Saline lakes: integrating ecology into their management future

Abstract

Defining the key temporal scales of variability in ecological processes is fundamental to saline lake management because the physical, chemical and biological characteristics of saline lakes undergo fluctuations at different time scales, compared to those of freshwater lakes. A long-term study of Lake Gallocanta (25 km² area inland saline lake in NE Spain) provides the ecological basis for its management. The coupling of the administrative framework with its ecological processes is examined. Limnological and climatological parameters were measured using standard methods during 1977–1995. Complete desiccation of the lake occurred in 1983–86 and in 1994–95. Water level fluctuations were strongly correlated with meteorological events, particularly rainfall for seasonal and decadal time scales. The relationship between salinity and water volume follows the typical model described for playa lakes. However, the intensity and frequency of the salinity and water volume fluctuations in Lake Gallocanta also change over time. Most species show pulsing population dynamics at the larger time scales (annual, decadal). However, many of these show a continuous population development at shorter time scales. Examples are provided for several phytoplankton and zooplankton species. Fluctuations in water level also influence phyto and zooplankton community structure. The combination of the number of species, S, and the number of individuals, N, as K=log S/log N indicates that the community structure also fluctuates at different time scales. Most of the present laws established for the management of saline lakes are centered on the conservation of waterfowl. Although some generic laws attempt to preserve the overall natural ecosystem, only those dealing with the protection of wild flora and fauna, and threatened species, are implemented. However, ecological knowledge now suggests that the major objective for the conservation of saline lakes should be to preserve the fluctuation of the hydrological balance, avoiding groundwater extraction in the catchment area and surface water. Generic laws regulate water use in Spain and in many other countries. These laws are not useful for saline lake management because they do not offer solutions to the frequent conflicts arising between the water demand for intensive agriculture and nature conservation, which are common in the semi-arid zones where saline lakes are located. Integrated management of the land and water resources in the catchment area is required to preserve saline lake characteistics. Recent legislation aims to promote such management. A model of conservation and development of the overall ecosystem is presented.