Hypoxia in Chesapeake Bay, 1950–2001: Long-term change in relation to nutrient loading and river flow

Hagy, James D.; Boynton, Walter R.; Keefe, Carolyn W.; Wood, Kathryn V.

doi:10.1007/bf02907650

Cited by 565 publications

(526 citation statements)

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“…The estuary has a surface area of 11,655 km 2 , yielding a land-to-water ratio of over 14:1. Such a high ratio helps to explain the significant influence that the watershed has on the water quality of the bay (e.g., Hagy et al 2004). Chesapeake Bay is a focus for major ecosystem rehabilitation efforts because it has been plagued by eutrophication for decades (Hagy et al 2004;Bricker et al 2014).…”

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confidence: 99%

“…Such a high ratio helps to explain the significant influence that the watershed has on the water quality of the bay (e.g., Hagy et al 2004). Chesapeake Bay is a focus for major ecosystem rehabilitation efforts because it has been plagued by eutrophication for decades (Hagy et al 2004;Bricker et al 2014). Increasing WT of streams significantly increases nutrient concentrations, which contribute to eutrophication (Duan and Kaushal 2013).…”

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confidence: 99%

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Rising air and stream-water temperatures in Chesapeake Bay region, USA

Rice

Jastram

2014

Climatic Change

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Monthly mean air temperature (AT) at 85 sites and instantaneous stream-water temperature (WT) at 129 sites for 1960-2010 are examined for the mid-Atlantic region, USA. Temperature anomalies for two periods, 1961-1985 and 1985-2010, relative to the climate normal period of 1971-2000, indicate that the latter period was statistically significantly warmer than the former for both mean AT and WT. Statistically significant temporal trends across the region of 0.023°C per year for AT and 0.028°C per year for WT are detected using simple linear regression. Sensitivity analyses show that the irregularly sampled WT data are appropriate for trend analyses, resulting in conservative estimates of trend magnitude. Relations between 190 landscape factors and significant trends in AT-WT relations are examined using principal components analysis. Measures of major dams and deciduous forest are correlated with WT increasing slower than AT, whereas agriculture in the absence of major dams is correlated with WT increasing faster than AT. Increasing WT trends are detected despite increasing trends in streamflow in the northern part of the study area. Continued warming of contributing streams to Chesapeake Bay likely will result in shifts in distributions of aquatic biota and contribute to worsened eutrophic conditions in the bay and its estuaries.

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Rising air and stream-water temperatures in Chesapeake Bay region, USA

Rice

Jastram

2014

Climatic Change

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“…It is found that freshwater discharge is a major factor in regulating stratification (Boicourt 1992) and is a predictor of the summertime hypoxic volume. High discharge increases stratification and nutrient supply, which enhances primary production (Hagy et al 2004;Murphy et al 2011). The observations showed that the time required for salinity in the upper Bay at latitude 38.4uN to respond to Susquehanna River discharge is about 1 month (Boicourt 1992).…”

Section: Discussionmentioning

confidence: 99%

“…They concluded that the variations in frequency, duration, and severity of hypoxia in Virginia tributaries are related to the net movement of bottom waters controlled by the strength of the gravitational circulation. In Chesapeake Bay, it has been found that freshwater discharge is a major factor in regulating stratification (Boicourt 1992) and is a predictor of summertime hypoxic volume (Hagy et al 2004) due to high nutrient input during spring runoff. In addition to the variation of freshwater, wind variations play a critical role in interannual DO variations in estuaries (Malone et al 1986;Scully 2010).…”

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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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“…It has been reported that hypoxia often causes problems in many eutrophic estuaries and coastal areas (e.g. Borsuk et al 2001;Hagy et al 2004;Gilbert et al 2005). More than 400 hypoxic waters have been reported in many coastal areas, including Baltic Sea, Mexico Bay and various estuaries.…”

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confidence: 99%

Hypoxia Controlled by Hydrodynamics

Kasai¹

2014

Aqua-BioSci. Monogr. (ABSM)

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In summer dissolved oxygen is often depleted in the lower and bottom layers in many coastal basins all over the world. This phenomena is called hypoxia. When the oxygen consumption exceeds oxygen supply, the water becomes hypoxic. The oxygen is consumed by decomposing organic matter by bacteria (biochemical processes), while the oxygen is supplied by physical processes such as convection, advection and diffusion. The primary cause of hypoxia is the consumption of oxygen in the water column, but physical processes mainly control its generation, distribution and configuration. In addition to the vertical supply of oxygen by mixing, horizontal transport by estuarine circulation plays the major role in the formation of hypoxia in regions of freshwater influence. As the hypoxic water contains a lot of nutrients, it plays an important role for primary production, producing middle layer chlorophyll maximum in summer and inducing bloom of phytoplankton in autumn.

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Hypoxia in Chesapeake Bay, 1950–2001: Long-term change in relation to nutrient loading and river flow

Cited by 565 publications

References 41 publications

Rising air and stream-water temperatures in Chesapeake Bay region, USA

Rising air and stream-water temperatures in Chesapeake Bay region, USA

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

Hypoxia Controlled by Hydrodynamics

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