Mozingo Studies I. Ice phenology and limnological legacies in a mid-continental reservoir

Long-term, integrated records of limnology are rare in the central United States.  Mozingo Lake is a reservoir in northwestern Missouri that was sampled regularly since its creation in 1994.  Physical data were collected during 121 visits and compared to meteorological observations. July hypolimnetic temperatures have risen rapidly (2.4°C / decade: P=0.037), suggesting weakened summer stratification in the future.  Winter conditions were rarely correlated with lake conditions in the following July; the exception is July epilimnion temperature, which correlated with ice-over date, January hypolimnion temperature, and ice duration (P=0.006, 0.010, and 0.024).  In contrast, winter ice-over date was best correlated with air temperature in the preceding July (P=0.006); other factors were not significantly correlated, including fall air temperatures, July epilimnion temperatures, and October water column temperatures. Analysis of air temperatures preceding ice-over revealed that the strongest correlation was with a 68-day average air temperature of 4.8°C. July air temperatures, along with ice-over date, correlated with January ice thickness and ice duration (P=0.014 and 0.001, respectively). This suggests that a warm July is associated with a mild winter, a relationship confirmed by a significant correlation (P=0.011). Ice thickness, ice duration, and ice-out date also correlated with winter air temperature (P≤0.003 for each). It therefore appears that summer conditions influence winter conditions which, in turn, influence certain lake conditions in the following summer; this observation indicates that winter conditions may not reset physical parameters in lakes.  Legacies thus may span various intervals, ranging from a week to a year or more.  Although the Mozingo Lake record is brief (20 years), it suggests directions for longer-term studies.  Multi-year legacy effects have rarely been documented, but in Mozingo Lake they suggest that a single strong climatic anomaly may affect the lake for several years.