Invertebrate drift densities in the Njoro and Kamweti Rivers in the Kenyan highlands that differ in the level of anthropogenic disturbances

Invertebrate drift is one of several fundamental ecological processes in streams. However, little is known about the dynamics of invertebrate drift in Kenyan streams. In this study, we assessed invertebrate drift in two rivers, i.e. Njoro and Kamweti, that differ in the level of anthropogenic disturbances, between February and March, 2016. The aim was to evaluate the effect of river sampling duration (5, 10, 15, 20 and 25 min) and sampling period (day or night) on invertebrate drift densities. The 5-minute sampling period resulted in significantly higher mean drift densities than the other time intervals in both rivers. The highest mean drift density (2.0 ± 0.9 individuals m−3) was recorded at the Njoro River during the day, whereas the lowest drift density (0.3 ± 0.2 individuals m−3) was recorded at the Kamweti River during the day. A strong nocturnal drift pattern was noted at the less disturbed river (Kamweti). The present results suggest that anthropogenic perturbations influence invertebrate drift densities, and sampling duration and sampling period are important factors to consider when sampling invertebrate drift.Keywords: anthropogenic impacts, drift, Kenya, sampling duration, sampling perio

Invertebrate drift densities in the Njoro and Kamweti Rivers in the Kenyan highlands that differ in the level of anthropogenic disturbances

<p>Invertebrate drift is one of several fundamental ecological processes in streams. However, little is known about the dynamics of invertebrate drift in Kenyan streams. In this study, we assessed invertebrate drift in two rivers, i.e. Njoro and Kamweti, that differ in the level of anthropogenic disturbances, between February and March, 2016. The aim was to evaluate the effect of river sampling duration (5, 10, 15, 20 and 25 min) and sampling period (day or night) on invertebrate drift densities. The 5-minute sampling period resulted in significantly higher mean drift densities than the other time intervals in both rivers. The highest mean drift density (2.0 ± 0.9 individuals m⁻³) was recorded at the Njoro River during the day, whereas the lowest drift density (0.3 ± 0.2 individuals m⁻³) was recorded at the Kamweti River during the day. A strong nocturnal drift pattern was noted at the less disturbed river (Kamweti). The present results suggest that anthropogenic perturbations influence invertebrate drift densities, and sampling duration and sampling period are important factors to consider when sampling invertebrate drift.</p

Does the exclusion of meiofauna affect the estimation of biotic indices using stream invertebrates?

<p>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.</p

Riparian plant litter quality increases with latitude

Plant litter represents a major basal resource in streams, where its decomposition is partly regulated by litter traits. Litter-trait variation may determine the latitudinal gradient in decomposition in streams, which is mainly microbial in the tropics and detritivore-mediated at high latitudes. However, this hypothesis remains untested, as we lack information on large-scale trait variation for riparian litter. Variation cannot easily be inferred from existing leaf-trait databases, since nutrient resorption can cause traits of litter and green leaves to diverge. Here we present the first global-scale assessment of riparian litter quality by determining latitudinal variation (spanning 107 degrees) in litter traits (nutrient concentrations; physical and chemical defences) of 151 species from 24 regions and their relationships with environmental factors and phylogeny. We hypothesized that litter quality would increase with latitude (despite variation within regions) and traits would be correlated to produce 'syndromes' resulting from phylogeny and environmental variation. We found lower litter quality and higher nitrogen: phosphorus ratios in the tropics. Traits were linked but showed no phylogenetic signal, suggesting that syndromes were environmentally determined. Poorer litter quality and greater phosphorus limitation towards the equator may restrict detritivore-mediated decomposition, contributing to the predominance of microbial decomposers in tropical streams.We thank the many assistants who helped with field work (Ana Chara-Serna, Francisco Correa-Araneda, Juliana Franca, Lina Giraldo, Stephanie Harper, Samuel Kariuki, Sylvain Lamothe, Lily Ng, Marcus Schindler, etc.), Cristina Grela Docal for helping with leaf chemical analyses, and Fernando Hiraldo (former director of EBD-CSIC) for his support. The study was funded by start-up funds from the Donana Biological Station (EBD-CSIC, Spain) and from Ikerbasque to LB, the Fundacao para a Ciencia e Tecnologia (FCT) strategic project ID/MAR/04292/2013 granted to MARE (Portugal), the 'BIOFUNCTION' project (CGL2014-52779-P) from the Spanish Ministry of Economy and Competitiveness (MINECO) and FEDER to LB and J. Pozo, and Basque Government funds (IT302-10) to J. Pozo