Analysis of distribution characteristics and pollution indicators of rural black and odorous water bodies in Anhui Province

To investigate the correlation between characteristics and pollution indicators of rural black and odorous water bodies (BOWBs) in Anhui Province, we analysed the spatial distribution patterns using the Nearest Neighbor Index method and compared the pollution indicators through K-Means clustering analysis, Spearman rank correlation analysis, non-parametric tests and Nemenyi method. Pollution driving factors were examined by Pearson chi-square test. The results indicated that the rural BOWBs in Anhui Province exhibited a clustered distribution pattern, with approximately 90.47% concentrated in Huaibei Plain region. While 62.72 percent of BOWBs had an area of less than 2 000 m², those over 10 000 m² accounted for 60.70 percent of the total BOWBs area. Pits/ponds and ditches were the main types of BOWBs in rural areas, accounting for 61.25% and 36.18% of the total, respectively. The primary pollution characteristics of BOWBs were elevated ammonia nitrogen (NH₃-N) concentrations coupled with depressed dissolved oxygen (DO) levels. Population size demonstrated a negative correlation with transparency (r=−0.083, P<0.01) in BOWBs, and a positive correlation with NH₃-N concentrations (r=0.071, P<0.01). The area of BOWBs showed a positive correlation with DO concentrations (r= 0.172, P<0.01) and a positive correlation with NH₃-N levels (r= 0.052, P<0.05). Transparency exhibited negative correlations with DO concentrations (r=−0.199, P<0.01) and NH₃-N levels (r=−0.192, P<0.01), respectively, in BOWBs. Transparency, DO concentrations, and NH₃-N levels showed significant differences among water body types (P<0.01). Pond-type and river-type water bodies exhibited statistically distinct patterns in both transparency and DO concentrations (P<0.01). Pits/ponds were primarily polluted by external sources, accounting for 66.95%, while mixed-source pollution was dominant in both ditch-type and river-type water bodies, constituting 56.49% and 58.06%, respectively. As black and odorous water bodies (BOWBs) expanded in area, the dominant pollution sources shifted progressively from predominantly exogenous inputs to mixed-source contributions. Rural domestic sewage constituted the primary driver of BOWBs, with 97.65% of these water bodies linked to this contamination source. Governance should target clustered regions, prioritizing source control and pollution interception, coordinated with sediment dredging and resource-recovery disposal of agricultural waste. Establishing public participation platforms and third-party evaluation mechanisms is critical to ensure sustainable remediation outcomes.