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Decadal trends and common dynamics of the bio-optical and thermal characteristics of the African Great Lakes.

Loiselle S, Cózar A, Adgo E, Ballatore T, Chavula G, Descy JP, Harper DM, Kansiime F, Kimirei I, Langenberg V, Ma R, Sarmento H, Odada E - PLoS ONE (2014)

Bottom Line: Lake surface temperature dynamics in nearly all lakes were found to be sensitive to the latitudinal position of the Inter Tropical Convergence Zone.Intra-lake differences in both surface temperature and phytoplankton dynamics occurred for many of the larger lakes.This inter-comparison of bio-optical and thermal dynamics provides new insights into the response of these ecosystems to global and regional drivers.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Biotecnologie, Chimica e Farmacia, Consorzio per lo Sviluppo dei Sistemi a Grande Interfase, Università degli Studi di Siena, Siena, Italy.

ABSTRACT
The Great Lakes of East Africa are among the world's most important freshwater ecosystems. Despite their importance in providing vital resources and ecosystem services, the impact of regional and global environmental drivers on this lacustrine system remains only partially understood. We make a systematic comparison of the dynamics of the bio-optical and thermal properties of thirteen of the largest African lakes between 2002 and 2011. Lake surface temperatures had a positive trend in all Great Lakes outside the latitude of 0° to 8° south, while the dynamics of those lakes within this latitude range were highly sensitive to global inter-annual climate drivers (i.e. El Niño Southern Oscillation). Lake surface temperature dynamics in nearly all lakes were found to be sensitive to the latitudinal position of the Inter Tropical Convergence Zone. Phytoplankton dynamics varied considerably between lakes, with increasing and decreasing trends. Intra-lake differences in both surface temperature and phytoplankton dynamics occurred for many of the larger lakes. This inter-comparison of bio-optical and thermal dynamics provides new insights into the response of these ecosystems to global and regional drivers.

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Lakes and lake sections included in the present analysis of the African Great Lakes.
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pone-0093656-g001: Lakes and lake sections included in the present analysis of the African Great Lakes.

Mentions: The Great Lakes of East Africa are among the world’s most important aquatic ecosystems from the point of view of ecosystem services, biodiversity and carbon cycling [1]. They are highly heterogeneous, presenting an array of hydrological and biological characteristics, ranging from shallow eutrophic water bodies (e.g. Lake Victoria) to deep oligotrophic lakes (e.g. Lake Tanganyika). Recent studies have demonstrated linkages between climate variability and productivity of several African lakes [2], [3], [4]. This is partially due to the importance of direct rainfall and evaporation in the water balances in the larger lakes (e.g. Lakes Tanganyika, Malawi and Victoria) and river flow in the smaller lakes (e.g. Lake Turkana) as well as climate driven lake stratification cycles [5], [6], [7]. Inter-annual variations in regional and global climate patterns have a strong influence on monsoon dynamics, in particular the Inter Tropical Convergence Zone (ITCZ) [8]. Local and regional impacts also play an important role on the chemical and biological dynamics of many of these lakes [9], [10], [11]. Remote measurements have been used to explore the spatio-temporal variability of the temperature and bio-optical properties in several of these lakes [12], [13], [14]. However, a systematic inter-lake comparison using a common methodology has yet to be performed. There are multiple reasons for this, geographical (e.g. altitude) and seasonal differences in atmospheric optical conditions and seasonal differences in aquatic optical properties. Most importantly, there are limited data for lake specific algorithm development and validation while standard bio-optical algorithms have been predominately developed for phytoplankton dominated water bodies found at sea level [15]. In the present study, we make a comparative analysis of the thermal and bio-optical dynamics of thirteen lakes lying in or between the two branches of the Great Rift in Eastern-Central Africa; Lakes Albert, Chilwa, Edward, Kivu, Kyoga, Malawi, Mweru, Naivasha, Rukwa, Tana, Tanganyika, Turkana and Victoria (Figure 1). Using site-specific seasonal smoothing of the time series, we examine their decadal trends. These trends are also compared to interannual climate drivers, allowing us to explore commonalities between lakes and potential drivers of change.


Decadal trends and common dynamics of the bio-optical and thermal characteristics of the African Great Lakes.

Loiselle S, Cózar A, Adgo E, Ballatore T, Chavula G, Descy JP, Harper DM, Kansiime F, Kimirei I, Langenberg V, Ma R, Sarmento H, Odada E - PLoS ONE (2014)

Lakes and lake sections included in the present analysis of the African Great Lakes.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3974808&req=5

pone-0093656-g001: Lakes and lake sections included in the present analysis of the African Great Lakes.
Mentions: The Great Lakes of East Africa are among the world’s most important aquatic ecosystems from the point of view of ecosystem services, biodiversity and carbon cycling [1]. They are highly heterogeneous, presenting an array of hydrological and biological characteristics, ranging from shallow eutrophic water bodies (e.g. Lake Victoria) to deep oligotrophic lakes (e.g. Lake Tanganyika). Recent studies have demonstrated linkages between climate variability and productivity of several African lakes [2], [3], [4]. This is partially due to the importance of direct rainfall and evaporation in the water balances in the larger lakes (e.g. Lakes Tanganyika, Malawi and Victoria) and river flow in the smaller lakes (e.g. Lake Turkana) as well as climate driven lake stratification cycles [5], [6], [7]. Inter-annual variations in regional and global climate patterns have a strong influence on monsoon dynamics, in particular the Inter Tropical Convergence Zone (ITCZ) [8]. Local and regional impacts also play an important role on the chemical and biological dynamics of many of these lakes [9], [10], [11]. Remote measurements have been used to explore the spatio-temporal variability of the temperature and bio-optical properties in several of these lakes [12], [13], [14]. However, a systematic inter-lake comparison using a common methodology has yet to be performed. There are multiple reasons for this, geographical (e.g. altitude) and seasonal differences in atmospheric optical conditions and seasonal differences in aquatic optical properties. Most importantly, there are limited data for lake specific algorithm development and validation while standard bio-optical algorithms have been predominately developed for phytoplankton dominated water bodies found at sea level [15]. In the present study, we make a comparative analysis of the thermal and bio-optical dynamics of thirteen lakes lying in or between the two branches of the Great Rift in Eastern-Central Africa; Lakes Albert, Chilwa, Edward, Kivu, Kyoga, Malawi, Mweru, Naivasha, Rukwa, Tana, Tanganyika, Turkana and Victoria (Figure 1). Using site-specific seasonal smoothing of the time series, we examine their decadal trends. These trends are also compared to interannual climate drivers, allowing us to explore commonalities between lakes and potential drivers of change.

Bottom Line: Lake surface temperature dynamics in nearly all lakes were found to be sensitive to the latitudinal position of the Inter Tropical Convergence Zone.Intra-lake differences in both surface temperature and phytoplankton dynamics occurred for many of the larger lakes.This inter-comparison of bio-optical and thermal dynamics provides new insights into the response of these ecosystems to global and regional drivers.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Biotecnologie, Chimica e Farmacia, Consorzio per lo Sviluppo dei Sistemi a Grande Interfase, Università degli Studi di Siena, Siena, Italy.

ABSTRACT
The Great Lakes of East Africa are among the world's most important freshwater ecosystems. Despite their importance in providing vital resources and ecosystem services, the impact of regional and global environmental drivers on this lacustrine system remains only partially understood. We make a systematic comparison of the dynamics of the bio-optical and thermal properties of thirteen of the largest African lakes between 2002 and 2011. Lake surface temperatures had a positive trend in all Great Lakes outside the latitude of 0° to 8° south, while the dynamics of those lakes within this latitude range were highly sensitive to global inter-annual climate drivers (i.e. El Niño Southern Oscillation). Lake surface temperature dynamics in nearly all lakes were found to be sensitive to the latitudinal position of the Inter Tropical Convergence Zone. Phytoplankton dynamics varied considerably between lakes, with increasing and decreasing trends. Intra-lake differences in both surface temperature and phytoplankton dynamics occurred for many of the larger lakes. This inter-comparison of bio-optical and thermal dynamics provides new insights into the response of these ecosystems to global and regional drivers.

Show MeSH