摘要：Shallow floodplain habitats connected to large rivers undergo seasonal flooding making them integral parts of large river ecosystems. In tropical and subtropical regions, water mixing in these habitats is described as polymictic, yet little description exists for other large river floodplain lakes. In this study, the effect of thermal input on die1 mixing was compared between subtropical Gar as Lake (GL)(1.2 m depth) connected to the Paran River, Brazil and temperate Crane Lake (CL)(0.5 m depth) connected to the Illinois River, USA. Physical, chemical, and microbial variables were measured at 3 h intervals on clear, nearly windless (avg. < 1.2 m s -1 ) days in summer (GL, 8-9 Jan 02; CL, 8-9 Aug 02). Nocturnal, convective mixing was evident for temperature (range: GL, 28-33 °C; CL, 23-32 °C) and oxygen (range GL: 23-196%; CL: 24-200%) in each system by nightfall (1930h) and correlated with differences in nitrate and ammonia. Although total bacterial density differed between surface and bottom water samples by afternoon, it was similar at both depths by evening (CL, 2230h) or early morning (GL, 430h)Diel mixing occurred in both systems and has important implications in nutrient cycling, coupling of oxic-anoxic processes, and distribution of microbiota.
