Estimation of N/P Ratios Levels in a Coastal Bay, Southern Adriatic Sea

Abstract

The DIN:DIP atomic ratio (N/P) considered optimal for phytoplankton growth is 16:1 (Redfield ratio). Significant deviations from 14 to low N/P ratio might indicate potential nitrogen limitation, the ratio between 14 and 16 indicates both nitrogen and phosphorus co-limitation, whereas from 16 to high N/P ratios indicates potential phosphorus limitation of phytoplankton primary production. This might affect the biological state of the ecosystem, in particular the phytoplankton biomass, species composition and food web dynamics. NO3- and PO43-concetrations in surface waters in six station samples were measured monthly by using spectrophotometer UV-VIS, whereas total Chl a was measured using flourometric method, from May - October 2011 and from June - October 2012. The data are converted on molar concentration (NO3-N and PO4-P) in order to calculate N/P ratios. The comparison of N/P ratios from 2011 to 2012 in Durres Bay, results in both N and P co-limitation for 2011 and N limitation of primary production in 2012. Comparing N:P ratio in Durres Bay to Southern Adriatic Sea for both 2011 and 2012, resulted in N limitation for Durres Bay and both N and P co-limitation of primary production in open waters. There is a strong positive relationship between primary production (total Chl a) and nitrogen in coastal waters and a moderate positive relationship of primary production and N/P ratio in coastal waters of Durres Bay.