Streams and rivers are significant sources of nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) globally, and watershed management can alter greenhouse gas (GHG) emissions from streams. We hypothesized that urban infrastructure significantly alters downstream water quality and contributes to variability in GHG saturation and emissions. We measured gas saturation and estimated emission rates in headwaters of two urban stream networks (Red Run and Dead Run) of the Baltimore Ecosystem Study Long-Term Ecological Research project. We identified four combinations of stormwater and sanitary infrastructure present in these watersheds, including: (1) stream burial, (2) inline stormwater wetlands, (3) riparian/floodplain preservation, and (4) septic systems. We selected two first-order catchments in each of these categories and measured GHG concentrations, emissions, and dissolved inorganic and organic carbon (DIC and DOC) and nutrient concentrations biweekly for 1 year. From a water quality perspective, the DOC : NO3− ratio of streamwater was significantly different across infrastructure categories. Multiple linear regressions including DOC : NO3− and other variables (dissolved oxygen, DO; total dissolved nitrogen, TDN; and temperature) explained much of the statistical variation in nitrous oxide (N2O, r2 = 0.78), carbon dioxide (CO2, r2 = 0.78), and methane (CH4, r2 = 0.50) saturation in stream water. We measured N2O saturation ratios, which were among the highest reported in the literature for streams, ranging from 1.1 to 47 across all sites and dates. N2O saturation ratios were highest in streams draining watersheds with septic systems and strongly correlated with TDN. The CO2 saturation ratio was highly correlated with the N2O saturation ratio across all sites and dates, and the CO2 saturation ratio ranged from 1.1 to 73. CH4 was always supersaturated, with saturation ratios ranging from 3.0 to 2157. Longitudinal surveys extending form headwaters to third-order outlets of Red Run and Dead Run took place in spring and fall. Linear regressions of these data yielded significant negative relationships between each gas with increasing watershed size as well as consistent relationships between solutes (TDN or DOC, and DOC : TDN ratio) and gas saturation. Despite a decline in gas saturation between the headwaters and stream outlet, streams remained saturated with GHGs throughout the drainage network, suggesting that urban streams are continuous sources of CO2, CH4, and N2O. Our results suggest that infrastructure decisions can have significant effects on downstream water quality and greenhouse gases, and watershed management strategies may need to consider coupled impacts on urban water and air quality.
more »
« less
Variability and drivers of CO 2 , CH 4 , and N 2 O concentrations in streams across the United States
Streams and rivers are major sources of greenhouse gases (GHGs) to the atmosphere, as carbon and nitrogen are converted and outgassed during transport. Although our understanding of drivers of individual GHG fluxes has improved with numerous site‐specific studies and global‐scale compilations, our ability to parse out interrelated physical and biogeochemical drivers of gas concentrations is limited by a lack of consistently collected, temporally continuous samples of GHGs and their associated drivers. We present a first analysis of such a dataset collected by the National Ecological Observatory Network across 27 streams and rivers across ecoclimatic domains of the United States. Average concentrations of CO2ranged from 36.9 ± 0.88 to 404 ± 33
- NSF-PAR ID:
- 10397014
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Limnology and Oceanography
- Volume:
- 68
- Issue:
- 2
- ISSN:
- 0024-3590
- Page Range / eLocation ID:
- p. 394-408
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
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 Streams and rivers are significant sources of carbon dioxide (CO2) and methane (CH4) to the atmosphere. However, the magnitudes of these fluxes are uncertain, in part, because dissolved greenhouse gases (GHGs) can exhibit high spatiotemporal variability. Concentration‐discharge (
C ‐Q ) relationships are commonly used to describe temporal variability stemming from hydrologic controls on solute production and transport. This study assesses how the partial pressures of two GHGs—p CO2andp CH4—vary across hydrologic conditions over 4 yr in eight nested streams and rivers, at both annual and seasonal timescales. Overall, the range ofp CO2was constrained, ranging from undersaturated to nine times oversaturated, whilep CH4was highly variable, ranging from 3 to 500 times oversaturated. We show thatp CO2exhibited chemostatic behavior (i.e., no change withQ ), in part, due to carbonate buffering and seasonally specific storm responses. In contrast, we show thatp CH4generally exhibited source limitation (i.e., a negative relationship withQ ), which we attribute to temperature‐mediated production. However,p CH4exhibited chemostasis in a wetland‐draining stream, likely due to hydrologic connection to the CH4‐rich wetland. These findings have implications for CO2and CH4fluxes, which are controlled by concentrations and gas transfer velocities. At highQ , enhanced gas transfer velocity acts on a relatively constant CO2stock but on a diminishing CH4stock. In other words, CO2fluxes increase withQ , while CH4fluxes are modulated by the divergentQ dynamics of gas transfer velocity and concentration. -
more » « less
Abstract Inland waters are important sources of the greenhouse gasses (GHGs) carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) to the atmosphere. In the framework of the second phase of the REgional Carbon Cycle Assessment and Processes (RECCAP‐2) initiative, we synthesize existing estimates of GHG emissions from streams, rivers, lakes and reservoirs, and homogenize them with regard to underlying global maps of water surface area distribution and the effects of seasonal ice cover. We then produce regionalized estimates of GHG emissions over 10 extensive land regions. According to our synthesis, inland water GHG emissions have a global warming potential of an equivalent emission of 13.5 (9.9–20.1) and 8.3 (5.7–12.7) Pg CO2‐eq. yr−1at a 20 and 100 years horizon (GWP20and GWP100), respectively. Contributions of CO2dominate GWP100, with rivers being the largest emitter. For GWP20, lakes and rivers are equally important emitters, and the warming potential of CH4is more important than that of CO2. Contributions from N2O are about two orders of magnitude lower. Normalized to the area of RECCAP‐2 regions, S‐America and SE‐Asia show the highest emission rates, dominated by riverine CO2emissions.
-
more » « less
Abstract Collectively, reservoirs constitute a significant global source of C‐based greenhouse gases (GHGs). Yet, global estimates of reservoir carbon dioxide (CO2) and methane (CH4) emissions remain uncertain, varying more than four‐fold in recent analyses. Here we present results from a global application of the Greenhouse Gas from Reservoirs (G‐res) model wherein we estimate per‐area and per‐reservoir CO2and CH4fluxes, by specific flux pathway and in a spatially and temporally explicit manner, as a function of reservoir characteristics. We show: (a) CH4fluxes via degassing and ebullition are much larger than previously recognized and diffusive CH4fluxes are lower than previously estimated, while CO2emissions are similar to those reported in past work; (b) per‐area reservoir GHG fluxes are >29% higher than suggested by previous studies, due in large part to our novel inclusion of the degassing flux in our global estimate; (c) CO2flux is the dominant emissions pathway in boreal regions and CH4degassing and ebullition are dominant in tropical and subtropical regions, with the highest overall reservoir GHG fluxes in the tropics and subtropics; and (d) reservoir GHG fluxes are quite sensitive to input parameters that are both poorly constrained and likely to be strongly influenced by climate change in coming decades (parameters such as temperature and littoral area, where the latter may be expanded by deepening thermoclines expected to accompany warming surface waters). Together these results highlight a critical need to both better understand climate‐related drivers of GHG emission and to better quantify GHG emissions via CH4ebullition and degassing.
