Estimating Hypoxic Volume in the Chesapeake Bay Using Two Continuously Sampled Oxygen Profiles

Abstract

Low levels of dissolved oxygen (DO) occur in many embayments throughout the world and have numerous detrimental effects on biota. Although measurement of in situ DO is straightforward with modern instrumentation, quantifying the volume of water in a given embayment that is hypoxic (hypoxic volume (HV)) is a more difficult task; however, this information is critical for determining whether management efforts to increase DO are having an overall impact. This paper uses output from a three-dimensional numerical model to demonstrate that HV in Chesapeake Bay can be estimated well with as few as two vertical profiles. In addition, the cumulative hypoxic volume (HV C ; the total amount of hypoxia in a given year) can be calculated with relatively low uncertainty (<10%) if continuous DO data are available from two strategically positioned vertical profiles. This is because HV in the Chesapeake Bay is strongly constrained by the geometry of the embayment. A simple Geometric HV calculation method is presented and numerical model results are used to illustrate that for calculating HV C , the results using two daily-averaged profiles are typically more accurate than those of the standard method that interpolates bimonthly cruise data. Bimonthly data produce less accurate estimates of HV C because high-frequency changes in oxygen concentration, for example, due to regional-weather-or storm-induced changes in wind direction and magnitude, are not resolved. The advantages of supplementing cruise-based sampling with continuous vertical profiles to estimate HV C should be applicable to other systems where hypoxic water is constrained to a specific area by bathymetry.Plain Language Summary The Chesapeake Bay supports a diverse range of recreational and commercial fisheries. However, every summer the amount of oxygen dissolved in the bay's bottom water decreases to levels lethal for fish and shellfish, termed a "dead zone." To make informed management decisions and understand the health of the ecosystem, it is important to understand the variability in the dissolved oxygen and the amount of water with low dissolved oxygen. In this study, we used both observations collected from boats and three-dimensional computer models to demonstrate that the region of low dissolved oxygen is strongly constrained by the geometry of the Chesapeake Bay. Because of this geometric constraint, the amount of low dissolved oxygen water can be accurately calculated if continually monitored with only two vertical profiles. In contrast, the current method uses numerous locations sampled only twice per month. This study demonstrated that continuous vertical profiles at as few as two locations provide a better estimate of the volume of hypoxia in any given year. This means that the amount of hypoxic water can be estimated in real time using an ocean observing system that efficiently supplements the current monitoring program, because only a few continuous monitoring locations are needed.While the determination of whether a certain location experiences hypox...

Transient Hypoxia Extent Off Changjiang River Estuary due to Mobile Changjiang River Plume

“…In contrast, the Changjiang River estuary and the adjacent sea are affected by monsoon, and the short‐time variability of wind occurs more frequently. Bever et al () used two continuously sampled oxygen profiles to estimate hypoxic volume for the Chesapeake Bay. These daily‐averaged profiles were considered to be more accurate in providing the estimations than the bimonthly cruise data because of the high‐frequency changes in oxygen concentration under the variable wind direction and magnitude.…”

“…With continuously increasing nutrient loads, coastal hypoxia is most likely to worsen in the foreseeable future. East China Sea (e.g., D. Li et al, ; H. Wang, Dai, et al; Wei et al, ; J. Zhang et al, ), North Gulf of Mexico (e.g., Feng et al, ; Hetland & DiMarco, ; Rabalais, Turner, Sen Gupta, Boesch, et al, ; Rabalais, Turner, Sen Gupta, Platon, et al, ; W. Zhang et al, ), and Chesapeake Bay (e.g., Bever et al, , ; M. Li et al, ; Scully, , ; Shen et al, ) are among the typical systems that are strongly influenced by massive nutrient loads introduced by riverine inputs.…”

“…Wang, Dai, et al2016;Wei et al, 2007; J. Zhang et al, 2016), North Gulf of Mexico (e.g., Feng et al, 2012;Hetland & DiMarco, 2008;Rabalais, Turner, Sen Gupta, Boesch, et al, 2007;Rabalais, Turner, Sen Gupta, Platon, et al, 2007; W. Zhang et al, 2015), and Chesapeake Bay (e.g., Bever et al, 2013Bever et al, , 2018M. Li et al, 2016;Scully, 2010Scully, , 2013Shen et al, 2013) are among the typical systems that are strongly influenced by massive nutrient loads introduced by riverine inputs.…”

Advancing estuarine ecological forecasts: seasonal hypoxia in Chesapeake Bay

“…As throughout the remainder of the year, with vertical profiles collected at about 1-2 m vertical resolution. These data have been used by numerous groups to estimate the extent of hypoxia in the Chesapeake Bay (Bever et al 2013(Bever et al , 2018Zhou et al 2014;Hagy et al 2004;Murphy et al 2011).…”

Effects of Short-Duration and Diel-Cycling Hypoxia on Predation of Mussels and Oysters in Two Tributaries of the Chesapeake Bay

“…The Bay also experiences diel-cycling hypoxia in its shallow-water tributaries [5,6]. The volume of the persistent hypoxia in the Chesapeake Bay is tracked annually [7], however, the volume of water exhibiting diel-cycling hypoxia is not monitored.…”