Correlates of Waterbody Characteristics and the Occurrence or Diversity of Larval Amphibians in Central Ontario, Canada.

Watershed acidification and poor water quality can deleteriously affect amphibian populations. Between 1990 and 2008, we sampled 333 small, permanent (inundated year round) waterbodies that drain forested areas in the Algoma, Muskoka and Sudbury regions of central Ontario, Canada to determine whether water chemistry parameters, fish presence, and waterbody area and depth predict amphibian presence or diversity. Amphibians were present in some low-pH waterbodies, contrasting earlier studies, and generally water chemistry was not a strong indicator of amphibian presence or diversity in central Ontario. We suspect that other biotic and abiotic factors have a stronger effect on amphibian presence, and that the relationships between chemical and physical attributes and amphibian presence are complex. Future research should focus on long-term habitat change in central Ontario waterbodies to determine how watershed degradation has affected amphibians.

The widespread threat of calcium decline in fresh waters.

Calcium concentrations are now commonly declining in softwater boreal lakes. Although the mechanisms leading to these declines are generally well known, the consequences for the aquatic biota have not yet been reported. By examining crustacean zooplankton remains preserved in lake sediment cores, we document near extirpations of calcium-rich Daphnia species, which are keystone herbivores in pelagic food webs, concurrent with declining lake-water calcium. A large proportion (62%, 47 to 81% by region) of the Canadian Shield lakes we examined has a calcium concentration approaching or below the threshold at which laboratory Daphnia populations suffer reduced survival and fecundity. The ecological impacts of environmental calcium loss are likely to be both widespread and pronounced.