Indole-3-acetic acid promotes growth in bloom-forming Microcystis via an antioxidant response.

Interactions between bacteria and phytoplankton in the phycosphere facilitate and constrain biogeochemical cycling in aquatic ecosystems. Indole-3-acetic acid (IAA) is a bacterially produced chemical signal that promotes growth of phytoplankton and plants. Here, we explored the impact of IAA on bloom-forming cyanobacteria and their associated bacteria. Exposure to IAA and its precursor, tryptophan, resulted in a strong growth response in a bloom of the freshwater cyanobacterium, Microcystis. Metatranscriptome analysis revealed the induction of an antioxidant response in Microcystis upon exposure to IAA, potentially allowing populations to increase photosynthetic rate and overcome internally generated reactive oxygen. Our data reveal that co-occurring bacteria within the phycosphere microbiome exhibit a division of labor for supportive functions, such as nutrient mineralization and transport, vitamin synthesis, and reactive oxygen neutralization. These complex dynamics within the Microcystis phycosphere microbiome are an example of interactions within a microenvironment that can have ecosystem-scale consequences.

Positive and negative impacts of flue gas desulfurization (FGD) gypsum on water quality.

Flue gas desulfurization (FGD) gypsum, a by-product of carbon-based energy sources, has typically been incorporated as a component of concrete mixes and wallboard and beneficially used as an agricultural amendment to enhance terrestrial crop production and improve the quality of runoff. These various uses for the by-product aid in reducing the amount that is ultimately landfilled. Limited studies have investigated its benefits when used directly in aquatic settings, such as ponds and lakes, to increase hardness and potentially mitigate eutrophication. A 36-day field mesocosm experiment tested a larger range of FGD gypsum concentrations (500-2000 mg/L) than those previously tested in the literature to investigate its desired and potentially undesired impacts on water quality, including the algal community. High FGD gypsum concentrations, 1000 and 2000 mg/L, were found to have more undesired impacts than the 500 mg/L treatment, including an initial spike in cyanobacteria, a decrease in total zooplankton abundance, and an increase in certain trace metals in the highest treatment. Ultimately, the 500 mg/L FGD gypsum treatment was found to have fewer undesired impacts while still resulting in significant desired effects, including those on hardness and pH, as well as moderate reductions in algal abundance. This experiment provides a better understanding of the effects of FGD gypsum when directly used in an aquatic setting, determines an optimal dose for future field experiments, and helps provide the groundwork for developing an upper threshold on FGD gypsum so as to not have the negative effects outweigh the positive.

Long-term missing role of small colloids and nanoparticles on the loading and speciation of phosphorus in catfish aquaculture ponds in west Alabama.

Increasing loading of phosphorus (P) into freshwater systems is deemed as one of the key drivers triggering harmful algal blooms (HABs). However, conventional water quality monitoring of P normally uses the operational cutoff (e.g., 450-nm filter membrane) to separate particulate and dissolved phases (entities passing through the 450-nm membrane are regarded as dissolved phase), which completely neglects the roles of small colloids (450-100 nm) and nanoparticles (100-1 nm). Herein, a new particle size separation approach was used to separate water samples collected from catfish aquaculture ponds in west Alabama into six size fractions: large particles (>1000 nm), large colloids (1000-450 nm), small colloids (450-100 nm), large nanoparticles (100-50 nm), small nanoparticles (50-1 nm), and the truly dissolved phase (<1 nm). The speciation and concentration of P in these six size fractions were then investigated using Hedley's sequential extraction method. The new particle size separation results showed that particle loading (mass) followed the order: >1000 nm, 450-100 nm, 1000-450 nm, 100-50 nm, and 50-1 nm. This is mainly due to the abundance of large-sized (>1000 nm) zooplankton and phytoplankton such as algae and cyanobacteria in the catfish aquaculture ponds. Importantly, the small colloid (450-100 nm) and nanoparticle (100-1 nm) size fractions, which were previously regarded as the dissolved phase using the 450-nm membrane filtration operation, accounted for ∼41.8% of the total particle mass. The Hedley's sequential extraction results showed that sodium hydroxide (NaOH)-extracted P represented the largest P pool, followed by water (H2O)- and sodium bicarbonate (NaHCO3)-extracted P pools. Smaller particles exhibited a higher loading of P due to their large surface areas. These new findings suggest that the new particle size separation approach needs to be adopted for future water quality monitoring and mitigation of HABs in freshwater ecosystems.

Complex effects of dissolved organic matter, temperature, and initial bloom density on the efficacy of hydrogen peroxide to control cyanobacteria.

Harmful cyanobacterial blooms plague reservoirs and lakes used for a variety of purposes, such as recreation and drinking water. Chemical controls are frequently used to mitigate the occurrence of cyanobacterial blooms given that many are fast-acting and effective at reducing cyanobacterial abundance. Recent research has identified hydrogen peroxide (H2O2) as an environmentally friendly alternative to algaecides that have typically been used, such as copper sulfate. To build on past studies, these experiments sought to further understand how well H2O2 treatments reduce cyanobacteria in complex eutrophic conditions, as well as to assess treatment effects on a non-target phytoplankter, a green alga. We assessed the effectiveness of H2O2 (at treatments of 2-16 mg L-1) under varying environmental conditions in a controlled laboratory setting, including (1) dissolved organic matter (DOM) concentrations (humic acid; 0-60 mg L-1), (2) temperature (20, 25, and 32 °C), and (3) initial algal biomass (chlorophyll-a; 82-371 µg L-1). In contrast to our expectations, neither DOM concentration nor temperature meaningfully impacted the effectiveness of H2O2 at reducing cyanobacteria. However, initial algal biomass as well as H2O2 treatment dose greatly influenced the effectiveness of the algaecide on cyanobacteria. Treatments of ≥ 8 mg H2O2 L-1 on algal biomass were significantly buffered with higher DOM and lower temperature, and the biological significance of these findings should be explored further. Across all experiments, H2O2 concentrations of 0.03-0.12 mg H2O2 L-1 µg chlorophyll L-1 were effective at significantly reducing cyanobacteria with varying effects on algal biomass. Thus, water resource managers are encouraged to consider how ambient levels of phytoplankton biomass may affect the ability of H2O2 to control cyanobacterial blooms prior to treatment.

Can correlational analyses help determine the drivers of microcystin occurrence in freshwater ecosystems? A meta-analysis of microcystin and associated water quality parameters.

Microcystin (MC) is a toxic secondary metabolite produced by select cyanobacteria that threatens aquatic and terrestrial organisms over a diverse range of freshwater systems. To assess the relationship between environmental parameters and MC, researchers frequently utilize correlational analyses. This statistical methodology has proved useful when summarizing complex water quality monitoring datasets, but the correlations between select parameters and MC have been documented to vary widely across studies and systems. Such variation within the peer-reviewed literature leaves uncertainty for resource managers when developing a MC monitoring program. The objective of this research is to determine if correlational analyses between environmental parameters and MC are helpful to resource managers desiring to understand the drivers of MC. Environmental (i.e., physical, chemical, and biological) and MC correlation data were retrieved from an estimated 2,643 waterbodies (largely from the north temperate region) and synthesized using a Fisher's z meta-analysis. Common water quality parameters, such as chlorophyll, temperature, and pH, were positively correlated with MC, while transparency was negatively correlated. Interestingly, 12 of the 15 studied nitrogen parameters, including total nitrogen, were not significantly correlated with MC. In contrast, three of the four studied phosphorus parameters, including total phosphorus, were positively related to MC. Results from this synthesis quantitatively reinforces the usefulness of commonly measured environmental parameters to monitor for conditions related to MC occurrence; however, correlational analyses by themselves are often ineffective and considering what role a parameter plays in the ecology of cyanobacterial blooms in addition to MC production is vital.

Field evaluation of seven products to control cyanobacterial blooms in aquaculture.

Harmful algal blooms negatively impact water quality in hypereutrophic systems that are common in aquaculture. However, few algaecides are approved for use in food-fish aquaculture. This study assessed the effectiveness of seven products, including hydrogen peroxide (as a concentrated liquid or in granular form (PAK-27)), peracetic acid (as VigorOx SP-15 and Peraclean), copper (as copper sulfate in unchelated (powder) or chelated (Captain) forms), and a clay-based product (as Phoslock) on phytoplankton (including cyanobacteria) and zooplankton biomass. Each product was tested in a 14-day laboratory and 35-day field experiment to assess their short- and long-term performance. Although some products (i.e., copper-based and liquid hydrogen peroxide) quickly reduced phytoplankton, effects were short-lived given that chlorophyll concentrations returned to starting concentrations within 21 days. In contrast, all but one product (i.e., concentrated liquid hydrogen peroxide) maintained low phycocyanin concentrations for 35 days. Zooplankton biomass trends showed large, negative effects for most algaecides; however, zooplankton rebounded for most treatments except for copper-based products. In general, copper-based products remain the most efficient and cheapest choice to reduce total phytoplankton biomass in aquaculture systems. However, peracetic acid-based products effectively and quickly reduced cyanobacteria while having marginal effects on beneficial algae and zooplankton. Such algaecides could be effective alternatives to copper-based products for aquaculture farmers.