Riparian plant litter is a major energy source for forested streams across the world and its decomposition has repercussions on nutrient cycling, food webs and ecosystem functioning. However, we know little about plant litter dynamics in tropical streams, even though the tropics occupy 40% of the Earth’s land surface. Here we investigated spatial and temporal (along a year cycle) patterns of litter inputs and storage in multiple streams of three tropical biomes in Brazil (Atlantic forest, Amazon forest and Cerrado savanna), predicting major differences among biomes in relation to temperature and precipitation regimes. Precipitation explained most of litter inputs and storage, which were generally higher in more humid biomes (litterfall: 384, 422 and 308 g m−2 y−1, storage: 55, 113 and 38 g m−2, on average in Atlantic forest, Amazon and Cerrado, respectively). Temporal dynamics varied across biomes in relation to precipitation and temperature, with uniform litter inputs but seasonal storage in Atlantic forest streams, seasonal inputs in Amazon and Cerrado streams, and aseasonal storage in Amazon streams. Our findings suggest that litter dynamics vary greatly within the tropics, but point to the major role of precipitation, which contrasts with the main influence of temperature in temperate areas.

Influence of land-use on structural and functional macroinvertebrate composition communities associated on detritus in Subtropical Atlantic Forest streamsInfluência do uso da terra sobre a composição estrutural e funcional da comunidade de macroinvertebrados associados a detritos em riachos subtropicais da Floresta Atlântica Abstract: Aim: Our aim in this study was to evaluate the effects of land use in drainage basins of the streams on the taxonomic and functional composition of aquatic invertebrate communities associated in leaf litter. Methods: We evaluated the colonisation of invertebrates in the incubated plant debris in streams with presence and absence of riparian vegetation and different land-uses in the drainage area. We used the litter bags approach. Results: The taxonomic and functional composition invertebrate associated with leaf litter ranged between streams. In addition, streams with presence of vegetation showed less variation taxonomic and functional composition communities. Still, the density of shredders invertebrates were lower in streams without vegetation. Conclusions: The riparian vegetation is an important environmental factor in the composition of invertebrates. However, the land-use throughout the drainage basin should be considered as relevant factor in structuring aquatic biota.

Metals from agricultural areas are responsible for soil contamination and are carried into aquatic ecosystems. In this context, we evaluated the incorporation of zinc and copper via three feeding strategies (shredding, herbivory and predators) in assemblages of stream insects. We collected aquatic insects in five agricultural streams and five natural streams in Atlantic forest biome to investigate the accumulation of copper and zinc in insects with different feeding strategies. We found no significant differences in the concentrations of copper and zinc between stream types among all insect-feeding groups compared. However, we observed that copper accumulate concentrations differed significantly among the shredders and predators in relation to their resource in streams, while zinc concentrations differed in the two feeding strategy. Therefore, the investigation of the transfer of copper and zinc by different feeding strategies in streams can contribute to the understanding of changes in aquatic insect assemblages related to agricultural activities around streams.

Lotic ecosystems are altered at various spatial scales leading to the simplification of water bodies and the dominance or exclusion of certain organisms. In streams, species may have limitations generated by the environment that result in a more abundant or rare occurrence. Thus, the aim of this study was to evaluate the influence of water physical-chemical variables and land use in the drainage basin on the composition of Ephemeroptera, Plecoptera and Trichoptera (EPT) assemblages in the streams of Atlantic Forest. We collected water samples and aquatic insects from 18 streams in Atlantic Forest in southern Brazil. We evaluated the relationship between physical-chemical variables of water and land use and the dissimilarity of EPT assemblages in three different situations: (i) matrix with all organisms collected, (ii) matrix containing only common genera and (iii) matrix containing only the rare genera. We collected 6 023 EPT larvae from 41 genera; 62 % of the individuals belonged to the order Trichoptera, 32 % to the order Ephemeroptera and 6 % to the order Plecoptera. The most common organisms (10 genera) accounted for 86 % of the total abundance of identified individuals. On the other hand, rare genera corresponded to 76 % of the total richness, but only 6 % of the total abundance. For the three matrices studied, the pH, electrical conductivity and riparian vegetation were correlated with the dissimilarity matrix of the three biological datasets used. In our study, we observed that the pH, electric conductivity, exposed soil and riparian vegetation variables were the most important for the dissimilarity of the EPT assemblages. In addition, our results demonstrated that variables at different scales (stream and riparian zone) structure stream insect assemblages.

ABSTRACT. Streams in urban areas are strongly impacted by the input of organic matter and metals, for instance copper (Cu) and zinc (Zn). These metals are essential for the aquatic biota, but when absorbed in excess they are toxic. In Chiro nomidae larvae, the deleterious effects of heavy metals can be ascertained by analyzing the morphological deformities of the larval mentum, a structure of the oral cavity. In this study, we evaluated I) the bioavailability of Cu and Zn in urban stream sediments and II) the relationship between Cu and Zn concentrations and the incidence of deformities in the mentum of Chironomus larvae. Chironomid flies were collected from four locations in two streams at an urban area in southern Brazil.They were identified and the incidence of deformities in the mentum was quantified. Sediment samples were collected at the same locations where larvae were collected, to quantify the bioavailable fractions of Cu and Zn. The concentrations of Cu in the sediment were similar between the collection sites. However, Zn concentrations varied among sites, being greater in the stretch directly influenced by the input of the organic waste. In total, 2,895 Chironomid larvae were collected. The incidence of deformities in the mentum was above 30% and was correlated with the concentrations of Cu (r = 0.68) and Zn (r = 0.87). This correlation indicates that the municipal waste that is thrown into the city's streams has influenced the occurrence of deformities.

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In this review, we present information about the presence of trace elements on streams and the consequences related to the increase of these chemical elements on aquatic systems. Although several studies on trace elements contamination in aquatic environments are conducted on point sources, non-point sources also have a high potential to contaminate water bodies. Some trace elements are important for the development of an organism. However, even essential elements, in high concentrations, may be toxic to aquatic organisms. In some cases, trace elements may accumulate and be transferred along food webs, generating changes in the structure and functioning of terrestrial ecosystems. The phytoremediation techniques could be an important tool in reducing the problems generated by trace elements. Thus, understanding the effects generated by the increase of trace elements concentrations on aquatic ecosystems becomes important to help public managers to apply solutions for the mitigation of this chemical pollution on natural resources.

A expansão das atividades agrícolas e, consequentemente, o uso de agrotóxicos e fertilizantes contendo metais pesados em sua composição podem afetar negativamente a estrutura das comunidades aquáticas. Diante disso, o objetivo do estudo foi avaliar as concentrações de cobre (Cu), cádmio (Cd) e cromo (Cr) em três níveis da cadeia trófica de invertebrados (i.e. detrito, fragmentadores e predadores). Para tanto, foram coletadas amostras de detritos foliares e insetos fragmentadores e predadores em seis riachos da região Norte do Estado do Rio Grande do Sul. A concentração média de Cu acumulada pelos detritos foi de 0,013±0,001 μg.g-1, enquanto que os predadores e fragmentadores acumularam 0,070±0,018 μg.g-1 e 0,077±0,022 μg.g-1, respectivamente. Para Cr, os fragmentadores apresentaram as maiores concentrações (0,753±0,218 μg.g-1) quando comparados aos predadores (0,583±0,169 μg.g-1) e detrito (0,027±0,002 μg.g-1). Para Cd, as concentrações foram maiores nos fragmentadores (0,056±0,021 μg.g-1) quando comparados aos predadores (0,046±0,025 μg.g-1) e detrito (0,004±0,000 μg.g-1). Concluímos que os insetos aquáticos fragmentadores estão acumulando metais pesados a partir da alimentação por detritos foliares, demonstrando, assim, potencial de acumulação de metais, podendo ser utilizados como bioindicadores da contaminação dos ambientes aquáticos por metais pesados.