Long-term trends in water chemistry of acid-sensitive Swedish lakes show slow recovery from historic acidification

Abstract

Long-term (1987–2012) water quality monitoring in 36 acid-sensitive Swedish lakes shows slow recovery from historic acidification. Overall, strong acid anion concentrations declined, primarily as a result of declines in sulfate. Chloride is now the dominant anion in many acid-sensitive lakes. Base cation concentrations have declined less rapidly than strong acid anion concentrations, leading to an increase in charge balance acid neutralizing capacity. In many lakes, modeled organic acidity is now approximately equal to inorganic acidity. The observed trends in water chemistry suggest lakes may not return to reference conditions. Despite declines in acid deposition, many of these lakes are still acidified. Base cation concentrations continue to decline and alkalinity shows only small increases. A changing climate may further delay recovery by increasing dissolved organic carbon concentrations and sea-salt episodes. More intensive forest harvesting may also hamper recovery by reducing the supply of soil base cations.

No long‐term trends in pCO2 despite increasing organic carbon concentrations in boreal lakes, streams, and rivers

“…Both DOC and p CO 2 are highly sensitive to acidification‐induced changes in ionic strength of soils [ Evans et al ., ; Lozanovska et al ., ]. In Sweden, recovery from acidification is also apparent, seen by decreasing SO 4 2− concentrations in waters [ Weyhenmeyer , ] and increasing alkalinity [ Futter et al ., ]. However, during the past years recovery from acidification has leveled out and instead climate change effects, in particular precipitation and runoff changes, seem to drive DOC concentration increases [ Weyhenmeyer et al ., ].…”

Species-specific roles of sulfolipid metabolism in acclimation of photosynthetic microbes to sulfur-starvation stress

“…Distinct from phosphate, sulfate, the preferred S-source for photosynthetic microbes, however shows extremely uneven distribution in aquatic habitats (reviewed in [15]): although the oceans typically contain sulfate at around 29 mM, i.e., supra-optimal concentrations for photosynthetic microbes, freshwater environments were highly variable in sulfate concentration such that lake sulfate ranged from as low as 10 to 1000 μM, dependent on the level of industrialization around the surrounding regions. Industrial emission of SO 2 into the atmosphere could elevate the sulfate content of freshwater environments, which have however been decreased with the enforcement of legislations that limit SO 2 emission in North America and Europe [16–18]. Therefore, there might be a growing trend that photosynthetic microbes in freshwater face S-deficiency.…”

Simple Models to Estimate Historical and Recent Changes of Total Organic Carbon Concentrations in Lakes

“…Based on VNIRS-TOC reconstruction and an independent validation dataset, it can be seen that surface water TOC concentrations have recovered back to reference condition levels just in a few decades (Figure 6). The recovery of TOC to reference condition levels is an anomaly compared to other water chemistry parameters that were affected by 55 Further work is needed to see if surface water TOC concentrations have returned to reference condition values in other regions that have experienced increases in surface water TOC over the last three decades. These results provide valuable information for future surface water management in Sweden and elsewhere.…”