Assessing the importance of a self-generated detachment process in river biofilm models

1. Epilithic biofilm biomass was measured for 14 months in two sites, located up- and downstream of the city of Toulouse in the Garonne River (south-west France). Periodical sampling provided a biomass data set to compare with simulations from the model of Uehlinger, Bürher and Reichert (1996: Freshwater Biology, 36, 249–263.), in order to evaluate the impact of hydraulic disturbance. 2. Despite differences in application conditions (e.g. river size, discharge, frequency of disturbance), the base equation satisfactorily predicted biomass between low and high water periods of the year, suggesting that the flood disturbance regime may be considered a universal mechanism controlling periphyton biomass. 3. However modelling gave no agreement with biomass dynamics during the 7-month long low water period that the river experienced. The influence of other biomass-regulating factors (temperature, light and soluble reactive phosphorus) on temporal biomass dynamics was weak. 4. Implementing a supplementary mechanism corresponding to a temperature-dependent self-generated loss because of heterotrophic processes allowed us to accurately reproduce the observed pattern: a succession of two peaks. This case study suggests that during typical summer low water periods (flow stability and favourable temperature) river biofilm modelling requires self-generated detachment to be considered

Leaf litter decomposition of native and introduced tree species of contrasting quality in headwater streams: How does the regional setting matter?

Terrestrial plant litter is important in sustaining stream food webs in forested headwaters. Leaf litter quality often decreases when native species are replaced by introduced species, and a lower quality of leaf litter inputs may alter litter decomposition at sites afforested with non-native species. However, since detritivore composition and resource use plasticity may depend on the prevalent litter inputs, the extent of the alteration in decomposition can vary between streams. We tested 2 hypotheses using 2 native and 3 introduced species of tree differing in quality in 4 Iberian regions with contrasting vegetational traits: 1) decomposition rates of all plant species would be higher in regions where streams normally receive litter inputs of lower rather than higher quality; 2) a higher resource-use plasticity of detritivores in regions vegetated with plants of lower litter quality will cause a greater evenness in decomposition rates among plant species compared to regions where streams normally receive higher-quality plant litter inputs. Results showed a highly consistent interspecific ranking of decomposition rates across regions driven by litter quality, and a significant regional effect. Hypothesis 1 was supported: decomposition rates of the five litter types were generally higher in streams from regions vegetated with species producing leaf litter of low quality, possibly due to the profusion of caddisfly shredders in their communities. Hypothesis 2 was not supported: the relative differences in decomposition rates among leaf litter species remained essentially unaltered across regions. Our results suggest that, even in regions where detritivores can be comparatively efficient using resources of low quality, caution is needed particularly when afforestation programs introduce plant species of lower litter quality than the native species

Life history and production of Caenis luctuosa (Burmeister) (Ephemeroptera, Caenidae) in two nearby reaches along a small stream

Population dynamics and production of C. luctuosa were compared in two reaches of the Agüera stream (northern Spain). This species showed univoltine winter life history in both sites. However, the start of the recruitment period, and the cohort production interval differed in 1 month between reaches. Secondary production of C. luctuosa ranged from 76 mg m-2 year-1 (upper site) to 93 mg m-2 year-1 (lower site). Although annual production seemed to be mainly influenced by the biomass found at each site, changes in life history may have also been important. The need to have accurate information about life history of the analysed species at the study sites when assessing secondary production is highlighted

Calidad del agua de los ríos de Bizkaia. I. Cuencas de Las Encartaciones

Se ha estudiado la alidad del agua de las cuencas de los ríos Mercadillo, Cadagua y Galindo, utilizándose macroinvertebrados bentónicos como indicadores. En base a estos datos y a la concentración de oxígeno en el agua se ha detectado una contaminación elevada en el arroyo Ballonti, perteneciente a la cuenca del Galindo y en el tramo final del río Cadagua. Está también bastante alterado el tramo final del Herrerías, mientras que la cuenca del Mercadillo solo experimenta una ligera eutrofización en su tramo fina

Calidad del agua de los ríos de Bizkaia. III. Cuencas del Oka, Lea y Artibai

Se ha estudiado la calidad del agua utilizando macroinvertebrados bentónicos como indicadores biológicos y la concentración de oxígeno como variable química, en las cuencas de los ríos Oka, Lea y Artibai, la más orientales de Bizkaia. Los ríos y arroyos de la cuenca del Oka presentan una fauna indicadora de buena calidad del agua a excepción del cauce principal, que en su último tramo se encuentra más eutrofizado. La cuenca del río Lea mantiene una elevada calidad incluso en su cauce principal, siendo la que se conserva en un estado más natural de todas las cuencas estudiadas en Bizkaia. La cuenca del Artibai, por el contrario, está bastante alterada a partir de Markina, lo que se pone de manifiesto no solo por la composición de la fauna, sino también por lo bajos valores de la concentración de oxígen

Calidad del agua de los ríos de Bizkaia. II. Cuencas del Nerbion-Ibaizabal

Se ha estudiado la composición de la fauna de macroinvertebrados bentónicos y se ha determinado la concentración de oxígeno en 54 estaciones de muestreo situadas en las cuencas del Nerbión-Ibaizabal. La calidad del agua es muy baja en los cauces principales, especialmente en el del Ibaizabal, donde se han registrado concentraciones de oxígeno inferiores a 2 mgl. También esta muy contaminado el río Elorrio con valores de oxígeno inferiores a 4 m

Spatio-temporal changes in the caddisfly (Trichoptera) communities of the river Lea basin (Basque Country, North Spain)

In the Lea River basin, 47 taxa of caddisflies have been found belonging to 32 genera and 15 families. Rhyacophilidae (5 species), Hydropsychidae (6 species), Limnophilidae (4 species) and Polycentropodidae (4 species) were the dominant families ; Hydropsyche pellucidula being the most abundant species. Using all these taxa as entities, an ordination of the River Lea Basin has been made by means of Correspondance Analysis. The ordinations with higher ecological meaning were obtained on the plane of the second and third axes, which explained about 21 % of the total variance. According to this ordination the following zones characterized by different communities of caddisflies could be identified in this basin : the headwater of the main river, the small tributaries and a downstream sequence from site 1 to site 5 of the main river as well as a downstream sequence from site 1 to site 2 of its principal tributary. Along the second axi,s a seasonal succession from spring to summer and autumn could be observed in the main river