Northeastern mountain ponds as sentinels of change: Current and emerging research and monitoring in the context of shifting chemistry and climate interactions

作者: S.J. Nelson ; J. Daly ; R.A. Hovel ; W.H. McDowell ; A. Gavin ; S. Dykema

Mountain ponds in the northeastern US have undergone acidification and subsequent recovery due to changes in atm. deposition, and also reflect phys. and biol. responses to climate change.These ponds are distinct from other lakes and ponds in the region as they are higher in elevation, relatively small, and have little direct impact from human land use in their watersheds.They are vulnerable to the increases in extreme weather events, overall warming, and shortening of winter that are occurring throughout the northeastern US.We compiled data collected from 1978 to 2019 for mountain ponds >500 m elevation and <60 ha surface area across the northeastern US (Northern Appalachians and Adirondack Mountains).The full dataset includes 257 ponds; 36% of the sites were sampled at sufficient frequency to conduct trend analyses from the 1980s through 2010s.We found widespread, significant declines in sulfate concentrations (95% of sites, ∼44% decline) and significantly increasing ANC at 53% of sites (46% of sites-no trend; 1%-significant decrease).Significant declining conductivity at 97% of sites (33% decline) suggested dilution (14.0μS/cm by the 2010s), and also reflected low chloride concentrations at these sites compared to others in the region affected by road salt contamination.DOC increased significantly in 54% of ponds (45% of sites-no trend; 1%-significant decrease).Increasing DOC has been attributed to both changing sulfate and climate related to increases in precipitation and air temperatureOther changes are occurring in these ponds alongside trends in water chem., such as thermal structures shifting as air temperature warms.Zooplankton communities are sensitive to water chem. parameters associated with acidification recovery, such as DOC, but climate change may complicate transitions back to pre-acidification community compositionBased on this synthesis and a case study that integrates chem., phys., and biol. research, we developed a conceptual model and framework for research and monitoring to support measurements of change in these ecosystems.The findings indicate the importance of eastern mountain ponds in understanding combined impacts of atm. deposition and climate change on lake ecosystems and highlight future research directions.

2021-11-01·Geoderma

Repeated freeze–thaw cycles increase extractable, but not total, carbon and nitrogen in a Maine coniferous soil

作者: Corianne Tatariw ; Tsutomu Ohno ; Kaizad F. Patel ; Sarah J. Nelson ; Jean D. MacRae ; Ivan J. Fernandez

Northeastern North America has been experiencing warmer winters with reduced snow accumulation, with more frequent winter freeze-thaw cycles.We conducted a laboratory experiment to investigate how increased frequency of freeze-thaw cycles (FTC) would alter soil C and N availability.Organic (O) and mineral (B) horizon soils were collected from a coniferous forest in Maine, processed to exclude roots, and then frozen in the laboratory (-10 °C) with one (FTC-1), two (FTC-2), or six (FTC-6) thaw periods (+5 °C).Soils were analyzed for extractable ammonium (NH₄-N), water extractable organic carbon (WEOC), carbon dioxide flux (respiration), and total C and N.Extractable NH₄-N increased following FTC (all levels), for both horizons.While WEOC concentrations did not change for FTC vs. control, the WEOC in O horizons had a lower SUVA₂₅₄ in FTC soils compared to control, indicating a stronger microbial influence (i.e., microbial cell lysis) in these soils after FTC.Respiration in O horizon soils decreased post-incubation and did not differ between FTC and Control soils.In the B horizon, however, FTC soils showed greater respiration than Control soils, suggesting that the newly available nutrients may have stimulated microbial activity.In contrast to these results, total C and N remained unaltered by FTC, presumably because the FTC disturbances represented mostly a translocation of C and N from one pool into another, and losses due to respiration were too small to significantly influence the large TC and TN pools.The effect of FTC on NH₄-N did not change with FTC frequency, suggesting that a single FTC is sufficient to alter both C and N availability and/or quality, and that addnl. FTC may not have a significant further effect.This study provides fresh insights on how organic and mineral horizon soils might respond to increased freeze-thaw frequency in winter.

2020-12-01·Biogeochemistry

Contrasting stream nitrate and sulfate response to recovery from experimental watershed acidification

作者: Sarah J. Nelson ; Stephen A. Norton ; Jacob Malcomb ; Kaizad F. Patel ; Ivan J. Fernandez

Abstract: Improvements in air quality have led to ecosystem recovery from acidic deposition, but the mechanisms and trajectories of this recovery are not fully understood.Here, we present long-term stream response and recovery data for paired watersheds at the Bear Brook Watershed in Maine (BBWM) during declining ambient SO₄ and NO₃ in precipitationEast Bear (EB) received ambient deposition from 1989 to 2018; West Bear (WB) received artificially elevated N + S from 1989 to 2016.The WB treatment was discontinued after 2016, the beginning of the recovery from both the exptl. N + S and ambient decline.Stream SO₄ in WB gradually declined after the treatment ended, from ∼147μeq L^-1 in 2010-16 to ∼126μeq L^-1 in 2017-18.The declining S inputs induced desorption of SO₄ from soil phase surfaces, with stream loss far exceeding precipitation input.At the current rate of recovery, it will be many decades before the WB stream returns to pre-treatment SO₄ concentrationsIn contrast, NO₃ is only weakly adsorbed in soil, and WB stream NO₃ concentrations rapidly declined from ∼39μeq L^-1 in 2010-16 to ∼5μeq L^-1 in 2017-18, comparable to the N-limited EB stream.The acid anions are strongly coupled to base cation chem. in streams, and there was a distinct hysteretic response of Ca and Mg to the chronic acidification, as (Ca + Mg) increased rapidly during the initial years, followed by declining values due to depletion of the soil exchange complex.This 30-yr monitoring study (1989-2019) provides insights into recovery mechanisms from acidic deposition and highlights the role of abiotic processes in soil that mediate nutrient cycling and retention.Documenting the rapid response of N alongside the slower recovery for S identifies the temporal resolution necessary for other whole-watershed recovery studies.

100 项与 Appalachian Mountain Club 相关的药物交易

登录后查看更多信息

100 项与 Appalachian Mountain Club 相关的转化医学

登录后查看更多信息