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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 (∼80nM) were low relative to other major rivers. Leachable and total particulate Al concentrations within the river reached concentrations greater than 1000nM and 18,000nM, 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 100km 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. [Copyright &y& Elsevier]

Abstract: The spatial distributions of dissolved manganese and nutrients were examined in the Columbia River plume off Oregon and Washington during the summer of 2004 and 2005 as part of the River Influence on Shelf Ecosystems (RISE) program. Factors influencing the hydrochemical characteristics of the freshly formed and aged Columbia River plume were investigated. Hydrographic data and nutrient concentrations were used to delineate three distinct water sources for the Columbia River Plume: California Current surface water, coastal upwelled water, and Columbia River water. The warm, intermediate salinity, nutrient poor California Current water contains low levels of dissolved manganese (<5 nM) and silicic acid (<5 μM), and is depleted in nitrate. The cold, high salinity, nutrient rich, freshly upwelled water is highly variable (2–20 nM) in dissolved manganese and can be as high as ∼45 μM in silicic acid and ∼30 μM nitrate. The variable Columbia River has summer temperatures ranging from ∼13 to 24 °C, high silicic acid concentrations (ranging from ∼120 to 200 μM), and lower nitrate concentrations (ranging from ∼2 to 20 μM). During the summer, the concentrations of silicic acid and dissolved manganese can exceed 100 μM and 200 nM, respectively, in near-field Columbia River plumes. These values are markedly greater than those of surface coastal waters (even during upwelling conditions). As the plume advects and mixes, the concentrations of these two constituents remain relatively high within plume waters. The concentrations of dissolved manganese in the near-field plume vary with tidal amplitude, exhibiting much higher concentrations for a given salinity during spring tides than during neap tides. For example, the Columbia River plume at a salinity of 20 has a concentration of dissolved manganese of ∼240 nM during spring tides, as compared to only ∼60 nM during low amplitude tides. Silicic acid concentrations in the near-field plume remain relatively constant throughout the tidal month. Calculations indicate there is roughly an equivalent yearly delivery of dissolved manganese and silicic acid to the coastal waters off Oregon and Washington by upwelled waters and by the Columbia River plume. [Copyright &y& Elsevier]

Abstract: The influence of the Columbia River plume on the distributions of nitrate and iron and their sources to coastal and shelf waters were examined. In contrast to other large estuaries, the Columbia River is a unique study area as it supplies very little nitrate (5 μM) and iron (14–30 nM) at salinities of 1–2 to coastal waters. Elevated nitrate and dissolved iron concentrations (as high as 20 μM and 20 nM) were observed, however, in the near field Columbia River plume at salinities of 20. Surface nitrate concentrations were higher than observed in the Columbia River itself and therefore must be added by entrainment of higher nitrate concentrations from subsurface coastal waters. Tidal flow was identified as an important factor in determining the chemical constituents of the Columbia River plume. During the rising flood tide, nitrate and iron were entrained into the plume waters resulting in concentrations of 15 μM and 6 nM, respectively. Conversely, during the ebb tide the concentrations of nitrate and total dissolved iron were reduced to 0.3–3 μM and 1–2 nM, respectively, with a concomitant increase in chlorophyll a concentrations. As these plume waters moved offshore the plume drifted directly westward, over a nitrate depleted water mass (<0.2 μM). The plume water was also identified to move southwards and offshore during upwelling conditions and nitrate concentrations in this far field plume were also depleted. Iron concentrations in the near-field Columbia River plume are sufficient to meet the biological demand. However, due to the low nitrate in the Columbia River itself, nitrate in the plume is primarily dependent on mixing with nitrate rich, cold, high salinity subsurface waters. Without such an additional source the plume rapidly becomes nitrate limited. [Copyright &y& Elsevier]

Abstract: This study examines the distribution of leachable particulate iron (Fe) in the Columbia River, estuary, and near-field plume. Surface samples were collected during late spring and summer of 2004–2006 as part of four River Influence on Shelf Ecosystems (RISE) cruises. Tidal amplitude and river flow are the primary factors influencing the estuary leachable particulate Fe concentrations, with greater values during high flow and/or spring tides. Near the mouth of the estuary, leachable particulate Fe [defined as the particulate Fe solubilized with a 25% acetic acid (pH 2) leach containing a weak reducing agent to reduce Fe oxyhydroxides and a short heating step to access intracellular Fe] averaged 770 nM during either spring tide or high flow, compared to 320 nM during neap tide, low flow conditions. In the near-field Columbia River plume, elevated leachable particulate Fe concentrations occur during spring tides and/or higher river flow, with resuspended shelf sediment as an additional source to the plume during periods of coastal upwelling and spring tides. Near-field plume concentrations of leachable particulate Fe (at a salinity of 20) averaged 660 nM during either spring tide or high flow, compared to 300 nM during neap tide, low flow conditions. Regardless of tidal amplitude and river flow, leachable particulate Fe concentrations in both the river/estuary and near-field plume are consistently one to two orders of magnitude greater than dissolved Fe concentrations. The Columbia River is an important source of reactive Fe to the productive coastal waters off Oregon and Washington, and leachable particulate Fe is available for solubilization following biological drawdown of the dissolved phase. Elevated leachable Fe concentrations allow coastal waters influenced by the Columbia River plume to remain Fe-replete and support phytoplankton production during the spring and summer seasons. [Copyright &y& Elsevier]