<p>Results from this study enables a better understanding of groundwater surface water interactions in the TMG, particularly regarding aquatic ecosystems. It has also highlighted the necessity to do proper impact assessments before proceeding with bulk abstraction from this important aquifer. The results also demonstrated the importance of differentiating between real groundwater and non-groundwater discharge contributions to surface hydrology and where these interface areas are located.</p>

Although there is much theoretical and empirical data about the life history responses of time constrained organisms, little is known about the latitude compensating mechanism that enables northern populations’ developmental rates to compensate for latitude. To investigate the importance of photoperiod on development and growth, I collected adults and raised the offspring of the obligatory univoltine damselfly Lestes sponsa from two populations at different latitudes (53º N and 63º N). The offspring were raised in a common laboratory environment at 21º C and at the two photoperiods corresponding to the sites of collection. Field data showed that adult and egg sizes decreased towards the higher latitude. This adult size difference was a genetically fixed trait since the same size difference between populations was also found when larvae where reared in the laboratory. All studied individuals expressed shorter development time and faster growth rates under northern photoperiod regimes. Northern damselflies showed fixed body size and mass at emergence despite being reared at different photoperiod conditions. Similarly, southern individuals kept body size at emergence constant at both photoregimes, but overcompensated shorter development time in the northern photoregime by gaining higher body mass than in original,southern photoregime. There was no difference in hatching synchronisation between larvae from the south and the north. I found evidence of higher synchrony at adult emergence among northern individuals. The previous investigation of L. sponsa phenology in natural conditions together with these laboratory results indicate the presence of the latitude compensating mechanism that is triggered by a response to photoperiod. A positive correlation between photoperiod and developmental rate in this damselfly, and probably in many other temperate insect species, might be adaptive since it optimises the life history stage transitions and body size/mass at each latitude.

Aquatic vegetation management and fisheries management are inseparable, however conflicts are often perceived between the two. We investigated the impact of biological, chemical, and no vegetation control on the ecology of private impoundments stocked with largemouth bass and bluegill sunfish. The primary purpose of this study was to determine if aquatic vegetation management had significant impact on pond ecology. A secondary purpose of this study was to collect data for a separate descriptive study on the impact of vegetation management on plankton populations. Nine 0.10 acre ponds were obtained at the Aquaculture Research and Teaching Facility of Texas A and M University in the fall of 2005. Southern naiad (Najas guadalupenis) was transplanted into each pond at a stocking rate of one ton per surface acre. One of three treatments was then randomly assigned to each pond. The treatments were replicated three times and consisted of: an herbicide treatment using Reward and Cutrine, a triploid grass carp treatment, and a control treatment. Fathead minnows (Pimephales promelas), bluegills (Lepomis macrochirus), and largemouth bass (Micropterus salmoides) fingerlings were stocked in each pond. The treatments were initiated on May 31, 2006. Prior to the initiation of the treatments, sampling of each pond occurred for hardness, total phosphorus, nitrite, nitrate, ammonia-nitrogen, dissolved oxygen, turbidity, pH, and temperature. Macroinvertebrate samples were collected from each pond. Post-treatment sampling was conducted on the herbicide treatment and the control at day 2, day 7, day 14, day 28, and monthly thereafter. Posttreatment sampling on the triploid grass carp treatment was conducted at day 14, day 28, and monthly thereafter. One-way ANOVA tests were conducted on the data using SPSS 15.0, and multivariate analysis was conducted using CANOCO software. Significant differences between treatments were found for the parameters turbidity, macrophyte percent coverage, macroinvertebrate species richness, largemouth bass mean weight, and largemouth mean length. Herbicide application and grass scarp stocking significantly decreased the percent coverage of macrophytes in the ponds. Turbidity was significantly increased in the herbicide and grass carp treatments. Largemouth bass mean weight and length were significantly higher in the grass carp ponds. No significant relationships were found in the multivariate analysis; however, there appeared to be several trends within the multivariate analysis that provide insight into potential ecological relationships between the various parameters. The results of this study provide great insight into the impact that various aquatic vegetation management strategies have on the ecology of small impoundments and will help private pond owners and managers conduct better pond management when dealing with aquatic vegetation problems.

Nutrient availability and herbivory can regulate primary production in ecosystems, but little is known about how, or whether, they may interact with one another. Here I investigate how nitrogen availability and insect herbivory interact to alter above- and belowground plant community biomass in an old-field ecosystem. In 2004, 36 experimental plots were established in which soil nitrogen (N) availability (at three levels) was manipulated and insect abundance (at two levels) in a completely randomized plot design. In 2009, after six years of treatment, I measured aboveground biomass and assessed root production at peak growth. Overall, I found a significant effect of soil N availability on both above- and belowground plant biomass while insects affected only aboveground biomass of subdominant plant species and coarse root production; there were no statistical interactions between N availability and insect herbivory for any response variable. Specifically, responses of aboveground and belowground community biomass to nutrients were driven by reductions in soil N, but not additions, indicating that soil N may not be primarily limiting production in this ecosystem. Insect herbivory altered the aboveground biomass of the subdominant plant species and altered allocation patterns to coarse root production belowground. Overall, the results of six years of nutrient amendments and insect removals suggest strong bottom-up influences on total plant community productivity.

Master's thesis. / Format: PDF. Bibl.

Thesis (M.S.)--University of North Texas, 2001. / Title from PDF title page (viewed on Dec. 9, 2004). Includes bibliographical references (p. 51-57).

No description available.

I examined the distribution of stable isotope ratios of nitrogen $( delta sp{15}$N) and carbon $( delta sp{13}$C) in fish and aquatic invertebrates. Animals are enriched in $ delta sp{15}$N compared to their diet and I hypothesized that among-lake variation in the $ delta sp{15}$N of a top predator should reflect variation in the length of the food chain leading to it. A comparative study of a biomagnifying contaminant, mercury, confirmed that the presence or absence of certain key organisms such as pelagic forage fish and the crustacean Mysis relicta determined among-lake variation in mercury in lake trout, a top predator in the lakes. Mercury levels from the longest food chains where pelagic forage fish and Mysis were present were higher than those from the shortest food chains where these last two components were missing. This biogeographic variation in food chain length was correlated with variation in the $ delta sp{15}$N of trout. The use of $ delta sp{15}$N as a continuous, integrative measure of trophic position was further supported by its correlation to mercury in lake trout. However, such cross-system comparisons in $ delta sp{15}$N can be complicated by differences in $ delta sp{15}$N at the base of the food chain. Using large primary consumers (unionid mussels) as bio-indicators, I showed that $ delta sp{15}$N increases markedly with the human population in the lake watershed, an effect of the high $ delta sp{15}$N of human sewage. Correcting for this baseline variation in $ delta sp{15}$N, I reported that food chains leading up to nearshore fish species varied by about only one trophic level among the 35 lakes studied. A study of the $ delta sp{15}$N of coral reef and intertidal organisms collected along the coast of the the Carribean island of Barbados extended these patterns observed in lakes to coastal systems: baseline variation in $ delta sp{15}$N was related to human density on the adjacent watershed and within-site variation $ delta sp{15}$N

<p>Results from this study enables a better understanding of groundwater surface water interactions in the TMG, particularly regarding aquatic ecosystems. It has also highlighted the necessity to do proper impact assessments before proceeding with bulk abstraction from this important aquifer. The results also demonstrated the importance of differentiating between real groundwater and non-groundwater discharge contributions to surface hydrology and where these interface areas are located.</p>

Over the past two decades, Lake Winnipeg has been experiencing increasingly rapid eutrophication, and large cyanobacterial blooms now form in the North Basin in most years in late summer or fall. Cyanobacteria are considered a relatively poor food source compared with other phytoplankton, but the impacts of these blooms upon the primary consumers in the lake have not previously been researched. A microscopic analysis of whole water samples found cyanobacteria to be scarcely present in summer 2012, with nitrogen-fixing and non-fixing cyanobacteria comprising 11.2% and 8.4% of the basin-wide biovolume, respectively, and all but absent in fall. Gut content analysis of chironomids found that cyanobacteria made up an almost negligible part of their diet. Stable isotope analysis revealed that nitrogen-fixing cyanobacteria reduced phytoplankton δ15N values, and that this same reduction could be traced through the zooplankton, but not down to the sediments or chironomids.