Seasonal differences

Production through much of the year will be subject to other constraints for example, the availability of light beneath the water surface. Seasonal differences in day length and periodic fluctuations in the depth of light penetration by active wavelengths often have an overriding effect on the net production rates and the supportive capacity. 

Water resources decision making in many areas, particularly arid and semi-arid climates such as the American West, depends on interannual to decadal variations in surface water availability. In addition to more predictable seasonal differences, runoff tends to exhibit long-term trends alternating between flood and drought periods. Figure 6-10 shows historical wet and dry periods based on streamflow records for 50 world rivers. For the most part, these periods are consistent on a regional basis, though they appear to alternate on a hemispheric scale. 

Gupta, P.L. Rorison, I.H. (1975). Seasonal differences in the availability of nutrients down a podzolic profile. Journal of Ecology, 63, 521-34. 

The kinetics of the various reactions have been explored in detail using large-volume chambers that can be used to simulate reactions in the troposphere. They have frequently used hydroxyl radicals formed by photolysis of methyl (or ethyl) nitrite, with the addition of NO to inhibit photolysis of NO2. This would result in the formation of 0( P) atoms, and subsequent reaction with Oj would produce ozone, and hence NO3 radicals from NOj. Nitrate radicals are produced by the thermal decomposition of NjOj, and in experiments with O3, a scavenger for hydroxyl radicals is added. Details of the different experimental procedures for the measurement of absolute and relative rates have been summarized, and attention drawn to the often considerable spread of values for experiments carried out at room temperature (-298 K) (Atkinson 1986). It should be emphasized that in the real troposphere, both the rates—and possibly the products—of transformation will be determined by seasonal differences both in temperature and the intensity of solar radiation. These are determined both by latitude and altitude. 

Recently, pulse labeling has frequently been applied to determine the fate of carbon in crops such as barley and wheat and the losses from roots and subsequent microbial transformations. In general, the results indicate that 15-25% of the net " C assimilation is transferred to the roots and that there are seasonal differences in the distribution of assimilated carbon. Meharg and Killham (25) measured the C distribution in perennial ryegrass (L perenne). At 8 days after the pulse with... 

Dawley E.M. (1998). Species, sex and seasonal differences in vomeronasal organ size. Micros Res Tech 41, 506-518. 

Table III shows seasonal differences of mean radon concentrations in the Mihama and Misasa areas. Mihama had higher mean values in winter and summer than Misasa had, but Misasa had a higher mean value in spring and autumn. Widespread use of air conditioners in Mihama area may account for the high values in summer. In general there was little seasonal variation in these two locations.

Table III. Seasonal Difference of Mean Radon Concentration (Arithmetic) in Mihama and Misasa Area ...

In addition seasonal differences were detected. Two specific substances were expressed by male fossas in higher concentrations during the breeding than during the non-breeding season. 

Leonard, S. T. and Ferkin, M. H. (2005) Seasonal differences in self-grooming in meadow voles, Microtus pennsylvanicus. Acta Ethologica. 8, 86-91. 

Borowski, Z. (2002) Individual and seasonal differences in antipredatory behaviour of root voles -a field experiment. Can. J. Zool. 80, 1520-1525. 

Particulate matter was also analysed during July and September 2001 at the same sampling points (Table 6.2.5). Significant levels of NPEO (0.18 - 5.2 pgg-1 d.w.) and NP (0.75 - 4.9 pgg-1 d.w.) were found in all samples of the rivers Rhine and Meuse. In the 30 samples investigated, from the NPECs only NPE2C could be detected and this was found only in two samples. No seasonal differences could be observed for NP or NPEO. 

Sampling rates for the case of total boundary layer-control can be expected to be nearly independent of temperature, since both the diffusion coefficients in air, and the kinematic viscosity of air are only weak functions of temperature (Shoeib and Harner, 2002). This leaves the air-flow velocity as the major factor that can be responsible for the seasonal differences among sampling rates observed by Ockenden et al. (1998). The absence of large R differences between indoor and outdoor exposures may be indicative of membrane-control, but it may also reflect the efficient damping of high flow velocities by the deployment devices used for SPMD air exposures (Ockenden et al., 2001). 

P002 drawdown based on seasonal differences in Pco2 concentrations in reference year 1995, corrected for temperature effects. This drawdown reflects the degree of biological utilization of CO2. Values exceeding 150 ji,atm (yellow-orange-red) are observed in the northwestern subarctic Pacific and Atlantic, the eastern equatorial Pacific, the northwestern Arabian Sea, and the Ross Sea. 

Other chemical studies did not find sex or seasonal differences in the composition of mammalian scents. No sex differences in the composition of mixtures of volatile compounds from glands have been found in the brushtailed possum, Trichosurus vulpecula, for example. The same profiles of low-molecular-weight branched carboxylic acids were found in paracloacal gland secretions of males and females (Woolhouse etal., 1994). Branched carboxylic acids also occurred in the preorbital gland secretion of a female sika deer [Ccrvus nippon) (Wood, 2004). Comparisons between the compositions of secretions in different, related species permit assumptions about functional adaptations and possible evolutionary pathways. Such comparisons are available for five Mustek species (Brinck etal., 1983), and three species of hyenas (Buglass etal., 1990). 

Ferrets, Mustek furo, distinguish between anal sac secretions of males and females. Males did not discriminate between the anal gland odors of estrous and anestrous females. Chemical sex differences were found, but no seasonal differences. Males had high concentrations of 2,3-dimethylthietane and/or 3,4-dimethyl-l,2-dithiolane (Fig. 7.6). Most individuals had 2-propylthietane. Clapperton etal. (1988) concluded that the odor of the anal gland provides sexual and territorial signals and cues to individual identity. 

As these examples show, different defenses among plant parts and seasonal differences have to be considered together. Coffee Coffea arabica) is a well-investigated example of increased chemical defenses when the plant is most vulnerable to herb ivory. The concentration of the alkaloid caffeine (Fig. 11.18) varies between plant parts and with the growth cycle. In the germinating seed, the... 

Ferkin, M. H. and Seamon, J. O. (1987). Odor preference and social behavior in meadow voles, Microtus pennsylvanicus seasonal differences. Canadian Journal of Zoology 65, 2931-2937. 

In view of the large seasonal differences in atmospheric dispersion in New York City and the improved models obtained, dispersion-normalized data based on 7 A.M. measurements were used in this first stage of development for all of the source apportion models reported here. In order to keep the notation as simple, as possible, this has not been indicated explicitly in the symbols used in the equations. Dispersion normalization, however, is implicit in all of the models reported. 

A residual of 20-30% (0.65-0.99 ug/m ) could not be attributed to any of the sources. Seasonal differences in temperature undoubtedly affect the vapor/particulate equilibrium for the nonpolar organics in this fraction and, thus, contribute to the unexplained portion of CYC. Attempts to take this into account... 

Seasonal Variation and the Influence of Temperature. In temperate latitudes, rather characteristic seasonal variations in milk composition are commonly observed. Both fat and solids-not-fat contents are lower in summer than in winter. In the survey by Overman (1945) of individual cows at the University of Illinois, monthly extremes for fat were 4.24 and 3.81% in January and August and for protein were 3.61 and 3.37% in January and July, respectively. Nickerson (1960) found significant seasonal differences in 18 components of bulk milks from six areas in California. Seasonal differences in fat and protein contents were similar to those observed in Illinois. Seasonal variations in milk composition could conceivably be caused by differences in temper-... 

Whitnah, C. H. 1962. The viscosity of milk in relation to the concentration of major constituents and to seasonal differences in the voluminosity of complexes of sedimentable nitrogen. J. Agr. Food Chem. 10, 295-296. 

There may be a strong seasonal cycle in the calculated impact of aircraft emissions on ozone. For example, using the same emission scenarios, the UIO and the UKMO models calculate a 40% larger increase of ozone in the NH in April compared to July (Stevenson et al. 1997 Bemtsen and lsaksen, 1998). Other models find much weaker seasonal cycles (e.g. IMAGES/BISA and ECHAM3/CHEM), or find the maximum increases in summer (e.g. TM3 and HARVARD). The reasons for these seasonal differences are probably associated with the different background NOx conditions in the different models (see next section). 

It can be seen from Table 7.11 that spinach, lettuce and beetroot had significantly higher nitrate contents than the other types of vegetables analysed. Tomatoes contained the lowest concentrations. Seasonal differences in nitrate concentrations were observed for potatoes, lettuce, carrot, cauliflower and onion samples. Nitrate concentrations in potatoes were lowest in the summer period... 

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