Carbon dynamics of pristine and hydrologically modified fens in the southern Rocky Mountains

We measured water table levels, above- and below-ground plant production, and CO 2 and CH 4 emissions for five fens in Rocky Mountain National Park, Colorado, to determine whether a water diversion project was adversely affecting carbon cycling. Two fens were located beneath the water diversion, and three fens were located in an adjacent pristine watershed. The diversion lowered water table levels in one fen, while the other fen was not hydrologically modified. Total NPP (net primary production) for all sites ranged from 130 to 316 g C·m –2 ·year –1 , with a mean of 217 g C·m –2 ·year –1 , and belowground NPP accounted for ~60% of the total. Maximum CO 2 emissions for pristine fens ranged between 170 and 273 mg CO 2 -C·m –2 ·h –1 , with annual emissions of 230–388 g CO 2 -C·m –2 ·year –1 . However, the hydrologically modified fen had maximum CO 2 emissions of 457 mg CO 2 -C·m –2 ·h –1 and had an annual flux of 573 g CO 2 -C·m –2 ·year –1 . Maximum CH 4 emissions ranged from 3 to 25 mg CH 4 -C·m –2 ·h –1 , with annual emissions of 9–61 g CH 4 -C·m –2 ·year –1 . The water diversion structure lowered water tables, increased CO 2 , decreased CH 4 and NPP, and resulted in the site likely becoming a net source of carbon.