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Headwater streams are reliant on riparian tree leaf litterfall to fuel brown food webs. Terrestrial agents like herbivores and contaminants can alter plant growth, litter production, litter quality, and the timing of litterfall into streams, influencing aspects of the brown food web. At Mount St. Helens (USA), early successional streams are developing willow (Salix sitchensis) riparian zones. The willows are attacked by stem-boring herbivores, altering litter quality and the timing of litterfall. Within a established experimental plots, willows (male and female plants) were protected from herbivores using insecticides and provided with experimental additions of nitrogen. This enabled us to test the interacting influences of herbivores, nitrogen deposition, and willow sex on leaf litter quality, aquatic litter decomposition, and microbial and invertebrate detritivores. We found weak litter quality effects (higher N and lower C:N) for the herbivore treatment, but no effect of nitrogen deposition. Although litter decomposition rates were not strongly affected by litter treatments, detritivore communities were altered by all treatments. Nitrogen deposition resulted in decreased bacterial richness and decreased fungal diversity in-stream. Aquatic macroinvertebrate communities were influenced by the interacting effects of herbivory and nitrogen addition, with abundances highest in herbivore litter with the greatest N addition. Shredders showed the highest abundance in male, herbivore-attacked litter. The establishment of riparian willows along early successional streams and their interacting effects with herbivores and nitrogen deposition may be influencing detritivore community assembly at Mount St. Helens. More broadly, global changes like increased wet and dry N deposition and expanded ranges of key herbivores might influence tree litter decomposition in many ecosystems. [ABSTRACT FROM AUTHOR]

Generally, deciduous and evergreen trees coexist in subtropical forests, and both types of leaves are attacked by numerous insect herbivores. However, trees respond and defend themselves from herbivores in different ways, and these responses may vary between evergreen and deciduous species. We examined both the percentage of leaf area removed by herbivores as well as the percentage of leaves attacked by herbivores to evaluate leaf herbivore damage across 14 subtropical deciduous and evergreen tree species, and quantified plant defenses to varying intensities of herbivory. We found that there was no significant difference in mean percentage of leaf area removed between deciduous and evergreen species, yet a higher mean percentage of deciduous leaves were damaged compared to evergreen leaves (73.7% versus 60.2%). Although percent leaf area removed was mainly influenced by hemicellulose concentrations, there was some evidence that the ratio of non-structural carbohydrates:lignin and the concentration of tannins contribute to herbivory. We also highlight that leaf defenses to varying intensities of herbivory varied greatly among subtropical plant species and there was a stronger response for deciduous trees to leaf herbivore (e.g., increased nitrogen or lignin) attack than that of evergreen trees. This work elucidates how leaves respond to varying intensities of herbivory, and explores some of the underlying relationships between leaf traits and herbivore attack in subtropical forests. [ABSTRACT FROM AUTHOR]

Small streams constitute the majority of the water courses in a catchment and have specific characteristics that distinguish them from larger streams and rivers. Despite their small size and frequently remote locations, small streams contribute to ecosystem services that are important for humans. Here, we have identified 27 ecosystem services that small streams provide: seven supporting services, eight regulating services, five provisioning services and seven cultural services. Small streams are especially important for the maintenance of biodiversity, which is the basis of many ecosystem services. Small streams also support ecosystem services provided by larger streams and rivers due to longitudinal connectivity resulting in the downstream transference of energy, water, sediments, nutrients, organic matter and organisms. Small streams are, however, highly vulnerable to disturbances, which can compromise the ecosystem services they supply. We see a global need to effectively protect small streams to safeguard biodiversity and human wellbeing. [ABSTRACT FROM AUTHOR]

Biodiversity at many scales (functional group, species, genetic) can result in emergent ecological patterns. Here we explore the influence of tree genotypic variation and diversity on in-stream ecosystem processes and aquatic communities. We test whether genetically diverse inputs of leaf litter interact with a keystone organism, anadromous salmon, to influence in-stream ecosystem function. We used reach-level manipulation of salmon carcasses and leaf litter bags to examine how nutrient inputs interact with genetic variation in leaf litter decomposition. Genotypic variation in black cottonwood (Populus balsamifera ssp. trichocarpa) significantly influenced leaf litter chemistry, litter mass loss, and fungal biomass, but these variables were only weakly influenced by salmon carcass presence or a genotype x salmon (G x E) interaction. Mixtures of genotypes tended to demonstrate antagonistic effects (slower than expected decomposition) in the absence of salmon, but synergistic effects (faster than expected decomposition) when salmon were present. Our findings suggest that the influence of plant genotypic variation in linking aquatic and terrestrial ecosystems may be altered and in some cases intensified in the presence of a keystone vertebrate species. Resume : La biodiversite a plusieurs echelles (groupe fonctionnel, espece, genetique) peut entrainer l'emergence de nouveaux motifs ecologiques. Nous explorons l'influence des variations et de la diversite genotypiques des arbres sur les processus ecosystemiques dans les cours d'eau et sur les communautes aquatiques. Nous examinons si d'eventuelles interactions des apports de litiere de feuilles mortes genetiquement varies avec un organisme cle, le saumon anadrome, peuvent influer sur la fonction de l'ecosysteme dans le cours d'eau. Nous utilisons des manipulations a l'echelle du troncon de carcasses de saumon et de sacs de feuilles mortes pour examiner l'interaction des apports de nutriments avec les variations genetiques dans la decomposition des feuilles mortes. Les variations genotypiques du peuplier de l'Ouest (Populus balsamifera ssp. trichocarpa) exercent une influence significative sur la chimie de la litiere de feuilles mortes, la reduction de la masse de cette derniere et la biomasse fongique, mais ces variables ne sont que faiblement influencees par la presence de carcasses de saumon ou une interaction genotype x saumon (G x E). Les melanges de genotypes ont tendance a presenter des effets antagonistes (decomposition plus lente que prevu) en l'absence de saumons, mais des synergistes (decomposition plus rapide que prevu) en presence de saumons. Nos resultats donnent a penser que l'influence des variations genotypiques des plantes sur le lien entre les ecosystemes aquatiques et terrestres pourrait etre modifiee, voire, dans certains cas, rehaussee par la presence d'une espece de vertebres cle. [Traduit par la Redaction], Introduction Over the last decade, a body of research has shown that genetic variation in several foundation species can influence associated communities and ecosystem functions, and these influences can be [...]

Fossil Creek had been dammed for the past 90 years, and plans were underway to restore the stream. The creek runs through Central Arizona and flows from the high plateaus to the desert, cutting through the same formations that form the Grand Canyon. This article discusses the Fossil Creek monitoring project. In this project, students and teachers of Sinagua High School in Arizona team up with Northern Arizona University to conduct a longitudinal study to monitor changes in the creek. The data collected will ultimately provide an invaluable annual record for students, working scientists, and the wider community as changes are monitored over time. This particular longitudinal study is important because it monitors not only change through time, but also through an extreme event--removing a dam and restoring a stream. Today, the project continues to be part of an ongoing Research Experience for Teachers (RET) grant funded by the National Science Foundation. Through the RET, teachers have gained the confidence to expand field research in environmental science classes. (Contains 2 figures.)

Marine-derived nutrients from salmon carcasses and leaf litter inputs from riparian vegetation may interactively support stream biodiversity and ecosystem functioning through enhanced resource heterogeneity. Using a full-factorial design of single- and mixed-species litters, we tested for influences of salmon carcasses on in-stream litter decomposition. Overall, nonadditive (synergistic and antagonistic) effects on decomposition were detected for litter species mixtures, and these effects were explained by litter species composition, but not species richness. In middle to late stages of decay, mixtures of labile (high-quality) litters showed faster than expected mass loss, and recalcitrant (low-quality) litter mixtures showed slower than expected mass loss. The presence or absence of each litter species differentially affected decomposition, but these patterns were stronger when salmon carcasses were available. Across all treatments, the influence of salmon carcasses on decomposition was most pronounced in mid-stages of litter decay, where deceleration of decomposition was likely caused by macroinvertebrates feeding on salmon carcasses and less on litter. Combined, these data demonstrate that salmon carcass inputs to streams can enhance detrital heterogeneity, alter interactions among species in litter mixtures, and influence ecosystem functioning (i.e., decomposition). Les nutriments d'origine marine provenant des carcasses de saumons et les apports de litieres de feuilles mortes a partir de la vegetation riveraine peuvent de facon interactive supporter la biodiversite des cours d'eau et le fonctionnement de l'ecosysteme en augmentant l'heterogeneite des ressources. A l'aide d'un plan factoriel complet de litieres d'une seule espece et d'especes mixtes, nous avons verifie les effets des carcasses de saumons sur la decomposition des litieres dans un cours d' eau. Globalement, on peut detecter des effets (synergiques et antagonistes) non additifs sur la decomposition des litieres d'especes mixtes et ces effets s'expliquent par la composition en especes de la litiere, mais non par la richesse en especes. Aux etapes moyenne et finale de la decomposition, les melanges de litiere labile (haute qualite) subissent une perte de masse plus rapide que prevu et les melanges de litiere recalcitrante (basse qualite) une perte de masse plus lente que prevu. La presence et l'absence de chaque espece de litiere affectent la decomposition de maniere differente, mais ces patrons sont plus marques lorsque des carcasses de saumons sont presentes. Sur l'ensemble des traitements, l'influence des carcasses de saumons sur la decomposition est plus prononcee aux etapes intermediaires de la decomposition de la litiere, au moment ou la deceleration de la decomposition s'explique vraisemblablement par l'alimentation des invertebres plus sur les carcasses de saumons et moins sur la litiere. Ces donnees reunies demontrent que les apports des carcasses de saumons dans les cours d' eau peuvent augmenter l'heterogeneite du detritus, modifier les interactions des especes dans les melanges de litieres et affecter le fonctionnement de l'ecosysteme (c.-a-d. la decomposition). [Traduit par la Redaction], Introduction Environmental changes are altering the biodiversity of ecosystems worldwide. The functional implications of species losses and the mechanisms of biodiversity effects are largely uncertain (Hooper et al. 2005), yet [...]