Highest Seasonal Values Research Articles

Respuesta productiva de trébol pata de pájaro en función del porcentaje de luz interceptada

La productividad de una especie forrajera puede ser descrita en términos del comportamiento de sus componentes morfológicos y la combinación con el ente en la pradera. El objetivo fue evaluar el comportamiento productivo de trébol pata de pájaro (L. corniculatus), bajo diferentes estrategias de defoliación. El experimento se llevó acabo en el Colegio de Postgraduados de septiembre 2015 a septiembre de 2016, en un diseño de bloques al azar, con tres repeticiones, con la hipótesis, que al cosechar la especie al 95% de luz interceptada (LI) se tiene un mejor comportamiento productivo. Un intervalo de corte fijo (CF), tuvo menor producción en invierno (3 441 kg MS ha-1), verano (5 024 kg MS ha-1) y anual acumulado (20 710 kg MS ha-1), respecto al resto de los tratamientos (26 689 kg MS ha-1, promedio anual). También, manifestó menor altura de planta (21 vs 26 cm, promedio en la LI). No obstante, el CF tuvo mayor relación hoja: tallo, tanto estacional como promedio anual (2.3 vs 1.5 promedio en la LI). Los valores estacionales más altos fueron en otoño e invierno (1.9). En primavera y verano se presentaron las alturas mayores con 29 cm vs invierno con 19 cm. La hoja aportó 51% al rendimiento anual, seguida por el tallo, maleza y material muerto con 32, 10 y 6%, respectivamente. En conclusión, el mejor comportamiento productivo de trébol pata de pájaro, genotipo 260012, se presentó en las estrategias de cosecha de LI respecto al CF.

Optical properties of atmospheric particles over an urban site in Mexico City and a peri-urban site in Queretaro

Optical properties of atmospheric particles at Mexico City (UNAM) and Queretaro (JQRO) were measured with a Photoacoustic Extinctiometer (PAX) at 870 nm. The Mexico City Metropolitan Area has around 21 million inhabitants and Queretaro Metropolitan Area has little more than a million. Observations of meteorological parameters (relative humidity, solar radiation, and wind speed) were used to identify the rainy and dry seasons and explain the daily and seasonal behaviors of particles optical properties. The measurements were made from November 1, 2014 to July 31, 2016. At UNAM, the mean values of the scattering coefficient (Bscat) in cold dry, warm dry, and rainy seasons were 35.8, 27.1, and 31.3 Mm−1, respectively; while at JQRO were 10.9, 11.9, and 15.0 Mm−1. The average values of the absorption coefficient (Babs) at UNAM during the cold dry, warm dry, and rainy seasons were 14.5, 12.7, and 12.7 Mm−1, respectively; whereas at JQRO were 4.9, 4.7, and 3.9 Mm−1. Both absorption and scattering coefficients showed similar diurnal behaviors, but at UNAM they are three times higher than JQRO. Concentrations of criteria gases (O3, NO, NO2 and NOx) were also measured. At UNAM no difference was observed between the seasonal values for the single scattering albedo (SSA); while in JQRO, the rainy season had the highest seasonal value, being 13% higher than in the dry seasons. The Mass Scattering Cross-Section (MSC) values at UNAM were close to 2 m2/g; on the other hand, at JQRO the MSC values were lower than 1 m2/g. The results suggest a seasonal variability in the aerosol optical properties in both sites, which should be verified with more long-term studies.

Seasonal and regional air quality and atmospheric deposition in the eastern United States

The atmospheric concentration, wet deposition, and inferred dry deposition of selected air pollutants reported over two 5‐year periods in the 1990s at or near 34 rural Clean Air Status and Trends Network (CASTNET) sites located in the eastern United States (U.S.) are adjusted for known biases, composed into seasonal values, and examined. Several terms are defined for the current study, where OxN is the measured oxidized nitrogen (i.e., airborne OxN is the sum of airborne HNO3 and NO3−, expressed as nitrogen), NH4 is the measured reduced nitrogen (i.e., airborne NH4 is the aerosol NH4+, expressed as nitrogen), N is the sum of measured oxidized and reduced forms of nitrogen, expressed as nitrogen, and S is the measured oxidized sulfur (i.e., airborne S is the sum of airborne SO2 and SO42−, expressed as sulfur). The atmospheric NH3 concentration is not monitored in the current study. Similar patterns of seasonal and regional behavior are found consistently in both periods. In the east, atmospheric concentration, estimated deposition velocity, precipitation rate, inferred dry deposition, wet deposition, and total (dry plus wet) deposition estimates of each of the monitored chemical constituents display regular seasonal cycles of behavior. High and low seasonal values occur in summer and winter, respectively, for atmospheric concentration and dry deposition of SO42−, NH4+, O3, HNO3, and N; for dry OxN deposition; for wet S and H+ deposition; and for total OxN and N deposition. In contrast, high seasonal values of SO2 concentration and dry deposition, and atmospheric NO3− concentration occur in winter. In the east, SO2 composes a major portion (≈70%) of the atmospheric S concentration and is the dominant (>85%) contributor to dry S deposition. Although aerosol NH4+ represents a major portion of the measured atmospheric N concentration (≈67%), HNO3 dominates estimates of both dry OxN (>90%) and N (>75%) deposition. Dry deposition contributes ≈15%, 38%, and 43% to total deposition of NH4, OxN, and S, and these appear to be conservative estimates. Wet deposition is a major contributor to total deposition, generally peaking in summer or spring. Total S, OxN, and N deposition peak in summer. Although mean O3 concentration is ≈70% larger in summer than winter, dry O3 deposition estimates in the east are >5 times higher in summer. Within the uncertainty of current conservative estimates, dry deposition of SO42−, HNO3, OxN, N, and O3 appears to be highest at the high‐elevation subset of sites. This underscores the potential importance of dry deposition as a stressor to high‐elevation ecosystems in the eastern U.S.

Characterization of methane emissions from rice fields in Asia. II. Differences among irrigated, rainfed, and deepwater rice.

Methane (CH4) emission rates were recorded automatically using the closed chamber technique in major rice-growing areas of Southeast Asia. The three experimental sites covered different ecosystems of wetland rice--irrigated, rainfed, and deepwater rice--using only mineral fertilizers (for this comparison). In Jakenan (Indonesia), the local water regime in rainfed rice encompassed a gradual increase (wet season) and a gradual decrease (dry season) in floodwater levels. Emission rates accumulated to 52 and 91 kg CH4 ha−1 season−1 corresponding to approximately 40% of emissions from irrigated rice in each season. Distinct drainage periods within the season can drastically reduce CH4 emissions to less than 30 kg CH4 ha−1 season−1 as shown in Los Banos (Philippines). The reduction effect of this water regime as compared with irrigated rice varied from 20% to 80% from season to season. Methane fluxes from deepwater rice in Prachinburi (Thailand) were lower than from irrigated rice but accumulated to equally high seasonal values, i.e., about 99 kg CH4 ha−1 season−1, due to longer seasons and assured periods of flooding. Rice ecosystems with continuous flooding were characterized by anaerobic conditions in the soil. These conditions commonly found in irrigated and deepwater rice favored CH4 emissions. Temporary aeration of flooded rice soils, which is generic in rainfed rice, reduced emission rates due to low CH4 production and high CH4 oxidation. Based on these findings and the global distribution of rice area, irrigated rice accounts globally for 70–80% of CH4 from the global rice area. Rainfed rice (about 15%) and deepwater rice (about 10%) have much lower shares. In turn, irrigated rice represents the most promising target for mitigation strategies. Proper water management could reduce CH4 emission without affecting yields.

Plasma sex steroid profiles and the seasonal reproductive cycle in male and female winter flounder, Pleuronectes americanus

The pattern of seasonal gonadal development and variations in plasma sex steroids were investigated in adult male and female winter flounder, Pleuronectes americanus (Walbaum), from Conception Bay Newfoundland beginning August 1987 to December 1988. The winter flounder reproductive cycle can be divided into five consecutive phases of relative reproductive activity including: (1) rapid gonadal recrudescence in the fall (August–December); (2) continued slow gondadal growth in females, or maintenance of the well developed gonads in males, during the winter (December–February); (3) a prespawning phase of gonadal maintenance in the spring (March–April); (4) spawning early in the summer (May–June) after the female gonads reach peak weight; and (5) the summer postspawned period (June–August) when the gonads remain regressed. Female gonadal recrudescence in August is characterized by small increases in plasma estrogen levels and recruitment of small oocytes (≥150 μm) into yolk accumulation. For the winter months, estradiol-17 β levels in the plasma remain stable, approximately 15 ng ml-1, until rising again together with testosterone to peak hormone levels just prior to spawning in conjunction with the highest seasonal values for the gonadosomatic index (GSI) and oocyte diameter. After spawning, the ovaries are regressed and sex steroids in the plasma fall to very low levels. Rapid seasonal recrudescence of the gonads in males is evident from rising GSI values, which reach a maximum in October, and from substantial early seasonal increases in plasma testosterone and 11-ketotestosterone. Afterwards, although GSI values subsequently decline presumably reflecting the process of spermiogenesis and/or onset of spermiation in some males, the testes remain relatively well developed with the presence of sperm throughout the spawning season. As the proportion of spermiating males increases, the plasma levels of the androgenic steroid hormones rise to peak circulating levels from April to June. At the end of the summer reproductive season, the testes of post-spawned males become regressed and plasma testosterone and 11-ketotestosterone levels fall, reaching the lowest seasonal values.

The energetics of the general circulation of the atmosphere in southern hemisphere during the IGY. Part I: The distribution of atmospheric energy

Results of evaluation of different forms of available potential energy and kinetic energy based on direct observations of temperature, wind and geopotential carried out in southern hemisphere during the IGY, are presented. The spatial distribution of various energy forms, for each of the three periods October–March (summer semester), April–September (winter semester) and the year is shown in tabular and graphical forms, including latitudinal and vertical cross sections. The theoretical framework this investigation is based on, consists of the general equations of atmospheric energetics in the space-time domain. It is found that the highest seasonal values occur generally in winter, the most important contributions to eddy energy forms being due to transient eddies.

Estimation of the production ofDaphnia longispinain a mountain lake

Abstract The parameters characterizing the processes of birth, growth, death, reproduction and production of Daphnia longispina in Lake Santo Parmense, a mountain lake in Northern Apennines (Italy), have been estimated for the period lasting from June to the beginning of September 1973: in this period the population is mainly constituted by parthenogenetic females and presents the highest seasonal values of density and biomass. The production of D. longispina has been calculated using the compartmental model proposed by De Bernardi and Di Cola (1976) for the study of the biomass dynamics in populations with continuous recruitment. The trend of death rates of the different size classes and in particular of the classes including newborn individuals has been explained by admitting that the population receives an input of individuals hatched from resting eggs over a long period (till the end of August). The total daily production is supplied mainly by the size classes including preadult individuals, over the ...