Base cations concentration, acidic episodes

Base cations are mobilized by weathering and cation exchange reactions that neutralize acids in the watershed. They respond therefore indirectly to changes in sulphate and nitrate concentrations. In fact, if acid anion concentrations (mainly sulphate) decrease, base cations are also expected to decrease. However, in the last few years an increase of the occurrence of alkaline rain episodes (probably due to climatic effects) has been observed and it is likely that calcareous Saharan dust, rich in base cations, is responsible for it [27]. Accelerated weathering, resulting from recent climate warming may also contribute to higher base cation concentrations [28]. 

Figure 10. Temporal patterns in lake-water N03, acid-neutralizing capacity (ANC), base cations (Ca + + Mg2+ + Na+ + K+), S042, and inorganic monomeric aluminum (Al ) at Constable Pond, a long-term monitoring site in the Adirondack Mountains. Trend lines are shown for variables with significant trends (p < 0.10 in seasonal Kendall tau test). Seasonal pattern is typical of Adirondack lakes, with seasonal minima in ANC coincident with seasonal maxima in NOf and Ah. Many Adirondack lakes exhibited upward trends in N03 in the 1980s the primary increase was in episodic N03 concentrations.

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