Dissolved Organic Matter Compositional Change and Biolability During Two Storm Runoff Events in a Small Agricultural Watershed. Issue 10 (20th October 2017)

• Record Type: Journal Article
• Authors: Eckard, Robert S.; Pellerin, Brian A.; Bergamaschi, Brian A.; Bachand, Philip A. M.; Bachand, Sandra M.; Spencer, Robert G. M.; Hernes, Peter J.
• Is Part Of: Journal of geophysical research. Volume 122:Issue 10(2017)
• Page Start: 2634
• Page End: 2650
• Publication Date: 2017-10-20
• Subjects: lignin -- water repellency -- dissolved organic carbon -- bioavailability -- overprinting -- dissolved organic matter; Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1002/2017JG003935
• Languages: English
• ISSNs: 2169-8953

Abstract

Abstract: Agricultural watersheds are globally pervasive, supporting fundamentally different organic matter source, composition, and concentration profiles in comparison to natural systems. Similar to natural systems, agricultural storm runoff exports large amounts of organic carbon from agricultural land into waterways. But intense management of upper soil layers, waterway channelization, wetland and riparian habitat removal, and postharvest vegetation removal promise to uniquely drive organic matter release to waterways. During a winter first flush and a subsequent storm event, this study investigated the influence of a small agricultural watershed on dissolved organic matter (DOM) source, composition, and biolability. Storm water discharge released strongly terrestrial yet biolabile (23 to 32%) dissolved organic carbon (DOC). Following a 21 day bioassay, a parallel factor analysis identified an 80% reduction in a protein‐like (phenylpropyl) component (C2) that was previously correlated to lignin phenol concentration, and a 10% reduction in a humic‐like, terrestrially sourced component (C4). Storm‐driven releases tripled DOC concentration (from 2.8 to 8.7 mg L −1 ) during the first flush event in comparison to base flow and were terrestrially sourced, with an eightfold increase in vascular plant derived lignin phenols (23.0 to 185 μg L −1 ). As inferred from system hydrology, lignin composition, and nitrate as a groundwater tracer, an initial pulse of dilute water from the upstream watershed caused a counterclockwise DOC hysteresis loop. DOC concentrations peaked after 3.5 days, with the delay between peak discharge and peak DOC attributed to storm water hydrology and a period of initial water repellency of agricultural soils, which delayed DOM leaching. Plain Language Summary: Human activities have transformed vast areas ofE arth's surface to agricultural use. Contemporary agricultural practices have vastly increased crop yield but have also greatly intensified agricultural land management practices, which deviate strongly from many of the basic processes that affect natural habitats. It follows, then, that agricultural land use could affect carbon cycling and water quality in agricultural watersheds very differently from how natural systems affect those same parameters. This study seeks to deepen scientific knowledge surrounding how storms drive carbon release from land to waterways, specific to an agricultural watershed. Results indicate that over a quarter of the carbon released from the subject agricultural watershed during storms has the potential to be used as energy by downstream ecosystems. This could support future management actions seeking to benefit downstream ecosystems or may pose a threat to ecosystem health. The study also suggests that the timing, amount, and quality of carbon released from the watershed depend on rainfall patterns and watershed plumbing, and on whether or not soil wetting has occurred recently, prior to the event in question. Key Points: Agricultural storm runoff can transfer large amounts of biolabile, terrestrial organic matter into waterways, supporting downstream heterotrophy or otherwise influencing downstream aquatic ecosystems Dilute upper watershed flows and water repellency of agricultural soils caused a counterclockwise organic carbon hysteresis loop Organic matter compositional change reflected differing watershed segment response, not an overprinting with downstream signatures