"what change may likely occur to chemistry of ocean if nutrient overload occurred causing historically unprecedented proliferation of algae in ocean ecosystem waters?"

Had to look that one up. Spent some time looking through my old textbooks, because they are more reliable than the internet.

'Quantitative Chemical Analysis' offered no information. Neither did 'Inorganic Chemistry'or 'Physical Chemistry'. 'Spectroscopic Methods in Organic Chemistry' wasn't helpful, nor was 'Molecular Symmetry and Group Theory'. My biology textbook might have something useful to say about algae, but it would be cheating to consult a biology textbook on a chemistry question. So once again I am forced to say dunno. You might have more luck asking an environmental chemist.