Seasonal variations of nutrients concentration in aquatic ecosystems from Danube Delta Biosphere Reserve

Nutrients (nitrites, nitrates, phosphates) are essentials for organisms life that use photosynthesis. An excessive growth of these aquatic organisms or contrary may cause an imbalance in the entire aquatic ecosystem. Therefore, the present study aims to determine seasonal dynamics of nitrogen concentrations from ammonia, nitrites, nitrates, total nitrogen, phosphorus from orthophosphates, and total phosphorus from 7 deltaic areas that included a number of 37 sampling points, representative for all types of aquatic ecosystems from Danube Delta Biosphere Reserve, during the year 2015. The investigations on nutrients concentrations highlighted significant variations from one season to other and also exceeding's of the maximum allowed concentrations, regulated by existing legislation. The highest exceeding was identified for nitrite concentrations. Concentrations for dissolved forms had minimum and maximum values as follows: nitrogen from ammonia (0.099 mg L-1 and 0.267 mg L-1), nitrogen from nitrate (0.164 mg L-1 and 1.961 mg L-1), nitrogen from nitrite (0.005 mg L-1 and 0.028 mg L-1), dissolved phosphorus (0.005 mg L-1 and 0.028 mg L-1). Total forms of nutrients varied in the range of 0.021-0.185 mg L-1 for total phosphorus and 3.913-6.359 mg L-1 for total nitrogen. Minimum concentrations in maritime area obtained for ammonia, nitrites, orthophosphates and total phosphorus can be attributed to the filter capacity of the Danube Delta.