Spatial distribution of zooplankton in response to ecological dynamics in tropical shallow lake: insight from Lake Malombe, Malawi

Abstract

This study assessed zooplankton density and Chl-a amount to understand their spatial and seasonal variation in Lake Malombe. Samples were collected for analysis during the hot, dry season (HDS) and cool, dry, windy season (CDWS). The zooplankton identified were Tropodiaptomus cunningtoni (TC), Mesocyclops aequatorialis aequatorialis (MAA), Thermocyclops neglectus (TN), Bosmina longirostris (BL), Diaphanosoma spp. (DS), and Nauplii. These zooplankton groups belong to copepods, Cyclopidae, Cladocera, Ctenopod, and Rotifers. Chl-a exhibited a substantial seasonal variation, with the highest concentration observed in HDS and lowest in CDWS. Zooplankton such as T. cunningtoni, M. aeq. aequatorialis, T. neglectus, B. longirostris, Diaphanosoma spp, Nauplii, and Rotifer increased during the HDS. The water temperatures (WT), pH, Dissolved Oxygen (DO), and Chl-a positively correlated with all zooplankton densities. Sodium (Na þ ) and Potassium (K þ ) ions positively correlated with TC, MAA, DS, Nauplii, and Rotifers. Chloride ion (Cl -) positively correlated with DS, Rotifers, while Carbonate ion (CO 3 2-) positively correlated with TC. Bicarbonate (HCO 3 -) correlated positively with DS and Rotifers, while TDS correlated negatively with BL, Nauplii, and Rotifers. Nitrite affected zooplankton density negatively, while SRP had a positive effect. The study revealed that physical-chemical variables, some significant ions, and Chl-a are the most critical factors influencing the spatial and seasonal variation of zooplankton density in the lake. These findings demonstrate the interaction between physical-chemical variables, Chl-a, and zooplankton and highlight the significance of ecological understanding of the complex dynamics of the food web system in shallow tropical lakes such as Lake Malombe-under the changing climate.

Application of DPSIR and Tobit Models in Assessing Freshwater Ecosystems: The Case of Lake Malombe, Malawi

“…Increased phytoplankton production, invasion of alien species, water quality degradation, drying up of rivers, over-exploitation of fisheries, increased erosion, shrinking of the lake, and a catastrophic decline in fish stocks, as reported by Hara [88], Dulanya et al [26], Froese et al [89], and Makwinja et al [35], have depressed the lake ecosystem's resilience. The depletion of high trophic level fish species in the 1980s led to what can be described as top-down cascading effects of human food web alterations [37]-a common scenario in many African inland freshwater shallow lakes' ecosystems [90][91][92].…”

“…as top-down cascading effects of human food web alterations [37]-a common scenario in many African inland freshwater shallow lakes' ecosystems [90][91][92].…”

“…Despite its ecological and economic significance, the lake has been overstretched due to human actions, climate variability, and landscape transformation [13,26]. Due to unprecedented economic pressures, rampant sedimentation, and water quality degradation [32,36,37], increased human population and climate change have further increased the burden on the lake [38]. Attempts were made to understand the socio-ecological systems and develop a sustainable ecosystem management plan for the lake [39,40].…”

Land use/land cover dynamics, trade-offs and implications on tropical inland shallow lakes’ ecosystems’ management: Case of Lake Malombe, Malawi

“…Lake Malombe is fed by water from Lake Malawi via a stretch of the Upper Shire River and shares the same aquatic ecology with Lake Malawi, including a high level of fish biodiversity, genetic plasticity, and endemism (FISH, 2015). Limnologically, Lake Malombe is a shallow, turbid, and nutrient-rich lake with shelving vegetated shores compared to Lake Malawi (Makwinja et al, 2021d). The lake is highly productive because of the water column, which mixes freely, recycling the bottom nutrients.…”

Assessment of trophic state in Lake Malombe, Malawi, using Sentinel-2 Multi-Spectral Instrument imagery

“…Satellite remote sensing is an effective inland water monitoring technique cheaper than the most di cult eld-based sampling method (Diamini et al, 2016). It offers valuable insights into phytoplankton distribution in the lake, a fundamental factor in understanding the inland water's trophic and limnological state (Makwinja 2021a). Time series remotely sensed re ectance provides a valuable opportunity to advance the basin-scale knowledge of the most productive lakes' ecosystems (Huang et al, 2014;Cózar et al, 2014).…”