This paper summarizes the results of years of research in the Nistru water content of
nutrients in the 2005-2010 years. The purpose of research is the identification of the spatial and
interannual dynamics of mineral forms of nitrogen and phosphorus content with the evaluation of
the influence limiting on the phytoplankton development. In the Nistru waters near Naslavcia for
the research period the forms of nitrogen NO3
-, NO2
-and phosphorus - PO4
3-, P2O5 were
constantly present. In 2005-2006 ammonium nitrogen was episodically absent.
The tendencies of the average concentration changes of inorganic nitrogen and
phosphorus for the period by the length of river portion from the Naslavchia to Dubasari
hydroelectric power station (HPP) dams and by years has been revealed. The average total
nitrogen (Ntot) and phosphorus (Ptot) content in Naslavcia was 1.896 and 0.14 mg / L,
respectively. Downstream of Cosauts there was reduced the total amount of mineral nitrogen up
to 1.712 mg/L and phosphorus in Mereshovca and the HPP dam to respectively 0.11 – 0.12
mg/L. Fluctuations by years of Ntot and Рtot average concentrations in the waters to Naslavcia and
Dubasari reservoir had the appearance of the trend polynomial with the coefficients of 0.59 and
0.36 respectively.
Estimation of influence of mineral biogenic elements on phytoplankton development was
performed in accordance with the Forsberg method by the ratio Ntot / Ptot [1]. According to the
analysis in the Naslavcia shutter of Nistru waters for 2005-2006 years the ratios Ntot / Ptot <10 in
2007 and Ntot / Ptot> 20 in 2009 were received. This indicated that in the first case the limitant of
primary production was mineral nitrogen, in the second - phosphorus. In the Dubasari reservoir
nitrogen was limited the algae development in 2005, 2007, 2009 years, phosphorus - in 2008.

Fig.1 Dynamics of annual values of Fig.2 Trend of the ratio Ntot/ Ptot in 2005-2010
the ratio Ntot/ Ptot
References:
[1] Forsberg, C. Die physiologischen Grundlagen der Gewassereutrophierung. In: Z. Wasser-und
Abwasser Forsch. 1979. Bd.2, H. 2.