Retention of Coarse Particulate Organic Matter on the Sediments of Njoro River, Kenya

Abstract

Retention of benthic organic matter (BOM) on the sediment surface of the Njoro River, Kenya was investigated between February 1998 and June 1999 at two sites, differing in channel morphology and riparian vegetation density and composition i.e. open-canopy and closed-canopy sites. Monthly accumulation of benthic organic matter (BOM) was highly variable, ranging from 97.3 to 6691.8 and from 206.6 to 1936.3 g ash free dry weight m -2 (AFDW) with a mean ± CL of 1133.3 ± 794.5 and 834.9 ± 275.8 g AFDW m -2 at the closed and open canopy sites, respectively. Pools retained higher amounts of particulate organic matter than riffles. Surprisingly, differences in retention of BOM at the two sites were not significant. Temporal distribution of benthic organic matter showed no distinct relationship with throughfall and bank runoff input patterns of particulate organic matter. Wood debris comprised 47% and 36% while leaves comprised 34% and 31% of the total BOM at the closed and open canopy sites, respectively; the rest was fruits and fine benthic organic matter (FBOM > 0.1 mm but < 1 mm). Out of 19 plant species recorded at both sites, only 8 species reflected their contribution in BOM with Syzygium cordatum contributing over 80% of the identifiable leaf litter. It is presumed that the variations in spatial and temporal distribution of BOM at the two sites is due to differences in discharge regimes, retention structures and riparian vegetation characteristics.

Dynamics of allochthonous organic matter in a tropical Brazilian headstream

“…Riparian plant species lose their leaves during different periods of the year and riverine characteristics of the studied stretch (bank inclination and stability, soil type, seasonal discharge, etc.) would influence the direction and location where the allochthonous organic matter deposits (Fleituch, 2001, Artmann et al, 2003, Magana and Bretschko, 2003. Our findings also suggested that major stocks of organic matter from soil were transferred to the stream.…”

Particulate Organic Matter (POM) in the Humid and Wet Zones of the Ellegirini River, Kenya

“…Also the bank slope is an important factor influencing the amount of litter in the humid zones (e.g. HILL and BROOKS, 1996;MAGANA and BRETSCHKO, 2003;MOSER, 1994). Although the downstream site has gentle slopes, the amounts of CPOM in the humid zones here were lower than in the upstream site.…”

Litter retention in Tasmanian headwater streams after clear-fell logging

“…A pilot study established the need for longer time scales than those used in the majority of published studies (e.g. Boulton & Boon, 1991;Magana & Bretschko, 2003;Banuelos et al, 2004), with leaves not moving from the upstream pool until after rain. A 4-mm mesh net was anchored to the stream bed at the downstream end of each study reach.…”