Nutrient Management Strategy - Government of Manitoba

Page 3Item 2 - Derive Numeric Objectives for NutrientVariablesResults from preliminary work on some of theissues in Item 1 indicate that the current ManitobaSurface Water Quality Objectives and objectivesin place elsewhere in the prairies for nutrients areinadequate. Because of this, the derivation of newnumeric objectives for nutrient variables is one ofthe first challenges in the development of anutrient management strategy for southernManitoba. Numeric objectives, as opposed tonarrative objectives, are important in controllingeutrophication because they allow water qualitymanagers to make informed, scientificallydefensible decisions with regard to regulatingnutrient inputs to surface waters.Two approaches to deriving numeric nutrientobjectives will be used simultaneously. These are:(1) Regional Based Objectives and (2) ObjectivesBased on Receiving Waters.(1) Regional Based ObjectivesThe chemical and physical characteristics of awaterway are determined in large part by thefeatures of its drainage basin or watershed.Topography, natural vegetation cover, land-usepractices, climate, geology, and soil type can varyconsiderably between watersheds, and as a result,no two waterways are exactly the same in terms offlow regime, physical characteristics, and waterchemistry. The growth of algae and macrophytesis dependent in large part on the availability ofphosphorus and nitrogen. However, primaryproductivity in streams is also influenced by lightexposure, temperature, water clarity, flow regime,grazing, the presence of toxic pollutants, andmicro-nutrient concentrations, all of which varybetween waterways.Given the considerable variation that existsbetween aquatic systems, it is unrealistic that asingle numeric objective for each nutrient variablecould be applicable to all the rivers and streams insouthern Manitoba. It is apparent that more sitespecificobjectives are required. Although theestablishment of nutrient objectives for individualwaterways is impractical at this time, it isreasonable to consider deriving nutrient objectivesat a regional scale.Regional boundaries for regionally-basednutrient objectives can be based on ecologicalunits such as ecozones or ecoregions, or ondrainage units such as drainage basins orwatersheds. The scale at which the regionalboundaries are set is dependent on the level ofenvironmental variability that is deemedacceptable, and the amount of the resources thatcan be devoted to the derivation process.Once regional boundaries are established theprocess of developing nutrient objectives for theregions can proceed. Major tasks to undertake inthe development of regional nutrient objectivesinclude:A. Identify the major problems associated witheutrophication within each region andprioritize which regions and waterwaysrequire the most immediate attention.B. Identify core variables used to assesseutrophication in southern Manitoba (these arethe variables for which objectives will beestablished).C. Develop focused monitoring programs orstudies, if required, to better define therelationship between nutrients and primaryproductivity and to identify any temporal orspatial trends in rivers within each region.D. Identify reference streams or reaches thatrepresent ambient of non-impacted conditionswithin each region.E. Analyze the data using acceptable statisticalmethods and empirical and simulation modelsto identify relationships between nutrientconcentrations and primary productivity.Nutrient objectives have to be scientificallydefensible; otherwise they will be of littlevalue when it comes to managing andregulating nutrient inputs to streams and riversfrom point and non-point sources.F. Derive nutrient objectives based on the resultsof the statistical analysis and modelling work.For Additional Information, Visit Manitoba Conservation’s Website for Current Issues - Latest Newswww.gov.mb.ca/environ/