Tidal Freshwater Research Articles

Forcing uncertainty and salinity response to dredging in a tidal freshwater river

ABSTRACT This study evaluates the salinity response to dredging under different forcing regimes for a 75-kilometer segment of the flood-prone Vermilion River located in coastal Louisiana, USA. The Vermilion is a tidal freshwater river affected by baseflow regulation, rapid urbanization, and hydromodification. This river also serves as major freshwater resource for the region. An efficient one-dimensional model calibrated previously for stage and water temperature is used to analyse the salinity impacts due to a large-scale flood control dredging. The analysis is based on 200 alternative scenarios based on combinations of uncertain key forcing variables for a critical 13-day intrusion period. The analysis reveals a nonlinear effect on mean salinities and position of the brackish water limit as a function of uncertain forcing variables. Dredging also increases the variability of salinity encroachment effects due to uncertainty in future forcing conditions (e.g. relative sea level rise, baseflow diversion volumes, and salinities at the river mouth). The robust analysis presented here provides a foundation for future model-based assessments of under-studied tidal freshwater rivers and provides key insights for coastal management and sustainability efforts in general.

Assessment of Methods to Control Invasive Reed Canarygrass (Phalaris arundinacea) in Tidal Freshwater Wetlands

Reed canarygrass (Phalaris arundinacea) is invasive in temperate freshwater wetlands throughout the United States and Canada and presents challenges to restoring tidal freshwater wetlands. Methods for the prevention or elimination of reed canarygrass in palustrine wetlands are generally well established, typically involving herbicide application, mechanical treatments, prolonged inundation, or establishment of competitive plant species. These methods are often not suitable for the unique conditions in tidal wetlands and alternative strategies remain poorly understood. Prolonging inundation of tidal wetlands requires a loss of habitat forming processes, connectivity, and other functions. Treatments such as mowing, discing, or fire are not feasible in the perpetually wet conditions of tidal wetlands. Restoration practitioners aiming to design self-sustaining wetlands in the lower Columbia River estuary and the U.S. Pacific Coast have found that reed canarygrass is widespread and quick to establish post-restoration creating a management burden and impacting restoration goals. Here we report the results of a comprehensive effort to develop methods for control in tidal wetlands through systematic review of the scientific literature, interviews with experienced practitioners, and field observations at nine Pacific Northwest sites. The review framework evaluated key environmental conditions affecting reed canarygrass, control methods, and practical considerations. Findings support an integrated long-term control strategy at the largest possible scale to establish effective and self-sustaining control. Appropriate and practical strategies for tidal freshwater wetlands include implementing control pre-restoration to suppress existing populations; topographic modification such as scrape-downs and mounds to support competitiveness of desired vegetation communities; seeding or planting strong native competitors; limiting nutrient availability; and periodic, targeted control to limit reinvasion. These strategies are supported by the study, but long-term results are generally not available. Formal field experiments are recommended by the authors to better evaluate factors that influence reed canarygrass control in tidal freshwater wetlands.

Influence of Invasive Submerged Aquatic Vegetation (E. densa) on Currents and Sediment Transport in a Freshwater Tidal System

AbstractWe present a field study combining measurements of vegetation density, vegetative drag, and reduction of suspended‐sediment concentration (SSC) within patches of the invasive submerged aquatic plant Egeria densa. Our study was motivated by concern that sediment trapping by E. densa, which has proliferated in the Sacramento–San Joaquin Delta, is impacting marsh accretion and reducing turbidity. In the freshwater tidal Delta, E. densa occupies shallow regions frequently along channel margins. We investigated two sites: Lindsey Slough, a muddy low‐energy backwater, and the lower Mokelumne River, with stronger currents and sandy bed sediments. At the two sites, biomass density, frontal area, and areal density of the submerged aquatic vegetation (SAV) were similar. Current attenuation within E. densa exceeded 90% and the vegetative drag coefficient followed , where is stem Reynolds number. The SAV reduced SSC by an average of 18% in Lindsey Slough. At the Mokelumne River the reduction ranged 0%–40%, with greatest trapping when discharge and SSC were elevated. This depletion of SSC decreases the transport of sediment to marshes by the same percentage, as the rising tide must pass through fringing SAV before reaching marshes. Sediment trapping in E. densa in the Delta is limited by low flux through the canopy and low settling velocity of suspended sediment (mostly flocculated mud). Sediment trapping by SAV has the potential to reduce channel SSC, but the magnitude and sign of the effect can vary with local factors including vegetative coverage and the depositional or erosional nature of the setting.

Belowground productivity varies by assessment technique, vegetation type, and nutrient availability in tidal freshwater forested wetlands transitioning to marsh.

Wetlands along upper estuaries are characterized by dynamic transitions between forested and herbaceous communities (marsh) as salinity, hydroperiod, and nutrients change. The importance of belowground net primary productivity (BNPP) associated with fine and coarse root growth also changes but remains the dominant component of overall productivity in these important blue carbon wetlands. Appropriate BNPP assessment techniques to use in various tidal wetlands are not well-defined, and could make a difference in BNPP estimation. We hypothesized that different BNPP techniques applied among tidal wetlands differ in estimation of BNPP and possibly also correlate differently with porewater nutrient concentrations. We compare 6-month and 12-month root ingrowth, serial soil coring techniques utilizing two different calculations, and a mass balance approach (TBCA, Total Belowground Carbon Allocation) among four tidal wetland types along each of two river systems transitioning from freshwater forest to marsh. Median values of BNPP were 266 to 2946 g/m2/year among all techniques used, with lower BNPP estimation from root ingrowth cores and TBCA (266–416 g/m2/year), and higher BNPP estimation from serial coring of standing crop root biomass (using Smalley and Max-Min calculation methods) (2336–2946 g/m2/year). Root turnover (or longevity) to a soil depth of 30 cm was 2.2/year (1.3 years), 2.7/year (1.1 years), 4.5/year (0.9 years), and 1.2/year (2.6 years), respectively, for Upper Forest, Middle Forest, Lower Forest, and Marsh. Marsh had greater root biomass and BNPP, with slower root turnover (greater root longevity) versus forested wetlands. Soil porewater concentrations of NH3 and reactive phosphorus stimulated BNPP in the marsh when assessed with short-deployment BNPP techniques, indicating that pulses of mineralized nutrients may stimulate BNPP to facilitate marsh replacement of forested wetlands. Overall, ingrowth techniques appeared to represent forested wetland BNPP adequately, while serial coring may be necessary to represent herbaceous plant BNPP from rhizomes as marshes replace forested wetlands.

Genomic data reveal the biogeographical and demographic history of Ammospiza sparrows in northeast tidal marshes

AbstractAimShaped by climate change and sea‐level rise, tidal salt marshes represent ephemeral systems that are home to only a few species. The dynamic ecological histories of these habitats, however, render it challenging to reconstruct the complete biogeographical histories of their endemic taxa. To better understand the evolutionary history of tidal marsh endemic sparrows, we employ genomic data to evaluate the timing and direction of tidal marsh colonization events and leverage these data to test a series of models describing the biogeographical history of our study taxa.LocationNorth America.TaxonAmmospiza Sparrows.MethodsWe sampled 54 individuals from the Ammospiza clade from freshwater and saltwater habitats. We sequenced whole genomes and generated a dataset containing 21 million SNPs. Detailed phylogenomic analyses were conducted to identify relationships between tidal marsh and freshwater species. These phylogenies were then used to date divergence times and reconstruct the biogeographical history of the clade as well as identify historic signals of introgression.ResultsPhylogenies based on several million SNPs supported well‐resolved clades that correspond to all previous species designations. Demographic modelling within A. nelsoni provided further resolution into the subspecies topology. Phylogenetic and biogeographical reconstructions support a series of saltwater to freshwater colonization events, with some endemic taxa exhibiting associations with tidal marsh habitat over longer evolutionary time‐scales and some habitat transitions occurring as recently as 5,000 years ago.Main ConclusionsBiogeographical and phylogenomic reconstructions support an original freshwater origin of the Ammospiza sparrows currently inhabiting tidal marshes in North America. We also found strong evidence for a saltwater to freshwater transition in A. n. subvirgatus as opposed to the long hypothesized freshwater origin of this group. We conclude that the increased resolution from genomic data paired with an integrative framework of phylogenomic, demographic and biogeographical reconstructions is important for resolving evolutionary histories in complex and ephemeral environments.

Contributions of Organic and Mineral Matter to Vertical Accretion in Tidal Wetlands across a Chesapeake Bay Subestuary

Persistence of tidal wetlands under conditions of sea level rise depends on vertical accretion of organic and inorganic matter, which vary in their relative abundance across estuarine gradients. We examined the relative contribution of organic and inorganic matter to vertical soil accretion using lead-210 (210Pb) dating of soil cores collected in tidal wetlands spanning a tidal freshwater to brackish gradient across a Chesapeake Bay subestuary. Only 8 out of the 15 subsites had accretion rates higher than relative sea level rise for the area, with the lowest rates of accretion found in oligohaline marshes in the middle of the subestuary. The mass accumulation of organic and inorganic matter was similar and related (R2 = 0.37). However, owing to its lower density, organic matter contributed 1.5–3 times more toward vertical accretion than inorganic matter. Furthermore, water/porespace associated with organic matter accounted for 82%–94% of the total vertical accretion. These findings demonstrate the key role of organic matter in the persistence of coastal wetlands with low mineral sediment supply, particularly mid-estuary oligohaline marshes.

Seasonal Changes in the Drivers of Water Physico-Chemistry Variability of a Small Freshwater Tidal River

Where rivers meet the sea, tides can exert a physical and chemical influence on the lower reaches of a river. How tidal dynamics in these tidal river reaches interact with upstream hydrological drivers such as storm rainfall, which ultimately determines the quantity and composition of material transferred from watersheds to estuaries, is currently unknown. We monitored a small freshwater tidal river in the Pacific Northwest, United States in high resolution over 1 year to evaluate the relative importance of tides vs. upstream hydrological flows (i.e., base flow and precipitation events) on basic physico-chemical parameters (pH, dissolved oxygen, turbidity, specific conductivity, and temperature), and how these interactions relate to the downstream estuary. Tidal variability and diurnal cycles (i.e., solar radiation) dominated water physico-chemical variability in the summer, but the influence of these drivers was overshadowed by storm-driven sharp pulses in river physico-chemistry during the remainder of the year. Within such events, we found incidences of counterclockwise hysteresis of pH, counterclockwise hysteresis of dissolved oxygen, and clockwise hysteresis of turbidity, although systematic trends were not observed across events. The dominance of storm rainfall in the river’s physico-chemistry dynamics, and similar pulses of decreased pH observed in adjacent estuarine waters, suggest that the linkage between tidal streams and the broader system is variable throughout the year. High-frequency monitoring of tidal river biogeochemistry is therefore crucial to enable the assessment of how the relative strength of these drivers may change with future sea level rise and altered precipitation patterns to modulate biogeochemical dynamics across the land-ocean-atmosphere continuum.

Sediment Accumulation, Elevation Change, and the Vulnerability of Tidal Marshes in the Delaware Estuary and Barnegat Bay to Accelerated Sea Level Rise

Tidal marshes are highly valued habitats, yet are vulnerable to loss from both anthropogenic and natural disturbances including sea-level rise (SLR). Many tidal marshes have kept pace with SLR over the last century; on average, however, recent escalations in SLR increase the vulnerability of marshes to submergence. Relative sea-level rise near our study sites in the Mid-Atlantic U.S. averaged 4.34 mm year−1 over the last 50 years, yet over the last 19 years, relative sea-level rise averaged 6.25 mm year−1 and the rise in high tide water levels averaged 8.13 mm year−1. We compared these rates of water rise to rates of marsh surface elevation change using surface elevation tables in ten tidal marshes—three tidal freshwater and four saline marshes in the Delaware Estuary and three salt marshes in Barnegat Bay, NJ, USA. We also examined the effects of marsh type and geomorphic setting on rates of elevation change, surface accretion, and subsurface change as well as the influence of marsh elevation, distance from a channel, and tidal range (n = 3 sites per marsh). Surface elevation change measured over the last 4 to 9 years averaged less than 6 mm year−1 in nine out of ten of the study stations, less than rates of relative SLR. Tidal freshwater marshes in the Delaware Estuary had greater rates of surface accretion and elevation change than salt marshes in Barnegat Bay. Marshes sitting lower in the tidal frame and experiencing higher tidal ranges tended to have higher surface accretion rates, but shallow subsidence had a stronger influence on these elevation change rates. We estimated time to submergence (i.e., lifespan) for using rates of marsh elevation change, a SLR rate of 10 mm year−1, and thresholds for conversion to open water using geospatial datasets. The calculated time to submergence for the majority of marshes was 60 to 80 years with some predicted to submerge in as few as 5 years. These data suggest that in order to keep pace with accelerating SLR, surface accretion in many of these marshes will have to increase at a rate that surpasses shallow subsidence (1–7 mm year−1).

Using Published Information to Predict Consumption by Northern Snakehead in Maryland

AbstractThe Northern Snakehead Channa argus, a species originating from Asia, was illegally introduced into ponds of Maryland in 2002. Later discovered in tidal freshwater of the Potomac River, the species has become successfully established in many Maryland rivers. The magnitude of impact on preferred prey of Northern Snakehead in North American ecosystems has not been widely studied, leaving unresolved whether there are deleterious effects owed to introduction. To add insight into potential impacts of Northern Snakeheads, we calibrated a published, temperature‐dependent maximum consumption model using field data and informed its results with diet and prey preference data to compare consumption levels among prey species. The total annual maximum consumption estimated from the model for a population of 600 Northern Snakeheads, which is an abundance approximated from published population sizes in streams of the Potomac basin, amounted to consumption of 2,189 kg of fish for the population per year. We found no evidence of strong prey preferences and partitioned this consumption to relative proportions of some fishes preyed on by Northern Snakehead as 661 kg/year of sunfishes Lepomis spp., 522 kg/year of Yellow Perch Perca flavescens, 332 kg/year of Goldfish Carassius auratus, 250 kg/year of White Perch Morone americana, and 174 kg/year of Banded Killifish Fundulus diaphanus. Some of these coastal fishes comprise important recreational and commercial fisheries. The maximum consumption estimates modeled here are greater than would be observed naturally, and whether predation affects persistence of the prey species in the ecosystem will depend upon the resiliency of the prey population and its current population size, which are unknown. We conclude that, as indicated by earlier risk assessments, the Northern Snakehead is an important predator in Maryland ecosystems because it is opportunistic and is capable of consuming significant biomasses of several recreationally and commercially important fish species.

Impact of Wetlands Loss and Migration, Induced by Climate Change, on Chesapeake Bay DO Standards

AbstractA predictive wetlands module is added to an existing eutrophication model of Chesapeake Bay in order to evaluate the impact of wetlands loss and migration on dissolved oxygen (DO) standards. Loss and migration are expected due to increases in sea level associated with climate change. The module calculates fluxes of carbon, nitrogen, and phosphorus between wetlands and the adjacent water column. Calculations are performed for a range of sea‐level increments up to 1 m. Wetlands areas, as a function of sea level, are obtained from an existing, independent, model applied to Chesapeake Bay. The results indicate two risks to DO standards. The first results from wetlands loss and simultaneous reductions in nutrient removal and burial by wetlands. Reduction in burial is the equivalent of a nutrient load increase and produces diminished DO in deep water and deep channel portions of the Bay. The second risk results from wetlands migration into upland areas adjoining shallow embayments and tidal fresh waters of the Bay. An increase in wetlands area in these regions may result in diminished DO concentration in adjacent open water due to direct wetlands respiration.

Estimates of Food Consumption Rates for Invasive Blue Catfish

AbstractAs a prolific invasive species, Blue Catfish Ictalurus furcatus threaten native organisms in numerous estuarine and tidal freshwaters along the Atlantic coast of the United States. However, no published estimates of consumption rates are available for Blue Catfish in the scientific literature. This information is critical for development of bioenergetics models or estimation of population‐level impacts on native species. Using a combination of field and laboratory studies, we provide the first estimates of daily ration, maximum daily ration, and consumption to biomass ratios for Blue Catfish populations. Ad libitum feeding trials conducted in our laboratory reveal that maximum daily ration in Blue Catfish varies by prey type, temperature, and fish size, with maximal feeding occurring in medium‐sized Blue Catfish (500–600 mm total length) and at temperatures ≥15°C. Furthermore, estimates of daily ration were higher for fish prey (Gizzard Shad Dorosoma cepedianum) than for crustacean prey (blue crab Callinectes sapidus). Diel feeding chronologies based on field‐collected diet samples from 1,226 Blue Catfish demonstrated river‐specific variability in daily ration and maximum daily ration. Blue Catfish daily ration ranged between 2.27% and 5.22% bodyweight per 24 h, while maximum daily ration ranges between 8.56% and 9.37% bodyweight per 24 h. Estimates of consumption to biomass ratios varied by river and Blue Catfish size groupings but range between 2.42 and 3.39, which is similar to other benthic omnivores. This research will inform the assessment of predatory impacts of invasive Blue Catfish in the Chesapeake Bay and beyond as it will enable researchers to estimate predatory impacts through the coupling of population models, food habit information, and consumption rate information (current study).

Population differentiation in the leaf shape and growth form of Cardamine scutata Thunb. in tidal and non‐tidal habitats

AbstractRiparian habitats are associated with diverse hydrological conditions that may enhance population differentiation in species inhabiting areas close to water. Cardamine scutata Thunb. is a widespread riparian herb that is typically characterized by compound leaves. On the Nohbi Plain in central Honshu, Japan, it has, however, been reported that plants of C. scutata occurring in tidal wetlands along the lower reaches of large rivers have simpler leaves than those inhabiting areas further upstream. In this study, we quantitatively describe environmental conditions, leaf shape and other phenotypic traits of populations in tidal and non‐tidal habitats. Measurements of the electrical conductivity of interstitial water and fluctuations in water levels indicated that tidal populations of C. scutata occurred in typical tidal freshwater wetlands. We found that tidal and non‐tidal populations are characterized by distinct leaf shapes, simple and compound, respectively, under both field and common growth conditions. These observations indicate that differences in leaf shape reflect a genetic differentiation between populations of the same species inhabiting distinct habitats. In addition to leaf shape, we found several phenotypic differences relating to growth form, with plants in tidal populations having elongated hollowed stems and elongated inflorescences. We conclude that tidal populations of C. scutata are a discrete ecotype inhabiting freshwater tidal wetlands, presumably derived either through adaptation or genetic drift.

Onset of runaway fragmentation of salt marshes

Summary Salt marshes are valuable but vulnerable coastal ecosystems that adapt to relative sea level rise (RSLR) by accumulating organic matter and inorganic sediment. The natural limit of these processes defines a threshold rate of RSLR beyond which marshes drown, resulting in ponding and conversion to open waters. We develop a simplified formulation for sediment transport across marshes to show that pond formation leads to runaway marsh fragmentation, a process characterized by a self-similar hierarchy of pond sizes with power-law distributions. We find the threshold for marsh fragmentation scales primarily with tidal range and that sediment supply is only relevant where tides are sufficient to transport sediment to the marsh interior. Thus the RSLR threshold is controlled by organic accretion in microtidal marshes regardless of the suspended sediment concentration at the marsh edge. This explains the observed fragmentation of microtidal marshes and suggests a tipping point for widespread marsh loss.

Nitrogen Dynamics of Inundated Sediments in an Emerging Coastal Deltaic Floodplain in Mississippi River Delta Using Isotope Pairing Technique to Test Response to Nitrate Enrichment and Sediment Organic Matter

Nitrate (NO3–) enrichment in rivers over the last four decades has potentially shifted how coastal ecosystems process nitrogen (N). Shifts in N dynamics may be particularly significant in coastal deltaic floodplains when sediments are inundated during river flood stage as this may change the fate of NO3– transported to the coastal ocean. We evaluated the relative importance of denitrification, dissimilative nitrate reduction to ammonium (DNRA), and anaerobic ammonium oxidation (anammox) in intact sediment cores of Wax Lake Delta (WLD) using continuous flow-through system. We manipulated this experimental system with two concentrations of riverine NO3– (lower concentration at 5 μM and ambient concentration at 100 μM) to test how nitrate-enriched waters may modify N cycling in coastal deltaic floodplains. Inundated sediments in a coastal deltaic floodplain removed bio-reactive N as a function of sediment organic matter (SOM) concentrations, indicating how N dynamics vary as a result of deltaic succession. Direct denitrification was the dominant N pathway in inundated sediments in WLD, which was several times greater than coupled nitrification-denitrification, DNRA, and anammox. Gross denitrification (direct denitrification + coupled nitrification-denitrification) rates generally increased with SOM concentrations and ranged from 4 to 12 μmol N m–2 h–1 under lower NO3– enrichment (5 μM) and 68 to 276 μmol N m–2 h–1 under higher NO3– enrichment (100 μM). Most of these changes in N fluxes with SOM and NO3– enrichment resulted from the increase in direct denitrification rates rather than coupled nitrification-denitrification rates. DNRA rates varied from 0 to 65 μmol N m–2 h–1, and the relative significance of DNRA increased as a percentage of total NO3– reduction (%DNRA) with increasing ratio of organic carbon to NO3– concentrations (OC/NO3–). Anammox rates increased among sites as SOM increased, but rates were lower from 0.0 to 38 μmol N m–2 h–1. The dominance of direct denitrification and increased anammox rates with SOM concentrations indicate that dynamic deltaic floodplains can permanently remove bio-reactive N in the proximal zone of river deposition of tidal freshwater wetlands.

Threat Posed by Future Sea-Level Rise to Freshwater Resources in the Upper Pearl River Estuary

The degradation of densely populated river delta environments due to the accelerating rise in sea level can affect the availability of freshwater for municipal supplies, irrigation, and industrial use. A fully calibrated three-dimensional numerical model is used in this study to evaluate the threat posed by the sea-level rise, which predicted to occur by 2100, to freshwater resources in the upper tributaries of Pearl River Estuary. The results indicate that both the intensity and duration of dry-season saltwater intrusion greatly increase as the sea level rises, making the water at drinking-water intake stations for the four waterworks no longer suitable for municipal supply. Flow modulation is performed to identify the threshold at which saltwater intrusion could be effectively suppressed in response to both sea-level rise and dry season hydrodynamics. The number of days for which water meets the drinking-water standard decreases as the sea level rises, but increases with increased river flow. The combined effect of future drought and sea-level rise would further limit the availability of freshwater in the upper tributaries. Stronger upstream salinity transport during flood tide are found in the sea-level rise case. The increased flood tidal salinity transport would have great impact on the tidal freshwater wetlands.

Long-term Salinity, Hydrology, and Forested Wetlands Along a Tidal Freshwater Gradient

Tidal freshwater forested wetlands (TFFWs) commonly occur along coastal rivers; however, sea level rise and changes to river discharge may impact these wetlands. Information that characterizes the hydrology and salinity regime of the TFFW zone is needed to assess risk and predict future viability. A combination of field data and modeling were used to characterize TFFW hydrology, salinity, and vegetation along two distributaries (the East River and St. Marks River) of the Apalachicola River in west Florida, USA. Six gaging stations were established (three per river) roughly equidistant along the TFFW tidal gradient to monitor salinity and water levels at the river-wetland interface. Eighteen 500-m2 forest survey stations (nine per river) were also established roughly equidistant between (and including) the upper and lower gaging stations to measure canopy trees (> 2.54 cm DBH) and calculate species importance values (IV200). Field measures, along with other monitoring and model data, were used to develop a 30-year salinity record (1985–2015) for each gaging station based on an artificial neural network (ANN) model. Optimal ANN models for each TFFW gaging station were selected based on Akaike’s Information Criteria, and 30-year mean daily salinity was interpolated to all forest survey stations based on river distance. Important input variables for the ANN models included daily Apalachicola River discharge, Apalachicola Bay tidal stage, and bay salinity, among others. Based on 30-year salinity models, mean daily salinity ranged between 0.30 and 0.63 ppt at the downriver stations of East and St. Marks Rivers, respectively, to 0.14 and 0.14 ppt at the upriver stations, respectively. Results showed a predictable reduction in mean salinity and salinity ranges further upriver at both rivers; however, the St. Marks River showed a distinct inflection point in reduced salinity compared with the East River. Evaluating tree species IV200, there was a shift to species indicative of non-tidal conditions midway up the study reach of the St. Marks River while tidal species remained prominent throughout the East River study reach. Comparison of salinity, tidal reach, and species IV200 for each river suggests hydrology may be the most important contributor to the downriver extent of TFFWs while salinity may be an important driver of TFFW community composition.

Tracking oxy-thermal habitat compression encountered by Chesapeake Bay striped bass through acoustic telemetry

Abstract In many coastal ecosystems, habitat compression is caused by seasonal combinations of hypoxia and supraoptimal temperatures. These conditions commonly induce avoidance behaviours in mobile species, resulting in the concentrated use of marginal habitats. Using 3 years of acoustic telemetry and high-resolution water quality data recorded throughout Chesapeake Bay, we measured the seasonal movements and exposure of striped bass (Morone saxatilis) to oxy-thermal habitat compression. Striped bass moved to tidal freshwaters in spring (March–May), mesohaline waters in summer (June–August) and fall (September–November), and mesohaline and polyhaline waters in winter (December–February): seasonal patterns consistent with known spawning, foraging, and overwintering migrations. Analyses of habitat selection suggest that during conditions of prevalent sub-pycnocline hypoxia (June–September), striped bass appeared to select surface waters (i.e. they may avoid bottom hypoxic waters). Striped bass detections indicated tolerance of a wide range of surface water temperatures, including those >25°C, which regional regulatory bodies stipulate are stressful for this species. Still, during summer and fall striped bass selected the lowest-available temperature and avoided water temperature >27°C, demonstrating that Chesapeake Bay striped bass can encounter habitat compressions due to the behavioural avoidance of bottom hypoxia and high temperatures.

Phosphorus mobilization and availability across the freshwater to oligohaline water transition in subtropical estuarine marshes

Internal phosphorus (P) released from sediments, which has been verified to be affected by iron (Fe) and sulfur (S) reactions, strongly influences P cycling and water eutrophication. However, minimal research has been performed to determine how increased low-level salinity in estuarine tidal marshes affects P mobility and its coupled processes. Herein, in situ high-resolution distributions of labile P, Fe, and S in sediment-overlying water profiles were simultaneously measured along an estuarine freshwater-oligohaline gradient (Min River Estuary, China) utilizing newly developed diffusive gradients in thin films technique. Significant variations in the P, Fe, and S concentrations were observed with significantly higher sediment labile P concentrations in the freshwater-oligohaline transition. The observed labile P and Fe coupling confirmed the Fe redox-driven P release mechanism in the sediment, although this coupling was weakened in the freshwater-oligohaline transition. The diffusion flux results revealed that the sediments shifted from P “sink” to “source” with the transition from a freshwater to an oligohaline environment, probably caused by the release of Fe-bonded P stimulated by sulfate reduction. This study determined that increased salinity and the associated environmental responses alter the P remobilization capacity and internal P cycling by changing the sediment P pool and the P-Fe-S couplings across the sediment–water interface. Furthermore, saltwater intrusion into tidal freshwater wetlands caused by strong typhoons or sea-level rise may increase internal P release from sediments, which could have future implications.

Rapid tidal marsh development in anthropogenic backwaters

AbstractTidal marsh restoration and creation is growing in popularity due to the many and diverse sets of services these important ecosystems provide. However, it is unclear what conditions within constructed settings will lead to the successful establishment of tidal marsh. Here we provide documentation for widespread and rapid development of tidal freshwater wetlands for a major urban estuary as an unintended result of early industrial development. Anthropogenic backwater areas established behind railroad berms, jetties, and dredge spoil islands resulted in the rapid accumulation of clastic material and the subsequent initiation of emergent marshes. In one case, historical aerial photos document this transition occurring in less than 18 years, offering a timeframe for marsh development. Accretion rates for anthropogenic tidal marshes and mudflats average 0.8–1.1 and 0.6–0.7 cm year−1, respectively, equivalent to two to three times the rate of relative sea level rise as well as the observed accretion rate at a 6000+ year‐old reference marsh in the study area. Paired historical and geospatial analysis revealed that more than half of all the tidal wetlands on the Hudson River were likely triggered by anthropogenic development since the onset of the industrial era, including two‐thirds of the emergent cattail marsh. These inadvertently constructed tidal wetlands currently trap roughly 6% of the Hudson River's sediment load. Results indicate that when sediment is readily available, freshwater tidal wetlands can develop relatively rapidly in sheltered settings. The study sites serve as useful examples to help guide future tidal marsh creation and restoration efforts.

Indexing habitat opportunity for juvenile anadromous fishes in tidal-fluvial wetland systems

In intertidal wetlands, habitat access by out-migrating juvenile anadromous fishes, such as salmon (Oncorhynchus spp.), is influenced by both physical and biological factors. Physical limits are set by inundation patterns and water quality parameters, while biological bounds are determined by species-specific migration timing and seasonal residency behaviors. We developed a new metric called the fish habitat opportunity index to quantify the total time (h) and volume-time (m3-h) per calendar year that salmon could access a given wetland, based on periods of inundation (volume) and seasonal migration period (time). The basic assumption of the index is that the volume of water inundating a restored wetland and the amount of time the wetland is inundated are both positively related to ecological benefits to juvenile salmon in terms of foraging success, growth, condition, and refuge from predators. We tested this index using data collected at a reconnected tidal freshwater wetland area in the lower Columbia River and estuary during 2006–2009. We found the wetland to be accessible to different salmon species for different lengths of time and periods of the year. On average, Chum Salmon (O. keta) had remarkably consistent opportunities to use wetland marsh habitat over the four years sampled, while opportunities were more variable for Chinook Salmon (O. tshawytscha), and Coho Salmon (O. kisutch). Inundation varied nonlinearly with tidal height. Fish had access to the productive marsh edge for approximately 40–50% of the time during out-migration periods. The fish habitat opportunity index is applicable to wetland systems throughout the tidal-fluvial continuum. It provides a metric for assessing fish habitat opportunity that is more realistic than simple wetted-area calculations or species presence/absence data. Most importantly, the fish habitat opportunity index affords a method for a priori comparison among potential restoration sites to help resource managers predict the likely relative effects on habitat opportunity from restoration aimed at benefiting juvenile anadromous fishes. Maximizing the fish habitat opportunity index should positively affect fish populations that use tidal-fluvial wetlands as vital habitats in their life cycle.