OMSAP Public MeetingSeptember 1999
Benthic Nutrient Cycling in Boston Harbor and Massachusetts Bay
Anne Giblin, Charles Hopkinson& Jane Tucker
The Ecosystems Center,Marine Biological LaboratoryWoods Hole, MA 02543
September 22, 1999
OMSAP Public MeetingSeptember 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
InflowOutflow
Light
ConcernsEcologicalEcological NutrientsNutrients Contaminants Organic MaterialOrganic 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
RegenerationRegeneration
DetritusDetritusParticulateParticulate
Microbes
Dissolved
WATER COLUMN
Sources Rivers BoundaryBoundary Nonpoint EffluentsEffluents
Gas ExchangeExchangeN2, | O2, CO2
ATMOSPHERE
N, P, Si, ON, P, Si, O22, CO, CO22 MicrobesMicrobes
OMSAP Public MeetingSeptember 1999
Nutrient Cycling Nitrogen Cycle in Coastal Waters
OMSAP Public MeetingSeptember 1999
$#
N
0 2 4km
BH02BH03
QB01 BH08A
Nutrient Cycling Boston Harbor Stations for Benthic Fluxes
OMSAP Public MeetingSeptember 1999
Nutrient Cycling Sediment Oxygen Demand - Northern Harbor
0
50
100
150
200
250
300
350
Jan-
92
Jul-9
2
Jan-
93
Jul-9
3
Jan-
94
Jul-9
4
Jan-
95
Jul-9
5
Jan-
96
Jul-9
6
Jan-
97
Jul-9
7
Jan-
98
Jul-9
8
Jan-
99
Jul-9
9
Jan-
00
mm
ol O 2
m2 d-1
a. BH02
0
50
100
150
200
250
300
350
Jan-
92
Jul-9
2
Jan-
93
Jul-9
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Jan-
94
Jul-9
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95
Jul-9
5
Jan-
96
Jul-9
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97
Jul-9
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Jul-9
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Jan-
99
Jul-9
9
Jan-
00
mm
ol O 2
m2 d-1
b. BH03
OMSAP Public MeetingSeptember 1999
Nutrient Cycling Sediment Oxygen Demand - Southern Harbor
050
100150200250300350
Jan-
95
Apr
-95
Jul-9
5
Oct
-95
Jan-
96
Apr
-96
Jul-9
6
Oct
-96
Jan-
97
Apr
-97
Jul-9
7
Oct
-97
Jan-
98
Apr
-98
Jul-9
8
Oct
-98
Jan-
99
Apr
-99
Jul-9
9
Oct
-99
Jan-
00
mm
ol O
2 m2 d
-1 c. BH08A
050
100150200250300350
Jan-
95
Apr
-95
Jul-9
5
Oct
-95
Jan-
96
Apr
-96
Jul-9
6
Oct
-96
Jan-
97
Apr
-97
Jul-9
7
Oct
-97
Jan-
98
Apr
-98
Jul-9
8
Oct
-98
Jan-
99
Apr
-99
Jul-9
9
Oct
-99
Jan-
00
mm
ol O 2
m2 d
-1 d. QB01
OMSAP Public MeetingSeptember 1999
Nutrient Cycling DIN Fluxes - Northern Harbor
-5
0
5
10
15
20
25Ja
n-92
Jul-9
2
Jan-
93
Jul-9
3
Jan-
94
Jul-9
4
Jan-
95
Jul-9
5
Jan-
96
Jul-9
6
Jan-
97
Jul-9
7
Jan-
98
Jul-9
8
Jan-
99
Jul-9
9
Jan-
00
mm
ol N
m2 d-1
NO3NH4
a. BH02
-5
0
5
10
15
20
25
Jan-
92
Jul-9
2
Jan-
93
Jul-9
3
Jan-
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Jul-9
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95
Jul-9
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96
Jul-9
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97
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Jul-9
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Jan-
99
Jul-9
9
Jan-
00
mm
ol N
m2 d
-1
NO3NH4
b. BH03
OMSAP Public MeetingSeptember 1999
Nutrient Cycling DIN Fluxes - Southern Harbor
-5
0
5
10
15
20
25Ja
n-95
Apr
-95
Jul-9
5
Oct
-95
Jan-
96
Apr
-96
Jul-9
6
Oct
-96
Jan-
97
Apr
-97
Jul-9
7
Oct
-97
Jan-
98
Apr
-98
Jul-9
8
Oct
-98
Jan-
99
Apr
-99
Jul-9
9
Oct
-99
Jan-
00
mm
ol N
m2 d
-1
NO3NH4
c. BH08A
-5
0
5
10
15
20
25
Jan-
95A
pr-9
5Ju
l-95
Oct
-95
Jan-
96A
pr-9
6Ju
l-96
Oct
-96
Jan-
97A
pr-9
7Ju
l-97
Oct
-97
Jan-
98A
pr-9
8Ju
l-98
Oct
-98
Jan-
99A
pr-9
9Ju
l-99
Oct
-99
Jan-
00
mm
ol N
m2 d
-1 NO3NH4
d. QB01
OMSAP Public MeetingSeptember 1999
0.02.04.06.08.0
10.012.014.016.0
Jan-
92
Jul-9
2
Jan-
93
Jul-9
3
Jan-
94
Jul-9
4
Jan-
95
Jul-9
5
Jan-
96
Jul-9
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97
Jul-9
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Jul-9
8
Jan-
99
mm
ol N
m2 d
-1 a. BH02
0.02.04.06.08.0
10.012.014.016.0
Jan-
92
Jul-9
2
Jan-
93
Jul-9
3
Jan-
94
Jul-9
4
Jan-
95
Jul-9
5
Jan-
96
Jul-9
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8
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99
mm
ol N
m2 d
-1
b. BH03
Nutrient Cycling Denitrification Losses
OMSAP Public MeetingSeptember 1999
0.0
2.0
4.0
6.0
8.0
10.0
12.0
May Jun Jul Aug Sep Oct
mm
ol N
m2 d
-1
StoichiometryGCDGA
a. BH02
0.0
2.0
4.0
6.0
8.0
10.0
12.0
May Jun Jul Aug Sep Oct
mm
ol N
m2 d
-1
StoichiometryGCDGA
b. BH03
0.0
2.0
4.0
6.0
8.0
10.0
12.0
May Jun Jul Aug Sep Oct
mm
ol N
m2 d
-1
StoichiometryDGA
c. BH08A
0.0
2.0
4.0
6.0
8.0
10.0
12.0
May Jun Jul Aug Sep Oct
mm
ol N
m2 d
-1
StoichiometryDGA
d. QB01
Nutrient Cycling Denitrification - Methods Comparisons
OMSAP Public MeetingSeptember 1999
-1.0
0.0
1.0
2.0
3.0
4.0
Jan-
92
Jul-9
2
Jan-
93
Jul-9
3
Jan-
94
Jul-9
4
Jan-
95
Jul-9
5
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96
Jul-9
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Jul-9
8
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99
mm
ol P
m-2 d
-1 7.8a. BH02
-1.0
0.0
1.0
2.0
3.0
4.0
Jan-
92
Jul-9
2
Jan-
93
Jul-9
3
Jan-
94
Jul-9
4
Jan-
95
Jul-9
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96
Jul-9
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Jul-9
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Jul-9
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99
mm
ol P
m-2 d
-1
b. BH03
-1.0
0.0
1.0
2.0
3.0
4.0
Jan-
95
Jul-9
5
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96
Jul-9
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Jul-9
7
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Jul-9
8
Jan-
99
Nutrient Cycling Phosphate Fluxes - Northern Harbor
OMSAP Public MeetingSeptember 1999
-1.0
0.0
1.0
2.0
3.0
4.0
Jan-
92
Jul-9
2
Jan-
93
Jul-9
3
Jan-
94
Jul-9
4
Jan-
95
Jul-9
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96
Jul-9
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Jul-9
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Jan-
99
-1.0
0.0
1.0
2.0
3.0
4.0Ja
n-95
Jul-9
5
Jan-
96
Jul-9
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Jan-
97
Jul-9
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Jul-9
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Jan-
99
mm
ol P
m-2 d
-1 c. BH08A
-1.0
0.0
1.0
2.0
3.0
4.0
Jan- 95 Jul-
95 Jan- 96 Jul-
96 Jan- 97 Jul-
97 Jan- 98 Jul-
98 Jan- 99
mm
ol P
m-2 d
-1
d. QB01
Nutrient Cycling Phosphate Fluxes - Southern Harbor
OMSAP Public MeetingSeptember 1999
a. DIC vs O2
020406080
100120140
0 20 40 60 80 100 120 140O2 (mmol m-2 d-1)
DIC
(mm
ol m
-2 d
-1)
DIC/O2=1BH02BH03BH08QB01
b. DIC vs DIN
020406080
100120140
0 4 8 12 16 20
DIN (mmol m-2 d-1)
DIC
(mm
ol m
-2 d
-1)
DIC/DIN = 6.6BH02BH03BH08AQB01
c. DIN vs DIP
-100
1020304050
-1 0 1 2 3
DIP (mmol m-2 d-1)
DIN
(mm
ol m
-2 d
-1) DIN/DIP=16
BH02BH03BH08AQB01
d. DIN vs Si
0
5
10
15
20
25
0 5 10 15 20 25Si (mmol m-2 d-1)
DIN
(mm
ol m
-2 d
-1) DIN/Si=1
BH02BH03BH08AQB01
Nutrient Cycling Flux Ratios
OMSAP Public MeetingSeptember 1999
a. BH02
-14
-12
-10
-8
-6
-4
-2
00.0 2.0 4.0 6.0
H2S (mM)
Dep
th (c
m)
JulyAug
b. BH03
-14
-12
-10
-8
-6
-4
-2
00.0 0.5 1.0 1.5
H2S (mM)
Dep
th (c
m)
JulyAug
c. BH08A
-14
-12
-10
-8
-6
-4
-2
00.0 0.5 1.0 1.5
H2S (mM)
Dep
th (c
m)
JulyAug
d. QB01
-14
-12
-10
-8
-6
-4
-2
00.0 0.5 1.0 1.5
H2S (mM)
Dep
th (c
m)
JulyAug
Nutrient Cycling Dissolved Sulfides in Porewaters
OMSAP Public MeetingSeptember 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
OMSAP Public MeetingSeptember 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)
OMSAP Public MeetingSeptember 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)
OMSAP Public MeetingSeptember 1999
Determine the role of the sediments in nutrient cyclingAmount of nutrients released relative to NPP needsRatios 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 dynamicsImportance as an oxygen sinkStorage 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
OMSAP Public MeetingSeptember 1999
Nutrient Cycling Benthic Flux Stations
BH02BH03
QB01
MB01MB02
MB03
MB05
BH08A
42°1
2'
42°12'
42°1
6'
42°16'
42°2
0'
42°20'
42°2
4'
42°24'
42°2
8'
42°28'
42°3
2'
42°32'
71°00'
71°00'
70°56'
70°56'
70°52'
70°52'
70°48'
70°48'
70°44'
70°44'
70°40'
70°40'
N
0 2 4 6 8 Kilometers
Benth ic Flux Stations
LEGEND
OMSAP Public MeetingSeptember 1999
Nutrient Cycling Sediment Oxygen Demand
05
101520253035
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Jul-9
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93
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Jul-9
9
Jan-
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O2 (
mm
ol m
-2 d
-1) MB01
05
101520253035
Jan-
92
Jul-9
2
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O2 (
mm
ol m
-2 d
-1) MB02
OMSAP Public MeetingSeptember 1999
05
101520253035
Jan-
92
Jul-9
2
Jan-
93
Jul-9
3
Jan-
94
Jul-9
4
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6
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Jul-9
8
Jan-
99
Jul-9
9
Jan-
00
O2 (
mm
ol m
-2 d
-1)
MB03
05
101520253035
Jan-
92
Jul-9
2
Jan-
93
Jul-9
3
Jan-
94
Jul-9
4
Jan-
95
Jul-9
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8
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Jul-9
9
Jan-
00
O2 (
mm
ol m
-2 d
-1)
MB05
Nutrient Cycling Sediment Oxygen Demand
OMSAP Public MeetingSeptember 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