Challenges to an Integrated Delta Approach: the case of the Tagus Estuary

The identification of phosphorus species in sediments is a useful approach for the assessment of potential sources or sinks of phosphorus in estuarine regions, and helps to understand the biogeochemical processes that control the availability of phosphorus in tropical areas. This study aimed to identify the spatial and seasonal distribution of the occluded, bioavailable and organic phosphorus fractions, in sediments of a polluted estuary (Botafogo river), and other considered as a background area (Carrapicho river), and determine the correlations between the concentration of phosphorus in sediments with the grain size, calcium carbonate, organic matter, dissolved phosphorus and salinity. No significant seasonal variation of phosphorus fractions concentrations was observed. The highest concentrations of occluded phosphorus was registered at Santa Cruz Channel sampling station with median value of 558,80 µg.g-1 . In the Botafogo river estuary were found the highest concentrations of organic, and bioavailable phosphorus with median values of 209,19 μg.g -1 and 398,09 µg.g-1 respectively, due to the high content of fine sediments in this area. The organic matter content was positively correlated with the organic, bioavailable and occluded phosphorus fractions r2 = 0.9335; 0.8882; and 0.7750 respectively. The occluded phosphorus was the major fraction of the total phosphorus in the whole study site and showed a high correlation (r= 0.8218) with the percentage of CaCO3 in sediments, unlike the others phosphorus fractions with r < 0.6.Weak correlations between the phosphorus fractions and the dissolved phosphorus were found, the bioavailable phosphorus showed the higher correlation with the water column concentrations (r= 0,5362).