Impacts of Climate Change on the Pacific Northwest

October 8, 2019

Ecology Blog 4: Water pollution and governance strategy of the lakes in Jiangsu and Washington

During our 10-day trip, we have learned a lot about ecology from different kinds of forests to wetlands and sea shores in the Pacific Northwest. Understanding human impacts on these various ecosystems are crucial to protect them. Where are the impacts most obvious? The lakes near the cities are good choices to study how human activities influence the ecosystems. When we visited Seattle, we saw very clear water in Lake Washington with a beautiful scenery. It reminded us of Lake Taihu in Jiangsu Province back in China. Lake Taihu is not so far from Nanjing, which means most of the geoscience students in Nanjing University would go there for field trips. It is similar to Lake Washington that Lake Taihu is also surrounded by cities.

Remote sensing images of two lakes(Google Earth)

So we would like to compare these two lakes and study the differences about the impacts of human activities and the methods to protect them.Besides,we will try to show the relationships between lake ecosystems and global climate change.

Lake Taihu is the third largest freshwater lake in China and is a typical subtropical shallow lake. In recent years, the problem of eutrophication in Lake Taihu and the outbreak of cyanobacteria have caused great concern. The outbreak of cyanobacteria in Lake Taihu is related to the geography, hydrology and meteorological characteristics. The Yangtze River scouring brings a lot of nutrients to the Lake Taihu, which provides a rich material basis for the large-scale growth of cyanobacteria. The hydrodynamic transmission causes the cyanobacteria to gather in a specific area, causing the cyanobacteria bloom.

Lake Tai in Jiangsu province,China

photo by Yuancong Gou

In order to ensure the safety of the Lake Taihu water environment , The government of China controls sewage discharge and intercepts sewage, such as closing most of the sewage outlets and strengthening the comprehensive management of point pollution sources and surface pollution sources. Second, cyanobacteria have been salvaged on a large scale, and silt that is seriously polluted by the cyanobacteria in Lake Taihu have been removed. In addition, ecological restoration has been used to improve the self-purification capacity of Lake Taihu.

Did Lake Washington have this kind of environmental issues in history?Through some readings, we learnt that in 1950s a great deal of sewage were poured into Lake Washington every day from Seattle and other communities surrounding the Lake, which induced predictions of blue-green algae blooms just like nowadays Lake Tai. Luckily, between 1963 and 1968, over 100 miles of sewer trunk lines and interceptors were laid to carry sewage to treatment plants, and effluent entering the lake was reduced to zero in February, 1968 . It is a good example that people took the scientific advices seriously and put into public actions. The protection project which cost nearly $140 million was considered the costliest pollution control program in the country at that time , but it also been seen as a very successful rescue.

When the lake water is polluted, lake management is needed. Lake restoration and algae management are two types of lake management. The focus is mainly on solving problems in the water body, such as improving the water environment or removing excess algae. Here are some possible ways:

  • Cold water layer extraction：Using a siphon to pump out the cold water layer that is rich in the bottom layer, reducing the amount of nutrients in the water and the water with less oxygen load.
  • Cold water layer aeration：The cold water layer is usually rich in nutrients, and the oxygen consumption is also large. The use of an aerator to convert oxygen into the cold water layer can maintain the oxygen load of the layer, inhibit the release of phosphorus from the bottom mud source.
  • Scooping up. Filamentous algae can be removed by the way of scooping up , and the effect is good, but it is only suitable for small-scale removal and specific algae species. It is also time-consuming and labor-intensive to eliminate it.
  • Lake bottom dredging:The dredging at the bottom of the lake can increase the depth and volume of the lake, clear the bottom mud that is rich and nourish, control the root water and produce plants, and achieve the purpose of improving water quality.
  • Water dye:It does not directly kill algae or sinking plants, but shields the light it needs to inhibit its growth.The concentration of the dye in the water should be maintained throughout the growing season to avoid sunlight and keep the light in the water darker, so as to control the growth of algae and sinking plants.
  • Algaecide:Rapidly inhibiting or remove algae from water

These measures can deal with the problem of the biological symptoms of the lake, but can not solve the problem fundamentally.Therefore, it is a quick and short-term solution.

In order to solve the problem of water pollution and water quality from the root, long-term management should be taken into consideration. Long-term management is concerned with factors such as the environment, culture and living that affect the lake, focusing on long-term strategies and long-term investment.The long-term management of algae is mainly to remove the source phosphorus in the water body and prevent the external source of phosphorus from entering the water body, reducing the nutrients in the water. Although it takes a lot of time to do this,the effect of improving water quality is very good.It requires joint efforts of community, individual, landowners, and government.

When it comes to Lake ecosystem, it is an important part of freshwater ecosystem. Its formation and development have a significant impact on the global climate which will affect these lakes in turn. The change of climate will further affect the lake, causing the water temperature to rise, the water body composition to change, and the water area to shrink.

Some researchers use a one-dimensional numerical lake model to assess climate change impacts on mixing regimes in 635 lakes worldwide. They run the lake model with input data from four state-of-the-art model projections of twenty-first-century climate under two emissions scenarios. Under the scenario with higher emissions (Representative Concentration Pathway 6.0), many lakes are projected to have reduced ice cover; about one-quarter of seasonally ice-covered lakes are projected to be permanently ice-free by 2080–2100. Surface waters are projected to warm, with a median warming across lakes of about 2.5°C, and the most extreme warming about 5.5°C.

Looking back at the cyanobacteria event in Lake Taihu: the discharge of a large amount of domestic sewage and industrial wastewater and the continuous high temperature weather created a perfect hotbed for the overproduction of cyanobacteria.

Nowadays, global warming on the one hand makes the temperature rise in the spring of Lake Taihu in advance and delay on the temperature drop in autumn, which prolongs the growth time of cyanobacteria. On the other hand, it raises the water temperature as a whole. Therefore, it is more difficult to control the blooms.

Furthermore, the changes in the water area of lakes also reveal the impact of climate and human activities on the structure and function of lake ecosystem, and have a guiding significance for lake health assessment and water ecological restoration. The water area of lakes is mainly dominated by two major factors: climate factors and human activities. Among them, the replenishment and evaporation of water have caused natural fluctuations in the water area of lakes since ancient times, and the increasing human activities have brought irreversible trauma to the lakes.

We generally compared two lakes in Washington and in Jiangsu. They have different environmental and climate conditions while having had similar pollution events. The successful rescue of Lake Washington set a good example for us to learn that science can help us to keep a fine environment. In fact, many lakes near cities are facing the same problems. The outbreaks of phytoplankton and bad smells make it very obvious so that people will focus on this issues. However, with rapid climate change and human activities, we may cause some similar trouble in other ecosystems which are not very noticeable. We need to observe them carefully and think seriously about how human impacts act on our world, and then take actions to prevent the bad results.

 

References:

[1]Liuyan, Yang , et al. “Mechanism and control strategy of cyanobacterial bloom in Lake Taihu.” Journal of Lake Sciences (2019).

[2]胡明明, 朱喜. “中国淡水湖泊蓝藻爆发现状及其治理思路.” 2014中国环境科学学会学术年会

[3]Sound Science: Synthesizing ecological and socioeconomic information about the Puget Sound ecosystem. 2007. Mary H. Ruckelshaus and Michelle M. McClure, coordinators; prepared in cooperation with the Sound Science collaborative team. U.S. Dept. of Commerce, National Oceanic & Atmospheric Administration (NMFS), Northwest Fisheries Science Center. Seattle, Washington. 93 p.

[4]Lake and Watershed Management and Blue-green Algae Control in California and Other States of the United States  Wei Zhiqi  Ministry of Science and Technology of People’s Republic of China, Beijing 100862

[5]R. lestyn Woolway, Christopher J. Merchant.  Worldwide alteration of lake mixing regimes in response to climate change[J]. Nature Geoscience. 2019(12):271-276.