We tracked carbon (C) and nitrogen (N) uptake into sediments in the presence and absence of benthic macroalgae using dual stable isotope tracers in combination with compound-specific isotope analyses of hydrolyzable amino acids and phospholipid-linked fatty acids to quantify the uptake and retention of C and N within bulk sediments, benthic microalgae (BMA), and heterotrophic bacteria. Stable isotope tracers (as 15NHz 4 and H13CO{3 ) were added to mesocosms either via the surface water or pore water for the first 14 d of the 42-d experiment. Macroalgae and sediments exposed to ambient light and dark cycles rapidly took up label from both sources and retained label for at least 4 weeks after isotope additions ended. BMA dominated sediment uptake of 13C and 15N, initially accounting for 100% of total uptake. Over time, heterotrophic bacterial uptake became relatively more important, increasing from 0% on day 1 to 20–50% on day 42, indicating a close coupling between BMA and bacterial production. In treatments with macroalgae, sediment 13C and 15N uptake was , 40% lower than treatments without macroalgae, likely because of shading of the sediment surface by macroalgae, which decreased BMA production, which in turn decreased bacterial production. Overall, sediments served as a sink for C and N through uptake and retention by the microbial community, but retention was lower in the presence of macroalgae.
Original languageEnglish
Pages (from-to)1489-1503
JournalLimnology and Oceanography
Issue number4
StatePublished - 2011

ID: 299779