Browsing by Subject "Nutrients."
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Item Assessing interactions between nutrients and aquatic toxicity : influences of nitrogen and phosphorus on ionic silver toxicity to the aquatic macrophyte Lemna gibba.(2011-05-12T15:18:27Z) Bian, Jingyi, 1985-; Brooks, Bryan W.; Environmental Science.; Baylor University. Dept. of Environmental Science.Though nutrients and silver often co-occur in aquatic ecosystems, the combined effects of these environmental stressors on aquatic plants are poorly understood. Such coexposures are important because nanosilver is increasingly released to the environment, and recent studies indicate that the dissolved fraction of nanosilver appears to be more acutely toxic to aquatic life. The primary objective of this study was to understand the effects of nitrogen (N) and phosphorus (P) concentrations and N : P ratios on the toxicity of ionic silver toxicity to the model aquatic macrophyte Lemna gibba over 7-d study periods. The experimental results indicated that L. gibba were more sensitive to silver (e.g., lower EC50 values) when N and P concentrations were higher. In addition, greater ionic silver toxicity occurred under higher P-availability (e.g., lower N : P ratios) conditions. L. gibba frond number and fresh weight were also differentially affected and showed variable sensitivity to different nutrient x silver treatment combinations, which highlights the importance of considering site-specific nutrient conditions during the prospective and retrospective assessment and management of silver impacts to primary producers.Item Effects of stream nutrient enrichment on aquatic insect stoichiometry : importance of life-history traits, sex, and ontogeny.(2014-01-28) Back, Jeffrey Alan.; King, Ryan Steven, 1972-; Biology.; Baylor University. Dept. of Biology.I investigated the effects of stream nutrient enrichment on aquatic insect stoichiometry, particularly in the context of species life-history traits, sex, and ontogeny. The majority of studies investigating nutrient content of organisms preceding this research had assumed that aquatic insect species maintain a homeostatic concentration of carbon, (C) nitrogen (N) and phosphorus (P) content with respect to developmental stage and nutrient enrichment of their food resources. However, P content was shown not to be homeostatic across the ontogeny of 19 species of aquatic insects and C and N were quasihomeostatic. Growth rates for Caenis mayflies were higher on P enriched foods, and smaller individuals grew faster than larger individuals. Further, female mayflies were equal to or larger than males and had equal or higher body P content than males, depending upon species. A phylogenetic pattern in body P content was found for baetid and leptophlebiid mayflies. Male and female baetids declined in % P across their ontogeny, whereas leptophlebiid females increased in the 3 species studied. Finally, a study of streams spanning a steep nutrient enrichment gradient revealed that females of Baetis sp. and Neochoroterpes nanita attained a much larger size than males and were more enriched in P. Body P content of both mayfly species was higher at low P sites, and body size was much larger at high P sites. In insects, P content is a good indicator of growth rate (higher P, faster growth), and body size is a good predictor of fecundity (bigger body, more fecund). Nutrients not only play a role in determining an organism’s reproductive success, growth rate and size. The effects of nutrients are seen in organism nutrient recycling rates, food web organization, and community structure and function.