DOI: 10.5061/dryad.8cz8w9gv0
title: Multi-proxy paleolimnological records provide evidence for a shift to a new ecosystem state in the Northern Great Plains, USA

description: Wetlands in the Prairie Pothole Region of the North American Northern
 Great Plains perform multiple ecosystem services and are biodiversity
 hotspots. However, climatological changes can result in sudden shifts in
 these important ecosystems. For example, marked increases in precipitation
 in the last few decades have resulted in a widespread shift in wetlands
 across the Prairie Pothole Region to a new ecohydrological state. We used
 multi-proxy analyses (diatom community composition and invertebrate stable
 isotopes) of 210Pb-dated sediment cores from two adjacent, but
 morphologically and hydrologically different, prairie-pothole wetlands to
 assess the effects of hydroclimatic variability on these wetland
 ecosystems. Our results provide evidence that the recent ecohydrological
 shift in the region’s wetlands is unprecedented over the past ca.178
 years. Oxygen stable isotopes in chironomid head capsules provide a record
 of paleo-hydrology changes. The most recent sediments (i.e., those
 deposited after the state shift) from both wetlands revealed novel changes
 in diatom communities that differed greatly from earlier community
 compositions. Additionally, a depleted signal in deuterium and 13C carbon
 stable isotopes observed in chironomid head capsules and Daphnia ephippia,
 respectively after 1993 is likely related to an increase in methane
 production in these wetlands. Our study highlights the importance of
 considering basin morphometry including whether a wetland has an overflow
 point, and multiple biological indicators to study climate-change
 influences on freshwater ecosystems. Research using these techniques can
 lead to an improved understanding of recent ecosystem shifts, an
 understanding that will be essential for future climate-change adaptation
 and mitigation in this ecologically important region.
description: Diatom community analyses Diatom frustules
 were prepared for enumeration following the methods of Battarbee et al.
 (2001). Briefly, hydrochloric acid (10%) was used to remove carbonates
 before processing. Hydrogen peroxide (30% concentration) was added at ~80
 °C to remove organic material. A portion of the digested slurry was dried
 on cover slips and mounted with Naphrax®. Diatom identification and
 enumeration were performed under oil immersion at 1,000X magnification
 using an Olympus model BX60 microscope with phase contrast. A minimum of
 400 diatom frustules were identified and counted from each sample. Diatom
 taxonomy followed Krammer and Lange-Bertalot (1986–1991). Updated naming
 conventions were obtained from Diatoms of North America (Spaulding et al.,
 2022). Community data were expressed as percent abundance of the total
 diatom sum in each sample. Diatom species were categorized as either
 planktonic or benthic following their habitat preferences based on Spaulding et al.
 (2022). Invertebrate stable-isotope analyses
 Stable isotope analyses of chironomid head capsules and Daphnia
 ephippia were conducted following the methods of Wang et al. (2008).
 Briefly, 2 to 4 g of freeze-dried sediment were treated with 10% KOH in a
 warm (60 – 70 °C) water bath for 15 to 20 min. After the sample cooled,
 sediments were rinsed with distilled water through a 100-μm sieve (Wang et
 al. 2008). Residual material was refrigerated at 4 °C in a 50-ml
 centrifuge tube until sorted. For sorting, small aliquots of aqueous
 residual material were transferred into a Bogorov counting tray using a
 pipette and examined under a dissecting microscope at 25X magnification.
 Chironomid heads capsules (0.05 – 2.5 mg) and Daphnia ephippia (0.07 – 0.6
 mg) were separately transferred using fine forceps into pre-weighed, tin
 capsules filled with distilled water. After all invertebrate remains were
 transferred into tin capsules, the open tin capsules were allowed to air
 dry overnight. The tin capsules were then crimped to leave a small opening
 and freeze dried for &gt; six days. The tin capsules were then
 reweighed, folded into a ball, and stored in a 96-well culture plate in a
 desiccator. Empty tin capsules were included every five samples in sample
 preparation (total eight empty tin capsules for 43 samples) for the oxygen
 and hydrogen isotopes blank correction (Wang et al. 2008). The mass of
 each sample was calculated by subtracting the tare weight (i.e., weight of
 the empty tin capsule). The chironomid samples were then loaded into a
 zero-blank auto sampler attached to an on-line pyrolysis thermochemical
 reactor (ThermoElectron TC/EA) coupled via a Conflo Ⅲ with a
 thermoFinnigan Deltaplus XP IRMS at the Alaska Stable Isotope Facility
 (University of Alaska Fairbanks, Fairbanks, Alaska, USA). Chironomid
 head-capsule results are reported in units of δ18O and δD per mil (‰)
 relative to Vienna Standard Mean Ocean Water (V-SMOW). Daphnia ephippia
 stable isotopes were quantified using a Costech ECS4010 elemental analyzer
 (EA) attached via a conflo Ⅲ to an IRMS (thermoFinnigan Deltaplus XL).
 δ13C values are reported relative to Vienna Pee Dee Belemnite (V-PDB) and
 δ15N values are expressed relative to atmospheric (atm.) nitrogen.
 Analytical precision for δ18O, δD, δ13C and δ15N were 0.6‰, 4‰, 0.2‰ and
 0.1‰, respectively. Invertebrate stable isotopes were quantified for
 wetland P1 and P8 to a core depth of 21 cm and 22 cm,
 respectively.