Taihu Region Research Articles

Bioaccumulation of microcystin congeners in soil-plant system and human health risk assessment: A field study from Lake Taihu region of China

A 120-day field study was carried out near Lake Taihu to evaluate the bioaccumulation of microcystin (MC) congeners in a soil-plant system, as well as to assess human health risk when consuming edible plants irrigated with MCs-contaminated water. Natural cyanobacteria bloom-containing lake water (lake water) and half-diluted natural cyanobacteria bloom-containing lake water with tap water (half-lake water) were used to irrigate lettuce and rice. An additional treatment involving fertilization with a cyanobacteria bloom was applied just to the lettuce experiment. MCs in soils, roots, leaves and grains (rice) were detected. In the soil-lettuce system, the three MC congeners in soils fertilized with a cyanobacteria bloom were not detected. The highest concentrations of MCs detected in soils, lettuce roots and leaves were 24.8 (MC-LR 10.1, MC-RR 10.5, MC-YR 4.2) μg kg−1, 424 (MC-LR 168, MC-RR 194, MC-YR 61.5) μg kg−1 and 183 (MC-LR 78.0, MC-RR 76.8, MC-YR 28.1) μg kg−1, respectively, in the lake water treatment. In the soil-rice system, the highest concentration of MCs was accumulated in roots 1504 (MC-LR 634, MC-RR 573, MC-YR 297) μg kg−1, in the lake water treatment. However, the concentration of MCs that accumulated in grains was extremely low with a total MCs concentration of 5.2 (MC-LR 2.1, MC-RR 2.0, MC-YR 1.1) μg kg−1 in the lake water treatment. According to the estimated daily intake (EDI) value, fertilizing with an appropriate amount (0.2% or less, w/w, dry weight (DW)) of a cyanobacteria bloom, as well as consuming rice irrigated with lake water would not pose a threat to human health. However, the EDI values for both adults and children reached tolerable daily intake (TDI) value, assuming they consumed lettuce irrigated with lake water. Results obtained from the growth and yield indicators suggest that MCs bioaccumulation in edible plants is not necessarily coupled with phytotoxic effects.

Combining emission inventory and isotope ratio analyses for quantitative source apportionment of heavy metals in agricultural soil

Two quantitative methods (emission inventory and isotope ratio analysis) were combined to apportion source contributions of heavy metals entering agricultural soils in the Lihe River watershed (Taihu region, east China). Source apportionment based on the emission inventory method indicated that for Cd, Cr, Cu, Pb, and Zn, the mean percentage input from atmospheric deposition was highest (62–85%), followed by irrigation (12–27%) and fertilization (1–14%). Thus, the heavy metals were derived mainly from industrial activities and traffic emissions. For Ni the combined percentage input from irrigation and fertilization was approximately 20% higher than that from atmospheric deposition, indicating that Ni was mainly derived from agricultural activities. Based on isotope ratio analysis, atmospheric deposition accounted for 57–93% of Pb entering soil, with the mean value of 69.3%, which indicates that this was the major source of Pb entering soil in the study area. The mean contributions of irrigation and fertilization to Pb pollution of soil ranged from 0% to 10%, indicating that they played only a marginally important role. Overall, the results obtained using the two methods were similar. This study provides a reliable approach for source apportionment of heavy metals entering agricultural soils in the study area, and clearly have potential application for future studies in other regions.

Urea deep placement in combination with Azolla for reducing nitrogen loss and improving fertilizer nitrogen recovery in rice field

Reducing environmental harm and improving fertilizer use efficiency is critical in Chinese agriculture. Azolla has particular value for paddy rice crop due to its biological nitrogen (N) fixation ability; however, the Chinese rice fields are highly fertilized, which will depress the N fixation of Azolla. Urea deep placement (UDP) reduces floodwater NH4+ and ammonia volatilization losses. To date, few studies have explored the effects of UDP combined with Azolla on the N uptake pattern, N recovery and N loss from 15N-labeled urea. Therefore, a 3-year field experiment was conducted with five treatments (control without urea (CK), urea broadcasting without Azolla (B) or with Azolla (BA), and UDP without Azolla (P) or with Azolla (PA)) in an intensive rice cropping system in the Taihu Region of China. The total 15N recovery (soil-plant system), crop 15N uptake (straw and grain) and 15N loss were assessed, and the ammonia (NH3) loss, rice yield, gross return and net economic benefit were measured. The results showed that the UDP treatments had delayed but long-lasting fertilization effects. The PA treatment resulted in the lowest 15N loss and highest total 15N recovery at harvest due to the prolonged N availability and negligible NH3 loss. The PA, P and BA treatments decreased 15N loss by 47%, 33% and 18% and increased total 15N recovery by 58%, 40% and 22%, respectively, compared to urea broadcasting alone. Almost all labeled Azolla-N was released within two months of which approximately 40% could be absorbed by the crop. Little labeled fertilizer N was absorbed by Azolla during the rice season. In addition, the PA, P and BA treatments increased rice yield and gross return by 13%, 10% and 9%, respectively, and they produced similar net economic benefit compared to urea broadcasting alone. In conclusion, UDP combined with Azolla is a potential strategy to further reduce fertilizer N loss and improve total fertilizer N recovery while maximizing rice yield if it can be widely adopted by Chinese rice farmers. However, widespread adoption will require improved technologies with lower labour requirement for mechanized deep placement of urea and for the propagation of Azolla.

Economics of social trade-off: Balancing wastewater treatment cost and ecosystem damage

We have developed a social optimization model that integrates the financial and ecological costs associated with wastewater treatment and ecosystem damage. The social optimal abatement level of water pollution is determined by finding the trade-off between the cost of pollution control and its resulting ecosystem damage. The model is applied to data from the Lake Taihu region in China to demonstrate this trade-off. A wastewater treatment cost function is estimated with a sizable sample from China, and an ecological damage cost function is estimated following an ecosystem service valuation framework. Results show that the wastewater treatment cost function has economies of scale in facility capacity, and diseconomies in pollutant removal efficiency. Results also show that a low value of the ecosystem service will lead to serious ecological damage. One important policy implication is that the assimilative capacity of the lake should be enhanced by forbidding over extraction of water from the lake. It is also suggested that more work should be done to improve the accuracy of the economic valuation.

Deteriorating water clarity in shallow waters: Evidence from long term MODIS and in-situ observations

Water clarity (Secchi disk depth: SDD), as a proxy of water transparency, provides important information on the light availability to the water or lake ecosystem. Shallow lakes have been experienced dramatic environmental and climatic change. This study demonstrated using combination of long-term MODIS and in-situ measurements to track the dynamics of SDD with these environmental and climate changes in shallow water environments. We selected a typical turbid shallow Lake Taihu as our case study. Based on MODIS-Aqua data, an empirical model for estimating SDD was developed and validated. Subsequently, we employed the proposed model to derive the spatial and temporal SDD distribution patterns of Lake Taihu from 2003 to 2015. Combining MODIS-derived SDD time series of 2003–2015 and long-term in-situ SDD observations dated back to 1993, we elucidated SDD long-term variation trends and driving mechanism. Deteriorating water clarity from the long-term SDD observations indicated that Lake Taihu became more and more turbid and water quality was decreasing. Increasing in cyanobacterial bloom area, as a result of decreasing in wind speed and eutrophication, may partially be responsible for the decreasing trend. A predicted future decrease in the wind speed in Lake Taihu region could enhance the formation of cyanobacterial blooms and consequently lead to a further decrease in water clarity. This study suggested that coupling remote sensing monitoring and long-term in-situ observations could provide robust evidence and new insights to elucidate long-term dynamics in aquatic ecosystem evolution.

Heavy metals in food crops, soil, and water in the Lihe River Watershed of the Taihu Region and their potential health risks when ingested

Environmental pollution by heavy metals resulting from rapid economic development is a major concern. Soil, water, wheat, and rice samples were collected from the Lihe River Watershed in the Taihu Region (east China). In this study area, many types of industrial plants, including ceramics factories, plants working with refractory materials, and chemical plants are densely distributed and cause serious heavy metal pollution. In addition, well-developed transportation and agricultural activities are also important sources of heavy metals. Thus, the concentrations of selected heavy metals including cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) in the samples were analyzed to evaluate their potential integral risk (IR) to the health of the local population. Accordingly, the spatial distribution pattern of the IR values was determined in the study. The soil in the study area showed heavy Cd pollution, whereas the pollution by other elements was relatively slight. When the proportions of grain samples in which the concentrations exceeded the tolerance limits were examined, the grains were primarily contaminated with Pb, Ni, Cd, and Zn; and less contaminated with Cu and Cr. The drinking water of the local inhabitants was safe. The average IR value was 3.53 for adults and 3.91 for children, indicating that both adults and children may experience adverse health effects. The spatial distribution pattern of the IR values among the exposed populations in the study area showed high values in the eastern and middle parts, with maximum values >5, and low values in the western part, with minimum values <2. This is consistent with the distributions of the industries and the population. The study may provide a basis for comparison to other regions both in China and worldwide.

Duckweed (Spirodela polyrhiza) as green manure for increasing yield and reducing nitrogen loss in rice production

Increasing rice production to feed the world’s growing population while protecting the environment requires more optimal use of fertilizers. In China, the current high input, high output and high reliance on synthetic nitrogen (N) fertilizer in agriculture has resulted in high N losses, especially ammonia (NH3) emission. Urea combined with green manure (GM) might be a promising approach to improve N fertilizer management. However, few studies have evaluated duckweed in this manner. Duckweed does not require arable land for cultivation and thus avoids competition with food crops. Therefore, a field experiment was conducted for three years with five treatments (CK, no N-fertilizer; CT, conventional practice, urea alone at 300kgNha−1; CTD, urea combined with duckweed at 300kgNha−1; RN, urea alone at 225kgNha−1; and RND, urea combined with duckweed at 225kgNha−1) in an intensive rice cropping system in the Taihu Region of China. The results for two years showed that urea combined with duckweed cover reduced NH3 loss by 36–52% over CT. This reduction was attributed primarily to the formation of a physical barrier and the uptake of NH4+ by duckweed. The 15N recovery for 15N balance conducted for one year was 38% higher and the 15N loss was 16% lower for CTD than that of CT. Furthermore, urea combined with duckweed increased N accumulation in the aboveground plants by 14–25% over CT for the 3 years. As a result, urea combined with duckweed achieved higher rice yield by 9–10%, and higher net economic benefit by 10–11% over CT for the 3 years; however, using the conventional rate of 300kgNha−1 did not increase rice yield over using the reduced N rate of 225kgNha−1, with or without duckweed. Thus, duckweed as GM combined with chemical fertilizer application provided an approach for increasing the rice yield without increasing inputs of N fertilizer and thereby provided a financially attractive option for farmers to achieve environmental integrity and ensure food security in rice production.

Equality testing for soil grid unit resolutions to polygon unit scales with DNDC modeling of regional SOC pools

Matching soil grid unit resolutions with polygon unit map scales is important to minimize the uncertainty of regional soil organic carbon (SOC) pool simulation due to their strong influences on the modeling. A series of soil grid units at varying cell sizes was derived from soil polygon units at six map scales, namely, 1:50 000 (C5), 1:200 000 (D2), 1:500 000 (P5), 1:1 000 000 (N1), 1: 4 000 000 (N4) and 1:14 000 000 (N14), in the Taihu Region of China. Both soil unit formats were used for regional SOC pool simulation with a DeNitrification-DeComposition (DNDC) process-based model, which spans the time period from 1982 to 2000 at the six map scales. Four indices, namely, soil type number (STN), area (AREA), average SOC density (ASOCD) and total SOC stocks (SOCS) of surface paddy soils that were simulated by the DNDC, were distinguished from all these soil polygon and grid units. Subjecting to the four index values (IV) from the parent polygon units, the variations in an index value (VIV, %) from the grid units were used to assess its dataset accuracy and redundancy, which reflects the uncertainty in the simulation of SOC pools. Optimal soil grid unit resolutions were generated and suggested for the DNDC simulation of regional SOC pools, matching their respective soil polygon unit map scales. With these optimal raster resolutions, the soil grid units datasets can have the same accuracy as their parent polygon units datasets without any redundancy, when VIV < 1% was assumed to be a criterion for all four indices. A quadratic curve regression model, namely, y =–0.80 × 10–6 x 2 + 0.0228x + 0.0211 (R 2 = 0.9994, P < 0.05), and a power function model R = 10.394Ŝ 0.2153 (R 2 = 0.9759, P < 0.05) were revealed, which describe the relationship between the optimal soil grid unit resolution (y, km) and soil polygon unit map scale (1:10 000x), the ratio (R, %) of the optimal soil grid size to average polygon patch size (Ŝ, km2) and the Ŝ, with the highest R 2 among different mathematical regressions, respectively. This knowledge may facilitate the grid partitioning of regions during the investigation and simulation of SOC pool dynamics at a certain map scale, and be referenced to other landscape polygon patches’ mesh partition.

Extremely high N 2 O but unexpectedly low NO emissions from a highly organic and chemical fertilized peach orchard system in China

Abstract In China, the rapid conversion of traditional rice-wheat rotation to orchard-induced management practices has resulted in changes in soil N 2 O and NO emissions. However, quantification of emissions from orchard fields characterized by a high rate of organic and chemical N fertilization application has not yet been widely carried out. In this study, we measured soil N 2 O and NO emissions from a typical peach orchard in the Taihu region over a 2-year period using a combination of static chamber and gas chromatography techniques. Four treatments were examined: organic manure alone (OM), chemical fertilizers alone (CF), organic manure plus chemical fertilizers (OF + CF), and no fertilizers as a control (CK). No significant effects of organic amendments × chemical fertilizer application on soil N 2 O and NO emissions were observed. The mean annual N 2 O emission over the 2-year period was 3.2 kg N ha −1 under CK treatment, and increased to 9.3, 10.3, and 20.1 kg N ha −1 under OF, CF and OF + CF treatment, respectively. In contrast, cumulative NO emissions were relatively low, ranging from 0.14 to 1.99 kg N ha −1 yr −1 . The NO emissions were enhanced by approximately eight fold following mineral fertilization application either alone or in combination with organic manure, and to a lesser extent (45%, nonsignificant) by organic manure application alone. Overall, NO accounted for approximately 14.5 and only 2.9% of the total (NO + N 2 O)-N emissions under CF and OF treatment, respectively. Over the 2-year observation period, the N 2 O emission factor averaged 1.69%, 1.32% and 1.86% and the NO emission factor averaged 0.03%, 0.27% and 0.17% under OF, CF and OF + CF treatment, respectively. Overall, our results suggest that fertilized peach orchard soil in the Taihu region is an important source of N 2 O emissions.

Urea deep placement for minimizing NH3 loss in an intensive rice cropping system

It is urgently necessary to reduce environmental harm while simultaneously ensuring food security from agriculture in China. Fertilizer deep placement, especially urea deep placement (UDP), has been widely recognized as an efficient way to increase rice yield with less N use in flooded rice fields; however, few studies have explored UDP as a way to abate N loss, particularly ammonia (NH3) volatilization, in intensive rice cropping systems. Therefore, a field experiment was performed in the Taihu Region with five treatments (two surface split broadcasting treatments: a current traditional practice with 300kgNha−1 (CT) and a reduced N practice with 225kgNha−1 (RN), two one-time UDP treatments: a current traditional practice under UDP (CTDP) and a reduced N practice under UDP (RNDP), and a CK treatment with no urea). The NH3 volatilization, grain yield and N use efficiency in terms of the N recovery efficiency (NRE) were investigated during the 2014–2016 rice growing seasons. Additionally, N diffusion and 15N-labeled urea experiments were conducted to explore the N release pattern and the fate of 15N under UDP. The results demonstrated that little NH4+-N could diffuse into surface water under UDP, thus, negligible floodwater NH4+-N was detected. The seasonally cumulative NH3 volatilization of the UDP accounted for only 1% of the total applied N, which decreased by 91% compared to surface broadcasting treatments. As a result, the NH3 intensity (NH3-N loss per crop yield) was reduced by 92% over surface broadcasting. Moreover, the deep placement of urea could supply a higher NH4+-N concentration in the soil during the early growth stage and prolong the duration of N availability for 2 months; as a result, UDP remarkably increased the N uptake by 28% compared with surface broadcasting treatments in the 3 years. The UDP treatments significantly increased the yield and NRE by 10% and 55% under favorable weather conditions (2015 and 2016 rice seasons), respectively. The RNDP treatment obtained the lowest N surplus (36kgNha−1), and the plant 15N uptake was 62% higher and the 15N loss was 38% lower with RNDP than surface broadcasting. Therefore, the deep placement of urea can be considered a slow release fertilizer, which better matches the N demand of rice plants and effectively minimizes N losses, especially NH3 volatilization. The RNDP treatment, with a 25% reduction in the N dose, can represent an effective and promising strategy to achieve environmental integrity and food security in intensive rice cropping systems.

Fine Mapping of a New Race-Specific Blast Resistance Gene, Pi-hk2, in Japonica Heikezijing from Taihu Region of China.

Heikezijing, a japonica rice landrace from the Taihu region of China, exhibited broad-spectrum resistance to more than 300 isolates of the blast pathogen (Magnaporthe oryzae). In our previous research, we fine mapped a broad-spectrum resistance gene, Pi-hk1, in chromosome 11. In this research, 2010-9(G1), one of the predominant races of blast in the Taihu Lake region of China, was inoculated into 162 recombinant inbred lines (RIL) and two parents, Heikezijing and Suyunuo, for mapping the resistance-blast quantitative trait loci (QTL). Three QTL (Lsqtl4-1, Lsqtl9-1, and Lsqtl11-1) associated with lesion scores were detected on chromosomes 4, 9, and 11 and two QTL (Lnqtl1-1 and Lnqtl9-1) associated with average lesion numbers were detected on chromosomes 1 and 9. The QTL Lsqtl9-1 conferring race-specific resistance to 2010-9(G1) at seedling stages showed logarithm of the odds scores of 9.10 and phenotypic variance of 46.19% and might be a major QTL, named Pi-hk2. The line RIL84 with Pi-hk2 derived from a cross between Heikezijing and Suyunuo was selected as Pi-hk2 gene donor for developing fine mapping populations. According to the resistance evaluation of recombinants of three generations (BC1F2, BC1F3, and BC1F4), Pi-hk2 was finally mapped to a 143-kb region between ILP-19 and RM24048, and 18 candidate genes were predicted, including genes that encode pleiotropic drug resistance protein 4 (n = 2), WRKY74 (n = 1), cytochrome b5-like heme/steroid-binding domain containing protein (n = 1), protein kinase (n = 1), and ankyrin repeat family protein (n = 1). These results provide essential information for cloning of Pi-hk2 and its potential utility in breeding resistant rice cultivars by marker-assisted selection.

Pudong White pig: a unique genetic resource disclosed by sequencing data

Pudong White (PW) pigs are distributed in the Taihu region of China and are characterized by their completely white coats. A heated debate concerning this genetic resource and its relationship to Taihu and western pig breeds has arisen, due to the white coat of the animals. To determine whether PW is a unique genetic resource, we performed a detailed assessment of the genetic relationships among PW, six breeds from the Taihu population and three western pig breeds, based on whole-genome single nucleotide polymorphism (SNP) data. A total of 68 102 SNPs were identified in the genomes of the tested populations by next-generation sequencing technology, of which, 64 were determined as the potentially specific to PW breed. The genetic distance between PW pigs and the Taihu population was shorter than that between PW and western breeds. The genetic distance within the PW population was small and neighbour-joining tree analysis revealed that all PW individuals clustered into a separated group, indicating a close genetic relationship among PW individuals which may result from a small effective population size (Ne) and inbreeding. The results of both principal component analysis and evaluation using fastSTRUCTURE demonstrated that PW was clearly differentiated from other breeds. Together, these results indicate that PW is a distinctive genetic resource with a unique genetic structure separate from other Taihu and western pig breeds. Furthermore, this genome-wide comprehensive survey of the relationships among PW, Taihu and western pig breeds, demonstrates the rationality of the current breed classification of PW. The results also provide evidence about the unique genetic resource of PW, based on genome-wide genetic markers. These data will improve our understanding of the genetic structure and current state of PW breed, and facilitate the development of a national project for the conservation and utilization of these pigs.

Long-Term Trends in Acid Neutralizing Capacity under Increasing Acidic Deposition: A Special Example of Eutrophic Taihu Lake, China.

While North America and Europe have been recovering from acidification, China is experiencing impacts of acid deposition. The Taihu region is a seriously impacted area by acid rain in China, with the average rainfall pH < 5. However, the acid neutralizing capacity (ANC) and pH of Taihu Lake have significantly increased over the past 60 years (p < 0.05). Analyses showed that watershed neutralization by carbonates and in-lake alkalinization by algae activities were the two major reactions responsible for the increase. In the Taihu basin, the dominant carbonate bedrocks are the major source of base cations (particularly Ca2+ and Mg2+) and act as the acidification buffer. In addition, our field measurements across the lake showed that the pH values were significantly higher in algal bloom waters than in areas without blooms. This observation was further supported by our statistical analysis showing that the Taihu ANC and pH were significantly correlated with the chlorophyll increase (p < 0.05; 1985-2015). However, our regression analysis indicated that the base cations in the watershed would be depleted by the early 2040s if the acid deposition continues at the current rate. Our results suggest that interactions between human accelerated weathering, watershed geochemistry, and in-lake algae activities significantly impact the water chemistry of the lake. We urgently recommend an "integrated and balanced" recovery plan for the lake ecosystem.

Since 2015 the SinoGerman research project SIGN supports water quality improvement in the Taihu region, China.

The Taihu (Tai lake) region is one of the most economically prospering areas of China. Due to its location within this district of high anthropogenic activities, Taihu represents a drastic example of water pollution with nutrients (nitrogen, phosphate), organic contaminants and heavy metals. High nutrient levels combined with very shallow water create large eutrophication problems, threatening the drinking water supply of the surrounding cities. Within the international research project SIGN (SinoGerman Water Supply Network, www.water-sign.de), funded by the German Federal Ministry of Education and Research (BMBF), a powerful consortium of fifteen German partners is working on the overall aim of assuring good water quality from the source to the tap by taking the whole water cycle into account: The diverse research topics range from future proof strategies for urban catchment, innovative monitoring and early warning approaches for lake and drinking water, control and use of biological degradation processes, efficient water treatment technologies, adapted water distribution up to promoting sector policy by good governance. The implementation in China is warranted, since the leading Chinese research institutes as well as the most important local stakeholders, e.g. water suppliers, are involved.

Phosphorus losses via surface runoff in rice-wheat cropping systems as impacted by rainfall regimes and fertilizer applications

Phosphorus (P) losses from agricultural soils contribute to eutrophication of surface waters. This field plot study investigated effects of rainfall regimes and P applications on P loss by surface runoff from rice (Oryza sativa L.) and wheat (Triticum aestivum L.) cropping systems in Lake Taihu region, China. The study was conducted on two types of paddy soils (Hydromorphic at Anzhen site, Wuxi City, and Degleyed at Xinzhuang site, Changshu City, Jiangsu Province) with different P status, and it covered 3 years with low, high and normal rainfall regimes. Four rates of mineral P fertilizer, i.e., no P (control), 30 kg P ha–1 for rice and 20 kg P ha–1 for wheat (P30+20), 75 plus 40 (P75+40), and 150 plus 80 (P150+80), were applied as treatments. Runoff water from individual plots and runoff events was recorded and analyzed for total P and dissolved reactive P concentrations. Losses of total P and dissolved reactive P significantly increased with rainfall depth and P rates (P<0.0001). Annual total P losses ranged from 0.36–0.92 kg ha–1 in control to 1.13–4.67 kg ha–1 in P150+80 at Anzhen, and correspondingly from 0.36–0.48 kg ha–1 to 1.26–1.88 kg ha–1 at Xinzhuang, with 16–49% of total P as dissolved reactive P. In particular, large amounts of P were lost during heavy rainfall events that occurred shortly after P applications at Anzhen. On average of all P treatments, rice growing season constituted 37–86% of annual total P loss at Anzhen and 28–44% of that at Xinzhuang. In both crop seasons, P concentrations peaked in the first runoff events and decreased with time. During rice growing season, runoff P concentrations positively correlated (P<0.0001) with P concentrations in field ponding water that was intentionally enclosed by construction of field bund. The relative high P loss during wheat growing season at Xinzhuang was due to high soil P status. In conclusion, P should be applied at rates balancing crop removal (20–30 kg P ha–1 in this study) and at time excluding heavy rains. Moreover, irrigation and drainage water should be appropriately managed to reduce runoff P losses from rice-wheat cropping systems.

Updating digital soil maps with new data: a case study of soil organic matter in Jiangsu, China

SummaryThe rapid developments in the acquisition of data on soil should enable pedologists to update existing digital soil maps readily. The methods by which that is done must take into account temporal change in soil properties and local differences in spatial variation. The common mapping techniques will have to be modified to make full use of digital data. We show what can be achieved with a case study on updating maps of soil organic matter (SOM) in Jiangsu Province, China, with three sets of soil data collected in the 1980s, 2000 and 2006. Our results showed that temporal changes in SOM between the three sampling periods occurred in only very small parts of the regions. Models of spatial variation of SOM based on the data collected in the 1980s and 2006 for the whole region differed somewhat, whereas models based on the data collected in the 1980s, 2000 and 2006 for the Taihu region (south Jiangsu) were significantly different. As updating with Bayesian maximum entropy continued, the accuracy of prediction increased and that of the prediction variance decreased. Finally, our study leads us to suggest improved technologies for updating digital soil maps with new data.

Hydrological behaviour and water balance analysis for Xitiaoxi catchment of Taihu Basin

With the rapid social and economic development of the Taihu region, Taihu Lake now faces an increasingly severe eutrophication problem. Pollution from surrounding catchments contributes greatly to the eutrophication of water bodies in the region. Investigation of surface flow and associated mass transport for the Xitiaoxi catchment is of a significant degree of importance as the Xitiaoxi catchment is one of the major catchments within the Taihu region. A SWAT-based distributed hydrological model was established for the Xitiaoxi catchment. The model was calibrated and verified using hydrometeorological data from 1988 to 2001. The results indicate that the modeled daily and annual stream flow match the observed data both in the calibration period and the verification period, with a linear regression coefficient R2 and a coefficient e for modeled daily stream flow greater than 0.8 at Hengtangcun and Fanjiacun gauge stations. The results show that the runoff process in the Xitiaoxi catchment is affected both by rainfall and human activities (e.g., reservoirs and polder areas). Moreover, the human activities weaken flood peaks more noticeably during rainstorms. The water balance analysis reveals the percentages of precipitation made up by surface flow, evapotranspiration, groundwater recharge and the change of soil storage, all of which are considered useful to the further understanding of the hydrological processes in the Xitiaoxi catchment. This study provides a good base for further studies in mass transport modeling and comparison of modeling results from similar hydrological models.

Nitrogen management in a rice–wheat system in the Taihu Region: Recommendations based on field experiments and surveys

Excessive use of mineral nitrogen (N) fertilizer has been a common practice in the high-yielding rice–wheat double-cropping system in the Taihu Region of southeastern China. As a consequence of high N balance surpluses and low N use efficiencies (NUEs), nitrogen losses to water bodies and to the atmosphere are high. Field experiments on five replicate farmers’ field sites were conducted in southern Jiangsu Province over three consecutive rice–wheat double-crop rotations with three different N fertilization treatments (‘conventional’ (farmers’ practice), ‘reduced’ (by 23% for rice and 32% for wheat) and zero N application). A parallel survey was carried out involving 43 farmers’ households, in order to calculate standard gross margins (SGM) and to conduct an environmental assessment of the rice–wheat farming system in the Taihu Region. The results of the field experiment showed that a distinct reduction in fertilizer N application rates to summer rice and winter wheat crops is possible without significant decrease in mean grain yields. Mean grain yields for the entire double-crop rotation were 14.7Mgha−1yr−1 under the conventional N fertilization practice and 14.1Mgha−1yr−1 under reduced N fertilization. A significant increase in NUEs could be achieved in most years and crops under reduced N fertilization compared to farmers’ practice, and N balance surpluses were significantly decreased from 142kgNha−1 to less than 60kgNha−1yr−1 under the reduced N fertilization regime. The residual mineral N contents in the soil profiles after winter wheat harvest showed a decreasing tendency over time with a reduction of N fertilization. Mineral N contents in fertilized fields were significantly higher than on the zero N plots. Concentrations of NH4+-N in soil extracts from the puddled layer during the summer rice in 2010 showed significant differences between the two N fertilization treatments and the zero N plots. Results of the agro-economic survey showed that production of rice was 50% more profitable than that of wheat, and that fertilizer costs made up less than 20% in the rice season, but almost 50% of the total production costs during the wheat season. It can be concluded that N losses to the environment can be efficiently decreased by reducing the overall N fertilization rates without any risk of decline in grain yield and related income for farmers. Based on the field experiments and investigations, a reduction in N fertilizer application rates by 15–25% for summer rice and by 20–25% for winter wheat, compared to present levels is recommended.

Impacts of Urbanization on River Systems in the Taihu Region, China

River systems are valuable to human beings; meanwhile, they are intensively influenced by human activities, especially urbanization. In this study, based on the data derived from topographic maps and remote sensing images, the temporal and spatial change of river system geomorphology in the Taihu Region over the past 50 years was investigated in conjunction with urbanization. Results demonstrated that the number of river systems decreased drastically, that the morphology of river channels changed into wider and straighter and that the structure of river network tended to simplify in the Taihu Region in recent 50 years. Meanwhile, the changes in river density, the water surface ratio, the river development coefficient, the main river area length ratio and the box dimension in the rapid urbanization period were much greater than those in the slow urbanization period, but the decrease of river sinuosity in the slow urbanization period was more intense. Moreover, the spatial differences of the changes in the river development coefficient were the largest, and the changes in the river indicators in the low-urbanized regions were the most intense. In addition, the changes in the water surface ratio had the closest correlation with urbanization, and the relational degrees between population urbanization and the changes in river systems were the largest. The results can provide a reliable basis to determine reasonable management and conservation strategies of river systems in the Taihu Region.

Nitrogen removal capacity of the river network in a high nitrogen loading region.

Denitrification is the primary process that regulates the removal of bioavailable nitrogen (N) from aquatic ecosystems. Quantifying the capacity of N removal from aquatic systems can provide a scientific basis for establishing the relationship between N reduction and water quality objectives, quantifying pollution contributions from different sources, as well as recommending control measures. The Lake Taihu region in China has a dense river network and heavy N pollution; however, the capacity for permanent N removal by the river network is unknown. Here, we concurrently examined environmental factors and net N2 flux from sediments of two rivers in the Lake Taihu region between July 2012 and May 2013, using membrane inlet mass spectrometry, and then established a regression model incorporating the highly correlated factors to predict the N removal capacity of the river network in the region. To test the applicability of the regression model, 21 additional rivers surrounding Lake Taihu were sampled between July and December 2013. The results suggested that water nitrate concentrations are still the primary controlling factor for net denitrification even in this high N loading river network, probably due to multicollinearity of other relevant factors, and thus can be used to predict N removal from aquatic systems. Our established model accounted for 78% of the variability in the measured net N2 flux in these 21 rivers, and the total N removed through N2 production by the river network was estimated at 4 × 10(4) t yr(-1), accounting for about 43% of the total aquatic N load to the river system. Our results indicate that the average total N content in the river water discharged into Lake Taihu would be around 5.9 mg of N L(-1) in the current situation, far higher than the target concentration of 2 mg of N L(-1), given the total N load and the N removal capacity. Therefore, a much stronger effort is required to control the N pollution of the surface water in the region.