Comparison of dissolved organic carbon bioavailability from native and invasive vegetation along the Wailuku River, Hawai'i

Riparian litterfall comprises a large fraction of the dissolved organic carbon (DOC) load in rivers. Shifts in riparian vegetation species composition should affect riverine DOC bioavailability. This study compared the bioavailability of DOC derived from several species of native riparian trees to that of invasive riparian trees. Dark bioassays were conducted using both freshwater and estuarine bacteria from the Wailuku River, Hawai'i. DOC bioavailability was similar among all vegetation types in fresh and estuarine waters. In contrast, DOC bioavailability was higher for treatments receiving vegetation derived DOC (52% +/- 4) versus the DOC present in the river (14% +/- 3). Combining DOC bioavailability data with leaf litter inputs suggests that the replacement of native M. polymorpha by the invasive F. moluccana increases the amount of bioavailable DOC entering Hawaiian rivers and streams via leaf litter. This has the potential to impact the metabolism and food webs of downstream ecosystems.