Natural variability in lake pH on seasonal, interannual and decadal time scales: Implications for assessment of human impact

Abstract

Reference values define the natural state with respect to environmental stressors and are commonly used for assessments of ecological impacts and to set restoration targets. These reference values are often treated as constants, whereas in reality they can be highly variable. Here, we study the significance of this variability for assessments of human impact on the environment, by using almost two decades of observations from 95 acid-sensitive Swedish lakes. Our approach was to first estimate the preindustrial, steady-state reference level of acid neutralization capacity (ANC) for each lake with the hydro-geochemical model MAGIC. Then the variability in pH around this "baseline" was reconstructed from the contemporary, "natural" variability in the ANC, total organic carbon (TOC) and Al-concentrations, and partial CO(2) pressure. The variability in reference pH was then examined for the period 1990-2004, on seasonal (single measurements), interannual (1-year median), and decadal (5-year median) scales. On the seasonal scale, the variability in reference pH ranged between 0.40 and 1.7. The range on the interannual time scale was up to 1.3 units and for the decadal scale up to 0.76 units. Since an anthropogenic pH decline of more than 0.4 units is deemed significant according to the Swedish Environmental Quality Criteria, this natural variability clearly needs to be accounted for when assessing acidification.

Published in

Environmental Science and Technology
2008, volume: 42, number: 15, pages: 5594-5599
Publisher: AMER CHEMICAL SOC

SLU Authors

• Erlandsson, Martin

  • Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences
    

• Fölster, Jens

  • Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences
    

• Laudon, Hjalmar

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

• Weyhenmeyer, Gesa

  • Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences
    

• Bishop, Kevin

  • Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences
    

Associated SLU-program

Acidification
Climate
Lakes and watercourses

Global goals (SDG)

SDG6 Clean water and sanitation

UKÄ Subject classification

Fish and Aquacultural Science
Forest Science
Environmental Sciences and Nature Conservation

Publication identifier

• DOI: https://doi.org/10.1021/es8005157

Permanent link to this page (URI)

https://res.slu.se/id/publ/18603