Effect of Warming on Solute Concentrations and Fluxes from Peatland Streams
Authors
Natalie A. Griffiths1* (griffithsna@ornl.gov), Stephen D. Sebestyen2, Keith C. Oleheiser1, Paul J. Hanson1, Melanie Mayes1, Daniel Ricciuto1
Institutions
1Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN; 2USDA Forest Service, Northern Research Station, Grand Rapids, MN
URLs
Abstract
Increased temperatures are altering biogeochemical processes in peatlands. Because many peatlands are hydrologically connected to downstream ecosystems, biogeochemical alterations within peatlands may also affect these connected environments. In the Spruce and Peatland Under Changing Environments (SPRUCE) experiment, the team is examining how warming affects solute concentrations and fluxes from peatland streams. At SPRUCE, each experimental enclosure is surrounded by a belowground corral, which hydrologically isolates each plot. Two lateral, slightly sloped, slotted pipes in the near-surface peat allow for lateral, passive drainage of water out of each enclosure, akin to stream flow.
Stream water drains into a subsurface basin, which is equipped with a water-level sensor to estimate stream flow and an automated sampler to collect flow-weighted water samples. Water samples are retrieved weekly and analyzed for total organic carbon (TOC), inorganic and total nutrients, anions, cations, and metals. After 7 years of warming, researchers have observed many changes in stream water solute concentrations. Notably, TOC concentrations have increased with warming, from 52 mg/L (+0°C enclosures) to 87 mg/L (+9°C enclosures). Concentrations of cations and metals (i.e., calcium, magnesium, aluminum, iron), several of which form complexes with TOC, have also increased with warming. While these increases in solutes may reflect evaporative concentration, there was a muted response of chloride concentrations (a conservative ion) to warming. Therefore, increased TOC, cation, and metal concentrations likely reflect warming-induced increases in peat mineralization, rather than a solely physical (evaporative concentration) response. While concentrations of many solutes have increased with warming, stream flow has decreased, likely due to increased evapotranspiration, resulting in an overall decrease in solute efflux from the peatland. In summary, climate change may alter the chemistry and volume of stream water flowing from peatlands, with potential cascading effects to downstream ecosystems.