Episodic variations in dissolved solutes are frequently complicated by a cyclical relationship between concentration and stream discharge. Established three-component models of runoff generation are used to explain this hysteresis effect and to illustrate how different component concentrations produce different hysteresis forms. It is demonstrated that a two-component model cannot reproduce all the hysteresis forms commonly observed. A method, based on the three-component system, is derived by which C/Q hysteresis can be used to predict relative component concentrations. This may provide a qualitative chemical description of sources supplying runoff for locations where these have not yet been directly established or a validation test where possible components have been sampled. The method has been tested using data collected at streams in the Adirondacks, New York, and the Northern Appalachian Plateau, Pennsylvania, during the Episodic Response Project of the U.S. Environmental Protection Agency. Predicted component compositions were in good agreement with measurements made during other studies and with those subsequently obtained from one of the Pennsylvania watersheds.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97WR01881

Causes of concentration/discharge hysteresis and its potential as a tool for analysis of episode hydrochemistry

Influence of land-use change on near-surface hydrological processes: Undisturbed forest to pasture

[1] End member mixing analysis (EMMA) is a commonly applied method to identify and quantify the dominant runoff producing sources of water It employs tracers to determine the dimensionality of the hydrologic system Many EMMA studies have been conducted using two to six tracers, with some of the main tracers being Ca, Na, Cl−, water isotopes, and alkalinity Few studies use larger tracer sets including minor trace elements such as Li, Rb, Sr, and Ba None of the studies has addressed the question of the tracer set size and composition, despite the fact that these determine which and how many end members (EM) will be identified We examine how tracer set size and composition affects the conceptual model that results from an EMMA We developed an automatic procedure that conducts EMMA while iteratively changing tracer set size and composition We used a set of 14 tracers and 9 EMs The validity of the resulting conceptual models was investigated under the aspects of dimensionality, EM combinations, and contributions to stream water From the 16,369 possibilities, 23 delivered plausible results The resulting conceptual models are highly sensitive to the tracer set size and composition The moderate reproducibility of EM contributions indicates a still missing EM It also emphasizes that the major elements are not always the most useful tracers and that larger tracer sets have an enhanced capacity to avoid false conclusions about catchment functioning The presented approach produces results that may not be apparent from the traditional approach and it is a first step to add the idea of statistical significance to the EMMA approach

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2011WR010604

How many tracers do we need for end member mixing analysis (EMMA)? A sensitivity analysis

The observation that "old" water dominates storm runoff suggests that release of low-solute water from soils rather than rainwater must cause storm runoff dilution. This inference is supported by sprinkling experiments in an 860-m 2 catchment in the Oregon Coast Range, in which .200 mm of both high and low ionic strength precipitation produced similar concentration-discharge trends. Rainwater chemistry was buffered as it traveled through catchment soils: the amount of sprinkling-derived water in the runoff increased during long periods of steady discharge but was not accompanied by a change in runoff solute concentrations. Stored water plays a role in runoff dilution as well. Nearly all runoff from the catchment passes through underlying weathered bedrock rather than perching and discharging only through soil. Bedrock water composition appears to vary through storm events, as the average contact time of water with rock declines with increasing discharge, a behavior at odds with the concept of stable end-members.

/pdf/concentration-discharge-relationships-in-runoff-from-a-steep-1gew35sqtc.pdf

Concentration-discharge relationships in runoff from a steep, unchanneled catchment

Size fractionation of ~40 major and trace elements (TE) in peat soil solutions from the Tverskaya region (Russia) has been studied using frontal filtration and ultrafiltration through a progressively decreasing pore size (5, 2.5, 0.22 μm, 100, 10, 5, and 1 kD) and in situ dialysis through 6–8 and 1 kD membranes with subsequent analysis by ICP-MS. In (ultra) filter-passed permeates and dialysates of soil solutions, Fe, Al, and organic carbon (OC) are well correlated, indicating the presence of mixed organo-mineral colloids. All major anions and silica are present in “dissolved” forms passed through 1 kD membrane. According to their behavior during filtration and dialysis and association with mineral or organic components, three groups of elements can be distinguished: (i) species that are weakly affected by size separation operations and largely (>50–80%) present in the form of dissolved inorganic species (Ca, Mg, Li, Na, K, Sr, Ba, Rb, Cs, As, Mn) with some proportion of small (1–10 kD) organic complexes (Ca, Mg, Sr, Ba), (ii) biologically essential elements (Co, Ni, Zn, Cu, Cd) mainly present in the fraction smaller than 1 kD and known to form strong organic complexes with fulvic acids, and, (iii) elements strongly associated with aluminum, iron and OC in all ultrafiltrates and dialysates with 30–50% being concentrated in large (>10 kD) colloids (Ga, Y, REEs, Pb, Cd, V, Nb, Sn, Ti, Zr, Hf, Th, U). For most trace metals, the proportion in the colloidal fraction correlates with their first hydrolysis constant. This implies a strong control of negatively charged oxygen donors present in inorganic/organic colloids on TE distribution between aqueous solution and colloid particles. It is suggested that these colloids are formed during plant uptake of Al, Fe, and TE from mineral matrix of deep soil horizons and their subsequent release in surface horizons after litter degradation and oxygenation on redox or acid/base fronts. Dissolved organic matter stabilizes Al/Fe colloids and thus enhances trace elements transport in soil solutions.

Fe–Al–organic Colloids Control of Trace Elements in Peat Soil Solutions: Results of Ultrafiltration and Dialysis

Previous hydrometric studies demonstrated the prevalence of overland flow as a hydrological pathway in the tropical rain forest catchment of South Creek, northeast Queensland The purpose of this study was to consider this information in a mixing analysis with the aim of identifying sources of, and of estimating their contribution to, storm flow during two events in February 1993 K and acid-neutralizing capacity (ANC) were used as tracers because they provided the best separation of the potential sources, saturation overland flow, soil water from depths of 03, 06, and 12 m, and hillslope groundwater in a two-dimensional mixing plot It was necessary to distinguish between saturation overland flow, generated at the soil surface and following unchanneled pathways, and overland flow in incised pathways This latter type of overland flow was a mixture of saturation overland flow (event water) with high concentrations of K and a low ANC, soil water (preevent water) with low concentrations of K and a low ANC, and groundwater (preevent water) with low concentrations of K and a high ANC The same sources explained the streamwater chemistry during the two events with strongly differing rainfall and antecedent moisture conditions The contribution of saturation overland flow dominated the storm flow during the first, high-intensity, 178-mm event, while the contribution of soil water reached 50% during peak flow of the second, low-intensity, 44-mm event 5 days later This latter result is remarkably similar to soil water contributions to storm flow in mountainous forested catchments of the southeastern United States In terms of event and preevent water the storm flow hydrograph of the high-intensity event is dominated by event water and that of the low-intensity event by preevent water This study highlights the problems of applying mixing analyses to overland flow-dominated catchments and soil environments with a poorly developed vertical chemical zonation and emphasizes the need for independent hydrometric information for a complete characterization of watershed hydrology and chemistry

/pdf/mixing-model-approaches-to-estimate-storm-flow-sources-in-an-20nnnbiz6m.pdf

Mixing Model Approaches to Estimate Storm Flow Sources in an Overland Flow-Dominated Tropical Rain Forest Catchment

Aluminium, iron and manganese in near-surface waters of a tropical rainforest ecosystem.

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Mixing Model Approaches to Estimate Storm Flow Sources in an Overland Flow-Dominated Tropical Rain Forest Catchment

Aluminium, iron and manganese in near-surface waters of a tropical rainforest ecosystem.