Ahealthy environment depends on biogeochemical cycles maintaining a balance of input and output. high levels of nitrogenous compounds in the waterways can cause an algal bloom. how does an algal bloom affect a marine ecosystem? a.) it decreases the carbon dioxide in the water, creating a toxic environment. b.) it decreases oxygen in the water, creating a toxic environment. c.) it increases the carbon dioxide in the water, stimulating plant growth. d.) it increases the oxygen in the water, stimulating plankton growth