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1.
Abstract

The chemistry of streamwater, bulk precipitation, throughfall and soil waters has been studied for three years in two plantation forest and two moorland catchments in mid-Wales. Na and CI are the major ions in streamwater reflecting the maritime influence on atmospheric inputs. In all streams, baseflow is characterised by high pH waters enriched in Ca, Mg, Si and HCO3. Differences in baseflow chemistry between streams reflect the varying extent of calcite and base metal sulphide mineralization within the catchments. Except for K, mean stream solute concentrations are higher in the unmineralized and mineralized forest catchments compared with their respective grassland counterparts. In the forest streams, storm flow concentrations of H+ are approximately 1.5 times and Al four times higher than in the moorland streams. Annual catchment losses of Na, Cl, SO4, NO3, Al and Si are greatest in the forest streams. In both grassland and forest systems, variations in stream chemistry be explained by mixing waters from different parts of the catchment, although NO3 concentrations may additionally be controlled by N transformations occurring between soils and streams. Differences in stream chemistry and solute budgets between forest and moorland catchments are related to greater atmospheric scavenging by the trees and changes in catchment hydrology consequent on afforestation. Mineral veins within the catchment bedrock can significantly modify the stream chemical response to afforestation.  相似文献   

2.
Josep Pi  ol  Anna   vila  Ferran Rod 《Journal of Hydrology》1992,140(1-4):119-141
Streamwater chemistry is described for three streams draining undisturbed, evergreen broad-leaved forested catchments on phyllites in NE Spain: two streams with no or negligible flow in summer are located in the Prades massif, and one perennial stream is in the wetter Montseny mountains. Weekly data for a study period of 2–4 years are provided to (1) describe the seasonal variations in streamwater chemistry, (2) analyse the relationship between stream discharge and solute concentrations using a two-component mixing model and (3) search for patterns of temporal variation in stream solute concentrations after discounting the effects of discharge. At Prades, concentrations of all analysed ions, except NO−3, showed marked seasonal variations in stream water, whereas at Montseny only ions related to mineral weathering (HCO−3, Na+, Ca2+ and Mg2+) showed strong seasonality. Ion concentrations were more closely dependent on instantaneous discharge at Montseny than at Prades. The residuals of the relationship between solute concentrations and discharge retained a strong seasonality at Prades, but not at Montseny. These differences are related to the major hydrochemical processes that determine the streamwater chemistry at each site. The same processes are probably operative in the three catchments, but are of varying relative importance. At Montseny, the mixing of waters of different chemical composition seems to be the major process controlling streamwater chemistry, although the soilwater end-member composition predicted by the mixing model applied did not match the measured soilwater chemistry. In the drier Prades catchments, the two major hydrochemical processes determining the seasonal variation of streamwater chemistry are (1) the restart of flow after the summer drought, which flushes out the solutes accumulated during the dry period, and (2) the seasonal changes in groundwater chemistry that result from the interplay of water residence time, temperature and CO2 partial pressure. In Mediterranean catchments with relatively high precipitation, such as Montseny, the seasonal variation in the streamwater chemistry is largely determined by the same processes as at humid-temperate sites, whereas in drier Mediterranean catchments, such as Prades, the major hydrochemical processes are clearly distinct.  相似文献   

3.
Stream chemistry is often used to infer catchment‐scale biogeochemical processes. However, biogeochemical cycling in the near‐stream zone or hydrologically connected areas may exert a stronger influence on stream chemistry compared with cycling processes occurring in more distal parts of the catchment, particularly in dry seasons and in dry years. In this study, we tested the hypotheses that near‐stream wetland proportion is a better predictor of seasonal (winter, spring, summer, and fall) stream chemistry compared with whole‐catchment averages and that these relationships are stronger in dryer periods with lower hydrologic connectivity. We evaluated relationships between catchment wetland proportion and 16‐year average seasonal flow‐weighted concentrations of both biogeochemically active nutrients, dissolved organic carbon (DOC), nitrate (NO3‐N), total phosphorus (TP), as well as weathering products, calcium (Ca), magnesium (Mg), at ten headwater (<200 ha) forested catchments in south‐central Ontario, Canada. Wetland proportion across the entire catchment was the best predictor of DOC and TP in all seasons and years, whereas predictions of NO3‐N concentrations improved when only the proportion of wetland within the near‐stream zone was considered. This was particularly the case during dry years and dry seasons such as summer. In contrast, Ca and Mg showed no relationship with catchment wetland proportion at any scale or in any season. In forested headwater catchments, variable hydrologic connectivity of source areas to streams alters the role of the near‐stream zone environment, particularly during dry periods. The results also suggest that extent of riparian zone control may vary under changing patterns of hydrological connectivity. Predictions of biogeochemically active nutrients, particularly NO3‐N, can be improved by including near‐stream zone catchment morphology in landscape models.  相似文献   

4.
Springs are the point of origin for most headwater streams and are important regulators of their chemical composition. We analysed solute concentrations of water emerging from 57 springs within the 3 km2 Fool Creek catchment at the Fraser Experimental Forest and considered sources of spatial variation among them and their influence on the chemical composition of downstream water. On average, calcium and acid neutralizing capacity (bicarbonate-ANC) comprised 50 and 90% of the cation and anion charge respectively, in both spring and stream water. Variation in inorganic chemical composition among springs reflected distinct groundwater sources and catchment geology. Springs emerging through glacial deposits in the upper portion of the catchment were the most dilute and similar to snowmelt, whereas lower elevation springs were more concentrated in cations and ANC. Water emerging from a handful of springs in a geologically faulted portion of the catchment were more concentrated than all others and had a predominant effect on downstream ion concentrations. Chemical similarity indicated that these springs were linked along surface and subsurface flowpaths. This survey shows that springwater chemistry is influenced at nested spatial scales including broad geologic conditions, elevational and spatial attributes and isolated local features. Our results highlight the role of overlapping factors on solute export from headwater catchments.  相似文献   

5.
Streamwater discharge and chemistry of two small catchments on Catoctin Mountain in north-central Maryland have been monitored since 1982. Repetitive seasonal cycles in stream-water chemistry have been observed each year, along with seasonal cycles in the volume of stream discharge and in groundwater levels. The hypothesis that the observed streamwater chemical cycles are related to seasonal changes in the hydrological flow paths that contribute to streamflow is examined using a combination of data on groundwater levels, shallow and deep groundwater chemistry, streamwater discharge, streamwater chemistry, soil-water chemistry, and estimates of water residence times. The concentrations of constituents derived from rock weathering, particularly bicarbonate and silica, increase in streamwater during the summer when the water table is below the regolith-bedrock interface and stream discharge consists primarily of deep groundwater from the fractured-bedrock aquifer. Conversely, the concentrations in streamwater of atmospherically derived components, particularly sulfate, increase in winter when the water table is above the regolith-bedrock interface and stream discharge consists primarily of shallow groundwater from the regolith. Tritium and chlorofluorocarbon (CFC) measurements suggest that the groundwater in these systems is young, with a residence time of less than several years. The results of this study have implications for the design of large-scale water-quality monitoring programs.  相似文献   

6.
Nitrate concentrations in streamwater of agricultural catchments often exhibit interannual variations, which are supposed to result from land‐use changes, as well as seasonal variations mainly explained by the effect of hydrological and biogeochemical cycles. In catchments on impervious bedrock, seasonal variations of nitrate concentrations in streamwater are usually characterized by higher nitrate concentrations in winter than in summer. However, intermediate or inverse cycles with higher concentrations in summer are sometimes observed. An experimental study was carried out to assess the mechanisms that determine the seasonal cycles of streamwater nitrate concentrations in intensive agricultural catchments. Temporal and spatial patterns of groundwater concentrations were investigated in two adjacent catchments located in south‐western Brittany (France), characterized by different seasonal variations of streamwater nitrate concentrations. Wells were drilled across the hillslope at depths ranging from 1·5 to 20 m. Dynamics of the water table were monitored and the groundwater nitrate and chloride concentrations were measured weekly over 2 years. Results highlighted that groundwater was partitioned into downslope domains, where denitrification induced lower nitrate concentrations than into mid‐slope and upslope domains. For one catchment, high subsurface flow with high nitrate concentrations during high water periods and active denitrification during low water periods explained the higher streamwater nitrate concentrations in winter than in summer. For the other catchment, the high contribution of groundwater with high nitrate concentrations smoothed or inverted this trend. Increasing bromide/chloride ratio and nitrate concentrations with depth argued for an effect of past agricultural pressure on this catchment. The relative contribution of flows in time and correlatively the spatial origin of waters, function of the depth and the location on the hillslope, and their chemical characteristics control seasonal cycles of streamwater nitrate concentrations and can influence their interannual trends. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

7.
Climate change is causing drastic landscape changes in the Arctic, but how these changes modify stream biogeochemistry is not clear yet. We examined how catchment properties influence stream nitrogen (N) and dissolved organic carbon concentrations (DOC) in a high-Arctic environment. We sampled two contrasting headwater streams (10–15 stations over 4.8 and 6.8 km, respectively) in Northeast Greenland (74°N). We characterized the geomorphology (i.e., bedrock, solifluction and alluvial types) and the vegetation (i.e., barren, fell field, grassland and tundra types) cover of each subcatchment area draining into each sampling station and collected water samples for hydrochemistry characterization. The two sampled streams differed in geomorphology and vegetation cover in the catchment. Aucellaelv catchment was mostly covered by a ‘bedrock’ geomorphology (71%) and ‘fellfield’ vegetation (51%), whereas Kæerelv was mostly covered by ‘alluvial’ geomorphology (65%) and ‘grassland’ and ‘tundra’ vegetation (42% and 41% respectively). Hydrochemistry also differed between the two study streams, with higher concentrations of inorganic N forms in Aucellaelv and lower DOC concentrations, compared to Kærelv. The results from the linear mixed model selection showed that vegetation and geomorphology had contrasting effects on stream hydrochemistry. Subcatchments with higher solifluction sheets and limited vegetation had higher nitrate concentrations but lower DOC concentrations. Interestingly, we also found high variability on the production and removal of nitrate across subcatchments. These results indicate landscape controls to nutrient and organic matter exports via flow paths, soil organic matter stocks and nutrient retention via terrestrial vegetation. Moreover, the results suggest that climate change induced alterations to vegetation cover and soil physical disturbance in high-Arctic catchments will affect stream hydrochemistry, with potential effects in stream productivity, trophic relations as well as change of solute export to downstream coastal areas.  相似文献   

8.
In order to investigate the relation between water chemistry and functional landscape elements, spatial data sets of characteristics for 68 small (0·2–1·5 km2) boreal forest catchments in western central Sweden were analysed in a geographical information system (GIS). The geographic data used were extracted from official topographic maps. Water sampled four times at different flow situations was analysed chemically. This paper focuses on one phenomenon that has an important influence on headwater quality in boreal, coniferous forest streams: generation and export of dissolved organic carbon (DOC). It is known that wetland cover (bogs and fens) in the catchment is a major source of DOC. In this study, a comparison was made between a large number of headwater catchments with varying spatial locations and areas of wetlands. How this variation, together with a number of other spatial variables, influences the DOC flux in the streamwater was analysed by statistical methods. There were significant, but not strong, correlations between the total percentages of wetland area and DOC flux measured at a medium flow situation, but not at high flow. Neither were there any significant correlations between the percentage of wetland area connected to streams, nor the percentage of wetland area within a zone 50 m from the stream and the DOC flux. There were, however, correlations between catchment mean slope and the DOC flux in all but one flow situations. This study showed that, considering geographical data retrieved from official sources, the topography of a catchment better explains the variation in DOC flux than the percentage and locations of distinct wetland areas. This emphasizes the need for high‐resolution elevation models accurate enough to reveal the sources of DOC found in headwater streams. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

9.
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   

10.
Although temporal variation in headwater stream chemistry has long been used to document baseline conditions and response to environmental drivers, less attention is paid to fine scale spatial variations that could yield clues to processes controlling stream water sources. We documented spatial and temporal variation in water composition in a headwater catchment (41 ha) at the Hubbard Brook Experimental Forest, NH, USA. We sampled every 50 m along an ephemeral to perennial stream network as well as groundwater from seeps and 35 shallow wells across varying flow conditions. Groundwater influences on surface water in this region have not been considered to be important in past studies as relatively coarse soils were assumed to be well drained in steep catchments with flashy runoff response. However, seeps displayed perennial discharge, upslope accumulated areas (UAA) smaller than those for channel initiation sites and higher pH, Ca and Si concentrations than streams, suggesting relatively long groundwater residence time or long subsurface flow paths not bound by topographic divides. Coupled with a large range in groundwater chemistry seen in wells, these results suggest stream chemistry variation reflects the range of connectivity with, and quality of, groundwater controlled by hillslope hydropedological processes. The magnitude of variations of solute concentrations seen in the first order catchment was as broad as that seen at the fifth order Hubbard Brook Valley (3519 ha). Reduction in variation in solute concentrations with increasing UAA suggested a representative elementary area (REA) value of less than 3 ha in the first order catchment, compared with 100 ha for the fifth order basin. Thus, the REA is not necessarily an elementary catchment property. Rather, the partitioning of variation between highly variable upstream sources and relatively homogenous downstream characteristics may have different physical significance depending on the scale and complexity of the catchment under examination. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

11.
Conservative solute injections were conducted in three first-order montane streams of different geological composition to assess the influence of parent lithology and alluvial characteristics on the hydrological retention of nutrients. Three study sites were established: (1) Aspen Creek, in a sandstone–siltstone catchment with a fine-grained alluvium of low hydraulic conductivity (1·3×10−4 cm/s), (2) Rio Calaveras, which flows through volcanic tuff with alluvium of intermediate grain size and hydraulic conductivity (1·2×10−3 cm/s), and (3) Gallina Creek, located in a granite/gneiss catchment of coarse, poorly sorted alluvium with high hydraulic conductivity (4·1×10−3 cm/s). All sites were instrumented with networks of shallow groundwater wells to monitor interstitial solute transport. The rate and extent of groundwater–surface water exchange, determined by the solute response in wells, increased with increasing hydraulic conductivity. The direction of surface water–groundwater interaction within a stream was related to local variation in vertical and horizontal hydraulic gradients. Experimental tracer responses in the surface stream were simulated with a one-dimensional solute transport model with inflow and storage components (OTIS). Model-derived measures of hydrological retention showed a corresponding increase with increasing hydraulic conductivity. To assess the temporal variability of hydrological retention, solute injection experiments were conducted in Gallina Creek under four seasonal flow regimes during which surface discharge ranged from baseflow (0·75 l/s in October) to high (75 l/s during spring snowmelt). Model-derived hydrological retention decreased with increasing discharge. The results of our intersite comparison suggest that hydrological retention is strongly influenced by the geologic setting and alluvial characteristics of the stream catchment. Temporal variation in hydrological retention at Gallina Creek is related to seasonal changes in discharge, highlighting the need for temporal resolution in studies of the dynamics of surface water–groundwater interactions in stream ecosystems. © 1997 by John Wiley & Sons, Ltd.  相似文献   

12.
This study examined stream water quality across a range of catchments which are representative of the key environments and land uses of rural south-west England. These catchments included: (a) an acidic upland headwater catchment, rising on the moorlands of Dartmoor, with low-intensity sheep rearing; (b) a headwater catchment rising on the weathered granite lower slopes of Dartmoor, with cattle farming; (c) a lowland headwater clay catchment with sub-surface drainage and high intensity livestock farming, fodder crop cultivation, and hard-standing/slurry storage; and (d) the main River Taw, a lowland river system receiving drainage from a range of tributaries, exemplified by the above catchment types. Variations in water chemistry and quality were observed along an upland–lowland transition, from headwater streams to the main river channel. Within the livestock-dominated headwater streams, total phosphorus (TP) was dominated by particulate phosphorus (PP). These PP concentrations appeared to be mainly linked to two sets of processes: (1) in-stream sediment precipitation with sorption/co-precipitation of phosphate and/or localised in-channel mobilisation of sediment (by cattle or channel-clearing operations) under low flow conditions, and (2) sediment erosion and transportation associated with near-surface runoff during storm events. Under baseflow conditions, in-stream and/or riparian processes played a significant role in controlling general nutrient chemistry, particularly in the headwater streams which were heavily impacted by livestock.  相似文献   

13.
Monitoring the temporal variation of solute concentrations in streams at high temporal frequency can play an important role in understanding the hydrological and biogeochemical behaviour of catchments. UV–visible spectrometry is a relatively inexpensive and easily used tool to infer those concentrations in streams at high temporal resolution. However, it is not yet clear which solutes can be modelled with such an in-situ sensor. Here, we installed a UV–visible spectrometer probe (200–750 nm) in a high-altitude tropical Páramo stream to record the wavelength absorbance at a 5-min temporal resolution. For calibration, we simultaneously sampled stream water at a 4-h frequency from February 2018 to March 2019 for subsequent laboratory analysis. Absorbance spectra and laboratory-determined solute concentrations were used to identify the best calibration method and to determine which solute concentrations can be effectively inferred using in situ spectrometry through the evaluation of six calibration methods of different mathematical complexity. Based on the Nash – Sutcliffe efficiency (NSE) and Akaike information criterion metrics, our results suggest that multivariate methods always outperformed simpler strategies to infer solute concentrations. Eleven out of 21 studied solutes (Al, DOC, Ca, Cu, K, Mg, N, Na, Rb, Si and Sr) were successfully calibrated (NSE >0.50) and could be inferred using UV–visible spectrometry even with a reduced daily sampling frequency. It is worth noting that most calibrated solutes were correlated with wavelengths (WLs) in the low range of the spectra (i.e., UV range) and showed relatively good correlation with DOC. The latter suggests that estimation of metal concentrations could be possible in other streams with a high organic load (e.g., peat dominated catchments). In situ operation of spectrometers to monitor water quality parameters at high temporal frequency (sub-hourly) can enhance the protection of human water supplies and aquatic ecosystems as well as providing information for assessing catchment hydrological functioning.  相似文献   

14.
Abstract

Knowledge of the hydrochemical dynamics of the trace metal manganese (Mn) in upland catchments is required for water quality management. Stream water Mn and other solutes and flow were monitored in two upland catchments in northern England with different soils: one dominated by peat (HS7), the other by mineral soils (HS4). Maximum Mn concentrations occurred at different times in the two catchments: in summer baseflow at HS4 and during late summer storm events at HS7. A two-component chemical mixing model was used to identify the hydrological processes controlling Mn concentrations in stream water. This approach was more successful for HS4 than HS7, probably because of different processes of Mn release in the two catchments and also difficulties in selecting conservative solutes. Factor analysis of the stream water chemistry data set for each catchment was more useful in identifying the controls on Mn release into runoff. The factors indicate that the main source of Mn at HS4 is the hydrological pathway supplying summer baseflow, whereas at HS7 Mn is released during the rewetting of dried peat soils. Manganese concentrations in stream water in upland catchments appear to depend on soil type and antecedent moisture conditions. This has implications for the design of sampling strategies in upland catchments and also for managing the quality of water supplies from such areas.  相似文献   

15.
Hydrological events transport large proportions of annual or seasonal dissolved organic carbon (DOC) loads from catchments to streams. The timing, magnitude and intensity of these events are very sensitive to changes in temperature and precipitation patterns, particularly across the boreal region where snowpacks are declining and summer droughts are increasing. It is important to understand how landscape characteristics modulate event-scale DOC dynamics in order to scale up predictions from sites across regions, and to understand how climatic changes will influence DOC dynamics across the boreal forest. The goal of this study was to assess variability in DOC concentrations in boreal headwater streams across catchments with varying physiographic characteristics (e.g., size, proportion of wetland) during a range of hydrological events (e.g., spring snowmelt, summer/fall storm events). From 2016 to 2017, continuous discharge and sub-daily chemistry grab samples were collected from three adjacent study catchments located at the International Institute for Sustainable Development-Experimental Lakes Area in northwestern Ontario, Canada. Catchment differences were more apparent in summer and fall events and less apparent during early spring melt events. Hysteresis analysis suggested that DOC sources were proximal to the stream for all events at a catchment dominated by a large wetland near the outlet, but distal from the stream at the catchments that lacked significant wetland coverage during the summer and fall. Wetland coverage also influenced responses of DOC export to antecedent moisture; at the wetland-dominated catchment, there were consistent negative relationships between DOC concentrations and antecedent moisture, while at the catchments without large wetlands, the relationships were positive or not significant. These results emphasize the utility of sub-daily sampling for inferring catchment DOC transport processes, and the importance of considering catchment-specific factors when predicting event-scale DOC behaviour.  相似文献   

16.
Variations in the concentration of Cl in rainfall and stream runoff are presented for two catchments in the Hafren forest of mid-Wales, Great Britain. Despite the large fluctuations in rainfall concentrations, Cl in the streamwater remains relatively constant. Using the two-reservoir Birkenes model, an attempt was made to simulate observed Cl in streamwater. The original model was unable to reproduce the observations and several modifications are suggested to provide better simulations. The resulting model is not the only one capable of reproducing the observations; other hydrochemical models will most probably also achieve this although emphasis will in each case be placed on different aspects. In this paper, it is suggested that the stochastic properties of water movement and chemical processes can account for the streamwater chemistry responses observed. On the catchment scale these processes will lead to an apparently deterministic behaviour that may well be described by simple relationships.  相似文献   

17.
Hydrological and hydrochemical processes in the critical zone of karst environments are controlled by the fracture‐conduit network. Modelling hydrological and hydrochemical dynamics in such heterogeneous hydrogeological settings remains a research challenge. In this study, water and solute transport in the dual flow system of the karst critical zone were investigated in a 73.5‐km2 catchment in southwest China. We developed a dual reservoir conceptual run‐off model combined with an autoregressive and moving average model with algorithms to assess dissolution rates in the “fast flow” and “slow flow” systems. This model was applied to 3 catchments with typical karst critical zone architectures, to show how flow exchange between fracture and conduit networks changes in relation to catchment storage dynamics. The flux of bidirectional water and solute exchange between the fissure and conduit system increases from the headwaters to the outfall due to the large area of the developed conduits and low hydraulic gradient in the lower catchment. Rainfall amounts have a significant influence on partitioning the relative proportions of flow and solutes derived from different sources reaching the underground outlet. The effect of rainfall on catchment function is modulated by the structure of the karst critical zone (e.g., epikarst and sinkholes). Thin epikarst and well‐developed sinkholes in the headwaters divert more surface water (younger water) into the underground channel network, leading to a higher fraction of rainfall recharge into the fast flow system and total outflow. Also, the contribution of carbonate weathering to mass export is also higher in the headwaters due to the infiltration of younger water with low solute concentrations through sinkholes.  相似文献   

18.
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19.
Rivers in the Mediterranean region often exhibit an intermittent character. An understanding and classification of the flow regimes of these rivers is needed, as flow patterns control both physicochemical and biological processes. This paper reports an attempt to classify flow regimes in Mediterranean rivers based on hydrological variables extracted from discharge time series. Long‐term discharge records from 60 rivers within the Mediterranean region were analysed in order to classify the streams into different flow regime groups. Hydrological indices (HIs) were derived for each stream and principal component analysis (PCA) and then applied to these indices to identify subsets of HIs describing the major sources of variations, while simultaneously minimizing redundancy. PCA was performed for two groups of streams (perennial and temporary) and for all streams combined. The results show that whereas perennial streams are mainly described by high‐flow indices, temporary streams are described by duration, variability and predictability indices. Agglomerative cluster analysis based on HIs identified six groups of rivers classified according to differences in intermittency and variability. A methodology allowing such a classification for ungauged catchments was also tested. Broad‐scale catchment characteristics based on digital elevation, climate, soil and land use data were derived for each long‐term station where these data were available. By using stepwise multiple regression analysis, statistically significant relationships were fitted, linking the three selected hydrological variables (mean annual number of zero‐flow days, predictability and flashiness) to the catchment characteristics. The method provides a means of simplifying the complexity of river systems and is thus useful for river basin management. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

20.
Dissolved organic carbon (DOC) was measured at four or eight hour intervals between mid-1989 and mid-1991 in two catchments in west central Scotland. The experimental catchment had been recently clear-felled and the control remained under forest. The amount of DOC varied during individual storm events following the stream hydro-graph. Maximum variations were found in the summer half-year and in the clear-felled catchment. There was also evidence of the exhaustion of DOC in the later events of a sequence. Differences between the catchments were related to catchment characteristics and to land-use change. The reduced magnitude of variation in DOC with discharge in the control stream was due to the influence of a wetland area through which the stream flowed. The mean DOC concentrations were similar in the two streams and annual exports were 15 g m?2 from the control and 16g m?2 from the felled catchment. The stream draining the clear-felled catchment had greater high flow DOC concentrations in the summer half-year, probably due to the effect of greater mean summer temperatures on DOC release and of the greater supply of organic debris in the stream channel.  相似文献   

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