Abstract
Organic matter in soils and sediments derives from a mixture of biological origins, often making it difficult to determine inputs from individual sources. Complicating the determination of source inputs to soil and sedimentary organic matter (OM) is the fact that physical and microbial processes have likely modified the initial composition of these sources. This study focused on identifying the composition of watershed-derived OM to better understand inputs to inland waters and improve our ability to resolve between terrigenous and aquatic sources in downstream systems, such as estuaries and coasts. We surveyed OM sources from the Yuba River watershed in northern California to identify specific biomarkers that represent aquatic and terrigenous OM sources. Multiple classes of organic proxies—including sterols, fatty acids (FA), lignin phenols and stable carbon and nitrogen isotope values (δ13C, δ15N)—were measured in soils, vegetation, charcoal, and freshwater plankton to characterize representative source endmembers. Sterols—including 27-nor-24-cholesta-5,22-dien-3β-ol, cholesta-5,22-dien-3β-ol, 24-methylcholesta-5,22-dien-3β-ol and cholesta-5-en-3β-ol, and positive δ15N values—were associated with aquatic OM (plankton, suspended particulate OM), whereas lignin phenols, long chain FA, and diacids characterized terrigenous sources (soils, charcoal, vegetation). Trends in organic carbon and biomarker signatures in soil samples showed a response to environmental disturbance (i.e., mining, agriculture) through an inverse relationship between OM content and land use. Results from this study demonstrate the utility of multi-biomarker studies for distinguishing between OM from different sources and land uses, offering new insights for biogeochemical studies in aquatic systems.
Highlights
Human land use—including deforestation, agriculture and urbanization—strongly modifies terrestrial landscapes by changing the amountsSAN FRANCISCO ESTUARY & WATERSHED SCIENCEVOLUME 20, ISSUE 1, ARTICLE 5 and types of vegetation, altering nutrient loadings, and increasing soil erosion and exposure to weathering processes (Regnier et al 2013; Bauer et al 2013)
This study focused on identifying the signatures of organic carbon (OC) from a variety of watershed sources to a small, mountainous river and its associated impounded lake
Lipid biomarkers have been identified for different organic matter (OM) sources, including short chain fatty acids and sterols like 24-methylcholesta-5,22dien-3β-ol, which are indicative of microalgae (Volkman 1986; Zimmerman and Canuel 2002), and branched fatty acids and specific amino acids of bacterial origin (Canuel and Martens 1993; Veuger et al 2007)
Summary
VOLUME 20, ISSUE 1, ARTICLE 5 and types of vegetation, altering nutrient loadings, and increasing soil erosion and exposure to weathering processes (Regnier et al 2013; Bauer et al 2013). In addition to these anthropogenic stressors, climate transforms the terrestrial landscape through drought, flooding, and wildfires, changing the composition and quantity of terrestrial organic matter (OM) (e.g., Harjung et al 2019; Walker et al 2019). This study focused on identifying the signatures of organic carbon (OC) from a variety of watershed sources to a small, mountainous river and its associated impounded lake. Lignin phenols have proven to be effective tools for quantifying terrestrial inputs to marine environments (e.g., Hedges and Mann 1979; Houel et al 2006; Blair and Aller 2012), fecal sterols (e.g., coprostanol) have been used to trace wastewater effluent and human contamination (Eganhouse and Sherblom 2001; Carreira et al 2015; Reichwaldt et al 2017), and lipid biomarkers have been used to determine the contribution of terrestrial and marine OM sources along the estuarine salinity gradient (Canuel 2001; Waterson and Canuel 2008; Freymond et al 2018)
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