Conservation of a permanent hypersaline lake: management options evaluated from decadal variability of Coleofasciculus chthonoplastes microbial mats

Abstract

‘La Salada de Chiprana’ (NE Spain) is a permanent athalassic saline lake, and as such unique in Western Europe. More than 20 years ago, it was recognized that this lake should be protected; particularly, because it supported extensive microbial mat communities built by the cyanobacterium Coleofasciculus (Microcoleus) chthonoplastes and submerged aquatic vegetation of an endemic form of the foxtail stonewort (Lamprothamnium papulosum var. papulosum f. aragonense).For centuries, the lake hydrology, salinity and water levels have been driven by the combined effects of anthropogenic activities (e.g. irrigation in the watershed) and climatic factors.In the early 1990s, the water level increased and salinity dropped as a consequence of excessive freshwater inputs from direct overflow via irrigation canals. As a result, the microbial mats and aquatic vegetation perished and water column turbidity increased. Based on these observations, since 1994 management measures were introduced aimed at reducing the freshwater input by stopping the direct overflow from irrigation canals. This resulted in a rapid recovery of the hypersaline features of the lake, particularly of the microbial mat communities and the aquatic vegetation.Since 2000, there has been a persistent trend of decreasing lake level and increasing salinity. The population of the endemic foxtail stonewort collapsed in 2006 and the area occupied by C. chthonoplastes mats has drastically decreased. This raises the important question on how to manage athalassic saline lakes in their agrocultural context and calls for a review of the management option taken in the early 1990s. While it could be argued that the current situation is closer to natural hydrological functioning than 20 years ago, we propose that management should seek to conserve the original microbial and aquatic vegetation communities.Copyright © 2012 John Wiley & Sons, Ltd.

Lake La Salada de Chiprana (NE Spain), an Example of an Athalassic Salt Lake in a Cultural Landscape

“…Such behavior is natural for these salt lakes as water levels rise during winter and spring and decrease during summer, thus achieving their annual minimum levels in late summer or autumn. The decreasing lake level between 1991 and 2008, corresponded to a 42% reduction in surface (from 36 to 21 ha) a 55 % reduction in volume (from 893,000 to 405,000 m 3 ) [9]. The decrease in the surface is illustrated in Figure 3.…”

“…In the early 1990s, the maximum depth reported for the lake was 5.6 m [8]. Between the early 1990s and early 2009, the lake level decreased overall by 1.75 m [9]. Hence, on 4 August 2007, the Confederación Hidrográfica del Ebro recorded a maximum depth of 3.7 m. The surface areas and volumes of the salt lake have been calculated from the topography of the landscape and the level and bathymetry of the lake [9,10].…”

“…Between the early 1990s and early 2009, the lake level decreased overall by 1.75 m [9]. Hence, on 4 August 2007, the Confederación Hidrográfica del Ebro recorded a maximum depth of 3.7 m. The surface areas and volumes of the salt lake have been calculated from the topography of the landscape and the level and bathymetry of the lake [9,10]. Superimposed on these trends, since 1998, the lake also showed repeatable intra-annual fluctuations with amplitude of 30-50 cm [9].…”

“…Hence, on 4 August 2007, the Confederación Hidrográfica del Ebro recorded a maximum depth of 3.7 m. The surface areas and volumes of the salt lake have been calculated from the topography of the landscape and the level and bathymetry of the lake [9,10]. Superimposed on these trends, since 1998, the lake also showed repeatable intra-annual fluctuations with amplitude of 30-50 cm [9]. Such behavior is natural for these salt lakes as water levels rise during winter and spring and decrease during summer, thus achieving their annual minimum levels in late summer or autumn.…”

“…This separated 822 tons of dissolved salt representing a loss of 2% of salt for the main lake. Nevertheless, the salinities in the lake showed remarkable conservative behavior, i.e., the mass of total dissolved salt in the lake was rather constant and variations of its salinities were directly related to the volume of the lake [9]. In conclusion, after a period of excessive water discharges in the lake in the early 1990s, since the introduction of the measures in 1993, the lake hydrology has been governed by high evapotranspiration (1000-1500 mm year -1 ), low rainfall (200-400 mm year -1 ), water runoff in its endorheic watershed, irrigation returns and groundwater flows.…”