Water resources occupy most of the earth’s area. Every change in water resources will have a serious impact on the earth, and human activities are drastically changing the quality of the earth’s water. We may not be able to see some of these changes, but their impact is not small at all.
How turbidity affects organisms?
Turbidity is an indicator of the water quality. The higher the turbidity, the more turbid the water. The lower the turbidity, the clearer and more transparent the water. According to relevant standards, when 1 liter of water contains 1 mg of silica gravel, the turbidity produced is 1 degree. When the turbidity reaches 10 degrees, the turbidity of the water will be clearly felt. In nature, due to the continuous circulation of water, the turbidity of water far away from land is not high. For example, the sea water in the ocean is very clear. However, with the increase in marine trade and activities, this situation is gradually changing. The discharge of sewage and the stirring of sediments have gradually increased the turbidity of seawater.
What are the effects of changes in turbidity? It cannot be said that it is definitely better or worse, because for aquatic organisms, whether low turbidity or high turbidity is more suitable for their survival is still undecided. Red algae and green algae need light for photosynthesis, so they live in clear water environments. Sponges, corals, and bryozoans also often live in clear water environments, and they will die due to turbid water. Aquatic organisms that feed on sediments, such as echinoderms and mollusks, prefer seawater with higher turbidity, which can transport food for them.
Changes in turbidity affect fish differently. Some small fish are more affected, such as the Delta Smelt. The Delta Smelt is a small, transparent fish that lives in the San Francisco Estuary in California, USA. The turbid water here is very suitable for its survival because it is small and transparent, so it can easily hide in the turbid water and avoid being eaten. However, on the other hand, turbid water is not very friendly to some predators, such as striped bass, which feed on Delta Smelt. Turbid water makes it more difficult for it to find food. Therefore, slight changes in turbidity can cause changes in the types and numbers of aquatic organisms, so the environmental protection department uses turbidity measurement as an important criterion for assessing water quality.
How temperature affects organisms?
Compared to turbidity, changes in temperature have a greater impact on aquatic organisms. We already know that global warming has caused rising temperatures on land, and the same changes are also happening in the water, which puts many aquatic organisms at risk.
Even if the ocean temperature rises only a little, it will have a serious impact on aquatic organisms. Rising water temperatures can cause errors in the connection of food chains and food webs in the ocean, causing changes in the composition of biological communities and ecosystems, or even destruction. In addition, high temperatures can provide a breeding ground for the growth of some pathogenic microorganisms in the water, causing the spread of certain diseases.
More dramatic changes in water temperature will cause some fish to change their habitats and look for cooler places to live. Studies have found that when the water temperature rises from 17°C to 21°C, delta smelt can no longer live safely in the mud and sand, making them more vulnerable to predators. For some cold-water fish, they will have nowhere to escape. Antarctic fish are the most numerous fish in the Southern Ocean. They have lived in a very narrow low-temperature range for more than 15 million years. When the ocean temperature rises to the physiological limit, they will become extinct.
If the temperature continues to rise, the lives of more aquatic organisms will be affected. According to research, when the ocean water temperature is 10-15°C, cold-water fish are the dominant population. When it exceeds 20°C, warm-water fish are the dominant population. When the water temperature is 25-30°C, hot-water fish are the dominant population. When it exceeds 33°C, most fish cannot survive. Aquatic mammals also don’t like high temperatures. A global distribution survey of 115 species, including pinnipeds and whales, showed that there are more whales in areas above 40° latitude, while as temperatures rise, the distribution of pinnipeds and whales in low latitudes decreases.
All aquatic life, from tiny organisms at the bottom of the food chain to high-level predators such as fish and marine mammals, will be affected by ocean warming.
How does the content of substances affect organisms?
For aquatic organisms, the most serious and direct impact is the change in the content of substances in the water.
The content of substances in water is actually changing all the time. Precipitation brings gases and impurities in the atmosphere, including but not limited to dust on land, oxygen and nitrogen compounds in the air, smoke and dust ejected by volcanic eruptions, and even waste gas emitted by industrial and mining enterprises. Inorganic ions in soil and rocks penetrate into water bodies. The organic matter generated by the decomposition of the remains of aquatic organisms constantly changes the composition of substances in the water.
Fortunately, aquatic organisms have adapted to these changes, and the dynamic balance of substances is beneficial to their lives. However, the drastic changes in the content of substances caused by human activities have greatly exceeded the adaptability of organisms. In 2010, an oil drilling platform off the coast of Louisiana in southern the United States caught fire and exploded, leaking about 1,000 barrels of crude oil into the Pacific Ocean every day, affecting the global ocean and the organisms in it. In the same year, a wastewater pond at an aluminum plant in Hungary burst, causing about 1 million cubic meters of toxic wastewater containing heavy metals such as lead to flow into the Danube River, and the creatures in some nearby small rivers were almost completely wiped out. Not long after, a similar tragedy occurred in China, when a wastewater pond at a tin mining company in Guangdong burst, and wastewater flowed into the Huanghua River, killing more than 100,000 kilograms of fish.
However, humans still don’t know how to deal with it. Due to practical factors such as financial and material resources, we cannot monitor the content of all substances in the water. We can only select some representative ones for monitoring, such as 68 toxic chemicals such as mercury, arsenic, chromium, sulfide and cyanide. But there are still many uncommon chemicals or chemicals whose harm to organisms is unknown and are still out of our control.
Not only harmful substances, but also drastic changes in nutrient content can cause disasters. Nitrogen and phosphorus are the most important nutrients for aquatic organisms. It is very important to maintain the balance of these nutrients, and human activities are changing the balance of nutrients. Under the scouring of rainwater, fertilizers containing a large amount of nutrients, especially nitrogen and phosphorus, will flow into the water body, and industrial wastewater will also introduce a large amount of nutrients into the water body.
Too much nutrients in the water can cause phytoplankton to proliferate and grow rapidly. Although phytoplankton is a very important type of aquatic life, dense phytoplankton is harmful, and they produce chemicals called microcystins. Aquatic life that drinks this sewage will be poisoned and die. Worse, the rapid proliferation of phytoplankton and the process of bacteria decomposing it when it dies will consume a lot of oxygen in the water, which will cause a large number of aquatic life to die due to lack of oxygen.
As you can see, water quality is composed of many different components, and these components must be kept in balance for aquatic life to live normally. How to make water “just right” is still a problem that humans have not yet solved.
