Purpose

Fate factors, for freshwater eutrophication, represent the route of a limiting-nutrient, phosphorus or nitrogen, and their degradation in the environment. Their value may vary according to the location and emission season; that is, they are site and temporal dependent. In this study, phosphorus fate factors for the freshwater eutrophication impact category were estimated in a native scale of state hydrographic units (SHU), considering its variability and applied in a case study for one hydrographic basin in the state of Bahia, Brazil.

Methods

The fate model considered the phosphorus removal processes of advection, retention, and agricultural and domestic water use, based on national databases (Geonetwork, HidroWeb, SAR, and SNIS). Heat maps and correlation networks allowed the assessment of fate factors’ spatiotemporal variability. The new generated fate factors were qualitatively and quantitatively assessed, then further applied in a case study of buffalo milk production at Leste SHU to determine the regionalization effects on the freshwater eutrophication potential impact.

Results and discussion

This study reconfirmed the spatial and temporal variability of the fate factors. The fate factor values found, in this study, for Pardo SHU are similar to those estimated with the non-regionalized data used by the adopted model, being within the range of 0 to 20 days. However, the fate factors for De Contas and, mainly, for Leste were underestimated, reaching a value up to five times higher, indicating that the model’s proposed changes impacted the final result. The temporal differentiation was mainly determined by periods of higher and lower water availability. Advection processes inversely determined the fate factors, and the phosphorus removal by retention processes became more prominent when the water availability was lower. On the other hand, the role of phosphorus removal through water use was minimum. Water availability was the largest contributor to the sensitivity analysis, followed by the total freshwater volume.

Conclusion

The fate modeling adopted in this study, with the use of data from national databases and native resolution, gave a more precise and detailed analysis perspective of the phosphorus fate in Brazilian SHUs, setting up site- and temporal-specific fate factors. Besides, this study provides a further understanding of the fate factors establishment by analyzing their relationship with the respective input parameters and highlighting one of the used model’s weaknesses: the estimation of phosphorus removals instead of phosphorus load underestimates the true freshwater eutrophication potential.

中文翻译：

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巴西巴伊亚州淡水富营养化的区域磷命运因素：时空变异性分析

目的

淡水富营养化的命运因素代表了有限营养，磷或氮的途径及其在环境中的降解。它们的值可能根据位置和排放季节而有所不同；也就是说，它们是位置和时间相关的。在这项研究中，考虑到水的富营养化影响因素的可变性，在当地规模的州水文单位（SHU）中估算了磷的命运因素，并将其应用于巴西巴伊亚州的一个水文盆地的案例研究中。

方法

命运模型基于国家数据库（Geonetwork，HidroWeb，SAR和SNIS）考虑了平流，保留以及农业和家庭用水的除磷过程。热图和相关网络可以评估命运因素的时空变异性。对新产生的命运因素进行定性和定量评估，然后进一步应用于Leste SHU的水牛乳生产案例研究中，以确定区域化对淡水富营养化潜在影响的影响。

结果和讨论

这项研究证实了命运因素的时空变异性。在本研究中发现的Pardo SHU的命运因子值与采用的模型使用的非区域化数据所估计的命运因子值相似，范围为0至20天。但是，低估了De Contas的命运因素，主要是Leste的命运因素，其命运值高达五倍，这表明模型的拟议变更影响了最终结果。时间上的差异主要由可用水量的高低决定。平流过程反过来决定了命运的因素，当水的利用率较低时，保留过程的除磷变得更加突出。另一方面，通过水去除磷的作用最小。

结论

这项研究采用的命运模型，利用国家数据库中的数据和原始分辨率，为巴西SHU中的磷命运提供了更为精确和详细的分析视角，建立了特定地点和特定时间的命运因素。此外，本研究通过分析命运因素与各个输入参数之间的关系并突出显示了所用模型的弱点之一，从而进一步了解了命运因素：估算的除磷量（而不是磷负荷量）会低估真正的淡水富营养化潜力。