Estuaries and Coasts最新文献

Tidal marsh plant communities in the Pacific Northwest are characterized by tall, perennial graminoids (TPGs), which provide forage for herbivores such as Canada geese. Excessive grazing by Canada geese leads to loss of marsh habitat, and removal of grazing pressure is required for the vegetation to recover. Grazing exclosures (fences) are used to allow time and space for vegetation to recover following intensive herbivory; however, their effects on native plant community recovery has not been tested. Generalized linear models were used to compare TPG abundance in aboveground vegetation and surface seed banks in 1-year-old and 10-year-old exclosures at Nanaimo River Estuary (NRE) and Little Qualicum River Estuary (LQRE), respectively, to areas of the marshes that had no known history of grazing (undisturbed) and areas still actively grazed (grubbed). Compared to undisturbed sites, grubbed sites had 187.3% less mean TPG vegetation cover and 190.7% lower proportion of TPG seeds. The 1-year-old exclosures at NRE had 105.0% less mean TPG vegetation cover and 193.2% lower proportion of TPG seeds. The 10-year-old exclosures at LQRE had 7.0% greater mean TPG cover and 55.7% greater proportion of TPG seed than all undisturbed sites; however, these exclosures had 110.0% greater mean relative abundance of non-native TPGs than undisturbed sites. These results indicate vegetation may not recover towards comparable historic conditions through grazing exclusion alone, and that active restoration methods may be required following intensive grazing, especially in estuaries where the vegetation community and surface seed bank has a high abundance of non-native, invasive species.

Rates of ecosystem metabolic properties, such as plankton community respiration, can be used as an assessment of the eutrophication state of a waterbody and are the primary biogeochemical rates causing oxygen depletion in coastal waters. However, given the additional labor involved in measuring biogeochemical rate processes, few monitoring programs regularly measure these properties, and thus, few long-term monitoring records of plankton respiration exist. An 8-year, biweekly plankton community respiration rate time series was analyzed as part of a monitoring program situated in the lower Patuxent River estuary, a tributary of Chesapeake Bay. We found that particulate nutrients (nitrogen and phosphorus) were the most highly correlated covariates with respiration rate. Additionally, statistical and kinetic models including variables both water temperature and particulate nitrogen were able to explain 74% of the variability in respiration. Over the long-term record, both particulate nutrients and respiration rate were elevated when measured at higher tides. Separate measurements of respiration rate during 10 consecutive days and during high and low tide on three separate days also support the enhancement of respiration with high tide. The enhancement was likely due to the import of particulate nutrients from the highly productive mid-bay region. This analysis of the longest consistently measured community respiration rate dataset in Chesapeake Bay has implications for how to interpret long-term records of measurements made at fixed locations in estuaries.

Recent large-scale spatial products have been developed to assess wetland position in the tidal frame, but nationwide comparisons and validations are missing for these products. Wetland position within the tidal frame is a commonly used characteristic to compare wetlands across biogeomorphic gradients and factors heavily into wetland vulnerability models. We utilize a dataset of 365 surface elevation table stations across the conterminous USA containing ground-surveyed tidal datum and elevation data to validate two gridded, conterminous USA–wide relative tidal elevation products. We identified substantial differences between our ground-surveyed dataset and the gridded products, with the Gulf coast exhibiting the greatest error (p < 0.0001, n = 140). Error in relative tidal elevation products varied by coast, tidal range, and latitude. These differences in errors indicate that gridded relative tidal elevation products may be more accurate in coastal wetlands with larger tidal ranges (> 30 cm) and are less accurate in freshwater wetlands near the coast. This paper makes advances in understanding why relative tidal elevation differences occur among national datasets and identifies areas of future work that could support more robust vulnerability models.

The common marsh snail Melampus bidentatus is an omnivore-detritivore that is typically restricted to the upper marsh zone in salt marshes of southern New England and further south. However, in Maritime Canadian salt marshes (specifically in the Northumberland Strait), M. bidentatus occurs throughout the high and low marsh zones (mean summer densities ~ 50 individuals m⁻²). This study determined the within-marsh distribution of M. bidentatus near its northern range limit and investigated the mechanisms responsible for this distribution. Intensive spatial and temporal sampling in 2015–2016 confirmed that all stages (adults, juveniles, and egg masses) occurred throughout the salt marsh. Investigations of snail survival (using tethering assays) and movement (using mark-recapture trials) indicated that mortality was very low and independent of marsh zone, and movement was moderate, random, and circuitous, generally maintaining snails in local areas. Thus, lack of differential survival and movement between marsh zones support an unrestricted distribution. This wide spatial distribution of M. bidentatus within salt marshes in north temperate latitudes is likely due to the species’ high physiological tolerances, absence of competition from other gastropod omnivores-detritivores, and low predation pressure in the low marsh zone. Given these findings, further research on the snails’ role in, for example, trophic dynamics would provide further insights as to latitudinal differences in the ecology of resident salt marsh fauna.

Up to 85% of shellfish reefs have been lost worldwide, resulting in declining ecosystem services, and increasing restoration demand. However, more information regarding the conditions which maximise oyster settlement and growth is required to optimise restoration. We deployed oyster settlement tiles at 21 intertidal sites throughout Moreton Bay, Australia; a region where > 96% of rock oyster reefs are lost and demand for restoration is high. We quantified effects of variables describing the spatial (from GIS), local habitat (using quadrats and water quality measures), and oyster predator (using underwater videography) characteristics of sites on oyster density and size on tiles. Oyster density was highest at sites with intermediate predator abundance and temperature, highest nearby invertebrate cover, and low and high values of turbidity and nearby rock and algae cover. Conversely, oyster size was highest at sites with intermediate predator density, higher fish species richness and turbidity, and lowest temperatures. Together, this showed that optimal restoration requires sites with 22 to 23 °C average water temperatures, between 10 and 15 oyster predators, and either low (< 2 NTU) or high (> 6 NTU) turbidity levels. Notably, we observed multiple peaks for several variables, suggesting the potential presence of multiple cryptic oyster species on settlement tiles. We found that oysters shared preferred environmental conditions with polychaetes, coralline algae, and tunicates, and were more prevalent and abundant at sites with lower turf algae, barnacle, and mussel cover. Identifying environmental variables influencing oyster population distribution, settlement, and growth can guide the selection and approach of oyster restoration sites.

The Atlantic sturgeon Acipenser oxyrinchus oxyrinchus is an anadromous species with a wide range along the Atlantic coast of North America. Because of overharvest and a variety of other anthropogenic stressors, the numbers of estuaries that currently host successful natural reproduction and the abundances of extant populations are depressed compared to historic numbers, resulting in its listing under the US Endangered Species Act as five Distinct Population Segments (DPS). Atlantic sturgeon are vulnerable to stressors not only within their natal estuaries but also at distant locales because of the highly migratory behavior of their subadult and adult life stages. In this study, we used our previously derived microsatellite DNA catalogue of 13 reference spawning populations and Individual-Based Assignment testing to determine the origin of 202 adult Atlantic sturgeon that were collected from the lower Altamaha River during spring, several months prior to their fall upriver spawning. We found that approximately one third (37%) of these adults assigned to populations other than the Altamaha, almost all (96%) to other populations within the South Atlantic DPS, a finding consistent with our earlier acoustic telemetry results. These results have management implications, including the likelihood of recolonization of depleted populations in the South Atlantic DPS and the compilation of reference population genetic profiles used in population delineation and mixed-stock analyses.

Previous work identified hurricane deposits in the back-barrier lagoon of Laguna Playa Grande (LPG) in Vieques, Puerto Rico, dating back over 5000 years, with periods of increased storm-induced overwash activity attributed to variability in regional hurricane climatology. In 2017, Hurricane Maria made direct landfall on LPG just below category 5 strength, providing the opportunity to revisit the site to improve upon interpretations of storm-induced deposition. Maria caused widespread wave-induced overwash of the barrier beach and extensive mangrove mortality with roughly a 40% reduction in vegetative cover along the barrier. Sediment trapping and overwash deposition occurred within ripped up and broken mangrove debris during the hurricane, which prevented sediments from being carried further landward into the lagoon. Thus, no measurable overwash deposition was observed in the larger, western portion of the lagoon where previous hurricane reconstructions are derived. Significant overwash deposition (1–27 cm thick) was observed in the smaller, eastern portion of the lagoon where human cut paths through the mangroves allowed for unobstructed flow. Early historical photos support 53% reduced vegetation in 1936 followed by revegetation towards present day that prevented sandy overwash deposits from Maria in the western side, explaining the discrepancy between previously observed hurricane overwash record compared to restricted deposition solely to locations with modern footpaths for Maria. Hurricanes occurring during the recovery-revegetation phase of such storms likely result in greater overwash deposition in back-barrier lagoons due to less barrier vegetation relative to periods with robust mangrove vegetation cover. Results highlight the important role of fringing mangrove forests in flood mitigation, and the vulnerability of back-barrier environments to enhanced flooding following both anthropogenic and event-driven vegetation loss.

The thematic issue entitled, “Current Advances in Coastal Wetland Elevation Dynamics,” draws on topics from two special sessions at the CERF 2021 conference plus additional recent research describing scientific insights gained from the Surface Elevation Table–Marker Horizon (SET–MT) method and its application across the globe to quantify and understand subsurface process influences on wetland elevation change and wetland responses to sea-level rise. The findings group articles within each of five thematic topics. (1) A 30-year retrospective on the scientific insights gained on surface and shallow subsurface process dynamics. (2) Investigations of the subsurface soil process influences on wetland elevation. (3) How the scientific community applies the SET–MH method to quantify and understand wetland responses to RSLR and other environmental drivers such as altered hydrology and sediment supply. (4) How SET–MH data are used in long-term monitoring networks at different geographic scales. (5) Pairing the SET-MH method with (a) survey techniques to increase lateral coverage of wetland elevation trends and (b) geodetic measurements to increase vertical coverage of vertical land motion.

Oxygen depletion in coastal waters is increasing globally due primarily to eutrophication and warming. Hypoxia responses to nutrient loading and climate change have been extensively studied in large systems like the Chesapeake Bay and the Baltic Sea, while fewer studies have investigated smaller, shallower hypoxic zones. Thus, an improved understanding of the interactions of eutrophication and warming on hypoxia expansion (or reduction) in the wide variety of different estuarine environments is needed. We examined interannual controls on oxygen depletion in the Patuxent River estuary, a eutrophic sub-estuary of Chesapeake Bay where seasonal hypoxia develops annually. We conducted a spatial and temporal analysis of dissolved oxygen (DO) trends, timing, and several metrics of depletion over a long-term record (1985–2021). We found an internally generated hypoxic zone that initiates in the middle estuary, spreading upstream and downstream as the summer progresses, and that hypoxic volume days (HVD) have been increasing (0.11 per year, p = 0.03) over the record despite reduced watershed nitrogen loads and stable phosphorus loads. River flow and temperature have been increasing and are major drivers of increased HVD, with river flow explaining 40% of the interannual variation in HVD (temperature has increased 0.03 and 0.06 °C per year in summer and fall, respectively). Apparent oxygen utilization (AOU) is increasing in bottom waters in the fall, consistent with increasing trends of both water temperature and stratification strength. HVD was negatively related (r² = 0.34, slope = −0.59*HVD) to the biomass of benthic invertebrates in the middle region of the estuary, suggesting that benthic forage for higher trophic levels will be limited by sustained hypoxia. These results indicate that current and future climate variability plays an important role in regulating oxygen depletion in the Patuxent River estuary, which reinforces the need to factor climate change into strategies for the restoration and management of estuaries.

Coastal ecosystems are recognized as important carbon reservoirs. However, assessments of coastal carbon dioxide (CO₂) fluxes often neglect unvegetated tidal flats, particularly in peri-urban areas. This study investigated the gross primary production (GPP), net primary production (NPP), and total respiration (TR) of three tidal flats in Hong Kong, one of the largest cities in South China, during both summer and winter seasons to understand their CO₂ fluxes. Results showed that GPP of three tidal flats was significantly higher in winter than in summer. However, no significant seasonal variations in TR were observed among the tidal flats. Structural equation modelling was used to examine the drivers of CO₂ fluxes in the three tidal flats. The model showed that temperature and microphytobenthos abundance were identified as positive drivers of GPP, while sediment mud content had a positive effect on TR. The estimated daily NPP of these tidal flats ranged from -0.853 to 0.112 g C m⁻² d⁻¹, which is lower than the mean value reported for global vegetated coastal wetlands. Despite some seasonal and spatial variations, those peri-urban tidal flats may be considered as weak CO₂ sources rather than CO₂ sinks.