The Effect of Artificial Destratification on Phytoplankton in a Reservoir

The effects of artificial destratification on limnological conditions and on phytoplankton were surveyed for 6 years (1995-2000) in Lake Dalbang (South Korea), a water supply reservoir receiving nutrients from agricultural non-point sources. In order to reduce odor problems caused by cyanobacterial blooms, six aerators were installed in 1996 and operated regularly during the warm season. Aeration destratified the water column of the reservoir and produced homogeneous physical and chemical parameters. The maximum surface temperature in summer decreased from 28.9 °C before aeration to 20.0-26.4 °C after aeration, whereas the maximum hypolimnetic temperature increased from 8.0 to 17.0-23.7 °C. Despite these changes, surface water concentrations of total phosphorus (TP) and chlorophyll a(CHLA) and their seasonal patterns did not change with destratification. Phosphorus loading was concentrated in heavy rain events during the summer monsoon, and TP and CHLA reached maximal concentrations in late summer after the monsoon. Because the hypolimnion was never anoxic prior to aeration, internal loading did not seem to be substantial. Cyanobacteria were the dominant phytoplankton in summer before aeration, but diatoms replaced them after operation of the aerator. Cyanobacteria blooms were eliminated. In contrast, total algal biomass in the water column (as CHLA integrated over depth) increased from 190 mg m^–2 in 1995 to 1150, 300, 170, and 355 mg m^–2 in 1997, 1998, 1999, and 2000, respectively. The increased ratio of mixing depth to euphotic depth to 2.5 may have resulted in a net reduction in the amount of underwater irradiance experienced by phytoplankton cells, and this may have favored the switch to diatom dominance. Furthermore, the mixing may have allowed diatoms to flourish in summer by lowering their settling loss that would be critical in stratified water columns. In conclusion, the destratification in this reservoir was effective in preventing cyanobacteria blooms, but not in reducing the total algal standing crop.     

Effects of phosphorus and nitrogen enrichment on the phytoplankton in a tropical reservoir (Lobo Reservoir,Brazil)

The effects of enrichment with phosphate (0–500 µg. 1^–1) and forms of nitrogen (nitrate, nitrite, ammonia an and urea) (0–3500 µgg. ^–1) on the phytoplankton growth of Lobo Reservoir (Brazil) were studied in July, 1979. Suspended matter, chlorophyll a, cell concentrations and the carotenoid:cchlorophyll ratio were estimated following 14 days of in situ incubation. Phosphate alone caused no significant effects, but enrichment with nitrogen caused a substantial increase on the growth of phytoplankton. Comparison between the different forms of nitrogen showed insignificant effects after their additions with 350 µg. ^–1 and in combination with phosphate. However, when nitrogen was added in large quantities (3 500 µg. ^–1), significant differences between the nitrogeneous forms were found, with urea causing the strongest effect. In July, nitrogen is mhe main limiting nutrient to phytoplankton growth of Lobo Reservoir.Supported by CNPq and FAPESP.     

Short term spatial and temporal variation of phytoplankton in a shallow tropical oligotrophic reservoir,southeast Brazil

Locally called IAG pond, system is a small, oligotrophic, shallow, urban reservoir located in the Parque Estadual das Fontes do Ipiranga Biological Reserve, south of São Paulo municipality, southeastern Brazil. Study was carried out in two phases to cover the two climatic periods (dry and rainy) that characterize the area. Daily samples were collected on seven consecutive days (dry = 20–26 August 1996; rainy = 22–28 January 1997), three times a day (07:00 h, 13:00 h, and 19:00 h), following the water column vertical profile at reservoir’s deepest site (Z _max = 4.7 m). The phytoplankton’s community structure’s diurnal variation was compared with environmental variables (thermal structure of the water column, pH, CO₂, dissolved oxygen, total phosphorus, and NH₄). Analysis of variance (ANOVA) showed significant variation among sampling hours and days but not among depths for most species, thus revealing a tendency towards a homogeneous vertical distribution of phytoplankton in the reservoir. Canonical Correspondence Analysis (CCA) showed a significant relationship between distribution of phytoplankton species and environmental variables used for ordination. Water temperature was the environmental variable that best explained distribution of sample units. Atelomixis was the only possible explanation for how a non-motile alga as, for example, the chlorococcal Oocystis lacustris Chodat and the diatom Cyclotella stelligera Cleve &; Grunow, can be so widespread and abundant in the IAG pond during the stratified period.     

The phosphorus status of sediments in a hypertrophic impoundment (Hartbeespoort Dam): implications for eutrophication management

The phosphorus status and distribution of sediments in a hypertrophic water supply reservoir (Hartbeespoort Dam) were investigated, with a view to assessing the role of sediments in counteracting the effects of reduced external phosphorus loading as a restoration measure. In comparison with similar water bodies in South Africa, the sediments in Hartbeespoort Dam contained high levels of both total and potentially mobile phosphorus. The potentially mobile fraction constituted about 60% of the total phosphorus content of the sediments, compared with about 11% in other reservoirs. The excessive eutrophication of Hartbeespoort Dam is clearly reflected in the phosphorus status of the sediments. Sediment distribution in the impoundment was found to be extremely heterogeneous, due to the combined influences of morphometry, hydrology and an imbalance in the nutrient loads entering via rivers at remote points in the water body. It is concluded that sufficient mobile phosphorus has accumulated in the sediments to prolong the response time of the impoundment to phosphorus load reductions. Since phosphorus release from sediments is dependent on dynamic processes not addressed in this study, the extent of the delays in trophic response to load reduction cannot be estimated.     

The Effect of Atmospheric Carbon Dioxide Elevation on Plant Growth in Freshwater Ecosystems

We developed a dynamic model to investigate the effect of atmospheric carbon dioxide (CO₂) increase on plant growth in freshwater ecosystems. Steady-state simulations were performed to analyze the response of phytoplankton and submerged macrophytes to atmospheric CO₂ elevation from 350 to 700 ppm. We studied various conditions that may affect this response, such as alkalinity, the air–water exchange rate of CO₂, the community respiration rate, and the phosphorus (P) supply rate. The increase in atmospheric CO₂ could affect submerged plant growth only under relatively eutrophic conditions and at a low community respiration rate. Alkalinity had little effect on the response of the different species. When the air–water exchange was low, the proportional effect of the CO₂ increase on plant growth was higher. Under eutrophic conditions, algae and macrophytes using CO₂ and HCO₃^– may double their growth rate due to atmospheric CO₂ elevation, while the growth of macrophytes restricted to CO₂ assimilation may be threefold. The differences in response of the species under various conditions indicate that the elevation of atmospheric CO₂ may induce drastic changes in the productivity and species dominance in freshwater systems.     

The Effect of Zostera noltii, Spartina maritima and Scirpus maritimus on Sediment Pore-water Profiles in a Temperate Intertidal Estuary

The objective of the present work was to study the effect of plants common in temperate latitudes (Zostera noltii, Spartina maritima and Scirpus maritimus) on sediment nutrient profiles, and to compare it to sand- and mud-flats without vegetation. The study focused on the organic matter contents, the concentration of dissolved inorganic nutrients (PO₄–P, NH₃–N, NO₃–N), an on the estimation of the total amount of these nutrients during day and night conditions and their potential net-fluxes. It was also hypothesised that in an estuarine system, different plants may have specific effects, and consequently different contributions to the system nutrient dynamics as a whole. Sediment profiles of loss on ignition (LOI) showed an increase of the organic matter contents from sand-flat, to Zostera, Spartina, mud-flat and Scirpus. Statistically, there were significant differences between sediment profiles of phosphate, ammonia and nitrate (Mann-Whitney test, p<0.05), during day and night periods. These results suggest that there is an intense mobility of nutrients in the sediment, showing a day-night variation of nutrient concentrations in the pore-water. In the plants’ rhizosphere, the day-night variation of nutrients seemed dependent on plant biomass and penetration of the roots. Additionally, coupling between plant and sediment seems to be a species-specific process. In spring, Scirpus salt marsh reaches the maximum density and biomass, and despite the higher organic matter contents in the plant covered sediment, Scirpus acts as a sink of nutrients. In contrast, the top 10 cm of the sediment in the Spartina salt marsh and in the Zostera beds may contribute to the efflux of nutrients during the night period, especially phosphate.     

The relationship between Chironomus plumosus burrows and the spatial distribution of pore-water phosphate, iron and ammonium in lake sediments

1. To study the influence of chironomids on the distribution of pore‐water concentrations of phosphate, iron and ammonium, we conducted a laboratory experiment using mesocosms equipped with two‐dimensional pore‐water samplers, filled with lake sediment and populated with different densities of Chironomus plumosus. 2. Specially designed mesocosms were used in the study. A 6‐mm deep space between the front plate and the pore‐water sampler at the back plate was just thick enough to allow the chironomids to live undisturbed, yet thin enough to force all the burrows into a two‐dimensional plane. 3. The courses of the burrows were observed during the experiment as oxidised zones surrounding them, as well as being identified with an X‐ray image taken at the end of the experiment. 4. We investigated the relationship between C. plumosus burrows and spatial patterns of pore‐water composition. Concentrations of the three ions were significantly less around ventilated burrows (54% to 24%), as bioirrigation caused a convective exchange of pore‐water enriched with dissolved species compared with the overlying water, and also because oxygen imported into the sediment resulting in nitrification of ammonium, oxidation of iron(II) and a co‐precipitation of phosphate with Fe(III) oxyhydroxides. 5. In mesocosms with chironomids, new (redox) interfaces occurred with diffusive pore‐water gradients perpendicular to the course of burrows and the site of major phosphate, ammonium and iron(II) release shifted from the sediment surface to the burrow walls.     

Influence of Water Hyacinth Cover on the Physico-chemical Characteristics of Water and Phytoplankton Composition in a Reservoir near Jaipur (India)

Water hyacinth (Eichhornia crassipes (Mart.) Solms.) invaded a eutrophic reservoir receiving domestic sewage near Jaipur (India) during 1975 and gradually developed a complete thick cover over the whole water body during Sept.–Oct. 1978. The physico-chemical characteristics of the water and the phytoplankton composition were studied during Sept. 1977–Sept. 1979 by fortnightly sampling. The changes observed during the second year of study are ascribed to the water hyacinth cover. The important changes were: lowering of water temperature, pH, dissolved oxygen content and nitrate nitrogen, and increase in total alkalinity, free carbon dioxide, chemical oxygen demand, ammonia nitrogen, sulphides, calcium, magnesium and phosphate phosphorus. The changes in the phytoplankton were both qualitative and quantitative. The green algae, particularly the species of Ankistrodesmus, Chlorella, Crucigenia and Selenastrum, increased considerably and replaced the blue-green algae, of which Oscillatoria and Microcystis disappeared totally. The densities of several other taxa changed significantly.     

The origin and recycling of sedimented biogenic debris in a subalphine eutrophic lake (Lake Bled, Slovenia)

The areal distribution of organic C contents, ¹³C values, total N and P and biogenic Si contents in surficial sediments were used to study the distribution, origin and diagenetic transformations of sedimented biogenic debris in the eutrophic subalpine Lake Bled (Slovenia), which for most of the yearhas an anoxic hypolimnion. The influence of an allochthonous input, restricted to the western basin, was clearly traced by higher organic C and total N and P contents, higher ¹³C values, and higher sedimentation rate in comparison to the eastern basin. The low ¹³C values of sedimentary organic matter in the major part of the lake, lower than the ¹³C values of different types of organic matter, suggest that this sedimentary organic matter is most probably the product of a microbial community and not a residue of primary production.The temporal variation of benthic diffusive fluxes of NH₄, Si and PO₄, derived from modelling the pore water profiles, was related to sedimentation of phytoplanktonic blooms, while the PO₄ fluxes were also dependent on changing redox conditions at the sediment-water interface in the period of the winter-spring overtum. The removal of PO₄ in pore waters is probably due to the adsorption of phosphate and precipitation of apatite and vivianite. The budget of C, N and P at the sediment-water interface revealed a high recycling efficiency (>70%), also confirmed by the rather uniform (or only slightly decreasing) vertical profiles of organic C, total N and P in sediment cores and C/N and C/P ratios. The percentage of biogenic Si recycling is low (<10%), suggesting its removal in sediments.     

The Effect of Phosphorus Availability on Decomposition Dynamics in a Seasonal Lowland Amazonian Forest

Once the weathering of parent material ceases to supply significant inputs of phosphorus (P), vegetation depends largely on the decomposition of litter and soil organic matter and the associated mineralization of organic P forms to provide an adequate supply of this essential nutrient. At the same time, the decomposition of litter is often characterized by the immobilization of nutrients, suggesting that nutrient availability is a limiting factor for this process. Immobilization temporally decouples nutrient mineralization from decomposition and may play an important role in nutrient retention in low-nutrient ecosystems. In this study, we used a common substrate to study the effects of native soil P availability as well as artificially elevated P availability on litter decomposition rates in a lowland Amazonian rain forest on highly weathered soils. Although both available and total soil P pools varied almost three fold across treatments, there was no significant difference in decomposition rates among treatments. Decomposition was rapid in all treatments, with approximately 50% of the mass lost over the 11-month study period. Carbon (C) and nitrogen (N) remaining and C:N ratios were the most effective predictors of amount of mass remaining at each time point in all treatments. Fertilized treatments showed significant amounts of P immobilization (P < 0.001). By the final collection point, the remaining litter contained a quantity equivalent to two-thirds of the initial P and N, even though only half of the original mass remained. In these soils, immobilization of nutrients in the microbial biomass, late in the decomposition process, effectively prevents the loss of essential nutrients through leaching or occlusion in the mineral soil.     

Interactions of Physical,Chemical and Biological Processes in Depth and Time within a Productive English Lake during Summer Stratification

A survey is given of physical, chemical and biological events in the water-mass of a productive lake (Esthwaite Water, N. England) during summer stratification. They are interrelated in terms of i) responses to meteorological changes (ii) susceptibility to density stratification (iii) participation in acid-base and redox systems, with interactions of these (iv) modification due to the generation of particulate material from soluble precursors (v) limiting factors in such bio-generation (vi) mechanisms of internal nutrient loading, and (vii) control by the characteristics of individual plankters. The significance is demonstrated of differential inputs of meteorological variables, and especially of biological production and degradation, for determining the overall structure and metabolism of the lake.     

The effects of disturbance events on phytoplankton community structure in a small temperate reservoir

1 The effects of disturbances, in the form of storm events, on phytoplankton community structure were examined over the course of four years in Eau Galle Reservoir, Wisconsin, USA.
2 Disturbances consistently brought about significant, but highly transient, increases in apparent phytoplankton species richness. It is likely that these resulted from temporary increases in the biomass of previously undetected rare species.
3 Substantial shifts in community dominance were confined to large, early season events, and were seldom long-lived. Later 'climax' communities were highly resistant to any changes in dominance, even when increases in species richness occurred.
4 Regardless of when they occurred, disturbances tended to favour species from a narrow range of the successional sequence.     

Use of Two Industrial Wastes as Soil Amendments: Effect on Dissolved Reactive Phosphorus in Runoff

To control the dissolved reactive phosphorus (DRP) concentration in a soil solution, a number of soil amendments were tested. In the current study, Blast Furnace Slag (BFS) and Water Treatment Residues (WTR) were tested on bare soil under two rainfall intensities and two soil roughness levels. The soil was fertilized with P (KH₂PO₄) at a rate of 400 kg ha^?1 while BFS and WTR were applied at a rate of 5 g per 100 g of soil. Two soil roughness levels were exposed to artificial rainfall intensities of 30 and 65 mm h^?1. Three rainfall events were performed on each treatment. The runoff water generated over an area of 0.5 m² with a slope of 8% was collected at different time intervals and analyzed for DRP, Al, Fe, and K concentrations. The results showed that, regardless of rainfall intensity and soil roughness, the concentration of DRP in the runoff water increased with increasing runoff time from the unamended plots. However, in the BFS- and WTR-amended soils, the DRP concentration decreased with runoff time. Dissolved reactive P and DRP loads were the lowest from the WTR-amended plots, followed by the control and the BFS treatment plots. Water treatment residues reduced the mean DRP concentration by 27.3% and the DRP load by 32% compared to unamended plots. The two rainfall intensities significantly affected the DRP concentration and load. Under the low rainfall intensity, the DRP concentration and load were higher compared to the high rainfall intensity. The overall DRP concentration was not affected by changes in soil roughness. However, the DRP loads were higher from the plots with low soil roughness levels, especially during the first and second runs. Both the BFS and WTR were also effective in reducing the DRP concentrations in the drain water collected during the runoff events. The concentrations of Al, Fe, and K in the runoff water were not affected by the soil amendments. However, the electrical conductivity and pH readings were higher from the BFS-amended plots.     

The influence of the North Atlantic Oscillation on the physical, chemical and biological characteristics of four lakes in the English Lake District

1. Thirty‐six years of winter meteorological and limnological measurements from four lakes in the English Lake District are analysed and related to variations in the North Atlantic Oscillation (NAO). Winter weather conditions were strongly influenced by the NAO with mild, wet winters being associated with strongly positive values of the NAO index (NAOI). 2. Lake surface and bottom temperatures were strongly positively correlated with the NAOI, with the highest correlations being recorded in the shallower lakes. 3. Variations in the NAOI also had a significant effect on the winter concentration of nitrate. In all the lakes, there was a significant negative correlation between the NAOI and the detrended winter concentration of nitrate. The key driving variable was the local air temperature, which appeared to limit the quantity of nitrate reaching the lake by increasing the amount assimilated in the surrounding catchment in mild winters. 4. Dissolved reactive phosphorus (DRP) concentrations were not significantly correlated with the NAOI in the two larger basins but significant positive correlations were recorded in the two smaller lakes. The key driving variable was the local rainfall with higher DRP concentrations being recorded after heavy rain in the lakes with a short retention time. 5. The NAOI‐related changes in rainfall also influenced the phytoplankton. In wet winters the concentration of chlorophyll in the two smaller lakes with the shortest retention time was lower and the spring growth of Asterionella formosa was delayed in the smallest lake. 6. These differential responses demonstrate how the large‐scale effects associated with the NAO can be ‘filtered’ by the physical characteristics of a particular site.     

Phosphorus and Nitrogen Budgets of Barton Broad and Predicted Effects of a Reduction in Nutrient Loading on Phytoplankton Biomass in Barton,Sutton and Stalham Broads,Norfolk, United Kingdom

Barton, Sutton and Stalham Broads are shallow, man-made lakes formed in mediaeval times when peat excavations were flooded. Recently, a once diverse submerged macrophyte flora has, in most broads, been replaced by large phytoplankton populations. This change has been attributed to increased nutrient loadings. The seasonal cycles of chlorophyll α, nitrogen and phosphorus in the three broads are described and the inputs of nitrogen and phosphorus to Barton Broad are budgeted. A reduction in the phosphorus loading is recommended as the best method of restricting phytoplankton populations in these broads. An equation relating phosphorus loading, flushing rate, mean depth and retention coefficient to mean standing phosphorus concentration is used to predict the reduction in phosphorus loading required to limit phytoplankton populations and permit the re-establishment of submerged macrophytes.     

The effects of water‐level manipulation on the benthic invertebrates of a managed reservoir

1. Reservoir creation and management can enhance many ecological services provided by freshwater ecosystems, but may alter the natural conditions to which aquatic biota have adapted. Benthic macroinvertebrates often reflect environmental conditions, and this community may be particularly susceptible to water‐level changes that alter sediment exposure, temperature regime, wave‐induced sediment redistribution and basal productivity. 2. Using a before–after control–impact experimental design, we assessed changes in macroinvertebrate community structure corresponding with changes in water‐level management in two lentic systems in the Voyageurs National Park, Minnesota, U.S.A. Littoral zone (depths 1–5 m) benthic macroinvertebrate assemblages were sampled in Rainy Lake (control system) and Namakan Reservoir (impact system) in 1984–85, and again in 2004–05 following a change in water‐level management that began in January 2000. The new regime reduced the magnitude of winter drawdown in Namakan Reservoir from 2.5 to 1.5 m, and allowed the reservoir to fill to capacity in late May, a month earlier than under the prior regime. Rainy Lake water levels were not altered substantially. 3. We found changes in macroinvertebrate community structure in Namakan Reservoir relative to Rainy Lake at 1–2 m depths but not at 3–5 m depths. These shallower depths would have been most directly affected by changes in sediment exposure and ice formation. 4. In 2004–05, Namakan Reservoir benthos showed lower overall abundance, more large‐bodied taxa and an increase in non‐insect invertebrates relative to 1984–85, without corresponding changes in Rainy Lake. 5. Changes in the benthic community in Namakan may reflect cooler water in spring and early summer as well as lower resource availability (both autochthonous production and allochthonous inputs) under the new regime.     

Recent sedimentation in a freshwater reservoir in SW-Finland: The diatomological and chemical evidence of sediments on the development of the water body

A freshwater reservoir was dammed from the Baltic Sea in 1965. The recent sediments and the processes of accumulation in the reservoir have been investigated. The physical, chemical and diatom analyses of the sediments were carried out at 5 sampling points in order to dinstinquish the freshwater sediments from the underlying brackish sediments as well as to date the freshwater sediments. The pattern of sedimentation in the reservoir is described on the basis of these results and conclusions are drawn regarding the development of the water body. In interpretating the diatomological and the chemical results from the recent sediments certain common features are highlighted.     

旱地小麦深施磷肥对土壤水分及植株氮素吸收、利用的影响

为探明磷肥在旱地小麦生产上的作用,寻求旱地小麦最佳施磷方式,在山西省闻喜县进行了低磷(75kg·hm~(-2))、中磷(112.5 kg·hm~(-2))、高磷(150 kg·hm~(-2))3个施磷量条件下20 cm、40 cm 2个深度施磷的田间试验,研究其对旱地麦田土壤水分及植株氮素吸收、利用的影响。结果表明:增加施磷量,越冬期-孕穗期0~100 cm土层土壤蓄水量提高,且深层施磷效果较好,尤其有利于返青期土壤蓄水量提高。增加施磷量,各生育时期植株含氮率提高,各生育时期植株氮素积累量显著提高,且深层施磷效果较好,尤其开花期含氮率。增加施磷量,花前各器官氮素运转量显著提高,深层施磷叶片氮素运转量对籽粒的贡献率提高,成熟期叶片氮素积累量及其所占比例显著降低。40 cm深度施磷150 kg·hm~(-2)花后氮素积累量最高。此外,越冬-孕穗期0~100 cm土层土壤蓄水量与花前氮素运转量关系密切,尤其与叶片氮素运转量关系密切,开花期土壤水分与花后氮素积累量关系系数最大。总之,增加施磷量,有利于提高花前1 m内土壤水分,有利于促进植株氮素积累、运转,且深层施磷效果显著,尤其可促进叶片氮素转移到籽粒,有利于开花期含氮率提高,有利于花后氮素积累。最终,40 cm深度施磷150 kg·hm~(-2)可显著提高旱地小麦氮肥吸收效率、氮肥生产效率、氮素收获指数。     

Effect of pollution on phytoplankton in the Ashar Canal,a highly polluted canal of the Shatt al-Arab Estuary at Basrah,Iraq

The effect of pollution on the phytoplankton in the Ashar Canal was studied during March and June 1976. Higher temperatures were recorded in June. The canal water was more turbid than that of the adjoining Shatt al-Arab estuary due to high algal populations and sewage disposal. The chlorosity values were remarkably high in the canal, due to sewage disposal. The flood waters in June lowered the chlorosity in both estuary and canal. Sewage disposal into the canal decreased its dissolved oxygen content. The lower oxygen values in the estuary in June were accompanied with higher temperatures. The pH values were generally higher in the estuary and were also higher in June than in March.Eighty-six algal taxa were recorded, 45 of which were diatoms. The phytoplankton in the estuary was more abundant in March, due to the increase in currents and turbidity in June. The Chlorophyta, Conjugatophyta, Myxophyta and Bacillariophyta in the estuary showed reverse seasonal trends from those of the total phytoplankton. These algal seemed to flourish during periods of high temperatures. The dense blue-green algae recorded in June is attributed to the high temperature and dissolved organic matter. The Chrysophyta recorded high populations in the estuary in March and were totally absent in June. Lower temperatures and high transparency in March might have led to their relative abundance.The total phytoplankton in the Ashar Canal followed two different seasonal trends, one resembling and the other differing from those in the estuary. The disposal of domestic sewage and agricultural wastes in the canal seemed to lead to such adverse seasonal variations. The diatoms only dominated the phytoplankton at one station in both months. The sewage and agricultural wastes disposal seemed to favour the abundance of the other phyla than the diatoms. Increased organic load in the canal has led to a considerable increase in the Myxophyta in June. Blooms of Chlamydomonas sp. and Euglena acus increased the phytoplankton densities in March at stations II and IV, respectively. Benthic or periphytic algae were found in the phytoplankton populations. Raised salinity seemed to restrict the distribution of the planktonic diatom Bacillaria paradoxa. Among the noticeable widespread planktonic algae in the study area are Dinobryon sertularia, Pediastrum duplex and P. simplex.     

初春马来眼子菜分解对水体和底泥碳、氮和磷积累及释放的影响

通过实验室模拟初春温度(17℃)条件,研究了沉水植物马来眼子菜(Potamogeton malaianus Miq.)分解过程对其有机碳、总氮和总磷的释放,水体和底泥中有机碳、总氮和总磷含量以及水体中铵态氮和硝态氮含量的影响,同时对水体N2和N2O的释放状况进行了分析。结果表明:在70 d的实验周期内,马来眼子菜分解迅速,至实验结束时植株失重率达到86.92%,植株中有机碳量、总氮量和总磷量分别较实验初始时降低了88.51%、88.93%和86.63%;底泥中有机碳、总氮和总磷含量分别较实验初始时增加了5.56%、17.06%和2.17%。在马来眼子菜分解过程中,水体中的溶解氧含量和氧化还原电位均较对照明显降低,并呈现在实验初期迅速下降然后逐渐增加并趋于稳定的趋势;水体中的有机碳、总氮、总磷以及铵态氮含量均较对照大幅度增加,并呈现在实验初期迅速上升然后逐渐下降并趋于稳定的趋势;而水体中的硝态氮含量则呈先下降后上升再下降的趋势。水体中N2和N2O释放通量较对照明显增加,且在实验中期N2和N2O释放通量达到峰值。研究结果表明:随时间推移,马来眼子菜向水体释放的磷大部分沉积到底泥中,而氮则部分沉积到底泥中、部分以气体形式(N2和N2O)逸出水体。