Meromixis Occurring in Mono Lake
by Heidi Hopkins
A study which has been submitted for publication in the scientific journal Ambio indicates that Mono Lake has entered a state of chemical stratification, or "meromixis," in which the upper, less saline layer of the lake fails to mix with the colder, more saline water below. The study has been funded by funded by the Department of Water and Power (DWP) and the National Science Foundation.
Usually, Mono Lake stratifies during the summer months due to solar heating and freshwater inflow, only to "turn over" in the fall, mixing completely from top to bottom. This mixing brings essential nutrients from the lake's lower levels into the surface waters. According to Dr. Robert Jellison, one of the scientists working on the study, in 1995 the great volume of water entering the lake combined with the low lake level and the lake's extremely high salinity to create a meromictic condition which persisted into 1996.
To project the duration of meromixis, Jellison used a lake-mixing model, applying it to 50-year simulations based on varying historic sequences of freshwater inflows. The model results suggest that the current management regime will result in long-term meromixis at Mono Lake in most cases. Jellison suggests that the stratification could lower lake productivity, reducing available food for the lake's birds.
While Jellison's study is no doubt credible, the actual implications of long-term meromixis on lake ecology remain unknown. Meromixis is a natural phenomenon that has occurred in the past, even before DWP's water diversions. In addition, the Jellison study analyzed deep water areas of the lake, not the readily mixing shoreline zone, which generates the majority of food resources for birds. Indeed, lower salinity caused by meromixis in this zone may be beneficial to productivity. Furthermore, meromixis must be assessed in the larger context of Mono Lake resources; suggestions that meromixis be averted by curtailing streamflows, for example, fail to consider the health of the streams themselves.
The Mono Lake Committee will continue to monitor the issue. Certainly, we want to know how lake productivity will be affected by the current restoration regime. On the other hand, we need to be cautious about this issue being used as a tool to reopen the Water Board decision and modify the lake level requirement.
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to learn more about meromixis.
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