1. 1 11/20/2015 Scott Libby, Battelle Candace Oviatt, URI Dave Borkman, URI Jeff Turner, UMD Water Column Overview OMSAP – June 29, 2009

2. 2 Water Column Results –“Typical” trends generally observed in WQ parameters –Driven by seasonal events -Winter/spring blooms (diatoms and Phaeocystis) -Alexandrium blooms -Seasonal stratification and upwelling -Fall blooms and mixing of water column Phaeocystis pouchetii Chaetoceros debilis Dactyliosolen fragilissima Ceratium tripos Asterionellopsis glacialisSkeletonema costatum Alexandrium fundyense DIN Areal Chla DO

3. 3 Monitoring Questions Have nutrients changed near the outfall or in the farfield? Has phytoplankton biomass changed? Have production rates changed in the nearfield and Boston Harbor? Has plankton community structure been altered? Has dissolved oxygen (DO) changed? Yes, as expected No Changes observed related to regional trends/blooms Yes No

4. 4 4 Nutrient Loading –Relatively constant load from outfall (<12K mt/yr) –Nitrogen load mostly ammonium (~75% NH 4 ; 5-10% NO 2 +NO 3 ) –Outfall contributes ~3% of TN entering the MB system –Flow from GoM contributes 92% of TN load to MB system –Dilution at outfall is as-designed - Plume surfaces in winter, but dilution is greater - Plume is isolated below pycnocline in summer - Net transport is generally to south with high local variability

5. 5 Outfall Plume – NH 4 signature (  M) Feb 2003 May 2003

6. 6 Physical processes Massachusetts Bay circulation influenced by seasonal and local winds plus runoff Nearfield area does not have a consistent mean flow Massachusetts Bay and the Gulf of Maine are coupled Interannual and regional factors contribute to spatial and temporal variability in key monitoring parameters (e.g. DO) Hemispheric scale processes imparting trends in MWRA monitoring data (e.g. NAO) Low-frequency Currents Winter Summer Butman et al. 2007

7. 7 Modeled and observed Nutrient distributions Model Predictions Monitoring Results WINTERSUMMER Harbor Outfall Bay Outfall (R. Signell, USGS)

8. 8 Annual Mean Nutrients – NH 4 Post Diversion –Large Decrease in Boston Harbor (red) –Decrease in Coastal area (green) –Initial doubling in nearfield (black) –Unchanged elsewhere MB and CCB After 2003 –Decrease across all areas –Current nearfield levels comparable to 90’s Ammonium has changed – what about the other nutrients?

9. 9 Annual Mean Nutrients – NO 3 NO 3 variable with a weak increasing trend over time in the bays (except Boston Harbor) SiO 4 and PO 4 (not shown) – more interannual variability and no long- term trends Have seasonal trends in nutrient concentrations changed?

10. 10 Nutrients – NO 3 Cape Cod Bay High NO 3 (& SiO 4 )in February and March 2008 across the Bays PCCS also observed higher NO 3 in CCB 2008 Late -February NO 3 higher post-diversion vs. Baseline in CCB and offshore MB Attributed to decrease/ delay in diatom bloom

11. 11 2008 Phytoplankton, Chla & POC

12. 12 POC – Baseline and Post-diversion Nearfield N. Boundary Offshore

13. 13 Boston Harbor Coastal Cape Cod Bay POC – Baseline and Post-diversion

14. 14 BACI Statistical Analysis (92-08) Grouped stations –“Impacted” area -Inner nearfield: N16, N18 & N20 –Control areas -Outer nearfield: N01, N04, N07 & N10 -MB Offshore: F12, F17, F19 & F28 -CCB: F01, F02 & F03 Pre vs. Post comparisons Comparisons of differences between impacted and control areas pre vs. post

15. 15 Nutrient Distribution – Pre-Post changes Ammonium – Baseline vs. 2001-2008   M NH 4 Winter/Spring SummerFall  Inner Nearfield  Outer Nearfield CCB & MB Off  Inner Nearfield  MB Off BACI analysis indicated increases (p≤0.05) in NH 4 above baseline levels in the Inner Nearfield compared to all three control areas for each season

16. 16 Nutrient Distribution – Pre-Post changes Nitrate – Baseline vs. 2001-2008   M NO 3 Winter/Spring Summer Fall  Inner Nearfield Outer Nearfield & MB Off  Inner Nearfield Outer Nearfield & CCB All groups trending in the same direction – no change (p>0.05) for Inner Nearfield compared to the three control areas for any season

17. 17 Chla Distribution – Pre-Post changes Areal Chla – Baseline vs. 2001-2008  mg m -2 Chla Winter/Spring SummerFall  Inner Nearfield Outer Nearfield & MB Off All groups trending in the same direction – no change (p>0.05) for Inner Nearfield compared to the three control areas for any season

18. 18 POC Distribution – Pre-Post changes POC – Baseline vs. 2001-2008   M POC Winter/Spring SummerFall  Inner Nearfield Outer Nearfield  Inner Nearfield All groups trending in the same direction – no change (p>0.05) for Inner Nearfield compared to the three control areas for any season

19. 19 Updated BACI by stations (92-08) Ran analysis based on proposed AMP revision Pre. vs. post station changes –Changes for NH 4 only (p≤0.05) -Increase at N18 all seasons -Decrease at F23 all seasons & W/S at F13 & N04 BACI results –Impact vs. Control sites –Only changes were for NH 4 -Increase at N18 (p≤0.05) relative to nearly all other stations/season groups -No differences for N18 in fall vs. F06, F13, and N04

20. 20 Monitoring Questions Have nutrients changed near the outfall or in the farfield? Has phytoplankton biomass changed? Have production rates changed in the nearfield and Boston Harbor? Yes, as expected Changes observed related to regional trends/blooms

21. 21 Seasonal and Annual Production Decreases in peak productivity on a seasonal basis Harbor summer peak productivity decreased by 56% (P=0.05) Harbor Annual production decreased >40% (P=0.03) Only a minor change in production at the nearfield stations

22. 22 Monitoring Questions Have nutrients changed near the outfall or in the farfield? Has phytoplankton biomass changed? Have production rates changed in the nearfield and Boston Harbor? Has plankton community structure been altered? Yes No Changes observed related to regional trends/blooms

23. 23 Phaeocystis Blooms (D. Borkman) Sept 2000 Transfer to Bay Outfall SeaWiFS April 2004

24. 24 March 21 – mixed Phaeocystis/ diatom/microflagellate assemblage in nearfield (<1 million cells/L) High flow into MB from Gulf of Maine (GoMOOS A buoy) in late March & April Elevated chlorophyll levels were also observed at the buoy over this period April 10-11 – Phaeocystis bloom observed from nearfield to CCB (1-9 million cells/L) April 21-22 – Bloom continues – maxima at depth from Cape Ann to nearfield (max 12 million/L at F22) Chlorophyll lower in early May and no Phaeocystis in nearfield on May 23 Phaeocystis also observed in Casco Bay and along NH coast – Regional Blooms 2007 Phaeocystis Bloom

25. 25 Diatom and Phaeocystis trends Diatom trend of long-term decline Phaeocystis increasing Inverse correlation (Pearson r = -0.54, P<0.0001)

26. 26 Alexandrium fundyense

27. 27 2005 Bloom Regional blooms – initiated in western Gulf of Maine and driven by physical forcing mechanisms Expect these blooms to continue with regularity in GoM and lead to frequent toxicity in Massachusetts Bay Conceptual Model

28. 28 Total zooplankton, 1992-2008 Similar abundance trends across areas Abundances ≤150,000 92-98 Peak abundances in 1999 & 2000 Lower post-diversion <100,000

29. 29 Cape Cod Bay Trends in total zooplankton abundance Long-term trend of decreased abundance since 2001 Increasing in recent years Similar trends observed throughout Massachusetts Bay and Boston Harbor No change in total zooplankton abundance in Cape Cod Bay Nearfield Time-series

30. 30 Monitoring Questions Have nutrients changed near the outfall or in the farfield? Has phytoplankton biomass changed? Have production rates changed in the nearfield and Boston Harbor? Has plankton community structure been altered? Has dissolved oxygen (DO) changed? Yes Changes observed related to regional trends/blooms Yes No

31. 31 Baseline vs. Post-discharge – Nearfield and Stellwagen Basin

32. 32 Monitoring Questions Have nutrients changed near the outfall or in the farfield? Has phytoplankton biomass changed? Have production rates changed in the nearfield and Boston Harbor? Has plankton community structure been altered? Has dissolved oxygen (DO) changed? Yes Changes observed related to regional trends/blooms Yes No

33. 33 Conclusions Obvious and expected changes in the nutrient regimes following diversion. –Ammonium decreased in Boston Harbor (80%) and nearby coastal waters –Increasing to a lesser degree in the nearfield –NH 4 signature of the plume confined to within 10-20 km of the outfall. –Consistent with predictions. In Boston Harbor, concurrent decreases in other nutrients, chlorophyll, and POC. In the nearfield, concurrent changes in chlorophyll, POC, and phytoplankton, but…. –BACI analysis found that the only change between impact and control areas and stations was for NH 4 concentrations –The analyses did not find statistically significant changes in chlorophyll –Primarily because the changes have been regional in nature – occurring throughout Massachusetts Bay and further offshore in the western Gulf of Maine

34. 34 Conclusions Productivity –Reduction (>40%) in Boston Harbor productivity since diversion –No change at nearfield stations Phytoplankton –Major observed trends occurring on a wider, western Gulf of Maine Scale -Decrease in diatoms and coincident increase in Phaeocystis blooms -Recent increase in occurrence of Alexandrium blooms and toxicity in the bays Zooplankton –Abundance and species composition generally similar interannually –Long-term decrease in total zooplankton in Massachusetts Bay 2001-2006 –Unchanged in Cape Cod Bay Dissolved Oxygen –Post-diversion comparable to baseline in the nearfield and Stellwagen Basin –No change in DO (interannual variability driven by regional processes)

35. 35 Acknowledgements The data presented are the result of the efforts from many HOM team members including: –Battelle Field and Logistics Operations Group –Battelle, subcontractor, and MWRA labs –Matt Fitzpatrick for helping with data analysis & graphics