Diel Variation In Temperature Research Articles

Performance of Spodoptera litura (Lepidoptera: Noctuidae) in responses to different amplitudes of alternating temperatures across permissive warm temperature regimes.

Climate change involves changes in the pattern of temperature fluctuations and the frequency and magnitude of thermal extremes. It is essential to investigate how insects respond to increased temperature variations, especially for species that usually experience diel temperature variations extending to thermal performance limits. To explicitly elucidate the effects of sizes of amplitudes of temperature variations, we used daily alternating temperatures with an equivalent mean of 28 °C to investigate the impact of different fluctuation amplitudes (± 0 °C, ± 2 °C, ± 4 °C, and ± 6 °C) across permissive temperature regimes on the performance of Spodoptera litura FabriciusFabricius, a highly destructive polyphagous pest of crops and vegetables in tropical and temperate climates. Amplitudes of temperature fluctuations significantly affected developmental durations, adult life spans, pupal weights, fecundity, and fertility of S. litura. The survival rates from the egg stage to the adult eclosion did not differ significantly across different temperature treatments. The developmental durations of individual life cycles significantly increased with larger amplitudes in 3 fluctuating temperature treatments. The pupal weight was significantly lower and the adult life span was significantly shorter in the ± 6 °C treatment in all treatments. Fecundity and fertility were significantly reduced in the ± 6 °C treatment, making the continuation of generations nearly impossible. The results should provide critical information for understanding the ecology of this widespread pest under diel, seasonal, and global climate changes.

Soil CO2 efflux fluctuates in three different annual seasons in a semideciduous tropical forest in Yucatan, Mexico

Tropical forest soils store a third of the global terrestrial carbon and control carbon dioxide (CO2) terrestrial effluxes to the atmosphere produced by root and microbial respiration. Soil CO2 efflux varies in time and space and is known to be strongly influenced by soil temperature and water content. However, little is known about the influence of seasonality on soil CO2 efflux, especially in tropical dry forests. This study evaluated soil CO2 efflux, soil temperature, and soil volumetric water content in a semideciduous tropical forest of the Yucatan Peninsula under two sites (flat areas close to and far from hills), and three seasons: dry, wet, and early dry (a transition between the rainy and dry seasons) throughout a year. Additionally, six 24-h periods of soil CO2 efflux were measured within these three seasons. The mean annual soil CO2 efflux was 4±2.2 μmol CO2 m-2 s-1, like the mean soil CO2 efflux during the early dry season. In all seasons, soil CO2 efflux increased linearly with soil moisture, which explained 45% of the spatial-temporal variation of soil CO2 efflux. Soil CO2 efflux was higher close to than far from hills in some months. The daily variation of soil CO2 efflux was less important than its spatial and seasonal variation likely due to small diel variations in temperature. Transition seasons are common in many tropical dry forests, and they should be taken into consideration to have a better understanding of the annual soil CO2 efflux, especially under future climate-change scenarios.

Diel and seasonal patterns of soil CO2 efflux in a temperate tidal marsh

Tidal marshes store large amounts of carbon; however, little is known about the patterns, magnitudes, and biophysical drivers that regulate CO2 efflux from these ecosystems. Due to harsh environmental conditions (e.g., flooding), it is difficult to measure continuous soil CO2 efflux in tidal marshes. These data are necessary to inform empirical and process-based models and to better quantify carbon budgets. We performed automated (30 min) and manual (bi-monthly) soil CO2 efflux measurements, for ~20 months, at two sites in a temperate tidal marsh: tall Spartina (TS; dominated by S. cynosuroides) and short Spartina (SS; dominated by S. alterniflora). These measurements were coupled with water quality, canopy spectral reflectance, and meteorological measurements. There were no consistent diel patterns of soil CO2 efflux, suggesting a decoupling of soil CO2 efflux with diel variations in temperature and tides (i.e., water level) showing a hysteresis effect. Mean soil CO2 efflux was significantly higher at SS (2.15 ± 1.60 μmol CO2 m−2 s−1) than at TS (0.55 ± 0.80 μmol CO2 m−2 s−1), highlighting distinct biogeochemical spatial variability. At the annual scale, air temperature explained >50% of the variability in soil CO2 efflux at both sites; and water level and salinity were secondary drivers of soil CO2 efflux at SS and TS, respectively. Annual soil CO2 efflux varied from 287-876 to 153-211 g C m−2 y−1 at SS and TS, respectively, but manual measurements underestimated the annual flux by <67% at SS and <23% at TS. These results suggest that measuring and modeling diel soil CO2 efflux variability in tidal marshes may be more challenging than previously expected and highlight large discrepancies between manual and automated soil CO2 efflux measurements. New technical approaches are needed to implement long-term automated measurements of soil CO2 efflux across wetlands to properly estimate the carbon balance of these ecosystems.

Effects of constant and diel cyclic temperatures on the liver and intestinal phospholipid fatty acid composition in rainbow trout Oncorhynchus mykiss during seawater acclimation

BackgroundRainbow trout is an economically important fish in aquaculture and is a model species in environmental physiology. Despite earlier research on the seawater adaptability of rainbow trout at different temperature regimes, the influence on the liver and intestine in this species is still unknown. Two trials were conducted to investigate the effects of constant and diel cyclic temperatures on phospholipid fatty acid (PLFA) composition in the liver and intestine of rainbow trout during seawater acclimation.ResultsAt the end of growth trial 1, fish at 9 and 12.5 °C showed significantly higher ratios of unsaturated to saturated (U/S) and unsaturation index (UI) than those at 16 °C in liver and intestine phospholipids. After day 1 of seawater acclimation, the U/S, UI, and average chain length (ACL) of liver and intestinal phospholipids in fish at 16 °C significantly increased. Two weeks after seawater acclimation, the liver and intestinal PLFA composition adapted to salinity changes. In trial 2, significantly higher U/S, UI, and ACL were found in intestinal phospholipids at 13 ± 2 °C. On the first day after seawater acclimation, UI and ACL in liver phospholipids significantly increased at 13 °C, while fish at 13 ± 2 °C showed significantly decreased U/S, UI, and ACL in the intestine. At the end of growth trial 2, liver PLFA compositions were stable, whereas intestinal PLFA at 13 and 13 ± 1 °C showed significantly decreased U/S, UI, and ACL. A two-way analysis of variance and principal component analysis revealed significant effects of different constant temperatures, seawater acclimation, and their interaction on the liver and intestinal phospholipids, a significant effect of diel cyclic temperature on intestinal phospholipids, and the effects of seawater acclimation and its interaction with diel cyclic temperature on liver phospholipids.ConclusionTemperatures of 9 and 12.5 °C could elevate membrane fluidity and thickness in the liver and intestine of rainbow trout in freshwater, whereas no significant effects were found with diel temperature variations. After seawater acclimation, constant and diel cyclic temperatures significantly influenced the membrane fluidity and thickness of the liver and intestine. Compared with constant temperature, diel temperature variation (13 ± 2 °C) can enhance the adaptability of rainbow trout during seawater acclimation.

Effects of seawater acclimation at constant and diel cyclic temperatures on growth, osmoregulation and branchial phospholipid fatty acid composition in rainbow trout Oncorhynchus mykiss.

The study investigated the effects of seawater acclimation at constant and diel temperatures on the growth, osmoregulation, and branchial phospholipid fatty acid (PLFA) composition in rainbow trout (Oncorhynchus mykiss). The fish (initial weight, 62.28 ± 0.41g) were reared at a constant 13.0°C (CT) or with a diel cycle of either 13.0 ± 1.0°C (VT2) or 13.0 ± 2.0°C (VT4) for 6weeks, and subsequently subjected to seawater acclimation. Diel temperature variations (of up to 4°C) did not affect the growth rate of rainbow trout maintained in freshwater, but alleviated the impairment on the growth after seawater challenge. Under all temperature conditions, rainbow trout were well prepared to seawater acclimation. The diel cyclic temperature resulted in fish with reduced fluctuations in plasma electrolyte levels, branchial Na+-K+ ATPase activity, and plasma osmolality. In freshwater, the sum of the monounsaturated fatty acids was significantly higher in the VT4 relative to CT and VT2 treatment. Conversely, the sum of polyunsaturated fatty acids was significantly lower in the VT4 fish. After seawater transfer, the branchial PLFA profiles of the fish significantly changed, but those in CT and VT2 did not recover afterwards (the degree of unsaturation was downregulated). The PLFA composition of fish in the VT4 treatment appeared to be steadier under seawater acclimation. This study suggests that a diel cyclic temperature (13.0 ± 2.0°C) can alleviate the impairment of growth, enhance osmoregulation capability, and improve the stability of the branchial PLFA composition in rainbow trout after seawater acclimation.

Rethinking temperature effects on leaf growth, gene expression and metabolism: Diel variation matters.

Plants have evolved to grow under prominently fluctuating environmental conditions. In experiments under controlled conditions, temperature is often set to artificial, binary regimes with constant values at day and at night. This study investigated how such a diel (24 hr) temperature regime affects leaf growth, carbohydrate metabolism and gene expression, compared to a temperature regime with a field‐like gradual increase and decline throughout 24 hr. Soybean (Glycine max) was grown under two contrasting diel temperature treatments. Leaf growth was measured in high temporal resolution. Periodical measurements were performed of carbohydrate concentrations, carbon isotopes as well as the transcriptome by RNA sequencing. Leaf growth activity peaked at different times under the two treatments, which cannot be explained intuitively. Under field‐like temperature conditions, leaf growth followed temperature and peaked in the afternoon, whereas in the binary temperature regime, growth increased at night and decreased during daytime. Differential gene expression data suggest that a synchronization of cell division activity seems to be evoked in the binary temperature regime. Overall, the results show that the coordination of a wide range of metabolic processes is markedly affected by the diel variation of temperature, which emphasizes the importance of realistic environmental settings in controlled condition experiments.

Impacts of diel temperature variations on nitrogen removal and metacommunity of anammox biofilm reactors

The influence of diel temperature variations (DTVs) on nitrogen removal and bacterial communities was investigated in two parallel anammox reactors (i.e., control and DTV reactors). The control reactor was operated at a constant temperature of 30 °C, whereas the DTV reactor was operated in a temperature fluctuation mode with a cycle of 12/12 h of high/low temperatures. Nine water temperature variations for the day/night periods were set from 30/30 °C (i.e., Δ0 °C) to 38/22 °C (i.e., Δ16 °C). An increase in DTVs from Δ8 °C (34/26 °C) to Δ16 °C (38/22 °C) caused a significant decline in reactor performance and a shift in bacterial diversity. Compared to the control reactor, for instance, nitrogen removal efficiency decreased (P < 0.05) when temperature fluctuations exceeded Δ8 °C in the DTV reactor with a decreasing ΔNO3−/ΔNH4+ ratio (from 0.21 ± 0.15 to 0.16 ± 0.04). The results of 16S rRNA gene sequencing showed that the initial disturbance of temperature variations led to increased levels of bacterial diversity (i.e., alpha diversity) and decreased community levels of anammox consortia whereas they slightly recovered at the end of each DTV phase. Notably, Candidatus Jettenia was more sensitive to strong water temperature fluctuations, with the lower relative abundance at Δ14 °C (17.11 ± 5.01%) and Δ16 °C (17.83 ± 7.22%) than at Δ4 °C (39.82 ± 0.01%). In contrast, Ca. Brocadia and Ca. Kuenenia had higher relative abundance at Δ14 °C (i.e., 0.24 ± 0.07% and 0.09 ± 0.02%, respectively) and Δ16 °C (i.e., 0.28 ± 0.05% and 0.12 ± 0.03%, respectively) compared to that at Δ4 °C (i.e., 0.15 ± 0.04% and 0.04 ± 0.01%, respectively). Nitrifiers (i.e., unidentified_Nitrospiraceae and Nitrosomonas) and denitrifiers (i.e., Denitratisoma) were also capable of tolerating high temperature perturbations. Overall this study furthers our knowledge of responses of the microbial ecology of anammox bacteria to DTVs in anammox processes, which could aid us in optimizing anammox-related wastewater treatment systems and in understanding the nitrogen cycles of natural ecosystems.

Diel Stream Temperature Effects on Nitrogen Cycling in Hyporheic Zones

AbstractStream temperature often varies diurnally and seasonally, and these variations propagate into hyporheic zones (HZs), forming dynamic and heterogeneous thermal patterns. The complex thermal distribution creates potential biogeochemical hotspots and hot moments. Yet, how diel temperature variations affect HZ nitrogen cycling is unknown. We thus conducted a series of multiphysics numerical simulations of nonisothermal fluid flow and multicomponent reactive solute transport to investigate this problem. We imposed a sinusoidally varying stream temperature representing diel warming and cooling and studied the effects of different temperature means and amplitudes on HZ nitrate removal efficiency inside a streambed with a dune. The results showed that the time‐variable nitrification, denitrification, and nitrate removal efficiency responded differently to the diel stream temperature signal. The temporal variation of spatially averaged nitrification rate tracks the stream temperature signal, whereas the spatially averaged denitrification variation pattern has a more complex connection to temperature. We observed a persistent hotspot where significant denitrification rates are present over the 24‐hr period. We further evaluated and estimated the bulk nitrate removal efficiency calculated by time integration of spatially averaged reaction rates over a day. For denitrification‐dominant systems, the bulk nitrate removal efficiency for cases with dynamic stream temperature was effectively the same as those with an equivalent constant mean temperature. Therefore, the bulk removal efficiency of a thermally dynamic diel system may be represented by an equivalent isothermal system given stable flow conditions. However, since large instantaneous variations in various rates were observed, the results imply that randomly timed field measurements are unlikely to be representative. This has to be considered for both past and future synoptic observational studies.

Mathematical Models for Predicting Development of Orius majusculus (Heteroptera: Anthocoridae) and Its Applicability to Biological Control.

Complete development of Orius majusculus Reuter (Heteroptera: Anthocoridae) at nine constant temperatures, between 12 and 34°C, was evaluated under laboratory conditions. The maximum developmental period of 90.75 d occurred at 12°C, whereas the minimum of 11.34 d occurred at 30°C. From 30 to 34°C, the developmental period increased to 13.50 d. Between 21 and 33°C the survival rate was more than 80%. The optimal temperature when considering developmental rate and survival was between 24 and 30°C. At constant temperatures, four models were developed, one of which was linear and three nonlinear (Logan type III, Lactin, and Brière). All models were validated under field conditions and diel temperature variations. The values of the adjusted determination coefficients of the linear (>0.77) and nonlinear models (>0.93) were high. The thermal requirement for complete development, from egg to adult, was 284.5 degree-days (DD). In all nonlinear models, elevated levels of accuracy (≥90.31%) in field validation were also obtained, especially in the Brière model. With the results obtained herein, the optimization of O. majusculus mass rearing, its ideal use, and field management in biological control strategies can be improved.

Temperature-dependent development of Macrolophus pygmaeus and its applicability to biological control

A linear model and three nonlinear models (Logan type III, Lactin and Briere) were applied to Macrolophus pygmaeus (Rambur) (Hemiptera: Miridae) at constant temperatures and validated under diel temperature variation, and field conditions. Complete development from egg to adult, with >80% survivorship, occurred at nine constant temperatures between 15 and 32 °C. Total developmental time decreased from a maximum at 15 °C (68.48 days) to a minimum at 30 °C (18.69 days) and then increased at 32 °C (23.44 days). Optimal survival and the highest developmental rate occurred within the range of 27–30 °C. The adjusted determination coefficients were high for linear and nonlinear models (>0.89). Field validation showed high levels of accuracy in all models (≥93.4%). These valid mathematical models contribute to optimal application, field management, and mass rearing of M. pygmaeus for its applicability to biological control.

Calculating water saturation from passive temperature measurements in near-surface sediments: Development of a semi-analytical model

A novel semi-analytical model for the calculation of water saturation levels in the near subsurface using passive temperature measurements is derived. The amplitude and phase of dominant natural diel temperature variations are exploited, although the solution is general so that a cyclical temperature signal of any period could be used. The model is based on the first-principles advection-conduction-dispersion equation, which is fully general for porous media. It requires a single independent soil moisture estimate, but directly considers the spatially variable saturation dependency of thermal conductivity which has been avoided in previous studies. An established empirical model for the thermal conductivity of variably saturated porous media is incorporated and two solutions for saturation are derived. Using data from numerical models, a spatially sequential implementation of one of these solutions is shown to predict the vertical saturation profile to within 2% for a hydraulically stable case and to within the saturation range observed over a single day for percolation rates up to 10 cm/day. The developed model and methodology can aid in the analysis of archived temperature data from the vadose zone and will serve as a powerful tool in future heat-tracing experiments in variably saturated conditions.

Insects in fluctuating thermal environments.

All climate change scenarios predict an increase in both global temperature means and the magnitude of seasonal and diel temperature variation. The nonlinear relationship between temperature and biological processes means that fluctuating temperatures lead to physiological, life history, and ecological consequences for ectothermic insects that diverge from those predicted from constant temperatures. Fluctuating temperatures that remain within permissive temperature ranges generally improve performance. By contrast, those which extend to stressful temperatures may have either positive impacts, allowing repair of damage accrued during exposure to thermal extremes, or negative impacts from cumulative damage during successive exposures. We discuss the mechanisms underlying these differing effects. Fluctuating temperatures could be used to enhance or weaken insects in applied rearing programs, and any prediction of insect performance in the field-including models of climate change or population performance-must account for the effect of fluctuating temperatures.

THE SOLAR‐TO‐STREAM POWER RATIO: A DIMENSIONLESS NUMBER EXPLAINING DIEL FLUCTUATIONS OF TEMPERATURE IN MESOSCALE RIVERS

ABSTRACTThe diel variation of temperature in mesoscale river reaches (catchment area &gt; 1000 km2) is analysed using concurrent measurements of water temperature and of those meteorological (incident short‐wave radiation, air temperature, relative humidity and wind speed variables) and hydraulic variables (streamflow, top width, channel slope and flow depth) controlling the thermal regime. Measurements were taken along two river reaches located in central Chile, on the Itata (11 290 km2, Strahler's order 6, reach length 30 km, Qbankfull = 400 m3 s−1) and Vergara (4340 km2, Strahler's order 5, reach length 20 km, Qbankfull = 85 m3 s−1) rivers. The measuring frequency was 15 min. The relevant energy fluxes at the air–water interface, that is, atmospheric long‐wave radiation, net short‐wave radiation, radiation emitted by the water body, evaporation (latent heat) and conduction heat are computed and analysed for four scenarios of 12 days duration each, representing typical conditions for the austral winter, spring, summer and autumn. We find large differences in the diel river temperature range between the two sites and across seasons (and thus, flows and meteorological conditions), as reported in previous studies, but no clear relationship with the controlling variables is overtly observed. Following a dimensional analysis, we obtain a dimensionless parameter corresponding to the ratio of solar‐to‐stream power, which adequately explains the diel variation of water temperature in mesoscale rivers. A number of our own measurements as well as literature data are used for preliminary testing of the proposed parameter. This easy‐to‐compute number is shown to predict quite well all of the cases, constituting a simple and useful criterion to estimate a priori the magnitude of temperature diel variations in a river reach, given prevailing meteorological (daily maximum solar radiation) and hydrologic–hydraulic (streamflow, mean top width) conditions. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Behavioral ecology of Heteragrion consors Hagen (Odonata, Megapodagrionidae): a shade-seek Atlantic forest damselfly

Behavioral ecology of Heteragrion consors Hagen (Odonata: Megapodagrionidae): a shade-seek Atlantic forest damselfly. The intensity of the inter and intra-sexual selection can affect male behavioral traits as territorial fidelity and aggressiveness allowing the existence of different strategies. However, its differential success could be affected by environmental - as the diel variation in temperature - and physiological constrains - as the variation in thermoregulatory abilities. In this context, we present a behavioral analysis of Heteragrion consors (Zygoptera, Megapodagrionidae) trying to characterize its mating system, diel activity pattern, temporal budget, territoriality and reproductive biology. These data were obtained based on field observations using the focal individual method and mark-recapture techniques in 120 m of a shaded Atlantic Forest stream in Brazil. The males of this species were territorial, varying in its local fidelity, while the females appear sporadically. Males were perched in the majority of the time, but were also observed in cleaning movements, longitudinal abdominal flexion, wing flexion and sperm transfer during perch. The males presented a perched thermoregulatory behavior related to an exothermic regulation. Foraging and agonistic interactions were rare, but dominate the other behavioral activities. Abdominal movements associated to long lasting copula pointed to the existence of sperm competition in this species. Males performed contact post-copulatory guarding of the females. These observations pointed to a non-resource mating system for this species.

The influence of riparian shade on lowland stream water temperatures in southern England and their viability for brown trout

AbstractSuitable thermal conditions in streams are necessary for fish and predictions of future climate changes infer that water temperatures may regularly exceed tolerable ranges for key species. Riparian woodland is considered as a possible management tool for moderating future thermal conditions in streams for the benefit of fish communities. The spatial and temporal variation of stream water temperature was therefore investigated over 3 years in lowland rivers in the New Forest (southern England) to establish the suitability of the thermal regime for fish in relation to riparian shade in a warm water system. Riparian shade was found to have a marked influence on stream water temperature, particularly in terms of moderating diel temperature variation and limiting the number of days per year that maximum temperatures exceeded published thermal thresholds for brown trout. Expansion of riparian woodland offers potential to prevent water temperature exceeding incipient lethal limits for brown trout and other fish species. A relatively low level of shade (20–40%) was found to be effective in keeping summer temperatures below the incipient lethal limit for brown trout, but ca. 80% shade generally prevented water temperatures exceeding the range reported for optimum growth of brown trout. Higher levels of shade are likely to be necessary to protect temperature‐sensitive species from climate warming. © Crown copyright 2010.

Diel time-courses of leaf growth in monocot and dicot species: endogenous rhythms and temperature effects.

Diel (24 h) leaf growth patterns were differently affected by temperature variations and the circadian clock in several plant species. In the monocotyledon Zea mays, leaf elongation rate closely followed changes in temperature. In the dicotyledons Nicotiana tabacum, Ricinus communis, and Flaveria bidentis, the effect of temperature regimes was less obvious and leaf growth exhibited a clear circadian oscillation.These differences were related neither to primary metabolism nor to altered carbohydrate availability for growth. The effect of endogenous rhythms on leaf growth was analysed under continuous light in Arabidopsis thaliana, Ricinus communis, Zea mays, and Oryza sativa. No rythmic growth was observed under continuous light in the two monocotyledons, while growth rhythmicity persisted in the two dicotyledons. Based on model simulations it is concluded that diel leaf growth patterns in mono- and dicotyledons result from the additive effects of both circadian-clock-controlled processes and responses to environmental changes such as temperature and evaporative demand. Apparently very distinct diel leaf growth behaviour of monocotyledons and dicotyledons can thus be explained by the different degrees to which diel temperature variations affect leaf growth in the two groups of species which, in turn, depends on the extent of the leaf growth control by internal clocks.

Direct and indirect coupling of primary production and diel nitrate dynamics in a subtropical spring‐fed river

We used high‐frequency in situ measurements of nitrate (NO3−) and dissolved oxygen (DO) from the springfed Ichetucknee River, Florida, to derive multiple independent estimates of assimilatory nitrogen (N) demand, and to evaluate the short‐term dependence of heterotrophic assimilation and dissimilation (e.g., denitrification) on gross primary productivity (GPP). Autotrophic N assimilation estimates derived from diel DO variability and GPP stoichiometry agreed closely with estimates based on integration of diel variation in NO3− concentration, although the correspondence of these metrics depended on the method used to estimate NO3− baselines. In addition, day‐to‐day changes in nocturnal NO3− concentration maxima were strongly negatively correlated with day‐to‐day changes in GPP. Diel temperature variation in the Ichetucknee River indicated that this pattern could not be explained by hydrologic dispersion, while relationships between N assimilation and O2 production at hourly intervals indicated minimal physiological lags. The estimated magnitude of heterotrophic assimilation was small, indicating that the relationship between changes in GPP and changes in nocturnal NO3− maxima reflects sensitivity of denitrification to variation in exudation of labile organic matter by primary producers. We estimate that ~ 35% of denitrification may be fueled by the previous day’s photosynthesis; this result is consistent with the broader hypothesis that the magnitude of autochthonous production in aquatic systems influences the fate of N via both direct and indirect mechanisms.

Thermal properties of artificial refuges and their implications for retreat-site selection in lizards

Artificial retreats or refuges (ARs) provide a useful method for sampling lizards and a possible means of restoring habitat to aid population persistence. Previous research suggests that preferences for ARs may vary among species and between different designs. To test these ideas further, we examined the influence of thermal and structural characteristics on use of three types of ARs by the nocturnal common gecko (Hoplodactylus maculatus) and diurnal McCann's skink (Oligosoma maccanni), two lizards endemic to New Zealand. The field study confirmed that the three ARs (triple-layered Onduline, triple-layered iron, solid concrete) differed in retreat-site temperatures provided during each of three seasons (winter, spring and summer). In their top spaces, Onduline ARs were the warmest by day, coolest by night, and thus displayed the largest diel variations in temperature. In the laboratory, common geckos showed a significant preference for Onduline whether ARs were exposed to a radiant overhead heat source or not, whereas skinks did not display any preference among the three types of ARs regardless of heating. The three types of ARs provided field temperatures within the thermal preference range of both species (data obtained from the literature) but only for the top spaces of the ARs and only during summer. Onduline was the only AR to consistently provide the temperatures preferred by pregnant females. Although this study suggests that structural properties alone may be sufficient to explain the preference of geckos for triple-layered Onduline stacks, it does not eliminate the possibility that attractive thermal properties also contribute. Long-term studies are needed to test the effects of artificial refuge supplementation on reptiles, and on their predators and competitors.

Thermal regime of dune‐covered sediments under gaining and losing water bodies

We investigate the effects of current–bed form induced flow and heat transport through permeable‐bottom sediments overlain by a marine or terrestrial water column that is gaining or losing deep groundwater. Heat transport is forced by the diel variation of temperature in the water column. The investigation utilizes sequentially coupled simulations of turbulent flow in the water column, and Darcy flow and heat transport in the sediments. The simulations address the question when, where, and by how much are diel water column temperature variations transmitted into sediments subjected to ambient‐groundwater discharge? This is crucial information for detecting, observing, and predicting temperature‐sensitive biogeochemical and ecological processes in the bottom sediments. When the groundwater gain or loss is small, it has no appreciable effect on temperatures in the sediments, which are controlled by heat conduction and current–bed form induced heat advection. As losing discharge increases, the temperature signal from the water column penetrates deeper into the sediments, with the largest temperature variations found under a downwelling zone along the stoss side of the bed form and damped temperature variations found near a narrow upwelling zone below the crest. Similar patterns are observed under gaining conditions, but with temperature variations penetrating to shallower depths; the interfacial exchange zone is diminished by upward movement of deep groundwater. Large gains or losses of deep groundwater prevent the formation of an interfacial exchange zone making heat transport almost vertically one‐dimensional. The sensitivity of the sediment‐thermal regime to hydrodynamic conditions increases with increasing water column current (Reynolds number) and with sediment permeability.

Patterns of vertical stratification in a subtropical constructed wetland in south Florida (USA)

The South Florida Water Management District (District) has built large treatment wetlands, known as Stormwater Treatment Areas (STAs), to reduce excess phosphorus loading to the Everglades. The District conducted research in a prototype treatment wetland, the Everglades Nutrient Removal Project (ENRP), to study biogeochemical processes that are important to treatment performance. Vertical profile measurements of water temperature, dissolved oxygen, pH, conductivity and transmission of photosynthetically active radiation (PAR) were made in open-water areas and sites dominated by emergent, floating or submersed vegetation over an annual cycle. Relative thermal resistance to mixing was used to infer the strength of thermal stratification. Long-term diel variation in temperature at the surface and bottom of an open-water and a vegetated site also was measured. Open-water sites were nearly isothermal and had minimal thermal stratification, while vegetated sites were all thermally stratified to some degree. The highest surface water temperatures (>35 °C) occurred in submersed vegetation where much of the light absorbed by leaves and stems was reflected as heat. Oxygen was uniformly low (<4 mg L −1) in emergent and floating vegetation and attributed to shading, high biological oxygen demand and limited reaeration at the surface. Depressed oxygen levels at open-water areas were attributed to high sediment oxygen demand. The highest oxygen concentrations occurred in submersed vegetation beds. Water column pH was unstratified and near circumneutral in the open water and at emergent and floating vegetation sites, while pH was markedly stratified in submersed vegetation, where surface values at times exceeded 9.0. High surface oxygen and pH levels in submersed vegetation were consistent with intense photosynthesis. Conductivity increased at the bottom of emergent and submersed vegetation but not at open-water or floating vegetation sites. PAR transmission was strongly reduced at all sites due to shading and/or absorption by dissolved organic carbon. Light extinction coefficients were markedly higher at vegetated sites compared to the open water. Peak irradiance shifted to longer wavelengths (538–643 nm) and both short (<400 nm) and long (>700 nm) wavelengths were largely attenuated at 60 cm relative to the surface. Long-term monitoring at a vegetated site revealed periods of inverse thermal stratification and dampened diel variation in temperatures at the bottom compared to open water.