Mabilde Lisa, De Neve Stefaan, Sleutel Steven
Department of Soil Management, Ghent University, Coupure Links 653, 9000, Gent, Belgium.
Department of Soil Management, Ghent University, Coupure Links 653, 9000, Gent, Belgium.
J Environ Manage. 2017 Dec 1;203(Pt 1):429-438. doi: 10.1016/j.jenvman.2017.07.058. Epub 2017 Aug 20.
Historic long-term P application to sandy soils in NW-Europe has resulted in abundant sorption, saturation and eventually leaching of P from soil to the groundwater. Although many studies recognize the control of site-specific factors like soil texture and phosphate saturation degree (PSD), the regional-scaled relevance of effects exerted by single factors controlling P leaching is unclear. Very large observational datasets of soil and groundwater P content are furthermore required to reveal indirect controls of soil traits through mediating soil variables. We explored co-variation of phreatic groundwater orthophosphate (o-P) concentration and soil factors in sandy soils in Flanders, Belgium. Correlation analyses were complemented with an exploratory model derived using 'path analysis'. Data of oxalate-extractable Al, Fe, P and pH, phosphate sorption capacity (PSC) and PSD in three depth layers (0-30, 30-60, 60-90 cm), topsoil SOC, % clay and groundwater depth (fluctuation) were interpolated to predict soil properties on exact locations of a very extensive net of groundwater monitoring wells. The mean PSD was only poorly correlated to groundwater o-P concentration, indicating the overriding control of other factors in the transport of P to the groundwater. A significant (P < 0.01) positive non-linear relationship was found between groundwater o-P concentrations and pH for all depth layers. Likewise, lower SOC% (P < 0.01) and shallower groundwater level (MHL or MLL) corresponded (P < 0.01) with higher o-P concentrations. Groundwater o-P unexpectedly correlated positively to clay% and path analysis indicated this to be an indirect effect of the groundwater level. Path analysis furthermore indicated an important indirect control of pH on groundwater o-P concentrations and a considerable direct effect of P, Al and MHL. The fact that groundwater o-P concentration was stronger controlled by soil pH and groundwater table depth than by PSD indicates the likely oversimplification of the latter index to measure the long-term potential risk of P leaching. Accounting for controls on leaching not included in PSD via an alternative index, however, seems problematic as in Flanders for example groundwater o-P turned out to be higher in finer textured soils or soils with higher pedogenic Fe content, probably because of their lower pedogenic Al content and higher soil pH. Path analysis of extensive soil and groundwater datasets seems a viable way to identify prime local determinants of soil P leaching and could be further on used for 'ground-truthing' more complex P-migration simulation models.
在欧洲西北部，长期以来一直向砂质土壤施用磷肥，这导致土壤对磷的大量吸附、饱和，最终磷从土壤淋溶到地下水中。尽管许多研究认识到诸如土壤质地和磷酸盐饱和度（PSD）等特定地点因素的控制作用，但单个因素对磷淋溶影响的区域尺度相关性尚不清楚。此外，还需要非常大的土壤和地下水磷含量观测数据集，以揭示通过中介土壤变量对土壤特性的间接控制。我们研究了比利时弗拉芒地区砂质土壤中潜水层地下水中正磷酸盐（o-P）浓度与土壤因素的协变关系。相关性分析辅以使用“路径分析”得出的探索性模型。对三个深度层（0-30、30-60、60-90厘米）中草酸盐可提取的铝、铁、磷和pH值、磷酸盐吸附容量（PSC）和PSD、表土有机碳、粘粒百分比和地下水位（波动）的数据进行插值，以预测非常广泛的地下水监测井网络精确位置处的土壤性质。平均PSD与地下水中o-P浓度的相关性很差，这表明在磷向地下水的迁移过程中，其他因素起主要控制作用。在所有深度层中，地下水中o-P浓度与pH值之间均发现了显著（P<0.01）的正非线性关系。同样，较低的有机碳百分比（P<0.01）和较浅的地下水位（平均高潮位或平均低潮位）与较高的o-P浓度相对应（P<0.01）。地下水中o-P与粘粒百分比意外地呈正相关，路径分析表明这是地下水位的间接影响。路径分析还表明，pH值对地下水中o-P浓度有重要的间接控制作用，而磷、铝和平均高潮位有相当大的直接影响。地下水中o-P浓度受土壤pH值和地下水位深度的控制比受PSD的控制更强，这一事实表明，用后一指标来衡量磷淋溶的长期潜在风险可能过于简单化。然而，通过替代指标来考虑PSD中未包括的对淋溶的控制因素似乎存在问题，例如在弗拉芒地区，质地较细的土壤或成土铁含量较高的土壤中，地下水中o-P含量较高，这可能是因为它们的成土铝含量较低且土壤pH值较高。对广泛的土壤和地下水数据集进行路径分析似乎是确定土壤磷淋溶主要局部决定因素的可行方法，并且可进一步用于对更复杂的磷迁移模拟模型进行“实地验证”。
