A common land and water management task is to determine where and by how much source loadings need to change to meet water quality limits in receiving environments. This paper addresses the problem of quantifying changes in loading when limits are specified in many locations in a large and spatially heterogeneous catchment, accounting for cumulative downstream impacts. Current approaches to this problem tend to use either scenario analysis or optimization, which suffer from difficulties of generating scenarios that meet the limits, or high complexity of optimization approaches. In contrast, we present a novel method in which simple catchment models, load limits, upstream/downstream spatial relationships and spatial allocation rules are combined to arrive at source load changes. The process iteratively establishes the critical location (river segment or lake) where the limits are most constraining, and then adjusts sources upstream of the critical location to meet the limit at that location. The method is demonstrated with application to New Zealand (268,000 km 2 ) for nutrients and the microbial indicator E. coli , which was conducted to support policy development regarding water quality limits. The model provided useful insights, such as a source load excess (the need for source load reduction) even after mitigation measures are introduced in order to comply with E. coli limits. On the other hand, there was headroom (ability to increase source loading) for nutrients. The method enables assessment of the necessary source load reductions to achieve water quality limits over broad areas such as large catchments or whole regions.

中文翻译：

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一种确定源负荷变化以符合流域水质限值的启发式方法

一项常见的土地和水资源管理任务是确定需要改变源负荷的位置和程度，以满足接收环境中的水质限制。本文解决了在大型和空间异质流域中的许多位置指定限制时量化负载变化的问题，并考虑了累积的下游影响。目前解决这个问题的方法倾向于使用场景分析或优化，这会导致生成满足限制的场景的困难，或者优化方法的高复杂性。相比之下，我们提出了一种新方法，其中将简单的集水模型、负荷限制、上下游空间关系和空间分配规则结合起来，以得出源负荷变化。该过程迭代地建立限制最受约束的关键位置（河段或湖泊），然后调整关键位置上游的源以满足该位置的限制。该方法在新西兰 (268,000 km 2 ) 的营养物质和微生物指标大肠杆菌中得到证明，该方法用于支持有关水质限制的政策制定。该模型提供了有用的见解，例如源负荷过剩（需要减少源负荷），即使在引入缓解措施以符合大肠杆菌限制之后也是如此。另一方面，养分有净空（增加源负荷的能力）。