6:15 PM - 7:30 PM
[ACG33-P02] Distribution of benthicmicroalgae and nutrients in tidalflat sediments estimating from chemical composition and delta13C
Keywords:benthic microalgae, nutrients, tidal flat sediments
Study site is located at Fujimae-higata inner part of Nagoya Port in Aich Prefecture, central Japan. Samples of surface sediments (1.5 cm depth, n=25) were subjected to analyses of chlorophyll a, TOC, TN, SiO2, TiO2, Al2O3, Fe2O3, MgO, MnO, CaO, Na2O, K2O, P2O5, Cr, Cu, Pb, Zn, Zr, δ13C and δ15N.
The surface sediments are characterized by high positive correlations of chlorophyll a with TN (r = 0.70, p<0.001) and TOC (r = 0.68, p<0.001). On the other hand the correlation between chlorophyll a and excess-P that is available for microalgae is very low (r = 0.09, p>0.5). Based on analysis of principal component chlorophyll a and other elements can be categorized into three groups, i) elements associated with coarse-grained materials, such as Al, Ca, and K, ii) elements adsorbed and /or bounded to fine-grained materials such as Cr, Cu, Pb, Zn, Fe, and P, iii) elements associated with organic matter, such as TOC, TN, and chlorophyll a. According to these results, three segments were identified for Fujimae-higata, including Segment 1 closest to the river mouth where sediments are dominated by coarse-grained materials, Segment 2 away from the river mouth, characterized by fine-grained materials, and Segment 3 between Segments 1 and 2, characterized with organic matter. Values of δ13C of surface sediments (average = -25.99 ‰, n = 25) are almost the same as those of suspended matter in the closest river (average = -25.94 ‰, n = 9). Benthic microalgae tend to have heavier δ13C ratio (approx. -18 ‰) than phytoplankton and the highest δ13C ratio in the analyzed sediment samples is -24.6 ‰. This suggests that the contribution of benthic microalgae to the sediment organic matter is small. The organic matter in Fujimae-higata sediments is likely supplied largely by riverine inflow.