Hydrodynamic and Microbial Processes Controlling Nitrate in a Fissured-Porous Karst Aquifer of the Franconian Alb, Southern Germany

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• 作者：Florian Einsiedl ; Bernhard Mayer
• 刊名：Environmental Science & Technology
• 出版年：2006
• 出版时间：November 1, 2006
• 年：2006
• 卷：40
• 期：21
• 页码：6697 - 6702
• 全文大小：115K
• 年卷期：v.40,no.21(November 1, 2006)
• ISSN：1520-5851

文摘

Concentrations and stable isotope compositions of nitratefrom 11 karst springs in the Franconian Alb (SouthernGermany) were determined during low flow and high flowconditions to assess sources and processes affectinggroundwater nitrate. During low flow, nitrate concentrationsin groundwater were around 0.10 mM in springs drainingforested catchments, whereas in agricultural areas nitrateconcentrations were typically higher reaching up to 0.93mM. The isotopic composition of groundwater nitrate duringlow flow (¹⁵N values of -3.1 to 6.7 ”, ¹⁸O values of+2.1 to 4.0 ”) in concert with concentration data suggeststhat nitrate is formed by nitrification in forest andagricultural soils. In addition, synthetic fertilizer N thathas undergone immobilization and subsequent remineralization likely constitutes an additional nitrate source inagriculturally used catchments. During recharge conditions,concentrations and ¹⁵N values of groundwater nitratechanged little, but ¹⁸O values were significantly elevated(up to 24.5”) suggesting that around 25% of the nitratewas directly derived from atmospheric deposition.Groundwater dating revealed that low nitrate concentrationsin groundwater (70 years) are consistent with a mixtureof old low nitrate-containing and young water, thelatter being affected by anthropogenic N inputs predominantlyin the agriculturally used catchment areas during thelast few decades. Thermodynamic and hydrogeologicalevidence also suggests that denitrification may have occurredin the porous rock matrix of the karst aquifer. This studydemonstrates that a combination of hydrodynamic, chemical,and isotopic approaches provides unique insights intothe sources and the biogeochemical history of nitrate inkarst aquifers, and therefore constitutes a valuable tool forassessing the vulnerability of karst aquifers to nitratepollution in dependence on land use and assessing their self-purification capacity.