Molecular and Isotopic Comparison of Aquatic Organic Matter Fractions With Associated Stream and Floodplain Sediments
Abstract
We conducted a pilot study to investigate the relationship between floodplain soils, and stream channel sediments with aquatic organic matter exported from a midwestern agricultural watershed. Similarities in source and relative state of degradation were assessed with molecular biomarkers (lignin) and bulk stable carbon isotope analysis. Sediments collected from the stream floodplain were characterized by greatest overall lignin yield and low relative degradation state. Molecular indicators and the relative state of degradation are similar between channel sediments and particulate organic matter suggesting a common source and degradation history. In contrast, colloidal and dissolved organic matter fractions are characterized by elevated yields and elevated relative degradation showing differences in either source or processing of these size fractions. Shifts in bulk stable carbon isotope values show that carbon-normalized differences in lignin yield are at least partly due to a dilution effect created by autochthonous production during low flow conditions when stream velocity is low and water clarity is high. Results from this work show that, for channel sediments and particulate organic matter in the water column, differences in terrestrial contributions (inferred from lignin yield) are mainly due to the presence/absence of autotrophic productivity in the stream. Floodplain and ditch deposits are most similar in molecular characteristics to agricultural fields; however, they are characterized by greater yield of lignin and are less degraded relative to the field soils. This may be due to selective mobilization of smaller particles during erosion events and subsequent protection from decomposition when deposited in the floodplain (removed from agricultural disturbance).
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2004
- Bibcode:
- 2004AGUFM.B13C0252G
- Keywords:
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- 1694 Instruments and techniques;
- 1860 Runoff and streamflow;
- 1030 Geochemical cycles (0330)