FACT SHEET

Monitoring pollution in 4 biodiversity hotspots in Lake

Victoria (Nyando, Awach, Nzoia and Yala river mouths

for informed decisions

May 2020

KMF/RS/2020/C1.20

KENYA MARINE AND FISHERIES RESEARCH INSTITUTE

FRESH WATER SYSTEMS

KMFRI Headquarters P.O. Box 81651 – 80100, Mombasa Tel: +254 (041475151/4) Email: kmfridirector@gmail.com

KMFRI Kisumu P.O. Box 1881 – 40100, Kisumu

Tel: +254 (0) 711 233774 Email: auramulanda@yahoo.com

AUTHORS

Mwamburi, J.,

Miruka J. B.,

Wawiye, P., Guya,

F., Aura C.M.

Nyamweya C.S.

Njiru J.M.

Major rivers of Lake Victoria

Kenya basin, are considered as

important hotspots of both

aquatic and terrestrial

biodiversity, besides the

numerous ecosystem services

to the surrounding lake basin

communities. Rivers

discharge contribute about

38% of the total water inputs

into the main lake. River water

also supports pond

aquaculture, irrigation

agriculture, industrial,

domestic and livestock water

uses, and energy generation,.

Many native and rare fish

species spawn in river mouth

areas. However, habitat loss

from pollution is of concerns

and a threat to sustainability of

both lotic and lentic

ecosystems services.

Background information

The Kenyan catchment area covers about 42,460 Km2 (about 22% of the whole Lake Victoria basin

catchment area). This covers areas in Busia, Siaya, Kisumu, Bungoma, Kakamega, Vihiga, Uasin

Gishu, Nandi, Kericho, Bomet, Kisii, Homa bay and Migori counties. Major river drainage systems

(Nyando, Sondu-Miriu, Awach Kibuon, Oluch, Kibos) discharge directly into the Winam Gulf,

whereas rivers Nzoia, Yala, Sio and Kuja are connected directly to the main lake. River discharge

contributes over 18% of the water inputs into Lake Victoria. In Kenya, this amounts to a mean

discharge of 292.1 m3s-1 representing 38%. The Nyando, Yala, Nzoia Sondu - Miriu, Awach and

Kuja drainage basins form key ecosystems supporting a diverse aquatic and terrestrial biodiversity,

and the river mouth areas are recognized as important critical fish habitats. These areas are hotspots

of biodiversity, and are demarcated as key fish breeding and nursery grounds.

Riverine ecosystems form extensive conduits for supply of particulate and dissolved chemical and

nutrient elements into recipient downstream lakes. A comparison of Landsat image from 1973 and

2001 shows a significant increase in suspended sediment in the gulf (UNEP 2014). Recent surveys

in Winam gulf showed high fluctuations in surface water coverage by water hyacinth. (Ongore et

al., 2018), with the highest peak infestations in September and November 2016 and river mouth

and sheltered bays as hotspots of the aquatic weed. Fish based Index of Biotic Integrity (FIBI)

provided a tool form monitoring of rivers within the Lake Victoria basin (Raburu and Masese,

2012; Raburu et al., 2009). Some fish species migrate up-to 80 Km upstream in major rivers

(Whitehead 1959; Cadwalladr, 1965).

Significant changes in landuse as a result of expanding human population, urbanization and

settlements, encroachment of forested lands and wetlands, has been accompanied by varying scales

of upstream land degradation and loss of ecosystem services, in different drainage basins. Notable

ecological changes within L. Victoria ecosystem with potential influences on aquatic biodiversity

includes the Nile perch ( now a major commercially important fish species) fish introductions of

1950’s and 1960’s, which preyed on the native haplochromine species.

Uncontrolled and poor solid waste disposal and management; untreated waste water discharge into

rivers; leaching of residual agricultural chemicals; diffuse surface runoffs and storm waters) from

anthropogenic activities and increasing river water demands are a threat to riverine ecosystems and

fish habitats.

Declining quality of water sources can lead to conflicts among different upstream and downstream

users and stakeholders, human – wildlife, irrigation farmers and water resources managers among

others. Expanding pond aquaculture will be sustained by protecting available water sources from

rivers and their recharge areas. Habitat loss can result from river channel modification,

sedimentation, poor water quality and other invasive species, and hence a cause of concern to the

aquatic biodiversity conservation and sustainability of the fisheries.

A

visual comparison of the colour of surface water in rivers Awach, Nyando, and Yala.

Monitoring of the pollution, key ecological components and indicators of water quality and

changes in environmental conditions in riverine habitats will ensure creation of more

awareness for protection of their ecological health and integrity, to the immediate

community users and other stakeholders, and for sustainable ecosystem services. Thirteen

of the most accessible sites representing the downstream and river mouth areas in each

river of the 4 river channels (Nyando, Yala, Awach and Nzoia) were studied and compared

to previously documented ecological and environmental conditions, for more informed

decisions in their development and overall water resources management. The field surveys

were conducted in November 2019 and March 2020 during the wet and dry seasons

respectively. Challenges often encountered in sampling of rivers were experienced, especially

during high flows and unaccessibility of some river mouth areas.

Clean water abstraction (left) and fish traps (right) in relatively un-degraded habitats.

Monitoring of pollution was undertaken through determination of the spatio - temporal

changes in the physico - chemical conditions; and their influence on the distribution of select indicator

taxa in the four-biodiversity hotspots. The composition, abundance and distribution of fish species,

zooplankton, phytoplankton, macroinvertebrates and other associated terrestrial and aquatic species

diversity; to try and assess how the taxa are affected by environmental and habitat changes.

The immediate communities perceptions of the on the historical changes in hydrological conditions,

potential pollution and ecological impacts affecting the riverine ecosystems within the lake Victoria

Kenya basin were also collected. This will help in understanding the challenges facing the immediate

communities, and other stakeholders around the hotspot areas; in protection of the biodiversity for a

sustainable fisheries and future development and management planning of the water resources within

the drainage basins.

Results

The results show a longitudinal variation the mean values of some of the physic-chemical parameters

The mean water pH lies within the acceptable range of 6.5 to 8.5. The surface water temperature

decreased upstream with a mean range of 23.7±1.6 to 25.6±1.1 °C in all rivers (March 2020) and

21.1±0.5 to 24.5±1.1 (November 2019). In both seasons, the lowest surface water temperatures were

21.7°C and 20.7 °C (R. Awach at Kokwanyo upstream); whereas the highest was recorded at the mouth

of rivers Yala (25.9 °C) and Nyando (27.5 °C).

High variations in D.O were evident. The river surface water was well oxygenated with mean

concentrations above 7.12 mgL-1, except for the lower concentrations at Goye, R. Yala, (4.18 mgL-1).

During November 2019, water conductivity and TDS decreased upstream, with rivers Nyando and

Awach recording the highest and lowest conductivity and TDS concentrations. Less defined trends in

R. Nyando were observed in March 2020. Water salinity showed a wide variation from 0.02 ‰ – 0.15

‰, with the lowest and highest concentrations in R. Awach and R. Nyando (Nyando at Chemelil)

respectively.

In general, all the water quality parameters determined were found to be lower than the drinking water

guideline values recommended by NEMA, except for the high concentration of suspended solids and

turbidity. Much higher total phosphorus concentrations, and which reflect eutrophic conditions were

observed in all rivers, but with lower river Yala (57.57±21.99 µgL-1) during November 2019. Lower

dissolved silica-Si and P were observed in March 2020 compared to the wet period.

The variations in total and soluble phosphorus in river water during Nov 2019 and Mar 2020

Seasonal and anthropogenic influences on the water quality were observed in all the river channels,

which is likely to impact resident species to some extent. River drainage basins are extensive and under

heavy agricultural and human activities with reduced soil cover which contributes to increasing loading

of eroded soils and materials which imparting a heavy visually evident brownish colouration in most

of the surface water. In contrast, clear waters of the Yala river mouth is an indication of reduced direct

surface transport of such materials into the lake waters, as it passes through the swampy areas.

Among the algal families, Diatoms, Chrophytes, Euglenophytes and Cynophyceaen were the most

dominant. 75 different species of algae identified. Of the 12 different species of cyanophytes

encountered, Chroococcus sp., Cylindrospermopsis, Planktolyngbya spp. and anabaena spp. were the

most common genera. Only one species of dinoflagellates (Glenoridinium spp.) was encountered in

Koru and Bondo water works. There were 29 different species of diatoms constituted mainly by of

Aulacoisera, Cyclotella, Chodatella spp., Fragillaria spp., Navicula spp., Surillella spp.

The most significant driving forces that cause predictable variations in phytoplankton composition is

due to algal species occupying different ecological niches within the sampling stations. The high

abundance of diatoms and chrophytes as dominant phytoplankton families, is an indication of cultural

eutrophication. High nutrients enrichment seems to enhance growth and increased algal density, and

more especially blue green algae which are proportionately high in most of the stations. Turbidly

favours the dominance of diatoms especially centric diatoms which are able to attach on detritus.

The percentage composition of phytoplankton groups during November 2019 and March 2020

There was a low zooplankton species diversity which is attributed to sampling during wet season.

However, the low diversity may also be attributed predation pressure from zooplanktivorous fish as

well as the carnivorous zooplankton which feeds on algae especially Merismopedia sp. The dominant

algae are not easily digested by zooplankton due to its fibrous nature and colonial formations. This

impacts the zooplankton community species especially rotifers found at Yala river mouth. Branchionus

spp. conditions only favour predation species on the large bodied zooplankters. The genus, Cyclopoida

genus is known to inhabit areas which are rocky, and could have a risen from sweeping effect of water

through adjacent macrophytes. The latter is a new finding in the river ecosystem health, there is need

to focus on the same in future sampling activities for temporal and spatial scales of the physico-

chemical environment that determine levels of primary production and plankton dynamics in aquatic

ecosystems hence affect the quantity and quality of food items available for invertebrates as well as

fish.

The Cyanophytes cell abundances were positively correlated with temperature (r = 0.701, p < 0.01)

and D.O (r = 0.711, p < 0.01), whereas diatoms were negatively and significantly associated with

water temperature (r= -0.740, p < 0.01).

Total zooplankton and copepods abundance of was positively and significantly correlated (p< 0.01)

with surface water temperature and D.O concentration. Abundances of zooplankton are often

regulated by temperature, food availability (phytoplankton) and predation. Temperature influences

the egg development time, growth rate, brood size and mortality of zooplankton (Herzig 1994).

The dissolved P, nitrate –N, and Nitrite N were all negatively associated with zooplankton

abundances. Among the nutrient elements, only ammonium –N was positively correlated with

Dinoflagellates. This may mean food availability was more important for regulating zooplankton,

than eutrophication, as reflected by the low contribution of rotifer (prefer more eutrophic

conditions) in the stations.

River channels are relatively of relatively shallow depths and with high water mixing rates due to

constant turbulence upstream, which decreases downstream. Most of the channels are exposed to

several diverse non-point (NP) anthropogenic pollution sources along the sub-basins. Known

industrial discharges (PS - point source pollution) are upstream rivers Nzoia and Nyando.

Normally, a combination of several abiotic and biotic factors influence algal production in water.

Light penetration, nutrients, zooplankton and fish grazers are factors influencing algae production.

Micro-invertebrates also prey on zooplankton. Increased presence of particulate mineral matter

reduce light availability for algae. However, the positive correlations with water temperature may

arise due to the increased heating effect from the high presence of suspended mineral matter which

reflects solar radiation within water. High river flows, high turbidity and inadequate sampling of

inaccessible river channels can contribute to the differences numerical abundances of zooplankton

observed. High turbidity may also reduce predation of smaller zooplankton by fish and micro-

invertebrates, resulting in variations numerical abundances and low diversity. In comparison, all

the peak abundances in the Kenyan portion of L. Victoria (lowest 41 Ind.L-1 and highest 474 ind.

L-1 at Kisumu pier), were reported at river mouths and bays (KMFRI 2013), with a similar

dominance by Copepoda.

Abundance of zooplankton du ring Nove 2019 and March 2020

Abundance of zooplankton in rivers during November 2019 and March 2020

The molar ratios of N:P were varied between March 2020 (dry) and November 2019 (wet) with a range

of 0.18 to 36.92, and suggested N –limitation in most of the rivers except for rivers Awach and Nzoia

in November 2019, where P limitation was observed.This may imply less variations in algal

compositions between the rivers. In total there were 75 different species of algae identified from rivers

during the November 2019 and 54 in March 2020.

A total number of 22 macroinveterbrate families representing 13 orders; the orders; Coleoptera,

Decapoda, Diptera, Ephemeroptera, Hemiptera, Hirudineae, Odonata, Plecoptera, Pulmonata,

Trichoptera, Tubificida, Unionoida and Veneroida.were recorded in November.

The percentage of tolerant and intolerant macroinvertebrates, Shannon’s and Simpson’s diversity

indices during March 2020

The percentage of the macroinvertebrate functional groups during March 2020

A total of 9 fish families were found in the study sites, which consisted of 19 fish species (wet season)

and 18 species (dry) from 8 families. The Cyprinidae formed the most dominant species, with the

Cichlids which were represented by O. niloticus and Haplochrois only encountered in rivers Nyando

and Yala. In both dry and wet season, the weight and numbers of fish caught was dominated by E.

nyanzae, E, cercops, L. altianalis, L. victorianus, Haplochromis and B. jacksonii fish species.

However, the fish are exposed to increasing degradation of the natural riverine habitats, and loading of

land derived materials, causing increasing turbidity, which affects aquatic productivity.

There exists a huge potential for conservation of non-commercial native fish species within the riverine

habitats, as indicated by the high diversity and abundance of some of the taxa. It is not possible to

effectively sample the riverine sites due to observed challenges of effective gears and accessibility.

Therefore in order to improve sample collection and representation of the extensive and diverse habitats

in rivers, more techniques and mixed gears need to be employed, with focus on the smaller streams and

tributaries. This should be accompanied by updated freshwater fish biodiversity hotspots guides for

specific river drainage basins to understanding effects of increasing ecological changes due to

degradation of riverine ecosystems. The riverine biodiversity hotspots should be clearly identified in

water resource management databases.

Most of the inflowing rivers serve as important sources of water into fish culture ponds, and receive

effluents from such ponds. Oreochromis niloticus and Clarias gariepinus are fish species widely

cultured in fish ponds within the lake basin. However, there are no reports of new species in the studied

rivers.

Previous biodiversity studies recorded 37, 28 and 25 fish species belonging to 11, 10 and 5 families in

Lake Victoria (Kenya), satellite lakes and dams (Masai et al., 2005) within the Kenyan catchment

respectively. Anabatidae and Propteridae, were the only families not represented in this riverine study.

Fish species composition (%) during November 2019mand March 2020.

Socio-economic aspects

Majority of the respondents were males (79%, n = 58) who are mostly involved in fishing, fish trade

and farming activities. The dominant age bracket indicates that the respondents were knowledgeable

on the historical trends within each river system. Almost over 80% were educated past primary level

of education, however, the income levels were low. Majority of them have adequate knowledge on the

river drainage basin (above 70% in all rivers).

The respondent’s perception on historical trends during the past 10 years revealed that floods are

increasing in rivers Yala, Nzoia and Awach. They felt that inter-seasonal variations were more less

stable (except for R. Awach Kibuon), but water levels tended to decrease during the drought. Changes

in amount of rainfall and water table rise between seasons has an impact of the variations in river water

flows.

Respondents occupation (%) Age of respondents (%)

In all the rivers, respondents felt the water sources are still very useful as there are still relied for most

of the historical domestic uses, fishing and livestock watering, with more potential demands of water

for irrigation and agriculture.

Silt, domestic washing and human and animal refuse were ranked highly as important pollutant sources

in the four inflowing rivers, except litter and obnoxious weeds.

0 10 20 30 40 50

<20

20 - 30

30 - 40

40 - 50

> 50

% of respondents

Age

in y

ears

The proportion of respondent’s perception on whether rivers are polluted.

Respondents in each river basin did not identify resource use conflicts as an impact of concerns.

However, poor river water quality was more perceived as the main impact from pollution. All pollution

impacts (poor water quality, unsafe water, high costs of purification) were of concerns in utilization of

water of river Awach, which reflects its overall low quality in comparison.

Conclusion

Seasonal and anthropogenic influences on the water quality were observed in all the river channels,

which is likely to impact resident species to some extent. River drainage basins are extensive and under

heavy agricultural and human activities with reduced soil cover which contributes to increasing loading

of eroded soils and materials which imparting a heavy visually evident brownish colouration in most

of the surface water. In contrast, clear waters of the Yala river mouth is an indication of reduced direct

surface transport of such materials into the lake waters, as it passes through the swampy areas.

River sites show a high concentrations of algal families dominated by Diatoms, Chrophytes,

Euglenophytes and Cynophyceae. The high abundance of diatoms and chrophytes as dominant

phytoplankton families, is an indication of cultural eutrophication.

High nutrients enrichment seems to enhance growth and increased algal density, and more especially

blue green algae which are proportionately high in most of the stations.

Turbidly favours the dominance of diatoms especially centric diatoms which are able to attach on

detritus.

A new occurrence of the Cyclopoida genus, known to inhabit areas which are rocky could be due to

the sweeping effect of water through adjacent macrophytes reported in this survey.

The high temporal variations in flow regimes in tropical areas necessitates the development of more

information on environmental flows in the rivers which is lacking for may basins and sub-basins.

Recommendations

Improved management of catchment area through improved agricultural practices and protection

existing forest areas with increased maintenance of vegetation cover through planting of perennial

crops and trees will reduce soil erosion and loading in rivers. Planned harvesting of sand minimizes

destruction of riverine aquatic habitats,, and also maintenance of the riparian zone vegetation traps

sediment and reduces suspended sediment loadinsg.-- This should be coupled with better

management of both solid and liquid waste discharges, and treatment of effluent discharged into

recipient river channels.

To address the increasing degradation of riverine ecosystems, and to reduce resource use conflicts,

which undermine biodiversity protection; there is need to develop, education, awareness and

sensitization programes, involving the communities and different stakeholders in improved

pollution control measures; adoption of cleaner production technologies and good agricultural

practices; sustainable use and management of specific river basins.

KMFRI to continue monitoring activities on impacts of pollution on riverine biodiversity (with a

wider focus to detail in smaller streams and tributaries) since non-point pollution sources are

diverse within the drainage basins.

A river monitoring program (gauged stations with long term data) for development of long-term

trends data on nutrients and for management of nutrient loadings and lake eutrophication is

required for the whole Lake Victoria Kenya basin, as some of the rivers lack gauge stations for

involvement of communities in river water quality monitoring activities..

Longterm flood management strategies are urgently required as part of development planning to

reduce associated risks.