Abstract
In this study, the characteristics and distribution of the organic phosphorus (Po) fractions in the surface sediments of seven inflow rivers around Hongze Lake in China were analyzed with a soil Po fraction method, as used by Ivanoff. The relationships between the Po fractions and physiochemical features of sediments were also discussed. The results showed that, the sediments of the rivers had been moderately pollution with certain ecological risk effects except the Waste Yellow River. The relative contribution order of the Po fractions in the sediments was residual Po > HCl-Po > fulvic acid-Po > humic acid-Po > labile organic phosphorus (LOP). Moderately labile organic phosphorus (MLOP) was the main part of the Po forms in the whole sediments. The risk of phosphorus released from river sediments was the highest in the western region, followed by the southwestern region, and finally the northwestern region. There were significant correlations between Po forms and total phosphorus (TP), inorganic phosphorus (Pi), and Po. Non labile organic phosphorus (NLOP) had the strongest correlation with TP. The distribution of Po forms in each region was different due to the impact of human activities, industrial and agricultural production and the land types; the heaver polluted sediments with higher Po fractions. It is suggested that most of the sediments of the inflow rivers in the regions have certain ecological risk effects and P of them have an important contributions on the eutrophication of Hongze Lake. Po forms can provide a reliable theoretical basis for dealing with the change of water quality and should be paid more attention in the lake eutrophication investigation. There was reciprocal transformation between different Po forms, especially non-bioavailable fraction can change into bio-available ones. The results can provide a basis for the earth cycle of phosphorus and a new perspective of eutrophication control of shallow lakes.
Highlights
Phosphorus (P) is an essential nutrient for aquatic organisms and is a limiting nutrient for primary production in lake ecosystems [1,2,3], so excessive phosphorus (P) is a key factor for eutrophication [4].Over the last few decades, the external inputs of P have been gradually reduced; the release of internal P from the sediments of lakes to the overlying water has become a significant source ofP [5,6]
The second national investigation surveyed 138 lakes with an area of more than 10 km2, and the results showed that 85.4% of the lakes have eutrophication issues, and almost half of them (>40%) are hyper-eutrophic lakes [29]
The concentration and the percentage of Non labile organic phosphorus (NLOP) increased with the increase of pollution degree, it was different from labile organic phosphorus (LOP)
Summary
Phosphorus (P) is an essential nutrient for aquatic organisms and is a limiting nutrient for primary production in lake ecosystems [1,2,3], so excessive phosphorus (P) is a key factor for eutrophication [4]. Not all the fractions of phosphorus can be released from sediments, and cause lake eutrophication [10,11,12]. Until now, investigations of the species, quantification, concentrations, dynamics, biogeochemical cycling and ecological significance of these organic P compounds have been limited due to its complexity and the limitations of analytical methods [19] For these reasons, in recent years, sequential extraction schemes have been developed based on the assumption that chemical extractants selectively dissolve discrete groups of Po [20]. The characteristics and distribution of nutrient elements especially the limiting nutrient P fractions in the sediments of the rivers flowing into the lake should be studied.
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