Biomonitoring of rivers is usually undertaken using information based on macroinvertebrate assemblages. However, exclusion of meiofauna (i.e. invertebrates less than 0.5 mm in size) when sorting benthic invertebrates can affect the estimation of densities and other biotic indices. In the present study, the effect of excluding the less than 0.5 mm fraction of invertebrates on estimation of benthic invertebrate indices was investigated in the Naro Moru River, Kenya. The Shannon-Wiener diversity index, Pielou's evenness index, a multimetric index, Simpson's diversity index, Margalef's diversity index, mean invertebrate density, taxa richness, and Ephemeroptera, Plecoptera and Trichoptera (EPT) densities were determined. Only mean invertebrate and EPT densities differed significantly between the greater than 0.5 mm and total fractions. In conclusion, exclusion of meiofauna from invertebrate samples can affect the estimation of some stream invertebrate biotic indices.

Small Clarias species (Clarias liocephalus (Boulenger) and C. alluaudi (Boulenger) movement patterns were analysed with Floy tags and through a structured questionnaire survey at the differently disturbed sites in the Mpologoma riverine wetland. Water physico-chemical characteristics, macroinvertebrate community and fish stomach content data were also collected.Water conductivity was higher at the highly disturbed sites while dissolved oxygen was lower at the highly disturbed sites than at the less disturbed sites (ANOVA, Tukey’s test p & lt; 0.05). Although floy tag recovery rate was low, a downstream movement during dry season and lateral movement in the rainy season were exhibited by the tagged fish. The fishermen (76.5%) concurred that these clariids move about and some fishermen (30.8 %) attributed the movement to reduction in waterrnlevel. The results were attributed to the species’ life history strategy, adaptation to change in environmental variables and avoidance of predators in deep waters.

Water quality information in aquatic ecosystems is crucial in setting up guidelines for resource management. This study explores the water quality status and pollution sources in Lake Naivasha, Kenya. Analysis of water quality parameters at seven sampling sites was carried out from water samples collected weekly from January to June and biweekly from July to November in 2011. Principal component analysis (PCA) and cluster analysis (CA) were used to analyse the dataset. Principal component analysis showed that four principal components (PCA-1 to PCA-4) explained 94.2% of the water quality variability. PCA-1 and PCA-2 bi-plot suggested that turbidity in the lake correlated directly to nutrients and iron with close association with the sampling site close to the mouth of Malewa River. Three distinct clusters were discerned from the CA analysis: Crescent Lake, a more or less isolated crater lake, the northern region of the lake, and the main lake. The pollution threat in Lake Naivasha includes agricultural and domestic sources. This study provides a valuable dataset on the current water quality status of Lake Naivasha, which is useful for formulating effective management strategies to safeguard ecosystem services and secure the livelihoods of the riparian communities around Lake Naivasha, Kenya.

Many forested headwater streams are heterotrophic ecosystems in which allochthonous inputs of plant litter are a major source of energy. Leaves of riparian vegetation entering the stream are broken down by a combination of biotic and abiotic processes and, in most temperate and boreal streams, provide food and habitat for dense populations of detritivorous invertebrates. However, tropical streams in different parts of the world show substantial variability in the number and diversity of leaf-shredding detritivores (hereafter detritivores). We used data obtained with standardized methods from multiple streams in Africa, the Americas, Asia, and Australia to test the hypothesis that this variability would lead to differences in the relative role of detritivores and microorganisms in the breakdown process. We also tested the hypotheses that variability in litter breakdown rates changes with litter type (native litter mixtures vs nonnative alder [Alnus glutinosa]) and is higher across regions within than outside the tropics. We found that litter breakdown rates were highly variable across sites, with no consistent pattern within geographic areas, although litter consumption by detritivores was negligible at several sites, all in America. Geographic patterns of litter breakdown also varied between litter types, with higher breakdown rates for alder than for native litter in most but not all regions. When litter breakdown rates at the tropical sites were compared to previously reported values from temperate and boreal regions, we found that differences in variability between tropical and temperate sites were inconsistent, with great differences among studies. Further global-scale studies will be needed to assess the extent to which latitudinal changes in the diversity and composition of microbial and detritivore assemblages contribute to variability in litter breakdown rates.

Understanding what mechanisms shape the diversity and composition of biological assemblages across broad‐scale gradients is central to ecology. Litter‐consuming detritivorous invertebrates in streams show an unusual diversity gradient, with α‐diversity increasing towards high latitudes but no trend in γ‐diversity. We hypothesized this pattern to be related to shifts in nestedness and several ecological processes shaping their assemblages (dispersal, environmental filtering and competition). We tested this hypothesis, using a global dataset, by examining latitudinal trends in nestedness and several indicators of the above processes along the latitudinal gradient. Our results suggest that strong environmental filtering and low dispersal in the tropics lead to often species‐poor local detritivore assemblages, nested in richer regional assemblages. At higher latitudes, dispersal becomes stronger, disrupting the nested assemblage structure and resulting in local assemblages that are generally more species‐rich and non‐nested subsets of the regional species pools. Our results provide evidence that mechanisms underlying assemblage composition and diversity of stream litter‐consuming detritivores shift across latitudes, and provide an explanation for their unusual pattern of increasing α‐diversity with latitude. When we repeated these analyses for whole invertebrate assemblages of leaf litter and for abundant taxa showing reverse or no diversity gradients we found no latitudinal patterns, suggesting that function‐based rather than taxon‐based analyses of assemblages may help elucidate the mechanisms behind diversity gradients.

AbstractSmall‐scale fisheries in developing countries are characterized by uncertain futures attributable to ever‐increasing pressures on wetland resources. Data on the interconnectivity between wetland fishery, land‐use changes and the socio‐economic situation in the Mpologoma wetland, Uganda, were obtained through interviews and structured questionnaire surveys at sampling sites exhibiting differing different levels of environmental disturbance (ranging from less disturbed to highly disturbed). Rice production was the major economic activity at the highly disturbed sites, while maize production was the major activity at the less‐disturbed sites. Of the secondary activities, the Clarias gariepinus (Burchell, 1815) and Protopterus aethiopicus (Heckel, 1851) fishery was more important at the less‐disturbed sites. The high daily fish sale income ranging from US$ 8 to 12 and the high‐percentage (52%) catch preference of all large wetland fish species were observed for the less‐disturbed sites. A high percentage of respondents from the area of the less‐disturbed sites had higher annual incomes, resulting in more accumulated wealth than for the highly disturbed Nsango site, whose fishery was affected by large‐scale rice schemes. The overall socio‐economic impact of the small‐scale fishery, based on the data regarding the number of fishermen and their dependents, and the income from fish sales and other wetland activities, was low, with differences between sites being attributed to the level of wetland disturbance. The Mpologoma wetland is threatened by overexploitation of its fisheries services, but also overlooked and undervalued by policymakers because of inadequate fisheries statistics. Thus, the information derived from this study will facilitate the formulation and design of riverine wetland‐specific and small‐scale fisheries management strategies.

The study was conducted in June and September 2011 in six rivers that drain Mt. Kenya and the Aberdare catchments, i.e. Honi, Naro Moru, Liki, Sirimon, Mariara and Karigu. The main objective was to determine the ecological status of these rivers and identify macroinvertebrates with potential applicability as biomonitors. South African Scoring System version 5 (SASS-5), Multimetric Index (i.e. MI; values ranging from 0 = poor to natural = 1) and the Qualitative Habitat Assessment (QHA) methods were used in this study. Values more than 80% indicate largely unmodified systems (class B and A) whilst values below 40% indicate largely modified systems (classes, D, E and F). Class C (moderately modified systems fall within 60 – 79%). The highest number (16) of macroinvertebrate taxa were recorded at the Naro Moru and Mariara Rivers, while the lowest (3) was recorded at Karigu River. Macroinvertebrate abundance differed significantly among the rivers (One-way ANOVA, (F (5,135) = 3.533, p 0.6) while Honi and Mariara Rivers were of moderate water quality (MI = 0.40.6). Monitoring with macroinvertebrates enabled identification of anthropogenically affected rivers and placement of the study sites in their respective management classes for future interventions. Key words: Assessment, habitat, anthropogenic, freshwater ecosystems, water quality

In densely populated areas such as those in Eastern Uganda where livelihoods demands create immense pressure on environmental resources, small scale wetland fisheries may be disturbed by agriculture practices. The study carried out between 2011 and 2012, investigated the variation of fish catch at the different wetland sites in relation to land use in Mpologoma riverine marsh. Four sites were identified to represent different land uses; intact wetland, minimally disturbed, highly disturbed with small scale farmers and one with a large scale irrigation scheme. Data was collected on water quality, wetland fish species catch and catch per unit effort from the different sites. Conductivity and dissolved oxygen levels significantly differed between sites and explained 72.03% of the variance among sites. Seven fish taxa dominated the wetland fishery. Large sized fish species catch, Clarias gariepinus and Protopterus aethiopicus (range of 0.45 to 38 and 0.25 to 20 kg/day, respectively) was higher at the less disturbed sites than at highly disturbed sites which accounted for over 91.5% of total wetland catch. Tilapia zillii and Oreochomis leucostictus catch were also higher at the less disturbed sites while the small fish species (Haplochomis sp, Clarias liocephalus and C. alluaudi) did not vary with site. Conductivity and dissolved oxygen significantly correlated with the two large fish species' catch but did not correlate with small fish species catch. Agricultural activities in the wetland negatively affected the life history strategies of large fish species, leading to low catch rates at the highly disturbed site. Therefore, there is need to control land use changes to secure high productivity of small scale fisheries in the riverine wetland. Key words: Papyrus wetland, fish, catch, water quality, disturbance.

AbstractThe spatio‐temporal dynamics of the trophic state of a lake are crucial in defining its water quality, as well as biodiversity. Accordingly, this study focused on the spatio‐temporal variations of the trophic state, and the possible causes of the heterogeneous turbidity in Lake Naivasha, Kenya. The trophic state of the lake oscillated between a eutrophic and hypereutrophic condition, being found to be more eutrophic than reported in previous studies, indicating a progressive deterioration of its water quality. Inferences from the graphical representation of the deviations of total phosphorus and Secchi depth from the chlorophyll‐a trophic state indices revealed that the lake is predominantly phosphorus limited. Furthermore, the turbidity in the northern part of the lake is dominated by suspended sediment and dissolved coloured material. Discriminant analysis resulted in identification of three distinct trophic state regions in Lake Naivasha, namely the northern region, the mid and southern part and the more or less isolated Crescent Lake. The results of this study provide a good basis for further investigation of the current loading magnitude of both nutrients and sediments, in order to facilitate sustainable management to ensure community integrity and ecosystem functions of the lake.

Lake Naivasha experiences frequent lake level fluctuations despite being on the decline in the last three decades. The main possible cause has been postulated to be increased abstraction around the lake. However, land use land cover changes (LULC) in the basin may be impacting on the level fluctuations and decline. The LULC interfere with runoff, evapotranspiration, and infiltration conditions of a catchment. The frequent lake levels fluctuations resulting from LULC impact significantly on riparian vegetation productivity and species composition. In addition, it has impact on the aquatic ecosystem water quality especially in terms of turbidity. Lake Naivasha basin has experienced significant LULC transformations predominantly caused by socio-economic drivers. Implications of past, present and future patterns of socio-economic drivers of LULC is vital to the understanding of social, ecological and limnological functioning of the basin. These factors are proposed to impact on the entire hydrological regime of the lake. In this study we present first results of the Earth Observation Integrated Assessment (EOIA) project for the governance of Lake Naivasha basin using Interdisciplinary approach that applies GIS and RS towards the understanding of the dynamics of Lake Naivasha ecosystem.

Restoration of the ecosystem services and functions of lakes requires an understanding of the turbidity dynamics in order to arrive at informed environmental management decisions. The understanding of the spatio-temporal dynamics of turbidity requires frequent monitoring of the turbidity components such as chlorophyll-a concentration. In this study, we explored the use of Moderate Resolution Imaging Spectroradiometer Aqua (MODIS-Aqua) satellite data in studying the spatio-temporal changes in chlorophyll-a concentration in Lake Naivasha, a turbid tropical system. The temporal trend of chlorophyll-a concentration over the study period in the lake was also evaluated. The temporal trend assessment was achieved through the removal of periodic seasonal interference using Seasonal-Trend decomposition based on the LOESS (Local Regression) procedure. The resultant chlorophyll-a concentration maps derived from MODIS-Aqua satellite data give an indication of the monthly spatial variation in chlorophyll-a concentration from 2002 to 2012. The results of regression analyses between satellite-derived chlorophyll-a and in situ measurements reveal a high level of precision, but with a measureable bias with the satellite underestimating actual in situ measurements (R2 = 0.65, P < 0.001). Although the actual values of the chlorophyll-a concentrations are underestimated, the significant relationship between satellite-derived chlorophyll-a and in situ measurements provides reliable information for studying spatial variations and temporal trends. In 2009 and 2010, it was difficult to detect chlorophyll-a from the MODIS-Aqua imagery, and this coincided with a period of the lowest water levels in Lake Naivasha. An inverse relationship between de-seasoned water level and chlorophyll-a concentration was evident. This study shows that MODIS-Aqua satellite data provide useful information on the spatio-temporal variations in Lake Naivasha, which is useful in establishing general trends that are more difficult to determine through routine ground measurements.

For the sustainable governance of river basins a wide range of variables from natural and human subsystems may need to be studied as the effectiveness of governance can be judged from a wide range of perspectives. Governance of natural resources is affected by processes that are taking place across various scales and by interventions from multiple levels of organization. Especially when there is competition over scarce resources among stakeholders and interests there is a need for Integrated Assessment (IA). An IA may result in indicators for sustainable governance through the integration over scientific disciplines in ways and at temporal and spatial scales meaningful to stakeholders. This implies that knowledge from different scientific disciplines, focusing on different subsystems, should be used for incorporating interdependencies that are of critical importance for overall system dynamics. The design of appropriate model structures (e.g. extent, resolution) depends on the spatial and temporal resolutions of the available data, levels at which process interactions take place and the desired level of output presentation for stakeholders. The quality of an Integrated Assessment approach relies on extensive datasets. In this regard, this study explores the added value of using detailed spatial information derived from Earth Observation (EO) time-series. As an example the Lake Naivasha basin (Kenya) is studied. In this study knowledge gaps are identified and discussed. The scientific disciplines covered in this study are hydrology, limnology, ecology, socioeconomics and governance. Finally a framework for IA is assembled around a proposed set of sustainability indicators for the Lake Naivasha basin.