The Influence of Dams on Downstream Larval and Juvenile Fish and Benthic Macroinvertebrate Community Structure and Associated Physicochemical Variables

The Influence of Dams on Downstream Larval and Juvenile Fish and Benthic Macroinvertebrate Community Structure and Associated Physicochemical Variables R. Daniel Hanks The influence of dams on downstream biotic and abiotic components of aquatic ecosystems has been largely studied within the context of the River Continuum (RCC) and Serial Discontinuity Concepts (SDC). Few of these studies have sufficiently studied how these variables change along the longitudinal gradient below the impoundments in a systematic manner, comparing equal distances below both epilimnetic and hypolimnetic dams to a reference condition. This is especially true of early life stages of fish (i.e., larval and juvenile stages) and macroinvertebrate functional groups. Here, we systematically evaluated the effects of dams at 16 sites downstream of dams for their impact on physicochemical (instream habitat [e.g., substrate, flow, etc.] and water quality [i.e., DO, pH, conductivity, and temperature], and landcover [i.e., % forested land, % developed land, and % grassland]) and various metrics for larval and juvenile fish and benthic macroinvertebrates.;Effective capture of larval and juvenile fish was paramount for the evaluation of dam influences on larval and juvenile. Sampling larval fish at various life stages can be difficult in shallow, structurally and spatially diverse streams. We evaluated three commonly employed methods (light traps, drift nets, and spot-and-sweep) for sampling larval fish in these systems. We found the spot-and-sweep method captured a higher abundance of larvae than either drift nets or light traps during both daytime and nighttime hours. Additionally the spot-and-sweep method captured as many different taxa as drift nets and more than light traps. The coefficient of variation was lower for spot-and-sweep than for either drift nets or light traps for both taxa richness and larval abundance. Richness for daytime and nighttime spot-and-sweep sampling was equal. Mean richness was also equal between the two periods, and mean CPUE was not significantly different between periods. The coefficient of variation was lowest for daytime spot-and-sweep sampling, suggesting it was less variable than nighttime sampling. The spot-and-sweep method showed promise for determining taxa presence and relative abundance. Discrepancies in the ability of personnel while performing spot-and-sweep sampling was investigated and found to be insignificant. Of the three methods evaluated for sampling structurally complex and spatially heterogeneous streams the spot-and-sweep method was found to be the most effective. We investigated the effects of dams on downstream larval and juvenile fish. Generalized additive models indicated that there was a general increase in abundance, genus richness, and Shannon diversity associated with increasing distance from dams. Principal component analysis (PCA) indicated three influential PC\u27s that were structured by landcover, habitat and water quality, and disturbance. Nonmetric multidimensional scaling (NMDS) indicated larval and juvenile fish communities were structured differently between epilimnetic and hypolimnetic releases and that habitat variables structuring those communities were more variable in epilimnetic releases than hypolimnetic releases. We systematically evaluated both the abiotic and biotic (i.e., benthic macroinvertebrates at the family level) along the stream continuum below impoundments with both epilimnetic and hypolimnetic releases and compared those findings to a reference stream. Generalized additive models (GAMs) identified six habitat variables (i.e., substrate coarseness, substrate diversity, pH, temperature, stream width, and stream depth) as significantly related to distance from dam. GAMs also indicated that abundance was not significantly related to distance from dam but both family level richness and Shannon diversity exhibited significant increases with increasing distance from dams. We evaluated patterns of changes in physicochemical and macroinvertebrate functional group components of aquatic systems along the longitudinal gradient below dams and compared changes in these variables to an undammed reference stream. Generalized additive models indicated that genus richness, functional richness, tolerance, dispersal, percent five dominant genera, EPT, and GLIMPSS were lower in dammed streams than in our reference stream. Genus and functional richness, percent 5 dominant genera, EPT, and GLIMPSS all increased as distance from dams increased while they remained relatively consistent within our reference stream. Tolerance and dispersal changed with distance from dams in dammed streams but showed little change in our reference stream. Percent composition of functional groups was different between dammed and reference streams; in dammed streams the percent composition changed with increasing distance from dams, but remained relatively stable in our reference stream. Genus and functional richness also exhibited two distinct gradients within the 5,100-m that we sampled below dams where a short, rapidly changing gradient existed immediately below dams to approximately 2,000-m, followed by a more gradual steadily increasing gradient that appeared to continue beyond our most distant sampling location below dams (i.e., 5,100-m). Important explanatory variables that varied in statistical significance between response variables but were commonly significant with distance from dams was substrate coarseness and percent forested land. Eighty five percent of our measured abiotic variables below dams had higher r values where curvilinear relationships were modeled as compared to linear relationships; whereas only 46% of the biotic variables had higher r values with curvilinear models. Nonmetric multidimensional scaling (NMDS) confirmed our GAM results indicating benthic macroinvertebrates below dams show structural changes along the stream continuum.;In all cases (larval and juvenile fish, family level aquatic macroinvertebrates, and genus level aquatic macroinvertebrate metrics) our findings generally agreed with the SDC but future studies should aim to sample in a spatially systematic manner, as this will improve our understanding of how dams influence abiotic and biotic components of aquatic systems. Additionally, our studies consistently indicated two gradients existed for most biotic measures. We believe further studies are required to understand the two recovery gradients that exist below dams and the extent of dam influences along the stream continuum

Interactive Online Tool for Educating the Public About Landscape Conservation

Landscape-scale conservation planning performed in a systematic and transparent manner is becoming more common as it is increasingly evident that ecological processes are being affected at large spatial scales. The Appalachian Landscape Conservation Cooperative undertook a 15-state landscape conservation planning project, resulting in a landscape conservation design called NatureScape. To facilitate NatureScape\u27s implementation by groups and individuals participating in on-the-ground landscape conservation, we developed an online decision support tool. This tool has the potential to assist Extension services in delivering research-based information to varied stakeholders as they make land use decisions

Design and Modeling of Membrane-Based Evaporative Cooling Devices for Thermal Management of High Heat Fluxes

We present a high-heat-flux cooling device for advanced thermal management of electronics. The device incorporates nanoporous membranes supported on microchannels to enable thin-film evaporation. The underlying concept takes advantage of the capillary pressure generated by small pores in the membrane, and minimizes the viscous loss by reducing the membrane thickness. The heat transfer and fluid flow in the device were modeled to determine the effect of different geometric parameters. With the optimization of various parameters, the device can achieve a heat transfer coefficient in excess of 0.05 kW/cm²-K, while dissipating a heat flux of 1 kW/cm². When applied to power electronics, such as GaN high-electron-mobility transistors, this membrane-based evaporative cooling device can lower the near-junction temperature by more than 40 K compared with contemporary single-phase microchannel coolers

Multiregional Emergence of Mobile Pastoralism and Nonuniform Institutional Complexity across Eurasia

In this article I present a new archaeological synthesis concerning the earliest formation of mobile pastoralist economies across central Eurasia. I argue that Eurasian steppe pastoralism developed along distinct local trajectories in the western, central, and (south)eastern steppe, sparking the development of regional networks of interaction in the late fourth and third millennia BC. The “Inner Asian Mountain Corridor” exemplifies the relationship between such incipient regional networks and the process of economic change in the eastern steppe territory. The diverse regional innovations, technologies, and ideologies evident across Eurasia in the mid-third millennium BC are cast as the building blocks of a unique political economy shaped by “nonuniform” institutional alignments among steppe populations throughout the second millennium BC. This theoretical model illustrates how regional channels of interaction between distinct societies positioned Eurasian mobile pastoralists as key players in wide-scale institutional developments among traditionally conceived “core” civilizations while also enabling them to remain strategically independent and small-scale in terms of their own sociopolitical organization. The development of nonuniform institutional complexity among Eurasian pastoralists demonstrates a unique political and economic structure applicable to societies whose variable political and territorial scales are inconsistent with commonly understood evolutionary or corporate sociopolitical typologies such as chiefdoms, states, or empires

Evaluating the potential for the environmentally sustainable control of foot and mouth disease in Sub-Saharan Africa

Strategies to control transboundary diseases have in the past generated unintended negative consequences for both the environment and local human populations. Integrating perspectives from across disciplines, including livestock, veterinary and conservation sectors, is necessary for identifying disease control strategies that optimise environmental goods and services at the wildlife-livestock interface. Prompted by the recent development of a global strategy for the control and elimination of foot-and-mouth disease (FMD), this paper seeks insight into the consequences of, and rational options for potential FMD control measures in relation to environmental, conservation and human poverty considerations in Africa. We suggest a more environmentally nuanced process of FMD control that safe-guards the integrity of wild populations and the ecosystem dynamics on which human livelihoods depend while simultaneously improving socio-economic conditions of rural people. In particular, we outline five major issues that need to be considered: 1) improved understanding of the different FMD viral strains and how they circulate between domestic and wildlife populations; 2) an appreciation for the economic value of wildlife for many African countries whose presence might preclude the country from ever achieving an FMD-free status; 3) exploring ways in which livestock production can be improved without compromising wildlife such as implementing commodity-based trading schemes; 4) introducing a participatory approach involving local farmers and the national veterinary services in the control of FMD; and 5) finally the possibility that transfrontier conservation might offer new hope of integrating decision-making at the wildlife-livestock interface

Prior and Present Evidence: How Prior Experience Interacts with Present Information in a Perceptual Decision Making Task

Vibrotactile discrimination tasks have been used to examine decision making processes in the presence of perceptual uncertainty, induced by barely discernible frequency differences between paired stimuli or by the presence of embedded noise. One lesser known property of such tasks is that decisions made on a single trial may be biased by information from prior trials. An example is the time-order effect whereby the presentation order of paired stimuli may introduce differences in accuracy. Subjects perform better when the first stimulus lies between the second stimulus and the global mean of all stimuli on the judged dimension ("preferred" time-orders) compared to the alternative presentation order ("nonpreferred" time-orders). This has been conceptualised as a "drift" of the first stimulus representation towards the global mean of the stimulus-set (an internal standard). We describe the influence of prior information in relation to the more traditionally studied factors of interest in a classic discrimination task.Sixty subjects performed a vibrotactile discrimination task with different levels of uncertainty parametrically induced by increasing task difficulty, aperiodic stimulus noise, and changing the task instructions whilst maintaining identical stimulus properties (the "context").The time-order effect had a greater influence on task performance than two of the explicit factors-task difficulty and noise-but not context. The influence of prior information increased with the distance of the first stimulus from the global mean, suggesting that the "drift" velocity of the first stimulus towards the global mean representation was greater for these trials.Awareness of the time-order effect and prior information in general is essential when studying perceptual decision making tasks. Implicit mechanisms may have a greater influence than the explicit factors under study. It also affords valuable insights into basic mechanisms of information accumulation, storage, sensory weighting, and processing in neural circuits

A Fluctuation-Driven Mechanism for Slow Decision Processes in Reverberant Networks

The spike activity of cells in some cortical areas has been found to be correlated with reaction times and behavioral responses during two-choice decision tasks. These experimental findings have motivated the study of biologically plausible winner-take-all network models, in which strong recurrent excitation and feedback inhibition allow the network to form a categorical choice upon stimulation. Choice formation corresponds in these models to the transition from the spontaneous state of the network to a state where neurons selective for one of the choices fire at a high rate and inhibit the activity of the other neurons. This transition has been traditionally induced by an increase in the external input that destabilizes the spontaneous state of the network and forces its relaxation to a decision state. Here we explore a different mechanism by which the system can undergo such transitions while keeping the spontaneous state stable, based on an escape induced by finite-size noise from the spontaneous state. This decision mechanism naturally arises for low stimulus strengths and leads to exponentially distributed decision times when the amount of noise in the system is small. Furthermore, we show using numerical simulations that mean decision times follow in this regime an exponential dependence on the amplitude of noise. The escape mechanism provides thus a dynamical basis for the wide range and variability of decision times observed experimentally

Expression of Constitutively Active CDK1 Stabilizes APC-Cdh1 Substrates and Potentiates Premature Spindle Assembly and Checkpoint Function in G1 Cells

Mitotic progression in eukaryotic cells depends upon the activation of cyclin-dependent kinase 1 (CDK1), followed by its inactivation through the anaphase-promoting complex (APC)/cyclosome-mediated degradation of M-phase cyclins. Previous work revealed that expression of a constitutively active CDK1 (CDK1AF) in HeLa cells permitted their division, but yielded G1 daughter cells that underwent premature S-phase and early mitotic events. While CDK1AF was found to impede the sustained activity of APC-Cdh1, it was unknown if this defect improperly stabilized mitotic substrates and contributed to the occurrence of these premature M phases. Here, we show that CDK1AF expression in HeLa cells improperly stabilized APC-Cdh1 substrates in G1-phase daughter cells, including mitotic kinases and the APC adaptor, Cdc20. Division of CDK1AF-expressing cells produced G1 daughters with an accelerated S-phase onset, interrupted by the formation of premature bipolar spindles capable of spindle assembly checkpoint function. Further characterization of these phenotypes induced by CDK1AF expression revealed that this early spindle formation depended upon premature CDK1 and Aurora B activities, and their inhibition induced rapid spindle disassembly. Following its normal M-phase degradation, we found that the absence of Wee1 in these prematurely cycling daughter cells permitted the endogenous CDK1 to contribute to these premature mitotic events, since expression of a non-degradable Wee1 reduced the number of cells that exhibited premature cyclin B1oscillations. Lastly, we discovered that Cdh1-ablated cells could not be forced into a premature M phase, despite cyclin B1 overexpression and proteasome inhibition. Together, these results demonstrate that expression of constitutively active CDK1AF hampers the destruction of critical APC-Cdh1 targets, and that this type of condition could prevent newly divided cells from properly maintaining a prolonged interphase state. We propose that this more subtle type of defect in activity of the APC-driven negative-feedback loop may have implications for triggering genome instability and tumorigenesis

Genetically defined elevated homocysteine levels do not result in widespread changes of DNA methylation in leukocytes

BACKGROUND:DNA methylation is affected by the activities of the key enzymes and intermediate metabolites of the one-carbon pathway, one of which involves homocysteine. We investigated the effect of the well-known genetic variant associated with mildly elevated homocysteine: MTHFR 677C>T independently and in combination with other homocysteine-associated variants, on genome-wide leukocyte DNA-methylation. METHODS:Methylation levels were assessed using Illumina 450k arrays on 9,894 individuals of European ancestry from 12 cohort studies. Linear-mixed-models were used to study the association of additive MTHFR 677C>T and genetic-risk score (GRS) based on 18 homocysteine-associated SNPs, with genome-wide methylation. RESULTS:Meta-analysis revealed that the MTHFR 677C>T variant was associated with 35 CpG sites in cis, and the GRS showed association with 113 CpG sites near the homocysteine-associated variants. Genome-wide analysis revealed that the MTHFR 677C>T variant was associated with 1 trans-CpG (nearest gene ZNF184), while the GRS model showed association with 5 significant trans-CpGs annotated to nearest genes PTF1A, MRPL55, CTDSP2, CRYM and FKBP5. CONCLUSIONS:Our results do not show widespread changes in DNA-methylation across the genome, and therefore do not support the hypothesis that mildly elevated homocysteine is associated with widespread methylation changes in leukocytes