江苏近岸海域营养盐类污染分布特征与评价

江苏沿海大多属于淤泥质平原海岸,开发利用方式以农业为主,海水中的营养盐类污染物质量浓度分布与入海河流和海岸区域农田化肥施用强度有重要的关系,因此,了解和探讨江苏近岸营养盐类污染的污染程度及其分布有重要的意义。根据江苏近海区域特征,选择近岸海域19个站点作为研究地点,分别对这些地点的总氮、总磷、无机氮和磷酸盐等营养盐类污染物质量浓度进行了分析,首先探讨了这些营养盐污染物在分布江苏近岸海域沿岸方向和向海方向的空间分布特点,然后结合海水水质标准,利用等标污染指数和综合污染指数等方法进行了污染程度评价,得出了江苏沿海营养盐类污染物在空间分布上具有南北两端和中间部位都比较高,而中部辐射沙洲附近和南北两端之间的质量浓度较低的"W"形分布特征,在向海方向上具有营养盐污染物质量浓度基本上都表现为靠近海岸质量浓度高,远离海岸略低的变化趋势,在污染程度评价方面,总磷等标污染指数普遍超过1,总氮等标污染指数大多小于1,综合污染指数在1.63～14.08之间,差异比较明显,一般表现为南北高中间低的特点,最后结合江苏沿海地区河流排污入海情况以及农田化肥农药施用强度,对江苏近岸海域营养盐类污染分布状况进行了讨论。     

Chlorophyll maxima in Kuroshio and adjacent area

Fluorometric determination of chlorophyll a and pheopigments was carried out in the sea area off southern Japan. Maximum concentration of chlorophyll pigments was determined to be at or below the lower limit of the euphotic zone, namely from 50 to 150 m depth. To estimate the activity of phytoplankton in this maximum chlorophyll layer, changes of chlorophyll concentration and number of cells were measured in samples taken from this layer before and after exposure to different light intensities. It was concluded that the growth of shade-adapted phytoplankton and the deterioration of chlorophyll pigments by light are the main factors causing the chlorophyll maximum to occur in a rather deep oceanic layer.     

Epipelagic planktonic bioluminescence in the marginal ice zone of the Greenland Sea

Epipelagic planktonic bioluminescence in the marginal ice zone of the Fram Strait was investigated during April and May 1989. Vertical profiles of bioluminescence potential were measured using a HIDEX (High Input Defined EXcitation) design bathyphotometer. Mesozooplankton samples were collected with oblique tows using a 153 m mesh net. The amount of bioluminescence produced by mechanical stimulation of individual organisms was measured using an integrating sphere and photon-counting system. These measures of bioluminescence potential along with estimated abundances of bioluminescent organisms allow an independent estimated of integrated epipelagic bioluminescence potential. The zooplankton community structure was relatively simple in this region and the number of bioluminescent species correspondingly small. The majority of epipelagic bioluminescence was produced by copepods (Metridia spp.), larvaceans (Oikopleura spp.), euphausiids (Thysanoeassa spp.) and ostracods (Conchoecia spp.), although the relative contribution of these organisms to the overall bioluminescence potential varied considerably with time and location over the 2 mo period. Bioluminescent dinoflagellates were rare and did not contribute significantly to epipelagic bioluminescence. Integrated bioluminescence potential in the water column was significantly correlated with zooplankton biomass, but not with any other measured environmental parameter. No enhancement of chlorophyll, zooplankton biomass or bioluminescence was observed in the marginal ice zone compared to the adjacent open waters of the Fram Strait during this spring cruise.     

Influence des conditions hivernales sur les productions phyto- et zooplanctoniques en Méditerranée Nord-Occidentale. II. Biomasse et production phytoplanctonique

Hydrological observations, and measurements of nutrient chemistry, plankton biomass, and production were carried out during the Médiprod I cruise of the R.V. “Jean-Charcot”. The March cruise was characterized by almost winter conditions, exhibiting strong vertical mixing of water masses in the offshore region and nutrient transport up to the photic zone. According to the working hypothesis, the strong vertically mixed area (e.g. Station 15) and the surrounding oligotrophic area are separated by an intermediate zone, where both nutrients and stability have produced phytoplankton-bloom conditions. During the April cruise, highest biomass and production rates were encountered everywhere in the offshore region, and especially in the previously mixed area of central divergence. Production was as high as 2 gC·m^-2 day^-1, and the standing crop of chlorophyll was 3 mg·m^-3; such values are rather important for the so called “poor” Mediterranean Sea. Salinity-phosphate and chlorophyll-phosphate diagrams are presented. Biomass and production rates are in agreement with the potential fertility based on the nutrient content of the waters. The disappearance of 1 μatg P·PO₄ by photosynthetic uptake corresponds to 7.7 mg chlorophyll a, which represents the autotrophic biomass remaining after grazing by the simultaneous zooplankton bloom. Biomass and production features are analyzed in regard to interaction of both nutrient availability and the stability of water masses. Stability conditions can be created either by intrusion of local mixing in a stratified oligotrophic area (“winter bloom”), or by thermal stratification of the upper layer (“spring bloom”). In the latter case, the highest biomasses are present in the zone where the nutrients were previously introduced by mixing. The oligotrophic situation remained constant during the two crunises in the surrounding coastal area, which is characterized by low-salinity water and, therefore, absence of vertical nutrient transport into the photic zone. Chlorophyll pigment concentration and photosynthetic rates in the “Cote d'Azur” region are similar to those in the “Provence” region; this situation may result more from upwelling of nutrient-rich intermediate water than from the mixing process which predominates in the latter region.     

Planktonic bioluminescence in the pack ice and the marginal ice zone of the Beaufort Sea

An icebreaker cruise into the Beaufort Sea in the fall of 1986 provided a unique opportunity for studying planktonic bioluminescence in ice fields and in the marginal ice zone. Bathyphotometer casts (bioluminescence intensity, seawater temperature, beam attenuation coefficient, and salinity) and biological collections were made to a depth of 100 m. A light budget, which describes the planktonic species responsible for the measured bioluminescence, and a dinoflagellate species budget were constructed from the mean light output from luminescent plankton and plankton counts. The vertical distribution of bioluminescence among the ice stations was similar. The maximum intensities were 2 to 8×10⁶ photons s^-1 cm^-3 in the upper 50 m of the sea-ice interface. The marginal ice zone station (MIZ) exhibited a maximum intensity of 2 to 3×10⁸ photons s^-1 cm^-3 between 5 and 30 m depth. At Ice Station 2, Metridia longa and their nauplii contributed approximately 80% of stimulable bioluminescence in the upper 10 m but, overall, Protoperidinium spp. dinoflagellates contributed most of the light to a depth of 100 m. In the MIZ, Protoperidinium spp. dinoflagellates contributed 90% of the light within the upper 10 m, decreasing to 43% of the contributed light at a depth of 40 m. Below 40 m, dinoflagellate bioluminescence decreased to a few percent of the total to a depth of 90 m. Metridia spp. copepods contributed more than 50% of the light at depths from 40 to 90 m. Ostracods, larvaceans, and euphausiid furcilia contributed <1% of all bioluminescence at all depths sampled. Correlation analyses between measured bioluminescence (photons s^-1 cm^-3), the number of bioluminescent dinoflagellates and the light budget for the MIZ indicated highly significant associations: r=0.919, p=0.001, and r=0.912, p<0.001, respectively (Student's two-tailed t-tests). Bioluminescence was negatively correlated with seawater salinity at all stations (p=0.001). Maximum bioluminescence was measured in the less saline surface waters at all stations.     

Influence des conditions hivernales sur les productions phyto- et zooplanctoniques en Méditerranée nord-occidentale. I. Structures hydrologiques et distribution des sels nutritifs

During two periods (1 to 15 March and 3 to 17 April, 1969), the R.V. “Jean Charcot” accomplished hydrological, chemical, and biological observations in the northern portion of the Western Mediterranean Sea. The main aim was to study the influence of the intensive vertical mixing of water masses on primary and secondary productions during winter. Earlier work in this area had revealed, in the offshore region, relatively large biomasses and high production rates during spring; considering the low potential fertility of Mediterranean waters, this finding may be explained by the effective vertical transport of nutrients upwards to the photic zone. The present paper discusses the hydrological features and the distribution of nutrients (phosphates and nitrates), in these areas, where, in winter, formation of deep water occurs. Observations were made down to 1,000 m on a grid of stations centred at 42°N; 5° E (“région provençale”) and another series of stations in the region “Corse-Côte d'Azur”. These two areas are characterized by cyclonic gyres, in which each centre shows a sector of high surface density (σ _t > 29.00). The surface mixed layer encountered is not deeper than 100 m; however, the Medoc Group (1970) has described formation of a homogeneous layer down to more than 1000 m. Many well-mixed water columns (maximum temperature and salinity at any depth do not exceed 13°C and 38.45‰, respectively) remain and occupy the western portion of the high surface density area; everywhere, the Mediterranean 3-layer system (superficial, intermediate and deep waters), more or less affected by mixing, remains well developed in the coastal region, and especially in the region of Côte d'Azur and Corsica. At some places, relatively high surface temperature (>13°C) associated with high salinity shows that the intermediate water fraction reaches the surface not only by direct vertical mixing, but also by any other dynamic lifting process, which constitutes another way of nutrient transport to the photic layer. The highest surface nutrient (0.3μ atg/l P?PO₄; 5 μ atg/l N?NO₃) and the lowest surface oxygen content (saturation <90%) are encountered in the mixed area; they are the best indicators of recently upwelled water. The surface layer around the cyclonic area is characterized by the low nutrient content of water of Atlantic origin. The lower salinity (<38%) of this water does not allow deep vertical mixing. During 3 to 17 April, 1969, the survey carried out on the same grid and sections reveals heating effects on all surface waters; the resulting stability in the most superficial layer accomodates the general spring bloom of phytoplankton. Nutrient consumption by photosynthesis in the upper 100 m layer of the surveyed area south of Marseilles was calculated to be: 129.1×10⁶ g-at P?PO₄ per 16,000 km² per month, converted on the atomic basis of P:C=1:106 represents almost 75% of the carbon production obtained by ¹⁴C-uptake measurements.     

Etude de la migration verticale quotidienne des larves de Mesochaetopterus sagittarius à Nosy-Bé (Madagascar)

The vertical distribution of the planktonic larvae of Mesochaetopterus sagittarius (Claparède, 1870) has been studied on the basis of samples taken with closing nets every 3 or 4 h, for periods of at least 24 h. The daily migration does not show the typical pattern. In the evening, the larvae begin to descend from the surface layer; they reach a maximum depth around midnight. The subsequent ascent ends at about noon, when the concentration again attains its maximum close to the surface. The biometric analysis of the samples shows that the migration range depends on the size of the larvae: the bigger they are, the higher is the respective amplitude of migration. Furthermore, there exists a size gradient independent of the time of capture which is most distinct during night time; at night, average size, as well as total number of larvae, decrease in the surface layer and, accordingly, increase in the greater depths. The techniques used allow a high degree of significance to be attached to the results obtained. The standard deviation calculated for each sampling series is lower when two parallel samples are taken at each depth, and in the same water mass, by using a parachute drogue set at 20 m depth and followed during the series.     

A spatial model of phytoplankton patchiness

The one-dimensional theory of critical-length scales of phytoplankton patchiness is developed to include phytoplankton growth and herbivore grazing as functions of time and space. The critical-length scale L _c for the pathch is then determined by the initial spatial distribution and concentration of the limiting nutrient and herbivores in addition to the daily averaged values of the growth and loss processes. The response of an initial phytoplankton patch to the stresses of turbulent diffusion, nutrient depletion, light periodicity, and nocturnal or continuous herbivore grazing is investigated numerically for several oceanic conditions. Nocturnal grazing, while less stressful on primary production than continous grazing, results in lower phytoplankton standing stocks. Increase in biomass of vertically migrating zooplankton results in a net loss of nutrient which might otherwise be egested, recycled, and utilized in the euphotic zone under continuous grazing conditions. The Ivlev constant is shown via sensitivity analysis to be a significant parameter ultimately influencing phytoplankton production. It is demonstrated numerically that diffusion of phytoplankton cells from areas of high concentration to low concentration prevents the local extinction of the standing stock, thereby rendering a positive herbivore grazing-threshold unnecessary for ecosystem stability.     

Depth-dependent changes in chlorophyll fluorescence number at a Sargasso Sea station

Chlorophyll a-specific in vivo fluorescence exhibited depth-dependent changes in a Sargasso Sea phytoplankton community, decreasing from a maximum value at the surface to a minimum at 90m, and then increasing again below 90 m. This distribution pattern was not explained by irradiance conditions, diurnal variability, senescence in the deep population, or changes in light-absorption efficiency of chlorophyll a. However, a significant positive correlation was found between mean phytoplankton cell size and fluorescence number in the upper euphotic zone, where nutrient concentrations were low. We hypothesize that the direct cause for this observed correlation was nutrient limitation. In this picoplankton-dominated community, packaging effect was minimal. Under nutrient-limiting conditions, as mean cell size increases photosynthetic efficiency decreases and therefore fluorescence number increases. In the lower euphotic zone where nutrients were not limiting, changes in fluorescence number exhibited weak size-dependence and appeared to be related to species compositional changes.     

Analysis of a two-layer cloud system with RAMS model and comparison to airborne observations

A three-dimensional numerical model (Regional Atmospheric Modeling System—-RAMS) was used to study the formation and evolution of water forms in a two-layer cloud structure observed during a field campaign over Brest (France). The model performance in regular operations, using conventional meteorological data as initial and lateral boundary conditions, was also examined. Remote sensing observations of the cloud system and in-situ aircraft data, selected during the campaign, were used to validate the model outputs. The model simulations showed that the lower cloud formation was characterized by high number concentration of pristine ice and snow, while the concentration of aggregates, graupel and hail were considerably lower. Hydrometeors in liquid phase appeared demonstrating high number concentration and water content on the top of this layer. The upper cloud layer consisted only of frozen water substances in lower amounts. The qualitative and quantitative comparison of the model-calculated meteorological and microphysical fields to the available observational data revealed that the model reflected fairly well the cloud structure (e.g., the spatio-temporal variability of the cloud parameters, the geometry of the cloud system). However, there were deviations as far as the model underestimating the ice water content (IWC) and number concentration (N_t) fields is concerned, especially at the atmospheric layer between 2.5 and 4 km of altitude. These deviations of the model simulated quantities from the measured ones may be attributed either to the performance of the model’s microphysics scheme, to instrument inaccuracies and to the local disturbance caused by the aircraft.     

Eddy-induced oscillations of the pycnocline affect the floristic composition and depth distribution of phytoplankton in the subtropical Pacific

Changes in the phytoplankton population caused by a wind-induced mesoscale eddy, first located off the Hawaiian chain on 29 August 1989, were examined from 6 to 12 September 1989. These cyclonic eddies produce upwelling of nutrient-rich water into the photic zone which may induce changes in the distribution of phytoplankton. The eddy affected the depth, magnitude and composition of the chlorophyll maximum. The eddy produced an upward shift in the distribution of phytoplankton, shoaling the chlorophyll maximum to 30 m. Pigment concentrations at the chlorophyll maximum were enriched up to 2.2 times inside the eddy. Outside the eddy, the upper mixed layer (UML, 50 m) was dominated by cyanobacteria whereas the deep chlorophyll maximum (DCM) was dominated by prochlorophytes, chlorophytes and chrysophytes. Inside the eddy, the UML showed an increase in deep water taxa but little change in cyanobacteria. The observed population changes probably resulted from increased growth rates and vertical transport of cells. Based on projections of the track of the eddy, we inferred that its trail created an area of enhanced chlorophyll that was not quickly consumed, and concluded that coupling between phytoplankton and grazers was weak. The presence of such cyclonic eddies may explain some of the variability in chlorophyll concentration found in the oligotrophic subtropical Pacific.     

Interaction Between Nutrient and Predator Limitation of Production in the Marine Euphotic Zone

Nutrient limitation of phytoplankton growth in nature is a complex phenomenon. the timing of nutrient limitation is a product of matching of algal growth with abiotic and/or biotic events regenerating nutrients, and mismatching with predator activity. the extent of production is governed by the concentration of atomic constituents which, in turn, is a function of the rapidity and quantity of nutrient regeneration by heterotrophs. Excess phytoplankton production over heterotroph demand is lost from the euphotic zone by sinking and from the ecosphere by sedimentation. Phytoplankton growth is therefore always limited by the size and activity of the regenerative food web, either directly through predation, or indirectly by inadequate nutrient regeneration. the open water column is a habitat deplete environment for metazoa, incapable of supporting simultaneous high predator and prey densities. Because of the incompatibility of the temporal and spatial scales of microbial and metazoan processes, and the presence of micro-habitats which can support a full recycling food web on microbial scales, the microbial loop is an important component of euphotic zone ecology. the total marine ecosystem runs at a nutrient sufficient level with nutrient deplete and replete phases dependent on matching of production with predation throughout the food web and subject to abiotic events. Man's release of N and P into coastal waters, if coupled with an increased incidence of mismatch resulting from climatic variation induced by the “greenhouse effect”, could have catastrophic effects on marine ecosystems.     

Simulation of Jeddah multi-port sea outfall

Jeddah wastewater multi-port outfall was analyzed using CORMIX2 for average ambient conditions. The numerical analysis of the outfall shows that the near-field mixing extends 187.5 m downstream of the diffuser and the dilution at the end of near-field reaches 1,047.8. The concentration of the plume drops sharply from 100 at the exit point to 0.0954 at the end of near-field zone. In the far-field zone the reduction in concentration is gradual and will reach 0.0061 at a distance of 20,000 m downstream of the diffuser, while dilution exceeds 16,440 at this point. The plume rises rapidly due to the buoyancy and touches the water surface at a distance of 187.5 m downstream. The thickness of the plume reaches a maximum value of 37.5 m at the interface of near-field and far-Field zones, and then it starts spreading horizontally maintaining a thickness of about 13 m over a distance of about 4 km. As the plume mixes with ambient sea water, it starts spreading again in vertical direction and fills the entire water depth at a distance of 18,927 m down stream. The plume maintains nearly a constant width in the near-field zone but spreads progressively horizontally in the far-field zone till the plume touches the left bank at a distance of 18,482.52 m downstream. The plume spreads at a distance of 2,069 m from the coastline at the end of simulation zone. It can be concluded from numerical results that if the discharged water meets local and international standards for treated wastewater, the plume will not pose any threats to the local venerable environment as the dilution is considerably high due to high exit momentum and favorable cross current.     

Observations of planktonic bioluminescence in the euphotic zone of the California Current

The distributions of bioluminescence, temperature, salinity, oxygen. pH, and chlorophyll a were measured at 10 m intervals, to a depth of 100 m at a station (33°46N; 119°36W) in the California Current from 17 to 20 July 1982. The distribution of bioluminescence showed a marked day-night change which was consistent over the sampling period. The nighttime maximum was at the surface, and the daytime maximum was between 30 and 40 m. The shapes of the day and night distributions were independent of the absolute intensity of bioluminescence and were also insensitive to advection, as inferred from changing temperature-salinity relationships. The nighttime depth distribution broadened during a period of high wind Day to night differences in the color spectrum at the depth of maximum bioluminescence suggest that the luminescent organisms differed from day to night.     

Deep Arabian Sea mesozooplankton distribution. Intermonsoon, October 1995

Mesozooplankton (<5 mm) collected by stratified oblique tows with a 1-m² MOCNESS was examined at four stations in the Arabian Sea, with special reference to the bathypelagic zone. The profiles commenced about 20 m above bottom, at 4430 m as a maximum depth. The highest mesozooplankton biomass concentrations (wet weight per cubic meter) were obtained from the surface layer during night. A secondary maximum was situated between 150 and 450 m, with maximum concentrations at daytime. This layer coincided with the daytime residence depth of the deep scattering layer. The standing crop of the mesozooplankton in the upper 1000 m was highest at station WAST at 16°N; 60°E (ca. 47 000 mg m⁻²); station CAST at 14°N; 65°E ranked second (ca. 22 500 mg m⁻²), followed by station SAST at 10°N; 65°E (11 420 mg m⁻²). The differences can be related to different productivity regimes at the sea surface generated by the Findlater Jet during the SW monsoon. The differences in surface production were also reflected below 1000 m depth, in the bathypelagic zone, with mesozooplankton wet weights of 5330 mg m⁻² at WAST, 3210 mg m⁻² at CAST, 3390 mg m⁻² at EAST (15°N; 65°E) and 2690 mg m⁻² at SAST. The decrease of mesozooplankton concentration with depth in the oxygen minimum zone (OMZ) was stronger than in comparable depths of open-ocean areas where an OMZ is absent. Among the discriminated four size classes of mesozooplankton, the largest fraction (2 to 5 mm) indicated a biomass peak at 1200 m depth, which coincided with the lower boundary layer of the OMZ. The rate of decrease of mesozooplankton biomass with depth in the bathypelagic zone was statistically similar between the sites, even though the absolute zooplankton biomass at the sites was different. There is no evidence that the presumed lower carbon degradation rates in the OMZ of the Arabian Sea caused a larger standing crop and less of a decrease in biomass with depth in the bathypelagic zone in comparison to other seas. Received: 16 May 1997 / Accepted: 5 June 1997     

Temporal variation of the concentration and biochemical composition of seston within the Humboldt Current System off northern Chile (21°S)

Seasonal differences in the concentration and biochemical composition of seston have been assessed for the first time in the Humboldt Current System off northern Chile (21°S). The study comprised four seasonal surveys in the Bay of Chipana, including the summer and winter of 2006 and 2007, when El Niño 2006 and La Niña 2007 developed. Protein, lipid, carbohydrate and biogenic silica contents were measured in samples collected at four selected depths. The highest protein, lipid and carbohydrate concentrations were found at the fluorescence maximum (between 10 and 15 m depth), whereas the highest biogenic silica concentration was found 1 m above the seabed. When El Niño started developing, every variable showed low values throughout the water column; however, the lowest values were found when La Niña conditions dominated, together with low oxygen concentrations. Samples collected within the oxygen minimum zone (65 m depth) showed the lowest values for the water column and the lowest seasonal variations. After the evident decline coincident with El Niño 2006, the abundance and biochemical quality (high protein and lipid contents) of seston recovered earlier in the surface layer (upper 15 m) than at other depths.     

三峡水库浮游植物群落特征及水体富营养化评价

基于2003—2017年三峡水库浮游植物群落结构、优势种群的变化和2017年水库干支流水质数据,全面分析浮游植物群落结构和演替特征,并运用综合营养状态指数法对水体富营养化程度进行评价。结果表明,三峡水库浮游植物种类丰富,监测期间共鉴定出浮游植物7门62属,细胞密度在7.5×10~4~2.8×10~7cell/L之间变化,Shannon-Wiener多样性指数为1.0~3.0,在α-中污带和β-中污带之间,说明三峡水库水生态环境健康状况相对较好;三峡水库浮游植物季节性演替特征呈硅藻和甲藻向蓝藻和绿藻演替的趋势,年际变化特征分析发现浮游植物密度在2008年175 m实验蓄水后大量增长,且优势藻类由河道型藻类向湖泊型藻类转化。通过监测数据分析,得出三峡水库干流处于中营养状态,支流在春季主要处于轻度富营养状态,秋季支流比春季支流的富营养化程度低,主要处于中营养状态,总氮(total nitrogen,TN)、总磷(total phosphorus,TP)和透明度(transparency,SD)为水质主要影响因子。     

论凤眼莲的是非功过

凤眼莲在城市河湖的污染与净化中的是非功过争议很大,双方意见均有部分正确,但各有片面性。凤眼莲耐污能力、净化能力强;生产力高,生产量大;从环境中吸收、转化的污染物种类多、量大;本身有一定的利用和经济价值.它本是水体中营养盐、有机质等污染物的迁移转化和输出链网中一个重要环节。目前一些地方水体中凤眼莲因未及时收获、输出水体,失控而过度发展、排斥其他多种生物的生存和发展,而成为外来入侵种,其残体留存水体中造成二次污染。决定它功过是非的关键是能否及时从其生长水体中收获和输出,防止他们疯长蔓延。而合理利用凤眼莲是促进它们的收获与输出一项条件.如能抓住这一关键,就可解决这一争论.发挥凤眼莲净化水体,变废为宝,化害为利.兼收生态环境和经济效益。     

Modeling compensated root water and nutrient uptake

Plant root water and nutrient uptake is one of the most important processes in subsurface unsaturated flow and transport modeling, as root uptake controls actual plant evapotranspiration, water recharge and nutrient leaching to the groundwater, and exerts a major influence on predictions of global climate models. In general, unsaturated models describe root uptake relatively simple. For example, root water uptake is mostly uncompensated and nutrient uptake is simulated assuming that all uptake is passive, through the water uptake pathway only. We present a new compensated root water and nutrient uptake model, implemented in HYDRUS. The so-called root adaptability factor represents a threshold value above which reduced root water or nutrient uptake in water- or nutrient-stressed parts of the root zone is fully compensated for by increased uptake in other soil regions that are less stressed. Using a critical value of the water stress index, water uptake compensation is proportional to the water stress response function. Total root nutrient uptake is determined from the total of active and passive nutrient uptake. The partitioning between passive and active uptake is controlled by the a priori defined concentration value c_max. Passive nutrient uptake is simulated by multiplying root water uptake with the dissolved nutrient concentration, for soil solution concentration values below c_max. Passive nutrient uptake is thus zero when c_max is equal to zero. As the active nutrient uptake is obtained from the difference between plant nutrient demand and passive nutrient uptake (using Michaelis–Menten kinetics), the presented model thus implies that reduced passive nutrient uptake is compensated for by active nutrient uptake. In addition, the proposed root uptake model includes compensation for active nutrient uptake, in a similar way as used for root water uptake. The proposed root water and nutrient uptake model is demonstrated by several hypothetical examples, for plants supplied by water due to capillary rise from groundwater and surface drip irrigation.     

利用农田系统中源汇型景观组合控制面源磷污染

通过田间调查、采样分析和小区试验,研究浙江省农田系统中源汇型景观组合及其控制面源磷污染的效果.调查表明,浙江省农田系统中源、汇配置的景观类型主要有:蔬菜地 - 稻田系统、蔬菜地 - 茭白田系统、桑园地 -稻田系统、旱地 - 稻田系统、高施肥稻田 - 低施肥稻田系统、农地(稻田、旱地) - 多塘系统、农地(稻田、旱地) - 植草水道(泥质排水沟)等.不同利用方式农田排水中磷含量有较大的差异,总磷平均含量为桑园>蔬菜地>稻田、小麦田、油菜田>休闲地>茭白田.小区试验表明,利用蔬菜地(旱地) - 稻田 - 茭白系统、蔬菜 - 稻田系统、桑园 - 稻田系统和蔬菜地 - (多)水塘系统可明显降低磷流失.建议对某些养分流失严重的农业流域,通过调整土地利用方式和增加养分汇型景观面积来控制农业面源污染.