DNR re­ports bay dead zones smaller than av­er­age

Maryland Independent - - Community Forum - DANDAN ZOU

Dis­solved oxy­gen con­di­tions in Mary­land wa­ters of the Ch­e­sa­peake Bay fared bet­ter than av­er­age in early Au­gust, the Mary­land De­part­ment of Nat­u­ral Re­sources re­ported this week.

Ar­eas with less than 2 mil­ligrams per liter oxy­gen, also known as the hy­poxic wa­ter vol­ume or dead zones, was 0.91 cu­bic miles, con­sid­er­ably smaller than the early Au­gust three-decade-av­er­age of 1.31 cu­bic miles, ac­cord­ing to DNR.

Dead zones are caused by ex­ces­sive nu­tri­ent pol­lu­tion, pri­mar­ily from hu­man ac­tiv­i­ties such as agri­cul­ture and waste­water, ac­cord­ing to the Na­tional Oceanic and At­mo­spheric Ad­min­is­tra­tion.

Ex­ces­sive nu­tri­ents can stim­u­late an over­growth of al­gae, which then sinks and de­com­poses in the wa­ter. That process uses oxy­gen in the wa­ter, leaves ar­eas of wa­ter with low oxy­gen and causes fish and other ma­rine life to die or leave the area.

Crabs, fish, oys­ters and other ma­rine life re­quire oxy­gen to sur­vive with lev­els higher than 5 mil­ligrams per liter to be con­sid­ered op­ti­mal to sup­port aquatic health, ac­cord­ing to DNR.

In a re­lease, DNR at­trib­uted the bet­ter-than-av­er­age re­sults this Au­gust in part to lower-than-av­er­age tem­per­a­tures in the week lead­ing up to the sam­pling.

“Higher tem­per­a­tures gen­er­ally cause more strat­i­fi­ca­tion of the wa­ter col­umn, which in­hibits oxy­gen from mix­ing into deeper wa­ters,” DNR said in a re­lease. “Wa­ters with higher tem­per­a­tures also hold less oxy­gen.”

Ear­lier in June, sci­en­tists had pre­dicted the size of dead zones in Ch­e­sa­peake Bay to be higher than av­er­age this sum­mer due to higher spring flows and ni­tro­gen load­ing from the Susque­hanna River.

The anoxic por­tion of the zone, which con­tains no oxy­gen, was ex­pected to be 0.35 cu­bic miles in early sum­mer, grow­ing to be 0.49 cu­bic miles by late sum­mer in the bay.

In the Au­gust re­port, DNR said no anoxic zones, namely ar­eas with less than 0.2 mil­ligrams per liter oxy­gen, were de­tected in Mary­land’s wa­ters.

Beth McGee, Ch­e­sa­peake Bay Foun­da­tion’s di­rec­tor of sci­ence and agri­cul­tural pol­icy, said in a state­ment the Au­gust re­port is good news be­cause it is an­other sign that shows the Bay may be be­com­ing more re­silient.

“All the cruises this sum­mer have found no anoxic con­di­tions, ar­eas of the bay with vir­tu­ally no oxy­gen,” McGee said. “If the trend con­tin­ues, it will be the third year in a row that sci­en­tists have found no anoxic con­di­tions, some­thing that hasn’t hap­pened since wa­ter qual­ity mon­i­tor­ing be­gan in 1985.”

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