Retrospective analysis of Chlorophyll-a and its correlation with climate and hydrological variations in Mindu Dam, Morogoro, Tanzania

Abstract

The measurement of Chlorophyll-a in aquatic systems has usually correlated to harmful algae in water bodies. Harmful algal blooms (HABs) are as a result of massive proliferation of blue-green algae (Cyanobacteria). Harmful algal blooms (HABs) pose threats to both the environment as well as human health, and despite this well-known fact, their monitoring and management are still challenging. Climate change, extreme weather events, and hydrological changes are the main drivers and predicted to benefits HABs dynamics in most parts of the world. In Tanzania, studies of HABs proliferation and their possible correlation with variability in climate and hydrology still lag behind despite high demand for developing predicting tools and prevention of HABs proliferation. The present study reports on the retrospective analysis of HABs variation in Mindu Dam located in Morogoro, Tanzania using remote sensing techniques. In the present study comparison between in situ measurement and ocean color (OC2) Chlorophyll-a with the surface reflectance's (band and band combinations) of Landsat 7 and Landsat 8 Operational Land Imager (OLI), was performed. Another approach involved searching for patterns and trends, and teleconnection between Chlorophyll-a index (best band ration) and the climate and hydrological variations in the catchment. The findings demonstrated that minimum and maximum temperatures, solar radiation, Chlorophyll-a concentration registered significant increasing trends. Wind speed and directions, water levels for Mindu Dam showed a significant decreasing trend. On the other hand, rainfall showed no trend. The patterns suggest that there are link and causality between the HABs variations and meteorological parameters such as temperatures, solar radiations, and water levels. The study, therefore, contributes to the application of recent advances in remote sensing and retrospectively analysis of bloom dynamics and search for their link with climate and hydrological changes.

Typhoon- and pollution-driven enhancement of reactive bromine in the mid-latitude marine boundary layer

“…Chlorophyll a (Chl-a) is an important indicator of algal biomass in aquatic ecosystems, which can be used as a proxy to provide an estimate of phytoplankton biomass in seawater [ 42 ]. Bromocarbons, e.g.…”

The implication of water accessibility challenges to urban water governance in Morogoro municipality, Tanzania

“…This vindicates that the public health for the urban dwellers who depend on water supply from the Mindu Dam is not at risk. However, recent studies including [ 31 , 35 , 36 ] demonstrate eutrophication due to high concentration of nitrate and phosphate despite efforts done by the water supply and sanitation authority to improve water quality [ 30 ]. Similarly, studies including [ 35 , 36 ] confirm brownish water colour because of soil erosion and sedimentation that are also attributed to a decreasing water level over time.…”

“…However, recent studies including [ 31 , 35 , 36 ] demonstrate eutrophication due to high concentration of nitrate and phosphate despite efforts done by the water supply and sanitation authority to improve water quality [ 30 ]. Similarly, studies including [ 35 , 36 ] confirm brownish water colour because of soil erosion and sedimentation that are also attributed to a decreasing water level over time. This is not good news because eutrophication may negatively affect public health while decreasing amount of water in the reservoir translates into water accessibility challenges.…”

Harmful Algal Blooms in Aquaculture Systems in Ngerengere Catchment, Morogoro, Tanzania: Stakeholder’s Experiences and Perception

“…Water quality status and trends in the catchment have also been studied with an indication that there is significant pollution contributed by agriculture, domestic, and industrial activities [ 12 , 28 , 29 , 30 , 31 ]. Furthermore, recent work on chlorophyll-a and variations in climate and hydrology has highlighted some possible causes of HABs in the catchment [ 32 ].…”