Nutrient concentration patterns in streams draining alpine and subalpine catchments, Fraser Experimental Forest, Colorado

Streamwater samples were collected during 1987–1988 from two adjacent gauged watersheds, the subalpine-alpine East St. Louis and the Fool Creek Alpine, in the Fraser Experimental Forest, Colorado. The study objective was to compare the relationships between streamwater discharge and ion concentration in alpine and alpine-subalpine watersheds at a site receiving low inputs of atmospheric contaminants. Streamwater discharge accounts for much of the variation in ion concentration. Trajectories of time, discharge, and ion concentration suggest that patterns of nutrient flux are controlled primarily by the magnitude of streamwater discharge, and seasonal differences in the relative contributions of snowmelt and soil water. In the subalpine catchment, increased streamwater discharge accounted for most of the decline in concentration of ions, with high concentrations in soil water relative to precipitation. This relationship was not seen in the alpine catchment, probably because of the influence of large diurnal variation in the ratio of snowmelt to soil water. In both catchments, ions with comparatively high concentrations in precipitation and the snowpack relative to soil water showed less concentration decline with increased streamwater discharge. The recurring nature of the trajectories, especially in the subalpine catchment, suggests that the time, discharge, and ion concentration patterns may represent a general characteristic in moderate-sized, undisturbed Rocky Mountain catchments which do not receive high inputs of airborne contaminants.     

Characterization of the groundwater flow regime and hydrochemistry of groundwater from the Buem formation,Eastern Ghana

This study demonstrates the application of multivariate statistical methods in definition of groundwater recharge and discharge areas in a sedimentary basin in Ghana. Q‐mode hierarchical cluster analysis (HCA) was applied to 57 hydrochemical data from the Buem formation in the northern part of the Volta Region in Ghana. R‐mode HCA and R‐mode factor analysis were then applied to the same dataset to reveal the processes controlling the hydrochemistry of groundwater from this hydrogeological formation. Results of both the Q‐ and R‐mode analyses were backed by graphical methods. The analyses revealed two major water types, differentiated by salinity levels into four spatial groundwater associations. The characteristics of the four groundwater types are discussed. The recharge areas are characterized by Ca? HCO₃ low salinity waters which evolve through rock–water interactions to Na? HCO₃ high salinity waters in the discharge areas. This study finds that the hydrochemistry of groundwater from this formation is mainly controlled by the weathering of minerals, principally silicates in the aquifer matrix. The effects of the chemistry of recharging precipitation are higher in the recharge areas, while mineral weathering tends to be severe close to the discharge areas in the groundwater flow regime. All the four spatial groundwater associations have low sodium content, but salinity levels increase towards the discharge areas, such that some of wells in the discharge areas may not be acceptable for irrigation on grounds of high salinities which might affect the osmotic potentials of plants. Copyright © 2011 John Wiley & Sons, Ltd.     

On long-term evolution of seasonal precipitation in southwestern Europe

Annual cycles in long time series of precipitation from sixteen southwest European observatories have been analysed using complex demodulation. The stations have been clustered into two distinct regions and a hybrid one. They are referred to as the southwestern Europe precipitation Atlantic regime (SEPAR) and the southwestern Europe precipitation Mediterranean regime (SEPMER), with the hybrid regime referred to in terms of the mean amplitude ratios between semiannual and annual rainfall components. Some evidence of linking between seasonal cycle harmonic amplitudes and the zonal circulation has been found for SEPAR stations and a more obscured relationship for the SEPMER region. Within the SEPAR region the strength of the relationship is diminished towards the north. A trend analysis of the amplitudes against time since 1920 has also been carried out and the results reveal a divergent pattern in trends between annual and semiannual component amplitudes for the SEPAR region. In fact, both an increasing annual-amplitude trend and a decreasing semiannual-amplitude trend are observed, in each case statistically significant. The fact that the seasonal cycle variability of rainfall in southwestern Europe becomes more sensitive southwards to changes in atmospheric zonal circulation over the North Atlantic might, in our opinion, be related to the swing of the circumpolar vortex.     

Groundwater flow and storage processes in an inactive rock glacier

Groundwater flow through coarse blocky landforms contributes to streamflow in mountain watersheds, yet its role in the alpine hydrologic cycle has received relatively little attention. This study examines the internal structure and hydrogeological characteristics of an inactive rock glacier in the Canadian Rockies using geophysical imaging techniques, analysis of the discharge hydrograph of the spring draining the rock glacier, and chemical and stable isotopic compositions of source waters. The results show that the coarse blocky sediments forming the rock glacier allow the rapid infiltration of snowmelt and rain water to an unconfined aquifer above the bedrock surface. The water flowing through the aquifer is eventually routed via an internal channel parallel to the front of the rock glacier to a spring, which provides baseflow to a headwater stream designated as a critical habitat for an at‐risk cold‐water fish species. Discharge from the rock glacier spring contributes up to 50% of basin streamflow during summer baseflow periods and up to 100% of basin streamflow over winter, despite draining less than 20% of the watershed area. The rock glacier contains patches of ground ice even though it may have been inactive for thousands of years, suggesting the resiliency of the ground thermal regime under a warming climate.     

Precipitation as a proxy for climate variables: application for hydrological modelling

It has been proposed that linear regression curves can be used to estimate monthly climate variables from observed precipitation. This approach was explored by applying the MGB hydrological model to the Paraná Basin (Brazil). Linear regressions were obtained for 54 climate gauges, and most of them showed at least six months of significant correlation between monthly climate variables (sunlight hours and relative humidity) and precipitation. The regression equations were applied to 5201 raingauges to estimate monthly climate variables and evapotranspiration, and the results were compared with a scenario using long-term climate averages only. The main differences occurred in wetter periods, where negative correlations between monthly precipitation and evapotranspiration were obtained when using precipitation as a proxy. Long-term changes in the hydrological regime were assessed and showed that the effect of precipitation on relative humidity and sunlight hours seems to have a minor effect on the alterations observed in river discharge in the Paraná Basin.     

Estimating ground water recharge using flow models of perched karstic aquifers

The fraction of rain that is annually recharged to ground water is a function of the transient quantities of precipitation (wet vs. dry years) as well as other meteorological and geologic factors, and thus it is very difficult to estimate. In this study, we have used long records (20 to 30 years) of precipitation and spring discharge to reconstruct the transient character of yearly recharge. These data sets were used to calibrate numerical ground water flow models on the less than 3 km(2) scale for four separate perched karstic aquifers in the Judean and Samarian Mountains of Israel. The stratification and karstic character of the local carbonate rock aquifers cause ground water to flow through discrete dissolution channels and to discharge at isolated springs. An innovative, dual-porosity approach was used where a finite-difference solution simulates flow in the rock matrix, while the karstic channels are simulated using computationally simple drains. Perched conditions are also simulated innovatively using MODFLOW by treating the bottom unsaturated layer as if it is saturated, but by assuming zero pressure head throughout the "unsaturated" layer. Best fitting between measured and computed spring hydrograph data has allowed us to develop a set of empirical functions relating measured precipitation to recharge to the aquifer. The generic methodology presented gives insight into the suspected changes in aquifer recharge rates between particularly wet or dry years.     

Coarse sediment supply sets the slope of bedrock channels in rapidly uplifting terrain: Field and topographic evidence from eastern Taiwan

The incision rate and steepness of bedrock channels depend on water discharge, uplift rate, substrate lithology, sediment flux, and bedload size. However, the relative role of these factors and the sensitivity of channel steepness to rapid (>1 mm yr⁻¹) uplift rates remain unclear. We conducted field and topographic analyses of fluvial bedrock channels with varying channel bed lithology and sediment source rock along the Coastal Range in eastern Taiwan, where uplift rates vary from 1.8 to 11.8 mm yr⁻¹ and precipitation is relatively consistent (1.5–2.7 m yr⁻¹), to evaluate the controls on bedrock channel steepness. We find that channel steepness is independent of rock uplift rate and annual precipitation but increases monotonically with sediment size and substrate strength. Furthermore, in reaches with uniform substrate lithology (mudstone and flysch), channel steepness systematically varies with sediment source rock but not with channel width. When applied to our data, a mechanistic incision model (saltation-abrasion model) suggests that the steepness of Coastal Range channels is set primarily by coarse-sediment supply. We also observe that larger particles are mainly composed of resistant lithologies derived from volcanic rocks and conglomerates. This result implies that hillslope bedrock properties in the source area exert a dominant control on the steepness of proximal channels through coarse-sediment production in this setting. We propose that channel steepness may be insensitive to uplift rate and flow discharge in fast-uplifting landscapes where incision processes are set by coarse sediment size and supply. Models assuming a proportionality between incision rate and basal shear stress (stream power) may not fully capture controls on fluvial channel profiles in landslide-dominated landscapes. Processes other than channel steepening, such as enhanced bedload impacts and debris-flow scour, may be required to balance rock uplift and incision in these transport-limited systems.     

Functioning of natural and natural-engineering systems formation conditions and natural state of the hydrothermal system in the Valley of Geysers (Kronotsky Nature Reserve, Kamchatka)

The formation of the hydrothermal system in the Valley of Geysers is shown to be governed by a structure of radial and circular faults of above-intrusion zone of a partially melted magmatic body with an epicenter near the Upper-Geyser Field, while the hydrothermal system is shown to receive its water from elevations of +500 to +900 m abs (according to isotopic data). The catastrophic landslide of June 3, 2007, was just a stage in the general scenario of the gradual hydrothermal transformation of the inclined Geyser unit (Q ₃ ⁴ grn), building up the roof of the hydrothermal reservoir, with a gradual decline of slide resistance. The slide was triggered by the increased pressure in the hydrothermal and magmatic systems and the saturation of the Geyser unit by moisture during spring flood. According to the data of continuous regime thermohydrodynamic observations carried out in the Valley of Geysers with the use of HOBO-loggers of temperature and pressure since July 2007 to April 2010, the mean time between eruptions of Velikan geyser was 348 minutes. The intensification of precipitation input directly into the geyser pool causes a short-time increase in the time between eruptions (up to the maximum of 32 h). According to observations at the “Plotina” gage, the total estimated mean annual discharge of thermal springs (by chlorine ion) in the Valley of Geysers is 263 kg/s; the discharge of thermal springs is governed by the level of Poldprudnoe Lake and its seasonal variations exceed 40%.     

Impacts of future land cover and climate change on the water balance in northern Iran

We evaluated the potential impacts of future land cover change and climate variability on hydrological processes in the Neka River basin, northern Iran. This catchment is the main source of water for the intensively cultivated area of Neka County. Hydrological simulations were conducted using the Soil and Water Assessment Tool. An ensemble of 17 CMIP5 climate models was applied to assess changes in temperature and precipitation under the moderate and high emissions scenarios. To generate the business-as-usual scenario map for year 2050 we used the Land Change Modeler. With a combined change in land cover and climate, discharge is expected to decline in all seasons except the end of autumn and winter, based on the inter-model average and various climate models, which illustrated a high degree of uncertainty in discharge projections. Land cover change had a minor influence on discharge relative to that resulting from climate change.     

Standard normal homogeneity test as a tool to detect change points in climate-related river discharge variation: case study of the Kupa River Basin

ABSTRACT

The study addresses homogeneity testing of annual discharge time series for eight hydrological stations and five annual climate time series for one weather station in the Kupa River Basin, between Slovenia and Croatia, and global annual average surface temperature time series for the period 1961–2010. The standard normal homogeneity test (SNHT) was used to detect both abrupt and gradual linear trend homogeneity breaks. The results reveal natural change points at the beginning of the 1980s. Absolute homogeneity testing of average annual weather station-level air pressure, annual precipitation, differences between precipitation totals and potential evapotranspiration and surface runoff from the independent observation time series confirmed an abrupt shift, also at the beginning of the 1980s. The trend of local air temperature for 1985–2000, which partly coincides with global surface temperature trend for 1974–2005, strengthened the river discharge regime shift since the beginning of the 1980s. These results could improve climate variation monitoring and estimation of the impact of climate variation on the environment in the area. Generally, an indication of climate regime change points and an assessment of their duration could provide significant benefits for the society.     

Sediment loads response to climate change:A preliminary study of eight large Chinese rivers

Climate change characterized by increasing temperature is able to affect precipitation regime and thus surface hydrology.However,the manner in which river sediment loads respond to climate change is not well understood,and related assessment regarding the effect of climate change on sediment loads is lacking.We present a quantitative estimate of changes in sediment loads(from 1.5 Gt yr^-1 pre-1990 to 0.6 Gt yr^-1 from 1991-2007) in response to climate change in eight large Chinese rivers.Over the past decades,precipitation change coupled with rising temperatures has played a significant role in influencing the sediment delivery dynamics,although human activities, such as reservoir construction,water diversion,sand mining and land cover change,are still the predominant forces. Lower precipitation coupled with rising temperatures has significantly reduced sediment loads delivered into the sea in semi-arid climates（4-61%）.In contrast,increasingly warmer and wetter climates in subtropical zones has yielded more sediment（0.4-11%）,although the increase was offset by human impact.Our results indicate that,compared with mechanical retention by reservoirs,water reduction caused by climate change or human withdrawals has contributed more sediment reduction for the rivers with abundant sediment supply but limited transport capacity（e.g.,the Huanghe）.Furthermore,our results indicate that every 1%change in precipitation has resulted in a 1.3%change in water discharge and a 2%change in sediment loads.In addition,every 1%change in water discharge caused by precipitation has led to a 1.6%change in sediment loads,but the same percentage of water discharge change caused largely by humans would only result in a 0.9%change in sediment loads.These figures can be used as a guideline for evaluating the responses of sediment loads to climate change in similar climate zones because future global warming will cause dramatic changes in water and sediment in river basins worldwide at rates previously unseen.     

Water quality and spatio-temporal hot spots in an effluent-dominated urban river

In arid and semi-arid regions, many rivers experience extremely low flow conditions during seasonal dry periods. During these times, effluent from wastewater treatment plants can make up the majority of flow in the river. However, water quality in urban systems can also be strongly influenced by the natural or human-influenced flow regime and discharge from other anthropogenic sources such as industrial operations and runoff from impervious surfaces. In this study, we aimed to determine whether water quality was controlled primarily by wastewater discharge in an effluent-dominated river. Between May 2016–May 2019, we systematically measured water temperature, pH, dissolved oxygen, biochemical oxygen demand, and the concentrations of nitrate-N, ammonia-N, and orthophosphate in the South Platte River in the Denver metropolitan area, Colorado, USA. We found that, despite being an effluent-dominated river, wastewater treatment plant discharge was not the principal factor controlling water quality in many of the sampled areas. Non-point source pollution from impervious surfaces, delivered to the river through storm drains and minor tributary streams, also contributed to the high nutrient conditions in several locations. We also noted a strong seasonality in water quality, with higher concentrations of nutrients and higher biochemical oxygen demand in the winter months when wastewater effluent can make up more than 90% of the flow in the river. Thus, the interaction of discharge location and reduced seasonal flow produced spatio-temporal hot spots of diminished water quality. More stringent enforcement of water quality regulations may improve water quality in this system. However, a large portion of the pollution seems to be from non-point sources, which are very difficult to control.     

Recent changes in the sediment regime of the Pearl River (South China): Causes and implications for the Pearl River Delta

Riverine sediments have played an important role in the morphological evolution of river channels and river deltas. However, the sediment regime in the many world's rivers has been altered in the context of global changes. In this study, temporal changes in the sediment regime of the Pearl River were examined at different time scales, that is, annual, seasonal, and monthly time scales, using the Mann–Kendall test. The results revealed that precipitation variability was responsible for monthly and seasonal distribution patterns of the sediment regime and the long‐term changes in the water discharge; however, dam operation has smoothed the seasonal distribution of water discharge and resulted in decreasing trends in the annual, wet‐season, and dry‐season sediment load series since the 1950s. Due to the different regulation magnitudes of dam operation, differences were observed in sediment regime changes among the three tributaries. In addition, human activities have altered the hysteresis of seasonal rating curves and affected hysteresis differences between increasing and decreasing water discharge stages. Sediment supply is an important factor controlling river channel dynamics, affecting channel morphology. From the 1950s to the 1980s, siltation was dominant in river channels across the West River and North River deltas in response to the sediment increases; however, scouring occurred in the East River deltas due to sediment reduction. Significant erosion occurred in river channels in the 1990s, which was mostly due to downcutting of the river bed caused by sand excavations and partly because of the reduced sediment load from upstream. Although sand excavations have been banned and controlled by authority agencies since 2000, the erosion of cross sections was still observed in the 2000s because of reduced sediment caused by dam construction. Our study examines the different effects of human activities on the sediment regime and downstream channel morphology, which is of substantial scientific importance for river management.     

Influence of a rock glacier spring on the stream energy budget and cold‐water refuge in an alpine stream

The thermal regimes of alpine streams remain understudied and have important implications for cold‐water fish habitat, which is expected to decline due to climatic warming. Previous research has focused on the effects of distributed energy fluxes and meltwater from snowpacks and glaciers on the temperature of mountain streams. This study presents the effects of the groundwater spring discharge from an inactive rock glacier containing little ground ice on the temperature of an alpine stream. Rock glaciers are coarse blocky landforms that are ubiquitous in alpine environments and typically exhibit low groundwater discharge temperatures and resilience to climatic warming. Water temperature data indicate that the rock glacier spring cools the stream by an average of 3 °C during July and August and reduces maximum daily temperatures by an average of 5 °C during the peak temperature period of the first two weeks in August, producing a cold‐water refuge downstream of the spring. The distributed stream surface and streambed energy fluxes are calculated for the reach along the toe of the rock glacier, and solar radiation dominates the distributed stream energy budget. The lateral advective heat flux generated by the rock glacier spring is compared to the distributed energy fluxes over the study reach, and the spring advective heat flux is the dominant control on stream temperature at the reach scale. This study highlights the potential for coarse blocky landforms to generate climatically resilient cold‐water refuges in alpine streams.     

Determining the relative contributions of climate change and multiple human activities to variations of sediment regime in the Minjiang River,China

In‐stream sediment transport plays an important role in delivery of sediment‐associated terrestrial elements. Investigating the history of fluvial sediment regime responding to changes in natural and anthropogenic driving forces provides a theoretical basis for establishment of optimal strategies on catchment management. The present study aims to systematically detect the patterns of change in sediment load at two key hydrological stations (Pengshan and Gaochang) in the Minjiang River and quantitatively evaluate the relative contributions of regional precipitation change and multiple local human activities to the observed sediment variations. Abrupt change in annual sediment load was detected in 1990 at Pengshan and in 1968, 1980 and 1992 at Gaochang. Compared with the baseline period of 1957–1990, precipitation decline and human activities had respectively contributed to 5 × 10⁶ t and 2 × 10⁶ t of reduction in mean annual sediment load at Pengshan during 1991–2007. For the entire Minjiang basin, taking 1956–1968 as the baseline period, precipitation decline and human activities had relatively contributed to 10 × 10⁶ t and 18 × 10⁶ t of reduction in mean annual sediment load at Gaochang during 1969–1980. During 1981–1992, precipitation decline had relatively contributed to 5 × 10⁶ t of reduction in mean annual sediment load, but human activities had led to 3 × 10⁶ t of increase in mean annual sediment load. During 1993–2009, 13 × 10⁶ t and 17 × 10⁶ t of reduction in mean annual sediment load may be attributed to precipitation decline and human activities, respectively. Copyright © 2012 John Wiley & Sons, Ltd.     

Diurnal dynamics of streamflow in an upland forested micro‐watershed during short precipitation‐free periods is altered by tree sap flow

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.     

Annual distribution of river runoff with estimated contribution of winter low-water season

Proportions of the overland, delayed, and groundwater runoff are given for different phases of the hydrological regimes of rivers under different landscape–climate conditions in Russia. The concept of runoff hydrological regime is in agreement with the formation features of the annual and seasonal runoff on small watersheds under current climate conditions. The increase in winter runoff is due to the impulse discharge regime of soil water and groundwater, which receive additional recharge during frequent thaws and at weak freezing of the aeration zone. Variations in the values of runoff, total precipitation, and mean temperature were shown to be both synchronous and periodic.     

Temporal variation of over‐bank flooding of Wei River and its impact on a riparian wetland in Xi'an,China

Over‐bank flooding is one of the driving forces controlling ecological integrity of riparian wetlands. Indentifying natural over‐bank flooding regime and its temporal variations is crucial for developing conservation and restoration plans and making water resources management policies for these ecosystems. Along the midstream of the Wei River in Xi'an, China lies the Jingwei riparian wetland, which was well preserved until the 1970s. Based on historical record of hydrological and morphological data of the Wei River from 1951 to 2000, we analysed temporal variations of over‐bank flooding frequency, duration, and timing in this paper. The natural annual over‐bank flooding regime was identified as having an occurrence frequency of 2·2 times a year and average duration of 5·3 days; these flooding events typically occur between June and September with occasional occurrence in late spring and late autumn. Over‐bank flooding occurrence frequency and duration decreased significantly during the 1990s, seasonal events of over‐bank floods were changed through reduced flooding frequency during summer and disappearing flooding events in late spring and late autumn. Further investigations showed that reduced discharge in the Wei River was the principal cause for these changes in over‐bank flooding dynamics. Our analysis also showed that decreased discharge of the Wei River during the 1990s was attributed near equally to disturbances from human activities and decreased regional precipitation. Results from this study may help reestablish natural over‐bank flooding dynamics in order to ensure successful restoration of Jingwei riparian wetland. Copyright © 2010 John Wiley & Sons, Ltd.     

Correlations between discharge and meteorological parameters and runoff forecasting from a highly glacierized Himalayan basin

Abstract

To assess the predictive significance of meteorological parameters for forecasting discharge from the Dokriani Glacier basin in the Himalayan region, discharge autocorrelation and correlations between discharge and meteorological factors were investigated on a monthly and a seasonal basis. Changes in correlations between discharge and meteorological variables, lagged by 0–3 days, were determined. Discharge autocorrelation was found to be very high for each individual summer month and for the melt season as a whole. This suggests that a substantial meltwater storage in the glacier, which results in a delayed response of runoff, and therefore discharge, from the highly glacierized basins is very much dependent on the previous day's discharge. A comparison of correlations between discharge and temperature, and discharge and precipitation shows that temperature has a better correlation with discharge during June and September, while precipitation has good correlation with discharge in July and August. Variations in the physical features of the glacier, weather conditions, and precipitation and its distribution with time over the basin account for changes in correlations. To forecast the runoff from the Dokriani Glacier basin, multiple linear regression equations were developed separately for each month and for the whole melt season. A better forecast was obtained using the seasonal regression equation. A comparison of correlations for the Dokriani Glacier with those for the Z'mutt Glacier basin, Switzerland, illustrates that, for both basins, the previous day's discharge (Q_i-1) shows maximum autocorrelation throughout the melt period. Whereas a good correlation between discharge and temperature was observed for the Z'mutt Glacier basin for the whole melt period, for the Dokriani Glacier basin it was strong at the beginning and end of the ablation season. Runoff delaying behaviour in the Dokriani Glacier basin is found more prominent than in the Z'mutt Glacier basin early in the melt season. Water storage appears to be less significant in the Dokriani Glacier than in the Z'mutt Glacier towards the end of the ablation season. The strength of correlation between discharge and precipitation is higher for the Dokriani Glacier basin than for the Z'mutt Glacier basin. This is due to higher rainfall in the Dokriani Glacier basin. In general, for both glacier basins, maximum correlation is found between discharge and precipitation on the same day.