The leaf breakdown of Picramnia sellowii (Picramniales: Picramniaceae) as index of anthropic disturbances in tropical streams.

M P Lopes,L S Silveira,R G Alves,R T Martins

doi:10.1590/1519-6984.00414

Abstract

There are few studies in tropical regions exploring the use of leaf breakdown process as a functional tool to assess anthropic disturbance on aquatic ecosystems. We assessed the effects of water pollution due to human activities on the leaf breakdown rate of Picramnia sellowii in streams of the southeastern Brazil. The experiment was carried out for 60 days in three reference streams and three streams impaired by organic pollution and absence of riparian vegetation. Three litter bags were incubated in each stream containing 3 ± 0.05 g of P. sellowii leaves. The reference streams presented higher values of dissolved oxygen and lower values of nutrients, turbidity, electrical conductivity, total impermeable area and water temperature. The leaf breakdown rate (k) differed significantly between the reference (k = 0.014 ± 0.003 d-1) and impaired streams (k = 0.005 ± 0.001 d-1). The leaves incubated in the reference streams contained greater fungal biomass (measured as ergosterol concentration) and abundance of invertebrates, as well as greater presence of shredders, with k values being related to the biomass of these organisms. Overall, there were clear differences between the leaf mass loss in the reference and impaired streams. These results reinforce the negative effect of urbanization on leaf breakdown and fungal and shredder biomass.

Highlights

The decomposition of the material from riparian vegetation is an important source of energy for low-order streams (Kominoski and Rosemond, 2011)
The values of electrical conductivity, water temperature, turbidity and NO2 were greater in the impaired streams (p < 0.05), while the dissolved oxygen values were higher in the reference streams (p < 0.05; Table 1)
The reference streams were positively related to axis 1 and were associated with dissolved oxygen and pH, while the impaired streams were negatively related to this axis and directly related to NH4, NO2, NO3, temperature, turbidity, water velocity, electrical conductivity and total impermeable area (TIA) (Figure 2)

Summary

Introduction

The decomposition of the material from riparian vegetation is an important source of energy for low-order streams (Kominoski and Rosemond, 2011). This process is influenced by the interaction of physical, chemical and biological factors (Brum et al, 1999). In tropical regions, shredders generally present low abundance and diversity in comparison with temperate regions. This is probably due to the low leaf quality, characterized high concentrations of lignin and polyphenols (Ligeiro et al, 2010; Boyero et al, 2011). Hyphomycete fungi are mainly responsible for accelerating the detritus degradation, either directly releasing enzymes able to degrade lignin (Fenoglio et al, 2006) or indirectly converting leaf carbon into microbial biomass (Gessner et al, 1999)

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