A space-time geostatistical model for probabilistic estimation of harmful algal bloom biomass and areal extent

• Published in: The Science of the total environment 2019-12, Vol.695, p.133776-133776, Article 133776
• Main Authors: Fang, Shiqi, Del Giudice, Dario, Scavia, Donald, Binding, Caren E., Bridgeman, Thomas B., Chaffin, Justin D., Evans, Mary Anne, Guinness, Joseph, Johengen, Thomas H., Obenour, Daniel R.
• Format: Article
• Language: English
• Subjects: Algal biomass and extent; Harmful algal blooms; Lake Erie; Probabilistic estimates; Space-time geostatistical model
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2019.133776

Harmful algal blooms (HABs) have been increasing in intensity worldwide, including the western basin of Lake Erie. Substantial efforts have been made to track these blooms using in situ sampling and remote sensing. However, such measurements do not fully capture HAB spatial and temporal dynamics due to the limitations of discrete shipboard sampling over large areas and the effects of clouds and winds on remote sensing estimates. To address these limitations, we develop a space-time geostatistical modeling framework for estimating HAB intensity and extent using chlorophyll a data sampled during the HAB season (June–October) from 2008 to 2017 by five independent monitoring programs. Based on the Bayesian information criterion for model selection, trend variables explain bloom northerly and easterly expansion from Maumee Bay, wind effects over depth, and variability among sampling methods. Cross validation results demonstrate that space-time kriging explains over half of the variability in daily, location-specific chlorophyll observations, on average. Conditional simulations provide, for the first time, comprehensive estimates of overall bloom biomass (based on depth-integrated concentrations) and surface areal extent with quantified uncertainties. These new estimates are contrasted with previous Lake Erie HAB monitoring studies, and deviations among estimates are explored and discussed. Overall, results highlight the importance of maintaining sufficient monitoring coverage to capture bloom dynamics, as well as the benefits of the proposed approach for synthesizing data from multiple monitoring programs to improve estimation accuracy while reducing uncertainty. [Display omitted] •We develop a space-time geostatistical approach for modeling algal bloom variability.•Model synthesizes data from an international suite of monitoring programs.•Trends characterize spatiotemporal patterns and effect of wind mixing on chl-a.•Model simultaneously estimates bloom surface area and overall biomass.•Results show potential to inform Lake Erie algal bloom monitoring design.