RESUMEN
Watershed water quality modeling is a valuable tool for managing ammonium (NH4+) pollution. However, simulating NH4+ pollution presents unique challenges due to the inherent instability of NH4+ in natural environment. This study modified the widely-used Soil and Water Assessment Tool (SWAT) model to simulate non-point source (NPS) NH4+ processes, specifically incorporating the simulation of land-to-water NH4+ delivery. The Jiulong River Watershed (JRW) is the study area, a coastal watershed in Southeast China with substantial sewage discharge, livestock farming, and fertilizer application. The results demonstrate that the modified model can effectively simulate the NPS NH4+ processes. It is recommended to use multiple sets of observations to calibrate NH4+ simulation to enhance model reliability. Despite constituting a minor proportion (5.6 %), point source inputs significantly contribute to NH4+ load at watershed outlet (32.4â¼51.9 %), while NPS inputs contribute 15.3â¼17.3 % of NH4+ loads. NH4+ primarily enters water through surface runoff and lateral flow, with negligible leaching. Average NH4+ land-to-water delivery rate is about 2.35 to 2.90 kg N/ha/a. High delivery rates mainly occur at agricultural areas. Notably, proposed NH4+ mitigation measures, including urban sewage treatment enhancement, livestock manure management improvement, and fertilizer application reduction, demonstrate potential to collectively reduce the NH4+ load at watershed outlet by 1/4 to 1/3 and significantly enhance water quality standard compliance frequency. Insights gained from modeling experience in the JRW offer valuable implications for NH4+ modeling and management in regions with similar climates and significant anthropogenic nitrogen inputs.
Asunto(s)
Compuestos de Amonio , Contaminantes Químicos del Agua , Fertilizantes , Aguas del Alcantarillado , Reproducibilidad de los Resultados , Monitoreo del Ambiente/métodos , Nitrógeno/análisis , Calidad del Agua , China , Ríos , Contaminantes Químicos del Agua/análisis , Fósforo/análisisRESUMEN
It is still a great challenge to address nutrient pollution issues caused by various point sources and non-point sources on the watershed scale. Source contribution analysis based on watershed modeling can help watershed managers identify major pollution sources, propose effective management plans and make smart decisions. This study demonstrated a technical procedure for addressing watershed-scale water pollution problems in an agriculture-dominated watershed, using the Dengsha River Watershed (DRW) in Dalian, China as an example. The SWAT model was improved by considering the constraints of soil nutrient concentration, i.e., nitrogen (N) and phosphorus (P), when modeling the nutrient uptake by a typical crop, corn. Then the modified SWAT model was used to quantify the contributions of all known pollution sources to the N and P pollution in the DRW. The results showed that crop production and trans-administrative wastewater discharge were the two dominant sources of nutrient pollution. This study further examined the responses of nutrient loss and crop yield to different fertilizer application schemes. The results showed that N fertilizer was the limiting factor for crop yield and that excessive levels of P were stored in the agricultural soils of the DRW. An N fertilizer application rate of approximately 40% of the current rate was suggested to balance water quality and environmental protection with crop production. The long-term impact of legacy P was investigated with a 100-year future simulation that showed the crop growth could maintain for 12 years even after P fertilization ceased. Our study highlights the need to consider source attribution, fertilizer application and legacy P impacts in agriculture-dominated watersheds. The analysis framework used in this study can provide a scientifically sound procedure for formulating adaptive and sustainable nutrient management strategies in other study areas.
Asunto(s)
Contaminantes Químicos del Agua , Calidad del Agua , Agricultura , China , Monitoreo del Ambiente , Nitrógeno/análisis , Nutrientes , Fósforo/análisis , Ríos , Contaminantes Químicos del Agua/análisis , Contaminación del AguaRESUMEN
To develop a sound ozone (O3) pollution control strategy, it is important to well understand and characterize the source contribution due to the complex chemical and physical formation processes of O3. Using the "Shunde" city as a pilot summer case study, we apply an innovative response surface modeling (RSM) methodology based on the Community Multi-Scale Air Quality (CMAQ) modeling simulations to identify the O3 regime and provide dynamic analysis of the precursor contributions to effectively assess the O3 impacts of volatile organic compound (VOC) control strategy. Our results show that Shunde is a typical VOC-limited urban O3 polluted city. The "Jiangmen" city, as the main upper wind area during July 2014, its VOCs and nitrogen oxides (NOx) emissions make up the largest contribution (9.06%). On the contrary, the contribution from local (Shunde) emission is lowest (6.35%) among the seven neighbor regions. The local VOCs industrial source emission has the largest contribution comparing to other precursor emission sectors in Shunde. The results of dynamic source contribution analysis further show that the local NOx control could slightly increase the ground O3 under low (10.00%) and medium (40.00%) reduction ratios, while it could start to turn positive to decrease ground O3 under the high NOx abatement ratio (75.00%). The real-time assessment of O3 impacts from VOCs control strategies in Pearl River Delta (PRD) shows that the joint regional VOCs emission control policy will effectively reduce the ground O3 concentration in Shunde.