Flocculation and sediment capping – fact sheet

Abstract

Sediment capping and flocculation are in-lake techniques designed to reduce internal nutrient loads from the bottom sediments of lakes. These loads are roughly equivalent in magnitude to external loads. Case studies of the Rotorua lakes (Figure 1) show that with careful design and management, sediment capping and flocculation can reduce nutrient concentrations and the likelihood of algal blooms. Relevant actions can include: (i) reducing bioavailable phosphorus in stream inflows through continuous addition of the active material to the stream, (ii) removing bioavailable phosphorus, and flocculation and sedimentation of nutrients, and (iii) altering sediment composition so that nutrients are more efficiently retained within the bottom sediments