Abstract
Expansion of agriculture is particularly worrying in tropical regions of the world, where native forests have been replaced by croplands and grasslands, with severe consequences for biodiversity conservation and ecosystem functioning. However, limited data exist on the effects of agriculture on the functioning of tropical streams. We conducted a leaf litter decomposition experiment in coarse- and fine-mesh litterbags using the three species of leaves (Eucalyptus globulus [non-native], Vernonia myriantha, and Syzygium cordatum [indigenous]) in three forested and agricultural streams to determine the effect of agriculture on instream leaf litter decomposition in headwater stream sites. We also examined the functional composition of macroinvertebrates in the streams through the contents of benthic kick samples. Agricultural streams had a less dense riparian canopy and smaller abundance of coarse organic particulate matter, and higher electric conductivity and suspended solids than forested streams. In terms of the effects of litter quality on decomposition rates, Vernonia had the fastest decomposition rates while Eucalyptus had the slowest in both forested and agricultural sites. Shredder invertebrates were less abundant in agricultural streams, and in both stream types, they were less diverse and abundant than other functional groups. Overall, leaf litter decomposition rates did not respond to agricultural land-use. The hypothesized negative effects of agriculture on organic matter processing were minimal and likely modulated by intact riparian zones along agricultural streams.
Highlights
Land-use change from native forestry to other uses is a major concern in many parts of the world because of its negative influence on water quality and quantity, biodiversity, and the structure and functioning of streams and rivers (Allan, 2004; Boyero et al, 2016; Masese et al, 2017; Jun et al, 2019)
There were no significant differences in habitat quality variables between forested and agricultural streams, except for the composition of the soft substrate whose percentage coverage of streambed was higher in agricultural streams (Table 1)
Insignificantly different between the two land-uses, mean coarse particulate organic matter (CPOM) standing stocks were higher in forested sites and different fractions of organic matter had higher standing stocks in forested sites
Summary
Land-use change from native forestry to other uses is a major concern in many parts of the world because of its negative influence on water quality and quantity, biodiversity, and the structure and functioning of streams and rivers (Allan, 2004; Boyero et al, 2016; Masese et al, 2017; Jun et al, 2019). Apart from agricultural land-use, plantation forestry is another common practice along riparian zones of streams and rivers. This has often introduced non-native trees with notable effects on aquatic and terrestrial ecosystems (Reinhart and Vandevoort, 2006). Nutrient enrichment and sediments from agricultural lands can stimulate microbial decomposition (Ferreira et al, 2006)Tank et al, 2010 and impair shredder assemblages and their role in leaf litter decomposition (Danger et al, 2012; Woodward et al, 2012; Mustonen et al, 2016), respectively
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