Spatial patterns in stream gross primary production in an agriculture-dominated watershed.

Stream metabolism, the balance of gross primary production (GPP) and ecosystem respiration, supports consumer production and is an important control on carbon, nitrogen, and phosphorus cycling. In forested watersheds, light is the dominant control on rates of GPP while nutrient concentrations and temperature frequently play a secondary role; often leading to a positive relationship between GPP and stream size. However, we have a limited understanding of factors controlling stream metabolism in agriculture-dominated watersheds where headwaters lack forested canopy cover. To address this knowledge gap, we estimated reach-scale metabolism in 20 streams spanning a stream size gradient from 3 to 1,959 km² in the Maumee River watershed using the single-station approach and examined potential controlling variables. Across all streams, GPP exhibited a spring peak and a second smaller peak during late summer. However, aside from the general seasonal patterns, there was no correlation in daily GPP among streams. Focusing on mid-summer base flow conditions, we found that mean daily GPP increased with conductivity, soluble reactive phosphorus, and watershed area, but decreased with canopy cover. The negative relationship between canopy cover and watershed area indicated that light plays an important role in determining GPP in this agriculture-dominated watershed. Our results indicate that patterns in whole-stream GPP in agriculture-dominated watersheds are controlled by light availability and exhibited similar relationships with stream size as in forested watersheds.

Primary Presenter: Matthew Sens, The Ohio State University Aquatic Ecology Lab (matthewlsens@gmail.com)

Authors:

Matthew Sens, Aquatic Ecology Laboratory, Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, Columbus, Ohio, USA  (matthewlsens@gmail.com)

Devan Mathie, Aquatic Ecology Laboratory, Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, Columbus, Ohio, USA  (mathie.22@buckeyemail.osu.edu)

Brittany Hanrahan, Soil Drainage Research Unit, USDA ARS, 590 Woody Hayes Drive, Columbus, OH 43210, United States  (bhanrahan@usgs.gov)

Laura Johnson, Heidelberg University, National Center for Water Quality Research, 310 East Market Street, Tiffin OH 44883, USA  (ljohnson@heidelberg.edu)

Kevin King, Soil Drainage Research Unit, USDA ARS, 590 Woody Hayes Drive, Columbus, OH 43210, United States  (kevin.king@usda.gov)

Rebecca Kreiling, U.S. Geological Survey, Upper Midwest Environmental Sciences Center, 2630 Fanta Reed Road, La Crosse, WI 54603, USA  (rkreiling@usgs.gov)

Nathan Manning, Heidelberg University, National Center for Water Quality Research, 310 East Market Street, Tiffin OH 44883, USA  (nmanning@heidelberg.edu)

James Hood, Aquatic Ecology Laboratory, Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, Columbus, Ohio, USA ; Translational Data Analytics Institute, The Ohio State University, Columbus, Ohio, USA  (hood.211@osu.edu)