Input, transport and storage of organic matter in two south Indian rivers

Abstract

The Achankovil and Pachayar Rivers in south India, the former in the Kerala State and the latter in Tamil Nadu, were studied with the aim of examining downstream patterns in organic matter dynamics and relating them to the predictions of the River Continuum Concept (RCC). Wet- and dry-season estimates of input, movement and storage of organic matter were made at sites on 1st-, 2nd-, 3rd- and 4th-order reaches in each river using comparable methods. Coarse benthic organic matter (CBOM) did not increase regularly from 1st- to 4th-order reaches in Achankovil River but there was evidence for such a downstream trend in Pachayar River. There was a general trend towards less CBOM and more fine benthic organic matter in 4th-order reaches during the dry season. Transported organic matter in the two rivers was dominated by coarse particulate material. The ratio of fine to coarse transported organic matter increased with stream order in both rivers except in 3rd-order reaches. Analysis of the interactions between benthic and transported organic matter indicated that the headwaters of the Achankovil and Pachayar Rivers were more retentive than downstream reaches. While there was concordance between the predictions of the RCC and some of the results of this study, not all of the data followed the expected patterns. Studies of larger Indian rivers and investigation of a wider range of stream types is needed before the RCC can be used as a basis for conservation and management decisions concerning Indian running waters.