Impact of nutrient enrichment in a waterchestnut ecosystem at Takahama-iri Bay of Lake Kasumigaura,Japan

The waterchestnut ecosystem of Lake Kasumigaura is at the climax stage of eutrophication. Organic debris in the ecosystem showed highly dynamic fluctuations throughout the year. This was chiefly attributed to high viable fractions of organic matter in the hypereutrophic water. The stability of steady-state equilibrium of organic debris was found to be maintained even in such a dynamic ecosystem, likely due to the precedence of heterotrophic processes over autotrophic processes. Using a mathematical model approximated by in situ data, the turnover time of organic solutes was analyzed to be between four and six months through these active heterotrophic processes.     

Impact of nutrient enrichment in a waterchestnut ecosystem at Takahama-Iri Bay of Lake Kasumigaura,Japan

The heaviest algal bloom that can be expected in an aquatic system was formed in a waterchestnut ecosystem in Lake Kasumigaura during the summer in 1978 when the water temperature was greater than 30°C, caused by the nutrient discharges from the River Koise and the River Sanno. The heavy bloom not only threatens the steady-state equilibrium of the eutrophic system of the Lake but also must accelerate the Lake transformation into a low moor by forming ooze on the lake bottom with the precipitation of a large amount of dead blue-green algae.     

Silicon budget of eutrophic Lake Kasumigaura, Japan

Purpose

Determining the dynamics of silicon in lakes, one of the essential nutrients for diatoms, is valuable for understanding aquatic environmental problems. The dissolved silicon (DSi) and biogenic silicon (BSi) budgets in Lake Kasumigaura, a shallow eutrophic lake in Japan, during the last three decades were assessed based on the analysis of dated sediment cores and a water quality database.

Materials and methods

Sediment cores (100?cm long) were taken at the center of Lake Kasumigaura in 2005, 2007, and 2009 and at two other sites in 2007. BSi contents of the dated sediments were determined by wet alkaline digestion. The net sedimentation rates of BSi were defined as the difference between the DSi load from inflowing rivers and the DSi and BSi loads from the outflow of the lake, calculated using DSi concentrations and diatom abundances in the lake from 1980 to 2007 and DSi concentrations of the inflowing rivers during 1994, 2007, and 2009. The gross sedimentation rates of BSi were estimated by multiplying BSi concentrations in lake water by the diatom sinking rate reported by previous studies.

Results and discussion

Budgetary calculations based on the database showed that 60?C70?% of DSi inputs from the inflowing rivers during the 27?years could ultimately be accumulated as diatom frustules in bottom sediments in the lake. The sediment analysis revealed that the amount of BSi accumulated in the lake from 1980 to 2007 was 2.0?C2.6?×?10¹¹?g, similar to the amount based on the database of 1.3?C2.4?×?10¹¹?g. Although the gross sedimentation rates of BSi likely increased, the net sedimentation rates of BSi decreased significantly from 6?C10?×?10⁹?g?year^?1 in the 1980s to 2?C6?×?10⁹?g?year^?1 in the 2000s, suggesting a fast recycling of BSi in recent years caused by an increase in sediment resuspension and regeneration.

Conclusions

The sediment core information and the water quality database can be used for calculating the long-term silicon budgets in Lake Kasumigaura. An increase in the DSi release rates was identified, which is consistent with recent sediment resuspension. Comparing the sediment core information with the database suggests the long-term dissolution of sediment BSi; however, analysis of the BSi content in sediment cores representing a much longer time period is needed to confirm this.     

Dynamics of dissolved oxygen in a hypereutrophic lake: Lake Kasumigaura,Japan

The dynamics of dissolved oxygen (DO) were studied during a typical wind condition for each season in Lake Kasumigaura, a hypereutrophic lake. Vertical and diel fluctuation of DO was extremely dynamic during the summer algal bloom in August. As the vertical transport of DO for the typical local-wind (1 to 2 m s^?1) was only one order of magnitude greater than for at the windless condition, the stability of oxygen conditions in the dysphotic zone could not be disturbed greatly by the wind stress.     

新疆艾比湖流域土地利用变化对生态系统服务价值的影响

在对流域可持续发展评估的研究中,生态系统服务价值的时空评估具有重要意义。以新疆艾比湖流域为研究区,基于1996-2016年的3期遥感影像和社会统计数据,对艾比湖流域土地利用和生态系统服务价值时空动态变化进行分析,并借鉴生态服务价值当量估算法定量探讨生态系统服务价值的变化特征,采用多元回归模型对流域土地利用和生态系统服务价值变化的驱动力进行分析。结果表明:1)1996-2016年,艾比湖流域耕地和建设用地面积变化最大,其占比分别从1996年的8.47%和0.42%,增加到2016年的15.28%和2.07%;林地、草地、湿地和水域的较少,但幅度较剧烈。2)近21a来,研究区生态系统服务价值总量呈持续减少的趋势,共减少了约85.863×108元,耕地、建设用地、盐碱地和沙地等土地利用类型的生态系统服务价值(ecosystem service value, ESV)值呈增加趋势;林地、草地、水域、湿地和未利用地等类型均呈减少趋势。3)空间上,21a间艾比湖流域ESV较高区面积逐渐减少,ESV较低区域面积逐渐增加,ESV中等区域呈现先减小后增大。4)回归分析表明影响艾比湖流域ESV变化的主要驱动因素是综合城镇化率、人口密度、气温和降水等指标,在未来的经济发展中,艾比湖流域要合理优化调整土地利用格局,保证生态系统的稳定-协调发展,实现经济-社会-生态的可持续发展。     

Impact of water percolation on nutrient leaching from an irrigated paddy field in Japan

Abstract. We examined the effect on soil nutrient status and sustainability of water percolation through an irrigated paddy field in Japan, to the depth of drainage (40 cm). The difference between amounts of nutrients leached by percolation and those supplied by irrigation indicated that 25–130 kg ha⁻¹ Ca, 8–24 kg ha⁻¹ Mg, from −1 to 9 kg ha⁻¹ K, and 8–17 kg ha⁻¹ Fe, respectively, were lost each year from the 0–40 cm soil layer during rice cultivation, when the supply from fertilization and rainfall and the loss in grain harvest were not accounted for. When the supply of K from rainfall and the loss in grain harvest were taken into account, a total K loss of about 10 kg ha⁻¹ was estimated. The electrical neutrality of inorganic ions in the percolating water was always maintained. From these results we estimate that the amounts of exchangeable Ca and Mg in the soil to a depth of 40 cm would decrease by 50% within 50–260 and 30–100 years, respectively, if similar management were continued without fertilization. The total amount of carbon dioxide (ΣCO₂) leached in percolating water during the period of rice cultivation was 120–325 kg C ha⁻¹, which corresponded to 0.47–0.94% of the soil organic carbon to 40 cm depth.     

Fine root decomposition,nutrient mobilization and fungal communities in a pine forest ecosystem

Despite its importance to energy flow and nutrient cycling the process of fine root decomposition has received comparatively little detailed research. Disruption of the fine root-soil interface during preparation of root litterbags for decomposition studies could affect decay rates and nutrient mobilization in part by altering the community of decay organisms. We compared rates of decomposition and nutrient release from fine roots of pine between litterbags and intact cores and characterized the fungal community in the decomposing roots. Fine root decomposition was about twice as fast overall for intact cores than litterbags, and rapid mobilization of N and P was observed for roots in cores whereas nutrients were immobilized in litterbags. Fungal communities characterized using 454 pyrosequencing were considerably different between decaying roots in intact cores and litterbags. Most interesting, taxa from ectomycorrhizal fungal orders such as Boletales, Thelephorales and Cantharellales appeared to be more common in decaying roots from cores than litterbags. Moreover, the rate of N and P mobilization from decaying fine roots was highly correlated with taxa from two orders of ectomycorrhizal fungi (Thelephorales, Cantharellales). Although we caution that DNA identified from the decaying roots cannot be conclusively ascribed to active fungi, the results provide tentative support for a significant role of ectomycorrhizal fungi in decomposition and nutrient mobilization from fine roots of pine.     

Mercury Speciation in the Water of Minamata Bay, Japan

The speciation of mercury (Hg) in Minamata Bay (Japan) was studied over a 2-year period (2006?C2008). Concentrations of dissolved total Hg, dissolved methylmercury (MeHg), particulate total Hg, and suspended solids were 0.43?±?0.14 ng/l (mean?±?standard deviation), 0.10?±?0.06 ng/l, 3.04?±?2.96 ng/l, and 5.94?±?2.10 mg/l, respectively. Correlations between concentrations of particulate total Hg and suspended solids at four depths (surface: 0 m; mid-depth: ?6 m, ?10 m; and bottom +1 m layer) were only significant in the bottom +1 m layer. The mean dissolved MeHg concentration and the ratio of dissolved MeHg to dissolved total Hg were considerably higher in summer compared to other seasons. The data suggest that bottom sediment was not the sole source of MeHg, and that MeHg may be produced in the water column by the conversion of divalent Hg eluted from resuspended bottom sediment. The correlation between seawater characteristics such as salinity, temperature, dissolved oxygen (DO), and dissolved MeHg concentration indicates that Hg methylation could be influenced by the heterotrophic activity of microorganisms in the seawater. In particular, inverse correlations were observed between DO, salinity, and MeHg concentration. However, dissolved MeHg concentrations did not correlate with seawater characteristics such as pH or chlorophyll-a.     

Heavy metal accumultations in a semi-enclosed hypereutrophic system: Lake Tefanuma,Japan

The abundance and distribution of Cd, Cu, Fe, Mn, and Zn in the water of Lake Teganuma, one of most hypereutrophic lakes in Japan, and from its two main inflow rivers were investigated. The heavy metal concentrations in Teganuma water were in the range of the world's ‘unpolluted’ lakes, although the Zn concentrations of inflow rivers were found to be clearly higher than those in the lake. Greater proportion of particulate heavy metals to dissolved in water of the lake than the two rivers shows the metal deposition process in the lake.     

Heavy metal accumulations in a semi-enclosed hypereutrophic system: Lake Teganuma,Japan

Heavy metal concentrations and other physical and chemical properties were studied so as to assess the heavy metal accumulation process in the sediments of a hypereutrophic lake, Lake Teganuma, Japan. The accumulations were most evident near the inflow inlets of two main inflow rivers in Kaminuma (the west part of Lake Teganuma) with the significant Zn accumulation. Except for Fe, the vertical distributions of heavy metals showed the highest concentrations in the surface 10 cm and decreased gradually with the sediment depth. The high concentrations in the upper layer was caused by an increase in the non-residual fractions. The large influx of heavy metal to Lake Teganuma seems to be due to the domestic effluents via the two rivers in last decades.     

日本北海道农村生态系统中N循环研究

This study of Mikasa City in 2001, which analyzed N flow between N production and N load in seven agricultural and settlement subsystems, i.e., paddy, onion, wheat, vegetable, dairy, chicken, and citizen subsystems, aimed to compare N flow in each subsystem, to determine the main sources of the N load, and to evaluate the influence of agricultural production and food consumption on N cycling in a rural area. The results showed that in Mikasa city, 38.5% of the N load came from point sources and the remainder from non-point sources with intensive vegetable farming imparting a serious N load. Because of the internal N cycling in the dairy subsystem, chemical fertilizer application was reduced by 70.2%, and 23.72 Mg manure N was recycled to the field; therefore, the N utilization efficiency was raised from 18.1% to 35.1%. If all the manure N in the chicken subsystem was recycled, chemical fertilizer application would be reduced by 8.1% from the present level, and the point sources of N pollution would be reduced by 20.8%.     

Natural acidification of lakes and rivers in Japan: The ecosystem of Lake Usoriko (ph 3.4–3.8)

Most of the acid lakes and rivers in Japan have been influenced by acid waters of volcanic origin. Acidophilic and acidotolerant organisms are observed in these natural acid lakes and rivers, each of which has its own ecosystem and history. Lake Usoriko (pH 3.4–3.8) is a lake which.has been acidified by strongly acid water containing sulfuric acid and hydrochloric acid. The ecosystem of Lake Usoriko consists of aquatic vascular plants, aquatic bryophytes (Drepanocladus fluitans, etc.), algae, fish (Tribolodon hakonensis), insects, Zooplankton, fungi and bacteria. The paleosediment distributed along Lake Usoriko's northern shore is partly silicified and it contains fossils of a moss (Drepanocladus fluitans) and diatoms such as Pinnularia braunii var. amphicephala which are also distributed in the present lake. ¹⁴C dating of the specimens in the paleosediment, shoots of D. fluitans and the wood and cones of Picea glehnii gave values in the range 11500–34000y B.P. This record shows how long Lake Usoriko has been an acid lake.     

CO2浓度升高、氮和水分对春小麦养分吸收和土壤养分的效应

研究了 2种CO2浓度水平 ,2种土壤水分处理和 5种N肥施用水平对春小麦 (TriticumaestivumL cv DingxiNo. 8654)养分吸收和土壤速效养分的影响。结果表明 ,高CO2浓度 (700 molmol-1)明显降低春小麦对氮(N)的吸收 ,低N时降低更为明显 ,但对磷 (P)、钾 (K)吸收的影响不明显。小麦对N、P、K吸收 ,干旱处理明显比湿润处理低。CO2浓度增高对土壤速效N的影响与土壤水分状况有关。湿润处理 ,CO2浓度增加的处理速效N量比当前CO2浓度的处理低 ;而干旱处理 ,施N 50、100、150mgkg-1时 ,速效N则较高。高CO2 浓度对土壤速效P、K量的影响不明显 ,而低N和水分不足 ,土壤速效P、K量较高     

The co-regulation of nitrate and temperature on denitrification at the sediment-water interface in the algae-dominated ecosystem of Lake Taihu,China

Journal of Soils and Sediments - Sediment denitrification is a dominant mechanism for nitrogen removal and can help to minimize lake eutrophication. However, the spatio-temporal variability of...     

土壤侵蚀过程中的养分富集率研究综述

伴随土壤流失过程的养分流失普遍存在着富集现象并可用富集率来表示。富集率是进行非点源污染评价与预报的重要参数。国内外氮、磷富集率大小和计算方法的研究成果表明：氮富集率变化于0.99～8.17之间,主要集中在1.11～2.99之间,磷富集率变化于0.84～16.12之间,主要集中在1.26～7.17之间;氮磷富集率的估算方法可以分为6种,可分别用土壤侵蚀量、含沙量、土壤质地、土壤比表面积、泥沙输移比和某种组合来计算。文中系统比较和分析了这些方法,对养分富集率的选用和研究有参考意义。     

Effects of litter addition and warming on soil carbon, nutrient pools and microbial communities in a subarctic heath ecosystem

Climatic warming leads to the expansion of deciduous shrubs and trees in the Arctic. This leads to higher leaf litter inputs, which together with warming may alter the rate of carbon and nutrient cycling in the arctic ecosystems. We assessed effects of factorial warming and additional litter on the soil ecosystem of a subarctic heath in a 7-year-long field experiment. Fine root biomass, dissolved organic carbon (DOC) and total C concentration increased in response to warming, which probably was a result of the increased vegetation cover. Litter addition increased the concentration of inorganic P in the uppermost 5 cm soil, while decreasing the pool of total P per unit area of the organic profile and having no significant effects on N concentrations or pools. Microbial biomass C and N were unaffected by the treatments, while the microbial biomass P increased significantly with litter addition. Soil ergosterol concentration was also slightly increased by the added litter in the uppermost soil, although not statistically significantly. According to a principal component analysis of the phospholipid fatty acid profiles, litter addition differed from the other treatments by increasing the relative proportion of biomarkers for Gram-positive bacteria. The combined warming plus litter addition treatment decreased the soil water content in the uppermost 5 cm soil, which was a likely reason for many interactions between the effects of warming and litter addition. The soil organic matter quality of the combined treatment was also clearly different from the control based on a near-infrared reflectance (NIR) spectroscopic analysis, implying that the treatment altered the composition of soil organic matter. However, it appears that the biological processes and the microbial community composition responded more to the soil and litter moisture conditions than to the change in the quality of the organic matter.     

Effectiveness of reducing external nutrient load entering a eutrophicated shallow lake ecosystem in the Naardermeer nature reserve, The Netherlands

This paper describes successes and complications in eutrophication abatement in the Naardermeer nature reserve, The Netherlands. Restoration of this lake started in 1985. The main measure was the reduction of external nutrient load by the supply of phosphate-free water. Water quality and aquatic vegetation were monitored and the usefulness of a modelling approach in designation of management programs was investigated. The monitoring showed that for the first 4 years, recovery was retarded, possibly because of phosphorus release from the lake-bed sediments. After 10 years, turbidity was reduced and characteristic vegetation with Najas marina and Characeae species had re-established in large parts of the lake. Due to spatial heterogeneity it appeared necessary to dredge the lake-bed sediments locally. The model predicted most changes in aquatic vegetation correctly, indicating its predictive value. However, to predict restoration perspectives for rare species, expert judgement still remains necessary. Suggestions are made for selection of successful management measures depending on the conditions of lake ecosystems.     

营养液动态液位法的原理及其增氧效果

经过对国内外水培技术中各自独具特色的增氧技术和方法的总结和分析，提出了营养液深液流栽培的动态液位增氧法(DSS)。DSS利用了滴液法、液流法、露根法、湿气根法等几方面增氧的原理和方法，在由水泵向栽培槽中供给营养液时，在回液套管的作用下，营养液向栽培槽底面流动，这种流动方式，有利于向植株根系更好地供应养分和氧气；在水泵停止工作时，随着液面的不断下降，植株的上层根系便暴露在空气中，可以充分进行氧气的吸收，以弥补营养液中氧含量的亏缺。     

Bioaccumulation of PCDD/Fs and Co-PCBs in Lower-Trophic-Level Organisms in Sendai Bay,Japan

In Sendai Bay, Japan, the total PCDD, PCDF, and Co-PCB (dioxins) concentrations in phytoplankton were equivalent to 150, 12, and 51 pg/g wet weight (ww), respectively. The average concentrations in seaweed were 3, 0.095, and 2.1 pg/g ww, respectively. The total concentrations in phytoplankton were much higher than those in seaweed, even though both groups are algae. The concentrations in zooplankton were 11, 1.1, and 110 pg/g ww, respectively. The total PCDD/F concentrations in zooplankton (primary consumers and lower-trophic-level invertebrates) were lower than in phytoplankton (primary producers), but the total Co-PCB concentration in zooplankton was higher than that in phytoplankton. The concentrations in mysids (secondary consumers and higher-trophic-level invertebrates) were 190, 18, and 290 pg/g ww, respectively. The average concentrations in shrimp (secondary consumers and higher-trophic-level invertebrates) were 120, 17, and 410 pg/g ww, respectively. The concentrations in higher-tropic-level invertebrates were higher than those in lower-trophic-level invertebrates. The average concentrations in sand lance were 4.5, 1.7, and 550 pg/g ww, respectively. The total PCDD concentration in sand lance was lower than that in zooplankton (prey of sand lance), but the total Co-PCB concentration in sand lance was higher than that in zooplankton. The bioaccumulation of PCDD congeners in sand lance differed from that of Co-PCB congeners. The bioaccumulation of PCDD/Fs from lower- to higher-trophic-level invertebrates through the food web differed from that from lower-trophic-level invertebrates to fish.