IMPACTOS DA INTENSIFICAÇÃO DO USO DO SOLO NA MULTIFUNCIONALIDADE DE RIACHOS INTERMITENTES
Pedro Victor Tavares Firmino da Silva
UFERSA
Rodrigo Fernandes
Eveline de Almeida Ferreira
Eulene Francisco da Silva
Palavras-chave: Eutrofização, Degradação Ambiental, Invasão biológica, Atividades Antrópicas
Resumo
Intermittent streams in the Brazilian semiarid region play a crucial role in maintaining aquatic and terrestrial biodiversity, in addition to performing essential functions such as nutrient cycling, water supply, and supporting primary and secondary production. Despite this, these systems are highly vulnerable to anthropogenic pressures associated with the intensification of land use and occupation, including agricultural expansion, urbanization, and deforestation of riparian vegetation. Given this scenario, understanding how these activities affect the multifunctionality (the ability to maintain multiple functions simultaneously) of streams is essential to inform conservation and sustainable management strategies for these ecosystems. In this study, we investigate the hypothesis that land use intensification negatively affects the multifunctionality of intermittent streams distributed across different land use and land cover classes (forest, agricultural, and urban) in the Apodi-Mossoró River basin. To quantify land use, we calculated the percentages of urban and agricultural areas, considering a circular buffer (500 m radius) around 34 stretches (50 m long) of intermittent streams distributed along a longitudinal gradient. To quantify the local land use intensity level, we calculated the buffer disturbance index (BDI) from the percentages of human activity classes. To quantify local ecosystem multifunctionality, we measured a set of physical, chemical, and ecological variables associated with nutrient cycling (nitrogen, nitrate, and phosphorus concentrations), decomposition (dissolved oxygen and total organic carbon in the sediment), primary productivity (chlorophyll-a concentration), and secondary productivity (benthic community biomass). All ecosystem variables were standardized, and multifunctionality was estimated as the mean value of all local functions. Additionally, we used the mean distance (m) to the nearest spring (DISMEF) as a spatial covariate, since the longitudinal position of the reaches can influence environmental variables and ecosystem functions independently of land use. The results of a multiple linear regression demonstrated a significant positive relationship between BDI and mean multifunctionality values, even after controlling for DISMEF. Contrary to our initial expectations, land use intensification was positively associated with higher mean multifunctionality values. Despite the observed positive relationship, this response reflects dysfunctional multifunctionality, driven by anthropogenic eutrophication processes, evidenced by increased nutrient concentrations, greater phytoplankton biomass (chlorophyll-a), and the expansion of an invasive mollusk species. These changes suggest a replacement of natural functional processes by dynamics dominated by tolerant organisms and exotic species, indicating a loss of resilience and a compromise in the ecological integrity of the systems. These results highlight the need to cautiously interpret multifunctionality in disturbed environments and reinforce the importance of integrating ecological quality metrics into management and conservation strategies for intermittent streams in the semiarid region.