Integrative monitoring strategy for marine and freshwater harmful algal blooms and toxins across the freshwater-to-marine continuum.

Many coastal states throughout the USA have observed negative effects in marine and estuarine environments caused by cyanotoxins produced in inland waterbodies that were transported downstream or produced in the estuaries. Estuaries and other downstream receiving waters now face the dual risk of impacts from harmful algal blooms (HABs) that occur in the coastal ocean as well as those originating in inland watersheds. Despite this risk, most HAB monitoring efforts do not account for hydrological connections in their monitoring strategies and designs. Monitoring efforts in California have revealed the persistent detection of cyanotoxins across the freshwater-to-marine continuum. These studies underscore the importance of inland waters as conduits for the transfer of cyanotoxins to the marine environment and highlight the importance of approaches that can monitor across hydrologically connected waterbodies. A HAB monitoring strategy is presented for the freshwater-to-marine continuum to inform HAB management and mitigation efforts and address the physical and hydrologic challenges encountered when monitoring in these systems. Three main recommendations are presented based on published studies, new datasets, and existing monitoring programs. First, HAB monitoring would benefit from coordinated and cohesive efforts across hydrologically interconnected waterbodies and across organizational and political boundaries and jurisdictions. Second, a combination of sampling modalities would provide the most effective monitoring for HAB toxin dynamics and transport across hydrologically connected waterbodies, from headwater sources to downstream receiving waterbodies. Third, routine monitoring is needed for toxin mixtures at the land-sea interface including algal toxins of marine origins as well as cyanotoxins that are sourced from inland freshwater or produced in estuaries. Case studies from California are presented to illustrate the implementation of these recommendations, but these recommendations can also be applied to inland states or regions where the downstream receiving waterbody is a freshwater lake, reservoir, or river. Integr Environ Assess Manag 2023;19:586-604. © 2022 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Spatial and temporal variability of river periphyton below a hypereutrophic lake and a series of dams.

Klamath River is described as an "upside-down" river due to its origins from the hypereutrophic Upper Klamath Lake (UKL) and hydrology that is heavily regulated by upstream dams. Understanding the lake and reservoir effects on benthic communities in the river can inform important aspects of its water quality dynamics. Periphyton samples were collected in May-November from 2004, 2006-2013 at nine long-term monitoring sites along 306 river km below UKL and a series of dams (n=299). Cluster analysis of periphyton assemblages identified three statistically different periphyton groups (denoted Groups 1-3). Group 1 occurred primarily in the upstream reach for June-October and had a higher percentage of sestonic species, including the cyanobacteria Aphanizomenon flos-aquae and Microcystis aeruginosa, consistent with the presence of upstream reservoirs. Group 2 had the highest relative biomass of diatoms and lowest relative biomass of cyanobacteria. Sites in the lower reach of the Klamath River fell into Group 2 in May-June and transitioning into Group 3 for July-October. Group 3 was dominated by nitrogen (N)-fixing species, including three diatoms (Epithemia sorex, Epithemia turgida, and Rhopalodia gibba) with cyanobacterial endosymbionts and the cyanobacterium Calothrix sp. Periphyton assemblages were strongly associated with temporal variations in flow conditions (e.g., decreasing flow from spring to fall) and spatial gradients in nutrient concentrations (e.g., decreasing from upstream to downstream). The inverse longitudinal relationship between periphyton biomass and nutrients may be explained by the ability of benthic N-fixers (Group 3) to overcome N limitation. Overall results showed a strong inverse relationship between the relative biomass of N-fixers and nitrogen concentrations and flow. This long-term dataset provides valuable insight into Klamath River's seasonal and longitudinal patterns of benthic algal communities and associated environmental variables. Our findings can inform river management decisions such as reducing upstream nutrient loads, setting flow regimes, and potential dam removals.