Using pedological knowledge to improve sediment source apportionment in tropical environments

Abstract

Purpose Soils are important regulators of Critical Zone processes that influence the development of geochemical signals used for sediment fingerprinting. In this study, pedological knowledge of tropical soils was incorporated into sediment source stratification and tracer selection in a large Brazilian catchment. Materials and methods In the Ingaí River basin (~1200 km 2), Brazil, three source end-members were defined according to the interpretation of soil and geological maps: the upper, mid, and lower catchment. A tributary sampling design was employed, and sediment geochemistry of three different size fractions was analyzed (2-0.2 mm; 0.2-0.062 mm, and < 0.062 mm). A commonly used statistical methodology to element selection was compared to a knowledge-based approach. The mass balance un-mixing models were solved by a Monte Carlo simulation. Modeled source contributions were evaluated against a set of artificial mixtures with known source proportions. Results and discussion For the coarse fraction (2-0.2 mm), both approaches to element selection yielded high errors compared to the artificial mixtures (23.8% and 17.8% for the statistical and the knowledge-based approach, respectively). The knowledgebased approach provided the lowest errors for the intermediate (0.2-0.062 mm) (10.9%) and fine (< 0.062 mm) (11.8%) fractions. Model predictions for catchment outlet target samples were highly uncertain for the coarse and intermediate fractions. This is likely the result of the spatial scale of the source stratification not being able to represent sediment dynamics for these fractions. Both approaches to element selection show that most of the fine sediments (median > 90%) reaching the catchment outlet were derived from Ustorthents in the lower catchment. Conclusions The different element selection methods and the artificial mixtures provide multiple lines of evidence for evaluating the fingerprint approaches. Our findings highlight the importance of considering pedogenetic processes in source stratification, and demonstrate that different sampling strategies might be necessary to model specific sediment fractions.

Preface—evaluating the response of critical zone processes to human impacts with sediment source fingerprinting

“…One of Uber et al's (2019) key findings is the importance of using multi-fingerprint and multimodel techniques to detect and quantify potential biases (e.g., source variability, particle-size selectivity) in order to obtain reliable and robust estimates of source contributions to target sediment. Batista et al (2019) examine how pedogenetic processes in soils help influence the development of the geochemical signals that are used in sediment source fingerprinting research. Their research in the Ingaí River Basin (Brazil) incorporated a tributary fingerprinting technique, multiple particle-size fractions, and artificial mixtures to understand erosion dynamics in three areas of this basin: the upper, middle, and lower regions.…”

“…Their research in the Ingaí River Basin (Brazil) incorporated a tributary fingerprinting technique, multiple particle-size fractions, and artificial mixtures to understand erosion dynamics in three areas of this basin: the upper, middle, and lower regions. In particular, Batista et al (2019) found that erosion processes on Ustorthrent soils from the lower catchment were dominating the supply of sediment at the basin outlet. In particular, these authors reported that using different techniques to select elements for inclusion in mixing models (e.g., knowledge and statistics based), along with artificial mixtures, helped provide multiple lines of evidence necessary to produce robust estimates of source contributions to target sediments.…”

“…In particular, these authors reported that using different techniques to select elements for inclusion in mixing models (e.g., knowledge and statistics based), along with artificial mixtures, helped provide multiple lines of evidence necessary to produce robust estimates of source contributions to target sediments. Batista et al (2019) illustrate the importance of understanding how pedogenetic processes drive source signal (i.e., fingerprint) development. In closing, Batista et al (2019) argue that the use of knowledge-based techniques to select fingerprints for modeling will encourage researchers to further develop their understanding of processes that drive erosion and sediment geochemistry across multiple spatial and temporal scales.…”

“…Batista et al (2019) illustrate the importance of understanding how pedogenetic processes drive source signal (i.e., fingerprint) development. In closing, Batista et al (2019) argue that the use of knowledge-based techniques to select fingerprints for modeling will encourage researchers to further develop their understanding of processes that drive erosion and sediment geochemistry across multiple spatial and temporal scales. Evrard et al (2019a) use colorimetric fingerprints to investigate the contribution of different erosion processes to material transiting the Mano and Niida catchments in the Fukushima Prefecture, Japan.…”

“…Furthermore, sediment source fingerprinting may help investigate sediment connectivity (Koiter et al 2013a;Chartin et al 2017) and help validate watershed sediment models. Even striving to understand the behaviour of sediment source fingerprints and whether or not they are conservative (Pawlowski and Karwan 2019) and how pedogenetic and/or geologic processes drive source signal (i.e., fingerprint) development (Batista et al 2019) will provide more information on a variety of different processes occurring in the critical zone. Indeed, more research is required to investigate the multitude of processes that Fig.…”