Doctor of Philosophy (PhD)
Renewable Natural Resources
Weak biotic responses to habitat gradients within Northern Gulf of Mexico streams have been attributed to spatial and temporal variability. Landscape and in-stream habitat descriptions are presented for watersheds within Pleistocene terraces of the Coastal Plains geomorphic province of Louisiana, USA. Geologic influences on stream habitat were inferred by comparing multivariate ordinations on physicochemical measurements between terraces. Seasonal variability was assessed during a drought year (2011) and a typical water year (2013). Within coastal plains of Louisiana, stream condition was more similar within terraces than within river basins. Permutational MANOVA models indicated significantly different stream habitat between Uplands and Prairie, with intermediate habitat in Flatwoods. Seasonal differences were detected more frequently during normal flow condition, suggesting that baseflow impacts habitat heterogeneity between adjacent terraces. Macroinvertebrates were collected throughout a drought year at stream sites stratified among coastal plain terraces to quantify spatial and temporal variability and identify functional habitat gradients. Macroinvertebrate assemblages differed between Uplands and Prairie terraces, especially regarding insect taxa, which were associated with better water quality and structurally complex habitat. Drought and other disturbances selected against lotic taxa expected in the intermediate Flatwoods terrace. Widening the lateral scope of the study landscape helped identify habitat thresholds and define regional habitat preference of individual taxa. Aquatic habitat improvement in Prairie terrace bayous should include restoring baseflow, increasing structural complexity and protecting macroinvertebrate source populations in the Uplands. Aquatic insect larvae are important bio-indicators and flexible life histories of many taxa may reflect regional or seasonal variability in environmental conditions. Larval development and reproductive strategy inferred from seasonal size distributions are presented for specimens of Caenis sp. (Ephemeroptera: Caenidae) in the coastal plain terraces of Louisiana. Influence of regional drought, landscape features and water quality on growth rate, terminal size and voltinism are examined. Caenis sp. in subtropical Louisiana exhibited bivoltine emergences in November and July. Size at instar development class did not differ by terrace, but was influenced by local water quality (e.g., orthophosphate concentration, specific conductance and biochemical oxygen demand). Maintenance of baseflow during drought enhanced abundance of Caenis larvae in streams with chronic disturbance from agriculture.
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Murphy, Catherine Elizabeth, "Temporal Dynamics of Benthic Responses to Habitat Disturbance in Coastal Plain Headwaters of Southwestern Louisiana" (2016). LSU Doctoral Dissertations. 4402.