Regional levels of high acidity in ponds and lakes are the result of wide-scale acid rain in the northeastern United States (Mason 1992, Likens 1996). Rain and snow in this region has had an annual pH of 4.05 and 4.3 since 1963 (Likens 1996), resulting in acidic ponds in areas such as the Black Rock Forest. This research examines the effects of acidification on populations of painted turtles (Chrysemys picta) and snapping turtles (Chelydra serpentina), in five different ponds of varying pH levels at Black Rock Forest, in New York State. Turtle foraging behavior, combined with sensitive hatching development and a long life span, make them particularly vulnerable to habitat quality (McKnight 1993).
From June 5, 1997 to August 6, 1997, two types of data were gathered and correlated: data on pond chemistry, and data on turtle populations. Pond chemistry analysis includes dissolved oxygen and pH measurements, inorganic ion concentration and chlorophyll analysis. Results from the pond chemistry data confirm distinct differences in water habitat quality between the five ponds.
Turtles were trapped with funnel turtle traps, using two methods of marking. Electronic PIT tags (Camper 1988), were used for permanent marking of individuals, and shell notching (Cagle 1939), was used for short term identification and for juveniles. Blood samples were taken, and shell notches preserved, for future molecular genetic analysis. Data on sex, age, and size of turtles was recorded.
Turtle populations were estimated from mark-recapture data using both simple graph analysis, and the Petersen-Lincoln estimator (White 1982), assuming closed populations. Abundance estimates were weakly correlated with pond chemistry data: highly acidic ponds have lower turtle populations than more neutral habitats. Analysis of sex ratio data and age structure in each pond correlated further: ponds of high acidity and low turtle populations tended to have skewed sex ratios and age structures, indicating a less robust breeding population. Knowledge gained will aid Black Rock Forest in creating and maintaining stable pond habitats necessary to support turtle populations.
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Last updated: 8 January 2001, KAK.