Direct and Indirect Effects of Dissolved Organic Matter Source and Concentration on Denitrification in Northern Florida Rivers
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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.
KeywordsDOC light limitation coupled biogeochemical cycles nitrogen cycle primary production browning humic substances
- Barnes RT, Smith RL, Aiken GR. 2012. Linkages between denitrification and dissolved organic matter quality, Boulder Creek watershed, Colorado. J Geophys Res 117:G01014.Google Scholar
- Cohen MJ, Heffernan JB, Albertin A, Martin JB. 2012. Inference of riverine nitrogen processing from longitudinal and diel variation in dual nitrate isotopes. J Geophys Res Biogeosci 117:G01021.Google Scholar
- Hamme RC, Emerson SR. 2004. The solubility of neon, nitrogen and argon in distilled water and seawater. Deep-Sea Res I 51:1517–28.Google Scholar
- McKnight DM, Bencala KE. 1990. The chemistry of iron, aluminum and dissolved organic material in 3 acidic, metal-enriched mountain streams, as controlled by watershed and in-stream processes. Water Resour Res 26:3087–100.Google Scholar
- Mulholland PJ, Helton AM, Poole GC, Hall RO Jr, Hamilton SK, Peterson BJ, Tank JL, Ashkenas LR, Cooper LW, Dahm CN, Dodds WK, Dodds WK, Findlay SEG, Gregory SV, Grimm NB, Johnson SL, McDowell WH, Meyer JL, Valett HM, Webster JR, Arango CP, Beaulieu JJ, Bernot MJ, Burgin AJ, Crenshaw CL, Johnson LT, Niederlehner BR, O’Brien JM, Potter JD, Sheibley RW, Sobota DJ, Thomas SM. 2008. Stream denitrification across biomes and its response to anthropogenic nitrate loading. Nature 452:202–7.PubMedCrossRefGoogle Scholar
- Myers RL, Ewel JJ, Eds. 1990. Ecosystems of Florida. Orlando (FL): First University Press of Florida. 765 p.Google Scholar
- R Development Core Team. 2012. R: A language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing http://www.r-project.org/. Accessed 30 Mar 2013.
- Scott TM, Means GH, Meegan RP, Means RC, Upchurch SB, Copeland JJ, Roberts T, Willet A. 2004. Bulletin No. 66: Springs of Florida. Florida Geological Survey.Google Scholar
- Sterner RW, Elser JJ. 2002. Ecological stoichiometry: the biology of elements from molecules to the biosphere. Princeton (NJ): Princeton University Press. p 439.Google Scholar
- Vitousek PM, Aber JD, Howarth RW, Likens GE, Matson PA, Schindler DW, Schlesinger WH, Tilman DG. 1997. Human alteration of the global nitrogen cycle: sources and consequences. Ecol Appl 7:737–50.Google Scholar