ScholarWorks at University of Montana

It's a drag: Understanding current and Cladophora

The ecology of the filamentous green algae Cladophora glomerata has been studied in the Clark Fork River for many years due to its influence on dissolved oxygen, pH, aquatic organisms, and recreational use. While a number of factors contribute to algal persistence and dominance, the influence of fluid velocity on resource acquisition (i.e., nutrient uptake) and removal by shear stress are important processes affecting Cladophora distribution in space and time. A basic introduction to mechanistic principles governing removal and nutrient uptake is provided, followed by techniques to examine such relationships in rivers. Techniques include use of low-cost unmanned aerial vehicles (UAVs) to remotely sense the spatial location of algae, and the use of acoustic Doppler current profilers (ADCPs) to assess habitat suitability and optimal/critical velocities for algal establishment. In 2013, a river site downstream of Deer Lodge exhibited percent algal cover that ranged from < 5 to > 50%, increasing immediately after vernal freshet, peaking midsummer, and declining in the fall. When paired with velocity observations from over 3,500 ADCP observations, the mean measured velocity profile in algal covered areas averaged 0.67 m s⁻¹, whereas it was found to be 0.41 m s⁻¹ in uncovered locations (p