Eutrophication simply implies the increase in nutrient or nutrient enrichment.
Commonly, waterways are connected to other water bodies. When water from farmlands washes fertilizers into them, there is an increase the available nutrient. Overtime, the water can be oversaturated with nutrients and this would lead to eutrophication. We can attribute eutrophication to human activities.
For the formation of the coal deposits the presence of the swampy vegetation and the needs a lot of moisture content and a plenty of warm temperatures for them to thrive. These conditions would have been near the today equator.
