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1.
Headwater streams are critical components of drainage systems, directly connecting terrestrial and downstream aquatic ecosystems. The amount of water in a stream can alter hydrologic connectivity between the stream and surrounding landscape and is ultimately an important driver of what constituents headwater streams transport. There is a shortage of studies that explore concentration–discharge (C‐Q) relationships in headwater systems, especially forested watersheds, where the hydrological and ecological processes that control the processing and export of solutes can be directly investigated. We sought to identify the temporal dynamics and spatial patterns of stream chemistry at three points along a forested headwater stream in Northern Michigan and utilize C‐Q relationships to explore transport dynamics and potential sources of solutes in the stream. Along the stream, surface flow was seasonal in the main stem, and perennial flow was spatially discontinuous for all but the lowest reaches. Spring snowmelt was the dominant hydrological event in the year with peak flows an order of magnitude larger at the mouth and upper reaches than annual mean discharge. All three C‐Q shapes (positive, negative, and flat) were observed at all locations along the stream, with a higher proportion of the analytes showing significant relationships at the mouth than at the mid or upper flumes. At the mouth, positive (flushing) C‐Q shapes were observed for dissolved organic carbon and total suspended solids, whereas negative (dilution) C‐Q shapes were observed for most cations (Na+, Mg2+, Ca2+) and biologically cycled anions (NO3?, PO43?, SO42?). Most analytes displayed significant C‐Q relationships at the mouth, indicating that discharge is a significant driving factor controlling stream chemistry. However, the importance of discharge appeared to decrease moving upstream to the headwaters where more localized or temporally dynamic factors may become more important controls on stream solute patterns.  相似文献   

2.
Stream temperature was recorded between 2002 and 2005 at four sites in a coastal headwater catchment in British Columbia, Canada. Shallow groundwater temperatures, along with bed temperature profiles at depths of 1 to 30 cm, were recorded at 10‐min intervals in two hydrologically distinct reaches beginning in 2003 or 2004, depending on the site. The lower reach had smaller discharge contributions via lateral inflow from the hillslopes and fewer areas with upwelling (UW) and/or neutral flow across the stream bed compared to the middle reach. Bed temperatures were greater than those of shallow groundwater during summer, with higher temperatures in areas of downwelling (DW) flow compared to areas of neutral and UW flow. A paired‐catchment analysis revealed that partial‐retention forest harvesting in autumn 2004 resulted in higher daily maximum stream and bed temperatures but smaller changes in daily minima. Changes in daily maximum stream temperature, averaged over July and August of the post‐harvest year, ranged from 1.6 to 3 °C at different locations within the cut block. Post‐harvest changes in bed temperature in the lower reach were smaller than the changes in stream temperature, greater at sites with DW flow, and decreased with depth at both UW and DW sites, dropping to about 1 °C at a depth of 30 cm. In the middle reach, changes in daily maximum bed temperature, averaged over July and August, were generally about 1 °C and did not vary significantly with depth. The pre‐harvest regression models for shallow groundwater were not suitable for applying the paired‐catchment analysis to estimate the effects of harvesting. However, shallow groundwater was warmer at the lower reach following harvesting, despite generally cooler weather compared to the pre‐harvest year. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

3.
The headwater catchments of the Yellow River basin generate over 35% of the basin's total stream flow and play a vital role in meeting downstream water resources requirements. In recent years the Yellow River has experienced significant changes in its hydrological regime, including an increased number of zero‐flow days. These changes have serious implications for water security and basin management. We investigated changes in stream flow regime of four headwater catchments since the 1950s. The rank‐based non‐parametric Mann–Kendall test was used to detect trends in annual stream flow. The results showed no significant trend for the period 1956 to 2000. However, change‐point analysis showed that a significant change in annual stream flow occurred around 1990, and hence the stream‐flow data can be divided into two periods: 1956–1990 and 1991–2000. There was a considerable difference in average annual stream flow between the two periods, with a maximum reduction of 51%. Wet‐season rainfall appears to be the main factor responsible for the decreasing trend in annual stream flow. Reductions in annual stream flow were associated with decreased interannual variability in stream flow. Seasonal stream flow distribution changed from bimodal to unimodal between the two periods, with winter stream flow showing a greater reduction than other seasons. Daily stream flow regime represented by flow duration curves showed that all percentile flows were decreased in the second period. The high flow index (Q5/Q50) reduced by up to 28%, whereas the reduction in the low flow index (Q95/Q50) is more dramatic, with up to 100% reduction. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

4.
Assessment of potential climate change impacts on stream water temperature (Ts) across large scales remains challenging for resource managers because energy exchange processes between the atmosphere and the stream environment are complex and uncertain, and few long‐term datasets are available to evaluate changes over time. In this study, we demonstrate how simple monthly linear regression models based on short‐term historical Ts observations and readily available interpolated air temperature (Ta) estimates can be used for rapid assessment of historical and future changes in Ts. Models were developed for 61 sites in the southeastern USA using ≥18 months of observations and were validated at sites with longer periods of record. The Ts models were then used to estimate temporal changes in Ts at each site using both historical estimates and future Ta projections. Results suggested that the linear regression models adequately explained the variability in Ts across sites, and the relationships between Ts and Ta remained consistent over 37 years. We estimated that most sites had increases in historical annual mean Ts between 1961 and 2010 (mean of +0.11 °C decade?1). All 61 sites were projected to experience increases in Ts from 2011 to 2060 under the three climate projections evaluated (mean of +0.41 °C decade?1). Several of the sites with the largest historical and future Ts changes were located in ecoregions home to temperature‐sensitive fish species. This methodology can be used by resource managers for rapid assessment of potential climate change impacts on stream water temperature. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

5.
Forest harvesting often increases catchment quickflow (QF, water delivered rapidly to the stream channel), a metric of high‐flow events controlling a catchment's solute and sediment export. Nevertheless, our understanding of QF responses to various silvicultural strategies (e.g., clearcutting, selection harvest, and shelterwood harvest) is incomplete. We present a 31‐year examination of QF delivery from treatment (clearcut, selection harvest, and shelterwood harvest) and control catchments in a deciduous forest landscape in central Ontario, Canada. Growing season root‐zone storage capacity was estimated using a water balance approach to evaluate temporal changes in QF response to precipitation (P) for pretreatment and posttreatment periods. Threshold relationships between QF and P were assessed for control and treatment catchments for pretreatment and posttreatment periods using piecewise regression. Root‐zone storage capacity demarcated shifts in the hydrologic regime arising from forest harvesting and subsequent regeneration. This was particularly pronounced for clearcutting where postharvest decline in root‐zone storage capacity was followed by a rise to preharvest values. Similar pretreatment threshold relationships between QF and P, and near‐identical P thresholds for producing significant QF, reflected similar soil and overburden depths in the catchments. Harvesting effects were indicated by increases in QF/P ratios for relative small P and the number of P events that generated QF, thus changing treatment QF vs. P threshold relationships. Prior to harvesting there was no significant increase in QF with P below a threshold P of 35–45 mm; however, there was a significant QF vs. P relationship below this threshold for all treatments postharvest. Clearcutting increased the number of QF events for the entire postharvest period and the first 9‐year postharvest compared to the other treatments; nevertheless, evidence for intertreatment differences in total QF depth delivered from the catchments during the growing season was inconclusive. Our work suggests that changes in threshold relationships between QF and P, coupled with knowledge of the physical processes underlying them, are useful when evaluating hydrologic responses to forest harvesting.  相似文献   

6.
This study investigates trends in bed surface and substrate grain sizes in relation to reach‐scale hydraulics using data from more than 100 gravel‐bed stream reaches in Colorado and Utah. Collocated measurements of surface and substrate sediment, bankfull channel geometry and channel slope are used to examine relations between reach‐average shear stress and bed sediment grain size. Slopes at the study sites range from 0·0003 to 0·07; bankfull depths range from 0·2 to 5 m and bankfull widths range from 2 to 200 m. The data show that there is much less variation in the median grain size of the substrate, D50s, than there is in the median grain size of the surface, D50; the ratio of D50 to D50s thus decreases from about four in headwater reaches with high shear stress to less than two in downstream reaches with low shear stress. Similar trends are observed in an independent data set obtained from measurements in gravel‐bed streams in Idaho. A conceptual quantitative model is developed on the basis of these observations to track differences in bed load transport through an idealized stream system. The results of the transport model suggest that downstream trends in total bed load flux may vary appreciably, depending on the assumed relation between surface and substrate grain sizes. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

7.
Water temperature is a key driver for riverine biota and strongly depends on shading by woody riparian vegetation in summer. While the general effects of shading on daily maximum water temperature Tmax are well understood, knowledge gaps on the role of the spatial configuration still exist. In this study, the effect of riparian buffer length, width, and canopy cover (percentage of buffer area covered by woody vegetation) on Tmax was investigated during summer baseflow using data measured in seven small lowland streams in western Germany (wetted width 0.8–3.7 m). The effect of buffer length on Tmax differed between downstream cooling and heating: Tmax approached cooler equilibrium conditions after a distance of 0.4 km (~45 min travel-time) downstream of a sharp increase in canopy cover. In contrast, Tmax continued to rise downstream of a sharp decrease in canopy cover along the whole 1.6 km stream length investigated. The effect of woody vegetation on Tmax depended on buffer width, with changes in canopy cover in a 10 m wide buffer being a better predictor for changes in Tmax compared to a 30 m buffer. The effect of woody vegetation on Tmax was linearly related to canopy cover but also depended on daily temperature range Trange, which itself was governed by cloudiness, upstream canopy cover, and season. The derived empirical relationship indicated that Tmax was reduced by −4.6°C and increased by +2.7°C downstream of a change from unshaded to fully shaded conditions and vice versa. This maximum effect was predicted for a 10 m wide buffer at sunny days in early summer, in streams with large diel fluctuations (large Trange). Therefore, even narrow woody riparian buffers may substantially reduce the increase in Tmax due to climate change, especially in small shallow headwater streams with low baseflow discharge and large daily temperature fluctuations.  相似文献   

8.
Forest harvesting activities, if not carefully carried out, can disturb the forest soils and can cause significant suspended solid concentration increases in receiving water. This study examined how harvesting, following forestry guidelines, influenced suspended solid concentrations and loads in the receiving water of a blanket peat salmonid catchment. The study site comprised of two forest coupes of 34‐year‐old conifers drained by a first‐order stream. The upper coupe was not felled and acted as a baseline ‘control’ catchment; the downstream coupe was completely harvested in summer 2005 and served as the ‘experimental’ catchment. Good management practices such as the proper use of brash mats and harvesting only in dry weather were implemented to minimize soil surface disturbance and streambank erosion. Stream flow and suspended solid measurements at an upstream station (US) and a downstream station (DS) in the study stream commenced over a year before felling took place. The suspended solid concentrations, yields and release patterns at US and DS were compared before and after harvesting. These showed that post‐guideline harvesting of upland blanket peat forest did not significantly increase the suspended solid concentrations in the receiving water and the aquatic zone need not be adversely affected by soil releases from sites without a buffer strip. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

9.
Although hydrologic responses to land cover changes are often studied using a paired watershed approach, it is not feasible to assess the hydrological effects of many different patterns of land cover alteration by empirical studies alone. An alternative is to use well validated, spatially explicit, physically based numerical models to estimate watershed storage and flux dynamics. The objectives of this study were to assess the sensitivity of watershed flow regimes to several spatial and temporal patterns of forest harvest and recovery in a snow‐dominated mountain watershed. The Distributed Hydrology Soil‐Vegetation Model (DHSVM) was parameterized using 1998–2007 climate data for the 28‐km2 Mica Creek Experimental Watershed (MCEW), a headwater catchment in the inland Pacific Northwest. The modelling experiment indicated that clear‐cutting the entire watershed would increase runoff volume by 79% and 5th percentile flows by 68%. Hydrologic recovery resulting from forest regeneration after clear‐cut harvesting is expected to take up to 25 years to return to baseline conditions, and 50 years to fully recover to preharvest conditions. A more realistic harvesting scenario where the watershed was gradually harvested in a series of clear‐cut blocks allowing for subsequent regeneration to occur was also assessed. This approach reduced the magnitude of hydrologic alteration. Analysis of several other scenarios, defined by aspect, elevation, and distance to the stream network, revealed that flow regime was more sensitive to the amount of alteration rather than pattern and landscape position of disturbance. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

10.
The stable isotopic composition of dissolved inorganic carbon (δ13C‐DIC) was investigated as a potential tracer of streamflow generation processes at the Sleepers River Research Watershed, Vermont, USA. Downstream sampling showed δ13C‐DIC increased between 3–5‰ from the stream source to the outlet weir approximately 0·5 km downstream, concomitant with increasing pH and decreasing PCO2. An increase in δ13C‐DIC of 2·4 ± 0·1‰ per log unit decrease of excess PCO2 (stream PCO2 normalized to atmospheric PCO2) was observed from downstream transect data collected during snowmelt. Isotopic fractionation of DIC due to CO2 outgassing rather than exchange with atmospheric CO2 may be the primary cause of increased δ13C‐DIC values downstream when PCO2 of surface freshwater exceeds twice the atmospheric CO2 concentration. Although CO2 outgassing caused a general increase in stream δ13C‐DIC values, points of localized groundwater seepage into the stream were identified by decreases in δ13C‐DIC and increases in DIC concentration of the stream water superimposed upon the general downstream trend. In addition, comparison between snowmelt, early spring and summer seasons showed that DIC is flushed from shallow groundwater flowpaths during snowmelt and is replaced by a greater proportion of DIC derived from soil CO2 during the early spring growing season. Thus, in spite of effects from CO2 outgassing, δ13C of DIC can be a useful indicator of groundwater additions to headwater streams and a tracer of carbon dynamics in catchments. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

11.
Erosion rates surveyed using 230 erosion pins on 24 occasions over eight years (1994–2001) on forested stream banks, tributaries and forest ditches in the 0·89 km2 Nant Tanllwyth catchment, part of the Hafren Forest on Plynlimon, mid‐Wales, showed statistically significant increases of up to 40 mm a?1 in mean erosion rates during the two‐year period in which environmentally sensitive plot‐scale timber harvesting operations took place (1996–97). In the four years following timber harvesting mean erosion rates at all sites recovered to levels that were lower than before the harvesting operations began. This is attributed to increased light levels, following canopy removal, allowing vegetation to colonize exposed banks. There was a statistically significant relationship (p < 0·05) between mean erosion rate in 2000–01 (four years after harvesting) and percentage vegetation cover at erosion monitoring sites in the clearfelled (south tributaries) area though the same relationship did not hold for sites on the mainstream banks or for sites on the north (mature forest) ditch sites. The implications of natural vegetation colonization for management of such streams are discussed. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

12.
We measured longitudinal spacing and wood volume of channel‐spanning logjams along 30 1‐km reaches of forest streams in the Colorado Front Range, USA. Study streams flow through old‐growth (> 200 year stand age) or younger subalpine conifer forest. Evaluating correlations between the volume and longitudinal spacing of logjams in relation to channel and forest characteristics, we find that old‐growth forest streams have greater in‐stream wood loads and more jams per kilometer than streams in younger forest. Old‐growth forests have a larger basal area close to the stream and correlate with larger piece diameters of in‐stream wood. Jam volume correlates inversely with the downstream spacing for ramp and bridge pieces that can act as key pieces in jams. Most importantly, old‐growth streams have shorter downstream spacing for ramp and bridge pieces (< 20 m). Our results suggest that management of in‐stream wood and associated stream characteristics can be focused most effectively at the reach scale, with an emphasis on preserving old‐growth riparian stands along lower gradient stream reaches or mimicking the effects of old growth by manipulating the spacing of ramp and bridge pieces. Our finding that average downstream spacing between jams declines as wood load increases suggests that the most effective way to create and retain jams is to ensure abundant sources of wood recruitment, with a particular emphasis on larger pieces that are less mobile because they have at least one anchor point outside the active channel. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

13.
Spatial and seasonal variations in CO2 and CH4 concentrations in streamwater and adjacent soils were studied at three sites on Brocky Burn, a headwater stream draining a peatland catchment in upland Britain. Concentrations of both gases in the soil atmosphere were significantly higher in peat and riparian soils than in mineral soils. Peat and riparian soil CO2 concentrations varied seasonally, showing a positive correlation with air and soil temperature. Streamwater CO2 concentrations at the upper sampling site, which mostly drained deep peats, varied from 2·8 to 9·8 mg l?1 (2·5 to 11·9 times atmospheric saturation) and decreased markedly downstream. Temperature‐related seasonal variations in peat and riparian soil CO2 were reflected in the stream at the upper site, where 77% of biweekly variation was explained by an autoregressive model based on: (i) a negative log‐linear relationship with stream flow; (ii) a positive linear relationship with soil CO2 concentrations in the shallow riparian wells; and (iii) a negative linear relationship with soil CO2 concentrations in the shallow peat wells, with a significant 2‐week lag term. These relationships changed markedly downstream, with an apparent decrease in the soil–stream linkage and a switch to a positive relationship between stream flow and stream CO2. Streamwater CH4 concentrations also declined sharply downstream, but were much lower (<0·01 to 0·12 mg l?1) than those of CO2 and showed no seasonal variation, nor any relationship with soil atmospheric CH4 concentrations. However, stream CH4 was significantly correlated with stream flow at the upper site, which explained 57% of biweekly variations in dissolved concentrations. We conclude that stream CO2 can be a useful integrative measure of whole catchment respiration, but only at sites where the soil–stream linkage is strong. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

14.
Eight small steep south-west facing catchments (1-63-8-26 ha) have been monitored in Westland, New Zealand since 1974. Two catchments were retained in native mixed evergreen forest and the rest were subjected to various harvesting and land preparation techniques before being planted with Pinus radiata between 1977 and 1980. Stream temperatures were measured in all catchments for 11 years, including up to four years before harvesting. The streamwater temperature regime under the native forest cover has a seasonal cycle, with an annual mean of about 9°C and mean daily temperatures ranging between a winter minimum of about 5.8°C and a summer maximum of 12.S°C. After harvesting, the winter minimum stream temperatures in all trials were unchanged as topography exerts the major control over incoming solar radiation. The largest rises in mean summer stream temperatures, up to 5.5°C, were in the catchments that had been clearcut and burnt before planting. The maximum stream temperature recorded was 22.8°C in a clearcut catchment with no riparian reserve. Summer stream temperatures in this catchment were up to 11°C higher than in an adjacent control catchment. Summer stream temperature rises in catchments with riparian reserves were less than 1.5°C. Seven years after harvesting, stream temperatures were dropping towards pre-treatments levels in only two of the six treated catchments as revegetation of the riparian areas occurred and the plantations became established. As these small headwater streams discharge into streams with flows one or two orders of magnitude larger, the increases in summer stream temperatures will be rapidly dissipated. However, the cumulative impact of harvesting many small headwater catchments that discharge into a larger stream could have a noticeable effect on stream temperature if intact riparian reserves were not retained in both headwater and main streams.  相似文献   

15.
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   

16.
Temperature observations at 25 sites in the 2000 km2 Dee catchment in NE Scotland were used, in conjunction with geographic information system (GIS) analysis, to identify dominant landscape controls on mean monthly maximum stream temperatures. Maximum winter stream temperatures are mainly controlled by elevation, catchment area and hill shading, whereas the maximum temperatures in summer are driven by more complex interactions, which include the influence of riparian forest cover and distance to coast. Multiple linear regression was used to estimate the catchment‐wide distribution of mean weekly maximum stream temperatures for the hottest week of the 2‐year observation period. The results suggested the streams most sensitive to high temperatures are small upland streams at exposed locations without any forest cover and relatively far inland, while lowland streams with riparian forest cover at locations closer to the coast exhibit a moderated thermal regime. Under current conditions, all streams provide a suitable thermal habitat for both, Atlantic salmon and brown trout. Using two climate change scenarios assuming 2·5 and 4 °C air temperature increases, respectively, temperature‐sensitive zones of the stream network were identified, which could potentially have an adverse effect on the thermal habitat of Atlantic salmon and brown trout. Analysis showed that the extension of riparian forests into headwater streams has the potential to moderate changes in temperature under climate change. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

17.
This study examined if riparian land use (forested vs agricultural) affects hydraulic transport in headwater streams located in an agriculturally fragmented watershed. We identified paired 50‐m reaches (one reach in agricultural land use and the other in forested land use) along three headwater streams in the Upper Sugar Creek Watershed in northeast Ohio, USA (40° 51′42″N, 81° 50′29″W). Using breakthrough curves obtained by Rhodamine WT slug injections and the one‐dimensional transport with inflow and storage model (OTIS), hydraulic transport parameters were obtained for each reach on six different occasions (n = 36). Relative transient storage (AS:A) was similar between both reach types (As: A = 0·3 ± 0·1 for both agricultural and forested reaches). Comparing values of Fmed200 to those in the literature indicates that the effect of transient storage was moderately high in the study streams in the Upper Sugar Creek Watershed. Examining travel times revealed that overall residence time (HRT) and residence time in transient storage (TSTO) were both longer in forested reaches (forested HRT = 19·1 ± 11·5 min and TSTO = 4·0 ± 3·8 min; agricultural HRT = 9·3 ± 5·3 min and TSTO = 1·7 ± 1·4 min). We concluded that the effect of transient storage on solute transport was similar between the forested and agricultural reaches but the forested reaches had a greater potential to retain solutes as a result of longer travel times. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

18.
Hemispherical photographs of forest canopies can be used to develop sophisticated models that predict incident below canopy shortwave radiation on the surface of interest (i.e. soil and water). Hemispherical photographs were collected on eight dates over the course of a growing season to estimate leaf area index and to quantify solar radiation incident on the surface of two stream reaches based on output from Gap Light Analyser and Hemisfer software. Stream reaches were shaded by a mixed‐deciduous Ozark border forested riparian canopy. Hemispherical photo model results were compared to observed solar radiation sensed at climate stations adjacent to each stream reach for the entire 2010 water year. Modeled stream‐incident shortwave radiation was validated with above‐stream pyranometers for the month of September. On average, the best hemispherical photo models underestimated daily averages of solar radiation by approximately 14% and 12% for E–W and N–S flowing stream reaches, respectively (44.7 W/m2 measured vs 38.4 W/m2 modeled E–W, 46.8 W/m2 vs. 41.1 W/m2N–S). The best hemispherical photo models overestimated solar radiation relative to in–Stream pyranometers placed in the center of each stream reach by approximately 7% and 17% for E–W and N–S stream reaches respectively (31.3 W/m2 measured vs 33.5 W/m2 modeled E–W, 31.5 W/m2 vs. 37.1 W/m2N–S). The model provides a geographically transferable means for quantifying changes in the solar radiation regime at a stream surface due to changes in canopy density through a growing season, thus providing a relatively simple method for estimating surface and water heating in canopy altered environments (e.g. forest harvest). Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

19.
To enhance the understanding of solute dynamics within the stream‐to‐riparian continuum during flood event‐driven water fluctuation (i.e., flood wave), a variable saturated groundwater flow and solute transport model were developed and calibrated against in situ measurements of the Inbuk stream, Korea, where seasonal flooding prevails. The solute dynamics were further investigated for flood waves (varying by amplitude [A], duration [T], roundness [r], and skewness [tp]) that were parameterised by real‐time stream stage fluctuations. We found that the solute transferred faster and farther in the riparian zone, especially within the phreatic zone, above which in the variable saturated zone the concentration required a significantly longer time, particularly at higher altitudes, to return to the initial state. By comparison, solute transferred shallowly in the streambed where the solute plume exhibited an exponential growth trend from the centre to the bank. The dynamic changes of solute flux and mass along the stream–aquifer interface and stream concentration were linked to the shape of flood wave. As the flood wave became higher (A↗), wider (T↗), rounder (r↘), and less skewed (tp↗), the maximum solute storage in aquifer increased. Maximum stream concentration (Cstr?max) not only presented a positive linear relationship with A or tp but also showed a negative logarithmic trend with increasing T or r. The sensitivity of Cstr_max to A was approximately two times that of tp, and between these values, the r was slightly more sensitive than T. Cstr?max linearly increased as hydraulic conductivity increased and logarithmically increased as longitudinal dispersivity increased. The former relationship was more sensitive than the latter.  相似文献   

20.
Dense understory thickets of the native evergreen shrub Rhododendron maximum expanded initially following elimination of American chestnut by the chestnut blight, and later in response to loss of the eastern hemlock due to hemlock woolly adelgid invasion. Rhododendron thickets often blanket streams and their riparian zones, creating cool, low-light microclimates. To determine the effect of such understory thickets on summer stream temperatures, we removed riparian rhododendron understory on 300 m reaches of two southern Appalachian Mountain headwater streams, while leaving two 300 m reference reaches undisturbed. Overhead canopy was left intact in all four streams, but all streams were selected to have a significant component of dead or dying eastern hemlock in the overstory, creating time-varying canopy gaps throughout the reach. We continuously monitored temperatures upstream, within and downstream of treatment and reference reaches. Temperatures were monitored in all four streams in the summer before treatments were imposed (2014), and for two summers following treatment (2015, 2016). Temperatures varied significantly across and within streams prior to treatment and across years for the reference streams. After rhododendron removal, increases in summer stream temperatures were observed at some locations within the treatment reaches, but these increases did not persist downstream and varied by watershed, sensor, and year. Significant increases in daily maxima in treatment reaches ranged from 0.9 to 2.6°C. Overhead canopy provided enough shade to prevent rhododendron removal from increasing summer temperatures to levels deleterious to native cold-water fauna (average summer temperatures remained below 16°C), and local temperature effects were not persistent.  相似文献   

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