Diagnostic Timescale Methods for the Aquatic Environment: Current Challenges, Recent Improvements, and Applications

A special issue of Water (ISSN 2073-4441). This special issue belongs to the section "Hydraulics and Hydrodynamics".

Deadline for manuscript submissions: 29 August 2024 | Viewed by 3224

Special Issue Editors

Institute of Mechanics, Materials and Civil Engineering (IMMC) & Earth and Life Institute (ELI), Université catholique de Louvain, Louvain-la-Neuve, Belgium
Interests: timescale diagnoses for geophysical and environmental fluid flows; river–sea continuum; reactive transport
Special Issues, Collections and Topics in MDPI journals
1. Resource Management Associates, Davis, CA, USA
2. Department of Civil and Environmental Engineering, University of California Davis, Davis, CA, USA
Interests: estuarine physics; hydrodynamic modeling; particle-tracking modeling; transport timescales; ecohydraulics
Department of Earth Sciences, National Natural Science Foundation of China, Beijing, China
Interests: water exchange; Lagrangian residual velocity; coastal physical oceanography; ocean modelling
Integrated Modeling and Prediction Division, Water Mission Area, U.S. Geological Survey, Menlo Park, CA, USA
Interests: surface water quality; aquatic ecosystems; estuarine ecosystems; freshwater ecosystems
Special Issues, Collections and Topics in MDPI journals
Virginia Institute of Marine Science, The College of William & Mary, Gloucester Point, VA, USA
Interests: hydrodynamic and water quality modeling; transport processes in estuaries and coasts; timescale diagnoses for interactions between hydrodynamics and biochemical processes
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Timescale diagnoses (e.g., age, residence/exposure time, inverse of reaction rate) are powerful tools helping to analyze and understand passive and reactive transport processes taking place in the aquatic environment (subsurface water, rivers, lakes, estuaries, seas, etc.). The aforementioned timescales, commonly derived from numerical modelling or from measurements, apply to water, natural and artificial tracers, and chemical and biological species. Regarding their integrative properties, timescale methods are potentially holistic, in that they include all of the available pieces of information about the underlying (reactive) transport processes taking place in environmental fluid flows.

This Special Issue aims at presenting recent advances in tracer and timescale methods. All types of contributions will be welcome, in particular those focusing on novel methodological developments (even if they are still being formulated) and applications aimed at addressing ecological problems. Numerical methods using Eulerian or Lagrangian approaches will be considered, as well as techniques based on remotely sensed or in situ data. We will seek a balance between contributions from natural sciences and engineering, as well as between numerical, observational and theoretical approaches.

Manuscripts dealing with issues falling outside the realm of the aquatic environment will also be considered provided they draw lessons that are of interest to the core of this Special Issue.

It is noteworthy that the publisher (MDPI) is willing to grant no less than ten publication fee waivers for this Special Issue. Potential authors are kindly invited to contact one of the guest editors, thereby outlining their article project and providing a tentative submission date.

This Special Issue is intended to be a follow-up to a recently completed Water Special Issue entitled “Tracer and Timescale Methods for Passive and Reactive Transport in Fluid Flows” (https://www.mdpi.com/journal/water/special_issues/Fluid_Flows).

Prof. Dr. Eric Deleersnijder
Dr. Edward S. Gross
Prof. Dr. Zhe Liu
Dr. Lisa V. Lucas
Prof. Dr. Jian Shen
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Water is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • aquatic environment
  • tracers
  • reactive transport
  • ecological modelling
  • diagnostic timescales
  • age
  • residence time
  • exposure time
  • flushing time
  • Lagrangian and Eulerian methods
  • adjoint model
  • geophysical and environmental flows
  • hydraulic engineering
  • hydrodynamics
  • biogeochemical

Published Papers (3 papers)

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Research

13 pages, 8010 KiB  
Article
Seasonality of Water Exchange in the Northern South China Sea from Hydrodynamic Perspective
Water 2024, 16(1), 10; https://doi.org/10.3390/w16010010 - 20 Dec 2023
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Abstract
In this study, we utilized exposure time (θ¯) as a key metric to investigate water exchange and its spatiotemporal variations in the Northern South China Sea (NSCS). The Eulerian adjoint method and Lagrangian tracking were adopted to capture a comprehensive [...] Read more.
In this study, we utilized exposure time (θ¯) as a key metric to investigate water exchange and its spatiotemporal variations in the Northern South China Sea (NSCS). The Eulerian adjoint method and Lagrangian tracking were adopted to capture a comprehensive view of water exchange in coastal regions. Our findings reveal distinct spatial and seasonal variations in θ¯. Spatially, a long θ¯ (exceeding 150 days) appears in the coastal region, and the largest values occur in the Beibu Gulf (300 days). Temporally, θ¯ exhibits clear seasonal patterns across the extensive shelf area, influenced by the seasonal monsoon which induced seasonally reversing shelf current and results in symmetrical distribution patterns of θ¯ across the board shelf during both winter and summer months. θ¯ is longer in winter than in summer. The study also revealed pronounced vertical contrasts in cross-isobath transport over the NSCS shelf, though significant vertical variations in net exchange time were noted only in specific locations, including the northeast side of Hainan Island, the Beibu Gulf mouth, and along the west side of Taiwan Island. The Beibu Gulf emerged as a critical factor in the NSCS’s water exchange dynamics in both seasons. In summer, it impacts more than 20% of the water exchange over adjacent areas, particularly through its westward transport against typical northeastward shelf currents. This highlights the combined effect of the westward spread of the Pearl River freshwater and the stable slope current on regional hydrodynamics. In winter, the Gulf’s retention characteristics profoundly affected even distant areas, contributing to up to 50% of water exchange, showing its broad impact on the NSCS’s water dynamics throughout the year. Full article
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17 pages, 3398 KiB  
Article
Longitudinal Mixing in Flows with Submerged Rigid Aquatic Canopies
Water 2023, 15(17), 3021; https://doi.org/10.3390/w15173021 - 22 Aug 2023
Viewed by 705
Abstract
The presence of dense submerged vegetation alters mixing characteristics in open channel flows as they cause differential velocities inside and above canopies. The prediction models for longitudinal mixing in the presence of submerged canopies often use the drag coefficient to represent the canopy, [...] Read more.
The presence of dense submerged vegetation alters mixing characteristics in open channel flows as they cause differential velocities inside and above canopies. The prediction models for longitudinal mixing in the presence of submerged canopies often use the drag coefficient to represent the canopy, which limits the usability of the models when the canopy properties are not fully understood. Here, attempts were made to present a methodology which can be used for deriving the coefficient of longitudinal dispersion in the presence of submerged vegetation based on velocity measurements, using a mixing length approach to model turbulence. An experimental study was conducted in a large-scale laboratory facility to investigate the longitudinal dispersion characteristics in open channel flow with submerged aquatic vegetation canopies. Detailed velocity and solute tracer measurements were undertaken for a representative range of flow velocities. The velocity measurements were used for deriving turbulent shear stress, mixing length, and diffusivity using established theoretical and empirical relationships to derive the longitudinal dispersion. The longitudinal dispersion measured in two locations in the water column for the two canopy submergences was discussed based on the amount of vertical mixing and differential advection. The canopy with a smaller stem length (i.e., higher submergence ratio) has a higher vertical diffusivity, resulting in increased vertical mixing in the water column. The canopy with the higher stem length (i.e., lower submergence ratio) consists of minimal vertical diffusivity, causing the longitudinal dispersion measured above the canopy to be significantly high, even though the longitudinal dispersion measured inside the canopy is much lower. The mathematical model which was adapted for calculating the coefficient of longitudinal dispersion and the tracer results show good agreement, indicating that the N-zone model can accurately predict the longitudinal dispersion in submerged aquatic canopies when used with the presented methodology. Full article
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26 pages, 5435 KiB  
Article
Using Age Tracers to Estimate Ecological Rates in a Phytoplankton Model
Water 2023, 15(11), 2097; https://doi.org/10.3390/w15112097 - 01 Jun 2023
Viewed by 1141
Abstract
The phytoplankton distribution in estuaries is influenced by multiple spatially variable growth and loss processes. As phytoplankton are transported by tidal and net flows, they are exposed to changing conditions of turbidity, depth, temperature, stratification, and grazing. Understanding the factors influencing the observed [...] Read more.
The phytoplankton distribution in estuaries is influenced by multiple spatially variable growth and loss processes. As phytoplankton are transported by tidal and net flows, they are exposed to changing conditions of turbidity, depth, temperature, stratification, and grazing. Understanding the factors influencing the observed phytoplankton distribution patterns will allow better-informed restoration and water management efforts. We developed a Lagrangian approach driven by three-dimensional hydrodynamic model results and a simple representation of the production and losses of phytoplankton, allowing a highly efficient closed-form solution for phytoplankton biomass. Our analysis used continuous observations of chlorophyll concentration at four stations and a near-synoptic chlorophyll dataset collected underway from a boat in the channels of Suisun Marsh in the San Francisco Estuary. We divided the study region into four compartments defined by the water depth and location. For each observation location, hydrodynamic model simulations calculated the time that water parcels spent in each of these compartments and the mean depth encountered by water parcels in those compartments. Then, using that information and continuous monitoring data, we inferred compartment-specific grazing rates and two additional ecological parameters. The underway chlorophyll dataset was used for model validation. The model predicted patterns of observed spatial and tidal variability in chlorophyll in Suisun Marsh. The modeling indicated that the chlorophyll concentration at a point in space in time depends largely on the relative exposure to shallow areas, with positive net productivity and deep areas having negative net productivity. Full article
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