Load Variance Research Articles

Stochastic structural control under earthquake excitations

SUMMARY Structural control is an alternative tool, which can be used for the reduction of the response caused by earthquake excitations. Research and implementation in practice have shown that seismic control of structures has not only a lot of potential but also many limitations. Many control strategies are based on the dynamic characteristics of buildings. During the life of the structures, these dynamic characteristics change. So there is a need of modifying the control algorithm. The question that arises is what would happen to the response of controlled structure if the parameters that influence the dynamic characteristics such as mass and stiffness would change while the control algorithm would remain the same. In this paper, this practical issue is discussed, using a stochastic control approach. The influence of the random character of the loads and the stiffness to the response of structures controlled by a modified pole placement algorithm are investigated. Loads and stiffness are considered as random variables, and the response of a structure subjected to dynamic loads is calculated using Monte Carlo methods (i) without control and (ii) controlled by the mentioned algorithm. The methodology is implemented for three characteristic buildings. The cumulative distribution function of acceleration, velocity, and displacement is obtained using the controlled and the uncontrolled analysis for the examined buildings. Deterministic results of the response are also calculated and compared with the random characteristics of the stochastic analyses. Conclusions regarding the influence of the variance of loads and stiffness to the response of structures are presented. Copyright © 2013 John Wiley & Sons, Ltd.

Trunk and Hip Biomechanics Influence Anterior Cruciate Loading Mechanisms in Physically Active Participants

Background: Excessive trunk motion and deficits in neuromuscular control (NMC) of the lumbopelvic hip complex are risk factors for anterior cruciate ligament (ACL) injury. However, the relationship between trunk motion, NMC of the lumbopelvic hip complex, and triplanar knee loads during a sidestep cutting task has not been examined. Purpose: To determine if there is an association between multiplanar trunk motion, NMC of the lumbopelvic hip complex, and triplanar knee loads with ACL injury during a sidestep cutting task. Study Design: Descriptive laboratory study. Methods: The hip and knee biomechanics and trunk motion of 30 participants (15 male, 15 female) were analyzed during a sidestep cutting task using an optoelectric camera system interfaced to a force plate. Trunk and lower extremity biomechanics were calculated from the kinematic and ground-reaction force data during the first 50% of the stance time during the cutting task. Pearson product moment correlation coefficients were calculated between trunk and lower extremity biomechanics. Multiple linear regression analyses were carried out to determine the amount of variance in triplanar knee loading explained by trunk motion and hip moments. Results: A greater internal knee varus moment (mean, 0.11 ± 0.12 N·m/kg*m) was associated with less transverse-plane trunk rotation away from the stance limb (mean, 20.25° ± 4.42°; r = −0.46, P = .011) and a greater internal hip adduction moment (mean, 0.33 ± 0.25 N·m/kg*m; r = 0.83, P < .05). A greater internal knee external rotation moment (mean, 0.11 ± 0.08 N·m/kg*m) was associated with a greater forward trunk flexion (mean, 7.62° ± 5.28°; r = 0.42, P = .020) and a greater hip internal rotation moment (mean, 0.15 ± 0.16 N·m/kg*m; r = 0.59, P = .001). Trunk rotation and hip adduction moment explained 81% (P < .05) of the variance in knee varus moment. Trunk flexion and hip internal rotation moment explained 48% (P < .05) of the variance in knee external rotation moment. Conclusion: Limited trunk rotation displacement toward the new direction of travel and hip adduction moment are associated with an increased internal knee varus moment, while a combined increase in trunk flexion displacement and hip internal rotation moment is associated with a higher internal knee external rotation moment. Clinical Relevance: Prevention interventions for ACL injury should encourage trunk rotation toward the new direction of travel and limit excessive trunk flexion while adjusting frontal- and transverse-plane hip NMC.

Stochastic Modeling and Optimization Scheduling for Electric Vehicle Charging

This paper commences with the investigation of the charging power of electric bus, and the charging profile is fitted by using Least Square Method. Then the charging modeling of private electric vehicles is established by way of statistical techniques and Monte Carlo simulation algorithm. According to the negative impact on planning and operation of the power system, as is brought by the popularity of electric vehicles (EVs), especially when implemented without control, an optimal control concept is put forward by combining a centralized optimal scheduling and a distributed scheduling scheme, and a coordinated scheduling model is also established. The centralized optimal scheduling scheme takes the network load variance minimization as the optimization objective. The optimization goal of distributed scheduling scheme is to minimize the deviation between charging load demand and the centralized optimization results, within each dynamic sliding window, considering the actual battery constraints and EV owners ′ benefits. Therefore, the dynamic control for EV charging and discharging is fulfilled. Take the planning data of Shandong for example, we analyze the impact of EV charging on the distribution network under different scenarios. Results are presented to verify the validity and feasibility of charging model and control algorithm.

How will renewable power generation be affected by climate change? The case of a Metropolitan Region in Northwest Germany

Energy systems that primarily use wind and solar power production are in need of long-term storage of electricity and fully developed transmission grids. Moreover, renewables-based energy systems may be strongly affected by climate change. We present two models that assess the impacts of climate change on solar and wind power generation and use these models to evaluate climate projections based on the A1B scenario for Germany's Northwest Metropolitan Region. For these projections the seasonal profile of solar power production is not affected despite less cloud cover during the summer, while the seasonal profile of wind power production has a more pronounced seasonal peak during the winter due to slightly increasing wind speeds. We compare the obtained seasonal profiles to different scenarios for electricity demand. For each scenario we identify the ratio of wind and solar power generation that minimizes the variance of the residual load at the monthly time scale under the premise of a full supply by wind and solar power. Our results suggest that the need for long-term storage of electricity and the need for extensions of the transmission grid will on the one hand decrease but on the other hand become more volatile because of climate change impacts in the Northwest Metropolitan Region over the next century.

A Collaborative and Scalable Platform for On-Demand IPTV Services

As a promising standard of television, Internet protocol television (IPTV) gains increasing popularity with its on-demand services. However, supporting scalable on-demand IPTV services remains to be an important challenge. Existing IPTV architecture dedicates a regional station to serve subscribers in the respective region regardless of temporal and spatial dynamics in service demand. This may cause significant imbalance of resource utilization and service provisioning delay among stations, especially with increasing subscribers and service catalog. In this paper, we propose CiTV, a collaborative Internet TV service platform that achieves efficient and scalable IPTV service delivery through interstation collaboration. First, CiTV employs a novel request dispatching algorithm that enables stations to autonomously dispatch requests among themselves and achieves low per-view cost and load variance at the same time. Second, CiTV also leverages a distributed content placement algorithm to globally optimize content utilization at multistation level, which is important for deployment scalability. Last but not the least, CiTV also ensures service delivery quality and efficiency through fine-grained collaboration scope control. We perform both theoretical and empirical analysis of CiTV. Our experiment results suggest that CiTV significantly improves the scalability of on-demand IPTV services for the existing IPTV architecture.

무선 센서 네트워크를 위한 비동기 적응형 메시지 전달 기법

본 논문에서는 무선 센서 네트워크에서 발생하는 에너지 효율성 문제를 해결하기 위해 S-MAC 기반의 비동기 적응형 메시지 전달 기법을 제안한다. 제안된 기법은 패킷 충돌이나 간섭에 의해 발생하는 전송오류와 버퍼 오버플로우로 인한 혼잡 손실을 구별하는 차별화 전략과 트래픽 부하 변화에 따라 단편의 크기를 적응적으로 조절하는 기법으로 구성된다. 특히, 패킷 전송 차별화 기법을 사용하여 단편의 크기가 필요 이상으로 축소하지 않도록 제어함으로써 메시지에 대한 총 전송시간이 증가되지 않도록 방지하여 전송을 위한 에너지 사용을 최소화하도록 한다. 마지막으로 시뮬레이션 분석결과를 통해 본 논문에서 제안한 기법이 에너지 효율성 및 전송 지연 측면에서 S-MAC 기반의 메시지 전달 기법보다 성능이 우수함을 보인다. In this paper, we propose an asynchronous and adaptive message passing scheme based on S-MAC for handling with the problem on energy efficiency in wireless sensor networks. The proposed scheme consists of a policy that differentiate transmission errors caused by packet collision or radio interference from congestion errors caused by buffer overflow and a method that adaptively controls the size of a fragment according to the variance of traffic loads. Especially, it presents a method that highly reduce the energy consumption by keeping the size of fragment not being excessively smaller than the one that may result in rapid increment of the total transfer time. Finally, with the simulation results we show that network throughput and delay are improved by using the proposed message passing scheme.

A utility‐based load‐balancing scheme with guarantee of users' rate for LTE self‐organization networks

SUMMARYMobility load balance is becoming increasingly crucial in the design of self‐organization networks for LTE (long‐term evolution), especially under dynamic scenarios. In this paper, we study the problem of load balance with guarantee of users' rate and formulate a general optimization model, where the weighted sum of the first‐order and second‐order statistics of load distribution (load variance and total load level) are considered directly. We prove the convexity of the model and derive the optimal user‐station association scheme in different weights. Based on analysis of the optimization model, a dynamic admission and handover scheme is proposed. Mobile users with rate requirement select a base station based on the load utility in a distributed way and handover to the selected station (if handover is triggered). Furthermore, a simulation platform with seven cells is developed to evaluate the dynamic admission and handover scheme. It is demonstrated that our proposed scheme outperforms the conventional counterpart. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Host nutrition alters the variance in parasite transmission potential.

The environmental conditions experienced by hosts are known to affect their mean parasite transmission potential. How different conditions may affect the variance of transmission potential has received less attention, but is an important question for disease management, especially if specific ecological contexts are more likely to foster a few extremely infectious hosts. Using the obligate-killing bacterium Pasteuria ramosa and its crustacean host Daphnia magna, we analysed how host nutrition affected the variance of individual parasite loads, and, therefore, transmission potential. Under low food, individual parasite loads showed similar mean and variance, following a Poisson distribution. By contrast, among well-nourished hosts, parasite loads were right-skewed and overdispersed, following a negative binomial distribution. Abundant food may, therefore, yield individuals causing potentially more transmission than the population average. Measuring both the mean and variance of individual parasite loads in controlled experimental infections may offer a useful way of revealing risk factors for potential highly infectious hosts.

Generating super-shedders: co-infection increases bacterial load and egg production of a gastrointestinal helminth

Co-infection by multiple parasites is common within individuals. Interactions between co-infecting parasites include resource competition, direct competition and immune-mediated interactions and each are likely to alter the dynamics of single parasites. We posit that co-infection is a driver of variation in parasite establishment and growth, ultimately altering the production of parasite transmission stages. To test this hypothesis, three different treatment groups of laboratory mice were infected with the gastrointestinal helminth Heligmosomoides polygyrus, the respiratory bacterial pathogen Bordetella bronchiseptica lux+ or co-infected with both parasites. To follow co-infection simultaneously, self-bioluminescent bacteria were used to quantify infection in vivo and in real-time, while helminth egg production was monitored in real-time using faecal samples. Co-infection resulted in high bacterial loads early in the infection (within the first 5 days) that could cause host mortality. Co-infection also produced helminth ‘super-shedders’; individuals that chronically shed the helminth eggs in larger than average numbers. Our study shows that co-infection may be one of the underlying mechanisms for the often-observed high variance in parasite load and shedding rates, and should thus be taken into consideration for disease management and control. Further, using self-bioluminescent bacterial reporters allowed quantification of the progression of infection within the whole animal of the same individuals at a fine temporal scale (daily) and significantly reduced the number of animals used (by 85%) compared with experiments that do not use in vivo techniques. Thus, we present bioluminescent imaging as a novel, non-invasive tool offering great potential to be taken forward into other applications of infectious disease ecology.

Wavelet Multiscale Analysis of a Power System Load Variance

Wavelet transform (WT) represents a very attractive mathematical area for just more than 15 years of its research in applications in electrical engineering. This is mainly due to its advantages over other processing techniques and signal analysis, which is reflected in the time-frequency analysis, and so it has an important application in the processing and analysis of time series. In this paper, for example, the analysis of the hourly load of a real power system over the past few years was performed by applying the continuous WT and using the Morlet wavelet function. The results show that this approach of data analysis can give a better insight into the basic characteristics of the consumption and identify the characteristic periods of the power system load variances over the past years, which can be very interesting for power system planners.

Cumulative impact of host and viral factors on HIV-1 viral-load control during early infection.

In HIV-1 infection, the early set-point viral load strongly predicts both viral transmission and disease progression. The factors responsible for the wide spectrum of set-point viral loads are complex and likely reflect an interplay between the transmitted virus and genetically defined factors in both the transmitting source partner and the seroconverter. Indeed, analysis of 195 transmission pairs from Lusaka, Zambia, revealed that the viral loads in transmitting source partners contributed only ∼2% of the variance in early set-point viral loads of seroconverters (P = 0.046 by univariable analysis). In multivariable models, early set-point viral loads in seroconverting partners were a complex function of (i) the viral load in the source partner, (ii) the gender of the seroconverter, (iii) specific HLA class I alleles in the newly infected partner, and (iv) sharing of HLA-I alleles between partners in a transmission pair. Each of these factors significantly and independently contributed to the set-point viral load in the newly infected partner, accounting for up to 37% of the variance observed and suggesting that many factors operate in concert to define the early virological phenotype in HIV-1 infection.

Resource concentration by insects and implications for plant populations

Summary1. The distribution of herbivores among plant patches may be an important factor determining plant population persistence. The resource concentration hypothesis proposes that herbivores are more abundant per unit plant at higher host plant densities and this has been found to occur in many systems. However, the opposite pattern, resource dilution, in which the herbivores are more abundant in low‐density patches and situations in which the number of insect herbivores per unit plant remains constant, also occurs.2. We developed a simulation model to explore how the distribution of insects per plant affects plant population decline and persistence. We varied the numbers of plants per patch and the distribution pattern, i.e. whether insects were found in a resource concentration distribution, a resource dilution distribution or a distribution in which insect abundance increased linearly with plant density.3. Resource concentration resulted in longer persistence of plant populations. Plant populations declined more rapidly with either weak resource dilution or directly proportional insect distribution patterns. As the intensity of resource concentration increased, the decline in plant population density was reduced, and plant persistence increased because of increasing variance in insect load. Under strong resource dilution, increasing variance in the insect load also led to a reduction in plant population decline and an increase in plant persistence.4. We complement our model with field data from the diffuse knapweed, Centaurea diffusa biocontrol system. We compared the relationship with plant density of a successful biocontrol agent, Larinus minutus, and an unsuccessful one, Urophora affinis. Larinus minutus density was directly proportional to plant density, while U. affinis showed a resource concentration pattern with higher rates of attack in high‐density patches.5. Synthesis: Patterns of insect distribution with host plant density will alter the extent to which patches of differing plant densities decline or persist. Resource concentration promotes persistence of the insect–plant system because increased herbivore pressure in high‐density patches leads to negative density‐dependent plant growth. Weak resource dilution and a distribution of insects that is directly proportionate to plant density can accelerate plant population decline. Strong resource dilution leads to positive density dependence with higher population growth in large patches. Our simulation model and field data demonstrate that the relationship between insect distribution and plant densities can influence plant population dynamics and has implications for choices of weed biological control agents.

A study on the electric power load of Beijing and its relationships with meteorological factors during summer and winter

Using the daily electric power load and meteorological data over the period from January 2006 to September 2010 in Beijing, the general features of the electric power load and the main factors affecting this load have been analysed. The results indicate that winter and summer are the two peak power consumption seasons in each year. This finding could be mainly attributed to the consumption of energy for urban residential cooling or heating. In the summer, the daily minimum temperature was most closely correlated with the maximum power load (correlation co-efficient of 0.65, significant at the 0.1% level); the primary effect of temperature on the maximum power load varied largely from 376 to 858 MW °C −1, and it increased sharply when the daily minimum temperature was higher than 24 °C or the daily maximum temperature was higher than 32 °C. In the winter, the daily maximum temperature was most closely correlated with the power load (−0.45, 0.1% significance), and the primary effect varied from 109 to 391 MW °C −1. However, the relationship between the power load and the temperature was more complicated in the winter: this relationship varied during the central heating period and its pre- and post-periods. Moreover, the temperature humidity index (THI) could explain more of the variance in the daily maximum power load than any single temperature factor in the summer, while the wind-chill temperature index (WCT) did not contribute to this variance in the winter. Finally, due to the rapid urbanization of Beijing, the power load and the priamry effect increased each year. Copyright © 2012 Royal Meteorological Society

Discernible rhythm in the spatio/temporal distributions of transatlantic dust

Abstract. The differences in North African dust emission regions and transport routes, between the boreal winter and summer, are thoroughly documented. Here we re-examine the spatial and temporal characteristics of dust transport over the tropical and subtropical North Atlantic Ocean, using 10 yr of satellite data, in order to better characterize the different dust transport periods. We see a robust annual triplet: a discernible rhythm of "transatlantic dust weather". The proposed annual partition is composed of two heavy loading periods, associated here with a northern-route period and southern-route period, and one light-loading period, accompanied by unusually low average optical depth of dust. The two dusty periods are quite different in character: their duration, transport routes, characteristic aerosol loading and frequency of pronounced dust episodes. The southern-route period lasts ~4 months. It is characterized by a relatively steady southern positioning, low frequency of dust events, low background values and high variance in dust loading. The northern-route period lasts ~6.5 months and is associated with a steady drift northward of ~0.1 latitude day−1, reaching ~1500 km north of the southern-route. The northern period is characterized by higher frequency of dust events, higher (and variable) background and smaller variance in dust loading. It is less episodic than the southern period. Transitions between the periods are brief. Separation between the southern and northern periods is marked by northward latitudinal shift in dust transport and by moderate reduction in the overall dust loading. The second transition, between the northern and southern periods, commences with an abrupt reduction in dust loading and rapid shift southward of ~0.2 latitude day−1, and ~1300 km in total. Based on cross-correlation analyses, we attribute the observed rhythm to the contrast between the northwestern and southern Saharan dust source spatial distributions. Despite the vast difference in areas, the Bodélé Depression, located in Chad, appears to modulate transatlantic dust patterns about half the time.

고력볼트 길이에 따른 체결 특성 평가

고력볼트 길이-직경비가 5d 이상인 경우, 시험을 통한 결과를 활용하여 현장에서 볼트 체결을 하도록 권고하고 있을뿐 길이-직경비에 따른 별도의 규정 및 지침은 없다. 국내에서는 고력볼트 체결법으로 너트회전법이 아닌 토크관리법이 적용하고 있고 최근에는 KS B 2819의 '구조물용 토크-전단형 고장력 볼트'(이하, TS 고력볼트)가 주로 사용되고 있기 때문에 길이 인자에 따른 규정이 국외 기준에 비해 미비한 것이 현실이다. 따라서, 본 논문에서는 TS 고력볼트의 길이인자에 따른 적정 축력 도입을 위한 소요 너트회전각 및 토크를 분석하여 길이변수에 따른 특성을 평가하고자 한다. 실험결과의 분석에서는 통계분석 프로그램 Minitab을 활용하여 길이변수에 대한 유효성을 정량적으로 분석했다. It has been reported that the length parameter of high strength bolts results in the variance in tensile loads. The required turn of nut for each length is specified in AISC RCSC specification. There is no specific regulation datum about the bolt length in the two national codes and specifications in Korea. Therefore this study focused on evaluating influence of the clamping torque subjected to length parameter of high strength bolts. Two types of high strength bolt specimens were manufactured and tested; High Strength Hexagon bolt specified in ASTM A490 and Torque Shear Bolt in KS B 2819. The length parameter ranged from 60mm(3d) to 140mm(7d). The torque, turn of nut, and the clamping force were analyzed to review whether length parameter affects on the required tensile strength. To evaluate the effects of the length parameter on the torque and turn of nut for the required strength and clamping force, statistical analysis was also carried out.

부하변동에 따른 유도전동기 전류와 전력 특성

Induction motor is most widely used as the driving power in the industrial site. Induction motor current is composed of two parts, magnetizing current and load current. Load current uses energy what is doing the work. Load current varies with load variance but magnetizing current is constant, regardless of load variation. Magnetizing current needs for establishing the rotating magnetic field of induction motor and lags behind the voltage. Generally capacitor is used for power-factor compensation of inductive load. Self-excitation occurs when the capacitive reactive current from the capacitor is greater than the magnetizing current of the induction motor. When this occurs, excessive voltages can result on the terminals of the motor. This excessive voltage can cause insulation degradation and ultimately result in motor insulation failure. In this paper, we analyzed that how the magnetizing current and condenser current is operating at the allowable limit by the load variation. Condenser current is below allowable limit of magnetizing current but magnetizing current is above allowable limit at the lower load operation condition.

Coordinated Charging of Plug-In Hybrid Electric Vehicles to Minimize Distribution System Losses

As the number of plug-in hybrid vehicles (PHEVs) increases, so might the impacts on the power system performance, such as overloading, reduced efficiency, power quality, and voltage regulation particularly at the distribution level. Coordinated charging of PHEVs is a possible solution to these problems. In this work, the relationship between feeder losses, load factor, and load variance is explored in the context of coordinated PHEV charging. From these relationships, three optimal charging algorithms are developed which minimize the impacts of PHEV charging on the connected distribution system. The application of the algorithms to two test systems verifies these relationships approximately hold independent of system topology. They also show the additional benefits of reduced computation time and problem convexity when using load factor or load variance as the objective function rather than system losses. This is important for real-time dispatching of PHEVs.

Hepatitis B viraemia: its heritability and association with common genetic variation in the interferon γ signalling pathway

ObjectiveHigh viraemia of hepatitis B virus (HBV) influences all phases in the development of hepatocellular carcinoma (HCC). This study was designed to estimate the overall contribution of host genetics to...

Interpretation of correlations in setpoint viral load in transmitting couples

Two interesting reports studying correlations in HIV-1 setpoint viral loads (spVLs) and early viral loads within transmitting couples [1,2] were published recently, an observation which was foreshadowed in Zambia [3] and which we also recently showed in Uganda [4]. We wish to highlight that even weak correlation between spVL of individuals in transmitting couples can correspond to a large estimate for the role of viral genetic factors in determining spVL. Our difference in interpretation can be clarified by consideration of the sources of variance contributing to spVL (Fig. 1).Fig. 1: Influences on setpoint viral load (a) Analysis of variance of within-couple and between-couple variance tries to estimate the proportion of variance in setpoint viral load (spVL) explained by shared viral factors. (b) Shared viral factors cause spVL to be correlated, but the proportion of variance in spVL of the secondary case explained by knowledge of the spVL of the index case will be lower than that shown in (a), as both are affected by nonviral factors. spVL, setpoint viral load.The spVL of index and secondary cases within transmitting couples may be determined by a combination of factors related to the broadly similar viral genotype (viral factors), and other nonviral factors including host factors, coinfections, specificity and nature of immunological response or chance effects (Fig. 1a). Nonviral factors affect the spVL of both index and the secondary cases in couples, explaining the difference between correlation between patients (Fig. 1b) and estimates of the strength of viral factors (Fig. 1a). Hecht et al.[1], van der Kuyl et al.[2] and Tang et al.[3] estimate the Pearson correlation coefficient, r, between spVL values of index cases and secondary cases in transmitting couples. We propose that if the aim is to infer the strength of viral factors on spVL, a better estimate can be obtained using analysis of variance (ANOVA) of within and between couple variance [4]. The coefficient of determination (R2) of the ANOVA is a lower-bound estimate for the proportion of variance in spVL explained by viral factors. An additional benefit of ANOVA is that the analysis is easily adjusted for confounders such as sex of the host and viral subtype. A drawback is that the method is less transparent and requires extra adjustments for the parameters introduced into the model. In an idealized case wherein spVL values are normally distributed with identical variance, the estimates are related in a simple manner: the coefficient of determination (R2) of the ANOVA, as used in [4], is equal to the correlation coefficient (r), as used in [1–3]. Thus, the raw numbers are unchanged, but their interpretation in terms of the strength of viral effects in determining spVL is radically altered. The unadjusted estimates for the proportion of variance in spVL explained by viral genotype in the four studies are 20% [3], 25% [2], 27% [4] and 55% [1]. These estimates are all higher than unadjusted estimates of 13% of variance in spVL explained by host genetic factors to date [5], although, of course, these latter estimates may increase as more host factors are discovered, and some host–virus interaction effects may be dually counted in individual analyses. The additional observation that the relationship between spVL in transmitting pairs may depend on the stage of infection of the recipient [2] (based on a small sample size) is plausible and interesting, and may aid the detailed elucidation of the mechanisms linking viral factors to spVL. The four published studies together represent 250 couples, and the link in spVL within couples seems consistent and robust. Attributing variation in viral load to viral, host and interaction effects will undoubtedly shed light on the mechanisms of HIV pathogenesis. These results also support the hypothesis that spVL has evolved at the population level [6].

Salmon-derived nutrients drive diatom beta-diversity patterns

SUMMARY 1. Pacific salmon are a textbook example of migratory animals that transfer nutrients between ecosystems, but little is known about how salmon-derived nutrients (SDN) affect the biodiversity of recipient freshwater ecosystems. We examined paleolimnological records from six Alaskan lakes to define how changes in SDN from sockeye salmon (Oncorhynchus nerka) influenced sedimentary diatom community structure and betadiversity among lakes and through time. 2. Using an isotopic mixing model, we showed that SDN loading could account for >80% of the lake total nitrogen budgets and strongly regulated diatom community composition. Spatial dissimilarity in diatom communities was positively related to differences in SDN among lakes (r 2 = 0.69, P < 0.01, n = 10). Likewise, temporal dissimilarity in diatom communities was positively related to differences in SDN in a sediment core with substantial variation in salmon spawner dynamics between 1700 and 1950 AD (r 2 = 0.34, P < 0.01, n = 19). Finally, beta-diversity metrics quantifying temporal turnover within each lake’s sediment record were also positively related to the variance in SDN loading among lakes (r 2 = 0.88, P < 0.05, n = 5). Mean SDN was only negatively correlated to temporal diatom beta-diversity. 3. Spatially subsidised systems often receive temporally variable resource inputs, and thus, it is not surprising that, unlike previous studies, we found that resource variability was the key driver of community composition and beta-diversity. In habitats that receive strongly fluctuating external nutrient loads, environment heterogeneity may overweigh stochastic community processes. In addition, freshwater diatoms are characterised by great dispersal capabilities and short life cycles and therefore may be a more sensitive indicator for evaluating the role of resource variability than previously used model organisms. These results suggest that productivity‐diversity relationship vary with the nature of nutrient loading and the life history of the community studied. 4. Overall, our study highlights that the transport of nutrients by sockeye salmon across ecosystem boundaries is a significant driver of algal community and biodiversity in nursery lakes, mainly through changing the magnitude of nutrient variation. As such, freshwater species diversity in regions like the U.S. Pacific Northwest may become