The influence of nitrogen and phosphorus on the growth of a diatom Skeletonema costatum (Greville) Cleve

Nitrogen and phosphorus requirements of a chain-forming diatom, Skeletonema costatum (Greville) Cleve, collected from Yatsushiro Sea, Japan, were investigated in a laboratory culture experiment. Sodium nitrate and sodium glycerophosphate were used as nitrogen and phosphorus sources, respectively. Cultures were grown in modified Provasoli's ASP2NTA medium (Provasoli et al. 1957) at 25±1°C, light intensity 60 µE mˉ² secˉ¹ and photoperiod 12:12-h, L:D cycle. Optimum growth was observed at nitrate concentrations of 3-10 mglˉ¹ and phosphate concentrations of 1.5-15 mglˉ¹. Adequate growth was also found at the nitrate concentration of up to as high as 300 mglˉ¹. Significantly poorer growth was found at lower nitrate (<3.0 mglˉ¹) and higher phosphate (>15 mglˉ¹) concentrations. From the present study, it is concluded that S. costatum can grow well at wide ranges of nitrate concentrations but is sensitive to higher phosphate concentrations.

Observations on changes in the major protein nitrogen fraction of prawns and sardines during ice storage

Changes in the major protein nitrogen fractions (sarcoplasmic, myofibrillar, stroma) have been studied in two species of prawns and in oil sardine held in ice storage. Myofibrillar proteins were observed to get denatured at a rapid rate as determined by salt extractability method. The sarcoplasmic proteins were not denatured to any considerable extent. With sardine however, the extraction of myofibrillar proteins was inhibited rather in the uniced condition itself presumably owing to the presence of free fatty acids.

Bonding regimes of nitrogen in amorphous carbon

Nitrogen can have numerous effects on diamond-like carbon: it can dope, it can form the hypothetical superhard compound C3N4, or it can create fullerene-like bonding structures. We studied amorphous carbon nitrogen films deposited by a filtered cathodic vacuum arc as a function of nitrogen content, ion energy and deposition temperature. The incorporation of nitrogen from 10-2 to 10 at% was measured by secondary ion mass spectrometry and elastic recoil detection analysis and was found to vary slightly sublinearly with N2 partial pressure during deposition. In the doping regime from 0 to about 0.4% N, the conductivity changes while the sp3 content and optical gap remain constant. From 0.4 to approximately 10% N, existing sp2 sites condense into clusters and reduce the band gap. Nitrogen contents over 10% change the bonding from mainly sp3 to mainly sp2. Ion energies between 20 and 250 eV do not greatly modify this behaviour. Deposition at higher temperatures causes a sudden loss of sp3 bonding above about 150 °C. Raman spectroscopy and optical gap data show that existing sp2 sites begin to cluster below this temperature, and the clustering continues above this temperature. This transition is found to vary only weakly with nitrogen addition, for N contents below 10%.

Salt and water balance in the Mundel Lake: a strongly choked coastal lagoon

The Mundel Lake is an extremely shallow lagoon on the west coast of Sri Lanka. It is connected to the Puttalam Lagoon through 15 km long Dutch Canal. Salinity measurements and daily sea level data were obtained fortnightly from January 1993 to March 1994 and they were used to quantify the salt and water budget along with precipitation, evaporation and freshwater runoff. Extreme fluctuations of salinity and sea level are striking features of the system. Salinity of the Mundel Lake and Dutch Canal varied from 5-46.5 and 6 61 ppt respectively while the sea level ranged from -0.25 to +1.2 m. Tidal variations were not seen in the lagoon due to its long narrow canal system. Salt budget showed that the deposition of salt on the lagoon bottom during periods of decreasing water level. During increasing water level, salt is dissolved again. Flow of water through the Dutch Canal between the Puttalam Lagoon and Mundel Lake is driven by the changes in sea level. These changes are mainly due to seasonal changes of net freshwater supply and, to a lesser degree, to seasonal changes in sea surface height. As the flow rates are small due to the long and narrow canal, the residence time ranges between two months and several months in the Mundel Lake, except during season of high freshwater supply. As the water exchange is weak, the Mundel Lake becomes hyper saline with strong fluctuations in salinity. This implies a stress to all lagoon dwelling aquatic organisms and also to aquaculture practices in the area.

Influence of nitrogen salts on growth and physiological responses of Rhizophora apiculata Blume in non-aerated water culture

Influence of two different forms of nitrogen on growth and physiological aspects of water-cultured seedlings of Rhizophora apiculata was studied. Of the two forms of nitrogen supplied to the growth medium, ammonium nitrogen was better than nitrate nitrogen by exhibiting increased dry matter production, shoot length, leaf area and also enhanced the contents of carotenoids, chlorophylls and their presence in photosystems and light harvesting protein complex.

Nitrogen-fixing aerobic bacteria and their nitrogenase activity in north Mumbai coastal waters

The effect of the physicochemical parameters of water and soil on the distribution of nitrogen-fixing bacteria and their nitrogen-fixing capacity was studied. Four species of nitrogen-fixing bacteria, e. g. Azotobacter chroococcum, A. vinelandii, A. beijerinckii and A. armeniacus, were recorded from water and soil samples of Mumbai coast. A higher number of bacterial populations were observed in sediment than in water samples. A positive correlation was observed between the dissolved organic matter and nitrogen fixing bacterial populations of water as well as between available phosphorus and the nitrogen-fixing bacteria of sediment. The nitrogen-fixing capacity of A. chroococcum was found to be 1.076 nmol C sub(2) H sub(4)/l/d and that of A. vinelandii was 0.965 nmol C sub(2) H sub(4)/l/d. Station 1 showed higher level of nitrogenase activity in comparison to other four stations.

The free alpha amino acid nitrogen contents of some common food fishes of Kakinada region, Andhra Pradesh

The moisture and free alpha amino nitrogen contents of some important food fishes and shell fishes of Kakinada region have been studied. Crustaceans and molluscs contain free alpha amino acids in quantities several times higher than all other aquatic animals examined in this study. Their probable role in the physiological activities of these animals has been discussed.