Relating hydrogeomorphic properties to stream buffering chemistry in the Neversink River watershed,New York State,USA

Monitoring the effects of acidic deposition on aquatic ecosystems in the Northeastern US has generally required regular measurements of stream buffering chemistry (i.e. acid‐neutralizing capacity (ANC) and calcium Ca²⁺), which can be expensive and time consuming. The goal of this paper was to develop a simple method for predicting baseflow buffering chemistry based on the hydrogeomorphic properties of ten nested watersheds in the Neversink River basin (2·0–176·0 km²), an acid‐sensitive basin in the Catskill Mountains, New York State. The tributaries and main reach watersheds have strongly contrasting mean baseflow ANC values and Ca²⁺ concentrations, despite rather homogeneous vegetation, bedrock geology, and soils. A stepwise regression was applied to relate 13 hydrogeomorphic properties to the mean baseflow ANC values and Ca²⁺ concentrations. The regression analysis showed that watersheds with lower ANC values had a higher mean ratio of ‘quickflow’ runoff to precipitation during 20 non‐snowmelt runoff events (referred to as mean runoff ratio). The mean runoff ratio could explain at least 80% of the variability in mean baseflow ANC values and Ca²⁺ concentrations among the ten watersheds. Greater mean runoff ratios also correlated with steeper slopes and greater drainage densities, thus allowing the prediction of baseflow ANC values (r² = 0·75) and Ca²⁺ concentrations (r² = 0·77) with widely available spatial data alone. These results indicate that hydrogeomorphic properties can predict a watershed's sensitivity to acid deposition in regions where the spatial sources of stream buffering chemistry from the bedrock mineralogy and soils are fairly uniform. Copyright © 2010 John Wiley & Sons, Ltd.     

Relating snow dynamics and balsam fir stand characteristics,Montmorency Forest,Quebec

Snow water equivalent was measured during three springs on north‐ and south‐exposed sites representing a range of stand structure and development stages of Quebec's balsam fir forest. Maximum snow water equivalent of the season, mean seasonal snowmelt rate, snowmelt season duration and total snowmelt season degree‐day factor were related to canopy height, canopy density, light interception fraction and basal area of the stands using random coefficient models. Seasonal mean snowmelt rate was better explained by stand characteristics (R² from 0·41 to 0·61) than was maximum snow water equivalent (R² from 0·08 to 0·23). The best relationship was found with light interception, which explained 61% of snowmelt rate variability between stands. These relationships were not significantly affected by stand aspect (Pr ≥ S = 0·14 or higher), as snow dynamics seemed less dependent on aspect than on stand characteristics. Snowmelt recovery rates could be used by forest planners to establish an acceptable time step for the harvesting of different parts of a watershed in order to prevent peak flow augmentations. Copyright © 2005 John Wiley & Sons, Ltd.     

Hydrologic and biogeochemical controls on the spatial and temporal patterns of nitrogen and phosphorus in the Kuparuk River,arctic Alaska

Nitrogen (N) and phosphorus (P) dynamics in the Kuparuk River in arctic Alaska were characterized in a 3‐year study using routine samples near the mouth of the river at the Arctic Ocean, synoptic whole‐river surveys, and temporally intense sampling during storms in three headwater basins. The Lower Kuparuk River has low nitrate concentrations (mean [NO₃]‐N] = 17 µg l^?1 ± 1·6 SE) and dissolved inorganic N (DIN, mean [N] = 31 µg l^?1 ± 1·2 SE) compared with rivers in more temperate environments. Organic forms constituted on average 90% of the N exported to the Arctic Ocean, and high ratios of dissolved organic N (DON) to total dissolved N (TDN) concentrations (mean 0·92) likely result from waterlogged soils formed by reduced infiltration due to permafrost and low hydrologic gradients. Annual export of TDN, DON, and particulate N averaged 52 kg km^?2, 48 kg km^?2, and 4·1 kg km^?2 respectively. During snowmelt, the high volume of runoff typically results in the highest nutrient loads of the year, although high discharge during summer storms can result in substantial nutrient loading over short periods of time. Differences in seasonal flow regime (snowmelt versus rain) and storm‐driven variation in discharge appear to be more important for determining nutrient concentrations than is the spatial variation in processes along the transect from headwaters towards the ocean. Both the temporal variation in nitrate:DIN ratios of headwater streams and the spatial variation in nitrate:DIN between larger sub‐basins and smaller headwater catchments is likely controlled by shifts in nitrification and soil anoxia. Copyright © 2008 John Wiley & Sons, Ltd.     

Channel precipitation dynamics in a forested Pennsylvania headwater catchment (USA)

Seasonal and event variations in stream channel area and the contributions of channel precipitation to stream flow were studied on a 106‐ha forested headwater catchment in central Pennsylvania. Variations in stream velocity, flowing stream surface width and widths of near‐stream saturated areas were periodically monitored at 61 channel transects over a two‐year period. The area of flowing stream surface and near‐stream saturated zones combined, ranged from 0·07% of basin area during summer low flows to 0·60% of total basin area during peak storm flows. Near‐stream saturated zones generally represented about half of the total channel area available to intercept throughfall and generate channel precipitation. Contributions of routed channel precipitation from the flowing stream surface and near‐stream zones, calculated using the Penn State Runoff Model (PSRM, v. 95), represented from 1·1 to 6·4% of total stream flow and 2·5–29% of total storm flow (stream flow–antecedent baseflow) during the six events. Areas of near‐stream saturated zones contributed 35–52% of the computed channel precipitation during the six events. Channel precipitation contributed a higher percentage of stream flow for events with low antecedent baseflow when storm flow generated by subsurface sources was relatively low. Expansion of channel area and consequent increases in volumes of channel precipitation with flow increases during events was non‐linear, with greater rates of change occurring at lower than at higher discharge rates. Copyright © 1999 John Wiley & Sons, Ltd.     

Concentrations and transport of different forms of phosphorus during snowmelt runoff from an illite clay soil

During a 16 day period with pronounced snowmelt via surface runoff, high water concentrations (usually 0·4–0·5 mg l^?1) of dissolved molybdate‐reactive phosphorus (MRP) were detected in surface runoff water from a clay soil of illite type. Other phosphorus fractions defined were: phosphorus in particles with a higher settling coefficient than 80 000 S (SPP); colloidal phosphorus caught on filters with a pore size of 0·2 µm but with a smaller settling coefficient (CPP); and dissolved phosphorus not reacting with molybdate (DUP). The order of concentrations was MRP > SPP > CPP > DUP. Nearly identical amounts of MRP, CPP, and DUP (in total 0·3 kg ha^?1) were lost from a grass–clover ley and a ploughed soil. However, more of the heavier phosphorus‐containing material was lost from the ploughed area. In drainpipe water, CPP was the largest fraction (28%), and in stream water from mixed arable/forest land, MRP dominated (33%). Loss on ignition of the settling material slowly decreased from 10 to 8% (dry weight) during the snowmelt period. Total phosphorus concentrations in the material followed the runoff pattern, with slightly higher phosphorus concentrations during fast runoff. The large amounts of readily dissolved or colloidal‐bound phosphorus (70–80%) transported from this clay soil during snowmelt are discussed with regard to the use of grass buffer strips as a measure against phosphorus losses from arable land. Copyright © 2002 John Wiley & Sons, Ltd.     

Dynamic evolution of nutrient discharge under stormflow and baseflow conditions in a coastal agricultural watershed in Ishigaki Island,Okinawa, Japan

Excessive terrestrial nutrient loadings adversely impact coral reefs by primarily enhancing growth of macroalgae, potentially leading to a phase‐shift phenomenon. Hydrological processes and other spatial and temporal factors affecting nutrient discharge must be examined to be able to formulate effective measures for reducing nutrient export to adjacent reefs. During storm events and baseflow periods, water samples were obtained from the tropical Todoroki River, which drains an intensively agricultural watershed into Shiraho coral reef. In situ nutrient analyzers were deployed for 6 months to hourly measure dissolved nutrient (NO₃⁻‐N and PO₄³⁻‐P) concentrations. Total phosphorus (TP) and suspended solid concentration (TSS) were increased by higher rainfall intensity (r = 0·94, p < 0·01) and river discharge Q (r = 0·88, p < 0·01). In contrast, NO₃⁻‐N concentration tends to decrease drastically (e.g. from 3 to 1 mg l⁻¹) during flood events. When base flow starts to dominate afterwards, NO₃⁻‐N manifested an increasing trend, but decreases when baseflow discharge becomes low. This counter‐clockwise hysteresis for NO₃⁻‐N highlights the significant influence of groundwater discharge. N delivery can therefore be considered a persistent process compared to sediment and P discharge, which are highly episodic in nature. Based on GIS analysis, nutrient concentration along the Todoroki River was largely affected by the percentage of sugarcane/bare areas and bedrock type. The spatial distribution of N concentration in the river reflects the considerable influence of subsurface geology—higher N levels in limestone‐dominated areas. P concentrations were directly related to the total length of artificial drainage, which enhances sediment transport. The use of high‐resolution monitoring data coupled with GIS‐based spatial analysis therefore enabled the clarification of control factors and the difference in the spatio‐temporal discharge characteristics between N and P. Thus, although erosion‐reduction schemes would reduce P discharge, other approaches (e.g. minimize fertilizer) are needed to reduce N discharge. Copyright © 2010 John Wiley & Sons, Ltd.     

Effects of 2003 wildfires on stream chemistry in Glacier National Park,Montana

Changes in stream chemistry were studied for 4 years following large wildfires that burned in Glacier National Park during the summer of 2003. Burned and unburned drainages were monitored from December 2003 through August 2007 for streamflow, major constituents, nutrients, and suspended sediment following the fires. Stream‐water nitrate concentrations showed the greatest response to fire, increasing up to tenfold above those in the unburned drainage just prior to the first post‐fire snowmelt season. Concentrations in winter base flow remained elevated during the entire study period, whereas concentrations during the growing season returned to background levels after two snowmelt seasons. Annual export of total nitrogen from the burned drainage ranged from 1·53 to 3·23 kg ha^?1 yr^?1 compared with 1·01 to 1·39 kg ha^?1 yr^?1 from the unburned drainage and exceeded atmospheric inputs for the first two post‐fire water years. Fire appeared to have minimal long‐term effects on other nutrients, dissolved organic carbon, and major constituents with the exception of sulfate and chloride, which showed increased concentrations for 2 years following the fire. There was little evidence that fire affected suspended‐sediment concentrations in the burned drainage. Sediment yields in subalpine streams may be less affected by fire than in lower elevation streams because of the slow release rate of water during spring snowmelt. Published in 2008 by John Wiley & Sons, Ltd.     

Improvement of distributed snowmelt energy balance modeling with MODIS‐based NDSI‐derived fractional snow‐covered area data

Describing the spatial variability of heterogeneous snowpacks at a watershed or mountain‐front scale is important for improvements in large‐scale snowmelt modelling. Snowmelt depletion curves, which relate fractional decreases in snow‐covered area (SCA) against normalized decreases in snow water equivalent (SWE), are a common approach to scale‐up snowmelt models. Unfortunately, the kinds of ground‐based observations that are used to develop depletion curves are expensive to gather and impractical for large areas. We describe an approach incorporating remotely sensed fractional SCA (FSCA) data with coinciding daily snowmelt SWE outputs during ablation to quantify the shape of a depletion curve. We joined melt estimates from the Utah Energy Balance Snow Accumulation and Melt Model (UEB) with FSCA data calculated from a normalized difference snow index snow algorithm using NASA's moderate resolution imaging spectroradiometer (MODIS) visible (0·545–0·565 µm) and shortwave infrared (1·628–1·652 µm) reflectance data. We tested the approach at three 500 m² study sites, one in central Idaho and the other two on the North Slope in the Alaskan arctic. The UEB‐MODIS‐derived depletion curves were evaluated against depletion curves derived from ground‐based snow surveys. Comparisons showed strong agreement between the independent estimates. Copyright © 2010 John Wiley & Sons, Ltd.     

Parameter sensitivity of automated baseflow separation for snowmelt‐dominated watersheds and new filtering procedure for determining end of snowmelt period

Automation in baseflow separation procedures allowed fast and convenient baseflow and baseflow index (BF and BFI) estimation for studies including multiple watersheds and covering large spatio‐temporal scales. While most of the existing algorithms are developed and tested extensively for rainfall‐ and baseflow‐dominated systems, little attention is paid on their suitability for snowmelt‐dominated systems. Current publishing practice in regional‐scale studies is to omit BF and BFI uncertainty evaluation or sensitivity analysis. Instead, “standard” and “previously recommended” parameterizations are transferred from rainfall/BF to snowmelt‐dominated systems. We believe that this practice should be abandoned. First, we demonstrate explicitly that the three most popular heuristic automated BF separation methods—Lyne–Hollick and Eckhardt recursive digital filters, and the U.K. Institute of Hydrology smoothed minima method—produce a wide range of annual BF and BFI estimates due to parameter sensitivity during the annual snowmelt period. Then, we propose a solution for cases when BF and BFI calibration is not possible, namely excluding the snowmelt‐dominated period from the analysis. We developed an automated filtering procedure, which divides the hydrograph into pre‐snowbelt, post‐snowmelt, and snowmelt periods. The filter was tested successfully on 218 continuous water years of daily streamflow data for four snowmelt‐dominated headwater watersheds located in Wyoming (60–837 km²). The post‐snowmelt BF and BFI metric can be used for characterizing summer low‐flows for snowmelt‐dominated systems. Our results show that post‐snowmelt BF and BFI sensitivity to filter parameterization is reduced compared with the sensitivity of annual BF and BFI and is similar to the sensitivity levels for rainfall/baseflow systems.     

Run‐off formation in a humid,temperate headwater catchment using a combined hydrological,hydrochemical and isotopic approach (Jizera Mountains,Czech Republic)

The formation of baseflow and stormflow was examined in the 1.18 km² part of the headwater catchment Uhlí?ská, Jizera Mountains, Czech Republic, over the period 2007–2011, by means of run‐off data and environmental tracers ¹⁸O and SiO₂. The baseflow, computed using the digital filter approach BFLOW, contributes 67% to total streamflow and has a mean residence time of 12.3 months. It is formed by groundwater discharge from the valley deluviofluvial granitic sediments, in combination with soil water in weathered layers on hillslopes during rainfall and snowmelt periods. The prevailing source of the groundwater is the infiltration of snowmelt water. Analysis of 20 run‐off events and their hysteretic patterns demonstrated that the stormflow water has a residence time of about 4 months and is generated by preferential flow on hillslopes combined by soil matrix drainage. Because of slower flow in the soil matrix, the enrichment of pore water in SiO₂ is more pronounced. The stormflow and snowmelt water flowing via preferential pathways of upslope minerals soils pushes the pre‐event groundwater through the pathways in wetlands to the stream, and the wetland can be therefore considered as groundwater supplied. This mechanism has been found to be typical for the groundwater‐supplied headwater catchments of the Jizera Mountains and can be also assumed in other mountainous headwaters of the granitic massif in Central Europe. The main methodological contribution of this study are the residence time calculations stratified by baseflow and event flow, identifying run‐off components of different travel times to streams and linking them with geochemical run‐off sources. This achievement was possible because of a comprehensive dataset on hydrology, stable isotopes and silica hydrochemistry in all relevant run‐off generation components. This concept indicates that a possible long‐term change in snowmelt may affect the run‐off regime of headwater catchments to climate or land‐use changes. Copyright © 2013 John Wiley & Sons, Ltd.     

Factors controlling nitrogen and dissolved organic carbon exports across timescales in two watersheds with different land uses

Investigating factors controlling the temporal patterns of nitrogen (N) and dissolved organic carbon (DOC) exports on the basis of a comparative study of different land uses is beneficial for managing water resources, especially in agricultural watersheds. We focused our research on an agricultural watershed (AW) and a forested watershed (FW) located in the Shibetsu watershed of eastern Hokkaido, Japan, to investigate the temporal patterns of N and DOC exports and factors controlling those patterns at different timescales (inter‐annual, seasonal, and hydrological event scales). Results showed that the annual patterns of N and DOC exports significantly varied over time and were probably controlled by climate. Higher discharge volumes in 2003, a wet year, showed higher N and DOC loadings in both watersheds. However, this process was also regulated by land use associated with N inputs. Higher concentrations and loadings were shown in the agricultural watershed. At the seasonal scale, N and DOC exports in the AW and the FW were more likely controlled by sources associated with land use. The Total N (TN) and Nitrate‐N (NO₃^?‐N) had higher concentrations during snowmelt season in the AW, which may be attributed to manure application in late autumn or early winter in the agricultural watershed. Concentrations of TN, NO₃^?‐N, dissolved organic nitrogen (DON), and DOC showed higher values during the summer rainy season in the FW, related to higher litter decomposition during summer and autumn and the fertilizer application in the agricultural area during summer. Higher DOC concentrations and loadings were observed during the rainy season in the AW, which is probably attributed to higher DOC production related to temperature and microbial activity during summer and autumn in grasslands. Correlations between discharge and concentrations differed during different periods or in different watersheds, suggesting that weather discharge can adequately represent the fact that N export depends on N concentrations, discharge level, and other factors. The differing correlations between N/DOC concentrations and the Si concentration indicated that the N/DOC exports might occur along different flow paths during different periods. During baseflow, the high NO₃^?‐N exports were probably derived from deep groundwater and might have percolated from uplands during hydrological events. During hydrological events, NO₃^?‐N exports may occur along near‐surface flow paths and in deep groundwater, whereas DOC exports could be related to near‐surface flow paths. At the event scale, the relationships between discharge and concentrations of N and DOC were regulated by antecedent soil moisture (shallow groundwater condition) in each watershed. These results indicated that factors controlling N and DOC exports varied at different timescales in the Shibetsu area and that better management of manure application during winter in agricultural lands is urgently needed to control water pollution in streams. Copyright © 2013 John Wiley & Sons, Ltd.     

Identifying and linking source areas of flow and P transport in dairy‐grazed headwater catchments,North Island,New Zealand

We examined the applicability of the critical‐source area (CSA) concept to the dairy‐grazed 192‐ha Upper Toenepi catchment and its 8·7‐ha Kiwitahi sub‐catchment, New Zealand. We evaluated if phosphorus (P) transport from land into stream is dominated by saturation‐excess (SE) and infiltration‐excess (IE) runoff during stormflow and by sub‐surface (<1·5 m depth) flows during baseflow. We measured stream flow and shallow groundwater levels, collected monthly stream, tile drain (TDA) and groundwater samples, and flow‐proportional stream samples from the Kiwitahi sub‐catchment, and determined their dissolved reactive phosphorus (DRP) and total phosphorus (TP) concentrations. In the Kiwitahi sub‐catchment, during storm events, IE contributions were significant. Contributions from SE appeared significant in the Upper Toenepi catchment. However, in both catchments, sub‐surface contributions dominated stormflow and baseflow periods. Absence of water table at the surface and the water table gradient towards the stream indicated that P transport during events was not limited to surface runoff. The dynamics of the groundwater table and the occurrence of SE areas were influenced by proximity to the stream and hillslope positions. Baseflow accounted for 42% of the annual flow in the Kiwitahi sub‐catchment, and contributed 37 and 52% to the DRP and TP loads, respectively. The P transport during baseflow appeared equally important as P losses from CSAs during stormflow. The close resemblance in P levels between groundwater and stream samples during baseflow demonstrates the importance of shallow groundwater for stream flow. In the Upper Toenepi catchment, contributions from effluent ponds (EFFs) dominated P loads. Management strategies should focus on controlling P release from EFFs, and on decreasing Olsen P concentrations in soil to minimize leaching of P via sub‐surface flow to streams. Research is needed to quantify the role of sub‐surface flow as well as to expand management strategies to minimize P transfers during stormflow and baseflow conditions. Copyright © 2010 John Wiley & Sons, Ltd.     

Spatial and temporal perspectives on spring break‐up flooding in the Slave River Delta,NWT

Spatial and temporal patterns of spring break‐up flooding in the Slave River Delta (SRD), Northwest Territories, are characterized during three years (2003–2005) using water isotope tracers and total inorganic suspended sediment (TSS) concentrations measured from lakewater samples collected shortly after the spring melt. Strongly contrasting spring melt periods led to a moderate flood in 2003, no flooding in 2004 and widespread flooding in 2005. Flooded lakes have isotopically‐depleted δ¹⁸O (δ²H) signatures, ranging between ? 19·2‰ (?145‰) and ? 17·1‰ (?146‰) and most have high TSS concentrations (>10 mg L^?1), while non‐flooded lakes have more isotopically‐enriched δ¹⁸O (δ²H) signatures, ranging between ? 18·2‰ (?149‰) and ? 10·6‰ (?118‰) and low TSS concentrations (<10 mg L^?1). These results, in conjunction with the isotopic signatures of Slave River water and snowmelt, are used to estimate the proportion of river‐ or snowmelt‐induced dilution in delta lakes during the spring of each study year. Calculations indicate river flooding caused dilution of ～70–100% in delta lakes, while snowmelt dilution in the absence of river flooding ranged from ～0–56%. A positive relationship exists between the spatial extent of spring flooding in the SRD and level and discharge on the Slave River and upstream tributaries, suggesting that upstream flow generation plays a key role in determining the magnitude of spring flooding in the SRD. Parallel variations in the 46‐year instrumental Slave River discharge record and flood stratigraphy in the active delta indicate that there is potential for extending the flood history of the SRD, a development that will contribute to a more robust understanding of the drivers of historic, contemporary and future flood frequency in the delta. Copyright © 2008 John Wiley & Sons, Ltd.     

Transformations of runoff chemistry in the Arctic tundra,Northwest Territories,Canada

The transformation of snowmelt water chemical composition during melt, elution and runoff in an Arctic tundra basin is investigated. The chemistry of the water flowing along pathways from the surface of melting snow to the 95·5 ha basin outlet is related to relevant hydrological processes. In so doing, this paper offers physically based explanations for the transformation of major ion concentrations and loads of runoff water associated with snowmelt and rainfall along hydrological pathways to the stream outlet. Late‐lying snowdrifts were found to influence the ion chemistry in adjacent reaches of the stream channel greatly. As the initial pulse of ion‐rich melt water drained from the snowdrift and was conveyed through hillslope flowpaths, the concentrations of most ions increased, and the duration of the peak ionic pulse lengthened. Over the first 3 m of overland flow, the concentrations of all ions except for NO increased by one to two orders of magnitude, with the largest increase for K⁺, Ca²⁺ and Mg²⁺. This was roughly equivalent to the concentration increase that resulted from percolation of relatively dilute water through 0·25 m of unsaturated soil. The Na⁺ and Cl^? were the dominant ions in snowmelt water, whereas Ca²⁺ and Mg²⁺ dominated the hillslope runoff. On slopes below a large melting snowdrift, ion concentrations of melt water flowing in the saturated layer of the soil were very similar to the relatively dilute concentrations found in surface runoff. However, once the snowdrift ablated, ion concentrations of subsurface flow increased above parent melt‐water concentrations. Three seasonally characteristic hydrochemical regimes were identified in a stream reach adjacent to late‐lying snowdrifts. In the first two stages, the water chemistry in the stream channel strongly resembled the hillslope drainage water. In the third stage, in‐stream geochemical processes, including the weathering/ion exchange of Ca²⁺ and Mg²⁺, were the main control of streamwater chemistry. Copyright © 2006 John Wiley & Sons, Ltd.     

Seasonal snowpack dynamics and runoff in a cool temperate forest: lysimeter experiment in Niigata,Japan

Seasonal snowpack dynamics are described through field measurements under contrasting canopy conditions for a mountainous catchment in the Japan Sea region. Microclimatic data, snow accumulation, albedo and lysimeter runoff are given through the complete winter season 2002–03 in (1) a mature cedar stand, (2) a larch stand, and (3) a regenerating cedar stand or opening. The accumulation and melt of seasonal snowpack strongly influences streamflow runoff during December to May, including winter baseflow, mid‐winter melt, rain on snow, and diurnal peaks driven by radiation melt in spring. Lysimeter runoff at all sites is characterized by constant ground melt of 0·8–1·0 mm day⁻¹. Rapid response to mid‐winter melt or rainfall shows that the snowpack remains in a ripe or near‐ripe condition throughout the snow‐cover season. Hourly and daily lysimeter discharge was greatest during rain on snow (e.g. 7 mm h⁻¹ and 53 mm day⁻¹ on 17 December) with the majority of runoff due to rainfall passing through the snowpack as opposed to snowmelt. For both rain‐on‐snow and radiation melt events lysimeter discharge was generally greatest at the open site, although there were exceptions such as during interception melt events. During radiation melt instantaneous discharge was up to 4·0 times greater in the opening compared with the mature cedar, and 48 h discharge was up to 2·5 times greater. Perhaps characteristic of maritime climates, forest interception melt is shown to be important in addition to sublimation in reducing snow accumulation beneath dense canopies. While sublimation represents a loss from the catchment water balance, interception melt percolates through the snowpack and contributes to soil moisture during the winter season. Strong differences in microclimate and snowpack albedo persisted between cedar, larch and open sites, and it is suggested further work is needed to account for this in hydrological simulation models. Copyright © 2005 John Wiley & Sons, Ltd.     

Hydrological heterogeneity of an alpine stream–lake network in Switzerland

Water source and lake landscape position can strongly influence the physico‐chemical characteristics of flowing waters over space and time. We examined the physico‐chemical heterogeneity in surface waters of an alpine stream‐lake network (>2600 m a.s.l.) in Switzerland. The catchment comprises two basins interspersed with 26 cirque lakes. The larger lakes in each basin are interconnected by streams that converge in a lowermost lake with an outlet stream. The north basin is primarily fed by precipitation and groundwater, whereas the south basin is fed mostly by glacial melt from rock glaciers. Surface flow of the entire channel network contracted by ～60% in early autumn, when snowmelt runoff ceased and cold temperatures reduced glacial outputs, particularly in the south basin. Average water temperatures were ～4 °C cooler in the south basin, and temperatures increased by about 4–6 °C along the longitudinal gradient within each basin. Although overall water conductivity was low (<27 µS cm^?1) because of bedrock geology (ortho‐gneiss), the south basin had two times higher conductivity values than the north basin. Phosphate‐phosphorus levels were below analytical detection limits, but particulate phosphorus was about four times higher in the north basin (seasonal average: 9 µg l^?1) than in the south basin (seasonal average: 2 µg l^?1). Dissolved nitrogen constituents were around two times higher in the south basin than in the north basin, with highest values averaging > 300 µg l^?1 (nitrite + nitrate‐nitrogen), whereas particulate nitrogen was approximately nine times greater in the north basin (seasonal average: 97 µg l^?1) than in the south basin (seasonal average: 12 µg l^?1). Total inorganic carbon was low (usually <0·8 mg l^?1), silica was sufficient for algal growth, and particulate organic carbon was 4·5 times higher in the north basin (average: 0·9 mg l^?1) than in the south basin (average: 0·2 mg l^?1). North‐basin streams showed strong seasonality in turbidity, particulate‐nitrogen and ‐phosphorus, and particulate organic carbon, whereas strong seasonality in south‐basin streams was observed in conductivity and dissolved nitrogen. Lake position influenced the seasonal dynamics in stream temperatures and nutrients, particularly in the groundwater/precipitation‐fed north‐basin network. Copyright © 2007 John Wiley & Sons, Ltd.     

Daily streamflow modelling and assessment based on the curve‐number technique

A cell‐based long‐term hydrological model (CELTHYM) that can be integrated with a geographical information system (GIS) was developed to predict continuous stream flow from small agricultural watersheds. The CELTHYM uses a cell‐by‐cell soil moisture balance approach. For surface runoff estimation, the curve number technique considering soil moisture on a daily basis was used, and release rate was used to estimate baseflow. Evapotranspiration was computed using the FAO modified Penman equation that considered land‐use‐based crop coefficients, soil moisture and the influence of topography on radiation. A rice paddy field water budget model was also adapted for the specific application of the model to East Asia. Model sensitivity analysis was conducted to obtain operational information about the model calibration parameters. The CELTHYM was calibrated and verified with measured runoff data from the WS#1 and WS#3 watersheds of the Seoul National University, Department of Agricultural Engineering, in Hwaseong County, Kyounggi Province, South Korea. The WS#1 watershed is comprised of about 35·4% rice paddy fields and 42·3% forest, whereas the WS#3 watershed is about 85·0% forest and 11·5% rice paddy fields. The CELTHYM was calibrated for the parameter release rate, K, and soil moisture storage coefficient, STC, and results were compared with the measured runoff data for 1986. The validation results for WS#1 considering all daily stream flow were poor with R², E² and RMSE having values of 0·40, ?6·63 and 9·69 (mm), respectively, but validation results for days without rainfall were statistically significant (R² = 0·66). Results for WS#3 showed good agreement with observed data for all days, and R², E² and RMSE were 0·92, 0·91 and 2·23 (mm), respectively, suggesting potential for CELTHYM application to other watersheds. The direct runoff and water balance components for watershed WS#1 with significant areas of paddy fields did not perform well, suggesting that additional study of these components is needed. Copyright © 2002 John Wiley & Sons, Ltd.     

Simulating short‐circuiting flow in a constructed wetland: the implications of bathymetry and vegetation effects

Short‐circuiting flow, commonly experienced in many constructed wetlands, reduces hydraulic retention times in unit wetland cells and decreases the treatment efficiency. A two‐dimensional (2‐D), physically based, distributed modelling approach was used to systematically address the effects of bathymetry and vegetation on short‐circuiting flow, which previously have been neglected or lumped in one‐dimensional wetland flow models. In this study, a 2‐D transient hydrodynamics with advection‐dispersion model was developed using MIKE 21 and calibrated with bromide tracer data collected at the Orlando Easterly Wetland Cell 7. The estimated topographic difference between short‐circuiting flow zone and adjacent area ranged from 0·3 to 0·8 m. A range of the Manning roughness coefficient at the short‐circuiting flow zone was estimated (0·022–0·045 s m^?1/3). Sensitivity analysis of topographical and vegetative heterogeneity deduced during model calibration shows that relic ditches or other ditch‐shaped landforms and the associated sparse vegetation along the main flow direction intensify the short‐circuiting pattern, considerably affecting 2‐D solute transport simulation. In terms of hydraulic efficiency, this study indicates that the bathymetry effect on short‐circuiting flow is more important than the vegetation effect. Copyright © 2009 John Wiley & Sons, Ltd.     

A temperature‐precipitation‐based model of thirty‐year mean snowpack accumulation and melt in Oregon,USA

High‐resolution, spatially extensive climate grids can be useful in regional hydrologic applications. However, in regions where precipitation is dominated by snow, snowmelt models are often used to account for timing and magnitude of water delivery. We developed an empirical, nonlinear model to estimate 30‐year means of monthly snowpack and snowmelt throughout Oregon. Precipitation and temperature for the period 1971–2000, derived from 400‐m resolution PRISM data, and potential evapotranspiration (estimated from temperature and day length) drive the model. The model was calibrated using mean monthly data from 45 SNOTEL sites and accurately estimated snowpack at 25 validation sites: R² = 0·76, Nash‐Sutcliffe Efficiency (NSE) = 0·80. Calibrating it with data from all 70 SNOTEL sites gave somewhat better results (R² = 0·84, NSE = 0·85). We separately applied the model to SNOTEL stations located < 200 and ≥ 200 km from the Oregon coast, since they have different climatic conditions. The model performed equally well for both areas. We used the model to modify moisture surplus (precipitation minus potential evapotranspiration) to account for snowpack accumulation and snowmelt. The resulting values accurately reflect the shape and magnitude of runoff at a snow‐dominated basin, with low winter values and a June peak. Our findings suggest that the model is robust with respect to different climatic conditions, and that it can be used to estimate potential runoff in snow‐dominated basins. The model may allow high‐resolution, regional hydrologic comparisons to be made across basins that are differentially affected by snowpack, and may prove useful for investigating regional hydrologic response to climate change. Published in 2011 by John Wiley & Sons, Ltd.     

Modified passive capillary samplers for collecting samples of snowmelt infiltration for stable isotope analysis in remote,seasonally inaccessible watersheds 2: field evaluation

Twelve modified passive capillary samplers (M‐PCAPS) were installed in remote locations within a large, alpine watershed located in the southern Rocky Mountains of Colorado to collect samples of infiltration during the snowmelt and summer rainfall seasons. These samples were collected in order to provide better constraints on the isotopic composition of soil‐water endmembers in the watershed. The seasonally integrated stable isotope composition (δ¹⁸O and δ²H) of soil‐meltwater collected with M‐PCAPS installed at shallow soil depths < 10 cm was similar to the seasonally integrated isotopic composition of bulk snow taken at the soil surface. However, meltwater which infiltrated to depths > 20 cm evolved along an isotopic enrichment line similar to the trendline described by the evolution of fresh snow to surface runoff from snowmelt in the watershed. Coincident changes in geochemistry were also observed at depth suggesting that the isotopic and geochemical composition of deep infiltration may be very different from that obtained by surface and/or shallow‐subsurface measurements. The M‐PCAPS design was also used to estimate downward fluxes of meltwater during the snowmelt season. Shallow and deep infiltration averaged 8·4 and 4·7 cm of event water or 54 and 33% of the measured snow water equivalent (SWE), respectively. Finally, dominant shallow‐subsurface runoff processes occurring during snowmelt could be identified using geochemical data obtained with the M‐PCAPS design. One soil regime was dominated by a combination of slow matrix flow in the shallow soil profile and fast preferential flow at depth through a layer of platy, volcanic rocks. The other soil regime lacked the rock layer and was dominated by slow matrix flow. Based on these results, the M‐PCAPS design appears to be a useful, robust methodology to quantify soil‐water fluxes during the snowmelt season and to sample the stable isotopic and geochemical composition of soil‐meltwater endmembers in remote watersheds. Copyright © 2009 John Wiley & Sons, Ltd.