Nutrient budgets in the Saigon–Dongnai River basin: Past to future inputs from the developing Ho Chi Minh megacity (Vietnam)

Ho Chi Minh City (HCMC, Vietnam) is one of the fastest growing megacities in the world. In this paper, we attempt to analyse the dynamics of nutrients, suspended sediments, and water discharges in its aquatic systems today and in the future. The work is based on nine sampling sites along the Saigon River and one on the Dongnai River to identify the reference water status upstream from the urban area and the increase in fluxes that occur within the city and its surroundings. For the first time, the calculated fluxes allow drawing up sediment and nutrient budgets at the basin scale and the quantification of total nutrient loading to the estuarine and coastal zones (2012–2016 period). Based on both national Vietnamese and supplementary monitoring programs, we estimated the water, total suspended sediment, and nutrients (Total N, Total P, and dissolved silica: DSi) fluxes at 137 m³ year^?1, 3,292 × 10³ tonSS year^?1, 5,323 tonN year^?1, 450 tonP year^?1, and 2,734 tonSi year^?1 for the Saigon River and 1,693 m³ year^?1, 1,175 × 10³ tonSS year^?1, 31,030 tonN year^?1, 1,653 tonP year^?1, and 31,138 tonSi year^?1 for the Dongnai River, respectively. Nutrient fluxes provide an indicator of coastal eutrophication potential (indicator of coastal eutrophication potential), using nutrient stoichiometry ratios. Despite an excess of nitrogen and phosphorus over silica, estuarine waters downstream of the megacity are not heavily impacted by HCMC. Finally, we analysed scenarios of future trends (2025–2050) for the nutrient inputs on the basis of expected population growth in HCMC and improvement of wastewater treatment capacity. We observed that without the construction of a large number of additional wastewater treatment plants, the eutrophication problem is likely to worsen. The results are discussed in the context of the wastewater management policy.     

Distribution and geochemical processes of boron in the multimedia of Lake Qinghai,China

Lake Qinghai on the Qinghai-Tibet plateau is the largest lake in China. This study investigated the concentration and geochemical processes of boron (B) in lake water, lake sediment and river samples collected from Lake Qinghai and the Buha River. In addition, lake sediment pore water samples were analyzed. The concentrations of B and major ions, including K⁺, Na⁺, Ca²⁺, Mg²⁺, Cl^? and SO₄^2?, were analyzed in all the water samples. The average concentration of B was 0.07?mg?L^?1, 6.37?mg?L^?1, 12.79) mg?L^?1 and 59.42?mg?kg^?1 for river water, lake water, pore water, and sediment, respectively. There were significant (p?<?0.05) and positive (r?=?0.70) relationships between the B concentrations in bottom water of the lake and in lake sediment, indicating that B diffusion from the sediment plays an important role in the concentration of B in bottom lake water. The differences in B concentrations and B/major ion molar ratios of the river water, lake water, and pore water indicated the following geochemical processes: 1) B is enriched in the lake water through evaporative concentration; 2) B is removed from the lake water through mineral precipitation as well as sorption onto colloids; 3) Solid-phase B in sediments was released through dissolution driven by organic matter mineralization. B/Cl and Na/Cl molar ratios alone are not enough to identify the sources of B in the water of inland closed-basin saline lakes because of these processes.     

Recruitment of Heliozoa, rhizopods and rotifers from the sediments of an extremely acidic lake during spring and early summer

The goal of this study was to investigate the recruitment of zooplankton from the littoral sediment of Lake 111, an acidic lake in north‐east Germany, in April (spring) and June (early summer), and its role in coupling the benthos and the pelagic. Maximum heliozoan and rhizopod recruitment occurred in early summer from sediment cores incubated at ambient water temperatures (20°C). Conversely, recruitment of the rotifer Cephalodella sp. was highest in spring at ambient spring temperatures of 12°C. A combination of passive and active recruitment processes is likely responsible. The seasonal abiotic and biotic sediment characteristics were relatively constant and therefore not likely responsible for the observed temporal recruitment pattern. The sediment water and carbon content ranged from 20 to 50% (mean = 29 ± 6% standard deviation) and 2–12% (mean = 5 ± 2% standard deviation), respectively. Similarly, there was little variation in the chlorophyll‐a (mean = 0.2 ± 0.2 µg Chl‐a g^?1 dry weight ≡ 6.1 ± 3.9 mg Chl‐a m^?2). The in situ sediment bacterial density (0.82 × 10⁹ ± 0.26 × 10⁹ g^?1 dry weight ≡ 1.01 × 10⁹ ± 0.34 × 10⁹ cells cm^?3) was high. In contrast, the abundance of zoobenthos and their resting stages was low (< 25 individuals cm^?3, and mean of 90 ± 75 cysts cm^?3, respectively), with no temporal pattern being observed. Temperature was the only abiotic factor influencing recruitment. This study suggests that, even in relatively young, chemically extreme lakes, the benthos can play an important role in whole lake microbial processes and zooplankton community composition. Such benthic repositories of resting stages potentially provide protection against adverse environmental changes.     

Mass Exchange Between Hamilton Harbour and Lake Ontario

The mass exchange between Hamilton Harbour and Lake Ontario waters through the Burlington Canal is important for estimating the dissolved oxygen budget of the harbour. Lake-harbour exchange is caused by either the oscillatory flow in the canal during isothermal conditions or the densimetric flow during thermal stratification. During the study period (September 1975), the canal water was found to be quasi-isothermal; consequently oscillatory flow existed. A computational method was developed to estimate the exchange based on excursion distance travelled for each limnological episode, and the final flow in each direction was checked with dissolved solids budget. An average of 2.04 × 10⁶ m³.d^?1 (24 m³.s^?l) of harbour water is estimated to flow into the lake, while 0.73 × 10⁶ m³.d^?1 (8 m³.s^?1) of lake water flowed toward the harbour during September 1975. This accounts for the total and net daily exchange of 0.98% and 0.48% of harbour volume, with net exchange being toward the lake. The total and net exchanges were respectively 8 and 4 times the natural drainage during the study period. On a monthly average, more water leaves than enters the harbour. The lake-harbour exchange is considered important for maintaining and even improving the existing harbour water quality. The harbour dilution factor was estimated as 0.0019 per day for the present study.     

Microbial processes at the land–water interface,and cross‐domain causal relationships,as influenced by atmospheric deposition of pollutants in three freshwater lakes in India

The effects of long‐term atmospheric deposition of pollutant elements on the trans‐surface causative relationships at three lake sites having different catchment characteristics were investigated in this study. The selected determinants included lake productivity, bottom sediment quality, and a suite of microbial variables (microbial biomass (C_mic); basal respiration; substrate‐induced respiration; bacterial:fungal ratio; metabolic quotient; and alkaline phosphatase and FDAase activities) measured at the land–water interface, in relation to atmospheric deposition of phosphate; nitrate; ammonium; sulphate; calcium; and magnesium. The results indicated significant between‐site differences (P < 0.001) in the atmospheric deposition of phosphate (0.21–1.96 kg.h^?1.year^?1); nitrate (2.77–28.05 kg.h^?1.year^?1); ammonium (0.58–11.60 kg.h^?1.year^?1); sulphate (5.64–32.15 kg.h^?1.year^?1); calcium (4.50–30.00 kg.h^?1.year^?1); and magnesium (1.50–12.15 kg.h^?1.year^?1), as well as a consistently increasing input of these ions across time. The catchment vegetation had important effects on microbial variables that, in turn, affected lake productivity. Interfaces of woodland lake were found to be rich in phenolics, supporting low C_mic and activities. Except for alkaline phosphatase, which declined over time, atmospheric deposition of pollutant elements increased the C_mic and activities at the land–water interface. The time lag correlation analysis indicated the C_mic and lake productivity relationships were significantly altered by atmospherically driven nitrogen and phosphorus inputs, with a time lag of 2–3 years. Despite being supportive, aerial nutrient inputs appeared to have a destabilizing effect on both, microbial biomass and lake productivity variables. These observations indicate that if present atmospheric deposition trends of pollutant elements continue, it will modify the cross‐domain causative relationships of inland lentic systems over the long term. These study results are relevant for the formulation of strategies for managing freshwater tropical lakes.     

Approach for Estimating Available Consumable Water for Human Activities in a River Basin

Water is vital for economic development and environmental sustainability in arid and semi-arid basins. Management of water resource requires good understanding of available water for human consumption. Evapotranspiration (ET) is an important component of the hydrological cycle and represents the amount of water lost to the atmosphere in a basin. This study proposes a new approach to estimate available consumable water for human activities (ACW) in a basin based on precipitation, natural ET, and uncontrollable outflow, thus capping water use for human consumption in a basin. The ACW is illustrated for the Hai Basin in North China, where the average ACW from 2001 to 2012 for the entire basin is estimated at 31.97?×?10⁹m³ yr.^?1, varying between 18.61?×?10⁹m³yr^?1 in 2002 and 42.60?×?10⁹m³yr^?1 in 2003. A water balance analysis for the basin indicates that the aquifer water depletion in Hai Basin for 2001–2012 is 5.23?×?10⁹m³yr^?1. Compared to existing water resources assessment, ACW provides an easier approach to water management planning as no hydrological data are required, only data on precipitation and ET, supported by landcover data.     

Limnological characteristics and trophic state of Paso de las Piedras Reservoir: An inland reservoir in Argentina

The current trophic status of Paso de las Piedras Reservoir was evaluated by analysing different physicochemical, biological and environmental variables, in relation to its water quality, and application of two different classification criteria. Water quality sampling was conducted at four sampling sites from June 2004 to June 2005. During this study, 183 phytoplankton taxa were identified. The phytoplankton abundance exhibited a maximum of 368.037 × 10³ cells.mL^?1 in February 2005, and at least 1.133 × 10³ cells.mL^?1 in October 2004. An almost exclusive dominance of Cyanobacteria was observed between December 2004 and May 2005, the product of a large relative abundance of Anabaena circinalis and Microcystis natans which, together with other companions, were the reason for an algal bloom characterized by an average density of 133.05 × 10³ cells.mL^?1, and an average chlorophyll concentration of 28.7 mg.m^?3. These study results indicate that the seasonal variations of physical, chemical and biological parameters in the waters of this reservoir were essentially a consequence of environmental and hydrological conditions in the dam area. In contrast, the spatial variations inside the lake were the result of the characteristics of the water inflow provided by its two main tributaries. The N:P ratio suggests neither nutrient is a limiting factor for maximum algal biomass in the lake, indicating that variations in the phytoplankton community structure, and development of phytoplankton blooms, would be more constrained by environmental and hydrological conditions than nutrient competition. The high concentration of measured nutrients could be attributed to the concurrence of various non‐point sources. The phytoplankton species richness was high, exhibiting values even higher than those mentioned in previous studies. Considering the two trophic classification systems, and based on total phosphorus data, the reservoir is classified within the hypertrophic category. In contrast, considering only the chlorophyll and turbidity data, the lake would be classified within the eutrophic category.     

若尔盖高原径流量变化与储水量计算

若尔盖高原的降水量微弱减少与蒸发量持续上升,使若尔盖高原径流量与储水量逐年降低,直接减少了若尔盖高原的湿地面积和对黄河上游径流量的补给。基于红原、若尔盖和玛曲站的气象数据和7个水文站的径流量数据(1981-2011年),并对数据序列进行插补与计算,获得若尔盖高原的径流量变化与气候因子的响应关系,进而计算储水量变化。计算结果表明:若尔盖高原向黄河年均补水(67. 08±14. 90)×108m3,并以0. 48×108m3/a速率持续减少。降水量每减少1 mm将导致黑河与白河的年径流量分别减少0. 02×108和0. 05×108m3。蒸发量每增加1 mm将导致黑河与白河的年径流量分别减少0. 12×108和0. 27×108m3。1981-2011年若尔盖高原的年均储水量为(59. 30±18. 69)×108m3,其年均递减速率为0. 49×108m3/a。本研究有助于认识若尔盖高原对于黄河上游水资源保障的重要性。     

Eutrophication of lakes in urbanized areas: The case of Yaounde Municipal Lake in Cameroon, Central Africa

A 1 year qualitative and quantitative evaluation of phytoplankton and chlorophyll‐a, as well as some physicochemical parameters, was recorded in a shallow tropical lake in Cameroon: the Yaounde Municipal Lake. Physicochemical measurements also were regularly made in its main tributary (Mingoa Stream). These analyses aimed to assess the lake's trophic status and to propose measures for controlling its degradation process. The Secchi disk transparency was low and rarely exceeded 100 cm. Conductivity was higher near the lake bottom. The oxygen deficiency, and sometimes anoxia, recorded from a 2.5 m depth leads to high quantities of ammonium‐nitrogen. The total phosphorus concentrations varied from 80–2290 µg P L^?1 and the total Kjeldhal nitrogen concentrations fluctuated between 3 and 15 mg  L^?1. Upstream to the lake, in the Mingoa Stream, total phosphorus concentrations ranged from 0.6–3.8 mg P L^?1 and total Kjeldhal nitrogen concentrations ranged from 10–22 mg  L^?1. There are up to 102 phytoplankton‐specific taxa, with Euglenophyta and Chlorophyta particularly more diversified. The phytoplankton biomass and chlorophyll‐a concentrations reached 225 µg mL^?1 and 566 mg m^?3, respectively. The analyses pointed out the allogenic nature of the functioning of this ecosystem as a result of bad waste management in the surrounding landscape. Urgent actions need to be undertaken in order to rehabilitate this lake, which rapidly shifted to a hypertrophic status.     

宁东能源化工基地水资源优化配置研究

宁东能源化工基地水资源极为贫乏,合理配置基地内的水资源对能源基地的发展极其重要。论文采用线性规划模型对宁东能源化工基地的联合供水方案进行了优化研究,提出了地表水和地下水联合供水方案,确定了供水方案中地下水的实际配额和供水路线,得到下述结论:陶乐傍河水源地可向平罗精细化工基地供水0.065×10~8m~3/a;骆驼井应急水源地向横城和鸳鸯湖工矿区供水0.019×10~8m~3/a;吴忠平原2号和3号备选水源地向灵武工矿区供水0.089×10~8m~3/a和0.067×10~8m~3/a;大泉地区的1号水源地向南部的马家滩和积家井工矿区供水0.054×10~8m~3/a。按地下水总供水量0.294×10~8m~3/a和最佳供水路线联合配置地下水,地表水配额只需供水3.136×10~8m~3/a,既能满足宁东能源化工基地2020年规划对水资源需求,又可实现社会经济和环境效益的最大化。     

Using 223Ra and 224Ra to estimate discharges of groundwater and associated nutrients into southeast of Qinghai Lake,in Qinghai–Tibet Plateau

With its important geographical location and status as the largest saltwater body in China, Qinghai Lake plays a vital role in the ecological environment of the northeastern part of the Qinghai-Tibet Plateau. Due to climate change and the subsequent adjustment of Qinghai Lake’s tourism policy, it is necessary to understand groundwater discharges in southeast of Qinghai lake both for ecological protection and risk prevention. This study used radium isotopes ²²³Ra and ²²⁴Ra to trace groundwater discharges and nutrients carried into the lake. The spatial characteristics of Ra isotopes with greater activity in the upper and bottom layers in the lake indicated that they were influenced by inputs of shallow groundwater and diffusion from sediments. The average ²²⁴Ra diffusion flux of the sediments in the Lake was 33.54 dpm m^?2 d^?1. Based on the ²²⁴Ra mass balance model, the discharge flux of shallow groundwater in this region was estimated to be 3.49 × 10⁶ ～ 3.68 × 10⁶ m³ d^?1. The PO₄^3? and SiO₂ fluxes carried into the southeastern of the lake by groundwater were 1.78 × 10¹¹ ～ 1.88 × 10¹¹ mg/y and 2.22 × 10¹² ～ 2.34 × 10¹² mg/y, respectively. It is thus essential to monitor shallow groundwater discharge into Qinghai Lake for the protection of the water environment and prevention of potential ecological risks.     

引调水改善玄武湖水质的水量优化方法

针对2012—2017年玄武湖增加生态补水量并不能让湖泊水质转好的问题,通过实测水量水质数据拟合、零维模型的推导和二维水环境数学模拟预测的方法研究玄武湖水质优化方法及应用。实测拟合发现湖区水质随着补水量的增加呈现先转好再变差的趋势。通过零维模型的公式推导及量化参数的方法,得出玄武湖污染物降解量与补水量呈负一次函数关系,玄武湖水质与补水量呈二次方关系,并得出丰水期优化补水量为20万t/d,枯水期优化补水量为15万t/d。运用水环境数学模型进行模拟预测,在枯水期近期削减现状入湖污水的40%水质最优时的补水量为12万t/d;在丰水期,近期削减现状入湖污水的40%时的水质最优补水量为18万t/d,远期削减现状入湖污水80%时的水质最优补水量为15万t/d。     

湖泊水体营养状态对沉积物好氧氨氧化菌异质性的影响

采用荧光定量PCR(real-time fluorescence quantitative polymerase chain reaction)和末端限制性片段长度多态性(terminal restriction fragment length polymorphism,T-RFLP)方法,对江苏7个湖泊沉积物中好氧氨氧化微生物进行分析,研究湖泊水体营养状态对沉积物好氧氨氧化微生物空间异质性的影响。综合营养指数分析结果表明,23个采样点中,61%的湖区为中营养状态,39%的湖区为轻度富营养状态。荧光定量PCR分析结果显示,每克底泥中氨氧化古菌(ammonia-oxidizing archaea,AOA)和氨氧化细菌(ammonia-oxidizing bacteria,AOB)amo A基因拷贝数虽然分别从中营养湖泊的3.91×10~6和3.82×10~6上升到轻度富营养湖泊的1.30×107和6.07×10~6,但湖泊水体营养状态并未显著影响沉积物AOA和AOB的丰度。T-RFLP分析结果表明,湖泊水体营养状态对AOA和AOB的优势种属及群落多样性也未产生显著影响。典范对应分析结果表明,湖泊水体营养盐浓度能解释AOA的群落结构差异的56.3%,而仅能解释27.2%的AOB的群落结构差异,TN和NO-3-N浓度是影响沉积物AOA分布异质性的主要环境因子,湖泊水体营养盐浓度比综合营养状态指数更能影响AOA和AOB的群落结构组成。     

The dying Dead Sea: The microbiology of an increasingly extreme environment

The Dead Sea, on the border between Israel and Jordan, currently contains around 348 g salt L^?1. Divalent cations (Mg²⁺, Ca²⁺) dominate over monovalent cations (Na⁺, K⁺), while Cl^? and Br^? are the main anions. The pH of the Sea is about 6. The water balance of the lake is negative, having dropped over 1 m year^?1 over the past decade. The water is supersaturated with Na⁺, with massive quantities of halite precipitating to the bottom of the lake. Biological monitoring since 1980 has indicated that blooms of the unicellular green alga Dunaliella and halophilic Archaea of the family Halobacteriaceae only develop following significant dilution of the upper water layers in the lake after very rainy winters. Such events occurred in 1980, and even more dramatically in 1992, when up to 3.5 × 10⁷ Archaea mL^?1 in the diluted upper 5–10 m of the water column coloured the lake red. Species isolated from the lake include Haloferax volcanii, Haloarcula marismortui, Halorubrum sodomense and Halobaculum gomorrense. Dunaliella was no longer observed in the lake after 1996, with prokaryote numbers remaining low. To characterize the residual microbial community in the lake, biomass was collected in February 2007 for environmental genomic analyses. The results were compared with the metagenome of microbial bloom material collected in 1992. The 16S rRNA archaeal phylotypes recovered from the 2007 sample were diverse, with phylotypes distantly related to the genera Halorhabdus, Haloplanus, Natronomonas and others. Halorhabdus sp. also was recovered in culture. The 1992 bloom sample was very homogeneous, however, with a single cluster remotely related to Halobacterium salinarum. These results illustrate that the microbial communities are dynamic, even in one of the most extreme environments on Earth, and exhibit strong shifts in species composition as conditions for life become increasingly adverse.     

Sediment greenhouse gases (methane and carbon dioxide) in the Lobo-Broa Reservoir, São Paulo State, Brazil: Concentrations and diffuse emission fluxes for carbon budget considerations

Carbon gases (methane, CH₄, and carbon dioxide, CO₂) were measured for the first time in sediments of the Lobo‐Broa Reservoir, near São Carlos in São Paulo State, Brazil. It is believed these are the first measurements of this kind in any of the many reservoirs located in Brazil. Even though the Lobo‐Broa Reservoir is classified as oligotrophic, the sediment gas concentrations were exceedingly high, ranging from 0.4–3 mmol L^?1 for CH₄ and 1–9 mmol L^?1 for CO₂. Both gases exceeded their in situ gas saturation values at these shallow water depths (7 m in central basin; 11 m at dam), resulting in numerous sediment bubbles. Organic matter was highly concentrated in the reservoir sediments, averaging 25.5% loss on ignition (LOI) (dam) to 26.9% LOI (central basin) for the 0–12 cm depth interval, with values as high as 29–30% LOI (12% organic carbon) in the surface 0–5 mm layer. The theoretical flux of dissolved pore water carbon gases to the sediment–water interface (SWI) averaged 3.4 mmol L^?1 m^?2 day^?1 CH₄ and 7.3 mmol L^?1 m^?2 day^?1 CO₂ for the surface 0–10 mm. From gas emission measurements at the water surface, it was calculated that 90% of CH₄ is consumed either at the SWI or in the water column, resulting in a loss of 0.31 mmol L^?1 m^?2 day^?1 of CH₄ to the atmosphere. However, only 20% of the total CO₂ gas transported across the water–atmosphere interface (36.3 mmol L^?1 m^?2 day^?1, or 1600 mg CO₂ m^?2 day^?1) was produced in the sediments. The remaining 80% of CO₂ probably comes from other carbon sources. With CH₄ oxidation in the aerobic water column, close to 30% of the carbon gas flux to the atmosphere could be accounted for by gas production of CO₂ and CH₄ in the sediments and their diffuse transport to the water column.     

Resolving Trans-jurisdictional Water Conflicts by the Nash Bargaining Method: A Case Study in Zhangweinan Canal Basin in North China

Trans-jurisdictional conflict in both water quantity and quality is a general concern in large river basins. In this paper, the relative utility function combined with the asymmetric Nash bargaining method was established to analyze the trans-jurisdictional conflict between water quantity and water quality in the Zhangweinan Canal Basin in China. The basin was divided into four conflict stakeholders, namely, Shanxi, Hebei, Henan, and Shandong Provinces, based on administrative unit. The water usage and pollutant discharge scheme for multiple stakeholders was optimized using the established model to satisfy the environmental flow and water quality objectives at the identified conflict sections. The results indicated that the total water consumption was reduced from 4.38?×?10⁹?m³ in 2007 to 1.97?×?10⁹?m³, and that the allowable COD and NH₃-N discharged into the river was less than 3.8?×?10⁴?t and 4.3?×?10³?t, respectively. About 81.1 % of COD and 76.1 % of NH₃-N should be further reduced compared with the values in 2007.     

面向供水对象转型的引大入秦工程水资源优化配置研究

引大入秦工程（以下简称引大工程）建成初期主要以秦王川农业供水为主,但随着兰州新区的建设发展,其供水对象开始向城市生活用水和工业用水转型,如何实现有限水资源的合理配置是目前研究的重点问题。基于此,依据引大工程供水区（以下简称引大供水区）可持续发展要求,构建以实现经济、社会、生态效益最大化为目标函数,可供水量、输水能力、用户需水量、排水系统排水量与变量非负为约束条件的多目标水资源优化配置模型,使用遗传算法进行求解。结果表明：2025年引大供水区不同用水部门配水量（保证率P=50%、P=75%）分别为生活用水8 323.85×10⁴、8 322.49×10⁴ m³,农业用水15 001.95×10⁴、15 631.53×10⁴ m³,工业用水11 111.00×10⁴、11 100.00×10⁴ m³,生态用水946.88×10⁴、947.02×10⁴ m³,各部门总配水量与优化前供水量4.23×10⁸ m³相比,达到供需平衡;2030年引大供水区不同用水部门配水量（保证率P=50%、P=75%）分别为生活用水12 650.51×10⁴、12 666.53×10⁴ m³,农业用水16 397.77×10⁴、17 019.70×10⁴ m³,工业用水20 498.00×10⁴、20 508.00×10⁴ m³,生态用水948.00×10⁴、948.88×10⁴ m³,不同保证率下各部门总体缺水率分别为12.27%、13.38%。2025—2030年引大供水区的非农业用水结构将大幅提升,农业灌溉用水量降低。研究结果可为引大供水区优化水资源配置决策提供参考依据。     

灞河流域气候因子对水沙变化的影响

利用灞河流域蓝田气象站和马渡王水文站1960—2012年的气象、水文实测资料,分析灞河流域气候及水沙变化规律,同时运用相关性分析、灰色关联分析、多元线性回归模型等多种方法探讨了该流域水沙变化与气候变化的关系。结果表明:灞河流域降雨量、蒸发量、径流量和输沙量皆呈显著下降趋势,而气温呈上升趋势;降雨量与水沙都有重要的相关关系,1960—1990年影响径流量的气候因子敏感度由大至小依次为降雨量、气温、蒸发量,而1991—2012年则为降雨量、蒸发量、气温,当气温和蒸发量不变时,降雨量每增加1 mm,两阶段的年径流量分别增加0.14亿m3和0.08亿m3;1960—2012年影响输沙量的气候因子敏感度由大至小依次为降雨量、气温、蒸发量,当气温和蒸发量不变时,降雨量每增加1 mm,年输沙量增加0.668万t。     

Sediment phosphorus characteristics in the clearwater state of Lake Mogan, Turkey

This study examined the vertical distributions of total phosphorus (TP) and phosphorus fractions, and the iron and organic matter, in the littoral sediment in a macrophyte‐dominated, clearwater state in Lake Mogan between September 2005 and August 2006. Benthic macroinvertebrates and total bacteria in the sediment also were determined. No clear seasonal or depth‐related (0–20 cm) patterns were found in sediment concentrations for the measured parameters. The phosphorus release was quantitatively very low, and a negative phosphorus release (–0.132 µg m^?2 day^?1) was measured during the summer months. The TP concentrations of the sediment samples ranged between 675.00 and 1463.80 µg g^?1 dry weight (DW), and the trophic level of the lake was eutrophic. On average, inorganic phosphorus fractions comprised the largest fraction (63%), while organic‐bound phosphorus (Org ≈ P) constituted 37% of the TP in Lake Mogan. The most important phosphorus‐immobilizing factors are high iron content (14 200–47 750 µg g^?1 DW), the sediment's clay content (47.80–51.80%), and an abundance of macrophytes at the sampling station. The low abundance of benthic macroinvertebrates (510–850 individuals m^?2), which depend on sediments with high iron and low organic matter (5.42–13.30%), played a role in the sediment phosphorus retention. Although bacterial abundance in the surficial sediment appeared to be positively correlated to temperature, the overlying water did not experience anoxic conditions, supporting a state in which bacteria were able to retain phosphorus in their cell structures. Long‐term changes in the sediments of Lake Mogan must be monitored lake. In order to optimize the management of the lake, and to determine the longevity of a clearwater state following management measures and continued external phosphorus loading, long‐term changes in the sediments of Lake Morgan must be monitored.     

Growth and population parameters of Nile tilapia,Oreochromis niloticus (L.) in the open waters of Lake Victoria,Kenya

The Nile tilapia (Oreochromis niloticus) was introduced into Lake Victoria in the early 1950s and 1960s and has since become the dominant tilapiine in the lake. This study investigated the growth and population parameters of O. niloticus in Lake Victoria on the basis of length–frequency data collected during the period June 2014 and June 2015. The asymptotic length (L_∞) had a mean (±SE) value of 46.24 ± 0.04 cm TL, growth curvature (K) of 0.69 ± 0.25 year^?1, total mortality (Z) of 2.18 ± 0.80 year^?1, a natural mortality (M) of 1.14 ± 0.28 year^?1, a fishing mortality (F) of 1.05 ± 0.53 year^?1, an exploitation rate (E) of 0.46 ± 0.08, a growth performance index (?) of 3.14 ± 0.17 and a length at first capture (L_C50) of 20.31 ± 0.40 cm TL. Comparing the results of this study with previous studies indicates the parameters K, Z and M have increased, whereas ?, F, E and L_C50 have decreased. Changes in these parameters could be attributed to the existing high fishing capacity, and changing lake conditions. Thus, management measures should include continued restriction on illegal fishing methods and gears, such as the use of undersized gillnets (<5 in. mesh size) and beach seines. More attention also should be directed to the implementation of measures to control pollution of the lake from its various sources.