Date of Award

10-5-2023

Publication Type

Dissertation

Degree Name

Ph.D.

Department

Earth and Environmental Sciences

Keywords

baselines;Ecopath;food webs;Lake Erie;stable isotopes

Supervisor

Aaron Fisk

Supervisor

Yingming Zhao

Rights

info:eu-repo/semantics/openAccess

Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

Abstract

Aquatic ecosystems are constantly adapting to fluxes in season, temperature, nutrient cycling, and prey availability. Consequently, aquatic food webs are dynamic, and relationships between species are perpetually changing as organisms and primary producer communities adapt to current environmental conditions both in time and space. Despite this knowledge however, many food web studies continue to use temporally static and spatially homogenous representations of food webs. This thesis proposes that a detailed investigation of temporal and spatial trends in a large lake ecosystem can improve our understanding of the mechanisms and drivers of spatial and temporal variation in food web structure and function. Lake Erie, the smallest of the Laurentian Great Lakes by volume, is divided into three bathymetrically distinct basins which are defined by unique environmental characteristics, and, as such, provides an excellent system to investigate spatio-temporal variation in food web structure. To this end, I investigated spatial and temporal variation in stable isotopes of δ13C, δ15N, and δ34S in lower trophic level organisms throughout Lake Erie, establishing an isotopic baseline which could be used to investigate larger spatial trends in food web structure using stable isotopes. Finally, I use the foundational food web structure provided by stable isotopes, and biomass data collected from annual community surveys to investigate how trophic transfer efficiency changes in each of Lake Erie’s three basins using Ecopath modelling. Unique environmental characteristics of each basin in Lake Erie influenced stable isotopes in lower trophic levels, and food web structure and function. Strong temporal variation in stable isotopes of δ13C, δ15N, and δ34S in seston, a suspended mixture of zooplankton, phytoplankton, and particulate and dissolved detritus, reflected seasonal changes in the plankton community. Likewise, dynamics of δ13C, δ15N and δ34S in zoobenthos, including Dreissena spp. and Oligochaeta, were influenced by nutrient gradients, hypoxia, and water flow throughout Lake Erie. Building off these observations, analysis of δ13C and δ15N of 23 of the most common invertebrates and fish species in Lake Erie revealed distinct differences in food web structure among basins, with the central basin food web being significantly influenced by annually recurring seasonal hypoxia. Finally, Ecopath models for each basin and the whole of Lake Erie showed that trophic transfer efficiency varied throughout the lake. The findings of this thesis expand the current comprehension of temporal and spatial dynamics in large lake food webs and reveal the importance of quantifying such variability to predict changes related to our fluctuating environment, particularly climate.

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