Dissolved and particulate aluminum in the Columbia River and coastal waters of Oregon and Washington: Behavior in near-field and far-field plumes

https://doi.org/10.1016/j.ecss.2009.05.031Get rights and content

Abstract

The distribution of dissolved (soluble and total) and particulate (leachable and total) aluminum was examined in the Columbia River and estuary, in near-field and far-field river plumes, and in adjacent coastal waters of Washington and Oregon during the River Influence on Shelf Ecosystems (RISE) cruise of May/June 2006. Dissolved and particulate aluminum (Al) concentrations were significantly greater in the river than in the coastal waters that mixed to form the plume. Dissolved Al concentrations in the Columbia River (∼80 nM) were low relative to other major rivers. Leachable and total particulate Al concentrations within the river reached concentrations greater than 1000 nM and 18,000 nM, respectively. Dissolved Al within the Columbia River estuary showed a significant removal (∼60%) at salinities between 0 and 10 with salt-induced flocculation of colloidal Al complexes and enhanced particle scavenging being probable explanations for aluminum removal. Dissolved and particulate Al concentrations were significantly greater in near-field plumes relative to surrounding coastal waters. As the plume advected from near-field to far-field away from the river mouth, dilution of the plume with lower dissolved Al surface waters as well as particle scavenging along the flow path appeared to be controlling dissolved Al distributions. Particle settling as well as dilution with lower particle-load waters led to observed decreases in particulate Al as the plume moved from near-field to far-field. However, the percent-leachable particulate aluminum in both near-field and far-field plumes was remarkably constant at ∼7%. Dissolved and particulate Al in a far-field plume over 100 km southwest of the Columbia River mouth were over an order-of-magnitude greater than surrounding waters, illustrating the importance of the Columbia River plume as a mechanism for transporting Al offshore. Aluminum could be used to trace the input of biologically-required elements such as iron into waters off the shelf.

Introduction

The Columbia River, originating some 820 m above sea level in British Columbia, is the largest river entering the northeast Pacific ocean, draining an area of approximately 665,000 km2 with an average discharge of 7300 m3 s−1 and annual river discharge of 260 km3 year−1(Barnes et al., 1972, Jay and Smith, 1990, Thomas and Weatherbee, 2006). A sustained maximum river flow generally occurs in May–June from interior snowmelt while shorter maxima occur during winter from storm events in the coastal basins. Minimum river flow occurs during August-September (Neal, 1972, Thomas and Weatherbee, 2006). During the late summer, the Columbia River accounts for ∼90% of the freshwater entering the sea between the Strait of Juan de Fuca and San Francisco Bay (Barnes et al., 1972).

The Columbia River plume forms as coastal seawater intrudes and mixes with river water at or near the mouth of the Columbia River estuary (Barnes et al., 1972). The Columbia River plume is a dominant hydrographic feature of the California Current system off the Washington and Oregon coasts and is observed as a shallow (∼2–20 m) surface lens of low-salinity water (Hickey et al., 1998). Because the chemistry of the river water and coastal seawater that mix to form the plume varies depending on time of year, tidal phase, and oceanographic conditions, the chemistry of the plume itself is expected to vary according to these changing conditions (Bruland et al., 2008). The Columbia River plume also plays a key role in the delivery of both macro- and micro-nutrients to offshore waters of Washington and Oregon (Hill and Wheeler, 2002, Lohan and Bruland, 2006, Aguilar-Islas and Bruland, 2006).

The movement of the plume is strongly influenced by seasonal variations in the local wind forcing. When dominant alongshore wind stress is to the south (upwelling conditions), Ekman transport is offshore and surface currents are to the southwest. Therefore, the plume separates from the coast and advects offshore and southward from the Columbia River mouth (Hickey et al., 1998). When dominant alongshore wind stress is to the north (downwelling conditions), Ekman transport is onshore and surface currents are to the north. This acts to keep the plume confined tightly along the Washington coast during strong northward wind events and more over the mid-Washington shelf during weaker wind events (Thomas and Weatherbee, 2006). Reversal of the wind forcing can lead to sudden changes between these two modes. Recent studies show that episodic relaxation or reversal of the northerly winds during summer can allow the Columbia River plume to strongly influence the Washington and Oregon coast with plumes moving north and south of the mouth of the Columbia River simultaneously (Garcia Berdeal et al., 2002).

Sources of aluminum (Al) to the world oceans include riverine inputs, atmospheric inputs, and, to a much lesser degree, dissolution from sediments while scavenging onto particle surfaces is regarded as the predominant mechanism for removal of Al. Oceanic levels of dissolved Al are found at trace concentrations, ranging from less than 0.50 nM in intermediate/deep waters of the North Pacific to >25 nM in surface and deep waters of the eastern North Atlantic where high eolian dust input from the Saharan desert is observed (Hydes, 1979, Orians and Bruland, 1986, Kramer et al., 2004, Measures et al., 2008). Higher surface water Al concentrations have been observed in the oligotrophic subtropical gyres of the ocean basins while lower concentrations have been observed in the more productive boundary regions (Orians and Bruland, 1986, Johnson et al., 2003, Measures et al., 2005). Concentrations of dissolved Al in riverine waters are highly variable, ranging from ∼50 nM to >1 μM (Hydes and Liss, 1977, Mackin and Aller, 1984a, Morris et al., 1986, Upadhyay and Sen Gupta, 1995, Takayanagi and Gobeil, 2000).

Conomos and Gross (1972) investigated the physical, geochemical, and biological processes governing suspended particulate material in the Columbia River estuary and nearby coastal ocean. Concentrations of riverine suspended particulate material varied from 8 to 40 mg L−1, of which 85–95% consisted of lithogenous particulate material. Assuming 8.2% Al by weight (Taylor, 1964) in crustal material, this equates to greater than 20 μM particulate Al. This suspended lithogenous particulate material consisted largely of feldspar and quartz with the aluminosilicates biotite [(K(Mg,Fe)3AlSi3O10(OH)2] and muscovite [Al2Si4O10(OH)2] dominating the larger particle size fractions (Conomos and Gross, 1972). Being that the high suspended particulate load of the river is dominated by aluminosilicates, it follows that the Columbia River is likely a major source of dissolved and particulate Al as well as silicic acid to coastal waters of Washington and Oregon. In contrast, California Current waters are low in both dissolved Al (<1 nM Al; Orians and Bruland, 1986) and silicic acid (∼2–4 μM; Hill and Wheeler, 2002, Aguilar-Islas and Bruland, 2006).

This study provided a unique opportunity to investigate dissolved and particulate Al and silicic acid distributions during both upwelling and downwelling conditions in May/June 2006 in the Columbia River, the river plume, and the adjacent coastal waters of Oregon and Washington. This paper describes the distributions of dissolved and particulate Al and silicic acid both within the Columbia River and estuary as well as in near- and far-field plumes both north and south of the Columbia River. The behavior of Al and silicic acid in river–ocean mixing within the estuary and during advection of the plume away from the river mouth is also discussed.

Section snippets

Sample collection and filtration

Seawater samples were collected aboard the R/V Wecoma off the Oregon and Washington coasts from May 21, 2006 to June 21, 2006 during the RISE-4W cruise, the last of five cruises associated with the RISE (River Influence on Shelf Ecosystems) program (see Bruland et al., 2008, for more detail). Surface (∼1 m) sampling was conducted using an underway clean surface pump “fish” system described in detail elsewhere (Bruland et al., 2005, Aguilar-Islas and Bruland, 2006, Lohan and Bruland, 2006).

Downwelling/northward plume transects

A period of strong south winds (∼12 m s−1) persisted from May 22, 2006 through May 27, 2006 and remained downwelling-favorable through the end of the month. This resulted in a narrow Columbia River plume moving northward and hugging the Washington coast over this time period. The locations of the downwelling northward plume surface transects (T1, T4, and T6) are shown in Fig. 1. Surface transect T4 was across the near-field plume close to the mouth of the Columbia River while transects T1 and T6

Comparison with previous data

Dissolved Al data from the Columbia River during May 2006 show significant differences from previously published results of river and estuarine studies. In a study of dissolved Al in the Zaire and Niger River plumes, Van Bennekom and Jager (1978) measured dissolved Al concentrations of 1.0–1.6 μM in the Zaire River and significantly lower values of 0.1–0.2 μM in the relatively higher suspended particulate matter (SPM) waters of the Niger River. In the Zaire River estuary, an increase in dissolved

Conclusions

The Columbia River is a significant source of dissolved and particulate Al to the coastal waters of Oregon and Washington with both dissolved Al and particulate Al being orders of magnitude greater in Columbia River plume waters than in Al-deplete California Current waters. Likely due to a combination of salt-induced flocculation of colloidal Al within the Columbia River estuary and Al scavenging onto particle surfaces in the turbidity maximum within the estuary, dissolved Al showed a

Acknowledgements

We thank the Captain and crew of the R/V Wecoma for their assistance on this research expedition. We deeply appreciate the efforts of Bettina Sohst for the nutrient analyses, Geoffrey Smith for help with the sampling, and Barbara Hickey as the chief scientist on-board. We are also appreciative of the efforts of two anonymous reviewers whose comments were constructive and greatly improved this manuscript. This work was supported by RISE program, funded by National Science Foundation CoOP

References (54)

  • J. Kramer et al.

    Distribution of dissolved aluminum in the high atmospheric input region of the subtropical waters of the North Atlantic Ocean

    Marine Chemistry

    (2004)
  • M.R. Landry et al.

    Broad-scale distributional patterns of hydrographic variables on the Washington/Oregon shelf

  • M.C. Lohan et al.

    The importance of vertical mixing for the supply of nitrate and iron to the Columbia River plume: implications for biology

    Marine Chemistry

    (2006)
  • J.E. Mackin et al.

    Processes affecting the behavior of dissolved aluminum in estuarine waters

    Marine Chemistry

    (1984)
  • J.E. Mackin et al.

    Dissolved Al in sediments and waters of the East China Sea: implications for authigenic mineral formation

    Geochimica Cosmochimica Acta

    (1984)
  • A.W. Morris et al.

    Dissolved aluminum in the Tamar Estuary, southwest England

    Geochimica Cosmochimica Acta

    (1986)
  • J. Nishioka et al.

    Size-fractionated iron concentration in the northeast Pacific Ocean: distribution of soluble and small colloidal iron

    Marine Chemistry

    (2001)
  • K.J. Orians et al.

    The biogeochemistry of aluminum in the Pacific Ocean

    Earth and Planetary Science Letters

    (1986)
  • E.R. Sholkovitz

    Flocculation of dissolved organic and inorganic matter during the mixing of river water and seawater

    Geochimica Cosmochimica Acta

    (1976)
  • S.R. Taylor

    Abundance of chemical elements in the continental crust: a new table

    Geochimica Cosmochimica Acta

    (1964)
  • A. Thomas et al.

    Cross-shelf phytoplankton pigment variability in the California Current

    Continental Shelf Research

    (2001)
  • S. Upadhyay et al.

    The behavior of aluminum in waters of the Mandovi estuary, west coast of India

    Marine Chemistry

    (1995)
  • A.J. Van Bennekom et al.

    Dissolved aluminum in the Zaire River plume

    Netherlands Journal of Sea Research

    (1978)
  • W.J. Walker et al.

    A kinetic study of aluminum adsorption by aluminosilicate clay minerals

    Geochimica Cosmochimica Acta

    (1988)
  • C.A. Barnes et al.

    Circulation and selected properties of the Columbia River effluent at sea

  • C.J.M. Berger et al.

    The application of a chemical leach technique for estimating labile particulate aluminum, iron, and manganese in the Columbia River plume and coastal waters off Oregon and Washington

    Journal of Geophysical Research

    (2008)
  • M.T. Brown et al.

    An improved flow-injection analysis method for the determination of dissolved aluminum in seawater

    Limnology and Oceanography Methods

    (2008)
  • Cited by (26)

    • Gallium-aluminum systematics of marine hydrogenetic ferromanganese crusts: Inter-oceanic differences and fractionation during scavenging

      2021, Geochimica et Cosmochimica Acta
      Citation Excerpt :

      Another fractionation step of the Ga-Al pair is assumed to occur when river water enters the marine environment (Shiller, 1988). To explain the higher Ga/Al ratios of seawater relative to river water, it has been suggested that Ga shows lower particle reactivity than Al which is known to be largely removed during aggregation and sedimentation of nanoparticles and colloids (NPCs) in estuaries (Hydes and Liss, 1977; van Bennekom and Jager, 1978; Mackin and Aller, 1984; Morris et al., 1986; Shiller, 1988; Takayanagi and Gobeil, 2000; Brown and Bruland, 2009). This further increases the Ga/Al ratio of continental runoff upon its entry into the ocean.

    • Spatial and temporal variability of dissolved aluminum and manganese in surface waters of the northern Gulf of Alaska

      2021, Deep-Sea Research Part II: Topical Studies in Oceanography
      Citation Excerpt :

      The dAl concentration calculated in Brown et al. (2010) for the Copper River, 1740 nM, falls within this range, which is much higher than estimates from other regions. Plots of dAl vs. salinity in the previously mentioned Columbia River and Yangtze River plume studies led to zero-salinity endmember values of ~85 nM and 220 nM dAl, respectively (Brown and Bruland 2009; Ren et al., 2006). This suggests that the lower dAl values observed in these regions at comparable (or lower) salinities to our plume study directly resulted from lower dAl in the rivers themselves.

    • Processes controlling the distribution of dissolved Al and Ga along the U.S. GEOTRACES East Pacific Zonal Transect (GP16)

      2019, Deep-Sea Research Part I: Oceanographic Research Papers
      Citation Excerpt :

      Given that Ga competes with Fe for binding to siderophores (Emery and Hoffer, 1980; Emery, 1986; Gascoyne et al., 1991), Ga could be removed via active scavenging. Low surface water dissolved Ga and Al concentrations in high productivity waters, relative to their concentrations in open gyre waters, are likely caused by intensive scavenging by biogenic particles (Orians and Bruland, 1986, 1988a; Shiller, 1998; Brown and Bruland, 2009). The advection of low or high dissolved Ga and Al from areas of low or high dust input also affects the distributions of these elements.

    View all citing articles on Scopus
    View full text