Multiple longshore sand bars in the upper Chesapeake Bay

In the upper Chesapeake Bay (Maryland, U.S.A.) field surveys were conducted at 18 multiple longshore sand bar sites. The multiple bar systems were found in water depths less than approximately 2 m (mean sea level), and exhibited mild bottom slopes of 0·0052 or less. The number of bars composing each system ranged from four to 17 and the spacing between the crests typically increased in the offshore direction, ranging from 12 to 70 m. Bar height also typically increased with distance offshore and ranged from 0·03 to 0·61 m. A grain size analysis of crest and trough sediment did not reveal any significant differences and the sediment was categorized as ‘fine sand’. A review of the literature data indicated that the Chesapeake Bay multiple bars possessed similar characteristics to those found in Gelding Bay (Baltic Sea); similarities in fetch, wave height and tidal range between the two bays may account for this finding. The surf-scaling parameter indicated that the multiple bar systems were extremely dissipative with regard to wave energy, and wave height appeared to be an important factor in controlling bar spacing and bar height. A multiple wave break point hypothesis was discussed as a possible mechanism for the formation of Chesapeake Bay multiple longshore bars, and limited observational evidence appeared to support such a mechanism.     

Particulate organic matter in the coastal and estuarine waters of Goa and its relationship with phytoplankton production

In the coastal and estuarine waters of Goa, particulate organic carbon (POC) varied from 0.52 to 2.51 mg l^?1 and from 0.28 to 5.24 mg l^?1 and particulate phosphorus (PP) varied from 0.71 to 5.18 μg l^?1 and from 0.78 to 20.34 μg l^?1, respectively. The mean values of chlorophyll and primary productivity were 1.94 mg m^?3 and 938.1 mg C m^?2 day^?1 in the coastal waters and 4.3 mg m^?3 and 636.5 mg C m^?1 day^?1 in the estuarine waters, respectively.$\text{POC}\text{chl}$ ratios were low in June and October even when POC values were quite high. The POC in surface waters was linearly correlated with the chlorophyll content. Also PP increased when chlorophyll and primary productivity remained high. The results suggest that the phytoplankton was sharply increasing and contributed to POC and PP content. The percentage of detritus calculated from the intercept values of chlorophyll on POC varied from 46 to 76% depending on season. Results indicate that the major portion of POC and PP during postmonsoon (October–January) is derived from phytoplankton production while the allochthonous matter predominate during monsoon (June–September).     

Contribution of storms to groundwater recharge in the semi‐arid region of Karnataka,India

This paper describes the application of environmental isotopes and injected tracer techniques in estimating the contribution of storms as well as annual precipitation to groundwater recharge and its circulation, in the semi‐arid region of Bagepalli, Kolar district, Karnataka. Environmental isotopes ²H, ¹⁸O and ³H were used to study the effect of storms on the hydrological system, and an isotope balance was used to compute the contribution of a storm component to the groundwater. Some of the groundwater samples collected during the post‐storm periods were highly depleted in stable isotope content with higher deuterium excess relative to groundwater from the pre‐storm periods. Significant variation in deuterium excess in groundwater from the same area, collected in two different periods, indicates the different origin of air masses. The estimated recharge component of a storm event of 600 mm to the groundwater was found to be in the range of 117–165 mm. There was no significant variation in environmental tritium content of post‐storm and pre‐storm groundwater, indicating the fast circulation of groundwater in the system. After completion of the environmental isotope work, an injected radiotracer ³H technique was applied to estimate the direct recharge of total precipitation to the groundwater. The estimated recharge to the groundwater is 33 mm of the 550 mm annual precipitation during 1992. Copyright © 2003 John Wiley & Sons, Ltd.     

The solubility of iron sulphides in synthetic and natural waters at ambient temperature

A critical evaluation of literature values for the solubility products, K _sp ^NBS = [Fe²⁺][HS^–] Fe²⁺ HS^– (H _NBS ⁺ )^–1, of various iron sulphide phases results in consensus values for the pKs of 2.95 ± 0.1 for amorphous ferrous sulphide, 3.6 ± 0.2 for mackinawite, 4.4 ± 0.1 for greigite, 5.1 ± 0.1 for pyrrhotite, 5.25 ± 0.2 for troilite and 16.4 ± 1.2 for pyrite.Where the analogous ion activity products have been measured in anoxic freshwaters in which there is evidence for the presence of solid phase FeS, the values lie within the range of 2.6–3.22, indicating that amorphous iron sulphide is the controlling phase. The single value for a groundwater of 2.65 (2.98 considering carbonate complexation) agrees. In seawater four values range between 3.85 to 4.2, indicating that mackinawite or greigite may be the controlling phase. The single low value of 2.94 is in a situation where particularly high fluxes of Fe (II) and S (–II) may result in the preferential precipitation of amorphous iron sulphide. Formation of framboidal pyrite in these sulphidic environments may occur in micro-niches and does not appear to influence bulk concentrations. Calculations show that the formation of Fe₂S₂ species probably accounts for very little of the iron or sulphide in most natural waters. Previously reported stability constants for the formation of Fe (HS)₂ and (Fe (HS)₃)^– are shown to be suspect, and these species are also thought to be negligible in natural waters. In completely anoxic pore waters polysulphides also have a negligible effect on speciation, but in tidal sediments they may reach appreciable concentrations and lead to the direct formation of pyrite. Concentrations of iron and sulphide in pore waters can be controlled by the more soluble iron sulphide phase. The change in the IAP with depth within the sediment may reflect ageing of the solid phase or a greater flux of Fe (II) and S (–II) nearer the sediment surface. This possible kinetic influence on the value of IAPs has implications for their use in geochemical studies involving phase formation.     

Trichodesmium erythraeum (Ehrenberg) bloom along the southwest coast of India (Arabian Sea) and its impact on trace metal concentrations in seawater

The incidence of a large scale Trichodesmium erythraeum bloom along the southwest coast of India (Arabian Sea) observed in May 2005 is reported. Around 4802 filaments of T. erythraeum ml⁻¹ seawater was observed and a colony consisted of 3.6 × 10⁵ cells. The bloom was predominant off Suratkal (12° 59′N and 74° 31′E) with a depth of about 47 m, covering an area of 7 km in length and 2 km width. The concentrations of Zinc, Cadmium, Lead, Copper, Nickel and Cobalt were determined in samples collected from the bloom and non-bloom sites using stripping voltammetry. The observed hydrographical and meteorological parameters were found to be favorable for the bloom. The concentrations of Zinc, Cadmium and Nickel were found to be higher at bloom stations, while the concentrations of Lead, Copper and Cobalt were found to be very low at bloom stations. Elevated concentrations of Cadmium and Cobalt were observed at Valappad mainly due to the decomposition of detrital material produced in the bloom. Statistically significant differences (P > 0.01) in metal concentrations between the bloom and non-bloom stations were not observed except for Copper. Metals such as Lead, Copper and Cobalt were removed from the seawater at all places where bloom was observed. Cadmium was found to be slowly released during the decaying process of the bloom.     

台湾山地的雨影效应及其表现

台湾岛的雨量受台湾山地的雨影效应影响明显,各地各月随着风向的不同,雨量表现出很大的差异。福建沿海一线存在着一个雨量低值区,主要是由于该地带所处的地理位置及地形条件所决定,与台湾山地的雨影效应无关。     

厦门筼筜港的形成与演变

本文根据实际调查的资料,概述了筼筜港区的地质地貌特征,重点论述了第四纪沉积物的成因和时代,阐述了该区的形成与演变过程,把它划分为5个发育阶段。     

A Classification of Hypersaline Waters, Based on Trophic Criteria

Abstract. A classification of hypersaline waters is proposed on the basis of the food chain structure of their biota. Four steps of increasing salinity and respective shortening of the food-chains are recognized, respectively named: alpha-, beta-, gamma- and delta-hypersaline waters.
Some general aspects, dealing with cosmopolitism of the biota, production, competition and benthic ecology in hypersaline waters are discussed.
The relevance of ecological studies in hypersaline waters to theoretical ecology and to the new technological uses of saline waters is briefly mentioned.