Data from 10 sampling sites along the River Njoro are used to examine the contribution of nutrients from upstream land uses draining each of the sampling sites. The data also are used to assess whether both the proportion of land uses and the size of the subwatersheds account for the variability in water quality in the River Njoro watershed. Geographical Information System analysis was used to determine the spatial distribution of land-cover types and subwatersheds contributing run-off to the sampling sites in the River Njoro. Standard Digital Elevation Model-based routines were used to establish the watershed area contributing run-off to each sampling site. Water and sediment samples were collected for chemical analysis, and the nutrient levels were related to the upstream land-use types and the size of the subwatersheds. The mid-stream portion of the River Njoro (near Egerton University) accounts for the highest nutrient contributions. The percentage contribution is magnified by additions from industrial, human settlements and agricultural land uses around the University. There is a significant decrease in nutrient levels downstream, however, indicating natural purification as the river flows through an area of large-scale farming with intense, well-preserved riparian and in-stream vegetation. Steep slopes of the land upstream of Egerton University enhance erosion and nutrient losses from those subwatersheds. Mixed small-scale agricultural and bare lands contribute over 55% of the phosphorus load to the upper and mid-reaches of the River Njoro. The size of the subwatershed accounts for about 53% of the variability in the soluble phosphorus in the river. The land-use subwatershed proportions are important for characterizing and modelling water quality in the River Njoro watershed. Upland land uses are as important as near-stream land uses. We suggest that conser vation of intact riparian corridor along the river and its tributaries contributes significantly to natural purification processes and recovery of the ecological integrity of the River Njoro ecosystem.

Populations of coexisting tropical forest rodents Praomys jacksoni and P. (Hylomyscus) stella were investigated to test whether lower relative densities in regenerating forest compared with mature forest were because of poor health and/or reduced chances for females to breed. Relative frequencies, litter size, mass, length of embryos, presence or absence of ecto-and/ or endoparasites, and liver condition were recorded and analysed. Higher numbers of either species occurred in the mature compared with regenerating forest. Mottled livers and endoparasites were associated with heavier rodents; litter size related positively to mass of pregnant females in both species. Litter size, embryo size, sex ratios, liver condition, and infestation of ecto-and endoparasites were independent of forest and species. Apparently, reduced female density in regenerating forest had no breeding cost on individual females occurring there. RésuméLes populations de rongeurs coexistants en forêt tropicale Praomys jacksoni et P. (Hylomyscus) stella ont été étudiées pour vérifier si les densités relatives, plus faibles dans les forêts en voie de régénération que dans les forêts mâtures, étaient dues à une moins bonne santé et/ou à de plus faibles chances de se reproduire pour les femelles. On a noté et analysé les fréquences relatives, la taille des portées, le poids, la taille des embryons, la présence ou l'absence d'ecto-et/ou d'endoparasites et l'état du foie.On a constaté des nombres plus importants des deux espèces dans les forêts mâtures que dans les forêts en voie de règénération. Des foies tachetés et des endoparasites étaient associés à des rongeurs plus lourds; la taille des portées était positivement liée au poids des femelles pleines dans les deux espèces. La taille de la portée, le poids des petits, le sex-ratio, l'état du foie et l'infestation par des ectoet endoparasites étaient indépendants de la forêt et de l'espèce. Apparemment, la densité réduite des femelles dans la forêt en voie de régénération n'avait aucun impact sur la reproduction locale des femelles prises individuellement.

The preliminary results of an assessment of land use effect on soil erosion and surface runoff in a severely degraded watershed in Kenya are presented here. Soil erosion and surface runoff was higher in the non-forested lands (deforested, agriculture and grazing lands) than in the forested (indigenous and exotic) lands.