Variation in water-mediated connectivity influences patch distributions of total N, total P, and TN:TP ratios in the Upper Mississippi River, USA

Abstract

AbstractFloodplain rivers have been conceptualized as patchwork mosaics of hydrogeomorphic zones that differ in hydrological, physiochemical, and ecological conditions. However, few investigators have empirically examined the extent to which basic ecological properties of large rivers, such as nutrient concentrations, are patchily distributed or the relationship between such distributions and water-mediated connectivity. We used global and local measures of spatial autocorrelation in 5 reaches of the Upper Mississippi River from 1994–2008 in spring (higher discharge) and summer (lower discharge) to examine distributions of total N (TN), total P (TP), and TN∶TP for evidence of patchiness. TN was distributed as discrete patches regardless of season, but the patches of TP and TN∶TP were more distinct during summer low-flow than spring high-flow conditions. The occurrence of patches of high TN, low TP, and high TN∶TP was highly predictable, generally occurring in backwater, low-velocity (0.1 m/s) environments...