Impacts of Water Clarity Variability on Temperature and Biogeochemistry in the Chesapeake Bay
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Impacts of Water Clarity Variability on Temperature and Biogeochemistry in the Chesapeake Bay Grace E. Kim1
· Pierre St-Laurent2 · Marjorie A. M. Friedrichs2 · Antonio Mannino1
Received: 16 December 2019 / Revised: 28 March 2020 / Accepted: 14 May 2020 © The Author(s) 2020
Abstract Estuarine water clarity depends on the concentrations of aquatic constituents, such as colored dissolved organic matter, phytoplankton, inorganic suspended solids, and detritus, which are influenced by variations in riverine inputs. These constituents directly affect temperature because when water is opaque, sunlight heats a shallower layer of the water compared to when it is clear. Despite the importance of accurately predicting temperature variability, many numerical modeling studies do not adequately account for this key process. In this study, we quantify the effect of water clarity on heating by comparing two simulations of a hydrodynamic-biogeochemical model of the Chesapeake Bay for the years 2001–2005, in which (1) water clarity is constant in space and time for the computation of solar heating, compared to (2) a simulation where water clarity varies with modeled concentrations of light-attenuating materials. In the variable water clarity simulation, the water is more opaque, particularly in the northern region of the Bay. This decrease in water clarity reduces the total heat, phytoplankton, and nitrate throughout the Bay. During the spring and summer months, surface temperatures in the northern Bay are warmer by 0.1 ◦ C and bottom temperatures are colder by 0.2 ◦ C in the variable light attenuation simulation. Warmer surface temperatures encourage phytoplankton growth and nutrient uptake near the head of the Bay, and fewer nutrients are transported downstream. These impacts are greater during higher river flow years, when differences in temperature, nutrients, phytoplankton, and zooplankton extend further seaward compared to other years. This study demonstrates the consequences of utilizing different light calculations for estuarine heating and biogeochemistry. Keywords Water clarity · Estuarine modeling · Chesapeake Bay · Phytoplankton · Temperature · Nutrients
Introduction Rivers flowing through watersheds collect sediment, colored dissolved organic material (CDOM), and nutrients from the surrounding landscape. These materials eventually reach estuaries and coastal ocean environments where they affect water clarity. CDOM is a major light absorber in Communicated by Neil Kamal Ganju Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12237-020-00760-x) contains supplementary material, which is available to authorized users. Grace E. Kim
[email protected] 1
NASA Goddard Space Flight Center, 8800 Greenbelt Rd, Greenbelt, MD 20771, USA
2
Virginia Institute of Marine Science, William, & Mary, Gloucester Point, VA 23062, USA
the energetic blue region of the visible spectrum, whereas sediment contributes to light scattering in the water column (Mobley 1994). Nutrients affect
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