An estuary, according to the National Water Act of 1998, is a partially or fully enclosed body of water which is open periodically or permanently to the sea within which the sea water can be diluted, to an extent that is measurable with freshwater from inland. Estuaries and the lands surrounding them are places of transition from land to sea, and from freshwater to saltwater. Although influenced by the tides, estuaries are protected from the full force of ocean waves, winds, and storms by the reefs, barrier islands, or fingers of land, mud, or sand that surround them. South Africa’s estuaries are important and irreplaceable habitats, especially for prawns, fish, wading birds and mangroves. They are home to numerous plants and animals that live in water that is partly fresh and partly salty. Estuaries are also homes to growing coastal communities as increasing number of people occupy watersheds. However, estuaries are also threatened. One of the threats is reduced river water inflow. This study applies the contingent valuation method (CVM) to elicit user’s willingness to pay to mitigate the negative impacts of reduced freshwater inflow into selected five Eastern Cape and Kwazulu-Natal estuaries: the Sundays, Gamtoos, Mdloti, Mgeni and Mvoti estuaries. In addition to the contingent valuation method, the travel cost method was used to generate comparative values. The contingent valuation method is a technique to establish the value of a good (or service) that is not bought or sold in an actual market. The CVM establishes the economic value of the good by asking the users of an environmental good to state their willingness to pay (WTP) for a hypothetical project to prevent, or bring about, a change in the current condition of the environmental good. The users’ WTP is aggregated to establish a total willingness to pay (TWTP) for the population of the users of the environmental good.

The trophic state of lakes is commonly defined by the concentration of nutrients in the water column. High nutrient concentrations generate high phytoplankton production, and lakes with low nutrient concentrations are considered low-productive. This simplified view of lake productivity ignores the fact that benthic primary producers and heterotrophic bacteria can be important basal producers in lake ecosystems. In this thesis I have studied clear-water and brown-water lakes with respect to primary production, respiration and bacterial production based on allochthonous organic carbon. These processes were quantified in pelagic and benthic habitats on temporal and spatial scales. I also calculated the net ecosystem production of the lakes, defined as the difference between gross primary production (GPP) and respiration (R). The net ecosystem production indicates whether a lake is net heterotrophic (GPP < R), net autotrophic (GPP > R) or in metabolic balance (GPP = R). Net heterotrophic lakes are sources of carbon dioxide (CO2) to the atmosphere since respiration in these lakes, by definition, is subsidized by an external organic carbon source. External organic carbon is transported to lakes from the terrestrial environment via inlets, and can serve as a carbon source for bacteria but it also limits light availability for primary producers by absorbing light. On a seasonal scale, four of the clear-water lakes studied in this thesis were dominated by primary production in the soft-bottom benthic habitat and by respiration in the pelagic habitat. Concentrations of dissolved organic carbon (DOC) were low in the lakes, but still high enough to cause the lakes to be net heterotrophic. However, the lakes were not low-productive due to the high production in the benthic habitat. One of the clear-water lakes was studied also during the winter and much of the respiration under ice was supported by the benthic primary production from the previous summer. This is in contrast to brown-water lakes where winter respiration is suggested to be supported by allochthonous organic carbon. By studying lakes in a DOC gradient (i.e. from clear-water to brown-water lakes) I could draw two major conclusions. The lakes became less productive since benthic primary production decreased with increasing light extinction, and the lakes became larger sources of CO2 to the atmosphere since pelagic respiration was subsidized by allochthonous organic carbon. Thus, lake carbon metabolism can have an important role in the global carbon cycle due to their processing of terrestrial organic carbon and to their possible feedback effects on the climate system.

This project covers the environmental issues of the proposed Lakes and Streams Project for the City of San Bernardino. The water history of San Bernardino, from the hot springs to the development of the current municipal water system, is also detailed. Two curriculum units teach students how to use environmental issue analysis skills. One focuses on the water history of San Bernardino and is aimed at grades three to five. The other immerses middle grade students directly into the Lakes and Streams issue.

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The prevalence of hypoxia in aquatic systems has increased in recent decades and climate change is expected to worsen the extent and severity of hypoxic phenomena worldwide. Moreover, aquatic hypoxia has produced adverse ecological consequences and stimulated research interest within the Laurentian Great Lakes. The physiological stress imposed by hypoxia reduces habitat quality for most aquatic biota and causes changes in patterns of resource use and food web dynamics. We conducted a review of the primary literature to identify trends in prevalence of Great Lakes hypoxia research and broadly classify the unique hypoxic conditions afflicting Great Lakes ecosystems. We found that the majority of research effort toward Great Lakes hypoxia is focused on the Lake Erie central basin. Our review further revealed that this does not characterize the breadth of hypoxic phenomena that occur throughout the Great Lakes region. We then utilized a long-term monitoring dataset provided by the U.S. Environmental Protection Agency Great Lakes National Program Office to quantify the impact of Lake Erie central basin hypoxia on habitat quality of several fish species. We found that bioenergetics-based growth-rate potential models have a potential application as the framework for the development of biological endpoints that measure the effects of hypoxia on aquatic biota. Finally, we utilized stable isotope analysis to look for broad spatial and temporal trends in resource utilization within distinct regions of the Lake Erie central basin, with hypoxia and large-scale hydrodynamic patterns serving as potential driving patterns for spatial differences.

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