Hydrological connectivity as most probable key driver of chlorophyll and nutrients in oxbow lakes of the Bug River (Poland)

Concentrations of chlorophyll, dissolved inorganic nitrogen and phosphorus, total phosphorus and suspended solids were analysed in 10 oxbow lakes of the Bug River in spring and summer. According to their connectivity with the river, all lakes were divided into 3 categories - lakes connected with the river channel but separated from the floodplain inputs, lakes connected with the river but receiving inputs from the floodplain and totally isolated lakes. Connected lakes showed significantly higher concentrations of available nutrients and chlorophyll but the relationship between the two variables was weak in the spring and non-existent in the summer. Suspended solids were also more abundant in connected than in isolated lakes. Analyses of the proportion of chlorophyll and particulate phosphorus in suspension led us to the conclusion that water movement in connected lakes inhibited sedimentation and kept algae in the water column. Isolated oxbow lakes devoid of wind-driven mixing were more susceptible to algal sedimentation which would explain the differences observed between the two lake categories.