Autochthonic and allochthonic plant detritus as zoobenthos habitat in anthropogenic woodland ponds

Regardless of origin, all water bodies situated inside forests form a unique habitat for many freshwater animals due to the allochthonous detritus covering the bottom, composed mostly of leaves from waterside trees. For many years these woodland ponds have been considered to be advantageous to regional biodiversity. Investigations were carried out in eight anthropogenic woodland ponds, formed as a consequence of coal mining activities, situated in forest complexes in Upper Silesia (Southern Poland), to evaluate the impact of allochthonic and autochthonic plant detritus on the formation of zoobenthic communities, together with insolation intensity. In sites covered by a layer of allochthonic plant matter, zoobenthos were more abundant compared to places covered by autochthonic detritus. The density of zoobenthos in sun-exposed sites was two to three times greater than in shaded sites.

Association of reduced riparian vegetation cover in agricultural landscapes with coarse detritus dynamics in lowland streams

Studies were conducted on streams flowing through agricultural floodplains in south-eastern Australia to quantify whether reductions in riparian canopy cover were associated with alterations to the input and benthic standing stocks of coarse allochthonous detritus. Comparisons were made among three farmland reaches and three reaches within reserves with intact cover of remnant overstorey trees. Detritus inputs to these reaches were measured monthly over 2 years using litter traps. Direct inputs to streams within the reserves were relatively high (550–617 g ash free dry weight (AFDW) m–2 year–1), but were lower at farmland reaches with the lowest canopy covers (83–117 gAFDW m–2 year–1). Only a minor fraction of the total allochthonous input (<10%) entered any of the study reaches laterally. The mean amounts of benthic detritus were lowest in the most open farmland reaches. Standing stocks of benthic detritus were found to be highly patchy across a large number of agricultural streams, but were consistently very low where the streamside canopy cover was below ~35%. Canopy cover should be restored along cleared agricultural streams because allochthonous detritus is a major source of food and habitat for aquatic ecosystems. Given the absence of pristine lowland streams in south-eastern Australia, those reaches with the most intact remnant overstorey canopies should be used to guide restoration.

Trophic relationships and food webs of the benthic invertebrate fauna of two aseasonal tropical streams on Bougainville Island, Papua New Guinea

ABSTRACTThe trophic ecology of Konaino Creek, a small mountain headwater stream draining rainforest in the aseasonal tropics on Bougainville Island, Papua New Guinea, was examined and a food web was constructed. The major source of energy in Konaiano Creek was allochthonous detritus, most of which had been terrestrially degraded to fine particulate organic matter rather than entering the stream as leaf litter. This fine detritus was collected by the filter-feeders (mostly Simuliidae and also Hydropsychidae) which formed the dominant functional feeding group (64.4% of the fauna). Thus filterers processed most of the allochthonous detritus and made the energy available to other trophic levels, rather than shredders (1.7% of the fauna) which perform this role in temperate headwater streams. Collector-gatherers made up 22.7% of the fauna, carnivorses, mostly Odonata, Decapoda (crabs) and Hydrobiosidae, comprised 2.8% of the fauna and grazer-scrapers made up 7.4%. The latter were inhibited by low instream production owing to heavy shading and the instability and abrasion of the substrate due to frequent spates. In comparison, the trophic ecology of the nearby, coastal, Bovo River (with a catchment mainly in rainforest but mostly cleared with introduced species at the study site) was quite different and it was dominated by collector-gatherers (74%) and grazer-scrapers (15%).

Benthic Bacterial Biomass and Production in Two Blackwater Rivers

Bacterial biomass and production in sediments of two blackwater rivers were measured via epifluorescent direct counts and rate of thymidine incorporation into DNA. Biomass ranged from 3 to 1500 mg C∙m−2 and production ranged from 0.01 to 22.0 mg C∙m−2∙h−1. Both biomass and production were correlated with organic content of the sediment. Neither biomass nor production was related to temperature. Allochthonous detritus apparently serves as a growth substrate for sediment bacteria. Despite differences in water chemistry and flow between the two rivers, comparison of similar sites between rivers showed similar bacterial standing stock and production. During most of the year these fourth- and sixth-order rivers are highly heterotrophic, yet at low water autochthonous carbon may serve as growth substrate for bacteria.