Plum Island Sound Research Articles

Above- and belowground plant mercury dynamics in a salt marsh estuary in Massachusetts, USA

Abstract. Estuaries are a conduit of mercury (Hg) from watersheds to the coastal ocean, and salt marshes play an important role in coastal Hg cycling. Hg cycling in upland terrestrial ecosystems has been well studied, but processes in densely vegetated salt marsh ecosystems are poorly characterized. We investigated Hg dynamics in vegetation and soils in the Plum Island Sound estuary in Massachusetts, USA, and specifically assessed the role of marsh vegetation for Hg deposition and turnover. Monthly quantitative harvesting of aboveground biomass showed strong linear seasonal increases in Hg associated with plants, with a 4-fold increase in Hg concentration and an 8-fold increase in standing Hg mass from June (3.9 ± 0.2 µg kg−1 and 0.7 ± 0.4 µg m−2, respectively) to November (16.2 ± 2.0 µg kg−1 and 5.7 ± 2.1 µg m−2, respectively). Hg did not increase further in aboveground biomass after plant senescence, indicating physiological controls of vegetation Hg uptake in salt marsh plants. Hg concentrations in live roots and live rhizomes were 11 and 2 times higher than concentrations in live aboveground biomass, respectively. Furthermore, live belowground biomass Hg pools (Hg in roots and rhizomes, 108.1 ± 83.4 µg m−2) were more than 10 times larger than peak standing aboveground Hg pools (9.0 ± 3.3 µg m−2). A ternary mixing model of measured stable Hg isotopes suggests that Hg sources in marsh aboveground tissues originate from about equal contributions of root uptake (∼ 35 %), precipitation uptake (∼ 33 %), and atmospheric gaseous elemental mercury (GEM) uptake (∼ 32 %). These results suggest a more important role of Hg transport from belowground (i.e., roots) to aboveground tissues in salt marsh vegetation than upland vegetation, where GEM uptake is generally the dominant Hg source. Roots and soils showed similar isotopic signatures, suggesting that belowground tissue Hg mostly derived from soil uptake. Annual root turnover results in large internal Hg recycling between soils and plants, estimated at 58.6 µg m−2 yr−1. An initial mass balance of Hg indicates that the salt marsh presently serves as a small net Hg sink for environmental Hg of 5.2 µg m−2 yr−1.

Recovery of salt marsh vegetation after ice-rafting

Sediment transport on salt marsh platforms is usually brought about through storm events and high tides. At high latitudes, ice-rafting is a secondary mechanism for sediment transport, redistributing sediment from tidal flats, channels, and ponds to marshland. In January 2018, winter storm Grayson hit the North Atlantic coast, producing a large storm surge and a significant decrease in temperature. The Great Marsh in Plum Island Sound, Massachusetts, USA, experienced an unprecedented sediment deposition due to ice-rafting, burying marsh vegetation. Plant vegetation recovery was investigated in 17 sediment patches, dominated by Spartina patens, Distichlis spicata, Juncus gerardi, and S. alterniflora. The analysis was carried out considering the number of stems and stem height for each vegetation species. D. spicata firstly occupied bare patches, while S. patens, once smothered by sediment, regrew slowly. The number of stems of S. patens inside the sediment patches recovered, on average, after 2 growing seasons. The number of J. gerardi stems was not significantly affected by ice-rafted sediment deposition. S. alterniflora dynamics were different depending on physical and edaphic conditions. At some locations, S. alterniflora did not recover after sediment deposition. The deposition of the sediment layer had a positive effect on vegetation vigor, increasing stem height and maintaining high stem density. The results suggest a beneficial effect of sediment deposition not only for marsh accretion, but also for marsh vegetation growth, both of which are fundamental for marsh restoration.

Following the Sand Grains

When longshore transport systems encounter tidal inlets, complex mechanisms are involved in bypassing sand to downdrift barriers. Here, this process is examined at Plum Island Sound and Essex Inlets, Massachusetts, USA. One major finding from this study is that sand is transferred along the coast—especially at tidal inlets—by parcels, in discrete steps, and over decadal-scale periods. The southerly orientation of the main-ebb channel at Plum Island Sound, coupled with the landward migration of bars from the ebb delta to the central portion of the downdrift Castle Neck barrier island, have formed a beach protuberance. During the constructional phase, sand is sequestered at the protuberance and the spit-end of the barrier becomes sediment starved, leading to shoreline retreat and a broadening of the spit platform at the mouth to Essex Bay (downdrift side of Castle Neck). Storm-induced sand transport from erosion of the spit and across the spit platform is washed into Essex Bay, filling channels and enlarging flood deltas. This study illustrates the pathways and processes of sand transfer along the shoreline of a barrier-island/tidal-inlet system and provides an important example of the processes that future hydrodynamic and sediment-transport modeling should strive to replicate.

Inorganic and methylated mercury dynamics in estuarine water of a salt marsh in Massachusetts, USA

Salt marsh estuaries serve as sources and sinks for nutrients and elements to and from estuarine water, which enhances and alleviates watershed fluxes to the coastal ocean. We assessed sources and sinks of mercury in the intertidal Plum Island Sound estuary in Massachusetts, the largest salt marsh estuary of New England, using 25-km spatial water sampling transects. Across all seasons, dissolved (FHg) and total (THg) mercury concentrations in estuarine water were highest and strongly enhanced in upper marshes (1.31 ± 0.20 ng L−1 and 6.56 ± 3.70 ng L−1, respectively), compared to riverine Hg concentrations (0.86 ± 0.17 ng L−1 and 0.88 ± 0.34 ng L−1, respectively). Mercury concentrations declined from upper to lower marshes and were lowest in ocean water (0.38 ± 0.10 ng L−1 and 0.56 ± 0.25 ng L−1, respectively). Conservative mixing models using river and ocean water as endmembers indicated that internal estuarine Hg sources strongly enhanced estuarine water Hg concentrations. For FHg, internal estuarine Hg contributions were estimated at 26 g yr−1 which enhanced Hg loads from riverine sources to the ocean by 44%. For THg, internal sources amounted to 251 g yr−1 and exceeded riverine sources six-fold. Proposed sources for internal estuarine mercury contributions include atmospheric deposition to the large estuarine surface area and sediment re-mobilization, although sediment Hg concentrations were low (average 23 ± 2 μg kg−1) typical of uncontaminated sediments. Soil mercury concentrations under vegetation, however, were ten times higher (average 200 ± 225 μg kg−1) than in intertidal sediments suggesting that high soil Hg accumulation might drive lateral export of Hg to the ocean. Spatial transects of methylated Hg (MeHg) showed no concentration enhancements in estuarine water and no indication of internal MeHg sources or formation. Initial mass balance considerations suggest that atmospheric deposition may either be in similar magnitude, or possibly exceed lateral tidal export which would be consistent with strong Hg accumulation observed in salt marsh soils sequestering Hg from current and past atmospheric deposition.

Largest marsh in New England near a precipice

The Great Marsh in northern Massachusetts and southern New Hampshire is the largest salt marsh in New England and includes the marsh surrounding Plum Island Sound, one of the most studied coastal wetlands in the United States. A primary goal in marsh research today is predicting their resilience in a regime of sea-level rise, which has become increasingly based on modeling studies with sparse or site-specific field data input. Here, we present the results of a vertical accretion study using 210Pb and 137Cs geochronology developed from 50-cm long auger cores taken at 15 locations throughout the PIS marsh. Two significant outliers were omitted from the final analyses due to their unusual depositional settings. The 137Cs spike produced the shortest-term record and lowest average accretion rate (2.5 mm/yr). Of the various 210Pb accretion models (Constant Flux-Constant Sedimentation: CF-CS, Constant Rate of Supply: CRS, Constant Initial Concentration: CIC), we chose the CF-CS model accretion rate for comparison to other environmental parameters and future marsh projections due to the robust R2 linear regression values and its wide use. The 13 stations exhibited an average accretion rate of 3.13 mm/yr, which is 0.6 mm/yr greater than the average rate reported elsewhere in New England. Individual accretion rates show no correlation with geography, elevation, bulk density, loss on ignition, distance to tidal channels, or peat thickness, indicating the complexity of the interacting factors that control marsh growth. Using moderate sea-level rise predictions, we show that large portions of the high marsh are likely to be converted to low marsh by 2050, and that the entire marsh high platform will become low marsh prior to 2070. This is the first time that wide spread field data are used to project a major transformation of the Plum Island Sound platform marsh that undoubtedly will lead to dramatic changes to marsh drainage, backbarrier hypsometry, tidal current dominance, and redistribution of sediment reservoirs, that will include the fronting barrier islands.

Fate of cohesive sediments in a marsh-dominated estuary

Deposition of fine sediments on a marsh platform favors accretion that counteracts Sea Level Rise. However, it is difficult to assess the sediment trapping capacity of a marsh given the heterogeneity of sediment sources and the geometric complexity of the system, with a network of dendritic and meandering creeks dissecting the intertidal area. Here we use a numerical model to study the sediment trapping capacity of a marsh-dominated estuary, Plum Island Sound, USA, and its variations across the landscape. The results highlight the importance of the timing between sediment inputs and tidal phase and show that sediment discharged from tidal rivers deposit within the rivers themselves or in adjacent marshes. Most sediment is deposited in shallow tidal flats and channels and is unable to penetrate farther inside the marshes because of the limited water depths and velocities on the marsh platform. Trapping capacity of sediment in different intertidal subdomains decreases logarithmically with the ratio between advection length and the typical length of channels and tidal flats. Moreover, sediment deposition on the marsh decreases exponentially with distance from the channels and marsh edge. This decay rate is a function of settling velocity and the maximum value of water depth and velocity on the marsh platform.

Can denitrification explain coastal wetland loss: A review of case studies in the Mississippi Delta and New England

There has been considerable discussion over the past several years about the potential negative effects of nutrient loading on coastal wetland stability. In particular, there have been concerns that high nitrate concentrations can fuel denitrification that can lead to soil organic matter loss and wetland deterioration. Here we review these issues for three case studies where there have been elevated levels of dissolved inorganic nitrogen, especially nitrate, coincident with wetland deterioration. These case studies include the Breton Sound estuary that receives diverted Mississippi River water at Caernarvon LA, a freshwater assimilation wetland that receives treated municipal effluent from a wastewater treatment plant at Hammond, LA, and a tidal creek in the Plum Island Sound estuary of northeastern Massachusetts where nitrate was introduced on each flood tide during the growing season for nearly ten years. We review the physical setting, ecology and biogeochemistry of these sites and use stoichiometric calculations to estimate how much soil organic matter decomposition could be accounted for by denitrification. Results of these calculations show that denitrification rates could not have caused the observed marsh deterioration at the two LA marshes. Denitrification may play a significant role in marsh loss at the MA site, however due to the unique hydrology of this site, denitrification rates induced by very high nitrogen loading rates in concert with the hydrology of the site may play a more significant role in marsh deterioration.

Lateral Marsh Edge Erosion as a Source of Sediments for Vertical Marsh Accretion

AbstractWith sea level rise accelerating and sediment inputs to the coast declining worldwide, there is concern that tidal wetlands will drown. To better understand this concern, sources of sediment contributing to marsh elevation gain were computed for Plum Island Sound estuary, MA, USA. We quantified input of sediment from rivers and erosion of marsh edges. Maintaining elevation relative to the recent sea level rise rate of 2.8 mm yr−1 requires input of 32,299 MT yr−1 of sediment. The input from watersheds is only 3,210 MT yr−1. Marsh edge erosion, based on a comparison of 2005 and 2011 LiDAR data, provides 10,032 MT yr−1. This level of erosion is met by <0.1% of total marsh area eroded annually. Mass balance suggests that 19,070 MT yr−1 should be of tidal flat or oceanic origin. The estuarine distribution of 14C and 13C isotopes of suspended particulate organic carbon confirms the resuspension of ancient marsh peat from marsh edge erosion, and the vertical distribution of 14C‐humin material in marsh sediment is indicative of the deposition of ancient organic carbon on the marsh platform. High resuspension rates in the estuarine water column are sufficient to meet marsh accretionary needs. Marsh edge erosion provides an important fraction of the material needed for marsh accretion. Because of limited sediment supply and sea level rise, the marsh platform maintains elevation at the expense of total marsh area.

Discontinuities in soil strength contribute to destabilization of nutrient-enriched creeks.

In a whole-ecosystem, nutrient addition experiment in the Plum Island Sound Estuary (Massachusetts), we tested the effects of nitrogen enrichment on the carbon and nitrogen contents, respiration, and strength of marsh soils. We measured soil shear strength within and across vegetation zones. We found significantly higher soil percent organic matter, carbon, and nitrogen in the long-term enriched marshes and higher soil respiration rates with longer duration of enrichment. The soil strength was similar in magnitude across depths and vegetation zones in the reference creeks, but showed signs of significant nutrient-mediated alteration in enriched creeks where shear strength at rooting depths of the low marsh–high marsh interface zone was significantly lower than at the sub-rooting depths or in the creek bank vegetation zone. To more closely examine the soil strength of the rooting (10–30 cm) and sub-rooting (40–60 cm) depths in the interface and creek bank vegetation zones, we calculated a vertical shear strength differential between these depths. We found significantly lower differentials in shear strength (rooting depth < sub-rooting depths) in the enriched creeks and in the interface zones. The discontinuities in the vertical and horizontal shear strength across the enriched marshes may contribute to observed fracturing and slumping occurring in the marsh systems. Tide gauge data also showed a pattern of rapid sea level rise for the period of the study, and changes in plant distribution patterns were indicative of increased flooding. Longer exposure times to nutrient-enriched waters and increased hydraulic energy associated with sea level rise may exacerbate creek bank sloughing. Additional research is needed, however, to better understand the interactions of nutrient enrichment and sea level rise on soil shear strength and stability of tidal salt marshes.

The effect of evaporation on the erodibility of mudflats in a mesotidal estuary

Large areas of mesotidal estuaries become subaerial during low tide. Here we study the effect of several meteorological and hydrodynamic parameters on the erodibility of mudflat substrates when they are subaerial. Field measurements carried out over a two-week period in September 2011 in Plum Island Sound, Massachusetts USA, indicate that high evaporation rates and long subaerial periods are associated to low sediment erodibility. Sediment concentrations in the water column during submergence depend on bottom shear stresses triggered by tidal currents. Surprisingly, they are also related to the total evaporation that occurred in the previous emergence period. We conclude that low erodibility of mudflat sediments is linked to subaerial desiccation at low tide. This strengthening effect is not lost during the following submerged period, thus limiting the erosive effect of tidal currents. We thus show that not only subaqueous but also subaerial processes might control the erodibility of mudflats. Long-term evaporation rates can therefore directly affect the stability of mudflats in mesotidal environments.

Varying Inundation Regimes Differentially Affect Natural and Sand-Amended Marsh Sediments.

Climate change is altering sea level rise rates and precipitation patterns worldwide. Coastal wetlands are vulnerable to these changes. System responses to stressors are important for resource managers and environmental stewards to understand in order to best manage them. Thin layer sand or sediment application to drowning and eroding marshes is one approach to build elevation and resilience. The above- and below-ground structure, soil carbon dioxide emissions, and pore water constituents in vegetated natural marsh sediments and sand-amended sediments were examined at varying inundation regimes between mean sea level and mean high water (0.82 m NAVD88 to 1.49 m NAVD88) in a field experiment at Laws Point, part of the Plum Island Sound Estuary (MA). Significantly lower salinities, pH, sulfides, phosphates, and ammonium were measured in the sand-amended sediments than in the natural sediments. In natural sediments there was a pattern of increasing salinity with increasing elevation while in the sand-amended sediments the trend was reversed, showing decreasing salinity with increasing elevation. Sulfide concentrations generally increased from low to high inundation with highest concentrations at the highest inundation (i.e., at the lowest elevations). High pore water phosphate concentrations were measured at low elevations in the natural sediments, but the sand-amended treatments had mostly low concentrations of phosphate and no consistent pattern with elevation. At the end of the experiment the lowest elevations generally had the highest measures of pore water ammonium. Soil carbon dioxide emissions were greatest in the sand-amended mesocosms and at higher elevations. Differences in coarse root and rhizome abundances and volumes among the sediment treatments were detected with CT imaging, but by 20 weeks the natural and sand-amended treatments showed similar total belowground biomass at the intermediate and high elevations. Although differences in pore water nutrient concentrations, pH, salinity, and belowground root and rhizome morphology were detected between the natural and sand-amended sediments, similar belowground productivity and total biomass were measured by the end of the growing season. Since the belowground productivity supports organic matter accumulation and peat buildup in marshes, our results suggest that thin layer sand or sediment application is a viable climate adaptation action to build elevation and coastal resiliency, especially in areas with low natural sediment supplies.

Variability of Mya arenaria growth along an environmental gradient in the Plum Island Sound estuary, Massachusetts, USA

An understanding of the environmental factors that determine how clam growth varies in space and time improves effective mariculture and shellfish management. We examined the importance of temperature, salinity and chlorophyll-a in controlling the spatial pattern of Mya arenaria growth, the commercially important soft-shell clam, in the Plum Island Sound estuary in northeastern Massachusetts, USA. We collected clams (>5.08 cm) monthly during the April to November growing season from which we determined growth rate, maximum size (L-infinity), and time to reach a harvestable size. We also surveyed selected sites along the estuary to estimate the relationship between clam size and weight. We collected environmental data along the estuary, and our data were complemented with data collected and maintained by the Plum Island ecosystems long-term ecological research project. Clams reached harvestable size fastest and had the greatest L-infinity at the most oceanic site (Yacht Club) in the estuary. Clams had the smallest L-infinity and were slowest to reach the harvestable size at the least oceanic site (Railroad Meander). The spatial patterns of clam growth were best explained by a positive distribution of salinity. Salinity significantly accounted for 95 % of the spatial variation of clam growth in the estuary. Snow melt in spring increases freshwater input to the estuary and results in the lowest spring salinity during a year, and this explained the upper estuary limit of clam distribution. IPCC-projected climate change will cause sea-level rise and increasing precipitation in the northeastern USA, which will modify the spatial pattern of salinity in the region’s estuaries. Our research therefore suggests that future management of M. arenaria, an important economic resource for the local economy, should be concerned with the changes of salinity distribution under climate and land-use change.

Influence of Physical Manipulations on Short-Term Salt Marsh Morphodynamics: Examples from the North and Mid-Atlantic Coast, USA

Along the mid- and north Atlantic coasts of the USA, over 90 % of salt marshes have been ditched. Ditching was largely abandoned by the mid-twentieth century; however, techniques that create permanent shallow water pools for mosquito control and bird habitat are increasingly being applied to marshes of the USA and elsewhere. Salt marshes in Plum Island Sound, Massachusetts, and Barnegat Bay, New Jersey, were used to examine differences between areas that have been ditched and those altered to increase the density of shallow pools in water table dynamics, salinity, soil and porewater chemistry, as well as short-term sedimentation, accretion, and elevation change rates. We found that the area with plugged ditches, berms, and pools in Plum Island had less drainage, higher salinity and porewater sulfide and ammonium concentrations, and higher soil organic matter than the adjacent ditched area. Despite averaging 8 cm lower in elevation, the Plum Island ditched area had less sediment deposition and was composed of higher elevation plant species than the area with plugged ditches, berms, and shallow pools. Elevation increased in the ditched area at a rate of 3.2 ± 0.5 mm/year, but elevation change was variable in the area with pools. In Barnegat Bay, the marsh area with pools and ditches had less sediment deposition and surface accretion than the ditch-only area, associated, in part, with the higher elevation. An average elevation difference of 4.5 cm was associated with a sixfold difference in mineral sediment deposition. Temporal sediment deposition and surface accretion was important in the ditch-only area but was absent or muted in the area with numerous pools. Elevation increased in both marsh areas at an average rate of 1.8 ± 0.8 mm/year, less than half the long-term average local rate of sea-level rise. Our results illustrate how physical manipulations including changes to tidal hydrology and surface topography interact with elevation to influence short-term biophysical feedbacks.

Elevated mercury levels in a wintering population of common eiders (Somateria mollissima) in the northeastern United States

In North America and Europe, sea ducks are important indicators of ecological health and inshore marine pollution. To explore spatial variation in mercury accumulation in common eiders in the northeastern United States, we compared concentrations of total mercury in common eider blood at several New England locations between 1998 and 2013. Eider food items (mollusks) were collected and analyzed to determine if mercury concentrations in eider blood were indicative of local mercury bioavailability. Eiders from Plum Island Sound, MA had a significantly higher mean blood mercury concentration (0.83μg/g) than those in other locations. Mean mercury levels in this population were also nearly three times higher than any blood mercury concentrations reported for common eiders in published literature. We observed consistent patterns in eider blood mercury and blue mussel mercury concentrations between sites, suggesting a tentative predictive quality between the two species.

The relationships among hydrodynamics, sediment distribution, and chlorophyll in a mesotidal estuary

Tidal bars and tidal flats in shallow, mesotidal estuaries are subject to the action of tidal currents and waves. This complex forcing gives rise to large variations in bottom sediments and related benthic ecosystems. In this research we study the spatial relationships among tidal currents, waves, sediment characteristics, chlorophyll a, and pheophytin in the shallow bars and flats of Plum Island Sound, Massachusetts, USA. Waves and tides have a mild effect on the sand grain size and percent of silt and mud of these shallow deposits. Average wave conditions are more important than extreme events, like Nor’easters, in sediment sorting. The spatial distribution of pheophytin, an indicator of dead microphytobenthos, mimics that of silt and mud whereas chlorophyll a, a proxy for the live microphytobenthos stock, is greatest in sandy areas characterized by intermediate values of tidal velocity.

Mummichog Fundulus heteroclitus responses to long-term, whole-ecosystem nutrient enrichment

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 492:211-222 (2013) - DOI: https://doi.org/10.3354/meps10495 Mummichog Fundulus heteroclitus responses to long-term, whole-ecosystem nutrient enrichment Konner C. Lockfield1, John W. Fleeger1,*, Linda A. Deegan2 1Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana 70803, USA 2The Ecosystems Center, Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA *Corresponding author. Email: zoflee@lsu.edu ABSTRACT: The effects of eutrophication on coastal plants and sessile animals are becoming well known, but responses of mobile species are less well studied. Here, we link variation in abundance, biomass, body size, growth rate, and resource utilization in mummichogs Fundulus heteroclitus >40 mm in length to experimental nutrient enrichment in Plum Island Sound, Massachusetts, USA. To mimic cultural eutrophication, dissolved fertilizer was released into replicate saltmarsh creeks on each rising tide throughout entire growing seasons. In the summer of the sixth year of enrichment, we released coded-wire tagged mummichogs into nutrient-enriched (n = 3733 fish) and reference (n = 3894 fish) creeks and recaptured them over the next 2 mo. We found increased abundance (by 37%), biomass (58%), body size (8%), and herbivory (115%, measured as photosynthetic gut pigment content) in nutrient-enriched creeks, although body condition was unaffected. However, individual growth rates were 43% lower in nutrient-enriched creeks. Nutrient enrichment stimulated primary production, causing a bottom-up enrichment of the food web which fostered increased biomass and body size. However, the reduction in growth rate indicates an adverse consequence of long-term nutrient enrichment. This negative effect occurred in the absence of increased hypoxia in these highly tidally (4 m amplitude) flushed study creeks. The mummichog is an important predator/grazer in salt marshes, and nutrient-induced alterations in biomass or resource utilization will directly or indirectly affect lower trophic levels, including benthic algae, thereby impacting the ecosystem-wide response to eutrophication. KEY WORDS: Fundulus heteroclitus · Mark and recapture · Eutrophication · Decimal coded-wire tags · Growth rate · Salt marsh Full text in pdf format PreviousNextCite this article as: Lockfield KC, Fleeger JW, Deegan LA (2013) Mummichog Fundulus heteroclitus responses to long-term, whole-ecosystem nutrient enrichment. Mar Ecol Prog Ser 492:211-222. https://doi.org/10.3354/meps10495 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 492. Online publication date: October 31, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Wetland‐estuarine‐shelf interactions in the Plum Island Sound and Merrimack River in the Massachusetts coast

Wetland‐estuarine‐shelf interaction processes in the Plum Island Sound and Merrimack River system in the Massachusetts coast are examined using the high‐resolution unstructured grid, finite volume, primitive equations, coastal ocean model. The computational domain covers the estuarine and entire intertidal area with a horizontal resolution of 10–200 m. Driven by five tidal constituents forcing at the open boundary on the inner shelf of the eastern coast of the Gulf of Maine, the model has successfully simulated the 3‐D flooding/drying process, temporal variability, and spatial distribution of salinity as well as the water exchange flux through the water passage between the Plum Island Sound and Merrimack River. The model predicts a complex recirculation loop around the Merrimack River, shelf, and Plum Island Sound. During the ebb tide, salt water in the Plum Island Sound is injected into the Merrimack River, while during flood tide, a significant amount of the freshwater in the Merrimack River is forced into Plum Island Sound. This water exchange varies with the magnitude of freshwater discharge and wind conditions, with a maximum contribution of ∼30%–40% variability in salinity over tidal cycles in the mouth of the Merrimack River. Nonlinear tidal rectification results in a complex clockwise residual recirculation loop around the Merrimack River, shelf, and Plum Island Sound. The net water flux from Plum Island Sound to the Merrimack River varies with the interaction between tide, river discharge, and wind forcing. This interaction, in turn, affects the salt transport from this system to the shelf. Since the resulting water transport into the shelf significantly varies with the variability of the wind, models that fail to resolve this complex estuarine and shelf system could either overestimate or underestimate the salt content over the shelf.

The effect of increased nitrate loading on nitrate reduction via denitrification and DNRA in salt marsh sediments

The effects of increased nitrogen loading on denitrification and dissimilatory nitrate reduction to ammonium (DNRA) in marsh sediments were studied in permanently submerged subtidal creek sediments and on the tidally inundated vegetated marsh platform in Plum Island Sound estuary, Massachusetts. DNRA and denitrification in surface sediments were measured at all sites using whole‐core incubations and the isotope pairing technique, which allows distinction between denitrification of water column nitrate and coupled nitrification‐denitrification. On the marsh platform, denitrification was also measured at depth in the rhizosphere, using a new approach that combined the push‐pull method and the isotope pairing technique. In tidal creek sediments, fertilization increased denitrification of water column nitrate by approximately one order of magnitude, and coupled nitrification‐denitrification threefold. Coupled nitrification‐denitrification made a significant contribution to the total N2 production in the unfertilized creek but was of minor importance in the fertilized creek due to increased rates of denitrification of water column nitrate. In the surface sediment of the marsh platform, fertilization increased denitrification of water column nitrate by an order of magnitude during inundation of the marsh platform, about 12% of the day. However, coupled nitrification‐denitrification occurring at depth in the rhizosphere was the main denitrification pathway, accounting for more than 50% of the total N2 production in the fertilized as well as in the reference marsh. DNRA was measured in the surface sediment only, where it was comparable in magnitude to denitrification in the fertilized as well as in the unfertilized marsh.

Seasonal Use of a New England Estuary by Foraging Contingents of Migratory Striped Bass

AbstractUsing acoustic telemetry on migratory striped bass Morone saxatilis in Plum Island Estuary (PIE), Massachusetts, we found that striped bass (335–634 mm total length) tagged in the spring and summer of 2005 (n = 14) and 2006 (n = 46) stayed in the estuary for an average of 66.0 d in 2005 and 72.2 d in 2006. Striped bass spent the most time in two specific reaches: middle Plum Island Sound and lower Rowley River. In both years, three different use‐groups of striped bass were observed in PIE. Short‐term visitors (n = 24) stayed in the estuary only briefly (range = 5–20 d). Two groups of seasonal residents stayed for more than 30 d, either in the Rowley River (n = 14) or in Plum Island Sound (n = 22). Within PIE, the two seasonal‐resident use‐groups may be foraging contingents that learn how to feed efficiently in specific parts of the estuary. These distinct within‐estuary use patterns could have different implications for striped bass condition and prey impact.

The effect of increased nitrate loading on nitrate reduction via denitrification and DNRA in salt marsh sediments

The effects of increased nitrogen loading on denitrification and dissimilatory nitrate reduction to ammonium (DNRA) in marsh sediments were studied in permanently submerged subtidal creek sediments and on the tidally inundated vegetated marsh platform in Plum Island Sound estuary, Massachusetts. DNRA and denitrification in surface sediments were measured at all sites using whole-core incubations and the isotope pairing technique, which allows distinction between denitrification of water column nitrate and coupled nitrification-denitrification. On the marsh platform, denitrification was also measured at depth in the rhizosphere, using a new approach that combined the push-pull method and the isotope pairing technique. In tidal creek sediments, fertilization increased denitrification of water column nitrate by approximately one order of magnitude, and coupled nitrification-denitrification threefold. Coupled nitrification-denitrification made a significant contribution to the total N2 production in the unfertilized creek but was of minor importance in the fertilized creek due to increased rates of denitrification of water column nitrate. In the surface sediment of the marsh platform, fertilization increased denitrification of water column nitrate by an order of magnitude during inundation of the marsh platform, about 12% of the day. However, coupled nitrification-denitrification occurring at depth in the rhizosphere was the main denitrification pathway, accounting for more than 50% of the total N2 production in the fertilized as well as in the reference marsh. DNRA was measured in the surface sediment only, where it was comparable in magnitude to denitrification in the fertilized as well as in the unfertilized marsh.