Mixing as a driver of temporal variations in river hydrochemistry: 2. Major and trace element concentration dynamics in the Andes‐Amazon transition

Baronas, J. Jotautas; Torres, Mark A.; Clark, K. E.; West, A. Joshua

doi:10.1002/2016wr019729

Cited by 38 publications

(36 citation statements)

References 115 publications

(179 reference statements)

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“…Previous studies show clear C–Q breakpoints or nonideal power‐law behaviour (e.g., Baronas, Torres, Clark, & Joshua, ; Clow & Mast, ; Godsey et al, ; Herndon et al, ; Smith et al, ) but tend to overlook the implications of these breakpoints. For example, Clow and Mast () show a breakpoint that shifts the silica C–Q slope from −0.1 to near dilution (−1), implying that although chemostasis dominates at low flows, dilution is a better description at high flows.…”

Section: Discussionmentioning

confidence: 96%

Complex patterns of catchment solute–discharge relationships for coastal plain rivers

Diamond

Cohen

2018

Hydrological Processes

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Riverine solute versus discharge (C–Q) relationships provide information about the magnitude and dynamics of material fluxes from landscapes. We analysed long‐term patterns of C–Q relationships for 44 rivers in Florida across a suite of geogenic, nutrient, and organic solutes and investigated land cover, watershed size, and surficial geology as controls on these patterns. Solute concentrations generally exhibited far less variability than did discharge, with coherent solute‐specific behaviours repeated across watersheds. Geogenic solutes generally diluted with increasing discharge, whereas organic solutes generally enriched; patterns for nutrients were highly variable across watersheds, but on average exhibited chemostasis. Despite strong evidence of both geologic and land cover controls on solute flow‐weighted concentrations, these variables were poor predictors of C–Q slopes (β) or relative coefficients of variation (CVC:CVQ). CVC:CVQ generally increased with watershed size, and wetland area appeared to influence C–Q patterns for base cations and organic solutes. Perhaps most importantly, we observed significant slope breaks in C–Q association in approximately half of our observations, challenging the generality of using single power functions to describe catchment solute export patterns. For all solutes except phosphorus (P), C–Q slopes decreased above statistically identified breaks (slopes for P increased), with breaks consistently at or near median flow (i.e., 50% flow exceedance probability). This common pattern significantly impacts solute load estimates; failing to account for slope breaks overestimates nitrate and total organic carbon loads as much as 125% and underestimates P loads as much as 35%. In addition to challenging generic power‐law characterization of C–Q relationships for these coastal plain rivers, and exploring the load estimate consequences thereof, our study supports emerging insights about watershed hydrochemical behaviours across a wide array of solutes.

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Section: Discussionmentioning

confidence: 96%

Complex patterns of catchment solute–discharge relationships for coastal plain rivers

Diamond

Cohen

2018

Hydrological Processes

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“…1). In particular, a number of dissolved and solid samples were collected along the Andes-Amazon elevation gradient in Peru, where previous studies on the geomorphic effects on weathering (Torres et al, 2015(Torres et al, , 2017Baronas et al, 2017b) provide a detailed context for the interpretation of Ge and Si isotope data.…”

Section: Sample Collectionmentioning

confidence: 99%

Ge and Si isotope signatures in rivers: A quantitative multi-proxy approach

Baronas

Torres

West

et al. 2018

Earth and Planetary Science Letters

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Solutes derived from the dissolution of silicate minerals play a key role in Earth's climate via the carbon and other biogeochemical cycles. Silicon (Si) is a unique constituent of silicate minerals and a biologically important nutrient, so tracing its behavior in near-surface environments may provide important insights into weathering processes. However, Si released by weathering is variably incorporated into secondary mineral phases and biota, obscuring signals derived from primary weathering processes. Due to chemical similarities, Germanium (Ge) may help better understand the Si cycle and its relationship to chemical weathering. With this aim, we report new measurements of the concentration and isotopic composition of Ge for both the dissolved and particulate phases of a variety of global rivers. These measurements are combined with analyses of concentration and isotopic ratio of Si on the exact same sample set in order to make direct comparisons of the behavior of these two elements in natural river systems. With this dataset, we develop a new modeling framework describing the full elemental and isotopic systems of these solutes in rivers (i.e., Ge/Si, δ74Ge, and δ30Si). This multi-proxy approach allows us to ascertain the relative importance of biological versus mineral uptake in modulating the fluxes of these elements delivered to the modern ocean. Dissolved δ74Ge composition of rivers studied thus far range from 0.9 to 5.5 ‰ with a discharge-weighted global average of 2.6±0.5 ‰. The Ge isotope composition of riverine suspended and bedload sediments is indistinguishable from silicate source rocks, which is consistent with mass balance expectations. The multi-proxy modeling suggests that, among the watersheds studied here, the isotopic fractionation of Si during secondary mineral phase precipitation (∆30Sisec) ranges from-2.7 to-0.2 ‰, which removes between 19-79% of the initial dissolved Si sequestration, while between 12-54% is incorporated by biota. For Ge, modeling indicates that 79-98% of the dissolved load is incorporated into secondary mineral phases with a ∆74Gesec ranging from-4.9 to-0.3 ‰. The fractionation induced by biological uptake is calculated to range from-2.6 to-1.3 ‰ for ∆30Sibio and-0.7±0.7 ‰ for ∆74Gebio. In addition to improving our understanding of the coupled Ge and Si cycles, our study provides a framework for Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site. using multiple isotopic tracers to elucidate the chemical behavior of solutes in natural waters Highlights ► Ge and Si isotope composition of water and sediments in various rivers is presented. ► Dissolved δ 74 Ge range 0.9-5.5‰, river sediment δ 74 Ge range 0.5-0.7‰. ► Dissolved δ 74 Ge is strongly fractionated due to low chemical Ge mobility. ► Ge/Si-isotope multi-proxy provides quantitative constraints on secondary vs biological fractionation.

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“…Thus, monitoring headwater catchments was necessary to disentangle both types of processes, as observed downstream export regimes may not describe well the dynamics of landto-stream transfer (Worrall et al, 2012;Minaudo et al, 2015;Temnerud et al, 2016;Baronas et al, 2017). Furthermore, both upstream processes (e.g., summer SRP release) and downstream contributions (e.g., point-source SRP contribution during summer) may lead to the same export regime (e.g., high SRP during low flow); this phenomenon creates epistemic uncertainty, which may lead to equifinality problems when calibrating catchment models to the data (Beven, 2013).…”

Section: Implications For Monitoring and Managementmentioning

confidence: 99%

Carbon and nutrient export regimes from headwater catchments to downstream reaches

et al. 2017

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Abstract. Excessive amounts of nutrients and dissolved organic matter in freshwater bodies affect aquatic ecosystems. In this study, the spatial and temporal variability in nitrate (NO − 3 ), dissolved organic carbon (DOC) and soluble reactive phosphorus (SRP) was analyzed in the Selke (Germany) river continuum from three headwaters draining 1-3 km 2 catchments to two downstream reaches representing spatially integrated signals from 184-456 km 2 catchments. Three headwater catchments were selected as archetypes of the main landscape units (land use × lithology) present in the Selke catchment. Export regimes in headwater catchments were interpreted in terms of NO − 3 , DOC and SRP land-to-stream transfer processes. Headwater signals were subtracted from downstream signals, with the differences interpreted in terms of in-stream processes and contributions from point sources. The seasonal dynamics for NO − 3 were opposite those of DOC and SRP in all three headwater catchments, and spatial differences also showed NO − 3 contrasting with DOC and SRP. These dynamics were interpreted as the result of the interplay of hydrological and biogeochemical processes, for which riparian zones were hypothesized to play a determining role. In the two downstream reaches, NO − 3 was transported almost conservatively, whereas DOC was consumed and produced in the upper and lower river sections, respectively. The natural export regime of SRP in the three headwater catchments mimicked a point-source signal (high SRP during summer low flow), which may lead to overestimation of domestic contributions in the downstream reaches. Monitoring the river continuum from headwaters to downstream reaches proved effective to jointly investigate land-to-stream and instream transport, and transformation processes.

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Mixing as a driver of temporal variations in river hydrochemistry: 2. Major and trace element concentration dynamics in the Andes‐Amazon transition

Cited by 38 publications

References 115 publications

Complex patterns of catchment solute–discharge relationships for coastal plain rivers

Complex patterns of catchment solute–discharge relationships for coastal plain rivers

Ge and Si isotope signatures in rivers: A quantitative multi-proxy approach

Carbon and nutrient export regimes from headwater catchments to downstream reaches

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