Nutrient characteristics in the Yangtze River Estuary and the adjacent East China Sea before and after impoundment of the Three Gorges Dam

From November 2002 to 2006, five cruises were undertaken in the Yangtze River Estuary and the adjacent East China Sea to compare the nutrient concentrations, ratios and potential nutrient limitation of phytoplankton growth before and after impoundment (June 2003) of the Three Gorges Dam (TGD). Concentrations of dissolved inorganic nitrogen (DIN), soluble reactive phosphorus (SRP) and total nitrogen (TN) exhibited an increasing trend from 2002 to 2006. In contrast, total phosphorus (TP) concentration exhibited a decreasing trend. The mean concentrations of DIN, SRP, and TN in the total study area increased from 21.4 mu M, 0.9 mu M, and 41.8 mu M in 2002 to 37.5 mu M, 1.3 mu M. and 82.2 mu M in 2006, respectively. while TP decreased from 2.1 mu M to 1.7 mu M. The concentration of dissolved reactive silica (DRSi) had no major fluctuations and the differences were not significant. The mean concentration of DRSi in the total study area ranged from 52.5 to 92.3 mu M. The Si:N ratio decreased significantly from 2.7 in 2002 to 1.3 in 2006, while TN: TP ratio increased from 22.1 to 80.3. The area of potential P limitation of phytoplankton growth expanded after 2003 and potential Si limitation appeared in 2005 and 2006. Potential P limitation mainly occurred in an area of salinity less than 30 after 2003, while potential Si limitation occurred where the salinity was greater than 30. By comparison with historical data, the concentrations of nitrate and SRP in this upper estuary during November 1980-2006 increased obviously after impoundment of TGD but DRSi decreased. Meanwhile, the ratios of N:P, Si:N and Si:P decreased obviously. (c) 2009 Elsevier B.V. All rights reserved.

Nutrient Dynamics in the Upwelling Area of Changjiang (Yangtze River) Estuary

Nutrient dynamics and its influence on the distribution of chlorophyll-a in the upwelling area of the Changjiang (Yangtze) River estuary were investigated in the spring (May) and summer (August) of 2004. In the spring, upwelling was apparent in the region of 122 degrees 20'-123 degrees 00' E, 31 degrees 00'-32 degrees 00' N and was associated with low temperature (16-21 degrees C), high salinity (24-33 practical salinity units [psu]), and low dissolved oxygen (2.5-6.0 mg L-1) in the upper 10 m of the water column. The spring upwelling increased the mixed-layer phosphate, nitrate, and silicate concentrations to roughly 1, 15, and 15 mu mol L-1, respectively, and improved the light transparency in the euphotic zone. This improvement in phytoplankton growing conditions was followed by an increase in chlorophyll-a concentrations. The summer upwelling was weaker and occurred over a smaller geographical area (122 degrees 20'-123 degrees 00' E, 31 degrees 15'-31 degrees 50' N). Strongly influenced by turbid Changjiang diluted water (CDW), it had little impact on the upper 10 m of the water column but instead increased nutrient concentrations at greater depths. The high concentration of particulates in the CDW reduced light transmission in the upper 10 m and, hence, limited phytoplankton growth throughout the water column. Chlorophyll-a concentrations in the summer upwelling area were roughly an order of magnitude lower than in the spring. Water clarity, as influenced by the CDW, appears to be the principal factor limiting the impact of upwelling on phytoplankton biomass in this area.

Historical changes in nutrient structure and its influences on phytoplantkon composition in Jiaozhou Bay

Due to the influence of human activities, nutrient concentrations, nutrient ratios and phytoplankton composition have notably changed in Jiaozhou Bay, China since the 1960s. From the 1960s to the 1990s, nutrient concentrations have increased 1.4 times for PO4-P, 4.3 times for NO3-N, 4.1 times for NH4-N and 3.9 times for DIN. The atomic ratio of DIN:PO4-P increased very rapidly from 15.9 +/- 6.3 for the 1960s, to 37.8 +/- 22.9 for the 1990s. SiO3-Si concentration has remained at a very low level from the 1980s to the 1990s. The high ratio of DIN: PO4-P and low ratios of SiO3-Si:PO4-P (7.6 +/- 8.9) and SiO3-Si:DIN (0.19 +/- 0.15) showed the nutrient structure of Jiaozhou Bay has changed from more balanced to unbalanced during the last 40 years. The possibility that DIN and/or PO4-P as limiting factors of Jiaozhou Bay phytoplankton has been lessened or eliminated and that of SiO3-Si limiting has been increased. The changes in nutrient structure may have led to the decrease of large diatoms and a shift of phytoplankton species composition. It is likely that there is a trend from large diatoms to smaller cells in Jiaozhou Bay. (C) 2001 Academic Press.

Nutrient structure of seawater and ecological responses in Jiaozhou Bay, China

Nutrient concentrations in seawater, and C, N, P, Si and chlorophyll a content in different-sized particulates were measured in Jiaozhou Bay, and C, N, P, Si composition in different-sized fractions of phytoplankton and their ecological responses to nutrient structure of the seawater were studied. Microphytoplankton and nanophytoplankton were dominant in Jiaozhou Bay. High C (16.50-20.97 unol L-1), N (2.46-2.99 mu mol L-1) and low P (0.06-0.12 mu mol L-1), Si (0.18-0.57 mu mol L-1) content, and high N/P (24.7-64.6) and low SUP (4.4-10.8), Si/N (0.06-0.20) ratios were found in all sized groups of particulates. These values reflected the elemental compositions of different-sized fractions of phytoplankton as being an ecological response to the nutrients in the seawater. The ratios deviated significantly from the Redfield values. The nutrient composition of seawater and particulates and their relationship to chlorophyll a showed that phytoplankton growth was possibly limited by Si. Si limitation appears favorable for controlling the ecological equilibrium of Jiaozhou Bay. Different-sized fractions of phytoplankton had different suitability to nutrient structures of the seawater. Among phytoplankton size groups, nanophytoplankton and microphytoplankton growths were more adaptable in eutrophic Jiaozhou Bay, and more competitive for assimilation of Si. This is consistent with their diatom-dominated composition, controlling the biomass and productivity of phytoplankton in Jiaozhou Bay. (c) 2006 Elsevier Ltd. All rights reserved.

A Review of Nontraditional Biomanipulation

The aim of this review is to identify problems, find general patterns, and extract recommendations for successful management using nontraditional biomanipulation to improve water quality. There are many obstacles that prevent traditional biomanipulation from achieving expectations: expending largely to remove planktivorous fish, reduction of external and internal phosphorus, and macrophyte re-establishment. Grazing pressure from large zooplankton is decoupled in hypereutrophic waters where cyanobacterial blooms flourish. The original idea of biomanipulation (increased zooplankton grazing rate as a tool for controlling nuisance algae) is not the only means of controlling nuisance algae via biotic manipulations. Stocking phytoplanktivorous fish may be considered to be a nontraditional method; however, it can be an effective management tool to control nuisance algal blooms in tropical lakes that are highly productive and unmanageable to reduce nutrient concentrations to low levels. Although small enclosures increase spatial overlap between predators and prey, leading to overestimates of the impact of predation, microcosm and whole-lake experiments have revealed similar community responses to major factors that regulate lake communities, such as nutrients and planktivorous fish. Both enclosure experiments and large-scale observations revealed that the initial phytoplankton community composition greatly impacted the success of biomanipulation. Long-term observations in Lake Donghu and Lake Qiandaohu have documented that silver carp (Hypophthalmichthys molitrix) and bighead carp (H. nobilis) (two filter-feeding planktivorous species commonly used in management) can suppress Microcystis blooms efficiently. The introduction of silver and bighead carp could be an effective management technique in eutrophic systems that lack macrozooplankton. We confirmed that nontraditional biomanipulation is only appropriate if the primary aim is to reduce nuisance blooms of large algal species, which cannot be controlled effectively by large herbivorous zooplankton. Alternatively, this type of biomanipulation did not work efficiently in less eutrophic systems where nanophytoplankton dominated.

Short-term effects of drawing water for connectivity of rivers and lakes on zooplankton community structure

During 28-29, September 2005, water was drawn from Hanjiang River and Houguan Lake to the Yangzi River via Sanjiao Lake and Nantaizi Lake in Wuhan in order to provide favorable conditions for ecosystem restoration. To evaluate the feasibility and validity of drawing water as a means of ecosystem restoration, zooplankton populations were studied 3 times (before, immediately after finishing and a month after drawing water) at seven locations from 27 Sept. 2005 to 2 Nov. 2005. Water quality in the lakes was mostly improved and zooplankton species richness decreased as soon as drawing water had finished but increased a month after drawing water. Zooplankton density and biomass was reduced in the lakes by drawing water but was increased at the entrance to Sanjiao Lake because of landform geometry change. Before drawing water, most species in Sanjiao Lake e.g., Brachionus sp. and Keratella sp. were tolerant of contamination. After drawing water oligotrophic-prone species such as Lecane ludwigii and Gastropus stylifer emerged. We conclude that drawing water could be important for improving water quality and favour ecosystem restoration. Dilution of nutrient concentrations may be an important role in the effect.

Calibration of alkenone unsaturation index with growth temperature for a lacustrine species, Chrysotila lamellosa (Haptophyceae)

Although long chain alkenones (LCKs) occur widely in lacustrine sediments, their origin is not clear. Here, we report a lacustrine source, the non-calcifying species Chrysotila lamellosa Anand (Haptophyceae), collected and isolated from an inland saline water body, Lake Xiarinur (Inner Mongolia, China). Its alketione pattern is similar to those of coastal marine strains of C lamellosa,but the relationship between U-37(K') index and culture temperature for the lacustrine species is quite different from that of the coastal species. A significant feature of the alkenones in this strain of C lamellosa is a lack of C-38 methyl alkenones, which might be used to distinguish the species from the marine haptophyte species Emiliania huxleyi and Gephyrocapsa oceanica. The higher C-38 tetraunsaturated compound abundance might be another important feature for distinguishing the C lamellosa alkenone producer from the coastal species Isochrysis galbana. This alkenone distribution pattern has been detected in many lakes, which suggests that C lamellosa or a closely related species might be a very common alkenone precursor in lacustrine systems. We examined U-37(K') and U-37(K) values for C lamellosa as a function of culture temperature in a batch culture experiment. The calibration for U-37(K') vs. culture temperature (T) was U-37(K') = 0.0011 x T-2 - 0.0157 x T + 0.1057(n = 14, r(2) = 0.99) from 10 degrees C to 22 degrees C or U-37(K') = 0.0257 x T - 0.2608(n = 9, r(2) = 0.97) from 14 degrees C to 22 degrees C. U-37(K) vs. culture temperature was U-37(K) = 0 0377 x T - 0.5992(n = 14, r(2) = 0.98) from 10 degrees C to 22 degrees C. Our experiments show that the alkenone unsaturation index (U-37(K')) is strongly controlled by culture temperature and can be used for palaeoclimate reconstruction. (C) 2007 Elsevier Ltd. All rights reserved.

Post-impoundment biomass and composition of phytoplankton in the Yangtze River

Damming, and thus alteration of stream flow, promotes higher phytoplankton populations and encourages algal blooms (density > 10(6) cells L-1) in the Three Gorges Reservoir (TGR). Phytoplankton composition and biomass were studied in the Yangtze River from March 2004 to May 2005. 107 taxa were identified. Diatoms were the dominant group, followed by Chlorophyta and Cyanobacteria. In the Yangtze River, algal abundance varied from 3.13 x 10(3) to 3.83 x 10(6) cells L-1, and algal biomass was in the range of 0.06 to 659 mg C m(-3). Levels of nitrogen, phosphorus and silica did not show consistent longitudinal changes along the river and were not correlated with phytoplankton parameters. Phytoplankton abundance was negatively correlated with main channel discharge (Spearman r = -1.000, P < 0.01). Phytoplankton abundance and biomass in the Yangtze River are mainly determined by the hydrological conditions rather than by nutrient concentrations.

Changes in the patterns of inorganic nitrogen and TN/TP ratio and the associated mechanism of biological regulation in the shallow lakes of the middle and lower reaches of the Yangtze River

The changes of NH3-N, NO3-N, NO2-N and TN/TP were studied during growth and non-growth season in 33 subtropical shallow lakes in the middle and lower reaches of the Yangtze River. There were significant positive correlations among all nutrient concentrations, and the correlations were better in growth season than in non-growth season. When TP > 0.1 mgL(-1), NH3-N increased sharply in non-growth season with increasing TP, and NO3-N increased in growth season but decreased in non-growth season with TP. These might be attributed to lower dissolved oxygen and low temperature in non-growth season of the hypereutrophic lakes, since nitrification is more sensitive to dissolved oxygen and temperature than anti nitrification. When 0.1 mgL(-1)> TP > 0.035 mgL(-1), TN and all kinds of inorganic nitrogen were lower in growth season than in non-growth season, and phytoplankton might be the vital regulating factor. When TP < 0.035 mgL(-1), inorganic nitrogen concentrations were relatively low and NH3-N, NO2-N had significant correlations with phytoplankton, indicating that NH3-N and NO2-N might be limiting factors to phytoplankton. In addition, TN/TP went down with decline in TIP concentration, and TN and inorganic nitrogen concentrations were obviously lower in growth season than in non-growth season, suggesting that decreasing nitrogen (especially NH3-N and NO3-N) was an important reason for the decreasing TN/TP in growth season. The ranges of TN/TP were closely related to trophic level in both growth and non-growth seasons, and it is apparent that in the eutrophic and hypertrophic state the TN/TP ratio was obviously lower in growth season than in non-growth season. The changes of the TN/TP ratio were closely correlated with trophic levels, and both declines of TN in the water column and TP release from the sediment were important factors for the decline of the TN/TP ratio in growth season.

Variation of benthic diatoms in a shallow, eutrophic Chinese Lake, Lake Donghu

Benthic diatom communities were sampled monthly from May 2004 to May 2005 at four different sites in the littoral zone of Lake Donghu, a shallow eutrophic lake of China. The seasonal patterns of the total abundance, which were lowest in summer and highest in spring, were found at all sites. Total densities of diatom assemblages were significantly higher at hyper-eutrophic sites than at moderately eutrophic sites. Melosira varians was the most abundant species and dominant contributor to total abundance at all sites during spring, autumn and winter, whereas Achnanthes exigua dominated benthic diatom assemblages at the site with the highest nutrient concentrations during the summer. Achnanthes lanceolata var. dubia, Gomphonema parvulum, Navicula similis, Navicula verecunda and Nitzschia amphibia were generally observed at all sites throughout the year and were dominant at higher-nutrient sites. The abundance of ambient nutrients was probably responsible for the spatial variation in biomass, composition and diversity of benthic diatom assemblages, and lake water temperature was the major factor that controlled seasonal distribution.

Negative effects of Microcystis blooms on the crustacean plankton in an enclosure experiment in the subtropical China

Effects of Microcystis blooms on the crustacean plankton were studied using enclosure experiments during July-September, 2000. Eight enclosures were set in the hypereutrophic Donghu Lake. Different nutrient concentrations through additional nutrient and sediment in enclosures were expected to result in different abundance of Micropystis. From July to early August, the phytoplankton community was dominated by Chlorophyta, Cryptophyta, Bacillariophyta and Cyanophyta other than Microcystis aeruginosa. M. aeruginosa showed a rapid increase during early August in all enclosures and predominated. Crustacean plankton was dominated by the herbivorous Moina micrura, Diaphanosoma brachyurum and Ceriodaphnia cornuta, and the predaceous Mesocyclops sp. and Thermocyclops taihokuensis. During the pre-bloom period, the dynamics of M. micrura population appeared to be mainly affected by the predaceous cyclopoids. With the development of Microcystis blooms, such interaction between M. micrura and cyclopoids seemed weakened, especially when the Microcystis biomass was high. But there was no apparent influence on the interaction between Leptodora kindti and its zooplanktonic prey. The density of two cyclopoids decreased with the enhancement of Microcystis. The density decline of M. micrura was caused by both predation and inhibition by Micropystis. The low food availability of other edible phytoplankton during the blooms led to low densities of both C. cornuta and D. brachyurum by late August. It appears that dense Microcystis blooms exert strong negative effects on the herbivorous cladocerans and the predaceous cyclopoids.

PLANKTON AND SESTON STRUCTURE IN A SHALLOW, EUTROPHIC SUBTROPICAL CHINESE LAKE

The seasonal dynamics in the nutrient concentrations, chlorophyll-a amount (Chl-a), total algal volume (CV), Chl-a/CV ratio, seston structure were studied at two sampling stations in a shallow, highly eutrophicated subtropic lake (the Guozheng Hu area of the East Lake) on the plain of the middle basin of the Chang Jiang (the Yangtze River) of China. The lake ecosystem of the Guozheng Hu area is dominated by two planktivorous fishes (silver carp and bighead carp), phytoplankton and zooplankton. Macrophytes are extremely scarce in this area. Concentrations of the total dissolved nitrogen and phosphorus in the Guozheng Hu area in 1990 were very high. Fish yield, of which, more than 90 % was composed of silver carp and bighead carp in the Guozheng Hu area was very high (ca. 1140 kg/ha or 45.6 g/m3 in 1990). Grazing pressure by the fishes on the plankton community is considered to be rather strong. The annual average biomass of zooplankton was ca. 1/3 - 1/2 that of phytoplankton. On the average, dry matter in the living plankton only constituted ca. 3-7 % of the total dry seston, and plankton carbon only constituted ca. 5 - 10 % of the seston carbon. The present results indicate that, in the Guozheng Hu area of the East Lake, of the organic part of the seston, detritus is quantitatively an important constituent, while living plankton is only a very small component.

干旱胁迫与施N条件下白刺花（Sophora davidii）幼苗生长及其适应机制

干旱环境常常由于多变的降水事件和贫瘠土壤的综合作用，表现出较低的生产力和较低的植被覆盖度。全球性的气候变暖和人类干扰必将使得干旱地区缺水现状越来越严竣。贫瘠土壤环境中已经很低的有效养分含量也将会随着干旱的扩大而越来越低。干旱与半干旱系统中不断加剧的水分与养分的缺失将严重限制植物的生长和植被的更新，必然会使得已经恶化的环境恶化速率的加快、恶化范围的加大。如何抑制这种趋势，逐步改善已经恶化的环境是现在和将来干旱系统管理者面临的主要关键问题。了解干旱系统本土植物对未来气候变化的适应机制，不仅是植物生态学研究的重要内容，也对人为调节干旱环境，改善干旱系统植被条件，提高植被覆盖度具有重要的实践意义。 本研究以干旱河谷优势灌木白刺花（Sophora davidii）为研究对象，通过两年大棚水分和施N控制实验和一个生长季野外施N半控制实验，从植物生长－生理－资源利用以及植物生长土壤环境特征入手，系统的研究了白刺花幼苗生长特性对干旱胁迫和施N的响应与适应机制，并试图探讨施N是否可调节干旱系统土壤环境，人工促进干旱条件下幼苗定居，最终贡献于促进植被更新实践。初步研究结论如下： 1）白刺花幼苗生长、生物量积累与分配以及水分利用效率对干旱胁迫和施N处理的适应白刺花幼苗株高、基径、叶片数目、叶面积、根长、生物量生产、相对含水量和水分利用效率随着干旱胁迫程度的增加而明显降低，但地下部分生物量比例和R/S随着干旱胁迫程度的增加而增加。轻度施N处理下幼苗株高、基径、叶片数目、叶片面积和生物量生产有所增加。但重度施N处理下这些生长指标表现出微弱甚至降低的趋势。严重干旱胁迫条件下，幼苗叶面积率、R/S、相对含水量和水分利用效率也以轻度施N处理为最高。 2）白刺花幼苗叶片光合生理特征对干旱胁迫和施N处理的适应叶片光合色素含量和叶片光合效率随着干旱胁迫程度的增加而显著降低，并且PS2系统在干旱胁迫条件下表现出一定程度的光损害。但是比叶面积随着干旱胁迫程度的增加而增加。在相对较好水分条件下幼苗净光合速率的降低可能是因为气孔限制作用，而严重干旱胁迫条件下非气孔限制可能是导致幼苗叶片光合速率下降的主要原因。叶片叶绿素含量、潜在光合能力、羧化效率、光合效率以及RUBP再生能力等在施N处理下得到提高，并因而改善干旱胁迫条件下光合能力和效率。虽然各荧光参数对施N处理并无显著的反应，但是干旱胁迫条件下qN和Fv/Fm在轻度施N处理下维持相对较高的水平，而两年连续处理后在严重干旱胁迫条件下幼苗叶片光合效率受到重度施N处理的抑制，并且Fv/Fm和qN也在重度施N处理下降低。 3）白刺花幼苗C、N和P积累以及N、P利用效率对干旱胁迫和施N处理的适应白刺花幼苗C、N和P的积累，P利用效率以及N和P吸收效率随干旱胁迫程度的增加而显著降低，C、N和P的分配格局也随之改变。在相同水分处理下，C、N和P的积累量、P利用效率以及N和P吸收效率在轻度施N处理下表现为较高的水平。然而，C、N和P的积累量和P利用效率在重度施N处理下不仅没有表现出显著的正效应，而且有降低的趋势。另外，在相同水分条件下白刺花幼苗N利用效率随着施N强度的增加而降低。 4）白刺花幼苗生长土壤化学与微生物特性对干旱胁迫和施N的适应白刺花幼苗生长土壤有机C、有效N和P含量也随干旱胁迫程度的增加而明显降低。干旱胁迫条件下土壤C/N、C/P、转化酶、脲酶和碱性磷酸酶活性的降低可能表明较低的N和P矿化速率。尽管微生物生物量C、N和P对一个生长季干旱胁迫处理无显著反应，但微生物生物量C和N在两年连续干旱胁迫后显著降低。土壤有机C和有效P含量在轻度施N处理下大于重度施N处理，但是有效N含量随着施N强度的增加而增加。微生物生物量C和N、碱性磷酸酶和转化酶活性也在轻度施N处理下有所增加。但是碱性磷酸酶活性在重度施N处理下降低。 5）野外条件下白刺花幼苗生长特征及生长土壤生化特性对施N的适应植物生长、生物生产量、C的固定、N、P等资源的吸收和积累、其它受限资源的利用效率（如P）在轻度施N处理下均有所增加，但N利用效率有所降低。幼苗生物生产量及C、N和P等资源的分配格局在轻度施N处理下也没有明显的改变。白刺花幼苗叶片数目、生物生产量和C、N、P的积累量在重度施N处理下虽然也相对于对照有所增加，但幼苗根系长度显著降低。生物量及资源（生物量、C、N、P）在重度施N处理下较多地分配给地上部分（主要是叶片）。另外，土壤有机C、全N和有效N含量随外源施N的增加而显著增加，土壤pH随之降低，但土壤全P含量并无显著反应。其中有机C含量和有效P含量以轻度施N处理最高。微生物生物量C、N和P在轻度施N处理下也显著增加，而微生物生物量C在重度施N处理下显著降低。同时，转化酶、脲酶、碱性磷酸酶和中性磷酸酶活性在施N处理下也明显的提高，但酸性磷酸酶和过氧化氢酶活性显著降低，其中碱性磷酸酶和中性磷酸酶活性以轻度施N处理最高。 综合分析表明，干旱河谷水分和N严重限制了白刺花幼苗的生长。施N不能完全改变干旱胁迫对白刺花幼苗的抑制的作用，但是由于施N增加土壤N有效性，改善土壤一系列生物与化学过程，幼苗的生长特性也对施N表现出强烈的反应，表现为植物结构与资源分配格局的改善，植物叶片光合能力与效率的提高，植物生长以及利用其他受限资源（如水分和P）的效率的增加，致使植物自身生长及其生长环境在干旱环境下得到改善。但是过度施N不仅不能起到改善干旱胁迫下植物生长环境、促进植物生长的作用，反而在土壤过程以及植物生长过程中加重干旱胁迫对植物的伤害。因此，建议在采用白刺花作为先锋种改善干旱河谷系统环境的实践中，可适当施加N以改善土壤环境，调节植物利用与分配资源的效率，促进植物定居，得到人工促进种群更新的目的。但在实践过程中也要避免过度施N。 Arid regions of the world are generally noted for their low primary productivity which is due to a combination of low, unpredictable water supply and low soil nutrient concentrations. The most serious effects of global climate change and human disturbances may well be those which related to increasing drought since drought stress has already been the principal constraint in plant growth. The decline in total rainfall and/or soil water availability expected for the next decades may turn out to be even more drastic under future warmer conditions. Nevertheless, water deficit is not the only limiting factor in arid and semiarid environments. Soils often suffer from nutrient (especially N and P) deficiencies in these ecosystems, which can also be worsened by climate change. How to improve the poor soil quality and enhance the vegetation coverage is always the problem facing ecosystem managers. The adaptive mechanisms of native plant to future climate change is always the focus in plant ecology, it also plays important roles in improving vegetation coverage by manual controlled programmes. Sophora davidii is a native perennial shrub of arid valleys, which is often predominant on eroded slopes and plays a vital role in retaining ecological stability in this region. It has been found that S. davidii was better adapted to dry environment than other shrubs, prompting its use for re-vegetation of arid lands. A two-years greenhouse experiment and a field experiment were conducted in order to understand the adaptation responses of Sophora davidii seedlings to different water and N conditions, and further explore if additional N supply as a modified role could enhance the adaptation ability of S. davidii seedlings to dry and infertile environment. Two-month old seedlings were subjected to a completely randome design with three water (80%, 40% and 20% water field capacity (FC)) and three N supply (N0: 0, Nl: 92 and Nh: 184 mg N kg-1 soil) regimes. Field experiment was arranged only by three N supplies in the dry valley. 1) The growth, biomass partitioning and water-use efficiency of Sophora davidii seedlings in respond to drought stress and N supply Seedlings height, basal diameter, leaf number, leaf area, root length, biomass production, relative water content (RWC) and WUE were decreased with increase of drought stress. An increase in below-ground biomass was observed indicating a higher root/shoot ratio (R/S) under drought stress conditions. Low N supply increased seedlings height, basal diameter, leaf number, leaf area, and biomass production, but decreased root length. In contrast, these growth characteristics showed little or negative effect to high N supply treatment. Leaf percentages increased with increase of N supply, but fine root percentages decreased. In addition, Low N supply rather than the other two N treatments increased leaf area ratio (LAR), leaf/fine root mass ratio (L/FR), R/S and RWC under severe drought stress (20%FC), even though these parameters could increase with the high N supply treatment under well-watered condition (80%FC). Moreover, Low N supply also increased WUE under three water conditions, but high N supply had little effect on WUE under drought stress conditions (40%FC and 20%FC). 2) Leaf gas exchange and fluorescence parameters of Sophora davidii seedlings in respond to drought stress and N supply Leaf area (LA), photosynthetic pigment contents, and photosynthetic efficiency were decreased with increase of drought stress, but specific leaf area (SLA) increased. Photodamage in photosystem 2 (PS2) was also observed under drought stress condition. The decreased net photosynthetic rate (PN) under relative well-watered water conditions might result from stomatal limitations, but the decreased PN under other hand, photosynthetic capacity by increasing LA, photosynthetic chlorophyll contents, Pnmax, CE, Jmax were increased with increase N supply, and photosynthetic efficiency was improved with N supply treatment under water deficit. Although N supply did a little in alleviating photodamages to PS2 caused by drought stress, low N supply enhanced qN and kept relative high Fv/Fm under drought stress condition. However, high N supply inhibited leaf photosynthetic efficiency, and declined Fv/Fm and qN under severe drought stress condition after two year continues drought stress and N supply. 3) Carbon accumulation, nitrogen and phosphorus use efficiency of Sophora davidii seedlings in respond to drought stress and N supply C, N and P accumulation, NUE , N and P uptake efficiency (NUtE and NUtE ) P N P were decreased with increase of drought stress regardless of N supply. On the other hand, the S. davidii seedlings exhibited strong responses to N supply, but the responses were inconsistent with the various N supply levels. Low N supply rather than the other two N treatments increased C, N and P accumulation, improved NUEP, NUtE and NUtE under corresponding water condition. In contrast, high N supply N P did few even depressed effects on C, N and P accumulation, and NUEP, although NUtEN and NUtEP could increase with high N supply under corresponding water conditions. Even so, a decrease of NUEN was observed with increase of N supply under corresponding water conditions. 4) Soil microbial and chemical characters in respond to drought stress and N supply The content of soil organic C, available N and P were decreased with increase of drought stress. Decreases in C/N and C/P, and invertase, urea and alkaline phosphatase activity were also observed under drought stress conditions, indicating a lower N and P mineralization rate. Although microbial biomass C, N and P showed slight responses to drought stress after one growth period treatment, microbial biomass C and N were also decreased with increase of drought stress after two year continuous treatment. The content of soil organic C and available P showed the stronger positive responses to low N supply than which to high N supply, although than the other two N treatments increased microbial biomass N and invertase activity under severe drought stress condition, even though invertase activity could increase with high N supply treatment under relative well-water conditions. Moreover, low N supply treatment also increased C/P and alkaline phosphatase activity which might result from higher P mineralization, but high N supply did negative effects on alkaline phosphatase activity. 5) The growth characteristics of Sophora davidii seedlings and soil microbial and chemical characters in respond to N supply under field condition Low N supply facilitated seedlings growth by increasing leaf number, basal diameter, root length, biomass production, C, N and P accumulation and absorption, and enhancing the use efficiency of other limited resources as P. Compared to control, however, low N supply did little effect on altering biomass, C, N and P portioning in seedlings components. On the contrary, high N supply treatment also increased leaf number, biomass and C, N and P accumulation relative to control, but significantly decreased root length, and altered more biomass and resources to above-ground, which strongly reduced the ability of absorbing water under drought condition, and thus which might deep the drought stress. In addition, N supply increased soil C, N and available N content, but declined pH and showed little effects on P content. Low N supply showed higher values of soil C and available P content. Low N supply also increased microbial biomass C, N and P, although high N supply decreased microbial biomass C. N supply significantly enhanced soil invertase, urea, alkaline and neutral phosphratase activity, while declined acid phosphratase and catalase activity. Low N supply exhibited higher alkaline and neutral phosphratase activity compared to the others. The results from this study indicated that both drought and N limited the growth of S. davidii seedlings and their biomass production. Regardless of N supply levels, drought stress dramatically reduced the seedlings growth and biomass production. Although plant growth parameters, including basal diameter, height, leaf number, and biomass and their components were observed to be positive responses to low N supply, N supply alone can not alter the diminishing tendency which is caused by drought. available N content increased with increase N supply. In addition, low N supply rather These findings imply that drought played a primary limitation role and N was only the secondary. Even so, appropriate N supply was seemed to enhance the ability that S. davidii seedlings adapted to the xeric and infertile environment by improving soil processes, stimulating plant growth, increasing recourses accumulation, enhancing use efficiency of other limited resources, and balancing biomass and resources partitioning. Appropriate N supply, therefore, would be recommended to improve S. davidii seedling establishment in this region, but excess N supply should be avoided.

Response of coastal marine eco-environment to river fluxes into the sea: A case study of the Huanghe (Yellow) River mouth and adjacent waters

The impact of the Huanghe (Yellow) River outflows on its estuary was investigated with river gauging and shipboard hydrographic observations. The river flux has been decreasing dramatically; the discharges of water and sediment in the 1990s dropped to 27.4% and 31.9% of those in the 1950s, respectively, resulting in frequent and lengthy events of downstream channel dry-up since the 1970s. There were accumulatively 897 zero-flow days during the 1990s in the river course below the Lijin Hydrological Station, 100 km upstream from the river mouth, which is 82.4% of that in 1972. As freshwater input decreases, river-borne nutrients to the estuarine increased significantly. Concentration of dissolved inorganic nitrogen (DIN) in the 1990s was four times of that in 1950s. Changes in amount and content of the riverine inputs have greatly affected the estuarine ecosystem. Over the past several decades, sea surface temperature and salinity in the estuary and its adjacent waters increased and their distribution pattern altered in response to the reduction of freshwater inflow. The distribution of and seasonal succession in nutrient concentrations in the surface layer have also changed with a shift of river outlet and the decrease in riverine nutrient loads. Furthermore, deterioration of estuarine ecosystem by less river input has decreased primary productivity in the deltaic region waters, and in turn depressed the fishery. (C) 2008 Published by Elsevier Ltd.

The status and characteristics of eutrophication in the Yangtze River (Changjiang) estuary and the adjacent East China Sea, China

Eutrophication has become increasingly serious and noxious algal blooms have been of more frequent occurrence in the Yangtze River Estuary and in the adjacent East China Sea. In 2003 and 2004, four cruises were undertaken in three zones in the estuary and in the adjacent sea to investigate nitrate (NO3-N), ammonium (NH4-N), nitrite (NO2-N), soluble reactive phosphorus (SRP), dissolved reactive silica (DRSi), dissolved oxygen (DO), phytoplankton chlorophyll a (Chl a) and suspended particulate matter (SPM). The highest concentrations of DIN (NO3-N+NH4-N+NO2-N), SRP and DRSi were 131.6, 1.2 and 155.6 mu M, respectively. The maximum Chl a concentration was 19.5 mg m(-3) in spring. An analysis of historical and recent data revealed that in the last 40 years, nitrate and SRP concentrations increased from 11 to 97 mu M and from 0.4 to 0.95 mu M, respectively. From 1963 to 2004, N:P ratios also increased from 30-40 up to 150. In parallel with the N and P enrichment, a significant increase of Chl a was detected, Chl a maximum being 20 mg m(-3), nearly four times higher than in the 1980s. In 2004, the mean DO concentration in bottom waters was 4.35 mg l(-1), much lower than in the 1980s. In comparison with other estuaries, the Yangtze River Estuary was characterized by high DIN and DRSi concentrations, with low SRP concentrations. Despite the higher nutrient concentrations, Chl a concentrations were lower in the inner estuary (Zones 1 and 2) than in the adjacent sea (Zone 3). Based on nutrient availability, SPM and hydrodynamics, we assumed that in Zones 1 and 2 phytoplankton growth was suppressed by high turbidity, large tidal amplitude and short residence time. Furthermore, in Zone 3 water stratification was also an important factor that resulted in a greater phytoplankton biomass and lower DO concentrations. Due to hydrodynamics and turbidity, the open sea was unexpectedly more sensitive to nutrient enrichment and related eutrophication processes.