Browsing by Author "McManamay, Ryan A."
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- The effect of resource stoichiometry on fish and macroinvertebrate nutrient excretionMcManamay, Ryan A. (Virginia Tech, 2007-11-27)Consumer-driven nutrient cycling has been shown to be an important process in supplying inorganic nutrients to autotrophic and heterotrophic organisms in aquatic ecosystems. Theory indicates that consumer nutrient excretion is influenced primarily by an organism's nutrient composition; however, an organism's diet should also play an important role in nutrient excretion, especially if the consumer is nutrient limited. This study asks the question, how does diet influence nutrient excretion of consumers at different trophic levels? Macroinvertebrates and fish were collected from six streams and nitrogen (N) and phosphorus (P) excretion were quantified. Epilithon, leaf detritus, and seston (fine particulate organic matter in transport) were collected and analyzed for carbon (C), nitrogen (N), and phosphorus (P) content in an attempt to qualitatively assess the nutritional status of the diet of primary consumers. Macroinvertebrates were also analyzed for C, N, and P content to assess their nutritional composition in relation to their excretion and also to assess the nutritional composition of the diet of predatory insects and fish. Fish were also analyzed for C, N, and P. Similar to theoretical predictions, fish and macroinvertebrate P excretion was negatively related to P content and the N:P excretion ratio was negatively related to the body N:P ratio. However, this relationship was driven primarily by two phosphorus rich species, mottled sculpin in the fish and crayfish in the macroinvertebrates. Some relationships did emerge between consumer excretion and diet. For example, hydropsychid caddisflies had the highest macroinvertebrate P excretion, possibly explained by the low N:P of seston. However, shredders, eating on a very low N and P diet of leaf detritus, had very low N and P excretion. The relationship between consumers, their food, and nutrient excretion is a matter of mass balance. If the food N:P ratio is higher than that of the consumer, then the N:P excretion should be higher than the consumer N:P and the food N:P, especially if organisms are P-limited. However, N:P excretion by macroinvertebrates and fish were very similar despite large differences in diet. The majority of macroinvertebrates and fish had a lower N:P excretion ratio than the predicted N:P of their food, possibly indicating that 1) consumers were either selectively consuming more P-rich foods than the diets that I assigned them or 2) consumers are generally not N or P limited or influenced by the N or P in their diet. Mottled sculpin and crayfish were the only organisms with a higher N:P excretion than their resources and both had a higher %P than the other fish and macroinvertebrates, respectively. High N:P excretion along with high phosphorus content is indicative of P-limitation. Macroinvertebrates and fish, excluding mottled sculpin and crayfish, had a lower N:P excretion and the N:P ratio of the water column. If consumers do play a role in nutrient dynamics, then consumers could alter the relative abundance of nitrogen and phosphorus by supplying more phosphorus. However, the presence of a P-limited organism, such as mottled sclupin or crayfish, could alter the relative abundance of nitrogen and phosphorus by supplying less phosphorus.
- Environmental flows in the context of unconventional natural gas development in the Marcellus ShaleBuchanan, Brian P.; Auerbach, Daniel A.; McManamay, Ryan A.; Taylor, Jason M.; Flecker, Alexander S.; Archibald, Josephine A.; Fuka, Daniel R.; Walter, M. Todd (2017-01)Quantitative flow-ecology relationships are needed to evaluate how water withdrawals for unconventional natural gas development may impact aquatic ecosystems. Addressing this need, we studied current patterns of hydrologic alteration in the Marcellus Shale region and related the estimated flow alteration to fish community measures. We then used these empirical flow-ecology relationships to evaluate alternative surface water withdrawals and environmental flow rules. Reduced high-flow magnitude, dampened rates of change, and increased low-flow magnitudes were apparent regionally, but changes in many of the flow metrics likely to be sensitive to withdrawals also showed substantial regional variation. Fish community measures were significantly related to flow alteration, including declines in species richness with diminished annual runoff, winter low-flow, and summer median-flow. In addition, the relative abundance of intolerant taxa decreased with reduced winter high-flow and increased flow constancy, while fluvial specialist species decreased with reduced winter and annual flows. Stream size strongly mediated both the impact of withdrawal scenarios and the protection-afforded by environmental flow standards. Under the most intense withdrawal-scenario, 75% of reference headwaters and creeks (drainage areas < 99 km(2)) experienced at least 78% reduction in summer flow, whereas little change was predicted for larger rivers. Moreover, the least intense withdrawal scenario still-reduced summer flows by at least 21% for 50% of headwaters and creeks. The observed 90th quantile flow-ecology relationships indicate that such alteration could reduce species richness by 23% or more. Seasonally varying environmental flow standards and high fixed minimum flows protected the most streams from hydrologic alteration, but common minimum flow standards left numerous locations vulnerable to substantial flow alteration. This study clarifies how additional water demands in the region may adversely affect freshwater biological integrity. The-results make clear that policies to limit or prevent water withdrawals from smaller streams can reduce the risk of ecosystem impairment.
- Providing a Restoration Framework for Regulated RiversMcManamay, Ryan A. (Virginia Tech, 2011-03-28)With over 800,000 dams occurring globally and the construction of thousands more being proposed, successful restoration of regulated rivers will depend on the creation of broadly applicable frameworks that provide management solutions by generalizing patterns in habitat and ecology. Based on the prevailing scientific literature, restoring natural stream flows in disturbed rivers is dependent upon developing quantitative, transferable stream flow-ecology relationships. The purpose of my dissertation was to apply a framework to regulated and unregulated streams within an eight-state region of the southeastern US to test its ability to generalize patterns in natural and altered stream flow and develop flow-ecology relationships. I created a simplified, 5-step version of the Ecological Limits of Hydrologic Alteration (ELOHA) framework (Poff et al. 2010). I carried out each of the steps in sequential order for unregulated and dam-regulated streams found in my region. The steps of my restoration framework are as follows: 1. Develop a natural flow classification of unregulated streams 2. Develop a tool that uses landscape characteristics to predict flow class membership 3. Use the predictive tool or pre-disturbance hydrologic information to classify regulated rivers to natural flow classes 4. Based on class membership, generalize patterns in hydrologic alteration 5. Relate ecological patterns to patterns in hydrologic alteration in relation tomorphology, temperature, and landscape disturbance Altogether, the results of steps 1-4 suggest that patterns in natural flow dynamics and hydrologic alterations can successfully be placed within a framework and generalized to provide the basis and context for environmental flow management; however, results of step 5 suggest that patterns in flow alteration were poorly related to fish assemblages relative to channel morphology, habitat fragmentation, temperature, and substrate. Thus, the development of patterns in hydrologic alteration using the existing frameworks (including mine) may not be ecologically-relevant. My results suggest that current regulated river restoration should not be dependent upon the development of flow-ecology relationships alone, but the interaction between flow, morphology, and temperature within a landscape disturbance context. These relationships should be incorporated within a hierarchical framework to guide restoration efforts in regulated rivers in the future.