Nutrient Criteria for Reservoirs – A Review of Missouri’s Proposed Approach Daniel V. Obrecht Dept. of Fisheries and Wildlife Sciences University of Missouri

Talk Outline Review approaches suggested in EPA guidance document Review some of the dead ends we visited Review how we came up with current proposal What it means in real terms

Suggested EPA Approaches

STEP APPROACH Designated Use Impairment of use Algal biomass Nutrient levels Criteria level

UMBRELLA APPROACH 1) Reference reservoirs and lakes – 75 th percentile 2) All reservoirs and lakes – 25 th percentile 3) EPA’s Regional criteria

Reference 75% = 58 All Reservoirs 25% = 31 EPA Regional Value = 40

Dead Ends

Relate current land use and hydrology to water quality

Dead Ends Relate current land use and hydrology to water quality Flow Chart – divide reservoirs up into various groupings

Dead Ends Relate current land use and hydrology to water quality Flow Chart – divide reservoirs up into various groupings Tried to identify impairment

Current Approach

Multi-Pronged Approach 1.Divide state into ecoregions 2.Use morphology and watershed characteristics to predict differences in total phosphorus concentrations among reservoirs 3.Identify reference reservoirs within each ecoregion

1. Ecoregions

2. Use morphology and watershed characteristics to predict differences in total phosphorus concentrations among reservoirs Reservoir surface area, reservoir volume, dam height (measure of depth), watershed area, pre-European settlement land cover (prairie, forest, etc.), and hydrology Did not include current land cover

Regional Equations for Predicting Total Phosphorus Plains ecoregion TP = (% prairie/4) + (16/residence time in years) + (570/dam height in feet) Ozark Border ecoregion TP = 15 + (740/dam height in feet) Ozark Highland ecoregion TP = 5 + (740/dam height in feet)

Plains Reservoirs (% prairie/4) + (16/ residence time) + (570/dam height in feet)

3. Reference Reservoirs 1. No point sources or CAFOs within the watershed 2. <20% of watershed in combined crop and urban coverage 3. >50% of watershed in dominant historic land cover (Ozark Highlands = forest; Plains = grassland)

3. Reference Reservoirs 1.Plains Region has 7 reference reservoirs 2.Ozark Border Region has 7 reference reservoirs 3.Ozark Highlands has 23 reference reservoirs

ReservoirTotal Phosphorus (μg/L) Marie14 Viking25 Hazel Creek27 Bethany30 Elmwood52 Harrison County52 Lamar72 Reference Reservoirs in the Plains Region

ReservoirTotal Phosphorus Marie14 Viking25 Hazel Creek27 Bethany30 Elmwood52 Harrison County52 Lamar72 Reference Reservoirs in the Plains Region 10 th percentile 75 th percentile (of range)

RegionParameter75%10% PlainsPhosphorus Nitrogen Chlorophyll BorderPhosphorus Nitrogen Chlorophyll OzarksPhosphorus 26 9 Nitrogen Chlorophyll *All values are micrograms per liter

Plains Reservoirs (% prairie/4) + (16/ residence time) + (570/dam height in feet)

Questions?