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The stated goal of Levi et al. (2011, Can. J. Fish. Aquat. Sci. 68: 1316-1329) was to determine the influence of geomorphic complexity on the dynamics of salmon-derived nutrients. We studied seven streams in Southeast Alaska with varying degrees of historical (mid-1900s) timber harvest and, as a result, differences in stream geomorphology. In a comment on our study, Jackson and Martin (2012, Can. J. Fish. Aquat. Sci. 69: this issue) suggest that the geomorphic complexity we ascribe to timber harvest may be due to natural variation in watershed characteristics and offer alternative hypotheses. We sought to reduce the natural variation among our study streams by using a stratified sampling design (i.e., selecting reaches classified as floodplain 4 or 5 by the USDA Forest Service), but acknowledge that, as with any ecological field study, alternative hypotheses may exist to explain observed patterns in ecological responses. We maintain that our study design was sufficiently robust (i.e., 300 m reaches studied in seven streams for 3 years, totaling 21 stream-years) to draw inferences about the influence of salmon on streamwater nutrients and, secondarily, the role of geomorphic variation in mediating nutrient dynamics. Our data also support our finding that the legacy of timber harvest altered nutrient dynamics in salmon-bearing streams via alterations to stream geomorphology that were quantifiable. Le but enonce de Levi et al. (2011, J. Can. Sci. Halieutiques Aquat. 68 : 1316-1329) consistait a determiner l'influence de la complexite geomorphologique sur la dynamique des nutriments provenant des saumons. Nous avons etudie sept cours d'eau du sud-est de l'Alaska presentant differentes intensites de coupe de bois historique (au milieu du 20e siecle) et, du coup, des differences sur le plan de leur geomorphologie fluviale. Dans un commentaire concernant notre etude, Jackson et Martin (2012, J. Can. Sci. Halieutiques Aquat. 69 : present numero) suggerent que la complexite geomorphologique que nous attribuons a la coupe de bois pourrait etre le fait de la variabilite naturelle des caracteristiques des cours d'eau et ces auteurs presentent d'autres explications possibles. Bien que nous ayons tente de limiter la variabilite naturelle parmi les cours d'eau etudies en utilisant un plan d'echantillonnage stratifie (c.-a-d. en choisissant des passages designes plaine inondable 4 ou 5 par le Service des forets du USDA), nous admettons que, comme il en va de toute etude ecologique de terrain, differentes hypotheses peuvent expliquer les patrons de reactions ecologiques observes. Nous maintenons cependant que notre methodologie etait assez robuste (c.-a-d. des passages de 300 m etudies dans sept cours d'eau pendant 3 ans, pour un total de 21 annees-cours d'eau) pour permettre de tirer des conclusions sur l'influence du saumon sur les nutriments dans l'eau et, secondairement, sur le role de la variabilite geomorphologique dans la mediation de la dynamique des nutriments. Nos donnees appuient egalement notre conclusion a l'effet que la coupe de bois a modifie la dynamique des nutriments dans les cours d'eau a saumons en modifiant de maniere quantifiable la geomorphologie de ces derniers. [Traduit par la Redaction], In Levi et al. (2011), our research objective was to 'explain spatial and temporal variation in the magnitude of nutrient enrichment' from salmon-derived nutrients during annual spawning runs. Numerous studies [...]

Streams often rely on nutrient subsidies, and variation in nutrient delivery may alter the ecosystem response. Pacific salmon (Oncorhynchus spp.) provide marine-derived nutrients to their natal streams but also cause benthic disturbance, with the net effect determined by watershed and stream characteristics. To understand the factors contributing to variation in salmon-derived nutrients (SDN), we studied nutrient concentration and export in seven streams with varying physical characteristics due to timber harvest (e.g., channel complexity) over three years in Southeast Alaska, USA. Salmon increased concentrations and export of dissolved and particulate nitrogen, phosphorus, and carbon, but the magnitude of increase varied up to 41-fold among streams. The density of live salmon best predicted the increase in nutrient concentration and export, whereas the density of carcasses had a negligible effect. Nutrient export was predicted by transient storage before and after the salmon run. Streams in harvested watersheds with simplified channels had greater nutrient export than those in pristine watersheds with complex channels. However, enrichment from salmon overrode the effect of timber harvest on export during the run. Our study demonstrates that enrichment via SDN is short-lived and related to run size, whereas timber harvest and carcasses exert little influence on SDN dynamics. Les cours d'eau dependent souvent de subsides de nutriments et la variation dans les apports de nutriments peut modifier les reactions de l'ecosysteme. Les saumons du Pacifique (Oncorhynchus spp.) procurent des nutriments d'origine marine a leur cours d' eau de naissance, mais ils causent aussi des bouleversements benthiques; l'effet net depend des caracteristiques du bassin versant et du cours d'eau. Afin de connaitre les facteurs qui contribuent a la variation dans les nutriments provenant des saumons (SDN), nous avons etudie les concentrations et les exportations de nutriments dans sept cours d' eau presentant des caracteristiques physiques differentes dues a la coupe du bois (par ex., complexite du chenal) pendant trois ans dans le sud-est de l'Alaska. Les saumons font augmenter les concentrations et l'exportation de l'azote dissous et particulaire, du phosphore et du carbone, mais l'importance de l'augmentation varie par un facteur pouvant atteindre 41 entre les cours d'eau. La densite des saumons est la meilleure variable predictive de l'augmentation des concentrations et de l'exportation des nutriments, alors que la densite des carcasses a un effet negligeable. L'exportation des nutriments peut etre predite en tenant compte de l'accumulation temporaire avant et apres la montaison des saumons. Les cours d'eau dans les bassins versants ayant subi la coupe forestiere qui ont un chenal simplifie exportent plus de nutriments que ceux dans des bassins versants non affectes avec un chenal plus complexe. Cependant, l'enrichissement apporte par les saumons surpasse l'effet de la recolte du bois sur l'exportation durant la montaison. Notre etude demontre que l'enrichissement en SDN est de courte duree et qu'il est relie a la taille de la montaison, mais que le recolte du bois et les carcasses ont peu d'influence sur la dynamique des SDN. [Traduit par la Redaction], Introduction Stream ecosystems often depend on nutrient subsidies to maintain their structure and function (Polis et al. 1997). In coastal watersheds and tributaries to large lakes, the migration of anadromous [...]

Using nutrient-diffusing substrata (NDS) in seven streams in southeast Alaska, USA, we tested whether (i) nutrient limitation of autotrophic and heterotrophic biofilms was alleviated by salmon resource subsidies, and (ii) whether the degree of alleviation could be predicted by environmental variables. Before salmon spawners arrived, autotrophic biofilms were nitrogen (N)-limited, or co-limited by N and phosphorus (P), whereas heterotrophic biofilms were either P-limited, or co-limited by N and P. Combined N and P amendments resulted in a 2.6-fold increase in biofilm chlorophyll a, and a 3.2-fold increase in community respiration. After salmon arrived, autotroph nutrient limitation was alleviated in six of the seven streams. Heterotrophs still exhibited nutrient limitation in six streams, but most streams shifted from co-limitation to P-limitation. Nutrient-diffusing substrata amended with salmon tissue indicated that salmon could also be an important source of organic carbon for biofilms. Autotrophs responded less to N and P amendments as streamwater ammonium concentration increased with the arrival of salmon. For heterotrophs, ammonium concentration and N:P ratio best predicted changes in response following the arrival of salmon. We provide the first direct evidence that biofilm nutrient limitation can be alleviated by salmon spawners in nutrient-poor streams. A l'aide de substrats diffuseurs de nutriments (NDS) dans sept cours d'eau du sud-est de l'Alaska, E.-U., nous avons teste (i) si la limitation par les nutriments des biofilms autotrophes et heterotrophes est reduite par les apports de ressources provenant des saumons et (ii) si l'importance de la reduction peut etre predite a partir des variables environnementales. Avant que les saumons n'arrivent pour frayer, les biofilms autotrophes sont limites par l'azote (N) ou limites conjointement par N et le phosphore (P), alors que les films heterotrophes sont limites par P ou conjointement par N et P. Des amendements combines en N et P entrainent une augmentation de la chlorophylle a des biofilms par un facteur de 2,6 et un accroissement de la respiration de la communaute par un facteur de 3,2. Apres l'arrivee des saumons, la limitation des autotrophes par les nutriments a ete reduite dans six des sept cours d'eau. Chez les heterotrophes, six des cours d'eau montraient encore une limitation par les nutriments, bien que la plupart des cours d'eau aient change d'une limitation conjointe pour une limitation par P. Les NDS amendes avec du tissu de saumons montrent que les saumons peuvent aussi representer une source importante de carbone organique pour les biofilms. Les autotrophes reagissent moins aux amendements en N et en P, alors que la concentration d'ammonium augmente dans l'eau des cours d'eau avec l'arrivee des saumons. Chez les heterotrophes, la concentration d'ammonium et le rapport N :P sont les meilleures variables predictives des changements consecutifs a l'arrivee des saumons. Nous presenteras les premieres donnees qui demontrent directement que la limitation des biofilms par les nutriments peut etre attenuee par les saumons reproducteurs dans les cours d'eau pauvres en nutriments. [Traduit par la Redaction], Introduction Ecological resource subsidies, the movements of material, energy, and organisms across ecosystem boundaries, are considered vital to the structure and function of many ecosystems (Polis et al. 2004). A [...]

In the present study we evaluated changes in phosphorus (P), nitrogen (N), and humic acid (HA) contents of vermicompost (VC) in response to temperature increases, and inoculation with N2-fixing and P-solubilizing microbes. Inoculants ofPseudomonasandAzotobacterwere prepared and used to inoculate VC that was kept at 28 and 41 °C. Biological and chemical parameters of the VC were evaluated at 0, 20, 40, and 60 days. As incubation duration increased, bacterial population, N, available P, and HA content increased while organic carbon and pH decreased. These changes were most rapid during the initial 40 days of the experiment, and slowed subsequently. Increasing temperature from 28 to 41 °C reduced bacterial population and the efficiency of these bacteria in improving VC quality. Overall, our results indicate that inoculation of VC with microbes holds promise as a means of increasing the quality of VC, while our increased temperature treatment was less effective. [ABSTRACT FROM PUBLISHER]

Migrations of animals can transfer energy and nutrients through and among terrestrial and aquatic habitats. Pool-breeding amphibians, such as the wood frog ( Lithobates sylvaticus), make annual breeding migrations to ephemeral wetlands in forest habitats in the eastern and midwestern United States and Canada., To model the influence of wood frogs on nutrient transport and transformation through time, we coupled long-term population monitoring data (1985-2005) from a wood frog population with estimates of the elemental composition of wood frog egg masses and emerging juveniles., Over the 21-year study period, 8.8 kg carbon (C), 2.0 kg nitrogen (N) and 0.20 kg phosphorus (P) were transported from the terrestrial to the aquatic habitat and approximately 21 kg C, 5.5 kg N and 1.2 kg P were exported to the surrounding terrestrial habitat by wood frogs., During the study period, the average net flux of C, N and P was from aquatic to terrestrial habitats, but the magnitude and direction of the net flux was element dependent. Thus, the net flux of C, N and P did not always flow in the same direction., Predicting long-term trends in nutrient and energy flux by organisms with biphasic life cycles should rely on long-term population data to account for temporal variability. This is especially true for organisms that are sensitive to long-term shifts in temperature and precipitation patterns, such as amphibians that breed in ephemeral pools. [ABSTRACT FROM AUTHOR]

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Summary 1. Variation in resource subsidies can create or reinforce heterogeneity in recipient ecosystems. Related activities of organisms delivering resource subsidies, such as ecosystem engineering by Pacific salmon spawners ( Oncorhynchus spp.), also alter heterogeneity. We studied whether heterogeneity in stream environmental conditions and spawner abundances were reflected in the net ecological effects of salmon (i.e. enrichment by resource subsidies and disturbance by ecosystem engineering) on benthic biofilm. 2. We sampled seven Southeast Alaska streams over 3 years, both before and during the salmon run. In each stream and year, stream environmental characteristics and their influence on responses of benthic biofilm [mean and coefficient of variation of chlorophyll a (chl a), ash-free dry mass (AFDM) and autotrophic index (AFDM:chl a)] to spawners were assessed. 3. Streams and periods before and during the salmon run were distinct based on their environmental characteristics. The responses of most biofilm metrics to spawners were stream- and year-specific, suggesting that the ecological effect of spawners ranged from net enrichment to net disturbance depending on the stream or year studied. The environmental context, especially temperature, large wood, and sediment size, explained >50% of biofilm variability during the run, but <30% over the entire study, suggesting that salmon can alter environmental constraints. 4. Precision of biofilm estimates improved by increasing either the number of streams or the number of years sampled (i.e. spatial or temporal replication). However, combining data from different North Pacific Rim ecoregions inflated the confidence interval as compared with a single ecoregion, indicating the importance of regional environmental contexts for net salmon effects. 5. Our results suggest that biofilm responses to salmon can vary greatly, even within a single ecoregion, and that environmental conditions can modify net salmon effects. Consequently, generalisations about biofilm responses across the native range of salmon may be challenging. [ABSTRACT FROM AUTHOR]