Abstract
Significant concern has emerged over the past decades regarding decreases in available base cations (that is, calcium, magnesium, potassium, and sodium) in forest soils and surface waters. Base cations (BCs) are important for buffering against changes in soil and water acidity, and their concentrations can be indicative of environmental management problems such as those linked to acid deposition and land use. Climate variability is also a potentially large factor influencing the dynamics of BCs in soils and surface waters, but our understanding of these interactions at broad scales remains elusive. We used a hierarchical Bayesian model to evaluate the long-term (1990–2010) patterns and drivers of BC concentrations for 60 stream and river monitoring stations across Sweden. Results indicated that the long-term trends in concentration, and the associated environmental drivers, differed among individual BCs and geographical regions. For example, we found that concentrations of Ca2+, Mg2+, K+, and Na+ have decreased in southern Sweden since 1990 and that this is strongly related to concurrent declines in sulfate (SO4 2−) over the same period of record. In contrast, concentrations of Ca2+, Mg2+, K+, and Na+ in northern Sweden did not exhibit significant directional trends, despite declines in SO4 2−, nitrate (NO3 −), and chloride (Cl−) over the same period. Instead, BC dynamics in the north are characterized by inter-annual variability that is most closely linked to climate variables. Results suggest that the interaction between climatic variability and historical acid deposition determines the regional pattern and long-term trends of BC concentrations across streams and rivers of Sweden. Understanding the strength of the interaction between climate features and historic deposition will greatly improve our ability to predict long-term trends of Ca2+, Mg2+, K+, and Na+ and their inter-annual dynamics in the future.
Highlights
IntroductionDecreases in available base cations (that is, calcium, magnesium, potassium, and sodium) in soils and waters have emerged as a significant concern in forest ecology over the past 20–30 years (Adams and others 2000; Berthrong and others 2009)
Decreases in available base cations in soils and waters have emerged as a significant concern in forest ecology over the past 20–30 years (Adams and others 2000; Berthrong and others 2009)
Our analysis indicated that concentrations of Ca2+, Mg2+, K+, and Na+ in southern, and Ca2+ and Mg2+ in central Sweden have declined significantly from their high points in the early 1990s to present day values (Figure 2)
Summary
Decreases in available base cations (that is, calcium, magnesium, potassium, and sodium) in soils and waters have emerged as a significant concern in forest ecology over the past 20–30 years (Adams and others 2000; Berthrong and others 2009). Base cations (BCs) are macrominerals critical for some of the most basic biological processes such as photosynthesis, energy storage, stomatal pore closure, and cell signaling (McLaughlin and Wimmer 1999). These minerals are important for buffering against changes in the acidity of soils and surface waters (Fernandez and others 2003). BCs are transported hydrologically through the soil matrix, accompanying dominant anions to maintain charge neutrality (Folster and Wilander 2002; Finer and others 2004; Molot and Dillon 2008). Because the primary source of BCs to ecosystems is the long-term weathering of parent materials (Sverdrup and Warfvinge 1988; Likens and others 1998), rapid losses of these elements can deplete soil pools and detrimentally affect ecological processes and acid buffering capacity for many years (SanClements et al 2010)
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