Sunday, 14 March 2021

RUSSO, Aeon1, JENCKES, Jordan2, BOUTT, David3 and MUNK, LeeAnn2, (1)Department of Geosciences, UMass Amherst, 627 North Pleasant Street, 233 Morrill Science Center, Amherst, MA 01003, (2)Department of Geological Sciences, University of Alaska, 3101 Science Circle, Anchorage, AK 99508, (3)Geosciences, University of Massachusetts at Amherst, 611 North Pleasant Street, 233 Morrill Science Center, Amherst, MA 01003

Global and near-global estimates of fresh submarine groundwater discharge (SGD) have provided drastically different results that vary over an order of magnitude. Narrowing the scope by focusing on regionally specific processes may prove to provide more reliable estimates of fresh SGD, as well as more effectively isolate potential SGD hotspots. This is especially true in the Gulf of Alaska (GOA), where complex topography, geology, and climate are coupled with recharge inputs derived from rainfall, snowmelt, glacial-melt, and glacier volume loss. This study estimates fresh SGD to the GOA with a simple water balance approach that integrates high temporal and spatial resolution recharge inputs over coastal recharge areas. Surficial geologic maps are incorporated to explore residence and transit times based on associated hydraulic conductivities that have not previously been conducted. By using recharge inputs that have been modeled over large timescales (1980-2019) at high temporal resolution (daily), we may begin to link fresh SGD with other physical and biological phenomena and observe how this flux is being altered by climate driven change over the last several decades. Although freshwater discharge to the GOA is well-constrained, the importance of fresh SGD to the GOA has, thus far, been overlooked.

CHASE, Alyssa, HATCH, Christine, YELLEN, Brian C., CASEY, Julia and DAWSON, Peter, Department of Geosciences, University of Massachusetts Amherst, Amherst, MA 01003

Foothills Preserve is a retired cranberry farm in Plymouth, Massachusetts. This work aims to measure success of wetland restoration sites. Collectively, we have gathered pre-restoration soil, vegetation, hydrology, water and soil chemistry data, and environmental conditions, which will all be re-assessed post-restoration. This portion of the study examines the subsurface and how elemental compositions of different soil types from the original wetland and subsequent cranberry farming impact water and soil chemistry of the restored wetland. Soil cores were taken from the pre-restoration site and scanned with an x-ray fluorescence machine. Elemental data were plotted versus depth and compared with core images to determine correlations between element abundance and soil type. Si, K and Os are abundant in the sand applied during farming over the last 200 years (~1 cm/ ~3 yr), Ti is abundant in peat (max age 9,100 yr). Ba was present in the (glacial outwash) sand and agricultural soil from farming, but not in pre-anthropogenic wetland peat, and was therefore used to demarcate the transition between them. Pb was present in higher amounts in the sand and agricultural soil but not in the peat, which may be an indicator of residual pesticides. From this analysis, it is possible to determine where the glacial history of the soil ceased at the termination of the native wetland peat, and where the anthropogenic period begins, denoted by agricultural soils intercalated with applied sand layers, using as clues the concentrations of Si, K, Os and Ti which serve as indicators of specific soil types. Demarcating different soil types allows us to image the thickness of the anthropogenic aquifer above the original peat, which is useful for the restoration process, as it allows decisions to be made about whether the agricultural soils and sand can be removed or if they need to be incorporated into the new wetland. The elemental composition of this anthropogenic aquifer is also important in determining whether these soils will produce troublesome chemical- or nutrient-laden runoff should water come into contact with these post-agricultural soils. Post-restoration wetting of the site could mobilize soil nutrients and impact wildlife, so a thorough characterization of the subsurface can help guide wetland restoration interventions.

HILLENBRAND, Ian, WILLIAMS, Michael L. and JERCINOVIC, Michael, Department of Geosciences, University of Massachusetts, Amherst, 627 N Pleasant St, Amherst, MA 01003-9354

Overprinting during multiple phases of high-grade metamorphism and regional variations in P, T, and deformation intensity stretch the limits of geochronologic tools, and have limited researchers’ ability to study rocks that have experienced multiple episodes of tectonism. To document distinct styles of tectonism associated with polyphase orogenesis in the Appalachian orogen of New England, we have utilized multi-scale compositional mapping, in-situ monazite and xenotime petrochronology, thermobarometry, and thermodynamic modeling. The data constrain distinct P-T-t paths from rocks across southern New England and show overprinting of progressively younger events from west to east. The earliest recognized garnet growth, ~470 Ma, is apparently limited and possibly associated with (soft?) accretion of the Moretown terrane. Widespread crustal thickening ~30 m.y. later may be related to late Taconic, Laramide-style tectonism and/or accretion of the Gander terrane. Thermal peaks ca. 400 and 380 Ma, associated with the Acadian and Neoacadian orogenies, respectively, are only recognized east of Cameron’s line. Abundant partial melting, high-pressure granulite facies metamorphism in gneiss domes, and very slow cooling associated with Neoacadian orogenesis provide further evidence for the existence of an orogenic plateau akin to the Pamir plateau. Garnet breakdown in all rocks east of Cameron’s line occurred at ca. 340-330 Ma and is interpreted to represent regional exhumation and plateau collapse. This may be associated with development of the 15 km high Moho step in western New England. Alleghanian-age tectonism is recognized in the vicinity of the Pelham dome with only minor and local reheating to the west. Together, these results provide quantitative constraints on polyphase orogenesis, define the spatial and temporal extent of overprinting, and track the evolution of eastern margin of Laurentia from terrane accretion to the rise and fall of a regional orogenic plateau.

ZUNIGA, Leann, 221 Strong St, Amherst, MA 01002-1801, RICHARDSON, Justin, Department of Geosciences, University of Massachusetts Amherst, 627 N. Pleasant St., Amherst, MA 01003-9354 and BOUTT, David, Geosciences, University of Massachusetts at Amherst, 611 North Pleasant Street, 233 Morrill Science Center, Amherst, MA 01003

Manganese in groundwater is ubiquitous in the U.S., with an estimated 2.6 million residents consuming groundwater with elevated Mn concentrations. All New England states have groundwaters with Mn concentrations over the USEPA secondary maximum contaminant limit of 50 ug/L. Studies often utilize point-sampling and do not capture temporal processes, which are suggested to be important as they relate to redox variability across seasons and may offer more insight to intermittent conditions driving Mn dissolution. We have collected surface, near surface, and groundwater samples, building a temporally variant dataset to determine the source of Mn in Massachusetts groundwater. Field parameters such as dissolved oxygen, pH, and ORP are measured in-situ for each sample, and samples are analyzed in the laboratory for trace metals, anions, and dissolved organic and inorganic carbon. Our preliminary data shows 61% of groundwater samples exceed the USEPA SMCL for Mn, with most of these samples coming from confined aquifer waters. This conflicts with other studies that observe higher Mn concentrations in shallow wells and groundwaters. Mn was not widely abundant in solid phase soils nor drilled rock fragments analyzed from the region, with mean Mn concentrations at 77 mg/kg and 122 mg/kg, respectively. We hypothesize that in geologic settings found in Massachusetts, Mn dissolution and transport behaves as a bottom-up process with transport playing an important role, rather than the localized top-down processes observed in aquifers in other regions. Using these preliminary findings along with stable water isotope data, we hope to further investigate the source of Mn to groundwaters and the role and importance of both transport and temporal redox variation. Private wells are often not extensively treated for Mn contamination, as many public groundwater supplies are, but offer an opportunity to better investigate the mechanisms behind manganese sourcing and transport across a wide range of geologic and soil conditions.

Monday, 15 March 2021

COOK, Tim, University of Massachusetts, Amherst, Amherst, MA and SNYDER, Noah, Earth and Environmental Sciences, Boston College, 140 Commonwealth Avenue, Chestnut Hill, MA 02467

Sedimentary archives in lakes and ponds are widely used to reconstruct past climatic and environmental conditions, as well as to quantify the environmental impacts of human activity. In this study, we summarize the characteristics of sedimentary deposits associated with different types of disturbances including floods, landslides, timber harvest, and conversion of forested land to agricultural use. We evaluated sediment cores from a network of lakes across the northeastern U.S. The watersheds span a range of topographic and surficial geologic characteristics, and have land-use histories with differing types, timing, intensity, and duration of anthropogenic disturbance. Cores were analyzed to identify distinct event deposits and changes in clastic sediment input indicative of landscape disturbances. While most records span the past millennium, we focus specifically on the period of record that overlaps with historical and instrumental records of events that can be linked to specific sedimentary deposits. Neither hydroclimatic nor human land-use signals are ubiquitous across all watersheds. The identification of distinct flood deposits was limited to higher relief, mountainous watersheds with abundant glacial-age sediment. Distal flood deposits are typically thin (mm to cm scale) and characterized by sharp contacts between dominant gyttja and fine-grained clastic flood layers. Hydrologic disturbances associated with landslide activation (such as occurred during tropical storm Irene in 2011) result in similarly sharp basal contacts between gyttja and clastic sediment. However, these deposits are commonly thicker (10s of cm) and characterized by compositional grading from more clastic to more organic rich sediment, and have complex patterns of textural variability. These signatures reflect a multi-year duration of elevated sediment delivery as the landscape gradually stabilizes and vegetation returns. In contrast, human land cover alteration typically manifests in sediments as a gradual and often prolonged increase in clastic content. Thick (up to 10s of cm), often sandy, texturally graded clastic deposits are distinct from those formed by both hydrologic and human disturbances, and interpreted as a consequence of subaqueous mass movements.

RICHARDSON, Justin and MISCHENKO, Ivan C., Department of Geosciences, University of Massachusetts Amherst, 627 N. Pleasant St., Amherst, MA 01003-9354

Lead in a toxic metal that has been widely dispersed across New England from industrial, commercial, and municipal processes. One of the largest emissions of lead occurred from the addition of tetra-ethyl lead to gasoline, which was phased out from the Clean Air Act of 1970 and Amendments of 1977 and 1990. However, the pollutant lead exists in the forests of New England with the potential to leach into ground and surface waters or remain enriched in surface soils from biological cycling by trees. We conducted a spatial gradient of 48 sites from Connecticut and Rhode Island up to central Vermont and New Hampshire to assess the bioavailability and its uptake by trees. At each site we collected forest floor samples and mineral soil samples (0-10cm, 10-20cm, 20-30cm, 30-40cm, 40-50cm) and four upper canopy hardwood tree leaf samples. Pseudototal soil digests yielded decreasing Pb concentrations with depths and an average Pb concentration of 37 mg/kg across the 48 sites. However, several sites had forest floor and surface mineral soil horizons with >100 mg/kg. Across all soil horizons, exchangeability of Pb was < 3% demonstrating high sorption of Pb to soil materials. Foliar concentrations were comparable across sugar maples, red maples, oaks, American beech, and birches at less than 0.3 mg/kg, suggesting either similar uptake rates or exposure to modern atmospheric Pb sources. Similar patterns demonstrate either modern or historical impacts on Pb in soils and foliage.

RICHARDSON, Justin, Department of Geosciences, University of Massachusetts Amherst, Amherst, MA 01003 and BUTLER, Mark J., Department of Geosciences, University of Massachusetts Amherst, 627 N. Pleasant St., Amherst, MA 01003-9354

Sequestration and transport of copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) are important due to its potential impacts on terrestrial and aquatic ecosystems and its sourcing from human activities. This is of particular importance in the Thames River Watershed of eastern Connecticut due to its abundant urban areas, historical pollution, and export to Long Island Sound. Forest soils in upland and riparian positions as well as adjacent to urban, agricultural, and forests were sampled across seven watersheds to investigate sequestration of metals. Further, river water samples from Feb 2019 to Jan 2020 were collected at least monthly. Upland, forest soils had lower metal concentrations than urban, riparian soils for Ni and Pb. Forest soil Cu and Zn concentrations were comparable between upland and riparian soils as well as forest, developed, and agricultural adjacent forest soils. River water sample concentrations were generally comparable across the watersheds. To account for differences river size and discharge, concentrations and discharge rates were used to estimate annual export rates. The larger Quinebaug and Shetucket watersheds had the highest annual export rates for Cu, Ni, Pb, and Zn. When normalized per square kilometer of watershed area, the Quinebaug watershed still had the highest Cu, Ni, Pb, and Zn exports, most likely due to the higher urban areas than the other watersheds. This agrees with the urban forest soil metal concentrations. However the normalized annual export results show some of the smaller, less urbanized watersheds had high exports of Cu and Ni. This could be due to modern point source pollution or export of historical pollution.