Determining patterns of stratification and mixing in tropical crater lakes through intermittent water-column profiling: A case study in western Uganda

Abstract. Equatorial East Africa has a complex, regional patchwork of climate regimes, with multiple interacting drivers. Recent studies have focussed on large lakes and reveal signals that are smoothed in both space and time, and, whilst useful at a continental scale, are of less relevance when understanding short-term, abrupt or immediate impacts of climate and environmental changes. Smaller-scale studies have highlighted spatial complexity and regional heterogeneity of tropical palaeoenvironments in terms of responses to climatic forcing (e.g. the Little Ice Age [LIA]) and questions remain over the spatial extent and synchroneity of climatic changes seen in East African records. Sediment cores from paired crater lakes in western Uganda were examined to assess ecosystem response to long-term climate and environmental change as well as testing responses to multiple drivers using redundancy analysis. These archives provide annual to sub-decadal records of environmental change. The records from the two lakes demonstrate an individualistic response to external (e.g. climatic) drivers, however, some of the broader patterns observed across East Africa suggest that the lakes are indeed sensitive to climatic perturbations such as a dry Mediaeval Climate Anomaly (MCA; 1000–1200 AD) and a relatively drier climate during the main phase of the LIA (1500–1800 AD); though lake levels in western Uganda do fluctuate. The relationship of Ugandan lakes to regional climate drivers breaks down c. 1800 AD, when major changes in the ecosystems appear to be a response to sediment and nutrient influxes as a result of increasing cultural impacts within the lake catchments. The data highlight the complexity of individual lake response to climate forcing, indicating shifting drivers through time. This research also highlights the importance of using multi-lake studies within a landscape to allow for rigorous testing of climate reconstructions, forcing and ecosystem response.

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Phytoplankton communities in the crater lakes of western Uganda, and their indicator species in relation to lake trophic status

Ecological Indicators ◽

10.1016/j.ecolind.2019.105563 ◽

2019 ◽

Vol 107 ◽

pp. 105563 ◽

Cited By ~ 5

Author(s):

Angela Nankabirwa ◽

Wannes De Crop ◽

Thijs Van der Meeren ◽

Christine Cocquyt ◽

Pierre-Denis Plisnier ◽

...

Keyword(s):

Indicator Species ◽

Trophic Status ◽

Crater Lakes ◽

Lake Trophic Status ◽

Phytoplankton Communities ◽

Western Uganda

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A BEM for the Hydrodynamic Analysis of Oscillating Water Column Systems in Variable Bathymetry

Energies ◽

10.3390/en13133403 ◽

2020 ◽

Vol 13 (13) ◽

pp. 3403 ◽

Cited By ~ 3

Author(s):

Kostas Belibassakis ◽

Alexandros Magkouris ◽

Eugen Rusu

Keyword(s):

Boundary Element Method ◽

Water Column ◽

Black Sea ◽

Bottom Topography ◽

The Black Sea ◽

Device Performance ◽

Oscillating Water Column ◽

Energy Potential ◽

Hydrodynamic Analysis

In this work, a novel Boundary Element Method (BEM) is developed and applied to the investigation of the performance of Oscillating Water Column (OWC) systems, taking into account the interaction of the incident wave field with the bottom topography. The modelling includes the effect of additional upwave walls and barriers used to modify the resonance characteristics of the device and improve its performance as the U-OWC configuration. Numerical results illustrating the effects of depth variation in conjunction with other parameters—such as chamber dimensions as well as the parameters associated with the turbine and power take-off system—on the device performance are presented and discussed. Finally, a case study is presented regarding the potential installation of an OWC in a selected port site in the Black Sea, characterized by a good wave energy potential, on the coast of Romania.

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Environmental Conditions in a Carpathian Deep Sea Basin During the Period Preceding Oceanic Anoxic Event 2 - A Case Study from the Skole Nappe

Geologica Carpathica ◽

10.1515/geoca-2015-0004 ◽

2015 ◽

Vol 65 (5) ◽

pp. 433-450 ◽

Cited By ~ 3

Author(s):

Krzysztof Bąk ◽

Marta Bąk ◽

Zbigniew Górny ◽

Anna Wolska

Keyword(s):

Water Column ◽

Deep Sea ◽

Silica Content ◽

Turbidity Currents ◽

Ecological Groups ◽

Deep Basin ◽

Oceanic Anoxic Event ◽

Plankton Production ◽

Basin Floor

Abstract Hemipelagic green clayey shales and thin muddy turbidites accumulated in a deep sea environment below the CCD in the Skole Basin, a part of the Outer Carpathian realm, during the Middle Cenomanian. The hemipelagites contain numerous radiolarians, associated with deep-water agglutinated foraminifera. These sediments accumulated under mesotrophic conditions with limited oxygen concentration. Short-term periodic anoxia also occurred during that time. Muddy turbidity currents caused deposition of siliciclastic and biogenic material, including calcareous foramini-fers and numerous sponge spicules. The preservation and diversity of the spicules suggests that they originate from disarticulation of moderately diversified sponge assemblages, which lived predominantly in the neritic-bathyal zone. Analyses of radiolarian ecological groups and pellets reflect the water column properties during the sedimentation of green shales. At that time, surface and also intermediate waters were oxygenated enough and sufficiently rich in nutri-ents to enable plankton production. Numerous, uncompacted pellets with nearly pristine radiolarian skeletons inside show that pelletization was the main factor of radiolarian flux into the deep basin floor. Partly dissolved skeletons indicate that waters in the Skole Basin were undersaturated in relation to silica content. Oxygen content might have been depleted in the deeper part of the water column causing periodic anoxic conditions which prevent rapid bacterial degra-dation of the pellets during their fall to the sea floor.

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