Environmental quality and fish community ecology in an agricultural mountain stream system of Taiwan

A 1.5 year environmental and faunal analysis was conducted in headwater streams of the upper Ta-chia River in mountainous central Taiwan. The area had distinct wet and dry seasons owing to monsoonal-typhoonal rainfall patterns. Compared to natural stream areas, agriculturally impacted reaches had greater discharge fluctuation, warmer temperatures, higher turbidity, increased nutrient loads, and reduced bedform diversity;Stream biotic communities varied according to local habitat characteristics. Coldwater algae existed mainly within natural stream reaches while eutrophication indicators occurred abundantly at agriculturally impacted sites. Large-bodies shredder-collector and predatory insects inhabited natural stream areas while smaller scraper-collectors were dominant in an agriculturally modified stream;Four fish species occur in the system: the endangered Taiwanese landlocked masu salmon (Oncorhynchus masou formosanus), kooye minnow (Varicorhinus barbatulus), Taiwanese tasseled-mouth loach (Crossostoma lacustre) and stream goby (Rhinogobius brunneus). Originally, this stream system was uniquely hospitable to the salmon owing to suitable cold water, a gentle gradient, moderate climate, and rich invertebrate food resources. In the last half-century, the salmon has become restricted because of overexploitation, population fragmentation by dams, and habitat deterioration caused by landslides and agricultural impacts;Multivariate analyses indicated that the minnow is a habitat generalist primarily associated with boulder cover while the loach is a specialist associated with boulder plus fast current. Both minnow and loach fed extensively upon attached algae and algal detritus, and small insect larvae; the latter ate significantly more insects than the former. Cyclical fluctuations of these food resources are chiefly determined by discharge events;There is no evidence that the salmon is detrimentally affected by any of its three ichthyofaunal associates because of their spatial and trophic segregation; however, its future could be imperiled by landslides, dams, and any expansion of row-crop agriculture. A comprehensive recovery plan for the salmon is proposed

Decoration of graphene nanoribbons by 5d5d transition-metal elements

Graphene is a famous truly two-dimensional (2D) material, possessing a cone-like energy structure near the Fermi level and treated as a gapless semiconductor. Its unique properties trigger researchers to find applications of it. The gapless feature shrinks the development of graphene nanoelectronics. Making one-dimensional (1D) strips of graphene nanoribbons (GNRs) could be one of the promising routes to modulating the electronic and optical properties of graphene. The electronic and optical properties of GNRs are highly sensitive to the edge and width. The tunability in electronic and optical properties further implies the possibilities of GNR application. However, the dangling bonds at ribbon edges remain an open question in GNR systems. Various passivation at the ribbon edge might change the essential physical properties. In this work, $5d$ transition-metal elements are considered as the guest atoms at the edges. The geometric structure, energy bands, density of states, charge distribution, and optical transitions are discussed