Recovery of organic-enriched sediments through microbial degradation: implications for eutrophic estuaries

Abstract

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 503:41-58 (2014) - DOI: https://doi.org/10.3354/meps10747 Recovery of organic-enriched sediments through microbial degradation: implications for eutrophic estuaries Thomas Valdemarsen1,*, Cintia O. Quintana1,2, Erik Kristensen1, Mogens R. Flindt1 1Institute of Biology, University of Southern Denmark, 5230 Odense M, Denmark 2Institute of Oceanography, University of São Paulo, São Paulo 05508-070, Brazil *Corresponding author: valdemarsen@biology.sdu.dk ABSTRACT: Sediments in eutrophic estuarine ecosystems may become heavily enriched with organic carbon (OC). This OC is primarily of low reactivity and, therefore, has moderate effects on sediment biogeochemical cycling. Nonetheless, OC levels of >1% reduce sediment stability and cause frequent resuspensions and high water turbidity, which affect the recovery of ecosystem functioning. Significant reduction of sediment OC content to <1% is, therefore, needed before ecosystems can fully recover. It was investigated whether organic-rich sediments with 2.5 to 4.4% OC (180–310 mol m–2) from the eutrophic Odense Fjord (Denmark) can recover by microbial degradation. Defaunated sediment cores from various habitats were subjected to long-term (~2 yr) degradation experiments. Total OC content was measured initially and OC degradation was measured regularly from CO2 effluxes and closed anoxic sediment incubations. OC degradation was high initially, but faded exponentially at all stations before stabilizing at 6 to 15 mmol OC m-2 d-1 after 100 to 150 d. Hence, over the 2 yr experiment OC degradation corresponded to only 3 to 5% reduction of initial OC. Temporal degradation patterns analyzed by exponential decay models suggested that sedimentary OC consisted of 2 pools with different reactivity plus a non-reactive pool. OC with the highest turnover (k = 0.5 × 10-2 to 5.5 × 10-2 d-1) was quantitatively the least important (0.3-4.3% of total OC), while OC with lower reactivity (k = 0.1 × 10-3 to 2.0 × 10-3 d-1) constituted a higher proportion (4-58% of total OC in organic-rich sediments). Furthermore, 43 to 95% of sediment OC was non-degradable. Our results suggest that partial recovery (5-57% reduction of initial OC) may occur within 23 to 50 yr. However, complete recovery of organic-rich sediments to <1% OC seems unlikely due to large pools of non-reactive OC. Eutrophication, therefore, leads to irreversible OC accumulation in sediments, which prolongs the recovery time for estuarine ecosystems after reductions in nutrient loading. KEY WORDS: Organic matter · Degradation · Mineralization · Oligotrophication · Recovery time · Exponential decay · G-model Full text in pdf format PreviousNextCite this article as: Valdemarsen T, Quintana CO, Kristensen E, Flindt MR (2014) Recovery of organic-enriched sediments through microbial degradation: implications for eutrophic estuaries. Mar Ecol Prog Ser 503:41-58. https://doi.org/10.3354/meps10747 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 503. Online publication date: April 29, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.