Study: Ch­e­sa­peake re­silient to pol­lu­tants pass­ing through dam

Baltimore Sun Sunday - - MARYLAND - By Scott Dance

New re­search shows that while stores of sed­i­ments be­hind the Conowingo Dam pose a grow­ing threat to Ch­e­sa­peake Bay health if they get washed out in a ma­jor rain­storm, dur­ing nor­mal Susque­hanna River flows the con­tam­i­nants aren’t hav­ing a large ef­fect on the es­tu­ary.

Look­ing at four decades of data, sci­en­tists at the Univer­sity of Mary­land Cen­ters for En­vi­ron­men­tal Science con­firmed fears that when Susque­hanna wa­ters swell, in­creas­ing amounts of sed­i­ments and nu­tri­ents are flow­ing through the dam and into the up­per Ch­e­sa­peake. They think that’s be­cause so much of the ma­te­rial has built up be­hind the dam, more of it is washed away with the cur­rent, and less gets trapped be­hind the 91-year-old struc­ture.

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But the rest of the time, they found, the po­ten­tial pol­lu­tants are mostly in­ert, get­ting trapped in grass beds at the river’s mouth and set­tling at the river bot­tom. The Ch­e­sa­peake ecosys­tem is re­silient enough to with­stand the or­di­nary flow of con­tam­i­nants, said Cindy Palinkas, lead au­thor of a study pub­lished this week in the journal Es­tu­ar­ies and Coasts.

“There’s al­ways been this idea that sed­i­ment is bad, and there’s go­ing to be all this sed­i­ment go­ing into the bay, and it’s go­ing to kill ev­ery­thing, and I just don’t think that’s true,” Palinkas said.

Still, the data does sup­port fears that a ma­jor storm like Trop­i­cal Storm Lee in 2011 or Hur­ri­cane Agnes in 1972 could send a “cat­a­strophic” amount of pol­lu­tion down the bay.

“None of us know if or when that will hap­pen, so I think the thing is to just keep do­ing the restora­tion work that we’re do­ing, and we give the bay its best chance of deal­ing with an event like that when it comes,” she said.

Sed­i­ment, and the nu­tri­ent par­ti­cles it car­ries, can spoil bay ecol­ogy, block­ing sun­light from reach­ing un­der­wa­ter plants and fu­el­ing mas­sive al­gae blooms that strip oxy­gen from the water when they die.

The Susque­hanna car­ries a heavy in­flu­ence on the bay’s health be­cause it drains more than 40% of the Ch­e­sa­peake wa­ter­shed. Since it was built in 1928, con­nect­ing Har­ford and Ce­cil coun­ties 10 miles north of where the river meets the bay, the Conowingo and other dams up­stream have col­lected much of the pol­lu­tion that washes into wa­ter­ways across much of Penn­syl­va­nia and parts of New York and Mary­land.

The re­search into how that flow of sed­i­ment has changed over time was con­ducted to in­form talks be­tween state en­vi­ron­men­tal of­fi­cials and Conowingo owner Ex­elon Corp. The Mary­land Depart­ment of the En­vi­ron­ment last year de­manded Ex­elon do more to ad­dress Susque­hanna pol­lu­tion, and the com­pany sued; the two sides reached a set­tle­ment last month un­der which Ex­elon says it will spend $200 mil­lion on en­vi­ron­men­tal ini­tia­tives.

Beth McGee, di­rec­tor of science and agri­cul­ture pol­icy for the Ch­e­sa­peake Bay Foun­da­tion, said the find­ings are en­cour­ag­ing and help show that broader ef­forts to re­duce water pol­lu­tion across the bay wa­ter­shed are more im­por­tant than fo­cus­ing on the dam’s role.

“There’s good news that what we’re do­ing up­stream is help­ing,” she said.

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