Seston, light, nutrients and chlorophyll in the lower missouri river, 1994–1998

Abstract

We collected data for five years from the lower Missouri River including discharge (819–10032 m3 s−1), mean depth (2.7–9.3 m), underwater irradiance (0.1–3.7 Ein m−2 d−1), suspended solids (19–2340 mg L−1), total phosphorus (131–1810 μg L−1), total nitrogen (0.9–4.2 mg L−1), nitrate-N (380–3050 μg L−1), silica (8.2–16.8 mg L−1) and chlorophyll (4.5–107 μg L−1). Suspended solids, phosphorus and light attenuation varied directly with discharge. Nitrate, ammonium-N, silica and chlorophyll were strongly seasonal. Chlorophyll was temperature dependent exhibiting winter minima (<8 μg L−1) and spring and fall maxima (>40 μg L−1). In the growing season, chlorophyll co-varied with light and varied inversely with silica and dissolved P. Poor light conditions (mixed depth:photic depth > 10) and rapid flow rates (≈ 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 transported by the river may be autochthonous. Algal uptake may reduce silica flux by >22%. © 2000, Copyright Taylor & Francis Group, LLC.