Philosophiae Doctor - PhD / The disposal of brine effluent from inland wastewater desalination plants is a growing global problem with adverse economic and environmental implications because of the substantial cost associated with its disposal and the potential for polluting groundwater resources. Currently, the best and most economical option for brine disposal from inland desalination plants is the use of evaporation ponds, which concentrate the liquid until getting a solid waste that can be valued or directly managed by an authorized company. The effectiveness of these ponds is therefore dependent on the evaporation rate, which has previously been improved by the addition of dyes such as methylene blue. However, the addition of chemical dyes to the evaporation ponds poses a threat to the environment, wildlife, and humans.

Integrating green or blue space into cities can provide environmental and public health benefits which maximize urban sustainability. One type of green/blue infrastructure that has been understudied is urban stormwater ponds, which are used to manage stormwater runoff. Their performance is typically only evaluated in terms of hydrological functions, with little focus on their capacity to provide ancillary benefits to communities. In this exploratory study, an online survey was distributed to six neighbourhoods in the City of Ottawa, ON to gain insight into the social value of urban stormwater ponds. The results revealed that despite some disadvantages, most respondents visited their neighbourhood stormwater ponds regularly and largely appreciated the cultural ecosystem services provided by these ponds, such as opportunities for experiencing nature, especially wildlife, and outdoor recreation. These findings can be used to improve the multifunctionality of stormwater ponds and optimize both environmental and social sustainability outcomes.

In the Southern Appalachians, there are growing concerns about Spotted Salamanders (Ambystoma maculatum) due to habitat destruction and the uncertain future of their forested riparian habitat. In this study, I establish baseline data of a population of Spotted Salamanders so future monitoring of this population can be performed. The study site is located in northeastern Tennessee, just east of the city of Bristol. It is a vernal pond at the Osceola Island Recreation Area one mile below the South Holston Dam on Holston View Dam road. A drift fence was established completely around the perimeter of the vernal pond to capture Spotted Salamanders entering and exiting the study pond. Individual Spotted Salamanders were identified using spot pattern recognition. An estimated population size of 2,449 Spotted Salamanders was determined to utilized the pond for breeding for the spring of 2003.

Algal blooms are a common occurrence in water bodies of all shapes and sizes throughout the United States and countries around the world. The State of Florida is no exception to this phenomenon. Cyanobacteria, or blue-green algae, have proven to be of special concern due to its proliferation and potential to produce toxins that are harmful to humans, livestock and wildlife. A casual drive along the roads and in the neighborhoods of central Florida will confirm algal conditions in many areas. The potential for exposure to harmful and possibly fatal toxins associated with these algal blooms are becoming more evident as urban development progresses. Detailed studies have been previously performed for large lakes and rivers in the State of Florida, but no studies have been performed regarding stormwater ponds. Since stormwater ponds in residential neighborhoods are a common source for irrigation, research in this area is warranted due to the potential health effects associated with Cyanobacteria. This research was conducted to determine if Cyanobacteria does exist in stormwater ponds and to what extent. Cyanobacteria were found to be in stormwater ponds of various sizes, locations and watersheds in the central Florida area. Even though the algae and its associated toxins were encountered in the stormwater ponds evaluated for this study, the levels detected were much lower than the values discovered in previous studies performed in the larger lakes and rivers around the State.

Exotic amphibians are often detrimental to native biotas. In Florida, the exotic Cuban Treefrog (Osteopilus septentrionalis) eats native frogs and may outcompete them for resources. Cuban Treefrogs thrive in disturbed areas and around buildings, and often breed in manufactured wetlands such as retention ponds and borrow pits. This study identified limnological, landscape, and biotic characteristics that discouraged pond use by Cuban Treefrogs and promoted use by native amphibian species. I sampled natural and manufactured ponds in Orange County, Florida, for one year, using standard methods to estimate the species richness and relative abundance of amphibians and their potential fish and macroinvertebrate predators. I determined the relationship between the presence of Cuban Treefrogs and twelve limnological (% vegetation, slope, pond age, pH, % dissolved oxygen, air temperature, water temperature, turbidity, conductivity, depth, perimeter, and area) and seven landscape characteristics (% canopy closure over ponds, building density, distance to nearest building, road density, distance to nearest road, distance to nearest forest stand, and % forest cover), plus five biotic factors (native amphibian richness and abundance, fish richness and abundance, and macroinvertebrate abundance). No relationship existed between native amphibian abundance or species richness and the presence or absence of Cuban Treefrogs. Ponds with a greater percentage of vegetation, large perimeters, and low pH and turbidity had greater native amphibian species richness. Cuban Treefrogs were more likely to be found in ponds with a greater percentage of aquatic vegetation and small perimeters. My results show that building large retention ponds containing low-turbidity water will restrict colonization by Cuban Treefrogs and maintain species richness of native amphibians.

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A floating treatment wetland (FTW) is an ecological approach which seeks to reduce point and nonpoint source pollution by installing substrate rooted plants grown on floating mats in open waters. While relatively novel, FTW use is increasing. A review of literature identified several research gaps, including: (1) assessments of the treatment performance of FTWs; (2) evaluations of FTWs in the U.S., particularly within wet ponds that receive urban runoff; and (3) plant temporal nutrient distribution, plant growth rate, and the long-term persistence of the FTWs in temperate regions with periodic ice encasement. An assessment model, i-FTW model, was developed, and its parameter s fitted based on data from 14 published FTW studies in the first research topic. The estimated median FTW apparent uptake velocity with 95% confidence interval were 0.048 (0.018 - 0.059) and 0.027 (0.016 - 0.040) m/day for total phosphorus (TP) and total nitrogen (TN), respectively. The i-FTW model provided a more accurate prediction in nutrient removal than two common performance metrics: removal rate (mg/m2/day) and removal efficiency (%). In the second research topic, the results of a mesocosm experiment indicated that FTWs with 61% coverage, planted with pickerelweed (Pontederia cordata L.) or softstem bulrush (Schoenoplectus tabernaemontani), significantly improved TP and TN removal efficiency of the control treatment by 8.2% and 18.2%, respectively. The pickerelweed exhibited significantly higher phosphorus and nitrogen removal than the softstem bulrush when water temperatures were greater than 25 deg C. Field observations in the third research topic found that pickerelweed demonstrated higher phosphorus removal performance (7.58 mg/plant) than softstem bulrush (1.62 mg/plant). Based on the observed seasonal changes in phosphorus distribution, harvest of above-ground vegetation is recommended to be conducted twice a year in June and September. Planted perennial macrophytes successfully adapted to stresses of the low dissolved oxygen (DO) concentrations (minimum: 1.2 mg/L), ice encasement, and relatively low nutrient concentrations in the water (median: 0.15 mg/L TP and 1.15 mg/L TN). Systematic observation of wildlife activities indicated eight classes of organisms inhabiting, foraging, breeding, nursing, or resting in the FTWs. Recommendations for FTW design and suggestions for further research are made based upon these findings. / Ph. D.

Benthic macroinvertebrate colonization of twelve 0.04-ha experimental ponds was studied for the 1st yr of their existence. The ponds were filled in late January 1988, and artificial substrate samples were retrieved at 4-wk intervals from February 25, 1988 to February 25, 1989. The first organisms (<u>Chironomus</u> and ceratopogonidae) were collected 4 wk after filling. Diptera, primarily several genera of chironomids, were followed in colonizing the ponds by Coleoptera, Ephemeroptera, and odonata. The arrival of new taxa corresponded to adult flight periods. Non-insect taxa (oligochaeta, Nematoda, Amphipoda) were collected in relatively low numbers and then only late in the year. A total of 29 taxa were collected, 13 of which were present in all 12 ponds. Mean number of taxa, diversity, and evenness increased rapidly during the first 7 mo but never became very high. Density increased slowly throughout the spring and summer, increased rapidly during the autumn and eventually became quite high. Density increased slowly throughout the spring and summer, increased rapidly during the autumn and eventually became quite high. Community structure was dominated by Chironomidae (ca. 85%) and Ephemeroptera (ca. 9%). Trophic function was dominated by detritus-feeding collectors (ca. 79%). Factors that influenced the structure and function of the new experimental ponds appeared to be: lack of connection to colonized waters, small size, and simple, homogeneous habitat and feod resources. Although at the end of the study the aquatic insect fauna was typical of shallow lentic environments, the mesocosms were not considered ready for use in chemical testing because of low densities of other macroinvertebrates. The mesocosms were somewhat variable in regard to community structure, however, no mesocosm was found to be a consistent outlier. Density could be measured less precisely than other structural parameters (number of taxa, diversity, and evenness). All of the structural parameters, however, could be estimated with reasonable precision (within 40%) using groups of three mesocosms. Greater numbers of replicate ponds would be required to precisely measure the density of individual taxa. Secondary production was measured for seven dominant taxa. Although the estimation of secondary production required more time, it could be done at a similar level of precision as density and was considered more ecologically meaningful than structural measurements. / Ph. D.

US catfish producers, seeking to reduce production costs, adopted technologies and production systems with the potential to increase the catfish pond productivity. Catfish pond intensification was accompanied by increased operating risk due to increased reliance on operating inputs. Split ponds were one adopted production system. The US catfish industry has adopted four split-pond variants differentiated by water circulation mechanism. Variants include the slow-rotating paddlewheel, the modified paddlewheel aerator, the screw pump, and the axial-flow turbine pump. Initial investment ranged from $54,400/4-ha ponds to $71,150/4-ha pond. Mean annual gross fish yield ranged from 12,876 kg/ha to 16,984 kg/ha. Net returns were positive for all designs under current economic conditions. The modified paddlewheel aerator and slow-rotating paddlewheel designs show the most promise for adoption. US catfish producers use multiple production strategies of varying intensity level, species produced, and pond design. Commercial farm data were used to quantify the economic risk of six commonly used catfish production strategies. Second order stochastic dominance (SOSD) was exhibited by multiple-batch and intensively aerated production of channel catfish over low intensity culture of channel catfish. Higher intensity hybrid catfish production strategies exhibited SOSD over medium intensity culture of hybrid catfish. Variations in fish yield, feed price, and feed conversion ratio were the primary contributors to variations in production cost. Hybrid catfish production strategies were dominated by yield (production) risk and channel catfish production strategies were dominated by price (market) risk. Off-flavor has been a persistent problem in the US catfish industry and contributes to economic risk. The cost of off-flavor was quantified at the farm level. A survey of catfish producers carried out in 2022 (n=54) revealed that farms representing 85% of the foodfish production area followed management practices for curbing off-flavor. The average annual off-flavor prevalence and the associated processing plant sample rejection rate was 27%. Off-flavor caused harvest delays averaged 23 days. Copper sulfate and diuron were used for managing off-flavor with diuron being the most popular choice used on 78% of the surveyed area. Direct annual cost associated with off-flavor management on catfish farms amounted to $39.9 million ($2,325/ha or $0.272/kg) in 2022.