Seasonal Environmental Variation Research Articles

Trophic niche breadth and niche overlap in a guild of flower-visiting bees in a Brazilian dry forest

Trophic niche breadth and niche overlap of bees were studied in a region of Caatinga (a deciduous dry thorn scrub forest) in Brazil with the lowest mean annual rainfall of the country, highly seasonal environmental variation, and an unpredictable rainy season. A null model approach was used to determine if the observed niche overlap in the community differed from that expected by chance. In general, even bee species with wider trophic niches concentrated foraging efforts on flowers of only a few of the available plant species, with low trophic niche overlap between pairs of species and among all species in the community. A randomization test showed niche overlap among the 10 common species in the guild to be significantly less than expected by chance, suggesting the existence of functional complementarity. The structure of communities defined by high functional complementarity is likely to be more sensitive to variation in available resources (e.g., richness and abundance of floral resources for bees). Ecosystem services provided by such communities may be more greatly affected by environmental changes (anthropogenic activities and climate change) than are services provided by communities with greater functional redundancy.

Abundance and Single-Cell Activity of Heterotrophic Bacterial Groups in the Western Arctic Ocean in Summer and Winter

Environmental conditions in the western Arctic Ocean range from constant light and nutrient depletion in summer to complete darkness and sea ice cover in winter. This seasonal environmental variation is likely to have an effect on the use of dissolved organic matter (DOM) by heterotrophic bacteria in surface water. However, this effect is not well studied and we know little about the activity of specific bacterial clades in the surface oceans. The use of DOM by three bacterial subgroups in both winter and summer was examined by microautoradiography combined with fluorescence in situ hybridization. We found selective use of substrates by these groups, although the abundances of Ant4D3 (Antarctic Gammaproteobacteria), Polaribacter (Bacteroidetes), and SAR11 (Alphaproteobacteria) were not different between summer and winter in the Beaufort and Chukchi Seas. The number of cells taking up glucose within all three bacterial groups decreased significantly from summer to winter, while the percentage of cells using leucine did not show a clear pattern between seasons. The uptake of the amino acid mix increased substantially from summer to winter by the Ant4D3 group, although such a large increase in uptake was not seen for the other two groups. Use of glucose by bacteria, but not use of leucine or the amino acid mix, related strongly to inorganic nutrients, chlorophyll a, and other environmental factors. Our results suggest a switch in use of dissolved organic substrates from summer to winter and that the three phylogenetic subgroups examined fill different niches in DOM use in the two seasons.

Seasonal environments, episodic density compensation and dynamics of structure of chiropteran frugivore guilds in Paraguayan Atlantic forest

Seasonal environmental variation experienced in the subtropics may contribute substantially to dynamics of community structure. This is particularly true for Neotropical bats because the geographic terminus of most families occurs there. Paraguayan Atlantic forest provides an ideal opportunity to evaluate effects of seasonality on structure of communities; it exhibits notable spatial and seasonal environmental variation and lies near the edge of the geographic distribution of most tropical bat species occurring there. We examined seasonality of bat populations and communities as well as correspondence to seasonal environmental conditions in eastern Paraguay. Most species exhibited lower abundances in the cool than in the warm season. Nonetheless, magnitude of differences was species-specific. Accordingly, highly significant differences between warm and cool seasons existed regarding species composition, evenness and diversity. Moreover, consistent with competition theory, magnitude of positive correlation between morphological distance and abundance and hence degree of structure was greater in the cool than warm season. Across the New World, seasonality assumes various forms (i.e. cold winters, dry and wet seasons) suggesting that better understanding of mechanistic bases of bat community structure in general may come from seasonal perspectives.

Environmental controls on microbial community cycling in modern marine stromatolites

Living stromatolites on the margins of Exuma Sound, Bahamas, are the only examples of modern stromatolites forming in open marine conditions similar to those that may have existed on Precambrian platforms. Six microbial mat types have previously been documented on the surfaces of stromatolites along the eastern side of Highborne Cay (Schizothrix, Solentia, heterotrophic biofilm, stalked diatom, tube diatom and Phormidium mats). Cycling of these communities create laminae with distinct microstructures. Subsurface laminae thus represent a chronology of former surface mats.The present study documents the effects of environmental factors on surface microbial communities of modern marine stromatolites and identifies potential causes of microbial mat cycling. Mat type and burial state at 43 markers along a stromatolitic reef on the margin of Highborne Cay were monitored over a two-year period (2005–2006). Key environmental parameters (i.e., temperature, light, wind, water chemistry) were also monitored.Results indicated that the composition of stromatolite surface mats and transitions from one mat type to another are controlled by both seasonal and stochastic events. All six stromatolite mat communities at Highborne Cay showed significant correlations with water temperature. Heterotrophic biofilms, Solentia, stalked diatom and Phormidium mats showed positive correlations with temperature, whereas Schizothrix and tube diatom communities showed negative correlations. A significant correlation with light (photosynthetically active radiation, PAR) was detected only for the heterotrophic biofilm community. No significant correlations were found between mat type and the monitored wind intensity data, but field observations indicated that wind-related events such as storms and sand abrasion play important roles in the transitions from one mat type to another.An integrated model of stromatolite mat community cycling is developed that includes both predictable seasonal environmental variation and stochastic events. The long-term monitoring of mat communities on Highborne Cay stromatolites and the resulting model are an important step in understanding morphogenesis of modern marine stromatolites, with implications for interpreting patterns of stromatolite lamination in the geologic record.

The ranging behaviour of a large sexually dimorphic herbivore in response to seasonal and annual environmental variation

AbstractThe allometric relationships of body size play a principle role in determining how large herbivores respond to the marked spatial and temporal heterogeneity of the savanna biome. Using location data collected over an 8‐year period from five distinct study sites, we investigated the influence of environmental variation (using phenological and rainfall data) on the ranging behaviour of the African elephant (Loxodonta africana), a species that exhibits pronounced sexual dimorphism. Both sexes expanded their annual ranges during years of high rainfall and contracted their ranges during periods of resource scarcity, concurring with the hypothesis that abiotic factors dictate the distribution of large generalist herbivores at the landscape scale. However, female elephant did not exhibit the same consistent response to rainfall at the seasonal scale. Furthermore, male elephant demonstrated a reduction in their daily displacement distances during the dry winter season, and altered their movement rates on the basis of seasonal rainfall. These results suggest that male elephant are able to consistently adapt their movement behaviour according to forage quality and abundance. Smaller‐bodied female elephant on the other hand, are unlikely to exhibit the same flexibility in their ranging behaviour because of their higher relative nutritional demands, lower tolerance to fibrous forage and the social and energetic constraints of group living with juveniles. Our study highlights the major role that body size and sociality plays in the decision making of sexually dimorphic herbivores. These differences can have important implications for effective conservation and management, particularly with regard to demographic (e.g. survival) and ecological (e.g. habitat use) factors.

The molecular physiology of increased egg desiccation resistance during diapause in the invasive mosquito,Aedes albopictus

Photoperiodic diapause is a crucial adaptation to seasonal environmental variation in a wide range of arthropods, but relatively little is known regarding the molecular basis of this important trait. In temperate populations of the mosquito Aedes albopictus, exposure to short-day (SD) lengths causes the female to produce diapause eggs. Tropical populations do not undergo a photoperiodic diapause. We identified a fatty acyl coA elongase transcript that is more abundant under SD versus long-day (LD) photoperiods in mature oocyte tissue of replicate temperate, but not tropical, A. albopictus populations. Fatty acyl CoA elongases are involved in the synthesis of long chain fatty acids (hydrocarbon precursors). Diapause eggs from a temperate population had one-third more surface hydrocarbons and one-half the water loss rates of non-diapause eggs. Eggs from a tropical population reared under SD and LD photoperiods did not differ in surface hydrocarbon abundance or water loss rates. In both a temperate and tropical population, composition of hydrocarbon chain lengths did not differ between eggs from SD versus LD conditions. These results implicate the expression of fatty acyl coA elongase and changes in quantity, but not composition, of egg surface hydrocarbons as important components of increased desiccation resistance during diapause in A. albopictus.

The odontocete community and its environment in the southwestern Gulf of California

Community structure is a function of the number of species, their relative abundance and the characteristics of the dominant, common and rare species that are part of it. It also can be described by changes in its physical and biological environment. The aim of the present work is to describe the odontocete community, its temporal changes and the relationship with environmental variability and food availability in the southwestern Gulf of California (GC). Information was obtained from 21 sampling trips from September 2003 to March 2006 between La Paz Bay and Loreto, with a sampling effort of 8769.1km. We recorded the presence, location and other biological parameters of odontocete sightings. Data on environmental variability was obtained from satellite images of sea surface temperature and chlorophyll concentration, and food availability from published reports. A total of 30201 odontocete cetaceans were recorded from 353 sightings, belonging to 10 different species. We observed a temporal lag between the peaks in productivity and an increased presence of odontocete species. The community structure showed a seasonal change in the abundance of the dominant (Tursiops truncatus and Delphinus sp.) and common species (Globicephala macrorhynchus and Kogia sp.), as well as by the absence or presence of scarce (Physeter macrocephalus and Orcinus orca) and rare species (Pseudorca crassidens and Lagenorhynchus obliquidens). This seasonal community change is in agreement with the known seasonal movements of its main prey inside the GC, which, in turn, is related to seasonal environmental variation. We observed that the community structure was dominated by fish-eating species during the temperate season and responded to the increased presence and aggregation of sardines (Sardinops sagax caerulea) in the southern GC, whereas the warm season was dominated by squid-eating species and related to the increased presence and aggregation of the jumbo squid (Dosidicus gigas) in the GC's west coast.

The maintenance of mixed mating by cleistogamy in the perennial violet Viola septemloba (Violaceae)

The production of both potentially outcrossed (chasmogamous) and obligately self-fertilized (cleistogamous) flowers presents a clear exception to the prediction that the only evolutionarily stable mating systems are complete selfing and complete outcrossing. Although cleistogamy has evolved repeatedly, the reason for its stability is not known for any species. We tested the hypothesis that the production of cleistogamous and chasmogamous flowers by a perennial violet constitutes adaptive phenotypic plasticity. We manipulated the season of flowering for each flower type and determined fruit set and the germination percentage of seeds produced by cleistogamous and chasmogamous flowers to test the hypothesis that adaptive plastic response to seasonal environmental variation makes mixed mating stable. Cleistogamous flowers had greater fruit set in all seasons and produced seeds with germination percentages as great as or greater than those from chasmogamous flowers. The consistent advantage of cleistogamous flowers is clearly not consistent with a role of adaptive plastic response to seasonal variation. The biomass cost of seed production by chasmogamous flowers was nearly three times that for cleistogamous flowers. Explaining why chasmogamous flower have not been eliminated by natural selection requires that this difference be balanced by an advantage to chasmogamous flowers that has not yet been identified.

Metal concentration of PM 2.5 and PM 10 particles and seasonal variations in urban and rural environment of Agra, India

Three monthly 24-hour samples of airborne aerosols (PM 10 and PM 2.5) were collected at an urban and a rural site of the North central, semi-arid part of India during May 2006 to March 2008. Seven trace metals (Pb, Zn, Ni, Fe, Mn, Cr and Cu) were determined for both sizes. The annual mean concentration for PM 10 was 154.2 µg/m 3 and 148.4 µg/m 3 at urban and rural sites whereas PM 2.5 mean concentration was 104.9 µg/m 3 and 91.1 µg/m 3 at urban and rural sites, respectively. Concentrations of PM 10 and PM 2.5 have been compared with prescribed WHO standards and NAAQS given by CPCB India and were found to be higher. Weekday/weekend variations of PM 10 and PM 2.5 have been studied at both monitoring sites. Lower particulate pollutant levels were found during weekends, which suggested that anthropogenic activities are major contributor of higher ambient particulate concentration during weekdays. Significant seasonal variations of particulate pollutants were obtained using the daily average concentration of PM 10 and PM 2.5 during the study period. PM 2.5/PM 10 ratios at urban and rural sites were also determined during the study period, which also showed variation between the seasons. Three factors have been identified using Principal Component Analysis at the sampling sites comprising resuspension of road dust due to vehicular activities, solid waste incineration, and industrial emission at urban site whereas resuspension of soil dust due to vehicular emission, construction activities and wind blown dust carrying industrial emission, were common sources at rural site.

Micropropagation of Populus trichocarpa ‘Nisqually-1’: the genotype deriving the Populus reference genome

Populus serves as a model tree for biotechnology and molecular biology research due to the availability of the reference genome sequence of Populustrichocarpa (Torr. & Gray) genotype ‘Nisqually-1’. However, ‘Nisqually-1’ has been shown to be very recalcitrant to micropropagation, regeneration and transformation. In this study, a highly efficient micropropagation protocol from greenhouse-grown shoot tips of ‘Nisqually-1’ was established. The optimal micropropagation protocol involves growing in vitro shoots in plant growth regulator-free Murashige and Skoog (MS) basal medium supplemented with 3% sucrose, 0.3% Gelrite® and 5–10 g L−1 of activated charcoal. Plants grown on this medium were significantly longer, and contained significantly higher concentrations of chlorophyll. This highly effective protocol provides a consistent supply of quality leaf and stem materials throughout the year for transformation experiments and other in vitro manipulations, therefore eliminating inconsistency due to seasonal and greenhouse environmental variations and the need for repetitive tissue sterilization.

Reproductive timing and patterns of development for the damselfly Coenagrion puella in the field

By a combination of detailed behavioral observations and molecular genetic approaches we have assessed development time, timing of first maturity, and the extent of genetic structure through the flying season in a wild population of the damselfly Coenagrion puella in England. This work provides the first estimate of development time (egg to mature adult) in the field based on individual damselflies. Development time was significantly longer for females than males. In contrast to reported laboratory studies, there was no difference in development times between different female color morphs. Development time ranged between 347 and 396 days and was negatively correlated with egg-laying date. As a result eggs laid early in one season reach adult maturity relatively late in the next; concurrently individuals developing from eggs laid late mature relatively early. We speculate that this pattern of development is a direct physiological response to seasonal environmental variation and results in reproductive synchrony within a population. Size, specifically hind wing length, declined with development time in males, but not in females. In one of the two years of the study there was evidence for weak clustering of related individuals during the reproductive season. This appeared to be the result of developmental synchronization within families: variance in timing of maturation was smaller in full-sib families than in half-sib families or randomly assigned unrelated groups.

Biometric, microstructural, and high-resolution trace element studies in Crassostrea gigas of Cantabria (Bay of Biscay, Spain): Anthropogenic and seasonal influences

Living Crassostrea gigas oysters of different ages and sizes were collected in three estuaries of Cantabria (Bay of Biscay, Spain): San Vicente de la Barquera Estuary, Santander Bay, and Marismas de Santoña Estuary. The main objective was to determine different shell responses to variable environmental parameters. A shell morphological study, based on three biometric indices, indicates that oysters of Santander Bay have two significant shell anomalies: abnormal thickening of the right valve and loss of vital cavity volume. These shell abnormalities are related with the presence in these waters of the chemical tributyltin. In the other two estuaries, the oysters show no detectable anomalies. Four shell microstructures have been distinguished: Regular Simple Prismatic, Regular Foliated, cone-Complex Cross Foliated, and Chalk. In Santander Bay oysters, the Chalk forms a “root-type” framework, whereas in the other two estuaries it forms a more compact microstructure. It is proposed that exposure to tributyltin has produced this modification. High-spatial-resolution geochemical transects have been carried out on the Regular Foliated microstructure in the umbo region in order to evaluate the distribution of Mg, Sr, and Na. The elements analysed exhibit clear cyclic variations in San Vicente de la Barquera Estuary and Marismas de Santoña Estuary oysters, related with seasonal periods, and characterised by broad maxima during months in which the waters are warmer and have higher salinity. These patterns are buffered in Santander Bay oysters. Our results demonstrate that biometric, microstructural, and high-resolution trace element studies in oyster shells can provide information about contaminants and seasonal variations in the estuarine environment.

Population dynamics of a freshwater calanoid copepod: Complex responses to changes in trophic status and climate variability

The long‐term dynamics of the calanoid copepod Eudiaptomus gracilis were analyzed in Lake Constance, a deep lake that has been influenced strongly by changes in trophic status and climate variability during the last few decades. Although copepod abundances remained rather stable throughout the study period (1970‐1995), the seasonal pattern changed strongly, including a seasonal shift in the timing of peak abundance from spring to late summer with increasing oligotrophication. This shift in seasonality resulted from seasonally opposing long‐term trends in abundances (a reduction in abundances in spring and an increase in summer) possibly due to seasonally opposing long‐term trends in naupliar mortality (an increase in late winter mortality and a decrease in early summer mortality). The changes in seasonality were most pronounced within the early copepodid stages, whereas the long duration of the adult stage seemed to buffer the adult dynamics against seasonal environmental variability. The effects of climate variability on population dynamics were more subtle and consisted of faster development in spring in years with faster vernal warming. Furthermore, the accelerated development in spring resulted in earlier occurrence of the population minimum in summer and subsequently in an earlier abundance increase in late summer/autumn. Hence, abundances in summer/autumn were still related to spring climate variability, which shows that spring environmental variability can be transferred further into the season by the cohort dynamics of continuously reproducing populations.

SELECTION ON HERITABLE SEASONAL PHENOTYPIC PLASTICITY OF BODY MASS

The ability to cope with environmental change is fundamental to a species' evolution. Organisms can respond to seasonal environmental variation through phenotypic plasticity. The substantial plasticity in body mass of temperate species has often been considered a simple consequence of change in environmental quality, but could also have evolved as an adaptation to seasonality. We investigated the genetic basis of, and selection acting on, seasonal plasticity in body mass for wild bighorn sheep ewes (Ovis canadensis) at Ram Mountain, Alberta, under two contrasting environmental conditions. Heritability of plasticity, estimated as mass-specific summer and winter mass changes, was low but significant. The additive genetic variance component of relative summer mass change was greater under good environmental conditions (characterized by a population increase and high juvenile survival) than under poor conditions (population decrease and low juvenile survival). Additive genetic variance of relative winter mass change appeared independent of environmental conditions. We found evidence of selection on summer (relative) and winter (relative and absolute) mass change. For a given mass, more plastic individuals (with greater seasonal mass changes) achieve greater fitness through reproduction in the following year. However, genetic correlations between mass parameters were positive. Our study supports the hypothesis that seasonal plasticity in body mass in vertebrates is an adaptation that evolved under natural selection to cope with environmental variation but genetic correlations with other traits might limit its evolutionary potential.

Crabeater seal diving behaviour in eastern Antarctica

Southern Ocean waters are highly productive and contain important food resources for many indigenous predators, including humans. Management of these resources has fallen under the regulation of the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR), which has identified a suite of predators as indicator species for monitoring ecosystem fluctuations, including crabeater seals. For crabeater seals to fulfil this role, however, they must respond predictably to fluctuations in krill distribution and abundance. Here, we investigated the validity of using the diving behaviour of this species as an indicator of krill distribution and abun- dance. We used behavioural data collected from 23 crabeater seals fitted with satellite-linked time- depth recorders off eastern Antarctica to quantify habitat use as a function of the amount of time they spent within geographic regions with varying environmental characteristics. This was then linked with diving behaviour in those regions. By integrating geographic location and diving parameters, we demonstrated that habitat use and foraging behaviour within eastern Antarctic waters fluctuated in response to seasonal and spatial environmental variability. Our attempts to use oceanographic variables to develop models of crabeater seal habitat use and behaviour demonstrated real limitations in inferring behaviour from a simple set of environmental factors, but we identified ocean depth and the proximity to the ice edge as factors influencing seasonal habitat use and diving behaviour. Whilst our understanding of the influences driving crabeater seal distribution has improved as a result of telemetry studies, it would appear premature to infer cross-species patterns in distribution and abun- dance with krill given the low predictive power of models derived in the present study. Furthermore, the dynamic and regionally variable use of pelagic habitat by this widely abundant Antarctic preda- tor has important implications for the estimation of crabeater seal biomass.

Patterns of tree growth in relation to environmental variability in the tropical dry deciduous forest at Mudumalai, southern India

Tree diameter growth is sensitive to environmental fluctuations and tropical dry forests experience high seasonal and inter-annual environmental variation. Tree growth rates in a large permanent plot at Mudumalai, southern India, were examined for the influences of rainfall and three intrinsic factors (size, species and growth form) during three 4-year intervals over the period 1988-2000. Most trees had lowest growth during the second interval when rainfall was lowest, and skewness and kurtosis of growth distributions were reduced during this interval. Tree diameter generally explained less than 10% of growth variation and had less influence on growth than species identity or time interval. Intraspecific variation was high, yet species identity accounted for up to 16% of growth variation in the community. There were no consistent differences between canopy and understory tree growth rates; however, a few subgroups of species may potentially represent canopy and understory growth guilds. Environmentally-induced temporal variations in growth generally did not reduce the odds of subsequent survival. Growth rates appear to be strongly influenced by species identity and environmental variability in the Mudumalai dry forest. Understanding and predicting vegetation dynamics in the dry tropics thus also requires information on temporal variability in local climate.

The dynamics of vulnerability: locating coping strategies in Kenya and Tanzania

We investigate how smallholder farmers at two sites in Kenya and Tanzania cope with climate stress and how constraints and opportunities shape variations in coping strategies between households and over time during a drought. On the basis of this analysis, we draw out implications for adaptation and adaptive policy. We find that households where an individual was able to specialize in one favoured activity, such as employment or charcoal burning, in the context of overall diversification by the household, were often less vulnerable than households where each individual is engaged in many activities at low intensity. Many households had limited access to the favoured coping options due to a lack of skill, labour and/or capital. This lack of access was compounded by social relations that led to exclusion of certain groups, especially women, from carrying out favoured activities with sufficient intensity. These households instead carried out a multitude of less favoured and frequently complementary activities, such as collecting indigenous fruit. While characterized by suitability to seasonal environmental variations and low demands on time and cash investments, these strategies often yielded marginal returns. Both the marginalization of local niche products and the commercialization of forest resources exemplify processes leading to differential vulnerability. We suggest that vulnerability can usefully be viewed in terms of the interaction of such processes, following the concept of locality. We argue that coping is a distinct component of vulnerability and that understanding the dynamism of coping and vulnerability is critical to developing adaptation measures that support people as active agents.

Diel feeding, daily food consumption and the predatory impact of whitemouth croaker (Micropogonias furnieri) in an estuarine environment

AbstractDiel feeding pattern and food consumption of whitemouth croaker (Micropogonias furnieri) were examined and related to seasonal variations in an estuarine environment. To determine diel feeding pattern whitemouth croaker were collected from the Patos Lagoon Estuary over 24 h (∼3‐h intervals) and their stomach contents were examined. Food consumption of whitemouth croaker was determined from evacuation rates estimated experimentally and in the field. The results suggested that whitemouth croaker in the Patos Lagoon estuary feed all day long. However, whitemouth croaker showed higher feeding intensity and food consumption during daylight hours when the water transparency increased than in others when water transparency was low. Thus, whitemouth croaker seemed to intensify their feeding when they could see their prey. Daily food consumption was between 0.9 and 5.3% of body wet weight (these being the lowest and highest consumption rates during the winter and summer, respectively). The maximum predation impact of whitemouth croaker on their preferential prey, the tanaid Kalliapseudes schubartii, was 27indiv·m−2·day−1. The results suggested that the changes in water transparency seem to affect the diel feeding pattern and food consumption of whitemouth croaker. This could have important consequences for fish growth.

Fish community alterations due to pollution and damming in Tietê and Paranapanema rivers (Brazil)

AbstractThe Tietê River crosses the metropolitan region of São Paulo (Brazil) and receives a large amount of pollution, in contrast to Paranapanema River which runs in a less populated area. In the inferior portions of the basins of these rivers, a series of reservoirs has been built for hydroelectric energy generation which improve the water quality due to the decantation of suspended soils and aeration in the water spills.Twenty‐nine sampling sites were established along the two rivers and in each sampling site, two groups of eight gillnets were used with standardized sizes in two seasons: winter (dry season: June–September 1994) and summer (rainy season: December–March 1995). The fishes were measured and weighed.Twenty‐five parameters related to the water were recorded. PCA and cluster analysis helped to identify two groups of sampling sites. The first one corresponds to the rainy season samples, while the second corresponds to the dry season samples, so evidencing strong seasonal environmental variation. However, the dry season group is still divided into polluted and non‐polluted sites, showing that during drought there are larger effects of pollutant concentration due to the decreased flow.A total of 415 kg of fish were caught, corresponding to 8324 individuals belonging to 64 different species, in 22 families and four orders of Teleostei. The largest catches occurred in the middle Tietê River. The catches in the reservoirs of the Tietê River during the rainy season are superior to those of the dry season. On the other hand, sampling sites located in running water presented an inverse pattern with the largest catches in the dry season. In river Paranapanema, catches are lower than in the Tietê River, except in Rosana Reservoir during the rainy season. Fish diversity was shown to be a good indicator of environmental stress. In Tietê River an expressive fall in species richness was detected in the polluted stretches, with dominance of one or two species. In the intermediary stretches, the presence of rapids increases the amount of dissolved oxygen, allowing the development of the most abundant and diverse fish community of the river. Fish communities in the reservoirs of the inferior stretch of Tietê River are more diverse. On the other hand, the damming of the superior reaches of Paranapanema River provoked a decrease in diversity. O the whole, types of local fish communities detected, showing different compositions and specific abundances, revealed different ecological situations. A discriminant analysis revealed that the parameters of the water influencing the fish community were: dissolved oxygen, conductivity, nitrogen (nitrate, ammoniacal and albuminoid), phosphate, alkalinity, hardness and iron. Copyright © 2003 John Wiley & Sons, Ltd.

Seasonality, water quality trends and biological responses in four streams in the Cairngorm Mountains, Scotland

Abstract. The chemical composition and invertebrate communities found in four streams in the Cairngorms, Scotland, were monitored between 1985-1997. Stream waters were mildly acidic (mean pH ca. 6.5), with low alkalinity (mean acid neutralising capacity varying from 35-117 meq l-1) and low ionic strength. Subtle differences in the chemistry of each stream were reflected in their invertebrate faunas. Strong seasonality in water chemistry occurred, with the most acid, low alkalinity waters observed during the winter and early spring. This was particularly marked during snowmelt between January and April. In contrast, summer flows were usually groundwater dominated and characterised by higher alkalinity and higher concentrations of most other weathering-derived solutes. Seasonality was also clear in the invertebrate data, with Canonical Correspondence Analysis (CCA) separating seasonal samples along axes related to water temperature and discharge characteristics. Inter-annual hydrological and chemical differences were marked, particularly with respect to the winter period. Invertebrate communities found in each of the streams also varied from year to year, with spring communities significantly more variable (P<0.01) than other seasons (quantified using Euclidean distance on CCA ordinations). Hydrochemical trends over the study period were analysed using a seasonal Kendall test, LOcally WEighted Scatterplot Smoothing (LOWESS) and graphical techniques. These indicated that a reduction in sulphate concentrations in stream water is occurring, consistent with declining levels of atmospheric deposition. This may be matched by increases in pH and declining calcium concentrations, though available evidence is inconclusive. Other parameters, such as chloride, total organic carbon and zinc, reveal somewhat random patterns, probably reflecting irregular variations in climatic factors and/or atmospheric deposition. Previous studies have shown that the stream invertebrate communities have remained stable over this period (i.e. no significant linear trends) and show no evidence of acid-related impoverishment. Thus, over longer timescales invertebrates in these streams appear robust to the short-term (seasonal and inter-annual) environmental variability and long-term (decadal) chemical changes identified. Keywords: hydrochemistry, hydrology, trends, macroinvertebrates, uplands, Cairngorms, acidification