Helinä Hartikainen

Phosphorus and its reactions in terrestrial soils and lake sediments

Introduction

Phosphorus and its reactions in terrestrial soils and lake sediments. Explore phosphorus reactions, availability, and eutrophication risk in terrestrial soils and lake sediments. Studies P forms, sorption/desorption, and environmental factors.

Abstract

The P status in some soils and sediments and the fate of P in various sorption and desorption tests was studied. The aim was to elucidate some factors possibly controlling the availability of soil P and the eutrophication risk owing to eroded soil material being carried into surface waters. Also the factors affecting the significance of bottom deposits in the P budget of lakes were discussed.The occurrence and reactions of various inorganic P forms were investigated by a modified CHANG and JAcKSON fractionation procedure which proved a suitable method also for sediment studies for limnological and paleolimnological purposes. In the sorption and desorption experiments the activities of the fractions varied. The extent of retention and the distribution of sorbed P in various fractions was closely related to amorphous oxides of Al and Fe in soils and sediments. In nature, the secondary phosphates seem to participate more actively in desorption processes than the acid soluble P, supposed to represent apatite-P. However, the ratio of secondary phosphates to their corresponding sorption components appeared primarily to control the extent of desorption. Further, the net release of P under desorptive conditions was dependent on the effectiveness of the resorption reactions. In addition to soil and sediment properties the environmental factors also affect the sorption and desorption of P. The immediate effect of temperature on sorption by different soils varied, but seemed to be generally quite unessential. A high content of active organic matter or oxygen depleted conditions may lower the sorption or even cause some desorption, while high concentrations of inorganic salts may enhance retention. Thus, the eutrophication risk owing to the eroded soil material is dependent also on conditions in the recipient ‘water.

Review

This study provides a comprehensive investigation into the intricate dynamics of phosphorus (P) in both terrestrial soils and lake sediments, addressing crucial environmental concerns related to P availability and eutrophication. The primary objectives were to identify factors controlling soil P availability, assess the eutrophication risk from eroded soil material, and elucidate the role of lake bottom deposits in the P budget of aquatic ecosystems. The research effectively utilized a modified Chang and Jackson fractionation procedure, validating its applicability for both limnological and paleolimnological sediment studies, thereby providing a robust methodological foundation for the subsequent analyses. The findings reveal several key mechanisms governing P behavior. The retention and distribution of sorbed P were strongly correlated with amorphous oxides of aluminum and iron in both soil and sediment matrices. Notably, secondary phosphates were found to be more active in desorption processes than acid-soluble P (presumed apatite-P), with their ratio to corresponding sorption components primarily dictating the extent of desorption. The net release of P under desorptive conditions was further influenced by the effectiveness of resorption reactions. Beyond intrinsic soil and sediment properties, environmental factors play a significant role: high organic matter content or anoxia can reduce sorption or induce desorption, while high inorganic salt concentrations may enhance retention. Interestingly, the immediate effect of temperature on sorption appeared to be generally minor. Overall, this research offers valuable insights into the complex interplay between chemical forms of P, soil/sediment characteristics, and environmental conditions. By highlighting that the eutrophication risk from eroded soil material is not solely dependent on the source material but also critically on the conditions within the recipient water body, the study provides a nuanced understanding essential for effective environmental management. The paper’s elucidation of these controlling factors significantly contributes to our knowledge of P cycling across the land-water interface, offering a strong basis for developing strategies to mitigate P-related environmental issues such as soil nutrient depletion and freshwater eutrophication.

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