Ammonium, nitrate and phytoplankton interactions in a freshwater tidal estuarine zone: potential effects of cultural eutrophication

摘要: Nitrate and ammonium are the most important nitrogen sources for phytoplankton growth. Differential utilization of inorganic nitrogenous compounds by has been observed may have significant impacts on primary productivity at local scales. We used enrichment experiments with natural populations from freshwater tidal zone Guadiana estuary, a coastal ecosystem increasingly subjected to anthropogenic influences, study effects nitrate N-consumption In addition, we combined additions understand inhibitory effect over uptake. Ammonium concentrations in reaches estuary throughout sampling period were too low exert an uptake or toxic was clearly main source site. Overall, seemed become limiting lower than 20 μM N-limitation particularly during summer. A trend decreasing increasing suggested overall preference ammonium. However, group-specific, it mainly green algae cyanobacteria. fact, cyanobacteria relied only as their N-source. On contrary, diatoms preferred nitrate, did not respond additions. The eutrophication increased inputs due urban waste effluents result shift community composition, towards dominance algae.