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Drought is common in rivers, yet how this disturbance regulates metabolic activity across network scales is largely unknown. Drought often lowers gross primary production (GPP) and ecosystem respiration (ER) in small headwaters but by contrast can enhance GPP and cause algal blooms in downstream estuaries. We estimated ecosystem metabolism across a nested network of 13 reaches from headwaters to the main stem of the Connecticut River from 2015 through 2017, which encompassed a pronounced drought. During drought, GPP and ER increased, but with greater enhancement in larger rivers. Responses of GPP and ER were partially due to warmer temperatures associated with drought, particularly in the larger rivers where temperatures during summer drought were > 10°C higher than typical summer baseflow. The larger rivers also had low canopy cover, which allowed primary producers to take advantage of lower turbidity and fewer cloudy days during drought. We conclude that GPP is enhanced by higher temperature, lower turbidity, and longer water residence times that are all a function of low discharge, but ecosystem response in temperate watersheds to these drivers depends on light availability regulated by riparian canopy cover. In larger rivers, GPP increased more than ER during drought, even leading to temporary autotrophy, an otherwise rare event in the typically light‐limited heterotrophic Connecticut River main stem. With climate change, rivers and streams may become warmer and drought frequency and severity may increase. Such changes may increase autotrophy in rivers with broad implications for carbon cycling and water quality in aquatic ecosystems.

The processes and biomass that characterize any ecosystem are fundamentally constrained by the total amount of energy that is either fixed within or delivered across its boundaries. Ultimately, ecosystems may be understood and classified by their rates of total and net productivity and by the seasonal patterns of photosynthesis and respiration. Such understanding is well developed for terrestrial and lentic ecosystems but our understanding of ecosystem phenology has lagged well behind for rivers. The proliferation of reliable and inexpensive sensors for monitoring dissolved oxygen and carbon dioxide is underpinning a revolution in our understanding of the ecosystem energetics of rivers. Here, we synthesize our current understanding of the drivers and constraints on river metabolism, and set out a research agenda aimed at characterizing, classifying and modeling the current and future metabolic regimes of flowing waters.

A critical analysis of the data for the specific heat from 15 K to 300 K of two samples of 241Am and one sample of 243Am leads to a set of “best” values. From these the thermodynamic functions are calculated, giving (Cp)298 = 25.5 ± 1 J mol-1 K-1 and S298 = 55.4 ± 2 J mol-1 K-1. The derived Debye characteristic temperature ?D is estimated as 120 ± 20 K and the electronic specific heat coefficient ? as 1 ± 1 mJ mol-1 K-2.

The thermal conductivity of a-plutonium has been measured over the range 3–100 K. For the highest purity material (~50 ppm metallic impurities) a small peak in the conductivity is seen at ~10 K, followed by a shallow minimum at 40 K. The maximum measured conductivity is 34.3 mW/K cm at 100 K. A decrease in conductivity occurs at low temperatures as a result of radioactive self-damage, which saturates with an exponential dependence. It is shown that most of the heat conduction is by phonons, electronic thermal conduction being small but rising with temperature.

The electrical resistivity and specific heat of samples of 241Am and 243Am are reported. The electrical resistivity at room temperature is reduced compared with the value for plutonium, while the power law exponent at low temperatures is increased. The electronic specific heat coefficient is lower than for the lighter actinides. These features lead to the conclusion that americium is the first of the actinides in which the 5 f electrons are essentially localized. Anomalies occur in the electrical resistivity and in the specific heat in the region of 60 K, the cause of which is unknown.

The electrical resistivity of protactinium metal has been measured between 0.90 and 300 K. The absolute value of the resistivity is between that of thorium and uranium, with ?298=19.28 µ ?-cm. A change in slope of the resistivity was observed at 103 K and remains unexplained. No superconductivity was observed down to 0.9 K. The resistivity ratio ?273/?o was 9.27, showing the sample to be reasonably pure.

The specific heat of polycrystalline a-uranium has been measured between 4.2 and 80 K. In addition to the second-order transition at 43 K, always seen in both polycrystalline and single-crystal uranium, a small effect was observed at 22 K. This had previously been seen only in single crystals. The larger, first-order change seen at 37 K in single-crystal uranium was not observed. The possible explanations for this difference are discussed.

The thermal and electrical conductivities of uranium have been measured over the temperature range 5–100 K. Both in the “as-received” condition and after annealing, the thermal conductivity results show a maximum at low temperatures followed by a shallow minimum with increasing temperature. Typical values for the annealed specimen were 65 W m-1 K-1 at 15 K and 35 W m-1 K-1 at 100 K. The temperature dependence can be explained by an electronic conductivity increasing with temperature, and a significant lattice contribution which is almost constant over the temperature range 40–100 K. A small secondary peak centered at 55 K is observed associated with the a-a0 phase transition.

The change in the resistitivity of high-purity a plutonium, due to self-irradiation damage with time of holding in liquid helium, has been measured. A small term, additional to the two terms previously reported, was found. A detailed analysis showed that a good fit was obtained using $$\begin{gathered} (\rho - \rho _0 ) = 1.920[1 - exp( - 0.65 \times 10^{ - 3} t)] - 0.400[1 - exp ( - 0.192 \times 10^{ - 2} t)] \hfill \\ - 0.230[1 - exp ( - 0.172 \times 10^{ - 3} t)]\mu \Omega m \hfill \\ \end{gathered} $$ This analysis was also applied to earlier results on lower purity a plutonium, and to a Pu-1% Np alloy.

SUPER-CONTRACTION induced in silk fibres by acid, and in wool by means of steam and chemical reagents, has been described by Farrell1, Astbury and Woods2and Speakman3respectively. I have recently obtained evidence of super-contraction in the guard hairs of raw pelts taken from fur-bearing animals, the phenomenon probably arising through oxidation of the disulphide link in keratin. As the furs had received neither heat nor chemical treatment, the condition described below apparently developed on the living animals. The fibres under consideration are distinguished by extra-normal curvature (Fig. 1a) which is generally greatest at the tip of the hair, and has been observed most frequently on the pelts of white and red foxes. The phenomenon may occur locally or be general to the whole skin, and when severe it gives a markedly frizzy appearance to the affected region.

THE authorities on cooking understand the effects of time and temperature1better than one might be led to suppose from Mr. Dufton's comments in his letter2under the above title.

UNDER the above title Mr. H. J. Woods1proposes three alternatives to the ‘weathering’ hypothesis tentatively advanced by me2to account for supernormal curvature in the apical region of certain guard hairs. Of the opposing evidence, it will suffice to point out that, in the light of a previous communication by Woods3, the fibres should, if his views are correct, easily acquire permanent set. If the phenomenon is due to extensive oxidative degeneration, this should be impossible. Straightening the fibres and steaming under various strains for periods up to one hour, then releasing and re-steaming resulted only in further contraction. Moreover, differential super-contraction does not follow strain in saturated sodium bicarbonate solution, which has a considerably higher pH than the maximum recorded for suint.

SINCE reading the interesting accounts of this phenomenon by Prof. W. Schmidt1and Prof. H. Stansfield2, I have noticed several striking instances which yield a clue to their cause. They occurred on the surfaces of clear country streams bridged by planks that touched the water, obstructions which, mechanically, resemble the mill-stream example described by Prof. Stansfield. Evidently the macroscopic agent causing the sudden change in velocity need penetrate only to a very small depth.