Car­bon from ponds

The Star Malaysia - Star2 - - ECOWATCH - By JIM SHEL­TON

TINY ponds play a dis­pro­por­tion­ately large role in global green­house gas emis­sions from in­land wa­ters. Al­though ponds less than a quar­ter of an acre in size make up only 8.6% of the sur­face area of the world’s lakes and ponds, they ac­count for 15.1% of car­bon diox­ide ( CO2) emis­sions and 40.6% of dif­fu­sive methane emis­sions. The find­ings by Yale Univer­sity’s School of Forestry and En­vi­ron­men­tal Stud­ies was re­cently pub­lished in jour­nal Na­ture Geo­science.

“Our study is the first to in­clude th­ese small ponds in global es­ti­mates of CO2 and methane emis­sions, largely be­cause they are dif­fi­cult to map and were thought to play a small role in car­bon cy­cling,” said study lead au­thor and doc­toral stu­dent Mered­ith Hol­ger­son.

Hol­ger­son and co- au­thor Peter Ray­mond, pro­fes­sor of ecosys­tem ecol­ogy, con­ducted their anal­y­sis by com­bin­ing re­cent es­ti­mates on the global num­ber of lakes and ponds with a com­pi­la­tion of di­rect mea­sure­ments of CO2 and methane con­cen­tra­tions from 427 lakes and ponds. They found that con­cen­tra­tions were great­est in smaller ponds and de­creased as the ponds and lakes grew larger.

The rea­son has to do with the phys­i­cal make- up of very small ponds and the way they cy­cle car­bon. Small ponds have a high perime­ter- to- sur­face- area ra­tio, for ex­am­ple, and ac­cu­mu­late a higher load of ter­res­trial car­bon from leaf lit­ter, sed­i­ment par­ti­cles and other ma­te­rial. Small ponds also tend to be shal­low, which means their ter- re­s­trial car­bon loads are highly con­cen­trated com­pared to larger lakes. Lastly, gases pro­duced at the bot­tom of th­ese ponds are able to reach the top more of­ten than what oc­curs in larger lakes, due to greater wa­ter mix­ing and shal­lower wa­ters. Be­cause of this, CO2 and methane gen­er­ated in sed­i­ments af­fects the en­tire pond.

“That makes small ponds an im­por­tant player in the car­bon cy­cle,” Hol­ger­son said.

The find­ings war­rant ad­di­tional re­search to more ac­cu­rately es­ti­mate the num­ber of tiny ponds around the world, she added. Such spots don’t typ­i­cally show up on satel­lite im­ages, but they can be mapped us­ing aerial im­ages and LiDAR, a re­mote sens­ing tech­nol­ogy that uses re­flected laser light. – Yale Univer­sity

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