The primary source of iron into the estuary is from geologic rock weathering and subsequent runoff delivery to the system. In addition, some iron may come from the Pacific Ocean and is transported into the estuary during tidal oscillation, enhanced seasonally during periods of upwelling. Iron inputs derived from riverine and oceanic origins are typically on the magnitude of 14-30 nM and 6 nM in concentration respectively. These sources of iron are generally sufficient to meet biological demands, including those of primary production, in the estuary and upriver. Consequently, iron is commonly not the limiting nutrient in the system; rather, the river depending on season and flow may serve as a net source of iron to iron-deficient coastal regions of the Northeast Pacific, sometimes referred to as areas of High Nutrient, Low Chlorophyll.
