1. OMSAP Public Meeting September 1999 Benthic Nutrient Cycling in Boston Harbor and Massachusetts Bay Anne Giblin, Charles Hopkinson & Jane Tucker The Ecosystems Center, Marine Biological Laboratory Woods Hole, MA 02543 September 22, 1999

2. OMSAP Public Meeting September 1999 Nutrient Cycling Boston Harbor – Goals Determine the role of the sediments in nutrient cycling  Amount of nutrients released relative to NPP needs  Ratios of nutrients released (e.g. N/Si)  Size of sink if appropriate (denitrification; N,P, and Si burial) Determine the role of the sediments in oxygen dynamics  Importance as an oxygen sink  Storage of reduced endproducts Determine how role of the sediments has changed over time  Sludge disposal ceased in 1991  Treatment being upgraded to secondary  Relocation of outfall to offshore

3. Inflow Outflow Light Concerns Ecological Nutrients Nutrients Contaminants Organic Material Food Chain Community Structure Living Resources Human Health Contaminants Bacteria Viruses Bioaccumulation SEDIMENT Mammals Infauna Piscivorous Fish Zooplankton Phytoplankton Planktivorous Fish Epibenthos Demersal Fish Regeneration Detritus Particulate Microbes Dissolved WATER COLUMN Sources Rivers Boundary Nonpoint Effluents Effluents Exchange Gas Exchange N 2, | O 2, CO 2 ATMOSPHERE N, P, Si, O 2, CO 2 Microbes

4. OMSAP Public Meeting September 1999 Nutrient Cycling Nitrogen Cycle in Coastal Waters

5. OMSAP Public Meeting September 1999 Nutrient Cycling Boston Harbor Stations for Benthic Fluxes

6. OMSAP Public Meeting September 1999 Nutrient Cycling Sediment Oxygen Demand - Northern Harbor

7. OMSAP Public Meeting September 1999 Nutrient Cycling Sediment Oxygen Demand - Southern Harbor

8. OMSAP Public Meeting September 1999 Nutrient Cycling DIN Fluxes - Northern Harbor

9. OMSAP Public Meeting September 1999 Nutrient Cycling DIN Fluxes - Southern Harbor -5 0 5 10 15 20 25 Jan-95 Apr-95 Jul-95 Oct-95Jan-96 Apr-96 Jul-96 Oct-96Jan-97 Apr-97 Jul-97 Oct-97Jan-98 Apr-98 Jul-98 Oct-98Jan-99 Apr-99 Jul-99 Oct-99Jan-00 mmol N m 2 d NO3 NH4 d. QB01

10. OMSAP Public Meeting September 1999 Nutrient Cycling Denitrification Losses

11. OMSAP Public Meeting September 1999 Nutrient Cycling Denitrification - Methods Comparisons

12. OMSAP Public Meeting September 1999 Nutrient Cycling Phosphate Fluxes - Northern Harbor

13. OMSAP Public Meeting September 1999 Nutrient Cycling Phosphate Fluxes - Southern Harbor

14. OMSAP Public Meeting September 1999 Nutrient Cycling Flux Ratios

15. OMSAP Public Meeting September 1999 Nutrient Cycling Dissolved Sulfides in Porewaters

16. OMSAP Public Meeting September 1999 The current four sites are representative of depositional and reworked areas in the Harbor and therefore may over-represent the role of the Harbor sediments somewhat. Based upon these four stations, we estimate that the sediments could supply 35% of the N and 58% of the P required for primary production. However, new inputs from the current Deer Island outfall contribute much more than needed for NPP. The importance of sedimentary recycled nutrients in supporting NPP will increase when the outfall moves offshore. Nutrient Cycling Harbor Role

17. OMSAP Public Meeting September 1999 Harbor sediments are an active site of denitrification and more than half of the nitrogen mineralized in the sediments is subsequently denitrified and lost from the ecosystem. Although the proportion of nitrogen lost from the sediments is high, it is typical of marine sediments. However, because most of the nitrogen entering Boston Harbor are not cycled through the sediments only a relatively minor percentage of the N inputs to Boston Harbor from sewage and other sources is lost by denitrification. Hence, moving the outfall should not have a large effect on the N budget of Massachusetts Bay as a whole. Nutrient Cycling Harbor Role (cont’d)

18. OMSAP Public Meeting September 1999 The ratio of N/Si is greater than 1.0 at most stations at most times of the year, therefore sediments are releasing nutrients with an N/Si ratio favorable to diatoms. Interannual oxygen uptake rates continue to be variable at most stations, however, the extremely high rates observed in the early part of the study (1993-1995) have not been repeated. Highest oxygen uptake rates are usually associated with a dense cover of tube building amphipods. Although the amphipods continue to be present the lower rates we are now observing near the Long Island sludge disposal site suggest some “mining” of sediments organic stores may have taken place. Nutrient Cycling Harbor Role (cont’d)

19. OMSAP Public Meeting September 1999 Determine the role of the sediments in nutrient cycling  Amount of nutrients released relative to NPP needs  Ratios of nutrients released (e.g. N/Si)  Size of sink if appropriate (denitrification; N,P, and Si burial) Determine the role of the sediments in oxygen dynamics  Importance as an oxygen sink  Storage of reduced endproducts Determine patterns of annual and interannual variability Determine how the role of the sediments changes with outfall relocation Nutrient Cycling Massachusetts Bay – Goals

20. OMSAP Public Meeting September 1999 Nutrient Cycling Benthic Flux Stations

21. OMSAP Public Meeting September 1999 Nutrient Cycling Sediment Oxygen Demand

22. OMSAP Public Meeting September 1999 Nutrient Cycling Sediment Oxygen Demand

23. OMSAP Public Meeting September 1999 Sediment fluxes were not measured in Massachusetts Bay during 1998. Previous measurements had shown that benthic respiration rates exhibited low interannual variability, less than 20%. This suggested that any change due to the outfall relocation would be readily detectable. Benthic respiration rates measured in 1999, however,have been higher than average, and may reflect greater carbon loading to the sediments from an unusually large diatom bloom, and warmer than usual bottom water temperatures. October rates will be needed to determine if this year’s rates would have fallen outside what was considered normal based upon the 1992-1997 data. Nutrient Cycling Bay Role