Apportioning sources of organic matter in streambed sediments: An integrated molecular and compound-specific stable isotope approach

Abstract

12We present a novel application for quantitatively apportioning sources of organic matter in streambed 13 sediments via a coupled δ 2 H and δ 13 C compound-specific isotope analysis (CSIA) of leaf wax n-14 alkane biomarkers using a Bayesian mixing model. Leaf wax extracts of 13 plant species were 15 collected from across three sub-environments (aquatic, bankside and terrestrial) and four plant 16 functional types (trees, herbaceous perennials and C 3 and C 4 graminoids) from the agricultural River 17Blackwater catchment, Norfolk, UK. Nine isotopic ratio and n-alkane chain length fingerprints were 18 derived, which successfully differentiated 93% of individual plant specimens by plant functional type. ranging from -259‰ to -221‰) providing the largest contrasts. The δ 13 C values provided strong 22 distinction between C 3 and C 4 plants, and successfully discriminated between natural and cultivated 23 vegetation. n-Alkane chain length metrics complemented hydrogen and carbon isotope data by 24 2 discriminating between aquatic, bankside and terrestrial sub-environments. Neither δ 2 H nor δ 13 C 25 could uniquely identify plants based on sub-environment, emphasizing a stronger plant 26 physiological/biochemical rather than environmental control over isotopic differences. Bayesian 27 source apportionment results for 18 streambed sediments collected between September 2013 and 28March 2014, revealed considerable temporal variability in organic matter sources. Median organic 29 matter contributions ranged from 22-52% for trees, 29-50% for herbaceous perennials, 17-34% for C 3 30 graminoids and 3-7% for C 4 graminoids. The results presented here clearly demonstrate the 31 effectiveness of an integrated stable isotope and molecular approach for quantitatively apportioning 32 plant specific organic matter contributions to streambed sediments. Future research could investigate 33 whether soils under particular vegetation types are tagged with unique δ 2 H and δ 13 C signatures that 34 would allow these isotopes to be used as direct land-use specific soil erosion tracers. 35 HIGHLIGHTS 36 Organic contributions from trees, herbs and C 3 /C 4 graminoids are apportioned. 37  δ 2 H provides strong discrimination between plant functional types. 38  δ 13 C provides strong contrasts between C 3 and C 4 plants. 39  δ 2 H and δ 13 C values were not influenced by sub-environment. 40  n-Alkane chain length metrics compliment isotopic discrimination. 41

Diverse Soil Carbon Dynamics Expressed at the Molecular Level

“…However, no such isotopic trend is observable within the lipid compound class as a function of depth (SI Figure S1). The 13 C-depleted nature of complex hydrocarbon lipids is known to reflect isotopic fractionation during their biosynthesis (Diefendorf & Freimuth, 2017), and the range in δ 13 C values found in this study falls within the typical range for C 3 terrestrial plants (Cooper et al, 2015;Hobbie & Werner, 2004). …”

Characterizing organic matter inputs to sediments of small, intermittent, prairie streams: a molecular marker and stable isotope approach

“…The importance of small streams is now recognized in the context of POM export from terrestrial to coastal environments, contributing to the estimations of the global ocean carbon cycle. However, while there are a growing number of studies on the detailed characterization of OM in small rivers (Jaffé et al 2001;Mead et al 2005;Medeiros and Simoneit 2008;Medeiros et al 2012;Cooper et al 2015;Giri et al 2015;Grewer et al 2015), more work is needed to characterize this material and link its sources, transport and transformations to spatially and temporally variable conditions that occur in stream networks. As we begin to understand how stream biogeochemistry varies across biome gradients at continental scales (Dodds et al 2015), a more complete model of OM sources, processing and transport may become possible and allow predictive ability related to anthropogenic changes such as woody vegetation expansion, climate change, and land use/land cover change.…”

“…While most of these studies focused on the bulk particulate OC (POC) isotopic composition, a more detailed characterization, through the molecular identification of source-specific biomarkers (Jaffé et al 2001;Medeiros and Simoneit 2008;Medeiros et al 2012;Cooper et al 2015;Giri et al 2015;Grewer et al 2015), could provide valuable information on the OM sources to and transport by small rivers. While detrital OM representative of the watershed could dominate supply to the stream network (Allan and Castillo 1995), a large portion of this material can originate from the vegetation comprising the riparian zone (Medeiros and Simoneit 2008).…”

Do forests represent a long-term source of contaminated particulate matter in the Fukushima Prefecture?

“…For researchers interesting in the mineral fraction, removal of organic debris by floating or density separation may be warranted. Moreover, additional analyses, such as compound specific isotopes (Blake et al, 2012;Cooper et al, 2015;Hancock and Revill, 2013) could provide increased source discrimination and insights into potential contributions from instream particulate matter. Analyses into the sources of carbon, including the use of vegetation as an end-member in particulate matter source tracing (Garzon-Garcia et al, in review) could provide additional significant insights into carbon sources in the catchment and potentially global carbon fluxes through the development of field based approaches that may be capable of validating desktop-based carbon flux models (e.g.…”