Human activities are altering the fundamental geography of biogeochemicals. Yet we lack an understanding of how the spatial patterns in organismal stoichiometry affect biogeochemical processes and the tools to predict the impacts of global changes on biogeochemical processes. In this contribution we develop stoichiometric distribution models (StDMs), which allow us to map spatial structure in resource elemental composition across a landscape and evaluate spatial responses of consumers. We parameterise StDMs for a consumer-resource (moose-white birch) system and demonstrate that we can develop predictive models of resource stoichiometry across a landscape and that such models could improve our predictions of consumer space use. With results from our study system application, we argue that explicit consideration of the spatial patterns in organismal elemental composition may uncover emergent individual, population, community and ecosystem properties that are not revealed at the local extents routinely used in ecological stoichiometry. We discuss perspectives for further developments and application of StDMs to advance three emerging frameworks for spatial ecosystem ecology in an era of global change; meta-ecosystem theory, macroecological stoichiometry and remotely sensed biogeochemistry. Progress on these emerging frameworks will allow for the integration of ecological stoichiometry and individual space use and fitness.

Abstract. Nutrient transport across ecosystem boundaries by migratory animals can regulate trophic and biogeochemical dynamics of recipient ecosystems. The magnitude and direction of net nutrient flow between ecosystems is modulated by life history, abundance and biomass, individual behavior, and body element composition of migrating individuals. We tested common assumptions applied to nutrient transport models regarding homeostasis of species' body element composition across space and ontogenetic stage. We quantified whole body phosphorus (P) concentration of three life stages of wild Atlantic salmon (Salmo salar L.) from three distinct populations in Newfoundland, Canada, to evaluate the importance of river of origin and life stage as predictors of salmon %P. We found that life stage was a more important predictor of salmon %P than river of origin, and that %P of post-spawn adults migrating downstream to the ocean (i.e., kelts) was more similar to %P of juveniles migrating downstream to the ocean (i.e., smolts) than it was to %P of adults migrating upstream to spawn. We then compared nutrient flux for the three rivers over a 20-year period calculated with body composition values extracted from existing literature and our direct measurements to evaluate how assumptions regarding spatial and ontogenetic homogeneity in salmon %P influenced the observed P fluxes. We demonstrate that assuming equality of kelt %P and adult %P results in an overestimate of net nutrient flux to rivers by Atlantic salmon and the erroneous conclusion that Atlantic salmon populations are unconditional sources of nutrients to their natal watersheds. Instead, Newfoundland's salmon populations are conditional sinks of freshwater P, which is the opposite functional role of Pacific salmon. Our results highlight that a better understanding of intraspecific variation in body element composition of fishes is a prerequisite to determining their role in global biogeochemical cycling.

Body-element content was measured for three life stages of wild Atlantic salmon Salmo salar from three distinct Newfoundland populations as individuals crossed between freshwater and marine ecosystems. Life stage explained most of the variation in observed body-element concentration whereas river of capture explained very little variation. Element composition of downstream migrating post-spawn adults (i.e. kelts) and juvenile smolts were similar and the composition of these two life stages strongly differed from adults migrating upstream to spawn. Low variation within life stages and across populations suggests that S. salar may exert rheostatic control of their body-element composition. Additionally, observed differences in trace element concentration between adults and other life stages were probably driven by the high carbon concentration in adults because abundant elements, such as carbon, can strongly influence the observed concentrations of less abundant elements. Thus, understanding variation among individuals in trace elements composition requires the measurement of more abundant elements. Changes in element concentration with ontogeny have important consequences the role of fishes in ecosystem nutrient cycling and should receive further attention.

Extensive research has been conducted on how large impoundments and reservoirs affect hydrologic, geomorphologic and ecological processes in downstream ecosystems. Surprisingly, few studies have addressed the effects of smaller impoundments and constructed ponds. Pond construction has been considered an important tool for managers seeking to reduce sediment, nutrient and pollutant loads, and increase habitat heterogeneity in streams in an effort to conserve or enhance aquatic species diversity. However, we lack information on the interaction between ponds and stream habitats, which may compromise the efficacy of conservation efforts. The objective of this review is to outline possible physical and biological changes to stream ecosystems resulting from pond construction. Greater understanding of how ponds influence watershed processes at various spatial scales is crucial to evaluating the effects of constructed ponds on stream ecosystems.

Dramatic declines of Pacific salmon (Oncorhynchus spp.) populations have decreased delivery of marine-derived material to Pacific Northwest streams where juvenile salmon reside. Managers use artificial nutrient additions to increase juvenile salmon growth and survival and typically assume nutrient-driven increases in biofilm production are an important pathway by which nutrients become available to higher trophic levels. To evaluate how biofilms respond to additions of salmon carcass analog, a pasteurized, processed form of nutrient mitigation materials, we quantified biofilm nutrient limitation, benthic and whole-stream metabolism, and biofilm standing crops before and following experimental additions in tributaries of the Salmon River, Idaho, USA. Biofilm nutrient limitation did not change and standing crop did not increase in response to analog additions at two different levels (low, 30 g·m −2 ; or high, 150 g·m −2 ) within 1 month of addition. In contrast, whole-stream and benthic primary productivity and respiration increased in a high-analog treated segment, but did not increase in a low-analog treated segment. Together, our results suggest that metabolism may be a more appropriate tool for assessing the ecosystem effects of nutrient additions than biofilm standing crop or nutrient limitation, which are constrained by a variety of abiotic and biotic factors like hydrology and grazing.Résumé : D'importantes diminutions des populations de saumons du Pacifique (Oncorhynchus spp.) ont entraîné une réduction des apports de matières d'origine marine dans les cours d'eau du Pacific Northwest où résident des saumons juvéniles. Les gestionnaires utilisent l'ajout de nutriments artificiels pour accroître la croissance et la survie des saumons juvéniles, présumant généralement que l'augmentation de la production de biofilm induite par les nutriments constitue une importante voie de transfert de nutriments vers des niveaux trophiques plus élevés. Afin d'évaluer la réaction des biofilms à l'ajout d'analogues de carcasse de saumon, une forme transformée et pasteurisée de matière utilisée pour compenser le manque de nutriments, nous avons quantifié la limitation des nutriments de biofilms, le métabolisme benthique et à l'échelle du cours d'eau et la biomasse de biofilm disponible avant et après des ajouts expérimentaux dans des affluents de la rivière Salmon (Idaho, États-Unis). La limitation des nutriments de biofilms n'a pas changé et la biomasse de biofilm disponible n'a pas augmenté en réaction à des ajouts d'analogue à deux taux différents (faible, 30 g·m −2 ; et fort, 150 g·m −2 ) durant le mois suivant ces ajouts. En revanche, la productivité primaire benthique et à l'échelle du cours d'eau et la respiration ont augmenté dans un tronçon ayant reçu un fort ajout d'analogue, mais n'ont pas augmenté dans un tronçon ayant reçu un faible ajout d'analogue. Nos résultats donnent à penser que le métabolisme pourrait être un outil mieux adapté pour évaluer les effets écosystémiques d'ajouts de nutriments que la biomasse de ...

Supplementing fish populations at the egg stage is a low‐cost alternative to hatchery rearing that is presumed to improve adaptation to local natural conditions. The Shoshone‐Bannock Tribes began supplementing Chinook Salmon Onchorynchus tschwytscha in Panther Creek, Idaho, at the eyed egg stage in 2014. The Chinook Salmon eggs were artificially fertilized and reared to eye‐up in the hatchery and then planted in custom‐made in‐stream incubators (egg boxes) for volitional release and natural rearing. Using data from three brood years, we evaluated the efficacy of this supplementation program solely in terms of juvenile production. We related juvenile production to the placement and retrieval of the egg boxes, assessed the relative contributions of offspring (parr and emigrants) from the egg boxes (HOR) to overall juvenile abundance, and compared the performance (length, condition, dispersal distance, and survival) of HOR versus natural‐origin (NOR) juveniles. Brood year and box placement within the stream (distance upstream) were the best predictors of whether or not an egg box was retrieved from its original location. Meanwhile, the condition of the box (i.e., intact, damaged, or missing) was the best single predictor of juvenile production. Supplemented eggs represented an estimated 42, 50, and 42% of the total egg deposition in Panther Creek in brood years 2014, 2015, and 2016, respectively. A parentage analysis revealed that the egg boxes accounted for 6, 22, and 35%, respectively, of the parr production for the respective brood years when the data were normalized to the estimated egg deposition—less than the egg‐to‐parr production that was estimated for natural redds. As fall parr, the HOR fish differed from the NOR fish in terms of their length and dispersal behavior, but they were of similar length and condition at their emigration from Panther Creek and exhibited no significant difference in downstream survival through the Federal Columbia River Power System (FCRPS). Collectively, our results provide useful insights to fisheries managers who are interested in initiating or refining egg supplementation programs.

No abstract

Variation in rearing conditions across hatcheries and basins can affect the performance of hatchery salmonids in the wild. In 2008, the Shoshone-Bannock Tribes began planning an out-of-basin hatchery facility on the eastern Snake River Plain for rearing threatened Chinook Salmon Oncorhynchus tshawytscha for release in tributaries of the upper Salmon River, Idaho, USA. To help determine the viability of the planned out-of-basin hatchery, we reared 100,000 juvenile Chinook Salmon from the same genetic stock at one in-basin (Sawtooth Fish Hatchery on the Salmon River) and one out-of-basin (Springfield Fish Hatchery on the Snake River Plain) site in Idaho that are characterized by significant differences in water hardness and temperature regime. In October 2018 and April 2019, we tested whether fish condition, stress physiology, acute mortality, and downstream survival differed between the two groups at the parr and smolt life stages upon release in the Yankee Fork Salmon River, which is characterized by low water hardness. For both release groups, parr experienced low acute mortality during the 48 h after release; however, the out-of-basin group had a downstream survival rate through an unimpounded portion of the migration corridor that was an order of magnitude lower than that for the in-basin group. During the smolt release, the out-of-basin group showed signs of extreme physiological stress, acute mortality rates of 40-80%, and low survival in the unimpounded portion of the migratory corridor. The in-basin group recovered from the stress of transport and release, had no acute mortality, and survived through the unimpounded migratory corridor at a rate comparable to that of previous years' releases. Based on the results of this comparative study, comanagers are evaluating alternatives to the proposed out-of-basin