Limnology of Lake Rerewhakaaitu

The limnology of Lake Rerewhakaaitu (36°18'S, 176° 30'E) was studied at various intervals between 1971 and 1974; comparisons were made between the main lake (area 6.32 km², mean depth 7 m, maximum depth 15 m), and the smaller (0.15 km²) and deeper (mean depth 15 m, maximum 31 m) crater which are connected by a narrow, 1 m deep channel. The main lake was usually homothermal, although temporary stratification periodically occurred, and the oxygen content of the deeper water could be as low as 2 g.m^‐3. The crater showed strong thermal and chemical stratification persisting well into the winter. Its heat budget and other factors related to lake stability are compared with those of some other New Zealand lakes. The failure of the crater to become fully re‐oxygenated during its brief period of homothermy is believed to be related to its morphometry, since the amount of phytoplankton did not appear to be great enough to explain the low levels of dissolved oxygen in the hypolimnion. The hypolimnetic oxygen deficit in 1973–74 was 0.038 mg. cm^‐2.day^‐1. Qualitatively the phytoplankton, usually dominated by desmids, was characteristic of oligotrophic waters, but quantitatively the main lake could be rated as mesotrophic. Differences were also found in the abundance of zooplankton between the crater and the main lake: there were usually more Bosmina but considerably fewer Ceriodaphnia in the main lake which had greater numbers of Piona. Adult Calamoecia were generally more abundant in the crater.     

Effects of fluctuations in water level and growth of Lagarosiphon major on the aquatic vascular plants in Lake Rotoma, 1973–80

Fluctuations in water level and the growth of the introduced exotic Lagarosiphon major (Ridley) Moss have significantly influenced the submerged vegetation of Lake Rotoma over the period 1973–80. Low lake levels temporarily reduced the proportion of native vascular plants by removing available shallow‐water habitats through erosion, siltation, or desiccation. High lake levels have allowed native vascular plants to re‐establish from seed and rhizomes. Fluctuations in water level appear to have reduced the long‐term replacement of native species by L. major, which has none the less spread progressively around the lake. Water‐level fluctuations enhanced its rate of fragmentation, and thus its dispersal and establishment. The annual increase in the proportion of L. major has been primarily at the expense of the shallow‐water characean algae, but also partly by competitive displacement of native vascular plants. The southwest inlet of Lake Rotoma had an exceptionally high plant density, with up to 3518 g/m² dry weight of L. major (believed to be a world record for submerged plant biomass); this is attributed to local enrichment and protection from wave exposure.     

Tropical seagrass-associated macroalgae distributions and trends relative to water quality

Tropical coastal marine ecosystems including mangroves, seagrass beds and coral reef communities are undergoing intense degradation in response to natural and human disturbances, therefore, understanding the causes and mechanisms present challenges for scientist and managers. In order to protect our marine resources, determining the effects of nutrient loads on these coastal systems has become a key management goal. Data from monitoring programs were used to detect trends of macroalgae abundances and develop correlations with nutrient availability, as well as forecast potential responses of the communities monitored. Using eight years of data (1996–2003) from complementary but independent monitoring programs in seagrass beds and water quality of the Florida Keys National Marine Sanctuary (FKNMS), we: (1) described the distribution and abundance of macroalgae groups; (2) analyzed the status and spatiotemporal trends of macroalgae groups; and (3) explored the connection between water quality and the macroalgae distribution in the FKNMS. In the seagrass beds of the FKNMS calcareous green algae were the dominant macroalgae group followed by the red group; brown and calcareous red algae were present but in lower abundance. Spatiotemporal patterns of the macroalgae groups were analyzed with a non-linear regression model of the abundance data. For the period of record, all macroalgae groups increased in abundance (Ab_i) at most sites, with calcareous green algae increasing the most. Calcareous green algae and red algae exhibited seasonal pattern with peak abundances (Φ_i) mainly in summer for calcareous green and mainly in winter for red. Macroalgae Ab_i and long-term trend (m_i) were correlated in a distinctive way with water quality parameters. Both the Ab_i and m_i of calcareous green algae had positive correlations with NO₃⁻, NO₂⁻, total nitrogen (TN) and total organic carbon (TOC). Red algae Ab_i had a positive correlation with NO₂⁻, TN, total phosphorus and TOC, and the m_i in red algae was positively correlated with N:P. In contrast brown and calcareous red algae Ab_i had negative correlations with N:P. These results suggest that calcareous green algae and red algae are responding mainly to increases in N availability, a process that is happening in inshore sites. A combination of spatially variable factors such as local current patterns, nutrient sources, and habitat characteristics result in a complex array of the macroalgae community in the seagrass beds of the FKNMS.     

Availability of soil and sediment phosphorus to a planktonic alga

Chlorophyll production by Chlorella vulgaris Beij. var. vulgaris was used to estimate alga‐available phosphorus in clays, soils, and lake sediments suspended in water at concentrations appropriate to lake inflows during floods (100–500 g/m³). Chlorella apparently used 24–81% of 0.5M H2SO4 extractable phosphorus in clays from topsoils, about 25% from lake sediments, and 0.3–1.0% from, subsoils low in phosphorus and with high phosphorus retention.

The presence of suspended soil material did not reduce the availability to Chlorella of inorganic phosphorus added to the cultures. Increasing the Chlorella population by adding inorganic phosphorus resulted in an apparent increase in availability of phosphorus from the soil, possibly as a result of enzymic mineralisation of organic soil phosphorus. The amount of available phosphorus in lake sediments was not a reliable guide to the trophic condition, of the lake.

Suspended material from sediments, soils, and especially clay eroded from fertilised topsoils may provide phosphorus for algal growth in lakes. If allophanic clays are applied to lakes to sorb phosphorus and hence control eutrophication, the particles must settle out before planktonic algae in the photic zone can use the adsorbed phosphorus.     

Changes in the limnological features of a meromictic Lake Suigetsu during the years, 1926–1967

Changes in the limnological features of a typical meromictic lake, Lake Suigetsu, from 1926 to 1967 are summarized. Until 1934, the lake was stratified due to the balance between the flushing of fresh water and the intrusion of salt water through a canal by which the lake was connected to a coastal polyhaline lake. Total chloride content of the lake had been within the range of 100–230×10³ tons and the thermal stratification had been well developed. In 1934, another channel was constructed, by which the lake was connected to another polyhaline coastal lake. This resulted in the influx of large quantities of salt water (maximum total chloride content of the lake: 790×10³tons), and characteristics of stratification were altered. In the data after 1951, a two-layered system was re-established (total chloride content of the lake: 470–620×10³tons), and distinct stratification began to appear.     

Water quality and phytoplankton communities in Lake Pontchartrain during and after the Bonnet Carré Spillway opening,April to October 2008, in Louisiana,USA

The Bonnet Carré Spillway, located 28 miles northwest of New Orleans, was constructed in the early 1930s as part of an integrated flood-control system for the lower Mississippi River system. From 11 April to 8 May 2008, Mississippi River water was diverted through the spillway into the 629-square-mile Lake Pontchartrain, which is hydraulically connected to the Gulf of Mexico. On 8 April, prior to the opening of the spillway, water-quality instruments were deployed and recorded hourly measurements of water temperature, dissolved oxygen, specific conductance, pH, and nitrate. Discrete water-quality and phytoplankton (algae) samples were collected in Lake Pontchartrain from 8 April to 3 October 2008 to assess the water-quality nutrient enrichment effects of the diversion on the lake. The maximum influence of river water in the southern portion of the lake was captured with continuous (hourly) monitoring of nitrate concentrations, and field measurements such as of specific conductance during the critical period in late April to early May. By late May, the deployed instruments had recorded the arrival, peak, and decline of selected constituents associated with the freshwater influx from the Mississippi River/Bonnet Carré Spillway diversion. The continuous monitoring data showed the short-term interactions of high-nitrate, low-specific conductance river water and low-nitrate, high-specific conductance lake water. The phytoplankton community composition, as an indicator of water quality, illustrated an extended response from the river water evident even after the continuous and discrete samples indicated that the lake had returned to pre-diversion conditions. The initial phytoplankton community response to nutrient increases was related to accumulations of diatoms. During periods of low nutrient concentrations, accumulations of blue-greens occurred by July and August. As blue-green algae cell densities and biovolumes increased in the summer, so did the species richness of blue-green algae, particularly the harmful algae bloom taxa. Cell densities and biovolume of the phytoplankton lake indicator taxa Skeletonema costatum, Anabaena sp., and Cylindrospermopsis raciborskii were highest and dominated the diatom and blue-green algae communities during the period of most river water influence on the lake and immediately following the freshwater inflows. The dominance and recession of these indictor taxa reflect the dramatic changes that occurred in the phytoplankton community in response to an increase in nutrient-rich freshwater from the diversion into the lake, and not normal seasonal phytoplankton compositional differences. Water-quality data indicated a gradual reversion to pre-diversion lake conditions by June to July, but shifts in the phytoplankton composition were still evident through August 2008. Observations from this study were similar to results from previous studies of Mississippi River/Bonnet Carré Spillway diversion opening in 1997.     

氢和氧稳定同位素示踪湖泊蒸发的对比研究

氢氧稳定同位素被广泛用于水文循环过程的研究。本文观测了2015年太湖湖水H~2HO和H_2~(18)O组分,分析了它们的时空变化规律及其控制因子,探讨亚热带大型浅水湖泊的同位素富集机制;基于稳定同位素质量守恒法计算太湖蒸发量;评价了动力分馏学系数的传统湖泊算法与海洋算法的适用性;重点分析了H~2HO和H_2~(18)O示踪湖泊蒸发的效果,对比二者之间的差异。研究结果表明,在空间上,太湖湖水和河水的氢氧同位素在南部特别是东南部较为富集但在北部区域较为贫化,这主要是受水流方向的控制,东南部湖水经历的蒸发时间较长,因此湖水中同位素累积较多;在季节上,冬季湖水同位素较贫化、春夏季较富集。对于2015年太湖的年蒸发量,用氢同位素示踪的结果与观测值较一致,为880mm;氧同位素的示踪结果略低,为690mm。使用传统湖泊研究中对动力学分馏系数的取值,会导致蒸发被显著低估,而氧稳定同位素的示踪结果对动力学分馏系数的取值更为敏感,同时氢稳定同位素在同位素分馏过程中主要是平衡分馏效应占主导,因此H~2HO在动力学分馏系数的参数化方案中影响较小,在实际应用中更为稳定。本文的研究结果表明了稳定同位素水文学研究中使用合适的动力学分馏系数的重要性。     

油藻混合水体遥感反射比光谱分析

辐射传输模式HydroLight是研究水体辐射传输特性的有效工具,同时也是进行石油类水体辐射传输特性的有效模型。本文基于2018年8月在辽宁大连港海域实测的石油类污染水体的表观及固有光学量数据,通过设置不同浓度的配比模拟试验,利用HydroLight对油类物质和藻类物质的单一组分和两者混合水体的遥感反射比（remote sensing reflectance,R_rs）光谱进行了模拟。模拟结果表明：（1）在仅含油类物质单一组分的水体中,R_rs随着油浓度C_oil的变化分为两个特征波段：400~480 nm和480~700 nm。在400~480 nm波段范围内R_rs随C_oil的增加而减小,在480~700 nm随C_oil的增大而增大;（2）在仅含藻类物质的单一成分水体中,叶绿素的光谱特性需要其浓度C_chl达到一定值才能表现出来,在低C_chl时的R_rs光谱特性反映为纯水的光谱特性;（3）在油藻混合水体中,随C_oil的增加会增大叶绿素的R_rs,但不会明显改变叶绿素的R_rs随波长的变化趋势,这说明油藻混合水体的光谱形状主要受叶绿素的影响,油类物质的存在只改变光谱的量值。利用HydroLight对石油类污染水体的R_rs展开研究,有助于丰富水色遥感基础研究,对完善各类水体生物光学模型研究具有重要的理论意义。     

Chlorophyll-specific absorption coefficients and pigments of phytoplankton off Sanriku, northwestern North Pacific

The variety in shape and magnitude of thein vivo chlorophyll-specific absorption spectra of phytoplankton was investigated in relation to differences in pigment composition off Sanriku, northwestern North Pacific. Site-to-site variations of the absorption coefficients,a _ph ^* (λ), and pigment composition were clearly observed. At warm-streamer stations, higher values ofa _ph ^* (440) anda _ph ^* (650) were found with relatively high concentrations of chlorophyllb (a green algae marker). At stations located in the Oyashio water (cold streamer),a _ph ^* (440) values were lower and fucoxanthin (a diatom marker) concentrations were higher, compared to the other stations. The peak in the absorption spectra at the Oyashio stations was shifted toward shorter wavelengths, which was probably due to the presence of phaeopigments. In a Kuroshio warm-core ring, the magnitude ofa _ph ^* (440) was in between those at the warm-streamer and Oyashio stations, and the diagnostic pigment was peridinin (a dinoflagellate marker). These findings indicated that major differences in phytoplankton absorption spectra of each water mass were a result of differences in the phytoplankton pigment composition of each water mass, which was probably related to the phytoplankton community.     

Faroe Bank Channel overflow 1995–2005

The Faroe Bank Channel (FBC) is the deepest passage across the Greenland–Scotland Ridge and there is continuous overflow of dense water through the channel, which provides a substantial contribution to the global thermohaline circulation. Since November 1995, Acoustic Doppler Current Profilers (ADCPs) have been moored at the sill of the channel continuously, except for short annual servicing periods. In addition to this, CTD sections have regularly been occupied across the channel and instruments, recording temperature and salinity, have been moored for short periods. These observations demonstrate that the channel, due to its small width, can be monitored fairly well with only one ADCP mooring and they allow the generation of a time-series of overflow volume flux for the 1995–2005 period. The kinematic overflow flux, defined solely from the velocity field, was found to have an average value of 2.1 ± 0.2 Sv with a seasonal and with inter-annual variations of approximately 10% amplitude, but with no discernible trend for the whole period. The average flux of water with potential density exceeding 27.8 kg m⁻³ was found to be 1.9 ± 0.3 Sv with average properties: θ = 0.25 °C, S = 34.93, γ_θ = 28.01 kg m⁻³ for this period. No evidence was found for a weakening overflow flux, but the salinity of the FBC-overflow, especially the warmer parts, has increased substantially during the period, which implies an increased average density on the order of 0.01 kg m⁻³. Previous observations of a helical cross-channel circulation are confirmed and may explain the thin pycnocline layer, but shear-instability induces intensive mixing that puts a lower limit on the layer thickness. Critical control at one point of the sill cross-section, rather than friction, seems to govern the overflow dynamics and simple layered models can explain much of the observed features as well as the seasonal variation, but potential vorticity, as defined for a single overflow layer, is not conserved. A previously suggested 1950–2000 weakening of the FBC-overflow, which was partly based on a subset of the data presented here, is not supported by the full dataset.     

Nitrogenase activity and estimates of nitrogen fixation by freshwater benthic blue‐green algae

The sandy substrate of Lake Taharoa (west coast, North Island, New Zealand ‐ 35°50'S, 173°41'E) is covered by communities of filamentous algae that extend from the exposed beach down to 21 m depth. The algae bind the sand to form crusts and mats which may break off as discrete plates. The dominant species are the blue‐greens Microcoleus, Nostoc, Phormidium, Lyngbya, Oscillatoria, Scytonema, Stigonema, Shizothrix, Calothrix, Dichothrix, Tolypothrix, and Anabaena, with occasional high concentrations of the desmid Cylindrocystis. Nitrogenase activity, measured by acetylene reduction, showed a wide range of rates (4–150 μmol C₂H₄ m^‐2h^‐1). Estimates of annual rates of nitrogen fixation by the Taharoa communities are comparable with those for periphytic blue‐green algae‐dominated systems reported elsewhere.     

Limnology of Lake Waikaremoana with special reference to littoral and pelagic primary producers

Lake Waikaremoana, the North Island's deepest lake (248 m), lies in a natural forested catchment, but the lake itself has been modified for hydro‐electric power generation and by the introduction of trout, smelt, and adventive aquatic plants. The lake is a warm monomictic water body of low conductivity (82 μS cm^‐1) and a high seasonal water column stability. The waters are oligotrophic, with epilimnetic dissolved reactive phosphorus concentrations typically < 1 mg m^‐3. The concentration of NO₃‐N is seasonally variable but generally high in winter and spring with maximum epilimnetic values approaching 70 mg m ³. This contrasts with other central North Island lakes. Horizontal variability in surface chlorophyll a is low as are the absolute values (< 1–2 mg m^‐3). A notable feature is the formation of a deep chlorophyll maximum within the metalim‐nion comprised largely of Sphaewcystis schweteri as opposed to diatoms and flagellates which normally dominate the epilimnion. Vascular macro‐phytes (maximum biomass 659 g m² dry weight) extended to 9 m and characeans (maximum biomass 447 g m²dry weight) to 16 m. Total phyto‐plankton primary production was calculated as 4524 tCy^‐1 and macrophyte production as 578 t C y^‐1. The proportion of macrophyte to phy‐toplankton production (0.14) is higher than in the other deep lakes of the central North Island.     

Limnology of Lake Rotokawa and its outlet stream

Abstract

The water chemistry, flora, and fauna of Lake Rotokawa (38° 37.8’ S, 176° 11.2'E) was studied in 1975–76. The mean pH is 2.1 and thermal inflows may elevate the mean summer temperature of the surface waters 4.2°c above that of nearby cold water Lake Rotongaio (18.9°c). The temperature range of surface water was from 10.1 °c in winter to 23.1°c in summer. The major anions were SO₄ ^2? 679 g.m^?3, and Cl‐ 314 g.m^?3. Mean concentrations of major cations were Na⁺ 224 g.m^?3, K⁺ 28.9 g.m^?3, Ca²⁺ 13.3 g.m^?3, and Mg²⁺ 2.6 g.m^?3.

Two species of flagellate algae were recorded, of which Euglena anabaena was predominant. Only two benthic macroinvertebrates were found, larvae of Chironomus zealandicus, mean density 253 per square metre, and Helobdella sp., 1.3 per square metre.

The Parariki Stream was influenced by thermal springs in its upper and lower reaches, being cooler (24–25°c) about halfway along its length than near its source (27.8–39.0°c) or confluence (26.5°‐28.0°c) with the Waikato River. In the cooler stretch of the stream where unidentified benthic algae were not limited by high temperature, chlorophyll and total pigment increased from 3.9 to 377.9 mg.m^?3 and from 17.5 to 534.4 mg.m^?3 respectively, and nutrient levels fell (NO₃‐N, 22–10.5 mg.m^?3; NH₄‐N, 6440–230 mg.m^?3; and PO₄‐P, 51–19 mg.m^?3).     

Submerged vegetation of the Rotorua and Waikato lakes

Five plant communities in Lake Rotoiti, North Island, New Zealand (38° 02’ S, 176° 24’ E) are described. In shallow water (0–2 m depth) partly protected from the prevailing westerly winds, some indigenous species form characteristic mounds. From 2 to 6 m depth the exotic macrophyte Lagarosiphon major (Ridley) Moss is the dominant and forms dense beds which appear to have completely replaced any native vegetation. Elodea canadensis Michx., a longer‐established exotic, may form a minor component of this zone, but may become the dominant species in water above and below the Lagarosiphon zone. Lagarosiphon appears to be primarily restricted to silty sand, but on pure silt areas it is replaced by Elodea and/or Nitella hookeri A. Braun. These zonations are probably static rather than successional. On underwater cliff faces and boulder shores a seasonal succession of algae was the major vegetation. Only filamentous cyanophytes grew within 1–2m of geothermal springs in the lake.     

Transverse mixing and surface heat exchange in the Waikato River: A comparison of two models

Abstract

Two mathematical models of different complexity were used to study transverse dispersion and surface heat transfer in the lower Waikato River. A simple analytical streamtube model (HPLUME) gave adequate temperature predictions in a reach where the channel was fairly regular but performed poorly where there were extensive shallows. In the latter reach, a two‐dimensional numerical model (SYSTEM21) gave good temperature and flow predictions once properly calibrated. Model calibration proved to be difficult in the Waikato River because the natural river temperature varied significantly along the channel. A search method was developed to estimate both the transverse dispersion and surface heat exchange coefficients from measured plume temperature profiles based on the observation that transverse variations in natural temperature were small. This method was used to calibrate SYSTEM21 in two separate reaches. Coefficient estimates were sensitive to measurement errors and slight departures in homogeneity of natural temperature and it would be desirable to corroborate the estimates of E_z using dye tests. In the upper reach, the average transverse dispersion coefficient was E_z/hu? = 1 which is high but within the range of published values. A sharp bend and buoyant spreading contributed to the high E_z value. E_z increased with river flow because both h and u? increase with flow. In the lower reach, E_z/hu? = 0.1 which is lower than expected but islands may have affected the model calibration. The surface heat exchange coefficient averaged K = 84–167 W m^?2 s^?1 °C^?1 which falls within the range of published values. No significant relationship could be found between surface heat exchange coefficient and meteorological variables.     

Chemistry of sediments in relation to trophic condition of eight Rotorua Lakes

Abstract

Chemical parameters (pH, Eh, carbon, Kjeldahl nitrogen, total phosphorus, 0.5M H₂SO₄‐extractable phosphorus, organic phosphorus, and water‐soluble phosphorus) were measured in the surface layers of sediments collected from various depths in Lakes Rotowhero, Okaro, Ngapouri, Rotokakahi, Okareka, Tikitapu, Okataina, and. Rotoma during October 1972. The sediments of the productive geothermal lake, Rotowhero, were markedly different from those of the cold‐water lakes: they had relatively low pH values, high carbon (mean 8.5%) and organic phosphorus (mean 4160 μg.g^?1) concentrations, and very high total phosphorus concentrations (mean 4770 μg.g^?1), probably as a result of enrichment by hot springs.

The mean concentrations in the sediments of the cold‐water lakes were carbon 3.2–7.9%, Kjeldahl nitrogen 3380–8310 μg.g^?1 and phosphorus 690–1780 μg.g^?1. These concentrations are within the ranges for New Zealand terrestrial topsoils, but the lake sediments appear enriched in phosphorus relative to local topsoils. Total carbon, nitrogen, and phosphorus concentrations of sediments tended to be highest in the eutrophic lakes (Okaro, Ngapouri) although the deep oligotrophic lakes (Okataina, Rotoma) had relatively high total phosphorus concentrations (means 1400, 1510 μg.g^?1). Overall, the carbon, nitrogen, and phosphorus concentrations of the sediments showed little relationship to the trophic state of the lake.

Organic phosphorus concentrations of the surface layers of sediments were similar in all the cold‐water lakes (mean 319 μg.g^?1). The proportion of the total phosphorus apparently ‘fixed’ in mineral material was minimal (0–1%) in sediments from the eutrophic and mesotrophic lakes, but in the oligotrophic lakes was similar to that in New Zealand topsoils (9–14%). Reducing conditions may cause solution of a high proportion of the ‘fixed’ phosphorus in the eutrophic lakes.

The water‐soluble phosphorus concentrations in the sediments of the five shallow cold‐water lakes (Okaro, Ngapouri, Rotokakahi, Okareka, Tikitapu) correlated positively with trophic state and with concentrations of dissolved phosphorus in the lake waters.

Carbon, nitrogen, and phosphorus concentrations in the sediments tended to vary with overlying water depth. This should be considered when comparisons are made between lakes.     

Terrestrial discharge influences microbioerosion and microbioeroder community structure in coral reefs

Microbioerosion rates and microbioeroder community structure were studied in four Kenyan protected coral-reef lagoons using shell fragments of Tridacna giant clams to determine their response to the influence of terrestrial run-off. Fourteen different microbioeroder traces from seven cyanobacteria, three green algae and four fungi species were identified. The river discharge-impacted reef and ‘pristine’ reef showed similar composition but higher microbioeroder abundance and total cyanobacteria- and chlorophyte-bioeroded areas when compared with the other study reefs. Cyanobacteria dominated during the north-east monsoon (NEM) relative to the south-east monsoon (SEM) season, with algae and cyanobacteria being major microbioeroders in the river-impacted and pristine reefs. The rate of microbioerosion varied between 4.3 g CaCO3 m^?2 y^?1 (SEM) and 134.7 g CaCO₃ m^?2 y^?1 (NEM), and was highest in the river-impacted reef (127.6 g CaCO₃ m^?2 y^?1), which was almost double that in the pristine reef (69.5 g CaCO₃ m^?2 y^?1) and the mangrove-fringed reef (56.2 g CaCO₃ m^?2 y^?1). The microbioerosion rates measured in this study may not be high enough to cause concern with regard to the health and net carbonate production of Kenya’s coral reefs. Nevertheless, predicted increases in the frequency and severity of stresses related to global climate change (e.g. increased sea surface temperature, acidification), as well as interactions with local disturbances and their influence on bioerosion, may be increasingly important in the future.     

Photochemical production of molecular hydrogen in lake water and coastal seawater

Samples of lake water and coastal seawater from Nova Scotia, Canada, were irradiated with natural or artificial sunlight to investigate the potential for photochemical hydrogen production. Hydrogen photo-production was observed in all natural water samples. Rates of hydrogen formation were highest in coloured lake water (range: 98–163 pmol L^− 1h^− 1) and lower in seawater (range: 19–45 pmol L^− 1 h ^− 1). Dilutions of the most highly coloured lake sample (Kejimkujik Lake) showed a positive linear relationship between H₂ production rates and CDOM concentration. Photo-production rates normalised to UV absorption coefficients at 350 nm indicated that the photochemical efficiency of hydrogen formation varied between samples, perhaps due to differences in the CDOM composition. Photochemical hydrogen formation was also seen in solutions of syringic acid and acetaldehyde: two low-molecular-weight carbonyl compounds found in natural waters. Photochemistry may therefore offer least a partial explanation for the persistently high levels of hydrogen observed in the low-latitude surface ocean.     

极大螺旋藻富积重金属机理的研究

于1993年5月由南京大学藻类培养室提供极大螺旋藻藻种,用Zarrouk培养基培养后,用活藻体和甲醛杀死的藻体分别进行吸附实验;过滤出的藻体置于6×10－3g／L左右浓度的Co2+,Ni2+,Cu2+,Zn2+离子混合液中。结果显示,死、活藻体都具有相似的吸附能力,对Co2+,Ni2+,Zn2+的富积大于203倍,对Cu2+的富积大于185倍;用热水提取、DEAE-纤维素D-23柱和SephadexG－200柱纯化后,获得了纯细胞外壁多糖,其分子量为52kD。将该糖溶液盛在透析袋内,并置于4种离子混合液中进行吸附实验,结果显示,核糖对Co2+,Ni2+,Cu2+,Zn2+的富积倍数分别达1744,1644,1340,1750。藻体和多糖对Co2+,Ni2+,Zn2+的吸附都高于对Cu2+的吸附。比较藻体与多糖对4种离子的吸附结果可见,藻体对离子的吸附主要是多糖的作用;多糖的红外光谱显示,金属离子改变OH和CO－NH的吸收峰,表明这两种基团与金属离子发生了络合作用;对Cu2+的络合滴定测定表明,Cu2+与多糖的结合度为0．40。     

The vertical attenuation of light in Charlotte Harbor, a shallow, subtropical estuary, south-western Florida

The relative contribution of different components to the attenuation of photosynthetically active radiation was determined in the Charlotte Harbor estuarine system based on laboratory and in situ measurements. Agreement between laboratory and in situ measurements of the attenuation coefficient (k_t) was good (r² = 0·92). For all in situ measurements (n = 100), suspended, non-chlorophyll matter accounted for an average of 72% of k_t, dissolved matter accounted for 21%, suspended chlorophyll for 4%, and water for the remaining 3%.For individual determinations, suspended non-chlorophyll matter, dissolved matter, suspended chlorophyll, and water, each accounted for as much as 99%, 79%, 21%, and 18% of k_t. Attenuation by suspended matter was greatest near the mouth of the northern tidal rivers and was variable over the rest of the estuarine system. Attenuation by dissolved matter was greatest in the brackish tidal rivers and decreased with increasing salinity. Attenuation due to dissolved matter was positively correlated with water color. The source of the color was basin runoff. Wavelength transmittance changed along the salinity gradient. Maximum transmittance shifted from 500 to 600 nm in gulf waters to 650 to 700 nm in colored, brackish waters. Dissolved matter was primarily responsible for the large attenuation at short wavelengths (400–500 nm).