Indiana Wetland and Lake Biogeochemistry Data

<p>Freshwater wetlands process large amounts of nutrients originating from agricultural fields. Yet, these systems also have the potential to produce substantial amounts of nitrous oxide (N<sub>2</sub>O) and methane (CH<sub>4</sub>), both potent greenhouse gasses (GHGs). Agricultural land use alters delivery of nutrients and carbon (C) to downstream wetlands, and changing climate is altering wetland hydroperiods. These drivers modulate wetland microbial processes responsible for GHG production including denitrification and methanogenesis. Studies have correlated GHGs to C quantity and nutrients independently; fewer studies identify how nutrients and C composition interact to modulate GHG concentrations in wetlands. In wetlands located in Indiana, USA, we studied how CH<sub>4</sub>, N<sub>2</sub>O, and carbon dioxide (CO<sub>2</sub>) correlated to C quantity and composition, nutrient concentrations, size, hydrology, and surrounding agricultural land use.</p>

<p>The dataset released here is a water chemistry dataset that includes nutrients (nitrogen, phosphorus, carbon, and sulfur), dissolved organic matter composition using ultra-violet visible absorbance and fluorescence spectroscopy, estimates of water body ecosystem metabolism (gross primary production, ecosystem respiration, and net ecosystem production) using dissolved oxygen time series, and concentrations of dissolved greenhouse gasses (i.e., methane, nitrous oxide, and carbon dioxide).</p>

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<p><strong>Data Collection</strong></p>

<p>We collected water and gas samples weekly at all ten sites from July 2021 to December 2021 and bi-weekly from January 2022 to August 2022 when water was present. This captured high temporal variation within the water column across wetlands. Water samples were filtered in the field to 0.45 µm and 0.2 µm and stored in amber Nalgene bottles at -20ºC until analysis, except for 0.2 µm samples used for DOC spectroscopy. DOC spectroscopy samples were kept at 4°C and analyzed within 2 weeks.</p>

<p>Gas samples for CH<sub>4</sub>, N<sub>2</sub>O, and CO<sub>2</sub> were collected at the same time water samples were collected. Dissolved concentrations of CH<sub>4</sub>, N<sub>2</sub>O, and CO<sub>2</sub> were measured using gas equilibration of water samples (Hamilton and Ostrom 2007, Aho and Raymond 2019). We collected 80 mL of water with minimal disturbance in a large syringe and added 20 mL of nitrogen gas (N<sub>2</sub>). The syringe was shaken to equilibrate dissolved gases in the water with the N<sub>2</sub>. 5 mL of the headspace was transferred to a 3 mL exetainer. At each site during each sampling event, we also collected atmospheric samples for analysis by transferring 5 mL of air to a 3 mL exetainer using a syringe. Gas samples were stored in darkness until analysis. Sensor data were collected using PME Minidot dissolved oxygen sensors.</p>

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