Three-component Hydrograph Separation Research Articles

Source and transport controls on nutrient delivery to tile drains

Apportioning sources, assessing flow pathways, and quantifying the interaction between source and transport factors are critical for decreasing nutrient loss from agricultural catchments. In this study, water, nutrient, and tracer (δ18O, electrical conductivity) fluxes were measured over two years from a tile-drained field in Indiana, USA to quantify linkages among water flow pathways, management practices, and nutrient delivery to tile drains. Three-component hydrograph separation showed that tile discharge was, on average, sourced from groundwater (65 ± 31%), shallow soil water (10–20-cm deep; 29 ± 28%), and precipitation (6 ± 8%). Daily nitrate-N (NO3-N) and dissolved reactive phosphorus (DRP) load ranged from 0.0 to 1.8 kg ha−1 and 0–101 g ha−1, respectively, while cumulative loads were 30.7 kg ha−1 and 1,040 g ha−1. Nutrient management practices (fertilizer rate, placement, timing) directly influenced the magnitude of incidental nutrient loss and proportion of load that was derived from a fertilizer source. It was estimated that 52% and 46% of cumulative NO3-N and DRP load, respectively, was incidental loss that occurred within 30 d of fertilizer application. Continuous re-distribution of NO3-N throughout the soil profile following fertilizer application resulted in a broad range of concentration across flow pathways and antecedent conditions. In contrast, dry conditions with tile water sourced from shallow soil water or precipitation resulted in greater, but more variable, DRP concentration compared to wetter conditions when tile water was largely comprised of groundwater. Findings suggest that groundwater table dynamics exerted a strong control over DRP concentration, as similar surface-tile hydrologic connectivity occurred during both dry and wet conditions but produced different water quality outcomes. Groundwater may therefore serve both as a chemical and hydrologic buffer of DRP concentration. Combined measurements of water, nutrient, and tracer fluxes revealed novel insights into processes controlling nutrient delivery to tile drains, with direct applicability for conservation practice implementation and improving process representation in models.

Applicability of Difference in Oxygen-18 and Deuterium of Water Sources and Isotopic Hydrograph Separation in a Bamboo Catchment during Different Rainfall Types

Typhoon storm and plum rain are two typical rainfall types in the lower regions of the Yangtze River Basin, which frequently cause flood disasters in China. New information in stable water isotopes offers the opportunity to advance understanding of runoff mechanisms and water source dynamics in response to these two typical rainfall types. We intensively monitored two representative rainfall events in a small bamboo forestry watershed in 2016. Results showed that precipitation isotopic variations during the event were generally larger than those of other monitored compartments (including throughfall, surface overland water, groundwater and river water) and also larger for the plum rain than for the typhoon event (δ18O varied in 5.2‰ and 3.7‰, respectively). Importantly, the differences of isotopic temporal variation between rainfall and throughfall showed significant impacts on the two-component hydrograph separation for both rainfall types (e.g., if not considered, the pre-event water fractions were 26.6% and 15.3% higher for the typhoon and plum rain events, respectively). Furthermore, we evaluated the role of soil water on the three-component isotopic hydrograph separation model; results revealed that soil water accounted for 10.9% and 28.3% of the total discharge in typhoon and plum rain events, respectively. This underpins the important role of soil water dynamics during the rainy season in this humid region.

Water storage, mixing, and fluxes in tile-drained agricultural fields inferred from stable water isotopes

Quantifying hydrological processes that control the upper critical zone water balance and contaminant transport in drained landscapes is needed, especially as precipitation patterns driving water balance dynamics continue to shift due to climate change. Here, hydrometric data are integrated with stable isotope signatures to quantify water storage, mixing, and fluxes to subsurface tile drainage at an agricultural field located in Indiana, USA. Over a 2-yr period, precipitation, soil water sampled with suction lysimeters (10–80 cm depth), groundwater (below tile depth; >1 m), and subsurface tile discharge were sampled 97 times. Results showed that isotopic variability in near-surface soil water (10–20 cm) reflected the seasonality of the precipitation input signal, while groundwater values were relatively consistent indicating that water stored below tile drain depth was recharged during winter. Soil water between 20 and 80 cm depth was a mixture of near-surface water and groundwater that varied seasonally depending upon groundwater hydrodynamics. Mean transit time of water ranged from 12 to 20 d for 10-cm soil water to 225–334 d for groundwater, with tile drainage exhibiting a mean transit time of 245 d. Both two- and three-component hydrograph separation indicated that groundwater was the primary source of water to the tile drain followed by soil water. Tile drain hydrograph response (i.e., celerity) was largely controlled by antecedent wetness. Comparison of tile drain celerities and velocities revealed however varying mechanisms controlling hydrograph response across a range of environmental conditions. Data sets of both water and tracer flux were, thus, useful to track the spatiotemporal variability of water fluxes within and from the critical zone. Such data provide valuable information to improve the representation of critical zone processes in these landscapes within spatially distributed hydrological models.

Hydrograph separation for a small agricultural watershed: The role of irrigation return flow

The streamflow components in a small agricultural watershed were determined using a three-component hydrograph separation model. Rainfall, throughfall, soil water, groundwater, irrigation water, and stream water samples were collected from a headwater catchment consisting of a natural forested area, and from the downstream agricultural catchment outlet, where rice paddy fields are developed extensively along the stream. The purpose of this study was to compare streamflow generation patterns between the forested and agricultural watersheds. We differentiated pre-event and event water contributions to streamflow for seven rainfall events using chemical and isotopic tracers. All of the stream water samples collected from the upper headwater station were plotted within the three-component end-members (groundwater, soil water, and precipitation); whereas, at the lower catchment outlet station, stream water samples collected during the agricultural season deviated clearly from the three-component mixing analysis, indicating the addition of a new water source (irrigation return flow) to the streamflow. Our findings indicate that pre-event groundwater was the major contribution to streamflow in the headwater catchment, whereas event rainwater and irrigation return flow were the major contributors to streamflow in the lower part catchment during the agricultural season.

Moisture Sources for Precipitation and Hydrograph Components of the Sutri Dhaka Glacier Basin, Western Himalayas

Himalayan glaciers are the major source of fresh water supply to the Himalayan Rivers, which support the livelihoods of more than a billion people living in the downstream region. However, in the face of recent climate change, these glaciers might be vulnerable, and thereby become a serious threat to the future fresh water reserve. Therefore, special attention is required in terms of understanding moisture sources for precipitation over the Himalayan glaciers and the hydrograph components of streams and rivers flowing from the glacierized region. We have carried out a systematic study in one of the benchmark glaciers, “Sutri Dhaka” of the Chandra Basin, in the western Himalayas, to understand its hydrograph components, based on stable water isotopes (δ18O and δ2H) and field-based ablation measurements. Further, to decipher moisture sources for precipitation and its variability in the study region, we have studied stable water isotopes in precipitation samples (rain and snow), and performed a back-trajectory analysis of the air parcel that brings moisture to this region. Our results show that the moisture source for precipitation over the study region is mainly derived from the Mediterranean regions (>70%) by Western Disturbances (WDs) during winter (October–May) and a minor contribution (<20%) from the Indian Summer Monsoon (ISM) during summer season (June–September). A three-component hydrograph separation based on δ18O and d-excess provides estimates of ice (65 ± 14%), snowpack (15 ± 9%) and fresh snow (20 ± 5%) contributions, respectively. Our field-based specific ablation measurements show that ice and snow melt contributions are 80 ± 16% and 20 ± 4%, respectively. The differences in hydrograph component estimates are apparently due to an unaccounted snow contribution ‘missing component’ from the valley slopes in field-based ablation measurements, whereas the isotope-based hydrograph separation method accounts for all the components, and provides a basin integrated estimate. Therefore, we suggest that for similar types of basins where contributions of rainfall and groundwater are minimal, and glaciers are often inaccessible for frequent field measurements/observations, the stable isotope-based method could significantly add to our ability to decipher moisture sources and estimate hydrograph components.

Water quality impacts of irrigation return flow on stream and groundwater in an intensive agricultural watershed

Irrigation return flow can include contaminants derived from agricultural practices, and then deteriorate the quality of surface and subsurface water within the watershed. Thus, it is important to estimate the effect of irrigation return flow on water chemistry/quality. To do that water samples were collected between November 2004 and December 2005 from stream and groundwater in a small watershed that contains extensive rice paddy fields. The water isotopic compositions represented seasonal variation, particularly in downstream of main channel and the tributary. In April and May, water samples in the downstream and tributary could not be explained by three-component (soil water, groundwater and rainfall) hydrograph separation models (THSM). These results indicated that the stream water was affected by high evaporation and that another water body (e.g. quick return flow) impacted on THSM. Plot of Cl/NO3 and NO3/HCO3 showed that the water chemistry of all water samples was mainly regulated by soil water and groundwater. In addition, the water chemistry was related to water derived from rice paddy fields (WR) and manure. Manure impacted the water chemistry in tributary, one of the shallow groundwaters and the deep groundwaters, whereas that water in downstream was affected by WR. On a plot of δ15NNO3 and δ18ONO3 values, many samples were in a cluster indicative of manure and on a denitrification line. These imply that irrigation return flow characterized by denitrification processes was involved in determining the water chemistry. We suggest that chemical and multi-isotopes approach combined with the THSM is useful to elucidate the sources and processes controlling water chemistry in stream associated with rice paddy fields.

Characterizing the climatic water balance dynamics and different runoff components in a poorly gauged tropical forested catchment, Nicaragua

ABSTRACTThe water balance dynamics and runoff components of a tropical forested catchment (46 km2) on the southwestern Pacific coast of Nicaragua were studied combining hydrometry, geological characterization and hydrochemical and isotopic tracers (three-component hydrograph separation). The climatic water balance was estimated for 2010/11, 2011/12 and 2012/13 with net values of 811 mm year-1, 782 mm year-1 and –447 mm year-1, respectively. Runoff components were studied at different spatial and temporal scales, demonstrating that different sources and temporal contributions are controlled by dominant landscape elements and antecedent rainfall. In forested sub-catchments, permeable soils, stratigraphy and steep slopes favour subsurface stormflow generation contributing 50% and 53% to total discharge. At catchment scale, landscape elements such as smooth slopes, wide valleys, deeper soils and water table allow groundwater recharge during rainfall events. Groundwater dominates the hydrograph (50% of total discharge) under dry prior conditions. However, low soil infiltration capacity generates a larger surface runoff component (42%) under wet prior conditions which dominates total discharge. Our results show that forested areas are important to reduce surface runoff and thus soil degradation, which is relevant for the design of water management plans.Editor D. Koutsoyiannis Associate editor D. Gerten

Streamwater hydrograph separation in an alpine glacier area in the Qilian Mountains, northwestern China

ABSTRACTGlacier-melt-induced changes in runoff are of concern in northwestern China where glacier runoff is a major source for irrigation, industries and ecosystems. Samples were collected in different water mediums such as precipitation, glacial ice/snowcover, meltwater, groundwater and streamwater for the analysis of stable isotopes and solute contents during the 2009 runoff season in the Laohugou Glacial Catchment. The multi-compare results of δ18O values showed that significant difference existed in different water mediums. Source waters of streamflow were determined using data of isotopic and geochemical tracers and a three-component hydrograph separation model. The results indicated that meltwater dominated (69.9 ± 2.7%) streamflow at the catchment. Precipitation and groundwater contributed 17.3 ± 2.3% and 12.8 ± 2.4% of the total discharge, respectively. According to the monthly hydrograph, the contribution of snow and glacier meltwater varied from 57.4% (September) to 79.1% (May), and that of precipitation varied from 0% (May) to 34.6% (September). At the same time, the monthly contribution of groundwater kept relatively steady, varying from 9.7% (June) to 20.9% (May) in the runoff season. Uncertainties for this separation were mainly caused by the variation of tracer concentrations. It is suggested that the end-member mixing analysis (EMMA) method can be used in the runoff separation in an alpine glacial catchment.Editor Z.W. Kundzewicz; Associate editor Not assigned

Understanding runoff processes in a semi-arid environment through isotope and hydrochemical hydrograph separations

Abstract. The understanding of runoff generation mechanisms is crucial for the sustainable management of river basins such as the allocation of water resources or the prediction of floods and droughts. However, identifying the mechanisms of runoff generation has been a challenging task, even more so in arid and semi-arid areas where high rainfall and streamflow variability, high evaporation rates, and deep groundwater reservoirs may increase the complexity of hydrological process dynamics. Isotope and hydrochemical tracers have proven to be useful in identifying runoff components and their characteristics. Moreover, although widely used in humid temperate regions, isotope hydrograph separations have not been studied in detail in arid and semi-arid areas. Thus the purpose of this study is to determine whether isotope hydrograph separations are suitable for the quantification and characterization of runoff components in a semi-arid catchment considering the hydrological complexities of these regions. Through a hydrochemical characterization of the surface water and groundwater sources of the catchment and two- and three-component hydrograph separations, runoff components of the Kaap catchment in South Africa were quantified using both isotope and hydrochemical tracers. No major disadvantages while using isotope tracers over hydrochemical tracers were found. Hydrograph separation results showed that runoff in the Kaap catchment is mainly generated by groundwater sources. Two-component hydrograph separations revealed groundwater contributions of between 64 and 98 % of total runoff. By means of three-component hydrograph separations, runoff components were further separated into direct runoff, shallow and deep groundwater components. Direct runoff, defined as the direct precipitation on the stream channel and overland flow, contributed up to 41 % of total runoff during wet catchment conditions. Shallow groundwater defined as the soil water and near-surface water component (and potentially surface runoff) contributed up to 45 % of total runoff, and deep groundwater contributed up to 84 % of total runoff. A strong correlation for the four studied events was found between the antecedent precipitation conditions and direct runoff. These findings suggest that direct runoff is enhanced by wetter conditions in the catchment that trigger saturation excess overland flow as observed in the hydrograph separations.

A three-component hydrograph separation based on relationship between organic and inorganic component concentrations: a case study in Eastern Siberia, Russia

Chemical monitoring data on two rivers draining small-scale and medium-scale watersheds were collected and analyzed. It was shown that the variability in stream water chemistry is explained mostly by two natural processes. The first process is the change in dominant water flow path in soil during the year and the second process is the change in water table depth. These changes are reflected in dissolved organic carbon (DOC) to base cations (BC) ratio (DOC/BC). The increase of DOC/BC ratio (or decrease of BC/DOC ratio) from winter to summer is due to proportional dilution of groundwater by near-surface flow. The decrease of DOC/BC ratio from summer to winter is due to dilution by interflow. The ratio values typical for hydrological periods, when one of the sources absolutely predominated over the others were used as end-member signatures. The solute concentrations calculated using discharge fractions derived from mixing equations were highly correlated to those measured in riverine water.

A three-component hydrograph separation based on geochemical tracers in a tropical mountainous headwater catchment in northern Thailand

Abstract. Land-use change in the mountainous parts of northern Thailand is reflected by an increased application of agrochemicals, which may be lost to surface and groundwater. The close relation between flow paths and contaminant transport within hydrological systems requires recognizing and understanding the dominant hydrological processes. To date, the vast majority of studies on runoff generation have been conducted in temperate regions. Tropical regions suffer from a general lack of data, and little is known about runoff generation processes. To fill this knowledge gap, a three-component hydrograph separation based on geochemical tracers was carried out in a steep, remote and monsoon-dominated study site (7 km2) in northern Thailand. Silica and electrical conductivity (EC) were identified as useful tracers and were applied to calculate the fractions of groundwater (similar to pre-event water), shallow subsurface flow and surface runoff on stormflow. K+ was a useful indicator for surface runoff dynamics, and Ca2+ provided insights into groundwater behaviour. Nevertheless, neither measure was applicable for the quantification of runoff components. Cl- and further parameters (e.g. Na+, K+, and Mg2+) were also not helpful for flow path identification, nor were their concentrations distinguishable among the components. Groundwater contributed the largest fractions to stormflow (62–80%) throughout all events, followed by shallow subsurface flow (17–36%) and surface runoff (2–13%). Our results provide important insights into the dynamics of the runoff processes in the study area and may be used to assess the transport pattern of contaminants (i.e. agrochemicals) here.

Identification of runoff generation processes using hydrometric and tracer methods in a meso-scale catchment in Rwanda

Abstract. Understanding of dominant runoff generation processes in the meso-scale Migina catchment (257.4 km2) in southern Rwanda was improved using analysis of hydrometric data and tracer methods. The paper examines the use of hydrochemical and isotope parameters for separating streamflow into different runoff components by investigating two flood events which occurred during the rainy season "Itumba" (March–May) over a period of 2 yr at two gauging stations. Dissolved silica (SiO2), electrical conductivity (EC), deuterium (2H), oxygen-18 (18O), major anions (Cl− and SO2−4) and major cations (Na+, K+, Mg2+ and Ca2+) were analyzed during the events. 2H, 18O, Cl− and SiO2 were finally selected to assess the different contributing sources using mass balance equations and end member mixing analysis for two- and three-component hydrograph separation models. The results obtained by applying two-component hydrograph separations using dissolved silica and chloride as tracers are generally in line with the results of three-component separations using dissolved silica and deuterium. Subsurface runoff is dominating the total discharge during flood events. More than 80% of the discharge was generated by subsurface runoff for both events. This is supported by observations of shallow groundwater responses in the catchment (depth 0.2–2 m), which show fast infiltration of rainfall water during events. Consequently, shallow groundwater contributes to subsurface stormflow and baseflow generation. This dominance of subsurface contributions is also in line with the observed low runoff coefficient values (16.7 and 44.5%) for both events. Groundwater recharge during the wet seasons leads to a perennial river system. These results are essential for better water resources planning and management in the region, which is characterized by very highly competing demands (domestic vs. agricultural vs. industrial uses).

Pesticide Transport Pathways from a Sloped Litchi Orchard to an Adjacent Tropical Stream as Identified by Hydrograph Separation

This study was performed to identify the transport pathways of pesticides from a sloped litchi ( Sonn.) orchard to a nearby stream based on a three-component hydrograph separation (baseflow, interflow, surface runoff). Dissolved silica and electrical conductivity were chosen as representative tracers. During the study period (30 d), 0.4 and 0.01% of the applied mass of atrazine and chlorpyrifos, respectively, were detected in the stream after 151 mm of rainfall. Baseflow (80-96%) was the dominant hydrological flow component, followed by interflow (3-18%) and surface runoff (1-7%). Despite its small contribution to total discharge, surface runoff was the dominant atrazine transport pathway during the first days after application because pesticide concentrations in the surface runoff flow component declined quickly within several days. Preferential transport with interflow became the dominant pathway of atrazine. Because chlorpyrifos was detected in the stream water only twice, it was not included in the hydrograph separation. A feature of the surface runoff pathway was the coincidence of pesticide and discharge peaks. In contrast, peak concentrations of pesticides transported by interflow occurred during the hydrograph recession phases. Stormflow generation and pesticide transport depended on antecedent rainfall. The combination of high-resolution pesticide concentration measurements with a three-component hydrograph separation has been shown to be a suitable method to identify pesticide transport pathways under tropical conditions.

Hydrograph separation in a mountainous catchment ? combining hydrochemical and isotopic tracers

Runoff components of the Zastler catchment (18\4 km2, southern Black Forest, Germany) were analysed with hydrograph separations using stable oxygen isotopes and dissolved silica. It was shown that event water and components with low silica contributed only small amounts to total runoff. In addition, comparison of the two-component hydrograph separations showed that the low-silica components are generated by both event water and pre-event water fractions, depending on the state of the system. A modified three-component hydrograph separation method was introduced using dissolved silica and 18O. During storm events an interaction of three runoff components having distinct silica concentrations could be shown. Based on the geological and geomorphological genesis of the study site, it was appropriate to assign (i) the low silica component to the riparian zones and impermeable areas, (ii) the medium silica component to the periglacial debris cover and (iii) the high silica component to the crystalline detritus and crystalline hard rock. Exact quantification of the runoff components remained difficult. However, runoff components with medium silica concentrations reacted very sensitively and intensely. The contribution of this component to total runoff is comparatively large. This shows the important role of the periglacial debris to runoff generation of the study site and emphasizes the importance of runoff generation processes occurring in this reservoir. Copyright © 2000 John Wiley & Sons, Ltd.

The role of event water, a rapid shallow flow component, and catchment size in summer stormflow

Seven nested headwater catchments (8 to 161 ha) were monitored during five summer rain events to evaluate storm runoff components and the effect of catchment size on water sources. Two-component isotopic hydrograph separation showed that event-water contributions near the time of peakflow ranged from 49% to 62% in the 7 catchments during the highest intensity event. The proportion of event water in stormflow was greater than could be accounted for by direct precipitation onto saturated areas. DOC concentrations in stormflow were strongly correlated with stream 18O composition. Bivariate mixing diagrams indicated that the large event water contributions were likely derived from flow through the soil O-horizon. Results from two-tracer, three-component hydrograph separations showed that the throughfall and O-horizon soil-water components together could account for the estimated contributions of event water to stormflow. End-member mixing analysis confirmed these results. Estimated event-water contributions were inversely related to catchment size, but the relation was significant for only the event with greatest rainfall intensity. Our results suggest that perched, shallow subsurface flow provides a substantial contribution to summer stormflow in these small catchments, but the relative contribution of this component decreases with catchment size.

The impact of land use on stream water quality in Slovakia

In the first part of this paper, the impact of forestry, agriculture and urban activities on the quality of surface water is analysed. Daily data from 15 forest and agricultural experimental catchments of the Institute of Hydrology, Slovak Academy of Sciences are used. It is shown, that the nitrate concentrations in surface water have decreased in Slovakia since 1989 as a result of decreased use of inorganic nitrogen fertilisers (lower intensity of agricultural production in Slovakia owing to recent economic changes). The annual nitrate specific load varies from 5.90 to 110 kg ha −1 year −1, the annual sulphate load varied from 29.16 to 509.60 kg ha −1 year −1 and the annual phosphate load varied from 0.0098 to 0.0224 kg ha −1 year −1 during 1990–1992. In the second part, a two-step method of three-component hydrograph separation of rain-, soil- and groundwater is proposed. The method is used in the Manelo-Gribov microbasin (O.95 km 2) in Eastern Slovakia. The annual contribution of surface runoff in total runoff volume was 57.5%, the contribution of interflow runoff was 21.1%, and the contribution of groundwater was 21.4%, during the period from 1 August to 31 July 1992. A deterministic regression model for predicting daily nitrate concentrations from values of stream daily discharge and flow component data was developed. A set of 1421 modelled NO 3 −1 data was compared with the set of measured data.

Analysis of storm hydrograph and flow pathways using a three-component hydrograph separation model

A three-component hydrograph separation model involving full chemical-isotopic mass balance equations is presented and tested using storm runoff and catchment hydrological and hydrochemical data from Allt a Mharcaidh catchment in Scotland. A key issue in the use of the model is the rational and objective selection of representative end-members given spatio-temporal variation in catchment hydrochemistry. In addition, a highly involved catchment sampling strategy should be adopted so that no key runoff source is omitted.End-member mixing analysis was used in determining the set of storm runoff end-members used in the model. Results show that incident precipitation, soil water and ground water contributed 15%, 19%, and 66%, respectively, of the June 1989 storm runoff. Maximum instantaneous contributions were 26%, 40%, and 78%, respectively.