Nitrogen may
1) promote growth and hence shading of phytoplankton ;
2) promote shading of periphyton ;and
3) exert toxic stress on plant metabolism, by generating oxidative stress , disturbing carbon and nitrogen metabolisms by accumulating free amino acids (FAA) and losing soluble carbohydrates (SC) , and by inhibiting photosynthesis (Su et al., 2012), resulting in chlorosis of leaves and suppressed growth