Winter Dry Season Research Articles

Eogenetic Karst Hydrology: Insights from the 2004 Hurricanes, Peninsular Florida

Eogenetic karst lies geographically and temporally close to the depositional environment of limestone in warm marine water at low latitude, in areas marked by midafternoon thunderstorms during a summer rainy season. Spring hydrographs from such an environment in north-central Florida are characterized by smooth, months-long, seasonal maxima. The passage of Hurricanes Frances and Jeanne in September 2004 over three field locations shows how the eogenetic karst of the Upper Floridan Aquifer responds to unequivocal recharge events. Hydrographs at wells in the High Springs area, Rainbow Springs, and at Morris, Briar, and Bat Caves all responded promptly with a similar drawn-out rise to a maximum that extended long into the winter dry season. The timing indicates that the typical hydrograph of eogenetic karst is not the short-term fluctuations of springs in epigenic, telogenetic karst, or the smoothed response to all the summer thunderstorms, but rather the protracted response of the system to rainfall that exceeds a threshold. The similarity of cave and noncave hydrographs indicates distributed autogenic recharge and a free communication between secondary porosity and permeable matrix-both of which differ from the hydrology of epigenic, telogenetic karst. At Briar Cave, drip rates lagged behind the water table rise, suggesting that recharge was delivered by fractures, which control the cave's morphology. At High Springs, hydrographs at the Santa Fe River and a submerged conduit apparently connected to it show sharp maxima after the storms, unlike the other cave hydrographs. Our interpretation is that the caves, in general, are discontinuous.

Spatial and temporal patterns of near-surface chlorophyll a in the Great Barrier Reef lagoon

Surface chlorophyll a concentrations in the Great Barrier Reef (GBR) lagoon were monitored at individual stations for periods of 6 to 12 years. The monitoring program was established to detect spatial and temporal changes in water quality resulting from increased loads of nutrients exported from the catchments adjoining the GBR. Sampling occurred monthly at up to 86 sites that were located in transects across the width of the continental shelf. In the central and southern GBR (16–21°S), there was a persistent cross-shelf chlorophyll a gradient, with higher concentrations near the coast. No cross-shelf gradient was observed in the far northern GBR (12–15°S). Mean chlorophyll a concentrations in the far northern GBR (0.23 µg L–1) were less than half those in the south and central GBR (0.54 µg L–1). Chlorophyll a varied seasonally within regions, with mean summer-wet season (December–April) concentrations ~50% greater than those in the winter-dry season (May–November). Sub-annual, inter-annual and event-related variations in chlorophyll a concentrations were observed in several zones. Multi-year patterns in concentrations suggest that relatively short (5–8 years) time series may give spurious estimates of secular trends. Higher chlorophyll a concentrations in inshore waters south of 16°S were most likely related to the levels of river nutrient delivery associated with agricultural development on adjacent catchments.

Kinematics of a Translational/Rotational Landslide, Central Andes, Northwestern Argentina

The eastern foothills of the Central Andes, known as the Subandean Ranges, in Peru, Bolivia, and northwestern Argentina, are characterized by heavy rainfall, weakly cemented substrate rocks, thick regoliths, and bedding planes parallel to mountain slopes, features that create serious landslide hazards (Multinational Andean Project: Geoscience for Andean Communities, http://www.pma-map.com). A moderately sized landslide (the Termas Hill landslide) occurred in August 2003 on a slope of the Andean foothills in northwestern Argentina (Figure 1). The slide disrupted regolith and rock, leaving a steep-walled scarp and severing a 130-m-long segment of forest road. The sliding block travelled downslope a few tens of meters, undergoing fragmentation and torsion. On the basis of a topographic survey and structural evidence, this article discusses the geometry and kinematics of the Termas Hill landslide. Figure 1. Location maps. (A) South America with Argentina outlined and square representing inset B (TC = Tropic of Capricorn). (B) Salta Province (S = Salta City; RF = Rosario de la Frontera; TC = Tropic of Capricorn; open rectangle shows location of map in inset C). (C) Simplified geologic map overlaid on a Thematic Mapper satellite image (white rectangle represents area of landslide; x = campsite adjoining large pond; r = topographic ridge; f = reverse fault affecting Termas Hill landslide; Q = Quaternary deposits; A = Anta Formation, geology taken from Seggiaro and others, 1997). (D) Average rainfall between 2000 and 2005, inclusive; meteorological station located 30 km north from landslide site, in similar geomorphic and climatic situation. The Subandean Ranges in northwestern Argentina (22–26°S; Figure 1A and B) have a humid subtropical climate with annual precipitation of 700–1,200 mm and an average air temperature of 20°C. The climate is mild with a dry winter season. Rainfall is concentrated in the austral summer months and is of the monsoonal type (Figure 1D). The Subandean Ranges …

Mineralogical and geochemical study of element mobility at the sulfide-rich Excelsior waste rock dump from the polymetallic Zn–Pb–(Ag–Bi–Cu) deposit, Cerro de Pasco, Peru

We present a mineralogical and geochemical study of the sulfide-rich waste rock dump Excelsior (size: 94 ha) originating from the Cerro de Pasco mine (altitude: 4300 m a.s.l.), Central Andes, Peru. The aims of this study were: to characterise (1) the secondary mineral assemblage and (2) the acid mine drainage (AMD) from this waste rock dump. (3) This information was used to create a model of the element transport in and out of the waste rock dump under the highly variable mountain climate with high precipitation during the wet season and high evaporation during the dry season. The main ore minerals found in the polymetallic Pb–Zn–(Ag–Bi–Cu) deposit are pyrite, sphalerite, galena and enargite with minor finds of tennantite, covellite and cerrusite. Gangue was dominantly quartz ± hematite ± siderite ± muscovite. The waste rocks had a high potential of acid generation with low neutralization potential (estimated > 60 wt.% pyrite, < 5 wt.% calcite/dolomite) with an already acidic environment (average paste – pH 2.8). Gypsum, different types of jarosite and a variety of Fe-sulfates (e.g. melanterite (Fe(SO 4)·7H 2O) and rozenite (Fe(SO 4)·4H 2O)) were the dominant secondary minerals. Less frequent secondary minerals were: Fe(III)-hydroxides (schwertmannite (Fe 16O 16(OH) 12(SO 4) 2) , fibroferrite (Fe(SO 4)(OH)·5H 2O)), and Mg-, Mn- and Zn-sulfates (e.g. starkeyite (Mg(SO 4)·4H 2O), mallardite (Mn(SO 4)·7H 2O), goslarite (Zn(SO 4)·7H 2O), respectively). For the primary mineral assemblage, X-ray fluorescence analyses displayed average concentrations of the heavy metals: Cu 0.1 wt.%, Zn 1.1 wt.%, Pb 1.2 wt.% and Cd 40 mg/kg and of the metalloid As 0.15 wt.%. In secondary minerals an average enrichment of Cu: 0.8 wt.%, Zn: 2.9 wt.%, As: 0.27 wt.% and Cd: 71 mg/kg was observed. Effects of rain events on the waste rocks were simulated by water-leach tests of (1) solid samples from the top, representing waste rocks leached by infiltrating rainwater and (2) solid samples around the base, representing waste rocks affected by outcropping AMD generated in the waste rock dump. The leachates showed stored acidity (pH 1.2–5.6 of the leachates) and high solubility of secondary minerals (average electrical conductivity: 9.7 mS/cm and average concentrations for Fe: 928 mg/L, Zn: 315 mg/L, Cu: 7.5 mg/L, As: 4.1 mg/L, Cd: 1.59 mg/L, and Pb: 0.31 mg/L). The AMD output at springs at the base of the waste rock dump is chemically similar to the leachates (acidic pH (2.78–5.10), oxidizing E h (319–684 mV)), but higher charged with maximum concentrations for Fe: 5640 mg/L, Zn: 3000 mg/L, Cu: 161 mg/L, As: 8.0 mg/L, Cd: 6.6 mg/L, and with higher electrical conductivity (19–26 mS/cm). The data suggest that AMD formation is strongly controlled by the local climate. During the dry winter season, high evaporation of outcropping pore solutions and subsequently precipitation of efflorescent salts resulted in a heavy metal-enrichment at the base of the Excelsior waste rock dump. During the wet summer season, rain events caused the dissolution of most efflorescent salts, removed the enrichment at the base and resulted in a washout of acid solutions rich in Fe, Mn, Zn, Cu, Cd, As and S.

Effects of aerosols on the surface solar radiation in a tropical urban area

Surface radiation measurements at an urban site in southern Taiwan during the dry winter season, December 2003 to March 2004, are used to investigate the aerosol properties and the effects of aerosols on the surface solar radiation in clear skies. The AERONET‐retrieved monthly mean aerosol optical thickness at 0.5 μm ranges from 0.52 to 1.18 with a mean of 0.73 for the four winter months. The single‐scattering albedo and asymmetry factor remain nearly constant with a mean of ∼0.95 for the former and ∼0.70 for the latter. Thus the air of Tainan during the winter is highly polluted, and the aerosols are moderately absorbing. A new approach is developed to estimate the effect of aerosols on the surface radiation from surface observations. The relationship between the surface radiation and the aerosol optical thickness is established for narrow intervals of the solar zenith angle by regression of the atmospheric path transmission against the aerosol optical path. It is found that the relationship is surprisingly linear. On the basis of the relationship the effect of aerosols on the surface radiation and the sensitivity of surface radiation to the aerosol optical thickness are computed. For the four‐month average, the effect of aerosols is to reduce the incident surface solar radiation by ∼39 W m−2, and the sensitivity of the surface radiation to aerosols undergoes a reduction of ∼53 W m−2 per unit increase of the aerosol optical thickness at 0.5 μm. These results are in good agreement with radiative transfer model calculations.

African elephant home range and habitat selection in Pongola Game Reserve, South Africa

The ranging behaviour and habitat occupancy by three elephant groups (cow herd, bulls, and an orphan group) were studied over a two-year period in a small, fenced reserve. No summer dispersal was observed. Distinct seasonal home ranges were exhibited for all groups, with the summer (wet season) ranges being smaller than the winter (dry season) ranges. Home range size was much smaller than in other locations. The dam and surrounding high density of patches of vegetation of high nutritional quality are thought to be the reasons. Habitat selection was strongly evident with all of the elephant groups selecting River Line habitats in the dry season. In the wet season the cow herd and orphans selected the more open Acacia habitats and the bulls exhibited no significant habitat preference.

Incorporation of Auxiliary Information in the Geostatistical Simulation of Soil Nitrate Nitrogen

In north‐central Florida the potential risk for movement of nitrate into the aquifer is high due to the large extent of well‐drained marine‐derived quartz sand overlying porous limestone material coupled with high precipitation rates. Our objective was to estimate spatio‐seasonal distributions of soil NO3–N across the Santa Fe River Watershed in north‐central Florida. We conducted spatially distributed synoptic and seasonal sampling (September 2003—wet summer/fall season, January 2004—dry winter season, May 2004—dry spring season) of soil NO3–N. Prior distributions of probability for NO3–N were inferred at each location across the watershed using ordered logistic regression. Explanatory variables included environmental spatial datasets such as land use, drainage class, and the Floridian aquifer DRASTIC index. These prior probabilities were then updated using indicator kriging, and multiple realizations of the spatial distribution of soil NO3–N were generated by sequential indicator simulation. Cross‐validation indicated that smaller prediction errors are obtained when secondary information is incorporated in the analysis and when indicator kriging is used instead of ordinary kriging to analyze these datasets characterized by the presence of extreme high values and a nonnegligible number of data below the detection limit. The NO3–N values were lowest in September 2003 as a result of excessive leaching caused by large, intense tropical storms. Overall the NO3–N values in January 2004 were high and could be attributed to fertilization of crops and pastures, low plant uptake, and low microbial transformation during the winter period. Despite seasonal trends reflected by the values of observed and estimated NO3–N, we found areas that showed consistently high soil NO3–N throughout all seasons. Those areas are prime targets to implement best management practices.

Effects of taxonomic and numeric resolution on the ability to detect ecological patterns at a local scale using stream macroinvertebrates

With 3 figures and 3 tables Abstract: The increasing demand for methods of rapid stream bioassessment has stim- ulated the evaluation of data simplification. In particular, these studies have assessed how much power is lost when species/morphospecies identification is replaced by family identifications or use of EPT (Ephemeroptera, Plecoptera and Trichoptera) taxa only. A second simplifying factor commonly evaluated is the use of presence/absence data instead of density. These simplifications have provided valid results in most cases where differences among groups are large, particularly in studies comparing impacted vs. non-impacted stream sites and ecological studies involving large spatial scales. Here I evaluate whether data simplification, both in terms of taxonomic (families, mor- phospecies of EPT) and numeric (presence/absence) resolutions, is valid for ecological studies done at local scales, where differences among groups are subtle. Datasets used are derived from a five-year study of five stream sites situated in a catchment in south- east Brazil. Streams were sampled twice a year, in the rainy (summer) and dry (winter) seasons. I used Analysis of Similarity (ANOSIM) to evaluate if differences i) among stream sites and ii) between seasons within a stream site, revealed by using the full data set (morphospecies, quantitative data), were also detected when using the sim- plified datasets. The effect of taxonomic resolution was not significant; the two sim- plified levels of this factor (morphospecies of EPT, families) were able to recover the same groups revealed by the full dataset. However, the use of presence/absence data had a strong negative effect on the ability to distinguish groups, particularly when dif- ferences were small (between seasons within a stream site). The success in recovering groups using simplified taxonomic data agrees with previous evaluations done using datasets from applied fields and those from ecological studies involving large spatial scales. However, in contrast to results observed in applied and large-scale studies, use of simplified data quantification in local datasets resulted in significant loss of infor-

Ecology of Chytridiomycosis in Rainforest Stream Frog Assemblages of Tropical Queensland

Abstract: In the wet tropics of Queensland, Australia, eight species of stream‐dwelling frogs have experienced population declines. Some declines were associated with an emerging infectious disease of amphibians (chytridiomycosis) caused by the fungus Batrachochytrium dendrobatidis. We examined the spatial and temporal pattern of infection prevalence in a sample of frog populations. Infected adults and tadpoles of all species were found, and infections occurred at every site. Infection prevalence varied among species and was always &lt; 10.0% in adults but ranged from 0.75 to 76.0% in tadpoles. In this system tadpoles and adults of some species may act as disease reservoirs, experiencing avirulent infections, whereas other hosts (declining species) experience virulent infections. Infection prevalence was higher during the cool, dry winter season (May to September) and at high elevations (600–800 m), suggesting regulation by environmental conditions, including temperature and precipitation. We found no relationships between infection prevalence and mean body condition, fluctuating asymmetry of hind limbs, population density, or the presence of metamorphosing tadpoles and juvenile frogs. Although it is not certain whether chytridiomycosis was responsible for past frog population declines in the wet tropics of Queensland, the pathogen is now endemic. Our data indicate that at the landscape level, environmental conditions have strong effects on host‐pathogen dynamics. These effects interact with species‐specific behavior or immune function and may be important underlying determinants of chytridiomycosis epizootics and emergence.

Estimating changes in heat energy stored within a column of wetland surface water and factors controlling their importance in the surface energy budget

Changes in heat energy stored within a column of wetland surface water can be a considerable component of the surface energy budget, an attribute that is demonstrated by comparing changes in stored heat energy to net radiation at seven sites in the wetland areas of southern Florida, including the Everglades. The magnitude of changes in stored heat energy approached the magnitude of net radiation more often during the winter dry season than during the summer wet season. Furthermore, the magnitude of changes in stored heat energy in wetland surface water generally decreased as surface energy budgets were upscaled temporally. A new method was developed to estimate changes in stored heat energy that overcomes an important data limitation, namely, the limited spatial and temporal availability of water temperature measurements. The new method is instead based on readily available air temperature measurements and relies on the convolution of air temperature changes with a regression‐defined transfer function to estimate changes in water temperature. The convolution‐computed water temperature changes are used with water depths and heat capacity to estimate changes in stored heat energy within the Everglades wetland areas. These results likely can be adapted to other humid subtropical wetlands characterized by open water, saw grass, and rush vegetation type communities.

Land‐surface, boundary layer, and cloud‐field coupling over the southwestern Amazon in ERA‐40

Models are powerful tools for understanding the coupling of physical processes. We illustrate this using averages from ERA‐40 for the Madeira River, a southwestern basin of the Amazon, which has a large seasonal cycle with a dry season in the austral winter. Daily‐mean land‐surface fluxes and state variables can be used to map the transitions of the surface “climate” of a model and to quantify the links between the soil moisture, the mean cloud‐base and cloud field, the shortwave and longwave radiation fields at the surface, the vertical motion field, the atmospheric precipitable water, and the surface precipitation. The links that are visible on a daily timescale can also be seen on the seasonal timescale. Several important surface processes are strongly influenced by soil moisture: relative humidity, which gives the mixed subcloud layer depth, low cloud cover, and the surface net long‐wave flux. The link between soil moisture and equivalent potential temperature can therefore be clearly seen once the temperature dependence is filtered. Surface evaporation is controlled as much by the feedback of the cloud field on the surface radiation budget as by soil moisture. Above the surface the cloud field and precipitation are coupled to the large‐scale dynamics, specifically the midtropospheric omega field. The shortwave cloud forcing of the atmosphere and the surface is given by the cloud field albedo at the top of the atmosphere to better than 1%. We have developed a new methodology for understanding the coupling and feedbacks between physical processes in models, so that different models can be compared with each other and with data.

Interannual Variations of Aerosol Optical Depth over Coastal India: Relation to Synoptic Meteorology

Abstract Interannual variations in spectral aerosol optical depths (AOD) were examined using the data obtained from a chain of ground-based multiwavelength solar radiometers from various locations of the Indian peninsula during the dry winter season (January–March) of 1996–2001. All of the stations revealed significant interannual variations, even though the spatial pattern of the variations differed over the years. These interannual variations were found to be significantly influenced by the extent of the southward excursion of the intertropical convergence zone (ITCZ). The years in which the southward excursion of the ITCZ was less (i.e., the years when the wintertime ITCZ was closer to the equator) showed higher AODs than the years in which the ITCZ moved far southward. The spatial variation was found to be influenced by large-scale vertical descent of an air mass over peninsular India, the Arabian Sea, the Indian Ocean, and the Bay of Bengal.

Effects of winter crop and supplemental irrigation on crop yield, water use efficiency and profitability in rainfed rice based cropping system of eastern India

Soil moisture availability is the main limiting factor for growing second crops in rainfed rice fallows of eastern India. Only rainfed rice is grown with traditional practices during the rainy season (June–October) with large areas (13 m ha −1) remaining fallow during the subsequent dry season (November–March) inspite of annual rainfall of the order 1000–2000 mm. In this study an attempt was made to improve productivity of rainfed rice during rainy season and to grow second crops in rice fallow during dry (winter) season with supplemental irrigation from harvested rainwater. Rice was grown as first crop with improved as well as traditional farmers’ management practices to compare the productivity between these two treatments. Study revealed that 87.1–95.6% higher yield of rice was obtained with improved management over farmers’ practices. Five crops viz., maize, groundnut, sunflower, wheat and potato were grown in rice fallow during dry (winter) season with two, three and four supplemental irrigations and improved management. Sufficient amount of excess rainwater (runoff) was available (381 mm at 75% probability level) to store and recycle for supplementary irrigation to second crops grown after rice. Study revealed that supplemental irrigation had significant effect ( P < 0.001) on grain yield of dry season crops and with two irrigation mean yields of 1845, 785, 905, 1420, 8050 kg ha −1 were obtained with maize (grain), groundnut, sunflower, wheat and potato (tuber), respectively. With four irrigations 214, 89, 78, 81, 54% yield was enhanced over two irrigations in respective five crops. Water use efficiency (WUE) of 13.8, 3.35, 3.39, 5.85 and 28.7 kg ha −1 was obtained in maize, groundnut, sunflower, wheat, potato (tuber), respectively with four irrigations. The different plant growth parameters like maximum above ground biomass, leaf area index and root length were also recorded with different levels of supplemental irrigation. The study amply revealed that there was scope to improve productivity of rainfed rice during rainy season and to grow another profitable crops during winter/dry season in rice fallow with supplemental irrigation from harvested rainwater of rainy season.

Leaf dynamics and above ground biomass growth in Dendrocalamus longispathus Kurz

Leaf production and culm growth as affected by different age groups of culms in a 10-year-old clump of Dendrocalamus longispathus Kurz were studied at Chittagong, Bangladesh. The total above ground biomass, bud break, branching pattern, leaf number and area produced by each age group of culms were investigated. The progressive increment of biomass-related morphometric parameters correlated optimally with the age of the clump. As the clumps become aged, the culms emerged in subsequent years were gradually taller with bigger diameter and more internodes. Leaf growth and defoliation are a dynamic process where leaf growth started in the first year of culm emergence but there is no defoliation. In 18–21-month-old culms the number and area of leaf, and biomass of branches, leaves and culm were highest; defoliation started at the end of the rainy season and continued in the winter dry season. In the third and fourth years leaf production and growth were getting low, but in the fifth and sixth years these sharply declined and ultimately the culm died. Thus harvesting of culm within 3 to 4 years of age could be an ideal management practice in the species.

Dilute Nectar in Dry Atmospheres: Nectar Secretion Patterns in Aloe castanea (Asphodelaceae)

Aloe species commonly flower during the winter dry season in southern Africa and produce abundant dilute nectar. We investigated variability in nectar production and availability in Aloe castanea because evaporation is more likely from its open flowers than from the tubular flowers of most other Aloe species. The greatest variability in nectar production was associated with flower age, and weather conditions and individual plants also had significant effects. However, when unscreened flowers of similar age were sampled throughout a clear day, nectar volumes and concentrations were remarkably constant, and concentrations did not exceed 10% w/w. Variability in concentration could be reduced by reabsorption of sugars, but there was no evidence of reabsorption after addition of relatively concentrated nectar (26.6%) to flowers. It appears that rapid secretion throughout the day accounts for the constant low concentration.

Photosynthetic responses to vapour pressure deficit in temperate and tropical evergreen rainforest trees of Australia

Rainforests occur in high precipitation areas of eastern Australia, along a gradient in seasonality of precipitation, ranging from a summer dry season in the temperate south to a winter dry season in the tropical north. The response of net photosynthesis to increasing vapour pressure deficit (VPD) was measured in a range of Australian rainforest trees from different latitudes to investigate possible differences in their response to atmospheric drought. Plants were grown in glasshouses under ambient or low VPD to determine the effect of growth VPD on the photosynthetic response. Temperate species, which experience low summer precipitation, were found to maintain maximum net photosynthesis over the measurement range of VPD (0.5-1.9 kPa). In contrast, the tropical species from climates with high summer precipitation showed large reductions in net photosynthesis with increasing VPD. Temperate species showed higher intrinsic water-use efficiencies under low VPD than the tropical species, whereas their efficiencies were similar under high VPD. Growing plants under a low VPD had little effect on either the photosynthetic response to VPD or the intrinsic water-use efficiency of the species. These different responses of gas exchange to VPD shown by the tropical and temperate rainforest species may reflect different strategies to maximise productivity in their respective climates.

A model of the plume front of the Pearl River Estuary, China and adjacent coastal waters in the winter dry season

The Princeton Ocean Model was employed for a detailed examination of the plume front dynamics of the Pearl River Estuary (PRE), China, and the small scale circulation associated with the plume front in the dry season during the winter. In general, the plume front in the PRE is formed by the salinity gradient between the riverine water and the higher salinity shelf waters. Although the basic features in the deeper waters of the plume front of the PRE are similar with respect to tidal variations and, wind and river discharge, both the tide and river discharge affect the subsurface front, while these dynamic factors modify the surface features of the plume front.A two-layer circulation in the vertical occurs within the plume front, while at the same time a horizontal circulation converges in the plume frontal zone. The density-driven current that is associated with the frontal dynamics plays a dominant role in modifying the dynamic behavior (both the strength and the scale) of the circulation. Basically, the small scale circulation associated with the plume front dynamics dominates the estuarine dynamics as well as the dynamic behavior of the western coastal part of the plume front. Moreover, most of the diluted water is transported along the plume front from the estuary to the western coastal region due to the fact that most of the water converges on two sides of the plume front. The sub-tidal current plays an important role in transporting suspended substances along the plume front during a spring tide due to the non-linear effect of the tide on the heterogeneous density field and on the topography.

Ecophysiology of the pitayo de Queretaro ( Stenocereus queretaroensis)

Pitayos ( Stenocereus spp.) are columnar cacti native to subtropical regions of Mexico that produce edible fruits. Vegetative and reproductive growth for S. qureretaroensis occurs in the dry season but not simultaneously. Most daily net CO 2 uptake by S. queretaroensis occurs at night, with the highest values during the late autumn and early winter dry season. Its fine roots are colonized by arbuscular mycorrhizal fungi that enhance stem and fruit growth, apparently due to better P nutrition. The seeds are small, and germinate in response to light. The fruits of S. queretaroensis are valuable resources to wild animals, and can help sequester atmospheric carbon during the dry season.

Stomatal sensitivity to vapour pressure deficit of temperate and tropical evergreen rainforest trees of Australia

Although rainforests of eastern Australia grow in regions of high precipitation, there is a shift from a summer dry season in the temperate south to a winter dry season in the tropical north. Therefore, rainforest trees of eastern Australia provide an opportunity to investigate stomatal sensitivity of mesic trees to vapour pressure deficit (VPD) along a gradient in seasonality of precipitation. Eight rainforest canopy tree species were selected to cover the latitudinal range of rainforests in eastern Australia. Seedlings of these species were grown for a year in glasshouses under ambient conditions or at low VPD and water vapour exchange of leaves was measured during summer. Tropical species, which experience summer-dominant precipitation, showed higher stomatal sensitivities to VPD than temperate species, which experience winter-dominant precipitation. Growing plants under a low VPD increased stomatal sensitivity to increasing VPD in most species. The high stomatal sensitivity to VPD of the tropical species is consistent with the infrequent water stress experienced during their growing season and suggests a high susceptibility to water deficits. In contrast, temperate species may use other mechanisms to maintain photosynthesis under the relatively drier conditions of the temperate growing season.

Chemical characterization of rainwater at a developing urban habitat of Northern India

A comprehensive study of the chemical composition of rainwater was carried out from June 1999 to September 2001 at Lucknow, India. The rainwater was found to be alkaline with a mean pH of 6.7 in winter season and 6.5 in monsoons. It was observed during the study that Ca was the most abundant ion and along with Mg and NH 4 it forms equilibrium reactions with acids. Analysis of Variation (ANOVA) indicates that concentration of major ions was higher during cold climatic conditions probably due to dry season in winter leading to low dilution phenomena. The data was subjected to factor analysis based on Principal Component Analysis using the SPSS software (Version 7.5). The rotated factor matrix was employed to group variables into four factors. The first factor included Ca, Mg, SO 4, NO 3 and NH 4 attributed to soil derivatives and biogenic activities. Factor 2 loaded with Na, K, and Cl, may be linked to emissions from traditional combustion activities. Factor 3 and 4 include Cu, Zn, Fe and Ni, which may be attributed to industrial activities and scavenging process cycles.