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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