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Early March (early + march)
Selected AbstractsSize-fractionated phytoplankton biomass and its implications for the dynamics of an oligotrophic tropical lakeFRESHWATER BIOLOGY, Issue 1 2008MARÍA FERNANDA ADAME Summary 1. Size-fractionated phytoplankton biomass was examined in relation to the hydrodynamics of tropical Lake Alchichica from 1999 to 2002. 2. Alchichica is a warm monomictic lake, in which mixing takes place from late December to early March. The lake is oligotrophic (mean total chlorophyll- a concentration 4.2 ± 4.2 ,g L,1) and its phytoplankton biomass is dominated (72.3 ± 16.4%) by large individuals (>2 ,m). The degree of dominance of the large size class (nano- and microplankton) over the small size class (picoplankton) throughout the year is mainly determined by the availability of silicate and the Si/N ratio in the hypolimnion prior to the mixing period. 3. This is the first record of an oligotrophic tropical lake dominated by large size fractions of phytoplankton. Because of this dominance, the fate of most primary productivity is rapid sedimentation to the bottom followed by decomposition that promotes an anoxic hypolimnion. 4. Our findings in tropical Lake Alchichica challenge the idea that oligotrophic waters are dominated by small phytoplankton, as has been well established for the oligotrophic ocean and temperate lakes. [source] Impacts of extreme winter warming in the sub-Arctic: growing season responses of dwarf shrub heathlandGLOBAL CHANGE BIOLOGY, Issue 11 2008S. BOKHORST Abstract Climate change scenarios predict an increased frequency of extreme climatic events. In Arctic regions, one of the most profound of these are extreme and sudden winter warming events in which temperatures increase rapidly to above freezing, often causing snow melt across whole landscapes and exposure of ecosystems to warm temperatures. Following warming, vegetation and soils no longer insulated below snow are then exposed to rapidly returning extreme cold. Using a new experimental facility established in sub-Arctic dwarf shrub heathland in northern Sweden, we simulated an extreme winter warming event in the field and report findings on growth, phenology and reproduction during the subsequent growing season. A 1-week long extreme winter warming event was simulated in early March using infrared heating lamps run with or without soil warming cables. Both single short events delayed bud development of Vaccinium myrtillus by up to 3 weeks in the following spring (June) and reduced flower production by more than 80%: this also led to a near-complete elimination of berry production in mid-summer. Empetrum hermaphroditum also showed delayed bud development. In contrast, Vaccinium vitis-idaea showed no delay in bud development, but instead appeared to produce a greater number of actively growing vegetative buds within plots warmed by heating lamps only. Again, there was evidence of reduced flowering and berry production in this species. While bud break was delayed, growing season measurements of growth and photosynthesis did not reveal a differential response in the warmed plants for any of the species. These results demonstrate that a single, short, extreme winter warming event can have considerable impact on bud production, phenology and reproductive effort of dominant plant species within sub-Arctic dwarf shrub heathland. Furthermore, large interspecific differences in sensitivity are seen. These findings are of considerable concern, because they suggest that repeated events may potentially impact on the biodiversity and productivity of these systems should these extreme events increase in frequency as a result of global change. Although climate change may lengthen the growing season by earlier spring snow melt, there is a profound danger for these high-latitude ecosystems if extreme, short-lived warming in winter exposes plants to initial warm temperatures, but then extreme cold for the rest of the winter. Work is ongoing to determine the longer term and wider impacts of these events. [source] Breeding biology and conservation of the Black-vented Shearwater Puffinus opisthomelasIBIS, Issue 4 2003Bradford S. Keitt The Black-vented Shearwater Puffinus opisthomelas is endemic to the Pacific coast of Baja California, Mexico. We studied the breeding biology of this species at Natividad Island in 1997 and 1998. The colony at Natividad Island covers approximately 2.5 km2 and we estimated there to be 114 455 (± 27 520 95% CI) burrows in the colony. In 1997 burrow occupancy was 66.9%, providing a population estimate of 76 570 (± 18 411 95% CI) breeding pairs, representing about 95% of the world's population of this species. In 1997 the peak in egg laying occurred in early March and hatching began on 7 May. The incubation period averaged 51 days (± 6 sd) and chick rearing averaged 69 days (± 3 sd). In 1998 burrow occupancy was lower (19.6%) and nest initiation was later (peak egg laying in mid-April), perhaps a result of El Niño conditions that prevailed in the Eastern Pacific at that time. We calculated that the development of the town and roads on Natividad Island have destroyed over 15% (26 532 burrows) of the breeding habitat on the island. [source] Effect of dietary ,-tocopherol + ascorbic acid, selenium, and iron on oxidative stress in sub-yearling Chinook salmon (Oncorhynchus tshawytscha Walbaum)JOURNAL OF ANIMAL PHYSIOLOGY AND NUTRITION, Issue 1 2009T. L. Welker Summary A three-variable central composite design coupled with surface-response analysis was used to examine the effects of dietary ,-tocopherol + ascorbic acid (TOCAA), selenium (Se), and iron (Fe) on indices of oxidative stress in juvenile spring Chinook salmon. Each dietary factor was tested at five levels for a total of fifteen dietary combinations (diets). Oxidative damage in liver and kidney (lipid peroxidation, protein carbonyls) and erythrocytes (erythrocyte resistance to peroxidative lysis, ERPL) was determined after feeding experimental diets for 16 (early December) and 28 (early March) weeks. Only TOCAA influenced oxidative stress in this study, with most measures of oxidative damage decreasing (liver lipid peroxidation in December and March; ERPL in December; liver protein carbonyl in March) with increasing levels of TOCAA. We also observed a TOCAA-stimulated increase in susceptibility of erythrocytes to peroxidative lysis in March at the highest levels of TOCAA. The data suggest that under most circumstances a progressive decrease in oxidative stress occurs as dietary TOCAA increases, but higher TOCAA concentrations can stimulate oxidative damage in some situations. Higher levels of TOCAA in the diet were required in March than in December to achieve comparable levels of protection against oxidative damage, which may have been due to physiological changes associated with the parr-smolt transformation. Erythrocytes appeared to be more sensitive to variation in dietary levels of TOCAA than liver and kidney tissues. Using the March ERPL assay results as a baseline, a TOCAA level of approximately 350,600 mg/kg diet would provide adequate protection against lipid peroxidation under most circumstances in juvenile Chinook salmon. [source] WINTER PHYTOPLANKTON BLOOMS UNDER ICE ASSOCIATED WITH ELEVATED OXYGEN LEVELS,JOURNAL OF PHYCOLOGY, Issue 6 2002Karen A. Phillips Many shallow lakes in north temperate zones experience reduced dissolved oxygen concentration under ice. However, some shallow lakes display supersaturated dissolved oxygen concentrations (>20 mg·L,1) in late winter under conditions of maximum ice thickness. During the winters of 1996, 1997, and 1999, we collected phytoplankton samples from Arrowwood Lake near Pingree, North Dakota to determine whether a specific alga was involved in dissolved oxygen supersaturation in this lake. Although dissolved oxygen supersaturation was not observed during this period, we did observe an increase in dissolved oxygen concentration that was associated with a phytoplankton bloom during late February and early March in both 1996 and 1997. In 1996, the bloom was composed of the dinoflagellate, Peridinium aciculiferum (Lemm.) Lemm. and several species of cryptomonads. A similar bloom of P. aciculiferum was followed by a bloom of several species of euglenoids in 1997. In contrast, P. aciculiferum was only a minor component of the winter phytoplankton, dissolved oxygen concentrations remained low, and no bloom event was observed in 1999. Statistical analyses indicated a significant relationship (rs = 0.57, P = 0.019) between dissolved oxygen levels and the density of the dinoflagellate, P. aciculiferum, but no significant relationship between dissolved oxygen levels and densities of other phytoplankton. These results suggest that the elevated levels of dissolved oxygen are associated with the dinoflagellate, P. aciculiferum. This bloom was most likely the result of an excystment event rather than a general growth response. [source] Competitive Interactions among First-Year and Second-Year Plants of the Invasive, Biennial Garlic Mustard (Alliaria petiolata) and Native Ground Layer VegetationRESTORATION ECOLOGY, Issue 5 2010Jonathan T. Bauer We studied the effects of hand weeding of second-year plants of the biennial garlic mustard (Alliaria petiolata) on first-year plants (seedlings) and native ground layer vegetation. Garlic mustard is a Eurasian species that has invaded deciduous forest ground layers in eastern North America. Treatments consisted of a control and an early or late weeding of second-year garlic mustard. The early treatment (early March) was applied before garlic mustard seeds had germinated and when most native species were dormant. The late treatment (mid-May) occurred after plants had bolted, flowering was occurring, and most native species and new garlic mustard seedlings were actively growing. Pre-treatment data were obtained in 2004 and treated and control plots were sampled in 2005, 2006, and 2007. No significant treatment effects were observed in 2004 or 2005. In 2006, mean cover of first-year plants was higher in the early weeding treatment than in the late weeding treatment and control. In 2007, mean cover of first-year garlic mustard was higher in the control than in either of the two weeding treatments. There were no significant treatment effects in any year on native vegetation cover, bare ground, or the five most abundant native species. Our data indicate that (1) late weeding of garlic mustard provided more effective control than early weeding because late weeding allows second-year plants to compete with garlic mustard seedlings for a longer period of time and (2) competition between first- and second-year plants is responsible for alternating dominance of first-year and second-year garlic mustard plants. [source] Life cycle of the QBO-modulated 11-year solar cycle signals in the Northern Hemispheric winterTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 641 2009Hua Lu Abstract This paper provides some insights on the quasi-biennial oscillation (QBO) modulated 11-year solar cycle (11-yr SC) signals in Northern Hemisphere (NH) winter temperature and zonal wind. Daily ERA-40 Reanalysis and ECMWF Operational data for the period of 1958,2006 were used to examine the seasonal evolution of the QBO-solar cycle relationship at various pressure levels up to the stratopause. The results show that the solar signals in the NH winter extratropics are indeed QBO-phase dependent, moving poleward and downward as winter progresses with a faster descent rate under westerly QBO than under easterly QBO. In the stratosphere, the signals are highly significant in late January to early March and have a life span of ,30,50 days. Under westerly QBO, the stratospheric solar signals clearly lead and connect to those in the troposphere in late March and early April where they have a life span of ,10 days. As the structure changes considerably from the upper stratosphere to the lower troposphere, the exact month when the maximum solar signals occur depends largely on the altitude chosen. For the low-latitude stratosphere, our analysis supports a vertical double-peaked structure of positive signature of the 11-yr SC in temperature, and demonstrates that this structure is further modulated by the QBO. These solar signals have a longer life span (,3,4 months) in comparison to those in the extratropics. The solar signals in the lower stratosphere are stronger in early winter but weaker in late winter, while the reverse holds in the upper stratosphere. Copyright © 2009 Royal Meteorological Society [source] The initial journey of juvenile emperor penguinsAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue S1 2007Gerald L. Kooyman Abstract 1.The first major journey of emperor penguins, among several in their lifetime, is the juveniles' dispersal from their natal colony on a trip that takes them beyond Antarctic waters. The route taken by fledglings from Cape Washington (74.5°,S; 165.4°,E) was studied by applying satellite transmitters to ten individuals during December 1994,1996. In January 2001 transmitters with longer transmission capacity were also applied to six hand-fed fledglings, which had been held captive for one month while attaining a body mass exceeding that of wild birds. These post-captive birds were released at the ice edge of McMurdo Sound (77.5°,S; 165.0°,E), which is in the vicinity of other emperor penguin colonies, and 320,km south of their natal colony of Cape Washington. 2.Independent of their parents, the wild birds travelled north-east for the next two months, reaching locations as low as 57°,S. The post-captive birds travelled north also, but their trek reached only to about 63°,S before they turned south, or remained near their most northerly position from March through May. 3.It was concluded that among colonies in the southern Ross Sea: (a) most healthy fledglings survive at least the first two months at sea, feeding themselves as they go; (b) the Cape Washington fledglings travelled as far north as 57°,S, and much of this journey was in ice free waters; (c) by April, the post-captive birds reached at least as far as the large-scale pack ice edge and possibly beyond the edge at 63°,S; (d) by early March the trend north ends, and by about late March the birds travel to, or remain near the northern ice edge. 4.The reason the birds travel so far north remains a mystery. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||