Allochthonous input and retention in a small mountain stream, South Africa

Abstract

Allochthonousinput and benthic coarse particulate organic matter (CPOM) standing stocks were investigated in a first-order stream in South Africa between May 1984 and April 1985. Monthly falls into the stream of all litter types (total) ranged from 11 (September) to 79 g rnM2 (March). Total annual litter fall was 426 g dry weight, which corresponds to 1.2 g m -2 d -'. Flowers, fruits and seeds contributed 37 g me2, woody debris, 122 g rnp2, and leaves 267 g me2 to this total. Leaf fall from native trees, which accounted for approximately 57 y0 of total litter input (244 g m-2 a-' ), was significantly higher in summer than in winter. The summer peak in leaf fall recorded is far smaller and more protracted than the autumnal peak recorded for many Northern Hemisphere streams.Monthly total standing stocks of CPOM ranged from 14 g dry weight me2 in January to 69 g m-2 in August, and a mean total CPOM standing stock of 41 g rnp2 mth-' was estimated. This comprised 18 g m -2 mth -r soft litter, and 23 g m -2 mth -' hard litter. CPOM standing stocks showed no seasonal trends, and with the exception of two species, standing stocks of endemic leaf species reflected their contributions to the total litter fall. Contrary to earlier reports for streams in the Fynbos Biome, Window Stream has CPOM standing stocks well within the ranges reported for low-order streams worldwide.

Uso do alimento por duas espécies simpátricas de Moenkhausia (Characiformes, Characidae) em um riacho da Região Centro-Oeste do Brasil

“…O sombreamento produzido pela vegetação arbórea limita a produção primária e os peixes se tornam dependentes dos recursos provenientes das encostas (LOWE-MCCONNELL, 1999), sendo esse tipo de alimento considerado como o principal recurso energético para habitantes destes ambientes (STEWART & DAVIES, 1990). No riacho Cancela, a elevada contribuição de recursos alóctones na dieta das espécies de Moenkhausia provavelmente está associada à mata ripária moderadamente preservada.…”

Allochthonous matter input in two different stretches of a headstream (Itatinga, São Paulo, Brazil)

“…It is expected that different forest ecosystems from various latitudes present differences in the litter production due to peculiar characteristics of the physical environment and the component plants. In forests from temperate zones, peaks on the litterfall occur in autumn due to the predominance of deciduous trees (Stewart & Davies, 1990;Weigelhofer & Waringer, 1994). In Eucalypt forests and temperate rainforests, the peak of litterfall is observed in the summer (Lake, 1995).…”

“…The litter can either fall to the streams directly from the canopy of the riparian vegetation or can be carried by the rainfall and the wind, providing a terrestrial input of organic matter (De La Rosa, 1995). Some researchers emphasize the role of allochthonous matter as a main resource of energy for the inhabitants of the small streams (Stewart & Davies, 1990). According to the "River Continuum Concept" (Vannotte et al, 1980), modified by Bretschko (1995), the allochthonous contribution is an important organic matter input for the aquatic community, specially in head streams with protected riparian forests.…”

The roles of grass leaf litter in streams draining tussock grassland in New Zealand: retention, food supply and substrate stabilization

“…New Zealand, beech forest stream of 107.6gm"^ in autumn and 269gm"î n winter. In a South African fynbos stream, Stewart & Davies (1990) reported monthly CPOM standing stocks of 15-17gm~^. By comparison, the tussock grassland streams had very low standing stocks (0.17-6.53gm"^).…”