Harte Research Institute for Gulf of Mexico Studies
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Browsing Harte Research Institute for Gulf of Mexico Studies by Author "Adams, Leslie"
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Item Determining Optimal Pumped Flows to Nueces Delta(2016-07) Montagna, Paul A.; Adams, Leslie; Chaloupka, Crystal; Del Rosario, Elizabeth; Kalke, Richard D.; Turner, Evan L.Item Effects of Pumped Flows into Rincon Bayou on Water Quality and Benthic Macrofauna(2015-08) Montagna, Paul A.; Adams, Leslie; Chaloupka, Crystal; Del Rosario, Elizabeth; Gordon, Amanda; Herdener, Meredyth; Kalke, Richard D.; Palmer, Terence A.; Turner, Evan L.Item Inorganic nitrogen release from sediment slurry of riverine and estuarine ecosystems located at different river regimes(Marine and Freshwater Research, 2016-10-29) Paudel, Bhanu; Montagna, Paul A.; Besonen, Mark; Adams, LeslieThe purpose of the present study was to compare the nature of dissolved inorganic nitrogen (DIN = ammonium (NH4+) and nitrite + nitrate (NO2+3 = (NO2– + NO3–)) release from aerobic sediment slurry at two different hydrologic flow regimes. The watershed of the Guadalupe River–Estuary system receives more freshwater inflow than does the watershed of the Nueces River–Estuary system; thus, the Nueces Estuary is more saline than is the Guadalupe Estuary. Sediment samples were collected using cores, analysed for organic matter and grain size, and used to perform laboratory experiments to measure DIN release. During the experiments, DIN concentrations in overlying water were measured for 48 h in five different salinity treatments. Ammonium concentrations were higher in the Nueces River and Estuary treatments than in similarly treated samples from the Guadalupe River and Estuary. An increase in NO2+3 concentrations along salinity gradients of the Nueces Estuary treatments indicated favourable condition for nitrification. The Guadalupe River sediments that were not exposed to salinity had an increase in NH4+ concentration at 7.5 ppt. The different DIN release among salinity treatments indicated that hydrologic forcing on organic matter deposition and salinity have an important role on the retention and release of inorganic nitrogen at the sediment–water aerobic layers in rivers and estuaries.Item Origin, composition and quality of suspended particulate organic matter in relation to freshwater inflow in a South Texas estuary(Estuarine, Coastal and Shelf Science, 2016-01-17) Montagna, Paul A.; Lebreton, Benoit; Pollack, Jennifer Beseres; Blomberg, Brittany; Palmer, Terence A.; Adams, Leslie; Guillou, GaelSouth Texas has a semi-arid climate with a large interannual variability of freshwater inflows. This study sought to define how changes in freshwater inflow affect the composition, quantity and quality of suspended particulate organic matter (SPOM) in a South Texas estuary: the Mission-Aransas estuary. The study was implemented 1.5 months after a large rain event in September 2010 and continued for 10 months of drought conditions. The composition of SPOM originating from rivers, the Gulf of Mexico and the estuary were determined using stable isotopes (δ13C, δ15N and δ34S). The quantity and quality of SPOM were assessed using organic carbon content, chlorophyll a concentrations and C/chl a ratios. Our results demonstrated that autochthonous phytoplankton was the dominant component of SPOM in the Mission-Aransas estuary during droughts. Benthic organic matter from local primary producers (i.e., seagrass, salt marsh plants, benthic microalgae) did not influence SPOM composition, either as fresh material or as detritus. A comparison with a positive estuary (i.e., Sabine-Neches estuary, TX) indicates that decreases in freshwater inflow may lead to decreases of terrestrial organic matter inputs and to increase the ratio of autochtonous phytoplanktonic material in SPOM.Item The relationship between suspended solids and nutrients with variable hydrologic flow regimes(Regional Studies in Marine Science, 2019) Paudel, Bhanu; Montagna, Paul A.; Adams, LeslieThe hypothesis that “freshwater inflow variability over space and time can drive suspended solids and nutrient concentrations” was tested by comparing three micro-tidal estuaries (Guadalupe, Lavaca-Colorado, and Nueces) in Texas with different hydrologic flow regimes over three years with wet and dry conditions. In all three estuaries, Total suspended solids (TSS) was less than 50 mg/L most of the time. In the Nueces Estuary, TSS of higher than 100 mg/L occurred during frontal events. Dissolved inorganic nitrogen (ammonia+nitrite+nitrate) concentrations were most of the time lowest in the Nueces Estuary (i.e. greater than or equal to 0.5 mol/L), with low inflow rates and high average salinity of 37.6. Salinity was highest in the river-estuary mouth (average salinity 38.3) of the Nueces Estuary relative to the other oceanic-side stations (average salinity 37), indicating that the system was a “reverse estuary” where evaporation exceeds freshwater inflow, resulting in net inflow of marine water into the estuary. The inverse correlation between ammonium and salinity in all three estuaries and the corresponding negative correlation between nitrite+nitrate concentrations and salinity in the Guadalupe Estuary indicate that the quantity of inflow controls nitrogen concentrations and transformations in the three estuaries. Drought conditions limited riverine transport of nitrogen and sediment to the three estuaries, demonstrating the importance of freshwater inflow to maintaining these constituents. Average silica and orthophosphate concentrations correlated positively with chlorophyll-a in combined data from all three estuaries. Silica and orthophosphate concentrations remained constant over the study period, but correlated with chlorophyll-a when suspended solid was low. Therefore, inflow dynamics drive changes in the salinity regime, suspended solids, and act to maintain nutrient concentrations.Item Variations in the release of silicate and orthophosphate along a salinity gradient: Do sediment composition and physical forcing have roles?(Estuarine, Coastal and Shelf Science, 2015-02-26) Paudel, Bhanu; Montagna, Paul A.; Adams, LeslieIt was hypothesized that sediment composition, i.e. organic matters and minerals, and physical forcing can influence retention and release of silicate (SiO4) and orthophosphate (o-PO4) along salinity gradients. An experiment was performed to measure nutrient release by using treatments with and without sediment organic matter from the Guadalupe and Nueces Estuaries at five different salinities. The sample mixtures were shaken at intervals over the course of 48 h to simulate wind and river forcing. The release of silicate from sediments increased with time from 2 min to 48 h in all five salinities. The added orthophosphate concentration was adsorbed in most of the sediment containing organic matter and calcium-rich shells from both estuaries. From the sediments without organic matter, the release of orthophosphate was as high as 52 μmol/L. The sediment minerals quartz and calcite were abundant in both estuaries. The average quartz to corundum peak intensities ratio were 14.04 and 13.36 and the average calcite to corundum peak intensities ratio were 3.06 and 1.32 in the Guadalupe and Nueces Estuaries respectively. The average organic matter in the Guadalupe and Nueces estuaries were 10.67% and 13.39% respectively. The retention and release of orthophosphate from the sediments may have been caused by the bonding with organic matter and calcite in the sediments. These findings indicate that sediment composition was a significant contributor in the low dissolved orthophosphate concentration in the estuaries. The release of silicate from the sediments containing quartz, and organic matter, when shaken, indicate that the combined forcing of river and wind may have been maintaining the estuaries silicate concentrations.