Proximity to research centers, fluvial accessibility, and dams presence drive sampling efforts for phytoplankton, zooplankton, and macrophytes in freshwater ecosystems

Abstract

Understanding biodiversity and monitoring ecosystems require robust sampling efforts for important bioindicators like phytoplankton, zooplankton, and aquatic macrophytes. This study quantified sampling efforts for these aquatic groups across the Tocantins-Araguaia Basin in Central Brazil, evaluating the influence of geographic and environmental factors such as human development, fluvial and terrestrial accessibility, elevation variation, and proximity to protected areas and research centers. These variables align with the appeal and accessibility hypotheses, which help explain sampling patterns observed across regions. A systematic review compiled 2,307 unique field collection records, allowing analysis of spatial and temporal sampling patterns. The sampling effort was quantified based on geographic coordinates per grid cell, with predictors analyzed using generalized linear mixed models. Results showed sampling was concentrated in the central-southern region, with phytoplankton covering 28.83% of the area, macrophytes 16.13%, and zooplankton 11.9%. Key drivers of sampling effort included proximity to research centers, dam presence, and fluvial accessibility. Additionally, protected areas and human development influenced sampling effort for specific biological groups. Despite these efforts, vast regions, especially in the northern Araguaia River, remain under-sampled, highlighting the need for comprehensive long-term sampling strategies to address critical biodiversity knowledge gaps.