Effects of retention site on breakdown of organic matter in a mountain stream

Abstract

Summary Organic matter inputs to streams can be retained in contrasting sites, from small leaf packs on top of cobbles to thick organic deposits trapped by wood jams. Differences in environmental conditions and in stability among sites can affect the biological communities, the quality of organic matter and its use by consumers. We measured the accumulation and composition of coarse organic matter and the breakdown of alder leaves on the surface of the streambed, inside gravel bars and in thick litter deposits trapped by log jams. We also monitored fungal sporulation rates and macroinvertebrate diversity and density in these retention sites. The amount of organic matter in these locations differed significantly among sites and ranged from 118 g m−2 in gravel to 11 562 g m−2 in jams. The biomass of shredders also differed significantly among retention sites, being highest in jams (1440 mg m−2) and lowest in gravel (86 mg m−2). Breakdown of alder leaves in fine‐mesh bags did not differ among retention sites. In coarse‐mesh bags, leaf breakdown rate was significantly lower in gravel bars than in surface sites or jams. Despite large differences in amount and quality of organic matter between surface sites and jams, alder leaves broke down at the same rate. Density of invertebrates in bags and fungal sporulation rates tended to be highest in surface sites and lowest in gravel bars. The contribution of microbes to breakdown was 67% in gravel, 52% in surface and only 28% in jams. Overall, the differences among sites in leaf breakdown were correlated with invertebrate density. Our results showed large differences in the amount and quality of organic matter accumulated, in biological communities and in the use of organic matter among retention sites of a single stream reach. This spatial variability should be taken into account in studies of ecosystem functioning related to organic matter.

Relationships of shredders, leaf processing and organic matter along a canopy cover gradient in tropical streams

“…In general, reference sites exhibit features that match with shredders demands, like litter accumulation and lower temperatures due riparian vegetation presence. Accumulated allochthonous organic matter can provide food for shredders and the positive correlation between these elements is well-established in temperate ecosystems (Richardson, 1992;Wallace et al, 1999;Rowe and Richardson, 2001;González and Graça, 2005;Flores et al, 2013). In this manner, as our studied sites are in the same well-preserved rainforest and accumulated leaves were not restricted to dense riparian covered sites, shredder biomass and abundance seem not restricted as well.…”

“…The stock of litter in streams can often reflect the organic matter input from adjacent vegetation (Bilby and Likens, 1980;Swanson et al, 1982), and exhibit similar patterns (Bambi et al, 2017). However, the presence and persistence of terrestrial material in the streambed is also related to several factors including composition, organization and densities of trees, seasonality and channel morphology (Fleituch, 2001;Gonçalves et al, 2006a;França et al, 2009;Tank et al, 2010;Flores et al, 2013;Lisboa et al, 2015;Bambi et al, 2017). Therefore, even with variation among sites in the degree of canopy cover and leaf input (Tab.…”

Decomposer communities in human‐impacted streams: species dominance rather than richness affects leaf decomposition

“…Additionally, several studies that have used a larger mesh size for the fine‐mesh treatment have reported a potential confounding factor, as these bags are often entered by small‐sized shredders (McKie, Petrin & Malmqvist ; Flores et al . ).…”

In-stream litter decomposition along an altitudinal gradient: does substrate quality matter?

“…The use of coarse and fine bags is recommended by Gessner & Chauvet (2002) and 5 mm and 0.5 mm mesh size bags have been broadly used in decomposition experiments and allows for distinguishing the relative importance and contribution of microbial decomposers from overall decomposition keeping the same environmental conditions (e.g. Flores et al, 2013;Ferreira & Canhoto, 2014;Mariluan et al, 2015). The bags were placed in the streams on November 21, 2011.…”