Spatial and Temporal Variabilities of Hypoxia in the Rappahannock River, Virginia

Kuo, Albert Y.; Park, Kyeong; Moustafa, M. Z.

doi:10.2307/1351684

Cited by 65 publications

(37 citation statements)

References 10 publications

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“…Development of the conceptual model-For a partially mixed estuary, the gravitational circulation can be described by a two-layer model (Pritchard 1952;Kuo and Neilson 1987;MacCready 2004) as shown in Fig. 1.…”

Section: Methodsmentioning

confidence: 99%

“…Kuo and Neilson (1987) analyzed DO budgets in Virginia tributary estuaries of Chesapeake Bay. They pointed out that gravitational circulation plays an important role in modulating DO in these tributaries.…”

Section: Introductionmentioning

confidence: 99%

“…Kuo and Neilson (1987) proposed a simplified model to examine the contribution of gravitational circulation to the bottomwater hypoxia in Virginia tributaries of Chesapeake Bay, which explains the differences among the hypoxia conditions in these tributaries. Although a strong gravitational circulation develops in the Bay, the strong stratification acts to decrease DO replenishment to the oxygen-depleted waters near the bottom.…”

Section: Introductionmentioning

confidence: 99%

“…Annual summertime occurrences of hypoxia in deep water are driven by seasonal stratification coupled with total respiration. Hypoxia develops when the DO consumption rate of biochemical processes exceeds the oxygen supply for the sub-pycnocline water of an estuary (Officer et al 1984).The variation of estuarine dynamics is the key factor controlling the development of hypoxia (Kuo and Neilson 1987;Boicourt 1992;Scully 2010). Kuo and Neilson (1987) analyzed DO budgets in Virginia tributary estuaries of Chesapeake Bay.…”

mentioning

confidence: 99%

“…The variation of estuarine dynamics is the key factor controlling the development of hypoxia (Kuo and Neilson 1987;Boicourt 1992;Scully 2010). Kuo and Neilson (1987) analyzed DO budgets in Virginia tributary estuaries of Chesapeake Bay.…”

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confidence: 99%

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Using timescales to interpret dissolved oxygen distributions in the bottom waters of Chesapeake Bay

Shen

Hong

Kuo

2013

Limnology & Oceanography

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A simplified conceptual model based on timescales of gravitational circulation, vertical exchange, and total oxygen consumption rate of the biochemical processes is presented to provide insight into the relationships between estuarine dynamics and bottom water dissolved oxygen (DO). Two dimensionless parameters are introduced to diagnose the relationship between the vertical exchange process and the biochemical DO consumption and the influence of gravitational circulation on replenishment of bottom DO. The relative magnitudes of these timescales provide a linkage between the physical and biochemical processes. The hypoxic and anoxic conditions in deep waters of Chesapeake Bay are successfully interpreted with these three proposed timescales. Because the Bay is a long estuary, the replenishment of the bottom DO due to gravitational circulation diminishes as the bottom water travels farther upstream. The bottom DO is mainly modulated by the vertical exchange process in the middle and upper portions of the Bay. In addition to other physical processes that affect vertical exchange, wind and freshwater are the major predictors of the vertical exchange time. The model is applicable to Chesapeake Bay and other estuaries with persistent gravitational circulation if the dimensionless parameters can be appropriately estimated.Hypoxia and anoxia occurrences in estuaries appear to be increasing and are most likely accelerated by human activities (Cloern 2001;Diaz 2001). Persistent seasonal hypoxia occurs in many stratified, partially mixed estuaries and shelf regions worldwide (Diaz 2001;Nixon 1995). The formation of chronic (days to months) hypoxic bottom waters in deep estuaries and coastal oceans is a common phenomenon of eutrophication in the aquatic environment and has been widely studied for many years (Diaz 2001;Kemp et al. 1992 Kemp et al. , 2005. Hypoxia and anoxia develop in Chesapeake Bay from the middle to upper Bay in summer (Kemp et al. 2005). The U.S. Environmental Protection Agency monitoring data (http://www.chesapeakebay.net/data/downloads/) also indicate that the hypoxic condition lessens in the lower Bay and that the bottom dissolved oxygen (DO) concentration at the Bay entrance is near saturation most of the time. Annual summertime occurrences of hypoxia in deep water are driven by seasonal stratification coupled with total respiration. Hypoxia develops when the DO consumption rate of biochemical processes exceeds the oxygen supply for the sub-pycnocline water of an estuary (Officer et al. 1984).The variation of estuarine dynamics is the key factor controlling the development of hypoxia (Kuo and Neilson 1987;Boicourt 1992;Scully 2010). Kuo and Neilson (1987) analyzed DO budgets in Virginia tributary estuaries of Chesapeake Bay. They pointed out that gravitational circulation plays an important role in modulating DO in these tributaries. High DO water at the estuarine mouth can be transported upstream by the gravitational circulation that replenishes the bottom-water DO. For an estuary with wea...

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Using timescales to interpret dissolved oxygen distributions in the bottom waters of Chesapeake Bay

Shen

Hong

Kuo

2013

Limnology & Oceanography

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Estimates of horizontal fluxes of oxygen, heat, and salt in western Long Island Sound

McCardell

O’Donnell

2014

JGR Oceans

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The dissolved oxygen (DO) concentration in the bottom waters of western Long Island Sound decreases to hypoxic levels between April and July. Since the rate of decline of DO is considerably less than measured respiration, there must be significant vertical transport of DO from oxygen richer waters near the surface and/or horizontal transport from the central Sound. Simple model budgets with either of these sources are able to provide predictions of the seasonal rate of decline that are consistent with the observed values. Although prior budget estimates indicated that vertical fluxes were a significant portion of the resupply of DO, these were not able to discount the possible importance of horizontal fluxes, nor have there been any measurements of horizontal fluxes in this region. We present an analysis of time series of moored conductivity, temperature, DO, and current observations in the hypoxic area of Long Island Sound during the summers of 2005 and 2006. We estimate the near-bottom along-channel flux divergences of salt, heat, and DO as 0.11 6 0.08 g kg 21 d 21 , 25 6 6 W m 23 , and 4 6 6 lM d 21 , respectively. Since this horizontal DO transport is only 25% of the magnitude of the mean rate of respiration, we conclude that vertical transport by mixing forms the bulk of the physical resupply of DO to the hypoxic zone of the western Sound.

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Decoupling the influence of biological and physical processes on the dissolved oxygen in the Chesapeake Bay

Shen

2015

JGR Oceans

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It is instructive and essential to decouple the effects of biological and physical processes on the dissolved oxygen condition, in order to understand their contribution to the interannual variability of hypoxia in Chesapeake Bay since the 1980s. A conceptual bottom DO budget model is applied, using the vertical exchange time scale (VET) to quantify the physical condition and net oxygen consumption rate to quantify biological activities. By combining observed DO data and modeled VET values along the main stem of the Chesapeake Bay, the monthly net bottom DO consumption rate was estimated for 1985-2012. The DO budget model results show that the interannual variations of physical conditions accounts for 88.8% of the interannual variations of observed DO. The high similarity between the VET spatial pattern and the observed DO suggests that physical processes play a key role in regulating the DO condition. Model results also show that long-term VET has a slight increase in summer, but no statistically significant trend is found. Correlations among southerly wind strength, North Atlantic Oscillation index, and VET demonstrate that the physical condition in the Chesapeake Bay is highly controlled by the large-scale climate variation. The relationship is most significant during the summer, when the southerly wind dominates throughout the Chesapeake Bay. The seasonal pattern of the averaged net bottom DO consumption rate (B

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Spatial and Temporal Variabilities of Hypoxia in the Rappahannock River, Virginia

Cited by 65 publications

References 10 publications

Using timescales to interpret dissolved oxygen distributions in the bottom waters of Chesapeake Bay

Using timescales to interpret dissolved oxygen distributions in the bottom waters of Chesapeake Bay

Estimates of horizontal fluxes of oxygen, heat, and salt in western Long Island Sound

Decoupling the influence of biological and physical processes on the dissolved oxygen in the Chesapeake Bay

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