Browsing by Subject "hypolimnetic withdrawal"

The particulate phosphorus flux consists of organic and inorganic matter as well as iron-phosphorus compounds, and often forms a significant portion of the total phosphorus flux in hypolimnetic waters. Phosphorus accumulated in hypolimnion can be removed by pumping phosphorus-rich water from areas where total phosphorus concentrations are high. The highest concentrations are typically measured in the hypolimnetic water of eutrophic and stratifying lakes particularly during the summer when anoxia occurs. Phosphorus bound to sediment iron oxides can be released due to changes in redox potential, pH, or resuspension. In hypolimnetic withdrawal, the importance of iron-bound phosphorus is emphasized, as it is essentially labile phosphorus. Therefore, the hypolimnetic withdrawal is not only limited to the removal of soluble phosphorus alone. The mobility of particles in the water column and their interaction with the sediment significantly affect the availability of phosphorus and its ecological impacts. By removing particulate phosphorus, the amount of phosphorus released in a potentially soluble form can be reduced. In this study, the flow of particulate phosphorus, i.e. the gross sedimentation of phosphorus, was investigated using sediment traps, in which the sinking particulate matter, including phosphorus accumulates. The study aimed to 1) examine how particulate phosphorus concentrations varied across three different depth zones (6 m, 9 m, 30 m) and the role of full circulation in the observed differences, 2) understand how iron-bound phosphorus moved between depth zones and the significance of its distribution, and 3) determine the magnitude of particulate phosphorus flow relative to soluble phosphorus flow. It was found that particulate phosphorus flow varied significantly during the full circulations and stratification period across different depth zones and times. The highest phosphorus flows were measured from the thermally stratified deep-water zone, particularly after the onset of spring and autumn full circulations. A similar trend was observed in the middle and shallow depth zones. The mixing during full circulations significantly increased both the rates of gross sedimentation of phosphorus and resuspension of phosphorus in the hypolimnion. Most of the particulate phosphorus in the water column of Lake Enonselkä was in the form of iron-bound phosphorus, although its proportion of the total particulate phosphorus flow did not differ between full circulation and stratification periods across the depth zones. Iron-bound phosphorus moved during full circulations in the water column of Enonselkä. The physical activity of the water body and peak in primary production in the spring after full circulation, supporting the conclusion that full circulations are a significant factor in the spread and release of phosphorus and iron-bound phosphorus, in the water column. Recognizing the proportion of particulate phosphorus is crucial for depleting the hypolimnetic phosphorus reserves, as the study found that particulate phosphorus accounted for over 90% of the total phosphorus flux both during the stratification season and after the onset of full circulations. The high proportions of particulate and iron-bound phosphorus in the total phosphorus flux are possible indicators that there is a connection between shallow and deep areas in terms of nutrient cycling. Additionally, the findings emphasize that considering particulate phosphorus is essential in assessing the theoretical potential of hypolimnetic water removal, especially during stratification and full circulation periods.