Hydrophysical and Hydrochemical Controls of Cyanobacterial Blooms in Coursey Pond, Delaware (USA).

Noxious cyanobacterial blooms are common in many ponds in the mid-Atlantic Coastal Plain. In Delaware, blooms normally occur between July and October, yet no in-depth analyses of the causes and predictors exist. A study using commercially available, high-frequency, continuous, and automated biogeochemical sensors at Coursey Pond, Delaware, a pond known for perennial summer blooms, was conducted to investigate how hydrophysical and hydrochemical conditions affect bloom dynamics. Cyanobacterial abundance (based on the in vivo phycocyanin fluorescence and phycocyanin/chlorophyll fluorescence ratios) increases during periods of high water temperatures (up to 32°C), low discharge through the pond (mean hydraulic residence time ≥5 d) with evaporative concentration of dissolved solids, and decreasing NO concentrations (reaching <0.1 mg L, the detection limit). These conditions lead to the uptake and depletion of bioavailable N in the pond surface waters and provide a competitive advantage for temperature-tolerant and N-fixing cyanobacteria. Irrigation water use within the watershed can exceed pond discharge during drier summer months, enhancing bloom-forming conditions. Bloom intensity varies due to storms but persists until mid-October to mid-November when temperatures cool, daylength decreases, and discharge and NO concentration recovers. Changes in these easily monitored physical and chemical parameters can serve to anticipate the onset, intensity, persistence, and the eventual dissipation of cyanobacterial blooms at Coursey Pond and similar ponds elsewhere. Therefore, the use of sensors and high-frequency data has the potential to assist in forecasting and management of blooms.

Community-Level and Species-Specific Associations between Phytoplankton and Particle-Associated Vibrio Species in Delaware's Inland Bays.

Vibrio species are an abundant and diverse group of bacteria that form associations with phytoplankton. Correlations between Vibrio and phytoplankton abundance have been noted, suggesting that growth is enhanced during algal blooms or that association with phytoplankton provides a refuge from predation. Here, we investigated relationships between particle-associated Vibrio spp. and phytoplankton in Delaware's inland bays (DIB). The relative abundances of particle-associated Vibrio spp. and algal classes that form blooms in DIB (dinoflagellates, diatoms, and raphidophytes) were determined using quantitative PCR. The results demonstrated a significant correlation between particle-associated Vibrio abundance and phytoplankton, with higher correlations to diatoms and raphidophytes than to dinoflagellates. Species-specific associations were examined during a mixed bloom of Heterosigma akashiwo and Fibrocapsa japonica (Raphidophyceae) and indicated a significant positive correlation for particle-associated Vibrio abundance with H. akashiwo but a negative correlation with F. japonica. Changes in Vibrio assemblages during the bloom were evaluated using automated ribosomal intergenic spacer analysis (ARISA), which revealed significant differences between each size fraction but no significant change in Vibrio assemblages over the course of the bloom. Microzooplankton grazing experiments showed that losses of particle-associated Vibrio spp. may be offset by increased growth in the Vibrio population. Moreover, analysis of Vibrio assemblages by ARISA also indicated an increase in the relative abundance for specific members of the Vibrio community despite higher grazing pressure on the particle-associated population as a whole. The results of this investigation demonstrate links between phytoplankton and Vibrio that may lead to predictions of potential health risks and inform future management practices in this region.

Reference library for microbial source tracking in the mid-Atlantic United States.

Microbial source tracking can determine fecal contamination but requires a relevant, sizable reference library for analysis. We provide a reference library of 100+ fecal microbiome samples relevant to mid-Atlantic United States ecosystems. Included are wild and domesticated fauna, wastewater, and septic samples applicable to Delaware source tracking studies.

Microbial Source Tracking in the Love Creek Watershed, Delaware (USA).

Fecal contamination of waterways in Delaware pose an ongoing problem for environmental and public health. For monitoring efforts, Enterococcus has been widely adopted by the state to indicate the presence of fecal matter from warm-blooded animals and to establish Primary and Secondary Contact Recreation criteria. In this study, we examined sites within the Love Creek watershed, a tributary of the Rehoboth bay, using next-generation sequencing and SourceTracker to determine sources of potential fecal contamination and compared to bacterial communities to chemical and nutrient concentrations. Microbial community from fecal samples of ten different types of animals and one human sample were used to generate a fecal library for community-based microbial source tracking. Orthophosphate and total dissolved solids were among the major factors associated with community composition. SourceTracker analysis of the monthly samples from the Love Creek watershed indicated the majority of the microbial community were attributed to "unknown" sources, i.e. wildlife. Those that attribute to known sources were primarily domestic animals, i.e. cat and dog. These results suggest that at the state level these methods are capable of giving the start for source tracking as a means to understanding bacterial contamination.

Interactive effects of light, CO2 and temperature on growth and resource partitioning by the mixotrophic dinoflagellate, Karlodinium veneficum.

There is little information on the impacts of climate change on resource partitioning for mixotrophic phytoplankton. Here, we investigated the hypothesis that light interacts with temperature and CO2 to affect changes in growth and cellular carbon and nitrogen content of the mixotrophic dinoflagellate, Karlodinium veneficum, with increasing cellular carbon and nitrogen content under low light conditions and increased growth under high light conditions. Using a multifactorial design, the interactive effects of light, temperature and CO2 were investigated on K. veneficum at ambient temperature and CO2 levels (25°C, 375 ppm), high temperature (30°C, 375 ppm CO2), high CO2 (30°C, 750 ppm CO2), or a combination of both high temperature and CO2 (30°C, 750 ppm CO2) at low light intensities (LL: 70 µmol photons m-2 s-2) and light-saturated conditions (HL: 140 µmol photons m-2 s-2). Results revealed significant interactions between light and temperature for all parameters. Growth rates were not significantly different among LL treatments, but increased significantly with temperature or a combination of elevated temperature and CO2 under HL compared to ambient conditions. Particulate carbon and nitrogen content increased in response to temperature or a combination of elevated temperature and CO2 under LL conditions, but significantly decreased in HL cultures exposed to elevated temperature and/or CO2 compared to ambient conditions at HL. Significant increases in C:N ratios were observed only in the combined treatment under LL, suggesting a synergistic effect of temperature and CO2 on carbon assimilation, while increases in C:N under HL were driven only by an increase in CO2. Results indicate light-driven variations in growth and nutrient acquisition strategies for K. veneficum that may benefit this species under anticipated climate change conditions (elevated light, temperature and pCO2) while also affecting trophic transfer efficiency during blooms of this species.