Spatial and temporal variations in coloured dissolved organic matter in large and shallow Estonian waterbodies

摘要

Spatial and temporal variations in coloured dissolved organic matter (CDOM) were studied in two large, shallow and eutrophic Estonian lakes (Peipsi and Vortsjarv), and in the CDOM-rich Parnu Bay (in the Gulf of Riga, Baltic Sea). The concentration of CDOM, determined by its absorption coefficient at wavelength λ = 380 nm, ranged from 4.17 to 22.3 m~(-1) in Peipsi, from 3.96 to 15.7 m~(-1) in Vortsjarv and from 2.24 to 32.9 m~(-1) in Parnu Bay. The amount of CDOM was spatially variable in all investigated waterbodies. It was highest in the coastal/onshore areas and in the estuaries of the main rivers. It usually decreased from spring towards autumn, and the seasonal patterns were most distinct in the onshore areas. In standing water bodies, the short-term dynamics of discharges had a more significant effect on CDOM concentration in onshore areas than in offshore areas, where the influence of the discharges became visible over a longer period. The results suggest that in large and shallow water bodies the share of the allochthonous component in the CDOM pool decreases towards offshore areas. The impact of CDOM discharged into the inflowing rivers reaches further from shores if the ratio of the catchment area to the volume of the standing water body (C/V) is larger. The influence of precipitation on CDOM absorption proved to be insignificant.