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Kopáček, Jiří; Hejzlar, Josef; Kaňa, Jiří; Porcal, Petr; Klementová, Šárka

Photochemical, Chemical, and Biological Transformations of Dissolved Organic Carbon and Its Effect on Alkalinity Production in Acidified Lakes

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  • Media type: E-Article
  • Title: Photochemical, Chemical, and Biological Transformations of Dissolved Organic Carbon and Its Effect on Alkalinity Production in Acidified Lakes
  • Contributor: Kopáček, Jiří; Hejzlar, Josef; Kaňa, Jiří; Porcal, Petr; Klementová, Šárka
  • imprint: The American Society of Limnology and Oceanography, 2003
  • Published in: Limnology and Oceanography
  • Language: English
  • ISSN: 0024-3590
  • Origination:
  • Footnote:
  • Description: <p>We evaluated the significance of photochemical and biological degradation of allochthonous dissolved organic carbon (DOC) on in-lake H&lt;sup&gt;+&lt;/sup&gt; budgets by laboratory experiments and with a mass budget study for major ions in three atmospherically acidified forest lakes in the Bohemian Forest. In the experiments, photodegradation of DOC from a lake tributary resulted in (1) a liberation of organically bound Al and Fe, which consumed an equivalent amount of H&lt;sup&gt;+&lt;/sup&gt;, (2) a minor decrease in concentrations of organic acid anions (A&lt;sup&gt;-&lt;/sup&gt;) despite a major decrease in DOC concentrations, and (3) the production of biologically available DOC. Biological degradation of the photochemically transformed DOC resulted in a lesser decrease in DOC concentrations than during photodegradation (28-45% of the total decline) but in a pronounced decrease in A&lt;sup&gt;-&lt;/sup&gt; concentrations (64-85% of the total decline), leading to a significant pH increase. Hydrolysis of photoliberated metals under increasing pH partly reduced net H&lt;sup&gt;+&lt;/sup&gt; consumption within the whole process. Watersheds of the lakes studied exported more SO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;2-&lt;/sup&gt;, NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt;, and H&lt;sup&gt;+&lt;/sup&gt; than they received by throughfall, and the lakes were the dominant acidity-consuming parts of the whole ecosystems, neutralizing 50-58% of H&lt;sup&gt;+&lt;/sup&gt; input. In-lake photochemical, biological, and chemical changes in A&lt;sup&gt;-&lt;/sup&gt; fluxes consumed 56-190 meq m&lt;sup&gt;-2&lt;/sup&gt;yr&lt;sup&gt;-1&lt;/sup&gt; of H&lt;sup&gt;+&lt;/sup&gt; and were the third major internal alkalinity-producing mechanism after the biochemical reduction of NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt; and SO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;2-&lt;/sup&gt; (333-396 and 143-214 meq m&lt;sup&gt;-2&lt;/sup&gt;yr&lt;sup&gt;-1&lt;/sup&gt;, respectively). In contrast, the hydrolysis of inorganic Al was the dominant in-lake H&lt;sup&gt;+&lt;/sup&gt;-producing process (144-340 meq m&lt;sup&gt;-2&lt;/sup&gt;yr&lt;sup&gt;-1&lt;/sup&gt;). The in-lake A&lt;sup&gt;-&lt;/sup&gt; removal was positively related to the DOC loading. Consequently, changes in DOC and A&lt;sup&gt;-&lt;/sup&gt; fluxes should not be omitted in alkalinity budgets in lakes with low or no bicarbonate concentration and elevated DOC input.</p>
  • Access State: Open Access