6.
The spatial and temporal variability of groundwater–surface‐water (GW–SW) interactions was investigated in an intensively utilized salmon spawning riffle. Hydrochemical tracers, were used along with high‐resolution hydraulic head and temperature data to assess hyporheic dynamics. Surface and subsurface hydrochemistry were monitored at three locations where salmon spawning had been observed in previous years. Temperature and hydraulic head were monitored in three nests of three piezometers located to characterize the head, the run and the tail‐out of the riffle feature. Hydrochemical gradients between surface and subsurface water indicated increasing GW influence with depth into the hyporheic zone. Surface water was characterized by high dissolved oxygen (DO) concentrations, low alkalinity and conductivity. Hyporheic water was generally characterized by high levels of alkalinity and conductivity indicative of longer residence times, and low DO, indicative of reducing conditions. Hydrochemical and temperature gradients varied spatially over the riffle in response to changes in local GW–SW interactions at the depths investigated. Groundwater inputs dominated the head and tail of the riffle. The influence of SW increased in the area of accelerating flow and decreasing water depth through the run of the riffle. Temporal GW–SW interactions also varied in response to changing hydrological conditions. Gross changes in hyporheic hydrochemistry were observed at the weekly scale in response to changing flow conditions and surface water inputs to the hyporheic zone. During low flows, caused by freezing or dry weather, hyporheic hydrochemistry was dominated by GW inputs. During higher flows hyporheic hydrochemistry indicated that SW contributions increased. In addition, high‐resolution hydraulic head data indicated that rapid changes in GW–SW interactions occurred during hydrological events. The spatial, and possibly the temporal, variability of GW–SW interactions had a marked effect on the survival of salmon ova. It is concluded that hyporheic dynamics and their effect on stream ecology should be given increased consideration by fisheries and water resource managers. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

7.
Stream–subsurface water interaction induced by natural riffles and constructed riffles/steps was examined in lowland streams in southern Ontario, Canada. The penetration of stream water into the subsurface was analysed using hydrometric data, and the zone of > 10% stream water was calculated from a chemical mixing equation using tracer injection of bromide and background chloride concentrations. The constructed riffles studied induced more extensive hyporheic exchange than the natural riffles because of their steeper longitudinal hydraulic head gradients and coarser streambed sediments. The depth of > 10% stream water zone in a small and a large constructed riffle extended to > 0·2 m and > 1·4 m depths respectively. Flux and residence time distribution of hyporheic exchange were simulated in constructed riffles using MODFLOW, a finite‐difference groundwater flow model. Hyporheic flux and residence time distribution varied along the riffles, and the exchange occurring upstream from the riffle crest was small in flux and had a long residence time. In contrast, hyporheic exchange occurring downstream from the riffle crest had a relatively short residence time and accounted for 83% and 70% of total hyporheic exchange flow in a small and large riffle respectively. Although stream restoration projects have not considered the hyporheic zone, our data indicate that constructed riffles and steps can promote vertical hydrologic exchange and increase the groundwater–surface water linkage in degraded lowland streams. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

8.
Biological and hydromorphological integrity of five reaches of the small urban stream were assessed. Because macroinvertebrate communities respond to both organic pollution and habitat change, impacts of both measures can be hardly separated. In our study on the urbanized small stream, an impact of organic pollution was excluded as all five sampling sites were assessed as moderately polluted. On the other hand differences in morphological degradation of banks and channel of selected sites enabled us to relate hydromorphological stress and biotic metrics and taxa. Physical habitat quality was assessed using River habitat survey (RHS) methodology. A downstream-upstream gradient of physical habitat degradation was observed and related to the macroinvertebrate community characteristics. Similarity analyses and biotic metrics were calculated and correlated with results of the RHS analyses. Composition of the macroinvertebrate assemblages did not follow the longitudinal pattern of habitat modification observed by the RHS analysis. However, some metrics corresponded well. Percentage of detritivores, percentage of Caenis luctuosa, number of individuals, percentage of EPT individuals were best predictors of changes in the physical habitat quality. However, the metric percentage of EPT individuals was negatively correlated to the habitat degradation, what is in contradiction with results from studies of other authors.  相似文献   

9.
Steven M. Wondzell 《水文研究》2011,25(22):3525-3532
Many hyporheic papers state that the hyporheic zone is a critical component of stream ecosystems, and many of these papers focus on the biogeochemical effects of the hyporheic zone on stream solute loads. However, efforts to show such relationships have proven elusive, prompting several questions: Are the effects of the hyporheic zone on stream ecosystems so highly variable in place and time (or among streams) that a consistent relationship should not be expected? Or, is the hyporheic zone less important in stream ecosystems than is commonly expected? These questions were examined using data from existing groundwater modelling studies of hyporheic exchange flow at five sites in a fifth‐order, mountainous stream network. The size of exchange flows, relative to stream discharge (QHEF:Q), was large only in very small streams at low discharge (area ≈ 100 ha; Q < 10 l/s). At higher flows (flow exceedance probability > 0·7) and in all larger streams, QHEF:Q was small. These data show that biogeochemical processes in the hyporheic zone of small streams can substantially influence the stream's solute load, but these processes become hydrologically constrained at high discharge or in larger streams and rivers. The hyporheic zone may influence stream ecosystems in many ways, however, not just through biogeochemical processes that alter stream solute loads. For example, the hyporheic zone represents a unique habitat for some organisms, with patterns and amounts of upwelling and downwelling water determining the underlying physiochemical environment of the hyporheic zone. Similarly, hyporheic exchange creates distinct patches of downwelling and upwelling. Upwelling environments are of special interest, because upwelling water has the potential to be thermally or chemically distinct from stream water. Consequently, micro‐environmental patches created by hyporheic exchange flows are likely to be important to biological and ecosystem processes, even if their impact on stream solute loads is small. Published in 2011 by John Wiley & Sons, Ltd.  相似文献   

10.
In‐channel rock vane structures are widely used in stream restoration as a way to reduce stream channel erosion and create pool or riffle features. When these structures change hydraulic gradients they may affect ecological stream functions, such as hyporheic exchange flow (HEF) patterns. A study of constructed in‐channel structure controls on HEF was conducted in the third‐order Batavia Kill, New York using stream and hyporheic temperature amplitude analysis and computational fluid dynamics (CFD) hydraulic simulations. Temperature monitors were installed in the water column and channel bed at six locations around each of seven in‐channel restoration structures (three cross‐vanes and four J‐hooks) at baseflow in 2007. Elevation surveys of the structures were then used to simulate HEF using CFD. The results indicate a pattern of pronounced upwelling in the run section just below the structure, upwelling transitioning to downwelling within the pool, and pronounced downwelling in the glide out of the pool. This pattern is consistent with natural riffle pool sequences. The direction of HEF inferred from the temperature amplitude analysis agreed with the direction of flow simulated with CFD at 80% of the locations, and the few disagreements were expected due to model limitations. CFD simulation demonstrated that increasing stream flows result in changes in HEF spatial patterns and magnitude at each structure. This work illustrates how CFD simulations can guide design of in‐channel restoration structures for HEF function. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

11.
Spatial and temporal variability in ground water–surface water interactions in the hyporheic zone of a salmonid spawning stream was investigated. Four locations in a 150‐m reach of the stream were studied using hydrometric and hydrochemical tracing techniques. A high degree of hydrological connectivity between the riparian hillslope and the stream channel was indicated at two locations, where hydrochemical changes and hydraulic gradients indicated that the hyporheic zone was dominated by upwelling ground water. The chemistry of ground water reflected relatively long residence times and reducing conditions with high levels of alkalinity and conductivity, low dissolved oxygen (DO) and nitrate. At the other locations, connectivity was less evident and, at most times, the hyporheic zone was dominated by downwelling stream water characterized by high DO, low alkalinity and conductivity. Substantial variability in hyporheic chemistry was evident at fine (<10 m) spatial scales and changed rapidly over the course of hydrological events. The nature of the hydrochemical response varied among locations depending on the strength of local ground water influence. It is suggested that greater emphasis on spatial and temporal heterogeneity in ground water–surface water interactions in the hyporheic zone is necessary for a consideration of hydrochemical effects on many aspects of stream ecology. For example, the survival of salmonid eggs in hyporheic gravels varied considerably among the locations studied and was shown to be associated with variation in interstitial chemistry. River restoration schemes and watershed management strategies based only on the surface expression of catchment characteristics risk excluding consideration of potentially critical subsurface processes. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

12.
Stream restoration goals include improving habitat and water quality through reconstruction of morphological features found at analogous, pristine stream reaches. Enhancing hyporheic exchange may facilitate achieving these goals. Although hyporheic exchange at restoration sites has been explored in a few previous studies, comparative studies of restored versus reference or control streams are largely absent. We hypothesized that restoration cross‐vanes enhance hyporheic exchange, resulting in biogeochemical alteration of stream water chemistry in the streambed. Two streams restored using cross‐vanes to control erosion and improve habitat were compared with their associated reference reaches, which provided the basis for the restoration design. Thirteen temperature profile rods with vertically stacked sensors were installed at each site for 2 weeks. Heat tracing was used to quantify vertical flux in the streambed from the diurnal temperature fluctuations in the subsurface. Stream water and bed pore waters from mini‐piezometers were analysed for ion and nutrient chemistry. In general, mean vertical flux rates through the streambed were small throughout reference sites (?0.3 to 0.3 m/day) and at most locations at restored sites. Immediately adjacent to cross‐vanes, vertical flux rates were larger (up to 3.5 m/day). Geochemistry of pore waters shows distinct differences in the sources for the reference and restored sites. Strong downwelling zones adjacent to cross‐vanes showed high dissolved oxygen (10.75 mg/l) and geochemistry in the streambed similar to surface water. Reference sites had lower dissolved oxygen in the streambed (0.66–5.14 mg/l), and geochemical patterns suggest a mixture of discharging groundwater and surface water in the hyporheic zone. Restored sites also clearly show sulfate and nitrate reduction occurring in the streambed, which is not observed at the reference sites. The stream restoration sites studied here enhance rapid hyporheic exchange, but upwelling of groundwater has a stronger influence on streambed geochemistry at reference sites. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

13.
Although there has been recent focus on understanding spatial variability in hyporheic zone geochemistry across different morphological units under baseflow conditions, less attention has been paid to temporal responses of hyporheic zone geochemistry to non‐steady‐state conditions. We documented spatial and temporal variability of hyporheic zone geochemistry in response to a large‐scale storm event, Tropical Storm Irene (August 2011), across a pool–riffle–pool sequence along Chittenango Creek in Chittenango, NY, USA. We sampled stream water as well as pore water at 15 cm depth in the streambed at 14 locations across a 30 m reach. Sampling occurred seven times at daily intervals: once during baseflow conditions, once during the rising limb of the storm hydrograph, and five times during the receding limb. Principal component analysis was used to interpret temporal and spatial changes and dominant drivers in stream and pore water geochemistry (n = 111). Results show the majority of spatial variance in hyporheic geochemistry (62%) is driven by differential mixing of stream and ground water in the hyporheic zone. The second largest driver (17%) of hyporheic geochemistry was temporal dilution and enrichment of infiltrating stream water during the storm. Hyporheic sites minimally influenced by discharging groundwater (‘connected’ sites) showed temporal changes in water chemistry in response to the storm event. Connected sites within and upstream of the riffle reflected stream geochemistry throughout the storm, whereas downstream sites showed temporally lagged responses in some conservative and biogeochemically reactive solutes. This suggests temporal changes in hyporheic geochemistry at these locations reflect a combination of changes in infiltrating stream chemistry and hyporheic flowpath length and residence time. The portion of the study area strongly influenced by groundwater discharge increased in size throughout the storm, producing elevated Ca2+ and concentrations in the streambed, suggesting zones of localized groundwater inputs expand in response to storms. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

14.
There is a need to identify measurable characteristics of stream channel morphology that vary predictably throughout stream networks and that influence patterns of hyporheic exchange flow in mountain streams. In this paper we characterize stream longitudinal profiles according to channel unit spacing and the concavity of the water surface profile. We demonstrate that: (1) the spacing between zones of upwelling and downwelling in the beds of mountain streams is closely related to channel unit spacing; (2) the magnitude of the vertical hydraulic gradients (VHGs) driving hyporheic exchange flow increase with increasing water surface concavity, measured at specific points along the longitudinal profile; (3) channel unit spacing and water surface concavity are useful metrics for predicting how patterns in hyporheic exchange vary amongst headwater and mid‐order streams. We use regression models to describe changes in channel unit spacing and concavity in longitudinal profiles for 12 randomly selected stream reaches spanning 62 km2 in the H.J. Andrews Experimental Forest in Oregon. Channel unit spacing increased significantly, whereas average water surface concavity (AWSC) decreased significantly with increasing basin area. Piezometer transects installed longitudinally in a subset of stream reaches were used to measure VHG in the hyporheic zone, and to determine the location of upwelling and downwelling zones. Predictions for median pool length and median distance between steps in piezometer reaches bracketed the median distance separating zones of upwelling in the stream bed. VHG in individual piezometers increased with increasing water surface concavity at individual points in the longitudinal profile along piezometer transects. Absolute values of VHG, averaged throughout piezometer transects, increased with increasing AWSC, indicating increased potential for hyporheic exchange flow. These findings suggest that average hyporheic flow path lengths increase—and the potential for hyporheic exchange flow in stream reaches decreases—along the continuum from headwater to mid‐order mountain streams. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

15.
This paper focuses on surface–subsurface water exchange in a steep coarse‐bedded stream with a step‐pool morphology. We use both flume experiments and numerical modelling to investigate the influence of stream discharge, channel slope and sediment hydraulic conductivity on hyporheic exchange. The model step‐pool reach, whose topography is scaled from a natural river, consists of three step‐pool units with 0.1‐m step heights, discharges ranging between base and over‐bankfull flows (scaled values of 0.3–4.5 l/s) and slopes of 4% and 8%. Results indicate that the deepest hyporheic flow occurs with the steeper slope and at moderate discharges and that downwelling fluxes at the base of steps are highest at the largest stream discharges. In contrast to findings in a pool‐riffle morphology, those in this study show that steep slopes cause deeper surface–subsurface exchanges than gentle slopes. Numerical simulation results show that the portion of the hyporheic zone influenced by surface water temperature increases with sediment hydraulic conductivity. These experiments and numerical simulations emphasize the importance of topography, sediment permeability and roughness elements along the channel surface in governing the locations and magnitude of downwelling fluxes and hyporheic exchange. Our results show that hyporheic zones in these steep streams are thicker than previously expected by extending the results from streams with pool‐riffle bed forms. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

16.
Hyporheic exchange increases the potential for solute retention in streams by slowing downstream transport and increasing solute contact with the substrate. Hyporheic exchange may be a major mechanism to remove nutrients in semi‐arid watersheds, where livestock have damaged stream riparian zones and contributed nutrients to stream channels. Debris dams, such as beaver dams and anthropogenic log dams, may increase hyporheic interactions by slowing stream water velocity, increasing flow complexity and diverting water to the subsurface. Here, we report the results of chloride tracer injection experiments done to evaluate hyporheic interaction along a 320 m reach of Red Canyon Creek, a second order stream in the semi‐arid Wind River Range of Wyoming. The study site is part of a rangeland watershed managed by The Nature Conservancy of Wyoming, and used as a hydrologic field site by the University of Missouri Branson Geologic Field Station. The creek reach we investigated has debris dams and tight meanders that hypothetically should enhance hyporheic interaction. Breakthrough curves of chloride measured during the field experiment were modelled with OTIS‐P, a one‐dimensional, surface‐water, solute‐transport model from which we extracted the storage exchange rate α and cross‐sectional area of the storage zone As for hyporheic exchange. Along gaining reaches of the stream reach, short‐term hyporheic interactions associated with debris dams were comparable to those associated with severe meanders. In contrast, along the non‐gaining reach, stream water was diverted to the subsurface by debris dams and captured by large‐scale near‐stream flow paths. Overall, hyporheic exchange rates along Red Canyon Creek during snowmelt recession equal or exceed exchange rates observed during baseflow at other streams. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

17.
This pilot study uses a chemical technique (KEtX) to establish vertical profiles of average monthly water temperature within river beds: the hyporheic zone at the interface between surface water and groundwater. Data are presented for two gravel-bed sites and one sand-bed site on the River Wissey, Norfolk, UK. From February to October 1992, average monthly temperatures were determined at 10cm intervals down 1 m profiles. A strong seasonal pattern was defined at all sites with hyporheic temperatures being relatively warm in winter and cool in summer. Isothermal periods occurred in March-April and September-October. Temperature ranges within the hyporheic were decreased (4.6–7.7°C) compared with those of surface waters (10 and 10.9°C). Temperature profiles were similar at all sites during winter, but the sand-bed site had relatively low temperatures at a standard depth within the hyporheic during summer and the temperature gradient became isothermal later in the autumn at this site. It is suggested that the influence of flows and substratum characteristics on temperature patterns, especially in regulated rivers, may have significant ecological implications, for example for determining the timing of salmonid fry and invertebrate emergence.  相似文献   

18.
Stream temperature is a key physical water‐quality parameter, controlling many biological, chemical, and physical processes in aquatic ecosystems. Maintenance of cool stream temperatures during summer is critical for high‐quality aquatic habitat. As such, transmission of warm water from small, nonfish‐bearing headwater streams after forest harvesting could cause warming in downstream fish‐bearing stream reaches with negative consequences. In this study, we evaluate (a) the effects of contemporary forest management practices on stream temperature in small, headwater streams, (b) the transmission of thermal signals from headwater reaches after harvesting to downstream fish‐bearing reaches, and (c) the relative role of lithology and forest management practices in influencing differential thermal responses in both the headwater and downstream reaches. We measured summer stream temperatures both preharvest and postharvest at 29 sites—12 upstream sites (4 reference, 8 harvested) and 17 downstream sites (5 reference, 12 harvested)—across 3 paired watershed studies in western Oregon. The 7‐day moving average of daily maximum stream temperature (T7DAYMAX) was greater during the postharvest period relative to the preharvest period at 7 of the 8 harvested upstream sites. Although the T7DAYMAX was generally warmer in the downstream direction at most of the stream reaches during both the preharvest and postharvest period, there was no evidence for additional downstream warming related to the harvesting activity. Rather, the T7DAYMAX cooled rapidly as stream water flowed into forested reaches ~370–1,420 m downstream of harvested areas. Finally, the magnitude of effects of contemporary forest management practices on stream temperature increased with the proportion of catchment underlain by more resistant lithology at both the headwater and downstream sites, reducing the potential for the cooling influence of groundwater.  相似文献   

19.
Riparian land use is a key driver of stream ecosystem processes but its effects on water quality are still a matter of debate when proposing measures to improve freshwater quality. The aim of this study was to examine the influence of riparian land use on stream habitat and water chemistry, and to assess in what extent stream habitat also affects water quality. To that end, we selected eight reaches in the Ave River basin (northwestern Portugal) and compared longitudinal variations in water chemistry and stream habitat between reaches with different land use (urban, agricultural and natural), and between reaches with natural riparian areas and different habitats. Stream habitat was assessed using the Fluvial Functional Index, the HABSCORE, and the Riparian Forest Quality Index. Longitudinal variations in water chemistry were determined measuring differences in concentrations of ammonium, nitrate, phosphate and oxygen, and conductivity, pH and temperature between the downstream and the upstream ends of each reach. Nitrate concentration tended to decrease along reaches with more natural riparian areas and to increase along reaches with more urban and agricultural land uses. Longitudinal variations in water chemistry also differed between reaches with natural riparian areas, suggesting that water quality also depends on stream habitat. Moreover, longitudinal variation in water chemistry was proven a simple, useful and low-cost approach to assess the influence of land cover and stream habitat on water quality. Overall results demonstrated that both riparian land use and stream habitat influence water quality and that riparian forests are essential to reduce nutrient export to downstream ecosystems.  相似文献   

20.
Temporal Hyporheic Zone Response to Water Table Fluctuations   总被引：1，自引：0，他引：1       下载免费PDF全文
Expansion and contraction of the hyporheic zone due to temporal hydrologic changes between stream and riparian aquifer influence the biogeochemical cycling capacity of streams. Theoretical studies have quantified the control of groundwater discharge on the depth of the hyporheic zone; however, observations of temporal groundwater controls are limited. In this study, we develop the concept of groundwater‐dominated differential hyporheic zone expansion to explain the temporal control of groundwater discharge on the hyporheic zone in a third‐order stream reach flowing through glacially derived terrain typical of the Great Lakes region. We define groundwater‐dominated differential expansion of the hyporheic zone as: differing rates and magnitudes of hyporheic zone expansion in response to seasonal vs. storm‐related water table fluctuation. Specific conductance and vertical hydraulic gradient measurements were used to map changes in the hyporheic zone during seasonal water table decline and storm events. Planar and riffle beds were monitored in order to distinguish the cause of increasing hyporheic zone depth. Planar bed seasonal expansion of the hyporheic zone was of a greater magnitude and longer in duration (weeks to months) than storm event expansion (hours to days). In contrast, the hyporheic zone beneath the riffle bed exhibited minimal expansion in response to seasonal groundwater decline compared to storm related expansion. Results indicated that fluctuation in the riparian water table controlled seasonal expansion of the hyporheic zone along the planar bed. This groundwater induced hyporheic zone expansion could increase the potential for biogeochemical cycling and natural attenuation.  相似文献   

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