What limits do anthropological studies of modern societies have as historical sources ?

Recall that areas with high net primary productivity not only produce high levels of biomass rapidly, they also take up large amounts of co2 and give off large amounts of oxygen. what is the likely result of the increasing amounts of sediments and fertilizers in the major rivers emptying into oceans and affecting algal beds, reefs, swamps, and estuaries? a fisheries will improve as the extra nutrients feed shellfish and fish. b eutrophication, followed by hypoxia, is a likely result, ultimately leading to less co2 uptake and more oxygen released. c productivity in these areas will increase permanently, leading to more co2 uptake and more oxygen released. d eutrophication, followed by hypoxia, is a likely result, ultimately leading to more co2 uptake and more oxygen released. e eutrophication, followed by hypoxia, is a likely result, ultimately leading to less co2 uptake and less oxygen released.