Nutrient Management Strategy - Government of Manitoba

Page 1IntroductionEutrophication is one of the most importantwater quality issues in the prairie and boreal plainecozones in western Canada. Water qualitymonitoring results indicate that most of the largeriver systems that flow across the prairie andboreal plain ecozones contain relatively highconcentrations of phosphorus and nitrogen, thetwo nutrients most commonly associated witheutrophication. The main factors that maycontribute to the high nutrient content in thesesystems include erosion of naturally fertile soils,surface run-off of fertilizers from cultivated fields,run-off from livestock pasture and feedlots, urbanrun-off and storm sewer discharges, andagricultural, industrial, and urban sewage effluentdischarges. Some of the larger river systems thatare of particular concern to southern Manitobainclude the Assiniboine, Souris, and Red Riversystems, all of which carry significant amounts ofnutrients into the province from the west andsouth.Concerns have been raised over the potentialfor eutrophication processes to not only negativelyimpact rivers and streams that flow through theregion, but also adversely affect the water qualityof Lake Winnipeg, since the lake is the eventualrecipient of the nutrient load transported by manyof these rivers and streams.growth of opportunistic species, resulting in anoverall decrease in biological diversity across theentire ecosystem. As well, the decay process thatfollows the decline or die-off of algal andmacrophyte populations uses up large amounts ofdissolved oxygen. This can have seriousconsequences on aquatic animals, such as fish andinvertebrates, which rely on an adequate supply ofdissolved oxygen for survival. Low oxygenconcentrations also result in the release of thenutrient phosphorus from the sediment, making itavailable for algal growth. Eutrophication mayalso decrease the suitability of a water supply fordomestic use (including human drinking),livestock watering, and recreational use. Algalblooms associated with eutrophic waters are oftendominated by species of blue-green algae, some ofwhich are known producers of potent nerve andliver toxins. Such a situation can present a healthrisk for humans, household pets, and livestock thatdrink the water, and for people who use the waterfor recreational purposes. There is also someevidence that the toxins produced by blue-greensmay be transferred up the food web, and mayadversely affect wildlife populations such as fishand water birds. Besides being potentially toxic,the presence of an algal bloom in a drinking watersource can clog treatment plant filters, and oftenimparts an unsightly appearance, and unpleasanttaste and odour to the finished water. Algalblooms and extensive macrophyte growth are alsoconsidered aesthetically unappealing and candetract from the recreational use of a surfacewater.The water quality problems that arise as aresult of eutrophication of drinking andrecreational waters are difficult and expensive toremedy. For drinking water sources the cost ofadditional treatment may be prohibitive in manyjurisdictions, while for recreational waterbodies, adecline in the aesthetic quality of the water canadversely affect tourism, and lead to decreasedland and cottage values.Nutrient enrichment can directly or indirectlyimpact the water quality of surface waters. Anoverabundance of nutrients can lead to excessivegrowth of algae and macrophytes within anaquatic system, which can greatly alter the overallstructure of the ecosystem by favouring theNutrient enrichment has long been recognizedas a major water quality issue. Many importantsteps have been implemented in Manitoba andelsewhere to better understand and to implementappropriate and feasible control options. Waterquality objectives were first developed forFor Additional Information, Visit Manitoba Conservation’s Website for Current Issues - Latest Newswww.gov.mb.ca/environ/