Separating natural acidity from anthropogenic acidification in the spring flood of northern Sweden

• Main Author: Laudon, Hjalmar
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2000
• Subjects: Oceanography; Hydrology; Water Resources; Northern Sweden
• Online Access: https://pub.epsilon.slu.se/11191/; https://pub.epsilon.slu.se/11191/1/laudon_h_140520.pdf

Spring flood is an occasion for transient hydrochemical changes that profoundly effect the biodiversity of the aquatic ecosystem. Spring flood is also very susceptible to anthropogenic acidification. Belief that acid deposition is primarily responsible for pH decline during spring flood has been an important factor in the decision to spend close to one billion Swedish crowns to lime surface waters in northern Sweden during the last decade. The objective of this work is to present an operational tool, the Boreal Dilution Model (BDM), for separating and quantifying the anthropogenic and natural contributions to episodic acidification during spring flood episodes in northern Sweden. The limited data requirements of 10-15 stream water samples before and during spring flood make the BDM suitable for widespread use in environmental monitoring programs. This creates a possibility for distinguishing trends and spatial patterns in the human impact as well as natural pH decline. The results from applying the BDM, and a one point "pBDM" version of the model, in northern Sweden demonstrate that the anthropogenic component associated with spring flood episodes is now generally limited. Instead it is the combination of natural organic acidity and dilution of the buffering capacity that is the major driving mechanism of episodic acidity during spring flood events in the region. While the anthropogenic component of episodic acidification generally contributes 0.1 to 0.3 pH units to the natural pH decline of up to 2.5 pH units, the current regional extent of areas that are severely affected by anthropogenically driven episodes is approximately 6%. Prior to the initiation of the Swedish Environmental Protection Agency's "Episode Project", the limited spring flood data together with lack of a systematic methodology for determining liming candidates forced the liming authorities to base the remediation strategy in northern Sweden on biological indications. But, since there are more reasons why acid sensitive species may be absent or not thriving, including natural acidity, physical habitat degradation, or an earlier period of anthropogenic acidification that ceased many years earlier, biological indicators are not a reliable guide to the contemporary acidification status. Instead hydrochemical models, such as the BDM, are needed.