Land use influences on cyanotoxin abundance in small south-central Saskatchewan water bodies
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Blooms of cyanobacteria that produce toxic compounds occur in ponds and wetlands in Saskatchewan, where they pose a risk to domestic livestock and wildlife. Most documented poisonings of animals that are caused by cyanotoxins result from exposure to the microcystins, which cause damage to the liver. The present study was intended to identify whether agricultural land use (arable land vs. permanent pasture), and/or geographic region were associated with the presence and abundance of toxins produced by cyanobacteria in small Saskatchewan water bodies in the Saskatchewan northern prairie ecozone. Cyanobacterial abundance and the risk of toxin production are thought to be associated with nutrient enrichment of water bodies, which might be linked to agricultural practices. Therefore, the study was also intended to determine if concentrations of nutrients in surface waters and/or soils were different for small water bodies and their surrounding drainage basins located within arable land compared with permanent pasture. Study sites were clustered in three regions of south-central Saskatchewan, including Saskatoon/Aberdeen, Elrose/Rosetown and Swift Current. These regions were located within two of the three main soil zones found within southern Saskatchewan. Each cluster consisted of eight small water bodies (natural ponds or wetlands, or farm dugouts) located within arable crop fields (mostly grain or pulse crops), and eight small water bodies located in permanent pasture land used for cattle grazing. Water was collected twice from all 48 sites, first in July and again in late August/September of 2009. Soil was collected once at all 48 sites. Samples collected included: 1) drainage basin soil cores for nutrient analysis, including available nitrate, ammonium, phosphorus and potassium; 2) integrated surface water samples for total phosphorus, soluble reactive phosphorus, nitrate, nitrite, total kjeldahl nitrogen, ammonia and chlorophyll-a; and 3) integrated surface water and algal bloom samples for cyanotoxin analyses and possible algal identification. Saxitoxins, which are neurotoxic cyanotoxins were identified and quantified by use of HPLC-MS/MS, while microcystins, which are hepatotoxins, were identified and quantified by use of both HPLC-MS/MS and a bioassay that measured inhibition of phosphatase activity. Results of the neurotoxin analyses indicated only trace amounts of saxitoxins present in any water bodies at the time of sampling. Although more work is necessary to determine the extent to which saxitoxins occur in small Saskatchewan water bodies, the results of the present study suggest that these neurotoxins pose little risk to humans, domestic animals or wildlife. Microcystins occurred consistently in lesser levels throughout the summer months in small water bodies in south central Saskatchewan. Although microcystins were detected in water bodies located within areas of both types of land use, the water bodies surrounded by arable land contained significantly greater concentrations of these toxins. This suggests that practices specific to arable land are influencing abundances of microcystins. Since there were no statistically significant differences in concentrations of microcystins between geographic regions, results were analyzed using data pooled from all areas. No significant differences between land uses were found for any water quality parameters. Concentrations of soluble reactive phosphorus in water and total phosphorus in water and soil were found to be significantly different between land uses, and were positively correlated with concentrations of microcystins in water. Nitrogenous compounds in soil and water were also positively associated with concentrations of microcystins. This result suggests that repeated fertilization with nitrogenous fertilizers is possibly leading to accumulation of nitrogen compounds in soil, which can be mobilized into local surface water, and potentially promote the growth of cyanobacteria. The triggers for formation of cyanobacterial blooms and subsequent production of microcystins are multi-factorial and complex, such that predicting formation of blooms at any given location is not currently possible. However, the results of this study of environmental factors and land use on the Canadian prairies generally confirms work done in other systems in that the presence of greater concentrations of nutrients, potentially due to fertilization practices, appears to be the critical factor affected by human activity that can be associated with the likelihood of production of microcystins.
DegreeMaster of Science (M.Sc.)
DepartmentWestern College of Veterinary Medicine
CommitteeDavies, John-Mark; Schoenau, Jeff; Blakley, Barry
Copyright DateJuly 2012
total kjeldahl nitrogen