Ecosystems

, Volume 17, Issue 1, pp 14–28

Direct and Indirect Effects of Dissolved Organic Matter Source and Concentration on Denitrification in Northern Florida Rivers

Article

DOI: 10.1007/s10021-013-9705-9

Cite this article as:
Fork, M.L. & Heffernan, J.B. Ecosystems (2014) 17: 14. doi:10.1007/s10021-013-9705-9

Abstract

Using a natural gradient of dissolved organic carbon (DOC) source and concentration in rivers of northern Florida, we investigated how terrestrially-derived DOC affects denitrification rates in river sediments. Specifically, we examined if the higher concentrations of DOC in blackwater rivers stimulate denitrification, or whether such terrestrially-derived DOC supports lower denitrification rates because (1) it is less labile than DOC from aquatic primary production; whether (2) terrestrial DOC directly inhibits denitrification via biochemical mechanisms; and/or whether (3) terrestrial DOC indirectly inhibits denitrification via reduced light availability to—and thus DOC exudation by—aquatic primary producers. We differentiated among these mechanisms using laboratory denitrification assays that subjected river sediments to factorial amendments of NO3 and dextrose, humic acid dosing, and cross-incubations of sediments and water from different river sources. DOC from terrestrial sources neither depressed nor stimulated denitrification rates, indicating low lability of this DOC but no direct inhibition; humic acid additions similarly did not affect denitrification rates. However, responses to addition of labile C increased with long-term average DOC concentration, which supports the hypothesis that terrestrial DOC indirectly inhibits denitrification via decreased autochthonous production. Observed and future changes in DOC concentration may therefore reduce the ability of inland waterways to remove reactive nitrogen.

Keywords

DOC light limitation coupled biogeochemical cycles nitrogen cycle primary production browning humic substances 

Supplementary material

10021_2013_9705_MOESM1_ESM.docx (56 kb)
Supplementary material 1 (DOCX 56 kb)

Copyright information

© Springer Science+Business Media New York 2013

Authors and Affiliations

  1. 1.Department of Biological SciencesFlorida International UniversityMiamiUSA
  2. 2.Nicholas School of EnvironmentDuke UniversityDurhamUSA

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