Lake Restoration by Dosing Aluminum Relative to Mobile Phosphorus in the Sediment

摘要

In the sediment of the shallow,hypertrophic Lake S0nderby,Denmark,potentially mobile phosphorus (P_(mobile)) was determined by a sequential extraction technique as the sum of porewater P,iron-bound P,and nonreactive P (i.e.,polyphosphates and organic P).A good agreement was observed between loss rates of P_(mobile) in the top 10 cm of the sediment from winter to summer,P release rates measured in undisturbed sediment cores,and rates of P accumulation in the lake water from winter to summer (22,32,and 30 mg of P m~(-2) day~(-1),respectively).This suggests that the operationally defined P_(mobile) was the sediment P fraction responsible for the internal loading in the lake.In autumn 2001,11 mg of aluminum (AI) L~(-1),equivalent to 31 g of Al m~(-2),was added to the lake water.This dosage represented a 4:1 molar ratio between Al and P_(mobile).The Al treatment significantly decreased lake water P,and P precipitated from the lake water was recovered as Al-bound P in the sediment after the treatment.Internal P loading was reduced by 93% in the two posttreatment years,relative to 2001.Accordingly,average summer concentrations of total P in lake water declined from 1.28 (SE=0.17) and 1.3 (SE=0.14) mg L~(-1) in the two pretreatment years to 0.09 (SE=0.01) and 0.13 (SE=0.01) mg L~(-1) in the posttreatment years.pH levels remained unchanged relative to pretreatment levels,while the total alkalinity was reduced from 3.2 (SE=0.04) to 2.7 (SE=0.03) mequiv L~(-1).