Monitoring the concentration, distribution, origin and size of suspended particles in the water column during harbour dredging in Pakri Bay, the Gulf of Finland

Dredging activities can influence ecological balance in the vicinity of developing ports. In the current study, monitoring of suspended matter load in the water column during dredging operations was performed using WetLabs AC-spectra instrument which allows for direct measurements of absorption and attenuation coefficients. The corresponding spectral scattering coefficients were calculated and used for the description of the concentration and composition of suspended matter. Also, concentrations of suspended matter (SPM) and chlorophyll a (Chl a) were determined from the water samples. The analysis showed that the particles were mainly of mineral origin in the south-eastern part of the bay near the harbour dredging area and mainly of organic origin in the central and open part of the bay. The current study also showed that the calculation of the Chl-a concentration from the absorption coefficient using the empirical regression method can sometimes produce questionable results.