Models, Muddles, & Management in Narragansett Bay, RI. Chris Deacutis NBEP, URI Coastal Institute May 18, 2011

Transcription

1 Models, Muddles, & Management in Narragansett Bay, RI Chris Deacutis NBEP, URI Coastal Institute May 18,

2 Narragansett Bay Watershed Watershed Area = 4,421 km 2 Bay Surface Area = 497 km 2 Watershed:Surface Area ~ 9:1 Vs. Casco Bay Watershed 2,551 km 2 Last Dam Surf Area 518 km 2 Ratio ~ 5:1 3 Major River Basins : Taunton ; Blackstone ; Pawtuxet Rivers Annual Mean Lynn Carlson, Mo. Flow Brown = U. GIS lab 104 m3/sec 61% of drainage basin in MA N-S Pollution Gradient STP N-S Pollution Gradients

3 August 20, 2003 Western Greenwich Bay T. Ardito, NBEP

4 July 6, 2006 Aug 14, 2008 Aug 4, Kill not perfect storm situation Upper half of Bay - serious hypoxia stress

5 WasteWater Treatment Facilities = 68-73% of load Tot. Diss.Inorganic Nitrogen (DIN) load to Narragansett Bay Narragansett Bay N Sources by % (Roman et al. 2000) 23 4 Atmos Incl.stormwtr Agri WWTF Pryor et al Worcester UBWPAD Cranston 73 Narragansett Bay P Sources by % (Roman et al. 2000) 5 2 Agri NBC Bucklin Pt NBC Fields Pt WWTF Backgrnd 93 Blackstone River WWTFs incl. Worcester, MA = 2 nd Lrgst srce N load after Direct Discharges to upper Bay.

6 Politicians Demand Action! Problem: Available hydrodynamic model available does NOT reproduce many aspects of Providence-Seekonk-Upper Bay area (most impacted zone) Top of the Bay (major WWTF + River input Other options to calculate approximate target for N load? URI Mar. Ecosystem Res Lab (MERL) exp 1980 s added sewage as DIN at various levels (Nixon, Oviatt & others) Upper Bay area below #1 WWTF

7 TN = 5 mg/l ~ 72% WWTF reduction to Prov.-Seekonk w/ MA UBWPAD (but only 58% at design flow) ; ~ 58% w/o MA (28% at design) ~ 42% (53% w/worc.ma) Total Load reduction to Prov.Seek loads (but 28% (42%w/MA) at design) W/O treatment = 55% incr load at design flows to Prov-Seekonk River area (= 39X MERL)

8 Projecting a decrease of 50% DIN from WWTF loads from new permit limits = ~ 35 % decrease Tot DIN to Bay (BUT > 35% decrease for Upper Bay) ~ 30% decrease in WWTF load so far 2014

9 Use of Models - Climate vs Weather Weather only short term (days)+ local (Boston vs Prov.) Climate - Long-term (decades & more) affected by major drivers: Sunlight Received + Amt. reflected (ice-snow) + amt. heat absorbed / radiated back to space etc. Prediction Level Differs! - Weather - Weather models only able to predict weather conditions max of ~ 1-2 wks due to chaos (nonlinear) behavior Climate - Global circulation models (GCM) target is over wide region - expect variability yr-to-yr and wider margin of prediction (e.g., ~ avg. annual temp. expect rise ~ +2 F over 20yrs across wide areas vs will be 60 F tomorrow in Prov.)

10 Mgt Needs : TMDL? (paper tigers?) -Driven by WQ criteria standard violations & halting violations - CWA does not deal with real world variability well Model that accurately predicts hrly D.O. criteria violations? - XXX Models cannot absolutely replicate real world - but are useful to give sense of direction / trend & whether you are in the ballpark you hope for

11 Jamie Vaudrey, James Kremer (UCONN), Mark Brush (VIMS), Dave Ullman (URI) CHRP October 8, 2009 Processes of a simplified 2 layer model & basis for formulations: (excluding macroalgae...) Temp, Light, Boundary Conditions Chl, N, P, Salinity Productivity BZI Phytoplankton O 2 coupled stoichiometrically DO2 Physics Surface layer Atmospheric deposition N N P Photic zone heterotrophy ƒ(chl 10d ) Flux to bottom ƒ[chl]. mixing flushing Deep layer Land-use N P Sediment organics Benthic heterotrophy Denitrification ƒ(om,t) % Bottom sediment.

12 Brown, CTD Surveys salinity oxygen Buoy Network salinity oxygen chlorophyll Nutrient Stations DIN DIP Model uses N, P loads & exchange between boxes from high res. ROMS hydrodynamic model Outputs for each box : Mean daily Chl a & Mean daily D.O.

13 Box 3 Current Conditions surface bottom e.g. prediction: N reduced 50% surface bottom Phytoplankton (ug Chl / L) Nitrogen (mg/l) Oxygen (mg/l) Values = daily avg /1 6/8 6/15 6/22 6/29 7/6 7/13 7/20 7/27 8/3 8/ /1 6/8 6/15 6/22 6/29 7/6 7/13 7/20 7/27 8/3 8/ Phytoplankton Nitrogen Oxygen /1 6/8 6/15 6/22 6/29 7/6 7/13 7/20 7/27 8/3 8/10

14 Mark Brush (VIMS) CHRP October 8, 2009 How use daily avgs for Mgt TMDL Needs? Test sites: SURFACE y = x R² = MinO2surf, mg/l TIMEsurf<2.9 mg/l TIMEsurf<1.4 mg/l Bullocks Reach 2003, Bottom Water instantaneous min. DO & time below DO thresholds appears predictable directly from daily mean DO BOTTOM y = 1.057x R² = MinO2bott, mg/l TIMEbott<2.9 mg/l TIMEbott<1.4 mg/l -Can plug in N load change - see predicted likely min bottom DO

15 A suggestion for Casco Bay : Concentrate on Gradients -for DO / chl a issues - look for hot spots using WQ surveys -Look into the role of local hydrodynamics in terms of geographic orientation & dominant wind directions on local FLUSHING -- Will highlight zones of greatest sensitivity to nutrient loads

16 Develop high resolution hydrodynamics/ flushing for the hot zones to understand major physical driving factors- perhaps couple to simplified ecol. models Kincaid coastal hydrodynamics lab (URI-GSO): Identified water retention zones coinciding with low oxygen hotspots

17 Success with multiple current meter methods (tilt meter + ADCP) High spatial-temporal hydrodynamic resolution in 2 hotspots: 1) Providence River 2) Greenwich Bay Save the Bay

18 Results of DATA, ROMS Modeling, LAB Modeling point to Bimodal Flushing of Urban Hotspots (not fully mixed Box Model Flushing) Channel water flushes ~ 1 day Shoal bottom water: can take days to go through cycle, a week to leave area tide does not flush! channel Fast flush Edgewood shoals Slow flush

19 Shoal bottom water floats can take > 6 days to exit the shoal Channel tracer flush < 1 day Shoal tracer > 5 days Cumulative track

20 Retention in Greenwich Bay: Wind matters at the local level! Residual flows - distinctly different in the 2 cases. (C Kincaid lab) 10 days of simulation No wind NNE-ward wind No sea breeze Applied sea breeze Slow flushing by ~ 10 X summer 2006 JUSTIN M. ROGERS, M.S URI

21 My Suggestions: Use WQ surveys to look for repeated hot spots then go w/ higher res hydrodynamics to see gyres etc. deal w/ input to these areas Suggestions from LIS special Symposium Port Jefferson, Long Island, NY - commit to long term monitoring at key pts in system Need understand key drivers of local hydrodynamics &eco. - Wind direction, speed & duration- correlated to flushing? - climate - may affect timing of stratification / hypoxia - changes in max temp?- affect nr-shore sp. max temp limits(e.g., lobster >20 C, metab.up ~50% betw C) Use models to understand which drivers have grtst infl. on the issue (hypoxia / stratification / flushing etc) - use nonproprietary models if possible more users to turn to for advice & more capable of revisions w/o huge cost

22 Discussion & Questions