COS 1-10
Changes in cyanotoxin concentrations from benthic cyanobacteria over space and time in a California river
Toxic cyanobacteria are often associated with eutrophic lakes and estuaries, but in the nitrogen-poor Eel River of Northern California, benthic cyanobacteria have been implicated in at least 11 dog deaths over the last decade. The Eel River is a ~10,000 sq. km watershed in Northern California that flows through Coast Range mountains in a Mediterranean climate. The summertime food web is fueled by epilithic diatoms and epiphytic diatoms, some diazotrophic, that grow on the green alga Cladophora glomerata. However, in extreme low flow summers, algal assemblages tip towards cyanobacterial dominance. Cyanobacteria, some also diazotrophic, are less edible and sometimes produce toxins. Knowledge of thermal, nutrient, and flow regimes that promote cyanobacteria is needed for management to sustain a fish-bearing food web and reduce public health threats from cyanotoxins. Working with volunteer citizen scientists in the record drought year of 2013, we established 7 monitoring sites, from the headwaters to the river mouth, to collect weekly cyanotoxin concentration, nutrient (N, P, and DOC), and temperature, data from July to September 2013. We monitored for two cyanotoxins (the liver toxin, microcystin, and the neurotoxin, anatoxin-a) using time integrative solid phase adsorption toxin tracking (SPATT) samplers.
Results/Conclusions
We observed potentially toxic benthic cyanobacterial assemblages throughout the watershed, primarily Anabaena spp. and Phormidium spp. Anatoxin-a was detected at all 7 sites, but only one site consistently produced microcystin. Concentrations of anatoxin-a were also higher than microcystin, with toxin concentrations varying up to 10x between weeks. The highest anatoxin-a concentrations were recorded at sites and dates with intermediate temperatures, of 20-24 C. The Eel River has low total dissolved nitrogen concentrations (< 250 µg / L), and higher nitrogen concentrations were not positively correlated with cyanotoxin concentrations. However, nutrient ratios may influence the production of anatoxin-a, as no anatoxin-a was produced at sites with molar N:P ratios greater than 40. Our observations are the first time-series of cyanotoxin concentrations in the Eel River. In general, our results show complex relationships between cyanotoxin concentrations, temperature, and nutrient concentrations, suggesting that multiple scales of environmental variation and local nutrient cycling in benthic habitats may play an important role in cyanobacterial growth and cyanotoxin production.