Temperature effects on potassium-calcium exchange and selectivity in selected soils, clay minerals, and cation exchange resins

Abstract

Leaf processing in the New River proceeds at rates approximately equivalent to those of small streams. The initial stages of New River leaf processing are mediated by microorganisms and enhanced by mechanical fragmentation, but macroinvertebrates, important to initial processing in small streams, are unimportant in the section of the New River studied. Four leaf species common to the New River Valley were selected for study: American sycamore (Platanus occidentalis), box elder (Acer negundo), sugar maple (Acer saccharum), and dogwood (Cornus florida). Chemical constituent analyses of leaves prior to river incubation showed that leaf fiber and lignin content was highest in sycamore, least in dogwood, and intermediate to sycamore and dogwood in sugar maple. Box elder and sycamore have similar high fiber contents, but box elder contain less lignin than sycamore. Box elder and sycamore were incubated concurrently for 4 and 8 week periods, respectively, over the entire study, but dogwood and sugar maple were only incubated for 4 week periods during the winter. Of the four species tested, box elder leaves were processed at the fastest rates. Processing rates for box elder, sugar maple, and dogwood were three to six times faster than processing rates for sycamore during simultaneous incubations. Differences in processing rates among the species tested were due to differences in the initial proportions of leaf chemical constituents and the rapidity of chemical constituent losses during incubation. Microbial presence (numbers, biomass) and activity (respiration, cellulase activity) were greater on faster decomposing leaves (box elder, sugar maple, and dogwood) than on sycamore. Observed differences in microbial colonization and activity were apparently due to the faster decomposing leaves being favored as nutritional substrates. Seasonal reductions in chemical constituent losses, microbial activity, and leaf processing speed occurred during winter incubations. As New River temperature increased during the spring (March), leaf chemical losses, microbial activity, and processing rates gradually increased, suggesting that seasonal temperature changes governed all processing mechanisms studied. The effect of thermal perturbation from a power plant on leaf processing in the New River was significant. Processing rates for faster decomposing species incubated in the thermal discharge were two to three times those of reference samples. While thermal perturbation enhanced sycamore leaf decomposition, processing rate increases were not as dramatic as those noted for the faster decomposing species under thermal stress. Leaf chemical constituents were more rapidly mobilized from the faster decomposing species than from sycamore in the thermal discharge. Microbial presence and activity were enhanced in the thermal discharge to the point that leaf processing and microbial activity dimunitions during winter at the reference station were obliterated in the thermal discharge. Faster decomposition at the thermally stressed station resulted in processing rates during January and February being similar to those observed at the reference station during October and November. Although a relatively minor perturbational sress of the New River was examined, the induction of rapid leaf decomposition could have more drastic effects on other aquatic systems receiving a greater thermal perturbation.