Particulate organic matter in a mountain stream in the south-western Cape, South Africa

Abstract

The quality and quantity of allochthonous inputs and of benthic organic matter were investigated in a secondorder, perennial mountain stream in the south-west Cape, South Africa, between April 1983 and January 1986. Although the endemic, riparian vegetation is sclerophyllous, low and evergreen, inputs of allochthonous detritus to the stream (434 to 500 g m-2y-1) were similar to those recorded for riparian communities worldwide, as were calorific values of these inputs (9548 to 10 032 KJ mm2y-'). Leaf fall of the riparian vegetation is seasonal, occurring in spring (November) as discharge decreases, resulting in retention of benthic organic matter (BOM) on the stream bed during summer and early autumn (maximum 224 g me2). Early winter rains (May) scoured the stream almost clean of benthic detritus (winter minimum 8 g mm2). Therefore, BOM was predictably plentiful for about half of each year and predictably scarce for the other half. Coarse BOM (CBOM) and fine BOM (FBOM) constituted 46 -64% of BOM standing stock, ultra-fine BOM (UBOM) 16 -33 070 and leaf packs 13 -24%. The mean annual calorific value of total BOM standing stock was 1709 KJ me2. Both standing stocks and total calorific values of BOM were lower than those reported for streams in other biogeographical regions. Values of C:N ratios decreased with decrease in BOM particle size with no seasonal trends. The stream is erosive with a poor ability to retain organic detritus. Its character appears to be dictated by abiotic factors, the most important of which is winter spates.

The influence of different litter bag designs on the breakdown of leaf material in a small mountain stream

“…This is illustrated by our results in so far as our two experimental leaf species exhibit very different fragmentation loss rates . The results of King et al (1987) which demonstrated that, in laboratory experiments, Ilex disintegrates easily compared to Cunonia supports this conclusion . Therefore, any future experiments which investigate the breakdown rates of leaves in streams must take care to estimate fragmentation losses ; each leaf species has different fragmentatioǹ qualities' .…”

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

“…PEARSON et al, (1989) collected standing stocks of benthic organic matter ranging between 38 and 184 g dry weight m -2 in Yuccabine Creek, Australia. While highest standing stock of benthic organic matter recorded by KING et al, (1987) ). This is surprising because unlike these rivers, the Njoro River has only a narrow strip of native riparian vegetation of about 20 metres covering either side of the river channel.…”

Seasonal Variability of Particulate Organic Matter in a Mountain Stream in Central Spain

“…Theoretically, SOM concentration is related to discharge and stream power, which is the ability of a stream to entrain suspended material and keep it in transport. Several studies have demonstrated this relationship for storm discharge (GOLLA- DAY et al, 1987;WALLACE et al, 1991;BROOKSHIRE and DWIRE, 2003), but the relationship during baseflow discharge is not as clear (WALLACE et al, 1982;WEBSTER and GOLLADAY, 1984;WEBSTER et al, 1987;VIDAL-ABARCA et al, 2001;ELLIOT et al, 2004). As was the case in some of the studies cited above, Pearson correlation coefficients in the Mediano stream indicated the absence of any significant relationship between discharge and SOM concentration (r = -0.70; p = 0.811).…”