Atmospheric acidic deposition introduces hydrogen ions to terrestrial and aquatic ecosystems, which become partially neutralized by chemical weathering. In the southern Alps of Switzerland, small catchments containing little or no soil and lacking carbonate minerals represent sensitive hydrological settings in which the relationship between alteration of granitic gneiss by acid deposition and the resulting composition of lake waters can be studied. Transmission and scanning electron microscopy, coupled with X-ray powder diffraction of lake sediments from such areas showed mainly unaltered minerals from parent rocks and no secondary silicate minerals. Element mapping indicated noncrystalline aluminum hydroxide as a product of the chemical weathering of silicates. Noncrystalline iron hydroxide was also observed. Mass balance calculations and the stoichiometry of suitable chemical reactions representing the weathering processes were used to derive a plausible reaction sequence on the interaction of the predominant reactive rock minerals with acid precipitation that accounted for the measured chemical composition of the acid lakes.

The Singapore freshwater crab Johora singaporensis is known only from three streams in Singapore and is among the top 100 most threatened species in the world. It is the only member of the genus Johora, endemic to the Malay Peninsula, to be categorized as Critically Endangered on the IUCN Red List. Extensive surveys conducted over 1 year to determine the extent of the species’ distribution revealed that the population has declined significantly at its type locality in Bukit Timah Nature Reserve, Singapore Island's oldest protected forest area. The species remains extant in two unprotected streams in Bukit Batok and Bukit Gombak, which are located outside the nature reserve. Acidification of streams as a result of acid precipitation may be a factor in the decline of the species. If so, this will be the first documented instance of a species being affected negatively by anthropogenic acidification of a tropical freshwater system. The occurrence of this threatened species in a protected area has not, therefore, guaranteed its survival. There is a need for long-term and continuous monitoring of species of high conservation value, together with other measures that focus on habitat protection. Conservation efforts by the National Parks Board of Singapore in collaboration with other government agencies are ongoing in an effort to ensure the survival of this important species.