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At least 181 records · Page 10Linked to original sources
USGS2007

Bora event variability and the role of air-sea feedback

A two-way interacting high resolution numerical simulation of the Adriatic Sea using the Navy Coastal Ocean Model (NCOM) and Coupled Ocean/ Atmosphere Mesoscale Prediction System (COAMPS??) was conducted to improve forecast momentum and heat flux fields, and to evaluate surface flux field differences for two consecutive bora events during February 2003. (COAMPS?? is a registered trademark of the Naval Research Laboratory.) The strength, mean positions and extensions of the bora jets, and the atmospheric conditions driving them varied considerably between the two events. Bora 1 had 62% stronger heat flux and 51% larger momentum flux than bora 2. The latter displayed much greater diurnal variability characterized by inertial oscillations and the early morning strengthening of a west Adriatic barrier jet, beneath which a stronger west Adriatic ocean current developed. Elsewhere, surface ocean current differences between the two events were directly related to differences in wind stress curl generated by the position and strength of the individual bora jets. The mean heat flux bias was reduced by 72%, and heat flux RMSE reduced by 30% on average at four instrumented over-water sites in the two-way coupled simulation relative to the uncoupled control. Largest reductions in wind stress were found in the bora jets, while the biggest reductions in heat flux were found along the north and west coasts of the Adriatic. In bora 2, SST gradients impacted the wind stress curl along the north and west coasts, and in bora 1 wind stress curl was sensitive to the Istrian front position and strength. The two-way coupled simulation produced diminished surface current speeds of ???12% over the northern Adriatic during both bora compared with a one-way coupled simulation. Copyright 2007 by the American Geophysical Union.

Journal of Geophysical Research C: Oceans↗
USGS2018

On the exchange of sensible and latent heat between the atmosphere and melting snow

The snow energy balance is difficult to measure during the snowmelt period, yet critical for predictions of water yield in regions characterized by snow cover. Robust simplifications of the snowmelt energy balance can aid our understanding of water resources in a changing climate. Research to date has demonstrated that the net turbulent flux ( F T ) between a melting snowpack and the atmosphere is negligible if the sum of atmospheric vapor pressure ( e a ) and temperature ( T a ) equals a constant, but it is unclear how frequently this situation holds across different sites. Here, we quantified the contribution of F T to the snowpack energy balance during 59 snowmelt periods across 11 sites in the FLUXNET2015 database with a detailed analysis of snowmelt in subarctic tundra near Abisko, Sweden. At the Abisko site we investigated the frequency of occurrences during which sensible heat flux ( H ) and latent heat flux ( λE ) are of (approximately) equal but opposite sign, and if the sum of these terms, F T , is therefore negligible during the snowmelt period. H approximately equaled - λE for less than 50% of the melt period and F T was infrequently a trivial term in the snowmelt energy balance at Abisko. The reason is that the relationship between observed e a and T a is roughly orthogonal to the “line of equality” at which H equals - λE as warmer T a during the melt period usually resulted in greater e a . This relationship holds both within melt periods at individual sites and across different sites in the FLUXNET2015 database, where F T comprised less than 20% of the energy available to melt snow, Q m , in 44% of the snowmelt periods studied here. F T / Q m was significantly related to the mean e a during the melt period, but not mean T a , and F T tended to be near 0 W m −2 when e a averaged ca . 0.5 kPa. F T may become an increasingly important term in the snowmelt energy balance across many global regions as warmer temperatures are projected to cause snow to melt more slowly and earlier in the year under conditions of lower net radiation ( R n ). Eddy covariance research networks such as Ameriflux must improve their ability to observe cold-season processes to enhance our understanding of water resources and surface-atmosphere exchange in a changing climate.

Agricultural and Forest Meteorology↗
USGS2015

Water-level measurements in Dauphin Island, Alabama, from the 2013 Hurricane Season

This report describes the instrumentation, field measurements, and processing methods used by the U.S. Geological Survey to measure atmospheric pressure, water levels, and waves on Dauphin Island, Alabama, in 2013 at part of the Barrier Island Evolution Research project. Simple, inexpensive pressure sensors mounted in shallow wells were buried in the beach and left throughout the hurricane season. Additionally, an atmospheric pressure sensor was mounted on the porch of a private residence to provide a local atmospheric pressure measurement for correcting the submerged pressure records.

Alabama↗
USGS1993

Acidic Depositions: Effects on Wildlife and Habitats

The phenomenon of 'acid rain' is not new; it was recognized in the mid-1800s in industrialized Europe. In the 1960s a synthesis of information about acidification began in Europe, along with predictions of ecological effects. In the U.S. studies of acidification began in the 1920s. By the late 1970s research efforts in the U.S. and Canada were better coordinated and in 1980 a 10-year research program was undertaken through the National Acid Precipitation Assessment Plan (NAPAP) to determine the causes and consequences of acidic depositions. Much of the bedrock in the northeastern U.S. and Canada contains total alkalinity of <200 ?eq 1-1, thus, it lacks acid-neutralizing capacity. In the U.S. about 5% of the land area and in Canada about 43 % of the land area is sensitive to acidic depositions. Further, these areas receive >20 kg/ha/yr of wet sulphate depositions and are vulnerable to acidifying processes. Acidic depositions contribute directly to acidifying processes of soil and soil water. Soils must have sufficient acid-neutralizing capacity or acidity of soil will increase. Natural soil-forming processes that lead to acidification can be accelerated by acidic depositions. Long-term effects of acidification are predicted, which will reduce soil productivity mainly through reduced availability of nutrients and mobilization of toxic metals. Severe effects may lead to major alteration of soil chemistry, soil biota, and even loss of vegetation. Several species of earthworms and several other taxa of soil-inhabiting invertebrates, which are important food of many vertebrate wildlife species, are affected by low pH in soil. Loss of canopy in declining sugar maples results in loss of insects fed on by certain neotropical migrant bird species. No definitive studies categorically link atmospheric acidic depositions with direct or indirect effects on wild mammals. Researchers have concentrated on vegetative and aquatic effects. Circumstantial evidence suggests that effects are probable for certain species of aquatic-dependent mammals (water shrew, mink, and otter) and that these species are at risk from the loss of foods or contamination of these foods by metals, especially methylmercury. Continued acidification of terrestrial habitats, to the extent that earthworm populations are broadly reduced, might expose some fossorial mammalian species to risk because of decline in their major prey species. Acidic deposition affects primarily aquatic habitats of avian species by disrupting food webs (ecological effects) and increasing amounts of available heavy metals (mercury, aluminum, cadmium) in prey of avian species (toxicological effects). The ecological effects of acidifying wetlands are to reduce acid-intolerant prey (invertebrates) and to change prey quality from high-calcium bearing prey to low-calcium bearing prey. The toxicological effects are to increase contamination by heavy metals, especially methylated mercury, in foods of breeding waterbirds. The combination of these 2 types of effects results in potentially lower survival of adults and reduced production, growth, or survival of young of many bird species. Effects of acidification on herpteofauna and their habitats are mainly reproductive failure of susceptible species and reduced or metal-contaminated foods for both amphibians and reptiles.

Wildlife Society Technical Review↗
USGS2018

Spatial distribution of halogen oxides in the plume of Mount Pagan volcano, Mariana Islands

Halogens are emitted from volcanoes primarily as hydrogen halides (HCl, HF, HBr, and HI). Upon mixing with the atmosphere, chlorine and bromine species are partially converted to the halogen oxides OClO and BrO. Here we report on the spatial distribution of BrO and OClO in the gas plume emitted from Mount Pagan volcano, Northern Mariana Islands. We found enhanced BrO/SO 2 ratios near the plume edges and a lack of OClO in the plume's core. Our results highlight the importance of in‐mixing of atmospheric oxidants for halogen oxide formation. They indicate that OClO can only be formed after most bromide dissolved in plume aerosols has been released to the gas phase. We conclude that Mount Pagan's gas emissions originated from a shallow magma body and were transported to the surface along dry degassing pathways and that the volcano's halogen emissions likely had significant impact on the oxidation capacity of the downwind atmosphere.

Geophysical Research Letters↗
USGS2013

Characterizing and estimating noise in InSAR and InSAR time series with MODIS

InSAR time series analysis is increasingly used to image subcentimeter displacement rates of the ground surface. The precision of InSAR observations is often affected by several noise sources, including spatially correlated noise from the turbulent atmosphere. Under ideal scenarios, InSAR time series techniques can substantially mitigate these effects; however, in practice the temporal distribution of InSAR acquisitions over much of the world exhibit seasonal biases, long temporal gaps, and insufficient acquisitions to confidently obtain the precisions desired for tectonic research. Here, we introduce a technique for constraining the magnitude of errors expected from atmospheric phase delays on the ground displacement rates inferred from an InSAR time series using independent observations of precipitable water vapor from MODIS. We implement a Monte Carlo error estimation technique based on multiple (100+) MODIS-based time series that sample date ranges close to the acquisitions times of the available SAR imagery. This stochastic approach allows evaluation of the significance of signals present in the final time series product, in particular their correlation with topography and seasonality. We find that topographically correlated noise in individual interferograms is not spatially stationary, even over short-spatial scales (<10 km). Overall, MODIS-inferred displacements and velocities exhibit errors of similar magnitude to the variability within an InSAR time series. We examine the MODIS-based confidence bounds in regions with a range of inferred displacement rates, and find we are capable of resolving velocities as low as 1.5 mm/yr with uncertainties increasing to ∼6 mm/yr in regions with higher topographic relief.

California↗
USGS2009

Transport of tritium contamination to the atmosphere in an arid environment

Soil–plant–atmosphere interactions strongly influence water movement in desert unsaturated zones, but little is known about how such interactions affect atmospheric release of subsurface water-borne contaminants. This 2-yr study, performed at the U.S. Geological Survey's Amargosa Desert Research Site in southern Nevada, quantified the magnitude and spatiotemporal variability of tritium (3H) transport from the shallow unsaturated zone to the atmosphere adjacent to a low-level radioactive waste (LLRW) facility. Tritium fluxes were calculated as the product of 3H concentrations in water vapor and respective evaporation and transpiration water-vapor fluxes. Quarterly measured 3H concentrations in soil water vapor and in leaf water of the dominant creosote-bush [ Larrea tridentat a (DC.) Coville] were spatially extrapolated and temporally interpolated to develop daily maps of contamination across the 0.76-km2 study area. Maximum plant and root-zone soil concentrations (4200 and 8700 Bq L−1, respectively) were measured 25 m from the LLRW facility boundary. Continuous evaporation was estimated using a Priestley–Taylor model and transpiration was computed as the difference between measured eddy-covariance evapotranspiration and estimated evaporation. The mean evaporation/transpiration ratio was 3:1. Tritium released from the study area ranged from 0.12 to 12 μg d−1 and totaled 1.5 mg (8.2 × 1010 Bq) over 2 yr. Tritium flux variability was driven spatially by proximity to 3H source areas and temporally by changes in 3H concentrations and in the partitioning between evaporation and transpiration. Evapotranspiration removed and limited penetration of precipitation beneath native vegetation and fostered upward movement and release of 3H from below the root zone.

Vadose Zone Journal↗
USGS2000

Calcium depletion in a Southeastern United States forest ecosystem

Forest soil Ca depletion through leaching and vegetation uptake may threaten long-term sustainability of forest productivity in the southeastern USA. This study was conducted to assess Ca pools and fluxes in a representative southern Piedmont forest to determine the soil Ca depletion rate. Soil Ca storage, Ca inputs in atmospheric deposition, and outputs in soil leaching and vegetation uptake were investigated at the Panola Mountain Research Watershed (PMRW) near Atlanta, GA. Average annual outputs of 12.3 kg ha −1 yr −1 in uptake into merchantable wood and 2.71 kg ha −1 yr −1 soil leaching exceeded inputs in atmospheric deposition of 2.24 kg ha −1 yr −1 The annual rate of Ca uptake into merchantable wood exceeds soil leaching losses by a factor of more than five. The potential for primary mineral weathering to provide a substantial amount of Ca inputs is low. Estimates of Ca replenishment through mineral weathering in the surface 1 m of soil and saprolite was estimated to be 0.12 kg ha −1 yr −1 The weathering rate in saprolite and partially weathered bedrock below the surface 1 m is similarly quite low because mineral Ca is largely depleted. The soil Ca depletion rate at PMRW is estimated to be 12.7 kg ha −1 yr −1 At PMRW and similar hardwood-dominated forests in the Piedmont physiographic province, Ca depletion will probably reduce soil reserves to less than the requirement for a merchantable forest stand in ≈80 yr. This assessment and comparable analyses at other southeastern USA forest sites suggests that there is a strong potential for a regional problem in forest nutrition in the long term.

Soil Science Society of America Journal↗
USGS1993

Integration of environmental simulation models with satellite remote sensing and geographic information systems technologies: case studies

Environmental modelers are testing and evaluating a prototype land cover characteristics database for the conterminous United States developed by the EROS Data Center of the U.S. Geological Survey and the University of Nebraska Center for Advanced Land Management Information Technologies. This database was developed from multi temporal, 1-kilometer advanced very high resolution radiometer (AVHRR) data for 1990 and various ancillary data sets such as elevation, ecological regions, and selected climatic normals. Several case studies using this database were analyzed to illustrate the integration of satellite remote sensing and geographic information systems technologies with land-atmosphere interactions models at a variety of spatial and temporal scales. The case studies are representative of contemporary environmental simulation modeling at local to regional levels in global change research, land and water resource management, and environmental simulation modeling at local to regional levels in global change research, land and water resource management and environmental risk assessment. The case studies feature land surface parameterizations for atmospheric mesoscale and global climate models; biogenic-hydrocarbons emissions models; distributed parameter watershed and other hydrological models; and various ecological models such as ecosystem, dynamics, biogeochemical cycles, ecotone variability, and equilibrium vegetation models. The case studies demonstrate the important of multi temporal AVHRR data to develop to develop and maintain a flexible, near-realtime land cover characteristics database. Moreover, such a flexible database is needed to derive various vegetation classification schemes, to aggregate data for nested models, to develop remote sensing algorithms, and to provide data on dynamic landscape characteristics. The case studies illustrate how such a database supports research on spatial heterogeneity, land use, sensitivity analysis, and scaling issues involving regional extrapolations and parameterizations of dynamic land processes within simulation models.

Pecora 12 Symposium↗
USGS2010

Paleoclimates: Understanding climate change past and present

The field of paleoclimatology relies on physical, chemical, and biological proxies of past climate changes that have been preserved in natural archives such as glacial ice, tree rings, sediments, corals, and speleothems. Paleoclimate archives obtained through field investigations, ocean sediment coring expeditions, ice sheet coring programs, and other projects allow scientists to reconstruct climate change over much of earth's history. When combined with computer model simulations, paleoclimatic reconstructions are used to test hypotheses about the causes of climatic change, such as greenhouse gases, solar variability, earth's orbital variations, and hydrological, oceanic, and tectonic processes. This book is a comprehensive, state-of-the art synthesis of paleoclimate research covering all geological timescales, emphasizing topics that shed light on modern trends in the earth's climate. Thomas M. Cronin discusses recent discoveries about past periods of global warmth, changes in atmospheric greenhouse gas concentrations, abrupt climate and sea-level change, natural temperature variability, and other topics directly relevant to controversies over the causes and impacts of climate change. This text is geared toward advanced undergraduate and graduate students and researchers in geology, geography, biology, glaciology, oceanography, atmospheric sciences, and climate modeling, fields that contribute to paleoclimatology. This volume can also serve as a reference for those requiring a general background on natural climate variability.

Book↗
USGS2004

Dust storms and their impact on ocean and human health: dust in Earth's atmosphere

Satellite imagery has greatly influenced our understanding of dust activity on a global scale. A number of different satellites such as NASA's Earth-Probe Total Ozone Mapping Spectrometer (TOMS) and Se-viewing Field-of-view Sensor (SeaWiFS) acquire daily global-scale data used to produce imagery for monitoring dust storm formation and movement. This global-scale imagery has documented the frequent transmission of dust storm-derived soils through Earth's atmosphere and the magnitude of many of these events. While various research projects have been undertaken to understand this normal planetary process, little has been done to address its impact on ocean and human health. This review will address the ability of dust storms to influence marine microbial population densities and transport of soil-associated toxins and pathogenic microorganisms to marine environments. The implications of dust on ocean and human health in this emerging scientific field will be discussed.

EcoHealth↗
USGS2000

Preface paper to the Semi-Arid Land-Surface-Atmosphere (SALSA) Program special issue

The Semi-Arid Land-Surface-Atmosphere Program (SALSA) is a multi-agency, multi-national research effort that seeks to evaluate the consequences of natural and human-induced environmental change in semi-arid regions. The ultimate goal of SALSA is to advance scientific understanding of the semi-arid portion of the hydrosphere-biosphere interface in order to provide reliable information for environmental decision making. SALSA approaches this goal through a program of long-term, integrated observations, process research, modeling, assessment, and information management that is sustained by cooperation among scientists and information users. In this preface to the SALSA special issue, general program background information and the critical nature of semi-arid regions is presented. A brief description of the Upper San Pedro River Basin, the initial location for focused SALSA research follows. Several overarching research objectives under which much of the interdisciplinary research contained in the special issue was undertaken are discussed. Principal methods, primary research sites and data collection used by numerous investigators during 1997-1999 are then presented. Scientists from about 20 US, five European (four French and one Dutch), and three Mexican agencies and institutions have collaborated closely to make the research leading to this special issue a reality. The SALSA Program has served as a model of interagency cooperation by breaking new ground in the approach to large scale interdisciplinary science with relatively limited resources.

Conference Paper↗
USGS2011

Doctorate time rising sharply: How long should it take?

The period 1967–1987 saw a 20% increase in the time it takes to complete the doctorate. That figure is based on data provided by the National Research Council from 11 scientific and engineering fields, including the Earth, atmospheric and marine sciences. The median time spent earning the degree rose from 5.4 years in 1967 to 6.1 years in 1977 to 6.9 years in 1987—an increase of 1.5 years in a single generation. Completion time still seems to be rising! All graduating doctoral students in 1987 had a median age of 33.6 years; chemistry students were youngest at 29, and education students were the oldsters at 39.8 years.

Eos, Transactions, American Geophysical Union↗
USGS2026

When best intentions are not enough - A collaboration between scientists, policymakers, and an agricultural community

Rocky Mountain National Park is a Congressionally mandated Clean Air Act Class I Area, but years of research have documented evidence of biogeochemical and ecological change caused by atmospheric deposition of nitrogen. A coalition of government agencies—National Park Service, the Environmental Protection Agency Region 8, and the State of Colorado—developed the 2007 Nitrogen Deposition Reduction Plan to reduce wet nitrogen deposition to the park from the baseline in 2006 by 50% by 2032. Fifty-four percent of wet nitrogen deposition is ammonium, primarily sourced from industrial cattle and dairy operations east of the park. An Agriculture Subcommittee, meeting with regulatory and management agencies and scientists since 2006, has explored voluntary options to reduce ammonia emissions. Ammonia emissions are unregulated in the U.S. Despite sustained efforts, neither ammonium deposition nor total inorganic nitrogen deposition have declined at the rate determined to reach the targeted value by 2032. In fact, ammonia is increasing over the Front Range agricultural area. Wet nitrogen deposition in 2024 was 2.81 kg N ha −1 yr −1 , 0.61 kg N ha −1 yr −1 higher than targeted in the Nitrogen Deposition Reduction Plan. The collaborative approach between agricultural producers, regulatory entities, and resource managers is not working, but not for lack of effort by all parties. Cattle process nitrogen inefficiently, and while management practices can somewhat reduce the proportion of ammonia emitted from feedlots, with more than one million head of cattle east of Rocky Mountain National Park, large-scale reductions are unlikely. New programs to reduce emissions of nitrogen oxides (46% of wet nitrogen deposition) may reduce nitrogen deposition that is changing park ecosystems. Improved integration of crop and livestock agriculture and valuation of the ecosystem services and economy of Rocky Mountain National Park alongside agricultural value are topics for further discussion. Implications : Nitrogen deposition in precipitation to Rocky Mountain National Park has changed natural ecosystems. To protect its Clean Air Act Class I status a 2007 Nitrogen Deposition Reduction Plan agreed upon by state and federal agencies set a goal to reduce wet nitrogen deposition to the Park by half by 2032. Industrial livestock operations are a large source of nitrogen; an Agriculture Subcommittee explored voluntary options to reduce emissions from cattle. Despite sustained efforts nitrogen deposition has not declined. Further reductions in industry and transportation emissions will be needed reduce nitrogen deposition to Rocky Mountain National Park.

Colorado↗
USGS2020

North Carolina State climate report

Our scientific understanding of the climate system strongly supports the conclusion that North Carolina’s climate has changed in recent decades and the expectation that large changes—much larger than at any time in the state’s history—will occur if current trends in greenhouse gas concentrations continue. Even under a scenario where emissions peak around 2050 and decline thereafter, North Carolina will experience substantial changes in climate. The projected changes with the highest level of scientific confidence include increases in temperature, increases in summer absolute humidity, increases in sea level, and increases in extreme precipitation. It is also likely that there will be increases in the intensity of the strongest hurricanes. A full appreciation for past and future changes in North Carolina’s climate requires a global perspective. Earth’s climate has warmed substantially since the late 19th century, with most of that warming occurring in the last 50 years. This warming trend is clear from global temperature records and many other indicators, including rising global sea levels and rapid decreases in arctic sea ice cover. Scientists have very high confidence that this warming is largely due to human activities that have significantly increased atmospheric concentrations of carbon dioxide (CO2) and other greenhouse gases. Exhaustive research has examined other potential causes of this warming, and the increase in greenhouse gas concentrations is the only plausible cause that is consistent with the observed data and the physics that governs the climate system.

North Carolina↗
USGS2024

Oxidation is a potentially significant methane sink in land-terminating glacial runoff

Globally, aquatic ecosystems are one of the largest but most uncertain sources of methane, a potent greenhouse gas. It is unclear how climate change will affect methane emissions, but recent work suggests that glacial systems, which are melting faster with climate change, may be an important source of methane to the atmosphere. Currently, studies quantifying glacial emissions are limited in number, and the role of methanotrophy, or microbial methane oxidizers, in reducing atmospheric emissions from source and receiving waters is not well known. Here we discuss three potential sites for methane oxidation that could mitigate emissions from glaciers into the atmosphere: under ice oxidation, oxidation within proglacial lakes, and oxidation within melt rivers. The research presented here increases the number of glacial sites with methane concentration data and is one of only a few studies to quantify the net microbial activity of methane production and oxidation in two types of land-terminating glacial runoff (lake and river). We find that oxidation in a glacial river may reduce atmospheric methane emissions from glacial melt by as much as 53%. Incorporating methane oxidation in estimates of glacial methane emissions may significantly reduce the estimated magnitude of this source in budgeting exercises.

Scientific Reports↗
USGS2016

Comparison of mercury mass loading in streams to atmospheric deposition in watersheds of Western North America: Evidence for non-atmospheric mercury sources

Annual stream loads of mercury (Hg) and inputs of wet and dry atmospheric Hg deposition to the landscape were investigated in watersheds of the Western United States and the Canadian-Alaskan Arctic. Mercury concentration and discharge data from flow gauging stations were used to compute annual mass loads with regression models. Measured wet and modeled dry deposition were compared to annual stream loads to compute ratios of Hg stream load to total Hg atmospheric deposition. Watershed land uses or cover included mining, undeveloped, urbanized, and mixed. Of 27 watersheds that were investigated, 15 had some degree of mining, either of Hg or precious metals (gold or silver), where Hg was used in the amalgamation process. Stream loads in excess of annual Hg atmospheric deposition (ratio > 1) were observed in watersheds containing Hg mines and in relatively small and medium-sized watersheds with gold or silver mines, however, larger watersheds containing gold or silver mines, some of which also contain large dams that trap sediment, were sometimes associated with lower load ratios (< 0.2). In the non-Arctic regions, watersheds with natural vegetation tended to have low ratios of stream load to Hg deposition (< 0.1), whereas urbanized areas had higher ratios (0.34–1.0) because of impervious surfaces. This indicated that, in ecosystems with natural vegetation, Hg is retained in the soil and may be transported subsequently to streams as a result of erosion or in association with dissolved organic carbon. Arctic watersheds (Mackenzie and Yukon Rivers) had a relatively elevated ratio of stream load to atmospheric deposition (0.27 and 0.74), possibly because of melting glaciers or permafrost releasing previously stored Hg to the streams. Overall, our research highlights the important role of watershed characteristics in determining whether a landscape is a net source of Hg or a net sink of atmospheric Hg.

Science of the Total Environment↗
USGS2016

Seasonal patterns in carbon dioxide in 15 mid-continent (USA) reservoirs

Evidence suggests that lakes are important sites for atmospheric CO 2 exchange and so play a substantial role in the global carbon budget. Previous research has 2 weaknesses: (1) most data have been collected only during the open-water or summer seasons, and (2) data are concentrated principally on natural lakes in northern latitudes. Here, we report on the full annual cycle of atmospheric CO 2 exchanges of 15 oligotrophic to eutrophic reservoirs in the Glacial Till Plains of the United States. With one exception, these reservoirs showed an overall loss of CO 2 during the year, with most values within the lower range reported for temperate lakes. There was a strong cross-system seasonal pattern: an average of 70% of total annual CO 2 efflux occurred by the end of spring mixis; some 20% of annual flux was reabsorbed during summer stratification; and the remaining 50% of efflux was lost during autumnal mixing. Net annual flux was negatively correlated with depth and positively correlated with both water residence time and DOC, with the smallest annual CO 2 efflux measured in shallow fertile impoundments. Strong correlations yield relationships allowing regional up-scaling of CO 2 evasion. Understanding lacustrine CO 2 uptake and evasion requires seasonal analyses across the full range of lake trophic states and morphometric attributes.

Missouri↗