Uptake of phosphate and inorganic nitrogen by a sediment-algal system in a subarctic lake

SUMMARY.

• 1 The uptake of phosphate and inorganic nitrogen by sediment and phytoplankton was studied under natural conditions (1977) and during lake fertilization with phosphorus and nitrogen (1978–79) in Lake Gunillajaure, a small, stratified, subarctic lake in northern Sweden. The experiments were performed in situ in plexiglass cylinders, to which additions of nutrients were made, and the uptake followed by consecutive sampling and analysis of the water phase.
• 2 Additions of HgCl₂ to the experimental vessels reduced the phosphate uptake to the sediment to less than 10% and it could therefore be concluded that the sediment uptake was mainly of biological nature.
• 3 Dark assimilation was 30–40% of that in light. Since light clearly stimulated the sediment uptake the epipelic algae were probably responsible.
• 4 The phosphate uptake to the sediment could be described by Michaelis-Menten kinetics and the calculated constants (V_max, ks) were very alike in 1977 and 1978 but appeared to have increased in 1979.
• 5 The sediment uptake of ammonium and nitrate was very slow indrcating that the epipelic algae were not nitrogen starved.
• 6 Even though the epipelic algae had a potential for efficient uptake of phosphorus, the phytoplankton took up 92–96% of the phosphate added to the lake on each fertilization occasion due to the relatively large water volume in the epilimnion in relation to the bottom area available for the epipelic algae.

     

Transformations between organic and inorganic sediment phosphorus in Lake Balaton

In order to estimate microbial P content and biological P uptake in sediments, the tungstate precipitation method of Orrett & Karl (1987) was used in sediment extracts. This method allows a simple and rapid separation of organic and inorganic ³²P radioactivity. Either inorganic ³²P (as carrierfree H₃ ³²PO₄) or organic ³²P (as ³²P-labelled algal material) was added to surface sediment suspensions of shallow Lake Balaton. Inorganic ³²P was rapidly transformed into organic ³²P, and this process was completely inhibited by formaline. P content of living benthic microorganisms was estimated from steady state distribution of the radioactivity. Transformation of algal organic P into inorganic P could also be detected.In extremely P limited Lake Balaton benthic microorganisms were shown to supplement their high P requirements by inorganic P uptake. The velocity of the inorganic into organic P transformation, i.e. the rate of microbial P uptake, was comparable to P uptake in the water column. Microbial P uptake contributed significantly to total P fixation by sediments, particularly at low ( 100 µg P l^–1) phosphate additions.     

Orthophosphate uptake of planktonic microorganisms in Lake Balaton

Seasonal orthophosphate uptake of natural plankton has been studied in hypertrophic and mesotrophic basins of Lake Balaton. Initial uptake of carrier-free labelled phosphoric acid followed first order kinetics in accordance with a single two-compartment model. In isotope equilibrium from 1.2 to 9.7 per cent of radioactivity was found in the filtrate. Turnover times of orthophosphate in water were some minutes in summer and two orders of magnitude longer in winter and April. Turnover time of phosphorus in microorganisms has been estimated on the basis of equilibrium isotope distribution between water and particular phases and turnover time in water. It ranged from 28 to over 1 000 min. The shortest times were found in summer, and the longest in winter. Turnover time of orthophosphate in water increased in relation to phosphate additions according to Michaelis-Menten kinetics. The values of Michaelis-constant plus the ambient orthophosphate concentration (K + S_n) suggested an overestimation of real phosphate concentrations by chemical measurements, being much lower than soluble reactive phosphorus contents in most cases, as it is well-known in many other lakes. Both K + S_n values and maximum uptake velocities (V) were significantly higher in the hypertrophic basin than in the mesotrophic one, in contrast to essentially similar values of turnover times. Maximum uptake velocity per unit chlorophyll-a P _opt:V ratio showed extreme to moderate phosphorus deficiency for Lake Balaton plankton, which seemed to decrease somewhat in the course of eutrophication.     

The Availability of Condensed Phosphates for the Algal Strain Scenedesmus obtusiusculus Chodat,with Special Regard to Conditions Characteristic in Lake Balaton

The limiting factor in the water of Lake Balaton was calculated by means of Verduin's equation. If only the orthophosphate-phosphorus concentration is inserted into the equation, phosphorus is the primary limiting factor. If, however, total phosphorus is considered, the factor intensity of nitrogen will be the least, i. e. nitrogen will be the primary limiting-factor of plant growth. According to measurements during 1976, average values for the total dissolved phosphorus and orthophosphate-phosphorus content of Balaton Lake water were 15,66 mg/m³ and 7.66 mg/m³, respectively. Experiments with the algal strain Scenedesmus obtusiusculus Chod. (Chlorophyceae, Chlorococcales). were designed to test the availability of the condensed phosphorus form for the algae. The experiments were performed partly with synthetic polyphosphates, partly, with polyphosphates isolated from Balaton Lake water. The results showed, contrary to our expectations, that phosphates present in the condensed form (irrespective of their structure and degree of condensation). were not utilized by the algae under sterile conditions, i. e. in the absence of bacterial activity. In the light of the above it is recommended to consider only orthophosphate-phosphorus when calculating the limiting factor.     

The impact of Chironomus plumosus larvae on organic matter decay and nutrient (N, P) exchange in a shallow eutrophic lake sediment following a phytoplankton sedimentation

The importance of Chironomus plumosus larvae onbenthic metabolism and nutrient exchange across thesediment–water interface was evaluated in a shalloweutrophic lake (Lake Arreskov, Denmark) following aphytoplankton sedimentation. Chironomus plumosuslarvae were added to laboratory sediment microcosms,corresponding to a density of 2825 larvae m⁻².Non-inhabited microcosms served as controls. Asedimentation pulse of organic matter was simulated byadding fresh algal material (Chlamydomonasreinhardii) to sediment cores (36 g dryweight m⁻²). The mineralization was followed bymeasuring fluxes of O₂, CO₂, dissolvedinorganic nitrogen and phosphate. A rapid clearance ofalgae from the water column in faunated microcosmssuggested that chironomids may be of major importancein controlling phytoplankton concentrations in shalloweutrophic lakes. Chironomids increased the sedimentO₂ uptake ≈ 3 times more than what wouldbe expected from their own respiration, indicating astimulation of microbial activity and decomposition oforganic matter in the sediment. Addition of algaeenhanced the release of CO₂, NH⁺ ₄ ando-P. The excess inorganic C, N and P released inamended non-inhabited sediment after 36 dayscorresponded to 65, 31 and 58% of the C, N and P inthe added algae. In sediment inhabited by Chironomus plumosus the corresponding numbers were147, 45 and 73%, indicating that mineralization oforganic matter also from the indigenous sediment poolwas stimulated by chironomids. This revised version was published online in July 2006 with corrections to the Cover Date.     

Experiments on Nitrogen and Phosphorus Release by Chironomus ex gr. plumosus from the Sediments of Lake Balaton,Hungary

Sediment-water systems of Lake Balaton mud and tap water were constructed in plexiglass tubes and boxes for evaluation of changes in the nitrogen and phosphorus contents of overlying water as influenced by chironomid density and light conditions. Nitrogen flux from sediment was greatly influenced by denitrification process. The amount of TN released by chironomids amounted to about half of the yearly nitrogen fixation rate in Lake Balaton. Omnivorous chironomids increased the phosphorus content of the overlying water. The rate of release was density dependent. TP release rates ranged between 1–17 mg m⁻² day ⁻¹ over a range of densities 500–20,000 larvae m⁻². It became evident that aerobic sediment cores can be an important nutrient source in lakes where chironomids inhabit them at densities above 1,000 larvae m⁻².     

Development and practical application of limiting values for the phosphate concentration in surface waters in the Netherlands

Summary To counteract eutrophication it is important to possess sufficient information (1) on the relationship between the content of nutrients and the algal biomass, and (2) on the cycling of nutrients in lakes.A comparative study of a large number of surface waters in the Netherlands has demonstrated that it is possible to derive a relationship between the nitrogen and phosphorus concentrations and the upper limit of the chlorophyll concentration, averaged over the summer season.For the authority in charge of water quality it is essential to know how far the phosphorus loading must be reduced to attain the desired phosphate concentration. The results of an extensive study of the nutrient budgets of Lake Wolderwijd-Nuldernauw over the period 1976–1979 demonstrate that in certain cases a relative high phosphate concentration can occur (approx. 0.30 mg/l) in spite of a low external phosphorus loading (approx. 0.7 g P/m² year). Such high concentrations can be explained by the continuous presence of a bloom of blue-green algae and the release of phosphate from the aquatic sediments during the summer. In such lakes it is necessary to take additional measures, such as flushing with water poor in algae and phosphates, or, where necessary, the removal of aquatic sediment rich in phosphate.     

Operation of the Kis-Balaton reservoir: evaluation of nutrient removal rates

As one of the major measures for controlling the man-made eutrophication of Lake Balaton, the Hidvég reservoir of 20 km² surface area was built near the mouth of River Zala, draining half the watershed of the lake, and representing the largest nutrient source for the lake. The reservoir, as the first element of the expected total system of 70 km² surface area (Kis-Balaton Control System), started to operate in June 1985, aiming at removing nutrients primarily through sedimentation, adsorption and uptake by macrophytes.Detailed investigations began with the operation. These cover the observation of upstream and downstream nutrient loads and the water quality in the reservoir, the study of major phosphorus removal processes, and analysis of the nitrogen cycle and of the behaviour of phytoplankton, zooplankton, fish and macrophytes. The research programme is completed by the evaluation of observations (including the use of phosphorus budget models), with special emphasis on future operation modes of the reservoir.The nutrient removal efficiencies in the reservoir came up to expectations. The removal rates for suspended solids, total-P, soluble reactive-P and nitrate-N exceeded 50 % in the first full year of operation (1986). As a result of reservoir operation, nutrient loads in the western basin of Lake Balaton have been significantly reduced. However, the improvement in water quality can be expected only with a lag time due to the internal P load of the basin.     

Seasonal Variations in Chlorophyll a Concentrations in Relation to Potentials of Sediment Phosphate Release by Different Mechanisms in a Large Chinese Shallow Eutrophic Lake (Lake Taihu)

The relationship between chlorophyll a and fractionation of sediment phosphorus, inorganic phosphate-solubilizing bacteria (IPB), and organic phosphate-mineralizing bacteria (OPB) was evaluated in a large Chinese shallow eutrophic lake (Lake Taihu) and its embayment (Wuli Bay). At the three study sites, the increase of chlorophyll a concentrations in April paralleled those of the iron bound phosphate accounting for major portion of sediment inorganic phosphate, and in June significantly higher OPB and IPB numbers (especially OPB) in sediment were main contributors to the peaks of chlorophyll a concentration. Even though IPB peaked from February to June, it should serve as an unimportant P source due to the irrelevancy with chlorophyll a and soluble reactive phosphorus (SRP). By contrast, at the other site in the embayment, the calcium-bound phosphate was predominant and solid, which was difficult to be released, and neither IPB nor OPB were detectable in the sediment, indicating weak potential for phosphorus release from the sediment, which was reflected in the small seasonal variation in SRP concentration in water column. Hence, the extents to which the three general mechanisms behind phosphate release from sediment (desorption of iron bound phosphate, solubilization by IPB and enzymatic hydrolysis by OPB) operated were different depending on seasons and sites in Lake Taihu, they may jointly drive phosphate release and accelerate the eutrophication processes.     

Transition from shallow lake to a wetland: a multi-proxy case study in Zalavári Pond,Lake Balaton,Hungary

Lake Balaton, the largest shallow lake in Central Europe, has no natural outlet, therefore, underwent water level changes during its 15,000–17,000 years of history. The lake is very sensitive to both climate changes and human impacts. Surroundings have been inhabited since the Stone Age; however, heavy human impact can be recognized during the past 6000 years. In this study, we established three different stages for and reconstructed water level changes of Lake Balaton by geochemical data, subfossil Cladocera and diatom remains in the sediments of the Zalavári Pond, a part of the Kis-Balaton wetland. In 9900–8600 cal. year BP, climate was dry, water level was low, and there was a wetland in this area. Although organic matter content was low in the sediment, the ratio of Fe/Mn was high. Between 5600 and 5000 cal. year BP, water level increased, Fe/Mn ratio shows that oxygen conditions of sediments was improved in agreement with the relatively low number of diatom remains and dense chydorid remains. About 5000 cal. year BP, water level of Lake Balaton decreased as indicated by high organic content with low carbonate and high Fe/Mn ratio in the sediments (oxygen depletion). At the bottom of this section, high Fe and S concentrations showed accumulation of pyrite (FeS₂) that is common in wetlands with very low redox potential. Low abundance of Cladocera remains together with rich and diverse diatom flora confirm the low water level hypothesis. Our data support that the water level of Lake Balaton was higher between 8600 and 5000 cal. year BP than it is at present.     

杭州西湖藻类动态模型研究

该模型按照年度来描述西湖四类藻类(蓝藻门、绿藻门、隐藻门、硅藻门)的动态变化.结果表明,模型作出的状态变量的描述是理想的,并且对于系统强制函数改变能给予合理响应.模型还对引水量,引水或溪流的含磷量及疏竣湖泥量的改变给水体带来的变化进行了预测.       

Stir-up effect of wind on a more-or-less stratified shallow lake phytoplankton community,Lake Balaton,Hungary

Microstratification of phytoplankton in the large shallow Lake Balaton (Hungary) was studied during a 24 h period. Dissolved O₂ showed biological stratification; flagellates exhibited a definite circadian rhythm. In the middle of the investigation a heavy storm broke out which was followed by the disappearance of differences between different layers of water. Storm-induced destratification is described by cluster-analysis. Abundances of dominant species changed differently in connection with the storm. Numbers of Nitzschia sp. increased due to stirring up from the sediment surface. Numbers of single-celled or colony-forming species (Cyclotella comta, Crucigenia quadrata, Coelosphaerium kuetzingianum) practically did not change. Numbers of all the three dominant filamentous species (Aphanizomenon fos-aquae f. klebahnii, Lyngbya limnetica, Planctonema lauterbornii) significantly decreased, which might be attributed to an unknown loss process and was followed by a competitive displacement by algae of small cell size.     

Production and Distribution of the Microphytobenthos in the Sediment of Lake Mikolajskie

Chlorophyll-α concentration, algal biomass and photosynthetic activity decrease with increasing sediment depth. Chlorophyll-α and biomass minima were found at the sediment surface on several occasions. This may be due to the removal of algae by wave action or vertical migrations of the algae in the sediment. By comparing stations with different degrees of exposure it was shown that wave action affects the size of the benthic populations. The epipsammic microphytobenthos is an important primary producer in the littoral zone of Lake Mikolajskie.     

Acidified lakes: sediment treatment with sodium carbonate — a remedy?

Until now, additions of lime have been used to restore the buffering capacity of acidified lakes, but an alternative method which is more effective in the treatment of lakes with organogenic sediments has recently been applied in a full-scale experiment. The method, called CONTRACID, is based on the cation exchange properties of lake sediment. A sodium carbonate (soda ash) solution is injected into the sediment (by a harrow), so that the sediment becomes sodium stocked. A reverse exchange occurs during subsequent acidification. Liming has a limited effect on humic lakes, since Ca-humates have a reduced reverse exchange ability and also the lime, which remains undissolved, is rendered inactive. Ionic exchange processes and nutrient transport were studied in water/sediment cores andin situ enclosures after additions of soda ash-, lye- and lime solutions with subsequent re-acidification. Sodium carbonate additions in laboratory systems resulted in a sorption to the sediment of 42–62% of the added sodium ions (5 eq m⁻²) and a release of 14–78 mg Pm⁻² sediment. Similar results were obtained in the enclosures where phosphorus release stimulated algal growth. Sediment pH, elevated by the sodium base addition, was lowered by re-acidification. Limed systems released no phosphorus and only about 25% of the added lime remained active for future neutralization. With the injection of the sodium carbonate solution into the sediment, only about 12% of the added sodium was recovered in lake water by spring circulation. Lake water alkalinity was then 0.12 meq l⁻¹ and pH 6.7. Total phosphorus had been raised by 0.007 mg P l⁻¹ causing an increase in phytoplankton biomass. Observations indicate that manipulations of acidic lake sediment according to the CONTRACID method create a long-lasting neutralizing capacity and a biological stimulation (through phosphorus release), which makes the method an attractive alternative to frequent liming.     

镉对固定化小球藻除磷效果的影响

采用人工配制污水进行静态模拟实验,研究了镉对被海藻酸钙凝胶包埋固定的小球藻去除磷能力的影响.结果表明:在各光照及pH条件下,镉对固定化小球藻吸收磷的效果随着实验时间的推移而变化,在实验的第一天时影响最大;总体而言,镉抑制了固定化小球藻的除磷能力,但在某些条件下镉反而提高了藻对磷的吸收;固定化处理减弱了镉对小球藻除磷能力的影响.具体的光照、pH值与镉的影响效果的关系尚待进一步探讨.     

Nitrogen uptake and the importance of internal nitrogen loading in Lake Balaton

1. The importance of various forms of nitrogen to the nitrogen supply of phytoplankton has been investigated in the mesotrophic eastern and eutrophic western basin of Lake Balaton.
2. Uptake rates of ammonium, urea, nitrate and carbon were measured simultaneously. The uptake rates were determined using N and C methodologies, and N2‐fixation was measured using the acetylene‐reduction method. The light dependence of uptake was described with an exponential saturation equation and used to calculate surface‐related (areal) daily uptake.
3. The contribution of ammonium, urea and nitrate to the daily nitrogen supply of phytoplankton varied between 11 and 80%, 17 and 73% and 1 and 15%, respectively. N2‐fixation was negligible in the eastern basin and varied between 5 and 30% in the western region of the lake. The annual external nitrogen load was only 10% of that utilized by algae.
4. The predominant process supplying nitrogen to the phytoplankton in the lake is the rapid recycling of ammonium and urea in the water column. The importance of the internal nutrient loading is emphasized.     

Ecotoxicological characterisation of sedimentation in the Kis-Balaton Water Protection System

The main function of the Kis-Balaton Water Protection System is to retain nutrients and total suspended solids, thus protecting the water quality of Lake Balaton. In this paper, the toxic nature of the sediment in the 2nd reservoir of the KBWPS has been characterised, using a battery of tests: Vibrio fischeri acute bioassay on whole sediment samples, and V. fischeri bioassay on pore water and elutriate samples. The latest version of the V. fischeri bioluminescence inhibition was applied, the Flash assay which uses a kinetic mode and is able to detect the toxicity of solid, turbid/coloured samples. Whole sediment toxicity showed a clear spatial distribution of toxicity, in parallel with elutriate toxicity. However, no pore water toxicity was detected, leading to the conclusion that contaminants are not water soluble.     

The effect of benthic algae on phosphorus exchange between sediment and overlying water in shallow lakes: a microcosm study using 32P as a tracer

Sediments are of key importance in determining the nutrient levels of water in shallow lakes as they can act as either source or sink for phosphorus (P) depending on environmental conditions, sediment characteristics, and external nutrient loading. We examined the role of benthic algae in the P cycling between sediment and overlying water in experiments using ³²P as a tracer. Sediment and water samples were collected from Huizhou West Lake, a shallow, eutrophic waterbody located in Huizhou City, South China. Laboratory cultured benthic algae were transferred to cover the sediment core in tubes. When ³²P was added to the water in experimental tubes containing sediment cores with and without benthic algae, ³²P activity after 48 h was significantly lower in the tubes with algae, indicating that benthic algae removed P from the overlying water. When the tracer was injected into the sediment, ³²P activity in the water overlying sediment with benthic algae was substantially lower than in tubes with naked sediment, suggesting that benthic algae reduce the release of sediment P. Oxygen levels were significantly higher in the upper 3 mm of the sediments covered by benthic algae; thus, we hypothesized that oxygen produced by the algae helps inhibit the release of P from the sediment. Our study demonstrates that benthic algae are capable of reducing P levels in water overlying the sediment, suggesting that loss of benthic algae during eutrophication triggered by impoverished light conditions may accelerate the shift in shallow lakes from a clear water to a turbid state.     

A bioassay to assess the potential effects of sediment resuspension on phytoplankton community composition

A laboratory assay (SAGA or Sediment Algal Growth Assay) was developed to assess the potential impact of sediment resuspension on the structure of phytoplankton communities, and to evaluate the effectiveness of various sediment treatments in decreasing the abundance of blue-green algae in the event of sediment resuspension during storms. In assays with sediment from eutrophic Akanoi Bay, Lake Biwa, Japan, 7–11 species of phytoplankton seeded from the sediments grew during the 3-week assay indicating that sediment resuspension has the potential to increase both phytoplankton biomass and species diversity. Treatment of sediments with Ca(NO3)2 substantially decreased phytoplankton biomass (measured as chlorophyll concentration) in assays with sediments from Akanoi Bay and the North Basin of Lake Biwa. Further, among various oxidation treatments of sediments, Ca(NO3)2 was most effective in decreasing or preventing filamentous blue-green algal growth in N- and P-replete media. In contrast, when sediments were added to P-limited phytoplankton dominated by green algae and diatoms, no growth of blue-green algae occurred regardless of sediment treatment. This revised version was published online in June 2006 with corrections to the Cover Date.     

Alga consumption of four dominant planktonic crustaceans in Lake Balaton (Hungary)

Between 1981–83 the gut contents ofDaphnia galeata, D. cucullata, Eudiaptomus gracilis, andCyclops vicinus were examined with light and scanning electron microscope to obtain information on the feeding of these species in Lake Balaton. The twoDaphnia species feed mainly on abioseston, and it is assumed that their primary nutrient source was organic matter adsorbed onto the surfaces of the abioseston granules plus bacteria and detritus.E. gracilis feeds on algae, showing a preference for green algae and diatoms.C. vicinus is also a prodigious consumer of algae in Lake Balaton, utilizing the whole size spectrum of phytoplankton. Concerning the trophic relationships between phytoplankton and zooplankton in Lake Balaton, that between diatoms and bothE. gracilis andC. vicinus is the most conspicouos. Convincing evidence for an extensive utilization of blue-green algae was not found. Though there is no firm evidence yet, it is likely that theDaphnia are dependent on organic matter adsorbed on the abioseston.