Late Winter Period Research Articles

Simulating soil freeze/thaw cycles typical of winter alpine conditions: Implications for N and P availability

Seasonally snow-covered alpine soils may be subjected to freeze/thaw cycles, particularly during years having little snow and during the late winter and early spring periods. Freeze/thaw cycles can stimulate soil mineralization and could therefore be one factor regulating nitrogen (N) and phosphorus (P) availability and cycling. In this study laboratory incubation experiments using four soils having contrasting properties have been used to characterize the change in N and P forms (microbial and soluble inorganic/organic) that occur after simulated freeze/thaw cycles. Soil samples were collected from locations representing extreme examples of either direct human management (grazed meadow (site M) and extensive grazing beneath larch (site L)) or those disturbed by more natural events (recent avalanche and colonisation by alder (site A)) and from beneath the expected forest climax vegetation beneath fir (site F). Topsoil from these sites, maintained at two different water contents (20 and 30%, w/w), were exposed to either a single (SF) or four sequential (4SF) freeze/thaw cycles. Each cycle consisted of 12 h at −9 °C and 12 h at +4 °C mimicking a diurnal pattern. A SF cycle reduced microbial N for soils from sites F and A and was accompanied by a significant increase in dissolved organic nitrogen (DON) at both moisture contents. In contrast, the microbial N of soils from M and L was not affected by the freeze/thaw cycles, suggesting a particular adaptation of soil microbes to these extremes in temperature. Freeze/thaw cycles resulted in a significant increase in the net ammonification in all soils. Extractable total dissolved N (TDN) and total dissolved P (TDP) increased in all soils after a SF cycle, however, the relative importance of the different N and P forms differed. At the lower soil moisture content, NO 3 − concentrations remained constant or slightly decreased in all soils, except that from site M. In all other soils DON appeared to replace NO 3 − as the potentially mobile N source after the freeze/thaw cycles. The relative contribution of dissolved organic P to TDP after freeze/thaw remained significant, and greater than 50% in all soils. Freeze/thaw cycles, in seasonally snow covered soils, are likely to have a selective effect on the microbial biomass. Freezing and thawing resulted in a pulse of net ammonification and DON release, which represent an important influence upon N cycling in these alpine systems.

Development of Practical Plant Factory with Artificial Supplemental Lighting System for the Growth of Vegetable Seedlings

For stable mass production of vegetable seedlings with good quality, a commercial greenhouse nursery needs a supplemental lighting system that is not affected by light fluctuations under natural solar conditions. Therefore, a practical plant nursery covering a 12 × 24 m area, and using a supplemental lighting system, was developed for the growth of vegetable seedlings. The developed lighting system had 400-W mercury-free, high pressure sodium lamps with reflectors, which produced a red radiation to far-red radiation photon flux (R/FR PF) ratio of 1.1. This is similar to that of solar radiation. And over about 60 μmol m-2 s-1 of PPFD was realized for stable and healthy growth of vegetable seedlings. By using a simulation model of horizontal distribution of PPFD on two cultivation beds (each bed area: 4.6 × 22.6 m) under 100 lamps, it was found that the system had high uniformity of lighting on the two beds. Observed value of illuminance and PPFD and uniformity also satisfied the planned specifications. By repeating a seedling growth experiment using various plants in this greenhouse, it is expected that the practical and effective use of this supplemental lighting system will be possible in rainy seasons or in the late winter period.

Variability in stream discharge and temperature: a preliminary assessment of the implications for juvenile and spawning Atlantic salmon

Abstract. This study focuses on understanding the temporal variability in hydrological and thermal conditions in a small mountain stream and its potential implication for two life stages of Atlantic salmon (Salmo salar) – stream resident juveniles and returning adult spawners. Stream discharge and temperature in the Girnock Burn, NE Scotland, were characterised over ten hydrological years (1994/1995–2003/2004). Attention was focussed on assessing variations during particular ecologically "sensitive" time periods when selected life-stages of salmon behaviour may be especially influenced by hydrological and thermal conditions. Empirical discharge data were used to derive hydraulic parameters to predict the Critical Displacement Velocity (CDV) of juvenile salmon. This is the velocity above which fish may no longer be able to hold station in the water column and thus can be used as an index of time periods where feeding behaviour might be constrained. In the Girnock Burn, strong inter- and intra-annual variability in hydrological and thermal conditions may have important implications for feeding opportunities for juvenile fish; both during important growth periods in late winter and early spring, and the emergence of fry in the late spring. Time periods when foraging behaviour of juvenile salmon may be constrained by hydraulic conditions were assessed as the percentage time when CDV for 0+ and 1+ fish were exceeded by mean daily stream velocities. Clear seasonal patterns of CDV were apparent, with higher summer values driven by higher stream temperatures and fish length. Inter-annual variability in the time when mean stream velocity exceeded CDV for 0+ fish ranged between 29.3% (1997/1998) and 44.7% (2000/2001). For 1+ fish mean stream velocity exceeded CDV between 14.5% (1997/1998) and 30.7% (2000/2001) of the time. The movement of adult spawners into the Girnock Burn in preparation for autumn spawning (late October to mid-November) exhibited a complex relationship with hydrological variability with marked inter-annual contrasts. In years when discharge in the period prior to spawning was low, fish movement was increasingly triggered by suboptimal flow increases as spawning time approached. In contrast, wet years with numerous events allowed a much more even distribution of fish entry. Elucidating links between discharge/temperature variability and foraging opportunities and upriver migration of adult Atlantic salmon have the potential to contribute to the improvement of conservation strategies in both regulated and unregulated rivers.

Relationship Between Rainfall and Stable Fly (Diptera: Muscidae) Abundance on California Dairies

Populations of adult stable flies, Stomoxys calcitrans (L.), were visually estimated by counting flies on the front legs of cattle on southern and central California confined dairy feedlots between late April and mid-June (encompassing the peak stable fly activity period). Fly counts on 45-90 animals (three to six dairies) per weekly sample date were conducted in 1985, 1986, 1993, 2002, and 2003. Average biting intensity (flies per front leg) for the peak fly season was not significantly related to early winter (December-January), late winter (February-March), or total period (December-March) rainfall, but it was strongly related (r2 = 0.726) to March rainfall. March rains probably moistened outside decaying manure habitats and similar substrates that are particularly suitable at that time for stable fly oviposition and larval development. Degree-day accumulations link the timing of significant (> or = 1.3 cm) late winter or early spring rains to peak adult stable fly activity two generations later in May and early June.

Effects of Nitrogen and Potassium Fertilization on Perennial Ryegrass Cold Tolerance During Deacclimation in Late Winter and Early Spring

Turf loss from freezing injury results in costly re-establishment, especially with turfgrasses such as perennial ryegrass (Lolium perenne L.) having poor low-temperature hardiness. Studies are limited as to the influence of N and K on cold tolerance during dehardening periods in late winter when grasses are most susceptible to freezing injury. The objective of this study was to evaluate perennial ryegrass low temperature hardiness during deacclimation in response to N and K and associated effects on crown hydration, median killing temperature (LT50), shoot growth rate, tissue K concentration, soil exchangeable K, and low temperature disease. Treatments included five rate levels of N (49, 147, 245, 343, and 441 kg·ha-1·yr-1) in all factorial combinations with 3 rate levels of K (49, 245, and 441 kg·ha-1·yr-1). Low temperature tolerance was assessed using whole plant survival and electrolyte leakage (EL). Interactions between N and K were detected for all field measurements. The effects of N and K on survival LT50 were detected only during late winter periods in February 2004, N and K differences were lost by March. Late winter cold survival was negatively correlated with crown moisture, growth rate, and tissue K. Tissue K concentrations ranged from 28.6 to 35.9 g·kg–1 DM while soil K ranged from 121 to 261 mg·kg–1. Soil extractable K was not correlated with tissue K. Survival and EL LT50 were uncorrelated due to N and K interaction. Survival LT50 ranged from –9.0 to –13.6 °C. Maximum cold hardiness occurred when low to moderate N (49 to 147 kg·ha-1·yr-1) was applied with medium-high to high levels of K (245 to 441 kg·ha-1·yr-1), which corresponded to soil exchangeable K levels ranging from 200 to 260 mg·kg–1. Alternatively, similar K fertilization and soil K levels combined with high rates of N (343 and 441 kg·ha-1·yr-1) increased freeze stress and low temperature fungi (Typhula incarnata). At N rates routinely applied to perennial ryegrass, higher soil extractable K beyond those levels currently recommended for optimum shoot growth could provide some benefit in enhancing cold hardiness. Late fall applied N did not appear to increase the potential for winter injury.

The effect of copper-amended fertiliser and copper oxide wire particles on the copper status of farmed red deer (Cervus elaphus) and their progeny

AIM: To determine changes in serum and liver copper concentrations in postnatal, weaner, yearling, and mature deer after grazing pasture topdressed with copper (Cu) at two rates of application of copper sulphate (CuSO4.5H2O), and following oral administration of copper oxide (CuO) wire particles to some of the deer. METHODS: In mid-March 2000 (Year 1), 1.1-ha paddocks (two/treatment) of ryegrass/white clover pasture received either 0 (Control), 6 (Low) or 12 (High) kg CuSO4.5H2O/ha applied with 250 kg potash superphosphate/ha. They were grazed by 4-month-old red deer hinds (n=11/treatment) from mid-April 2000 until early March 2001. In mid-March 2001 (Year 2), the pastures were topdressed again as for Year 1, and the original hinds, now yearlings which had grazed as a single group between studies, were returned to their respective treatments in mid-April 2001 and remained on the trial until mid-March 2002. They were mated during April/May. The pastures were also grazed by pregnant mature hinds (n=8/treatment) from mid-May 2001. As the Cu status (i.e. liver Cu concentration) of the yearling hinds on the pasture treated with 6 kg CuSO4.5H2O/ha was not significantly different from the untreated animals, in late July 2001 the yearling and mature deer on this treatment were treated orally with 10 g CuO wire particles. The mature hinds calved in November and the yearling hinds in December. Pasture samples were collected at about monthly intervals to determine concentrations of Cu and other minerals. In Year 1, liver biopsies and blood samples were collected at 4–6-weekly intervals for determination of Cu concentrations. In Year 2, samples were collected similarly at 6–12-weekly intervals. Liver biopsies and blood were also collected from progeny, along with milk from their dams. Liveweights were determined at 3–7-monthly intervals, as well as data on calving/mortality rates. RESULTS: Pasture Cu concentrations before the application of CuSO4.5H2O were 6–9 mg Cu/kg dry matter (DM) and remained at this level in the untreated Control paddocks throughout the study. In Year 1, 28 days after treatment, pasture Cu concentration was 25 and 35 mg Cu/kg DM for the Low and High treatments, respectively; while at the same time for the same treatments in Year 2 it was 20 and 60 mg/kg DM, respectively. A second 60 mg Cu/kg DM peak also occurred on Day 85 in Year 2 with the High treatment. The pasture Cu concentration returned to 6–9 mg/kg DM, and there were no differences between treatments at Days 80 and 150 in Years 1 and 2, respectively. In Years 1 and 2, the Low treatment had no significant effect on the Cu status of the weaner and yearling hinds, respectively, when compared with that of animals grazing the untreated Control pastures. Weaner (Year 1) and yearling (Year 2) deer on the High treatment had significantly higher mean serum and liver Cu concentrations in the late winter and spring period when compared with those on untreated Control pastures. CuO wire particles increased the mean serum Cu concentration at Days 60 and 180, and liver Cu concentration at Day 60, in yearling hinds. A similar effect was observed in mature hinds. Regardless of Cu treatment, the liver Cu concentration of the 1–4-week-old progeny was markedly greater (p<0.001) than that of their dams, and then decreased significantly until weaning in March. In progeny of treated yearling hinds, but not mature hinds, serum and liver Cu concentrations were significantly higher (p=0.013) than progeny of untreated dams. CONCLUSION: Topdressing pastures with CuSO4.5H2O at a rate of 12 kg/ha, but not 6 kg/ha, in mid-March was effective in increasing the Cu status of weanling hinds; while pastures topdressed with 12 kg CuSO4.5H2O/ha in mid-March and dosing hinds with 10 g CuO in late July were effective in increasing the Cu status of pregnant hinds, and in the case of the yearling hinds, significantly improved the Cu status of their progeny from birth to weaning.

Acute otitis media and season of birth

This study examines the question whether season of birth is associated with acute otitis media (AOM) and recurrent AOM (rAOM) and whether season of birth is associated with early age of AOM onset. This was done in a population-based survey of 591 unselected Greenlandic children aged 3-5 and 8 years, living in the two largest towns in Greenland. The overall attendance rate was 86%. Information of AOM episodes was obtained from the parents and cross-checked in medical records available for 95% of the children. In total, 67% reported AOM at least once and 30% of those had rAOM. According to season of birth, the frequency of history of AOM in general varied between 63% and 70% lowest for birth in the autumn and highest for birth in the spring but without any significant statistical difference (p=0.51). The similar variation in rAOM according to season of birth was between 21% and 35%, highest for children born in autumn and winter and lowest for children born in the spring (p=0.09). Additionally, there was no difference in age at onset of the first AOM episode according to season of birth. However, AOM children born in the summer and autumn periods have a significantly higher relative risk (RR=1.44, CI=1.04-1.99) of attracting rAOM than AOM children born in the winter and spring periods. This may be due to a higher risk of being quickly reinfected in the late autumn and winter period with another episode of upper respiratory tract infection. Season of birth do not seem to be a predictor of AOM episodes or early onset of AOM but children born in the summer and autumn periods who attracts AOM have a higher risk of developing rAOM.

Effects of tillage systems in dryland farming on near-surface water content during the late winter period

Tillage systems modify, at least temporarily, some of the physical properties of soil, such as soil porosity. Tillage also has an indirect effect on soil water content throughout the growth cycle, particularly in areas with a Mediterranean climate. This paper presents the results of monitoring the water content in the topsoil (0–0.20 m) of three adjacent plots during February to May cycles starting in 1994–1995 and ending in 1998–1999. Each of the plots had a surface area of 2700 m 2, an 8% slope and Calcic Cambisol soil. Starting in 1994, three different tillage systems were applied: conventional tillage, which is typical of the area (CT); minimum tillage (MT); and no-tillage (NT). Two vertical 200 mm TDR probes were permanently installed in each plot and measurements were taken every week. The results show that, under an NT system, the soil had significantly higher water content than the other two soil plots. However, this increased quantity of water did not denote increased crop production; on the contrary, these preliminary data point to a decrease in crop production.

Effect of increased flow on the behaviour of Atlantic salmon parr in winter

The effect of increased flow on movement and microhabitat use of Atlantic salmon Salmo salar parr in winter was investigated using radiotelemetry. To simulate hydropeaking operations, flow was increased four‐fold from 1·3 m3 s−1 to 5·2 m3 s−1 for 24 h periods. Flow did not affect fish habitat use or displacement and had little effect on fish activity within diel periods. During high flow periods in late winter, fish reduced night‐time activity. Stranding rates during flow reduction were also very low (only one fish).

WINTER PREY SELECTION AND ESTIMATION OF WOLF KILL RATES IN YELLOWSTONE NATIONAL PARK, 1995–2000

Wolf (Canis lupus) impacts on prey are a central post-wolf-reintroduction issue in the greater Yellowstone ecosystem (GYE) of the western United States. Further, estimates of wolf kill rates, used to understand these impacts, can be biased due to unrecovered kills. In Yellowstone National Park (YNP), visibility of wolves allowed us to combine independent aerial and ground observations and use a double-count method to estimate the probability of recovering kills. We consequently used these data to adjust estimates of wolf kill rates. We conducted monitoring annually from 1995 to 2000 during 2 30-day periods in early (15 Nov–14 Dec) and late winter (Mar). Estimated recovery rates of wolf kills for ground and aerial crews were 50% and 45%, respectively, although we determined that this varied by location (distance from road) and possibly age (calf or adult) of the kill. The estimated combined recovery rate was 73%. Estimated wolf kill rates were higher in late winter (2.2 kills/wolf/month) compared to early winter (1.6 kills/wolf/month), with an overall estimated rate of 1.9 kills/wolf/month. The primary prey of wolves in winter was elk (Cervus elaphus; 90%). During our study, 43% of the elk killed were calves, 28% were adult females (cows), 21% were adult males (bulls), and 9% were of unknown age/sex. Comparing prey selection to prey availability, wolf packs residing on the northern range (NR) of the GYE selected for calves, against cows, and approximately proportional to availability for bulls. Prey use was different for wolf packs occupying the NR compared to packs residing in other areas (non-northern range [NNR]) and varied seasonally for NR packs. Variation in wolf kill rates by season, and the relative stability of the northern Yellowstone elk herd during a series of mild winters despite increases in wolf density, suggest that kill rates and ultimately elk population size are influenced by winter weather. Management of ungulates should reflect the addition of wolves combined with the unpredictability of winter weather in the mountainous terrain of the western United States.

Induced resistance to infection of lobsters Homarus americanus by Aerococcus viridans (var.) homari, the bacterium causing gaffkemia

A vaccine composed of steam sterilized (autoclaved) cells of a virulent strain of Aerococcus viridans (var.) homari was effective in protecting lobsters Homarus americanus against gaffkemia. At 15 degrees C the heat-killed vaccines (HKV) at concentrations between 1 and 5 x 10(7) particles kg(-1) lobster body wt induced maximal protection in induction periods ranging from 7 to 11 d. Protection was substantial over the course of a 30 d post-induction trial period. Spring-caught lobsters (i.e. those more fully rehabilitated following ecdysis) gained more protection (LD50 = 1.9 x 10(4)) from the vaccination than did those caught in the late fall-early winter period (lobsters that were not yet fully recovered from ecdysis) (LD50 = 3.2 x 10(3)). The protection offered by the HK vaccine was comparable to that induced by a vaccine produced by incubating the pathogen with low concentrations (2 pg ml(-1)) of the antibiotic vancomycin. The bacterins produced by both methods exhibited similar new properties: (1) agglutination at low titres by lobster hemolymph serum, suggesting an impaired capsule layer, and (2) increased permeability to the large Alcian Blue molecule. With both vaccines, the protection may be a direct result of increased exposure to intact bacterial cell structures by the lobster defences, an exposure which otherwise would be prevented by an intact capsule.

Delayed post-fire seedling emergence linked to season: a case study with Leucopogon species (Epacridaceae)

In many fire-prone habitats around the world, natural fire regimes have shaped the evolution of the associated flora. Critical life history stages are often linked to fire in species that occur in these fire-prone habitats but many species are unstudied. We investigated seedling emergence patterns over time, after several fires in south-eastern Australia, for three obligate seeders in the Genus Leucopogon (Family Epacridaceae): L. setiger, L. esquamatus and L. exolasius. Fixed quadrats were monitored for 12 to 30 months for newly emerged seedlings, both after fire and in unburnt L. exolasius and L. esquamatus habitats. There was a flush of seedling emergence in the first year after fire for all three Leucopogon species, with smaller pulses recorded in subsequent years. Time elapsed between fire and the onset of emergence differed between fires, but not between Leucopogon species. Whatever the timing of the fire, seedling emergence was restricted to the late autumn and winter periods, coinciding with emergence in unburnt habitat. This contrasts with patterns of emergence previously reported for other taxa, and also in this study, where emergence of the Leucopogon species after fire was delayed compared with co-occurring species in other genera. Our results suggest that seasonal factors are important to the germination ecology of these species and that combinations of fire-related and seasonal factors are necessary to maximise germination. Rainfall has a non-seasonal pattern in the study region and seasonal emergence post-fire has not previously been recorded. The magnitude of delay to emergence of species with seasonal emergence patterns will be determined by the season of fire but not by a seasonal pattern of rainfall in the post-fire year. A shift of the peak fire season could increase this delay, possibly affecting plant population recovery.

Productivity, Protein Content and Nutrient Removal from Anaerobic Effluents of Coffee Wastewater in Salvinia minima Ponds, under Subtropical Conditions

AbstractSalvinia minima is an aquatic fern which presents several advantages for the phytoremediation of wastewater. However, there is no information available for the operation of Salvinia‐based systems (SBS) for nutrient removal from organic matter enriched wastewater. The objective of this work was to establish the optimum range of some key parameters for the operation of Salvinia minima ponds treating anaerobic effluents of coffee wastewater (AECWW). Batch cultures were performed outdoors, under subtropical conditions (Xalapa, Veracruz, Mexico). At the first stage, various pH levels were tested. After choosing the optimum pH, two pond depths were evaluated (0.10 m and 0.27 m). It was found that the productivity in AECWW was strongly affected by the pH, as it decreased with the increase in the pH. In fact, growth was completely inhibited at pH 8.0. In contrast, productivity at a pH of 6.0 and a pond depth of 0.27 m during the summer was equivalent to 27.92 ton/ha × year. The percentage of TKN removal increased with the pH value: 51 ± 2.28% at pH 5.0; 78 ± 1.47% at pH 6.0 and. 97 ± 0.80% at pH 8.0. A similar situation was found for the case of NH4‐N removal: (55 ± 0.44%, 80 ± 1.1%, 99 ± 0.02%). The depth of the culture had influence on the productivity, protein content and nutrient removal. It was concluded that Salvinia minima is an adequate choice for the treatment and recovery of nutrients from AECWW. The pH for optimal operation of this type of pond was 6.0. The depth of the water column should be adjusted to 0.10 m for attaining a maximum relative removal efficiency (in terms of g NH4‐nitrogen/l × d), although the productivity would not be at its maximum under these conditions. On the contrary, depth should be adjusted to 0.27 m for reaching the maximum absolute removal efficiency (considering the total volume of the reactor) and the maximum productivity. During the late autumn and winter period, the AECWW should be diluted 1:2 in order to enhance ammonia nitrogen removal.

Sources of C and N contributing to the flush in mineralization upon freeze–thaw cycles in soils

In mid-latitude climatic regions (35–65°) soils may be subjected to freeze–thaw cycles (FTC) which can occur frequently in late winter and early spring. FTC often results in flushes in C and N mineralization and could therefore be an important factor controlling C and N mineralization rates. Laboratory experiments were carried out to characterize the source of organic matter that becomes available upon FTC. Soils, differing in the quantity and quality of organic matter inputs they had received since 1956, were sampled, pre-incubated to reduce amounts of labile organic matter and subsequently exposed to repeated FTC. Each FTC consisted of 6 h at −2 °C, 16 h at −5 °C, 4 h at +2 °C and 22 h at +5 °C, giving a total of 48 h for each FTC. The contribution of microbial biomass C to the C flush upon FTC was determined by labeling the native microbial biomass with a small amount of 14C-labeled glucose and comparing the specific activity of the C flush upon FTC with that upon chloroform fumigation. Temperature corrected amounts of C and N mineralized in soil incubated at constant temperatures acted as control in the calculation of the flush. FTC increased the amounts of C and N mineralized 2–3 fold. The flush was short-lived and highest in the first four FTC, suggesting that easily decomposable material became available upon FTC and that the size of the freeze–thaw susceptible pool was limited. The C flush was linearly related to organic C, water-soluble organic C, microbial biomass C and basal respiration, but only proportional to the latter two. Labeling the native microbial biomass with a small amount of glucose suggested that microbial biomass C contributed ca. 65% to the C flush upon FTC, while representing only about 5% of microbial biomass C. We have no direct evidence for the source of the remaining 35% of the C flush or for the mechanism of its release. In soils subjected to chloroform fumigation prior to being exposed to FTC organic matter released by fumigation became a more important source to the flush than the microbial biomass, suggesting that labile organic matter is highly susceptible to FTC. From our results, effects of FTC have little consequence for annual C and N budgets, but may need to be taken into account when modeling C and N mineralization during the late winter and early spring period in mid-latitude climatic regions.

Seasonal variations of net CO 2 exchange in European Arctic ecosystems

The carbon dioxide exchange in arctic and subarctic terrestrial ecosystems has been measured using the eddy-covariance method at sites representing the latitudinal and longitudinal extremes of the European Arctic sea areas as part of the Land Arctic Physical Processes (LAPP) project. The sites include two fen (Kaamanen and Kevo) and one mountain birch ecosystems in subarctic northern Finland (69° N); fen, heathland, and snowbed willow ecosystems in northeastern Greenland (74° N); and a polar semidesert site in Svalbard (79° N). The measurement results, which are given as weekly average diurnal cycles, show the striking seasonal development of the net CO2 fluxes. The seasonal periods important for the net CO2 fluxes, i.e. winter, thaw, pre-leaf, summer, and autumn can be identified from measurements of the physical environment, such as temperature, albedo, and greenness. During the late winter period continuous efflux is observed at the permafrost-free Kaamanen site. At the permafrost sites, efflux begins during the thaw period, which lasts about 3–5 weeks, in contrast to the Kaamanen site where efflux continues at the same rate as during the winter. Seasonal efflux maximum is during the pre-leaf period, which lasts about 2–5 weeks. The summer period lasts 6 weeks in NE Greenland but 10–14 weeks in northern Finland. During a high summer week, the mountain birch ecosystem had the highest gross photosynthetic capacity, GPmax, followed by the fen ecosystems. The polar semidesert ecosystem had the lowest GPmax. By the middle of August, noon uptake fluxes start to decrease as the solar elevation angle decreases and senescence begins within the vascular plants. At the end of the autumn period, which lasts 2–5 weeks, topsoil begins to freeze at the end of August in Svalbard; at the end of September at sites in eastern Greenland; and one month later at sites in northern Finland.

Feeding habits of wild and escaped farmed Atlantic salmon, Salmo salar L., in the Northeast Atlantic

Jacobsen, J. A., and Hansen, L. P. 2001. Feeding habits of wild and escaped farmed Atlantic salmon, Salmo salar L., in the Northeast Atlantic. – ICES Journal of Marine Science, 58: 916–933. The stomach contents of 2992 wild and 863 putative escaped farmed Atlantic salmon caught on floating long-lines in a Faroese research fishery in the late autumn (November–December) and winter (February–March) in the Northeast Atlantic (63–66N and 1–10W) during three consecutive fishing periods 1992/1993–1994/1995 were analysed. Hyperiid amphipods of the genus Themisto, euphausiids and mesopelagic shrimps are important sources of food for salmon in the autumn period and various mesopelagic fish as lantern fishes, pearlsides and barracudinas become equally important during the late winter period. The occasional presence in the stomachs of larger fish such as herring, blue whiting and mackerel is not considered to be evidence that these fish are a main source of food for salmon in the sea north of the Faroes. The proportion of stomachs containing food was significantly lower during autumn (53%) than during winter (78%). However, temperature-dependent evacuation rates could partly explain the apparent lower stomach content during the autumn, since the average ambient sea-surface temperature is 7C in autumn compared to 3C in winter. There was evidence of selective foraging. Fish were preferred over crustaceans, and amphipods were chosen over euphausiids. Large salmon (3+SW) tended to be more piscivorous than smaller fish. There was no difference in condition factor, number and weight proportions of prey, or in diet between wild and escaped farmed salmon, which suggests that escaped farmed salmon adapt well to the ‘‘wild’’ life in the ocean. 2001 International Council for the Exploration of the Sea

Seasonality of feeding and nutritional status during the austral winter in the Antarctic sea urchin Sterechinus neumayeri

The seasonal pattern of food intake and tissue energy status was measured over a 2 year period for two populations of the common Antarctic echinoid Sterechinus neumayeri living on contrasting substrata at Rothera Point, Adelaide Island, Antarctica. Food intake was estimated from faecal egestion, and both tissue mass and energy content assessed. Food availability was intensely seasonal, in that water column chlorophyll content and sediment pigment content varied markedly throughout the year. In response, both urchin populations showed an extremely seasonal cycle of faecal egestion, indicating a strong seasonality of feeding activity. Urchins from North Cove living on soft sediment fed at a considerably higher rate, and had a significantly larger Aristotle's lantern, than those in South Cove, 1 km away, living on hard substrata and taking a more cosmopolitan diet. Faecal egestion in both populations was zero for a 7 month period in the austral winter of 1997, and again for a 4 month period in 1998. During the austral summer of 1997/1998, 84% of the total annual energy intake took place in the period January to March. Significant decrease in gut tissue mass provided energy for maintenance in early winter, although progressive reduction of both gonad energy content (but without a detectable change in gonad mass) and body wall organic mass provided energy during the late winter period. The mass of reproductive tissue showed large differences between the two sites, but there was no marked decrease associated with spawning. Tissue proximate composition was assessed stoichiometrically from elemental composition and also checked by direct assay; gonad tissue was richer in lipid than gut tissue, though both were dominated by protein and contained only small amounts of carbohydrate. These data suggest that the very strong seasonality of food intake does not pose a significant energetic challenge for this species.

Seasonal differences in the origin of Atlantic salmon ( Salmo salar L.) in the Norwegian Sea based on estimates from age structures and tag recaptures

To test if the population structure of Atlantic salmon ( Salmo salar L.) at the feeding areas in the Norwegian Sea north of the Faroes is stable throughout early (November–December) and late (February–March) winter, river and sea age distributions were estimated from 2350 scale samples obtained in the early and late winter during four consecutive fishing periods 1991/1992–1994/1995. The origin of recaptures of salmon tagged as smolts in different European countries were also compared between early and late winter. The fish were classified as being of wild or fish farm origin from scale characteristics, and farmed salmon were excluded from the analyses. Age compositions in samples from the four fishing periods showed consistent patterns. The average smolt age (±S.E.) was significantly lower in the early than in the late winter (2.5±0.04 and 2.7±0.03, range 1–5) as was average sea age (1.9±0.03 and 2.2±0.02, range 1–6). As salmon from southern European countries tend to smolt at an earlier age and produce more one sea-winter salmon than in northern Europe, we suggest that a significant proportion of the salmon caught in the Faroes area during early winter originate from southern European countries and that fish from northern regions appear to be more abundant in the late winter period. Recaptures in the Faroese fishery during early and late winter of salmon tagged as smolts in different countries support this.

Interannual Seesaw between the Aleutian and Icelandic Lows. Part I: Seasonal Dependence and Life Cycle

Abstract The seasonal dependence and life cycle of the well-known interannual seesawlike oscillation between the intensities of the surface Aleutian and Icelandic lows (AL and IL, respectively) are investigated, based on the National Meteorological Center operational analyses for the period from 1973 to 1994. It is found that the correlation between the AL and IL intensities is significantly negative only from February to mid-March. It is also found that the seesaw exhibits an equivalent barotropic structure within the troposphere. For this late-winter period an index is defined that measures the intensity difference between the two lows. A linear lag regression analysis between this index and circulation anomalies averaged in each of the nine 45-day periods from early winter to midspring reveals that the stationary AL and IL anomalies constituting the seesaw do not start developing simultaneously over the respective ocean basins in the course of a particular winter season. Rather, the seesaw formation is...

The seasonal variations of dimethyl sulphide and carbon disulphide in surface waters of the Venice lagoon

Abstract The seasonal variation in the concentration of dimethyl sulphide (DMS) and carbon disulphide (CS2) in the surface water of the Venice lagoon was determined at two stations in the period from 3 June 1996 (3 March 1997 for CS2) to 26 November 1997. Other parameters such as chlorophyll a, water temperature, and wind speed were also measured. DMS concentration (ranges 0.85–15.0 nmol S l−1 at Stn. 1 and 0.40–16.3 nmol S l−1 at Stn. 2) showed two relative maxima in the spring–summer period, probably connected to phytoplanktonic and macro-algal blooms. Low and constant values were observed in autumn, whereas the maximum concentration was observed in the late winter period. The CS2 concentration (ranges 0.17–2.8 nmol S l−1 at Stn. 1 and 0.08–2.0 nmol S l−1 at Stn. 2) increased in the spring, was maximal in summer and then decreased in autumn, with a different trend from that of DMS, suggesting that the production and the fate of CS2 and DMS in water are different. Interpretation of the seasonal trends, based on current knowledge of possible formation and transformation processes, is reported. The mean flux of DMS to the atmosphere is estimated to be 0.34 μmol S (DMS) m−2 day−1, which is about one order of magnitude lower than that observed in the open sea, due mainly to lower wind speed. The CS2 flux (March to November average 0.086 μmol S(CS2) m−2 day−1) may represent, at least in lagoon environments, an appreciable fraction of the total natural reduced sulphur emitted to the atmosphere.