The activity of decomposers (microorganisms and invertebrates) is crucial not only in leaf litter breakdown, but also in indicating ecosystem quality (Ferreira et al. 2021; Brosed et al. 2022). The occurrence (Ferreira et al. 2021), frequency (Rezende et al. 2014a), and distribution (Correa-Araneda et al. 2022) of decomposers organisms can provide essential information about the conservation status of the environment they inhabit (Chauvet et al. 2016; Ferreira et al. 2021; Brosed et al. 2022). Identifying the organisms that make up the decomposer fauna of each environment allows for an understanding of the organic matter dynamics within a particular ecosystem, which can facilitate its management and conservation (Tank et al. 2010; Graça et al. 2015).
One advantage over other methods (e.g. bioindicators based only in invertebrate communities) is that leaf litter breakdown is a continuous process (Ferreira and Graça 2006; Rezende et al. 2019), involving both biotic factors as microorganisms and invertebrates decomposers organisms (Graça 2001; Cararo et al. 2023), and abiotic factors as i) litter species quality (by nutrients and leaf hardness), ii) water chemical (e.g. N, F, temperature, dissolved oxygen and electrical conductivity), and iii) water flow abrasion power (Rezende et al. 2014a). Also, the vegetation surrounding water bodies plays a fundamental role in supplying organic matter to the aquatic system (Bambi et al. 2017), which can undergo anthropogenic alterations due to changes in land use (Bambi et al., 2022; Inhamuns et al., 2021; Brandão et al., 2022).
Several studies have examined the impact of human activities on leaf litter breakdown and invertebrate communities (Chauvet et al. 2016; Ferreira et al. 2021; Brosed et al. 2022). Litter breakdown rates typically show a variable pattern (Hill et al. 2022), accelerating with moderate nutrient input in water (Tagliaferro et al. 2022), remaining neutral (Smith and Chadwick 2014), or decreasing due to the harmful effect of pollutants on decomposer communities (Torres and Ramírez 2014; Classen-Rodríguez et al. 2019; Wymore et al. 2021). Changes in litter breakdown rates may alter trophic relationships in response to the type and intensity of anthropogenic impact (Docile and Rosa 2016).
However, the invertebrate community consistently shows lower diversity in the face of anthropogenic impact (Iñiguez-Armijos et al. 2016; Classen-Rodríguez et al. 2019). In semi-arid regions, information about litter breakdown in aquatic systems is scarce (Rezende et al. 2018). Additionally, due to low water availability in semi-arid areas, many aquatic systems already experiences some form of anthropogenic interference (Barbosa et al. 2012; Taye et al. 2013; Ammar et al. 2016). Moreover, many aquatic systems are perennial or have become intermittent due to human interference (Barbosa et al. 2012), such as the construction of dams, thus altering decomposer communities (Ammar et al. 2016; Rezende et al. 2018).
It is crucial to recognize that urbanization actively contributes to the degradation of aquatic environments (Keinath et al. 2023). Urban land uses can reduce soil permeability (Booth et al. 2004), making water systems more susceptible to the input of heavy metals and domestic effluents (Del Arco et al. 2012; Burdon et al. 2023), thereby altering the physical and chemical properties of the water, including oxygen levels, pH, and electrical conductivity (Del Arco et al. 2012; Akamagwuna et al. 2022; Keinath et al. 2023). As a result, urbanization directly impacts species richness within the ecosystem (Classen-Rodríguez et al. 2019; Keinath et al. 2023), as organisms sensitive to these changes may disappear (Akamagwuna et al. 2022). Since urbanization can lead to changes in water physicochemical properties and invertebrate species diversity (Keinath et al. 2023), mass loss may also vary between more urbanized environments and natural ones (Iñiguez-Armijos et al. 2016; Classen‐Rodríguez et al. 2019).
The present study aims to: i) compare how urbanization and the presence of leaves from five plant species (Erythrina velutina, Anacardium occidentale, Tabebuia aurea, Croton sonderianus, and Hymenaea courbaril) affect leaf litter mass loss and invertebrate communities; and ii) determine whether the city's presence or the type of leaf litter is more influential in driving the leaf litter breakdown process (by mass loss) in a semi-arid river. Notably, that the number of studies in aquatic systems on semi-arid zones is deficient, especially in the Neotropics (Rezende et al. 2018). We base our study on the following premises: i) anthropogenic land uses have a strong negative impact on invertebrate communities (Del Arco et al. 2012; Akamagwuna et al. 2022; Keinath et al. 2023), which consequently affects litter breakdown rates (Classen-Rodríguez et al. 2019; Keinath et al. 2023); and ii) litter breakdown rates result from a combination of biotic and abiotic factors (Graça 2001; Tank et al. 2010), with leaf quality being crucial for the entire decomposer community (Rezende et al. 2019; Cararo et al. 2023). We hypothesize that: i) anthropogenic land uses in urban areas will accelerate leaf mass loss due to nutrient input; but ii) the identity of the leaf litter (higher litter quality) will be more important than the city effect in driving the mass loss process.