Small ponds account for a disproportionately high percentage of carbon dioxide emissions relative to their small surface area. It is therefore crucial to understand carbon flow in these ponds to refine the current global carbon budget, especially because climate change is affecting pond hydrology. High elevation ponds in the Elk Mountains of western Colorado are drying more frequently as the timing of snowmelt advances. We compared CO2 concentrations and fluxes among ponds of different hydroperiods over diel sampling periods during the course of the 2017 open-water period. CO2 concentrations were significantly negatively correlated with pond depth and averaged 77.6 ± 24.5 μmol L−1 (mean ± S.E.) across all ponds and sampling events. Ponds were up to twenty times supersaturated in CO2 with respect to the atmosphere. Flux was highly variable within individual ponds but correlated with time of sampling and was highest at night. Flux averaged 19.7 ± 18.8 mg CO2 m−2 h−1 across all ponds and sampling events. We also compared flux values obtained using modeled and empirical methods and found that widely-applied models of gas exchange rates using wind-based gas exchange (K) values yielded estimates of CO2 flux that were significantly higher than those obtained using the floating chamber approach, but estimates of CO2 flux using globally averaged convection-based K values were lower than those obtained using the floating chambers. Lastly, we integrated soil vs. water efflux measurements with long-term patterns in hydrology to predict how total season-long efflux might change under the more rapid drying regimes and longer seasons that are already occurring in these systems. Because soil CO2 efflux averaged 277.0 ± 49.0 mg CO2 m−2 h−1, temporary ponds emitted 674.1 ± 99.4 kg CO2 m−2 over the course of the 2017 season from ice-out to refreezing, which was over twice as much as permanent and semi-permanent ponds. Our results emphasize that contributions of CO2 from small ponds to the global carbon budget estimates will vary with pond hydroperiod and sampling methodology, which have been overlooked given that most previous estimates were collected from limited sampling periods and from pond waters alone. Furthermore, pond CO2 contributions are predicted to increase over time as pond areas transition from efflux from water to efflux from soil.
more »
« less
Biogeochemical characteristics and hydroperiod affect carbon dioxide flux rates from exposed high‐elevation pond sediments
While inundated, small ponds (< 1000 m2area) account for disproportionately large contributions of CO2efflux to the global carbon budget and also store carbon in anoxic sediments. However, pond hydrology is shifting toward increasingly dry conditions in alpine and temperate zones, which might lead to increased exposure of shallow pond sediments. We analyzed sediment CO2efflux rates in dried sediments of multiple ponds of varying hydrology and sediment characteristics at montane and subalpine elevations near the Rocky Mountain Biological Laboratory in Colorado. Average CO2efflux rates from exposed sediments, 331.5 ± 11.5 mmol m−2d−1at the montane sites and 142.8 ± 45.1 mmol m−2d−1at the subalpine sites, were 10 times higher than average CO2efflux rates from pond water. Principal components analysis to reduce dimensionality of sediment characteristics revealed that random inter‐pond differences rather than exposure timing or hydroperiod drove variation among sediments. In linear mixed effects models of CO2flux rates, significant predictors included sediment moisture and temperature, pH, total organic carbon, and organic matter content at all pond hydroperiod classifications and sites. However, the sediment characteristics explaining the most variance differed among sites and hydroperiods and included nitrate concentrations, pH, bulk density, and temperature. We conclude that pond sediments are heterogeneous both within and among ponds in close proximity, and drivers of relatively high CO2efflux rates differ among pond hydroperiods and elevations. This work emphasizes that local differences can impact predictions of CO2flux from lentic sediments which are becoming increasingly exposed.
more » « less- NSF-PAR ID:
- 10452137
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Limnology and Oceanography
- Volume:
- 66
- Issue:
- 4
- ISSN:
- 0024-3590
- Page Range / eLocation ID:
- p. 1050-1067
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)In many lentic ecosystems, hydroperiod, or the duration of inundation, controls animal community composition and biomass. Although hydroperiod-imposed differences in wetland animal communities could cause differences in animal-driven nutrient supply, hydroperiod has not been considered as a template for investigating patterns of animal-driven nutrient cycling. Here, we use nutrient excretion rates (NH4-N and SRP) and biomasses of pelagic and benthic invertebrates and salamanders and nutrient uptake rates in a simulation model to estimate animal-driven nutrient supply and pond-level demand along a hydroperiod gradient of 12 subalpine ponds in the U.S. Rocky Mountains that are vulnerable to climate change. We found that animal biomass increased with hydroperiod duration and biomass predicted animal-driven supply contributions among hydroperiod classifications (temporary-permanent). Consequently, community-wide supply was greatest in permanent ponds. Animal-driven N supply exceeded demand in permanent and semi-permanent ponds, whereas P supply equaled demand in both. Conversely, temporary ponds had large deficits in N and P supply due to lower community biomass and hydroperiod-induced constraints on dominant suppliers (oligochaetes and chironomids). The distribution of taxon-specific supply also differed among hydroperiods, with supply dominated by a few taxa in permanent ponds and supply more evenly distributed among temporary pond taxa. The absence or lower biomass of dominant suppliers in temporary ponds creates nutrient deficits and possible limitation of productivity. Thus, as climate warming causes hydroperiods to become increasingly temporary and indirectly prompts biomass declines and compositional shifts, animal-driven nutrient supply will decrease and strong nutrient limitation may arise due to loss of animal-driven supply.more » « less
-
more » « less
Abstract Ponds play a larger role in the global freshwater methane (CH4) budget than predicted from surface area alone. To improve our understanding of pond CH4dynamics, we measured summer CH4production, concentrations, and emissions to the atmosphere in nine Alaskan wetland ponds along with potential physical, chemical, and biological regulators. Pond CH4production (0.64, 0.086–1.3 mmol m−2d−1; median, interquartile range), as assessed with slurry incubations, was positively related to water‐column temperature and chlorophyll
a (Chla ), negatively influenced by oxygen levels, and varied with microbial community structure. Average water‐column CH4concentrations (0.39, 0.21–0.87μ mol L−1) were lower in deeper ponds and at higher oxygen levels, and as expected, they were correlated with diffusive emissions (0.055, 0.024–0.20 mmol m−2d−1) assessed with flux chambers. Based on a mass balance approach, 39–99% of CH4produced in ponds was oxidized. Pond ebullition (3.7, 0.60–24 mmol m−2d−1) was higher and more variable than diffusive emissions. Additionally, pond ebullition rates were better correlated with production rates from the previous month. We also systematically compared the ratio of ebullition to diffusive CH4emissions in our ponds and other northern lakes, which was negatively related to water depth (n = 71), but positively related to Chla (n = 28). Our study sheds light on the factors that influence pond CH4dynamics and demonstrates that pond ebullition is a significant CH4source worthy of continued study. -
more » « less
Abstract Coastal salt marshes store large amounts of carbon but the magnitude and patterns of greenhouse gas (GHG; i.e., carbon dioxide (CO2) and methane (CH4)) fluxes are unclear. Information about GHG fluxes from these ecosystems comes from studies of sediments or at the ecosystem‐scale (eddy covariance) but fluxes from tidal creeks are unknown. We measured GHG concentrations in water, water quality, meteorological parameters, sediment CO2efflux, ecosystem‐scale GHG fluxes, and plant phenology; all at half‐hour intervals over 1 year. Manual creek GHG flux measurements were used to calculate gas transfer velocity (
k ) and parameterize a model of water‐to‐atmosphere GHG fluxes. The creek was a source of GHGs to the atmosphere where tidal patterns controlled diel variability. Dissolved oxygen and wind speed were negatively correlated with creek CH4efflux. Despite lacking a seasonal pattern, creek CO2efflux was correlated with drivers such as turbidity across phenological phases. Overall, nighttime creek CO2efflux (3.6 ± 0.63 μmol/m2/s) was at least 2 times higher than nighttime marsh sediment CO2efflux (1.5 ± 1.23 μmol/m2/s). Creek CH4efflux (17.5 ± 6.9 nmol/m2/s) was 4 times lower than ecosystem‐scale CH4fluxes (68.1 ± 52.3 nmol/m2/s) across the year. These results suggest that tidal creeks are potential hotspots for CO2emissions and could contribute to lateral transport of CH4to the coastal ocean due to supersaturation of CH4(>6,000 μmol/mol) in water. This study provides insights for modeling GHG efflux from tidal creeks and suggests that changes in tide stage overshadow water temperature in determining magnitudes of fluxes. -
more » « less
Abstract Arctic regions are experiencing rapid warming, leading to permafrost thaw and formation of numerous water bodies. Although small ponds in particular are considered hot spots for methane (CH4) release, long‐term studies of CH4efflux from these surfaces are rare. We have collected an extensive data set of CH4ebullition (bubbling) measurements from eight small thaw ponds (<0.001 km2) with different physical and hydrological characteristics over four summer seasons, the longest set of observations from thaw ponds to date. The measured fluxes were highly variable with an average of 20.0 mg CH4· m−2· day−1(median: 4.1 mg CH4· m−2· day−1,
n = 2,063) which is higher than that of most nearby lakes. The ponds were categorized into four types based on clear and significant differences in bubble flux. We found that the amount of CH4released as bubbles from ponds was very weakly correlated with environmental variables, like air temperature and atmospheric pressure, and was potentially more related to differences in physical characteristics of the ponds. Using our measured average daily bubble flux plus the available literature, we estimate circumpolar thaw ponds <0.001 km2in size to emit between 0.2 and 1.0 Tg of CH4through ebullition. Our findings exemplify the importance of high‐frequency measurements over long study periods in order to adequately capture the variability of these water bodies. Through the expansion of current spatial and temporal monitoring efforts, we can increase our ability to estimate CH4emissions from permafrost pond ecosystems now and in the future.
