Puget Sound Oceanography Jan. 24, 2011

†All but the Fraser River are dammed. Comparison among rivers: River mean flow (m3/s) range   Peak flow Min flow mean NO3 (uM) tonnes NO3 per day Mississippi 12,000 7,000–20,000 m3/s Spring Sept/Oct 100 2500 *nitrate conc. and flow timing directly correlated Susquehanna 1,200 50-5,500 m3/s Winter/spring Summer 50 (summer) – 100 (spring) 60 (summer)- Fraser 3,500 1,700-3,700 m3/s early Summer Jan/Feb 2 (summer) – 15 (winter) <50 *nitrate conc. and flow timing inversely correlated Skagit 450 50-200 m3/s 7 †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 Coral Reefs Estuaries Continental Shelf Coastal Upwelling Predictability Open Ocean 100 300 1000 Productivity (g C m-2 y-2)

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%) % of surface irradiance 100 Beers-Lambert law: Iz is irradiance at depth I0 is surface irradiance kz is the extinction coefficient z is depth Depth The euphotic zone is defined as the depth to which 1% of the surface irradiance penetrates. Extinction of light in water follows an exponential decrease, with the rate of decrease dependent on the extinction coefficient. Attenuators: Water CDOM Particles (sediments, phytoplankton, etc.)

Light penetration into water Light intensity at depth (W m-2) Depth (m) Light penetrates even less into coastal water than it does into clear water at night! kz m-1 Clarke and Denton 1962

Phytoplankton specific-growth rate, d-1 Temperature [°C] Matrix of phytoplankton growth rates as f(I,N,T) Nitrate [µM] Irradiance [µmol m-2 s-1] R. Reynolds

Sverdrup’s Critical Depth Hypothesis: Metabolism (photosynthetic rate) Depth Critical Depth Net increase Net decrease (includes all losses, respiration, grazing, mortality)

Depth of the mixed layer Well-mixed conditions: Stratified conditions: Salinity profile Salinity profile Depth Depth Well-mixed - MLD is deeper than Critical depth, so no bloom can form. Stratified – relationship between MLD and CD determines whether plankton can bloom.

Observations: Classic illustration of critical depth theory from observations (from Sverdrup, 1953)

Controls on chlorophyll biomass: (growth – respiration – grazing) Horizontal advection Mixing depth 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: 5 10 15 20 25 1 2 3 4 6 7 8 9 11 12 Month 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) Which basin is which?

Differences in Residence Time: [from Babson et al, 2006] Basin Residence time (days) Rank order (longest to shortest) Main Surface 22 2 Deep 38 3 South Sound Surface 24 1 Deep 23 4 Whidbey Surface 5 5 Deep 36 2 Northern Hood Canal Surface 8 4 Deep 15 5 Southern Hood Canal Surface 16 3 Deep 73 1

For more info see Newton et al, 2002 Washington State Marine Water Column Quality Report

(short residence time) Categorization of PS basins: Hood Canal Main Basin Whidbey Basin Strait of Juan de Fuca Dabob Bay Sills Well-mixed (long residence time) Poorly-flushed (short residence time) Well-flushed 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. Main basin has perfect balance of stratification, mixing, and flushing. Strongly-stratified From Strickland, The Fertile Fjord

Seasonal cycles of chlorophyll across the basins: 5 10 15 20 25 1 2 3 4 6 7 8 9 11 12 Month 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) Which basin is which?