**4. Conclusion**

around Kisumu and Homa Bay areas are considered more vulnerable to fecal contamination, than open lake sites. Safe water quality implies low risk from bacteriological pollution and acceptable properties in terms of chemical, oduor, and taste [121]. Under the World Health Organization (WHO) guidelines, the bacterium *E. coli* should not be detected in a given 100 ml sample of drinking water [122]. Increased nutrients from atmosphere, land and fecal contamination, fuel the growth, and proliferation of algal blooms in surface water. Cyanobacteria are potentially toxic to humans and animals and can also degrade the ecological and esthetic values of water. From previous phytoplankton surveys in Kisumu Bay of the Nyanza Gulf of *L. Victoria* (Kenya), cyanobacteria were the most dominant, contributing 50% to the total phytoplankton biovolume. The highest MC concentrations were recorded between November and March coinciding with the wet season when rainfall and nutrient enrichment from the catchment increased [13]. Algal blooms were thicker and more frequent in Murchison Bay than Napoleon Gulf. Highly toxic blue-green algal scums (*Microcystis* and *Anabaena* spp.) and water hyacinth (*Eichhornia crassipes*) congregated along the shores of the city of Gaba (Uganda)

*L. Victoria* (Tanzania), the level of water exchange from individual bays to the main basin is an important factor influencing eutrophication and microcystin production in nearshore habitats [124]. Microcystins were found in closed bay sites, and concentrations ranged from 0.4 to

Particulate matter fluxes into the bottom sediments remove and incorporate particulate-bound metals from the water column, where they can become permanently buried or reintroduced back through sediment resuspension, especially in shallower areas. Similarly types of feed and sources are important factors which can contribute to accumulation of non-essential metals and other organics in aquatic food chains and caged fish. Supplementary fish diets improve fish nutrition. However, understanding how dietary MeHg affects its bioaccumulation in caged fish fed from marine based feeds is unknown but of importance. Variations in sediment metal contents have been reported in the lake from different surveys in 2010, 2012, and 2013. Total mercury concentration in sediments fell within the range of values recorded elsewhere but with low ng/l concentrations in the water. There is paucity of data on Hg contents in biota from the gulf, apart from initial results by Campbell et al. [103]. Recent research indicates that heavy metals do tend to accumulate in the sediments below fish farms. However, most studies have found that concentrations are within acceptable environmental guidelines even at farms that have been in production for many years [125]. Toxic metals that bioaccumulate and magnify along food chains are a concern to human health worldwide. Improvement in feed formulations is expected to decrease Zn loading to the marine environment, as many manufacturers are adding lower amounts of a more available form, zinc methionine [126]. Recently moderate to high levels of sum of seven PCB concentration were provided in sediments and

respectively. Fish cestode endoparasites biomagnified PCB levels than levels in fish hosts. These levels were found to be comparable with ranges of the PCB values found in other places of the world [127]. In a recent study, Abong'o et al. [128] indicates occurrences of some OCs around island waters of *L. Victoria*, supporting previous reports of use of the same pesticides in the wider catchment by Musa et al. [129]. Antibiotics and therapeutants are administered to recover sick fish, but this has declined in marine aquaculture. Commercially medicated feed

microcystin-LR equivalent and coincided with high abundance of *Microcystis* spp.

and 3 μgL−<sup>1</sup>

dry weight and 300 to 3000 μgKg−<sup>1</sup>

[123]. In bays of

lipid weight,

water intake sites. Microcystin levels were between <0.5 μgL−<sup>1</sup>

fish, with median values of 2.2 to 96.3 μgKg−<sup>1</sup>

13 μg l −1

56 Persistent Organic Pollutants

Sediments eroded from watersheds are important determinant factors in water quality and integrated water resource management. Increased concentrations in surface water causes increased turbidity, reduced under water light transmission and siltation, and reduced water storage in dams and shallow lakes.

Maintaining good sediment and water quality today is prioritized due to human health related concerns from faecal contamination from untreated and partially treated domestic wastewaters; discharge of industrial chemical effluents; increased use of pesticides, fertilizers, and herbicides for crop production and livestock rearing; and persistent organic pollutants and pharmaceutical residues which are endocrine disruptors and carcinogens.

Bottom lake sediments are important archives of the lake and anthropogenic indicators of their catchment. In *L. Victoria*, although the deeper (> 40 m) depositional areas are in the open lake, visual observations show that most of the offshore sediments consists of muddy deposits plus significant shell remains, with more sandy type of sediments in some of the areas off river-mouths.

**Author details**

Address all correspondence to: jjmghanga@yahoo.co.uk

Kenya Marine and Fisheries Research Institute (KMFRI), Kisumu Research Centre, Kisumu,

Lake Sedimentary Environments and Roles of Accumulating Organic Matter in Biogeochemical…

http://dx.doi.org/10.5772/intechopen.79395

59

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The sediment organic carbon contents varied spatial, but there were no significant variations between the different sampling periods. The surficial sediments are organic rich and are characterized by a relatively high water content, with over 89% of the samples containing water contents of greater than 75%. In 2012 survey, sediment organic matter contents were more variable and ranged from 1.90 to 33.47%.

An evaluation of the SOM at different heating durations at constant temperature 550°C and at very high temperatures of 950°C did not show any significant differences. High primary production and greater settling in deeper area contribute to the nature of sediments deposited and also are reflected in the relatively high OC contents.

The importance of sediments in adsorption of contaminant substances and influencing geochemical processes within the lake are also emphasized. It is recommended that continuous monitoring strategies are adopted in view of the new cage culture developments initiated in most of the African tropical lakes, including Lake Victoria, as uneaten feeds and operations may influence water and sediment quality in cases where designed best management practices are not fully implemented. There is a need to prioritize sediment research including the microbial component, porewater exchanges, and sediment fluxes which are rarely incorporated in major projects.
