Waquoit Bay Research Articles

Pollutant dynamics in a subterranean estuary (Waquoit Bay, MA, USA) via mathematical modeling

Minerals and nutrients are vital to life, but their excess can harm health and sometimes lead to life risks. Harmful impact of nutrients in water can be a threat to marine life as well. Waquoit Bay linked with its eight rivers and ponds is becoming the reason for excess nutrient passage into the Bay. Excess amounts of nutrients were found in Waquoit Bay from coastal areas and therefore analyzed in this work by a system of nine differential equations. The main objective of this paper is to develop a mathematical model to assess the situation of pollution in Waquoit Bay and suggest some solutions using optimal control theory with Hamiltonian system. Mathematical Model of water pollution will be evaluated numerically, with different input models to track environmental contamination in a water body. To prove the accuracy of this model, its numerical results will be compared with real data and the impact of control strategies i.e. nutrient control from housing area and bio dredging will be studied. Benefit of developing such mathematical models can be a decision support for planning restrictions in coastal areas near Waquoit Bay.

Dead molluscan shells from multiple trophic groups as archives of nitrogen isotopic evidence of wastewater gradients in estuaries

Increased coastal urbanization worldwide has resulted in increased nitrogen inputs to ecosystems, leading to eutrophication and other negative effects. We assessed δ15N in the dead-collected shells of three molluscan species in two estuaries in order to evaluate their ability to identify known gradients in wastewater nitrogen input, namely from private septic systems feeding directly into Waquoit Bay and from a groundwater plume reflecting wastewater injection at a municipal treatment plant in West Falmouth Harbor, Massachusetts, USA. Shells of a suspension-feeder (Geukensia demissa), a micro-algal grazer (Littorina littorea), and an omnivore (Nassarius obsoletus) were collected from lower intertidal sediments near the taxon's life habitat. We found that δ15N in dead-collected shells decreased significantly along the gradients of wastewater pollution in both estuaries, with similar results across all three trophic groups. These positive results demonstrate the potential of dead-shell assemblages for detecting spatial gradients of wastewater pollution.

Deoxygenation, Acidification and Warming in Waquoit Bay, USA, and a Shift to Pelagic Dominance

Coastal nutrient pollution, or eutrophication, is commonly linked to anthropogenic influences in terrestrial watersheds, where land-use changes often degrade water quality over time. Due to gradual changes, the management and monitoring of estuarine systems often lag environmental degradation. One example can be found at the Waquoit Bay National Estuarine Research Reserve, where we developed an analysis framework to standardize and analyze long-term trends in water quality and submerged vegetation data from monitoring programs that began in the 1990s. These programs started after the nearly complete loss of historically extensive Zostera marina (eelgrass) meadows throughout the estuary. Recently, eelgrass only persisted in small, undeveloped sub-embayments of the estuary, with conservative declines of over 97% in areal coverage. Over the past 2 decades, the average deoxygenation, acidification, and warming were −24.7 µmol O2 kg−1 (−11%), 0.006 µmol H+ kg−1 (+ 34%), and 1.0 °C (+ 4%), respectively. Along with the loss of eelgrass, there was also a decline in macroalgal biomass over 3 decades, resulting in a system dominated by pelagic metabolism, indicated by a 71% increase in water column chlorophyll a concentrations since 2009. This recent increase in phytoplankton biomass, which is highly mobile and transported throughout the estuary by tides, has resulted in recent degradation of isolated embayments despite their lower nutrient loads. This shift toward pelagic dominance in Waquoit Bay may indicate that other eutrophic and warming estuaries may also shift toward pelagic dominance in the future, as the Northeastern US is one of the fastest warming regions across the world.

Measuring and modeling nitrogen export from cranberry farms

AbstractNitrogen (N) pollution is arguably the single greatest threat to coastal water quality in the United States. In the state of Massachusetts, sustainable management of cranberry agriculture requires detailed understanding of potential sources and losses of N, which can contribute to impaired coastal waters. Given the complexity of N transport processes, models are often used to quantify the amount of N delivered from cranberry farms to coastal waters. However, ambiguities in model parameters, inconsistencies in deriving N loading rates, and inaccuracies in spatial coverages leave open questions about the contribution of cranberry agriculture to impaired coastal waters. In this study, we synthesize the methods, assumptions, and results of all N budget studies conducted in cranberry farms from 1995 to 2019. We propose a new analytical framework for measuring N fertilizer export from cranberry farms which includes our best understanding of N retention and transport in cranberry farms. We then apply our results to two watershed land‐use models (Massachusetts Estuaries Project Linked Watershed‐Embayment Model, LM; the Waquoit Bay Nitrogen Loading Model, NLM) to quantify N loads contributed by cranberry farms to the highly eutrophic Wareham River estuary. We find that the LM and NLM are in close agreement with respect to the amount of N delivered from cranberry farms to the Wareham River estuary. In our application of the LM, we estimated that 7791 kg N·yr−1 from cranberry farms, or 15% of the total N load, reached the estuary. By comparison, we found that the NLM estimated slightly higher N loads contributed by cranberry farms to the estuary: 8365 kg N·yr−1, or 16% of the total N load. However, the models gave contrasting estimates of unattenuated N loads from cranberry farms (9670 kg N·yr−1, LM; 12,870 kg N·yr−1, NLM) and the amount of N transmitted through the watershed to the estuary (81% LM; 65% NLM).

Comparison of Oyster Aquaculture Methods and Their Potential to Enhance Microbial Nitrogen Removal From Coastal Ecosystems

Coastal ecosystems are impacted by excessive nutrient inputs that cause degradation of water quality and impairments of ecosystem functioning. Regulatory and management efforts to enhance nutrient export from coastal ecosystems include sustainable oyster aquaculture that removes nitrogen in the form of oyster biomass and increases particulate export to underlying sediments where increased organic material may enhance microbial denitrification. To better understand the impacts of oyster aquaculture on nitrogen removal, we examined bacterial processes in sediments underlying three of the most common aquaculture methods that vary in the proximity of oysters to the sediments. Sediment samples underlying sites managed with these different aquaculture methods were examined using the 16S rRNA gene to assess microbial community structure, gene expression analyses to examine nitrogen and sulfur cycling genes, and nitrogen gas flux measurements. All sites were located in the same hydrodynamic setting within Waquoit Bay, MA during 2018 and 2019. Although sediments under the different oyster farming practices showed similar communities, ordination analysis revealed discrete community groups formed along the sampling season. Measured N2 fluxes and expression of key genes involved in denitrification, anaerobic ammonium oxidation (anammox), and dissimilatory nitrate reduction to ammonium (DNRA) increased during mid-summer and into fall in both years primarily under bottom cages. While all three oyster growing methods enhanced nitrogen removal relative to the control site, gene expression data indicate that the nitrogen retaining process of DNRA is particularly enhanced after end of July under bottom cages, and to a lesser extent, under suspended and floating bags. The choice of gear can also potentially increase processes that induce nitrogen retention in the form of ammonia in the underlying sediments over time, thus causing deviations from predicted nitrogen removal. If nitrogen removal is a primary objective, monitoring for these shifts is essential for making decisions about siting and size of aquaculture sites from year to year.

Control of N Concentrations in Cape Cod Estuaries by Nitrogen Loads, Season, and Down-Estuary Transit: Assessment by Conventional and Effect-Size Statistics

To assess effects of N loads, season, and down-estuary transit on estuarine concentrations of nitrate (NO3), ammonium (NH4), dissolved organic nitrogen (DON), and total dissolved nitrogen (TDN), we sampled three estuaries within Waquoit Bay, MA (USA), subject to different N loads, from spring to fall, at nine stations spanning the salinity range. Conventional statistical analysis on the basis of entire data for the three estuaries suggested significant effects of N loads on concentrations, but comparisons with effect size measures suggested that the effects were minor, largely an artifactual result from the large number of samples. Constraining variation by binning data into weekly means, and partitioning data by season (summer vs. spring-fall) and down-estuary transit (based on salinity) improved interpretations, allowing emergence of detectable increases in NO3 concentrations in estuaries subject to larger N loads, confirmed interactions between N load and season (seasonal increases in NO3 larger in estuaries subject to higher N loads), and down-estuary gradients (highest NO3 concentrations in fresher reaches and significant down-estuary decreases in NO3). NH4 and DON were less responsive to N loads, with rapid uptake of NH4 and seasonal trajectories of DON subject to within-estuary features. TDN concentrations decreased down-estuary, with 13–36% of loss attributable to within-estuary interception, a considerable effect in spite of short water residence times. Management implications include the need to sample seasonally and cover the salinity gradient, checking conventional statistical analyses of pooled data from large databases, using effect size measures to ensure meaningful biological and management results, and attention to the limited lability of DON often included in considering estuarine TDN and N loads.

Ecological parameter reductions, environmental regimes, and characteristic process diagram of carbon dioxide fluxes in coastal salt marshes

We investigated the ecological parameter reductions (termed “similitudes”) and characteristic patterns of the net uptake fluxes of carbon dioxide (CO2) in coastal salt marshes using dimensional analysis method from fluid mechanics and hydraulic engineering. Data collected during May–October, 2013 from four salt marshes in Waquoit Bay and adjacent estuary, Massachusetts, USA were utilized to evaluate the theoretically-derived dimensionless flux and various ecological driver numbers. Two meaningful dimensionless groups were discovered as the light use efficiency number (LUE = CO2 normalized by photosynthetically active radiation) and the biogeochemical number (combination of soil temperature, porewater salinity, and atmospheric pressure). A semi-logarithmic plot of the dimensionless numbers indicated the emergence of a characteristic diagram represented by three distinct LUE regimes (high, transitional, and low). The high regime corresponded to the most favorable (high temperature and low salinity) condition for CO2 uptake, whereas the low regime represented an unfavorable condition (low temperature and high salinity). The analysis identified two environmental thresholds (soil temperature ~ 17 °C and salinity ~ 30 ppt), which dictated the regime transitions of CO2 uptake. The process diagram and critical thresholds provide important insights into the CO2 uptake potential of coastal wetlands in response to changes in key environmental drivers.

Estuarine Sediments Exhibit Dynamic and Variable Biogeochemical Responses to Hypoxia

AbstractEstuarine ecosystems are considered among the most valuable regions worldwide because of the wealth of ecosystem services they provide. Given their proximity to the land, they are also vulnerable to excessive nutrient inputs, which can lead to eutrophication and hypoxia. Water column hypoxia can dramatically alter sediment biogeochemistry, yet the response of specific processes varies widely. Predicting whether sediments are sources or sinks of ecologically and climatologically relevant nutrients and gases remains elusive, particularly for shallow coastal regions. In this study, we conducted experiments with sediments collected from Waquoit Bay (Massachusetts, United States) and measured dissolved nutrient and gas fluxes across the sediment‐water interface to investigate the impact of water column hypoxia (defined here as dissolved oxygen ≤3 mg/L) on three important ecosystem functions: nutrient regeneration, removal of reactive nitrogen, and the regulation of greenhouse gases. Under hypoxia we observed variable responses in sediment biogeochemical cycling, including little to no change in important nitrogen cycling processes such as ammonium efflux and nitrogen removal through denitrification. As expected, low oxygen conditions stimulated sediment phosphate efflux. This caused nutrient ratios for both nitrogen to phosphorus and silica to phosphorus in the overlying water to decrease by 50%. Such changes can alter both the composition of water column primary producers as well as the rate of primary production. Hypoxia led to an almost 60% decrease in sediment nitrous oxide consumption but had little impact on sediment methane emissions. Taken together, these experimental results suggest sediment biogeochemical cycling has variable and dynamic responses to hypoxia.

Dissolved silica in the subterranean estuary and the impact of submarine groundwater discharge on the global marine silica budget

Groundwater's role in the global marine budget of dissolved silica (DSi), an essential nutrient, is constrained using DSi groundwater concentrations from multiple endmember lithologies and a global terrestrial submarine groundwater discharge (SGD) model. We report new DSi concentrations in nine subterranean estuaries throughout the world, including Panama, Mauritius, Guam, Yucatan (Mexico), Chile, Argentina, Southwest Florida (USA), Long Island Sound (USA) and Waquoit Bay (USA). These new data are augmented with a literature survey of DSi endmember concentrations in the subterranean estuary to determine the global DSi endmember in SGD, classified by the regional lithology (carbonate, shale, sandstone, extrusive igneous, shield and “complex”). DSi fluxes to the ocean from terrestrial (fresh) SGD equal 0.7 ± 0.1 Tmol y−1, more than half of which enters the Pacific Ocean. Non-conservative DSi enrichment was observed in marine groundwaters circulated through extrusive igneous and complex lithology sediments for twenty different study sites. Dissolution rate calculations indicate that non-conservative DSi enrichments in marine groundwaters can be supported, in part, by lithogenic dissolution of the coastal sediment, rather than biogenic silica dissolution. We make preliminary estimates of DSi inputs via marine SGD in shallow coastal aquifers of ~3 Tmol y−1. Considering recent revisions to the marine silica budget (e.g., increased estimates of biogenic silica storage via reverse weathering reactions, increased estimates of standing stocks of biogenic silica, and changing estimates of silica burial efficiency), sources and sinks in the marine Si budget can be balanced when taking into account estimates of new DSi inputs from total SGD (terrestrial and marine flow paths). These findings impact the residence time of oceanic Si and mass balances of the stable Si isotopes, as well as associated silicate weathering products, including Li and Ge.

Germination responses to abiotic stress shape species distributions on coastal dunes

Plant species occupy distinct zones on coastal dunes, but the mechanisms limiting their distributions have not been fully explained. We combined field surveys of plant distributions and abiotic conditions with controlled germination experiments to assess the contribution of germination requirements to plant zonation. Species presence and abiotic conditions were measured in ten transects across the barrier dune at Waquoit Bay, Massachusetts. Germinating seeds of six species were exposed to four fully crossed treatments: pre-treatment (soaked in fresh water, soaked in salt water, or not soaked), temperature (low, moderate, or high), soil salinity (none, moderate, or high), and light (full light, shade, dark). Species distributions in the field were affected by both distance from the shore and presence of dominant shrubs. Germination tolerance of soil salinity reflected species zonation: species found on the front slope of the dune tolerated salinity, while germination of other species was limited by salinity alone or by salinity in combination with high temperature. Shrubs reduced soil surface temperature and decreased light, but these conditions had limited effects on germination. These results indicate that limitations to germination can contribute to explaining species distributions on coastal dunes.

Environmental Controls, Emergent Scaling, and Predictions of Greenhouse Gas (GHG) Fluxes in Coastal Salt Marshes

AbstractCoastal salt marshes play an important role in mitigating global warming by removing atmospheric carbon at a high rate. We investigated the environmental controls and emergent scaling of major greenhouse gas (GHG) fluxes such as carbon dioxide (CO2) and methane (CH4) in coastal salt marshes by conducting data analytics and empirical modeling. The underlying hypothesis is that the salt marsh GHG fluxes follow emergent scaling relationships with their environmental drivers, leading to parsimonious predictive models. CO2 and CH4 fluxes, photosynthetically active radiation (PAR), air and soil temperatures, well water level, soil moisture, and porewater pH and salinity were measured during May–October 2013 from four marshes in Waquoit Bay and adjacent estuaries, MA, USA. The salt marshes exhibited high CO2 uptake and low CH4 emission, which did not significantly vary with the nitrogen loading gradient (5–126 kg · ha−1 · year−1) among the salt marshes. Soil temperature was the strongest driver of both fluxes, representing 2 and 4–5 times higher influence than PAR and salinity, respectively. Well water level, soil moisture, and pH did not have a predictive control on the GHG fluxes, although both fluxes were significantly higher during high tides than low tides. The results were leveraged to develop emergent power law‐based parsimonious scaling models to accurately predict the salt marsh GHG fluxes from PAR, soil temperature, and salinity (Nash‐Sutcliffe Efficiency = 0.80–0.91). The scaling models are available as a user‐friendly Excel spreadsheet named Coastal Wetland GHG Model to explore scenarios of GHG fluxes in tidal marshes under a changing climate and environment.

Carbonate system biogeochemistry in a subterranean estuary – Waquoit Bay, USA

Quantifying carbon fluxes associated with submarine groundwater discharge (SGD) remains challenging due to the complex biogeochemistry of the carbonate system in the subterranean estuary (STE). Here we conducted time series measurements of total alkalinity (TAlk) and dissolved inorganic carbon (DIC) in a well-studied coastal aquifer (Waquoit Bay, Massachusetts, USA). Groundwater samples were collected monthly from May 2009 to June 2010 across the freshwater-saltwater mixing zone of the Waquoit Bay (WB) STE. The concentrations of both TAlk and DIC in zero-salinity groundwater were variable, but were lower than those in the bay water (S∼28). DIC underwent slightly non-conservative mixing between low and intermediate salinities while there was an apparent additional DIC source at high salinity (>20) in all seasons. TAlk concentrations exhibited even stronger variations, with evidence of both production and consumption in high salinity zones, and consistent TAlk consumption at intermediate salinity in summer and fall (June–December, 2009). The increases in DIC and TAlk at high salinity were attributed to aerobic respiration and denitrification in WB sediments during bay water recharge of the STE. We infer that the loss of TAlk at intermediate salinity reflects H+ production as reduced compounds (e.g. Fe2+) are oxidized within the STE. In terms of impacts on surface water inorganic carbon budgets, the SGD-derived DIC flux was mainly controlled by seasonal changes in SGD while a combination of TAlk concentration variability and SGD drove the TAlk flux. SGD-derived DIC, aqueous CO2, and H+ fluxes to the bay were ∼40–50% higher in summer vs. in winter, a result of enhanced marine groundwater flux and significant TAlk removal (proton addition) during periods of high seawater intrusion. Furthermore, the SGD-derived DIC flux was consistently greater than TAlk flux regardless of season, indicating that SGD serves to reduce the CO2 buffering capacity of surface water. Our results highlight the importance of seasonality and subsurface biogeochemical processes on the subterranean estuary carbonate system and the resulting impact on SGD-derived TAlk, DIC, aqueous CO2, and H+ fluxes to the coastal ocean.

Sediment dynamics and hydrographic conditions during storm passage, Waquoit Bay, Massachusetts

The impact of storm events on the sediment dynamics of the shallow groundwater fed estuaries of Cape Cod, Massachusetts, USA is little understood. To address this, the objectives of this study are to assess sediment dynamics during storm passage and determine whether shallow back-barrier lagoons like Waquoit Bay have the preservation potential for a sedimentary archive of hurricanes. When setting out in this study, it was unclear whether paleotempestological methods could be applied successfully to cores collected from the landward reaches of shallow estuaries of southern New England. Water level and bottom current data using Arm-and-Float tide gauges and SeaHorse Tilt Current Meters was collected during Tropical Storm Irene (2011) and coupled with storm surge modeling projections to better elucidate storm-induced sediment transport mechanisms. Three sediment cores were collected at the head of Waquoit Bay, located 2.8km from the barrier beach. Grain size analysis of sediment cores was conducted with a laser particle size analyzer at 1cm increments in order to identify coarse grain anomalies, which can act as a storm event proxy. Bayesian statistics were applied to develop age models of two of the cores based on three Pb pollution chronomarkers and 21 continuous flow 14C AMS ages. The results yield variable sediment accumulation rates between 2mm/yr to 10mm/yr, with significantly higher rates occurring in the upper 1m of sediments. Grain size results are highly variable, and contain numerous large amplitude, short duration fluctuations suggesting that during storm passage coarse sand is deposited in the coring site. The sensitivity of the site to both tropical and extratropical storm events, uncertainties in the age model, and the multiple sediment sources and transport pathways limits the utility of using the Waquoit sediments to determine long-term hurricane frequencies. Results nonetheless provide insights into how extreme storm events impact coastal lagoons.

Sediment Nitrogen Fixation: a Call for Re-evaluating Coastal N Budgets

Coastal ocean primary productivity is often limited by nitrogen (N) availability, which is determined by the balance between N sources (e.g., N-fixation, groundwater, river inputs, etc.) and sinks (e.g., denitrification, sediment burial, etc.). Historically, heterotrophic N-fixation in sediments was excluded as a significant source of N in estuarine budgets, based on low, indirectly measured rates (e.g., acetylene reduction assay) and because it was unnecessary to achieve mass balance. Many recent studies using net N2 flux measurements have shown that sediment N-fixation can equal or exceed N2 loss. In an effort to quantify N2 production and consumption simultaneously, we measured N-fixation and denitrification directly in sediment cores from a temperate estuary (Waquoit Bay, MA). N-fixation, dissimilatory nitrate reduction to ammonium, and denitrification occurred simultaneously, and the net N2 flux shifted from uptake (N-fixation) to efflux (denitrification) over the 120-h incubation. Evidence for N-fixation included net 28N2 and 30N2 uptake, 15NH4 + production from 30N2 additions, 15Norganic matter production, and nifH expression. N-fixation from 30N2 was up to eight times higher than potential denitrification. However, N-fixation calculated from 15NO3 − was one half of the measured fixation from 30N2, indicating that 15NO3-isotope labeling calculations may underestimate N-fixation. These results highlight the dynamic nature of sediment N cycling and suggest that quantifying individual processes allows a greater understanding of what net N2 fluxes signify and how that balance varies over time.

Sediment Nitrous Oxide Fluxes Are Dominated by Uptake in a Temperate Estuary

Coastal marine ecosystems are generally considered important sources of nitrous oxide (N2O), a powerful greenhouse gas and ozone depleting substance. To date most studies have focused on the environmental factors controlling N2O production although N2O uptake has been observed in a variety of coastal ecosystems. In this study, we examined sediment fluxes of N2O during two years (2012-2013) in a shallow temperate estuary (Waquoit Bay, MA, USA). Overall sediments were a net N2O sink (-23 ±5.2 nmol m-2 h-1, mean ±SE, significantly less than zero p<0.0001). N2O fluxes were significantly correlated to water column dissolved N2O (% saturation) (p<0.0001), inorganic phosphorus (DIP) (p=0.0017) and nitrogen (DIN) (p=0.0019), as well as to temperature (p=0.0192). Additionally, there was a positive correlation between sediment N2O uptake and both oxygen (O2) and DIP uptake (p=0.0002 and p<0.0001, O2 and DIP sediment uptake, respectively). Results from this study indicate that sediments in shallow coastal ecosystems can be a strong sink of dissolved N2O, and therefore may mitigate N2O efflux to the atmosphere and export to the coastal ocean. Establishing the nature and strength of relationships between environmental conditions and sediment N2O fluxes moves us towards better-constrained models that will improve ecosystem management strategies, N2O budgets, and our ability to predict the response of coastal ecosystems to local and global change. Establishing the nature and strength of relationships between environmental conditions and sediment N2O fluxes moves us towards better-constrained models that will improve ecosystem management strategies, N2O budgets, and our ability to predict the response of coastal ecosystems to local and global change.

Molecular evidence for sediment nitrogen fixation in a temperate New England estuary.

Primary production in coastal waters is generally nitrogen (N) limited with denitrification outpacing nitrogen fixation (N2-fixation). However, recent work suggests that we have potentially underestimated the importance of heterotrophic sediment N2-fixation in marine ecosystems. We used clone libraries to examine transcript diversity of nifH (a gene associated with N2-fixation) in sediments at three sites in a temperate New England estuary (Waquoit Bay, Massachusetts, USA) and compared our results to net sediment N2 fluxes previously measured at these sites. We observed nifH expression at all sites, including a site heavily impacted by anthropogenic N. At this N impacted site, we also observed mean net sediment N2-fixation, linking the geochemical rate measurement with nifH expression. This same site also had the lowest diversity (non-parametric Shannon = 2.75). At the two other sites, we also detected nifH transcripts, however, the mean N2 flux indicated net denitrification. These results suggest that N2-fixation and denitrification co-occur in these sediments. Of the unique sequences in this study, 67% were most closely related to uncultured bacteria from various marine environments, 17% to Cluster III, 15% to Cluster I, and only 1% to Cluster II. These data add to the growing body of literature that sediment heterotrophic N2-fixation, even under high inorganic nitrogen concentrations, may be an important yet overlooked source of N in coastal systems.

Possible cryptic invasion of the Western Pacific toxic population of the hydromedusa Gonionemus vertens (Cnidaria: Hydrozoa) in the Northwestern Atlantic Ocean

We describe a possible cryptic invasion of the toxic Western Pacific hydromedusa Gonionemus vertens (Cnidaria, Hydrozoa, Limnomedusae) in the Northwest Atlantic Ocean. G. vertens was first noticed in Eel Pond in Woods Hole (Cape Cod), Massachusetts in 1894, but nearly disappeared in the 1930s, coincident with a large scale die-off of its preferred eelgrass habitat. During the 1894–1930 period, G. vertens was the object of numerous studies by local scientists, and was not reported as stinging. In contrast, Western Pacific G. vertens are known for their toxic sting symptoms, which include severe pain, respiratory distress, and paralysis. Here, we report new sightings in the northwest Atlantic from the late twentieth century onwards. Sightings are most frequent in Waquoit Bay on the southern-facing shore of Cape Cod, Massachusetts, and on the island of Martha’s Vineyard, Massachusetts, but medusae have also been found in locations ranging from Long Island (New York) to Wellfleet Harbor on the north side of Cape Cod. We also describe reports of stings with symptoms similar to those produced by the toxic Western Pacific strain. The first sting report that we are aware of occurred in 1990 in Waquoit Bay, and stings have since occurred in most of G. vertens’ known Northwest Atlantic locations. It appears likely that the recent sightings associated with toxic stings represent a new, cryptic invasion of the Western Pacific form. These new observations are cause for public health concern, particularly as warmer temperatures associated with climate change may promote G. vertens blooms and thus the likelihood of dangerous human-jellyfish interactions in a populated, tourism-dependent region.

Land use and nitrogen loading in seven estuaries along the southern Gulf of St. Lawrence, Canada

Nitrogen loading from coastal watersheds is a principal factor associated with the decline in eelgrass bed health and cover in estuaries worldwide. We apply the Nitrogen Loading Model (NLM) framework developed in Waquoit Bay, Massachusetts to 7 estuaries in eastern New Brunswick. Using watershed-specific information on human population, wastewater production, atmospheric deposition, and land use in each watershed we estimate annual input of Total Dissolved Nitrogen (TDN) from point and non-point sources. We also estimate flushing time of each estuary using available hydrodynamic and bathymetric data incorporated in a tidal prism model. Finally, we validate the NLM results by testing the link between estimated nitrogen loading, flushing time and nitrogen signals in eelgrass tissue including nitrogen content and stable isotopes. Overall, total nitrogen load (kg TDN yr−1) was strongly dependent on watershed and estuary size, while loading rate per unit watershed area (yield) was linked to watershed population density. Atmospheric deposition was the largest contributor of nitrogen to all estuaries except one, where seafood processing effluent was the greatest source. Stable isotope analysis of eelgrass tissue reflected this distinction, with high δ15N values of 8–10‰ related to high wastewater loading, compared to 2–6.5‰ in the other estuaries that receive proportionally more atmospheric deposition. Tissue nitrogen content was positively related to nitrogen yields and loading rate per volume of estuary, highlighting the influence of variable watershed:estuary size ratio. Multiple regression analysis identified a significant interaction between nitrogen yield and flushing time on eelgrass tissue nitrogen content and isotopes, pointing to the mitigating effect an estuary's quick flushing time can have on the expression of nitrogen enrichment in primary producers. The compilation of new information on nitrogen loading to east Canadian estuaries is a novel contribution from a region where human influences are still at a relatively low level, and hence will add to existing information from cold temperate, mainly forested watershed-estuary environments.

Permeable Reactive Barriers Designed To Mitigate Eutrophication Alter Bacterial Community Composition and Aquifer Redox Conditions.

Permeable reactive barriers (PRBs) consist of a labile carbon source that is positioned to intercept nitrate-laden groundwater to prevent eutrophication. Decomposition of carbon in the PRB drives groundwater anoxic, fostering microbial denitrification. Such PRBs are an ideal habitat to examine microbial community structure under high-nitrate, carbon-replete conditions in coastal aquifers. We examined a PRB installed at the Waquoit Bay National Estuarine Research Reserve in Falmouth, MA. Groundwater within and below the PRB was depleted in oxygen compared to groundwater at sites upgradient and at adjacent reference sites. Nitrate concentrations declined from a high of 25 μM upgradient and adjacent to the barrier to <0.1 μM within the PRB. We analyzed the total and active bacterial communities filtered from groundwater flowing through the PRB using amplicons of 16S rRNA and of the 16S rRNA genes. Analysis of the 16S rRNA genes collected from the PRB showed that the total bacterial community had high relative abundances of bacteria thought to have alternative metabolisms, such as fermentation, including candidate phyla OD1, OP3, TM7, and GN02. In contrast, the active bacteria had lower abundances of many of these bacteria, suggesting that the bacterial taxa that differentiate the PRB groundwater community were not actively growing. Among the environmental variables analyzed, dissolved oxygen concentration explained the largest proportion of total community structure. There was, however, no significant correlation between measured environmental parameters and the active microbial community, suggesting that controls on the active portion may differ from the community as a whole.

Oxygen metabolism and pH in coastal ecosystems: Eddy Covariance Hydrogen ion and Oxygen Exchange System (ECHOES)

An aquatic eddy covariance (EC) system was developed to measure the exchange of oxygen (O2) and hydrogen ions (H+) across the sediment-water interface. The system uses O2 optodes and a newly developed micro-flow cell H+ ion selective field effect transistor; these sensors displayed sufficient precision and rapid enough response times to measure concentration changes associated with turbulent exchange. Discrete samples of total alkalinity and dissolved inorganic carbon were used to determine the background carbonate chemistry of the water column and relate the O2 and H+ fluxes to benthic processes. The ECHOES system was deployed in a eutrophic estuary (Waquoit Bay), and revealed that the benthos was a sink for acidity during the day and a source of acidity during the night, with H+ and O2 fluxes of ± 0.0001 and ± 10 mmol m−2 h−1, respectively. H+ and O2 fluxes were also determined using benthic flux chambers, for comparison with the EC rates. Chamber fluxes determined in 0.25 h intervals co-varied with EC fluxes but were ∼ 4 times lower in magnitude. This difference was likely due to suppressed pore-water advection in the chambers and changes in the chemistry of the enclosed chamber overlying water. The individual H+ and O2 fluxes were highly correlated in each dataset (EC and chambers), and both methods yielded H+ fluxes that could not be explained by O2 metabolism alone. The ECHOES system provides a new tool for determining the influence of benthic biogeochemical cycling on coastal ocean acidification and carbon cycling.