Virginia Institute of Marine Science
As three-dimensional (3-D) aquatic ecosystem models are used more frequently for operational water quality forecasts and ecological management decisions, it is important to understand the relative strengths and limitations of existing 3-D models of varying spatial resolution and biogeochemical complexity. To this end, 2-year simulations of the Chesapeake Bay from eight hydrodynamic-oxygen models have been statistically compared to each other and to historical monitoring data. Results show that although models have difficulty resolving the variables typically thought to be the main drivers of dissolved oxygen variability (stratification, nutrients, and chlorophyll), all eight models have significant skill in reproducing the mean and seasonal variability of dissolved oxygen. In addition, models with constant net respiration rates independent of nutrient supply and temperature reproduced observed dissolved oxygen concentrations about as well as much more complex, nutrient-dependent biogeochemical models. This finding has significant ramifications for short-term hypoxia forecasts in the Chesapeake Bay, which may be possible with very simple oxygen parameterizations, in contrast to the more complex full biogeochemical models required for scenario-based forecasting. However, models have difficulty simulating correct density and oxygen mixed layer depths, which are important ecologically in terms of habitat compression. Observations indicate a much stronger correlation between the depths of the top of the pycnocline and oxycline than between their maximum vertical gradients, highlighting the importance of the mixing depth in defining the region of aerobic habitat in the Chesapeake Bay when low-oxygen bottom waters are present. Improvement in hypoxia simulations will thus depend more on the ability of models to reproduce the correct mean and variability of the depth of the physically driven surface mixed layer than the precise magnitude of the vertical density gradient.
EASTERN NORTH-AMERICA; ECOSYSTEM MODELS; EUTROPHICATION MODEL; BIOGEOCHEMICAL MODEL; PHYSICAL CONTROLS; DATA ASSIMILATION; DISSOLVED-OXYGEN; SKILL ASSESSMENT; ATLANTIC-OCEAN; FOOD-WEB
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This work is licensed under a Creative Commons Attribution 4.0 License.
Data sets Chesapeake Bay Operational Forecast System (CBOFS) National Oceanic and Atmospheric Administration http://www.tidesandcurrents.noaa.gov/ofs/cbofs/cbofs.html Chesapeake Bay Program Water Quality Database (1984-present) USGS http://www.chesapeakebay.net/data/downloads/cbp_water_quality_database_1984_present
This work was supported by the NOAA IOOS program as part of the Coastal Ocean Modeling Testbed. We thank Yun Li and Younjoo Lee for help with the ROMS-RCA simulations used in this analysis and Ray Najjar for his insights and comments. This is VIMS contribution 3520 and UMCES contribution 5130.
Irby, I. D., Friedrichs, M. A. M., Friedrichs, C. T., Bever, A. J., Hood, R. R., Lanerolle, L. W. J., Li, M., Linker, L., Scully, M. E., Sellner, K., Shen, J., Testa, J., Wang, H., Wang, P., and Xia, M.: Challenges associated with modeling low-oxygen waters in Chesapeake Bay: a multiple model comparison, Biogeosciences, 13, 2011-2028, https://doi.org/10.5194/bg-13-2011-2016, 2016.