Wednesday, 9 September 2020

Low-Fe lake sediments recycled to agriculture improved grass growth- and hardwood biochar reduced leaching of N and P


In AgriChar research group, we are trying to find ways to best close the phosphorus (P) cycles in the environment by recycling nutrients in sediments back to the agriculture and restoring eutrophic lakes.

The nutrients including Phosphorus (P) in upstream agricultural soils are washed out by erosion and reach the bottom of the lake sediment. Excessive load of (P) causes eutrophication problems in many lakes. One of the effective restoration methods especially for small shallow lakes is removal of sediments enriched with nutrients. We examined the factors behind P release from sediment to lake water after removal of sediments from a 1-ha shallow eutrophic lake during two-year follow up period. Removing 7 500 m3 of nutrient-rich sediment removed 6 400 kg of P, including the potential source of P for algae. 


However, high pool of releasable P was rebuilt soon after the removal of sediment due to high external P loading, resulting in high internal P loading which sustained eutrophication of the lake. So ways that help to control nutrient losses from fields upstream are of great importance! Our study documented clear strong linkage between sediment P and iron dynamics after the restoration. We also found that the Fe-P and labile P fractions were the most important sources of P release evidenced by their considerable seasonal and interannual changes after the sediment removal.