Previous Autumn Research Articles

Predictability of winter temperature in China from previous autumn Arctic sea ice

The potential predictability of winter temperature in China from autumn Arctic sea ice anomalies is studied by examining and statistically modeling the large–scale interannual covariability between them on the basis of singular value decomposition analysis. It is demonstrated that an intimate relationship exists between September and October sea ice anomalies in the Eurasian Arctic and following winter temperature anomalies in China, except in the Tibetan Plateau. When the autumn sea ice anomalies decline in the Eurasian Arctic, above-normal pressure anomalies appear to prevail over the region from the Eurasian Arctic to Eastern Europe and Mongolia, and below-normal anomalies prevail over the mid-latitudes of Asia and Northwestern Pacific in the following winter. Consequently, the winter Siberian High and East Asian trough are both strengthened, favoring the southward invasion of high–latitude cold air masses and thus cold temperature anomalies in China. It is found that the Siberian High plays a crucial role in delivering effects of the autumn Arctic sea ice anomalies on winter temperature variability in China. Based on this evidence, a statistical model is established to examine the potential predictability of winter temperature anomalies in China by taking the autumn Arctic sea ice signals as a predictor. Validation shows considerable skill in predicting winter temperature anomalies over a large part of China, indicating a significant potential for improving winter climate prediction in China.

Interannual variations of the dominant modes of East Asian winter monsoon and possible links to Arctic sea ice

Two dominant modes of the winter temperature over East Asia, a northern mode and a southern mode, and their links with Arctic climate conditions are analyzed. The relationships of the two modes with Arctic sea ice are different. The northern mode is closely linked to variations in sea ice of the Arctic Barents–Laptev Sea in previous autumn and most of the Arctic in concurrent winter. The southern mode seems independent from the Arctic sea ice variations, but is associated with sea surface temperature (SST) anomalies in the equatorial central-eastern Pacific. Results suggest an effect of Arctic sea ice variation on the northern mode and an influence of tropical SST anomalies on the southern mode. Reduced sea ice over the Arctic increases 1000–500-hPa thickness over the high-latitudes of Eurasian continent, which reduces the meridional thickness gradient between the middle and high latitudes and thus weakens the extratropical upper-level zonal wind. The weakened zonal wind provides a favorable dynamic condition for the development of a high-latitude ridge around the Ural Mountain. Reduced Arctic sea ice also tends to enhance the Siberian high through both thermodynamic and dynamic processes. The above atmospheric circulation patterns provide a favorable condition for the intrusion of cold air to northern East Asia.

Response of degraded vegetation to introduction of prescribed burning or mowing management in a Mongolian steppe

AbstractThe understanding of the effectiveness of prescribed burning and mowing as restoration tools of degraded grasslands is important for dryland rangeland management. We examined the effects of spring prescribed burning or seasonal mowing treatments on the degraded vegetation dominated by an unpalatable subshrub, Artemisia adamsii, in grazed Mongolian steppe. Spring burning was conducted in 2013, and three types of mowing treatments (spring, previous summer, and previous summer and autumn) were conducted with varying seasons and frequency, respectively. Soil samples were collected immediately after the spring treatments. Four months after the spring treatments, total plant biomass, the numbers of flowering shoots and florets per shoot of A. adamsii were compared among the treatments. Plant biomass was divided into A. adamsii and herbaceous plants (forbs and graminoids) with different Raunkiaer life forms (chamaephytes, hemicryptophytes and geophytes). Soil properties and total plant biomass were not different among the treatments. For A. adamsii, the biomass and number of flowering shoots were decreased by spring burning and growing‐season mowing, owing to the disappearance of woody‐shoots of A. adamsii. On the other hand, spring mowing had less negative impact on the biomass of A. adamsii due to an increase of the newly‐formed shoots. The biomass of perennial herbaceous‐plants was not affected by spring burning, regardless of the life form, whereas that of the geophytic sedge Carex duriuscula increased in the summer‐and‐autumn mowing. Thus, spring burning and growing‐season mowing have the potential to control undesirable subshrubs due to loss of the woody shoots, while spring mowing may not be recommended as a useful management tool in the Mongolian steppe. Our results emphasize that the introduction of these management tools for degraded‐grassland restoration in dryland rangelands needs more long‐term evaluation considering the relation with external factors such as climate variation and grazing impact.

Flowering and fruiting responses to climate change of two Arctic plant species, purple saxifrage (Saxifraga oppositifolia) and mountain avens (Dryas integrifolia)

In temperate regions, there are clear indications that spring flowering plants are flowering earlier due to rising temperatures of contemporary climate change. Temperatures in temperate regions are rising predominantly in spring. However, Arctic regions are seeing unprecedented temperature increases, predominantly towards the end of the growing season. We might, therefore, expect to see earlier flowering of later-season flowering Arctic plants. Parks Canada has been monitoring purple saxifrage (Saxifraga oppositifolia) and mountain avens (Dryas integrifolia) flowering and fruiting times for 20 years at Tanquary Fiord, Quttinirpaaq National Park, Ellesmere Island. Saxifraga oppositifolia flowers in early spring, while D. integrifolia flowers in midsummer. Over the 20-year period, Tanquary Fiord's annual and late-summer temperatures have risen significantly. During the same timeframe, D. integrifolia showed a trend towards earlier flowering and fruiting, but S. oppositifolia showed no changes in flowering or fruiting time. Flowering time was related to monthly temperatures just prior to flowering. The number of flowers produced was related to the previous autumn's monthly temperatures. We found no relationship between flowering time and snowmelt date. Our findings suggest that Arctic community level ecological effects from climate change induced phenology changes will differ from those in temperate regions.

Food availability in spring affects smolting in brown trout (Salmo trutta)

Prior to out-migration, salmonid fish typically undergo physiological and morphological changes — a process known as smolting. This study indicates that smolting in brown trout (Salmo trutta) is affected by feeding conditions in spring immediately prior to out-migration. This conclusion was reached after experimentally testing the effect of seasonal variation in food availability on smolt status in the spring. A migratory strain of trout was administered either high or low food rations in the autumn, winter, or spring prior to release in the spring. While fish growth or condition could be affected in any season, it was spring rationing that reduced growth and growth-related variables and that caused increased smolting. Our result supports the idea that smoltification and the decision to migrate is affected by spring food availability regardless of conditions in the previous autumn or winter.

Bridging tree rings and forest inventories: How climate effects on spruce and beech growth aggregate over time

Tree growth is strongly influenced, among other factors, by climate. Much knowledge regarding climate–growth relationships has been gained by studying tree rings. However, sufficient tree-ring data is rarely available if climate effects are required to be representative for large spatial scales, for example, in order to be used in scenario models to estimate forest development under climate change. Alternative data sources include large-scale forest inventories, although these usually provide lower temporal resolutions than tree rings. When working with temporally sparsely-resolved growth data, the question of how climate–growth relationships aggregate over time becomes relevant. To overcome this trade-off between spatial representativeness and temporal resolution, this study aims at optimally using the information contained in the annual resolution of tree rings to derive recommendations regarding the choice of climate variables for modeling tree growth based on forest inventories. We evaluated for Picea abies and Fagus sylvatica, which part of the year (spring, summer, vegetation period, whole year) and whether mean or extreme climatic conditions within inventory intervals should be taken into consideration. A three-step approach was used: (1) we used response functions to quantify the effect of monthly precipitation and temperature on annual basal area increments, (2) we temporally aggregated the annual basal area increments to hypothetical intervals of five and ten years, and correlated them with climate means and extremes – from different parts of the year – within the aggregated intervals, and (3) we fitted linear mixed-effects models to simultaneously quantify the effects of the climate variables, site characteristics and the years of the hypothetical inventories. The results did not generally differ between both species. Variables based on conditions during the whole year and partly during spring performed better than variables based on conditions during summer or the vegetation period. Defining the year as the period between October of the previous year and September of the current year allows possible lag effects of previous autumn and winter conditions to be taken into consideration. Mean climatic conditions reached or exceeded the correlations of the extremes and mostly performed similar to or better than the extremes in the models. Our results indicate that these relationships are insensitive to the often arbitrarily determined years, in which inventories take place. These findings can serve as basic recommendations for the choice of climate variables when modeling climate effects on multi-year growth of P. abies and F. sylvatica in the European lowlands.

Tree rings reflect growth adjustments and enhanced synchrony among sites in Iberian stone pine (Pinus pinea L.) under climate change

We used tree ring analysis to assess the response of Pinus pinea to climate change in South Iberia. Climate–growth relationships changed over time, with greater sensitivity in recent years due to increasing aridity. A common dendroclimatic signal among sites was found, suggesting that climate change is the main responsible for the observed variation in tree growth. Understanding the response of Mediterranean forests to climate change is required to assess their vulnerability and to develop measures that may limit the impact of future climate change. We analyzed the sensitivity of several populations of Pinus pinea (Stone pine) in Southern and Central Spain and Portugal to climate and identified some responses to climate change. We constructed tree ring chronologies and studied the dendroclimatic signal over the last century. There were similarities in tree ring growth and response to climate among sites. Growth was enhanced after precipitation during the previous autumn and the current spring and was limited by water shortage. In recent decades, aridity increased in the study region and the sensitivity of tree ring growth to water availability increased at all study sites. We also observed an enhanced growth synchrony among chronologies as well as an increase in ring width variability during the last decades. The radial growth of P. pinea indicated strong effects of climate change. The climatic signal in tree ring chronologies suggested a plastic growth response to climate of this species, although the enhanced growth synchrony and variability in recent years suggest the presence of conditions that are limiting for growth. This study provides the first assessment of the responses of Iberian populations of P. pinea to changes in climate.

Individual Variations of Winter Surface Air Temperature over Northwest and Northeast China and Their Respective Preceding Factors

AbstractBased on monthly mean surface air temperature (SAT) from 71 stations in northern China and NCEP/NCAR and NOAA-CIRES (Cooperative Institute for Research in Environmental Sciences) twentieth century reanalysis data, the dominant modes of winter SAT over northern China were explored. The results showed that there are two modes that account for a majority of the total variance over northern China. The first mode is unanimously colder (warmer) over the whole of northern China. The second mode is characterized by a dipole structure that is colder (warmer) over Northwest China (NWC) and warmer (colder) over Northeast China (NEC), accounting for a fairly large proportion of the total variance. The two components constituting the second mode, the individual variations of winter SAT over NWC and NEC and their respective preceding factors, were further investigated. It was found that the autumn SAT anomalies are closely linked to persistent snow cover anomalies over Eurasia, showing the delayed effects on wi...

Timing and duration of the life cycle of Asian longhorn beetle Anoplophora glabripennis (Coleoptera: Cerambycidae) in southern England

AbstractIn March 2012, an outbreak of Asian longhorn beetle Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae), a quarantine pest that is highly damaging to broadleaved trees, was discovered at Paddock Wood in southern England. Infested trees were felled as part of an eradication programme, but material that contained A. glabripennis life stages was retained and analyzed to provide information on the timing and length of the life cycle, as an aid to future management and surveillance. A total of 366 A. glabripennis larvae were recovered, including 69 first‐ and second‐instar larvae found in June and July before any adults were found in the samples or had emerged, which indicated that the majority of eggs were laid in the previous autumn and over‐wintered before hatching. Tree ring analysis and predictions of the timing of adult emergence based on degree‐day accumulation also indicated that adults emerged late in the season, from August onwards, when lower temperatures would have caused most eggs to delay hatching until the next year. Two cohorts of older, established larvae were present in the samples, corresponding to larvae that had over‐wintered once and twice, respectively. Thus, most larvae required two seasons to complete their development after hatching and a total of 3 years to complete the full life cycle from egg to adult.

Population-Wide Failure to Breed in the Clark's Nutcracker (Nucifraga columbiana).

In highly variable environments, conditions can be so stressful in some years that entire populations forgo reproduction in favor of higher likelihood of surviving to breed in future years. In two out of five years, Clark’s nutcrackers (Nucifraga Columbiana) in the Greater Yellowstone Ecosystem exhibited population-wide failure to breed. Clark’s nutcrackers at the study site experienced substantial interannual differences in food availability and weather conditions, and the two nonbreeding years corresponded with low whitebark pine (Pinus albicaulis) cone crops the previous autumn (≤ an average of 8 ± 2 cones per tree versus ≥ an average of 20 ± 2 cones per tree during breeding years) and high snowpack in early spring (≥ 61.2 ± 5.5 cm versus ≤ 51.9 ± 4.4 cm during breeding years). The average adult body condition index during the breeding season was significantly lower in 2011 (-1.5 ± 1.1), a nonbreeding year, as compared to 2012 (6.2 ± 2.0), a breeding year. The environmental cues available to the birds prior to breeding, specifically availability of cached whitebark pine seeds, may have allowed them to predict that breeding conditions would be poor, leading to the decision to skip breeding. Alternatively, the Clark’s nutcrackers may have had such low body energy stores that they chose not to or were unable to breed. Breeding plasticity would allow Clark’s nutcrackers to exploit an unpredictable environment. However, if large-scale mortality of whitebark pines is leading to an increase in the number of nonbreeding years, there could be serious population-level and ecosystem-wide consequences.

Planting window requirements for Bt cotton in Australia: do they limit the exposure ofHelicoverpaspp. (Lepidoptera: Noctuidae) to Bt toxins?

The threat of Bt resistance in Helicoverpa armigera (Hubner 1808) and H. punctigera (Wallengren 1860) (Heliothinae) is a major impediment to the sustainability of transgenic (Bt) cotton crops in Australia. A resistance management plan has, therefore, been instigated that in part requires farmers to sow their Bt cotton within specified dates to limit the number of generations of Helicoverpa spp. that are exposed to Bt toxins during the growing season. This study evaluated this strategy by utilising industry-wide databases of planting dates and other cropping/pest management events throughout 11 growing seasons. The analysis included model predictions of when Helicoverpa is likely to enter winter (pupal) diapause and emerge as moths in spring, and the long-term pheromone trapping records of moths. In New South Wales and southern Queensland (Qld), most first-generation moths were caught at the same time, or before, cotton was planted (mostly in October). This generation was, therefore, unlikely to have been exposed significantly to Bt toxins as feeding larvae in spring, but some individuals (especially H. armigera) may have been exposed to Bt prior to pupating in the previous autumn. Three subsequent generations, which could have been exposed to Bt during summer–autumn, were recognisable in trap catches before moths became very rare in early April. By then, the majority of Helicoverpa had entered winter diapause as pupae and cotton harvest was well underway. We conclude that the current planting window (pre-mid-November in these regions) achieves little in limiting the exposure of Helicoverpa to Bt. However, insufficient is known of the population dynamics of Helicoverpa in central Qld to be as definitive about the need for planting windows there. Importantly, Helicoverpa are active all year round in central Qld and cotton can be grown over a longer period, thus increasing the risks of greater exposure to Bt.

C depletion and tree dieback in young peach trees: a possible consequence of N shortage?

Bud burst disruption, carbon depletion and tree dieback in spring were experimentally linked to N shortage the previous autumn. Dieback occurred despite tree N concentrations were compatible with plant survival: their N stores being blocked in the roots and woody axes. Tree dieback is generally linked to hydraulic failure or carbon (C) starvation but seldom to poor nitrogen (N) resources. We provide here an experimental evidence linking autumn N shortage, C depletion and tree dieback in spring. Young peach trees were either N deprived or fertilised in autumn, and then fed in excess in spring. Spring supplies were 15N-labelled. The effects of the deprivation on tree development, N uptake and C status were then assessed by coupling in situ measurements of shoot development with organ biochemical and isotopic determinations. All deprived trees died within 3 months after burst. Bud burst was severely disrupted, and vegetative growth limited to the expansion of a few leaves. The dead trees absorbed between 39 and 117 mg 15N in spring, and their roots and axes contained 758 mg more nitrogen than the fertilised trees, suggesting that they did not mobilise their N reserves in spring. They also had lower non-structural carbohydrate concentrations ( 15.4 % DW), which were below the threshold accepted for plant survival. Two possible causes of total non-structural carbon (or TNC) depletion are discussed: insufficient storage due to advanced leaf senescence or increase in the C costs regarding winter embolism recovery.

Predicting a change in the order of spring phenology in temperate forests.

The rise in spring temperatures over the past half‐century has led to advances in the phenology of many nontropical plants and animals. As species and populations differ in their phenological responses to temperature, an increase in temperatures has the potential to alter timing‐dependent species interactions. One species‐interaction that may be affected is the competition for light in deciduous forests, where early vernal species have a narrow window of opportunity for growth before late spring species cast shade. Here we consider the Marsham phenology time series of first leafing dates of thirteen tree species and flowering dates of one ground flora species, which spans two centuries. The exceptional length of this time series permits a rare comparison of the statistical support for parameter‐rich regression and mechanistic thermal sensitivity phenology models. While mechanistic models perform best in the majority of cases, both they and the regression models provide remarkably consistent insights into the relative sensitivity of each species to forcing and chilling effects. All species are sensitive to spring forcing, but we also find that vernal and northern European species are responsive to cold temperatures in the previous autumn. Whether this sensitivity reflects a chilling requirement or a delaying of dormancy remains to be tested. We then apply the models to projected future temperature data under a fossil fuel intensive emissions scenario and predict that while some species will advance substantially others will advance by less and may even be delayed due to a rise in autumn and winter temperatures. Considering the projected responses of all fourteen species, we anticipate a change in the order of spring events, which may lead to changes in competitive advantage for light with potential implications for the composition of temperate forests.

Diverse Responses of Remotely Sensed Grassland Phenology to Interannual Climate Variability over Frozen Ground Regions in Mongolia

Frozen ground may regulate the phenological shifts of dry and cold grasslands at the southern edge of the Eurasian cryosphere. In this study, an investigation based on the MODIS Collection 5 phenology product and climatic data collected from 2001 to 2009 reveals the diverse responses of grassland phenology to interannual climate variability over various frozen ground regions in Mongolia. Compared with middle and southern typical steppe and desert steppe, the spring (start of season; SOS) and autumn (end of season; EOS) phenological events of northern forest steppe with lower air temperature tend to be earlier and later, respectively. Both the SOS and EOS are less sensitive to climate variability in permafrost regions than in other regions, whereas the SOS of typical steppe is more sensitive to both air temperature and precipitation over sporadic permafrost and seasonal frozen ground regions. Over various frozen ground regions in Mongolia; the SOS is mainly dominated by the prior autumn precipitation, and frozen ground plays a vital role in storing the precipitation of the previous autumn for the subsequent grass green-up. The EOS is mainly dominated by autumn air temperature. These findings could help to improve phenological models of grasslands in extremely dry and cold regions.

Estimation of annual forest evapotranspiration from a coniferous plantation watershed in Japan (2): Comparison of eddy covariance, water budget and sap-flow plus interception loss

Evapotranspiration (ET) was estimated from a planted coniferous forest in southwestern Japan by applying three methods: the eddy covariance method; the measurement of rainfall (P) and runoff (Q) in a small watershed; and a combination of rainfall interception loss (IC), upper canopy transpiration based on a sap-flux density measurement in Japanese cedar (Cryptomeria Japonica D. Don) stands (EUC), and modeled sub-canopy ET (ESC). After inverse multiplication of the energy imbalance ratio, ET by the eddy covariance method (ETEC) was 839.9 mm in 2007 and 811.8 mm in 2008. The yearly values of P–Q were partially affected by P in the previous autumn. After continuous data collection for more than 5 years, P–Q became stable. The 9-year (2000–2008) average P–Q, which was considered most reliable in this study, was 897.5 mm y−1. The cumulative ETEC during the daylight hours from the right stream bank, covered mainly with large Japanese cedars, was 894.1 mm from April 2007 to March 2008. The value was almost the same as that calculated as the components sum (ETCOMP = IC + EUC + ESC: 911.4 mm), and the comparison suggested that the annual totals of ETEC with an energy imbalance correction provide a reliable estimate of ET in a forest stand on a complex topography. Spatial variation in the watershed was likely caused by differences in soil water retention at each slope position. The slight difference in annual ETEC in 2007 compared with 2008 was attributed to differences in the radiative energy input. In the monthly–weekly analysis, ETCOMP was frequently higher than ETEC after heavy rainfall, while ETEC was higher under dry conditions and during active ET. Even under dry canopy conditions, daily ETEC was often higher than EUC + ESC. The results suggested a time-lag in evaporation from the ecosystem and/or under-estimated ETEC after rainfall.

Effect of fertilization rate and ploughing time on nitrous oxide emissions in a long-term cereal trail in south east Norway

Fertilization and soil tillage are important factors for crop production and N2O emissions. Nothing is known about fertilizer-induced N2O emissions (FIEs) in cereal production under cool-temperate conditions in Norway. Here, we report N2O emissions measured throughout two vegetation periods in a long-term cereal trail in SE Norway, comparing three nitrogen (N) fertilization rates (0, 60 and 120 kg N ha−1) under long-term autumn and spring-ploughing regimes. Emission rates were higher in undisturbed plots directly after spring thaw before ploughing (35–52 μg N2O-N m−2 h−1) than those in plots ploughed in previous autumn (18–26 μg N2O-N m−2 h−1), suggesting that ploughing date affected post-thaw availability of N from crop residues in the following year. In contrary, autumn-ploughed plots had higher N2O emissions during drying–rewetting events in summer, cancelling out any effect of ploughing date on growing season N2O emissions. Averaged FIE differed greatly between the years, with 0.37–0.40 and 0.72–0.96 % of fertilizer N lost as N2O in 2009 and 2010, respectively, reflecting different weather conditions in the 2 years. Growing season N2O emission response was not stable over the tested fertilization range but increased disproportionally above an optimum fertilization rate of 90–100 kg N ha−1, probably because of incomplete N uptake by the crop. This would suggest that decreasing the N fertilization rate by 25 % (from 120 to an optimum level of 90 kg N ha−1) could reduce N2O emission by 30 % with only minor reduction in grain yield (6–8 %).

Extreme cold and warm events over China in wintertime

The characteristics of extreme cold and warm events (ECE; EWE) over the whole China in December, January and February are investigated using the observed daily surface air temperature for 1961–2012. Among the 3 months, both the EWE and ECE in February are most frequent and strongest and least frequent in December and weakest in January. More than 50% of the EWE and ECE in February and less than 40% of the EWE and ECE in January exhibit persistent feature (lasting at least 5 days). Generally, the persistent ECE are more frequent than the persistent EWE. The EWE (ECE) in February exhibit intensive increasing (decreasing) tendency and show more (less) persistent feature in 1961–1986 than that in 1987–2012. The persistent feature of the EWE (ECE) in December and January is more (less) obvious in 1961–1986 than that in 1987–2012 although the EWE (ECE) in 1961–1986 is less (more) frequent than that in 1987–2012. The significant weakening (strengthening) Siberia high and East Asia trough are the two main key factors for the EWE (ECE) in January and February and they can be found up to 5 days before the occurrence of the EWE (ECE). The ECE (EWE) in December are associated with the three-wave structure anomalies in troposphere, but these anomalies cannot be found before the occurrence of the ECE (EWE). The warm North Atlantic and tropical central-eastern Pacific in previous autumn (SON, September–October–November) trigger significant weakening of Siberia high and East Asia trough in February and thereby cause the occurrence of the EWE. On decadal time scale, the increasing EWE in February seem to be the consequence of the warming North Atlantic. The cold SON Indian Ocean corresponds to significant atmospheric circulation anomalies in December similar to those associated with the ECE in December, indicating its importance in the ECE in December.

Early 21st century snow cover state over the western river basins of the Indus River system

Abstract. In this paper we assess the snow cover and its dynamics for the western river basins of the Indus River system (IRS) and their sub-basins located in Afghanistan, China, India and Pakistan for the period 2001–2012. First, we validate the Moderate Resolution Imaging Spectroradiometer (MODIS) daily snow products from Terra (MOD10A1) and Aqua (MYD10A1) against the Landsat Thematic Mapper/Enhanced Thematic Mapper plus (TM/ETM+) data set, and then improve them for clouds by applying a validated non-spectral cloud removal technique. The improved snow product has been analysed on a seasonal and annual basis against different topographic parameters (aspect, elevation and slope). Our results show a decreasing tendency for the annual average snow cover for the westerlies-influenced basins (upper Indus basin (UIB), Astore, Hunza, Shigar and Shyok) and an increasing tendency for the monsoon-influenced basins (Jhelum, Kabul, Swat and Gilgit). Seasonal average snow cover decreases during winter and autumn, and increases during spring and summer, which is consistent with the observed cooling and warming trends during the respective seasons. Sub-basins at relatively higher latitudes/altitudes show higher variability than basins at lower latitudes/middle altitudes. Northeastern and northwestern aspects feature greater snow cover. The mean end-of-summer regional snow line altitude (SLA) zones range from 3000 to 5000 m a.s.l. for all basins. Our analysis provides an indication of a descending end-of-summer regional SLA zone for most of the studied basins, which is significant for the Shyok and Kabul basins, thus indicating a change in their water resources. Such results are consistent with the observed hydro-climatic data, recently collected local perceptions and glacier mass balances for the investigated period within the UIB. Moreover, our analysis shows a significant correlation between winter season snow cover and the North Atlantic Oscillation (NAO) index of the previous autumn. Similarly, the inter-annual variability of spring season snow cover and spring season precipitation explains well the inter-annual variability of the summer season discharge from most of the basins. These findings indicate some potential for the seasonal stream flow forecast in the region, suggesting snow cover as a possible predictor.

Effects of feeding regimes and early maturation on migratory behaviour of landlocked hatchery-reared Atlantic salmon Salmo salar smolts.

The migratory behaviour of hatchery-reared landlocked Atlantic salmon Salmo salar raised under three different feeding regimes was monitored through the lower part of the River Klarälven, Sweden. The smolts were implanted with acoustic transmitters and released into the River Klarälven, 25 km upstream of the outlet in Lake Vänern. Early mature males, which had matured the previous autumn, were also tagged and released. To monitor migration of the fish, acoustic receivers were deployed along the migratory route. The proportion of S. salar that reached Lake Vänern was significantly greater for fish fed fat-reduced feed than for fish given rations with higher fat content, regardless of ration size. Fish from the early mature male group remained in the river to a greater extent than fish from the three feeding regimes. Smolt status (degree of silvering), as visually assessed, did not differ among the feeding regime groups, and moreover, fully-silvered fish, regardless of feeding regime, migrated faster and had a greater migration success than fish with less developed smolt characteristics. Also, successful migrants had a lower condition factor than unsuccessful ones. These results indicate that the migration success of hatchery-reared S. smolts released to the wild can be enhanced by relatively simple changes in feeding regimes and by matching stocking time with smolt development.

Disruption of the naturally evolved N conservation strategy in soil under grassland at a sports field in York, UK

Water- and KCl-extractable ammonium–N and nitrate–N concentrations have been monitored at approximately monthly intervals over a year in soils from 0–10 and 10–20cm depths under permanent grass at a sports field in York, UK. Measurements were made on both fresh, field-moist soils and after the same soils had been incubated for 7days at ambient outdoor temperatures, to assess seasonal changes in the capacity of the soils to produce mineral-N species in the absence of plant uptake and other effects. Water extracts allowed potential mobility of N species to be assessed. Comparison of seasonal trends in mineral-N species concentrations in pre- and post-incubation soils confirmed depletion of exchangeable ammonium–N from the winter to summer. Mineral-N in fresh and incubated soils displayed summer minima and also low production in winter, associated with the effects of low temperature on nitrate production and probably microbial immobilization of nitrate produced by residual senescent plant litter with a higher C:N ratio from the previous autumn. The results support the concept that plant/soil systems co-evolved under more pristine conditions to conserve soil N by matching the dynamics of soil mineral N production and plant N uptake, but now N pollution has resulted in a dynamic mismatch.