Summer Formation Research Articles

Light absorption, fluorescence properties and sources of brown carbon aerosols in the Southeast Tibetan Plateau

Brown carbon (BrC) has been proposed as an important driving factor in climate change due to its light absorption properties. However, our understanding of BrC’s chemical and optical properties are inadequate, particularly at remote regions. This study conducts a comprehensive investigation of BrC aerosols in summer (Aug. 2013) and winter (Jan. 2014) at Southeast Tibetan Plateau, which is ecologically fragile and sensitive to global warming. The concentrations of methanol-soluble BrC (MeS-BrC) are approximately twice of water-soluble BrC (WS-BrC), demonstrating the environmental importance of water-insoluble BrC are previously underestimated with only WS-BrC considered. The mass absorption efficiency of WS-BrC (0.27–0.86 m2 g−1) is lower than those in heavily polluted South Asia, indicating a distinct contrast between the two sides of Himalayas. Fluorescence reveals that the absorption of BrC is mainly attributed to humic-like and protein-like substances, which broaden the current knowledge of BrC’s chromophores. Combining organic tracer, satellite MODIS data and air-mass backward trajectory analysis, this study finds BrC is mainly derived from bioaerosols and secondary formation in summer, while long-range transport of biomass burning emissions in winter. Our study provides new insights into the optical and chemical properties of BrC, which may have implications for environmental effect and sources of organic aerosols.

Spatiotemporal variation of atmospheric nitrated polycyclic aromatic hydrocarbons in semi-arid and petrochemical industrialized Lanzhou City, Northwest China.

Polyurethane foam-based passive air sampler (PUF-PAS) and passive dry deposition sampler (PAS-DD) were adopted, for thefirst timeever in China, to investigate the atmospheric levels and spatial-temporal distributions of air burdens and dry deposition fluxes of 12 nitrated polycyclic aromatic hydrocarbons (NPAHs) during winter and summer seasons in a multiple site field campaign in a petrochemical industrialized capital city in Northwest China. The results showed that the highest air concentration and dry deposition fluxes of ∑12NPAHs occurred at a heavy traffic site among 18 sampling sites in both winter and summer season. The lowest air concentration and dry deposition fluxes were observed at the background site. The mean concentrations of ∑12NPAHs in the ambient air were 8.6 ± 8.1ngm-3 in winter and 15 ± 11ngm-3 in summer. The mean dry deposition fluxes of ∑12NPAHs were 1.8 × 103 ± 1.9 × 103ng(m2day)-1 in winter and 1.4 × 103 ± 1.3 × 103ng(m2day)-1 in summer, respectively. The total concentration of 12 NPAHs was mainly dominated by 1-nitro-naphthalene (1N-NAP) and 2-nitro-naphthalene(2N-NAP) in air, accounting for 32% in winter and 45% in summer of ∑12NPAHs. 7-Nitro-benzo [a] anthracene (7N-BaA) made the largest contribution to dry deposition fluxes of ∑12NPAHs, accounting for 28% in winter and 24% in summer. The ratios of ∑12NPAHs/∑15pPAHs (parent polycyclic aromatic hydrocarbons) were calculated to identify potential sources of NPAHs across the city. The results revealed that the main atmospheric air concentration and dry deposition fluxes of 12 NPAHs could be attributed to the primary emissions in winter and the secondary reaction formation in summer. The sources of primary emissions could be traced back to petrochemical, steel mills, as well as aluminum industries in winter and vehicle exhaust in summer. Higher ∑12NPAH/∑15pPAH concentration ratios in summer indicated that the oxidation of pPAHs contributed to the secondary formation of NPAHs via atmospheric chemical reactions in this petrochemical industrialized mountain-valley city.

Seasonal cycles of secondary organic aerosol tracers in rural Guangzhou, Southern China: The importance of atmospheric oxidants

Thirteen secondary organic aerosol (SOA) tracers of isoprene (SOAI), monoterpenes (SOAM), sesquiterpenes (SOAS) and aromatics (SOAA) in fine particulate matter (PM2.5) were measured at a Pearl River Delta (PRD) regional site for one year. The characteristics including their seasonal cycles and the factors influencing their formation in this region were studied. The seasonal patterns of SOAI, SOAM and SOAS tracers were characterized over three enhancement periods in summer (I), autumn (II) and winter (III), while the elevations of SOAA tracer (i.e., 2,3-dihydroxy-4-oxopentanoic acid, DHOPA) were observed in Periods II and III. We found that SOA formed from different biogenic precursors could be driven by several factors during a one-year seasonal cycle. Isoprene emission controlled SOAI formation throughout the year, while monoterpene and sesquiterpene emissions facilitated SOAM and SOAS formation in summer rather than in other seasons. The influence of atmospheric oxidants (Ox) was found to be an important factor of the formation of SOAM tracers during the enhancement periods in autumn and winter. The formation of SOAS tracer was influenced by the precursor emissions in summer, atmospheric oxidation in autumn and probably also by biomass burning in both summer and winter. In this study, we could not see the strong contribution of biomass burning to DHOPA as suggested by previous studies in this region. Instead, good correlations between observed DHOPA and Ox as well as [NO2][O3] suggest the involvement of both ozone (O3) and nitrogen dioxide (NO2) in the formation of DHOPA. The results showed that regional air pollution may not only increase the emissions of aromatic precursors but also can greatly promote the formation processes.

The first case of anoxia in waters of the Far East Marine Biosphere Reserve

In August 2013, anoxia of the bottom waters was established in the southern region of the Far East Marine Biosphere Reserve, Far East Branch, Russian Academy of Science, in the depression between Furugelm Island and coastal waters. Death of the benthic community was registered using a remotely operated underwater vehicle. The hydrochemical studies revealed that the area of the absence and/or presence of low oxygen contents corresponds to an area of anomalously high contents of ammonium, phosphates, and silicates, a high partial pressure of carbon dioxide and normalized alkalinity, and the presence of hydrogen sulfide. The microbiological decomposition of diatoms precipitated on the seafloor in the absence of oxygen regeneration was the reason for anoxia. Its formation in summer of 2013 was caused by anomalously abundant precipitates in the Far East.

Role of secondary aerosols in haze formation in summer in the Megacity Beijing

A field experiment from 18 August to 8 September 2006 in Beijing, China, was carried out. A hazy day was defined as visibility<l0km and RH (relative humidity)<90%. Four haze episodes, which accounted for ~60% of the time during the whole campaign, were characterized by increases of SNA (sulfate, nitrate, and ammonium) and SOA (secondary organic aerosol) concentrations. The average values with standard deviation of SO42−, NO3−, NH4+ and SOA were 49.8 (±31.6), 31.4 (±22.3), 25.8 (±16.6) and 8.9 (±4.1)μg/m3, respectively, during the haze episodes, which were 4.3, 3.4, 4.1, and 1.7 times those in the non-haze days. The SO42−, NO3−, NH4+, and SOA accounted for 15.8%, 8.8%, 7.3%, and 6.0% of the total mass concentration of PM10 during the non-haze days. The respective contributions of SNA species to PM10 rose to about 27.2%, 15.9%, and 13.9% during the haze days, while the contributions of SOA maintained the same level with a slight decrease to about 4.9%. The observed mass concentrations of SNA and SOA increased with the increase of PM10 mass concentration, however, the rate of increase of SNA was much faster than that of the SOA. The SOR (sulfur oxidation ratio) and NOR (nitrogen oxidation ratio) increased from non-haze days to hazy days, and increased with the increase of RH. High concentrations of aerosols and water vapor favored the conversion of SO2 to SO42− and NO2 to NO3−, which accelerated the accumulation of the aerosols and resulted in the formation of haze in Beijing.

Near-surface internal melting: a substantial mass loss on Antarctic Dry Valley glaciers

AbstractThe McMurdo Dry Valleys, southern Victoria Land, East Antarctica, are a polar desert, and melt from glacial ice is the primary source of water to streams, lakes and associated ecosystems. Previous work found that to adequately model glacier ablation and subsurface ice temperatures with a surface energy-balance model required including the transmission of solar radiation into the ice. Here we investigate the contribution of subsurface melt to the mass balance of (and runoff from) Dry Valley glaciers by including a drainage process in the model and applying the model to three glacier sites using 13 years of hourly meteorological data. Model results for the smooth glacier surfaces common to many glaciers in the Dry Valleys showed that sublimation was typically the largest component of surface lowering, with rare episodes of surface melting, consistent with anecdotal field observations. Results also showed extensive internal melting 5–15 cm below the ice surface, the drainage of which accounted for ~50% of summer ablation. This is consistent with field observations of subsurface streams and formation of a weathering crust. We identify an annual cycle of weathering crust formation in summer and its removal during the 10 months of winter sublimation.

Temporal dynamics of nonstructural carbohydrates and xylem growth inPinus sylvestrisexposed to drought

Wood formation requires a continuous supply of carbohydrates for structural growth and metabolism. In the montane belt of the central Austrian Alps, we monitored the temporal dynamics of xylem growth and nonstructural carbohydrates (NSC) in stem sapwood of Scots pine ( Pinus sylvestris L.) during the growing season of 2009, which was characterized by exceptional soil dryness within the study area. Soil water content dropped below 10% at the time of maximum xylem growth at the end of May. Histological analyses have been used to describe cambial activity and xylem growth. Determination of NSC was performed using specific enzymatic assays revealing that total NSC ranged from 0.8% to 1.7% dry matter throughout the year. Significant variations (P &lt; 0.05) of the size of the NSC pool were observed during the growing season. Starch showed persistent abundance throughout the year, reaching a maximum shortly before onset of late wood formation in mid-July. Seasonal dynamics of NSC and xylem growth suggest that (i) high sink activity occurred at the start of the growing season in spring and during late wood formation in summer and (ii) there was no particular shortage in NSC, which caused P. sylvestris to draw upon stem reserves more heavily during the drought in 2009.

Maximum urban heat island intensity in a medium-sized coastal Mediterranean city

This paper studies the maximum intensity of the urban heat island (UHI) that develops in Volos urban area, a medium-sized coastal city in central Greece. The maximum temperature difference between the city center and a suburb is 3.4°C and 3.1°C during winter and summer, respectively, while during both seasons the average maximum UHI intensity is 2.0°C. The UHI usually starts developing after sunset during both seasons. It could be attributed to the different nocturnal radiative cooling rate and to the different anthropogenic heat emission rate that are observed at the city center and at the suburb, as well as to meteorological conditions. The analysis reveals that during both seasons the daily maximum hourly (DMH) UHI intensity is positively correlated with solar radiation and with previous day’s maximum hourly UHI intensity and negatively correlated with wind speed. It is also negatively correlated with relative humidity during winter but positively correlated with it during summer. This difference could be attributed to the different mechanisms that mainly drive humidity levels (i.e., evaporation in winter and sea breeze (SB) in summer). Moreover, it is found that SB development triggers a delay in UHI formation in summer. The impact of atmospheric pollution on maximum UHI intensity is also examined. An increase in PM10 concentration is associated with an increase in maximum UHI intensity during winter and with a decrease during summer. The impact of PM10 on UHI is caused by the attenuation of the incoming and the outgoing radiation. Additionally, this study shows that the weekly cycle of the city activities induces a weekly variation in maximum UHI intensity levels. The weekly range of DMH UHI intensity is not very large, being more pronounced during winter (0.4°C). Moreover, a first attempt is made to predict the DMH UHI intensity by applying regression models, whose success is rather promising.

Seasonal reversal at Miryang Eoreumgol (Ice Valley), Korea: observation and monitoring

We investigate an anomalous phenomenon evident in the Miryang Eoreumgol (Ice Valley), Korea: The wind and water are cold during summer and warm during winter, and ice formation does not occur in winter but in summer. We have initiated observations and investigations into the origin of heat sources particularly with regard to the mechanism of ice formation in summer. Previous theories, e.g., concerning underground gravity currents, water evaporation, diurnal and seasonal respirations of the talus, effects of ground heat, radiation and topography, etc., are considered. After a calculation of heat sources, we propose two new concepts—a repetitious heat separation mechanism and a positive feedback mechanism of cold air generation—to demonstrate that the heat mechanism of the seasonal reversal of the ice valley may be controlled by the use of the phase change between ice and water vapor with only a small amount of additional unknown energy.

Application of OMI observations to a space-based indicator of NO x and VOC controls on surface ozone formation

We investigated variations in the relative sensitivity of surface ozone formation in summer to precursor species concentrations of volatile organic compounds (VOCs) and nitrogen oxides (NO x) as inferred from the ratio of the tropospheric columns of formaldehyde to nitrogen dioxide (the “Ratio”) from the Aura Ozone Monitoring Instrument (OMI). Our modeling study suggests that ozone formation decreases with reductions in VOCs at Ratios <1 and NO x at Ratios >2; both NO x and VOC reductions may decrease ozone formation for Ratios between 1 and 2. Using this criteria, the OMI data indicate that ozone formation became: 1. more sensitive to NO x over most of the United States from 2005 to 2007 because of the substantial decrease in NO x emissions, primarily from stationary sources, and the concomitant decrease in the tropospheric column of NO 2, and 2. more sensitive to NO x with increasing temperature, in part because emissions of highly reactive, biogenic isoprene increase with temperature, thus increasing the total VOC reactivity. In cities with relatively low isoprene emissions (e.g., Chicago), the data clearly indicate that ozone formation became more sensitive to NO x from 2005 to 2007. In cities with relatively high isoprene emissions (e.g., Atlanta), we found that the increase in the Ratio due to decreasing NO x emissions was not obvious as this signal was convolved with variations in the Ratio associated with the temperature dependence of isoprene emissions and, consequently, the formaldehyde concentration.

The Impact of the Eastward Propagation of Convective Systems over the Tibetan Plateau on the Southwest Vortex Formation in Summer

AbstractBased on the temperature of the black body (TBB), station observed and NCEP reanalysis data, the impacts of the eastward propagation of convective cloud systems over the Tibetan Plateau on the southwest vortex (SWV) formation that occurred at 1800 UTC on 29 June 2003 are analyzed by using the Zwack-Okossi (Z-O) equation to diagnose the thermal and dynamic processes. It is found that, in summer, severe convective activities often occur over the Tibetan Plateau due to the abundant supply of moisture. The convective cloud near the east edge of the plateau could move eastward with a short-wave trough in the westerly. The divergent center that is induced by latent heat release, which is associated with severe convective activities, moves out with the convective cloud and contributes to the low level decompression which is favorable for the formation of plateau edge cyclogenesis (PEC). The Z-O equation indicates that, in this case, the latent heat release and convergence are the two most important facto...

Determination of Dicarboxylic Acids and Levoglucosan in Fine Particles in the Kanto Plain, Japan, for Source Apportionment of Organic Aerosols

Fine particles were collected at a suburban site in the inland Kanto plain, Japan, in the spring and winter of 2007, and the summer of 2008. Organic carbon (OC), water-soluble organic carbon (WSOC), elemental carbon (EC), inorganic ions, and water-soluble organic compounds (dicarboxylic acids and levoglucosan) were analyzed. The WSOC/OC ratio was the highest in summer, followed by in spring, suggesting that organic aerosols were influenced by aging. The concentrations of total diacids (C2–C9) in spring and summer were higher than in winter. In each season, WSOC showed a strong positive correlation with the total diacids. Levoglucosan, which is recognized as a biomass burning tracer, was observed in a considerably higher concentration in winter than in spring or summer. In winter, WSOC also showed a strong positive correlation with levoglucosan. These results indicate that secondary formation is important as a source of WSOC and OC especially in the warm seasons, although emissions from biomass burning also contribute to WSOC in winter. By using the combination of source profile for biomass burning emission and EC tracer method, OC derived from biomass combustion in winter was calculated to be 47% of OC and OC derived from secondary formation in summer was calculated to be 75% of OC.

Seasonal and spatial variations in characteristics of Lake Biwa dissolved organic matter: sorption of pyrene and its derivatives and fluorescence properties

The objectives of this research were to investigate seasonal and spatial variations in (1) sorption of pyrene and its derivatives onto dissolved organic matter (DOM) and (2) fluorescence properties of DOM in Lake Biwa, Japan. In the case of pyrene, sorption coefficient (Kdoc) of Lake Biwa DOM seasonally changed from 1,200 to 3,800 L/kgC. Vertical distribution of Kdoc was affected by thermocline formation in summer, while it was uniformly distributed as a result of vertical mixing in winter. Functional groups affected sorption of pyrene onto Lake Biwa DOM in different manner from that onto Suwannee River fulvic acid. Three-dimensional excitation emission matrices (3D-EEMs) fluorescence spectroscopy was applied to characterize Lake Biwa DOMs and indicated the existence of at least two fluorophores. The two major peaks at Ex230/Em300 and Ex230/Em425 originated from protein-like and fulvic/humic-like substances, respectively. The peak at Ex230/Em300 showed the maximum fluorescence intensity at a depth of 5 m and could be affected by stratification of the water column in summer. On the other hand, the peak at Ex230/Em425 showed similar profiles both in summer and in winter. These results demonstrably showed that sorption of micropollutants and fluorescence properties of Lake Biwa DOMs were seasonally and spatially varied.

Spatial and temporal variability in the snowpack of a High Arctic ice cap: implications for mass-change measurements

AbstractInterpretation of ice mass elevation changes observed by satellite altimetry demands quantification of the proportion of elevation change which is attributable to variations in firn densification. Detailed stratigraphic logging of snowpack structure and density was carried out at ~1km intervals along a 47 km transect on Devon Ice Cap, Canada, in spring (pre-melt) and autumn (during/ after melt) 2004 and 2006 to characterize seasonal snowpack variability across the full range of snow facies. Simultaneous meteorological measurements were gathered. Spring (pre-melt) snowpacks show low variability over large spatial scales, with low-magnitude changes in density. The end-of-summer/ autumn density profiles show high variability in both 2004 and 2006, with vastly different melt regimes generating dissimilar patterns of ice-layer formation over the two melt seasons. Dye-tracing experiments from spring to autumn 2006 reveal that vertical and horizontal distribution of meltwater flow within and below the annual snowpack is strongly affected by the pre-existing, often subtle stratigraphic interfaces in the snowpack, rather than its bulk properties. Strong interannual variability suggests that using a simple relationship between air temperature, elevation and snowpack densification to derive mass change from measurements of elevation change across High Arctic ice caps may be misguided. Melt timing and duration are important extrinsic factors governing snowpack densification and ice-layer formation in summer, rather than averaged air temperatures.

Temporal Variation of Air Temperature in Ice-Valley at Milyang in Association with Ice Formation

A long-term in situ observation was carried out in the Ice-valley at Milyang in order to explain the factors and processes associated with the summertime ice formation. The variation of temperature inside Ice-valley in relation with ice formation in summer time was found to depend on precipitation rate in spring and cold air sinking in autumn and winter. The rate of temperature rising tends to correspond to sensible heat release depending on the precipitation amount at the freezing location. The reason of the cold air accumulation in a talus in the Ice-valley is the cold air sinking over the surface of talus due to the occurrence of outside clod air mass and the accumulated cold air from autumn to spring flow outside at the bottom of talus. The out-flowing cold air can result in the ice formation in the hot summer.

Number concentration and size distributions of submicron particles in Jinan urban area: Characteristics in summer and winter

The aerosol number concentration and size distribution were measured with the newly developed Wide-range Particle Spectrometer in summer and winter of 2006 at the urban site of Jinan City. Here reported the characteristics of fine particles of the different observation seasons. Relative high number concentrations for the particles in the diameter range of 10–500 nm were observed in both seasons. It was found that the dominant number distributed in particle diameter smaller than 100 nm and the percentage over the number concentration of all air particles is much higher than what has been measured in other urban sites over the world. The number mean diameter in summer was much smaller than in winter, strongly suggesting the different origin of ultrafine particles in different seasons. That is, particles in ultrafine mode mainly came from nucleation and new particle formation in summer while from traffic emission in winter. The diurnal variation also supported this point. Number concentration in the diameter range of 10–200 nm got their peak values at noontime, well correlated with the mixing ratio of SO 2 and the intensity of solar radiation in summer. While in winter, those in the same diameter range showed the main peaks during the traffic hours happened in the morning and evening.

Hydrological and biogeochemical dynamics of the minor and trace elements in the St. Lawrence River

Surface water samples from the St. Lawrence River were collected in order to study the processes controlling minor and trace elements concentrations (Al, Fe, Mn, Cd, Co, Cu, Ni and Zn), and to construct mass balances allowing estimates of the relative importance of their natural and anthropogenic sources. The two major water inputs, the upper St. Lawrence River, which drains waters originating from the Lake Ontario, and the Ottawa River were collected fortnightly over 18 months. In addition, other tributaries were sampled during the spring floods. The output was monitored near Quebec City at the river mouth weekly between 1995 and 1999. Dissolved metal concentrations in the upper St. Lawrence River carbonated waters were lower than in the acidic waters of the tributaries draining the crystalline rocks of the Canadian shield and the forest cover. Biogeochemical and hydrodynamic processes occurring in Lake Ontario drive the seasonal variations observed in the upper St. Lawrence River. Biogeochemical processes relate to biological uptake, regeneration of organic matter (for Cd and Zn) and oxyhydroxide formation (for Mn and Fe), while hydrodynamic processes mainly concern the seasonal change in vertical stratification (for Cd, Mn, and Zn). In the Ottawa River, the main tributary, oxyhydroxide formation in summer governs seasonal patterns of Al, Fe, Mn, Cd, Co and Zn. The downstream section of the St. Lawrence River is a transit zone in which seasonal variations are mainly driven by the mixing of the different water masses and the large input of suspended particulate matter from erosion. The budget of all dissolved elements, except Fe and Zn, was balanced, as the budget of particulate elements (except Cd and Zn). The main sources of metals to the St. Lawrence River are erosion and inputs from tributaries and Lake Ontario. Direct anthropogenic discharges into the river accounted for less than 5% of the load, except for Cd (10%) and Zn (21%). The fluxes in transfer of dissolved Cd, Co, Cu and Zn species from the river to the lower St. Lawrence estuary were equal to corresponding fluxes calculated for Quebec City since the distributions of dissolved concentrations of these metals versus salinity were conservative. For Fe, the curvature of the dilution line obtained suggests that dissolved species were removed during early mixing.

Superimposed-ice formation in summer on Ross Sea pack-ice floes

AbstractAustral summer sea-ice processes were investigated in January 1999 during a cruise of the R.V. Nathaniel B. Palmer in the central and eastern Ross Sea, Antarctica. The crystal texture, 18O/16O ratios, density and salinity of ice cores and of ice blocks ‘perched’ on slush at the ice surface were studied. The perched ice blocks had a distinctive polygonal granular (PG) crystal texture and very negative isotope signature that were also characteristic of layers at the top of first-year floes and of layers ‘buried’ below the surface in multi-year floes. The PG ice is superimposed ice that results from melting in the snow cover and refreezing at the slush surface and directly on top of ice floes. If PG ice is buried after the ice surface floods and the resultant slush freezes, then snow ice forms above the PG ice. The contribution of superimposed ice to floe surface mass balance and some implications with respect to weather and climate are discussed.

Sowing date and nitrogen rate effects on growth, yield and yield components of two summer rapeseed cultivars

Rapeseed ( Brassica napus L.) has potential to become an alternate oilseed crop in eastern Anatolia, Turkey. Information on sowing date and nitrogen rate for rapeseed is not available in this region. Therefore, a study was initiated to investigate the effects of sowing date and nitrogen rate on the yield and agronomic characteristics of two genotypes of spring rapeseed (Tower and Lirawell) in Erzurum, eastern Anatolia, during 1994 and 1995. Four sowing dates were established at about 10-day intervals from mid April to lately May (19 April, 29 April, 9 May, and 18 May 1994; and 29 April, 9 May, 18 May, and 27 May 1995). Four N fertilizer rates established; 0, 80, 160, and 240 kg N ha −1. In both years, there were effects on plant growth, yield, and yield components due to sowing dates, nitrogen rates, and cultivars. Cultivars tended to respond similarly to sowing date and nitrogen rate for seed yield in both years of the study. In general, early sowings gave higher yields than late sowings in both years, except the first sowing (9 April) in 1994 growing season. From this study, it appears that seeding rapeseed from 29 April to 9 May gives a greater assurance for higher yields. The present results highlight the practical importance of adequate N fertilization in yield formation in summer oilseed rape and suggest that the rate of 160 kg N ha −1 will be about adequate for the crop to meet its N requirements. The yield differences measured for both sowing dates and nitrogen rates were primarily due to the changes in branch numbers, pod numbers per plant, and 1000 seed weights.

Summer diapause in Daphnia as a reaction to the presence of fish

A chemical signal, released by a fish predator under summer-like high water temperature and long-day photoperiod, caused the formation of resting eggs in a clone of Daphnia magna. No ephippial females were recorded and no ephippia were released in the control treatment during 45 days of the experiment. When exposed to fish water, the fraction of ephippial females reached a maximum of 3.7%, a value comparable to that registered in summer in the GroBer Binnensee (North- ern Germany), a hypertrophic lake inhabited by fish, which was the source lake for our experimental clone. The number of ephippia released within 45 days was on average 34 ± 22. Ephippia formation could not result from the between-treatment differences in population density, and related patterns of food depletion, since no substantial difference between control and fish treatment was observed. Instead, specific information on the presence of a predator provided a cue which induced the formation of resting eggs in Daphnia. Under heavy predation and very low survival probability of parthenogenetic females, ephippia formation in summer can be adaptive, i.e. higher fitness can be achieved through sur- vival in the diapausing state than through the immediate reproductive gain via parthenogenesis.