Seasonal variation of nitrate-N in surface and ground-waters of South Western Nigeria: a preliminary survey

Two surveys of nitrate-N concentrations in surface and ground water in Ogun and parts of Lagos and Oyo States of south-western Nigeria were undertaken between October 1997 and December 1998, and between July 2000 and May 2001 (covering both dry and rainy seasons). The study was conducted to ascertain the extent of nitrate-N pollution of the surface/ground water in some parts of the three states. Seventy-two water points (33 rivers/streams, 21 wells and 18 boreholes) were sampled three times during each of the two seasons. Nitrate-N was detected in all the river/stream samples analysed with concentrations ranging from 0.5 to 15.3 mg/l and 1.0 to 7.7 mg/l during the rainy and dry seasons, respectively (average value 2.7 and 2.4 mg/l for rainy and dry season, respectively). 98.5% of the rivers/streams sampling points contained nitrate-N in amounts equal to or less than 10 mg/l. 88.1% of wells and 97.2% of boreholes had a nitrate-N content less than 5 mg/l. Nitrate-N concentrations in the sampled wells ranged from 1.4 to 7.4 mg/l and 1.1 to 6.0 mg/l during the rainy and dry seasons, respectively (average value 2.6 and 2.2 mg/l, respectively). The sampled boreholes had a lower nitrate-N concentration ranging from 0.1 to 5.2 mg/l and from below the detection limit to 5.0 mg/l during the rainy and dry seasons, respectively (average value 1.8 and 1.6 mg/l, respectively). Nitrate-N concentrations in boreholes were below detection limit in 22% of the samples. Generally, for most of the sampling points, nitrate-N concentrations were slightly higher during the rainy season compared with the dry season. The present results indicated that nitrate-N concentrations in all the water points (except one) were below the World Health Organization (WHO) maximum acceptable limit in potable waters (10 mg/l). Therefore, contamination of the surface and ground water of the study area is not indicated. This study provides background data against which future changes in nitrate-N concentrations of surface and ground waters in the study area can be measured.     

Anthropogenic influence on surface water quality of the Nhue and Day sub-river systems in Vietnam

In order to investigate the temporal and spatial variations of 14 physical and chemical surface water parameters in the Nhue and Day sub-river systems of Vietnam, surface water samples were taken from 43 sampling sites during the dry and rainy seasons in 2007. The results were statistically examined by Mann–Whitney U-test and hierarchical cluster analysis. The results show that water quality of the Day River was significantly improved during the rainy season while this was not the case of the Nhue River. However, the river water did not meet the Vietnamese surface water quality standards for dissolved oxygen (DO), biological oxygen demand (BOD₅), chemical oxygen demand (COD), nutrients, total coliform, and fecal coliform. This implies that the health of local communities using untreated river water for drinking purposes as well as irrigation of vegetables may be at risk. Forty-three sampling sites were grouped into four main clusters on the basis of water quality characteristics with particular reference to geographic location and land use and revealed the contamination levels from anthropogenic sources.     

Seasonal variations in trace metal levels,speciation and physicochemical determinants of metal availability in dumpsite soils within Akwa Ibom State,Nigeria

Physicochemical properties, total metals and metal species were investigated in surface soil samples from six urban dumpsites within Akwa Ibom State, Nigeria. Results obtained indicated that Pb, Cd and Cr levels were higher in the dry season than in wet season, whereas Ni levels were higher during the wet season. Soil pH, organic matter and cation-exchange capacity (CEC) showed higher values in wet season than in dry season, whereas sand and clay levels were higher in the dry season. Speciation analysis showed the principal fraction of the metals to be Pb (reducible), Cd (acid extractable) and Ni (residual), whereas Cr existed in the residual fraction during the dry season and in the acid-extractable fraction during the wet season. Soil pH was positively correlated at p<0.1 with all metals in both seasons, sand was negatively correlated with the metals in both seasons, and CEC was negatively correlated with all metals in both seasons, except Pb in the wet season. Organic matter showed variable relationships with metals in both seasons. Seasonal variations affected metal availability and physicochemical properties of the soil. Total metal concentrations followed the order Pb>Ni>Cd>Cr, whereas their bioavailability followed the trend Cd>Pb>Cr>Ni.     

Competition, resources, and vegetation during 10 years in native grassland

A 10-year experiment tested for variation in competition intensity over time in a natural grassland at the northern edge of the Great Plains. Growing-season precipitation varied fivefold during the study. All ecosystem-level variables varied significantly among years, and most covaried in expected ways. The covers of all common grasses possessing the C3 photosynthetic pathway varied significantly among years; in contrast, all common species with traits associated with drought tolerance (a C4 grass, a lichen, a spikemoss, and a subshrub) did not vary. Annual transplant experiments measured the competitive effects of neighbors on the growth of individuals of the native grass Bouteloua gracilis. A significant interaction between year and competition showed that competition intensity varied among years. The size of this effect, however, was small (eta2 = 0.074) relative to the size of the direct effect of competition (eta2 = 0.20) or the year in which the experiment was conducted (eta2 = 0.51). Further, competition intensity was not significantly related to any variable describing standing crop or resources, or species richness. Species richness was highest in years with high precipitation, standing crop, and individual growth, due to the recruitment of rare species that were absent from dry years. In summary, variation in competition intensity was statistically significant but had small effects relative to the direct effects of climate.     

Airborne bacteria associated with particulate matter from a highly urbanised metropolis: A potential risk to the population’s health

• The airborne bacteria of Mexico City are representative of urban environments. • Particle material<10 µm influenced the type and quantity of airborne bacteria. • The diversity and richness of bacteria were higher in the rainy season. • The emission & transport of airborne bacteria determine the atmosphere’s microbiome. • Bacterias as Kocuria, Paracoccus, and Staphylococcus were in the air of Mexico City. Bacteria in the air present patterns in space and time produced by different sources and environmental factors. Few studies have focused on the link between airborne pathogenic bacteria in densely populated cities, and the risk to the population’s health. Bacteria associated with particulate matter (PM) were monitored from the air of Mexico City (Mexico). We employed a metagenomic approach to characterise bacteria using the 16S rRNA gene. Airborne bacteria sampling was carried out in the north, centre, and south of Mexico City, with different urbanisation rates, during 2017. Bacteria added to the particles were sampled using high-volume PM₁₀ samplers. To ascertain significant differences in bacterial diversity between zones and seasons, the Kruskal-Wallis, Wilcoxon tests were done on alpha diversity parameters. Sixty-three air samples were collected, and DNA was sequenced using next-generation sequencing. The results indicated that the bacterial phyla in the north and south of the city were Firmicutes, Cyanobacteria, Proteobacteria, and Actinobacteria, while in the central zone there were more Actinobacteria. There were no differences in the alpha diversity indices between the sampled areas. According to the OTUs, the richness of bacteria was higher in the central zone. Alpha diversity was higher in the rainy season than in the dry season; the Shannon index and the OTUs observed were higher in the central zone in the dry season. Pathogenic bacteria such as Kocuria, Paracoccus, and Micrococcus predominated in both seasonal times, while Staphylococcus, Corynebacterium, and Nocardioides were found during the rainy season, with a presence in the central zone.     

Phytoextraction potential of Sporobulus pyramidalis found in an abandoned battery industry environment in Nigeria

The levels of heavy metals (Cd, Cr, Ni, Pb, Sb and V) in Sporobulus pyramidalis plant species from an abandoned battery industry environment were determined during the wet and dry seasons as follows: The ranges in metal concentrations during the wet and dry seasons were 0.002, 0.420, 0.036 and 36.10?µg?g^?1, respectively. The coefficients of variation for the metals during wet and dry seasons ranged between none to 151.724% and 13.838–214.935%, respectively. The results showed higher levels of the metals in S. pyramidalis during the dry than wet season. Results obtained from both wet and dry season when compared with background values, Federal Environmental Protection Agency and other international standards revealed that the plant species accumulated high levels of these heavy metals which was evident in concentrations exceeding maximum tolerable limits. The health implications of consuming this plant and any other plant or crop within this environment are discussed.     

Community composition of aquatic birds in lakes of Bangalore, India

Observations were made on the occurrence, abundance, richness, and diversity of waterbirds in 15 major lakes in Bangalore city during 2008 - 2009. During the study period 35 species of aquatic birds were recorded. The number of aquatic bird species recorded at various lakes ranged from 23 to 35. The percent abundance of waterbirds recorded in the study lakes ranged from 2.46 to 21.49 and itwas significantly different (p < 0.05). The diversity and species evenness of waterbirds in the lakes ranged from 2.07 to 3.16 and 0.32 to 0.76, respectively. There was a significant difference (p < 0.05) in the diversity and species evenness of waterbirds among different lakes. Species richness of the bird population ranged from 2.89 to 4.01 in the different study lakes and it was not significantly different (p > 0.05). There was a variation in number of waterbird species recorded during summer, monsoon and winter seasons. Of the 35 waterbird species, Bubulcus ibis showed cent percent frequency, whereas less frequently (4.44%) observed species was Anas platyrhynchos. Among various waterbird species, Bubulcus ibis, Fulica atra, Tringa hypoleucos, Motacilla maderaspatensis, Phalacrocorax niger Egretta garzetta, Charadrius dubius, Ardeola grayji, Halcyon smymensis and Motacilla alba were frequently encountered in most of the study lakes.     

Extrinsic and intrinsic controls of zooplankton diversity in lakes

Pelagic crustacean zooplankton were collected from 336 Norwegian lakes covering a wide range of latitude, altitude, lake area, mean depth, production (as chlorophyll a), and fish community structure. Mean zooplankton species richness during the ice-free season was generally low at high latitudes and altitudes. Further, lower species richness was recorded in western lakes, possibly reflecting constraints on migration and dispersal. However, despite obvious spatial limitations, geographic boundaries were only weak predictors of mean zooplankton richness. Similarly, lake surface area did not contribute positively to mean richness such as seen in other ecosystem surveys. Rather, intrinsic factors such as primary production and fish community (planktivore) structure were identified by regression analysis as the major predictors of zooplankton diversity, while a positive correlation was observed between species richness and total zooplankton biomass. However, in spite of a large number of variables included in this study, the predictive power of multiple regression models was modest (<50% variance explained), pointing to a major role for within-lake properties, as yet unidentified intrinsic forces, stochasticity, or dispersal as constraints on zooplankton diversity in these lakes.     

Use of data on avian demographics and site persistence during overwintering to assess quality of restored riparian habitat

Monitoring responses by birds to restoration of riparian vegetation is relatively cost-effective, but in most assessments species-specific abundances, not demography, are monitored. Data on birds collected during the nonbreeding season are particularly lacking. We captured birds in mist nets and resighted banded birds to estimate species richness and diversity, abundance, demographic indexes, and site-level persistence of permanent-resident and overwintering migrants in remnant and restored riparian sites in California. Species richness in riparian remnants was significantly higher than in restored sites because abundances of uncommon permanent residents were greater in remnants. Species richness of overwintering migrants did not differ between remnants and restored sites. Responses among overwintering migrants (but not permanent residents) to remnant and restored riparian sites differed. Capture rates were higher in remnant or restored riparian sites for 7 of 10 overwintering migratory species. For Lincoln's Sparrows (Melospiza lincolnii) and White-crowned Sparrows (Zonotrichia leucophrys) proportions of older birds were significantly higher in remnants, even though capture rates of these species were higher in restored sites. Overwinter persistence of 4 migrant species was significantly higher in remnant than in restored sites. A higher proportion of Hermit Thrushes (Catharus guttatus, 56.3%), older Fox Sparrows (Passerella iliaca, 57.1%), Lincoln's Sparrows (59.7%), and White-crowned Sparrows (67.8%) persisted in remnants than restored sites. Our results suggest restored riparian sites provide habitat for a wide variety of species in comparable abundances and diversity as occurs in remnant riparian sites. Our demographic and persistence data showed that remnants supported some species and age classes to a greater extent than restored sites.     

Seasonal variations in abundance of nitrifying bacteria in fish pond ecosystem

Seasonal changes in abundance of nitrifiers (ammonia-oxidizing and nitrite-oxidizing bacteria) in surface and bottom water of freshwater ponds were examined with respect to temperature, DO, pH as well as concentration of ammonia and nitrite. The most probable number (MPN) of ammonia-oxidizers in different ponds varied from 1297 +/- 3.6 to 1673.23 +/- 0.36 ml(-1) in bottom and 720.5 +/- 8.1 to 955.3 +/- 10.8 ml(-1) in surface water during the rainy season while the MPN ranged from 1074 +/- 1.07 to 1372.17 +/- 4.6 ml(-1) in bottom and 515 +/- 10.1 to 678 +/- 11.8 ml(-1) in surface water in winter. However, the MPN were greatly reduced in summer and ranged from 435.05 +/- 15.7 to 547.54 +/- 2.12 ml(-1) in bottom and 218.7 +/- 7.3 to 368.4 +/- 9.32 ml(-1) in surface water. Similar seasonal trends were also observed in MPN of nitrite-oxidizers. Among all the physico-chemical parameters, abundance of nitrifiers was more positively correlated with ammonia and nitrite concentration in all the seasons. The abundance of nitrifiers in surface and bottom water was highest in rainy season followed by winter and modest in summer. The potential nitrification activities and oxidation rates were shown to be linear and activity of ammonia-oxidizing and nitrite-oxidizing bacteria was highest during rainy season.     

Habitat use pattern of tidal mud and sand flats by shorebirds (charadriiformes) wintering in southern India

Habitat use pattern and status of shorebirds in southern India were investigated in six tidal flats comprising three mudflats and three sand flats on the east coast of southern India. Totally, 7757 shorebirds belonging to 21 species were recorded during September 2000–March 2002. The birds preferred mudflats over sand flats. Density, diversity and richness of shorebirds were relatively higher in tidal flats, especially in mudflats. The shorebirds preferred mudflats over sand flats as stopover sites and sites for refueling the required energy during migration. Rhythmic changes in tidal pattern also influenced the allochthonous nutrients and prey species, which also attracted the migratory shorebirds. However, the abundance of shorebirds with reference to tidal flats *season*tide and habitats*seasons * tide had strong variations (P < 0.001). During migratory season, bird density, diversity and species richness were observed higher than in other seasons.     

Seasonal variations in physicochemical characteristics and cyanobacterial diversity of a lake in Northern India

Physicochemical analyses and cyanobacterial diversity of Ramgarh Lake water were performed at five sampling sites during winter, summer, and monsoon seasons. Higher load of solids, carbon, and nutrients were persistent throughout the analysis that indicates the conversion of lake from oligotrophic to eutrophic nature. High nutrients load enhanced cyanobacterial biomass, while low nutrients load produced relatively less biomass. The physicochemical parameters of water samples revealed minimum 2.9 mg L^?1 dissolved oxygen (DO) at site-1 during summer, while maximum (5.6 mg L^?1) at site-4 in monsoon season. Maximum biochemical oxygen demand (BOD) (40 mg L^?1) and chemical oxygen demand (COD) (126 mg L^?1) were recorded at site-1 during summer, whereas minimum BOD (18 mg L^?1) and COD (52 mg L^?1) were evident at site-3 in monsoon season. Minimum concentration of nitrate (0.72 mg L^?1) was recorded at site-3 in summer, whereas maximum 2.7 mg L^?1 was present at site-5 in winter season. The phosphate concentration was maximum (0.52 mg L^?1) at site-5 in summer, and minimum (0.18 mg L^?1) was observed at site-4 in monsoon season. Cyanobacterial diversity was higher during all the seasons, and dominated by the species of Microcystis at all the five sampling sites.     

富营养化对浅水湖泊轮虫种群结构影响研究

石臼湖和固城湖是长江中下游两个浅水湖泊,富营养化问题日益突出。为探索湖泊富营养化对轮虫的影响,于2012年平水期和枯水期对这两个湖泊轮虫种群结构进行了调查,并检测水体理化因子,分析轮虫分布与水环境因子及水体富营养状况的关系。水质检测结果显示,平水期石臼湖除个别点水体综合营养状态指数（TLI）〉50为轻度富营养状态外,大多数站点TLI50,处于轻度-中度富营养化状态。水生生物调查检出轮虫35种,其中石臼湖33种,固城湖27种,平水期种类多于枯水期。出现的轮虫以臂尾轮虫（Brachionus）和异尾轮虫（Trichocerca）居多,优势种主要有螺形龟甲轮虫（Keratella cochlearis）、广生多肢轮虫（Polyarthra vulgaris）、疣毛轮虫（Trichocerca sp.）、沟痕泡轮虫（Pompholyx sulcata）、异尾轮虫属和臂尾轮虫属等。轮虫平均密度3023.19 ind·L-1,平均生物量745.72μg·L-1。现存量季节变动明显,大部分站点平水期大于枯水期。轮虫多样性指数也是平水期大于枯水期,石臼湖轮虫多样性大于固城湖。水体综合营养状态指数（TLI）与轮虫种类数和多样性成显著负相关,随着富营养化加剧,轮虫种类减少,多样性降低。典范对应分析（Canonical Correspondence Analysis,CCA）表明,影响轮虫种群分布的主要环境因子为NH4＋-N、TN、TP和CODMn。按轮虫丰度分布与水环境因子的关系排序,2次调查的24个站点可大致分成3个组。轮虫种群结构受水体富营养状态影响,每组站点的代表性种类对水体营养状态有较好的指示作用。组1的代表性种类为曲腿龟甲轮虫,指示营养级别O-β;组2代表性种类萼花臂尾轮虫,指示的营养级别为β-α;组3以O营养级种类为主。     

Physicochemical and microbiological assessment of Oko-oba--a Nigerian abattoir

The physicochemical and microbiological assessments of Oko-oba abattoir were carried out during dry and wet season to determine whether the waste discharges are within tolerable limits. All the physicochemical parameters studied showed seasonal variations. Higher temperature and lower pH values were recorded during the dry season than wet season. Similarly, the BOD of wastewater from the slab decreases from 10000 mg/ml during the dry season to 6000 mg/ml in the wet season. Conversely, the BOD of the final waste discharge was 4000 mg/ml during the dry season and 3,500 mg/ml during the wet season. The COD showed similar trend, with values ranging from 12,200 to 18,500 mg/ml depending on the season. The suspended solid values ranged from 1200 to 1950 mg/ml. The phosphate and nitrate ions were in the range of 41-75 mg/l and 22.5- 960 mg/ml respectively. Heavy metals detected were Chromium at 104 -114 mg/ml, Copper 16 -75 mg/ml and Iron 55- 114 mg/ml. The following bacteria species were also encountered: B. cereus, E. coli, P. aeruginosa, S. aureus, S. faecalis, S. lactis, Micrococcus sp, A. aerogenes, P. vulgaris, and S. typhi. The results showed significantly high level of pollutants in the waste discharged.     

近50年广东省降雨时空变化及趋势研究

基于1959-2008年广东省境内25个雨量站的逐日降雨观测资料,在SQL SERVER2000中编写相关代码,对次降雨、月、雨季、年、10年、50年等6个不同时间尺度的降雨量、降雨次数、降雨类型进行统计分析。研究表明：广东省境内存在3个多雨带和3个少雨带,降雨量在空间上大致呈现东、西、北部少,中、南部多的格局,年均降雨天数内陆多于沿海,而降雨量沿海大于内陆。近50年广东省年均降雨量为1758.8 mm,降雨量由南向北呈带状递减,其降雨量最多、最少的区域分别为阳江、徐闻。年降雨天数的年际变化幅度小于降雨量的年际变化幅度。年降雨量变化不大,但降雨总天数呈现减少趋势,且减少的降雨类型以小雨、中雨为主,大雨、暴雨的降雨次数有增加的趋势,降雨量在时间分布上更为集中,旱涝灾害将会更为频繁。研究区80.0%以上的降雨量在雨季产生,其中沿海雨季降雨量占年降雨量的比重要大于内陆,且内陆（沿海）雨季降雨量一般集中在前汛期（后汛期）。在月尺度上,降雨量随月份变化呈现双峰型,两个峰值分别处于6月、8月。其中1-4月、6-8月、12月降雨量整体呈现增大趋势,5月、9-11月降雨量整体呈现减少趋势。在次降雨尺度,小雨、中雨、暴雨的平均次降雨强度有增大的趋势,而大雨、大暴雨降雨强度有微度减少的趋势。     

Effects of nutrients, herbivory, and depth on the macroalgal community in the rocky sublittoral

We studied the interacting roles of nutrient availability and herbivory in determining the macroalgal community in a rocky littoral environment. We conducted a factorial field experiment where we manipulated nutrient levels and herbivory at two sublittoral depths and measured macroalgal colonization and the following young assemblage during the growing season. At the community level, grazing reduced algal colonization, though the effect varied with depth and its interaction with nutrient availability varied in time. In shallow water, the total density of macroalgae increased in response to nutrient enrichment, but the ability of grazers to reduce macroalgal density also increased with the nutrient enrichment, and thus, the community could not escape from the top-down control. In deep water, the algal density was lower, except in July when nutrient enrichment caused a very dense algal growth. Grazing at the greater depth, though effective, was generally of smaller magnitude, and in July it could not limit algal recruitment and growth. Species richness peaked at the intermediate nutrient level in deep but not in shallow water during most of the growing season. Grazing had no effect on diversity of the algal community at either depth and only a minor effect on species richness at the greater depth. Opportunistic and ephemeral algae benefited from the nutrient enrichment but were also grazed to very low densities. Slowly growing and/or perennial species colonized poorly in the nutrient enriched treatments, and depending on the species, either suffered or indirectly benefited from herbivory. For all species, effects of nutrients on colonization depended on depth; usually both nutrient and herbivory effects were more pronounced at the shallow depth. We conclude that grazers are able to reduce macroalgae over a large range of nutrient availabilities, up to 12-fold nutrient enrichment in the current experiment, and that the sublittoral depth gradient generates variation in the algal community control exerted by both herbivory and nutrient availability. Thus temporal and spatial variability in both top-down and bottom-up control and in their interaction, especially along the depth gradient, may be crucially important for producer diversity and for the successional dynamic in a rocky sublittoral environment.     

Platinum in PM2.5 of the metropolitan area of Mexico City

The increase in platinum (Pt) in the airborne particulate matter with size ≤2.5 µm (PM_2.5) in urban environments may be interpreted as result of the abrasion and deterioration of automobile catalyst. Nowadays, about four million vehicles in Mexico City use catalytic converters, which means that their impact should be considered. In order to evaluate the contribution of Pt to environmental pollution of the metropolitan area of Mexico City (MAMC), airborne PM_2.5 was collected at five different sites in the urban area (NW, NE, C, SW, SE) in 2011 during April (dry-warm season), August (rainy season) and December (dry-cold season). Analytical determinations were carried out using a ICP-MS with a collision cell and kinetic energy discrimination. The analytical and instrument performance was evaluated with standard road dust reference material (BCR-723). Median Pt concentration in the analyzed particulate was is 38.4 pg m^?3 (minimal value 1 pg m^?3 maximal value 79 pg m^?3). Obtained Pt concentrations are higher than those reported for other urban areas. Spatial variation shows that SW had Pt concentration significantly higher than NW and C only. Seasonal variation shows that Pt median was higher in rainy season than in both dry seasons. A comparison of these results with previously reported data of PM₁₀ from 1991 and 2003 in the same studied area shows a worrying increase in the concentration of Pt in the air environment of MAMC.     

地形因子对暖温带森林群落物种丰富度-地上生物量关系的影响

地形因子是森林群落物种丰富度与生产力的重要影响因素,可以修正物种丰富度-生产力两者之间的关系。为了厘清地形因子对物种丰富度-生产力关系的修正效应,以东灵山暖温带天然次生林为研究对象,基于20 hm2样地DEM地图,提取海拔、坡度、坡向、凹凸度等地形因子,用GLM模型探讨了地形因子对群落丰富度与地上生物量的影响。结果表明,群落地上生物量与物种丰富度分别受不同地形因子的影响,群落地上生物量受Ea、El2、El3、Co34个因子的显著影响（P〈0.05）,而物种丰富度则受Sl、El、El2、El34个因子的显著作用（P〈0.05）,两者受海拔相关因子的影响最大,分别解释了两者3.99%和11.09%的变异。地形因子修正了物种丰富度-地上生物量之间的单峰曲线关系,使其朝着单调与直线化趋势变化。以后在探讨森林群落物种丰富度-生产力关系时,地形因子的修正作用应该受到重视。     

Development of contemporary Eastern Pacific coral reefs

An overview of oceanographic conditions prevailing in the tropical Eastern Pacific Ocean suggests that the entire region is environmentally marginal for coral-reef development. The principal features of this environment are a strong, permanent, shallow thermocline and an annual north-south migration of the Intertropical Convergence resulting in wet and dry seasons. Along tropical Eastern Pacific continental margins structural coral reefs are best developed in the Gulf of Chiriquí off western Panamá. These reefs are relatively small, with reef formation taking place at a maximum depth of roughly 10 m. All of the reefs are judged to have formed since sea level approached its present height some 5,000 years ago. A study of the physical environment in the Gulf of Chiriquí revealed the following. Seasonal differences in surface temperatures were small but significant (P0.01), with the dry-season median (Md) of 28.9°C higher than the rainy season one of 28.0°C. At all times, surface-water temperatures were within the range considered optimal for coral growth. There were also significant (P<0.05) seasonal differences in the depths of the 25°, 20°, and 18°C isotherms. The first was shallowest (Md=18.5 m) during the rainy season due to vertical mixing, while the latter two were shallowest (Mds=31.5 and 33.0 m, respectively) during the dry season due to a generalized shoaling of the thermocline. All three isotherms are closely associated with the thermocline and showed remarkable variability in depth, most likely connected with internal waves. Salinities were reduced down to depths greater than 20 m and for distances of more than 50 km from the coast. Seasonal differences were slight (0.7% S) but statistically significant (P<0.01). Turbidity during the rainy season reduces the amount of light reaching the bottom at 10 m depth roughly by a factor of three compared to the dry season. Even the dry season amount is only about one half as much as would be expected to reach the same depth on the seaward reef of a Westen Pacific atoll. These conditions of cool water a short distance below the surface, reduced salinities, and high seasonal turbidity combine to make the region a poor one for coral-reef formation. The history of the Eastern Pacific coral fauna is traced from the Cretaceous to the Holocene. The present fauna is of Indo-Western Pacific origin, having become established following (1) the final closure of the connections between the Caribbean and Eastern Pacific (Pliocene), (2) movement of the northern Line Islands by sea-floor spreading into the path of the North Pacific Equatorial Countercurrent (Pliocene), and (3) the loss of all Eastern Pacific hermatypes during the Pleistocene.     

内蒙古乌梁素海水质时空分布特征

将地质统计学理论与地理信息系统相结合对乌梁素海富营养化指标、有机污染指标和盐化污染指标进行了kriging空间插值,结果表明：从时间角度分析,冬季总氮浓度、总磷浓度、化学需氧量质量浓度明显高于其他季节;叶绿素a质量浓度浓度冬季最低;时空电导率平均值在4.0 ms.cm-1左右波动。从空间角度分析,总氮浓度、总磷浓度、叶绿素a质量浓度呈现出由北向南递减的趋势;夏秋季化学需氧量空间分布与春冬季节相反;冬季电导率空间分布与其他季节明显不同。从浓度大小分析,乌梁素海复合污染已十分严重。