Seston, light, nutrients and chlorophyll in the lower Missouri River, 1994-1998

We collected data for five years from the lower Missouri River including di scharge (819-10032 m(3) s(-1)), mean depth (2.7-9.3 m), underwater irradian ce (0.1-3.7 fin m(-2) d(-1)), suspended solids (19-2340 mg L-I), total phos phorus (131-1810 mu g L-1), total nitrogen (0.9-4.2 mg L-1), nitrate-N (380 -3050 mu g L-1), silica (8.2-16.8 mg L-1) and chlorophyll (4.5-107 mu g L-1 ). Suspended solids, phosphorus and light attenuation varied directly with discharge. Nitrate, ammonium-N, silica and chlorophyll were strongly season al. Chlorophyll was temperature dependent exhibiting winter minima (<8 mu g L-1) and spring and fall maxima (>40 mu g L-1). In the growing season, chl orophyll co-varied with light and varied inversely with silica and dissolve d P. Poor light conditions (mixed depth:photic depth >10) and rapid flow ra tes (approximate to 150 km d(-1)) suggest that in situ production of algae is less important than flux of biomass from upstream. Chlorophyll flux and pheophytin increased with discharge indicating contributions of benthic or terrestrial inputs. About a fourth of the particulate organic nitrogen tran sported by the river may be autochthonous. Algal uptake may reduce silica f lux by >22%.