Tidal Pulses Research Articles

Driving force of tidal pulses on denitrifiers-dominated nitrogen oxide emissions from intertidal wetland sediments

Intertidal wetland sediments are an important source of atmospheric nitrogen oxides (NOx), but their contribution to the global NOx budget remains unclear. In this work, we conducted year-round and diurnal observations in the intertidal wetland of Jiaozhou Bay to explore their regional source-sink patterns and influence factors on NOx emissions (initially in the form of nitric oxide) and used a dynamic soil reactor to further extend the mechanisms underlying the tidal pulse of nitric oxide (NO) observed in our investigations. The annual fluxes of NOx in the vegetated wetland were significantly higher than those in the wetland without vegetation. Their annual variations could be attributed to changes in temperature and the amount of organic carbon in the sediment, which was derived from vegetated plants and promoted the carbon-nitrogen cycle. Anaerobic denitrifiers had advantages in the intertidal wetland sediment and accounted for the major NO production (63.8 %) but were still limited by nitrite and nitrate concentrations in the sediment. Moreover, the tidal pulse was likely a primary driver of NOx emissions from intertidal wetlands over short periods, which was not considered in previous investigations. The annual NO exchange flux considering the tide pulse contribution (8.93 ± 1.72 × 10–2 kg N ha–1 yr–1) was significantly higher than that of the non-pulse period (4.14 ± 1.13 × 10–2 kg N ha–1 yr–1) in our modeling result for the fluxes over the last decade. Therefore, the current measurement of NOx fluxes underestimated the actual gas emission without considering the tidal pulse.

Offshore Spreading of a Supercritical Plume Under Upwelling Wind Forcing: A Case Study of the Winyah Bay Outflow

In this study, we present observations of the Winyah Bay (WB) plume (SC, United States) formed by high freshwater discharge and a moderate upwelling-favorable wind acting continuously for ∼1.5 days prior to the shipboard survey. If a similar wind forcing persists over a longer period, the plume turns upstream (against its natural propagation) and curves offshore forming a “filament” with minimal transverse spreading, as seen in numerous satellite images. The observed plume comprises a train of tidal sub-plumes undergoing rotational adjustment and being transported offshore by Ekman dynamics. The WB outflow is supercritical in terms of the interior Froude number. Moderate wind extends this supercritical regime farther offshore. The plume is characterized by interior fronts associated with consecutive tidal pulses. Age of the buoyant water can be distinguished by the buoyant layer mixing (evident in the layer’s thickness and salinity anomaly) along with the transformation of its TS properties. However, relatively little transverse (lateral) spreading of buoyant water occurs: the equivalent freshwater layer thickness remains surprisingly consistent, approximately 0.8 m, over more than 20 km in the direction of the bulge extension. It is hypothesized that the supercritical regime constrains the transverse spreading of a plume. Microstructure measurements reveal higher dissipation rates below the base of the older (offshore) part of the plume. This is attributed to internal wave radiation from a newly discharged tidal pulse into an older plume, with the buoyant layer acting as a waveguide. Theoretical estimations of the internal wave properties show that the interior front is highly supercritical, while the observed dissipation maximum agrees with the theoretical wave structure.

Assessment of Nutrient Supply by a Tidal Jet in the Northern Strait of Georgia Based on a Biogeochemical Model

AbstractWe present a coupled three‐dimensional biological‐physical model for the Salish Sea and evaluate it by comparison to nitrate, silicate, and chlorophyll observations. It accurately reproduces nitrate concentrations with Willmott skill scores, root‐mean‐square error, and bias ranging from 0.84–0.95, 4.02–6.5 μM, and −2.33–1.84 μM, respectively, compared to three independent discrete sample data sets. A prominent feature of the model output is a tidal jet emanating from Discovery Passage producing a downstream plume of elevated surface nitrate. The signal is present from April to September, when surface nitrate is otherwise drawn down. It has a weak but statistically significant correlation to Discovery Passage tidal velocity (R=0.37, p<0.01). Within the turbulent jet and associated plume, the average rate of vertical nitrate supply due to mixing and advection across a depth of roughly 6 m is 0.46 μmol m−2 s−1 between 15 May and 20 August 2015, compared to 0.10 μmol m−2 s−1 for the northern Strait of Georgia as a whole. Close to Discovery Passage, where velocities and shear are strongest, the majority of the vertical nitrate flux is due to mixing. As velocities weaken downstream, vertical advection becomes more important relative to mixing, but vertical velocities also decrease. The tidal pulses out of Discovery Passage drive waves that contribute net upward nitrate flux as far south as Cape Lazo, 40 km away. The nitrate supply drives new production, consistent with existing observations. Similar dynamics have been described in many other tidally influenced coastal systems.

The Impact of the Degree of Aquifer Confinement and Anisotropy on Tidal Pulse Propagation.

Oceanic tidal fluctuations which propagate long distances up coastal rivers can be exploited to constrain hydraulic properties of riverbank aquifers. These estimates, however, may be sensitive to degree of aquifer confinement and aquifer anisotropy. We analyzed the hydraulic properties of a tidally influenced aquifer along the Meghna River in Bangladesh using: (1) slug tests combined with drilling logs and surface resistivity to estimate Transmissivity (T); (2) a pumping test to estimate T and Storativity (S) and thus Aquifer Diffusivity (DPT ); and (3) the observed reduction in the amplitude and velocity of a tidal pulse to calculate D using the Jacob-Ferris analytical solution. Average Hydraulic Conductivity (K) and T estimated with slug tests and borehole lithology were 27.3 m/d and 564 m2 /d, respectively. Values of T and S determined from the pumping test ranged from 400 to 500 m2 /d and 1 to 5 × 10-4 , respectively with DPT ranging from 9 to 40 × 105 m2 /d. In contrast, D estimated from the Jacob-Ferris model ranged from 0.5 to 9 × 104 m2 /d. We hypothesized this error resulted from deviations of the real aquifer conditions from those assumed by the Jacob-Ferris model. Using a 2D numerical model tidal pulses were simulated across a range of conditions and D was calculated with the Jacob-Ferris model. Moderately confined (Ktop /Kaquifer < 0.01) or anisotropic aquifers (Kx /Kz > 10) yield D within a factor of 2 of the actual value. The order of magnitude difference in D between pumping test and Jacob-Ferris model at our site argues for little confinement or anisotropy.

Point Source Nutrient Fluxes from an Urban Coast: the Boynton (Florida) Inlet

The Boynton Inlet (SE Florida, USA) is one of two tidal inlets connecting the Lake Worth Lagoon to the Atlantic Ocean. To quantitate the amount of anthropogenic materials reaching the South Florida coastal ocean and reef track, nutrient fluxes through the Boynton Inlet were measured during two 48-hour intensive studies conducted on June 4-6 and September 26-28, 2007. These studies combined analyses of water samples taken at regular intervals in the Boynton Inlet with acoustic Doppler current profiler (ADCP) measurements of the flow through the inlet. Data collected include concentrations of nutrients (silicate [Si], orthophosphate [PO 4 ], ammonium [NH 4 ], nitrate+nitrite [N+N]), isotope ratios of nitrogen, and physical parameters that included pH, salinity, total suspended solids (TSS), and turbidity. The study found a significant but highly variable flux of nutrients in the eight outgoing (ebb) tidal pulses sampled. Daily fluxes of nitrate+nitrite ranged from 16 to 565 kg N, silicate from 564 to 5197 kg Si, phosphate from 154 to 309 kg P, and ammonium from 34 to 354 kg N. These results are compared with other sources of nutrient inputs into the coastal environment. Inlets are a significant source of offshore nutrients.

PCBs refocused: Correlation of PCB concentrations in Green Bay legacy sediments with adjacent lithophilic, invasive biota

Green Bay sediments exhibit a gradient of polychlorinated biphenyl (PCB) concentrations from the mouth of the Fox River to the northern end of the bay. This study explored whether the sediment concentration gradient was reflected along Green Bay's rocky (non-depositional) eastern coast in a suspension feeder, the invasive quagga mussel (Dreissena bugensis), as well as in the main predator on quagga mussels, the invasive round goby (Neogobius melanostomus). We performed congener-specific PCB analyses on quagga mussels and round gobies collected from ten sites along the east shore of Green Bay. PCB results were compared with sediment data. Regression analyses showed that mussel tissue PCB concentrations followed sediment PCB concentrations (F1,6=16.4, P=0.007) except at two sites near Sturgeon Bay where cleaner Lake Michigan water enters in tidal pulses. Round goby PCB concentrations also followed the sediment trends (F1,7=8.17, P=0.024). However, only a weak relationship between PCB concentrations in quagga mussel and round goby was found (P=0.085), even though the species are trophically linked. Here, ontogenetic and seasonal details of round goby diet strongly influenced PCB concentrations such that in areas adjacent to high sediment PCB concentrations, fish length dictated round goby's PCB concentration (F1,14=7.46, P=0.016). Overall, our findings indicate that these exotic benthos refocus PCBs in near-shore regions in a pattern similar to that observed in sediments. Our results also highlight the need to understand trophic details in order to track contaminant bioaccumulation accurately.

Tidal, Riverine, and Wind Influences on the Circulation of a Macrotidal Estuary

Abstract The effect of tides, river, wind and Earth’s rotation on the three-dimensional circulation in the Dee, a macrotidal estuary, are investigated using a fine-resolution model. The interactions of the large tidal amplitude, currents, river, and wind-generated circulation require baroclinic and unsteady studies to properly understand the estuarine dynamics. Assessment of the model skill has been carried out by model–observation comparisons for salinity, which is the main control for density, surface elevation, current, and turbulence. Stationary nondimensional numbers were only partially able to characterize the dynamics in this (real) complex macrotidal estuary. At low water, tidal straining and constrained river flow cause stratification. Large spatial variability occurs in the current and residual patterns, with flood-dominated maximum values occurring within the tidal channels. The tides control residual circulation by modulating stratification through tidal straining and bathymetric constraint on river flow. Tide–stratification–river interaction causes an unsteady pattern of residual circulation and tidal pulses. River-induced pulses are enhanced near low tide–inducing density-driven circulation. Wind effects are concentrated near the surface, mainly occurring at high tide because of increased fetch. Even though Coriolis has, overall, a small contribution it produces tidal pulses modifying the current and salinity distribution.

The role of turbulence stress divergence in decelerating a river plume

Turbulence controls the composition of river plumes through mixing and alters the plume's trajectory by diffusing its momentum. While believed to play a crucial role in decelerating river‐source waters, the turbulence stress in a near‐field river plume has not previously been observationally quantified. In this study, finely resolved density, velocity, and turbulence observations are combined with a control‐volume technique to describe the momentum balance in the Columbia River's near‐field plume during 10 tidal cycles that encompass both large and small river flow. Turbulence stress varies by 2–3 orders of magnitude, both within a given ebb and between ebbs with different tidal or river forcing; its magnitude scales with the strength of the instantaneous ebb outflow, i.e., high stresses occur during peak flow of strong ebbs. During these periods, the momentum equation is represented by a balance between stress divergence and plume deceleration. As the flow relaxes, the stress divergence weakens and other terms (pressure gradient and Coriolis) may become appreciable and influence plume deceleration. While the momentum balance could not be closed during these weaker flow periods, during strong tidal pulses the time scale for decay based on observed stress is significantly less than a tidal half‐period, indicating that stress divergence plays a fundamental role in the initial deceleration of the plume.

Sea‐tide effects on flows in the lower reaches of the Amazon River

AbstractThe physical influence of sea tides on the lower reaches of the Amazon River can be identified more than 1000 km upstream from the sea. Analysis of upstream tidal wave propagation on the Amazon River contributes to the understanding of the hydrodynamics of the lower reaches and to the quantification of the influence of sea level on sedimentation rates. Continuous over‐the‐year recording of water levels has been undertaken at eight locations along the lower reaches of the Amazon River and flow measurement campaigns have been organized for different river discharge rates (100 000 m3 s−1, 190 000 m3 s−1 and 250 000 m3 s−1) and sea‐tide amplitudes (2–3·5 m). Damping, time‐delay and deformation of the tidal wave signals, depending on water regimes and distances from the sea, have been analyzed. The physical processes of wave propagation and cyclic water storage and release have been investigated both through data analysis and the application of mathematical hydrodynamic models. The impact of tidal pulses on sediment transport to the sea has been assessed. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Variability of the Columbia River plume observed in visible and infrared satellite imagery

Variability of the Columbia River plume in coastal waters off the northwestern United States, 1979-1985, was observed in sea surface temperature and phytoplankton pigment images derived from Advanced Very High Resolution Radiometer and Coastal Zone Colour Scanner data. The orientation, shape, intensity and relative temperature of the plume vary in response to coastal winds and wind-driven surface currents. From October to April, plume water is oriented northward along the coast. Following the spring transition in April or May, the plume is oriented southward, either adjacent to the coast or offshore. Transition between the winter and summer forms can be observed in the satellite imagery. Brief reversals of the prevailing seasonal winds cause rapid changes in the orientation and shape of the plume. Remote sensing of the Columbia River plume offers valuable information for oceanographic studies and fisheries management in the region. Derivation of an appropriate visible-infrared signature for plume waters and tracking of tidal pulses in the plume is suggested as a promising direction for future research.

Phase-Responsiveness of the Circatidal Locomotor Activity Rhythm of Hemigrapsus Edwardsi (Hilgendorf) to Simulated High Tide

Phase-responsiveness to single pulses of simulated high tide has been tested for in the locomotor activity rhythm of Hemigrapsus edwardsi, a grapsid crab from a locality of equal semi-diurnal tides. The crab exhibits endogenous circatidal locomotor rhythmicity with only a weak circadian component. Exposure to a single 3 h ‘pulse’ of simulated high tide (immersion and low temperature, with or without light) in crabs kept otherwise in constant conditions (moist air; dim red light; 15°C), resulted in slight phase delays in the free-running rhythm when the tidal ‘pulse’ was applied in the first 2–3 h of the ‘expected’ high tide period. Tidal pulses initiated at and just after the expected time of high tide induce a phase advance. The results support the hypothesis of a phase-responsive curve on a tidal (12·4 h) rather than 24 h time-base. However, the phase advances and delays are small when compared with circadian phase response curves. It is suggested that the circatidal rhythms depend mainly upon repeated exposure to tidal variables for entrainment and that each individual tide is able to adjust the behavioural rhythm only slightly from its endogenous pattern. In this way, behaviour of populations of coastal animals is less susceptible to environmental perturbations associated, for example, with severe storms.