In large groups, duck and geese can contribute heavy loads. Nitrogen in the forms of ammonia and nitrates functions as a plant nutrient and initiates eutrophication . Sewage is the main source of human-influenced nitrate addition to streams. Nitrates are introduced by inadequately treated wastewater from sewage treatment plants, effluent from illegal sanitary sewer connections, and poorly functioning septic systems. Fertilizers from fields and runoff from cattle feedlots, dairies, and barnyards are other nitrate sources.
Phosphates accumulate from living plants and animals, their byproducts, and their remains.
Phosphate ions bonded to soil particles and in laundry detergents also end up in streams. Other sources of phosphorus include sewage, animal waste, soil erosion, fertilizers, and drained swamps and marshlands. Excess phosphate creates blooms of extensive algal growth. Forest fires and fallout from volcanic eruptions are responsible for natural eutrophication in streams, while humans are the instigators of cultural eutrophication. Phosphorus initially stimulates aquatic plant growth, which unlocks even more phosphorus from bottom sediments.