Assessment of the conventional molybdenum-blue and magnesium-induced coprecipitation procedures in phosphorus measurement in various aquatic environments

Phosphorus (P) is an essential nutrient utilized by all organisms for energy transport and growth. Both the conventional molybdenum-blue method and the magnesium-induced coprecipitation (MAGIC) procedures were applied for the measurement of dissolved inorganic phosphorus (DIP) and total dissolved phosphorus (TDP) in more than 840 water samples collected between 2003 and 2005, including seawater (the Huanghai Sea, the East China Sea, and the northern South China Sea), water from rivers and estuaries (the Changjiang, the Huanghe, and the major rivers emptying into the Jiaozhou Bay), groundwater (in the drainage basin surrounding the Jiaozhou Bay), rain- water, and aquaculture water samples. The MAGIC method allows the investigation of phosphorus distributions and cycling for systems in which DIP is below the detection limits of conventional methods. Comparison between the two methods demonstrated that the concentrations obtained with both methods were signiˉcantly correlated. The di?erences of DIP and TDP concentrations measured with the two methods were higher when the concentrations of DIP and TDP were lower, implying the lower reproducibility at low concentrations. The concentration di?erences increase with the increase in the proportion of DOP in TDP, which indicates that the discrepancy of DIP concentrations measured with the two methods increases when the DOP concentration is high. The discrepancies indicated that the composition of P compounds di?ers depending on sample sources and water type; it would be useful to infer the presence of di?erent phosphorus compound pools from di?erences between the two methods. This study indicates the potential presence of a pool of alkaline-labile compounds for samples from rainwater and rivers and estuaries surrounding the Jiaozhou Bay; the potential presence of acid-labile compounds that were adsorbed by Mg(OH)2 for samples from the Changjiang Estuary, Huanghai Sea, East China Sea, and groundwater; the po- tential presence of a substantial pool of acid-labile compounds that were not adsorbed by Mg(OH)2 for samples from the Huanghe Estuary, aquaculture water, the East China Sea algal bloom water, and the northern South China Sea.     

The evolution and depth structure of shelf and slope temperatures and velocities during the 1997–1998 El Niño near Point Conception, California

Moored, survey, and drifter observations are used to describe the evolution of temperature, sea level, velocity and salinity from 1997 to 1998 over the California shelf, between San Luis Obispo Bay and the eastern entrance to the Santa Barbara Channel. The dominant event during this time was the 1997–1998 El Niño. Its relation to background seasonal and interannual variability depended on which property is considered. Subsurface temperature and local sea level showed extreme anomalies between March 1997 and October 1998. Three distinct peaks occurred. The first two are associated with the regional response to El Niño, while the cause of the third remains unclear. The first peaked in June 1997, and decayed until August. The main El Niño peak reached maximum amplitude between November 1997 and January 1998. After the collapse of the regional El Niño anomaly in February 1998, a final peak occurred locally during the summer of 1998.The central result presented here concerns the spatial structure of temperature during these events. The initial peak was surface intensified and was barely detectable at 45 m. Its amplitude varied with position along the coast, decaying with distance north. The main peak showed a strong signal down to at least 200 m. The amplitude and timing of temperature anomalies during this event were depth dependent. The largest absolute amplitudes relative to seasonal cycles were in excess of 4 °C and occurred between 45 and 65 m depth. The anomalies reached their maximum values at later time with increasing depth, between October 1997 and January 1998. The amplitude of this main peak was comparable at all mooring sites. The final peak in August 1998 had a comparable amplitude at all mooring sites to a depth of 100 m. Temperature increases during the three events were accompanied by a corresponding rise in sea level.The El Niño signals in currents and salinity are more difficult to distinguish from background variability than those in temperatures and sea level. However, stronger than average poleward flow was observed at the eastern entrance to the Santa Barbara Channel between 5 and 100 m depth for most of 1997, and there are indications for greater than usual poleward flow over the Santa Maria Basin in fall 1997. Surface drifter evidence, although qualitative, also suggests greater than usual poleward displacement in November 1997 relative to other years. Along with increased temperature, survey observations of salinity suggest changes to the regional temperature–salinity relation during November 1997 with greater than usual salinity at temperatures below 12 °C.     

Discussion of “A function to determine wavelength from deep in to shallow water based on the length of the cnoidal wave at breaking” by J.P. Le Roux

An empirical modification to the Airy equation for wave celerity reduces to the expression for solitary waves in shallow water whilst retaining its usual form for deep water. The equation yields celerities in reasonable agreement with those for cnoidal waves in intermediate water depths. In this aspect, it is similar to the work described by Le Roux [Le Roux, J.P., 2007. A function to determine wavelength from deep into shallow water based on the length of the cnoidal wave at breaking. Coastal Engineering 54, 770–774]. The empirical modification has been widely applied in computer programs over the past 30 years.     

Discussion on “Soft computing approach for real-time estimation of missing wave heights” by S.N. Londhe [Ocean Engineering 35 (2008) 1080-1089]

The paper studied by Londhe (2008) utilizes genetic programming (GP) for estimation of missing wave heights. The paper includes some problems about the fundamental aspects and use of the GP approach. In this discussion, some controversial points of the paper are given.     

Morphology and distribution of the marine diatom Azpeitia africana(Janisch ex A. Schmidt) G. Fryxell & T. P. Watkins in the South China Sea

The purpose of the present paper is to study the morphological structure and variability of Azpeitia africana and to determine its geographical distribution in the surface sediments of the South China Sea(SCS). Sediment samples were collected with grabs or box corers in one cruise in 2001 and two cruises in 2007. The sampling stations were located between 3°56.61′–20°59.37′N and 108°30.68′–116°46.70′E,where the water depth ranged from 72 m to 4 238 m. The diatom was observed by phase contrast microscopy and scanning electron microscopy. Microscopical observation showed that A. africana had circular valves with the areolar lines radiating from the eccentric ring. The central rimoportula had an external tube recessed on the edge of a central ring. The marginal rimoportulae were not evenly spaced, and they were positioned more closely together in one quadrant than in the others. Azpeitia africana is the most abundant diatom species in the southern region of the SCS, and accounted for 0.9%–5.6% of all diatom species in the Xisha Islands area. Average cell density of A. africana was 1.1×10~5 valves/g. The percentage abundance of A.africana was low(0%–2.5%) in the northern regions of the SCS and the Sunda Shelf, and it was not detected in the northwestern continental shelf(shallow water area) and northern Kalimantan Island shelf. Our results suggested that A. africana is a typical warm water species and that it could be used as an indicator of the warm Paci?c Ocean water, including the Kuroshio Current, ?owing into the SCS.     

A function to determine wavelength from deep into shallow water based on the length of the cnoidal wave at breaking—Reply to discussion by T.S. Hedges

The equations of Hedges [Hedges, T.S., 2009. Discussion of “A function to determine wavelength from deep into shallow water based on the length of the cnoidal wave at breaking” by J.P. Le Roux, Coastal Eng.], although yielding similar wavelengths, are not consistent with the fact that the horizontal water particle velocity in the wave crest should equal the wave celerity at breaking over a nearly horizontal bottom.     

Monitoring of the chemical pollution of the river Rhône through measurement of DNA damage and cytochrome P4501a induction in chub (Leuciscus cephalus)

The in vivo response of freshwater fish exposed to pollutants was assessed using two biomarkers, 7-ethoxyresorufin-O-deethylase (EROD) induction and DNA single strand breaks. Chub (Leuciscus cephalus) were caught in spring and in fall at various locations in the river Rhône watershed. EROD activity was measured in the liver while DNA damage was evaluated in chub erythrocytes using the recently developed Comet assay. Chemical contamination was evaluated both in fish muscle (PCBs) and in sediment (PCBs, PAHs, heavy metals) collected at each sampling station. Sex of individuals was shown to influence the level of EROD activity but not the level of DNA damage. The EROD activity as well as the DNA damage were found to be higher in the mostly contaminated stations compared to the reference one. This study shows that multibiomarker-based approach provides complementary informations about early effects in feral fish exposed to complex chemical pollution and highlights the interest of the Comet assay in genotoxicity assessment.     

Spatial and temporal variability of microplankton and detritus, and their export to the shelf sediments in the upwelling area off Concepción, Chile (∼36°S), during 2002-2005

Seasonal variations in diversity and biomass of diatoms, tintinnids, and dinoflagellates and the contribution of microplankton and faecal material to the vertical flux of particulates were investigated at one time series station T (station 18) between 2002 and 2005 and at a grid of stations during November 2004 in the coastal and oceanic area off Concepción (36°S), Chile. The variations were analysed in relation to water column temperature, dissolved oxygen, nutrient concentration, offshore Ekman transport, and chlorophyll-a concentration. Abundance was estimated as cell numbers per litre and biomass in terms of biovolume and carbon units.A sharp decrease with depth was observed in the abundance of both phytoplankton and microzooplankton during the whole annual cycle; over 70% of their abundance was concentrated in the upper 10 m of the water column. Also, a clear seasonality in microplankton distribution was observed at station T, with maxima for diatoms, tintinnids, and dinoflagellates every summer (centred on January) from 2002 to 2005.On the grid of stations, the maximum integrated (0-50 m) micro-phytoplankton abundances (>1 × 10⁹ cells m⁻²) occurred at the coastal stations, an area directly influenced by upwelling. A similar spatial distribution was observed for the integrated (0-200 m) faecal carbon (with values up to 632 mg C m⁻²). Tintinnids were distributed in all the first 300 miles from the coast and dinoflagellates were more abundant in oceanic waters.At station T, the average POC export production (below 50 m depth) was 16.6% (SD = 17%; range 2-67%; n = 16). The biological-mediated fluxes of carbon between the upper productive layer and the sediments of the continental shelf off Concepción depend upon key groups of phytoplankton (Thalassiosira spp., Chaetoceros spp.) and zooplankton (euphausiids) through the export of either cells or faecal material, respectively.