Societal benefits of floodplains in the Chesapeake Bay and Delaware River watersheds: Sediment, nutrient, and flood regulation ecosystem services.

Floodplains provide critical ecosystem services to people by regulating floodwaters and retaining sediments and nutrients. Geospatial analyses, field data collection, and modeling were integrated to quantify a portfolio of services that floodplains provide to downstream communities within the Chesapeake Bay and Delaware River watersheds. The portfolio of services included floodplain sediment and nutrient retention and flood regulation. Sediment and nutrient retention were quantified and valued for all non-tidal wadable streams in the Chesapeake Bay and Delaware River watersheds. Predicted nitrogen fluxes from measurements of streambanks and floodplain geomorphic changes were summarized at various scales (river basin, state, and county) and valued using a benefits transfer approach. Floodplain flood regulation services were assessed through a pilot study focused on the Schuylkill River watershed in the Delaware River watershed. Geospatial analysis and published flood frequency estimates were used to assess baseline and counterfactual (i.e., floodplain storage removed) scenarios. Flood regulation was valued using the Federal Emergency Management Agency's Hazus model to compare differences in structural damage to private residences under baseline and counterfactual scenarios. The estimated value of floodplain sediment and nutrient retention was $223 million United States dollars (USD) per year in the Chesapeake Bay watershed and $38 million USD per year in the Delaware River watershed. Sediment and nutrient retention benefits were offset by a streambank erosion cost of $123 million and $14 million USD annually in the Chesapeake and Delaware watersheds, respectively. In the Schuylkill River watershed floodplain flood regulation was valued at $860,000 USD per year, with an additional $7.2 million USD annually provided through floodplain sediment and nutrient retention. Together this portfolio of floodplain ecosystem services indicates that floodplains provide substantial benefits to people by trapping nutrients and storing floodwaters.

Toward effective river basin management (RBM): The politics of cooperation, sustainability, and collaboration in the Delaware River basin.

Creating institutions to manage shared waterways at the basin scale, instead of as a patchwork of fragmented political jurisdictions, has long held attraction for water managers and political scientists. Basin-scale planning, management, and governance, the scholarly consensus runs, can promote cooperative management of shared water resources, facilitate management on an ecological rather than political basis, and better engage a diverse set of stakeholders. Yet in practice, River Basin Management (RBM) has proven difficult to institute and often produced disappointing results, being either too weak to be effective or too technocratic. The case of the Delaware River basin in the United States is a noteworthy exception. RBM in the Delaware basin has taken the form of a capable but inclusive inter-jurisdictional commission that has almost eliminated previously widespread conflict between riparian states; generally improved water quality and ecosystem protection; and empowered civil society. Yet this effectiveness stemmed from a messy political process marked by tension and competition between central, state, and local levels of government. Harnessing this tension to forge a durable, adaptable institutional framework proved to be key to the relative success of RBM in the Delaware basin, providing lessons to inform the management of shared watersheds elsewhere.

Spatial patterns and seasonal timing of increasing riverine specific conductance from 1998 to 2018 suggest legacy contamination in the Delaware River Basin.

Increasing salinization of freshwater threatens water supplies that support a range of human and ecological uses. The latest assessments of Delaware River Basin (DRB) surface-water-quality changes indicate widespread salinization has occurred in recent decades, which may lead to meaningful degradation in water quality. To better understand how and when salinity transport occurs and implications for DRB streams, this study: 1) explores the variability of specific conductance (SC) trends spatially and seasonally from 1998 to 2018, and 2) investigates how trends relate to streamflow, land disturbance, and impervious surface area to better understand regional salinization drivers. We find widespread increases in SC across the DRB, with several sites in the lower basin exceeding thresholds for aquatic life and experiencing increasing frequencies of exceedance over time. In general, the greatest basin wide increases in SC occurred during low flow conditions, indicating that a legacy component resulting from subsurface retention and transport processes has driven observed changes in riverine SC. For a subset of sites in the lower basin, where impervious area and cumulative land disturbance are higher, the greatest SC increases occurred during high flow conditions in winter months. Given the patterns of SC and watershed changes across the basin, as well as strong relationships between SC trends and sodium and chloride trends, deicing salt appears to be a likely driver of observed SC change. Even if deicing salt application plateaus or declines in coming years, the continued release and transport of the legacy subsurface component may still contribute to elevated DRB riverine SC.