Turning water quality data into lake-specific nutrient standards

Transcription

1 Turning water quality data into lake-specific nutrient standards 2015 Tribal Lands and Environment Forum Nancy Schuldt, Water Projects Coordinator Fond du Lac Reservation

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4 Current Narrative Standard: Reservation waters shall be free from nutrients (nitrogen and phosphorus) from entering the waters as a result of human activity in concentrations that create nuisance growths of aquatic weeds and algae

5 Traditional paradigm Stressor/response relationships (increasing nutrient, sediment loads lead to increased primary productivity, decreased transparency) Causal and response variables State of Minnesota (MPCA) has developed lake nutrient criteria for northern lakes and forests ecoregion, establishing a reference condition (29 lakes) But, for our lakes, dissolved organic carbon or color confounds that relationship (also seen in Florida)

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7 Parameters: Secchi depth Hydrolab profile (DO, ph, specific conductance, turbidity, temperature) TSS Total hardness Alkalinity Color (true & apparent) Sulfate Sediment nutrients (wild rice lakes) Macrophytes (spp. lists) Nutrients (TKN, ammonia, nitrate-nitrite, total phosphorus ortho phosphorus Chlorophyll a, algal community Zooplankton (fisheries lakes) Annual toxics/metals Mercury

8 Potential Differences between tribal, state WQS: Number of waterbodies for which criteria will be developed, applied Type of data available to robustly quantify or calculate numerical criteria States work on large spatial scales, but little temporal variability Tribes work on smaller spatial scales, may have extensive long-term data

9 Basis for our approach: Stressor/response relationship has not been well studied in highly stained lakes (shallow or deep) natural geomorphic setting of lakes sets the stage for the expected or natural condition expected condition is defined as the nutrient concentrations in least disturbed areas most of our lakes have experienced limited human disturbance in their watersheds

10 Numeric Nutrient Criteria Nine priority fisheries lakes: pilot project for lakespecific nutrient criteria Dr. Pat Soranno: Biopredictive modeling to determine healthy (relatively unimpacted) condition; relate nutrient levels to biological response Considers natural hydrogeomorphic setting of lake; sets the stage for natural or expected condition of nutrients Single criterion will not work across all lakes; too variable

11 Our approach (FDL, GP): Biological Thresholds/Predictive Modeling Assume P is the main stressor to lakes Natural variation in P due to watershed, lake morphometry, geology, climate Establish biological benchmarks that relate to the lake s designated uses Biological response (lake clarity as a function of algae biomass/primary productivity) Human disturbance can be approximated as human land use within the watershed

12 Approach (continued) Assumption: lakes are in relatively unimpacted state Current biological conditions assumed to be indicative of meeting designated uses Using nutrient data from each lake, the expected condition is calculated as the full range of expected concentrations for each variable (TN, TP, chlorophyll a) within each lake Nutrient criteria calculated as upper 90 th %tile of each variable within a season, across all years

13 Results (90 th percentile) TP criteria range from µg/l TN criteria range from µg/l Chlorophyll a criteria range from 3 44 µg/l TP TN chlorophyll a Median Fond du Lac criteria Median Grand Portage criteria Median NLF reference lakes 30 9

14 FDL, GP compared to MN NLF Secchi transparency is much lower for FDL, GP TN is higher for both FDL, GP than NLF Chlorophyll a is NOT higher than NLF FDL lakes are variable; single criterion would not work GP lakes: TP is only weakly correlated to chl a

15 But need to validate Using algal community data

16 Phase 2: PhycoTech study Evaluate whether phytoplankton rapid assay data ( ) support the finding that FdL lakes are unique, minimally impacted, and that lake specific criteria are appropriate Algae generally considered sensitive indicators of changes to nutrient loading, at either high (chrysophytes, diatoms, cryptophytes) or low (toxin-producing cyanobacteria) water quality Other taxonomic divisions convey information, such as high organic matter, low ph, or higher nitrogen

17 Objectives Compare FdL lakes to moderately-highly impacted lakes in MN Do FdL lakes have algal assemblages that are associated with more color, higher WQ? *opportunity to evaluate Phytoplankton Rapid Assay (PRA) as a good alternative to full algal counts with biovolume estimates, when time/resources are limiting (calibration study)

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24 Calibration study: 2014 Fond du Lac samples Good agreement between quantitative (relative % biovolume) and PRA, and two independent taxonomists

25 Additional Results: Also compared rainfall, ice-out dates, air temperature; FdL lakes experience colder temps and later ice-out (shorter growing season; affects HAB potential) No increasing or decreasing trends in FdL lakes over time (MDS, Cluster analysis) FdL lakes were stable ecologically in their algal community response

26 Issues to consider Chlorophyll a is a useful and broadly used indicator, but different algal divisions have distinct differences in pigment composition Might not be as sensitive an indicator of ecosystem change in lakes with different relative percents of contrasting algal divisions, as would the relative changes among those divisions measured directly

27 Issues (cont.) Our proposed lake-specific nutrient criteria (from Soranno), which are higher than the state s ecoregional criteria, are corroborated by the PRA analysis The best way to track subtle changes in water quality involves multiple indicators, especially when we are trying to manage nutrients before water quality noticeably degrades

28 Next steps: Submit technical supporting documents for lake-specific nutrient criteria for nine primary fisheries lakes Propose adopting these criteria during triennial review Calculate criteria for other fisheries lakes Consider approach for wild rice lakes Consider approach for streams

29 Questions?