The Bay After Nutrient
Reduction
Habitat Indicators: Primary Production, Winter Spring Diatom
Bloom, Summer Hypoxia and Fish Biomass
Candace Oviatt, Heather Stoffel, Laura Reed, Edwin Requintina
Graduate School of Oceanography, URI
CHRP Presentation – Coastal Institute Hazzard Rooms
May 19, 2016
Improvements in the Bay due to the Clean Water Act of 1972
and Amendments of 1977, 1987
1988
Used Oil Recycling Program
Heavy Metal Recycling Program
Millions of gallons of used oil collected and recycled.
Heavy metals at low background concentrations during 2001
Providence River Survey.
1993-
Combined Sewer Over-Flow Abatement Program
Phase I and 2 completed in 2008 and 2014.
Reduced bacterial contamination of Bay beaches and new shell-fishing
grounds opened.
2005-
30% Reduction in Standing Stock nitrogen concentrations in the Bay
2013
50% Reduction in Standing Stock nitrogen concentrations in the Bay
Summer Production 2013
How did the gradient in Dissolved Inorganic Nitrogen (DIN) Change during Nitrogen Reduction?
50
45
DIN 1980, 06-10, 2012, 2013, 2014
40
35
DIN, µM
30
25
20
15
10
5
0
FP
BR
CP
NP
MHB
GB
PQ
TW
QP
Fox Is
GSO NewPt
RIS
Summer Surface System Apparent Production, g O2 m-3 d-1
4
PD
3.5
BR
3
CP
2.5
NP
Series5
2
GB
1.5
PQ
MV
1
QP
0.5
GSO
0
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
Winter-Spring Diatom Bloom 2014 in the Upper Bay (CP), Mid Bay (GB & TW) and Lower Bay
(GSO)
Chlorophyll a Fluorescence (ug l-1)
110
TW
100
GSO
90
CP
80
GB
70
60
50
40
30
20
10
0
1/1/14
1/2/14
1/3/14
1/4/14
1/5/14
1/6/14
1/7/14
1/8/14
1/9/14
1/10/14
1/11/14
1/12/14
1/13/14
1/14/14
1/15/14
J
1/16/14
1/17/14
1/18/14
1/19/14
1/20/14
1/21/14
1/22/14
1/23/14
1/24/14
1/25/14
1/26/14
1/27/14
1/28/14
1/29/14
1/30/14
1/31/14
2/1/14
2/2/14
2/3/14
2/4/14
2/5/14
2/6/14
2/7/14
2/8/14
2/9/14
2/10/14
2/11/14
2/12/14
2/13/14
2/14/14
2/15/14
2/16/14
2/17/14
2/18/14
2/19/14
2/20/14
F
2014
2/21/14
2/22/14
2/23/14
2/24/14
2/25/14
2/26/14
2/27/14
2/28/14
3/1/14
3/2/14
3/3/14
3/4/14
3/5/14
3/6/14
3/7/14
3/8/14
3/9/14
3/10/14
3/11/14
3/12/14
M
3/13/14
3/14/14
3/15/14
3/16/14
3/17/14
3/18/14
3/19/14
3/20/14
3/21/14
3/22/14
3/23/14
3/24/14
3/25/14
3/26/14
3/27/14
3/28/14
3/29/14
3/30/14
3/31/14
The Number of Summer Days of Hypoxia has Decreased.
Days of Hypoxia (Based on RIDOCS)
60
50
40
30
20
10
0
PD
BR
NP
GB
SR
MV QP GD
PP
MH TW
2001-2012
2013-2015
Average Seasonal Hypoxic Days (June-Aug)
CP
Stations
Percent Reduction in Hypoxia from 2012 to 2013 - 2014
Phillipsdale
Bullock Reach
Conimicut Pt
North Prudence
Popposquash Pt
Greenwich Bay
Mt. View
T-Wharf
Quonset Pt
GSO Dock
27
46
19
43
37
32
32
100
37
100
DEM Fish Trawl at Bay Station Before and After Nitrogen
Reduction
1995-2004
600
Warwick Light
Fish Weight, Kg
500
400
2005-2014
Fox Is
Ohio Ledge
Bonnet Pt
Hope Is
300
200
100
0
41.67
41.66
41.6
North to South Lattitude
41.55
41.47
Total Fish Biomass Before and After Nitrogen Reduction.
DEM Trawl Narragansett Bay (6 sta) All Species
2500
Average Total Wet Weight per year, Kg
30% N Reduction
2000
Before N
Reduction
50% N Reduction
1500
1000
500
0
1995-04
2005-12
2013-14
Conclusions
 Managed DIN reduction has achieved about a 60% reduction.
 Primary Production in the Bay has declined in mid Bay by 31-45%.
 The Winter-Spring Diatom Bloom has declined by over 50%.
 Summer hypoxia has declined in the upper Bay by 30%.
 Fish biomass in the Bay has increased particularly in upper Bay areas prone to
hypoxia.
 The fish biomass after the 50% nitrogen reduction has decreased but is still
higher than the decade prior to nitrogen reduction. This trend bears watching.
 Overall water quality in the Bay has improved.