Harvey Jud, Gomez-Velez Jesus, Schmadel Noah, Scott Durelle, Boyer Elizabeth, Alexander Richard, Eng Ken, Golden Heather, Kettner Albert, Konrad Chris, Moore Richard, Pizzuto Jim, Schwarz Greg, Soulsby Chris, Choi Jay
Earth Surface Processes Division (Harvey, Schmadel, Choi), and Integrated Modeling and Prediction Division (Alexander, Eng, Schwarz), U.S. Geological Survey, Reston, Virginia, USA; Civil and Environmental Engineering (Gomez-Velez), Vanderbilt University, Nashville, Tennessee, USA; Department of Biological Systems Engineering (Scott), Virginia Tech, Blacksburg, Virginia, USA; Department of Ecosystem Science and Management (Boyer), Pennsylvania State University, State College, Pennsylvania, USA; Office of Research and Development (Golden), U.S. Environmental Protection Agency, Cincinnati, Ohio, USA; Institute of Arctic and Alpine Research (Kettner), University of Colorado, Boulder, Colorado, USA; Washington Water Science Center (Konrad), U.S. Geological Survey, Tacoma, Washington, USA; New England Water Science Center (Moore), U.S. Geological Survey, Pembroke, New Hampshire, USA; College of Earth, Ocean, and the Environment (Pizzuto), University of Delaware, Newark, Delaware, USA; and School of Geosciences (Soulsby), University of Aberdeen, Aberdeen, Scotland, GRB.
J Am Water Resour Assoc. 2019 Apr 1;55(2):369-381. doi: 10.1111/1752-1688.12691.
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.
河流中的下游水流会因与发生生物地球化学过程的河道外蓄水区进行水文交换而反复延迟。我们提出了一个无量纲指标，将河流连通性量化为下游水流与河床、河岸和洪泛区之间的水交换平衡。连通程度直接影响下游水质——连通性过低会限制河水交换量，导致生物地球化学不活跃的水体储存；而连通性过高则会限制与沉积物的接触时间，影响反应进行。基于河流连通性，我们使用一个反应显著性指标，证明中等连通水平而非最高或最低水平，对于美国东北部河流的脱氮最为有效。中等连通性平衡了与活性沉积物的接触频率、停留时间和接触体积，从而能使溶解污染物的反应处理最大化，并保护下游水质。我们的模拟表明，反硝化作用主要发生在溪流和小河流的河床潜流带，而在中型到大型河流中，与沉积物接触的垂直湍流混合起主导作用。这里提出的连通性和反应显著性指标有助于基于科学依据对河流管理策略进行优先排序，以保护河流廊道的价值和功能。
