Pathways of Transport of Microcystin-LR from Microcystis aergonisa to the Benthic Environment

Cyanobacterial harmful algal blooms (CHAB’s) are a global concern that affect humans and wildlife. Microcystis aeruginosa (Microcystis) is a freshwater photosynthetic cyanobacterium that is planktonic during warm months but has an overwintering benthic phase. Microcystis create toxins, including microcystins that can lead to liver damage and cancer in aquatic life, livestock and humans. Microcystins can be stored intracellularly or released into the water column in a dissolved form. Most studies focus on Microcystis in its planktonic state, but not on transport of microcystins. More recently, microcystins have become a threat to coastal systems that are linked to freshwater inputs. The goal of this paper is to determine pathways of transport of Microcystis and microcystins in estuary systems. This paper synthesizes literature on environmental factors that increase Microcystis blooms and how their microcystins accumulate in sediments and bivalves. The interaction between the water column and sediments is an important role for predicting future Microcystis blooms. Bivalves are known to be bioindicators of contaminants, since they are sessile organisms that are filter feeders and deposit feed from sediment bottoms. To current knowledge, there is no mandated CHAB monitoring in California, which is important to predict or mitigate future blooms. The results of this paper indicate remote sensing, water quality monitoring, and sediment monitoring are useful strategies to not only predict but mitigate blooms. Freshwater and marine bivalves should also be monitored since they are bioindicators of potential impacts to ecological health. By incorporating multiple monitoring components, the data can be integrated into models to not only predict future CHAB’s but also determine the drivers of blooms

Delta Blue(green)s: The Effect of Drought and Drought-Management Actions on Microcystis in the Sacramento–San Joaquin Delta

Cyanobacterial phytoplankton blooms are more prevalent in the freshwater Sacramento-San Joaquin Delta (Delta) since the late 1990s, including blooms driven by overgrowths of potentially toxigenic organisms of the genus Microcystis. Data from 2014 to 2021 were used to show how flow dynamics, water temperature, and water clarity drive occurrence of Microcystis. We used a Microcystis bloom in the central Delta from 2021 as a case study for how novel monitoring tools can track blooms in real-time and be used post hoc to evaluate the effects of management actions.Microcystis was detected throughout the Delta in all but the highest-flow years, and bloom incidence and severity increased during drier years. In the South Delta, Franks Tract, lower San Joaquin River, and Old River regions, where blooms are most prevalent, higher water temperatures and clarities combined with lower exports from state and federal water projects were the best explanatory factors for the occurrence of Microcystis blooms. Nutrient concentrations were lower in summer than in winter, but only became limiting at high phytoplankton concentrations.We used satellite data and in situ continuous monitoring of flow, phytoplankton communities, and water quality to track hydro-biogeochemical conditions during the 2021 case study Microcystis bloom in the Central Delta. We did not find evidence that changes to Delta outflow regulatory standards contributed to this bloom, but changes in flow caused by a salinity barrier placed in west False River may have exacerbated the bloom. The frequency and severity of droughts are expected to increase in the future as a result of climate change, and our study demonstrates how continued monitoring of cyanotoxins, water quality, and phytoplankton communities could help improve management of cyanobacterial blooms in the Delta and other estuaries