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Article

Impact of Global Warming on Dissolved Oxygen and BOD Assimilative Capacity of the World’s Rivers: Modeling Analysis

1
Department of Civil and Environmental Engineering, Tufts University, Medford, MA 02155, USA
2
Environmental Engineering Research Center (CIIA), Civil and Environmental Engineering Department, Universidad de los Andes, Bogotá 111111, Colombia
3
National Institute of Water and Atmospheric Research (NIWA), P.O. Box 11-115, Hamilton 3251, New Zealand
*
Author to whom correspondence should be addressed.
Academic Editor: Chin-Pao Huang
Water 2021, 13(17), 2408; https://doi.org/10.3390/w13172408
Received: 27 May 2021 / Revised: 16 August 2021 / Accepted: 26 August 2021 / Published: 1 September 2021
(This article belongs to the Special Issue Water-Quality Modeling)
For rivers and streams, the impact of rising water temperature on biochemical oxygen demand (BOD) assimilative capacity depends on the interplay of two independent factors: the waterbody’s dissolved oxygen (DO) saturation and its self-purification rate (i.e., the balance between BOD oxidation and reaeration). Although both processes increase with rising water temperatures, oxygen depletion due to BOD oxidation increases faster than reaeration. The net result is that rising temperatures will decrease the ability of the world’s natural waters to assimilate oxygen-demanding wastes beyond the damage due to reduced saturation alone. This effect should be worse for nitrogenous BOD than for carbonaceous BOD because of the former’s higher sensitivity to rising water temperatures. Focusing on streams and rivers, the classic Streeter–Phelps model was used to determine the magnitude of the maximum or “critical” DO deficit that can be calculated analytically as a function of the mixing-point BOD concentration, DO saturation, and the self-purification rate. The results indicate that high-velocity streams will be the most sensitive to rising temperatures. This is significant because such systems typically occur in mountainous regions where they are also subject to lower oxygen saturation due to decreased oxygen partial pressure. Further, they are dominated by salmonids and other cold-water fish that require higher oxygen levels than warm-water species. Due to their high reaeration rates, such systems typically exhibit high self-purification constants and consequently have higher assimilation capacities than slower moving lowland rivers. For slow-moving rivers, the total sustainable mixing-point concentration for CBOD is primarily dictated by saturation reductions. For faster flowing streams, the sensitivity of the total sustainable load is more equally dependent on temperature-induced reductions in both saturation and self-purification. View Full-Text
Keywords: streams; water quality; climate change; saturation; oxygen metabolism; sustainability streams; water quality; climate change; saturation; oxygen metabolism; sustainability
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MDPI and ACS Style

Chapra, S.C.; Camacho, L.A.; McBride, G.B. Impact of Global Warming on Dissolved Oxygen and BOD Assimilative Capacity of the World’s Rivers: Modeling Analysis. Water 2021, 13, 2408. https://doi.org/10.3390/w13172408

AMA Style

Chapra SC, Camacho LA, McBride GB. Impact of Global Warming on Dissolved Oxygen and BOD Assimilative Capacity of the World’s Rivers: Modeling Analysis. Water. 2021; 13(17):2408. https://doi.org/10.3390/w13172408

Chicago/Turabian Style

Chapra, Steven C., Luis A. Camacho, and Graham B. McBride 2021. "Impact of Global Warming on Dissolved Oxygen and BOD Assimilative Capacity of the World’s Rivers: Modeling Analysis" Water 13, no. 17: 2408. https://doi.org/10.3390/w13172408

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