Changes in soil microbial biomass and aggregate stability under different land uses in the northeastern Turkey

The characteristics of three neighboring soils from the NE of Turkey were evaluated in order to elucidate the effect of different land-use management on the soil aggregate stability and microbial biomass in Galyan-Atasu dam watershed. Three experimental sites corresponding to three land uses were selected. The first site is a hazelnut orchard (agriculture), the second site is a forest dominated by mature coniferous trees, and the third site is grassland. Soil aggregate stability values for the 1–2-mm aggregates increased from forest (lowest) to agriculture (highest) in the current study. The percentage of clay was highest in agriculture soils with 33.57 %, and overall stability values increased according to soil clay content. The lower aggregate stability in the forest soils probably reflects the highly silty texture soils with 11.95 % compared to agriculture and grassland. However, in our study, there were no significant correlations between aggregate stability and organic C concentrations either in cultivated or forested soils. Aggregate stability depended more on the organic matter content when the organic matter content was greater than 50 or 60 mg g^?1. Below that threshold, aggregate stability may be mainly related to clay content. Furthermore, the results confirmed that higher percentages of Cmic/Corg in agricultural soils are the result of more labile organic substrates maintained in the soil, allowing a higher microbial biomass C per unit of soil organic C. This work gives a better understanding of the relationships between land-use type and soil aggregation and allows to know the soil response to different types of management in humid environments.     

Hydrology, suspended sediment dynamics and nutrient loading in Lake Takkobu, a degrading lake ecosystem in Kushiro Mire, northern Japan

Suspended sediment and nutrient loadings from agricultural watersheds have lead to habitat degradation in Lake Takkobu. To examine their relationships with land-use activities, we monitored sediment, nutrient and water discharges into the lake for a 1-year sampling period. The Takkobu River contributed the largest portion of the annual water discharge into the lake, compared with the other tributaries. During dry conditions, lake water flowed into the Kushiro River, and conversely during flooding, Kushiro River water flowed into the lake. Inflows from the Kushiro River had a high proportion of inorganic matter, with high concentrations of total nitrogen and total phosphorus, attributed to agricultural land-use development and stream channelization practiced since the 1960s in the Kushiro Mire. Nutrient loadings from these two rivers were significantly higher during flooding than in dry conditions. However, there was no clear correlation between river discharge and nutrient concentrations. Since land-use activities in the Kushiro River and Takkobu River watersheds were concentrated near rivers, nutrients easily entered the drainage system under low flow conditions. In contrast, water discharged from small, forest-dominated watersheds contained a low proportion of inorganic matter, and low nutrient concentrations. The suspended sediment delivered to the lake during the sample period was estimated as approximately 607 tons, while the total nitrogen and total phosphorus inflows were about 10,466 and 1,433 kg, respectively. Suspended sediment input into the lake was 65%, and total nitrogen and total phosphorus were 40% and 48%, respectively, being delivered by the Kushiro River.     

High-frequency nutrient monitoring to infer seasonal patterns in catchment source availability, mobilisation and delivery

To explore the value of high-frequency monitoring to characterise and explain riverine nutrient concentration dynamics, total phosphorus (TP), reactive phosphorus (RP), ammonium (NH₄-N) and nitrate (NO₃-N) concentrations were measured hourly over a 2-year period in the Duck River, in north-western Tasmania, Australia, draining a 369-km² mixed land use catchment area. River discharge was observed at the same location and frequency, spanning a wide range of hydrological conditions. Nutrient concentrations changed rapidly and were higher than previously observed. Maximum nutrient concentrations were 2,577 μg L^?1 TP, 1,572 μg L^?1 RP, 972 μg L^?1 NH₄-N and 1,983 μg L^?1 NO₃-N, respectively. Different nutrient response patterns were evident at seasonal, individual event and diurnal time scales—patterns that had gone largely undetected in previous less frequent water quality sampling. Interpretation of these patterns in terms of nutrient source availability, mobilisation and delivery to the stream allowed the development of a conceptual model of catchment nutrient dynamics. Functional stages of nutrient release were identified for the Duck River catchment and were supported by a cluster analysis which confirmed the similarities and differences in nutrient responses caused by the sequence of hydrologic events: (1) a build-up of nutrients during periods with low hydrologic activity, (2) flushing of readily available nutrient sources at the onset of the high flow period, followed by (3) a switch from transport to supply limitation, (4) the accessibility of new nutrient sources with increasing catchment wetness and hydrologic connectivity and (5) high nutrient spikes occurring when new sources become available that are easily mobilised with quickly re-established hydrologic connectivity. Diurnal variations that could be influenced by riverine processes and/or localised point sources were also identified as part of stage (1) and during late recession of some of the winter high flow events. Illustrated by examples from the Duck River study, we demonstrate that the use of high-frequency monitoring to identify and characterise functional stages of catchment nutrient release is a constructive approach for informing and supporting catchment management and future nutrient monitoring strategies.     

Nutrient spatial pattern of the upstream,mainstream and tributaries of the Three Gorges Reservoir in China

A comprehensive monitoring program was conducted to investigate the nutrient spatial pattern in the mainstream of the Yangtze River from the Baihetan Dam down to the Three Gorges Dam located at the upper region of the Yangtze River in China. Samples were taken from 33 different sites from July 30 to August 19, 2011. The nutrient patterns of the three representative tributaries of the Three Gorges Reservoir (TGR)—the Modao, the Daning, and the Xiangxi Rivers—were also investigated. The results show that the mainstream of the TGR has a higher concentration of nitrogen and a lower concentration of phosphorus than that of the upper mainstream before the TGR. Moreover, it was found that nitrate-nitrogen (NO₃-N) is the main nitrogen component, while particulate phosphorus predominates the total phosphorus (TP). It was found that the three representative tributaries of the TGR have lower total nitrogen (TN) concentrations compared to the corresponding sections of the mainstream TGR. Based on the nutrient spatial pattern, the nutrient flux was calculated. The total fluxes of TN, NO₃-N, TP, and orthophosphate (PO₄-P) from the upstream reach into the TGR are 2,155.06, 1,674.97, 212.98, and 83.42 t day^?1, respectively. The amount of nutrients imported from the TGR into its tributaries is more than the amount exported. It was determined that the Xiangxi River has the largest net rate of imported nitrogen at 7.66 t day^?1, whereas the Daning River has the largest net rate of imported phosphorus at 1.75 t day^?1. In addition, compared with the nutrients imported from the TGR into its tributaries, the nutrient flux from the upstream reach into the TGR contributes approximately less than 3 %.     

Estimating reference nutrient criteria for Maryland ecoregions

Management of stream nutrients is becoming increasingly important in order to protect both water quality and aquatic resources throughout the USA. Using an extensive water quality database from the long-term Maryland Biological Stream Survey (MBSS), we describe nutrient relationships to landscape characteristics as total nitrogen (TN) and total phosphorus (TP) of small-order, non-tidal streams in USEPA L2 and L3 ecoregions in Maryland and by MBSS stream order at the L2 and L3 ecoregion levels. To protect stream ecosystem integrity, preliminary reference nutrient estimates (TN and TP) as percentiles (25th of all stream reaches and 75th of stream reference reaches) for the six Maryland L3 ecoregions are: Blue Ridge TN 0.29 and 0.64 mg/L, TP 0.0065 and 0.0090 mg/L; Central Appalachians TN 0.40 and 1.0 mg/L, TP 0.0060 and 0.015 mg/L; Middle Atlantic Coastal Plains TN 0.93 and 2.5 mg/L, TP 0.094 and 0.065 mg/L; Northern Piedmont TN 1.6 and 1.8 mg/L, TP 0.010 and 0.015 mg/L; Ridge and Valley TN 0.40 and 0.98 mg/L, TP 0.0063 and 0.012 mg/L; and Southeastern Plains TN 0.33 and 0.82 mg/L, TP 0.016 and 0.042 mg/L. High levels of both TN and TP are present in many streams found in non-tidal watersheds associated with all Maryland ecoregions, but are especially elevated in the Northern Piedmont and Middle Atlantic Coastal Plain ecoregions, with the latter second-order streams (average TN?>?2.9 mg/L) significantly higher than all other ecoregion–order combinations. Across all six ecoregions, mean nutrient loading for both TN and TP was generally equivalent in first-order streams to nutrient concentrations seen in both second- and third-order streams, indicating a definite need to increase efforts in preventing nutrients from entering first-order streams. Small-order stream nutrient levels are the drivers for subsequent TN and TP inputs into the upper freshwater tidal reaches of the Chesapeake Bay, resulting in a potential risk for altered estuarine ecosystems.     

Water quality status and trends in agriculture-dominated headwaters; a national monitoring network for assessing the effectiveness of national and European manure legislation in The Netherlands

Large nutrient losses to groundwater and surface waters are a major drawback of the highly productive agricultural sector in The Netherlands. The resulting high nutrient concentrations in water resources threaten their ecological, industrial, and recreational functions. To mitigate eutrophication problems, legislation on nutrient application in agriculture was enforced in 1986 in The Netherlands. The objective of this study was to evaluate this manure policy by assessing the water quality status and trends in agriculture-dominated headwaters. We used datasets from 5 agricultural test catchments and from 167 existing monitoring locations in agricultural headwaters. Trend analysis for these locations showed a fast reduction of nutrient concentrations after the enforcement of the manure legislation (median slopes of ?0.55 mg/l per decade for total nitrogen (N-tot) and ?0.020 mg/l per decade for total phosphorus (P-tot)). Still, up to 76 % of the selected locations currently do not comply with either the environmental quality standards (EQSs) for nitrogen (N-tot) or phosphorus (P-tot). This indicates that further improvement of agricultural water quality is needed. We observed that weather-related variations in nutrient concentrations strongly influence the compliance testing results, both for individual locations and for the aggregated results at the national scale. Another important finding is that testing compliance for nutrients based on summer average concentrations may underestimate the agricultural impact on ecosystem health. The focus on summer concentrations does not account for the environmental impact of high winter loads from agricultural headwaters towards downstream water bodies.     

Contribution of point sources and non-point sources to nutrient and carbon loads and their influence on the trophic status of the Ganga River at Varanasi,India

To determine the possible contributions of point and non-point sources to carbon and nutrient loading in the Ganga River, we analyzed N, P, and organic carbon (OC) in the atmospheric deposits, surface runoff, and in the river along a 37-km stretch from 2013 to 2015. We also assessed the trophic status of the river as influenced by such sources of nutrient input. Although the river N, P, and productivity showed a declining trend with increasing discharge, runoff DOC and dissolved reactive phosphorus (DRP) increased by 88.05 and 122.7% between the Adpr and Rjht sites, indicating contributions from atmospheric deposition (AD) coupled with land use where agriculture appeared to be the major contributor. Point source input led to increased river concentrations of NO₃ ^?, NH₄ ⁺, DRP, and DOC by 10.5, 115.9, 115.2, and 67.3%, respectively. Increases in N, P, and productivity along the gradient were significantly negatively correlated with river discharge (p < 0.001), while river DOC and dissolved silica showed positive relationships. The results revealed large differences in point and non-point sources of carbon and nutrient input into the Ganga River, although these variations were strongly influenced by the seasonality in surface runoff and river discharge. Despite these variations, N and P concentrations were sufficient to enhance phytoplankton growth along the study stretch. Allochthonous input together with enhanced autotrophy would accelerate heterotrophic growth, degrading the river more rapidly in the near future. This study suggests the need for large-scale inter-regional time series data on the point and non-point source partitioning and associated food web dynamics of this major river system.     

Seasonal and spatial distribution of 4-tert-octylphenol, 4-nonylphenol and bisphenol A in the Huangpu River and its tributaries, Shanghai, China

The seasonal variations and spatial distributions of 4-tert-octylphenol (OP), 4-nonylphenol (NP) and bisphenol A (BPA) in surface waters, suspended solids and surface sediments in the Huangpu River and its tributaries (Suzhou River and Yunzao Brook) were firstly investigated. The mean concentrations of OP, NP and BPA in the three rivers were 10.59, 120.96 and 22.93 ng L^?1 in surface waters, 199.87, 2,300.87 and 84.11 ng g^?1 in suspended solids and 9.49, 119.44 and 7.13 ng g^?1 dry weight in surface sediments, respectively. The concentrations of NP and OP were higher in summer than in winter in the suspended solids and surface sediments, while the reverse was true in surface waters. Similarly, the levels of BPA were lower in summer than in winter in surface sediments, while the opposite was true in surface waters and suspended solids. These seasonal variations might be attributed to temperature and stream flows. High levels of OP, NP and BPA were found in surrounding river intersections, residential and industrial areas. Their concentrations decreased gradually with increasing distance from those areas, while the lowest levels were measured in near less urbanized and agricultural areas. These phenomena might indicate that the stream current and pollutant source were the major factors that affect the spatial distributions of OP, NP and BPA in the three rivers. Ecological risk assessment indicated that NP was the only one of the three pollutants with the potential to influence local aquatic organisms. The results of this study provide scientific support for control of these pollutants.     

Determination of Cadmium Levels in Agricultural Areas of Çarşamba and Bafra Plains

Cadmium pollution resulted from fertilizer applications were studied by determining cadmium levels in agricultural and non-agricultural soils of Bafra and Çar?amba plains. Soil samples of 68 were collected from agricultural (34) and non-agricultural (34) areas. The sample of 2 g was placed in a test tube and digested with hydrochloric acid and nitric acid mixture (3:1, v/v) in an aluminum block. Taking up the evaporated residue was dissolved in 1% nitric acid and total cadmium concentrations were determined with GF-AAS. Mean level of cadmium contents were found in agricultural areas 0.162?±?0.078 for Çar?amba and 0.433?±?0.288 mg kg^?1 for Bafra. The accuracy of the method was tested with determining cadmium contents of standard reference material and cadmium spiked soil samples.     

Spatial Patterns of Water Quality in the Cuiabá River Basin, Central Brazil

This study evaluates the spatial patterns of land occupation and their relationship to water quality in the Cuiabá River watershed, one of the main affluents of the Pantanal floodplain. The impact of farming and other land occupation forms were studied using a three year time series. Monitoring included 15 parameters at 21 stations with a total of 1266 different samples. Ten stations along the Cuiabá River were ordinated by Principal Component Analysis (PCA). For an exploratory analysis in the spatial domain, sub-basins of the Cuiabá watershed were classified according to mean concentrations of selected water quality parameters. Supervised classification of digital Landsat ETM imagery and standard GIS techniques were applied to parameterize land use and occupation according to a watershed scale. Redundancy Analysis (RDA) was then used to evaluate impacts of environmental and socio-economic factors on water quality.A Cuiabá headwater station only shows slightly elevated total coliform counts and concentrations of nutrients in the river after it passes regions of extensive cattle farming. After the confluence with the Manso River, nutrient and COD concentrations increase significantly, receiving loads from sub-basins under intensive agricultural land use, with mean annual concentrations up to 1.74 mg/L of total nitrogen (Kjedahl). Sub-watersheds with intensive fishing culture activities were shown to have significant impact on nitrogen concentrations, reaching mean concentrations of 2.66 mg/L of total nitrogen in the affluents. Most serious biological and chemical water pollution can be observed at stream outlets in the urban agglomeration of Cuiabá/Várzea Grande. Affluent pollution is reflected in the water quality of the Cuiabá River: subsequent monitoring stations in the urban area are ordinated on a gradient of increasing degradation of chemical and biological water quality. The auto-depuration capacity of the Cuiabá River is intact, but elevated concentrations of Phosphorous and Chemical Oxygen Demand can be observed as far away as the Pantanal floodplain, about 120 km downstream from the urban agglomeration.     

Assessing the influence of nutrient reduction on water quality using a three-dimensional model: case study in a tidal estuarine system

A coupled three-dimensional hydrodynamic and water quality model has been developed and applied to the Danshuei River estuarine system and adjacent coastal sea. The water quality model considers various species of nitrogen, phosphorus, organic carbon, and phytoplankton as well as dissolved oxygen and is driven by a three-dimensional hydrodynamic model. The hydrodynamic and water quality models were validated with observations of water surface elevation, velocity, salinity distribution, and water quality parameters. Statistical error analysis shows that predictions of hydrodynamics, salinity, dissolved oxygen, and nutrients from the model simulation quantitatively agreed with the observed data. The validated model was then applied to predict water quality conditions as a result of a reduction in nutrient loadings based on different engineering strategies. The simulated results revealed that the dissolved oxygen concentration would increase significantly and would be higher than 2 mg/L in the main stream and in three tributaries to meet the minimum statutory requirement for dissolved oxygen. Active estuarine management focused on the reduction of anthropogenic nutrient loads is needed for improvement in water quality.     

Distribution of phthalate esters in topsoil: a case study in the Yellow River Delta, China

The Yellow River Delta (YRD) is a typical agricultural and petrochemical industrial area of China. To assess the current status of phthalate esters (PAEs) of soil residues, soil samples (0～20 cm) (n?=?82) were collected in Bincheng District, at the geographic center of the YRD. PAEs were detected in all topsoil samples analyzed, which indicated that PAEs are ubiquitous environmental contaminants. Concentrations of 11 PAEs are in the range of 0.794～19.504 μg g^?1, with an average value of 2.975 μg g^?1. It was presented that PAEs pollution in this area was weak and monotonously increasing along the rural–urban gradient. Higher concentrations were observed from roadsides (and/or gutters), densely anthropogenic activities areas (such as the urbanization and industrialization), and agriculture influence district, which mainly originated from construction waste, municipal sewage, agricultural waste and pesticide, discarded plastic effusion and atmospheric depositions. Concentrations of PAEs were weakly positivity correlated with soil organic carbon content and pH, which suggested both of them can affect the distribution of PAEs. The concentration of di (2-ethylhexyl) phthalate and di-n-butyl phthalate dominated in the 11 PAEs, with the average values of 0.735 and 1.915 μg g^?1, respectively, and accounted for 92.1 % of the whole PAEs’ concentrations. No significant differences of PAE congeneric profiles were observed between our work and others previously reported, which is consistent with the use of similar commercial PAEs around the world.     

Investigating the impacts of treated effluent discharge on coastal water health (Visakhapatnam,SW coast of Bay of Bengal,India)

The present study investigated the impacts of treated effluent discharge on physicochemical and biological properties of coastal waters from three pharmaceuticals situated along the coast of Visakhapatnam (SW Bay of Bengal). Seawater samples were collected (during the months of December 2013, March 2014 and April 2014) from different sampling locations (Chippada (CHP), Tikkavanipalem (TKP) and Nakkapalli (NKP)) at 0- and 30-m depths within 2-km radius (0.5 km = inner, 1 km = middle and 2 km?=?outer sampling circles) from the marine outfall points. Physicochemical and biological parameters, which differed significantly within the stations, were likely to be influenced by strong seasonality rather than local discharge. Dissolved oxygen variability was tightly coupled with both physical and biological processes. Phytoplankton cell density and total chlorophyll (TChla) concentrations were significantly correlated with dissolved inorganic nutrient concentrations. CHP (December) represented a diatom bloom condition where the highest concentrations of diatom cells, total chlorophyll (TChla), dissolved oxygen coupled with lower zooplankton abundance and low nutrient levels were noticed. The centric diatom, Chaetoceros sp. (>?50%) dominated the phytoplankton community. TKP (March) represented a post-diatom bloom phase with the dominance of Pseudo-nitzschia seriata; zooplankton abundance and nutrient concentrations were minimum. Conversely, NKP (April) represented a warm well-stratified heterotrophic period with maximum zooplankton and minimum phytoplankton density. Dinoflagellate abundance increased at this station. Relatively higher water temperature, salinity, inorganic nutrients coupled with very low concentrations of dissolved oxygen, TChla and pH were observed at this station. Copepods dominated the zooplankton communities in all stations and showed their highest abundance in the innermost sampling circles. Treated effluent discharge did not seem to have any significant impact at these discharge points.     

A geographical approach to tracking Escherichia coli and other water quality constituents in a Texas coastal plains watershed

Diffuse sources of surface water pathogens and nutrients can be difficult to isolate in larger river basins. This study used a geographical or nested approach to isolate diffuse sources of Escherichia coli and other water quality constituents in a 145.7-km² river basin in south central Texas, USA. Average numbers of E. coli ranged from 49 to 64,000 colony forming units (CFU) per 100 mL depending upon season and stream flow over the 1-year sampling period. Nitrate-N concentrations ranged from 48 to 14,041 μg?L^?1 and orthophosphate-P from 27 to 2,721 μg?L^?1. High concentrations of nitrate-N, dissolved organic nitrogen, and orthophosphate-P were observed downstream of waste water treatment plants but E. coli values were higher in a watershed draining an older part of the city. Total urban land use explained between 56 and 72 % of the variance in mean annual E. coli values (p?<?0.05) in nine hydrologically disconnected creeks. Of the types of urban land use, commercial land use explained most of the variance in E. coli values in the fall and winter. Surface water sodium, alkalinity, and potassium concentrations in surface water were best described by the proportion of commercial land use in the watershed. Based on our nested approach in examining surface water, city officials are able to direct funding to specific areas of the basin in order to mitigate high surface water E. coli numbers and nutrient concentrations.     

Different hydrodynamic processes regulated on water quality (nutrients,dissolved oxygen,and phytoplankton biomass) in three contrasting waters of Hong Kong

The subtropical Hong Kong (HK) waters are located at the eastern side of the Pearl River Estuary. Monthly changes of water quality, including nutrients, dissolved oxygen (DO), and phytoplankton biomass (Chl-a) were routinely investigated in 2003 by the Hong Kong Environmental Protection Department in three contrasting waters of HK with different prevailing hydrodynamic processes. The western, eastern, and southern waters were mainly dominated by nutrient-replete Pearl River discharge, the nutrient-poor coastal/shelf oceanic waters, and mixtures of estuarine and coastal seawater and sewage effluent of Hong Kong, respectively. Acting in response, the water quality in these three contrasting areas showed apparently spatial–temporal variation pattern. Nutrients usually decreased along western waters to eastern waters. In the dry season, the water column was strongly mixed by monsoon winds and tidal currents, which resulted in relatively low Chl-a (<5 μg l^?1) and high bottom DO (>4 mg l^?1), suggesting that mixing enhanced the buffering capacity of eutrophication in HK waters. However, in the wet season, surface Chl-a was generally >10 μg l^?1 in southern waters in summer due to halocline and thermohaline stratification, adequate nutrients, and light availability. Although summer hypoxia (DO <2 mg l^?1) was episodically observed near sewage effluent site and in southern waters induced by vertical stratification, the eutrophication impacts in HK waters were not as severe as expected owing to P limitation and short water residence time in the wet season.     

Determining storm sampling requirements for improving precision of annual load estimates of nutrients from a small forested watershed

This study sought to determine the lowest number of storm events required for adequate estimation of annual nutrient loads from a forested watershed using the regression equation between cumulative load (∑L) and cumulative stream discharge (∑Q). Hydrological surveys were conducted for 4 years, and stream water was sampled sequentially at 15-60-min intervals during 24 h in 20 events, as well as weekly in a small forested watershed. The bootstrap sampling technique was used to determine the regression (∑L-∑Q) equations of dissolved nitrogen (DN) and phosphorus (DP), particulate nitrogen (PN) and phosphorus (PP), dissolved inorganic nitrogen (DIN), and suspended solid (SS) for each dataset of ∑L and ∑Q. For dissolved nutrients (DN, DP, DIN), the coefficient of variance (CV) in 100 replicates of 4-year average annual load estimates was below 20% with datasets composed of five storm events. For particulate nutrients (PN, PP, SS), the CV exceeded 20%, even with datasets composed of more than ten storm events. The differences in the number of storm events required for precise load estimates between dissolved and particulate nutrients were attributed to the goodness of fit of the ∑L-∑Q equations. Bootstrap simulation based on flow-stratified sampling resulted in fewer storm events than the simulation based on random sampling and showed that only three storm events were required to give a CV below 20% for dissolved nutrients. These results indicate that a sampling design considering discharge levels reduces the frequency of laborious chemical analyses of water samples required throughout the year.     

Quantifying nickel in soils and plants in an ultramafic area in Philippines

In this study, concentrations of nickel (Ni) were quantified in the soils and plants in the agricultural areas of Salcedo watershed in Eastern Samar Island, Philippines. The quantity of total Ni in soils (TS-Ni) was significantly high with a mean of 1,409 mg kg^?1, while the soil available Ni (SA-Ni) was low with a mean of 8.66 mg kg^?1. As the levels of TS-Ni in the Salcedo watershed greatly exceeded the maximum allowable concentrations for agricultural soils, the site is not suitable for agricultural purposes. Despite significant TS-Ni levels, SA-Ni levels were very low due to tight binding between Ni and soil components. Consequently, all plants investigated did not meet the criterion for a Ni hyperaccumulator plant with low Ni contents (mean TP-Ni of 14.7 mg kg^?1). Comparison of Ni levels between food plants and its recommended daily intake (RDI) suggests that consumption of food-plants grown in the study area is unlikely to pose health risks. However, caution must be taken against combined consumption of food plants with high Ni levels or their prolonged consumption, as it can induce accumulation of Ni above RDI.     

Spatial variability of soil total and DTPA-extractable cadmium caused by long-term application of phosphate fertilizers, crop rotation, and soil characteristics

Increasing cadmium (Cd) accumulation in agricultural soils is undesirable due to its hazardous influences on human health. Thus, having more information on spatial variability of Cd and factors effective to increase its content on the cultivated soils is very important. Phosphate fertilizers are main contamination source of cadmium (Cd) in cultivated soils. Also, crop rotation is a critical management practice which can alter soil Cd content. This study was conducted to evaluate the effects of long-term consumption of the phosphate fertilizers, crop rotations, and soil characteristics on spatial variability of two soil Cd species (i.e., total and diethylene triamine pentaacetic acid (DTPA) extractable) in agricultural soils. The study was conducted in wheat farms of Khuzestan Province, Iran. Long-term (27-year period (1980 to 2006)) data including the rate and the type of phosphate fertilizers application, the respective area, and the rotation type of different regions were used. Afterwards, soil Cd content (total or DTPA extractable) and its spatial variability in study area (400,000 ha) were determined by sampling from soils of 255 fields. The results showed that the consumption rate of di-ammonium phosphate fertilizer have been varied enormously in the period study. The application rate of phosphorus fertilizers was very high in some subregions with have extensive agricultural activities (more than 95 kg/ha). The average and maximum contents of total Cd in the study region were obtained as 1.47 and 2.19 mg/kg and DTPA-extractable Cd as 0.084 and 0.35 mg/kg, respectively. The spatial variability of Cd indicated that total and DTPA-extractable Cd contents were over 0.8 and 0.1 mg/kg in 95 and 25 % of samples, respectively. The spherical model enjoys the best fitting and lowest error rate to appraise the Cd content. Comparing the phosphate fertilizer consumption rate with spatial variability of the soil cadmium (both total and DTPA extractable) revealed the high correlation between the consumption rate of P fertilizers and soil Cd content. Rotation type was likely the main effective factor on variations of the soil DTPA-extractable Cd contents in some parts (eastern part of study region) and could explain some Cd variation. Total Cd concentrations had significant correlation with the total neutralizing value (p?<?0.01), available P (p?<?0.01), cation exchange capacity (p?<?0.05), and organic carbon (p?<?0.05) variables. The DTPA-extractable Cd had significant correlation with OC (p?<?0.01), pH, and clay content (p?<?0.05). Therefore, consumption rate of the phosphate fertilizers and crop rotation are important factors on solubility and hence spatial variability of Cd content in agricultural soils.     

Pollution of intensively managed greenhouse soils by nutrients and heavy metals in the Yellow River Irrigation Region,Northwest China

The present study aimed to assess the potential ecological risk of heavy metals and nutrient accumulation in polytunnel greenhouse soils in the Yellow River irrigation region (YRIR), Northwest China, and to identify the potential sources of these heavy metals using principal component analysis. Contents of available nitrogen (AN), phosphorus (AP), and potassium (AK) in the surface polytunnel greenhouse soils (0–20 cm) varied from 13.42 to 486.78, from 39.10 to 566.97, and from 21.64 to 1,156.40 mg kg^?1, respectively, as well as AP, soil organic matter (SOM) and AK contents tended to increase significantly at the 0–20- and 20–40-cm soil layers. Heavy metal accumulations occurred in the polytunnel greenhouse soils as compared to arable soils, especially at a depth of 20 cm where Cd, Zn and Cu contents were significantly higher than arable soil. Cd and As were found to be the two main polluting elements in the greenhouse soils because their contents exceeded the thresholds established for greenhouse vegetable production HJ333-2006 in China and the background of Gansu province. It has been shown that Cd, Cu, Pb and Zn at the 0–20-cm soil layer were derived mainly from agricultural production activities, whereas contents of Cr and Ni at the same soil layer were determined by ‘natural’ factors and As originated from natural sources, deposition and irrigation water.     

Trace element concentration and speciation in selected urban soils in New York City

A long history of urbanization and industrialization has affected trace elements in New York City (NYC) soils. Selected NYC pedons were analyzed by aqua regia microwave digestion and sequential chemical extraction as follows: water soluble (WS); exchangeable (EX); specifically sorbed/carbonate bound (SS/CAR); oxide-bound (OX); organic/sulfide bound (OM/S). Soils showed a range in properties (e.g., pH 3.9 to 7.4). Sum of total extractable (SUM_TE) trace elements was higher in NYC parks compared to Bronx River watershed sites. NYC surface horizons showed higher total extractable (TE) levels compared to US non-anthropogenic soils. TE levels increased over 10 year in some of the relatively undisturbed and mostly wooded park sites. Surface horizons of park sites with long-term anthropogenic inputs showed elevated TE levels vs. subsurface horizons. Conversely, some Bronx River watershed soils showed increased concentrations with depth, reflective of their formation in a thick mantle of construction debris increasing with depth and intermingled with anthrotransported soil materials. Short-range variability was evident in primary pedons and satellite samples (e.g., Pb 253?±?143 mg/kg). Long-range variability was indicated by Pb_TE (348 versus 156 mg/kg) and Hg_TE (1 versus 0.3 mg/kg) concentrations varying several-fold in the same soil but in different geographic locations. Relative predominance of fractions: RES (37 %)?>?SS/CAR (22 %)?>?OX (20 %)?>?OM/S (10 %)?>?EX (7 %)?>?WS (4 %). WS and EX fractions were greatest for Hg (7 %) and Cd (14 %), respectively. RES was predominant fraction for Co, Cr, Ni, and Zn (41 to 51 %); SS/CAR for Cd and Pb (40 and 63 %); OM/S for Cu and Hg (36 and 37 %); and OX for As (59 %).