Occurrence of phosphorus and its potential remohilization in the littoral sediments of a productive English lake

SUMMARY. 1. Vertical profiles of pH were measured at nine shallow water (<5m) locations in Esthwaite Water. These indicate strong gradients of pH near the sediment water interface suggesting a marked buffering capacity of the sediments.
2. Thirteen littoral sediment cores were horizontally sectioned and sequentially extracted (0.5 M NaHCO₃, 0.1 M NaOH, 1 M HCI) and analysed for soluble reactive phosphorus. The core sections were also analysed for total phosphorus and per cent organic content to determine the vertical and areal variability of phosphorus within the littoral sediments of Esthwaite Water.
3. The rate of release of phosphorus from intact sediment cores was measured in the laboratory as a function of the pH of overlying water, yielding the relationship log K=0.54 pH−3.94, K=mg Pm⁻²day⁻¹. The maximum release rate measured was 75 mg P m⁻² day⁻² at pH = 10.5.
4. Experiments on sediment slurries indicate that the release of phosphorus at pH 10 is rapid with approximately 50% of the total NaHCO₃+ NaOH extractable phosphorus being released within 3 h.
5. Phosphorus release from the littoral sediments may equal or exceed external sources plus hypolimnetic inputs during periods of high pH associated with times of maximum algal biomass.