Assessment of Anthropogenic Impacts on Water Quality and Microbial Communities in the Heilongjiang Maolan Gou National Nature Reserve

Freshwater ecosystems within protected areas play a vital role in maintaining biodiversity and ecological stability, yet they are increasingly threatened by anthropogenic disturbances such as agriculture and tourism. Understanding the impacts of human activities on water quality and microbial community dynamics is essential for the effective conservation and management. This study investigates the spatial variability of water quality and microbial communities across the core, buffer, and experimental zones of the Heilongjiang Maolan Gou National Nature Reserve. Twelve water samples were collected and analyzed for key physicochemical parameters (turbidity, electrical conductivity (EC), chemical oxygen demand (COD), biochemical oxygen demand (BOD), NH₄⁺, PO₄³⁻ and heavy metals). The core zone exhibited excellent water quality with low turbidity (0.4-0.5 NTU), EC (45-130 µS/cm), COD (8-10 mg/L), BOD (1.5-2.2 mg/L). In contrast, the experimental zone showed significant contamination due to agriculture and tourism, with high COD (up to 35 mg/L), BOD (up to 6.5 mg/L), NH₄⁺ (0.18-0.35 mg/L), and PO₄^3- (0.008-0.035 mg/L). Heavy metal concentrations, particularly Cd (up to 0.24 µg/L), were elevated in the experimental zone, correlating with higher Pollution and Water Quality Indices (HPI up to 96.4, WQI up to 61.28). According to standard classifications, HPI values > 100 indicated heavy pollution and WQI scores between 50 and 100 denoted moderate to poor water quality, highlighting degraded conditions in the experimental zone. Microbial analysis revealed distinct community structures across zones, with enhanced pollutant-degrading taxa such as Pseudomonas (noted for aromatic hydrocarbon degradation) and members of Bacteroidota (associated with organic matter breakdown) in the experimental zone. These findings highlight the need for sustainable management to mitigate human impacts and preserve ecological health within the reserve.