20 Oct 2022
20 Oct 2022
Status: this preprint is open for discussion.

Impacts and uncertainties of climate-induced changes in watershed inputs on estuarine hypoxia

Kyle E. Hinson1, Marjorie A. M. Friedrichs1, Raymond G. Najjar2, Maria Herrmann2, Zihao Bian3, Gopal Bhatt4,5, Pierre St-Laurent1, Hanqin Tian6, and Gary Shenk7,5 Kyle E. Hinson et al.
  • 1Virginia Institute of Marine Science, William & Mary, Gloucester Point, VA 23062, USA
  • 2Department of Meteorology and Atmospheric Science, The Pennsylvania State University, University Park, PA 16802, USA
  • 3International Center for Climate and Global Change, Auburn University, Auburn, AL 36849, USA
  • 4Department of Civil & Environmental Engineering, The Pennsylvania State University, State College, 16801, USA
  • 5United States Environmental Protection Agency Chesapeake Bay Program Office, Annapolis, 21401, USA
  • 6Schiller Institute for Integrated Science and Society, Department of Earth and Environmental Sciences, Boston College, Chestnut Hill, MA 02467, USA
  • 7United States Geological Survey, Virginia/West Virginia Water Science Center, Richmond, VA 23228, USA

Abstract. Multiple climate-driven stressors, including warming and increased nutrient delivery, are exacerbating hypoxia in coastal marine environments. Within coastal watersheds, environmental managers are particularly interested in climate impacts on terrestrial processes, which may undermine the efficacy of management actions designed to reduce eutrophication and consequent low-oxygen conditions in receiving coastal waters. However, substantial uncertainty accompanies the application of Earth System Model (ESM) projections to a regional modeling framework when quantifying future changes to estuarine hypoxia due to climate change. In this study, two downscaling methods are applied to multiple ESMs and used to force two independent watershed models for Chesapeake Bay, a large coastal-plain estuary of the eastern United States. The projected watershed changes are then used to force a coupled 3-D hydrodynamic-biogeochemical estuarine model to project climate impacts on hypoxia, with particular emphasis on projection uncertainties. Results indicate that all three factors (ESM, downscaling method, and watershed model) are found to contribute significantly to the uncertainty associated with future hypoxia, with the choice of ESM being the largest contributor. Overall, in the absence of management actions, there is a high likelihood that climate change impacts on the watershed will expand low-oxygen conditions by 2050, relative to a 1990s baseline period; however, the projected increase in hypoxia is quite small (4 %) because only climate-induced changes in watershed inputs are considered and not those on the estuary itself. Results also demonstrate that the attainment of established nutrient reduction targets will reduce annual hypoxia by about 50 % compared to the 1990s. Given these estimates, it is virtually certain that fully implemented management actions reducing excess nutrient loadings will outweigh hypoxia increases driven by climate-induced changes in terrestrial runoff.

Kyle E. Hinson et al.

Status: open (until 19 Dec 2022)

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Kyle E. Hinson et al.


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Short summary
Climate impacts are essential for environmental managers to consider when implementing nutrient reduction plans designed to reduce hypoxia. This work highlights relative sources of uncertainty in modeling regional climate impacts on the Chesapeake Bay watershed and consequent declines in Bay oxygen levels. The results demonstrate that planned water quality improvement goals are capable of reducing hypoxia levels by half, offsetting climate-driven impacts to terrestrial runoff.