Vertical variations in kinetics of alkaline phosphatase and P species in sediments of a shallow Chinese eutrophic lake (Lake Donghu)

The vertical distribution of the variables relevant to P forms in sediments were studied in a shallow Chinese freshwater lake (Lake Donghu) in 1997, 1998, 1999 and 2000, to assess the contribution of enzyme to P availability in sediment cores. Sediment P was fractionationd into iron-bound P, calcium-bound P, acid soluble organic P (ASOP) and hot NaOH extractable residual organic P. The former two species made the largest contribution to the sediment P pool. All P species exhibited significantly higher concentrations in different depths at Station I, compared with those found at Station II, except for ASOP. Coupled with these lower ASOP concentrations, the V _max data of alkaline phosphatase, measured on the same samples, were significantly higher at station I. Taken together, ASOP were probably important in supplying the enzymatic substrate (Phosphatase Hydrolyzable Phosphorus, PHP) into interstitial water. Dissolved orthophosphate and PHP concentrations were highly heterogeneous , but peaked in subsurface, paralleled by higher V _max and lower K _m values of alkaline phosphatase, throughout the sediment core. Sediment in the eutrophic lake is not only enriched in available P (iron-bound P), or stores residual P, but also tends to release PHP, thereby inducing the production of alkaline phosphatase and releasing o-P into water column by enzymatic hydrolysis. The latter process may also occur in relatively deep sediment layers.     

UV-sensitive P compounds: release mechanism, seasonal fluctuation and inhibitory effects on alkaline phosphatase activity in a shallow Chinese freshwater lake (Donghu Lake)

Filtrable phosphorus compounds in a shallow Chinese freshwater lake (Donghu Lake) were fractionated by Sephadex G-25 gel-filtration chromatography. Some portions of those compounds released soluble reactive phosphorus upon irradiation with low dose ultraviolet light. Catalase and a hydroxyl radical scavenger (mannitol) markedly prevented photosensitive phosphorus release. The observed effects may be explained by the action of oxidizing reagents such as hydroxyl radicals, produced in photochemical reactions between UV irradiation and humic substances in the water. There was a strong seasonality in UV-sensitive P (UVSP) release. Michaels constants (K _m) of total alkaline phosphatase in the lake water showed a direct positive relation to UVSP Plot of K _m against the UVSP/phosphomonoester ratio reveals a strong relationship between the two variables. These results suggest that in some situations UVSP may be a competitive inhibitor of alkaline phosphatase activity in the lake. The competitive inhibition of fractionated UVSP on alkaline phosphatase reagent (Sigma) apparently supports this hypothesis.     

菹草对湖泊沉积物磷状态的影响

武昌野芷湖湾菹草(PotamogetoncrispusL.)生物量较高位置的沉积物显示明显较高的磷吸附指数,以及据Langmuir方程:C/X=C/Xm+K×1/Xm导出的最大吸附量与吸附强度,这一结果在不同时期与不同采样深度均有体现,故提高沉积物磷的吸附能力应为菹草维持水体较低营养水平的重要机制。铁结合态磷是沉积物磷的主要存在形式,吸附能力的提高可由有机质及其与铁的相互作用部分地得到解释。不同时期菹草生物量较高的沉积物表现明显较低的碱性磷酸酶活性与最大反应速度,降低沉积物有机磷的酶促分解速率应为菹草维持水体低营养水平的另一机制。     

The effect of wave-reduction engineering on sediment resuspension in a large, shallow, eutrophic lake (Lake Taihu)

Frequent resuspension of sediments is recognized as an important process in large shallow lakes, impeding the recovery of eutrophic lakes. A large-scale project, including a wave barrier (3.3 km long) and a soft enclosure, was implemented to reduce wave energy and sediment resuspension in Lake Taihu, eastern China. The effects of the wave-reduction engineering on sediment resuspension and internal nutrient loading were investigated. Results showed that sediment resuspension rates as well as suspended solids (SS) in the areas protected by the wave barrier and the soft enclosure were significantly lower than in the unprotected areas. There was a positive relationship between total phosphorus (TP) and SS; thus internal loading of phosphorus was significantly reduced by the wave-reduction structure. High nutrient levels and phytoplankton biomass persisted during the experiment period, suggesting that additional measures, such as re-establishment of the macrophyte community, must be included to help restore the water quality in such a large, shallow and eutrophic lake.     

太湖大型底栖动物群落结构及多样性

为揭示现阶段太湖大型底栖动物群落现状及其对生态环境变化的响应, 于2007年2月至2008年11月对太湖大型底栖动物进行为期两周年的季度调查。30个采样点共记录底栖动物3门7纲19科40种, 底栖动物平均密度和生物量空间差异较大, 平均密度高值出现在梅梁湾、竺山湾及河口, 主要为寡毛纲颤蚓类; 平均生物量高值出现在贡湖湾、西湖区、东太湖和东部湖湾, 主要为软体动物。霍甫水丝蚓(Limnodrilus hoffmeisteri)、中华河蚓(Rhyacodrilus sinicus)、河蚬(Corbicula fluminea)、铜锈环棱螺(Bellamya aeruginosa)、中国长足摇蚊(Tanypus chinensis)和钩虾属一种(Gammarus sp.)是现阶段太湖大型底栖动物的优势种。聚类分析将30个采样点分成3组, 相似性分析检验表明各聚类组大型底栖动物群落具有显著差异(P<0.05)。多样性分析结果表明, 东太湖和东部湖湾物种多样性、丰富度和均匀度最高, 优势种为腹足纲螺类; 梅梁湾、竺山湾及河口多样性最低、密度最高, 霍甫水丝蚓和中华河蚓在该区占据绝对优势; 贡湖湾、湖心和西湖区多样性处于中等水平, 其优势种为河蚬。研究结果表明营养水平、底质类型以及水生植被的分布是决定太湖大型底栖动物群落结构及多样性的关键因子。     

Stratification of alkaline phosphatase in sediments of two urban lakes and its effect on phosphorus cycle

Phosphorus loadings in sediments play an important role in lake eutrophication and the progress of its recovery. The phosphorus release is controlled by physical, chemical and biological mechanisms. Alkaline phosphatase catalyzes remineralization of organic phosphorus and then it may be an important factor accelerating phosphorus cycling in sediments. In this paper, distributions, properties and function of alkaline phosphatase with depths in sediments of two urban lakes were discussed. Alkaline phosphatase activity (APA) in the sediments of Lake Yuehu decreased with the sediment depth. APA in sediments of Lake Yuehu was, mostly, inhibited by Phe and L-Cys; and inhibiting ability of Phe could be stronger than L-Cys. APA in deeper layer (20–30 cm) of sediments was more sensitive to the inhibitors than other layers, but range of variation in APA was most wide in the subsurface layer (10–20 cm). All the facts implied that alkaline phosphatase occurred in various forms (isoenzymes). APA in the sediments with different depths of Lake Donghu responded Phe differently. Reacted with Phe and incubated for 1 day, the amounts of SRP released by these sediments varied correspondingly. SRP on the overlying water in deeper layers (5–10 cm and 15–20 cm) of Site T1 was higher than that in surface layer (0–5 cm) of the same site, 1 day after incubation. Hence, the SRP release resulted, at least partially, from the hydrolysis of some liable organic phosphorus mediated by APA. Alkaline phosphatase in lake sediments plays an important role in the release of internal phosphorus loadings and eutrophication. A possible explanation for the sensitivity at deeper layers could be another active region of hydrolysis by alkaline phosphatase from organic phosphorus, which added a new dimension in phosphorus cycling mediated by some biochemical mechanisms.     

Mobility of phosphorus fractions in the sediments of Lake Balaton

Sediment phosporus was studied by a combination of the fractionation procedure of Hieltjes & Lijklema and the isotopic dilution technique in a mesotrophic (Tihany) and a hypertrophic (Keszthely) basin of Lake Balaton.In the calcareous sediments the largest part of phosphorus was bound to calcium. Iron-bound and residual P showed higher concentrations at Keszthely than at Tihany. There was little loosely adsorbed P at both locations. Vertical differences in P fractions of the sediments were more pronounced at Keszthely than at Tihany. Exchangeability of the fractions decreased in the following sequence: iron-bound > loosely adsorbed > calcium-bound > residual. Phosphorus, particularly in the calcium-bound fraction, was more mobile at Keszthely, and its exchangeability decreased rapidly downwards at both stations. Four times more potentially mobile phosphorus has been accumulated by the upper sediment layer at Keszthely than at Tihany.     

Phosphorus availability to maize as influenced by organic manures and fertilizer P associated phosphatase activity in soils

Laboratory incubation and green house studies were conducted to compare the P availability of organic manures and P uptake from organic manures by maize. Various organic manures viz. Poultry manure (PM), Farmyard manure (FYM), Green manure (GM) and Crop residue (CR) and graded levels of fertilizer P were applied in Samana sandy loam and Ladhowal silt loam soils and incubated for 7, 15, 30, 60 and 90 days. Samples were analyzed for P availability, P uptake and alkaline phosphatase activity. The overall, phosphatase activity, Paranitrophenyl phosphate (PNP h⁻¹ g⁻¹), in the Ladhowal silt loam soil was higher than in the Samana sandy loam soil. As the level of inorganic P increased, the release of PNP h⁻¹ g⁻¹ soil also increased. Among different organic manures, PM registered the highest enzyme activity followed by FYM, GM and CR. Compared to 7 days incubation a slightly higher increase in PNP was noticed in samples from 90 days incubation in both soils. The differential phosphatase activity in the organic manures was further reflected in dynamic P availability. The highest amount of Olsen extractable P was in PM-treated soil followed by FYM, GM and field pea crop residue. Organic manure addition along with inorganic P, irrespective of the source, increased the Olsen extractable P throughout the incubation period. Total P uptake by maize increased with the increasing level of inorganic P in both soils. The highest uptake was obtained in PM-treated soil and lowest in the CR-amended soil. We conclude that PM more readily supplies P to plants than other organic manure sources.     

Kinetics of inactivation of green crab (Scylla Serrata) alkaline phosphatase during removal of zinc ions by ethylenediaminetetraacetic acid disodium

Green crab (Scylla Serrata) alkaline phosphatase (EC 3.1.3.1.) is a metalloenzyme, the each active site in which contains a tight cluster of two zinc ions and one magnesium ion. The kinetic theory of the substrate reaction during irreversible inhibition of enzyme activity previously described by Tsou has been applied to a study on the kinetics of the course of inactivation of the enzyme by ethylenediaminetetraacetic acid disodium (EDTA). The kinetics of the substrate reaction with different concentrations of the substrate p-nitrophenyl phosphate (PNPP) and inactivator EDTA suggested a complexing mechanism for inactivation by, and substrate competition with, EDTA at the active site. The inactivation kinetics are single phasic, showing the initial formation of an enzyme-EDTA complex is a relatively rapid reaction, followed a slow inactivation step that probably involves a conformational change of the enzyme. Zinc ions are finally removed from the enzyme. The presence of metal ions apparently stabilizes an active-site conformation required for enzyme activity.     

The distributions and effects of nutrients in the sediments of a shallow eutrophic Chinese lake

The temporal and spatial distribution of total nitrogen and total phosphate in the sediments of a shallow eutrophic Chinese lake (Lake Chao), and their relationships with the physical and chemical features of sediments, and their effects on the lake water quality and trophic state, are presented in this paper. The following results were obtained: (1) higher concentration of Tot-N and Tot-P in the sediments occurred in the summer and the autumn seasons; (2) higher annual average Tot-N and Tot-P concentrations were observed in the sediments near the various river mouths and in the western part of the lake; (3) Tot-N and Tot-P concentration in the lake sediments generally increased with increase in lake sediment Eh, pH, and Al₂O₃, and declined with decrease in lake sediment size diameters and SiO₂; and, (4) correlations were observed in both the temporal and spatial distributions between the trophic state, Tot-N and Tot-P concentration in the lake water, and the Tot-N and Tot-P concentration found in the lake sediments.     

Effects of hydrodynamics on phosphorus concentrations in water of Lake Taihu,a large,shallow, eutrophic lake of China

To understand the effect of hydrodynamical process on water phosphorus concentration, wind, wave, and several water quality indices were observed in Meiliang Bay, a shallow and eutrophic bay locates in north of Lake Taihu. During the 7 day observation period, wind speed and significant wave height were recorded more than 3 h per day, and water samples were collected in five water-depth layers once a day. Hydrodynamical disturbance had no significant correlationship with the water quality at the top layer when the significant wave height was smaller than 30 cm, but it significantly increased suspended solids (SS) concentration of the bottom water layer. Concentrations of nutrients showed no positive correlationship with SS concentration in the water body. Intensive sediment resuspension may not have occurred when the hydrodynamic stress on sediment was only a little higher than the critical stress for sediment resuspension. A new method for confirming the critical stress for intensive sediment resuspension and nutrient release still needs to be developed. The range of the water quality indices was quite high during the seven days of observation. High variation seems to be a common character of large shallow lakes like Taihu.     

The role of periphytes in the shift between macrophyte and phytoplankton dominated systems in a shallow, eutrophic lake (Lake Taihu, China)

Based on experiments of periphyte response to different trophic levels and their impact on macrophyte production, it was found that the periphyte biomass increased with the nutrient concentrations. Increased trophic level and periphyte biomass resulted in decreased macrophyte photosynthesis. It was suggested that the periphytes could cause resilience and hysteresis in the system shifts between macrophyte and phytoplankton domination. Other factors, such as fish farming, storm induced waves and mechanical destruction, and high water levels could be the perturbations during the system shifts, but these are not the key factors. Instead, the nutrient loading and periphyte abundance could determine the shift in lake ecosystem between macrophyte and phytoplankton domination. This finding could theoretically elucidate the mechanism of ecosystem shifts between macrophyte and phytoplankton domination.     

The role of periphytes in the shift between macrophyte and phytoplankton dominated systems in a shallow, eutrophic lake (Lake Taihu, China)

Based on experiments of periphyte response to different trophic levels and their impact on macrophyte production,it was found that the periphyte biomass increased with the nutrient con-centrations. Increased trophic level and periphyte biomass resulted in decreased macrophyte photo-synthesis. It was suggested that the periphytes could cause resilience and hysteresis in the system shifts between macrophyte and phytoplankton domination. Other factors,such as fish farming,storm induced waves and mechanical destruction,and high water levels could be the perturbations during the system shifts,but these are not the key factors. Instead,the nutrient loading and periphyte abundance could determine the shift in lake ecosystem between macrophyte and phytoplankton domination. This finding could theoretically elucidate the mechanism of ecosystem shifts between macrophyte and phytoplankton domination.     

Stimulation of alkaline phosphatase activity in Ishikawa cells induced by various phytoestrogens and synthetic estrogens

Xenoestrogens, phytoestrogens and synthetic estrogens, are able to bind to estrogen receptors, and to mimic estrogenic activities in a cell and tissue specific manner. For the characterization of environmental estrogens mainly mammary derived and yeast based models have been used. The aim of this study was therefore to assess selected natural and synthetic compounds in an endometrial derived model. We measured the relative estrogenic potency of phytoestrogens (genistein, daidzein, coumestrol, some naringenins), synthetic estrogens (bisphenol A, octylphenol, nonylphenol, o,p′-DDT), mycoestrogen (zearalanone) as well as extracts of Cimicifuga racemosa on alkaline phosphatase (AlkP) activity in the endometrial derived adenocarcinoma cell line Ishikawa. We used a modified multiwell plate in vitro bioassay based on the estrogen-specific and dose-dependent enhancement of AlkP activity in this cell line. Estradiol, which induced AlkP at levels as low as 10⁻⁸ M, was used as positive control. Most of the compounds studied showed a clear dose-dependent estrogenic effect. Compared to the vehicle control (ethanol) all phyto- and mycoestrogens, stimulated the AlkP activity 2–4-fold at a concentration of 10⁻⁶ M. The synthetic chemicals bisphenol A and nonylphenol showed an effect at 10⁻⁶ M, octylphenol at 10⁻⁵ M. Effects of o,p′-DTT could not be measured. ICI 182,780, a pure estrogen receptor antagonist, significantly inhibited these effects. The latter result demonstrated the estrogen receptor dependency of this process. In summary, most of the phytoestrogens and industrial chemicals tested, behaved as estrogen receptor agonists in terms of the stimulation of AlkP activity.     

Composition and distribution of bottom oligochaete fauna of a north Italian eutrophic lake (Lake Ledro)

The profundal macroinvertebrates, particularly the oligochaetes, of Lake Ledro (Trento, Italy), that has recently undergone eutrophication, were studied.A statistical approach of random sampling was used to study the distribution and abundance of the oligochaete species. The optimum sample number was calculated from a preliminary sample series. The oligochaete community was made up of five tubificid species, one naidid and one lumbriculid species that on average represents more than 80% of the macrobenthic community. Population density was correlated with depth and decreasing oxygen concentration. The role of Tubifex tubifex as a eutrophic, tolerant species was confirmed; and in fact it was the only species found (although at low density) in the deepest and anoxic zone. No comparable data are available for the lake prior to eutrophication, but these data will be valuable for future comparison once a remediation program for the lake has been implemented.     

Inhibition of protein tyrosine phosphatase 1B and alkaline phosphatase by bis(maltolato)oxovanadium (IV)

Vanadate has been recognized as a specific and potent phosphatase inhibitor since its structure is similar to that of phosphate. In this study, we measured the inhibition of glutathione S-transferase-tagged protein tyrosine phosphatase 1B (GST-PTP1B) and alkaline phosphatase (ALP) by the insulin enhancing compounds, bis(maltolato)oxovanadium(IV) (BMOV). The results showed that the activity of GST-PTP1B was reversibly inhibited by solutions of BMOV with an IC₅₀ value of 0.86 ± 0.02 μM. Steady state kinetic studies showed that inhibition of GST-PTP1B by BMOV was of a mixed competitive and noncompetitive type. In addition, incubation of GST-PTP1B with BMOV showed a time-dependent biphasic inactivation of the protein. On the other hand, the inhibitory behavior of BMOV on ALP activity was reversible and competitive with an IC₅₀ value of 32.1 ± 0.6 μM. Incubation with BMOV did not show biphasic inactivation of ALP. The reversible inhibition of GST-PTP1B by BMOV is more potent than that of ALP, but solutions of BMOV inhibited both enzymes. This data support the suggestion that mechanisms for the inhibitory effects of BMOV on GST-PTP1B and ALP are very different.     

Study on ecological restoration in near-shore zone of a eutrophic lake, Wuli Bay, Taihu Lake

A two-year restoration period, large-scale ecological restoration demonstration engineering project was carried out in the near-shore zones of Wuli Bay, Taihu Lake. Various methods to restore the aquatic biodiversity and prevent ecological degradation were employed and their effects on water quality and aquatic plants were investigated. The results showed that water quality had been significantly improved in the demonstration zones. The concentrations of TN and TP were about half of those of the reference site in Wuli Bay. The water transparency was 30 cm higher than that in the reference site. The species, cover and biomass of aquatic plants were also significantly increased in the demonstration zones.     

Bacterial and archaeal assemblages in sediments of a large shallow freshwater lake, Lake Taihu, as revealed by denaturing gradient gel electrophoresis

Aims:  To explore the association of microbial community structure with the development of eutrophication in a large shallow freshwater lake, Lake Taihu.
Methods and Results:  The bacterial and archaeal assemblages in sediments of different lake areas were analysed using denaturing gradient gel electrophoresis (DGGE) of amplified 16S rDNA fragments. The bacterial DGGE profiles showed that eutrophied sites, grass-bottom areas and relatively clean sites with a eutrophic (albeit dredged) site are three respective clusters. Fifty-one dominant bacterial DGGE bands were detected and 92 corresponding clones were sequenced, most of which were affiliated with bacterial phylotypes commonly found in freshwater ecosystems. Actinobacteria were detected in the centre of the lake and not at eutrophied sites whereas the opposite was found with respect to Verrucomicrobiales . Twenty-five dominant archaeal DGGE bands were detected and 31 corresponding clones were sequenced, most of which were affiliated with freshwater archaeal phylotypes.
Conclusions:  The bacterial community structures in the sediments of different areas with similar water quality and situation tend to be similar in Taihu Lake.
Significance and Impact of the Study:  This study may expand our knowledge on the relationship between the overall microbial assemblages and the development of eutrophication in the shallow freshwater lake.     

Isolation and Characterization of Organic Phosphorus-Mineralizing Bacteria in Sediment of a Chinese Large Shallow Eutrophic Lake (Lake Taihu)

The organic phosphorus mineralizing bacteria (OPB) play an important role in phosphorus cycling in lake sediment, to which less attention has been paid. Monthly sediment samples in 2009 ending in October, together with the samples from different seasons (May, July, October, and December) in 2008, were collected at 6 sites in a Chinese large shallow eutrophic lake (Lake Taihu). The sediment OPB numbers ranged from 2.2 × 10⁶ to 1.79 × 10⁸ cells g^?1 (dry weight) at different sampling sites and in different seasons, with the average being 3.88 × 10⁷ cells g^?1 (dry weight). Its number was highest at the most polluted site and peaked in spring and summer, which can be explained by the enrichment of organic matter in sediment. Furthermore, there existed a significant positive relationship between the OPB numbers and alkaline phosphatase activities in the sediment. The 6 OPB strains isolated from the sediment were distinct in terms of their colony morphology on the yolk agar, biochemical characteristics and phosphorus release abilities. According to the 16S rDNA sequences, these OPB belong to Bacillus cereus, Stenotrophomonas maltophilia, Stenotrophomonas sp., Bacillus cereus, Xanthomonas sp., Pseudomonas sp. They were distinguished from the OPB species recorded in a Chinese small shallow eutrophic lake whose sediment organic content was remarkably higher. Taken together, organic matter shaped the OPB community not only quantitatively but also qualitatively, which in concert facilitated the enzymatic hydrolysis of organic phosphorus in lake sediment.     

Morphospecies and genospecies of Microcystis during blooms in eutrophic Lake Taihu (China) in autumn

Microcystis colonies collected in a hypertrophic lake (Lake Taihu, China) in October and November 2012 were divided into five subsamples according to colony size (<75, 75–150, 150–300, 300–500, and >500 μm). All the subsamples collected in November were dominated with Microcystis ichthyoblabe and the percentages of M. ichthyoblabe exceeded 83%. The percentages of Microcystis aeruginosa of the subsamples in >500 μm class collected in October was 93.5%. For the sample collected in October, the percentage of M. ichthyoblabe was more than 58% in <75, 75–150, 150–300 μm classes. The 16S rDNA as well as some polysaccharide biosynthesis-related genes were analyzed to understand the phylogeny of Microcystis species. There was no variant site presented in each Microcystis subsample but a single nucleotide polymorphism (SNP) was found in 16S rDNA alignment tested using MSR1 in subsamples between the two months in the current study. Our results also showed that samples collected in two months can by divided into two parts by the phylogenetic analysis using two polysaccharide biosynthesis-related genes (espL and TagH). All the results suggested that 16S rDNA was valuable to identify seasonal succession of Microcystis genospecies and the diversity of Microcystis morphospecies would be explained by these polysaccharide biosynthesis-related genes.