Seminar

Eutrophication and harmful algal blooms (HABs) are global threats to lakes, especially shallow lakes (with a depth < 5m), and may further induce environmental consequences such as greenhouse gas emissions. The occurrences of these problems are governed by various biogeochemical, climatological and anthropogenic factors. Groundwater may play a key role in controlling HABs and mediating the related biogeochemical processes of carbon and nitrogen, but the underlying mechanisms remain unclear. Basin-wide field data of Lake Taihu, China’s largest eutrophic lake, were leveraged, and multiple environmental isotopes were applied. The dominance of evaporation on lacustrine groundwater discharge (LGD) in the shallow lake was demonstrated. HABs were found to promptly consume ubiquitous groundwater-borne nutrients, while LGD effects on inventories and pathways of carbon and nitrogen could be dampened by the enhanced productions from organic matter degradation with the increasing eutrophication. The evaporation dominated LGD is an unraveled but crucial regulator of nutrient states and HABs in the shallow lake, and significantly mediated the internal biogeochemical processes. This study advocates the need for synergistical studies from climatological, hydrogeological and biogeochemical perspectives when restoring aquatic ecosystems and reducing global warming.

Additional information: Ms. SHI Xiaoyan, shixyan@connect.hku.hk