Browsing by Subject "freshwater inflow"
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Item Freshwater Flow, Saltwater Intrusion, Paper Mill Effluent, and Fish Assemblage Structure in the Lower Neches River, Texas(2013-06-11) Pizano, Rebecca IIn 2011, Texas experienced the worst drought in recorded history. This has escalated concerns regarding environmental flows needed to sustain freshwater and estuarine systems as human needs are addressed during drought periods. In this thesis, I analyze fish assemblages and water quality variables in order to observe the effects of drought in the lower Neches River below the saltwater barrier located upstream from Beaumont, Texas. Fish and water quality samples were taken during drought conditions during fall 2011 and summer 2012, after a season of rain. During fall 2011, sites surveyed above the barrier had lower salinity but similarly low dissolved oxygen (DO) levels compared with sites surveyed below the barrier. Salinity levels during fall 2011 were relatively high (reaching up to 15 ppt), whereas salinity during summer 2012 never rose above 1.5 ppt. For gillnet samples obtained during fall 2011, fish species richness was higher in December following a series of rain events than during drought conditions in October and November. Although fish species richness was similar between fall 2011 and summer 2012, species composition varied greatly. For seine samples obtained during summer 2012, species richness was higher during May and July (when the barrier was open) than during June and August (when the barrier was closed). Species richness was lowest for sites in closest proximity to a paper mill effluent discharge pipe located below the barrier. Also, species richness was higher at sites above the barrier than at sites below the barrier regardless of whether or not the barrier was closed. Multivariate statistical analyses of gillnet samples revealed a large amount of compositional overlap among fish assemblages, regardless of time period and location; however, analyses of seine samples revealed that fish assemblages above the barrier were different than those from samples obtained below the barrier and that fish assemblages varied based on time period. Results indicate that, during periods of low flow, water quality deteriorates in the Lower Neches River below the saltwater barrier. During these periods of environmental degradation, fish assemblages have reduced diversity and sensitive freshwater species decline in abundance, with some absent from survey samples.Item Is Salinity Variability a Benthic Disturbance?(2014-05-07) Van Diggelen, AmandaEstuaries are subjected to variable salinity regimes governed by variable freshwater inflow and tidal regimes. Estuaries are less saline near the river (source of fresh water); salinities increase towards the inlet of the adjacent sea or ocean. Freshwater inflow is a driver to the functioning of estuaries, and average salinity is usually measured to identify the effects of inflow. However, salinity variability could act as a disturbance by producing unstable habitats. The purpose of this research was to determine if salinity variance is an indicator of benthic disturbance, and therefore a driver of community stability. The macrofauna communities of the five most southern estuaries on the Texas coastline were analyzed using a long-term data set. The estuaries lie in a climatic gradient and have different long-term salinity dynamics, thus salinity variance within and between estuaries can be compared. Benthic diversity, evenness, and richness (i.e., total number of species) were calculated and compared to salinity average and salinity variance to determine the efficacy of each diversity measure for determining community changes within and between estuarine systems. Salinity variance, rather than salinity average, was found to be more correlated to benthic diversity for each estuarine system. Freshwater inflow acts as a benthic disturbance both within and between estuaries. As salinity variance decreased (i.e. reduced freshwater inflow) diversity levels of benthic communities increased, while areas with more freshwater inflow displayed lower levels of benthic diversity. These findings advance a general theory of diversity maintenance. When communities are not influenced by persistent stressors, such as salinity variance, multiple stages of succession may occur with more species available to occupy the resulting open niches, thereby increasing diversity.Item Suspended Sediment Dynamics of Texas EstuariesReisinger, Anthony Sherman