Question

Suppose a large number of dead fish are found floating in a lake. how would you determine whether they died from cultural eutrophication or from exposure to toxic chemicals?

Answer 1

To determine if dead fish in a lake died due to cultural eutrophication or toxic chemical exposure, assess signs of algae growth and test for oxygen levels, indicating eutrophication, or analyze fish tissues for toxic substances, suggesting chemical exposure. Factors like temperature and point-source pollution should also be considered.

Step-by-step explanation:

Determining Cause of Fish Deaths in a Lake

To determine whether dead fish found in a lake died from cultural eutrophication or from exposure to toxic chemicals, one would need to investigate several environmental factors and conduct specific tests. Observations of excessive algae growth, water clarity, and oxygen levels could indicate cultural eutrophication, as nitrogen (N) and phosphorus (P) from agricultural runoff and sewage can lead to algal blooms. These blooms decrease water quality and lower dissolved oxygen, creating dead zones.

Conversely, if toxic chemicals such as polychlorinated biphenyls (PCBs) or heavy metals (mercury, lead, cadmium) are suspected, tissue samples from the dead fish should be analyzed for these substances. These chemicals can biomagnify up the food chain and lead to fish kills. Additional considerations include water temperature, the presence of unusual substances on the water's surface, and any known industrial discharge points nearby.

Moreover, eutrophication often happens gradually while chemical spills may cause sudden fish kills. Identifying the source as point or nonpoint is also crucial in distinguishing between the two causes.

Answer 2

To determine the reason for the fish death, do the following:
1. Test the water for the presence of organic substances that may be poisonous to the fish.
2. Test the dissolved oxygen concentration of the lake at different locations and at different depths.
3. Perform full toxicological examination of the lake to determine if any pollutant or poisonous chemical is present in the lake.