A prolonged drought in southeastern Connecticut reduced the stability of microorganisms responsible for a critical step in the nitrogen cycle in a coastal salt marsh, according to research led by a Connecticut College scientist and published in Estuaries and Coasts.
The study was led by Anne Bernhard, professor of biology at Connecticut College. Bernhard and her co-author analyzed microbial communities in a salt marsh at the Barn Island Wildlife Management Area in Stonington, Connecticut, from 2006 to 2019. The period included a severe regional drought from 2013 to 2018.
Researchers measured the abundance of microbial groups involved in nitrogen and carbon cycling. While most groups declined during dry periods, ammonia-oxidizing archaea and ammonia-oxidizing bacteria showed the largest fluctuations.
Archaeal amoA gene abundances were nearly 35 times higher in wet conditions than in dry conditions. Over the course of the study, abundances of ammonia-oxidizing archaea and bacteria varied by as much as 30,000-fold and 9,500-fold, respectively. Both groups showed lower temporal stability during dry conditions compared with other microbes measured.
Nitrification — the conversion of ammonium to nitrate — plays an important role in regulating nitrogen in coastal ecosystems. Salt marshes buffer storm surge, store carbon and provide habitat for fish and shellfish.
After drought conditions eased in 2018 and 2019, abundances of ammonia-oxidizing archaea and bacteria returned to levels more similar to those observed before the drought.
The findings provide long-term, field-based evidence that extended dry conditions can alter the stability of microbial communities central to nitrogen cycling in coastal marshes.
