Investigation of the Combined Effects of Temperature and Nutrients on Chlorophyll-a Concentration in the Tigris River, Baghdad

Rivers are exposed to global warming and eutrophication, which in turn affect phytoplankton biomass in rivers. This study investigates the changes in Chl-a concentration, an indicator of phytoplankton biomass. A microcosm experiment was conducted, with water sampling from the Tigris River in Baghdad during the wet season. Temperature increase was based on raising the temperature by 3 °C higher than the ambient temperature, while nutrient enrichment was based on the mean values of soluble reactive NO3-1 and PO4-3 verified in the Tigris River. Variations in Chl-a concentration are associated with changes in WT and nutrient enrichment; NO3-1 and PO4-3. Our results showed that the Chl-a concentration was 0.8 μg/l in the control microcosm. Temperature increase led to an increase in Chl-a of Temperature microcosm 1 μg/l, enrichment of nutrient, in turn, led to an increase in Chl-a of NO3-1 and PO4-3 microcosms to 1.2 and 0.8 μg/l, respectively, so the temperature increase and nutrient enrichment together led to a greater increase in Chl-a of T+NO3-1 and T+PO4-3 microcosms 1.2 and 1.1 μg/l, respectively, than if it were a single effect, which constitutes the highest concentration of Chl-a during the experiment. The effects of temperature and/ or nutrient can change the concentration of Chl-a. Nutrient enrichment. NO3-1 and PO4-3, were identified as key contributors to Chl-a concentration, while warming influences the growth of Chl-a by enhancing metabolic and photosynthetic processes under nutrient-enriched conditions.