Connections among Land Use, Water Quality, Biodiversity of Aquatic Invertebrates, and Fish Behavior in Amazon Rivers

Amazon rivers host some of the highest biodiversity globally, yet human activities increasingly threaten these ecosystems. The Xingu River, a major Amazon tributary, flows through a region that has historically remained relatively undisturbed. However, recent changes in land use, particularly from mining and livestock farming, have altered water quality and habitat integrity. Prior research has shown that habitat fragmentation can reduce biodiversity and affect aquatic life. Yet, the specific effects of land use changes on river invertebrates and fish behavior remain unclear. This gap motivated the need to study how land use patterns influence water quality and biodiversity in Amazonian rivers. The Xingu River has been preserved compared to the Fresco River, which has experienced significant degradation. This contrast offers a unique opportunity to examine ecological impacts. No prior work had resolved how fish behavior responds to degraded water inputs. This study aimed to address these uncertainties.

The study aimed to evaluate the ecological consequences of land use changes on river systems in the Amazon. Specifically, the researchers compared the preserved Xingu River with the impacted Fresco River to understand how altered land use affects biodiversity and water quality. The primary goal was to assess land use patterns in the Xingu River basin and compare them with those in the Fresco River. A secondary aim was to measure water quality parameters, including turbidity, total solids, and metal concentrations. Another objective was to compare zooplankton biodiversity between the two rivers. The final goal was to evaluate fish avoidance behavior in response to water from each river. By analyzing these factors, the study sought to determine how human activities influence aquatic ecosystems. The focus was on invertebrate biodiversity and fish responses as indicators of environmental health. This approach allowed for a comprehensive assessment of land use impacts on river ecosystems.

The study focused on two rivers—the Xingu and the Fresco—and their confluence. Researchers assessed land use patterns in the hydrographic basin using satellite imagery and historical data. Water quality was measured through field sampling and laboratory analysis of turbidity, total solids, and metal concentrations. Zooplankton biodiversity was evaluated by collecting samples and identifying species down to the family level. Fish avoidance behavior was tested using a multi-compartment system to observe responses to water from each river. The study compared data from three sampling points (P1XR, P2FR, P3XFR) to track changes over time. Historical land use data from 1985 was compared with current data to assess deforestation rates. This approach allowed for a detailed understanding of how human activities affect river ecosystems. The combination of ecological and behavioral assessments provided a holistic view of the study area.

The preserved Xingu River had nearly 300% more invertebrate families than the impacted Fresco River. Fish populations showed a strong preference for Xingu River water, with over 50% avoidance of Fresco River water in behavioral tests. Land use data revealed that forests still dominated the study areas, covering 57.6%, 60.8%, and 63.9% of the total area at P1XR, P2FR, and P3XFR, respectively. However, since 1985, forest cover had decreased by 31.3%, 25.7%, and 27.9% at these points. Water quality measurements showed higher turbidity and total solids in the Fresco River compared to the Xingu River. Metal concentrations, including Cd, Cu, Fe, Mn, Pb, Zn, and Hg, were elevated in the Fresco River. Zooplankton biodiversity was significantly lower in the Fresco River, indicating environmental stress. These findings suggest that land use changes have degraded the Fresco River's ecosystem, impacting biodiversity and fish behavior.

The study found that land use changes in the Fresco River led to reduced invertebrate biodiversity and altered fish behavior. The preserved Xingu River maintained higher biodiversity and better water quality, highlighting the importance of conservation efforts. Fish avoidance of Fresco River water suggests that degraded water quality affects aquatic life. The reduction in forest cover since 1985 indicates ongoing habitat fragmentation. The study supports the idea that anthropic factors, such as mining and livestock farming, negatively impact river ecosystems. The results emphasize the need to protect rivers like the Xingu to maintain biodiversity and ecological health. The observed differences between the two rivers underscore the sensitivity of aquatic systems to environmental changes. These findings align with the authors' hypothesis that land use changes significantly affect river ecosystems.