Influences of Land Reclamation Near the River Mouth on River Plume Spreading

Abstract. Nitrification is a series of processes that oxidizes ammonia to nitrate, which contributes to hypoxia development in coastal oceans, especially in eutrophicated regions. The nitrification rate of bulk water (NRb) and particle free water (NRpf, particle > 3 μm eliminated) were determined along the Chang Jiang River plume in August 2011 by nitrogen isotope tracer technique. Measurements of dissolved oxygen (DO), community respiration rate (CR), nutrients, dissolved organic nitrogen (DON), total suspended matter (TSM), particulate organic carbon/nitrogen (POC / PON), acid-leachable iron and manganese on suspended particles and both archaeal and β-proteobacterial ammonia monooxygenase subunit A gene (amoA) abundance on size-fractioned particles (> 3 μm and 0.22–3 μm) were conducted. The NRb ranged from undetectable up to 4.6 μmol L−1 day−1, peaking at a salinity of ~ 29. NRb values were positively correlated with ammonium concentration, suggesting the importance of substrate in nitrification. In the river mouth and the inner plume, NRb was much higher than NRpf, indicating that the nitrifying microorganism is mainly particle associated, which was supported by its significant correlation with amoA gene abundance and TSM concentration. The estimated oxygen demands of nitrification accounted for 0.32 to 318% of CR, in which 50% samples demanded more oxygen than that predicted by by the Redfield model (23%), indicating that oxygen might not be the sole oxidant though DO was sufficient (> 58 μmol kg−1) throughout the observation period. The excess nitrification-associated oxygen demand (NOD) showed a tendency to occur at lower DO samples accompanied by higher acid-leachable Fe / Mn, which implied reactive Fe3+ / Mn4+ may play a role as oxidant in the nitrification process. Stoichiometric calculation suggested that reactive Fe on particles was 10 times the oxidant demand required to complete ammonia oxidation in the entire plume. The potential involvement of reactive iron and manganese in the nitrification process in oxygenated water further complicated nitrogen cycling in the turbid river plume.

Download Full-text

Two-layer hydraulics at the river–ocean interface

Journal of Fluid Mechanics ◽

10.1017/jfm.2018.688 ◽

2018 ◽

Vol 856 ◽

pp. 633-672 ◽

Cited By ~ 3

Author(s):

Anthony R. Poggioli ◽

Alexander R. Horner-Devine

Keyword(s):

Free Surface ◽

Near Field ◽

Full Range ◽

River Estuary ◽

Surface Profile ◽

River Mouth ◽

River Plume ◽

Gravitational Acceleration ◽

Wide Range ◽

Experimental Apparatus

Liftoff is the hydraulically forced detachment of buoyant freshwater from the channel bottom or seabed that occurs as river water discharges into the coastal ocean. It is a key feature of strongly stratified systems, occurring well upstream in the channel or seaward of the river mouth under sufficiently strong forcing. We present a two-layer hydraulic solution for the river–ocean interface that considers the river, estuary and near-field river plume as a single interlinked system, extending previous work that considered them separately. This unified approach provides a prediction of the liftoff location and free-surface profile for a wide range of forcing conditions, which are characterized in terms of the freshwater Froude number $F_{f}\equiv Q/b_{0}\sqrt{g_{0}^{\prime }h_{0}^{3}}$. Here, $Q$ is the river discharge, $b_{0}$ is the channel width, $g_{0}^{\prime }\equiv (\unicode[STIX]{x0394}\unicode[STIX]{x1D70C}_{0}/\unicode[STIX]{x1D70C}_{2})g$ is the reduced gravitational acceleration, $\unicode[STIX]{x0394}\unicode[STIX]{x1D70C}_{0}$ is the density contrast between fresh and ocean water and $h_{0}$ is the total water depth at the river mouth. The solution is validated with laboratory experiments using an experimental apparatus consisting of a long, sloping river channel that discharges into a deep, wide saltwater basin. The experiments simulate the full range of hydraulic behaviours predicted by the model, from saltwater intrusion to offshore liftoff. For $F_{f}<1$, liftoff occurs in the estuary channel and our results show that the relationship between intrusion length and $F_{f}$ depends on the channel slope. For $F_{f}>1$, corresponding to flood conditions in many natural systems, liftoff is forced outside the river mouth and the hydraulic coupling between the channel and shelf becomes more important. For these conditions and for intermediate to steeply sloped shelves, the offshore liftoff distance varies linearly with $F_{f}-1$, a particularly simple scaling given the nonlinearity and relative complexity of the governing equations. The model and experimental results support a conceptual description of the river–ocean interface that relates the liftoff location, free-surface elevation and the spreading rate of the buoyant river plume.

Download Full-text

Mixing Characteristics of the Niagara River Plume in Lake Ontario

Water Quality Research Journal ◽

10.2166/wqrj.1989.008 ◽

1989 ◽

Vol 24 (1) ◽

pp. 143-162 ◽

Cited By ~ 2

Author(s):

C. R. Murthy ◽

K. C. Miners

Keyword(s):

General Circulation ◽

River Mouth ◽

Lake Ontario ◽

Intermediate Stage ◽

River Plume ◽

Thermal Front ◽

Niagara River ◽

Initial Stage ◽

Mixing Characteristics ◽

Lagrangian Drifter

Abstract Data collected between 1982 and 1985 from Lagrangian drifter experiments in which about ten drifters were tracked for ten to twelve hours from their release across the Niagara River mouth, and from concurrently taken ship-based temperature soundings at fixed grid stations off the river mouth, are used to develop a conceptual model of the mixing characteristics of the Niagara River in Lake Ontario. The data obtained suggest a three-stage mixing process. In the initial stage, the river inflow momentum dominates and the plume is well mixed vertically. In the intermediate stage, the interaction of the well mixed, buoyant river plume with colder water from deeper depths of the lake generates a sharp thermal front. In the final stage, the river plume responds to the prevailing winds and the general circulation of the lake. The correlation between these observed plume characteristics and the distribution of toxic contaminants such as mercury and mirex in Lake Ontario sediments attributed to Niagara River outflow is illustrated.

Download Full-text

Studies of Internal Waves in the Strait of Georgia Based on Remote Sensing Images

Remote Sensing ◽

10.3390/rs11010096 ◽

2019 ◽

Vol 11 (1) ◽

pp. 96 ◽

Cited By ~ 2

Author(s):

Caixia Wang ◽

Xin Wang ◽

Jose C. B. Da Silva

Keyword(s):

Remote Sensing ◽

Internal Waves ◽

River Mouth ◽

Temporal Distribution ◽

Tidal Currents ◽

River Plume ◽

Remote Sensing Images ◽

Strait Of Georgia ◽

Narrow Channels ◽

Propagating Waves

This paper analyzes over 500 sets of internal waves in the Strait of Georgia (British Columbia, Canada) based on a large number of satellite remote sensing images. The spatial and temporal distribution of internal waves in the central region of the strait are discussed via statistical analysis. Possible generation origins of the observed internal waves are divided into three categories based on their different propagation directions and geographical locations: (1) the interaction between the narrow channels to the south of the Strait and the tidal currents, leading to the formation of mainly eastward and northward propagating waves; (2) the interaction between the tidal currents and the topography near Point Roberts, resulting in mainly westward propagating waves; (3) excitation by river plume, mainly near Fraser River mouth, leading to the formation of mainly westward waves along the direction of the river plume. The relation between the occurrence of internal waves in remote sensing images and wind or tide level is also discussed. It is found that most of the observed internal waves occur at low tides. However, due to the influence of the river, the eastward propagating internal waves near the river mouth seldom occur at the lowest tide. Also, internal waves are captured more easily by remote sensing images in summer due to the lower wind speed than winter and therefore the seasonal distribution of internal waves in remote sensing images may not be able to completely represent the real situation in the study area. Finally, combining the in situ measured data and model output data, the Benjamin-Ono equation is found to satisfyingly simulate the characteristic parameters of the studied internal waves.

Download Full-text

Numerical Modelling of the Grand River Plume in Lake Erie during Unstratified Period

Water Quality Research Journal ◽

10.2166/wqrj.2006.002 ◽

2006 ◽

Vol 41 (1) ◽

pp. 16-23 ◽

Cited By ~ 12

Author(s):

Cheng He ◽

Yerubandi R. Rao ◽

Michael G. Skafel ◽

Todd Howell

Keyword(s):

Lake Erie ◽

River Mouth ◽

River Plume ◽

Open Boundary ◽

Closed Domain ◽

Eastern Basin ◽

Receiving Waters ◽

Plume Transport ◽

Grand River ◽

The Impact

Abstract The Grand River is a major contributor of nutrients and dissolved and suspended solids to the eastern basin of Lake Erie. To better understand the impact of the Grand River plume on the surrounding receiving waters, we integrated data analysis and modelling of the Grand River plume transport in the eastern basin of Lake Erie using a high-resolution depth-integrated nonlinear barotropic finite element model. An extended domain of receiving waters with closed boundary was applied in this numerical study due to the lack of observations needed for specifying the open boundary conditions. The size of closed domain was chosen by considering balance between the computing time and stabilizing the hydrodynamic flow. Numerical simulations of the influence of wind on the plume transport in the vicinity of the Grand River mouth were performed. The root mean square error values of alongshore and cross-shore current components were 5 and 2.85 cm s-1, respectively. The transport simulations compare favorably (±20%) with observations of conductivity in the vicinity of the Grand River mouth. This study demonstrates that a two-dimensional numerical model can reasonably predict the river plume transport in a large lake during unstratified periods. Plume movement is primarily controlled by the wind-driven coastal current. Our simulations indicate that the frequent reversals of this current should effectively limit the plume's alongshore extent and may result in a continuous coastal band of turbid water extending alongshore in either direction in the vicinity of the river mouth.

Download Full-text

Ballooning of River-Plume Bulge and Its Stabilization by Tidal Currents

Journal of Physical Oceanography ◽

10.1175/jpo2837.1 ◽

2005 ◽

Vol 35 (12) ◽

pp. 2337-2351 ◽

Cited By ~ 39

Author(s):

Atsuhiko Isobe

Keyword(s):

River Mouth ◽

Tidal Currents ◽

River Plume ◽

Boundary Current ◽

Inertial Instability ◽

Long Time ◽

Coastal Boundary ◽

Ambient Currents ◽

The Right ◽

Coastal Boundary Current

Abstract When freshwater debouches into an adjacent ocean, an anticyclonic eddy (bulge) is formed in front of the river mouth. It is well known that a bulge growing offshore (ballooning) hardly reaches a steady state in the absence of either ambient currents or wind forcing. This study provides a physical interpretation for the ballooning of river-plume bulges by conducting numerical experiments in which a river plume is induced by a coastal freshwater source. Part of the freshwater released to the model ocean undergoes inertial instability. Near-inertial oscillations are predominant when disturbances are not forced in ambient waters of the river plume. These isotropic disturbances are amplified by inertial instability, so that unstabilized freshwater can move in arbitrary directions. Thus, unstabilized freshwater does not need to move toward the coastal boundary current on the right-hand side of the river mouth. Freshwater unstabilized for a long time can stay in the bulge for a long time. Unstabilized freshwater accumulates gradually in the bulge, and so ballooning occurs. When the direction of disturbances is prescribed in ambient waters, unstabilized freshwater is forced to move in the same direction. Thereby, the motion of unstabilized freshwater is restricted in the alongshore direction when background disturbances are induced by alongshore tidal currents. It is therefore concluded that tidal currents play a role in stabilizing the offshore growth of river-plume bulges in coastal and shelf waters.

Download Full-text

Mycoplankton Biome Structure and Assemblage Processes Differ Along a Transect From the Elbe River Down to the River Plume and the Adjacent Marine Waters

Frontiers in Microbiology ◽

10.3389/fmicb.2021.640469 ◽

2021 ◽

Vol 12 ◽

Author(s):

Yanyan Yang ◽

Stefanos Banos ◽

Gunnar Gerdts ◽

Antje Wichels ◽

Marlis Reich

Keyword(s):

River Mouth ◽

Well Being ◽

River Plume ◽

Transport Systems ◽

Minor Role ◽

Rrna Gene ◽

Stream Order ◽

Marine Waters ◽

Elbe River ◽

The Elbe River

Rivers are transport systems and supply adjacent ecosystems with nutrients. They also serve human well-being, for example as a source of food. Microorganism biodiversity is an important parameter for the ecological balance of river ecosystems. Despite the knowledge that fungi are key players in freshwater nutrient cycling and food webs, data on planktonic fungi of streams with higher stream order are scarce. This study aims to fill this knowledge gap by a fungi-specific 18S ribosomal RNA (rRNA) gene tag sequencing approach, investigating mycoplankton diversity in the Elbe River along a transect from shallow freshwater, to the estuary and river plume down to the adjacent marine waters (sections of seventh stream order number). Using multivariate analyses and the quantitative process estimates (QPEs) method, questions (i) of how mycoplankton communities as part of the river continuum change along the transect, (ii) what factors, spatial and environmental, play a role, and (iii) what assembly processes, such as selection or dispersion, operate along the transect, were addressed. The partitioning of mycoplankton communities into three significant distant biomes was mainly driven by local environmental conditions that were partly under spatial control. The assembly processes underlying the biomes also differed significantly. Thus, variable selection dominated the upstream sections, while undominated processes like ecological drift dominated the sections close to the river mouth and beyond. Dispersal played a minor role. The results suggest that the ecological versatility of the mycoplankton communities changes along the transect as response, for example, to a drastic change from an autotrophic to a heterotrophic system caused by an abrupt increase in the river depth. Furthermore, a significant salinity-dependent occurrence of diverse basal fungal groups was observed, with no clade found exclusively in marine waters. These results provide an important framework to help understand patterns of riverine mycoplankton communities and serve as basis for a further in-depth work so that fungi, as an important ecological organism group, can be integrated into models of, e.g., usage-balance considerations of rivers.

Download Full-text