Warm Sunny Days Research Articles

Comparison of Flight Periods of Solitary and Primitively Eusocial Bees in Urban Environments and Nature Conservation Areas: a Preliminary Report

Solitary and primitively eusocial bees, an important group of pollinators, have declined in the past few decades. In view of the recent focus on safeguarding pollinating insects, it is vital to understand the basic ecology of species for their conservation, for example their phenologies. We observed the flight periods of solitary and primitively eusocial bees in both the urban core of a large British town and nearby nature conservation areas. The bee surveys were conducted with standardised methods, on warm sunny days from the first appearance of bees in March 2012 and continued until October 2012. This study confirmed that a high number of species are active in the spring season. The emergence dates of species in urban areas and nature sites varied; about 26 of the 35 species were recorded at least one week earlier in urban areas; in contrast, only four species were seen earlier in nature conservation sites. When comparing this with the expected flight periods recorded (largely in nature sites) in the literature, many species were recorded at their expected time. However, a few individuals were recorded after their usual flight activity time, suggesting that the populations were possibly affected by the microclimate in urban areas. More urban phenological data are needed to understand the phenological trends in bees in urban habitats.

Primary and Secondary Organic Aerosol Formation from Asphalt Pavements.

Asphalt is ubiquitous across cities and a source of organic compounds spanning a wide range of volatility and may be an overlooked source of urban organic aerosols. The emission rate and composition depend strongly on temperature, but emissions have been observed at both application temperatures and surface temperatures during warm sunny days. Here we report primary organic aerosol (POA) emissions and secondary organic aerosol (SOA) production from asphalt. We reheated real-world asphalt samples to application-relevant temperatures (∼130 °C) and typical summertime road-surface temperatures (∼55 °C) and then flushed the emitted vapors into an environmental oxidation chamber containing ammonium sulfate seed particles. SOA was then formed following the photo-oxidation of emissions under high-NOx conditions typical of urban atmospheres. We find that POA only forms at application temperature as it does not require further oxidation, whereas SOA forms under both conditions; with the resulting POA and SOA both being semi-volatile. While total OA formation rates were substantially greater under the limited time spent under application conditions, SOA formation from passive asphalt heating presents a potential long-term source, as heating continues for the lifetime of the road surface. This suggests that persistent asphalt solar heating is likely a considerable and continued source of summertime SOA in urban environments.

Snížení základního odtoku kvůli evapotranspiraci povrchové a podzemní vody z mokřadu v povodí Liběchovky: porovnání měření a výpočtu Oudinovou metodou

This study is focused on the base flow decrease due to surface water and groundwater evapotranspiration (ET) in wetlands of the Liběchovka catchment. Evapotranspiration in wetlands can significantly affect stream discharge, and its influence will probably still increase in the future due to the global rise of temperatures caused by climate change. The study site is located in the upper part of Liběchovka catchment (Fig. 1). This wetland hosts a small stream supplied by rather steady groundwater inflow, representing the favourable site for detection of the effect of ET. V notch weir and two piezometers were used to monitor stream discharge and wetland water table in 30 minute periods (Fig. 2). Diurnal periodical oscillations of water flow and water table caused by ET were observed (Fig. 3). They occurred in the summer part of the year, especially on sunny days without rain. The amplitude of water table level oscillation was increasing with increasing temperature (Fig. 4). Calculation showed that evapotranspiration reduced the water flow, on average, by 15 % on the warm sunny days. The maximum daily reduction was up to 32 %. Direct measurements were compared with the potential ET calculated using the Oudin’s method (Oudin 2005). The ET from the measurement was 45 % of the potential ET calculated by Oudin’s method. In the next step, the Oudin’s method was used to calculate the potential ET of all wetlands in Liběchovka catchment upstream from the Želízy village, where gauging station of ČHMÚ is situated. The original discharge not reduced by the wetland ET was defined as the sum of the wetland potential ET and the mean annual measured discharge. Due to the ET from wetlands (years 2015–2020), the discharge was reduced on average by 13 %. If only the summer months of July and August were considered, it was reduced, on average, by 26 % and by 39 % in the driest day recorded in this period. To estimate the role of groundwater abstraction on the Liběchovka stream during the period of 2015–2020, the sum of measured stream discharge, groundwater abstraction and wetland ET was calculated. From this sum, 71.5 % represented the directly measured water flow, 18.2 % was the groundwater abstraction, and 10.3 % was the wetland ET (Fig. 8).

Honeybee clusters seethe to keep cool as air temperatures rise

Packing up to relocate is always daunting, but imagine uprooting an entire community and setting forth with no final destination in mind. This is the prospect faced by swarming honeybees as they depart in search of pastures new. Having located a nearby tree, the swarm settles while scouts venture off in search of a new home, yet the cluster continually seethes and churns to maintain a stable temperature within. However, no one had detailed the precise changes that a swarm makes as air temperatures rise and fall. To learn more, Jacob Peters and L. Mahadevan from Harvard University, USA, with Orit Peleg from the University of Colorado, USA, secured a box containing a queen bee to an inverted weighing scale and encouraged the colony to swarm around her, to find out how they adapted as the temperature rose and fell.However, the team quickly found that they were best conducting their experiments at night. ‘On warm sunny days the bees would fly off as if to a new nest site’, recalls Peters. So he and Peleg warmed the clusters from 15°C to 30°C at different rates before keeping the insects warm for 5 h. During that time, the duo took 360 deg snapshots of the clusters every 4 min by swinging a camera around the cluster, taking a picture every 9 deg, to build a 3D profile. Then the duo cooled the air around each cluster at the same rate, to find out how the bees reacted. In addition, James MacArthur from Harvard University designed a bespoke temperature sensor for the bees to cluster around that recorded the temperatures experienced within the colony as it churned in response to the changing air temperatures.Reconstructing time-lapse movies of the clusters, the team could see them become longer and broader as the temperature rose, almost doubling their volume at the highest temperature. ‘A quick look at the time lapse showed dramatic and predictable changes’, says Peters. However, even after 5 h at 30°C, the swarm never achieved a stable structure, continuing to ripple and pulse until Peters and Peleg turned the thermostat down. Yet, the time-lapse movies of the cooling colonies appearing to deflate weren't simple rewinds of the warming expansions. ‘The cluster shrinks quickly in response to cooling but expands sluggishly to its original size as it warms back up’, says Peters.The team also noticed that at one point during the heating process the cluster stopped lengthening and began shortening instead, even though the base continued to broaden, probably because there is a stage when the honeybees within are at full stretch and can no longer cling on to each other if the cluster continues growing longer to avoid overheating. ‘This [manoeuvre] allows them to increase their surface area without a dramatic decrease in density’, says Peters. And, when the temperature around the colony fell, the colony shortened more rapidly than it narrowed, probably because it is easier for bees to climb up and down chains of their sisters than it is for the insects to move inward carrying their colony mates suspended below. The colonies’ pulsating manoeuvres also successfully maintained relatively warm temperatures within (30–36°C), while remaining cooler at the periphery.So, honeybees are able to regulate the temperature within a cluster by spreading apart as air temperatures rise, but they can only go so far before the swarm is in danger of disintegrating. Peters also warns that if environmental temperatures continue to rise, the forces within expanding clusters may be too great for resting swarms to withstand shattering as they attempt to avoid overheating.

A Bayesian network approach to modelling rip-current drownings and shore-break wave injuries

Abstract. A Bayesian network (BN) approach is used to model and predict shore-break-related injuries and rip-current drowning incidents based on detailed environmental conditions (wave, tide, weather, beach morphology) on the high-energy Gironde coast, southwest France. Six years (2011–2017) of boreal summer (15 June–15 September) surf zone injuries (SZIs) were analysed, comprising 442 (fatal and non-fatal) drownings caused by rip currents and 715 injuries caused by shore-break waves. Environmental conditions at the time of the SZIs were used to train two separate Bayesian networks (BNs), one for rip-current drownings and the other one for shore-break wave injuries. Each BN included two so-called “hidden” exposure and hazard variables, which are not observed yet interact with several of the observed (environmental) variables, which in turn limit the number of BN edges. Both BNs were tested for varying complexity using K-fold cross-validation based on multiple performance metrics. Results show a poor to fair predictive ability of the models according to the different metrics. Shore-break-related injuries appear more predictable than rip-current drowning incidents using the selected predictors within a BN, as the shore-break BN systematically performed better than the rip-current BN. Sensitivity and scenario analyses were performed to address the influence of environmental data variables and their interactions on exposure, hazard and resulting life risk. Most of our findings are in line with earlier SZI and physical hazard-based work; that is, more SZIs are observed for warm sunny days with light winds; long-period waves, with specifically more shore-break-related injuries at high tide and for steep beach profiles; and more rip-current drownings near low tide with near-shore-normal wave incidence and strongly alongshore non-uniform surf zone morphology. The BNs also provided fresh insight, showing that rip-current drowning risk is approximately equally distributed between exposure (variance reduction Vr=14.4 %) and hazard (Vr=17.4 %), while exposure of water user to shore-break waves is much more important (Vr=23.5 %) than the hazard (Vr=10.9 %). Large surf is found to decrease beachgoer exposure to shore-break hazard, while this is not observed for rip currents. Rapid change in tide elevation during days with large tidal range was also found to result in more drowning incidents. We advocate that such BNs, providing a better understanding of hazard, exposure and life risk, can be developed to improve public safety awareness campaigns, in parallel with the development of more skilful risk predictors to anticipate high-life-risk days.

Exogenous Calcium Alleviates Nocturnal Chilling-Induced Feedback Inhibition of Photosynthesis by Improving Sink Demand in Peanut (Arachis hypogaea).

Arachis hypogaea (peanut) is a globally important oilseed crop with high nutritional value. However, upon exposure to overnight chilling stress, it shows poor growth and seedling necrosis in many cultivation areas worldwide. Calcium (Ca2+) enhances chilling resistance in various plant species. We undertook a pot experiment to investigate the effects of exogenous Ca2+ and a calmodulin (CaM) inhibitor on growth and photosynthetic characteristics of peanut exposed to low night temperature (LNT) stress following warm sunny days. The LNT stress reduced growth, leaf extension, biomass accumulation, gas exchange rates, and photosynthetic electron transport rates. Following LNT stress, we observed larger starch grains and a concomitant increase in nonstructural carbohydrates and hydrogen peroxide (H2O2) concentrations. The LNT stress further induced photoinhibition and caused structural damage to the chloroplast grana. Exogenous Ca2+ enhanced plant growth following LNT stress, possibly by allowing continued export of carbohydrates from leaves. Foliar Ca2+ likely alleviated the nocturnal chilling-dependent feedback limitation on photosynthesis in the daytime by increasing sink demand. The foliar Ca2+ pretreatment protected the photosystems from photoinhibition by facilitating cyclic electron flow (CEF) and decreasing the proton gradient (ΔpH) across thylakoid membranes during LNT stress. Foliar application of a CaM inhibitor increased the negative impact of LNT stress on photosynthetic processes, confirming that Ca2+–CaM played an important role in alleviating photosynthetic inhibition due to the overnight chilling-dependent feedback.

Appropriate Time to Measure Leaf and Stem Water Potential in North-South Oriented, Vertically Shoot-Positioned Vineyards

The diurnal changes in vine water status and the appropriate time of day to measure leaf water potential (LWP) and stem water potential (SWP) were examined in Willamette Valley vineyards with north-south (N-S) oriented rows employing a single curtain, vertically shoot-positioned (VSP) canopy. Measurements of LWP and SWP were performed on Chardonnay and Pinot noir grapevines on seven cloudless days between bloom and harvest over two years. On warm days, LWP reached the daily minimum value by midday (1300 hr) and remained there for a longer duration when vines experienced moderate water stress (LWP -1.20 MPa). However, on cool days, LWP reached the daily minimum later in the day (1400 hr to 1500 hr) in both stressed and unstressed vines. SWP reached the daily minimum level late in the day (1400 hr to 1600 hr) under all conditions and even increased between late morning and midday on two occasions. Thus, measuring SWP at midday consistently underestimates the greatest level of water stress experienced by vines in N-S oriented, VSP canopies. Results of this study show that LWP can be determined over a four-hour period starting at midday on warm sunny days when vines experience a moderate level of water stress: conditions when it is most critical to assess vine water status to schedule irrigation. SWP should be measured in the two-hour period between 1500 hr and 1700 hr under all conditions tested here in N-S oriented, VSP canopies.

Wave and Tide Controls on Rip Current Activity and Drowning Incidents in Southwest France

Castelle, B.; Scott, T.; Brander, R.W.; McCarroll, R.J.; Tellier, E.; de Korte, E.; Tackuy, L.; Robinet, A.; Simonnet, B. and Salmi, L.-R., 2020. Wave and tide controls on rip current activity and drowning incidents in Southwest France. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 769–774. Coconut Creek (Florida), ISSN 0749-0208.The meso-macrotidal sandy surf beaches of southwest France are a popular destination visited by millions of tourists each summer, who potentially expose themselves to surf zone hazards and particularly to rip currents flowing through the inner-bar rip channels. 281 non-fatal and fatal drowning incidents, most of them caused by rip currents, recorded by lifeguards during the summer 2007, 2009 and 2015 were combined with measured and hindcast wave and tide data. Results show that drownings occur disproportionally near neap low tide, under shore-normal incident waves and average to above-average height and period, with drowning incidents tending to occur in clusters with particular days of mass incidents. An XBeach model is implemented on measured rip-channelled bathymetries to address the influence of offshore wave conditions and tidal elevation on rip flow dynamics and resulting hazard. Simulations show that rip flow increases with increasing wave height, increasing wave period and increasingly shore-normal incidence, which is consistent with the increased number of drowning incidents for such conditions. Although more incidents also tend to occur on warm sunny days with light winds, presumably driving more exposure to the rip current hazard, this highlights the dominance of the physical hazard on the life risk along this stretch of coast.

Environmental controls on surf zone injuries on high-energy beaches

Abstract. The two primary causes of surf zone injuries (SZIs) worldwide, including fatal drowning and severe spinal injuries, are rip currents (rips) and shore-break waves. SZIs also result from surfing and bodyboarding activity. In this paper we address the primary environmental controls on SZIs along the high-energy meso–macro-tidal surf beach coast of southwestern France. A total of 2523 SZIs recorded by lifeguards over 186 sample days during the summers of 2007, 2009 and 2015 were combined with measured and/or hindcast weather, wave, tide, and beach morphology data. All SZIs occurred disproportionately on warm sunny days with low wind, likely because of increased beachgoer numbers and hazard exposure. Relationships were strongest for shore-break- and rip-related SZIs and weakest for surfing-related SZIs, the latter being also unaffected by tidal stage or range. Therefore, the analysis focused on bathers. More shore-break-related SZIs occur during shore-normal incident waves with average to below-average wave height (significant wave height, Hs = 0.75–1.5 m) and around higher water levels and large tide ranges when waves break on the steepest section of the beach. In contrast, more rip-related drownings occur near neap low tide, coinciding with maximised channel rip flow activity, under shore-normal incident waves with Hs >1.25 m and mean wave periods longer than 5 s. Additional drowning incidents occurred at spring high tide, presumably due to small-scale swash rips. The composite wave and tide parameters proposed by Scott et al. (2014) are key controlling factors determining SZI occurrence, although the risk ranges are not necessarily transferable to all sites. Summer beach and surf zone morphology is interannually highly variable, which is critical to SZI patterns. The upper beach slope can vary from 0.06 to 0.18 between summers, resulting in low and high shore-break-related SZIs, respectively. Summers with coast-wide highly (weakly) developed rip channels also result in widespread (scarce) rip-related drowning incidents. With life risk defined in terms of the number of people exposed to life threatening hazards at a beach, the ability of morphodynamic models to simulate primary beach morphology characteristics a few weeks or months in advance is therefore of paramount importance for predicting the primary surf zone life risks along this coast.

Pest categorisation of Popilliajaponica.

The Panel on Plant Health performed a pest categorisation of Popillia japonica (Coleoptera: Scarabaeidae) for the EU. P. japonica is a distinguishable species listed in Annex IAII of Council Directive 2000/29/EC. It is native to Japan but established in the USA in the early 20th century. It spreads from New Jersey to most US states east of the Mississippi, some to the west and north into Canada. P. japonica feeds on over 700 plant species. Adults attack foliage and fruit surfaces. They can cause serious injury to tree fruits and soft fruit, vegetable crops, ornamental herbaceous plants, shrubs, vines and trees. Larvae are root feeders regarded as serious pests of lawns and turf, vegetables and nursery stock. Adults emerge during the summer and can fly short distances on warm sunny days. The life cycle is usually completed in one year. In cooler regions, development takes two years. P. japonica occurs in the EU in the Azores (Portugal), Lombardy and Piedmont (Italy) where it is under official control. Adults are suspected of being able to spread on aircraft as hitchhikers, i.e. without host plants. Soil accompanying plants for planting provides a pathway for further introductions. Hosts are widely available within the EU. Climatic conditions across central and parts of southern EU are suitable for development in one year. Across parts of northern Europe development over two years is likely. Without control, impacts could be expected on a range of plants. Phytosanitary measures are available to reduce the likelihood of introduction of P. japonica. All criteria assessed by EFSA for consideration as a potential Union quarantine pest are met. Plants for planting are not necessarily the main means of spread so P. japonica does not satisfy all criteria necessary for it to be regarded as a Union regulated non‐quarantine pest (RNQP).

Visual approach computation in feeding hoverflies.

ABSTRACTOn warm sunny days, female hoverflies are often observed feeding from a wide range of wild and cultivated flowers. In doing so, hoverflies serve a vital role as alternative pollinators, and are suggested to be the most important pollinators after bees and bumblebees. Unless the flower hoverflies are feeding from is large, they do not readily share the space with other insects, but instead opt to leave if another insect approaches. We used high-speed videography followed by 3D reconstruction of flight trajectories to quantify how female Eristalis hoverflies respond to approaching bees, wasps and two different hoverfly species. We found that, in 94% of the interactions, the occupant female left the flower when approached by another insect. We found that compared with spontaneous take-offs, the occupant hoverfly's escape response was performed at ∼3 times higher speed (spontaneous take-off at 0.2±0.05 m s−1 compared with 0.55±0.08 m s−1 when approached by another Eristalis). The hoverflies tended to take off upward and forward, while taking the incomer's approach angle into account. Intriguingly, we found that, when approached by wasps, the occupant Eristalis took off at a higher speed and when the wasp was further away. This suggests that feeding hoverflies may be able to distinguish these predators, demanding impressive visual capabilities. Our results, including quantification of the visual information available before occupant take-off, provide important insight into how freely behaving hoverflies perform escape responses from competitors and predators (e.g. wasps) in the wild.

Warm coffee, sunny days, and prosocial behavior.

This commentary discusses the research finding that warmer temperatures are associated with more prosocial outcomes. It calls for future research and theory on climate-related variables and social behavior to allow for both positive and negative emotional and behavioral responses to warmer temperatures.

The influence of increasing tree cover on mean radiant temperature across a mixed development suburb in Adelaide, Australia

The implementation of trees in urban environments can mitigate outdoor thermal stress. Growing global urban population and the risk of heatwaves, compounded by development driven urban warmth (the urban heat island), means more people are at risk of heat stress in our cities. Effective planning of urban environments must minimise heat-health risks through a variety of active and passive design measures at an affordable cost. Using the Solar and Longwave Environmental Irradiance Geometry (SOLWEIG) model and working within the bounds of current urban design, this study aimed to quantify changes in mean radiant temperature (Tmrt) from increased tree cover at five different 200×200m urban forms (including compact mid-rise development, residential and open grassy areas) within a suburb of Adelaide, Australia during summer. Following a successful validation of SOLWEIG, street trees were strategically distributed throughout each of the five urban forms and the model run over five warm sunny days (13–17 February 2011). Results showed spatially averaged daytime (7:30–20:00) Tmrt reduced by between 1.7°C and 5.1°C at each site, while under peak heating conditions (16 February, 14:00) Tmrt reduced by between 2.0°C and 7.1°C. The largest reduction in Tmrt under peak warming conditions was at the residential site, despite having the fewest number of trees added. Directly below clusters of trees, Tmrt could be reduced by between 14.1°C and 18.7°C. SOLWEIG also highlighted that more built-up sites showed higher Tmrt under peak warming conditions due to increased radiation loading from 3D urban surfaces, but over the course of the day, open sites were exposed to greater and more uniform Tmrt. This study clearly demonstrates the capacity of street trees to mitigate outdoor thermal stress and provides guidance for urban planners on strategic street tree implementation.

Natural ultraviolet-b exposure of the Texas Horned Lizard (Phrynosoma cornutum) at a North Texas Wildlife Refuge

Abstract We monitored daily patterns of natural ultraviolet-B (UVB) exposure (measured using the ultraviolet index [UVI]) of the Texas horned lizard (Phrynosoma cornutum) in North Central Texas. The animals were active on unpaved road surfaces on warm sunny days in May and June in the morning (0800–1200 h) and in late afternoon and early evening (1800–2100 h). The UVI was high during the morning and was positively correlated with hour of the day and body temperature. The UVI was lower during the late afternoon and early evening and was negatively correlated with hour of the day. Body temperatures of the animals were higher than air temperature during both periods of road activity. On warm sunny days between the two periods of high road activity, lizards remained active in shaded off-road areas and received variable amounts of UVB exposure. Two lizards that were followed most hours on warm sunny days had similar UVB exposure doses (irradiance × time) for the day but showed different patterns of UVI irradia...

Influence of weather variables on methane and carbon dioxide flux from a shallow pond

Freshwaters are important sources of the greenhouse gases methane (CH4) and carbon dioxide (CO2) to the atmosphere. Knowledge about temporal variability in these fluxes is very limited, yet critical for proper study design and evaluating flux data. Further, to understand the reasons for the variability and allow predictive modeling, the temporal variability has to be related to relevant environmental variables. Here we analyzed the effect of weather variables on CH4 and CO2 flux from a small shallow pond during a period of 4 months. Mean CH4 flux and surface water CH4 concentration were 8.0 [3.3–15.1] ± 3.1 mmol m−2 day−1 (mean [range] ± 1 SD) and 1.3 [0.3–3.5] ± 0.9 µM respectively. Mean CO2 flux was 1.1 [−9.8 to 16.0] ± 6.9 mmol m−2 day−1. Substantial diel changes in CO2 flux and surface water CH4 concentration were observed during detailed measurements over a 24 h cycle. Thus diel patterns need to be accounted for in future measurements. Significant positive correlations of CH4 emissions with temperature were found and could include both direct temperature effects as well as indirect effects (e.g. related to the growth season and macrophyte primary productivity providing organic substrates). CO2 flux on the other hand was negatively correlated to temperature and solar radiation, presumably because CO2 consumption by plants was higher relative to CO2 production by respiration during warm sunny days. Interestingly, CH4 fluxes were comparable to ponds with similar morphometry and macrophyte abundance in the tropics. We therefore hypothesize that CH4 and CO2 summer emissions from ponds could be more related to the morphometry and dominating primary producers rather than latitude per se. Data indicate that CH4 emissions, given the system characteristic frameworks, is positively affected by increased temperatures or prolonged growth seasons.

The butterfly rash of lupus: An example of aposematism?

The butterfly rash of lupus: An example of aposematism?

Assessing detectability for monitoring of rare species: a case study of the cobblestone tiger beetle (Cicindela marginipennis Dejean)

Interpreting data on distribution or population trends may be difficult unless detection probability is accounted for. We wished to determine the detectability of the rare and patchily distributed cobblestone tiger beetle (Cicindela marginipennis) along the upper Genesee River in western New York for development of a monitoring strategy. We used occupancy surveys and distance sampling to examine two types of detectability. The first type was site-level detectability: the probability of detecting a single cobblestone tiger beetle on an occupied cobble bar, calculated using program PRESENCE. The second type was individual-level detectability: the probability of detecting an individual cobblestone tiger beetle in a population on a single cobble bar, calculated using program DISTANCE. Our occupancy surveys consisted of collecting presence and absence data on cobble bars along the Genesee River; these showed a relatively narrow range of site-level detection probabilities (0.60–0.68) for cobblestone tiger beetles in 2008 and 2009. Three visits were necessary to detect cobblestone tiger beetles on 90% of occupied cobble bars. Individual cobblestone tiger beetles were detectable one-half of the time (0.50) in our surveys. It is important for ecologists to distinguish between the two kinds of detectability, as monitoring implications could differ substantially depending on which is calculated. Our monitoring recommendations include (1) continuing occupancy surveys with at least three visits to each cobble bar; (2) conducting occupancy surveys between 10:00 and 17:00 on warm sunny days in mid-July and mid-August; and (3) conducting surveys at three- to five-year intervals depending on the study objective.

Delays of supraglacial runoff from differently defined microbasin areas on the Peyto Glacier

AbstractMicrobasin runoff experiments were conducted on ice surfaces of the Peyto Glacier during the 1971 and 2008 ablation seasons, when half‐hourly measurements of net radiation, wind speed, temperature, vapour pressure, and supraglacial runoff were obtained on warm sunny days with daily mean temperatures 6·1–10·1 °C and daily total ablation amounts of 43–95 mm. Net radiation contributed almost 70% of the melt energy in 1971 and nearly 60% in 2008, with the remainder supplied by turbulent transfers of sensible and latent heat. Thus, the two experiments are similar in finding that radiation dominates surface melt energy inputs to microbasin runoff outputs. They differ with respect to area definitions and microbasin shapes: (1) a purposely delineated rhomboidal area, 30 m long × 15 m wide, covering 386 m2 in 1971; (2) a naturally delineated elongated area, approximately 600 m long × 2 m wide, covering an estimated 1200 m2 in 2008. Three 24‐hour periods beginning at 0700 h were obtained for experimental work in 1971, and 8 such periods in 2008. Supraglacial runoff was modelled by passing melt energy water equivalents through a simple storage reservoir and forcing closure with measured runoff by optimising for delay time. Optimal times of 1–2 h were found for 1971, and 7·5–11·5 h for 2008, thus indicating a major difference between the runoff responses of the two microbasins. It is possible that different basin shapes may explain the contrasting delay times, perhaps because different shapes signify different flow connections to meltwater storage in the weathering crust. If the elongated microbasin response is typical of the elemental hydrological response unit of the melting ice surface, distributed glacier runoff models should incorporate it as part of the model structure. Copyright © 2011 John Wiley & Sons, Ltd.

Water relations of climbing ivy in a temperate forest

Ivy (Hedera helix) is the most important liana in temperate European forests. We studied water relations of adult ivy in a natural, 35 m tall mixed deciduous forest in Switzerland using a construction crane to access the canopy. Predawn leaf water potential at the top of climbing ivy ranged from -0.4 to -0.6 MPa, daily minima ranged from -1.3 to -1.7 MPa. Leaf water potentials as well as relative sap flow were held surprisingly constant throughout different weather conditions, suggesting a tendency to isohydric behaviour. Maximum stomatal conductance was 200 mmol m⁻² s⁻¹. The use of a potometer experiment allowed us to measure absolute transpiration rates integrated over a whole plant of 0.23 mmol m⁻² s⁻¹. Nightly sap flow of ivy during warm, dry nights accounted for up to 20% of the seasonal maximum. Maximum sap flow rates were reached at ca. 0.5 kPa vpd. On the other hand, the host trees showed a less conservative stomatal regulation, maximum sap flow rates were reached at vpd values of ca. 1 kPa. Sap flow rates of ivy decreased by ca. 20% in spring after bud break of trees, suggesting that ivy profits strongly from warm sunny days in early spring before budbreak of the host trees and from mild winter days. This species may benefit from rising winter temperatures in Europe and thus become a stronger competitor against its host trees.

Autumn

Marking the change from warm sunny days to the cold, dark days of winter, autumn is a wonderful time of year, with so many changes happening in the natural world for children to investigate.