Intra-annual variability in nutrients in the Godavari estuary,India

Daily variations in nutrients were monitored for 15 months (September 2007–November 2008) in the Godavari estuary, Andhra Pradesh, India, at two fixed locations. River discharge has significant influence on nutrients loading to the estuary, which peaks during June–August (peak discharge period; monsoon) whereas exchanges at the sediment–water interface, groundwater and rainwater contribute significantly during other period. Despite significant amount of nutrients brought by discharge to the study region, phytoplankton biomass, in terms of chlorophyll-a (Chl a), did not increase significantly due to high suspended load and shallow photic depth. Nutrients showed downward gradient towards downstream of the estuary from upstream due to dilution by nutrient poor seawater and biological uptake. The N:P ratios were higher than Redfield ratio in both upstream and downstream of the estuary during no discharge period suggesting PO₄ to be a limiting nutrient for phytoplankton production, at levels <0.10 μmol L⁻¹. On the other hand, Si:N ratios were always more than unity during entire study period at both the stations indicating that Si(OH)₄ is not a limiting nutrient. Our results suggest that suspended matter limits phytoplankton biomass during peak discharge period whereas PO₄ during no discharge period.     

A sedimentological study of the dredged material deposit in the New York Bight

A variety of sediment types were identified in sediment cores taken at the dredged material dumpsite in the New York Bight. Black sandy mud is characteristic of dumped dredged material while glauconitic and quartzose sands are typical of the naturally deposited sediments underlying the deposit. The sedimentological investigation indicates that largescale differentiation of dumped material occurs at the dumpsite. Laminated sediments and discrete beds are typical of the central part of the deposit, the area that receives the bulk of direct dumping. Relatively homogeneous, fine-grained sediments, presumably derived from the area of direct dumping, are characteristic of the material present at the periphery of the deposit. Preferential transport of fine-grained material to the fringes of the deposit may be an important contaminant transport mechanism in the area. Incursion of glauconitic sand, derived from surrounding areas, onto the edges of the deposit is also believed to occur. Based on bathymetric surveys of the area conducted in 1936, 1973, and 1978, rates of dredged material accumulation at the dumpsite have been estimated for the period 1936–1978. The calculated rates range from 50 cm/yr at the apex of the deposit to 6 cm/yr at the periphery. Contribution 294 of the Marine Sciences Research Center (MSRC) of the State University of New York at Stony Brook.     

Stability of ion-acoustic waves in a pair-ion plasma with a third species of ions: application to cometary plasmas

A popular model of a cometary plasma is hydrogen (H⁺) with positively charged oxygen (O⁺) as a heavier ion component. However, the discovery of negatively charged oxygen (O^?) ions enables one to model a cometary plasma as a pair-ion plasma (of O⁺ and O^?) with hydrogen as a third ion constituent. We have, therefore, studied the stability of the ion-acoustic wave in such a pair-ion plasma with hydrogen and electrons streaming with velocities $V_{d\mathrm{H}^{+}}$ and V _de , respectively, relative to the oxygen ions. We find the calculated frequency of the ion-acoustic wave with this model to be in good agreement with the observed frequencies. The ion-acoustic wave can also be driven unstable by the streaming velocity of the hydrogen ions. The growth rate increases with increasing hydrogen density $n_{\mathrm{H}^{+}}$ , and streaming velocities $V_{d\mathrm{H}^{+}}$ and V _de . It, however, decreases with increasing oxygen ion densities $n_{\mathrm{O}^{+}}$ and $n_{\mathrm{O}^{-}}$ .