Patterns of productivity during eutrophication: a mesocosm experiment

In a 28 mo mesocosm experiment, levels and patterns of productivity and respiration were observed for a range of nutrient additions selected to provide a gradation from conditions in lower Narragansett Bay, Rhode Island, USA. to maximum impact for an urbalJ. t\!ary receiving present day leve1s of sewage effluents. For a 3Z. fold increase in nutrients, system apparent prod.uction increased by only a factor of 3, 5. Seasonal patterns of . autotrophy during the winter-spring diatom bloom and , heterolrophy during summer and early fall occurred at all treatment levels. With the exception of the 8 x treci\ment, all treatments above 2 X had a greater respiratory demand in the water column than the benthos. The highest treatment mesocosm (32 X) wentbrieny anoxic during the second summer of the experiment during a period when little productivity was occurring in the water column.