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John Wesley Powell Center for Analysis and Synthesis

Powell Center Products

The Natural Capital Accounting Opportunity: Let's Really Do the Numbers

Powell Center Working Group Products - Thu, 11/01/2018 - 11:10
"The nation's economic accounts provide objective, regular, and standardized information routinely relied on by public and private decision-makers. But they are incomplete. The United States and many other nations currently do not account for the natural capital--such as the wildlife, forests, grasslands, soils, and water bodies--on which all other economic activity rests. By creating formal natural capital accounts (NCA) and ecosystem goods and service (EGSA) accounts, governments and businesses could better understand the past, peer into the future, innovate, conserve, and plan for environmental shocks. They would standardize, regularly repeat, and aggregate diverse natural resource, environmental, and social and economic data and could thereby play a significant role in advancing the science of coupled biophysical and social systems...."

How Hydrologic Connectivity Regulates Water Quality in River Corridors

Powell Center Working Group Products - Thu, 11/01/2018 - 10:46

Downstream flow in rivers is repeatedly delayed by hydrologic exchange with off‐channel storage zones where biogeochemical processing occurs. We present a dimensionless metric that quantifies river connectivity as the balance between downstream flow and the exchange of water with the bed, banks, and floodplains. The degree of connectivity directly influences downstream water quality--too little connectivity limits the amount of river water exchanged and leads to biogeochemically inactive water storage, while too much connectivity limits the contact time with sediments for reactions to proceed. Using a metric of reaction significance based on river connectivity, we provide evidence that intermediate levels of connectivity, rather than the highest or lowest levels, are the most efficient in removing nitrogen from Northeastern United States’ rivers. Intermediate connectivity balances the frequency, residence time, and contact volume with reactive sediments, which can maximize the reactive processing of dissolved contaminants and the protection of downstream water quality. Our simulations suggest denitrification dominantly occurs in riverbed hyporheic zones of streams and small rivers, whereas vertical turbulent mixing in contact with sediments dominates in mid‐size to large rivers. The metrics of connectivity and reaction significance presented here can facilitate scientifically based prioritizations of river management strategies to protect the values and functions of river corridors.

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