Predicting the transfer of 137Cs to rice plants by a dynamic compartment model with a consideration of the soil properties

The factors governing chlorine transfer from Phaeozem and Greyzem soils to various important crop species (foodstuff and forage) were determined in natural conditions in the Kiev region of Ukraine. The stable chlorine concentration ratio (CR) values were the lowest in apple (0.5+/-0.3) and strawberry (2+/-1), higher in vegetables (5+/-3), seeds (15+/-7) and reached a maximum in straw (187+/-90). The average CR values of 36Cl were estimated for the most important crops using all experimental data on 36Cl and stable chlorine transfer into plants from various soils. It was experimentally shown that boiling potatoes in water leads to an equilibrium between 36Cl specific content in the water and moisture in the cooked potato. The 36Cl processing factor (PF) for boiling various foodstuffs is equal to the ratio of water mass in the cooked foodstuff to the total water mass (in the food and the decoction). 36Cl PF for cereal flour can be estimated as 1. The 36Cl processing factor for dairy products is equal to the ratio of residual water mass in the product to initial water mass in milk. At a 36Cl specific activity in soil of 1 Bq kg-1, the estimated annual dietary 36Cl intake into human organism (adult man) is about 10 kBq. Sixty to seventy percent of the above amount will be taken in via milk and dairy products, 7-16% via meat, 14-16% via bread and bakery items and 8-12% via vegetables. The highest annual 36Cl intake, 10.7 kBq, is predicted for 1-year-old children. The expected effective doses from annual 36Cl intake are higher for younger age groups, increasing from 0.008 mSv in adults to 0.12 mSv in 1-year-old children.     

Characterisation of submarine groundwater discharge offshore south-eastern Sicily

A complex approach in characterisation of submarine groundwater discharge (SGD) off south-eastern Sicily comprising applications of radioactive and non-radioactive tracers, direct seepage measurements, geophysical surveys and a numerical modelling is presented. SGD fluxes in the Donnalucata boat basin were estimated by direct seepage measurements to be from 4 to 12Ls(-1), which are comparable with the total SGD flux in the basin of 17Ls(-1) obtained from radon measurements. The integrated SGD flux over the Donnalucata coast estimated on the basis of Ra isotopes was around 60m(3)s(-1) per km of the coast. Spatial variations of SGD were observed in the Donnalucata boat basin, the average (222)Rn activity concentration in seawater varied from approximately 0.1kBqm(-3) to 3.7kBqm(-3) showing an inverse relationship with salinity. The continuous monitoring carried out at the site closest to the coast has revealed an inverse relationship of (222)Rn activity concentration on the tide. The (222)Rn concentrations in seawater varied from 2.3kBqm(-3) during high tides to 4.8kBqm(-3) during low tides, thus confirming an influence of the tide on submarine groundwater discharge. Stable isotopes (delta(2)H and delta(18)O) showed that SGD samples consist up to 50% of groundwater. Geo-electrical measurements showed a spatial variability of the salt/fresh water interface and its complex transformation in the coastal zone. The presented results imply that in the studied Donnalucata site there are at least two different sources of SGD, one superficial, represented by mixed fresh water and seawater, and the second one which originates in a deeper limestone aquifer.     

The use of carbon and nitrogen isotope ratios to identify landfill leachate contamination: Green Island Landfill, Dunedin, New Zealand

A study was undertaken to determine whether the isotopic ratios of C and N could be used to uniquely identify municipal solid waste landfill leachate as a source of contamination in the Kaikorai Estuary, Dunedin, New Zealand. Leachate samples were taken from the adjacent Green Island Landfill (GILF), and surface water samples were collected over an 8-month period from the stream and estuary, upstream and downstream of the landfill. Samples were analysed for delta(13)C-dissolved inorganic carbon (DIC), delta(15)N-NO(3)(-), delta(15)N-NH(4)(+), and particulate organic matter (POM) delta(13)C and delta(15)N. Plant material collected along the Kaikorai Stream was analysed for POM delta(13)C and delta(15)N. Leachate was found to have a distinct isotopic signature characterised by a highly enriched delta(13)C-DIC (as much as 16.11+/-0.23 per thousand ) and highly enriched delta(15)N-NH(4)(+) (as much as 27.42+/-0.90 per thousand ). Evidence of leachate contamination was found in the isotopic signatures of downstream delta(13)C-DIC, delta(15)N-NH(4)(+), and delta(13)C and delta(15)N of plant material POM. Other potential sources of enriched delta(13)C-DIC and delta(15)N-NH(4)(+) present in the study area, such as estuarine waters and livestock effluent, were eliminated on the basis of their isotopic characteristics.     

Revision and meta-analysis of selected biosphere parameter values for chlorine, iodine, neptunium, radium, radon and uranium

There is a continual supply of new experimental data that are relevant to the assessment of the potential impacts of nuclear fuel waste disposal. In the biosphere, the traditional assessment models are data intensive, and values are needed for several thousand parameters. This is augmented further when measures of central tendency, statistical dispersion, correlations and truncations are required for each parameter to allow probabilistic risk assessment. Recent reviews proposed values for 10-15 key element-specific parameters relevant to (36)Cl, (129)I, (222)Rn, (226)Ra, (237)Np and (238)U, and some highlights from this data update are summarized here. Several parameters for Np are revised downward by more than 10-fold, as is the fish/water concentration ratio for U. Soil solid/liquid partition coefficients, Kd, are revised downward by 10-770-fold for Ra. Specific parameters are discussed in detail, including degassing of I from soil; sorption of Cl in soil; categorization of plant/soil concentration ratios for U, Ra and Np; Rn transfer from soil to indoor air; Rn degassing from surface water; and the Ca dependence of Ra transfers.     

Radiochlorine concentration ratios for agricultural plants in various soil conditions

Long-term field experiments have been carried out in the Chernobyl exclusion zone in order to determine the parameters governing radiochlorine ((36)Cl) transfer to plants from four types of soil, namely, Podzoluvisol, Greyzem, Phaeozem and Chernozem. Radiochlorine concentration ratios (CR=concentration of (36)Cl in the fresh plant material divided by its concentration in the dried soil in the upper 20 cm layer) were obtained in green peas (2.6+/-0.4), onions (1.5+/-0.5), potatoes (8+/-1), clover (90+/-26) and ryegrass (158+/-88) hay, oat seeds (36+/-23) and straw (305+/-159), wheat seeds (35+/-10) and straw (222+/-82). These values correlate with the stable chlorine values for the same plants. It was shown that (36)Cl plant/soil CR in radish roots (CR=9.7+/-1.4) does not depend on the stable chlorine content in the soil (up to 150 mgkg(-1)), soil type and thus, that stable chlorine CR values (9.4+/-1.2) can also be used for (36)Cl. Injection of additional quantities of stable chlorine into the soil (100 mgkg(-1) of dry soil) with fertilizer does not change the soil-to-plant transfer of (36)Cl. The results from a batch experiment showed that chlorine is retained in the investigated soils only by live biota and transfers quickly (in just a few hours) into the soil solution from dry vegetation even without decomposition of dead plants and is integrated in the migration processes in soil.     

A study on the arsenic concentration in groundwater of a coastal aquifer in south-east India: an integrated approach

The occurrence of arsenic in drinking water and its detrimental effects have drawn much attention in recent years. Several studies have been conducted in the deltaic plains of River Ganga, NE part of the India, and in other countries, but no systematic study was conducted in South India on occurrence of arsenic in groundwater. The main aim of this study is to determine the level of arsenic in groundwater and to understand the relation with other geochemical parameters of groundwater in the south-eastern coastal aquifer at Kalpakkam region, India. This region is represented by three different lithologies, viz. charnockites, flood plain alluvium and marine alluvium. Twenty-nine representative samples of groundwater were collected and analysed for major ions, metals and isotopes such as ²H and ¹⁸O. In addition, geophysical method was also attempted to understand the subsurface condition. The spatial variation in arsenic (As) indicates that higher concentration was observed around the landfill sites and irrigated regions, which was supported by geochemical, statistical and isotopic inferences. The variation in the As with depth, lithology and sources has been clearly brought out. Though the values of As does not exceed the drinking water permissible limit (10 mg/l), it has reached a near permissible level of 8.7 ppb. Hence, it is essential to understand the geochemical behaviour of As for a proper future management of the water resource in the study area.     

Acid mine drainage pollution in the Tinto and Odiel rivers (Iberian Pyrite Belt, SW Spain) and bioavailability of the transported metals to the Huelva Estuary

The Tinto and Odiel rivers are seriously affected by acid mine drainage (AMD) from the long-term mining activities in Iberian Pyrite Belt (IPB). As a consequence, the Huelva estuary is heavily contaminated by metals and metalloids. This study presents an estimation of the seasonal variation, and the dissolved contaminant load transported by both rivers from February 2002 to September 2004. Besides, toxicity and bioaccumulation tests with the sediments of the estuary have been conducted in order to measure the mobility of the toxic metals. Results show that the Tinto and Odiel rivers transport enormous quantities of dissolved metals to the estuary: 7900 t yr(-1) of Iron (Fe), 5800 t yr(-1) Aluminium (Al), 3500 t yr(-1) Zinc (Zn), 1700 t yr(-1) Copper (Cu), 1600 t yr(-1) Manganese (Mn) and minor quantities of other metals and metalloids. These values represent 37% of the global gross flux of dissolved Zn transported by rivers in to the ocean, and 15% of the global gross flux of dissolved Cu. These metals and metalloids usually sink in the estuarine sediments due to pH and salinity changes. The increase of salinity in the estuary favours the adsorption and trapping of metals. For this reason, the mobility and bioavailability of metals such as Zn, Cd and Cu is higher in sediments located in the area of fresh water influence that in sediments located in the marine influenced area of the estuary, showing a higher percentage of fractionation and bioaccumulation of these metals in the station influenced by the fresh water environment.     

Stable carbon isotope ratios of POPs--a tracer that can lead to the origins of pollution

An elemental analyzer in combination with stable isotope ratio mass spectrometry (EA-IRMS) was used to demonstrate that two samples of the chloropesticide Melipax discovered in two countries varied only by 0.1 per thousand in their delta 13C values. Gas chromatography interfaced to a stable isotope mass spectrometer (GC-IRMS) was used to study the delta 13C values of individual congeners in two technical polybrominated diphenyl ether products, i. e. DE-71 and DE-79, at three different concentration levels. Injections of 4 microg and 5.2 microg of DE-71 and DE-79 were most suited for the determinations. In both products, the delta 13C values were usually the more negative the higher the degree of bromination was. The delta 13C values of three hexabromo isomers BDE 138, BDE 153, and BDE 154 could be determined in both products. In all cases the delta 13C values of the three hexaBDEs were more depleted in delta 13C in the higher brominated technical octabromo diphenyl ether DE-79.     

Soil-to-plant halogens transfer studies 2. Root uptake of radiochlorine by plants

Long-term field experiments have been carried out in the Chernobyl exclusion zone in order to determine the parameters governing radiochlorine (36Cl) transfer to plants from four types of soil, namely, podzoluvisol, greyzem, and typical and meadow chernozem. Radiochlorine concentration ratios (CR) in radish roots (15+/-10), lettuce leaves (30+/-15), bean pods (15+/-11) and wheat seed (23+/-11) and straw (210+/-110) for fresh weight of plants were obtained. These values correlate well with stable chlorine values for the same plants. One year after injection, 36Cl reached a quasi-equilibrium with stable chlorine in the agricultural soils and its behavior in the soil-plant system mimicked the behavior of stable chlorine (this behavior was determined by soil moisture transport in the investigated soils). In the absence of intensive vertical migration, more than half of 36Cl activity in arable layer of soil passes into the radish, lettuce and the aboveground parts of wheat during a single vegetation period.     

Isotope tracing of submarine groundwater discharge offshore Ubatuba, Brazil: results of the IAEA-UNESCO SGD project

Results of groundwater and seawater analyses for radioactive ((3)H, (222)Rn, (223)Ra, (224)Ra, (226)Ra, and (228)Ra) and stable (D and (18)O) isotopes are presented together with in situ spatial mapping and time series (222)Rn measurements in seawater, direct seepage measurements using manual and automated seepage meters, pore water investigations using different tracers and piezometric techniques, and geoelectric surveys probing the coast. This study represents first time that such a new complex arsenal of radioactive and non-radioactive tracer techniques and geophysical methods have been used for simultaneous submarine groundwater discharge (SGD) investigations. Large fluctuations of SGD fluxes were observed at sites situated only a few meters apart (from 0cmd(-1) to 360cmd(-1); the unit represents cm(3)/cm(2)/day), as well as during a few hours (from 0cmd(-1) to 110cmd(-1)), strongly depending on the tidal fluctuations. The average SGD flux estimated from continuous (222)Rn measurements is 17+/-10cmd(-1). Integrated coastal SGD flux estimated for the Ubatuba coast using radium isotopes is about 7x10(3)m(3)d(-1) per km of the coast. The isotopic composition (deltaD and delta(18)O) of submarine waters was characterised by significant variability and heavy isotope enrichment, indicating that the contribution of groundwater in submarine waters varied from a small percentage to 20%. However, this contribution with increasing offshore distance became negligible. Automated seepage meters and time series measurements of (222)Rn activity concentration showed a negative correlation between the SGD rates and tidal stage. This is likely caused by sea level changes as tidal effects induce variations of hydraulic gradients. The geoelectric probing and piezometric measurements contributed to better understanding of the spatial distribution of different water masses present along the coast. The radium isotope data showed scattered distributions with offshore distance, which imply that seawater in a complex coast with many small bays and islands was influenced by local currents and groundwater/seawater mixing. This has also been confirmed by a relatively short residence time of 1-2 weeks for water within 25km offshore, as obtained by short-lived radium isotopes. The irregular distribution of SGD seen at Ubatuba is a characteristic of fractured rock aquifers, fed by coastal groundwater and recirculated seawater with small admixtures of groundwater, which is of potential environmental concern and has implications on the management of freshwater resources in the region.     

长江入海水沙通量变化过程分析及变化趋势

针对河流入海水沙通量变化问题,以长江为研究对象,基于1950~2017年大通站及各组分实测水沙和降雨量数据,在分析入海水沙和各组分变化过程及各组分贡献比例的基础上,确定主要贡献组分,进而预测入海水沙通量的变化趋势。结果表明：（1）各组分年径流量和降雨量的多年变化均不大,使得大通站入海年径流量多年变化不大,宜昌站对入海年径流量的贡献比例为48%。（2）大通站入海流量年内分配过程逐渐坦化,其中宜昌站为主要贡献组分,洪枯季平均贡献比例分别为233.79%和80.36%;宜昌站的主要贡献作用体现了其上游梯级水库群对大通站入海流量过程的调平效应。（3）流域水库建设将使得大通站入海流量过程坦化和年径流量稳定的趋势得以维持。（4）大通站年入海沙量自1985年起显著减少,三峡水库蓄水前大通站泥沙主要来自宜昌,其贡献比例为116.04%,三峡水库蓄水后,大通站泥沙主要来自宜昌—大通区间的河床补给,其贡献比例为53.29%;水库下游河床补给逐渐减少和水库淤积平衡时间延长将使得大通站多年平均入海沙量在较长时期内（>300年）不超过1.5×108 t/a。     

长江口前缘沙洲演变与流域泥沙要素关系

为了研究河口前缘沙洲演变过程与流域入海泥沙要素关系,建立了长江口前缘沙洲面积冲淤速率和流域入海泥沙要素关系曲线,并预测沙洲发展趋势。结果表明：长江河口前缘沙洲1958~1989年-5 m以浅面积表现为淤涨,1989~2000年为淤涨和侵蚀交替变化,但幅度较小,自2000年起为冲刷趋势发展,这一过程伴随流域入海泥沙量和含沙量的减少而产生。同时沙洲面积的锐减过程中存在临界泥沙要素条件,并建立了相应的经验曲线,当沙洲面积冲刷和淤涨达到平衡时,临界入海沙量和含沙量临界值分别为283×10⁸t/a,0318 kg/m3。依据以往三峡水库蓄水后入海沙量预测数据,三峡水库蓄水后60 a左右前缘沙洲-5 m以浅面积将侵蚀到1958年水平,其后沙洲面积增加趋势,面积逐渐恢复。2003~2011年长江流域入海泥沙量小于三峡水库蓄水前的预测数值,沙洲面积的冲刷趋势将加剧,应引起有关机构和部门重视     

Evolutionary social and biogeophysical changes in the Amazon,Ganges–Brahmaputra–Meghna and Mekong deltas

Policy-making in social-ecological systems increasingly looks to iterative, evolutionary approaches that can address the inherent complexity of interactions between human wellbeing, provision of goods, and the maintenance of ecosystem services. Here, we show how the analysis of available time-series in tropical delta regions over past decades can provide important insight into the social-ecological system dynamics in deltaic regions. The paper provides an exploratory analysis of the recent changes that have occurred in the major elements of three tropical deltaic social-ecological systems, such as demography, economy, health, climate, food, and water. Time-series data from official statistics, monitoring programmes, and Earth observation data are analysed to explore possible trends, slow and fast variables, and observed drivers of change in the Amazon, Ganges–Brahmaputra–Meghna and Mekong deltas. In the Ganges–Brahmaputra–Meghna delta zone, increasing gross domestic product and per capita income levels since the 1980s mirror rising levels of food and inland fish production. In contrast, non-food ecosystem services, such as water availability, water quality, and land stability appear to be deteriorating. In the Amazon delta, natural and anthropogenic perturbations are continuously degrading key ecosystem services, such as carbon storage in biomass and soils, the regulation of water balance, and the modulation of regional climate patterns. In the Mekong delta, rapid economic development, changing land-use practices, and salinity intrusion are progressively putting more pressure on the delivery of important provisioning services, such as rice and inland aquaculture production, which are key sources of staple food, farm incomes, and export revenue. Observed changes in many key indicators of ecosystem services point to a changing dynamic state and increased probability of systemic threshold transformations in the near future.     

A general methodology for structuring models to predict the long-term migration of radionuclides from catchments

In the present paper a generic model for predicting the long-term migration of radionuclides and heavy metals from catchments is described. The model subdivides the catchment into a number of homogeneous, infinitesimal sub-catchments and integrates the radionuclide contributions from such sub-catchments to calculate the total flux of contaminant. It relates the radionuclide behaviour to the statistical distribution of the pollutant partition coefficient on the "ensemble" of sub-catchments. The methodology was validated for 90Sr and 137Cs by using data for water contamination in some European rivers. Values of migration parameters for Pu, Tc, I and Cd isotopes were obtained.     

太湖辐射和能量收支的时间变化特征

湖泊的辐射和能量收支的观测研究对于气象学和水文学研究都具有重要的意义。于2012年采用涡度相关系统和小气候观测系统观测太湖表面的辐射平衡、湖泊与大气之间的感热和潜热通量、水温廓线和常规气象要素数据,分析太湖表面辐射及能量收支的时间变化特征以及环境控制因子。结果表明:(1)太湖2012年辐射收支四分量(向下短波辐射、向上短波辐射、向下长波辐射和向上长波辐射)的年均值分别为146.5、9.4、359.7和405.4 W/m~2,反照率的年均值为0.06,各辐射分量日变化和季节变化特征明显;(2)净辐射和热储量日变化趋势相同,正午最高,午夜最低;湍流能量通量的日变化幅度较小;不同天气条件下能量分配具有一定差别:晴天条件下能量分配以潜热通量为主,阴天净辐射能量主要被水体吸收转换为热储量;(3)通过分析湍流能量通量与环境因子的相关性发现:感热通量变化最主要的相关因子是风速与湖–气界面温度差的乘积;风速与湖-气界面水汽压的乘积是潜热通量的主要驱动因子。本研究结果能为边界层气象学、全球能量和物质循环以及湖泊生态环境治理等研究提供理论基础和数据支持。     

鄱阳湖区地下水位动态及其与湖水侧向水力联系分析

基于野外定点监测数据,运用统计学方法解析鄱阳湖区地下水位年内分布特征和动态变化,辨析湖水和典型区地下水之间的侧向水力联系与程度。统计结果表明,不同洲滩地下水埋深变化范围约–8.1~–0.1 m,洲滩地下水和湖水在6~9月份保持完全水力连通。湖水位和洲滩地下水位动态变化呈现高度一致性,表明了洲滩地下水和湖水具有密切的侧向水力联系。湖岸带不同典型区的地下水埋深变化范围介于–10~–2.2 m。湖岸带地下水位与湖水位并不具有日时间尺度变化上的高度一致性,但两者却很好呈现了月尺度上的较好一致性,表明了湖岸带地下水与湖水之间具有一定的相互关系和水力联系。小波分析得出,湖水位和洲滩、湖岸带不同典型区的地下水位均在60 d尺度的周期上存在着极大可能的显著相关,总体上两者呈正相关关系变化,表明湖水和洲滩地下水具有密切的水力联系,但与湖岸带地下水的侧向水力联系可能体现在个别典型时段。为今后鄱阳湖地下水方面的相关研究奠定基础,也为鄱阳湖湿地生态环境保护、水资源评价等方面提供科学依据和参考。     

鄱阳湖流域水化学环境参数的变化特征

分别于2010年2月和7月,对鄱阳湖湖区和入湖河流的pH、TDS以及主要离子浓度进行了测定,分析了主要离子组成的时空变化特征及其影响机制。结果表明,鄱阳湖流域水体属于弱矿化度软水,Ca2+是湖水和河水的主要阳离子,分别占阳离子总数〖JP〗的5935%、4989%;HCO-3是湖水和河水的主要阴离子,分别占阴离子总数的5337%、5937%,水质类型为Ca-HCO-3型水;主要离子组成和TDS浓度具有明显的季节和沿程变化特征,这与降雨季节性变化以及不同水系的地质背景有关;从河流水系上游至湖区的水化学特征依次为HCO-3型、HCO-3-SO2-4和SO2-4型。从水化学控制机制上看,鄱阳湖丰水期受大气降水作用和地质条件影响显著,而枯水期降雨量大大减少,主要受岩石风化、蒸发沉淀作用和人为输入的影响。除此之外,SO2-4型水的增加与长江干流酸化以及丰水期长江顶托倒灌现象有密切关系     

汉江堵河流域地表水质时空变化特征

对汉江堵河流域9个点位为期1年的地表水水质理化特性进行时空特征分析，应用〖WTBX〗t〖WTBZ〗检验进行水质季节性变化分析，聚类分析进行空间相似性分析以确定空间尺度的分类情况，判别分析识别显著性指标，并以此反映上述空间聚类分析结果的差异性。结果表明:①Cl-、总溶解性固体（TDS）及浊度（Turbidity） 3项指标没有表现出显著的时间差异性；②温度、pH、NO-3、TP表现为丰水季显著大于枯水季，而SO2-4、HCO-3、NH+4、 DO则表现出相反的变化趋势，即枯水季显著大于丰水季；③空间聚类分析将采样点分为4类；④判别分析体现出良好的指标降维能力，仅需4个指标（NO-3、TDS、SO2-4、HCO-3）即可反映整体水质的空间差异性。     

Time-series sampling of Ra and Ra at the inlet to Great South Bay (New York): a strategy for characterizing the dominant terms in the Ra budget of the bay

Ra isotopes are a powerful tool for quantifying the flux of submarine groundwater discharge (SGD) into the sea. Previous studies of ²²³Ra and ²²⁴Ra mass balances in coastal embayments have shown that the Ra balance is dominated by supply via SGD, exchange with the open ocean and radioactive decay. The current study shows that a single time series over a tidal cycle at the principal inlet to Great South Bay (NY, US) is sufficient to determine the net flux of Ra across the inlet, and also can be used to estimate the decay of short-lived Ra in the bay. Estimates of the net Ra flux obtained from a single tidal time-series by using three different approaches agree with those determined from a more time-consuming survey of Ra within the bay, and may represent a first step of estimating SGD in bays and coastal lagoons.     

Environmental externalities in relation to agricultural sector in Thailand with trade-linked analysis

Thailand plays an important role in the international trade of food and agricultural products, which is in alignment with its national strategy of serving as the “kitchen of the world.” When looking at its agricultural promotion and export policies, the country only counts the value gains from exports while neglecting environmental externalities related to plantation practices. The purpose of this study was to perform a trade-off analysis between consumptive water, land, and fertilizer use together with the economic values of major crops for export and consumption in the country. The results show that to gain income from agricultural exports, the country has exploited various natural resources. The area used to harvest rice, sugarcane, cassava, and rubber adds up to approximately 15.3 million ha: 7.2 million ha of which is for domestic consumption and 8.1 ha for export. To produce Thailand’s agricultural exports, total water use is estimated to be 49.8–67.5 billion m³ per year (61–65 %), while the amount used to produce crops for domestic consumption is 26.5–43.7 billion m³ per year (35–39 %). Meanwhile, 1,056–1,826 thousand tons (54 %) of fertilizer was used on crops for domestic consumption, and 1,222–1,370 thousand tons (46 %) of fertilizer was used on export crops. The best crop choice for export in terms of its export value, land use, fertilizer use, and water consumption is rubber. The worst crop choices for export are rice and cassava. More sustainable agricultural practices are needed to effect improvements such as increased yields and reduced fertilizer and water use.