Maximum In May Research Articles

Near-bottom particle concentration and flux: Temporal variations observed with sediment traps and nepholometer on the Meriadzek Terrace, Bay of Biscay

The Meriadzek Terrace (a 2100m deep plateau on the North-East Atlantic continental slope) was chosen as the experimental site for a multidisciplinary programme to observe the parameters needed for a better understanding of biological processes in the benthic environment. Two approaches were used to study the input of particulate matter to the bathyal seabed: sediment traps and indirect particle concentration measurements with nephelometry. These two technologies do not measure particles of the same size range, but as we are interested in the fluctuations of the particle supply, their results are complementary. Vertical profiles of nephelometry show that over the Meriadzek Terrace there is 125m thick nepheloid layer immediately above the bottom. The dynamics in the deep layer has been determined by measurements made with a Module Autonome Pluridisciplinaire (MAP), an in situ monitoring device developed at IFREMER which measures currents, nephelometry, temperature vertical profile near the bottom. Throughout six months of measurements in 1984, the currents at 0.5m and 120m above the bottom were subject to semi-diurnal tidal oscillations. The intensity of light scattering recorded with the nephelometer on the MAP was highly correlated with current velocities especially with semidiurnal tidal oscillations which seem to induce local resuspension. There are also longer term fluctuations, notably a very strong event which lasted several days during August. This event lagged behind a period of high intensity of internal waves correlated with a reversal in current direction. The sediment trap (Pièges à Particules “PAP”) observations showed that the particle fluxes on the Meriadzek Terrace have a cycle of variation similar to primary production which is characterized by a maximum in May during the phytoplankton bloom and a minimum during January. There was also interannual fluctuation. These two kinds of results point out the different time scales (from some hours to several months) of the large temporal fluctuations which affect the near-bottom particle behaviour.

A 3‐year continuous record on the influence of daytime, season, and fertilizer treatment on methane emission rates from an Italian rice paddy

CH4 emission rates have been measured in an Italian rice paddy between 1984 and 1986, covering three vegetation periods. For these measurements a fully automated, computerized sampling and analyzing system was developed which allowed the simultaneous determination of CH4 emission rates at 16 different field plots. CH4 emission rates showed strong diurnal and seasonal variations. Diurnal changes correlated with changes in soil temperature. During the season, CH4 emission rates showed a first maximum in May–June before tillering and a second maximum in July during the reproductive stage of the rice plants. In 1985 and 1986 two maxima were observed during summer in addition to the first maximum in the rate of CH4 emission during spring. Application of mineral and/or organic fertilizer strongly influenced the CH4 emission rates, depending on the type, rate, and mode of fertilizer application. Thus the rates decreased by at most 40% and 60% after fertilization by deep incorporation with 200 kg N/ha urea and 200 kg N/ha ammonium sulfate, respectively. Application of 200 kg N/ha calcium cyanamide led to a reduction of the first maximum of CH4 emission but caused the second maximum to increase, the overall result being that the seasonally averaged CH4 emission rate was comparable to that observed in unfertilized fields. Application of rice straw at a rate of 12 t/ha enhanced the rate of CH4 emission by a factor of 2 compared with the control. Higher application rates of rice straw did not cause a further increase in CH4 emission. The complete records of CH4 emissions over three vegetation periods indicate an average seasonal CH4 emission rate from unfertilized fields of 0.28 g CH4/m2 d, with a range of 0.16–0.38 g CH4/m2 d. Based on this value and applying the observed temperature dependence of the CH4 emission rates, the global annual CH4 emission from rice paddies is estimated to be in the range of 50–150 Tg, with a likely average of 100 Tg. This figure represents between 19% and 25% of the global CH4 emission, indicating that rice paddies are one of the most important individual sources of atmospheric CH4.

Mass Flux and "Nutritional Composition" of settling Epilimnetic Particles in Lake Michigan

A series of sediment-trap samples, collected at a 30-m depth in southeastern Lake Michigan, was analyzed to evaluate the seasonal flux and nutritional value of settling epilimnetic particles as potential food for benthic organisms. Flux was highest in the spring (due in part to resuspension), lowest in the summer during stratification, and intermediate during autumn months. Organic content of the particles ranged from 10% ash free dry weight (AFDW) in March through May samples to 17–19% in July–August samples. During the summer, microbial degradation of organic materials occurred in the trap bottles without added preservative, as evidenced by less AFDW in nonpreserved trap bottles than in similar chloroform-preserved bottles. The percentage of AFDW occuring as lipid ranged from 3.5% in April–May up to 14% during May through August. Dominant lipid classes were hydrocarbons, polar lipids including phospholipids and chlorophyll a, and free fatty acids. The ratio of n-alkane C-17 (algal indicator) to n-alkane C-29 (terrestrial or resuspension indicator) and the ratio of biogenic silica to AFDW in preserved samples both reached a maximum in May, shortly before lipid content peaked in the benthic amphipod, Pontoporeia hoyi. This observation agrees with the hypothesis that P. hoyi receives much of its nutrition from the spring algal bloom.

Zur chemischen Zusammensetzung der CtenophorePleurobrachia pileus in der Kieler Bucht

The chemical composition of the ctenophorePleurobrachia pileus was investigated in March, May and July 1981 in Kiel Bight, western Baltic. The results of all determinations yielded low values compared with other zooplankton groups. Dry weight made up 1.95 to 2.28% wet weight with a minimum occurring in may. Ash-free dry weight amounted to 28–37% of the dry weight but exhibited a maximum in May. Carbon and nitrogen analyses yielded amounts of between 2.6–4.7% of the dry weight and 0.5–1.0% of the dry weight, respectively. Both elements reached lowest levels in May. Proteins reached a minimum in May, too, and values ranged between 2.5 and 5.1% of the dry weight. However, lipids as well as carbohydrates exhibited highest values in May and ranged from 0.8 to 1.6% and 0.8–1.1% of the dry weight, respectively. The C∶N values increased between March and July from 3.7∶1 to 6.7∶1, indicating a decline in protein content. To relate the biochemical compounds to organic matter I used three different approaches: (1) On the basis of ashfree dry weight, carbohydrates remained constant whereas lipids increased from March to July. A minimum of proteins occurred in May. The three compounds made up only 14–22% of ash-free dry weight. (2) Organic matter approximately equals organic carbon content multiplied by 2. Proteins, lipids and carbohydrates summed up reached 61–100% of this reference value and the seasonal course of these compounds changed in a drastic way: proteins decreased, whereas lipids as well as carbohydrates showed a relative maximum in May. (3) Finally, the carbon content of each biochemical compound was calculated in relation to total carbon content measured via C/N analysis. On this basis, 63–105% of total carbon were recovered, and the course of seasonal changes agreed with that of the second approach. A comparison of these three approaches suggests that comparative calculations based on carbon measurements are more valid than those based on ash-free dry weight. The results show that seasonal changes in the amount of organic matter and the biochemical composition occurred. Dry weight was lowest in May, which could be due to the low salinity environment recorded at that time and the corresponding low salt content of the tissue. The observed relative maxima of lipids and carbohydrates in May may be explained by good food conditions since high zooplankton densities are characteristic for this month in Kiel Bight.

Urban and rural ozone concentrations in Alberta, Canada

Ozone concentrations in Alberta cities typically exhibit a maximum in May (up to 35 ppb) and a minimum in November (as low as 4 ppb). This behaviour is similar to that of rural Alberta O 3 concentrations. Annual O 3 concentrations at six urban monitoring stations vary from 11 ppb to 22 ppb and are about one-half the values at rural stations. In winter, urban O 3 concentrations are always smaller than rural concentrations and the cities act as sinks for O 3. Although urban stations do not exceed Canada's maximum acceptable levels of daily (25 ppb) and annual (15 ppb) O 3 concentrations as often as rural stations, the frequency is still quite large. Canada's hourly maximum desirable level (50 ppb) is exceeded 11 times more often at the remote (rural) station than at the downtown (urban) stations.

Seasonal nutrient status of Banjara lake, Hyderabad

Seasonal and diel variations of nutrients viz. nitrate, nitrite, ammonia, soluble reactive phosphorus and silica in Banjara lake (identified by Andhra Pradesh Fisheries Department for pisciculture) during August 1986 to July 1987 were reported. Nitrate, nitrite and ammonia reached highest concentrations in March (3·76±1·74 mg l−1), July (575±77 μg l−1) and April (404·6±127 μg l−1) respectively. However, fish kills through nitrite toxicity was not observed at the reported nitrite concentrations. Ammonia decreased during summer mainly due to utilization by phytoplankton blooms. The highest value of soluble reactive phosphorus was observed in April (956±44 μg l−) attributed to sewage, domestic effluents and also release from sediments. Silica was at a maximum in October and decreased during diatom blooms in December. Clear pattern of diel variation was not observed for nitrate, nitrite and phosphorus. However, ammonia showed diel variation having higher concentrations at 6 h than 12, 18 and 24h due to its slower uptake by phytoplankton during nights. Chlorophylla was at a maximum in May (32 mg m−3) at N/P ratio of 5·3 with the dominance of cyanophyceae and chlorophyceae.

Estimating biomass and production of pelagic larvae of brachyuran decapods in western European shelf waters

Methods are described for estimating the dry weight biomass, production due to growth, production due to moults, flux to the plankton from the benthos of hatching zoeae and from the plankton to the benthos of settling megalopae of common Brachyura from north-western European waters. These methods are applied to brachyuran larvae taken in Continuous Plankton Records in the Irish Sea during 1981–1983 and from the Longhurst Hardy Plankton Recorder over Great Sole Bank in June 1983. The former provided estimates of input of hatching zoeae to the plankton at 10 m depth from the benthos of 0.41 mg dry weight · m −3 · a −1 with a peak in April, a mean standing stock of 0.19 mg · m −3 with a maximum in May. The peak in production was in July and the annual ratio of production to biomass ( P: B) was 23.2:1 excluding moults, or 26.1:1 including moults. The estimated flux of settling megalopae from the plankton at 10 m depth to the benthos was 1.33 mg · m −3 · a −1 with a peak in July. The data from the LHPR haul gave instantaneous daily values of an input of 0.004 mg · m −2 · day −1 to the plankton and a mean biomass 6.696 mg · m −2 of brachyuran larvae in the plankton. The daily P: B ratio was 0.067:1 excluding moults and 0.073:1 including moults and an estimated 0.07 mg · m −2 · day −1 was returning to the benthos.

Seasonal variation of transmission risk of Lyme disease and human babesiosis.

The seasonal host-seeking pattern of nymphal Ixodes dammini infected with Babesia microti or Borrelia burgdorferi was determined on Nantucket Island, Massachusetts, during 1985. The peak period of host-seeking by infected nymphal I. dammini occurred in May and June. On a per person-hour basis, the number of infected ticks collected reached a maximum in May (Babesia = 17.3; Borrelia = 16.2). The number of infected ticks remained high in June, but decreased notably in July, August, and September. Transmission risk of the tick-borne etiologic agents of Lyme disease and human babesiosis in Massachusetts is greatest during the late spring-early summer months of May and June.

The effect of shoot growth stage of Pinus contorta and Pinus sylvestris on the growth and survival of Panolis flammea larvae.

Young Panolis flammea (Lepidoptera: Noctuidae) larvae were unable to survive on the mature (one-year old) needles of Pinus contorta and Pinus sylvestris. Larval growth and survival on the current year's shoots of the 2 pine host plants first incresed, and then decreased as pine shoot development progressed, the effect on survival being more marked at 10° C that 18° C. The survival of larvae on lodgepole pine on field-grown plants transferred to 10° C rose from 26% in March to 87% in mid May, and rose from 3% to 82% on Scots pine in the same period. Larval survival exceeded 70% for about 8 weeks on lodgepole pine and about 6 weeks on Scots pine, this period starting and ending earlier on lodgepole than on Scots pine. The nitrogen, water and phosphorus contents of both pines were at a maximum in May and decline gradually thereafter; the soluble tannin content showed a more complex pattern. These results are discussed in relation to the possible importance of phenological coincidence on the population dynamics of P. flammea with emphasis on its greater abundance on lodgepole pine in Scotland.

Influence of domestic sewage on growth and nitrogen fixation of Azolla pinnata R. Br.

Biomass production of Azolla pinnata R.Br., cultured in sewage effluents under full sunlight, correlated closely with the changes of orthophosphate phosphorus (P) in the medium: it was highest (13.18 g m −2) in August as opposed to 6.34 g m −2 in January, though the environmental influence was also remarkable. Phosphorus contents in different media, particularly in one receiving a higher quantity of sewage effluents, gradually increased to 20.30 μg 1 −1 in January, reaching a maximum in May (37.60 μg 1 −1), followed by a gradual decline with a further rise in August (32.70 μg 1 −1). The seasonal variation in phosphorus content of the medium was closely associated with the carbon, phosphorus and nitrogen contents of plant tissue, as well as the heterocyst frequency of the symbiont, Anabaena azollae Strasb. The respective increases in nitrogen, carbon and phosphorus contents of plant tissue in mg 1 −1 during August were 39.80, 280.00 and 2.20, compared with values of 28.20, 245.00 and 1.50 during January, while the heterocyst frequencies were 15.96 and 10.92, respectively.

Ecology and Bioproduction in the Microphytobenthos of the Chain of Shallow Inlets (Boddens) South of the Darss‐Zingst Peninsula (Southern Baltic Sea)

AbstractThe significance of epipsammic microphytobenthos bioproduction in a shallow estuary was investigated by the oxygen method. Bioproduction reached a maximum in May or June. A close correlation was found between the gross production rate and algal biomass at station K. The biomass and production rates were distinctly lower at station B than at station K as station B was more exposed. Circadian variations and depth profiles of the gross production rate correlated best with irradiation intensity. Mean gross production from April to October was 1761 O2.m−2 and 75 g C·m−2.

Gill (Na+K)-ATPase activity and plasma thyroxine concentrations do not predict time of release of hatchery coho ( Oncorhynchus kisutch) and chinook salmon ( Oncorhynchus tshawytscha) for maximum adult returns

The timing of cyclic changes in gill (Na+K)-ATPase activity and plasma thyroxine (T 4) concentrations in coho ( Oncorhynchus kisutch) and spring chinook ( O. tshawytscha) salmon were compared with the time of release from hatcheries promoting maximal survival. In coho salmon from Big Creek reared in the laboratory, thyroxine reached a maximum concentration in April, and gill (Na+K)-ATPase activities reached a maximum in May. Plasma thyroxine in coho salmon reared at Big Creek Hatchery had two peaks in concentration in April and mid-May. Only fish released in June had a peak in gill (Na+K)-ATPase activity in mid-May. Coho salmon reared at Cascade Hatchery showed no cyclic changes in either plasma thyroxine or gill (Na+K)-ATPase activity. Greatest returns from coho salmon released from Big Creek Hatchery and from Cascade Hatchery occurred from fish released in June. Juvenile spring chinook salmon reared at Cole Rivers Hatchery had peaks in gill (Na+K)-ATPase activity in June or July, September, and November. In the same strain of fish reared in the laboratory, gill (Na+K)-ATPase activity reached a peak in October, and thyroxine concentration reached a maximum in November. Greatest adult returns occurred in fish released from Cole Rivers Hatchery in August. Spring chinook salmon reared at Round Butte Hatchery had variable peaks in gill (Na+K)-ATPase activity, depending on the year and rearing conditions. The time of release providing greatest adult returns did not correlate well with peaks in gill (Na+K)-ATPase activity. Results from these studies indicated that gill (Na+K)-ATPase activity and plasma T 4 levels were poor predictors for release of juvenile coho and spring chinook salmon to produce maximal adult returns. The relationship of oceanic factors to survival of hatchery fish is discussed.

Evaporation from coastal and open waters of the central zone of the red sea

Abstract Monthly evaporation was estimated from the coastal and open waters in the central region of the Red Sea between latitudes 21 and 22°N. A recent equation based on the bulk aerodynamic method was used to calculate the evaporation using two sets of observations collected over the coastal and open waters. The annual evaporation from coastal water was 194 cm with a maximum in May and a minimum in October; from open water, it was 144 cm with a maximum and a minimum in November and September, respectively. The application of Sverdrup's (1937) equation was attempted, first when the roughness parameter z0 in his equation was set equal to 0.6 cm as he proposed, and when z0 was set equal to the most acceptable value of 0.01 cm. Our study shows that the evaporation values obtained in the first case are closer to those obtained either from the recent equation or from direct measurements than those obtained in the second case.

Primary productivity and biomass of epiphytes on Phragmites australis in a eutrophic Danish lake

A field incubator based on a closed flow system was applied for primary productivity measurements in situ. The seasonal development of epiphytes showed a pronounced productivity maximum in May (610 mg C m−2Phragmites stand d−1) and a maximum chlorophyll a content of 414 mg m−2Phragmites stand. Substratum limitation was indicated during the spring maximum. Primary productivity and biomass decreased to low values in late summer, mainly due to shading from the aerial shoots. Significant quantitative heterogeneities in epiphyte biomass occurred over a few decimeter of Phragmites stem. Productivity and biomass were higher on old stems than on new ones throughout the growth period. The annual epiphyte production (23,7 g C m−2Phragmites stand) was mainly a result of the spring maximum. The fact that 64% was produced on old stems emphasizes the importance of the highly variable degree to which these may be destroyed. The host plant phenology appears from this investigation to be a key factor affecting epiphyte growth in the emergent vegetation determined by (1) the amount of available substratum and (2) the light penetration through the canopy.

An evaluation of sulfate in European precipitation 1955–1982

More than 25 years of data on sulfate in precipitation from the European Air Chemistry Network (EACN) are analysed for seasonal and long-term trends and their spatial variability. The number of stations has varied between about 50 and 100, all of them located in the central and northern parts of western Europe. Despite considerable shortcomings of the data (indicated among other things by poor ionic balance during several years, particularly in the late 1950s and the early 1960s) the following conclusions are drawn. In Norway, Sweden, Denmark and Finland, the sulfate concentration increased by roughly 50 per cent between the late 1950s and the late 1960s. A further increase during the 1970s is indicated at the Danish stations but most stations in Sweden and Norway show a decline by on the average about 20 per cent since the early 1970s. Sulfate data from the U.K. and the European continent seem to exhibit less systematic variations. A comparison between the long-term changes in the Scandinavian data on sulfate in precipitation and the corresponding changes in anthropogenic SO 2 emission in Europe indicates a fair agreement with regard both to the increase in emission during the 1950s and 1960s and, except for the Danish stations, also the subsequent decrease in emission in several of the West European countries. In most parts of the network the annual cycle of concentration of sulfate exhibits a maximum in February through May and a minimum in July to October, whereas the wet deposition normally has its maximum in May to August and minimum in December to March. A comparison with the annual cycle of anthropogenic emission, which has a clear maximum in December to March, indicates that the fraction of sulfur exported out of the region is larger in winter than in summer.

Primary productivity of the River Ely, South Wales, U.K.

The present study was carried out on the non-tidal reaches of the River Ely, South Wales, from October 1979 to October 1980. The seasonal variations of the chlorophyll-a content of the phytoplankton was unimodal with one maximum in May and a minimum in December. The chlorophyll-a content varied from 0.277 to 41.259 mg m−3. The primary productivity showed a bimodal seasonal distribution with two maxima in May and September and lower values throughout the remainder of the year, particularly in winter. The value for the primary productivity varied from 0.269 to 24.302 mg C m−3 h−1. A positive correlation was obtained between chlorophyll-a content and primary productivity. The seasonal distribution of the dominant algal species and the saprobity of the River Ely were also studied. The diatom species almost showed a similar seasonal periodicity. Their concentrations were low during the winter months and high during most of the spring and summer months. Many of the dominant diatom species found in the phytoplankton populations were either considered by the other authors as saprobic (Nitzchia palea) or as inhabitants of eutrophic waters (Gomphonema parvulum, Navicula cryptocephala and Synedra ulna). Chlamydomonas spp. were the most abundant green algae followed by Chlorella vulgaris. The effect of sewage effluent disposal and cattle excreta at three of the sampling sites might partly explain the presence of high Chlamydomonas spp. populations at those sites. Physical factors (low flow rates, high transparency and water temperature) and organic pollution at some sampling sites seemed to play an important role in increasing the number of algal species during spring and summer. The non-tidal reaches of the River Ely were found to be β-mesosaprobic above and below Station 5 and α-mesosaprobic at the latter station and therefore, the river can be considered as polluted at Station 5 and mildly polluted at the others.

Temperature and relative humidity inside the mound ofOdontotermes obesus (Rambur) (Isoptera: Termitidae)

No diurnal fluctuation in temperature and relative humidity inside the mound ofOdontotermes obesus (Rambur) has been noticed and the fluctuations through the year were within a narrow range (4° C; 4%). Sudden fall in temperature from the maximum in May to the minimum in June, July and August was probably due to emergence of alates in June.

Seasonal Periodicity of Diatoms, and Silicon Limitation in Offshore Lake Michigan, 1975

Diatom biomass maxima occurred in spring and fall and produced a bimodal bloom sequence at an offshore Lake Michigan station. The maximum in May was preceded by rapid growth as indicated by increased values of primary productivity and pigment concentration. As the spring bloom progressed, decreasing nutrient levels apparently slowed diatom growth. The diatom-biomass accumulation rate declined, assimilation quotients were minimal, and soluble reactive silicon was reduced from 13 to 6.8 μmol/ℓ. In summer, after the bloom, diatom biomass and silicon reached seasonal minima of < 250 mg C/m2 and ~ 1.0 μmol/ℓ, respectively. Diatom biomass increased again in October when silicon supplies were replenished and the concentration exceeded 6.6 μmol/ℓ. A critical silicon concentration of ~ 6.5 μmol/ℓ, may control the development and timing of offshore diatom populations in Lake Michigan. Key words: Lake Michigan, diatoms, growth, biomass, periodicity, silicon, uptake, limitation

Seasonal variation in casting activity and in the amounts and release to solution of phosphorus forms in earthworm casts

Production of surface casts of earthworms (dominantly Allolobophora caliginosa) varied markedly during 1975. Casting activity was restricted to the April to September period and reached a maximum in early June. Seasonal variations in cast production were attributed to fluctuations in soil moisture and temperature, and in food supply. Although the total P content of casts was essentially constant throughout the year, the inorganic P content decreased from a maximum in May to a minimum in August. The progressive decrease in the amount of inorganic P between May and August is attributed to a reduction in the conversion of organic to inorganic P because of the lower microbial and phosphatase enzyme activity as a result of declining soil temperature. Seasonal variations in the release of inorganic P from casts to solution and in the amounts of rapidly-exchangeable P were more closely related to the seasonal pattern of cast production than to changes in the amount of inorganic P in the casts. In contrast, seasonal changes in the release of inorganic P to solution and in the amount of rapidly-exchangeable P in underlying soil were small. A greater amount of inorganic P was extracted by 0.5 m NaHCO 3 than by water from freshly-deposited casts collected at different times of the year, indicating that NaHCO 3 extracts some chemisorbed inorganic P from casts. Water-extractable inorganic P accounted for approximately 90% of the difference between inorganic P in casts and underlying soil. Consequently, essentially all of the additional inorganic P in casts is retained by a more-physical sorption type. The results obtained are discussed in terms of the likely effects of surface casting on the P cycle in a soil-plant system.

Observations on the age, growth, reproduction and food of the pike Esox lucius (L.) in two rivers in southern England

Opercular bones of 261 pike from the River Stour and 117 from the River Frome were used for age and back‐calculated growth determinations. The annuli were laid down during late April and early May and most growth occurred between May and September. Pike growth in the two rivers was comparable with the fastest growth in other waters, though Frome pike grew slightly faster than Stour pike. Spawning occurred from the end of March into May. Elaboration of the ovaries commenced in September and was virtually completed by February, whereas the testes reached their maximum weight in October and maintained it until spawning. Immature pike had an annual cycle of condition reaching a maximum in May and a minimum during the winter. The gonad cycle affected the condition of mature females which had their minimum condition in mid‐summer. The fecundity of Stour pike is expressed by the formula: log10 egg number =3.56 log10 fish length (mm) – 5.40. Approximately 75% of all Stour pike were sexually mature by age II and these fish were, on average, larger than immature pike of the same age. The most numerous items in the diet of pike were small cyprinids, 30–80 mm fork length, although pike over 700 mm long ate larger fish. Few salmonids appeared in the diet of either Frome or Stour pike. The percentage of empty stomachs was highest in Stour samples taken during the summer, shorter digestion times and longer feeding periods in this period are suggested as reasons for the apparent anomaly.