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Mora J.W.,Waquoit Bay National Estuarine Research Reserve | Burdick D.M.,University of New Hampshire
Wetlands Ecology and Management

In New England salt marshes, man-made earthen barriers, or berms, are generally historic, small-scale (average height = 0.71 m ± 0.12 SE; average length = 166 m ± 41 SE) tidal restrictions which originated from past agricultural, industrial, and environmental practices. The orientation and size depends primarily on the original purpose of the barrier, but this study examines the effects of berms oriented parallel to the incoming tide such that some landward portion of the marsh receives a different tidal signal than the seaward portion. Our hypotheses considered the impacts of the altered hydrology on pore water chemistry and edaphic characteristics. The results indicate that the effect of berms on salt marsh physical structure varies significantly by site. Where the tidal flooding frequency is restricted and drainage is poor, the landward marsh shows pool development, high salinity and sulfide concentrations, and low vegetation cover. In contrast, where tidal flooding is inhibited but the marsh soils are well-drained, salinity and sulfide concentrations decrease and accelerated decomposition results in subsidence and reduced soil organic matter. Given these findings, impacts from berms may impair salt marsh function and resilience to invasive plants and sea level rise. © 2013 Springer Science+Business Media Dordrecht. Source

Mora J.W.,Waquoit Bay National Estuarine Research Reserve | Burdick D.M.,University of New Hampshire
Wetlands Ecology and Management

New England has an extensive history in restricting salt marsh tidal flooding to promote agricultural, industrial, and environmental endeavors. While previous research has focused on the physical and biological impacts of large-scale tidal restrictions, such as dikes and undersized culverts, the effect of smaller historic earthen barriers (average height = 0. 71 m ± 0. 12 SE; average length = 166 m ± 41 SE), or berms, is less understood. Here, we investigate how salt marsh plant communities respond to berms located in the interior of the marsh and oriented parallel to tidal rivers or creeks. Based on the observations from a descriptive study, the landward side of the berm consistently shows a distinct plant species assemblage from the reference areas (ANOSIM: R = 0. 541, p = 0. 001), which is most likely a result of landward pool development. A follow-up manipulative transplant experiment considers how the landward pools affect the governing factors (e. g., physical stress, competition, etc.) controlling the distribution and abundance of Schoenoplectus maritimus and Spartina patens in the landward and seaward zones. The experimental results show that while physical stress seems to prevent robust S. patens growth in the landward zone (ANOVA: F = 24. 697; p < 0. 001), herbivory seems to be the main driving factor behind the low S. maritimus cover found in the seaward zone (Mann-Whitney: U = 56, p = 0. 015). The combined results from the two studies show that berm-associated pools have the potential to impact biological interactions within and across trophic levels in salt marshes. © 2013 Springer Science+Business Media Dordrecht. Source

Maio C.V.,University of Massachusetts Boston | Gontz A.M.,University of Massachusetts Boston | Weidman C.R.,Waquoit Bay National Estuarine Research Reserve | Donnelly J.P.,Woods Hole Oceanographic Institution
Palaeogeography, Palaeoclimatology, Palaeoecology

Extra-tropical storms in the spring of 2010 swept the New England coastline resulting in significant erosion along South Cape Beach, a barrier system located on Cape Cod, Massachusetts. The erosion revealed 111 subfossil stumps and a preserved peat outcrop. We hypothesize that the stumps represent an ancient Eastern Red cedar, Juniperus virginiana, stand growing in a back-barrier environment and drowned by episodic storm events and moderate rates of sea-level rise. Stumps, bivalves, and organic sediments, were radiocarbon dated using traditional and continuous-flow Atomic Mass Spectroscopy methods. Six sediment cores elucidated subsurface stratigraphy and environmental setting. Subfossil stumps ranged in age from 413±80 to 1239±53 calibrated years before present. We assume that this age represents the time at which the ancient trees were drowned by marine waters. Based on elevation and age, an 826year rate of submergence was calculated at 0.73mm/yr with an R2 value of 0.47. Core stratigraphy, microfossil assemblages, and radiocarbon ages indicate a dynamic barrier environment with frequent overwash and breaching events occurring during the past 500years. Shoreline change analysis showed that between 1846 and 2008, the shoreline retreated landward by 70m at a long-term rate of 0.43m/yr. Future increases in the rate of sea-level rise, coupled with episodic storm events, will lead to the destruction of terrestrial environments at rate orders of magnitude greater than that during the time of the paleoforest. © 2013 Elsevier B.V. Source

Vadopalas B.,University of Washington | Weidman C.,Waquoit Bay National Estuarine Research Reserve | Cronin E.K.,University of Washington
Journal of Shellfish Research

Geoduck clams (Panopea generosa Gould 1850) are large, deep-burrowing bivalves distributed from southeast Alaska to Baja California. This species supports a lucrative fishery in the states of Washington and Alaska, as well as in British Columbia, Canada, and geoduck aquaculture currently supplies approximately 30% of the market. To manage this species effectively, it is important to elucidate the population age structure. Geoduck ages are currently estimated by counting valve growth rings. We used bomb radiocarbon ( 14C) to validate geoduck age estimates derived from counts of growth bands in thin-sectioned valve inner hinge plates. Seven specimens with presumed birth years before, during, and after the bomb testing period (1957 to 1967) were sampled from the first 35 y of growth, and subsequently assayed for 14C using accelerator mass spectrometry. The 14C values from each of our specimens compared with reference 14C chronologies for the northeast Pacific were in accord at estimated birth years. The temporal concordance validates current age estimation methods, and provides a first record of marine bomb radiocarbon in Puget Sound. Source

Scourse J.D.,Bangor University | Wanamaker Jr A.D.,Iowa State University | Weidman C.,Waquoit Bay National Estuarine Research Reserve | Heinemeier J.,University of Aarhus | And 4 more authors.

Marine radiocarbon bomb-pulse time histories of annually resolved archives from temperate regions have been underexploited. We present here series of Δ 14C excess from known-age annual increments of the long-lived bivalve mollusk Arctica islandica from 4 sites across the coastal North Atlantic (German Bight, North Sea; Tromsø, north Norway; Siglufjordur, north Icelandic shelf; Grimsey, north Icelandic shelf) combined with published series from Georges Bank and Sable Bank (NW Atlantic) and the Oyster Ground (North Sea). The atmospheric bomb pulse is shown to be a step-function whose response in the marine environment is immediate but of smaller amplitude and which has a longer decay time as a result of the much larger marine carbon reservoir. Attenuation is determined by the regional hydrographic setting of the sites, vertical mixing, processes controlling the isotopic exchange of 14C at the air-sea boundary, 14C content of the freshwater flux, primary productivity, and the residence time of organic matter in the sediment mixed layer. The inventories form a sequence from high magnitude-early peak (German Bight) to low magnitude-late peak (Grimsey). All series show a rapid response to the increase in atmospheric Δ 14C excess but a slow response to the subsequent decline resulting from the succession of rapid isotopic airsea exchange followed by the more gradual isotopic equilibration in the mixed layer due to the variable marine carbon reservoir and incorporation of organic carbon from the sediment mixed layer. The data constitute calibration series for the use of the bomb pulse as a high-resolution dating tool in the marine environment and as a tracer of coastal ocean water masses. © 2012 by the Arizona Board of Regents on behalf of the University of Arizona. Source

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