基于流域水环境响应的城市建设用地面积阈值模拟

城市扩张影响流域水环境质量.从水环境响应出发,模拟预测流域范围内城市建设用地的扩张阈值,可为城市建设用地规划提供客观依据.本文选取完全城市化的筼筜湖流域、半城市化的马銮湾流域和城市化起步阶段的杏林湾流域作为对比研究对象,结合2009—2012年实测数据,运用区域污染物管理模型(ReNuMa),计算3个流域水体污染物总氮(TN)和总磷(TP)环境容量上限,确定流域内城市建设用地面积阈值,并预测城市景观格局演变产生的水环境效应.结果表明: 筼筜湖、马銮湾和杏林湾的TN年负荷上限值分别为12900、42800和43120 kg,TP年负荷上限值分别为340、420和450 kg;现实情境下,筼筜湖水体污染物环境容量尚未饱和,马銮湾与杏林湾的污染物年负荷均接近上限值,杏林湾的TN和TP年负荷存在明显的上升趋势;3个流域污染物年负荷均在模拟情境1下未超标、情境3下超标,情境2下,筼筜湖污染物年负荷均未超标,而马銮湾TN与TP年负荷均处于超标;筼筜湖、马銮湾和杏林湾流域的城市建设用地面积阈值分别为1320、5600和4750 hm²,并据此提出景观格局调整对策建议.

Simulation on area threshold of urban building land based on water environmental response in watersheds.

Urban sprawl has impacted increasingly on water environment quality in watersheds. Based on water environmental response, the simulation and prediction of expanding threshold of urban building land could provide an alternative reference for urban construction planning. Taking three watersheds (i.e., Yundang Lake at complete urbanization phase, Maluan Bay at peri-urbanization phase and Xinglin Bay at early urbanization phase) with 2009-2012 observation data as example, we calculated the upper limit of TN and TP capacity in three watersheds and identified the threshold value of urban building land in watersheds using the regional nutrient management (ReNuMa) model, and also predicted the water environmental effects associated with the changes of urban landscape pattern. Results indicated that the upper limit value of TN was 12900, 42800 and 43120 kg, while that of TP was 340, 420 and 450 kg for Yundang, Maluan and Xinglin watershed, respectively. In reality, the environment capacity of pollutants in Yundang Lake was not yet satura-ted, and annual pollutant loads in Maluan Bay and Xinglin Bay were close to the upper limit. How-ever, an obvious upward trend of annual TN and TP loads was observed in Xinglin Bay. The annual pollutant load was not beyond the annual upper limit in three watersheds under Scenario 1, while performed oppositely under Scenario 3. Under Scenario 2, the annual pollutant load in Yundang Lake was under-saturation, and the TN and TP in Maluan Bay were over their limits. The area thresholds of urban building land were 1320, 5600 and 4750 hm² in Yundang Lake, Maluan Bay and Xinglin Bay, respectively. This study could benefit the regulation on urban landscape planning.