Centre for Landscape & Climate Research, School of Geography, Geology and the Environment, University of Leicester, UK.
Environ Sci Process Impacts. 2020 Apr 29;22(4):956-972. doi: 10.1039/c9em00492k.
Pesticide losses from agricultural land to water can result in the environmental deterioration of receiving systems. Mathematical models can make important contributions to risk assessments and catchment management. However, some mechanistic models have high parameter requirements which can make them difficult to apply in data poor areas. In addition, uncertainties in pesticide properties and applications are difficult to account for using models with long run-times. Alternative, simpler, conceptual models are easier to apply and can still be used as a framework for process interpretation. Here, we present a new conceptual model of pesticide behaviour in surface water catchments, based on continuous water balance calculations. Pesticide losses to surface waters are calculated based on the displacement of a limited fraction of the soil pore water during storm events occurring after application. The model was used to describe the behaviour of metaldehyde in a small (2.2 km2) under-drained catchment in Eastern England. Metaldehyde is a molluscicide which has been regularly detected at high concentrations in many drinking water supply catchments. Measured peak concentrations in stream water (to about 9 μg L-1) occurred in the first few storm events after application in mid-August. In each event, there was a quasi-exponential decrease in concentration during hydrograph recession. Peak concentrations decreased in successive events - responding to rainfall but reflecting an effective exhaustion in soil supply due to degradation and dissipation. Uncertain pesticide applications to the catchment were estimated using land cover analysis of satellite data, combined with a Poisson distribution to describe the timing of application. Model performance for both the hydrograph (after calibration of the water balance) and the chemograph was good and could be improved via some minor adjustments in assumptions which yield general insights into the drivers for pesticide transport. The use of remote sensing offers some promising opportunities for estimating catchment-scale pesticide applications and associated losses.
农业用地向水体流失的农药会导致受纳系统的环境恶化。数学模型可以为风险评估和集水区管理做出重要贡献。然而，一些机械模型需要大量的参数，这使得它们难以在数据匮乏的地区应用。此外，使用运行时间长的模型很难考虑农药特性和应用的不确定性。替代的、更简单的概念模型更容易应用，仍然可以作为过程解释的框架。在这里，我们提出了一种基于连续水量平衡计算的地表水集水区农药行为的新概念模型。根据应用后发生的暴雨事件中土壤孔隙水中有限部分的位移，计算农药向地表水的流失。该模型用于描述在英格兰东部一个 2.2 平方公里的排水不良集水区中，灭多威的行为。灭多威是一种杀螺剂，在许多饮用水供应集水区中经常以高浓度检测到。在 8 月中旬施药后的头几次暴雨事件中，溪水中的峰值浓度（约 9μg/L）达到。在每次事件中，浓度在退水期间呈准指数下降。随着降雨的发生，浓度逐渐降低，但反映了土壤供应的有效耗尽，这是由于降解和消散造成的。利用卫星数据的土地覆盖分析，并结合泊松分布来描述施药时间，估算了集水区内不确定的农药施用量。对水文（在水量平衡校准后）和化学图谱的模型性能都很好，并且可以通过对假设进行一些微小的调整来进一步提高，这可以深入了解农药输运的驱动因素。遥感的使用为估算集水区尺度的农药应用和相关损失提供了一些有希望的机会。
