Restoration of Nutrient Rich Lakes - Towards Better Understanding of Sediment Phosphorus Availability and Management

Sammanfattning: Lakes are important for many reasons as they provide valuable ecological and human services, such as drinking water and recreational use. Eutrophication, a result of excess nutrients (e.g. phosphorus (P)) in lakes, is a threat to these resources, causing impairment of water quality. Excess P loading to lakes accumulates in the sediment, consequently making sediment a potential source of P via release (internal loading). One way of counteracting effects caused by internal loading is to inactivate the pool of potentially available P in the sediment. Better information is needed for optimizing most in-lake P reduction methods, including aluminum (Al)-treatment. One of these areas is better knowledge about the availability of different P fractions, and which fractions to target with a specific dose of Al under certain environmental conditions such as bioturbation (e.g. sediment mixing by carp). We also need to deepen the knowledge about modern Altreatment methods, with respect to both treatment techniques and dosing. Knowledge about factors affecting how long the positive effects from an Al-treatment last also needs to be improved. This thesis presents results concerning optimization of Al application methods, where a novel application method that injects Al into the sediment was evaluated and a model for optimal Al dose determination is presented. Factors affecting treatment longevity were evaluated, using historical water quality records and knowledge about a previously assumed recalcitrant P form being bioavailable due to bioturbation by benthic feeding fish like carp and bream. Al-treatment methods, including practical Al application methods as well as dosing methods are developing rapidly and being applied in the field, and further work is needed to keep up with evaluating the progress of lake restoration results using methods like Al-treatment.

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