Effects of physical dynamics on the water column structure of Lake Bosomtwe/Bosumtwi, Ghana (West Africa)

Puchniak, M.; Awortwi, F. E.; Sanful, Peter O.; Frempong, E.; Hall, Roland I.; Hecky, Robert E.

doi:10.1080/03680770.2009.11902305

Cited by 7 publications

(34 citation statements)

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“…In Lake Bosumtwi, stratification patterns and seasonal water column fluctuations are mediated by strong climatic forcing (Puchniak et al, ). Important factors dictating stratification patterns include atmospheric temperature, convective heat exchanges and wind stress (Puchniak et al, ; Sanful, Aikins, Frempong, Hall, & Hecky, ). The seasonal variations in regional meteorology are a consequence of the latitudinal displacement of the Intertropical Convergence Zone (ITCZ) between the Atlantic Ocean to the south and Sahara desert to the north (Mamoudou, Frouin, & Nicholson, ).…”

Section: Limnology Of Lake Bosumtwimentioning

confidence: 99%

“…Lake Bosumtwi possesses a band of chlorophyll a (Chl a ) in the metalimnetic layer that persists throughout the year, develops an exceptionally high peak concentration each year in April under conditions of high transparency and water column stability, but rapidly disaggregates to normal levels in July (Puchniak et al, ). Reconnaissance survey of the water column properties of this meromictic, mesotrophic lake first detected the DCM with YSI fluorescence probes (and confirmed with HPLC analysis) in hypoxic‐anoxic water between the lower and upper boundary of the metalimnion, just below the oxycline and within the nutricline at 12 m depth (Verburg, ).…”

Section: Introductionmentioning

confidence: 99%

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Occurrence and seasonal dynamics of metalimnetic Deep Chlorophyll Maximum (DCM) in a stratified meromictic tropical lake and its implications for zooplankton community distribution

Sanful

Otu

Kling³

et al. 2017

Internat Rev Hydrobiol

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Deep Chlorophyll Maxima (DCM) is an important feature of stratified lakes and oceans but very little is known about the phenomenon in tropical systems. Proximate factors accounting for DCM presence include light, thermal stratification and nutrients but biotic interactions such as zooplankton grazing can actively support DCM formation, structure and maintenance. We examined DCM characteristics in tropical Lake Bosumtwi at biweekly intervals between April and July of 2005 and 2006 and also assessed zooplankton herbivore interactions with the DCM. The onset and development of the seasonal DCM peak was based on stable water column, steep thermocline, availability of a nutricline and nutrient limitation in the epilimnion. Euphotic depth doubled during DCM formation and increasing transparency tripled DCM Chl a in the metalimnion just below the oxycline. DCM, however, disaggregated with seasonally induced deeper mixing. The range of variability in surface chlorophyll did not differ significantly between seasonal and aseasonal DCM period. There was about one‐fourth difference between mean surface and metalimnetic chlorophyll concentrations but this shift in resource location did not trigger a descent to deeper waters by herbivores. Herbivore grazing could not be linked to surface variations in water clarity and deep‐water irradiance needed for DCM formation and maintenance. DCM presence therefore was not enhanced by surface water grazing activities of zooplankton. This suppressed biotic influence indicated that DCM dynamics is driven by lake clarity, thermal and nutrient gradients which constitute key abiotic drivers. Direct consumption of the DCM by herbivorous zooplankton was not evident and the energy therein is possibly lost to the anoxic deep waters of the lake through sedimentation. The sinking organic matter could be returned to the pelagic food web via the microbial loop represented by bacteria, ciliates and heterotrophic/mixotrophic flagellates inhabiting the lake's deep layers.

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Section: Limnology Of Lake Bosumtwimentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Occurrence and seasonal dynamics of metalimnetic Deep Chlorophyll Maximum (DCM) in a stratified meromictic tropical lake and its implications for zooplankton community distribution

Sanful

Otu

Kling³

et al. 2017

Internat Rev Hydrobiol

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“…The lake is mesotrophic and permanently stratified. The deep water below 15 m is persistently deoxygenated except during August of certain years when mixing sometimes redistributes oxygen to greater depths but the water column is never oxygenated throughout its depth (Puchniak et al 2009). Strong mixing in August sometimes result in fish kills.…”

Section: Introductionmentioning

confidence: 98%

“…Highest transparency occurs from April to July each year allowing the development of the deep water chlorophyll maximum by the green sulphur bacterium, cf. Pelodictyon clathratiforme (Puchniak et al 2009). Cyanobacteria dominate the phytoplankton community in the mixed layer (Poste, Hecky and Muir 2008;Awortwi 2009 Eleven fish species, mainly cichlids, inhabit the lake.…”

Section: Introductionmentioning

confidence: 98%

“…This amount of chlorophyll excludes contributions from the seasonal deep water plate of green-sulphur photosynthetic bacteria. Mean pH is 8.9; average conductivity measured was 1150 mS cm 71 , alkalinity recorded was 10320 mmol l 71 , salinity averaged 0.32 g l 71 and the amount of carbon dioxide measured was 59 mol l 71 (Puchniak et al 2009). Mean surface water temperature is 27.768C.…”

Section: Introductionmentioning

confidence: 99%

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Secondary production of Chaoborus ceratopogones (Diptera: Chaoboridae) in Lake Bosumtwi, Ghana

et al. 2012

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Preliminary surveys of the zooplankton of Lake Bosumtwi revealed copious amounts of larval stages of Chaoborus ceratopogones in the water column. Secondary production was subsequently determined to assess its role in the zooplankton community. Head capsule length distinguished consecutive larval instars without overlaps. Growth rates were low in instar I and pupae. Instars II and III were the focal points of population growth. Growth equations were used to compute stage-specific biomass and production. Mean larval density was 16,053+15,865 organisms per m 3 . Daily standing stock varied from 80 to 4180 mg dw m 73 and an annual average production of 920 mg dw m 73 yr 71 . Prey biomass was weakly correlated with Chaoborus biomass so most of the variance in Chaoborus production was controlled by mechanisms external to food abundance. Transfer efficiency of Chaoborus production to planktivorous fish may be low because of intense fishing pressure on the lake.

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Depth distribution of zooplankton in relation to limnological gradients under different stratification and interannual regimes in a deep, tropical crater lake

Sanful

Aikins

Hecky

2017

Ann. Limnol. - Int. J. Lim.

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Zooplankton vertical distribution was studied in Lake Bosumtwi to understand how spatial and temporal variations in the water column affected diurnal and nocturnal patterns. Biweekly samples were collected for 24 consecutive months at the deepest point from 2005 to 2006. Water column properties shaping habitat suitability, namely temperature, light intensity, dissolved oxygen and phytoplankton biomass, varied markedly with depth but less with season. Most zooplankton stayed in the epilimnion continuously and their distribution was unaltered by lake stratification, mixing and restratification. Species dwelt permanently in the epilimnion without any necessity to migrate. Reduced water column variability and resultant weak selective pressures suppressed greater dispersion of species. Chaoborus ceratopogones (Theobald) was the main invertebrate predator and performed upward and downward movements on a diel cycle. Competing prey species overlapped extensively in spatial and temporal degree of habitat use. Chaoborus, however, segregated in deep water during the day, thereby minimizing prey vulnerability and promoting coexistence among predators and prey. During night-time residence, prey species may be exposed to increased predation risk from Chaoborus but gains in reproductive potential in warm, food-rich surface waters may offset losses to mortality. Our results suggest that high degree of habitat constancy and consequently weak selective pressures contributed to the lowered behavioural responses of zooplankton. The persistently skewed distribution of zooplankton is adaptive to predation and competition and promotes species coexistence. This behaviour will optimize growth and reproductive benefits over the cost of descent to suboptimal conditions in deep water.

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Effects of physical dynamics on the water column structure of Lake Bosomtwe/Bosumtwi, Ghana (West Africa)

Cited by 7 publications

References 10 publications

Occurrence and seasonal dynamics of metalimnetic Deep Chlorophyll Maximum (DCM) in a stratified meromictic tropical lake and its implications for zooplankton community distribution

Occurrence and seasonal dynamics of metalimnetic Deep Chlorophyll Maximum (DCM) in a stratified meromictic tropical lake and its implications for zooplankton community distribution

Secondary production of Chaoborus ceratopogones (Diptera: Chaoboridae) in Lake Bosumtwi, Ghana

Depth distribution of zooplankton in relation to limnological gradients under different stratification and interannual regimes in a deep, tropical crater lake

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