Links between stream reach hydromorphology and land cover on different spatial scales in the Adour-Garonne Basin (SW France)

We report an investigation aimed at improving the understanding of the relationships between hydromorphology and land cover, and in particular aimed at identifying the spatial scale on which land cover patterns best account for the hydromorphology at a stream reach. This investigation was carried out in the Adour-Garonne basin. Several key findings emerged from the use of a new modeling procedure called “Random Forests”. Firstly, we established a typology of sites showing an upstream/downstream gradient structured by geographical descriptors and catchment hydromorphological features. Secondly, we found that the relationships between hydromorphology and the different spatial scales of land cover responded to a longitudinal gradient. Upstream, no noticeable difference was observed whatever the land cover pattern considered, whereas downstream, larger scales were strongly related to the hydromorphology. Thirdly, a specific land cover effect on each hydromorphological type was seen. Along the gradient, the contribution of the land cover variables structuring the hydromorphological types decreased and become homogeneous. Fourthly, stronger correlations were established with individual hydromorphological variables using the larger scales of land cover. This paper contributes to a better understanding of landscape ecology and fits well with the European Water Framework Directive that requires long-term sustainable management. In the context of natural conditions, we advise that the catchment scale should be given high priority when connected with land cover/uses; local and riparian environments being more valuable and complementary in the case of impacted sites

Adlafia diahotensis et Kobayasiella enigmatica, deux espèces nouvelles de Nouvelle-Calédonie

International audienceLa flore diatomique de Nouvelle-Calédonie a sans doute un des plus hauts taux d'endémisme au monde ; cela ne constitue donc pas un exploit de découvrir des espèces nouvelles pour la science. Adlafia diahotensis sp. nov. se caractérise par des valves linéaires aux extrémités cunéiformes, ce qui la distingue des autres espèces d'Adlafia (L : 9-16 µm ; l : 2,8-3,8 µm ; nombre de stries : 36-42 en 10 µm). Avec Adlafia muscora (Kociolek & de Reviers) Gerd Moser, Lange-Bertalot & Metzeltin, espèce typique du genre, et Adlafia djibaoui Le Cohu, Marquié & M.Coste, c'est la troisième espèce d'Adlafia détectée en Nouvelle-Calédonie. Dans le genre Adlafia, nous pouvons distinguer deux groupes. Le premier rassemble les espèces dont les extrémités proximales du raphé sont droites en vue interne. Le second groupe inclut les espèces dont ces mêmes extrémités proximales sont incurvées du côté primaire de la valve. A l'intérieur du second groupe, nous pouvons distinguer un sous-groupe suivant que les extrémités proximales sont proches (Adlafia muscora) ou éloignées (A. djibaoui). Adlafia diahotensis se range dans le sous-groupe du deuxième groupe avec les extrémités proximales du raphé incurvées et écartées. Kobayasiella enigmatica est un nom provisoire donné à cette espèce très rare, qui n'a pu être clairement détectée en M.O. alors que des observations ont été faites en M.E.B. Les valves sont linéaires-lancéolées avec les extrémités arrondies ou légèrement cunéiformes (L : 12-26 µm ; l : 3,0-3,8 µm). Les stries d'abord radiantes deviennent abruptement convergentes au voisinage des extrémités de la valve. Ce changement d'orientation des stries est marqué par une strie ramifiée simulant un candélabre de chaque côté de la valve. Cette strie ramifiée en candélabre est un critère générique fiable du genre Kobayasiella par rapport au genre Adlafia où le changement d'orientation des stries est déterminé par une strie simplement bifurquée ou très rarement trifurquée. Kobayasiella enigmatica se distingue de toutes les autres espèces du genre par un nombre très élevé de stries (58-62 en 10 µm)

Links between stream reach hydromorphology and land cover on different spatial scales in the Adour-Garonne Basin (SW France)

We report an investigation aimed at improving the understanding of the relationships between hydromorphology and land cover, and in particular aimed at identifying the spatial scale on which land cover patterns best account for the hydromorphology at a stream reach. This investigation was carried out in the Adour-Garonne basin. Several key findings emerged from the use of a new modeling procedure called “Random Forests”. Firstly, we established a typology of sites showing an upstream/downstream gradient structured by geographical descriptors and catchment hydromorphological features. Secondly, we found that the relationships between hydromorphology and the different spatial scales of land cover responded to a longitudinal gradient. Upstream, no noticeable difference was observed whatever the land cover pattern considered, whereas downstream, larger scales were strongly related to the hydromorphology. Thirdly, a specific land cover effect on each hydromorphological type was seen. Along the gradient, the contribution of the land cover variables structuring the hydromorphological types decreased and become homogeneous. Fourthly, stronger correlations were established with individual hydromorphological variables using the larger scales of land cover. This paper contributes to a better understanding of landscape ecology and fits well with the European Water Framework Directive that requires long-term sustainable management. In the context of natural conditions, we advise that the catchment scale should be given high priority when connected with land cover/uses; local and riparian environments being more valuable and complementary in the case of impacted sites

Trois nouvelles espèces de Delicata de Nouvelle-Calédonie et quelques observations complémentaires sur Delicata nepouiana Krammer et D. neocaledonica Krammer

International audienceDe nombreux prélèvements ont été effectués en Nouvelle-Calédonie en vue d’élaborer un indice diatomique ; ils ont permis de mettre au jour 3 espèces nouvelles du genre Delicata : D. pouentensis, D. gobinii et D. karembeui. Delicata pouentensis se caractérise par un côté dorsal fortement convexe et un rapport longueur/largeur assez faible, compris entre 3,4 et 4,7. Delicata gobinii présente une morphologie aciculaire, presque naviculoïde, son rapport longueur/largeur reste toujours élevé entre 7,1 et 8,7. Delicata karembeui est un cas particulier ; la structure des stries est originale pour le genre et la face valvaire présente des sortes de gouttières peu profondes le long du côté dorsal et ventral. Delicata karembeui peut être différenciée des autres genres cymbelloïdes par une combinaison de plusieurs facteurs incluant la forme, la taille, la course du raphé et la structure des stries. Par ailleurs, des observations en microscopie électronique de D. neocaledonica Krammer et de D. nepouiana Krammer, décrites seulement en microscopie optique, confirment leur placement dans le genre Delicata. Suite à ces observations sur les Delicata de Nouvelle-Calédonie, il faut noter que le genre se répartit en deux groupes. Dans le premier groupe, les stries se poursuivent sans interruption de la face valvaire au manteau ; dans le second, le manteau est délimité par un bourrelet longitudinal interrompant les stries. Il est remarquable d’observer que sur les 22 espèces de Delicata décrites à ce jour, 8 sont endémiques de Nouvelle-Calédonie

Modeling the Stream Water Nitrate Dynamics in 60,000-km(2) European Catchment, the Garonne, Southwest France

The spatial and temporal dynamics in the stream water NO3-N concentrations in a major European river-system, the Garonne (62,700 km(2)), are described and related to variations in climate, land management, and effluent point-sources using multivariate statistics. Building on this, the Hydrologiska Byrans Vattenbalansavdelning (HBV) rainfall-runoff model and the Integrated Catchment Model of Nitrogen (INCA-N) are applied to simulate the observed flow and N dynamics. This is done to help us to understand which factors and processes control the flow and N dynamics in different climate zones and to assess the relative inputs from diffuse and point sources across the catchment. This is the first application of the linked HBV and INCA-N models to a major European river system commensurate with the largest basins to be managed tinder the Water Framework Directive. The simulations suggest that in the lowlands, seasonal patterns in the stream water NO3-N concentrations emerge and are dominated by diffuse agricultural inputs, with an estimated 75% of the river load in the lowlands derived from arable farming. The results confirm earlier European catchment studies. Namely, current semi-distrubuted catchment-scale dynamic models, which integrate variations in land cover, climate, and a simple representation of the terrestrial and in-stream N cycle, are able to simulate seasonal NO3-N patterns at large spatial (> 300 km(2)) and temporal (>= monthly) scales using available national datasets

Lacuneolimna gen. nov., Lacuneolimna zalokariae comb. nov. and Lacuneolimna novagallia spec. nov. (Bacillariophyceae) from the French Guiana diatom freshwater flora

International audienceThe freshwater diatoms of the French Guiana have received little attention so far. A new diatom genus, Lacuneolimna, based on the species Eolimna zalokariae, is described from a small rainforest stream. Numerous ultrastructural features differ from the genus Eolimna, notably the pluriseriate striae lying between relief-like elevated virgae and depressed externally. In addition, another species new to science, L. novagallia, belonging to this new genus, was discovered in the same place. Detailed light and scanning electron microscope observations are used to characterize the morphology and the ultrastructure of these two new taxa

Modeling the Stream Water Nitrate Dynamics in 60,000-km(2) European Catchment, the Garonne, Southwest France

The spatial and temporal dynamics in the stream water NO3-N concentrations in a major European river-system, the Garonne (62,700 km(2)), are described and related to variations in climate, land management, and effluent point-sources using multivariate statistics. Building on this, the Hydrologiska Byrans Vattenbalansavdelning (HBV) rainfall-runoff model and the Integrated Catchment Model of Nitrogen (INCA-N) are applied to simulate the observed flow and N dynamics. This is done to help us to understand which factors and processes control the flow and N dynamics in different climate zones and to assess the relative inputs from diffuse and point sources across the catchment. This is the first application of the linked HBV and INCA-N models to a major European river system commensurate with the largest basins to be managed tinder the Water Framework Directive. The simulations suggest that in the lowlands, seasonal patterns in the stream water NO3-N concentrations emerge and are dominated by diffuse agricultural inputs, with an estimated 75% of the river load in the lowlands derived from arable farming. The results confirm earlier European catchment studies. Namely, current semi-distrubuted catchment-scale dynamic models, which integrate variations in land cover, climate, and a simple representation of the terrestrial and in-stream N cycle, are able to simulate seasonal NO3-N patterns at large spatial (> 300 km(2)) and temporal (>= monthly) scales using available national datasets