Please use this identifier to cite or link to this item: http://hdl.handle.net/2440/113583
Type: Theses
Title: Food web dynamics in the benthic habitat of a groundwater-fed, freshwater pond
Author: Liu, Yang
Issue Date: 2017
School/Discipline: School of Biological Sciences
Abstract: Human activities have significantly altered biogeochemical cycles of major elemental nutrients and hydrological cycles of water all over the world, causing degradation of many freshwater ecosystems. Enrichment in essential nutrients, especially nitrogen (N) and phosphorus (P), has been accused to progressively reduce the resilience of systems and pave the way to regime shifts in freshwater environments. Regime shifts mark profound changes in ecosystem structure and function, many of which have been carefully evaluated in certain types of habitat, for example, pelagic zones of lakes. However, the consequences of potential regime shifts are understudied in some unique inland waterbodies, such as groundwater-fed freshwater ponds. In the southeast of South Australia, vast areas of peat swamps were drained and transferred into managed pastures, and remanent wetlands are highly valuable because of their importance in delivering critical ecological and socio-economic services. Even so, many of the remaining wetlands are under the threat of increasing nutrient concentrations due to pollution of groundwater by applied fertilizers and decreasing incoming flows owing to extraction of groundwater for agricultural use. Ewens Ponds, is an example of such wetland systems with deteriorated condition, as evidenced by gradual replacement of submerged vascular plants by benthic filamentous algae and episodic occurrence of algal blooms. Traces of upcoming regime shifts may hide in gradual changes of key ecological processes, and many of these processes are connected through the energy and material flowing within the ecosystem. Determining trophic links and transfer efficiencies between food-web components, thus is critical to the understanding of how ecosystems are influenced by changes in environmental factors. Resources supporting the major benthic macroinvertebrate and fish consumers and their respective contribution to specific consumers were investigated in Ewens Ponds using a combination of gut content, stable isotope and fatty acid composition analysis. The results demonstrated that epiphytes and filamentous cyanobacteria were the most important sources of organic carbon for benthic macroinvertebrates and fish, with substantial supplement of macrophytes to the diet of these consumers. Contributions of different basal resources to consumer biomass were affected by their availability and quality. Disparity of stoichiometric ratios between primary producers and primary consumers were greater than that between fish and their prey, and population size of several consumers may be constrained by the low availability of P in Ewens Ponds. Periphyton production was unlikely to be limited by light intensity, but was certainly limited by P concentration. It is likely that there is competition between benthic macroinvertebrates for epiphytes as a high-quality food resource. Accumulation of massive biomass of benthic filamentous algae was associated with the low transfer rate of this form of organic carbon production to animals. Complex trophic interactions related to feeding preferences and habitat selection between components of the food web in the benthic habitat of Ewens Ponds regulated the production of organisms at different trophic levels. Ecosystem dynamics in freshwater environments may be greatly reshaped after the occurrence of regime shifts. This thesis emphasized the importance of considering trophic interactions among multiple groups of the members of the food web when assessing ecosystem responses to environmental factors and also generated information that are useful in an applied sense.
Advisor: Brookes, Justin D.
Dissertation Note: Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Biological Sciences, 2018
Keywords: Research by publication
food web
stable isotope
fatty acids
ecological stoichiometry
benthic
freshwater pond
Provenance: This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at http://www.adelaide.edu.au/legals
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