Chinese scientists: Model involving native macrophytes, fishes, benthons, and birds effective for lake wetlands restoration

Scientists from the Kunming Institute of Zoology, Chinese Academy of Sciences (CAS), published information related to an innovative lake wetlands restoration model involving native macrophytes, fishes, benthons, and birds that gives full play to the role of native creatures in ecological restoration and its implementation in the Bulletin of Chinese Academy of Sciences (BCAS, in Chinese), a think tank journal focused on strategic and decision-making research that is supervised and sponsored by the CAS, in 2023. The information below comes from their report.

One of the three most productive ecosystems in the world, wetlands play an important role in maintaining the balance of natural ecosystems due to their water conservation, water purification, flood and drought prevention, climate regulation, and biodiversity maintenance functions. Lake wetlands account for 16.03% of China’s total wetland area, according to its second national wetland resources survey, which was conducted from 2009 to 2013 and compiled early in 2014.

Yunnan Province’s lake wetlands are home to abundant and unique species, and several of them have been listed as internationally important wetlands. The wetlands in Yunnan cover 5,636 sq. km, accounting for 1.05% of China’s wetland area, with lake wetlands comprising 1,185 sq. km of the total, or 21.03% of Yunnan’s wetland area.

The ecological systems associated with the province’s lake wetlands have been experiencing many problems as human activities and resulting climate change have intensified, and economic and social development have led to environmental changes, and a decline in biodiversity, however. Located in Kunming, Yunnan’s capital and largest city, Dianchi – the largest inland lake on the Yunnan-Guizhou Plateau – has experienced a sharp decline in biodiversity, for example. The number of indigenous fish species present in the lake decreased from 26 in the 1960s to just 11 in 2001, while aquatic plant coverage declined from 90% in the 1960s to 12.6% in the 1980s and has stood at only around 1.4% since 2000, and the number of aquatic plant species detected fell from 44 in 1957 to 30 in 1977 and just 22 in 1997.

The Chinese Ministry of Ecology and Environment has developed a Roman numeral-based surface water grading system with six categories, with grade I representing the highest quality and water that falls in the grade-I to grade-III range being considered to be of at least “fairly good quality.” Grade I refers to water that comes directly from natural sources; grade II refers to water that is suited to centralized drinking projects and can sustain aquatic life; grade III is also suited to centralized drinking projects, can sustain some aquatic life, and can be swam in; grade IV is suited to industrial use and recreation but should not make direct contact with people; grade V is only suited to irrigation and landscaping purposes; and water that does not fall into any of these categories is not suitable for any use.

Dianchi Lake’s water quality deteriorated from the grade-I level in the 1950s to the grade-III to grade-IV range in the 1970s and was even worse than grade V in the 1990s. Eventually water management measures were implemented and the situation began to improve, which resulted in its water quality rising to the grade-V level in 2016 and the grade-IV level in 2019, where it has remained. The lake’s surface area has gradually decreased as well, falling from 510 sq. km as of the early Yuan Dynasty (1271 to 1368) to 410 sq. km by the end of it and then to 323 sq. km in 1938. Reclamation efforts began being implemented at this point, which brought the surface area to 361.8 sq. km by 1978, though it began to shrink again after the 1980s and stands at 309 sq. km at present.

The “algae-fishes-birds/humans” and “macrophytes-fishes-birds/humans” paths are two of the main ways that eutrophic elements, such as phosphorus and nitrogen, are removed from wetlands. A decline in biodiversity damages them and thus causes eutrophication. Reconstructing and restoring lake wetlands’ ecological food chains in order to rebuild the paths is thus an urgent aspect of ecological restoration.

In the past, Yunnan mainly employed three models that were designed to reduce endogenous pollution by introducing alien species. The first entailed using silver and bighead carps to control algae, which is effective in controlling algae blooms in water that is worse than the grade-V level. The second entailed planting reeds and willows in order to improve lakeside zones’ landscapes. The third entailed introducing water hyacinths, which play a positive role in reducing nitrogen and phosphorus but create a dark and anaerobic environment in the area that they cover, making it impossible for fish, shrimp, shellfish, and aquatic plants to survive.

The Kunming Institute of Zoology research team that wrote the report created the macrophytes-fishes-benthons-birds restoration model as a means of reducing phosphorus and nitrogen after studying the theory of the paths by which they are ushered out of wetlands. The model connects native flagship aquatic plants, fish, and benthic animals in order to reconstruct broken ecological chains and create a path by which phosphorus and nitrogen can be removed from the water. It has been implemented at Dianchi Lake and Yunnan’s second largest lake – an alpine lake in Dali City known as Erhai Lake – and good results have been achieved.

The researchers suggest dividing plateau lake wetlands into three categories and conducting targeted ecological restoration and management measures in accordance with local conditions in order to promote the model.

Implementing the macrophytes-fishes-benthons-birds restoration model is recommended for lake wetlands with good ecological environments where native species are well-preserved and water quality is in the grade-I to grade-III range, such as the Erhai Lake, Fuxian Lake, which is the third largest lake in Yunnan, and Lugu Lake, which is the highest lake in Yunnan, in order to engender the two main paths by which phosphorus and nitrogen are removed.

Introducing silver and bighead carps in lakes where some native creatures have disappeared and the water quality is in the grade-IV to worse-than-grade-V range, such as Dianchi, a plateau lake that connects to karst caves known as Qilu, a plateau lake that connects to Fuxian Lake by river known as Xingyun, a mesotrophic plateau lake located in western Yunnan known as Chenghai, and a lake that is known for its colorful lotus flowers and other scenery known as Yilong, is suggested so that they can consume algae present in them. The “macrophytes-fishes-benthons-birds” restoration model can be used in a supplementary manner in this case.

Reducing and removing heavy metals is the top priority for lake wetlands that have this problem, such as the Yangzonghai Lake area, which features underwater springs and is one of Yunnan’s scenic regions. The best way of doing so is by increasing the population of benthic shellfish, such as the Chinese pond mussel (Anodonta woodiana), Chinese round snails, and river clams, since shellfish adsorb heavy metals and deposit them in their shells as they grow. Lakeside zones should also be restored and native fish species that consume filamentous algae should be released as appropriate.