Global patterns and drivers of ecosystem functioning in rivers and riparian zones

River ecosystems receive and process vast quantities of terrestrial organic carbon, the fate of which depends strongly on microbial activity. Variation in and controls of processing rates, however, are poorly characterized at the global scale. In response, we used a peer-sourced research network and a highly standardized carbon processing assay to conduct a global-scale field experiment in greater than 1000 river and riparian sites. We found that Earth's biomes have distinct carbon processing signatures. Slow processing is evident across latitudes, whereas rapid rates are restricted to lower latitudes. Both the mean rate and variability decline with latitude, suggesting temperature constraints toward the poles and greater roles for other environmental drivers (e.g., nutrient loading) toward the equator. These results and data set the stage for unprecedented "next-generation biomonitoring" by establishing baselines to help quantify environmental impacts to the functioning of ecosystems at a global scale.peerReviewe

Global Patterns and Controls of Nutrient Immobilization On Decomposing Cellulose In Riverine Ecosystems

Microbes play a critical role in plant litter decomposition and influence the fate of carbon in rivers and riparian zones. When decomposing low-nutrient plant litter, microbes acquire nitrogen (N) and phosphorus (P) from the environment (i.e., nutrient immobilization), and this process is potentially sensitive to nutrient loading and changing climate. Nonetheless, environmental controls on immobilization are poorly understood because rates are also influenced by plant litter chemistry, which is coupled to the same environmental factors. Here we used a standardized, low-nutrient organic matter substrate (cotton strips) to quantify nutrient immobilization at 100 paired stream and riparian sites representing 11 biomes worldwide. Immobilization rates varied by three orders of magnitude, were greater in rivers than riparian zones, and were strongly correlated to decomposition rates. In rivers, P immobilization rates were controlled by surface water phosphate concentrations, but N immobilization rates were not related to inorganic N. The N:P of immobilized nutrients was tightly constrained to a molar ratio of 10:1 despite wide variation in surface water N:P. Immobilization rates were temperature-dependent in riparian zones but not related to temperature in rivers. However, in rivers nutrient supply ultimately controlled whether microbes could achieve the maximum expected decomposition rate at a given temperature

The bear in Eurasian plant names: Motivations and models

Ethnolinguistic studies are important for understanding an ethnic group's ideas on the world, expressed in its language. Comparing corresponding aspects of such knowledge might help clarify problems of origin for certain concepts and words, e.g. whether they form common heritage, have an independent origin, are borrowings, or calques. The current study was conducted on the material in Slavonic, Baltic, Germanic, Romance, Finno-Ugrian, Turkic and Albanian languages. The bear was chosen as being a large, dangerous animal, important in traditional culture, whose name is widely reflected in folk plant names. The phytonyms for comparison were mostly obtained from dictionaries and other publications, and supplemented with data from databases, the co-authors' field data, and archival sources (dialect and folklore materials). More than 1200 phytonym use records (combinations of a local name and a meaning) for 364 plant and fungal taxa were recorded to help find out the reasoning behind bear-nomination in various languages, as well as differences and similarities between the patterns among them. Among the most common taxa with bear-related phytonyms were Arctostaphylos uva-ursi (L.) Spreng., Heracleum sphondylium L., Acanthus mollis L., and Allium ursinum L., with Latin loan translation contributing a high proportion of the phytonyms. Some plants have many and various bear-related phytonyms, while others have only one or two bear names. Features like form and/or surface generated the richest pool of names, while such features as colour seemed to provoke rather few associations with bears. The unevenness of bear phytonyms in the chosen languages was not related to the size of the language nor the present occurence of the Brown Bear in the region. However, this may, at least to certain extent, be related to the amount of the historical ethnolinguistic research done on the selected languages

Benthic diatom communities in Estonian rivers

Epilithic, epiphytic and epipelic (soft bottom) diatom communities were studied in three rivers (Ahja, Selja and Valgejõgi). Although the total number of recorded diatom taxa was 165, the studied diatom assemblages consisted of 32, 26, or 28 constant taxa in the three studied rivers, respectively. The dominating diatoms were Achnanthidium minutissimum, Cocconeis placentula, Amphora pediculus, Staurosirella pinnata, Planothidium lanceolatum, and Diatoma moniliformis. The cluster analysis of three different diatom communities yielded different results. The clustering of the composition and structure of the epilithic diatom community brought out three principal groups of river reaches differing in the trophic status of water. Hence the epilithic community of diatoms can be recommended for the monitoring of Estonian running waters

Régressions entre 3 indices diatomiques existants et les teneurs en nutriments inorganiques pour 3 pays européens

[Departement_IRSTEA]Eaux [TR1_IRSTEA]BELCA [ADD1_IRSTEA]Systèmes aquatiques soumis à des pressions multiplesInternational audienceMonitoring eutrophication from benthic diatoms is a common practice in Europe, since this key-compartment is one of the most sensitive to the nutrient enrichment of hydrosystems. However, they have rarely been used to model nitrogen and phosphorus nutrient contents from the responses of diatomic bioindicators. The aim of this talk is therefore to try to model nutrient contents from the scores obtained by 3 diatom indices, PSI, BDI and TDI. This comparative prediction approach is useful for implementing the WFD because it would make it possible to infer nutrient contents from the responses of the diatomic compartment, clearly more integrative of the temporal dimension than an instantaneous water sampling. After log transformation of the nutrient contents, the responses of the PSI and of the BDI follow a linear adjustment and are consistent (R2 of 0.39 versus 0.35). The linear relationship with the TDI is weaker (0, 20), but fits better with a polynomial regression of degree 2 (0.30). The type of watercourse makes a significant influence on the physiognomy and the quality of the relationships found. The responses of these 3 indices to nitrates are weaker, PSI being the most correlated to this nutrient (0.19). It is difficult to find a convincing pattern from graphics for this relationship (large, feathered cloud shape, probably very influenced on some sites by the presence of other more biologically active nutrients). A need for indices more sensitive to the specific effects of this nutrient is therefore felt and constitutes a working track to be pursued, in REBECCA or other future works.Le monitoring de l'eutrophisation à partir des diatomées benthiques est une pratique courante en Europe, vu que ce maillon-clé est l'un des plus sensibles à l'enrichissement des hydrosystèmes en nutriments. Cependant, ils ont rarement été utilisés pour modéliser des teneurs en nutriments azotés et phosphorés à partir des réponses des bio-indicateurs diatomiques. Le but de la présente communication est donc d'essayer de déduire des teneurs en nutriments à partir des notes obtenues par 3 indices diatomiques, l'IPS, l'IBD et le TDI. Cette approche comparée de prédiction est utile à la mise en application de l'DCE car elle permettrait d'inférer des teneurs en nutriments à partir des réponses du compartiment diatomique, nettement plus intégrateur de la dimension temporelle qu'un prélèvement d'eau instantané. Après transformation log des teneurs en nutriments, les réponses de l'IPS et de l'IBD suivent un ajustement linéaire et sont consistantes (R2 de 0,39 versus 0,35), la relation linéaire avec le TDI est plus faible (0,20), mais s'ajuste mieux avec une régression polynomiale de degré 2 (0,30). Le type de cours d'eau influe sensiblement sur la physionomie et la qualité des relations trouvées. Les réponses des 3 indices aux nitrates sont plus faible, l'IPS étant le plus corrélé des 3 à ce nutriment (0,19). Il est difficile de dégager un patron convaincant des graphiquespour cette relation (forme du nuage large et en drapeau, probablement très influencée sur certains sites par la présence d'autres nutriments plus biologiquement actifs). Un besoin en indices plus sensibles aux effets de ce nutriment est donc ressenti et constitue une piste de travail à poursuivre, dans REBECCA ou dans d'autres travaux futurs