Impactos do descarte de efluentes da carcinicultura nas frações da matéria orgânica de solos de manguezais do semiárido

Abstract

Mangroves are highly important ecosystems and play a fundamental role in mitigating climate change, mainly due to their capacity to sequester carbon (C). However, the expansion of shrimp farming in estuarine areas has promoted significant changes in soil physicochemical conditions, with potential impacts on the dynamics and stability of organic matter. Therefore, this study aimed to evaluate the effects of shrimp farming effluent discharge in three impacted areas, in comparison with non-impacted sections of the same sites. Soils were analyzed to quantify total organic carbon (TOC), particulate organic carbon (POC), and mineral-associated organic carbon (MAOC), as well as to characterize the chemical composition of organic matter using diffuse reflectance infrared Fourier transform spectroscopy (FTIR-DRIFT). Recalcitrance indices and multivariate analyses were used to integrate the results and identify the main factors associated with the observed changes. The results indicate that impacted areas present lower TOC contents (21.66 g kg⁻¹) compared to non-impacted areas (23.16 g kg⁻¹), suggesting that the input of organic material and nutrients from shrimp farming enhances organic matter decomposition. However, a higher accumulation of particulate organic carbon was observed in impacted areas, especially in surface layers, confirming the input of recent and labile material. FTIR-DRIFT analyses revealed a reduction in aliphatic compounds and polysaccharides and a relative increase in aromatic and carbonyl groups, indicating faster degradation processes in impacted areas. Recalcitrance indices indicated lower carbon stability in impacted areas compared to non-impacted ones, with mean values for all combined fractions of 57.49% and 59.74%, respectively, confirming the intensification of mineralization processes associated with increased soil redox potential. It is concluded that shrimp farming alters the distribution and quality of soil organic matter in mangroves, promoting an increase in the labile carbon fraction without favoring its long-term stabilization in the soil. These results demonstrate that impacted mangroves are less efficient as carbon sinks, highlighting the need for management practices that consider not only carbon stocks but also soil conservation and ecosystem preservation.