Significance of groundwater discharge along the coast of Poland as a source of dissolved metals to the southern Baltic Sea

© The Author(s), 2016. This is the author's version of the work and is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Marine Pollution Bulletin 109 (2016): 151–162, doi:10.1016/j.marpolbul.2016.06.008.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.The study reports the results obtained within the framework of the following projects: the statutory activities of the Institute of Oceanology Polish Academy of Sciences theme 2.2, research project No. 2012/05/N/ST10/02761 sponsored by the National Science Centre, and AMBER, the BONUS+ EU FP6 Project. We would like to thank Polish-U.S. Fulbright Commission for funding Szymczycha B. post-doctoral studies at USGS.2017-06-1

The magnitude and origin of groundwater discharge to Eastern U.S. and Gulf of Mexico coastal waters

Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 44 (2017): 10,396–10,406, doi:10.1002/2017GL075238.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.National Science Foundation Grant Number: EPS-1208909; NASA Carbon Cycle Science Grant Number: NNX14AM37G2018-04-2

Depth of the vadose zone controls aquifer biogeochemical conditions and extent of anthropogenic nitrogen removal

© The Author(s), 2017. This is the author's version of the work and is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Water Research 123 (2017): 794-801, doi:10.1016/j.watres.2017.06.048.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.Project supported by the Polish-U.S. Fulbright Commission, the USGS Coastal and Marine Geology Program, the National Fish and Wildlife Foundation, and the USGS/National Park Service Water-Quality Assessment and Monitoring program.2019-06-1

Molecular signature of organic nitrogen in septic-impacted groundwater

Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of Royal Society of Chemistry for personal use, not for redistribution. The definitive version was published in Environmental Science: Processes & Impacts 16 (2014):2400-2407, doi:10.1039/C4EM00289J.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.The Deep Ocean Exploration and Coastal Ocean Institutes at WHOI and the University of Minnesota Institute on the Environment are thanked for financial support.2015-02-0

Macrophytes as indicators of land-derived wastewater : application of a δ15N method in aquatic systems

Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Water Resources Research 41 (2005): W01014, doi:10.1029/2004WR003269.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.This work was supported by funds from the Woods Hole Oceanographic Institution Sea Grant Program, from the Cooperative Institute for Coastal and Estuarine Environmental Technology, from a Massachusetts Department of Environmental Protection grant to Applied Science Associates, Narragansett, Rhode Island, and from a National Oceanic and Atmospheric Administration National Estuarine Research Reserve fellowship and Palmer/McCleod fellowship to K.D.K

Oxygen-controlled recirculating seepage meter reveals extent of nitrogen transformation in discharging coastal groundwater at the aquifer-estuary interface

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Brooks, T. W., Kroeger, K. D., Michael, H. A., & York, J. K. Oxygen-controlled recirculating seepage meter reveals extent of nitrogen transformation in discharging coastal groundwater at the aquifer-estuary interface. Limnology and Oceanography, 66, (2021): 3055-3069, https://doi.org/10.1002/lno.11858.Nutrient loads delivered to estuaries via submarine groundwater discharge (SGD) play an important role in the nitrogen (N) budget and eutrophication status. However, accurate and reliable quantification of the chemical flux across the final decimeters and centimeters at the sediment–estuary interface remains a challenge, because there is significant potential for biogeochemical alteration due to contrasting conditions in the coastal aquifer and surface sediment. Here, a novel, oxygen- and light-regulated ultrasonic seepage meter, and a standard seepage meter, were used to measure SGD and calculate N species fluxes across the sediment–estuary interface. Coupling the measurements to an endmember approach based on subsurface N concentrations and an assumption of conservative transport enabled estimation of the extent of transformation occurring in discharging groundwater within the benthic zone. Biogeochemical transformation within reactive estuarine surface sediment was a dominant driver in modifying the N flux carried upward by SGD, and resulted in a similar percentage of N removal (~ 42–52%) as did transformations occurring deeper within the coastal aquifer salinity mixing zone (~ 42–47%). Seasonal shifts in the relative importance of biogeochemical processes including denitrification, nitrification, dissimilatory nitrate reduction, and assimilation altered the composition of the flux to estuarine surface water, which was dominated by ammonium in June and by nitrate in August, despite the endmember-based observation that fixed N in discharging groundwater was strongly dominated by nitrate. This may have important ramifications for the ecology and management of estuaries, since past N loading estimates have generally assumed conservative transport from the nearshore aquifer to estuary.This work was supported by an award from Delaware Sea Grant (award No. NA100AR4170084 to J.K.Y. and K.D.K.), and by the USGS Coastal and Marine Hazards and Resources Program

Water salinity and inundation control soil carbon decomposition during salt marsh restoration: An incubation experiment.

© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Wang, F., Kroeger, K. D., Gonneea, M. E., Pohlman, J. W., & Tang, J. Water salinity and inundation control soil carbon decomposition during salt marsh restoration: An incubation experiment. Ecology and Evolution, 9(4), (2019):1911-1921, doi:10.1002/ece3.4884.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.We acknowledge collaboration and support from Tim Smith of the Cape Cod National Seashore, James Rassman and Tonna‐Marie Surgeon‐Rogers of the Waquoit Bay National Estuarine Research Reserve, Margot McKlveen of the Marine Biological Laboratory, Jennifer O'keefe Suttles, Wally Brooks and Michael Casso of the USGS, and Amanda Spivak of the Woods Hole Oceanographic Institution. This study was funded by the NOAA National Estuarine Research Reserve Science Collaborative (NA09NOS4190153 and NA14NOS4190145) awarded to JT and KK, MIT Sea Grant (2015‐R/RC‐141), and USGS‐Land Carbon and Coastal & Marine Geology projects. F.W. was also supported by funding from Natural Science Foundation of China (31300419, 31670621, 31870463). Any use of trade names is for descriptive purposes and does not imply endorsement by the U.S. government

Detection and characterization of coastal tidal wetland change in the northeastern US using Landsat time series

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Yang, X., Zhu, Z., Qiu, S., Kroeger, K. D., Zhu, Z., & Covington, S. Detection and characterization of coastal tidal wetland change in the northeastern US using Landsat time series. Remote Sensing of Environment, 276, (2022): 113047, https://doi.org/10.1016/j.rse.2022.113047.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.This study was supported by USGS North Atlantic Coast Cooperative Ecosystem Studies Unit (CESU) Program for Detection and Characterization of Coastal Tidal Wetland Change (G19AC00354)

Deciphering the dynamics of inorganic carbon export from intertidal salt marshes using high-frequency measurements

© The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Marine Chemistry 206 (2018): 7-18, doi:10.1016/j.marchem.2018.08.005.The lateral export of carbon from coastal marshes via tidal exchange is a key component of the marsh carbon budget and coastal carbon cycles. However, the magnitude of this export has been difficult to accurately quantify due to complex tidal dynamics and seasonal cycling of carbon. In this study, we use in situ, high-frequency measurements of dissolved inorganic carbon (DIC) and water fluxes to estimate lateral DIC fluxes from a U.S. northeastern salt marsh. DIC was measured by a CHANnelized Optical Sensor (CHANOS) that provided an in situ concentration measurement at 15-min intervals, during periods in summer (July – August) and late fall (December). Seasonal changes in the marsh had strong effects on DIC concentrations, while tidally-driven water fluxes were the fundamental vehicle of marsh carbon export. Episodic events, such as groundwater discharge and mean sea water level changes, can impact DIC flux through altered DIC concentrations and water flow. Variability between individual tides within each season was comparable to mean variability between the two seasons. Estimated mean DIC fluxes based on a multiple linear regression (MLR) model of DIC concentrations and high-frequency water fluxes agreed reasonably well with those derived from CHANOS DIC measurements for both study periods, indicating that high-frequency, modeled DIC concentrations, coupled with continuous water flux measurements and a hydrodynamic model, provide a robust estimate of DIC flux. Additionally, an analysis of sampling strategies revealed that DIC fluxes calculated using conventional sampling frequencies (hourly to two-hourly) of a single tidal cycle are unlikely to capture a representative mean DIC flux compared to longer-term measurements across multiple tidal cycles with sampling frequency on the order of tens of minutes. This results from a disproportionately large amount of the net DIC flux occurring over a small number of tidal cycles, while most tides have a near-zero DIC export. Thus, high-frequency measurements (on the order of tens of minutes or better) over the time period of interest are necessary to accurately quantify tidal exports of carbon species from salt marshes.This work was funded by NSF Graduate Research Fellowship Program, NSF Ocean Sciences Postdoctoral Fellowship (OCE-1323728), Link FoundationOcean Engineering and Instrumentation Fellowship, National Institute of Science and Technology (NIST no. 60NANB10D024), the USGS LandCarbon and Coastal & Marine Geology Programs, NSF Chemical Oceanography Program (OCE-1459521), NSF Ocean Technology and Interdisciplinary Coordination program (OCE-1233654) and NOAA Science Collaborative (NA09NOS4190153)

Intertidal salt marshes as an important source of inorganic carbon to the coastal ocean

© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Limnology and Oceanography 61 (2016): 1916–1931, doi:10.1002/lno.10347.Dynamic tidal export of dissolved inorganic carbon (DIC) to the coastal ocean from highly productive intertidal marshes and its effects on seawater carbonate chemistry are thoroughly evaluated. The study uses a comprehensive approach by combining tidal water sampling of CO2 parameters across seasons, continuous in situ measurements of biogeochemically-relevant parameters and water fluxes, with high-resolution modeling in an intertidal salt marsh of the U.S. northeast region. Salt marshes can acidify and alkalize tidal water by injecting CO2 (DIC) and total alkalinity (TA). DIC and TA generation may also be decoupled due to differential effects of marsh aerobic and anaerobic respiration on DIC and TA. As marsh DIC is added to tidal water, the buffering capacity first decreases to a minimum and then increases quickly. Large additions of marsh DIC can result in higher buffering capacity in ebbing tide than incoming tide. Alkalization of tidal water, which mostly occurs in the summer due to anaerobic respiration, can further modify buffering capacity. Marsh exports of DIC and alkalinity may have complex implications for the future, more acidified ocean. Marsh DIC export exhibits high variability over tidal and seasonal cycles, which is modulated by both marsh DIC generation and by water fluxes. The marsh DIC export of 414 g C m−2 yr−1, based on high-resolution measurements and modeling, is more than twice the previous estimates. It is a major term in the marsh carbon budget and translates to one of the largest carbon fluxes along the U.S. East Coast.USGS Coastal & Marine Geology Program; U.S. National Science Foundation Grant Number: OCE-1459521; NOAA Science Collaborative Grant Number: NA09NOS4190153; USGS LandCarbon Progra