The ecology of river, lake, and wetland ecosystems is strongly affected by the routing of their source waters. As the interface between rivers and terrestrial landscapes, riparian ecosystems are uniquely situated to influence, and be influenced by, hydrologic variation. The primary objective of this research was to characterize the range and spatial variation of riparian ecotypes throughout Lower Michigan using readily available digital maps and an extensive inventory of riparian forests. Utilizing a terrain-based model of groundwater delivery and regression analysis, I accounted for significant proportions of variance in stream baseflow yield (48-54%, N=58), summer stream temperatures (23-40%, N=171), and discharge accrual (59-65%, N=48). Using network summaries of groundwater delivery and water table proximity to augment mapped agricultural and wetland information, I demonstrated that accounting for variation in riparian hydrology improved regressions of nutrient export across Lower Michigan (N=290) between 6-20%. As a proxy for variation in riparian site conditions, I sampled forest composition from 94 locations throughout Lower Michigan. Based on ordinations and autecological interpretations of tree species occurrence, I developed a causal hypothesis of soil saturation and flood dynamics using macroclimate, local landscape, and catchment influences on hydrologic character using covariance structure analysis. The model exhibited an excellent fit with the observed data (chi-square=18.11, p=0.382) and accounted for nearly 65% of observed variation in the probability of correct riparian classification. Map-based models explained large portions of natural variation in the compositional and structural character of riparian areas. I therefore conclude that relatively simple, yet process-specific interpretations of existing spatial data sets have enormous potential for predicting complex, yet ecologically relevant hydrologic processes at the land-water interface. (email: baker@serc.si.edu)