Contributed Session.
Lead Organizer: Serghei Bocaniov , University of Waterloo (sbocaniov@uwaterloo.ca)
Presentations
02:30 PM
Importance of horizontal heterogeneity of lake morphometry in modeling algal production and biomass (9113)
Primary Presenter: Hugo Harlin, Umeå University (hugo.harlin@umu.se)
To explore the importance of the horizontal component of lake morphometry in modeling algal production and biomass, we developed a 2D-approximation of a 3D-model of a radially symmetric, cone-shaped lake and compared it with its 1D-analog, i.e. a flat-bottomed, cylindrical lake of identical mean depth. The model consists of coupled reaction-diffusion partial differential equations and considers mineral nutrients and light as potentially limiting to algal growth. When compared across a 5-dimensional parameter space covering a wide range in lake area and depth, water clarity, nutrient content and vertical mixing intensity, outcomes from the 2D- and 1D-models at the whole lake scale differ as a rule, the most common deviations being that the 1D-model underestimates the biomass of benthic algae and overestimates the biomass of pelagic algae. Moreover, the horizontally sloping bottom topography produces phenomena that are not possible in 1D, and which depend on other physical properties such as water clarity and lake depth. For example, in shallow, clear lakes pelagic algal biomass decreases and benthic algal biomass increases with lake area, whereas in less transparent and deeper lakes, the opposite can be observed, potentially leading to a switch from benthic to pelagic algal dominance along a gradient of increasing lake size. These findings highlight the importance of considering horizontal heterogeneity in lake ecosystems and emphasize the need for higher dimensional modeling approaches to accurately capture the complex influence of abiotic factors on algal dynamics.
02:45 PM
Modeling the impact of chemical and physical processes of PFOA on their LRT in the global ocean (9693)
Primary Presenter: Elena Mikheeva, Hereon (elena.mikheeva@hereon.de)
Per- and polyfluoroalkyl substances (PFAS), a class of anthropogenic organic pollutants, are of critical societal concern due to their persistence and toxic properties. One of the most widely known PFAS, perfluorooctanoic acid (PFOA), has been produced on an industrial scale since the 1950s. Due to its persistence and toxicity, PFOA has been gradually replaced by alternative PFAS in recent decades. However, between 200 and 300 tons of PFOA are still released into the environment annually, from both air and water sources. As an acid, PFOA dissociates to its ionic form in water, increasing its tendency to accumulate in the ocean. To explore PFOA's environmental behavior, we developed a mechanism to simulate its chemical and physical transformations in the ocean and implemented it in the fully resolved 3D global ocean model ICON-O. This Icosahedral Nonhydrostatic (ICON) model is a next-generation, multi-compartment Earth System Sodel that includes atmospheric transport. We assessed the influence of these processes on the long-range transport (LRT) of PFOA compared to passive tracer simulations. The model simulates PFOA’s photochemical degradation under UV light, partitioning into organic matter matrices, and re-emission from the surface layer via sea salt aerosols. These factors, combined with primary production, light exposure, salinity, and wind speed, shape PFOA's global distribution, enhancing our understanding of PFAS fate in the ocean.
03:00 PM
USING LONG TERM MONITORING DATA TO INVESTIGATE WATER QUALITY IN BUZZARDS BAY, MA – FROM NITROGEN TO DISSOLVED OXYGEN (9196)
Primary Presenter: Kristin Huizenga, Woodwell Climate Research Center and Buzzards Bay Coalition (khuizenga@woodwellclimate.org)
Buzzards Bay is a shallow estuary in Massachusetts whose coastline consists of a variety of river-fed and groundwater-fed embayments, many of which the state has classified as nutrient impaired. For more than thirty years, the Buzzards Bay Coalition has maintained a water quality monitoring program using a combination of laboratory analyzed nutrient samples and field measurements taken by trained citizen scientists. Baywatchers data provides incredible spatial resolution and insight into local ecosystem dynamics. However the data must also be assessed carefully due to natural variability across embayments, the periodic nature of the measurements, and occasional data gaps at some locations. To better understand trends in nutrients and dissolved oxygen in Buzzards Bay, data was grouped and analyzed by spatial and environmental factors. Embayments varied in both the frequency of low dissolved oxygen measurements (<6 mg/L) as well as if low dissolved oxygen was becoming more or less prevalent. This variability highlights the importance of carefully considering environmental impacts and nutrient sources within embayments as opposed to a more generalized bay-wide approach.
03:15 PM
IMPACT OF VERTICAL COORDINATE SYSTEMS ON THE ACCURACY OF SIMULATING THERMAL STRUCTURE AND SEASONAL CIRCULATION IN LAKE MICHIGAN-HURON (9341)
Primary Presenter: Meena Raju, University of Michigan (meena1982@gmail.com)
In hydrodynamic modeling, the choice of vertical coordinate system (VCS) directly influences vertical processes, including vertical mixing, density stratification, and overturning circulation. VCS choice is particularly important for steep bathymetry (e.g. continental slopes, rift lakes) and weak stratification, which is especially relevant for large freshwater lakes, like the Laurentian Great Lakes, where contemporary operational hydrodynamic models simulate overly diffuse metalimnions. This is problematic for simulating many key ecosystem processes, such as phytoplankton growth and hypolimnetic hypoxia, the latter of which is directly correlated with hypolimnetic water volume. This study uses the Modular Ocean Model version 6.0 (MOM6) to simulate the thermal structure and seasonal circulation of Lake Michigan-Huron. MOM6 applies vertical Lagrangian remapping, a type of Arbitrary Lagrangian Eulerian (ALE) algorithm, enabling flexibility in using various VCSs, including geopotential (z or z*), isopycnal, sigma, or hybrid configurations. This study tests z*, sigma, isopycnal, and hybrid coordinates to assess the strengths and limitations of these VCS for simulating thermal structure and vertical mixing in baroclinic simulations of large, seasonally stratified freshwater lakes, which are novel systems for MOM6 applications. A well-validated hydrodynamic model will aid in coupling with next-generation biogeochemical (COBALT), climate (CM4), and ecosystem (Atlantis) models, improving the understanding of lake-atmosphere interactions, carbon cycling, and ecosystem dynamics.
03:30 PM
PHYTOPLANKTON TRAIT TRADEOFFS INFLUENCE PRODUCTIVITY AND ASSEMBLAGE COMPOSITION IN A SPECIES-RICH BAY MODEL (9804)
Primary Presenter: Sierra Cagle, Texas A&M University at Galveston (scagle1414@gmail.com)
Historically, ecosystem and earth-system models have focused on 1-3 phytoplankton groups, and therefore left assemblage structure unresolved. Considering processes that support ecosystem functioning (e.g. biomass production, maintenance of water quality), differentiating between bulk phytoplankton biomass and species (or functional group) specific biomass is important, as phytoplankton taxa respond differently to environmental fluctuations and potential changes in composition may not reflect changes in bulk biomass. In cases where the traits of an altered assemblage are less desirable, as in the case with harmful algae blooms, such distinctions become critical. In the work presented here, we discuss further development of the spatially-explicit, multispecies, multi-nutrient plankton model for shallow bay systems (MUMPS), focused on incorporation of a self-organized, species-rich phytoplankton assemblage shaped by life history traits and ecological trade-offs. Here, tradeoffs include reduced maximum growth rate for low half-saturation growth coefficients and reduced edibility to a dynamic zooplankton population. Preliminary results show that shifts in phytoplankton assemblage composition to dominance by slower growing species were largely dependent on extended periods of nutrient limitation that occurred during prolonged low inflow conditions. In simulations still to come, we anticipate altered freshwater inflows and nutrient loading conditions to reveal nuanced interactions between bottom-up and top-down (grazer-driven) controls on productivity and community composition.
CS11 - Models and Modelling
Description
Time: 2:30 PM
Date: 31/3/2025
Room: W206A