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Puget Sound Oceanography
Jan. 24, 2011
Comparison among rivers:
Peak
flow
Mississippi
Spring
Susquehanna
Fraser
River
mean flow
(m3/s)
range
12,000
7,000–20,000 m3/s
*nitrate conc. and flow timing directly correlated
1,200
50-5,500 m3/s
*nitrate conc. and flow timing directly correlated
3,500
1,700-3,700 m3/s
*nitrate conc. and flow timing inversely correlated
Skagit
m3/s
450
50-200
*nitrate conc. and flow timing inversely correlated
Min flow
mean
NO3 (uM)
tonnes NO3 per
day
Sept/Oct
100
2500
Winter/spring
Summer
50 (summer) –
100 (spring)
60 (summer)100 (spring)
early
Summer
Jan/Feb
2 (summer) –
15 (winter)
<50
Jan/Feb
2 (summer) –
15 (winter)
7
early
Summer
†All but the Fraser River are dammed.
Puget Sound nutrients:
• Primarily come from the ocean (>90%)
• Relatively minor inputs from rivers, run-off, and sewage treatment
plants
• Seasonality of rivers (low flow and low nutrient conc. in summer) limits
influence
• Limited threat of eutrophication in PS as a whole
BUT –
• ocean water comes in deep and must be mixed to surface
• Rivers/run-off come in at surface
• Many smaller rivers/run-off come into sheltered, stratified inlets/bays
with limited connection to the ocean
•So, some areas vulnerable to effects of anthropogenic nutrient inputs
Primary Production
Productivity and Predictability of Marine Habitats
Predictability
Estuaries
Coral Reefs
Continental
Shelf Coastal
Upwelling
Open
Ocean
100
300
Productivity (g C m-2 y-2)
1000
g C m-2 d-1
Phytoplankton
Production
across different
systems
g C m-2 d-1 (net)
min season to max
season range and
median ( • )
From Mann (2000) Ecology of Coastal Waters, 2nd Ed.,
Blackwell Science, MA, 406 pp.
Main Controls on Primary Production
• Light
• Nutrients
• Temperature
Extinction of light in water follows a negative exponential:
Depth of the euphotic zone is defined by the 1% light depth (z1%)
0
% of surface irradiance
100
Beers-Lambert law:
Depth
I z  I 0 e  kz
•Iz is irradiance at depth
•I0 is surface irradiance
•kz is the extinction coefficient
•z is depth
Attenuators:
•Water
•CDOM
•Particles (sediments, phytoplankton, etc.)
Light penetration into water
Depth (m)
Light intensity at depth (W m-2)
kz m-1
Clarke and Denton
1962
Temperature [°C]
Phytoplankton specific-growth rate, d-1
R. Reynolds
Sverdrup’s Critical Depth Hypothesis:
Depth
Metabolism (photosynthetic rate)
(includes all losses, respiration, grazing, mortality)
Net increase
Critical Depth
Net decrease
Depth of the mixed layer
Well-mixed conditions:
Stratified conditions:
Salinity profile
Depth
Depth
Salinity profile
Observations:
Classic illustration of critical depth theory from observations (from Sverdrup, 1953)
Controls on chlorophyll biomass:
chlorophyll
depth
(growth –
respiration –
grazing)
Horizontal advection
Mixing
Vertical advection
and sinking
Growth = (Light, Nutrients, Temp.)
temperature
Chlorophyll = growth – respiration +/- horizontal advection – vertical advection
– mixing – sinking - grazing
How do circulation differences in Puget Sound effect phytoplankton
production and biomass?
Seasonal cycles of chlorophyll across the basins:
25
Three Tree Point, Main Basin
Gedney Island, Whidbey Basin
N.Admiralty Inlet
Sisters Point, Hood Canal
Oakland Bay, South Sound
Chl a (µg L-1)
20
15
10
5
0
1
2
3
4
5
6
7
8
9
10
Month
Which basin is which?
11
12
Differences in Residence Time:
Basin
[from Babson et al, 2006]
Residence time (days)
Rank order
(longest to shortest)
Main
Surface
Deep
22
38
2
3
South Sound
Surface
Deep
24
23
1
4
Whidbey
Surface
Deep
5
36
5
2
Northern Hood Canal
Surface
Deep
8
15
4
5
Southern Hood Canal
Surface
Deep
16
73
3
1
For more info see Newton et al, 2002 Washington State Marine Water Column Quality Report
Categorization of PS basins:
Well-mixed
Strait of
Juan de
Fuca
Hood Canal
Main Basin
Dabob Bay
Whidbey Basin
Stronglystratified
Well-flushed
(short residence time)
Poorly-flushed
(long residence time)
Sills
Figure 5.9 Relative productivities
of Puget Sound inlets. Compared
to the main basin, which seems to
have a nearly optimal balance of
mixing and flushing for
phytoplankton growth, other areas
of the Sound are less productive.
They may be flushed and mixed
too much (as at the sills) or not
enough (as in inlets), or another
combination of suboptimal
conditions.
From Strickland, The Fertile Fjord
Seasonal cycles of chlorophyll across the basins:
25
Three Tree Point, Main Basin
Gedney Island, Whidbey Basin
N.Admiralty Inlet
Sisters Point, Hood Canal
Oakland Bay, South Sound
Chl a (µg L-1)
20
15
10
5
0
1
2
3
4
5
6
7
8
9
10
Month
Which basin is which?
11
12