Diurnal Ones Research Articles

Pollen load, pollen species diversity and conspecific pollen carried by pollinators across 24-hour cycles

Plant-pollinator interactions are key for the reproduction of wild plants and for food security. However, the role nocturnal pollinators play in wild plant communities is not yet clear. Specifically, it has rarely been studied whether nocturnal pollinators are comparable to diurnal ones in the pollination services they deliver in plant communities. We tested whether nocturnal pollinators have the potential to provide high pollination services to the plants they visit by carrying high conspecific pollen loads. We studied pollen loads carried by nocturnal and diurnal pollinators captured over 24-hour cycles in co-flowering plant communities in Swiss ruderal meadows. Pollen load was less diverse at night, and the proportion of conspecific pollen carried by nocturnal pollinators was higher than that of diurnal ones. Because the majority of plant species visited at night were also visited during the day, floral resource availability could drive the observed patterns in pollen load and amount of conspecific pollen. Nevertheless, nocturnal pollinators do not only carry pollen but can remove and potentially deposit conspecific pollen to the plants they visit. Therefore, pollinators active at night might be an important pollination vector for more plant species than previously thought and should not be neglected in pollination studies.

Evolution of Avian Eye Size Is Associated with Habitat Openness, Food Type and Brain Size.

The eye is the primary sensory organ that obtains information from the ecological environments and specifically bridges the brain with the extra environment. However, the coevolutionary relationships between eye size and ecological factors, behaviours and brain size in birds remain poorly understood. Here, we investigate whether eye size evolution is associated with ecological factors (e.g., habitat openness, food type and foraging habitat), behaviours (e.g., migration and activity pattern) and brain size among 1274 avian species using phylogenetically controlled comparative analyses. Our results indicate that avian eye size is significantly associated with habitat openness, food type and brain size. Species living in dense habitats and consuming animals exhibit larger eye sizes compared to species living in open habitats and consuming plants, respectively. Large-brained birds tend to possess larger eyes. However, migration, foraging habitat and activity pattern were not found to be significantly associated with eye size in birds, except for nocturnal birds having longer axial lengths than diurnal ones. Collectively, our results suggest that avian eye size is primarily influenced by light availability, food need and cognitive ability.

RESPONSE OF RICE VARIETIES GROWN ON CALCAREOUS AND ACID MIXED SOILS AMENDED BY VERMICOMPOST UNDER VARIABLE CLIMATES

A field experiment was conducted to explore how rice (BINA Dhan 11 and BRRI Dhan 34) responds in modified soil and climatic conditions. They were planted on artificially prepared soil beds by mixing calcareous and acid soils in 1:1 and 1:3 ratios. Soil temperature (St) was elevated up to 20C over the diurnal ones. Moisture (M) was maintained at 50%, 70%, and saturated (100%) soil conditions. Vermicompost (V) was applied at the rates of 0, 10, and 15 tha-1. The number of tillers and plant height were recorded at 25 days intervals. The maximum number of 26 and 27 tillers for BINA Dhan 11 and BRRI Dhan 34 were recorded. The longest plant height was observed with the T10 (V15M100) treatment. The treatment T3 (V15M100) resulted in maximum fresh weight of shoot and shoot dry matter production for both rice varieties in 1:3 mixed soil. Both varieties performed well in 1:3 mixed soils and elevated temperature conditions, as observed for normal soils. This evidence concluded that the improvement of calcareous and acid soils through their mixing is a successful approach and confirmed by the treatments' usual responses on different rice growth parameters under these mixed soils.

ГЛЯЦИОКЛИМАТИЧЕСКИЕ ИССЛЕДОВАНИЯ ИНСТИТУТА ГЕОГРАФИИ РАН В КРАТЕРЕ ВОСТОЧНОЙ ВЕРШИНЫ ЭЛЬБРУСА В 2020 Г

During the field campaign in August 18–30, 2020 the meteorological regime and heat balance of the glacier surface were investigated in the crater of Mt Elbrus Eastern Summit (5600 m a.s.l.) together with the GPR measurements of the ice thickness and seasonal snow cover. Preliminary data analysis allowed the following features: the predominance of synoptic fluctuations over the diurnal ones; the high values of average and maximum wind speed associated with the impact of jet streams and with influence of leeward storms; extremely high temporal variability of relative humidity and its very high deficit in cloudless conditions conducive to intensive evaporation and sublimation from the snow surface. The maximum thickness of ice in the crater reaches 100 m, and the average is 34 m. A new ice core with a length of 96.01 m from the glacier surface to its bed had been obtained. The drilling speed varied from 11 to 1 m/h, decreasing with depth from 4.5 to 4.0 m/h on average. The thickness of the snow-firn mass is about 20 m, which is three times less than on the Western Plateau of Mt Elbrus. According to measurements in the borehole, temperature at the glacier bed is −0.6 °C. The calculated heat flux is 0.39 W/m2. Air sampling was carried out in the crater of the Eastern Summit of Elbrus and on the Garabashi glacier. Repeated measurements of the soil temperature in the fumarole field on the outer edge of the crater of the Elbrus Eastern Summit allow the conclusion that the temperature regime is stable.

Moonlight triggers nocturnal display in a diurnal bird

The importance of nocturnal display in diurnal birds has been neglected for a long time, owing to the difficulties in recording behaviour by night. Using loggers with an accelerometer (ACC) we studied nocturnal display in male African houbara bustards, Chlamydotis undulata, ssp. fuertaventurae. Diurnal display of male houbaras consists of a visual component, the display run, and an acoustic component, the boom. Nocturnal display runs were only recorded twice, both on full moon nights. Nocturnal booming intensity was highest on full moon nights when it reached similar levels to those during peak diurnal display at dawn. The more favourable physical conditions for sound transmission and the reduced acoustic competition with wind and other birds at night have been proposed to explain nocturnal vocalizing. Minimizing copulation disruptions, a frequent intramale competition mechanism in bustards, could be an additional advantage of nocturnal display. However, these factors do not explain why vocal activity is highest on full moon nights. We suggest that moonlight may help displaying males to detect predators, as well as to communicate visually with approaching females. Moonlight also allows males to combine booms with visual signals produced by the white neck feathers exposed during booming into more efficient multimodal signals. Moonlight would thus ultimately lead to males achieving nocturnal copulations, which indeed might be more frequent than previously thought, according to rates of nocturnal ACC-recorded precopulatory movements. Finally, nocturnal booming sequences had almost twice as many booms as diurnal ones, which suggests that nocturnal vocalizations transmit higher-quality information about signalling males than diurnal vocalizations. Nocturnal booming significantly increased the total display time of male houbara bustards; thus, future studies should investigate whether nocturnal vocal activity represents an important contribution to individual fitness in this and other nocturnally vocalizing diurnal species.

Detection of UHI bias in China climate network using Tmin and Tmax surface temperature divergence

Near-surface temperature records show that China warmed by about 0.8 °C from 1950 to 2010. However, there exists an ongoing debate about whether this warming might have been partially due to urbanization bias. In fact, homogenization approaches may be inefficient in densely populated provinces that have experienced a significant urban development since the 1940s. This paper aims to complement previous research on the topic by showing that an alternative approach based on the analysis of the divergence between the minimum (Tmin) and maximum (Tmax) near-surface temperature records since the 1940s could be useful to clarify the issue because urban heat island (UHI) effects stress the warming of nocturnal temperatures more than the diurnal ones. Then, the significance of the divergence observed in the data could be evaluated against the expectations produced by the CMIP5 general circulation model simulations. From 1945–1954 to 2005–2014, on average and over China, these models predict that Tmin had to warm 0.19 ± 0.06 °C more than Tmax. However, during the same period, the climatic records show that Tmin warmed 0.83 ± 0.15 °C more than Tmax. A similar analysis demonstrates that the effect is more pronounced during the colder months from November–April than during the warmer ones from May to October. A comparison versus China urbanization records demonstrates that the regions characterized by a large Tmin-Tmax divergence are also the most densely populated ones, such as north-east China, that have experienced a diffused and fast urbanization since the 1940s. The results are significant and may indicate the presence of a substantial uncorrected urbanization bias in the Chinese climate records. Under the hypothesis that Tmax is a better metric for studying climatic changes than Tmean or Tmin, we conclude that about 50% of the recorded warming of China since the 1940s could be due to uncorrected urbanization bias. In addition, we also find that the Tmax record from May to October over China shows the 1940s and the 2000s equally warm, in contrast to the 1 °C warming predicted by the CMIP5 models.

Water vapor transport to material surfaces-Simplified analytical expressions for non-linear material properties

The water vapour transfer between the indoor air and material surfaces is of importance for the moisture balance of the room. It can also be important for the moisture content and durability of the material surface layer such as artefacts in churches and historical buildings. For most building materials the penetration depth due to short time fluctuations, such as diurnal ones, is very limited. For these cases the assumption of semi-infinite analysis gives accurate results even for a rather thin material layer. In the paper, the moisture profile and surface moisture uptake are modelled in detail for isothermal cases and strongly non-linear material properties for the sorption isotherm and vapor permeability. An approximative formula is given for a quite accurate estimate of the moisture up take for a demonstration case with a strongly non-linear material.

The evolution of iris colour in relation to nocturnality in owls

Birds, due to their multiple colourful displays, constitute a classic paradigm for the study of colour evolution. Although avian eyes are remarkably coloured, the functional basis behind inter‐specific variability in iris colouration remains poorly understood. Owls are an ideal system to shed light on the role of ecology in promoting iris colour evolution as they show inter‐specific variation in iris colour and in niche specialization with some species being strictly nocturnal and others active during the day. Owls perching for hunting at night might be unnoticed by both predators and their prey if they had dark irises, which would predict that dark irises were more likely to evolve in strictly nocturnal species than in diurnal ones. Using phylogenetic comparative models, we tested the camouflage hypothesis for eye colour. The proportion of dark‐eyed owl species is higher among strictly nocturnal owls than among diurnal ones. Ancestral state reconstruction revealed that the owl ancestor of the family Strigidae was more likely bright‐irided whereas the ancestor of the family Tytonidae was more likely dark‐irided. Our results show robust support for the coevolution of iris coloration and nocturnality in the owls, and suggest that shifting to a nocturnal niche would be a prerequisite leading to the evolution of dark eyes in owls. The specific evolutionary pathway by which iris coloration and activity rhythm coevolve, however, remains to be investigated further as we have found only partial support for the idea that dark irises in birds might be an adaptive feature evolved due to the selective advantage of concealment from undesired visual receptors.

Long-Term Trends and Variability of Water Levels and Tides in Buenos Aires and Mar del Plata, Argentina

We present an analysis of the long-term trends and variability of extreme water and tidal levels and the main tidal constituents using long-term records from two tide gauges in the wider region of the Rio de la Plata estuary: Buenos Aires (1905–2013) and Mar del Plata (1956–2013). We find significant long-term trends in both tidal levels and the main tidal constituents (M2, S2, K1, O1, and the overtide M4) from a running harmonic analysis in both locations. The tidal range decreased on average 0.63 mm y−1, as a result of an increase of the low water levels and a decrease of the high water levels. We also find a secular decrease in the amplitude of the semi-diurnal constituents and an increase of the diurnal ones, but of different magnitudes at each location, which suggests that different processes are producing these changes. In Buenos Aires, an increase of river discharge into the estuary seems to reduce the tidal range by hampering the propagation of the tidal wave into the estuary, whereas no influence of river discharge on water and tidal levels can be detected in Mar del Plata. We believe that other factors such as thermohaline changes or the rise of mean sea-level may be responsible for the observed tidal range decrease. Despite the tidal long-term trends, we find no significant trends in the meteorological component of the tide-gauge records other than an increase in the mean sea-level. In addition, we explore teleconnections between the variability of the meteorological component of the tide-gauge records and climate drivers.

Comparative Feeding Ecology of Cardinalfishes (Apogonidae) at Toliara Reef, Madagascar.

Bruno Frédérich, Loïc N. Michel, Esther Zaeytydt, Roger Lingofo Bolaya, Thierry Lavitra, Eric Parmentier, and Gilles Lepoint (2017) Despite their importance in coral reef ecosystem function and trophodynamics, the trophic ecology of nocturnal shes (e.g. Apogonidae, Holocentridae, Pempheridae) is by far less studied than diurnal ones. The Apogonidae (cardinal shes) include mostly carnivorous species and evidence of trophic niche partitioning among sympatric cardinal shes is still limited. The present study combines stomach contents and stable isotope analyses to investigate the feeding ecology of an assemblage of eight cardinal shes from the Great Reef of Toliara (SW Madagascar). δ13C and δ15N of shes ranged between -17.49‰ and -10.03‰ and between 6.28‰ and 10.74‰, respectively. Both stomach contents and stable isotopes showed that they feed on planktonic and benthic animal prey in various proportions. Previous studies were able to group apogonids in di erent trophic categories but such a discrimination is not obvious here. Large intra-speci c variation in the stomach contents and temporal variation in the relative contribution of prey to diet support that all apogonids should be considered as generalist, carnivorous shes. However the exploration of the isotopic space revealed a clear segregation of isotopic niches among species, suggesting a high level of resource partitioning within the assemblage. According to low inter-speci c variation in stomach content compositions, we argue that the di erences in isotopic niches could be driven by variation in foraging locations (i.e. microhabitat segregation) and physiology among species. Our temporal datasets demonstrate that the trophic niche partitioning among cardinal shes and the breadth of their isotopic niches are dynamic and change across time. Factors driving this temporal variation need to be investigated in further studies.

Temporal patterns of CO2 and CH4 in a rural area in northern Spain described by a harmonic equation over 2010–2016

The present paper seeks to improve our knowledge concerning the evolution of CO2 and CH4 in terms of monthly trends, growth rate and seasonal variations in the lower atmosphere. Dry continuous measurements of CO2 and the CH4 mixing ratio were carried out over five and a half years (from 15 October 2010 to 29 February 2016) by multi-point sampling at 1.8, 3.7 and 8.3m, using a Picarro analyzer at a rural site in the Low Atmosphere Research Centre (CIBA), on the upper Spanish plateau. Data were divided into diurnal and nocturnal records. The mathematical equation proposed to analyze the overall data was a harmonic one, comprising a polynomial (trend) and a series of harmonics (seasonal cycle). Amplitude was considered as a constant and variable term over time. Quite different behaviour was found between day and night measurements in both climate forcing agents. CO2 showed an accelerating trend in autumn, whereas CH4 trends were higher during the winter. Increasing growth rates were reported for CO2 and CH4 over the whole study period. Nocturnal CO2 amplitudes are higher than diurnal ones except in winter for both gases, and also in the autumn for CH4.

Food items of Macrotus waterhousii (Chiroptera: Phyllostomidae) in central Mexico

Macrotus waterhousii is a phyllostomid bat whose diet is poorly known, particularly in semiarid and temperate central Mexico. In this work additional information is reported from food remains discarded by this bat, including taxonomic composition, frequencies and size range of consumed insects; the assessment of a prediction on prey hardness of food insects, at the ordinal level; relative energy reward of insect prey in the sample; a comparison of the composition of the food sample from the arid study locality against one from a subtropical-temperate site; and brief comments on the known ecological importance of particular prey in the arid site. A sample of insect food remains discarded by Macrotus waterhousii bulleri, was recovered from under a roost in semiarid northern Queretaro, Mexico. The taxonomic identity, estimated relative abundance, size, hardness, and ecological relations of prey species in the sample were studied and results were compared with reference to feeding ecology. A comparison of the data with available information on food taken by Macrotus waterhousii mexicanus in temperate-subtropical central Mexico was made. Information on the importance of the most relevant identified insects was extracted from literature and analyzed. In Queretaro, Lepidoptera, Hymenoptera, and Coleoptera were frequent; moths dominated but, as a single species, the (winged) ant, Atta mexicana was most frequent. Nocturnal insects were frequent; diurnal ones may have been gleaned at night. A sample from Estado de Mexico featured Orthoptera, Coleoptera, and Lepidoptera. Wingspan range of frequent prey in Queretaro was 25-80 mm, but moths over 70 mm were over one fifth of the sample. Prey hardness estimation was similar to that for Macrotus californicus. Some insects identified are of ecologic and agricultural relevance. Insects known to be seasonally abundant in the environment were also abundant in the sample, presumably captured according to that availability. However this bat, aside from eating insects of moderate size in proportion to its jaw size, is also capable of capturing large moths and these may represent a significant energy intake. Most insects are nocturnal species. The taxonomic composition of the food samples from both areas suggests that M. waterhousii (sensu lato) may be mostly an opportunistic predator. Local insect fauna composition and dynamics may be hypothesized to influence food taken by M. waterhousii. Several insect species consumed by this bat in semiarid Queretaro have crucial roles in the ecology of arid land vegetation, as well as some economic importance for agriculture as pests.

A new halisaurine mosasaur (Squamata: Halisaurinae) from Japan: the first record in the western Pacific realm and the first documented insights into binocular vision in mosasaurs

A specimen of a halisaurine mosasaur is reported from Japan for the first time, closing the pre-existing biogeographical gap between the Middle East and the eastern Pacific. Phosphorosaurus ponpetelegans sp. nov., from the lowermost Maastrichtian of Hokkaido, has been assigned to the genus Phosphorosaurus for sharing the following suite of major cranial characters with P. ortliebi, the type species from Belgium: apex of posterodorsal triangular plateau on frontal reaching level of interorbital constriction; frontal lateral border forming a step-like junction between interorbital and preorbital segments of frontal; preorbital segment of frontal sloping anteroventrally; and stapedial meatus parallel-sided in latero-medial view. Potential autapomorphies that distinguish P. ponpetelegans from other members of Halisaurinae include: postorbitofrontal jugal process elongate and stalk-like, projecting laterally; this process distally bearing a ventrally facing depression for jugal articulation; and lateral surangular–articular suture angular rather than round. The long and laterally projecting jugal processes, when combined with a depressed as well as narrow snout, provide compelling evidence for well-developed binocular vision for the new mosasaur, with an estimated binocular field of view (BFoV) of 35°. This value is unusually high for non-ophidian squamates that typically exhibit a BFoV of 10—20°, and is higher than those of other measured mosasaur taxa by at least 5°. Among colubrid snakes, nocturnal species exhibit greater BFoV than diurnal ones in both arboreal and terrestrial taxa. Known also from the Maastrichtian of Hokkaido are fossils of lantern fish (myctophids) and 10-armed cephalopods (coleoids), both of which are typically bioluminescent today. It is hence proposed that the exceptionally large, forward-facing eyes of P. ponpetelegans may well have been a special adaptation for a nocturnal lifestyle, where they hunted small, bioluminescent prey at night while avoiding direct competition with larger, more piscine mosasaurine taxa such as Mosasaurus hobetsuensis that co-existed with P. ponpetelegans.http://zoobank.org/urn:lsid:zoobank.org:pub:3EF73BE7-B3FE-4441-BA5E-29C5D5FCCBC9

Point-diversity, a critical tool for assessing dynamics of guilds of scavenging ants (Hymenoptera: Formicidae): an example from a eucalypt woodland

Point diversity provides essential information about structuring of assemblages and interactions of component species, not achieved using other scales of analysis. A baited grid was used (1) to ascertain number of species of scavenging ants at point resources of food in an Australian eucalypt woodland at three times in the diel cycle and (2) to assess the nature of interactions and ecological impact of each species. Nineteen measures of assemblage structure and species’ interactions were implemented. Ants covered the entire area during a single diel cycle. Eurydielic species foraged over the largest area and showed least overlap. Nocturnal species foraged over the smallest area, with half the space not visited. Many foraging ranges of species-pairs, both of nocturnal and of diurnal ants, overlapped as expected by chance but half the eurydielic species-pairs overlapped less than expected; some abutted. Foraging ranges of eurydielic and nocturnal species did not overlap more than by chance. Overlap between eurydielic and diurnal species-pairs varied from less to more overlap than by chance. Simultaneous co-occurrences of all eurydielic species-pairs and many of nocturnal and diurnal ones were random. Members of pairs of nocturnal and of diurnal species were negatively associated except for one positive association. Early occupancy by diurnal ants did not guarantee persistence. Eurydielic species fed a higher percentage of their time than did diurnal or nocturnal species. Incidence of mobilization decreased with increasing number of simultaneously co-occurring species. Some species may be attracted by other species’ activities. Eurydielic species dominated two tiers of diurnal species by day and two tiers of nocturnal species by night. Eurydielic species were most important in determining assemblage structure. Formicines had the greatest species richness but myrmicines and dolichoderines were more important ecologically.

Composition and structure of the molluscan assemblage associated with a Cymodocea nodosa bed in south-eastern Spain: seasonal and diel variation

The molluscan taxocoenosis associated with a Cymodocea nodosa seagrass bed was studied throughout 1 year in Genoveses Bay, in the MPA “Parque Natural Cabo de Gata-Níjar” (south-eastern Spain). A total of 64,824 individuals were collected and 54 species identified. The molluscan fauna was mainly composed of gastropods (99.56% of individuals, 43 spp.). The families Rissoidae (72.98%, 11 spp.) and Trochidae (16.93%, 7 spp.) were the most abundant and diversified in terms of number of species. Rissoa monodonta (47.1% dominance), Rissoa membranacea (25.1%) and Gibbula leucophaea (11.6%) proved the top dominant species in both diurnal and nocturnal samples. Bivalves (0.41%, 10 species) and cephalopods (0.03%, 1 species) represented only a low percentage of the molluscan taxocoenosis. The molluscan assemblage was mainly composed of species with a wide geographical distribution in Europe, followed by strictly Mediterranean species. The abundance was significantly higher in the cold (December, March) than in the warm months (June, July). Species richness (S) was higher in nocturnal than in diurnal samples, reaching maximal values in diurnal samples of March and June. Shannon–Wiener diversity (H′) values were generally higher in nocturnal samples than in diurnal ones, displaying minimum values in December and June, respectively. Evenness was similar in diurnal and nocturnal samples, with maximum values in July in both groups. S and H′ were also significantly different between diurnal and nocturnal samples. Multivariate analyses based on both qualitative and quantitative data showed a significant seasonal and diel variation. Diel changes revealed to be more distinct than seasonal ones.

Nocturnal Hypertension and Special - Period Hypertension in Type 1 Diabetes Mellitus

Nocturnal Hypertension and Special - Period Hypertension in Type 1 Diabetes MellitusBackground: One of the unique aspects of continuous ambulatory arterial-tension monitoring is the ability of recording the diurnal variations. The patients suffering from Type 1 Diabetes Mellitus (T1DM) may present higher nocturnal values of arterial tension and this rise can be determined by hyperinsulinism. The first hours in the morning (6 a.m. - 9 a.m.), the so-called special period, is correlated with a rise in the incidence of cardiovascular events and a rise in plasmatic catecholamine and of platelet aggregability. The main goal of this study is to analyze the particularities of the tensional profile with regard to nocturnal behavior and behavior in the special period, reported to glycemic variations. Material and method: The study analysed 351 patients known with T1DM, who have been suffering from this disease for more than 10 years, who were in the records of the Center of Diabetes, Nutrition and Metabolic Diseases of Iaşi and Suceava. The patients were assesssed from a tensional and glycemic point of view, by continuous blood-tension (ABPM) and glycemia (CGMS) monitoring. Results: The occurrence of nocturnal hypertension in patients suffering T1DM is by 29.24 higher than in the case of hypertensive persons compared to the risk presented by the persons without blood hypertension. The continuous recording of blood hypertension during the asymptomatic hypoglycemia period showed increased values both for systolic blood tension and for diastolic one (p<0.05). The hypertension risk is by 3.24 higher during the hypoglycemia period compared to the normoglycemic one. Tension variations during the special period were noticed in 87 patients who have been suffering from diabetes mellitus for 19.75 ± 4.57 years. These tension values are higher than the nocturnal ones, but lower than the diurnal ones. Conclusions: Hypoglycemia duration and magnitude induces increased tension values which adds another hemodynamic stress factor to the patient suffering from T1DM. In T1DM, in the first morning hours, in particular conditions, we can notice increased tension values, higher in patients with blood hypertension, which induces a stressed cardiovascular risk. Tension value increase during the special period overlaps the morning hyperglycemias. Therefore, there appears an apparently invisible impact on the cardiovascular condition of diabetes mellitus.

Fortnightly oscillations observed in the Adriatic Sea

This paper documents the occurrence of strong fortnightly oscillations in the Adriatic Sea frequently observed in the current measurements. For that purpose, we analyzed half-decadal sea level series and long-term currents collected within different parts and layers of the Adriatic Sea. Harmonic analysis and band-pass filter with cutoff periods at 10 and 20 days have been applied to the series. The sea level Mf tide is found to be the only significant tidal constituent over periods between the diurnal and semi-annual ones, having no significant phase variations in the Adriatic Sea. Moreover, the currents on periods between 10 and 20 days could only partially be explained by atmospheric forcing. The fact that they are in-phase with the Mf tide gives a hint on a possible mechanism responsible for the generation of these oscillations. Additionally, these currents are usually strongly amplified during a weakly stratified season, indicating a baroclinic mechanism responsible for the multiplication of the fortnightly currents.

Assessing residence times of hyporheic ground water in two alluvial flood plains of the Southern Alps using water temperature and tracers

Abstract. Water temperature can be used as a tracer for the interaction between river water and groundwater, interpreting time shifts in temperature signals as retarded travel times. The water temperature fluctuates on different time scales, the most pronounced of which are the seasonal and diurnal ones. While seasonal fluctuations can be found in any type of shallow groundwater, high-frequency components are more typical for freshly infiltrated river water, or hyporheic groundwater, and are thus better suited for evaluating the travel time of the youngest groundwater component in alluvial aquifer systems. We present temperature time series collected at two sites in the alpine floodplain aquifers of the Brenno river in Southern Switzerland. At the first site, we determine apparent travel times of temperature for both the seasonal and high-frequency components of the temperature signals in several wells. The seasonal signal appears to travel more slowly, indicating a mixture of older and younger groundwater components, which is confirmed by sulphate measurements. The travel times of the high-frequency component qualitatively agree with the groundwater age derived from radon concentrations, which exclusively reflects young water components. Directly after minor floods, the amplitude of temperature fluctuations in an observation well nearby the river is the highest. Within a week, the riverbed is being clogged, leading to stronger attenuation of the temperature fluctuations in the observation well. At the second site, very fast infiltration to depths of 1.9 m under the riverbed could be inferred from the time shift of the diurnal temperature signal.

Numerical simulation of the Adriatic Sea principal tidal constituents

Abstract. The primary goal of this study was to incorporate data-derived harmonic constants into a complex dynamic model using a form of variational data assimilation, with a view to improve the prediction of 7 dominant tidal constituents in the Adriatic Sea. Firstly, harmonic-constant data for 6 Adriatic stations were fed into a steady-state, 3-D, forward/inverse model to furnish optimal boundary conditions (OBCs). Calculated OBCs were then used to derive individual constituent responses, as well as to synthesise seven-constituent boundary conditions for the time stepping, 3-D model. A separate set of 25 stations provided control harmonic constant data. In validating the model output particular attention has been given to the often-ignored tidal currents. To that end 14 current meter data records were processed into tidal current ellipse parameters and used to examine the comparable model output. Comparison to gauge data has shown that the present solution is better than our own previous one, and shows an improvement over recent solutions by other authors. The model accurately reproduces available data with individual station amplitude differences rarely exceeding 1cm, and with the phase error commonly staying well below 10°. For all tidal constituents individual station differences result in RMSE in the 0.33-0.71-cm range for amplitude, and the 5.6°-19.2° range for phase. Semidiurnal currents appear to be modelled better than the diurnal ones (generally over-predicted). High eccentricity of both data and model-derived ellipses often impaired calculating the proper sense of rotation; inclination of the ellipses proved to be the most robust parameter, successfully predicted for most constituents at all depths.

Barotropic tide and baroclinic waves observations in the Río de la Plata Estuary

The first long‐period ADCP series collected in two locations of the salinity front of the Río de la Plata estuary are explored for periods less than 30 hours. Barotropic velocity shows tidal and mean currents consistent with what is known about the estuarine circulation in tidal and seasonal scales. Baroclinic currents provide the first evidence of the occurrence of internal waves, which can account for half of the total variance. In the northernmost location, predominantly zonal oscillations with semidiurnal period, and oscillations with a dominant meridional component and diurnal period, are found. Whereas the first ones can be related to the semidiurnal tide, the second ones seem to be atmospherically forced by the land/sea breeze. In the southernmost location, more rotational oscillations are observed, with periods around the inertial and diurnal ones. Inertial oscillations could result from wind relaxation, whereas diurnal oscillations also seem to be forced by breeze. Wave activity in the diurnal band was less frequent in the northernmost than in the southernmost location. This can be attributed to less frequent favorable stratification conditions in that area during the observed period. Wave activity in the southernmost location resulted weaker during the observed fall than during the summer. This could be a typical feature given that in autumn both the number of storms destroying the thermohaline structure increases and land/sea breeze is less frequent. This suggests a likely seasonal cycle in the diurnal wave activity in this area, given that those unfavorable conditions are even more marked during winter.