大汶河典型干流段不同水平年溶解氧与氨氮时空分布特征研究OA

To understand the spatiotemporal distribution characteristics of DO and NH3-N in the typical mainstream section of the Dawen River under different level years,this study constructs a hydrodynamic water quality model for the typical river section based on the EFDC model.It quantitatively reveals the spatiotemporal distribution patterns of DO and NH3-N concentrations,and identifies the key pollution periods and river sections.The results show that in a normal year,DO concentration drops to its annual minimum of 5 mg/L in August,while NH3-N reaches its peak of 0.3 mg/L.In a dry year,NH3-N concentration reaches a peak of 0.843 mg/L in March,and decreases significantly with precipitation increased to 42.2 mm in April,while DO concentration remains stable within 7.0-8.6 mg/L.In a wet year,runoff lags behind precipitation by about one month;after precipitation peaks at 228 mm in August,DO drops to its lowest value of 6.3 mg/L in September,while NH3-N increases to its highest value of 0.318 mg/L,showing a negative correlation between the two.Spatially,during the non-flood season,in normal and dry years,DO concentration generally increases from Dawenkou to the estuary,with an increase of about 1.2-1.8 mg/L,while in wet increases from Dawenkou to the estuary,with an increase of about 1.2-1.8 mg/L,while in increases increases from Dawenkou to the estuary,with an increase of about 1.2-1.8 mg/L,while in wet years,DO is concentrated in the Daicun Dam area,with the midstream section being 0.5-0.9 mg/L higher than upstream and downstream sections.During the flood season,in normal years,DO shows a pattern of"Dawenkou>estuary>midstream",while in dry years,concentrations in the Daicun Dam area are 0.4-0.7 mg/L higher than in upstream and downstream sections.NH3-N concentration generally exhibits a decreasing spatial pattern,with reductions of 48%-67%from Dawenkou to the estuary,except during the flood season in wet years when it is enriched in the midstream,exceeding upstream and downstream sections by 0.3-0.5 mg/L.Under the combined influence of natural factors and human activities,water quality in the river reach shows spatial and temporal heterogeneity.The study provides a modeling foundation and scientific basis for formulating effective water pollution control measures and water resource management strategies.