Annual variation in water column structure and its implications for the behaviour of Deep Chlorophyll Maximum (DCM) in a stratified tropical lake

The occurrence and dynamics of Deep Chlorophyll Maxima (DCM) in stratified water bodies has implications for aquatic productivity, biogeochemistry, and energy flow. Attributes of the DCM related to structure and function have been well studied in temperate systems but substantial knowledge gaps exist in tropical lakes due to limited studies. We investigated the seasonal and annual patterns of vertical chlorophyll distribution and behaviour of DCM along the water column of a tropical lake by monitoring Chl-a vertical profile biweekly over a two-year period. The aim was to understand the factors controlling seasonal variability of DCM and the functional relationship between DCM and epilimnetic Chl-a and changes in the physicochemical environment influencing these dynamic relationships. We found remarkable persistence of the DCM all year round with high average Chl-a and was not dissipated by lake mixing despite precipitous seasonal decline in euphotic depth. The persistence of DCM was linked with prolonged thermal stratification and high nutrient enrichment below the thermocline. DCM and epilimnetic algal chlorophyll were controlled by differing regulating mechanisms affected by stratification, mixing and restratification cycles of the lake. The euphotic depth and TP were the strongest predictors of DCM dynamics. Doubling of euphotic depth during thermal stratification increased DCM chlorophyll by 85 % above epilimnetic chlorophyll. These limnological patterns could be predicted from year to year to a high degree of certainty.