Great Plains rivers are characterized by water discharge flashiness, shallow depths, and ephemeral sandbars. The system flashiness, combined with the unstable substrate of the sandbars, create constant changes in hydrogeomorphic complexity. The Kansas River, a prairie river, displays hydrogeomorphic complexity both longitudinally and laterally, with the degree of complexity dependent on the flow pulse. In situ studies on effects of hydrogeomorphic variability on primary producers and, in turn, net ecosystem production, were conducted during summer 2007. Pelagic and benthic algal samples were collected across lateral habitats (main channel, side channel, backwater), counted, and identified. Initial data analyses indicate a change in algal abundance and community composition across the habitat gradient. The backwater areas typically showed greater algal abundance and more species diversity.  Net ecosystem production was measured in three longitudinal habitats varying in geomorphic complexity (point bar, braided area, and single channel). Diel changes in dissolved oxygen concentration and other variables were measured with data recording sondes for 48 hr periods in responses to changes in river discharge. Preliminary analyses indicate the sites undergo daily fluctuations in net ecosystem production. At some sites, these daily net fluctuations are due to fluctuations in community respiration rather than production and vice versa.