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Arid subtropical climates often oscillate between drought and wet conditions, leading to a "flood or famine" paradigm for estuarine freshwater inflow, in which sporadic storm events drive dynamic changes in salinity and nutrient availability. Transitioning from prolonged drought to wet conditions can impact phytoplankton communities. The Mission‐Aransas Estuary, located on the south Texas coast, transitioned from a 5‐yr drought (2010–2015) to wet conditions (2015–2020), punctuated by several large flood events and the direct impact of category 4 Hurricane Harvey. Using an 8‐yr bimonthly sample set (2012–2019), we evaluated particulate organic carbon, chlorophyll a, nutrient concentrations, and accessory pigments to characterize the response of the phytoplankton community to these climate events. We found that phytoplankton biomass was diminished during severe drought and increased during prolonged wet conditions. The phytoplankton community switched from being diatom‐dominated during drought to cyanobacteria‐dominated following estuarine freshening, driven by lower salinity and increased nutrient availability. Seasonal fluctuations between taxa persisted regardless of climate condition. The drought‐to‐wet transition prompted a regime shift of the estuarine phytoplankton community to a new quasi‐steady state in the studied estuary. Globally, changing climate regimes may cause longer periods of extreme drought or wet conditions for estuarine systems. Detailed, long‐term ecosystem monitoring is necessary to fully evaluate ecological responses to extreme weather events, especially links between biogeochemical cycling and ecosystem function. These results suggest that oscillations between distinct wet and dry periods have lasting effects on primary productivity, phytoplankton community composition, and organic matter cycling in subtropical estuaries with long residence times. [ABSTRACT FROM AUTHOR]

Abiotic filters that interact with wetland plant communities along tidal–fluvial gradients are highly dynamic, and understanding their quantitative thresholds and relationships to interspecific competition is important during an era of sea‐level rise and watershed hydrologic change. Yet, landscape‐scale studies of major coastal rivers from the river mouth to the head of tide, such as this study, remain rare. Here, we develop a new predictive framework for estuarine–tidal river research and management using a river‐specific low‐water datum and the wetland inundation indicator SEVg, the growing‐season sum exceedance value of hourly surface‐water depth. The distribution and variability of the wetland species pool (n = 203) on the 234 river kilometer (rkm) lower Columbia River and estuary floodplain are described for the first time. 4,940 quadrats at 50 marshes were surveyed (2005–2016). Throughout the estuarine–tidal river system, SEVg was well suited to describe the wetland inundation regime and its variability based on the combination of longitudinal river position and elevation. SEVg increased significantly landward. Two primary wetland inundation regimes were identified: the seaward‐tidal, usually greatest during the winter months, and landward‐fluvial, greatest during the growing season. Nearest the ocean, salinity is the abiotic factor limiting species richness and non‐native species. Farther upriver, the daily, seasonal, and interannual variability of the wetting and drying cycle encourage disturbance‐tolerant species and non‐natives and limit the number of hydrophytes and total vegetative cover. Hence, the average between‐year similarity of site‐scale areal cover significantly decreased landward. Hierarchical cluster analysis indicated five vegetative groups and five ecohydrologic zones between rkm 0 and 234 were discriminated with 76 significant species–zone associations. All zones had unique indicator species. Species with high indicator values were Carex lyngbyei throughout the estuarine zones, and Eleocharis palustris, Sagittaria latifolia, and the invasive non‐native Phalaris arundinacea in the upper estuarine and lower, middle, and upper tidal river zones (IV > 0.90). Competition from C. lyngbyei nearest the ocean and P. arundinacea in the tidal river was associated with reduced species richness when total cover was >65%. This framework of filters informs the design and prediction of future wetland plant communities on coastal river floodplains. [ABSTRACT FROM AUTHOR]

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Polylactide-co-glycolide (PLGA) foams of tubular shape were assessed for their use as soft- tissue engineering scaffolds in vitro and in vivo. Porous membranes were fabricated by a thermally induced phase separation process of PLGA solutions in dimethylcarbonate. The parameters investigated were the PLGA concentration and the casting volume of solution. Membranes produced from 5 wt/v % polymer solutions and a 6 ml casting volume of polymer solution were selected for fabricating tubes of 3 mm diameter, 20 mm length and a nominal wall thickness of 1.5 mm. Scanning electron microscopy revealed that the structure of the tubular foams consisted of radially oriented and highly interconnected pores with a large size distribution (50–300 μm). Selected tubes were implanted subcutaneously into adult male Lewis rats. Although the lumen of the tubes collapsed within one week of implantation, histological examination of the implanted scaffolds revealed that the foam tubes were well tolerated. Cellular infiltration into the foams, consisting mainly of fibrovascular tissue, was evident after two weeks and complete within eight weeks of implantation. The polymer was still evident in the scaffolds after eight weeks of implantation. The results from this study demonstrate that the PLGA tubular foams may be useful as soft-tissue engineering scaffolds with modification holding promise for the regeneration of tissues requiring a tubular shape scaffold such as intestine. [ABSTRACT FROM AUTHOR]