Spatial distribution study of phosphorus forms in lake sediment

The objective of this work is the study of spatial variations of the different phosphorus forms, collected from 56 surficial sediment samples which were performed during four seasons in spring, summer, autumn 2013, and winter 2014, such as inorganic forms (Fe (OOH)-P and CaCO3-P) and organic forms (ASOP et ROP), in the retaining of Sidi Chahed dam (Morocco), as well as the elaboration of spatial distributions maps of these phosphorus forms by the use of geographic information system (GIS). To obtain more information on the correlations and the geochemical links that may exist between these forms on the one hand and between sampling stations and these forms on the other hand, we carried out a principal components analysis (PCA) and a factorial correspondence analysis (FCA) of the data collected on these phosphorus forms. The results of phosphorus extractions have shown that the sedimentary phosphorus is mainly in the inorganic forms (Fe (OOH)-P + CaCO3-P). These mineral forms represent nearly 88% on average of total phosphorus, with the predominance of the CaCO3-P fraction that represents almost 76%. However, organic forms (POSA + POR) represent only 12% of the total phosphorus. The thematic maps elaborated by the geographical information systems allow having more accurate distribution of phosphorus forms concentrations. These maps show that the different phosphorus forms are distributed in a homogeneous way at the retaining dam studied. These results raise the hypothesis of a similar behavior of each fraction concerning the physicochemical processes that take place in the environment. The principal components analysis shows that the (POR, Fe (OOH) -P) forms are highly correlated with each other (R = 0.80), and that the CaCO3-P form is positively correlated with the total phosphorus (R = 0.71). The factorial correspondence analysis allowed us to clearly identify three seasons (spring, autumn, and winter), with interpenetration of summer between spring and autumn.