Organic carbon transport in the Columbia River

Keywords: dissolved organic compounds; particulate matter; TOC;annual variations; exports; river discharges; Columbia River estuary
Total organic carbon (TOC) levels in the Columbia River measured monthlyfrom May 1973 to December 1974 ranged from a maximum of 270 gmol l -1during late spring and early summer to a minimum of 550 1=01 1 duringlate autumn. Sampling locations were directly behind the spillway at theBonneville Dam, 23o km upstream, and at Kalama, Washington, 128 kmupstream from the river mouth. The average annual TOC contributionfrom the Columbia River drainage to the north-eastern Pacific is4.9 x to" mol with an average concentration of approximately 195 p.mol 1-1.Of this TOC annual export, 89% is dissolved organic carbon (DOC) andIt% is particulate organic carbon (POC). The TOC and DOC levels weremost highly correlated with increased oxygen saturation and discharge,while POC correlated more closely to high instream primary productivityas indicated by higher pH and oxygen supersaturation.
Variability of DOC in the main channel of the Columbia River fromPortland, Oregon, to the estuary during a June 1974 cruise was minimal.The DOC concentrations ranged from 221-260 1.1M01 1-1 with no signifi-cant upstream or downstream gradients. Diel variation also was slight,varying randomly during 24 h between 235-257 mol 1 -1. The relativeannual constancy of the DOC is indicative of the refractory nature of asignificant proportion of the dissolved organic load of the Columbia River.