Kroeger Kevin D.

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Kevin D.

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  • Article
    Author Correction : Accuracy and precision of tidal wetland soil carbon mapping in the conterminous United States
    (Nature Publishing Group, 2018-10-09) Holmquist, James R. ; Windham-Myers, Lisamarie ; Bliss, Norman B. ; Crooks, Stephen ; Morris, James T. ; Megonigal, J. Patrick ; Troxler, Tiffany G. ; Weller, Donald ; Callaway, John ; Drexler, Judith ; Ferner, Matthew C. ; Gonneea, Meagan E. ; Kroeger, Kevin D. ; Schile-Beers, Lisa ; Woo, Isa ; Buffington, Kevin ; Breithaupt, Joshua ; Boyd, Brandon M. ; Brown, Lauren N. ; Dix, Nicole ; Hice, Lyndie ; Horton, Benjamin P. ; MacDonald, Glen M. ; Moyer, Ryan P. ; Reay, William ; Shaw, Timothy ; Smith, Erik ; Smoak, Joseph M. ; Sommerfield, Christopher K. ; Thorne, Karen ; Velinsky, David ; Watson, Elizabeth ; Wilson Grimes, Kristin ; Woodrey, Mark
    This Article corrects an error in Equation 1
  • Preprint
    Depth of the vadose zone controls aquifer biogeochemical conditions and extent of anthropogenic nitrogen removal
    ( 2017-06) Szymczycha, Beata ; Kroeger, Kevin D. ; Crusius, John ; Bratton, John F.
    We investigated biogeochemical conditions and watershed features controlling the extent of nitrate removal through microbial dinitrogen (N2) production within the surficial glacial aquifer located on the north and south shores of Long Island, NY, USA. The extent of N2 production differs within portions of the aquifer, with greatest N2 production observed at the south shore of Long Island where the vadose zone is thinnest, while limited N2 production occurred under the thick vadose zones on the north shore. In areas with a shallow water table and thin vadose zone, low oxygen concentrations and sufficient DOC concentrations are conducive to N2 production. Results support the hypothesis that in aquifers without a significant supply of sediment-bound reducing potential, vadose zone thickness exerts an important control of the extent of N2 production. Since quantification of excess N2 relies on knowledge of equilibrium N2 concentration at recharge, calculated based on temperature at recharge, we further identify several features, such as land use and cover, seasonality of recharge, and climate change that should be considered to refine estimation of recharge temperature, its deviation from mean annual air temperature, and resulting deviation from expected equilibrium gas concentrations.
  • Article
    Water salinity and inundation control soil carbon decomposition during salt marsh restoration: An incubation experiment.
    (Wiley Open Access, 2019-02-10) Wang, Faming ; Kroeger, Kevin D. ; Gonneea, Meagan E. ; Pohlman, John W. ; Tang, Jianwu
    Coastal wetlands are a significant carbon (C) sink since they store carbon in anoxic soils. This ecosystem service is impacted by hydrologic alteration and management of these coastal habitats. Efforts to restore tidal flow to former salt marshes have increased in recent decades and are generally associated with alteration of water inundation levels and salinity. This study examined the effect of water level and salinity changes on soil organic matter decomposition during a 60‐day incubation period. Intact soil cores from impounded fresh water marsh and salt marsh were incubated after addition of either sea water or fresh water under flooded and drained water levels. Elevating fresh water marsh salinity to 6 to 9 ppt enhanced CO2 emission by 50%−80% and most typically decreased CH4 emissions, whereas, decreasing the salinity from 26 ppt to 19 ppt in salt marsh soils had no effect on CO2 or CH4 fluxes. The effect from altering water levels was more pronounced with drained soil cores emitting ~10‐fold more CO2 than the flooded treatment in both marsh sediments. Draining soil cores also increased dissolved organic carbon (DOC) concentrations. Stable carbon isotope analysis of CO2 generated during the incubations of fresh water marsh cores in drained soils demonstrates that relict peat OC that accumulated when the marsh was saline was preferentially oxidized when sea water was introduced. This study suggests that restoration of tidal flow that raises the water level from drained conditions would decrease aerobic decomposition and enhance C sequestration. It is also possible that the restoration would increase soil C decomposition of deeper deposits by anaerobic oxidation, however this impact would be minimal compared to lower emissions expected due to the return of flooding conditions.
  • Article
    Detection and characterization of coastal tidal wetland change in the northeastern US using Landsat time series
    (Elsevier, 2022-04-26) Yang, Xiucheng ; Zhu, Zhe ; Qiu, Shi ; Kroeger, Kevin D. ; Zhu, Zhiliang ; Covington, Scott
    Coastal tidal wetlands are highly altered ecosystems exposed to substantial risk due to widespread and frequent land-use change coupled with sea-level rise, leading to disrupted hydrologic and ecologic functions and ultimately, significant reduction in climate resiliency. Knowing where and when the changes have occurred, and the nature of those changes, is important for coastal communities and natural resource management. Large-scale mapping of coastal tidal wetland changes is extremely difficult due to their inherent dynamic nature. To bridge this gap, we developed an automated algorithm for DEtection and Characterization of cOastal tiDal wEtlands change (DECODE) using dense Landsat time series. DECODE consists of three elements, including spectral break detection, land cover classification and change characterization. DECODE assembles all available Landsat observations and introduces a water level regressor for each pixel to flag the spectral breaks and estimate harmonic time-series models for the divided temporal segments. Each temporal segment is classified (e.g., vegetated wetlands, open water, and others – including unvegetated areas and uplands) based on the phenological characteristics and the synthetic surface reflectance values calculated from the harmonic model coefficients, as well as a generic rule-based classification system. This harmonic model-based approach has the advantage of not needing the acquisition of satellite images at optimal conditions (i.e., low tide status) to avoid underestimating coastal vegetation caused by the tidal fluctuation. At the same time, DECODE can also characterize different kinds of changes including land cover change and condition change (i.e., land cover modification without conversion). We used DECODE to track status of coastal tidal wetlands in the northeastern United States from 1986 to 2020. The overall accuracy of land cover classification and change detection is approximately 95.8% and 99.8%, respectively. The vegetated wetlands and open water were mapped with user's accuracy of 94.6% and 99.0%, and producer's accuracy of 98.1% and 93.5%, respectively. The cover change and condition change were mapped with user's accuracy of 68.0% and 80.0%, and producer's accuracy of 80.5% and 97.1%, respectively. Approximately 3283 km2 of the coastal landscape within our study area in the northeastern United States changed at least once (12% of the study area), and condition changes were the dominant change type (84.3%). Vegetated coastal tidal wetland decreased consistently (~2.6 km2 per year) in the past 35 years, largely due to conversion to open water in the context of sea-level rise.
  • Article
    Identifying nutrient sources to three lagoons at Ofu and Olosega, American Samoa using δ15N of benthic macroalgae
    (Elsevier B.V., 2007-11-01) Garrison, Virginia ; Kroeger, Kevin D. ; Fenner, Douglas ; Craig, Peter
    Degradation of nearshore habitats is a serious problem in some areas of American Samoa, such as in Pago Pago Harbor on Tutuila Island, and is a smaller but chronic problem in other areas. Sedimentation, pollution, nutrient enrichment from surface runoff or groundwater, and trampling are the major factors causing the changes. On the outer islands of Ofu and Olosega, there is an interesting contrast between relatively pristine lagoon habitats not far from comparatively degraded lagoon habitats. To’aga lagoon on the southeast side of Ofu Island has clear waters, a high diversity of corals and fishes, no human habitations, and an undeveloped watershed with no streams. To’aga lagoon is within the boundaries of the National Park of American Samoa and is the site of long-term research on coral reef resilience and global climate change. Only 3 km to the east of To’aga is a degraded lagoon that fronts Olosega Village. The Olosega lagoon is similar in size but has significantly less live coral than To’aga, and blooms of filamentous algae have been reported to cover the Olosega lagoon/reef flat bottom. The islands are influenced by the same regional-scale and biogeochemical regimes, and both islands are remnants of a volcanic caldera.
  • Preprint
    Molecular signature of organic nitrogen in septic-impacted groundwater
    ( 2014-08) Arnold, William A. ; Longnecker, Krista ; Kroeger, Kevin D. ; Kujawinski, Elizabeth B.
    Dissolved inorganic and organic nitrogen levels are elevated in aquatic systems due to anthropogenic activities. Dissolved organic nitrogen (DON) arises from various sources, and its impact could be more clearly constrained if specific sources were identified and if the molecular level composition of DON were better understood. In this work, the pharmaceutical carbamazepine was used to identify septic-impacted groundwater in a coastal watershed. Using ultrahigh resolution mass spectrometry data, the nitrogen-containing features of the dissolved organic matter in septic-impacted and non-impacted samples were compared. The septic impacted groundwater samples have a larger abundance of nitrogen-containing formulas. Impacted samples have additional DON features in the regions ascribed as ‘protein-like’ and ‘lipid-like’ in van Krevelen space and have more intense nitrogen-containing features in a specific region of a carbon versus mass plot. These features are potential indicators of dissolved organic nitrogen arising from septic effluents, and this work suggests that ultrahigh resolution mass spectrometry is a valuable tool to identify and characterize sources of DON.
  • Article
    Carbon dioxide fluxes reflect plant zonation and belowground biomass in a coastal marsh
    (John Wiley & Sons, 2016-11-15) Moseman-Valtierra, Serena M. ; Abdul-Aziz, Omar I. ; Tang, Jianwu ; Ishtiaq, Khandker S. ; Morkeski, Kate ; Mora, Jordan ; Quinn, Ryan K. ; Martin, Rose M. ; Egan, Katherine E. ; Brannon, Elizabeth Q. ; Carey, Joanna C. ; Kroeger, Kevin D.
    Coastal wetlands are major global carbon sinks; however, they are heterogeneous and dynamic ecosystems. To characterize spatial and temporal variability in a New England salt marsh, greenhouse gas (GHG) fluxes were compared among major plant-defined zones during growing seasons. Carbon dioxide (CO2) and methane (CH4) fluxes were compared in two mensurative experiments during summer months (2012–2014) that included low marsh (Spartina alterniflora), high marsh (Distichlis spicata and Juncus gerardii-dominated), invasive Phragmites australis zones, and unvegetated ponds. Day- and nighttime fluxes were also contrasted in the native marsh zones. N2O fluxes were measured in parallel with CO2 and CH4 fluxes, but were not found to be significant. To test the relationships of CO2 and CH4 fluxes with several native plant metrics, a multivariate nonlinear model was used. Invasive P. australis zones (−7 to −15 μmol CO2·m−2·s−1) and S. alterniflora low marsh zones (up to −14 μmol CO2·m−2·s−1) displayed highest average CO2 uptake rates, while those in the native high marsh zone (less than −2 μmol CO2·m−2·s−1) were much lower. Unvegetated ponds were typically small sources of CO2 to the atmosphere (<0.5 μmol CO2·m−2·s−1). Nighttime emissions of CO2 averaged only 35% of daytime uptake in the low marsh zone, but they exceeded daytime CO2 uptake by up to threefold in the native high marsh zone. Based on modeling, belowground biomass was the plant metric most strongly correlated with CO2 fluxes in native marsh zones, while none of the plant variables correlated significantly with CH4 fluxes. Methane fluxes did not vary between day and night and did not significantly offset CO2 uptake in any vegetated marsh zones based on sustained global warming potential calculations. These findings suggest that attention to spatial zonation as well as expanded measurements and modeling of GHG emissions across greater temporal scales will help to improve accuracy of carbon accounting in coastal marshes.
  • Preprint
    Significance of groundwater discharge along the coast of Poland as a source of dissolved metals to the southern Baltic Sea
    ( 2016-06) Szymczycha, Beata ; Kroeger, Kevin D. ; Pempkowiak, Janusz
    Fluxes of dissolved trace metals (Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn) via groundwater discharge along the southern Baltic Sea have been assessed for the first time. Dissolved metal concentrations in groundwater samples were less variable than in seawater and were generally one or two orders of magnitude higher: Cd (2.1-2.8 nmolL−1), Co (8.70-8.76 nmolL−1), Cr (18.1-18.5 nmolL−1), Mn (2.4-2.8 μmolL−1), Pb (1.2-1.5 nmolL−1), Zn (33.1-34.0 nmolL−1). Concentrations of Cu (0.5-0.8 nmolL−1) and Ni (4.9-5.8 nmolL−1) were, respectively, 32 and 4 times lower, than in seawater. Groundwater-derived trace metal fluxes constitute 93% for Cd, 80% for Co, 91% for Cr, 6% for Cu, 66% for Mn, 4% for Ni, 70% for Pb and 93% for Zn of the total freshwater trace metal flux to the Bay of Puck. Groundwater-seawater mixing, redox conditions and Mn-cycling are the main processes responsible for trace metal distribution in groundwater discharge sites.
  • Preprint
    Hydrogeologic controls on groundwater discharge and nitrogen loads in a coastal watershed
    ( 2016-05-02) Russoniello, Christopher J. ; Konikow, Leonard F. ; Kroeger, Kevin D. ; Fernandez, Cristina ; Andres, A. Scott ; Michael, Holly A.
    Submarine groundwater discharge (SGD) is a small portion of the global water budget, but a potentially large contributor to coastal nutrient budgets due to high concentrations relative to stream discharge. A numerical groundwater flow model of the Inland Bays Watershed, Delaware, USA, was developed to identify the primary hydrogeologic factors that affect groundwater discharge rates and transit times to streams and bays. The distribution of groundwater discharge between streams and bays is sensitive to the depth of the water table below land surface. Higher recharge and reduced hydraulic conductivity raised the water table and increased discharge to streams relative to bays compared to the Reference case (in which 66% of recharge is discharged to streams). Increases to either factor decreased transit times for discharge to both streams and bays compared to the Reference case (in which mean transit times are 56.5 and 94.3 years, respectively), though sensitivity to recharge is greater. Groundwaterborne nitrogen loads were calculated from nitrogen concentrations measured in discharging fresh groundwater and modeled SGD rates. These loads combined with long SGD transit times suggest groundwater-borne nitrogen reductions and estuarine water quality improvements will lag decades behind implementation of efforts to manage nutrient sources. This work enhances understanding of the hydrogeologic controls on and uncertainties in absolute and relative rates and transit times of groundwater discharge to streams and bays in coastal watersheds.
  • Article
    Higher Temperature Sensitivity of Ecosystem Respiration in Low Marsh Compared to High Elevation Marsh Ecosystems
    (American Geophysical Union, 2022-10-22) Carey, Joanna C. ; Kroeger, Kevin D. ; Tang, Jianwu
    Salt marsh habitats contain some of the highest quantities of soil organic carbon (C) per unit area, but increasing anthropogenic stressors threaten their ability to maintain themselves as large C reservoirs in some regions. We quantify rates of C gas exchange (methane [CH4] and carbon dioxide [CO2]) monthly across a 16‐month period from a low nitrogen “reference” salt marsh on Cape Cod in New England using static chambers. While the summer period is the most dynamic period of marsh C gas exchange, we observed substantial fluxes in the early summer through late fall, highlighting the importance of including shoulder seasons in studies of marsh C exchange. We estimate annual ecosystem respiration between 108 and 252 g C m−2 yr−1, which varied based on temperature and elevation. This flux is lower than in other nearby marshes, which we attribute to the frequently inundated, microtidal nature of the site, resulting in the majority of respired CO2 being exported via lateral, not vertical, fluxes from this marsh. We observed significantly higher temperature sensitivity from the low elevation of the marsh compared to the high marsh. Recent acceleration in the rate of sea level rise is leading to a well‐documented expansion of low marsh into high marsh vegetation zones in this marsh system and others in the region. While rates of C burial are higher in the low marsh compared to the high marsh, the higher temperature sensitivity of respiration in the low marsh may diminish the longevity of marsh C stocks with climate warming.
  • Dataset
    Discrete bottle sample measurements for carbonate chemistry from samples collected in the Sage Lot Pond salt marsh tidal creek in Waquoit Bay, MA from 2012 to 2015
    (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact:, 2019-05-29) Wang, Zhaohui Aleck ; Gonneea, Meagan ; Kroeger, Kevin D.
    Discrete bottle sample measurements for carbonate chemistry from samples collected in the Sage Lot Pond salt marsh tidal creek in Waquoit Bay, MA from 2012 to 2015. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at:
  • Article
    Macrophytes as indicators of land-derived wastewater : application of a δ15N method in aquatic systems
    (American Geophysical Union, 2005-01-25) Cole, Marci L. ; Kroeger, Kevin D. ; McClelland, James W. ; Valiela, Ivan
    We measured δ15N signatures of macrophytes and particulate organic matter (POM) in six estuaries and three freshwater ponds of Massachusetts to assess whether the signatures could be used as indicators of the magnitude of land-derived nitrogen loads, concentration of dissolved inorganic nitrogen in the water column, and percentage of N loads contributed by wastewater disposal. The study focused specifically on sites on Cape Cod and Nantucket Island, in the northeastern United States. There was no evidence of seasonal changes in δ15N values of macrophytes or POM. The δ15N values of macrophytes and POM increased as water column dissolved inorganic nitrogen concentrations increased. We found that δ15N of macrophytes, but not of POM, increased as N load increased. The δ15N values of macrophytes and groundwater NO3 tracked the percent of wastewater contribution linearly. This research confirms that δ15N values of macrophytes and NO3 can be excellent indicators of anthropogenic N in aquatic systems.
  • Preprint
    Effects of watershed land use on nitrogen concentrations and δ15 Nitrogen in groundwater
    ( 2005-07-18) Cole, Marci L. ; Kroeger, Kevin D. ; McClelland, James W. ; Valiela, Ivan
    Eutrophication is a major agent of change affecting freshwater, estuarine, and marine systems. It is largely driven by transportation of nitrogen from natural and anthropogenic sources. Research is needed to quantify this nitrogen delivery and to link the delivery to specific land-derived sources. In this study we measured nitrogen concentrations and δ15N values in seepage water entering three freshwater ponds and six estuaries on Cape Cod, Massachusetts and assessed how they varied with different types of land use. Nitrate concentrations and δ15N values in groundwater reflected land use in developed and pristine watersheds. In particular, watersheds with larger populations delivered larger nitrate loads with higher δ15N values to receiving waters. The enriched δ15N values confirmed nitrogen loading model results identifying wastewater contributions from septic tanks as the major N source. Furthermore, it was apparent that N coastal sources had a relatively larger impact on the N loads and isotopic signatures than did inland N sources further upstream in the watersheds. This finding suggests that management priorities could focus on coastal sources as a first course of action. This would require management constraints on a much smaller population.
  • Article
    Submarine groundwater discharge to Tampa Bay : nutrient fluxes and biogeochemistry of the coastal aquifer
    (Elsevier B.V., 2007-01-10) Kroeger, Kevin D. ; Swarzenski, Peter W. ; Greenwood, Wm. Jason ; Reich, Christopher
    To separately quantify the roles of fresh and saline submarine groundwater discharge (SGD), relative to that of rivers, in transporting nutrients to Tampa Bay, Florida, we used three approaches (Darcy's Law calculations, a watershed water budget, and a 222Rn mass-balance) to estimate rate of SGD from the Pinellas peninsula. Groundwater samples were collected in 69 locations in the coastal aquifer to examine biogeochemical conditions, nutrient concentrations and stoichiometry, and salinity structure. Salinity structure was also examined using stationary electrical resistivity measurements. The coastal aquifer along the Pinellas peninsula was chemically reducing in all locations sampled, and that condition influences nitrogen (N) form and mobility of N and PO43−. Concentrations of NH4+, PO43− and ratio of dissolved inorganic N (DIN) to PO43− were all related to measured oxidation/reduction potential (pε) of the groundwater. Ratio of DIN: PO43− was below Redfield ratio in both fresh and saline groundwater. Nitrogen occurred almost exclusively in reduced forms, NH4+ and dissolved organic nitrogen (DON), suggesting that anthropogenic N is exported from the watershed in those forms. In comparison to other SGD studies, rate of PO43− flux in the seepage zone (μM m− 2 d− 1) in Tampa Bay was higher than previous estimates, likely due to 1) high watershed population density, 2) chemically reducing conditions, and 3) high ion concentrations in fresh groundwater. Estimates of freshwater groundwater flux indicate that the ratio of groundwater discharge to stream flow is not, vert, similar 20 to 50%, and that the magnitudes of both the total dissolved nitrogen and PO43− loads due to fresh SGD are not, vert, similar 40 to 100% of loads carried by streams. Estimates of SGD based on radon inventories in near-shore waters were 2 to 5 times greater than the estimates of freshwater groundwater discharge, suggesting that brackish and saline SGD is also an important process in Tampa Bay and results in flux of regenerated N and P from sediment to surface water.
  • Article
    Restoring tides to reduce methane emissions in impounded wetlands : a new and potent Blue Carbon climate change intervention
    (Nature Publishing Group, 2017-09-20) Kroeger, Kevin D. ; Crooks, Stephen ; Moseman-Valtierra, Serena M. ; Tang, Jianwu
    Coastal wetlands are sites of rapid carbon (C) sequestration and contain large soil C stocks. Thus, there is increasing interest in those ecosystems as sites for anthropogenic greenhouse gas emission offset projects (sometimes referred to as “Blue Carbon”), through preservation of existing C stocks or creation of new wetlands to increase future sequestration. Here we show that in the globallywidespread occurrence of diked, impounded, drained and tidally-restricted salt marshes, substantial methane (CH4) and CO2 emission reductions can be achieved through restoration of disconnected saline tidal flows. Modeled climatic forcing indicates that tidal restoration to reduce emissions has a much greater impact per unit area than wetland creation or conservation to enhance sequestration. Given that GHG emissions in tidally-restricted, degraded wetlands are caused by human activity, they are anthropogenic emissions, and reducing them will have an effect on climate that is equivalent to reduced emission of an equal quantity of fossil fuel GHG. Thus, as a landuse-based climate change intervention, reducing CH4 emissions is an entirely distinct concept from biological C sequestration projects to enhance C storage in forest or wetland biomass or soil, and will not suffer from the non-permanence risk that stored C will be returned to the atmosphere.
  • Article
    The magnitude and origin of groundwater discharge to Eastern U.S. and Gulf of Mexico coastal waters
    (John Wiley & Sons, 2017-10-28) Befus, Kevin Martin ; Kroeger, Kevin D. ; Smith, Christopher G. ; Swarzenski, Peter W.
    Fresh groundwater discharge to coastal environments contributes to the physical and chemical conditions of coastal waters, but the role of coastal groundwater at regional to continental scales remains poorly defined due to diverse hydrologic conditions and the difficulty of tracking coastal groundwater flow paths through heterogeneous subsurface materials. We use three-dimensional groundwater flow models for the first time to calculate the magnitude and source areas of groundwater discharge from unconfined aquifers to coastal waterbodies along the entire eastern U.S. We find that 27.1 km3/yr (22.8–30.5 km3/yr) of groundwater directly enters eastern U.S. and Gulf of Mexico coastal waters. The contributing recharge areas comprised ~175,000 km2 of U.S. land area, extending several kilometers inland. This result provides new information on the land area that can supply natural and anthropogenic constituents to coastal waters via groundwater discharge, thereby defining the subterranean domain potentially affecting coastal chemical budgets and ecosystem processes.
  • Article
    Observations of nearshore groundwater discharge : Kahekili Beach Park submarine springs, Maui, Hawaii
    (Elsevier, 2016-01-14) Swarzenski, Peter W. ; Dulai, Henrietta ; Kroeger, Kevin D. ; Smith, Christopher G. ; Dimova, Natasha T. ; Storlazzi, Curt D. ; Prouty, Nancy G. ; Gingerich, Stephen B. ; Glenn, Craig R.
    The study region encompasses the nearshore, coastal waters off west Maui, Hawaii. Here abundant groundwater—that carries with it a strong land-based fingerprint—discharges into the coastal waters and over a coral reef. Coastal groundwater discharge is a ubiquitous hydrologic feature that has been shown to impact nearshore ecosystems and material budgets. A unique combined geochemical tracer and oceanographic time-series study addressed rates and oceanic forcings of submarine groundwater discharge at a submarine spring site off west Maui, Hawaii. Estimates of submarine groundwater discharge were derived for a primary vent site and surrounding coastal waters off west Maui, Hawaii using an excess 222Rn (t1/2 = 3.8 d) mass balance model. Such estimates were complemented with a novel thoron (220Rn, t1/2 = 56 s) groundwater discharge tracer application, as well as oceanographic time series and thermal infrared imagery analyses. In combination, this suite of techniques provides new insight into the connectivity of the coastal aquifer with the near-shore ocean and examines the physical drivers of submarine groundwater discharge. Lastly, submarine groundwater discharge derived constituent concentrations were tabulated and compared to surrounding seawater concentrations. Such work has implications for the management of coastal aquifers and downstream nearshore ecosystems that respond to sustained constituent loadings via this submarine route.
  • Article
    Submarine groundwater discharge to a small estuary estimated from radon and salinity measurements and a box model
    (Copernicus Publications, 2005-06-24) Crusius, John ; Koopmans, D. ; Bratton, John F. ; Charette, Matthew A. ; Kroeger, Kevin D. ; Henderson, Paul B. ; Ryckman, L. ; Halloran, K. ; Colman, John A.
    Submarine groundwater discharge was quantified by a variety of methods for a 4-day period during the early summer of 2004, in Salt Pond, adjacent to Nauset Marsh, on Cape Cod, USA. Discharge estimates based on radon and salinity took advantage of the presence of the narrow channel connecting Salt Pond to Nauset Marsh, which allowed constructing whole-pond mass balances as water flowed in and out due to tidal fluctuations. The data suggest that less than one quarter of the discharge in the vicinity of Salt Pond happened within the pond itself, while three quarters or more of the discharge occurred immediately seaward of the pond, either in the channel or in adjacent regions of Nauset Marsh. Much of this discharge, which maintains high radon activities and low salinity, is carried into the pond during each incoming tide. A box model was used as an aid to understand both the rates and the locations of discharge in the vicinity of Salt Pond. The model achieves a reasonable fit to both the salinity and radon data assuming submarine groundwater discharge is fresh and that most of it occurs either in the channel or in adjacent regions of Nauset Marsh. Salinity and radon data, together with seepage meter results, do not rule out discharge of saline groundwater, but suggest either that the saline discharge is at most comparable in volume to the fresh discharge or that it is depleted in radon. The estimated rate of fresh groundwater discharge in the vicinity of Salt Pond is 3000-7000 m3 d-1. This groundwater flux estimated from the radon and salinity data is comparable to a value of 3200-4500 m3 d-1 predicted by a recent hydrologic model (Masterson, 2004; Colman and Masterson, 2004), although the model predicts this rate of discharge to the pond whereas our data suggest most of the groundwater bypasses the pond prior to discharge. Additional work is needed to determine if the measured rate of discharge is representative of the long-term average, and to better constrain the rate of groundwater discharge seaward of Salt Pond.
  • Article
    Natural climate solutions for the United States
    (American Association for the Advancement of Science, 2018-11-14) Fargione, Joseph E. ; Bassett, Steven ; Boucher, Timothy ; Bridgham, Scott D. ; Conant, Richard T. ; Cook-Patton, Susan C. ; Ellis, Peter W. ; Falcucci, Alessandra ; Fourqurean, James W. ; Gopalakrishna, Trisha ; Gu, Huan ; Henderson, Benjamin ; Hurteau, Matthew D. ; Kroeger, Kevin D. ; Kroeger, Timm ; Lark, Tyler J. ; Leavitt, Sara M. ; Lomax, Guy ; McDonald, Robert I. ; Megonigal, J. Patrick ; Miteva, Daniela A. ; Richardson, Curtis J. ; Sanderman, Jonathan ; Shoch, David ; Spawn, Seth A. ; Veldman, Joseph W. ; Williams, Christopher A. ; Woodbury, Peter B. ; Zganjar, Chris ; Baranski, Marci ; Elias, Patricia ; Houghton, Richard A. ; Landis, Emily ; McGlynn, Emily ; Schlesinger, William H. ; Siikamaki, Juha V. ; Sutton-Grier, Ariana E. ; Griscom, Bronson W.
    Limiting climate warming to <2°C requires increased mitigation efforts, including land stewardship, whose potential in the United States is poorly understood. We quantified the potential of natural climate solutions (NCS)—21 conservation, restoration, and improved land management interventions on natural and agricultural lands—to increase carbon storage and avoid greenhouse gas emissions in the United States. We found a maximum potential of 1.2 (0.9 to 1.6) Pg CO2e year−1, the equivalent of 21% of current net annual emissions of the United States. At current carbon market prices (USD 10 per Mg CO2e), 299 Tg CO2e year−1 could be achieved. NCS would also provide air and water filtration, flood control, soil health, wildlife habitat, and climate resilience benefits.
  • Article
    Soil carbon consequences of historic hydrologic impairment and recent restoration in coastal wetlands
    (Association for the Sciences of Limnology and Oceanography, 2022-08-06) Eagle, Meagan ; Kroeger, Kevin D. ; Spivak, Amanda C. ; Wang, Faming ; Tang, Jianwu ; Abdul-Aziz, Omar I. ; Ishtiaq, Khandker S. ; O'Keefe Suttles, Jennifer A. ; Mann, Adrian G.
    Coastal wetlands provide key ecosystem services, including substantial long-term storage of atmospheric CO2 in soil organic carbon pools. This accumulation of soil organic matter is a vital component of elevation gain in coastal wetlands responding to sea-level rise. Anthropogenic activities that alter coastal wetland function through disruption of tidal exchange and wetland water levels are ubiquitous. This study assesses soil vertical accretion and organic carbon accretion across five coastal wetlands that experienced over a century of impounded hydrology, followed by restoration of tidal exchange 5 to 14 years prior to sampling. Nearby marshes that never experienced tidal impoundment served as controls with natural hydrology to assess the impact of impoundment and restoration. Dated soil cores indicate that elevation gain and carbon storage were suppressed 30–70 % during impoundment, accounting for the majority of elevation deficit between impacted and natural sites. Only one site had substantial subsidence, likely due to oxidation of soil organic matter. Vertical and carbon accretion gains were achieved at all restored sites, with carbon burial increasing from 96 ± 33 to 197 ± 64 g C m−2 y−1. The site with subsidence was able to accrete at double the rate (13 ± 5.6 mm y−1) of the natural complement, due predominantly to organic matter accumulation rather than mineral deposition, indicating these ecosystems are capable of large dynamic responses to restoration when conditions are optimized for vegetation growth. Hydrologic restoration enhanced elevation resilience and climate benefits of these coastal wetlands.