J M Burke

Hepatotoxic Cyanobacteria: A Review of the Biological Importance of Microcystins in Freshwater Environments

Cyanobacteria possess many adaptations to develop population maxima or “blooms” in lakes and reservoirs. A potential consequence of freshwater blooms of many cyanobacterial species is the production of potent toxins, including the cyclic hepatotoxins, microcystins (MCs). Approximately 70 MC variants have been isolated. Their toxicity to humans and other animals is well studied, because of public health concerns. This review focuses instead on the production and degradation of MCs in freshwater environments and their effects on aquatic organisms. Genetic research has revealed the existence of MC-related genes, yet the expression of these genes seems to be regulated by complex mechanisms and is influenced by environmental factors. In natural water bodies, the species composition of cyanobacterial communities and the ratio of toxic to nontoxic species and strains are largely responsible for total toxin production. Cyanobacteria play vital roles in aquatic food webs, yet production, accumulation, and toxicity patterns of MCs within aquatic food webs remain obscure. R. Zurawell was supported by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant to E. Prepas. The authors wish to thank D. G. Dixon for the inspiration to write this review and S. Pinder for assisting with figure preparation. Thorough reviews of earlier drafts by two anonymous reviewers greatly improved the content and logical development of this article.Current address for Ronald W. Zurawell is Environmental Monitoring and Evaluation Branch, Environmental Assurance Division, Alberta Environment, 10th Floor, Oxbridge Place, 9820-106 St., Edmonton, AB T5K 2J6, Canada.

Riparian areas in the Canadian boreal forest and linkages with water quality in streams

Riparian areas in the Canadian boreal forest represent the transition zone between terrestrial and aquatic ecosystems. We review factors that influence riparian vegetation communities and the associated interactions with boreal streams. Regional and local drivers (e.g., climate, edaphic factors, and natural disturbances) that affect upland boreal vegetation also operate in riparian areas. However, the proximity of riparian areas to the stream channel not only modifies some of these drivers, but it means that the stream itself becomes a driver of riparian vegetation dynamics. For example, hydrological disturbances like flooding and ice scour affect soil texture and alter successional pathways, sometimes completely denuding streambanks of vegetation. Even in riparian areas unaffected by such catastrophic disturbances, saturated soil conditions can influence riparian forest composition and nutrient cycling. Saturated soils support lower mineralization rates, therefore organic layers store relatively more car...

First assessment of cyanobacterial blooms and microcystin-LR in the Canadian portion of Lake of the Woods

Abstract Cyanobacterial blooms containing the hepatotoxin microcystin-LR (MC-LR) occurred at least once at each of 5 sites sampled in June, July and August 2004 in the Boreal Shield (Ont., Canada) portion of Lake of the Woods. In June, cyanobacteria constituted 3.5–49% (median 25%) of total phytoplankton biomass and consisted largely of Aphanothece spp. (median 98% of total cyanobacterial biomass). In July and August, cyanobacteria comprised 54–98% (median 77%) of total phytoplankton biomass in surface water samples and consisted largely of Aphanizomenon flos-aquae (median 82% of total cyanobacterial biomass). Three species of Anabaena (A. flos-aquae, A. lemmermannii, and A. mendotae), as well as Homeothrix janthina, Pseudanabaena spp., Aphanocapsa spp., and Woronichinia spp. were also present during the study period. Among study sites, total phosphorus concentrations in surface grab samples ranged from 11 to 31 μg/L and were positively associated with total cyanobacterial biomass (r = 0.64, P = 0.01). MC-LR concentrations (μg/g dry weight) in bloom material collected with a 64-μm tow net and analyzed by High Performance Liquid Chromatography were positively related to ammonium concentrations in surface grab samples (r = 0.94, P = 0.001), but not to the total biomass of cyanobacteria or any cyanobacterial taxon. In the isolated Boreal Shield basins of this lake, cyanobacterial blooms and cyanotoxins like MC-LR may have ecological and human health consequences and may be sensitive indicators of human disturbance in the drainage basin.