Using Graph Networks to Quantify the Cumulative Importance of Riparian Wetlands within a Watershed

Abstract Wetlands provide many valuable ecosystem functions including nutrient cycling and retention, sediment capture, flood reduction, carbon storage, and habitat for water-dependent plant and wildlife species. The alteration of landscapes and the deterioration of upstream wetlands have been determined to be detrimental to downstream stream and watershed health. The position of the wetland in the landscape and its quality and size can significantly change the influence it has on stream condition. This research tests the efficacy of graphed networks created from the terrestrial-wetland-stream landscape to quantify the cumulative benefits of riparian wetlands within a watershed. We tested a combination of network parameters such as node degree, betweenness centrality, and the integral index of connectivity. Graphed networks are created by nodes that are connected by edges. Nodes were defined as stream reaches that extend out to the riparian landscape and edges as the stream confluences that connect them. Nodes were weighted by their capacity to perform ecosystem functions and the opportunity for such functions. We found that the network-based approach can quantify the impact of riparian wetland loss revealing that some riparian losses within the watershed were inherently worse than others at reducing connectivity and cumulative wetland function within the watershed. Incorporating these network metrics into wetland assessments can quantify the cumulative influence of geographic position, wetland function and size on overall wetland benefits within the watershed. This new approach can be applied to watershed planning efforts to assist managers with identifying wetlands for protection, enhancement, and re-establishment.