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Tropical alpine areas may be highly sensitive to climate change. Yet, because high-resolution palaeoenvironmental studies in these regions are scant, patterns of environmental change over the last few centuries, and linkages with regional changes, remain poorly resolved. This article presents a 400-year palaeolimnological record from Lower Kitandara Lake (3,989 m above m.a.s.l.), located in the Rwenzori Mountains of Uganda, where marked glacial recession has been recorded over much of the twentieth century. An age model is produced for a 57.5 cm sediment core based on 210Pb and 14C dating, suggesting a basal date of approximately 1600 AD. Diatom and organic geochemistry (%TOC, C/N ratios, δ13C) analyses are carried out at an approximately decadal resolution. Twentieth-century glacial recession does not appear to have significantly impacted either the diatom or geochemical records. However, large ecological changes have occurred during the past 400 years, particularly shown by the diatom fluxes and geochemical data. Throughout the core, the diatom record reveals only minor changes in assemblage composition, which may be related to the dominance of Staurosira construens var. venter in the lake’s diatom flora, a tychoplanktonic taxon which is highly adaptive to environmental change. Geochemical analyses, however, reveal a marked change at around the end of the eighteenth century, when C/N ratios suggest an increase in the dominance of algal aquatic sources to lacustrine organic matter, concomitant with a stabilisation of catchment inputs and increased diatom productivity, which may have been caused by reduced glacial inputs. The relationship between these changes at Lower Kitandara Lake and wider regional climate change that occurred at the end of the eighteenth century is not well understood, but this study highlights the need for additional research to link drivers of alpine ecosystem change with those operating at low altitudes. [ABSTRACT FROM AUTHOR]

This study describes the physical and chemical properties of 17 Afroalpine lakes (>2 m deep) and 11 pools (<2 m deep) in the Rwenzori mountains, Uganda-DR Congo, with the aim to establish the baseline conditions against which to evaluate future environmental and biological changes in these unique tropical ecosystems, and to provide the foundation for lake-based paleoenvironmental studies. Most Rwenzori lakes are located above 3,500 m elevation, and dilute (5–52 μS/cm specific conductance at 25°C) open systems with surface in- and outflow. Multivariate ordination and pairwise correlations between environmental variables mainly differentiate between (1) lakes located near or above 4,000 m (3,890–4,487 m), with at least some direct input of glacial meltwater and surrounded by rocky catchments or alpine vegetation; and (2) lakes located mostly below 4,000 m (2,990–4,054 m), remote from glaciers and surrounded by Ericaceous vegetation and/or bogs. The former group are mildly acidic to neutral clear-water lakes (surface pH: 5.80–7.82; Secchi depth: 120–280 cm) with often above-average dissolved ion concentrations (18–52 μS/cm). These lakes are (ultra-) oligotrophic to mesotrophic (TP: 3.1–12.4 μg/l; Chl- a: 0.3–10.9 μg/l) and phosphorus-limited (mass TN/TP: 22.9–81.4). The latter group are mildly to strongly acidic (pH: 4.30–6.69) waters stained by dissolved organic carbon (DOC: 6.8–13.6 mg/l) and more modest transparency (Secchi-disk depth: 60–132 cm). Ratios of particulate carbon, particulate nitrogen and chlorophyll a in these lakes indicate that organic matter in suspension is primarily derived from the lakes’ catchments rather than aquatic primary productivity. Since key features in the Rwenzori lakes’ abiotic environment are strongly tied to temperature and catchment hydrology, these Afroalpine lake ecosystems can be expected to respond sensitively to climate change and glacier melting. [ABSTRACT FROM AUTHOR]