Lake of the Woods TMDL: Internal Loading Update November 23, 2016

Transcription

1 Lake of the Woods TMDL: Internal Loading Update November 23, 216 Outline HSPF update Bathtub update Internal loading update Next steps 1

2 HSPF Update Completed in September 7, km 2 ~ 615 HUC12s >3, Waterbodies 9 Linked HSPF models HSPF Update Update incorporated University of Minnesota 21 land use update Very small changes in Q and TP loading 2.7% increase in Q 4% decrease in TP load to Lake of the Woods Changes due largely to vast ungauged areas coupled with changes in land use Land Use Area by Model (km 2 ) Aggregated Land Use NLCD/LCC 21 UMN 21 Change Open Water 12,943 12, Developed Barren Forest 4,531 38, Hay/Pasture 3,781 1, Cropland Wetland 1,84 16,

3 Bathtub Update Bathtub has been updated with updated HSPF Q and FWMCs for each tributary and lakeshed Bathtub Update: Next Steps Need final estimate for internal loading TP model selection update based on new analysis Complex system that is not well represented by any one Bathtub model option Calibration 3

4 Internal Loading: Past Work Bill James 212 Dissolved oxygen-mediated sediment P release Aerobic release:.2 to.6 mg P m -2 d to 272 tons/yr from Big Traverse (1,243 km 2 ) Anaerobic release: 8.3 to 12.5 mg P m -2 d -1 Internal Loading: Past Work Bill James 215 Temperature- and dissolved oxygen-mediated sediment P release 1 Sediment P Release Rate vs. Water Temperature Sediment P Release Rate (mg/m 2 /d) Water Temperature (⁰C) Aerobic release rate Anaerobic release rate 4

5 Internal Loading: Past Work Bill James 215 Aerobic release:.12 mg P m -2 d tons/yr from Big Traverse Based on bottom water temperature by month Anaerobic release: 7.3 mg P m -2 d -1 (assumed T = 17 ⁰C) 9 tons/d from Big Traverse Total annual sediment P release is very sensitive to anoxia Internal Loading: Past Work Science Museum of Minnesota Dissolved oxygen measuremens 5cm above lake bottom Show depletion (.4 to.5 mg L -1 d -1 ) during calm periods No anoxia observed It is unknown if/how often anoxic conditions occur Observed Bottom Dissolved Oxygen Concentration (mg/l) Bottom Dissolved Oxyen Concentration, 215 6/21/215 6/26/215 7/1/215 7/6/215 7/11/215 7/16/215 7/21/215 7/26/215 7/31/215 MPCA Muskeg Big Traverse 5

6 TP Mass Balance Approach Δ Σ Σ Unexplained residual internal loading, or more accurately Net TP release, resuspension, and settling We know that both TP release and sedimentation/settling are happening all the time, but TP release dominates during the growing season due to warmer temperatures, biological activity, and wind mixing Monthly net estimates are therefore minimums for TP release into the water column TP Mass Balance Approach Approach to determine approximate long-term mean annual water and TP budgets Corresponds to Bathtub: mean annual Q and loading Water balance Volumes and surface areas by bay (Zhang et al (213), MPCA) HSPF tributary and lakeshed runoff (HSPF) Precipitation (HSPF) Evaporation (HSPF/literature data) Outflow at Kenora (LWCB) 6

7 TP Mass Balance Approach TP mass balance Loading from tributaries and lakesheds (HSPF) Atmospheric deposition Observed TP concentrations by month (US/Canadian monitoring data) to determine: in-lake TP mass TP flow through and between bays Outflow at Kenora (LWCB) Water Balance 4, Lake of the Woods Overall Monthly Water Balance Summary 3, Monthly Inflow/Discharge (hm 3 ) 2, 1, 1, 2, 3, Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total Inflow Total Outflow Change in Volume 7

8 Water Balance 3, Lake of the Woods Overall Monthly Water Balance Summary 2,5 2, Monthly Inflow/Discharge (hm 3 ) 1,5 1, 5 5 1, 1,5 2, Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Precipitation Tributary Inflow Evaporation Outflow Change in Volume Monthly Water Surface Fluctuation.5 Relative Water Surface Elevation Relative Water Level (m).1.1 Error = 3 cm (122 hm 3 ) < 1% of outflow at Kenora /1 1/31 3/1 4/1 5/1 6/1 7/1 8/1 8/31 1/1 1/31 11/3 12/31 8

9 TP Mass Balance Pathway Mean Annual TP Load (25-214), metric tons Atmospheric Deposition 69 Tributary Inflow (includes lakeshed 44 & PS loading) SSTS Loading Direct to LOTW.6 Bank Erosion (Houston) 72 Internal Loading??? Total Inflow >582 Outflow at Kenora 32 Entire Lake TP Budget 14, Monthly TP Inflow and Outflow 12, 1, TP Flux (kg) 8, 6, 4, 2, Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec TP Inflow TP Outflow 9

10 Observed TP Concentrations 8 Big Traverse Observed TP Concentration 7 6 TP Concentration (μg/l) Ordinal Day 6 day Rolling Mean Observed Concentration Observed TP Concentrations 8 Little Traverse Observed TP Concentration 7 6 TP Concentration (μg/l) Ordinal Day 6 day Rolling Mean Observed Concentration 1

11 Observed TP Concentrations 8 Muskeg Observed TP Concentration 7 6 TP Concentration (μg/l) Ordinal Day 6 day Rolling Mean Observed Concentration Observed TP Concentrations 6 6 Day Rolling Mean TP Concentration 5 TP Concentration (μg/l) Ordinal Day Big Traverse Little Traverse Muskeg 11

12 Monthly TP Budget 2, Entire Lake Monthly TP Budget Net P release 15, 1, 5, Monthly TP Flux (kg) - (5,) (1,) (15,) (2,) (25,) (3,) Net sedimentation May Jun Jul Aug Sep Oct Total Surface Inflow (kg) Total Outflow Net Inflow Unexplained Residual Observed Change in In-Lake TP Monthly TP Budget Big Traverse 15, Big Traverse Bay Monthly TP Budget 1, Monthly TP Flux (kg) 5, - (5,) (1,) (15,) May Jun Jul Aug Sep Oct Total Inflow Total Outflow Net Inflow Unexplained Residual Observed Change in In-Lake TP 12

13 Net Internal Loading Summary Net Unexplained Residual TP Load (tons) Month Sabaskong Four Mile Muskeg Big Traverse Little Traverse May 7.8 (17.3) (5.5) (24.2) 5.1 June (3.4) July (33.4) August (.7) (7.6) September (13.3) (8.1) October (27.8) 2.3 (9.9) (12.) 3.4 Total Mass* (44.4) Loading Rate (mg/m 2 /d) ^ * calculated as net loading from June to Sept, ignoring Oct May, when settling dominates ^ limited data available, analysis suggests settling dominates all year Internal Loading Summary Performed detailed hydrologic and nutrient mass balance with HSPF outputs Monthly mass balance compared to observed in-lake TP mass Resulted in redefinition of internal loading as net of TP release, resuspension, and settling Mean annual internal loading: 282 tons 13

14 Next Steps Develop draft TMDL Load allocation table Reasonable assurance Monitoring plan Implementation strategy Thank you! Questions/Comments? Julie Blackburn: Geoff Kramer: 14