Loss of submerged macrophytes and high biomass of benthivorous/planktivorous fish are main factors contributing to the resistance of shallow lakes to the reduction in external nutrient loadings in tropical and subtropical China. Our large scale (30 hectares) experiment in subtropical Lake Yanglan showed that removal of benthivorous/planktivorous fish and flocculation by polyaluminium chloride (PAC) and lanthanum modified bentonite (Phoslock®) resulted in an immediate increase in water transparency (secchi depth up to 2 m) and decrease in total phosphorus (TP) (down to 50 µg/L), creating conditions for macrophyte growth. Follow-up transplanting of submerged macrophytes re-established a clear-water state in this urban lake. Although the restoration led to occurrence of large sized cladoceran Daphnia sp., but they disappeared in early summer which likely due to the recovery of young-of-the year fish in the restored area. Our results suggest that submerged macrophyte dominance could be restored by fish removal plus chemical flocculation followed by plant transplantation in this warm lake.

Primary Presenter: Zhengwen Liu, Nanjing Institute of Geography and Limnology (zliu@niglas.ac.cn)

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