Limnological and ecological sensitivity of Rwenzori mountain lakes to climate warming

Abstract

An increasing number of studies forecast that anthropogenic climate change poses serious consequences for the biodiversity and ecosystem functioning of high-elevation mountain lakes, through a series of both direct and indirect effects. The impacts of future climate warming on alpine ecosystems are of particular concern, given that warming is expected to be most pronounced at high elevations around the globe. Here, we evaluate the limnological and ecological sensitivity of high-ele- vation lakes in the Rwenzori Mountains (Uganda-D. R. Congo) to climate change. This is done by comparing the species assemblages of larval chiron- omid remains deposited recently in lake sediments with those deposited at the base of short cores (dated to within or shortly after the Little Ice Age) in 16 lakes. Chironomid-based reconstructions of mean annual air temperature (MATemp) are made using a variety of inference models (with transfer functions based on weighted averaging, weighted-averaging partial least squares, and a weighted modern analogue technique), and two different calibration data sets, one covering the full regional temperature gradient and one comprising only high-elevation Rwenzori lakes and ponds. The reconstructed historical temperature change ranges between a cooling of -2.03C and a warming of ?3.22C (with n = 16 lakes 9 3 models 9 2 calibration data sets). How- ever, excluding the atypical mid-elevation lake Mahoma (2,990 m altitude), we find a three-to-one ratio of cases of inferred warming against inferred cooling, and of the 24 D MATemp values exceeding 0.60C, 23 are positive and only one is negative. Chironomid-inferred temperature changes mostly fall within the error range of the regional temperature inference models. A generalized linear mixed model analysis of the combined result from all lakes (except Mahoma) nevertheless indicates significantly warmer MATemp (on average ?0.38 ± 0.11C) at present