Controlling Factors of Phytoplankton Productivity in Marshes in a Hot Climate with High Seasonal Variation

In this work the Auda marsh, which is part of a system of Iraqi marshes, was sampled to assess the seasonal dynamics and controlling factors of microalgae productivity. The marshes are situated in a hot climate with high seasonal variation near the Arabian Gulf. Physicochemical and biological measurements were taken for water in three areas. Bio-optical models were constructed to describe the primary productivity and chlorophyll-a concentrations in the wet and dry seasons separately and also for the entire area of the Iraqi marshes. The models, as well as almost all measurements, showed high seasonal variation. The mean water temperature was 16 °C in the wet season and 28 °C in the dry season. An almost twofold difference was measured for turbidity and the concentrations of dissolved oxygen and chlorophyll-a for the two seasons. Chlorophyll-a appeared to be a better indicator of ecosystem conditions than primary productivity or biological oxygen demand, according to the results obtained from canonical correlation analysis. Nitrogen or phosphorous did not explain primary productivity or chlorophyll-a to an appreciable extent. Biological variables were related most strongly to water temperature and turbidity, which were the factors most important for controlling phytoplankton productivity in the marshes.