Paavel, B; Arst, H; Metsamaa, L; Toming, K; Reinart, A (2011). Optical investigations of CDOM-rich coastal waters in Parnu Bay. ESTONIAN JOURNAL OF EARTH SCIENCES, 60(2), 102-112.
Parnu Bay in the Eastern Baltic Sea was chosen for studying the spatial-temporal variability of water parameters as an optically complex and semi-enclosed coastal area. The water properties of Parnu Bay are influenced by the town of Parnu with its 70 000 inhabitants and by the high inflow from the Parnu River. The in situ database was collected during the ice-free period of 2006-2007 (11 sampling stations, 10 series of field trips). According to the results, the main factor influencing the light attenuation in the water was coloured dissolved organic matter (CDOM) which overshadows the relationships between the radiation characteristics and organic/inorganic particles. In April and May, when the freshwater discharge of the Parnu River was highest, the values of a(CDOM)(380) were between 4.6 and 31.8 m(-1), while in September they varied only within 2.52-10.2 m(-1). The concentrations of chlorophyll a (including its metabolite phaeophytin a) generally ranged from 4 to 12 mg m(-3) but during algal blooms they rapidly increased to 31.8 mg m(-3). The temporal and spatial irregularity of suspended matter concentrations was caused by the loading of unpacked peat at the Parnu River mouth as well as by undulation and ship traffic in Parnu Bay. MODIS level 1 data with 250 m resolution were used for illustrative comparison of spatial and temporal variations in the water properties in Parnu Bay and the Gulf of Riga. An attempt to perform the quantitative analysis with the purpose of estimating the concentrations of different optically significant substances separately gave statistically incorrect results.