The flux of CO2 and CH4 from lakes and rivers in arctic Alaska

Partial pressures of CO₂ and CH₄ were measured directly or calculated from pH and alkalinity or DIC measurements for 25 lakes and 4 rivers on the North Slope of Alaska. Nearly all waters were super-saturated with respect to atmospheric pressures of CO₂ and CH₄. Gas fluxes to the atmosphere ranged from −6.5 to 59.8 mmol m⁻² d⁻¹ for CO₂ and from 0.08 to 1.02 mmol m⁻² d⁻¹ for CH₄, and were uncorrelated with latitude or lake morphology. Seasonal trends include a buildup of CO₂ and CH₄ under ice during winter, and often an increased CO₂ flux rate in August due to partial lake turnover. Nutrient fertilization experiments resulted in decreased CO₂ release from a lake due to photosynthetic uptake, but no change in CO₂ release from a river due to the much faster water renewal time. In lakes and rivers the groundwater input of dissolved CO₂ and CH₄ is supplemented by in-lake respiration of dissolved and particulate carbon washed in from land. The release of carbon from aquatic systems to the atmosphere averaged 24 g C m⁻² y⁻¹, and in coastal areas where up to 50% of the surface area is water, this loss equals frac 1/5 to 1/2 of the net carbon accumulation rates estimated for tundra.     

The Release of CO<Subscript>2</Subscript> from Riverwaters – the Contribution of Excess CO<Subscript>2</Subscript> from Groundwater

The dissolved CO ₂ concentration of stream waters is an important component of the terrestrial carbon cycle and an important pathway for release of CO₂ to the atmosphere. This study uses data from the UK's largest groundwater monitoring network to estimate the importance of groundwater in contributing excess dissolved CO₂ to the atmosphere. The study shows that:

Dissolved oxygen and nutrient budgets in a phytotreatment pond colonised by <Emphasis Type="Italic">Ulva</Emphasis> spp.

Net daily budgets of dissolved oxygen (O₂), dissolved inorganic carbon (DIC), dissolved inorganic nitrogen (DIN = NH₄⁺+NO₂⁻+NO₃⁻) and soluble reactive phosphorus (SRP) were determined in a pond colonised by Ulva spp. This pond received wastewater from a land-based fish farm and was used as a phytotreatment plant. Three consecutive 24-h cycles of measurements were performed with 8–14 samplings per day. Water samples were collected at the inlet and outlet of the pond and budgets were estimated from differences between inlet and outlet loadings. The first cycle was started when Ulva biomass was 8 kg m⁻², as wet weight. The second cycle was performed after the harvest of ~20% of the macroalgal biomass and the third after the harvest of another ~20% of the remaining biomass. Ulva removal was very fast (<1 h) and samplings for cycles 2 and 3 were started two hours after harvesting, so that the whole experiment lasted ~80 h. When Ulva biomass was at its maximum, the aquatic system was heterotrophic with an O₂ demand of 519 mol d⁻¹ and a net regeneration of DIC (2686 mol d⁻¹), NH₄⁺ (49 mol d⁻¹) and SRP (2.5 mol d⁻¹). The DIC to O₂ ratio was an indicator of persistent anaerobic metabolism. Following the first harvest intervention, this system displayed a prompt response and shifted toward a lower O₂ demand (from −519 to −13 mol d⁻¹), with a lesser regeneration degree of NH₄⁺ (11.4 mol d⁻¹) and DIC (1066 mol d⁻¹). After the second Ulva removal the net budget of SRP became negative (−1.0 mol d⁻¹). By integrating these results over the three days cycle we estimated that in order to operate an efficient nutrient control and maintain macroalgal mats in a healthy status the optimal Ulva biomass should be well below ~4 kg m⁻² as wet weight. Above this threshold, self-limitation would render most of the algal mat unable to exploit light and nutrients. An efficient removal of nitrogen and phosphorus could be attained through the management of macroalgal biomass only with an optimisation of recipient surface to nutrient loading ratio.     

不同年龄雄性北山羊发情期时间分配特征

前人研究表明,可多次繁殖的反刍物种其雄性个体在发情期采食时间显著减少。目前有两个假说解释这一现象,即能量摄入最大化假说和能量保存假说。为验证雄性北山羊在不同发情阶段所采取的能量保存策略,作者于2014年10-12月在新疆天山中部采用焦点动物取样法采集数据,采用Kruskal-Wallis检验和Spearman秩相关性检验分析数据。研究发现雄性北山羊成体和亚成体发情期采食时间均显著低于发情前期和发情后期,但二者在不同发情阶段卧息时间无显著变化,发情期采食和卧息时间比亦显著降低。发情期发情行为时间显著高于发情前期和发情后期,非发情时间主要用于采食。发情期采食时间和卧息时间都与发情行为时间呈显著的负相关关系。雌性北山羊发情期采食时间亦显著低于发情前期和发情后期,发情期和发情后期卧息时间显著高于发情前期。本研究结果表明,发情期不同年龄阶段雄羊都主要采取能量摄入最大化策略,但同时也具有部分能量保存策略的特征。     

The effects of acid deposition on the biogeochemical cycles of major nutrients in miniature red spruce ecosystems

As part of an experimental study of air pollution effects on tree growth and health, we combined process studies with an ecosystem approach to evaluate the effects of acidic deposition on soil acidification, nutrient cycling and proton fluxes in miniature red spruce ecosystems. Ninety red spruce saplings were transplanted into 1-m diameter pots containing reconstructed soil profiles and exposed to simulated acid rain treatments of pH 3.1, 4.1 and 5.1 for four consecutive growing seasons. All the principal fluxes of the major elements were measured. During the first year of treatments, the disturbance associated with the transplanting of the experimental trees masked any treatment effects by stimulating N mineralization rates and consequent high N0₃ ⁻ cation, and H⁺ flux through the soil profile. In subsequent years, leaching of base cations and labile Al was accelerated in the most intensive acid treatment and corresponding declines in soil pH and exchangeable pools of Ca and Mg and increases in exchangeable Al concentrations were observed in the organic horizon. Leaching of Ca²⁺ and Mg²⁺ also was significantly higher in the pH 4.1 than in the pH 5.1 treatment. Flux of Ca from foliage and soil was increased in response to strong acid loading and root uptake increased to compensate for foliar Ca losses. In contrast, K cycling was dominated by root uptake and internal cycling and was relatively insensitive to strong acid inputs. Cation leaching induced by acidic deposition was responsible for the majority of H⁺ flux in the pH 3.1 treatment in the organic soil horizon whereas root uptake accounted for most of the H⁺ flux in the pH 4.1 and 5.1 treatments. Although no measurable effects on tree nutrition or health were observed, base cation leaching was significantly accelerated by acidic deposition, even at levels below that observed in the eastern U.S., warranting continued concern about acid deposition effects on the soil base status of forested ecosystems.     

In situ metabolic budget for the calanoid copepod Acartia clausi in a tropical brackish water lagoon (Ebrié Lagoon,Ivory Coast)

Simultaneous measurements of respiration, excretion and production rates were carried out several times over a year period at five representative stations of the Ebrié Lagoon. Assuming a constant assimilation efficiency rate of 69.4%, we derived metabolic budgets for carbon, nitrogen and phosphorus. Daily specific ingestion rates calculated were rather generally high, and ranged between 54 and 159% of body carbon, between 26 and 102% of body nitrogen and between 108 and 307% of body phosphorus. Regional and seasonal variations depended mainly upon variations in trophic conditions. Curvilinear relationships between ingestion production, or net production efficiency K2, and food concentration (as chlorophyll-a + phaeopigments) showed that food could have been a limiting factor. Furthermore, K2 were low when compared with data from the literature (mean of 21% in carbon, 39% in nitrogen and 11% in phosphorus).Complementary laboratory experiments carried out on adults fed with enriched natural particles or algal cultures (Tetraselmis sp. or Dunaliella sp.) showed similar production (egg-production) vs food concentration curvilinear relationships as in the field. However, considerably higher maximal ingestion and production rates were obtained for animals fed algal cultures suggesting that optima for food acquisition and transformation were not reached in field conditions.Consequently, A. clausi, which represents more than 50% of the zooplankton biomass, appears to be rather inefficient in transforming the abundant particulate organic matter produced in the lagoon. This results from its high level of metabolic expenditure through respiration or excretion (about 50% of ingestion in terms of carbon) and from the small size and poor trophic value of food particles (high percentage of detritus).     

Pelagic food web processes in an oligotrophic lake

Major pelagic carbon pathways, including primary production, release of extracellular products (EOC), bacterial production and zooplankton grazing were measured in oligotrophic Lake Almind (Denmark) and in enclosures (7 m³) subjected to artificial eutrophication. Simultaneous measurements at three days interval of carbon exchange rates and pools allowed the construction of carbon flow scenarios over a nineteen day experimental period.The flow of organic carbon was dominated by phytoplankton EOC release, which amounted from 44 to 58% of the net fixation of inorganic carbon. Gross bacterial production accounted for 33 to 75% of the primary production. The lower values of EOC release (44%) and bacterial production (33%) were found in the enclosures with added nutrients. The release of recently fixed photosynthetic products was the most important source of organic carbon to the bacterioplankton. Uptake of dissolved free amino acids was responsible for 52 to 62% of the gross bacterial production. Thus, amino acids constituted a significant proportion of the EOC. Zooplankton (< 50 µm) grazing on algae and bacteria accounted only for a minor proportion of the particulate production in May. Circumstantial evidence is presented that suggests the chrysophycean alga Dinobryon was the most important bacterial remover.The results clearly demonstrated EOC release and bacterial metabolism to be key processes in pelagic carbon cycling in this oligotrophic lake.     

Inter-population differences in the time budgets of bonnet monkeys (Macaca radiata)

Time budgets for five major activities viz., Passive Sitting, Locomotion, Foraging, Social Behaviour, and Self-directed Behaviours were recorded for bonnet monkeys inhabiting forest, urban, and rural habitats. The time budgets were further classified into those of various age-sex classes. Significant inter-population differences were found in group size, social behaviour, foraging, and locomotion, which are discussed in relation to the habitat features.     

Activity budgets in a group of Sichuan snub-nosed monkeys in Shennongjia Nature Reserve, China

We examined time allocation by Sichuan snub-nosed monkeys Rhinopithecus roxellana in the montane,temperate and highly seasonal forests of the Shennongjia Nature Reserve in China,in order to improve our understanding of the ecological and social influences on monkey behavior.We collected data on activity budgets in relation to food availability in a group of monkeys from July 2003 to September 2004(except February 2004),using instantaneous scan samples.The monkeys spent 36.21% of daytime moving(n=21,269 reco...