Influence of Major Storm Events on the Quantity and Composition of Particulate Organic Matter and the Phytoplankton Community in a Subtropical Estuary, Texas

Abstract

Variations in the freshwater inflow regimes of estuaries due to perturbations, such as storm events, alter the source, and composition of particulate organic matter (POM) and the phytoplankton community which are key links in estuarine carbon and nitrogen cycling. To evaluate the impact of varying freshwater discharge on POM quantity and composition and the phytoplankton community, monthly samples of surface water were collected at four long-term monitoring stations from 2012-2015 in a subtropical estuarine system, the Mission-Aransas Estuary, Texas (USA). This system is characterized by a semiarid climate, drought, and sporadic precipitation events. We analyzed organic carbon and nitrogen content, carbon and nitrogen stable isotopes, and chlorophyll a and accessory pigments of the POM samples. Following a prolonged dry spell (2012)(2013)(2014)(2015), consecutive major storm events in spring 2015 led to a dramatic freshening of the entire estuary. Large increases in particulate organic carbon (POC) concentrations and decreases in δ 13 C values of POC over several weeks following the storms suggest an increase in in-situ production at lower salinities as a result of increased freshwater inflow. These changes in bulk POM coincided with an increase in chlorophyll a concentration, further indicating a significant contribution by phytoplankton to the elevated POM. Concurrently, pigment biomarkers revealed a significant (10-fold) increase in the cyanobacterial pigment, zeaxanthin, and further 16S rRNA analysis showed that Cyanobium spp. was responsible for the observed bloom. The combination of environment conditions, including freshening, high temperature, and high nutrients, likely contributed to the cyanobacteria bloom. These results show that episodic rain events can substantially affect estuarine phytoplankton community composition, which impacts the available energy resources for secondary production and thus may have ecosystem-wide implications on productivity.

Responses of carbonate system and CO2 flux to extended drought and intense flooding in a semiarid subtropical estuary

“…), which was in favor of CO 2 production. In flooding season, non‐thermal effect dramatically increased (Table 4) air–water CO 2 flux at CW, whereas CO 2 degassing was maintained at similar level or even decreased in other part of this estuary, due presumably to nutrient‐enhanced primary production (Reyna et al ).…”

Molecular Level Analysis Reveals Changes in Chemical Composition of Dissolved Organic Matter From South Texas Rivers After High Flow Events

“…Overall, DOM at high-flow appears to contain relatively higher percentages of aromatic structures, which may represent a recalcitrant nature under certain conditions, but can be very reactive when conditions change. Therefore, the high-flow events can relocate a large amount of terrestrial photo-active DOM to coastal region, where it could be rapidly utilized by microbes and further fuel primary production in brackish water (e.g., Liu et al, 2011;Mooney and McClelland, 2012;Bruesewitz et al, 2013;Reyna et al, 2017). High flow DOM also seems to contain a fraction of highly bioavailable DOM in the form of hydrolyzable amino acids, which can further supply labile substrates to estuaries and bays.…”

“…Besides the direct impact on the landfall area (e.g., Han et al, 2018), high-flow events after hurricane could subsequently change the hydrology and water quality in subtropical regions (e.g., Nesbit and Mitsch, 2018). Characterized by a semiarid climate and sporadic rainfalls, South Texas is known for very intense precipitation events cropping up within relatively short period of time (Bomar, 1983(Bomar, , 2017Mooney and McClelland, 2012;Bruesewitz et al, 2013;Reyna et al, 2017). For instance, Hurricane Harvey, a category four major hurricane that made landfall near University of Texas Marine Science Institute (UTMSI) on August 25, 2017, caused unprecedented flooding in nearby areas.…”

An expanded rating curve model to estimate river discharge during tidal influences across the progressive-mixed-standing wave systems

“…Elevated summer temperatures often result in summer evaporation exceeding local annual precipitation [18,45,47]. However, warm summer waters from the Gulf of Mexico and El Niño Southern Oscillation (ENSO) events promote storms, leading to flash flooding and freshets in coastal bays [14,18,21,22,45,48,49]. This typically baseflow, yet wide-ranging set of riverine conditions, when combined with tidal forces, provided an ideal test case for the new tidal rating curve method.…”

“…Furthermore, long-term discharge records aid in predictions of hyporheic exchange rates that control groundwater inputs of nitrogen (N) in these costal environments; understanding such exchange rates will further inform management and policy surrounding TMDLs [19,20]. Complete long-term tidal volumetric discharge records also inform increasingly precise relationships between terrestrial physical parameters and downstream ecology and biota over a range of timescales, from flashy, short-term event timescales to longer global climate trends [11,14,16,21,22].…”