Bimodal transparency as an indicator for alternative stable states in South-American lakes

KOSTEN, SARIAN; VERNOOIJ, MARTINE ; VAN NES, EGBERT H.; GONZÁLEZ SAGRARIO, M. A.; CLEVERS, JAN G.P.W. ; SCHEFFER, MARTEN

FRESHWATER BIOLOGY (PRINT)

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Wiley Services Singapore Pte Ltd 1 Fusionopolis Walk #07-01 Solaris South Tower Singapore ; Año: 2012 vol. 57 p. 1191 - 1201

0046-5070

Evidence for the alternative state theory that claims that shallow lakes may be either clear and submerged vegetation dominated or turbid and phytoplankton dominated comes mostly from studies in temperate or boreal regions in Europe. Because of climate related differences in trophic interactions, however, it is not straight forward that this state theory applies to other regions as well. Here we focus on South American lakes combining field and Landsat satellite data. We study the frequency distribution of primary producers and water transparency for potential bimodality separating clear and turbid lakes. Possible shifts in alternative states were analyzed by comparing satellite data of two different years. Analyses of our field data indicate a bimodal pattern in primary producers, especially for submerged vegetation, and in water transparency. The satellite data analyses confirm this pattern with a strong bimodality in the reflectance data from 2005, but much less so in the 1987 data. In 1987 the lakes were generally more clear and the transition to higher turbidities was more gradual than in 2005. The temporal character of the bimodality and the underlying changes in lake transparency may be caused by increase in fertilizer use and subsequent eutrophication or by strong changes in hydrology. The 1987 situation was much wetter than 2005 which may have caused dilution leading to clearer water. Although a bimodal distribution in primary producer abundance and water clarity in not an absolute proof, the occurrence of bimodality in both our field data and satellite data suggests that alternative states are present in South American lakes.