Hurricane Harvey (category four storm) made landfall along the coast of Texas (United States) and then stalled out over Texas and Louisiana, releasing 1.29 × 10¹¹ m³ of precipitation over 5 days. This caused extensive flooding that elevated freshwater river discharge and land runoff into Galveston Bay and eventually into the Gulf of Mexico. The floodwaters delivered a significant influx of dissolved organic carbon (DOC), organic pollutants and nutrients along with terrestrial and freshwater associated microbes. Over the 24 days following the flooding event, samples were collected on five cruises across Galveston Bay from the mouth of the San Jacinto River (Houston, TX, United States) to the Gulf of Mexico. Parameters measured for this study include: water quality (temperature, salinity, pH, and dissolved oxygen), nutrients (NO₃^–, NO₂^–, NH₄⁺, P_i, and HSiO₃^–), polycyclic aromatic hydrocarbons (PAHs), pharmaceuticals (cotinine, carbamazepine, carbamazepine-epoxide, and prednisone), biocide (imidacloprid), DOC, bacteria, and the eukaryotic community composition (16S and 18S rRNA genes). In the week after the flood event, bay-wide salinities decreased to 0–5 compared to the higher pre-Harvey salinities of 20–30 (recorded 5 days before the flood). Water treatment facilities and petrochemical plants were compromised due to the heavy flooding in the region. Increased concentrations of DOC, nutrients, PAHs, pharmaceuticals, and biocides were observed across Galveston Bay immediately following the storm. During the 4 weeks after Harvey, concentrations of DOC, nutrients, and organic pollutants began to decrease coinciding with rising salinities as the freshwater was flushed into the Gulf of Mexico and seawater began moving back into the Bay. Successive blooms of Chlorophyta, diatoms (Bacillariophyta), and dinoflagellates (Dinophyta) occurred similar to post-storm communities from past hurricanes that have impacted estuarine systems along the Gulf of Mexico. The bacterial community showed an increase in the abundance of bacteria associated with terrestrial soils and freshwater at the initial time point and then decreased over time and were replaced by their estuarine and marine relatives within the month following the hurricane. The eukaryotic community changed substantially following Harvey and did not recover to pre-Harvey conditions during our study period, suggesting a longer recovery time compared to the prokaryotes. Although the water quality parameters and prokaryotic community showed signs of returning to pre-Harvey conditions within the month following the flood event, long-term impacts need to be measured in the years following the flood.

Phytoplankton form the base of the food web and are often the main primary producer in estuaries. Freshwater inflow variability will modulate phytoplankton biomass and production in estuaries through effects on nutrient delivery and cycling in estuaries, as well as on light availability and flushing rates. The goal of this chapter is to build upon the conceptual framework of inflow-nutrient-phytoplankton dynamics proposed by Longley (1994) by highlighting advances that have been made since then. Specific objectives are to: quantify coast-wide relationships between inflow, nutrients, and phytoplankton biomass (chlorophyll a; hereafter “chlorophyll”) in Texas estuaries; quantify variability in phytoplankton biomass in relation to inflow variability; identify key drivers of this variability in individual systems where sufficient data exists (Galveston Bay, Matagorda Bay, Baffin Bay); and highlight deficiencies and future data needs. The overarching conclusion is that freshwater inflow plays a major role in external nutrient loadings to Texas estuaries, but its influence on phytoplankton dynamics is complicated because of effects on not only nutrient availability but also flushing rates and the light environment within estuaries. One recommendation based on the synthesis here is that there is a strong need for more system-specific studies to elucidate mechanistic linkages between inflow, nutrients, and phytoplankton, because this information will be vital for developing management plans in areas where inflow rates are changing and/or where nutrient pressures may be a growing concern.

Estuarine phytoplankton communities are acclimated to environmental parameters that change seasonally. With climate change, they are having to respond to extreme weather events that create dramatic alterations to ecosystem function(s) on the scale of days. Herein, we examined the short term (<1 month) shifts in phytoplankton communities associated with four pulse disturbances (Tax Day Flood in 2016, Hurricane Harvey in 2017, Tropical Storm Imelda in 2019, and Winter Storm Uri in 2021) that occurred in Galveston Bay (TX, USA). Water samples collected daily were processed using an Imaging FlowCytobot (IFCB), along with concurrent measurements of temperature, salinity, and chlorophyll-a. Stronger storm events with localized heavy precipitation and flooding had greater impacts on community composition, increasing diversity (Shannon–Weiner and Simpson Indices) while a cold wave event lowered it. Diatoms and dinoflagellates accounted for the largest fraction of the community, cyanobacteria and chlorophytes varied mostly with salinity, while euglenoids, cryptophytes, and raphidophytes, albeit at lower densities, fluctuated greatly. The unconstrained variance of the redundancy analysis models pointed to additional environmental processes than those measured being responsible for the changes observed. These findings provide insights into the impact of pulse disturbances of different magnitudes, durations, and timings on phytoplankton communities.

Plankton (phytoplankton, zooplankton) form the base of the food web. Inflow variability modulates plankton concentration, community composition, and productivity in estuaries. This chapter synthesizes data on plankton and their relationship with inflow from individual bay systems along the Texas coast where sufficient data exists. This will be primarily the Trinity-San Jacinto Estuary (also known as Galveston Bay) and Baffin Bay (located in the Upper Laguna Madre complex) with some details for San Antonio Bay, Mission Aransas Estuary, and Nueces-Corpus Christi Bay. In the former two systems, there is a lot of knowledge on key harmful algal bloom-forming taxa. This chapter will also highlight deficiencies in our current knowledge and future data needs. Given the general lack of data on zooplankton in Texas estuaries, this part of chapter is descriptive in nature. We end with providing a synthesis and recommendation for future efforts.