Nutrient Criteria Development for Lakes: Minnesota’s Approach & Timeline

1. Nutrient Criteria Development for Lakes: Minnesota’s Approach & Timeline Steve Heiskary, Research Scientist III Minnesota Pollution Control Agency Environmental Analysis & Outcomes Div. MDNR Meeting April 2007

2. Background & Overview 1. Present draft criteria 2. Overview of our approach, which considers: • Assessment of ecoregion patterns; • Varying uses of lakes; • Considerations for shallow lakes (collaboration w/ Ecoservices & Wildlife); • Fishery considerations (Collaboration w/ Fisheries) • Use of sediment cores to reconstruct WQ (collaboration w/ Science Museum); • Criteria for both “causative” (TP) & “response” (Secchi & chlorophyll-a) variables; • Allowance for site specific criteria, e.g. reservoirs; 3. Application of criteria – from TMDLs to protection; 4. Timeline for rulemaking

3. Minnesota’s Draft Eutrophication Criteria.

4. Definitions (include in rule) • Need to differentiate among lakes (shallow vs. deep), reservoirs, wetlands & rivers • “Lake” – enclosed basin…max. depth > 15 ft. (4.5m) -- 10 acres (4 ha) minimum size for “lakes”; • “Shallow lake” - max. depth 15 ft. (4.5 m) or less or 80% or more littoral (drawn from Schupp); generally not wetlands; • “Reservoir” – natural or artificial basin where outlet is controlled by control structure. Differentiated from rivers based on Tw of 14 days or more as determined based on a summer “120 day Q10”; • Index period – summer (June – September);

5. Minnesota’s Ecoregions & Reference Lakes: 98% of MN lakes located in these 4 ecoregions; Reference lake monitoring began in 1985 - ~ 90 “minimally-impacted, representative lakes (candidates to consider for long-term or trend monitoring) WQ & morphometry varies among regions; 6 – 17 m. deep 20 – 140 ha 5 – 15 m deep 25 – 160 ha 2.5 – 5 m deep 45 – 283 ha

6. Basis for “Response” Criteria • Relationships among TP, chlorophyll-a, Secchi, nuisance blooms & HOD; • User perception data from CLMP observers • Regional patterns in lake trophic status, fishery composition; lake morphometry, soils, land form & land use

8. Fish species vary relative to lake trophic status Based on work of Dennis Schupp & paper by Schupp & Wilson 1993

9. Burntside Kabekona TP 10 12 Chl 3 3 Secchi 6.1 m 3.6 m • Lake Trout Lakes – consider: • Unique DO & temp. requirements – DO 6 or more, temp. 8-15 C preferred (12 C or less deemed suitable habitat, Siesennop 2000); • We Charted “optimal habitat”

10. Number of Fish Species as a function of TSI (Schupp) TP =12 ppb TP = 90 ppb

11. Percent Piscivores as a function of TSI (Schupp) TP ~20-25 ppb

12. Percent of lakes with lake trout or carp as a function of TSI (Schupp). Implies no lake trout lakes when TP > 15 ppb. TP=12 ppb

13. % of lakes with NP or LMB as a function of TSI (Schupp). Distinct decline in % lakes w/ NP as TP >40-50 ppb

14. Northern pike & black bullhead as a function of TSI (Adapted from Schupp) Argues for keeping TP < ~50 – 60 ppb where possible

15. Worked to identify thresholds for shallow lakes

16. Floating-leaf SAV Pelican Note: as TP increases above ~60-90 ppb, floating-leaf generally absent & 10 or fewer species present

17. At Secchi < 1.0 m floating-leaf uncommon & generally < 10 species of submergents

18. As P increased above ~60-90 ppb floating-leaf plants disappeared, & increased risk of loss of plant diversity & algal dominance.

19. “55 lakes study” lakes from NLF, CHF & WCP regions (mid 1990s); • SW MN study focused on 22 shallow lakes, 6 with deep cores (2002); • West-central focused on shallow CHF lakes with a gradient in modern-day P and macrophytes; 6 deep cores (2003);

21. Northern Lakes & Forests ecoregion: Generally low P, minimal change over time; predominately forested land use; P criteria noted

22. North Central Hardwoods Forests ecoregion: large range, distinct differences between shallow and deep lakes. , dramatic change for many lakes over time shallow deep

23. Western Corn Belt Plains 90% or more considered shallow, highly agricultural land use, vast majority eutrophic -hypereutrophic shallow deep

24. Rulemaking timeline for Lake Criteria • Finish SONARs by end of March • Compare our version of rule to Revisor's version - complete by end of January. • Submit rule to to Governor's Office and Commissioner's Office April • Publish in State Register, late April • Public hearings in May-June, 2007 • Close of hearing record in late August • ALJ report - probably at least 60 days after record closes.

25. Main Features & Approach Draft criteria (TP, chla, & Secchi) based on weight-of-evidence approach that considers: • Regional patterns in lake morphometry, water quality, & watershed characteristics. • Within-ecoregion distributions of TP, chl-a & Secchi - reference & overall populations; • Varying uses of lakes & differences among deep & shallow lakes; • Fishery (aquatic life) requirements; • Shallow lakes - plant communities relative to P, chl-a, & Secchi; • Use of sediment cores to re-affirm regional patterns & estimate background; • User perceptions;

26. Summary • Ecoregion-based TP criteria first developed in 1988; • MPCA developed rules for 303(d) listing of nutrient-impaired lakes (2002) – using the 1988 P criteria & corresponding chlorophyll-a & Secchi thresholds; • Listing requires exceedance of causal plus one response (will maintain this approach in standards); • Draft criteria are in WQ standards now being promulgated; • Standards language reinforces need to protect high quality lakes (non-degradation) and account for naturally poor quality lakes; • Differentiate among shallow & deep lakes; • Allows for site-specific criteria for reservoirs & other cases where deemed necessary (have guidance)

27. Track progress on adoption of lake standards on our triennial review web page & Nutrient criteria-related reports on lake assessment web page MPCA Home Water -- Regulations Proposed Water Quality Standards Rule Revision http://www.pca.state.mn.us/water/standards/rulechange.html Water -- Lakes -- Lake Water Quality Assessment Report: Developing Nutrient Criteria http://www.pca.state.mn.us/water/lakequality.html#reports steven.heiskary@pca.state.mn.us 651-296-7217