ABSTRACT
HRBS-GLWNB 2020 presents the first open-source and high-resolution bathymetry, shoreline, and water level data for Lakes Victoria, Albert, Edward, and George in East Africa. For each Lake, these data have three primary products collected for this project. The bathymetric datasets were created from approximately 18 million acoustic soundings. Over 8,200 km of shorelines are delineated across the three lakes from high-resolution satellite systems and uncrewed aerial vehicles. Finally, these data are tied together by creating lake surface elevation models collected from GPS and altimeter measures. The data repository includes additional derived products, including surface areas, water volumes, shoreline lengths, lake elevation levels, and geodetic information. These data can be used to make allocation decisions regarding the freshwater resources within Africa, manage food resources on which many tens of millions of people rely, and help preserve the region's endemic biodiversity. Finally, as these data are tied to globally consistent geodetic models, they can be used in future global and regional climate change models.
ABSTRACT
Microplastic pollution of aquatic systems is a widely recognised environmental challenge. In this study, the occurrence, abundance, distribution and chemical nature of microplastics within the size range 0.3-4.9 mm, was assessed in the surface water of northern Lake Victoria. Lake surface transects in the sites were sampled using a floating manta net and analysed for microplastics. The various sites examined were grouped into three: Group A- sites in vicinity of fish landing and recreational beaches, and within urban or semi urban setting; Group B - sites in vicinity of only fish landing beaches within a rural community setting, and Group C - Sites in the vicinity of river inflows. Our results show occurrence of microplastics in all sites (range: 2834-329,167 particles/km2 or 0.02-2.19 particles/m3), with the abundance highest in group A (range: 103,333-329,167 particles/km2 or 0.69-2.19 particles/m3) and lowest in group C (range: 2834-20,840 particles/km2 or 0.02-0.14 particles/m3). All the microplastics were secondary in nature being derived from plastic materials utilised by the community. The largest proportion (36%) of microplastic counts were of the size <1 mm which poses a threat to water quality and fisheries of the lake. Analysis of the chemical composition of microplastics indicated dominance by the low density polymers: Polyethylene and Polypropylene across the microplastic types. The occurrence of microplastics derived from degradation of large plastic debris implies that proper plastic waste management measures be implemented in the communities operating on the lake and in its vicinity, in order to safeguard the ecosystem benefits derived from the lake.
ABSTRACT
An investigation was conducted on the macro-benthic fauna of the Napoleon Gulf in the northern part of Lake Victoria from March 2011 to December 2016 at the cage fish farm. The aim was to examine the likely impact of cage aquaculture on macro-benthic invertebrates. Cage aquaculture is now a common practice on Lake Victoria yet little is known about its long-term effect on macro-benthic faunal assemblages. Temporal variation indicated a general decline in annual faunal density at the farm area with corresponding stability at upstream (control) and downstream sites. Arthropods remained numerically dominant at the control and downstream sites. The percentage abundance of EPT (Ephemeroptera, Plecoptera, and Trichoptera) and Malacostraca was highest at the upstream and lowest at the farm area. The farm area which initially was dominated by molluscs became dominated by arthropods after 3 years. The decrease in density of molluscs at the farm area was attributed to the general decrease in density of two species: Bellamya unicolor (Gastropoda) and Corbicula africana (Bivalvia). These two species were initially abundant but showed decline within the farm area with corresponding stability at the upstream and downstream areas. Oligochaete annelids were more abundant within the farm area than at the upstream and downstream sites. These findings suggested that molluscs offered better prediction of the impact of cages on the environment than arthropods. Besides that, in a community dominated by pollution-tolerant organisms, the impact of aquaculture may not be immediate especially when organic loading from aquaculture is moderate.
