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

Abstract

[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 À , 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.

Hydrological connectivity inferred from diatom transport through the riparian-stream system

“…Catchment end-members included shallow groundwater (GW1-4), soil water (SS1 20 , SS1 60 , SS2 60 ), soil water from the riparian zone (SSr), rainfall (R), throughfall (TH1-2), snow (SN) and overland flow (OF). We applied the diagnostic tools of Hooper (2003), which have been recently applied in the literature (James and Roulet, 2006;Barthold et al, 2011;Neill et al, 2011;Inamdar et al, 2013). Our approach followed three main steps.…”

“…In this study, stream water concentrations and isotopic compositions (of all samples collected during storm events and low flows at the catchment outlet) were considered conservative when they exhibited at least one linear trend with one other tracer (i.e. r 2 > 0.5, p value < 0.01) (James and Roulet, 2006;Barthold et al, 2011).…”

Exploring water cycle dynamics by sampling multiple stable water isotope pools in a developed landscape in Germany

“…Particularly in catchment hydrology, stable water isotopes play a major role since they can be utilized for hydrograph separations (Buttle, 2006), to calculate the mean transit time (McGuire and McDonnell, 2006), to investigate water flow paths (Barthold et al, 2011), or to improve hydrological model simulations . However, most of our current under-standing results from studies in forested catchments.…”

Impact of elevation and weather patterns on the isotopic composition of precipitation in a tropical montane rainforest

“…to validate hydrological models (Birkel et al, 2009;Koivusalo et al, 2000;Liebminger et al, 2007;Rodgers et al, 2005b), identify areas of groundwater recharge (Cortés et al, 1997;Gonfiantini et al, 2001;Kattan, 2006), investigate flow paths (Barthold et al, 2011;Goller et al, 2005;Rodgers et al, 2005a) or to calculate the mean transit time (MTT) of water (Garvelmann et al, 2012;Kabeya et al, 2007;McGuire et al, 2002McGuire et al, , 2005Rodgers et al, 2005b).…”