Dead zones are low-oxygen areas that develop on the sea floor. scientists hypothesize that phytoplankton blooms cause these dead zones. phytoplankton blooms occur when excess nutrients are introduced by pollution from fertilizers, sewage plants and the burning of fossil fuels. which of the following would most likely cause an increase in these contributors to dead zones? rainfall patterns that increase freshwater runoff from terrestrial ecosystems replacing coal-fired power plants with windmills farming practices that reduce nitrate and phosphate applications constructing efficient water-recovery and treatment plants