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Task 128

Pilot Applications of the Chesapeake Bay Forecast System

Principal Investigator(s):

A. Busalacchi


J. Bryson

Last Updated:

October 26, 2012 15:25:30

Description of Problem

A project aimed at demonstrating the value and utility of applications of the Chesapeake Bay Forecast System (CBFS), a prototype regional integrated Earth System Model being developed and implemented at the University of Maryland Earth System Science Interdisciplinary Center. This pilot effort will develop several Pilot User Collaborations aimed at identifying and testing methods for applying CBFS forecast products to sector-specific needs.

Scientific Objectives and Approach

Rising temperatures have important implications for estuarine ecosystem structure and metabolism. Although elevated nutrient loadings are the dominant cause of eutrophication and hypoxia in coastal waters, rising temperatures can increase rates of oxygen consumption and further reduce the solubility of atmospheric oxygen in coastal waters, ultimately driving deoxygenation. Furthermore, global climate change may increase coastal stratification and inhibit vertical mixing, thereby reducing ventilation of subsurface coastal and ocean waters. The Chesapeake Bay is the largest estuary in the North American region and is facing severe summer hypoxia and anoxia problems. Moreover, changes in land-use and climate amplify the terrestrial nutrient loadings to the Bay that subsequently affects the water quality. The aim of this research is to understand the impacts of climate change induced rising temperatures on dissolved oxygen (DO) dynamics and to develop the ecosystem models to understand intricate interactions among various ecological processes and to predict DO in the Chesapeake Bay.

We collected the long term water temperature, dissolved oxygen and dissolved nutrients (nitrogen and phosphorus) data were collected from various stations of the Chesapeake Bay from the Chesapeake Bay Program. Each station is sampled once a month during the colder late fall and winter months and twice each month in the warmer months. At each station, a hydrographic profile is made and water samples for chemical analysis are collected at the surface and the bottom, and (for deeper stations) at two additional mid-water depths depending on the existence and location of the pycnocline. Long-term (1979-2009) air temperatures over the Chesapeake Bay were collected from the National Centers for Environmental Prediction (NCEP)-North American Regional Reanalysis (NARR) data. In this study, air temperatures for the central axis stations were computed by interpolating temperatures from the neighboring grid points, if the air temperature was not available for that particular station. The long-term trends in air- and water temperatures and DO were analyzed using SAS to depict the interactive control of rising temperatures on DO dynamics and depletion of DO in the Chesapeake Bay. Furthermore, the multivariate statistical model was developed using a set of environmental variable (water temperature, salinity, nitrogen and phosphorus). The developed model was validated for the operational prediction of DO in the Chesapeake Bay.

Earth’s surface temperatures are likely to increase by 1.1-6.4 °C by the end of the 21st century relative to the 1980-1990 base periods, with a best estimate of 1.8-4.0 °C for a wide range of greenhouse gas emission scenarios. An increase in air temperature will likely be reflected in higher water temperatures, which has implications for the structure and metabolism of coastal ecosystems. Statistically significant long-term trends in air temperatures were observed in CB with a measured rate of warming of 0.05 °C yr-1 (r = 0.63, p<0.05; Fig. 1). An increase in air temperature will likely be reflected in higher water temperatures, which impact estuarine ecological processes, water circulation and nutrient dynamics. Weak increasing trends in water temperatures (0.0145 °C/yr; p<0.47, see Fig. 1) are observed in CB, and the air- and water temperatures are also strongly correlated (Fig. 2). This clearly describes that the heat balance and distribution of heat in shallow estuaries are largely controlled by meteorological forcings at the air–water interface.

An important regulator of dissolved oxygen concentrations in coastal surface waters is its solubility, which decreases with increasing temperatures. Strong negative correlations between temperature (both air and water) and DO in both estuaries clearly demonstrate that climate induced variability in temperatures drives down the DO levels in coastal waters (Fig. 3). Moreover, distributions of oxygen levels in coastal and marine waters are also controlled by both rates of photosynthesis and heterotrophic respiration. Rising temperature could accelerate the metabolism of large quantities of terrestrial organic matter delivered to coastal waters from watersheds and have a profound effect on bacterial heterotrophic respiration and oxygen levels. In addition, sinking of organic matter due to eutrophication demands substantial oxygen levels for microbial respiration in the bottom waters of CB that further exacerbate the bottom water hypoxia and anoxia, and these rates of respiration may also be influenced by temperature.

The spatially-explicit ecological model was developed for prediction of DO in the Chesapeake Bay using a suite of environmental variables like water temperature, salinity, nitrogen and phosphorus. The developed model was well validated with the observations (Fig. 4). The developed model is an effective ecological tool can be used to describe the response of ecosystem to changing environmental variables, like rise in temperature and salinity and increase in terrestrial nutrient loadings.

Other Publications and Conferences

Prasad, M.B.K., Kaushal, S.S., Momem, B., Murtugudde, R., 2012. Rising temperature drives deoxygenation in coastal waters. Proceedings of National Academy of Sciences of the United States of America, in review.

Prasad, M.B.K., Long, W., Zhang, X., Wood, R.J., Murtugudde, R., 2011. Predicting dissolved oxygen in the Chesapeake Bay: Applications and implications. Aquatic Sciences, 73: 437-451.

Task Figures

Fig. 1 – Long-term analysis of air- and water temperatures of the Chesapeake Bay (1985-2008).

Fig. 2 – Correlation between air- and water temperatures in Chesapeake Bay.

Fig. 3 – Dynamic interactions of dissolved oxygen with air- and water temperatures in Chesapeake Bay.

Fig. 4 – Correlation (R2) between observed and predicted DO concentrations for both surface and bottom layers
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