Distributional Patterns of Diatoms andLimnodrilus Oligochaetes in a Kenyan Dry Streambed Following the 1999-2000 Drought Conditions

Abstract

Drought is a natural phenomenon experienced by many intermittent and also seasonal lotic systems. It has diverse effects on the structure and distribution of biological communities through habitat transition from wetted to terrestrial conditions. The Njoro River, a tropical stream, was drought-stressed between late 1999 and mid 2000, providing an opportunity to sample and describe the distributional patterns of diatoms and Limnodrilus oligochaetes in the vertical sediment profile. The dispersion of Limnodrilus oligochaetes with sediment depth profile varied from quasi-random (i.e. exponent k of the negative binomial distribution >2.0 or <0) at the surface to strong aggregation (0 < k < 1.0) in the deeper sediments. Diatoms were heterogenous, with most species contributing less than 1% of all the diatoms collected from the riverbed. Contagious dispersion was a common feature among the diatom species. The distribution of Fragilaria ulna was largely quasi-random in all sites, with Nitzschia amphibia and Cocconeis placentula demonstrating quasi-random distribution in the Kerma vertical sediment profile. Escape from stranding to deeper sediment strata as the drought progressed was not a universal response among the diatom species. Our results showed that drought-stress altered the structure of biological assemblages and also emphasized the need for the management of tropical lotic systems and their catchments for flow permanence.

Macroinvertebrate Community Structure in Three‐Gorges Reservoir, China

“…The Nais-Polypedilum community type, occurring in winter and spring, was followed by the Limnodrilus community type that occurred in autumn and summer. It is not surprising that the Limnodrilus community type occurred during seasons with high inflow discharge and low transparency, because it has been reported that Limnodrilus is tolerant of harsh environments (e.g., MATHOOKO et al, 2005). Before reservoir construction, N. inflata was also the most common species throughout the Yangtze River (LIANG, 1987).…”

Flow intermittency decreases nestedness and specialisation of diatom communities in Mediterranean rivers

“…Specifically, droughts are known to have a profound impact on the densities and size-or age-structure of populations, on community composition and diversity, and on ecosystem processes (Lake, 2003). For instance, it has been suggested that very few diatom species are abundant and dominant in dry riverbeds, with these remaining species being highly tolerant (Mathooko et al, 2005). Disturbances caused by local flow fluctuations confer heterogeneity to the structure of benthic algae, with successional age being inversely related to disturbance frequency (Ledger et al, 2008).…”

Bioassessment of multiple stressors in Afrotropical rivers: Evaluating the performance of a macroinvertebrate-based index of biotic integrity, diversity, and regional biotic indices

“…The abundance of burrowing taxa is negatively related to discharge and flow velocities in streams and rivers (Masese et al, 2021). In the Njoro River, drying of the river resulted in a tremendous increase in oligochaetes while other sensitive taxa among the EPT were eliminated (Shivoga, 2001;Mathooko et al, 2005). In the Moiben River, the peak of the dry season coincided with a significant decline in sensitive taxa and a proliferation of burrowing and pool-associated taxa, such as Belostomatidae, Corixidae, Gomphidae, and oligochaetes (Masese et al, 2009a;Masese et al, 2009b).…”