Ecohydrology is a growing field of science that aims to quantify the interplay between water as a nutrient carrier and bio-assimilation processes (Zalewski 2001). Its basic assumption relies on the fact that water pollution can be processed efficiently by biota along the water pathways by regulating abiotic and biotic controlling factors at key locations. The most important feature to design the so called dual regulation is the non linear time response of biota to controlling factors. Biota refer either to aquatic vegetation or micro-organisms. We here develop a method to analyze and model the response dynamic of biota to abiotic factors evolution at a reach scale. In a first step a natural growing function is fitted to observed biotic data. Then residues to this model are processed in a second step with a memory analysis technique that helps to identify key abiotic factors. In a third step, a dynamic model is build by combining the natural growth functionl with its abiotic controlling factors. Model is then run at a daily time step. Data come from a reach of the river Dordogne. Reach was 250 m long and 100 m wide. Vegetation species and abundance, water level, velocity and temperature were sampled during five years several times a year. Most abundant taxonomic groups of aquatic macrophytes in our samplings were phanerogams and algae. The good model fitting over years with observed data confirms the mixing methodology of biotic and abiotic factors can serve the dynamic process analysis. An equivalent N uptake function is then processes considering the macrophyte biomass. Memory analysis results indicate that Phanerogam are mainly linked to water temperature and water depth variations that occurred in the past 10 days but also depend on a seasonal time scale. Algae variations are closely linked to the antecedent day(s) variations in flow velocity. First conclusions are drawn on the methodology and a discussion is open on controlling factors of the nitrogen uptake that would be regulated to increase the yearly overall natural N uptake at the reach scale.