Periodic Reporting for period 1 - BLOOMTOX (Global change impacts on cyanobacterial bloom toxicity)
Reporting period: 2022-10-01 to 2025-03-31
Think of a hot summer day. Imagine getting a glass of cold water, but no water is coming, or it is brownish with a foul odor. Imagine being a farmer, and your cattle need water but there is only smelly (blue-)green water. Imagine going for a cooling swim, but the lake is closed for recreation. For millions of people, this is not imagination, but a recurring reality caused by toxic cyanobacterial blooms. Scarcity of clean and healthy water is among the biggest societal challenges for the 21st century, listed as one of the United Nations Sustainable Development Goals (SDG2), and among the main concerns of the European Union. The quantity and quality of surface waters are declining at a high rate by increased societal demands and global environmental change. Notably, eutrophication may lead to harmful cyanobacterial blooms, which are expected to be further promoted by elevated pCO2 and warming. Although studies focusing on individual global change factors are relatively common, studies on combined stressors on harmful cyanobacterial blooms are remarkably rare. Importantly, harmful cyanobacteria produce toxins, which are the major cause of their threat to human health. Overall bloom toxicity is thus not only driven by the biomass of cyanobacteria, but also depends on the amounts and types of toxins produced by the dominant species and genotypes. The aim of this project is to mechanistically understand the processes underlying bloom toxicity, and their response to the complex interplay of multiple global change factors. It follows a unique approach crossing all scales that determine bloom toxicity, from cellular processes to ecosystem dynamics. The project will technologically scale from cell the ecosystem using a novel high-throughput flow-cytometry based multi-trait pipeline. It will experimentally scale from traits to population and community interactions using a novel lab-on-a-chip experimental platform for massive parallel screening of key traits, and state-of-the-art flat panel chemostat experiments. These experiments will provide the mechanisms underlying natural community dynamics that will be tested in microcosms, large-scale indoor mesocosms, and the field. Overall, being able to mechanistically scale from cells to the ecosystem will advance the ecological field, and by revealing key indicators that determine the toxicity of cyanobacterial blooms may support water management actions.
At the start of the project in the summer of 2023, field work was performed to study the relationship between eutrophication, local climate conditions and the toxicity of cyanobacterial blooms. This work was performed by two Doctoral Candidates funded by the ERC, where one has been focusing on the relationship between cyanobacterial bloom toxicity with the overall plankton community and food-web. The other studied population dynamics and genomic diversity, for example looking at the presence of genes involved in toxin production. This study included a selection of three lakes that differed in their concentrations of nitrogen and phosphorus, two main nutrients that are closely linked to cyanobacterial blooms. The field work consisted of weekly sampling from the shore, and was supplemented by automated high frequency buoy measurements of oxygen and cyanobacterial biomass assess key lake functions including primary production and respiration. Besides these three lakes, field work was also performed on the Lake IJsselmeer, which is the largest freshwater reservoir in the Netherlands but dominated by cyanobacteria. This lake is sampled over 2023, 2024 and will be continued during 2025, and is performed in collaboration with the national water authority and a regional drinking water company. During the first part of the project, we established a high throughput metho based on flow cytometry, which is a machine that measures the fluorescence of single cells at a rate of up to 1,000 particles per second. Each cell is exposed to five lasers, and we receive up to 19 signals of each particle. This allows us to acquire individual cell-based information in complex natural communities. We tested how these signals together can tell something about the health and physiological status of the cells. For example, we showed that the fluorescence signals change with nutrient limitation, light limitation, and elevated CO2 levels. We confirmed this by using laboratory cultures and scaled these to the field. We furthermore developed a novel lab-on-a-chip system, where up to 40 culture chambers of microscopic size fit on a small glass plate of 2x6 cm (i.e. two post-stamps). This collaboration with engineers allowed us to use microfluidic wafers for fabricating our own lab-on-a-chip systems. These are currently being tested for growing cyanobacterial cells for high throughput parallel screening of cyanobacterial growth characteristics.
Our collaboration between ecologists and engineers allowed for the development of beyond state-of-the-art technology, where we use microfluidic lab-on-a-chip systems for high throughput parallel screening of toxic cyanobacterial growth characteristics. Further success and use will depend on the accuracy of the developed gradient generators that will allow us to assess the non-linearity of responses to environmental gradient. Results from various components of this project may be used by water management for mitigation and risk assessment. This includes the high throughput multi-trait pipeline to establish the physiological status of cyanobacterial in natural samples, which may inform management actions and guide targets for mitigation strategies. The results from experiments testing the different scales determining bloom toxicity will inform best approaches, or combination of approaches, to establish and improve risk assessment. This includes an explicit test of a two-tiered risk assessment strategy first targeting fast and cheap but generic approaches such as overall cyanobacterial biomass, toxic species and/or functional groups, and when needed a more specific but costly approach targeting toxins.