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Speculations on Human and Climate-Change Alteration of Iron Input to Upwelling Areas off Oregon and Washington. David A. Jay, Philip M. Orton and Thomas A. Chisholm Department of Environmental Science and Engineering, OGI School of Science and Engineering, Oregon Health & Science University

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Speculations on Human and Climate-Change Alteration of Iron Input to Upwelling Areas off Oregon and Washington

David A. Jay, Philip M. Orton and Thomas A. Chisholm

Department of Environmental Science and Engineering, OGI School of Science and Engineering, Oregon Health & Science University

Research supported by the National Science Foundation and Bonneville Power Administration. Thanks to Ken Bruland (UCSC) and Valerie Kelly ( US GS, Portland)

why study columbia river cr fe input
Why Study Columbia River (CR) Fe Input?
  • CR Plume supports juvenile salmon productivity
  • CR Fe supply may be a major factor in determining plume and coastal productivity
  • CR flow regime and fine sediment transport have been greatly altered; likely Fe input also
  • Region has spent more than $5 billion on salmon, but:
    • Mechanisms of plume productivity are poorly understood
    • Effects of CR power system on plume not examined
    • Role of plume for salmon barely understood
  • Changing hydropower system to restore Fe input may be economical relative to other “fixes”
why are ideas about cr fe input speculative
Why are Ideas about CR Fe Input Speculative?
  • Is Fe input supply or transport capacity limited?
  • Which particulate fractions are bioavailable?
  • What about transformations in marshes, mudflats and floodplain?
  • USGS trace metal database is limited, transport models uncertain
  • Don’t know whether delivery of particulate Fe to shelf sediments or dissolved Fe (dFe) is more important
  • N input is also important and has been altered
  • The problem is important – so we forge ahead!
observations suggest
Observations Suggest --
  • dFe may be input to surface waters from (Chase et al, 2002):
    • Upwelling (appear to be enriched by terrigenous particles on shelf; Johnson et al, Nature, 1999)
    • Offshore sub-surface waters
    • CR plume
  • All three sources may reflect CR input
  • The OR coast is mildly Fe-stressed (Hutchins et al., Type 2)
  • This level of Fe limitation can disadvantage the large diatoms that support juvenile salmonids’ food web
  • WA productivity is higher than OR -- is this partially explained by deposits of Fe-rich CR sediments on WA shelf?
  • This might require a greater degree of Fe limitation…
  • More questions than answers!
dfe in the cr plume area
dFe in the CR Plume Area --
  • dFe can be plentiful in the plume (Chase et al, Bruland et al)
  • Fe decreases offshore, but may be elevated at fronts
  • Chl peaks as N is supplied to plume by mixing; again fronts may be important

June 1997 observations Bruland et al., in preparation

Bruland et al., in preparation

hydrologic change and the cr plume
Hydrologic Change and the CR Plume --
  • CR spring flow is down >40% due to flow regulation, irrigation
  • Plume volume is much smaller, 1961 vs. 1999 as example:
    • June 1961 and 1999 “virgin” flows both very high (>20,000 m3 s-1)
    • Actual 1999 flow was ~ 11,000 m3 s-1, 1961 was ~20,000 m3 s-1
    • 1999 plume covered only ~65% of area covered in 1961,
    • Fe input likely reduced

June 1961 Plume

June 1999 Plume

hindcasting cr dfe supply
Hindcasting CR dFe Supply:
  • Use USGS data and transport models to define sources, seasonality of dFe
  • The Cascades are a potent dFe source, highest dFe concentrations are found in Willamette (reservoir removal??)
  • USGS models: CR delivers as much dFe as Mississippi
  • Particulate Fe is near crustal abundance (~5%), but much is not available (e.g., in black sands). Not useful to model
  • Can dFe model be used in historical, hindcast mode?
1880 vs 1997 input compare two very high flow years
1880 vs. 1997 input: Compare Two Very High-Flow Years


  • Almost all 1997 Fe input was in winter
  • Big winter freshets are of short duration
  • 1880 input was mostly in spring; winter inputs low
  • 95% confidence limits indicate high levels of uncertainty
  • Controls on fluvial Fe inputs not understood

Beaver Fe transport,

Hindcast from US GS model,

95% confidence limits shaded


Beaver Fe transport,

Hindcast from US GS model,

95% confidence limits shaded

1880 vs 1997 seasonal comparison
1880 vs. 1997 Seasonal Comparison --
  • 1880 had ~twice the total input (150,000 vs 70,000 tons), and 7x the spring input (140,000 vs. 20,000 tons)
  • 1997 had much larger winter input (50,000 vs 10,000 tons)
  • 1880 vs. 1997 spring freshet change is typical of long-term change: less dFe input, occurs earlier in season (May vs. June)
  • There were actually more winter floods before 1940

Seasonal Totals

important factors for spring freshet
Important Factors for Spring Freshet --
  • Estuary residence time has increased:
    • due to dredged channel (increases exposure of water to peripheral areas)
    • due to reduced spring freshet, no zero-salinity estuary during spring freshet
  • River residence time has increased:
    • nutrient utilization = F (temperature, clarity, time)
    • particles are lost in storage reservoirs
  • Need to understand historical changes in geochemistry from:
    • Decreases in SPM transport
    • 70% loss of floodplain and marshes through diking
  • Changes to N and Si may also be important
changes in n and si inputs
Changes in N and Si Inputs --
  • Eutrophication is NOT aCR issue
  • N, POM inputs to river have increased, but:
    • Reservoirs increase T & residence time, decrease turbidity
    • Fluvial production up ~4x
    • Changes in flow have increased estuary residence time and use of N
  • Annual export of N to plume may have decreased
  • Biggest decrease in N supply in spring, because there was historically little production in cold, turbid, high-flow river
  • Si input likely not changed very much – always in excess

Chl data from Larry Small, OSU

Summary --
  • Primary production in CR plume area is mildly Fe stressed
  • CR is a huge Fe source to OR-WA shelf, differentiating Pacific NW from California coast
  • DEFINITE: Flow regulation has made plume smaller, earlier in season
  • LIKELY: There has been a decrease in spring freshet CR dFe, affecting plume, OR and WA shelves
  • POSSIBLE: Impact may also extend further into California Current, to N. California
  • This may have reduced total primary production and altered food web structure; unfavorable for salmon
fe input and the cr power system
Fe Input and the CR Power System --
  • How can decreased dFe input be reversed?
  • Maybe impossible to quantify the benefit… thus, the approach should be low cost!
  • If spring dFe input is critical, this is another reason to increase spring flows. BUT this is costly.
  • If winter particulate input to WA shelf is critical, then there is an “easy” fix:
    • Time winter reservoir drawdown to coincide with northward flow on shelf
    • Concentrate reservoir drawdown in a few high-flow periods, to flush SPM and Fe
  • Hutchins, D.A., G.R. DiTullio, Y. Zhang, and K.W. Bruland, An iron limitation mosaic in the California upwelling regime, Limnol. Oceanogr., 43, 1037-1054, 1998.
  • Johnson, K.S., F.P. Chavez, and G.E. Friederich, Continental-shelf sediment as a primary source of iron for coastal phytoplankton, Nature, 398, 697-700, 1999.
  • Chase, Z., A. van Geen, P.M. Kosro, J. Marra, P.A. Wheeler, 2002. Iron, nutrient and phytoplankton distributions in Oregon coastal waters. Journal of Geophysical Research, Oceans. ?? Volume, page??
fe in the cr plume area conceptual
Fe in the CR Plume Area (Conceptual) --
  • WA productivity generally higher, winter Fe input??
  • Plume moves south and offshore during upwelling
  • Fe from river, BBL and from plume frontal mixing

Rating curve approach (Crawford, 1991):F = function(Q,T); Q is flow; T is decimal year multiplied by 2pF = exp [ k1 + k2*ln(Q) + k3*sin(T) + k4*cos(T) + k5*T ]Problems: 1. handling of “below detection” data 2. short data set (1992-date) and secular change 3. CR landward of Portland has low dFe levels

US GS dFe Hydrologic Model for Beaver --

Nonlinear multivariate least-squares regression, with seasonal variability:

historic changes in columbia flow
CR virgin flow is estimated from resevoir and agricultural withdrawals

WR virgin flow is not known, thus the winter flow shown is likely much lower

Climate change responsible for most of the freshet timing change

however, 1880 was an unusually cool PDO- year

Historic Changes in Columbia Flow
Role of marshes and tidal flats unclear
    • lower CR marshes have been diked (75% loss)
    • estuary tidal flat area has increased slightly (which is more important to dFe?)