Humans use many chemical substances for farming that consequently affect biodiversity. These compounds, which are rich in nitrogen and phosphorus, are used to fertilize crops. Excessive use of these compounds causes

eutrophication and algal growth

Explanation:

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algal growth due to eutrophication

Explaination:

Eutrophication is where these nutrient rich compounds mix with nearby water sources and promote the growth of large amounts of algae. Algae go through respiration and take up the dissolved O2 in water which causes these areas to experience low O2 levels. Everything needs O2 to survive thus nearby organisms and plants die out creating dead zones.