丹江口水库消落区农业种植对库湾水质的影响评估OA

[Objective]Danjiangkou Reservoir is the core water source of China's South-to-North Water Diversion Middle Route Project,with a 378.82 km2 water-level-fluctuation zone(WLFZ)where agricultural planting covers 45.39％of the 158-170 m area,threatening adjacent reservoir bay water quality.Existing studies lack clarity on re-gion-specific planting impacts and risks from pathways like rainfall runoff and submergence.This study aimed to:(1)quantify total nitrogen(TN)and total phosphorus(TP)changes in soils and bay waters before/after planting and rainfall;(2)measure TN/TP release rates from soils under submergence via simulations;(3)provide targeted support for WLFZ water quality protection.[Methods]A total of 10 topsoil samples(0-15 cm)and 9 bay water samples(0.5 m below surface)were collected during pre-planting(Sept.6-7,2024),post-planting/pre-rainfall(Oct.22-23,2024),and post-planting/post-rainfall(Nov.16-17,2024).Soil TN/TP and water quality indica-tors were tested following national standards.Static immersion experiments used soil columns(5 cm height)with 2 L reservoir water,sampling every other day until concentration stabilization.[Results](1)Soil TN concentrations rose by 159-890 mg/kg,with the mean value increasing from 790 mg/kg(pre-planting,mostly Grade Ⅴ-Ⅵ,low nutrient level)to 1 246 mg/kg(post-planting,mostly Grade Ⅲ-Ⅳ,medium level).Soil TP concentrations in-creased by 46-546 mg/kg,with the mean rising from 608 mg/kg(pre-planting)to 669 mg/kg(post-planting);only unfertilized sites showed no increase or a decrease.After rainfall,soil TN decreased by an average of 266 mg/kg(range:80-698 mg/kg),with the largest drop(698 mg/kg)in Shengwan Town.Soil TP decreased by an av-erage of 149 mg/kg(range:58-332 mg/kg),with the largest decline(332 mg/kg)in Jiuchong Town.(2)Rain-fall led to significant water quality deterioration:the proportion of Ⅰ-Ⅱ class water(per GB3838-2002)dropped from 88.81％(pre-rainfall)to 33.33％(post-rainfall).Water TN increased by an average of 14％(range:0.07-0.47 mg/L).Water TP surged by an average of 255％(range:0.01-0.10 mg/L).This indicated that TP(domi-nated by particulate phosphorus)was more vulnerable to rainfall erosion than TN.(3)Planting significantly en-hanced TN and TP release from soils.Annual TN release rates increased by 65％-386％:from 16.1 mg/(m2·d)to 26.62 mg/(m2·d)(Jiuchong Town D2-166),16.77 mg/(m2·d)to 81.51 mg/(m2·d)(Xianghua Town D1-166),and 7.36 mg/(m2·d)to 33.1 mg/(m2·d)(Cangfang Town D3-163).Annual TP release rates in-creased by 6％-232％:from 3.59 mg/(m2·d)to 3.79 mg/(m2·d)(Jiuchong Town D2-166),0.38 mg/(m2·d)to 1.26 mg/(m2·d)(Xianghua Town D1-166),and 0.48 mg/(m2·d)to 1.10 mg/(m2·d)(Cangfang Town D3-163).Nutrient release followed a consistent pattern:rapid release in the early stage and gradual stabiliza-tion later,though release amounts varied significantly across different planting sites.[Conclusion]This study inno-vatively clarifies region-specific pollution risks and nutrient release of agricultural planting in the Danjiangkou Res-ervoir WLFZ.Agricultural planting increases soil TN/TP accumulation,while rainfall runoff and submergence ac-celerate their migration to water bodies—with TP more susceptible to rainfall erosion.The marked rise in nutrient release rates post-planting elevates water quality risks during WLFZ submergence.Targeted recommendations in-clude:(1)strengthening intensive water quality monitoring in high-risk bays(Xianghua,Shengwan,Jiuchong Towns)during peak planting seasons(April-May,October-November);(2)implementing strict fertilizer controls and regular inspections in these key regions;(3)prioritizing measures to reduce particulate phosphorus loss and mitigate eutrophication.These findings fill gaps in region-and pathway-specific pollution risk assessments and pro-vide critical support for safeguarding the South-to-North Water Diversion Project's water quality.