Catchment-Scale Variation in the Nitrate Concentrations of Groundwater Seeps in the Catskill Mountains,New York,U.S.A.

Forested headwater streams in the Catskill Mountains of New York show significant among-catchment variability in mean annual nitrate (NO₃ ^-) concentrations. Large contributions from deep groundwater with high NO₃ ^-concentrations have been invoked to explain high NO₃ ^-concentrations in stream water during the growing season. To determine whether variable contributions of groundwater couldexplain among-catchment differences in streamwater, we measuredNO₃ ^- concentrations in 58 groundwater seeps distributed across six catchments known to have different annual average streamwater concentrations. Seeps were identified based on release from bedrock fractures and beddingplanes and had consistently lower temperatures than adjacentstreamwaters. Nitrate concentrations in seeps ranged from neardetection limits (0.005 mg NO₃ ^--N/L) to 0.75 mg NO₃ ^--N/L. Within individual catchments, groundwaterresidence time does not seem to strongly affect NO₃ ^-concentrations because in three out of four catchments therewere non-significant correlations between seep silica (SiO₂) concentrations, a proxy for residence time, andseep NO₃ ^- concentrations. Across catchments, therewas a significant but weak negative relationship betweenNO₃ ^- and SiO₂ concentrations. The large rangein NO₃ ^- concentrations of seeps across catchmentssuggests: 1) the principal process generating among-catchmentdifferences in streamwater NO₃ ^- concentrations mustinfluence water before it enters the groundwater flow system and 2) this process must act at large spatial scales becauseamong-catchment variability is much greater than intra-catchmentvariability. Differences in the quantity of groundwater contribution to stream baseflow are not sufficient to account for differences in streamwater NO₃ ^- concentrationsamong catchments in the Catskill Mountains.     

Occurrence of High In-Stream Nitrite Levels in a Temperate Region Agricultural Watershed

This study is the first to report nitrite occurrence and variability in surface water across an agricultural watershed in the province of Quebec, Canada. Nitrite (NO₂ ^?) concentrations were monitored across a 2.4 km² watershed during 2 years. Water samples were collected at the outlet from April to November and in three contrasted stream branches (six stations) during three hydrological regimes (summer low water levels, fall recharge, and snowmelt). Our study clearly demonstrates that NO₂ ^? levels observed at the outlet are not representative of NO₂ ^? variability across the micro-watershed. Surface water collected in cropped areas presents high NO₂ ^? concentrations during summer low water levels, often exceeding guidelines for aquatic life, with NO₂ ^? means ranging from 0.022 to 0.107 mg N L^?1 and maximum value reaching 0.156 mg N L^?1. Furthermore, the two stream branches in cropped area have demonstrated significant differences in NO₂ ^? concentrations and other water quality parameters. The importance of groundwater discharge to streams in the micro-watershed Bras d’Henri may potentially generate different in-stream sources of NO₂ ^? and water quality parameters. However, further studies are essential to determine sources and processes related to in-stream NO₂ ^? peaks.     

Denitrification Efficiency in Groundwater Adjacent to Ditches within Constructed Riparian Wetlands: Kankakee Watershed,Illinois-Indiana,U.S.A.

Dual isotope evaluations of NO₃ ^- in groundwater adjacentto ditches within constructed riparian wetlands across the Kankakee watershed may assist the determination of denitrificationefficiency. Groundwater sampling indicates that NO₃ ^--N exceeded 10 mg L^-1 in constructed riparian wetlands but not innative wetlands within the riparian zones of the Kankakee basin. Anapparent local empirical threshold for nitrification occurs in groundwater near ditches with less then 1:11 depth to width dimensions within similar hydrogeology. The ¹⁵N and ¹⁸Ocomposition of groundwater nitrate varies widely in these constructed riparian wetlands. Groundwater nitrate associated with broader ditches (e.g. 1:35) most closely matches the denitrification isotope signature of native riparian wetlands in the basin. The geometry of various cut and fill landforms may need evaluation in engineering designs for constructed riparian wetlands to ensure the establishment of local natural groundwaterflow conditions for efficient nitrate attenuation.     

Column Studies on Nitrate Removal from Potable Water

Biological processes can achieve nitrate removal from groundwater. The sulfur/limestone autotrophic denitrification by Thiobacillus denitrificans was evaluated with three laboratory-scale column reactors. The optimum sulfur/limestone ratio was determined to be 2:1 (mass/mass). Different hydraulic retention times were used during the column tests to examine nitrate removal efficiencies. Under an HRTs of 13 h, nitrate concentration of 60 mgNO₃ ^--N L^-1 was reduced to less than 5 mg NO₃ ^--N L^-1. On a higher HRT of 26 h the nitrate removal efficiency was close to 100% for all nitrate-nitrogen loading rates. Different initial nitrate-nitrogen concentrations (30, 60, and 90 mg NO₃ ^--N L^-1) were used in the study. Column tests showed that the nitrate-nitrogen loading rate in this study was between 50 to 100 g NO₃ ^--N m^-3 d^-1 to obtain a removal efficiency of 80–100%. It was found that approximately 6 mg SO₄ ^2- was produced for 1 mg NO₃ ^--N removed. Nitrite-nitrogen in all cases was less than the maximum allowable concentration of 1 mg NO₂ ^--N L^-1. Effluent pH was stable in the range of 7 to 8; the effluent dissolved oxygen was less than 0.15 mg L^-1 and the oxidation-reduction potential in all columns was in the range of –110 to –250 mV.     

成都平原农区地下水中NO3--N含量变化规律研究

采用硝酸根电极法对成都平原温江县天府乡农区田间和水井的地下水NO-3 N含量进行了一年多的连续测定 ,探讨了该农区地下水中NO-3 N的变化规律和氮肥用量的影响。结果表明 :(1)田间地下水NO-3 N含量周年变化规律是冬春枯水季较高 ,且变幅较大 (0 3 6～ 2 62mgL- 1) ,平均值为 2 59mgL- 1;夏秋丰水季较低 ,且变幅较小 (0 84～ 5 48mgL- 1) ,平均值为 1 10mgL- 1。 (2 )前作麦季氮肥施用量 ,对稻季地下水中NO-3 N含量有明显影响 ,当前作施纯氮达 3 75kghm- 2 时 ,稻季地下水NO-3 N含量最高达 3 4 6mgL- 1,其平均值为 17 97mgL- 1,是施纯氮 150kghm- 2 平均值 1 3 0mgL- 1的 13 7倍。 (3 )井水中NO-3 N含量变化幅度为 0 14～ 16 53mgL- 1,3口井水平均值分别为 2 54、3 60、6 52mgL- 1,未超出我国生活饮用水卫生标准 ,但明显高于灌溉水NO-3 N含量的平均值 1 81mgL- 1。 (4)地下水位的高低与井水中NO-3 N含量没有线性关系     

Long-Term Annual and Seasonal Patterns of Acidic Deposition and Stream Water Quality in a Great Smoky Mountains High-Elevation Watershed

The recovery potential of stream acidification from years of acidic deposition is dependent on biogeochemical processes and varies among different acid-sensitive regions. Studies that investigate long-term trends and seasonal variability of stream chemistry in the context of atmospheric deposition and watershed setting provide crucial assessments on governing biogeochemical processes. In this study, water chemistries were investigated in Noland Divide watershed (NDW), a high-elevation watershed in the Great Smoky Mountains National Park (GRSM) of the southern Appalachian region. Monitoring data from 1991 to 2007 for deposition and stream water chemistries were statistically analyzed for long-term trends and seasonal patterns by using Seasonal Kendall Tau tests. Precipitation declined over this study period, where throughfall (TF) declined significantly by 5.76?cm?year^?1. Precipitation patterns play a key role in the fate and transport of acid pollutants. On a monthly volume-weighted basis, pH of TF and wet deposition, and stream water did not significantly change over time remaining around 4.3, 4.7, and 5.8, respectively. Per NDW area, TF SO₄ ^2- flux declined 356.16?eq?year^?1 and SO₄ ^2- concentrations did not change significantly over time. Stream SO₄ ^2- remained about 30???eq L^?1 exhibiting no long-term trends or seasonal patterns. SO₄ ^2- retention was generally greater during drier months. TF monthly volume-weighted NH₄ ⁺ and NO₃ ^- concentrations significantly increased by 0.80???eq L^?1?year^?1 and 1.24???eq L^?1?year^?1, respectively. TF NH₄ ⁺ fluxes increased by 95.76?eq?year^?1. Most of NH₄ ⁺ was retained in the watershed, and NO₃ ^- retention was much lower than NH₄ ⁺. Stream monthly volume-weighted NO₃ ^- concentrations and fluxes significantly declined by 0.56???eq L^?1?year^?1 and 139.56?eq?year^?1, respectively. Overall, in NDW, inorganic nitrogen was exported before 1999 and retained since then, presumably from forest regrowth after Frazer fir die-off in the 1970s from balsam wooly adelgid infestation. Stream export of NO₃ ^- was greater during winter than summer months. During the period from 1999 to 2007, stream base cations did not exhibit significant changes, apparently regulated by soil supply. Statistical models predicting stream pH, ANC, SO₄ ^2-, and NO₃ ^- concentrations were largely correlated with stream discharge and number of dry days between precipitation events and SO₄ ^2- deposition. Dependent on precipitation, governing biogeochemical processes in NDW appear to be SO₄ ^2- adsorption, nitrification, and NO₃ ^- forest uptake. This study provided essential information to aid the GRSM management for developing predictive models of the future water quality and potential impacts from climate change.     

Effects of Nitrogen Fertilization on Stream Chemistry of Japanese Forested Watersheds

Steam chemistry was investigated from May 1991 through April 1992 for 13 Japanese forested watersheds and from May 1990 through August 1994 for two of these watersheds. Nine watersheds were treated over different periods (1983–1991) with different amounts of N (nitrogen) fertilizer as urea and ammonium salts. Total N additions ranged from 20 to 375 kg ha^-1. There were no distinct seasonal differences in stream NO₃ ^- concentrations in either the treated or untreated watersheds, but concentrations tended to be somewhat higher during periods of high discharge. The annual average NO₃ ^- concentrations in streams had a significant, positive (p < 0.001, r = 0.84) relationship to the total amount of N applied from 1985–1991. The application of 330 kg N ha^-1 raised annual average stream NO₃ ^- concentration to about 300 μeq L^-1 compared to less than 160 μeq L^-1 in untreated watersheds. The concentrations of K⁺, Ca²⁺, and Mg2+ in stream water also increased in those watersheds with high rates of N fertilizer as a result of nitrification that increased the generation of the mobile nitrate anion. The lack of seasonality in stream NO₃ ^- concentrations and the large rates of N loss with N addition both suggest that these watersheds were ‘nitrogen saturated’     

Soil C/N Ratio as Affected by Climate: An Ecological Factor of Forest NO3 − Leaching

The soil nitrogen cycle was investigated for several watershed forests of which stream waters have distinctively different nitrate (NO₃ ^?) concentrations. In a watershed with stream water NO₃ ^? of more than 100 µM, soil NO₃ ^? content increased even beneath the rooting zone, revealing "nitrogen saturation" status. A laboratory soil experiment demonstrated that the proportion of net NO₃ ^? production to CO₂ production was largely regulated by a soil C/N ratio, suggesting a key parameter for NO₃ ^? abundance. In the respective watershed soils, little nitrogen was actually present as NO₃ ^? above a soil C/N ratio of 20. The annual mean soil temperature recorded at the sites was correlated with a shift in the C/N ratio in watershed soils (a soil C/N ratio increase of 0.5 per 1°C decrease) along the stream NO₃ ^? gradient of 30 fold. The results suggest that soil microbial metabolisms affected by C/N ratio may be a direct agent regulating NO₃ ^? leaching from watersheds under the influence of an atmospheric nitrogen load and climate.     

太湖地区稻麦高产的氮肥适宜用量及其对地下水的影响

通过田间定位试验与土壤渗漏仪 (Lysimeter)模拟试验 ,研究太湖地区稻麦生产中氮肥过量施用带来氮肥利用率低与环境污染问题 ,探讨本区稻麦高产与减少氮肥淋洗的适宜氮肥用量。初步试验结果表明 ,氮肥适宜用量随着稻麦产量的提高而增加 ,本区两种主要土壤水稻、小麦高产的氮肥适宜用量(以N计 )分别为 2 2 5～ 2 70kghm- 2 与 1 80～ 2 2 5kghm- 2 ;适宜的氮肥用量使单位面积的有效穗数和每穗的结实颖花数均高 ,因而产量高。氮素的淋洗以NO- 3 N为主 ,主要发生在麦季与泡田插秧初期 ,其含量随着施氮量的增加而增加 ,每hm2 施N 2 2 5kg的模拟试验 ,麦季渗漏液的NO- 3 N浓度在 5 4～ 2 1 3mgL- 1,有60 %的样次超过污染标准 (NO- 3 N 1 0mgL- 1) ;田间试验 ,麦季施N量在 2 70～ 31 5kghm- 2 范围内 ,地下水NO- 3 N浓度在 1 9～ 1 1 0mgL- 1,有 2 0 %的样次接近 ,1 0 %的样次超过污染标准。长期NO- 3 N渗漏累积 ,势必对地下水构成潜在威胁。     

再生水灌溉区农田包气带及地下水中硝酸盐分布特征及来源研究

本文通过对华北平原典型再生水灌溉区(河北省石家庄洨河流域)的包气带土壤、地表水和地下水进行采样分析,对硝酸盐在多种环境介质中的来源与环境行为进行了研究,识别了再生水灌溉区地下水硝酸盐污染来源,明确了不同灌溉条件对包气带土壤中硝酸盐迁移的影响。在受到城市再生水严重影响的洨河流域,地下水中的硝酸盐浓度分布范围在4.0 mg·L?1到156.6 mg·L?1之间,已经形成了距离河道2 km、深度70 m的硝酸盐高值区域,经过计算硝酸盐的垂向扩散速率为每年1～2 m。硝酸盐与氯离子的相关性表明,城市再生水是再生水灌溉区包气带、地表水和地下水中硝酸盐的主要来源。利用Geoprobe获取利用不同灌溉水农田土壤剖面样品,研究再生水对厚包气带NO3?-N垂向分布影响,再生水灌溉区和地下水灌溉区中包气带土壤的NO3?-N的平均含量为137.0 mg·kg-1和107.7 mg·kg-1,最高含量523.2 mg·L?1和725.9 mg·L?1,分别出现1.20 m和0.85 m深度,分布规律有着明显的差别。包气带土壤硝酸盐与氯离子的相关性分析表明,再生水灌溉区土壤硝酸盐主要来源于城市再生水,而地下水灌溉区可能来源于农田氮肥。地下水年龄和硝酸盐之间关系表明,地下水中1975年以前补给的硝酸盐浓度低于1975年以后补给,地下水硝酸盐污染与包气带氮入渗的历史过程密切相关。在华北平原特殊的地质水文背景下,农田面源污染对地下水的影响有限,但再生水灌溉区地下水硝酸盐污染的风险较高。     

Evaluating the Validity of a Nitrate Quick Test in Different Chinese Soils

Because laboratory tests are expensive and time-consuming and may not be available to farmers, soil nitrate quick tests are required for optimal nitrogen management strategies in China to increase nitrogen use effciency and to reduce nitrogen losses. A total of 328 soil samples were collected at different soil depths from 225 sites in China, which covered a wide range of climatic and geographic regions, soil types, croplands and soil textures, to evaluate the suitability of a quick reflectometer test method for analysing soil NO-3-N in a wide range of soil NO-3 concentrations, soil types and cropping systems in China, mainly by comparison of soil NO-3-N assessed by a quick-test method (a reflectometer) and a standard laboratory method, i.e., high-performance liquid chromatography (HPLC). The reflectometer showed excellent agreement with the laboratory HPLC method with regard to soil nitrate contents for all analysed soil samples. The linear regression had slopes of 1 ± 0.08 and intercepts of ±1.38 mg NO-3-N L-1 among different soil types and croplands. Compared with the 1:1 lines, the regression analysis for each soil type showed statistically significant but small differences in slope; the relative difference between the values measured using the two analytical systems varied from -8% to 6%, and there were no differences in intercept except for paddy soil. The reflectometer showed adequate, statistically significant precision in determining soil nitrate contents, and it could therefore be directly used instead of the laboratory methods for soil NO-3-N measurement in China.     

Contribution of dissolved organic nitrogen deposition to nitrogen saturation in a forested mountainous watershed in Tsukui, Central Japan

Nitrogen (N) budget was estimated with dissolved inorganic N (DIN) and dissolved organic N (DON) in a forested mountainous watershed in Tsukui, Kanagawa Prefecture, about 50 km west of Tokyo in Central Japan. The forest vegetation in the watershed was dominant by Konara oak (Quercus serrata) and Korean hornbeam (Carpinus tschonoskii), and Japanese cedar (Cryptomeria japonica). Nitrate (NO₃ ^?) concentration in the watershed streamwater was averagely high (98.0 ±± 19 (±± SD, n = 36) μmol L^?1) during 2001–2003. There was no seasonal and annual changes in the stream NO^? ₃ concentration even though the highest N uptake rate presumably occurred during the spring of plant growing season, a fact indicating that N availability was in excess of biotic demands. The DON deposition rates (DON input rates) in open area and forest area were estimated as one of the main N sources, accounting for about 32% of total dissolved N (TDN). It was estimated that a part of the DON input rate contributed to the excessive stream NO^? ₃ output rate under the condition of the rapid mineralization and nitrification rates, which annual DON deposition rates were positively correlated with the stream NO₃ ^? output rates. The DON retention rate in the DON budget had a potential capacity, which contributed to the excessive stream NO^? ₃ output rate without other N contributions (e.g. forest floor N or soil N).     

Spatial and Temporal Variability of Groundwater Nitrate Concentrations in Irrigated Mediterranean Agriculture

As nitrogen (N) fertilizer-use efficiency rarely exceeds 50% in most agricultural systems, the potential leaching of N to the groundwater, particularly under irrigated conditions, has economic, health, and environmental implications. Research in the Akarsu irrigation district in the Lower Seyhan Plain in southern Turkey sought to determine spatial and temporal variability of groundwater (GW) nitrate (NO₃) concentrations in 2007–2008. Shallow groundwater observation wells 3 m deep were installed at different locations to represent the whole irrigation district. Groundwater samples were collected (February, April, July, October) and analyzed for ammonium (NH₄) and NO₃ concentrations. Because NH₄ values were negligible, only NO₃ data were processed to determine spatial and temporal variability and then used to develop regional NO₃ maps using geographic information systems. Groundwater NO₃ concentrations ranged between 0.17 and 55.96 mg L^–1 during the 2 years, only exceeding the critical 50 mg L^–1 concentration in 1% of the area sampled. The areal mean of NO₃ concentration was greatest in February, indicating a potential N leaching of unused N from the early season with intensive rainfall, especially in wheat-growing areas. Groundwater NO₃ concentrations decreased after February; however, during the peak irrigation season in July, NO₃ was relatively low because of crop uptake during spring and summer. In about half the area, groundwater NO₃ concentrations ranged between 20 and 50 mg L^–1 and were thus marginal relative to the critical pollution level. As N fertilizer use will continue to increase, especially with the expanded irrigation that is now occurring in the Mediterranean region, regular monitoring of groundwater NO₃ is advisable under such conditions.     

Nitrogen and Phosphorus Leaching from Fertilizer Applied on Golf Course: Lysimeter Study

Fertilizers applied to turfgrass may pose a threat to surface and groundwater quality, and hence, a study was carried out to evaluate the fate of fertilizer applied to turfgrass of the Clearwater Bay Golf and Country Club in Hong Kong. Lysimeters with reconstituted soils collected from fairways and greens with Bermudagrass (Cynodon dactylon) growing in the surface were used to evaluate the leaching loss of nitrate (NO₃ ^-), ammonium (NH₄ ⁺), and phosphate (PO₄ ^3-) for 22 weeks under greenhouse condition. Both soils received a slow release fertilizer at an application rate of 25 (low) or 50 (high) kg N ha^-1, and an application frequency of monthly and fortnightly for fairways and greens, respectively, simulating the fertilizer application strategy of the golf course. Both low and high fertilizer application rate supported the same amount of biomass production for each soil type. Breakthrough of NO₃ ^- occurred only in greens after 11 weeks of leaching, but the total amount of NO₃ ^- leached did not differ significantly for the two different fertilizer application rates. The continued addition of fertilizer to greens resulted in a final leachate NO₃ ^- concentration exceeding 45 mg L^-1, while fairways maintained a concentration below 5 mg L^-1. Also PO₄ ^3- concentration in leachate of greens exceeded the surface water standard of 0.3 mg L^-1. The results of the lysimeter study showed that the current application rate on greens would create adverse environmental impacts on the surface water and groundwater due to leaching loss of PO₄ ^{3 -} and NO₃ ^-.     

凉水国家级自然保护区溪流水化学特征分析

 采用集水区对比分析方法,探讨凉水国家级自然保护区不同森林类型对溪流水化学特征的影响。结果表明:保护区内各集水区溪流水均呈弱酸性至中性;主要离子中阳离子均以Ca2+的质量浓度最高,Na+次之,阴离子均以HCO3-的质量浓度最高,SO2-4次之;不同集水区溪流水中TP月平均质量浓度为0.031～0.077mg/L,TN为0.682～0.942 mg/L,NO-3-N的质量浓度高于NH+4-N;Fe的月平均质量浓度为0.030～0.037mg/L,Mn为0.010～0.012 mg/L。溪流水化学季节变化规律表现为:除HCO-3、SO2-4、Ca2+、Fe和Mn外,其他元素在融雪（4、5月）含量均较高;大多数元素在雨季的质量浓度比9月份低,而TN、TP、Fe、Mn表现为9月份的质量浓度低于雨季。保护区内原始阔叶红松林集水区溪流水质为最优,其他研究集水区溪流中的溶解物质含量增高,但除TP和SO2-4（p<0.05）外,差异性均不显著。说明凉水国家级自然保护区内虽进行过森林采伐和人工造林等人为干扰,但对于溪流水质并没有显著影响。     

Nitrate removal from ground water — use of a nitrate selective resin and a low concentrated regenerant

A new, strong base, macro-porous anion exchange resin, Amberlite IRA 996, appeared to be more nitrate selective than sulfate selective in treating high nitrate concentrations (18 mg NO _inf3 ^sup? -N L^?1) in potable water. When regeneration is carried out in a closed circuit in which a biological denitrification reactor is incorporated to remove nitrate from the regenerant, regeneration salt requirement and brine production can be minimized. In this combination of ion exchange and biological denitrification, regeneration with 30 g NaHCO₃ L^?1) is possible in 6 hr at a flow rate of 11 BV hr^?1. Accumulation of sulfate in the closed regeneration circuit does not affect the nitrate capacity of the resin.     

Effects of tile drainage repair on nutrient leaching from a field under ordinary cultivation in Sweden

Leaching losses of nitrogen (N), phosphorus (P) and potassium (K) from arable land can be high, with N and P contributing significantly to the eutrophication of lakes and coastal waters. This study examined whether agriculture management and drain repair changed the chemical properties of shallow groundwater and affected nutrient leaching in the field. The hydrology of a subsurface-drained agricultural observation field included in the Swedish water quality monitoring programme was simulated for the period 1976–2006 using the process-based, field-scale model DRAINMOD. On the assumption that the drainage system operated similarly before and after repair, 54% more water was assigned to low-moderate flow events. Measured concentrations of sulphate-sulphur (SO₄-S), sodium (Na), chloride (Cl) and potassium (K) were significantly lower in shallow groundwater in the period before drainage system repair (1980–1998) than afterwards (1998–2010). The concentrations were also significantly correlated with the corresponding concentrations in near-simultaneously sampled drain water. A similar connection was not observed for Na and Cl in the period before drain repair. Elevated concentrations of nitrate-nitrogen (NO₃-N) were recorded both in shallow groundwater and in drainage water from 1998 to 2010, especially after incorporation of chicken manure into the soil in 1998. Based on simulated discharge (assuming a functioning measuring station throughout), estimated flow-weighted mean NO₃-N concentration in drainage water increased from 5.6 mg L^?1 (1977–1998) to 15.7 mg L^?1 in the period 1998–2000. Simultaneously, mean NO₃-N concentration in shallow groundwater increased from 0.2 to 4.0 mg L^?1, and then to 4.8 mg L^?1 in the period 2000–2012. It was estimated that after drain repair, a greater proportion of infiltrated NO₃-N entered the receiving stream directly via the outlet of the tile drainage system close to the field's monitoring station than was the case before repair.     

不同水稻品种根尖吸收NO3-过程中表皮细胞膜电位变化特征

越来越多的结果表明给水稻提供部分硝酸盐营养可促进水稻的氮素总吸收量并明显改善水稻的生长发育。利用微电极技术分别测定了4个水稻品种即农垦57(粳稻)、泗优917(杂粳)、扬稻6号(籼稻)和汕优63(杂籼)幼苗根尖表皮细胞在3种NO3^-浓度(0．1mmol L^-1、1mmol L^-1、10mmol L^-1)处理过程中膜电位的变化特征。结果表明：水稻根系吸收NO3^-引起膜的去极化，去极化到一定程度出现复极化。去极化程度随外界处理液中NO3^-浓度的增加而加强，0．1mmol L^-1 NO3^-处理产生的去极化值平均为7mV，1mmol L^-1 NO3^-处理的平均为11mV，10mmol L^-1 NO3^-处理的平均为21mV；就复极化来说，0．1mmol L^-1 NO3^-处理自动出现复极化，1mmol L^-1 NO3^-处理和处理10mmol L^-1 NO3^-处理只有当除去NO3^-时才出现复极化。就单位时间膜电位变化大小而言，扬稻6号对外界NO3^-较敏感，3种NO3^-浓度引起的去极化值均高于其他3个品种，表现出对NO3^-的吸收能力较强；泗优917和汕优63表现出相似的去极化大小和相似的反应时间，而农垦57对NO3^-相对不敏感，3种NO3^-浓度引起的去极化值均低于其他3个品种，表现出对NO3^-的吸收能力较弱。另外，有部分品种的水稻根在吸收NO3^-以后表现为膜电位先超极化后去极化。上述结果表明用根系对NO3^-响应的细胞膜电位变化来研究水稻的硝酸盐营养是有可行性的。     

Comparison of Nitrate Leaching under Silver Birch (Betula Pendula) and Corsican Pine (Pinus Nigra SSP. Laricio) in Flanders (Belgium)

In a forest in Flanders (Belgium), situated in a region of intensive livestock production, comparable stands of Corsican pine and silver birch were studied for (1) NH₄ ⁺ and NO₃ ^- concentrations in throughfall water and soil solution and (2) depositions and leaching of NH₄ ⁺ and NO₃ ^- to groundwater. In each stand, throughfall collectors and porous cup lysimeters at three depths (0.1m, 0.5m and 1m) were installed in three replicated sets. Throughfall concentrations of ammonium and nitrate were significantly different for both species as well as soil solution concentrations of nitrate at all depths. Under pine, nitrate concentrations of the soil solution at 1m depth clearly exceeded the Belgian critical level for drinking water (50 mg.1^-1). Under birch, this level was only sporadically exceeded. During the sampling period, the depositions of NH₄ ⁺-N and NO₃ ^--N reached respectively 21.6 kg/ha and 6.3 kg/ha under birch and 81.3 and 15.2 kg/ha under Corsican pine. Nitrate-N leaching under silver birch amounted 25.4 kg/ha whereas 56.4 kg/ha was measured under Corsican pine.     

Sulfate and Nitrate Loads on a Forest Ecosystem in Kochi in Southwest of Japan

To assess the influence of acidic deposition on the forest ecosystem, it is necessary to evaluate the gross amount of acidic deposition. In this paper, we discuss the variation of sulfate (SO₄ ^2?) and nitrate (NO₃ ^?) loads as well as related concentration from 1991 to 1999 in the Hinoki (Chamaecyparis obtusa) plantation in Kochi, southwest Japan. The annual precipitation varied significantly from 1,700 to 3,900 mm during the study period. The annual sulfate concentration of rainfall was about 15 µmol L^?1, including about 80% non sea salt sulfate, while the annual nitrate concentration of rainfall was increased. The sulfate and nitrate concentrations of the through fall and the nitrate concentration of the stem flow were equal to or slightly higher than those of rainfall. However, the sulfate concentration of the stem flow was higher than that of rainfall, 21 to 55 µmol L^?1. The sulfate and nitrate loads of rainfall were measured to be 27 to 46 and 14 to 43 mmol m^?2 y^?1, respectively. The sulfate and nitrate loads of the through fall were the same or slightly higher than those of rainfall. In contrast, the sulfate and nitrate loads of the stem flow were less than those of rainfall. Combined sulfate loads of the through fall and the stem flow reached about 1.5 times that of the sulfate load of rainfall.