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1.
Water yields increased after logging by 150–250 mm per year in small catchments of moist old-growth eucalypt at Karuah in central New South Wales. The magnitude of this initial increase was directly related to the percentage of the catchment logged (29–79%). Where substantial vegetation removal took place in less than 20% of one catchment no increased water yield was observed. Water yields began to decline in all catchments 2–3 years after logging as regrowth eucalypts became established, and the rate of this decline was related to the mean stocking rate of eucalypt regeneration during the next 4 years. This water yield decline exceeded 250 mm in the sixth year after logging in the catchment with the highest stocking of regeneration and the highest regrowth basal area. Water yields in this catchment had declined to levels significantly below pre-logging levels by this time, supporting the notion that regrowth evapotranspiration had begun to exceed that of the old-growth forest. Patterns of declining water yield in the other catchments suggest that yields in some may also decline below pre-logging levels as regrowth evapotranspiration increases in line with increases in the basal area of the regrowth forest. Further study is required to determine the magnitude and duration of water yield reductions in these regrowth catchments, and to quantify the eucalypt growth rates and stand conditions responsible for the reductions. Nevertheless, these early results are consistent with water yield changes observed in mountain ash forest in Victoria, and support the concept of greater water use by a rapidly regenerating forest.  相似文献   

2.
Few long-term studies have explored how intensively managed short rotation forest plantations interact with climate variability. We examine how prolonged severe drought and forest operations affect runoff in 11 experimental catchments on private corporate forest land near Nacimiento in south central Chile over the period 2008–2019. The catchments (7.7–414 ha) contain forest plantations of exotic fast-growing species (Pinus radiata, Eucalyptus spp.) at various stages of growth in a Mediterranean climate (mean long-term annual rainfall = 1381 mm). Since 2010, a drought, unprecedented in recent history, has reduced rainfall at Nacimiento by 20%, relative to the long-term mean. Pre-drought runoff ratios were <0.2 under 8-year-old Eucalyptus; >0.4 under 21-year-old Radiata pine and >0.8 where herbicide treatments had controlled vegetation for 2 years in 38% of the catchment area. Early in the study period, clearcutting of Radiata pine (85%–95% of catchment area) increased streamflow by 150 mm as compared with the year before harvest, while clearcutting and partial cuts of Eucalyptus did not increase streamflow. During 2008–2019, the combination of emerging drought and forestry treatments (replanting with Eucalyptus after clearcutting of Radiata pine and Eucalyptus) reduced streamflow by 400–500 mm, and regeneration of previously herbicide-treated vegetation combined with growth of Eucalyptus plantations reduced streamflow by 1125 mm (87% of mean annual precipitation 2010–2019). These results from one of the most comprehensive forest catchment studies in the world on private industrial forest land indicate that multiple decades of forest management have reduced deep soil moisture reservoirs. This effect has been exacerbated by drought and conversion from Radiata pine to Eucalyptus, apparently largely eliminating subsurface supply to streamflow. The findings reveal tradeoffs between wood production and water supply, provide lessons for adapting forest management to the projected future drier climate in Chile, and underscore the need for continued experimental work in managed forest plantations.  相似文献   

3.
Forest species composition may change following a disturbance. This change can affect long term water yield from forested catchments when the replaced and replacement species have different evapotranspiration rates. Following strip‐thinning experiments that removed 50% of the overstorey basal area in several Eucalyptus regnans water supply catchments in south eastern Australia, Acacia spp. (Acacia dealbata and Acacia melanoxylon) became the dominant overstorey species in most of the cut strips. More recently, low regeneration of E. regnans following wildfires in 2009 may result in mixed Acacia and E. regnans stands in some catchments. We compared transpiration of E. regnans and Acacia stands in the uncut and cut strips of a catchment that was strip‐thinned in early 1980s (Crotty Creek). We also compared transpiration and throughfall in a mixed E. regnans–A. dealbata regrowth stand 20 years after clear‐fell logging (Road 8). Sap flow was measured for 13 and 6 months at Crotty Creek and Road 8, respectively. In both studies, mean daily sap flow density of Acacia spp. was lower than of E. regnans. Estimated Leaf Area Index of E. regnans stands was slightly greater than that of Acacia spp. Stomatal conductance (gc), estimated by inverting the Penman–Monteith equation, differed between the species suggesting species‐level physiological differences with Acacia being more sensitive to vapour pressure deficit than E. regnans. Throughfall measurements at Road 8 indicated interception was slightly higher in A. dealbata but only enough to offset about 13% of the difference in transpiration. Replacement of E. regnans by Acacia dominated stands may, therefore, decrease catchment evapotranspiration and increase streamflow.  相似文献   

4.
Streamflow is the runoff response integrated in space and time over a complex system involving climatic and catchment physiographic factors. In the Andes, accelerating runoff process understanding is hampered by the inability to quantify heterogeneity of surface and subsurface catchment properties. Here, we present a statistical approach based on regression models and correlation analysis that links hydrological signatures and catchment properties to unveil processes in a set of volcanic mountain catchments (latitude 0°30'N) in Ecuador. The catchments represent form and function diversity in the same hydrological unit. We found that despite of similar atmospheric-water inputs the water yield in the north-east region is about 5× larger than in the south-west region and their flow regimes are asymmetric. The soil-bedrock interface and lithology exert a first-order control on hydrologic partitioning, and this allowed us to hypothesize two hydrological mechanisms. Firstly, in the north-east region, the perennial streamflow is associated with seasonal rainfall patterns, and subsequent drainage processes taking place at the surface and subsurface level. The amount of streamflow is related to landform characteristics, high canopy density and root development of forest as well as water holding capacity of organic soils. From a mechanistic standpoint, the low concentration time, steep slopes and shallow infiltration limited by high-consolidated deposits of sedimentary and volcanics suggest a lateral movement of the flow. Secondly, in the south-west region the streamflow regime is mostly groundwater-dependent and it becomes seasonally enhanced by rainfall. Larger seasonal variations of precipitation and temperature result into enhanced evapotranspiration in the drier months, limiting shallow soil infiltration. Under the soil layers, highly permeable pyroclastic deposits and andesitic lavas promote deep percolation. The results highlight the degree of dissimilarity of hydrological processes in Andean settings, but unravelling their complexity seems plausible using streamflow signatures and causal explanatory models.  相似文献   

5.
Periods of summertime low flows are often critical for fish. This study quantified the impacts of forest clear‐cutting on summertime low flows and fish habitat and how they evolved through time in two snowmelt‐dominant headwater catchments in the southern interior of British Columbia, Canada. A paired‐catchment analysis was applied to July–September water yield, the number of days each year with flow less than 10% of mean annual discharge, and daily streamflow for each calendar day. The postharvest time series were divided into treatment periods of approximately 6–10 years, which were analysed independently to evaluate how the effects of forestry changed through time. An instream flow assessment using a physical habitat simulation‐style approach was used to relate streamflow to the availability of physical habitat for resident rainbow trout. About two decades after the onset of logging and as the extent of logging increased to approximately 50% of the catchments, reductions in daily summertime low flows became more significant for the July–September yield (43%) and for the analysis by calendar day (11–68%). Reductions in summertime low flows were most pronounced in the catchment with the longest postharvest time series. On the basis of the temporal patterns of response, we hypothesize that the delayed reductions in late‐summer flow represent the combined effects of a persistent advance in snowmelt timing in combination with at least a partial recovery of transpiration and interception loss from the regenerating forests. These results indicate that asymptotic hydrological recovery as time progresses following logging is not suitable for understanding the impacts of forest harvesting on summertime low flows. Additionally, these reductions in streamflow corresponded to persistent decreases in modelled fish habitat availability that typically ranged from 20% to 50% during the summer low‐flow period in one of the catchments, suggesting that forest harvest may have substantial delayed effects on rearing salmonids in headwater streams.  相似文献   

6.
Forest biomass reductions in overgrown forests have the potential to provide hydrologic benefits in the form of improved forest health and increased streamflow production in water-limited systems. Biomass reductions may also alter evaporation. These changes are generated when water that previously would have been transpired or evaporated from the canopy of the removed vegetation is transferred to transpiration of the remaining vegetation, streamflow, and/or non-canopy evaporation. In this study, we combined a new vegetation-change water-balance approach with lumped hydrologic modelling outputs to examine the effects of forest biomass reductions on transpiration of the remaining vegetation and streamflow in California's Sierra Nevada. We found that on average, 102 mm and 263 mm (8.0% and 20.6% of mean annual precipitation [MAP]) of water were made available following 20% and 50% forest biomass-reduction scenarios, respectively. This water was then partitioned to both streamflow and transpiration of the remaining forest, but to varying degrees depending on post-biomass-reduction precipitation levels and forest biomass-reduction intensity. During dry periods, most of the water (approximately 200 mm [15.7% on MAP] for the 50% biomass-reduction scenario) was partitioned to transpiration of the remaining trees, while less than 50 mm (3.9% on MAP) was partitioned to streamflow. This increase in transpiration during dry periods would likely help trees maintain forest productivity and resistance to drought. During wet periods, the hydrologic benefits of forest biomass reductions shifted to streamflow (200 mm [15.7% on MAP]) and away from transpiration (less than 150 mm [11.8% on MAP]) as the remaining trees became less water stressed. We also found that streamflow benefits per unit of forest biomass reduction increased with biomass-reduction intensity, whereas transpiration benefits decreased. By accounting for changes in vegetation, the vegetation-change water balance developed in this study provided an improved assessment of watershed-scale forest health benefits associated with forest biomass reductions.  相似文献   

7.
Ashley A. Webb 《水文研究》2009,23(12):1679-1689
Streamflows were measured in two Pinus radiata plantation catchments and one native eucalypt forest catchment in Canobolas State forest from 1999 to 2007. In 2002/2003, clearfall harvesting of 43·2 and 40·3% of two plantation catchments occurred, respectively. Water yields increased by 54 mm (52%), 71 mm (35%) and 50 mm (19%) in the first three years post‐harvest in treated catchment A and by 103 mm (118%), 157 mm (82%) and 119 mm (48%) in treated catchment B relative to the native forest control catchment. In the fourth post‐harvest water year annual rainfall was only 488 mm, which resulted in negligible run‐off in all catchments, regardless of forest cover. In both plantation catchments, monthly streamflows increased significantly (p = 0·01, p < 0·001) due to a significant increase in baseflows (p < 0·001) after harvesting. Monthly stormflows were not significantly affected by harvesting. Flow duration curve analyses indicated a variable response between the two plantation catchments. Treated catchment A was converted from an ephemeral stream flowing 42% of the time pre‐harvest to a temporary stream flowing 82% of the time post‐harvest. These changes occurred throughout all seasons of the year but were most pronounced during summer and autumn when baseflows were maintained post‐harvest but were not observed under native forest or mature pine plantations. By contrast, flow duration increased in treated catchment B from 12% of the time pre‐harvest to 38% of the time post‐harvest with the greatest changes measured during the winter and spring months when streamflow would normally occur under native forest conditions. These observations have important implications for the development of models of plantation water use to be utilized in water resource planning in Australia. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

8.
Global increases in intensive forestry have raised concerns about forest plantation effects on water, but few studies have tested the effects of plantation forest removal and native forest restoration on catchment hydrology. We describe results of a 14-year paired watershed experiment on ecological restoration in south central Chile which documents streamflow response to the early stages of native forest restoration, after clearcutting of plantations of exotic fast-growing Eucalyptus, planting of native trees, and fostering natural regeneration of native temperate rainforest species. Precipitation, streamflow, and vegetation were measured starting in 2006 in four small (3 to 5 ha) catchments with Eucalyptus globulus plantations and native riparian buffers in the Valdivian Coastal Reserve. Mean annual precipitation is 2500 mm, of which 11% occurs in summer. Streamflow increased, and increases persisted, throughout the first 9 years of vigorous native forest regeneration (2011 to 2019). Annual streamflow increased by 40% to >100% in most years and >150% in fall and summer of some years. Streamflow was 50% to 100% lower than before treatment in two dry summers. Base flow increased by 28% to 87% during the restoration period compared to pre-treatment, and remained elevated in later years despite low summer precipitation. Overall, these findings indicate that removal of Eucalyptus plantations immediately increased streamflow, and native forest restoration gradually restored deep soil moisture reservoirs that sustain base flow during dry periods, increasing water ecosystem services. To our knowledge this is the first study to assess catchment streamflow response to native forest restoration in former forest plantations. Therefore, the results of this study are relevant to global efforts to restore native forest ecosystems on land currently intensively managed with fast-growing forest plantations and may inform policy and decision-making in areas experiencing a drying trend associated with climate change.  相似文献   

9.
Elevated wildfire activity in many regions in recent decades has increased concerns about the short- and long-term effects on water quantity, quality, and aquatic ecosystem health. Often, loss of canopy interception and transpiration, along with changes in soil structural properties, leads to elevated total annual water yields, peak flows, and low flows. Post-fire land management treatments are often used to promote forest regeneration and mitigate effects to terrestrial and aquatic ecosystems. However, few studies have investigated the longer-term effects of either wildfire or post-fire land management on catchment hydrology. Our objectives were to quantify and compare the short- and longer-term effects of both wildfire and post-fire forest management treatments on annual discharge, peak flows, low flows, and evapotranspiration (AET). We analyzed ten years of pre-fire data, along with post-fire data from 1 to 7 and 35 to 41 years after wildfire burned three experimental catchments in the Entiat Experimental Forest (EEF) in the Pacific Northwest, USA. After the fire, two of the catchments were salvage logged, aerially seeded, and fertilized, while the third catchment remained as a burned reference. We observed increases in annual discharge (150–202%), peak flows (234–283%), and low flows (42–81%), along with decreases in AET (34–45%), across all three study catchments in the first seven year period after the EEF wildfire. Comparatively, annual discharge, peak flows, lows flows, and AET had returned to pre-fire levels 35–41 years after the EEF fire in the two salvage logged and seeded catchments. Surprisingly, in the catchment that was burned but not actively managed, the annual discharge and runoff ratios remained elevated, while AET remained lower, during the period 35–41 years after the EEF fire. We posit that differences in long-term hydrologic recovery across catchments were driven by delayed vegetation recovery in the unmanaged catchment. Our study demonstrates that post-fire land management decisions have the potential to produce meaningful differences in the long-term recovery of catchment-scale ecohydrologic processes and streamflow.  相似文献   

10.
Forestal Arauco (FA), a global manufacturer of forest products, manages more than 1 million ha of forest plantations and oversees the conservation of more than half a million hectares of native forest and vegetation in Brazil, Argentina and Chile. In 2008, FA responded to local concerns about the effect of plantations on water resources and commenced streamflow monitoring in catchments in the coastal range of central-southern Chile between 35° and 39° of latitude south. This data note presents an overview of daily streamflow and rainfall records for 10 small catchments (18–112 ha) from 2008 to 2018. The catchments are covered by three different forest types, namely native forest (2), pine plantations of different ages (6) and eucalypt plantations (2). All of these catchments share similar metamorphic geology. A 90° V notch weir was built at each catchment outlet and data collected at 5 min interval using a pressure transducer that was calibrated monthly. The dataset is part of a research programme aiming to improve our understanding about the role of forest plantations on water balance at a stand and catchment level. It also includes the rainfall data from these catchments estimated using a combination of local rain gauges and data from the longer term records of the Chilean Directorate of Water. This dataset can be used in hydrological modelling and in a wide range of research questions and water management issues regarding forest plantations in a Mediterranean climate.  相似文献   

11.
Sixteen small catchments in the Maroondah region of Victoria, Australia were analysed using rainfall, temperature and streamflow time series with a rainfall–runoff model whose parameters efficiently characterize the hydrological response of a catchment. A set of catchment attributes for each of these catchments was then compared with the associated set of hydrological response characteristics of the catchments as estimated by the model. The time constant governing quickflow recession of streamflow (τq) was related to the drainage network and catchment area. The time constant governing slowflow recession of streamflow (τs) was related to the slope and shape of the catchment. The parameter governing evapotranspirative losses ( f ) was related to catchment gradient and vegetative water use. Forestry activities in the catchments changed evapotranspirative losses and thus total volume of streamflow, but did not affect the rate of streamflow recession.  相似文献   

12.
This study is focused on the analysis of the relationship between sap‐flow‐derived transpiration measured in a Scots pine stand in the Vallcebre research catchments (NE Iberian Peninsula) and meteorological and rainfall data. The first part of the study is focused on the analysis of temperature and rainfall anomalies. Then, the Scots pine transpiration response to inter‐annual rainfall variability, soil water stress and water table depth variations during the period 1997–2000 is analysed. This period includes the extremely dry year of 1998, which allows us to infer the response of Scots pine transpiration to severe droughts. Scots pine transpiration during the summer presented a high inter‐annual variability, largely related to rainfall amounts. Daily transpiration during dry summers was 40% of the transpiration of a summer day with average rainfall. Moreover, during dry summers, transpiration rates were not fully recovered even after significant rainfall events. The analysis of the dependence of Scots pine transpiration on available water indicated the strong limitation on transpiration induced by water content in the whole soil profile as well as by water table position. Under these drought conditions, a reduction of runoff and deep water stores was observed at the catchment scale, suggesting that the predicted increase in the frequency of severe summer droughts may threaten the current role of Mediterranean mountain catchments as suppliers of water resources for lowland areas. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

13.
Understanding the role of forest fires on water budgets of subarctic Precambrian Shield catchments is important because of growing evidence that fire activity is increasing. Most research has focused on assessing impacts on individual landscape units, so it is unclear how changes manifest at the catchment scale enough to alter water budgets. The objective of this study was to determine the water budget impact of a forest fire that partially burned a ~450 km2 subarctic Precambrian Shield basin. Water budget components were measured in a pair of catchments: one burnt and another unburnt. Burnt and unburnt areas had comparable net radiation, but thaw was deeper in burned areas. There were deeper snow packs in burns. Differences in streamflow between the catchments were within measurement uncertainty. Enhanced winter streamflow from the burned watershed was evident by icing growth at the streamflow gauge location, which was not observed in the unburned catchment. Wintertime water chemistry was also clearly elevated in dissolved organics, and organic-associated nutrients. Application of a framework to assess hydrological resilience of watersheds to wildfire reveal that watersheds with both high bedrock and open water fractions are more resilient to hydrological change after fire in the subarctic shield, and resilience decreases with increasingly climatically wet conditions. This suggests significant changes in runoff magnitude, timing and water chemistry of many Shield catchments following wildfire depend on pre-fire land cover distribution, the extent of the wildfire and climatic conditions that follow the fire.  相似文献   

14.
Diurnal variations in streamflow are becoming acknowledged as a way of analysing how changing climatic conditions and land use affects watersheds but also as a way to understand watersheds as a whole. Yet not many studies from uplands below 900 mm mean annual precipitation zone are available from European countries. During the 2012 growing season, a sampling campaign took place in an upland forested micro‐watershed, Czech Republic (65 ha). Tree sap flow, rainfall and temperature were measured continuously, while streamflow at the discharge point and soil moisture were estimated from short‐term measurements. Short precipitation‐free periods lasting several days were identified for evaluation of trends in diurnal dynamics of both sap flow and streamflow. The results demonstrated that during these periods, the main factor altering streamflow was almost exclusively tree sap flow. A decrease in streamflow was observed during the day and an increase at night. The decline in sap flow after sunset was accompanied by a continuous increase in streamflow throughout the night up to its initial maximum in the morning. The amplitude in diurnal variations reached 18%. The observed time lag between the diurnal variations of sap flow and streamflow was approximately 2 h. Relatively low changes in diurnal dynamics of streamflow pointed out a strong regulatory role of the forest in buffering water discharge from the catchment. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

15.
Water yield issues in the jarrah forest of south-western Australia   总被引：2，自引：0，他引：2  
The jarrah forest of south-western Australia produces little streamflow from moderate rainfall. Water yield from water supply catchments for Perth, Western Australia, are low, averaging 71 mm (7% of annual rainfall). The low water yields are attributed to the large soil water storage available for continuous use by the forest vegetation. A number of water yield studies in south-western Australia have examined the impact on water yield of land use practices including clearing for agricultural development, forest harvesting and regeneration, forest thinning and bauxite mining. A permanent reduction in forest cover by clearing for agriculture led to permanent increases of water yield of approximately 28% of annual rainfall in a high rainfall catchment. Thinning of a high rainfall catchment led to an increase in water yield of 20% of annual rainfall. However, it is not clear for how long the increased water yield will persist. Forest harvesting and regeneration have led to water yield increases of 16% of annual rainfall. The subsequent recovery of vegetation cover has led to water yields returning to pre-disturbance levels after an estimated 12–15 years. Bauxite mining of a high rainfall catchment led to a water yield increase of 8% of annual rainfall, followed by a return to pre-disturbance water yield after 12 years. The magnitude of specific streamflow generation mechanisms in small catchments subject to forest disturbance vary considerably, typically in a number of distinct stages. The presence of a permanent groundwater discharge area was shown to be instrumental in determining the magnitude of the streamflow response after forest disturbance. The long-term prognosis for water yield from areas subject to forest thinning, harvesting and regeneration, and bauxite mining are uncertain, owing to the complex interrelationship between vegetation cover, tree height and age, and catchment evapotranspiration. Management of the forest for water yield needs to acknowledge this complexity and evaluate forest management strategies both at the large catchment scale and at long time-scales. The extensive network of small catchment experiments, regional studies, process studies and catchment modelling at both the small and large scale, which are carried out in the jarrah forest, are all considered as integral components of the research to develop these management strategies to optimise water yield from the jarrah forest, without forfeiting other forest values.  相似文献   

16.
Six small, steep, south-west facing catchments (1.63–4.62 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. The 11-year water balance for the native forest catchments was: rain = streamflow + interception loss + transpiration + seepage (2370mm = 1290mm + 620mm + 360mm + 100mm). In the year after treatment streamflow generally increased by 200–250 mm, except for one treatment (clearfelling, herbicide application, no riparian reserve) where the increase was 550 mm. The catchments were planted with Pinus radiata, but rapid colonization by bracken (Pteridium esculentum) and Himalayan honeysuckle (Leycesteria formosa) led to a rapid decline in streamflow, which returned to pre-treatment levels after an average of about five years. Streamflow yields then continued to decline for another two to three years before stabilizing at a level about 250mm yr?1 lower than pre-treatment levels. At this time the catchments had a dense bracken/honeysuckle understorey beneath 5 m tall pine trees.  相似文献   

17.
The extensive afforestation of the Mediterranean rim of Europe in recent decades has increased the number of wildfire disturbances on hydrological and sediment processes, but the impacts on headwater catchments is still poorly understood, especially when compared with the previous agricultural landscape. This work monitored an agroforestry catchment in the north-western Iberian Peninsula, with plantation forests mixed with traditional agriculture using soil conservation practices, for one year before the fire and for three years afterwards, during which period the burnt area was ploughed and reforested. During this period, continuous data was collected for meteorology, streamflow and sediment concentration at the outlet, erosion features were mapped and measured after major rainfall events, and channel sediment dynamics were monitored downstream from the agricultural and the burnt forest area. Data from 202 rainfall events with over 10 mm was analysed in detail. Results show that the fire led to a notable impact on sediment processes during the first two post-fire years, but not on streamflow processes; this despite the small size of the burnt area (10% of the catchment) and the occurrence of a severe drought in the first year after the fire. During this period, soil loss at the burnt forest slopes was much larger than that at most traditionally managed fields, and, ultimately, led to sediment exhaustion. At the catchment scale, storm characteristics were the dominant factor behind streamflow and sediment yield both before and after the fire. However, the data indicated a shift from detachment-limited sediment yield before the fire, to transport-limited sediment yield afterwards, with important increases in streamflow sediment concentration. This indicates that even small fires can temporarily change sediment processes in agroforestry catchments, with potential negative consequences for downstream water quality.  相似文献   

18.
A study of the hydrologic effects of catchment change from pasture to plantation was carried out in Gatum, south‐western Victoria, Australia. This study describes the hydrologic characteristics of two adjacent catchments: one with 97% grassland and the other one with 62% Eucalyptus globulus plantations. Streamflow from both catchments was intermittent during the 20‐month study period. Monthly streamflow was always greater in the pasture‐dominated catchment compared with the plantation catchment because of lower evapotranspiration in the pasture‐based catchment. This difference in streamflow was also observed even during summer 2010/2011 when precipitation was 74% above average (1954–2012) summer rainfall. Streamflow peaks in the plantation‐based catchment were smaller than in the pasture‐dominated system. Flow duration curves show differences between the pasture and plantation‐dominated catchments and affect both high‐flow and low‐flow periods. Groundwater levels fell (up to 4.4 m) in the plantation catchment during the study period but rose (up to 3.2 m) in the pasture catchment. Higher evapotranspiration in the plantation catchment resulted in falling groundwater levels and greater disconnection of the groundwater system from the stream, resulting in lower baseflow contribution to streamflow. Salt export from each catchment increases with increasing flow and is higher at the pasture catchment, mainly because of the higher flow. Reduced salt loading to streams due to tree planting is generally considered environmentally beneficial in saline areas of south‐eastern Australia, but this benefit is offset by reduced total streamflow. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

19.
Mountain front catchment net groundwater recharge (NR) represents the upper end of mountain block recharge (MBR) groundwater flow paths. Using environmental chloride in precipitation, streamflow and groundwater, we apply chloride mass balance (CMB) to estimate NR at multiple catchment scales within the 27 km2 Dry Creek Experimental Watershed (DCEW) on the Boise Front, southwestern Idaho. The estimate for average annual precipitation partitioning to NR is approximately 14% for DCEW. In contrast, as much as 44% of annual precipitation routes to NR in ephemeral headwater catchments. NR in headwater catchments is likely routed to downgradient springs, baseflow, and MBR, while downgradient streamflow losses contribute further to MBR. A key assumption in the CMB approach is that the change in stored chloride during the study period is zero. We found that this assumption is violated in some individual years, but that a 5‐year integration period is sufficient. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

20.
Annual streamflows have decreased across mountain watersheds in the Pacific Northwest of the United States over the last ~70 years; however, in some watersheds, observed annual flows have increased. Physically based models are useful tools to reveal the combined effects of climate and vegetation on long‐term water balances by explicitly simulating the internal watershed hydrological fluxes that affect discharge. We used the physically based Simultaneous Heat and Water (SHAW) model to simulate the inter‐annual hydrological dynamics of a 4 km2 watershed in northern Idaho. The model simulates seasonal and annual water balance components including evaporation, transpiration, storage changes, deep drainage, and trends in streamflow. Independent measurements were used to parameterize the model, including forest transpiration, stomatal feedback to vapour pressure, forest properties (height, leaf area index, and biomass), soil properties, soil moisture, snow depth, and snow water equivalent. No calibrations were applied to fit the simulated streamflow to observations. The model reasonably simulated the annual runoff variations during the evaluation period from water year 2004 to 2009, which verified the ability of SHAW to simulate the water budget in this small watershed. The simulations indicated that inter‐annual variations in streamflow were driven by variations in precipitation and soil water storage. One key parameterization issue was leaf area index, which strongly influenced interception across the catchment. This approach appears promising to help elucidate the mechanisms responsible for hydrological trends and variations resulting from climate and vegetation changes on small watersheds in the region. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

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