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Influence of Cadmium and Zinc on Carbon Dioxide Evolution from Litter and Soil from a Black Oak Forest¹

ABSTRACT

Studies have shown that heavy metals can reduce decomposition rates. Since litter decomposition is an essential part of forest mineral cycles, understanding the degree of impact that these substances have on such a key process is important. Two similar black oak forests, East Chicago (impacted) and Willow Slough (background), were chosen as study areas. Microcosms containing litter and mineral soil were collected at each site and returned to the laboratory where comparative measurements of carbon dioxide evolution were taken at 0, 12, 36, and 84 hours, and at 23 days. Measurements indicated a higher decomposition rate for the Willow Slough microcosms (138 mg CO₂/hour per kg at 23 days) compared to the East Chicago microcosms (94 mg CO₂/hour per kg). Additional microcosms from Willow Slough were treated with solutions containing all possible combinations of 0, 0.1, or 10 ppm CdCl₂ and 0, 100, or 1,000 ppm ZnCl₂. Metal concentrations applied were equivalent to litter and soil levels at East Chicago. Statistically significant differences were detected only 36 hours and 23 days after treatment. Reduced respiration rates were associated with high concentrations of CdCl₂/ZnCl₂. Suppression of respiration rates due to osmotic effects of metal salts was rejected after microcosms treated with KCl and CaCl₂ exhibited no change in respiration. While high levels of cadmium and zinc produced reductions in respiration rates compared to controls, low level treatments may have stimulated decomposition slightly.

Key Words: microcosm • litter decomposition • respiration

¹ Contribution from Purdue Univ. Agric. Exp. Stn. J. Pap. no. 6835. Financial support was provided by Natl. Sci. Found. (RANN) Grant GI-35106.

² Associate Professor, Research Associate, and Graduate Research Assistant, respectively, Dep. of For. and Nat. Resour., Purdue Univ., West Lafayette, IN 47907. Second author's present address: Div. of Environ. Planning, Tennessee Valley Auth., Muscle Shoals, AL 35660.

Received for publication May 12, 1977.