Photocatalytic Decolorization of Commercial Acid Dyes using Solar Irradiation

Four wetland plants were selected to study the effect of Fe plaque formation on phosphorus (P) accumulation in the rhizosphere and P uptake. There were significant positive correlations between the sorbed Fe content in the rhizosphere and the Fe plaque concentration (r ²?=?0.8454, p?<?0.01) and between P accumulation and the amount of the sorbed Fe in the rhizosphere (r ²?=?0.8460, p?<?0.01). The concentration of the Fe plaque on the root surface of four wetland plants species tested followed the order of Zizania cedu Ciflora Turez > Scirpus tabernaemontani Gmel > Iris pseudacorus Linn > Canna indica Linn. The Fe plaque formation increased P uptake, apparently through enhancing the diffusion of P into the roots of the wetland plants; this resulted in increased P concentration in shoots. However, this effect decreased in the higher Fe plaque concentration status, apparently due to physical blocking and immobilization of P by Fe plaque. Therefore, adequate surface coverage of roots of wetland plant by the Fe plaque would increase the uptake of P by wetland plants, which depend on the optimum amendment of Fe. These effects also varied with wetland plant species.     

Total cadmium concentrations in the water and littoral sediments of Central Ontario Lakes

Lakes within 20 km of Sudbury, Ontario, have significantly higher Cd concentrations in surface waters (geometric mean 122 ng L^?1; n = 7) than lakes elsewhere in central Ontario (10.8 ng L^?1; n = 57). Cadmium concentrations in water from lakes beyond the Sudbury halo were negatively correlated (r = 0.797; p < 0.001) with pH. A weak correlation between fluoride and Cd concentrations leads to speculation that some Cd may be mobilized from watersheds with Al. Cadmium concentrations in littoral sediments are not elevated near Sudbury. The geometric mean Cd concentration of littoral sediments in central Ontario lakes is 0.08 mg Cd kg^?1 dry mass (n = 75). Cadmium concentrations in littoral sediments are strongly correlated with sediment loss on ignition (r = 0.860; p < 0.001). After correction for differences in organic content, littoral sediments are less enriched with Cd than profundal sediments, as reported in the literature. The difference between littoral and profundal sediments, and the sensitivity of Cd concentrations in water to pH, may be due to the importance of Cd binding by Fe/Mn hydrous oxides in the profundal zone, while organic matter binds Cd in the littoral zone. The lack of sensitivity of Cd concentrations in littoral sediments to acidification may be due to the incorporation of much of the Cd in those sediments into organic particulates.     

Mercury and Organic Carbon Dynamics During Runoff Episodes from a Northeastern USA Watershed

Mercury and organic carbon concentrations vary dynamically in streamwater at the Sleepers River Research Watershed in Vermont, USA. Total mercury (THg) concentrations ranged from 0.53 to 93.8 ng/L during a 3-year period of study. The highest mercury (Hg) concentrations occurred slightly before peak flows and were associated with the highest organic carbon (OC) concentrations. Dissolved Hg (DHg) was the dominant form in the upland catchments; particulate Hg (PHg) dominated in the lowland catchments. The concentration of hydrophobic acid (HPOA), the major component of dissolved organic carbon (DOC), explained 41–98% of the variability of DHg concentration while DOC flux explained 68–85% of the variability in DHg flux, indicating both quality and quantity of the DOC substantially influenced the transport and fate of DHg. Particulate organic carbon (POC) concentrations explained 50% of the PHg variability, indicating that POC is an important transport mechanism for PHg. Despite available sources of DHg and wetlands in the upland catchments, dissolved methylmercury (DmeHg) concentrations in streamwaters were below detection limit (0.04 ng/L). PHg and particulate methylmercury (PmeHg) had a strong positive correlation (r ²?=?0.84, p?<?0.0001), suggesting a common source; likely in-stream or near-stream POC eroded or re-suspended during spring snowmelt and summer storms. Ratios of PmeHg to THg were low and fairly constant despite an apparent higher methylmercury (meHg) production potential in the summer. Methylmercury production in soils and stream sediments was below detection during snowmelt in April and highest in stream sediments (compared to forest and wetland soils) sampled in July. Using the watershed approach, the correlation of the percent of wetland cover to TmeHg concentrations in streamwater indicates that poorly drained wetland soils are a source of meHg and the relatively high concentrations found in stream surface sediments in July indicate these zones are a meHg sink.     

Distribution of total mercury in coastal sediments from Jade Bay and its catchment, Lower Saxony, Germany

Purpose

Sediment cores provide a reliable record of mercury (Hg) contamination and can be used to study long-term Hg pollution and relevant environmental change. In the last hundred years, there were several events which may have contributed to the accumulation of Hg in Jade Bay and its catchment. This work was undertaken to assess the record in total Hg (THg) content in sediments of cores from Jade Bay and its catchment.

Materials and methods

A 5-m sediment core from Jade Bay, Lower Saxonian Wadden Sea, southern North Sea and a 12-m core from its catchment area (Wangerland, coastal zone of the Jade Bay) were used to study Hg contents in sediments. Total Hg, grain size distribution, aluminium (Al) and total organic carbon (TOC) were analysed on subsamples of both sediment cores. Total Hg was determined by oxygen combustion-gold amalgamation using DMA-80.

Results and discussion

As THg contents of the Jade Bay core were positively correlated to the sum of TOC and Al contents (r ²?=?0.86, p?<?0.001), the Hg data were interpreted using a regional normalisation function with the sum of Al and TOC as the normalisation parameters. Total Hg contents of the Wangerland core were correlated better to Al contents (r ²?=?0.70, p?<?0.001) than to the sum of TOC and Al contents (r ²?=?0.63, p?<?0.05). Therefore, Hg contents in sediments of the Wangerland core were normalised to Al contents. Comparison between enrichment factors and the background range of the sediment cores suggested that Jade Bay was contaminated about 50 years ago, and that Wangerland, or the catchment area of Jade Bay, was contaminated about 300 years ago, if no diagenetic remobilization occurred.

Conclusions

Total Hg contents of both cores were low and of no concern to the aquatic environment of Jade Bay. The Hg record was in good agreement with the history of industrial development in the region; thus, Hg deposition could have occurred through atmospheric input, ammunition residues of the Second World War and volcanic emanations, as well as through diagenetic remobilization.     

Biochemical Oxygen Demand Relationships in Typical Agricultural Effluents

Understanding the variables controlling biochemical oxygen demand (BOD) of effluents from agricultural systems is essential for predicting and managing the water quality risks associated with agricultural production. In this study, short- and long-term oxygen demand behaviors of waters from primarily agricultural sources and their relationships with other parameters were evaluated. A total of 46 water samples were generated from diverse organic sources commonly associated with agricultural activities and analyzed for BOD and other various water quality parameters. Short-term BOD (BOD₂ and BOD₅) were significantly correlated with total organic carbon (TOC), particulate organic carbon (POC), and dissolved organic carbon (DOC) (R ²?=?0.62–0.77, p?<?0.001), likewise to total nitrogen, total Kjeldahl nitrogen, and nitrite–nitrogen (NO₂–N) (R ²?=?0.40–0.55, p?<?0.001). Long-term BOD (BOD₆₀) was generally poorly correlated with these C and N fractions. Phosphate (PO₄–P) exhibited a positive and linear relationship with both short- and long-term BOD, whereas chloride (Cl) tended to inhibit oxygen demand. Multivariate combinations of each of TOC, POC, and DOC with NO₂–N, and Cl or PO₄–P improved the predictions of both short- and long-term BOD. The ultimate BOD (BOD_u) derived from the first-order kinetics was highly correlated with BOD₆₀ (R ²?=?0.81, p?<?0.001) whereas BOD₆₀ was correlated with BOD₅ (R ²?=?0.60, p?<?0.001). Overall the results indicated that C and N forms along with PO₄–P and Cl were the dominant factors controlling the oxygen demand behaviors of agricultural effluents.     

Phosphorus Release and Equilibrium Dynamics of Canal Sediments within the Everglades Agricultural Area, Florida

High phosphorus (P) in surface drainage water from agricultural and urban runoff is the main cause of eutrophication within aquatic systems in South Florida, including the Everglades. While primary sources of P in drainage canals in the Everglades Agricultural Area (EAA) are from land use application of agricultural chemicals and oxidation of the organic soils, internal sources from canal sediments can also affect overall P status in the water column. In this paper, we evaluate P release and equilibrium dynamics from three conveyance canals within the EAA. Incubation and flux experiments were conducted on intact sediment cores collected from four locations within the Miami, West Palm Beach (WPB), and Ocean canal. After three continuous exchanges, Miami canal sediments reported the highest P release (66?±?37 mg m^?2) compared to WPB (13?±?10 mg m^?2) and Ocean (17?±?11 mg m^?2) canal over 84 days. Overall, the P flux from all three canal sediments was highest during the first exchange. Miami canal sediments showed the highest P flux (2.4?±?1.3 mg m^?2 day^?1) compared to WPB (0.83?±?0.39 mg m^?2?d^?1) and Ocean canal sediments (0.98?±?0.38 mg m^?2 day^?1). Low P release from WPB canal sediments despite having high TP content could be due to carbonate layers distributed throughout the sediment column inhibiting P release. Equilibrium P concentrations estimated from the sediment core experiment corresponded to 0.12?±?0.04 mg L^?1, 0.06?±?0.03 mg L^?1, and 0.08?±?0.03 mg L^?1 for Miami, WPB, and Ocean canal sediments, respectively, indicating Miami canal sediments behave as a source of P, while Ocean and WPB canal sediments are in equilibrium with the water column. Overall, the sediments showed a significant positive correlation between P release and total P (r?=?0.42), Fe_ox (r?=?0.65), and Al_ox (r?=?0.64) content of sediments. The contribution of P from the three main canals sediments within the EAA boundary corresponded to a very small portion of the total P load exiting the EAA. These estimates, however, only take into consideration diffusive fluxes from sediments and no other factors such as canal flow, bioturbation, resuspension, and anaerobic conditions.     

Dissolved Organic Nitrogen Concentrations and Ratios of Dissolved Organic Carbon to Dissolved Organic Nitrogen in Throughfall and Soil Waters in Norway Spruce and Scots Pine Forest Stands Throughout Norway

Dissolved organic nitrogen (DON) plays an important ecological role in forest ecosystems, and its concentration is related to that of dissolved organic carbon (DOC). We investigated DON concentrations and ratios of DOC to DON in throughfall and soil waters in 16 Norway spruce and two Scots pine forest stands sampled at weekly intervals between 1996 and 2006. The stands are all included in the ICP Forests Level II monitoring program and are located throughout Norway. DON concentrations were significantly and positively related to DOC concentrations in throughfall (r ²?=?0.72, p?<?0.0001) and soil water at 5, 15, and 40 cm (r ²?=?0.86, 0.32, and 0.84 and p?<?0.0001, 0.04, and <0.0001, respectively). At most sites, the annual median DOC/DON ratio in throughfall ranged from 20.3 to 55.5, which is lower than values in soil water, which ranged from 24.5 to 81.3, gradually decreasing with soil depth. DON concentrations varied seasonally in throughfall at many plots and in soil water at 5-cm depth at one plot only, with higher values in the growing season, but there was no noticeable seasonality at greater depth. The ratios of DOC/DON in soil water were significantly positively related to the C/N ratio in soil at the same depth. Above-ground litter input was the main factor having a significant, negative relationship to DOC/DON in soil water at all depths studied. This might reflect the effect of site conditions on both DOC/DON ratios and litter quantity.     

Increasing the Knowledge of Heavy Metal Contents and Sources in Agricultural Soils of the European Mediterranean Region

This paper contributes to increase the knowledge of the contents and sources of heavy metals (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) to agricultural soils in Castellón province (Spain), a representative area of the European Mediterranean region. The surface horizons of 77 agricultural soils under vegetable crops were sampled and heavy metals were analysed by atomic absorption spectroscopy (AAS) after microwave extraction using the USEPA 3051A method. Mean heavy metal contents were similar to those obtained in other areas of this region. However, heavy metal contents (e.g. Cr, Pb) in some soils were above the maximum limit set in the 86/278/CEE Directive. Multivariate analysis (correlation analysis and principal component analysis – PCA) was performed so as to identify the sources of heavy metals to soils. Co, Fe and Ni were highly correlated amongst them (r?>?0.800; p?<?0.01), whereas Cr and Mn were less correlated with Co, Fe and Ni (r?>?0.500; p?<?0.01). Other relationships among heavy metals (i.e. Cu, Pb and Zn) were also identified, although correlation coefficients were not so high as those among Co, Fe and Ni (r?<?0.500; p?<?0.01). Contents of Co, Fe, Mn and Ni were interpreted to be mainly associated with parent rocks corresponding to the first principal component (PC1). On the other hand, Cd, Cu, Pb and Zn were interpreted to be mainly related to anthropogenic activities and comprised the second (Pb and Zn) and the third (Cd and Cu) principal components (PC2 and PC3, respectively), designated as anthropogenic components. Remarkably, Cr appears to be related in the study area to both the lithogenic and the anthropogenic components. Lithogenic elements were highly correlated with soil properties. Positive relationships with CEC (r?>?0.200; p?<?0.05) and clay (r?>?0.400; p?<?0.01), and negative relationships with carbonates (r?>??0.400; p?<?0.01) and sand (r?>??0.300; p?<?0.01) were observed. Anthropogenic elements were less correlated with soils properties, since these elements are generally more mobile because they form more soluble chemical species associated to anthropogenic sources. Particularly, no correlation was found between Cd and Zn and soil properties. These findings extend results achieved in other parts of the region, highlighting the need to set soil quality standards in order to declare soils affected by anthropogenic pollution, particularly in the case of anthropogenic metals such as Cd, Cu and Pb, and also Cr and Zn in some areas. Further knowledge from other areas in this region would improve the basis for proposing such standards at regional level, which is a priority objective in Europe according to the European Thematic Strategy for Soil Protection.     

Response of selected drought tolerant wheat (Triticum aestivum L.) genotypes for agronomic traits and biochemical markers under drought-stressed and non-stressed conditions

ABSTRACT

Genetic improvement of wheat for drought tolerance can be achieved by developing suitable ideotypes with enhanced yield-response associated with agronomic traits and biochemical markers. The objective of this study was to determine drought response of elite drought tolerant wheat genotypes using agronomic and biochemical traits to select promising lines for breeding. Fourteen wheat genotypes selected from the International Maize and Wheat Improvement Center’s heat and drought tolerance nursery and one standard check variety were evaluated under drought-stressed (DS) and non-stressed (NS) conditions using a randomised complete block design in three replications. Significant (P?<?0.05) genotype, drought condition and genotype?×?drought condition interaction effect were detected for the tested traits suggesting differential response of genotype for selection. Grain yield positively correlated with sucrose (r?=?0.58; P?<?0.05), fructose (r?=?0.52; P?<?0.05) and total sugar (r?=?0.52; P?<?0.05) contents under NS condition and with sucrose (r?=?0.80; P?<?0.001), total sugar (r?=?0.84; P?<?0.001) content, proline content (r?=?0.74; P?<?0.001) and number of grains per spike (r?=?0.58; P?<?0.05) under DS condition. Genetically unrelated wheat genotypes such as SM04, SM19, SM29, SM32, SM45 and SM97 possessing key agronomic and biochemical traits were selected for cultivar development for drought-stressed environments.     

Nutrient And Particulate Inputs Into The Mar Menor Lagoon (Se Spain) From An Intensive Agricultural Watershed

The Mar Menor is a Mediterranean coastal lagoon of high conservation interest, but highly threatened by non-point pollution derived from agricultural lands. This is the first comprehensive study that evaluates the inputs into the Mar Menor from a drainage channel and the Albujón wadi, the main watercourse, and their influence on the trophic state of the lagoon. Discharge variation during the study period was closely related to the precipitation pattern. Suspended sediments and particulate organic matter loads greatly increased with flash floods. Nitrate concentrations, too, increased after heavy autumn rains through washing of the nitrates accumulated in soils, although no significant correlations were found between nitrate concentrations and precipitation or discharge. The nitrate load depended on several factors including the intensity and frequency of precipitation, and the nitrates accumulated in soils as a result of fertilisation. Phosphate concentrations decreased with higher flows. The total input into the lagoon from the two discharges estimated for the period September 2002–October 2003 were 10,142 t.yr^?1of suspended sediments, 389 t.yr^?1 of particulate organic matter, 2,010 t.yr^?1 of dissolved inorganic nitrogen (93 % as NO^? ₃) and 178 t.yr^?1 of soluble reactive phosphorus. The Albujón wadi exported about 80% of the N load and 70% of the P load. Higher flows contributed approximately 80% of the total discharge and nutrient loads, 99% of suspended sediment and 88% of the particulate organic matter. Mean suspended solids and nutrient concentrations in the lagoon followed a spatial pattern, decreasing with distance from the mouth of the Albujón wadi. Water nitrate and phosphate concentrations in the Mar Menor lagoon were lower than reference limits for eutrophic conditions, except after heavy rains. Nutrient concentrations were positively correlated with precipitation variables and particulate and nutrient inputs. Phosphorus was the most limiting nutrient in the Mar Menor, the DIN:SRP ratios found being higher than the Redfield ratio on all sampling dates. Phytoplankton bloom in the lagoon was only found next to the Albujón mouth during late summer and extending 5000 m into the lagoon in autumn as a consequence of large freshwater discharge caused by flash floods. Around 53.6% of the variation in chlorophyll a in the lagoon was explained by the NH₄ and NO₃ inputs and distance from the Albujón mouth. A good deal of P input into the lagoon is retained in the sediments, supporting a high biomass of the benthic macroalga Caulerpa prolifera in spring and summer.     

Short-term impact of a wildfire on net and gross N transformation rates

Wildfires often modify soil properties, including the N status and net N mineralization rates, but their impacts on gross N fluxes have been scarcely evaluated. We aimed to ascertain the immediate effects of a medium–high severity wildfire on soil N transformations. Net and gross N rates were analytically and numerically (FLUAZ) quantified in burned (BS) and unburned (US) topsoils from the temperate–humid region (NW Spain). Analytical and numerical solutions were significantly correlated for both gross N mineralization (m) (r ²?=?0.815; p?<?0.001) and gross nitrification (n) (r ²?=?0.950; p?<?0.001). In BS, all NH₄ ⁺-N fluxes (net m, gross m and gross NH₄ ⁺-N immobilization, ‘ia’) increased, while those of NO₃ ^?-N decreased (gross n and gross NO₃ ^?-N immobilization, ‘in’) or did not vary (net n). In US and BS, gross m (0.26–3.60 and 4.70–15.42 mg N kg^?1 day^?1, respectively) predominated over gross n (0.026–2.45 and 0.001–0.002 mg N kg^?1 day^?1, respectively), and the same was true for the net fluxes. Compared with the few available data on recently burned soils (m?=?8–55 mg N kg^?1 day^?1; n?=?0.50–1.83 mg N kg^?1 day^?1), our gross m and n rates were similar and very low, respectively; gross n showed that nitrifiers were active in US and also in BS, despite the 98 % reduction observed immediately after the fire. For gross fluxes, m increased more than ia suggesting an NH₄ ⁺-N accumulation, but there is no risk of NO₃ ^?-N leaching because n decreased more than in.     

Assessment of plant nutrients’ dynamics in organically and conventionally managed soils by means of different extraction methods

The aim of this study was to investigate what kind changes in the soil fertility parameters occur depending on different farming methods. The field experiment was performed on sandy loam Luvisol during 2008–2014. The following treatments were carried out: organic (ORG), organic with farmyard cattle manure (ORGFYM) and conventional with farmyard cattle manure and mineral fertilizers (CONFYM). Soil samples were collected yearly in September and analyzed for P, K, Mg and Ca by the Mehlich III method. In parallel, ammonium lactate extractable P and K (AL method), and ammonium acetate extractable Mg and Ca (NH₄OAc-method) were determined. The Pearson correlation coefficients between the analysis results achieved by the Mehlich III method and alternative methods were calculated. In all the treatments, no significant changes in soil Corg content were established over seven years. A significant (p?AL in the soil but considerable decrease in the soil K_AL content was revealed. The application of cattle manure (60?t?ha^?1 for the 5-year crop rotation) in both organic and conventional treatments sustained the status of available nutrients in the soil. The Pearson correlation coefficients between Mehlich III and AL methods for P (r?=?0.770, p?r?=?0.922, p?4OAc-methods was found in the case of Mg (r?=?0.951, p?r?=?0.841, p?Mehlich III/P_AL quotient was inversely proportional with the Ca_{Mehlich III} values.     

Soil organic carbon stocks in Veracruz State (Mexico) estimated using the 1:250,000 soil database of INEGI: biophysical contributions

Purpose

In this study, we quantified soil organic carbon (SOC) stocks and analyzed their relationship with biophysical factors and soil properties.

Materials and methods

The study region was Veracruz State, located in the eastern part of Mexico, covering an area of 72,410 km². A soil database that contains physicochemical analyses of soil horizons such as carbon concentration data was the source of information used in this study. The database consisted of 163 soil profiles representing 464 genetic horizons. Statistical analysis was used to investigate the effect of each factor (climate, altitude, slope) on SOC stock to 0.50 m depth and to assess differences in the distribution of SOC stock in terms of soil depth (0.0–0.20, 0.20–0.40, 0.40–0.60, 0.60–0.80, 0.80–1.0 m) and land use. In order to compute the spatial distribution of SOC stock to 0.50 m depth based on the soil sampling location, the kriging method was used.

Results and discussion

Results indicated that SOC stock (0.50 m depth) ranged between 0.44 and 41.2 kg C m^?2. Regression analysis showed that SOC stocks (0.50 m depth) are negatively correlated with temperature (r?=??0.38; P?<?0.001) and positively correlated with altitude (r?=?0.40; P?<?0.001) and slope (r?=?0.40; P?<?0.001). In addition, by multiple regression, temperature combined with precipitation explained more SOC stock variations (r?=?0.43; P?<?0.001) than the regression model with precipitation (r?=?0.13; P?=?0.16) alone. Also, slope combined with temperature and precipitation explained more SOC stock variations (r?=?0.46; P?<?0.001) than the regression model with slope alone. Forest lands, grasslands, and croplands have higher SOC stocks in the 0.0–0.20-m soil layer than in deeper layers. On average, forest lands, grasslands, croplands, and other lands (wetland and dunes) had a SOC stock of 13.6, 14.6, 15.1, and 8.5 kg C m^?2 at 1 m depth, respectively. Soil color correlated (?0.25 ≤ r ≤ ?0.89) with SOC content.

Conclusions

Overall, these results indicate the influence of major interactions between biophysical factors and SOC stocks. This research indicated that SOC stock decreased with soil depth, but with slight variations depending on land use. Thus, there remains a need for more SOC data that include an improved distribution of soil sampling points in order to entirely understand the contributions of biophysical factors to SOC stocks in Veracruz State.     

Control of Algal Scum Using Top-Down Biomanipulation Approaches and Ecosystem Health Assessments for Efficient Reservoir Management

The objectives of this study were algal control and health assessments in a temperate eutrophic reservoir. Laboratory and mesocosm-scale in situ top-down biomanipulation experiments using planktivorous fishes and filter-feeding macroinvertebrates were conducted along with identification of the limiting nutrient using nutrient enrichment bioassays (NEBs), and ecosystem health evaluation based on the modified index of biological integrity model (Reservoir Ecosystem Health Assessment; REHA). Nutrients and N/P ratio analyses during 5 years revealed that the reservoir was in a eutrophic–hypertrophic state and that the key limiting nutrients, based on the NEBs, varied among seasons. Reservoir trophic guilds indicated declines in sensitive and endemic fish species and dominance of tolerant omnivores. Model values from multimetric REHAs averaged 25.8, indicating that the ecological health was in “fair to poor” condition. Overall microcosm biomanipulation tests suggested that macroinvertebrates, specifically Palaemon paucidens and Caridina denticulata, were effective candidates for phytoplankton control, compared to fishes. In situ mesocosm experiments revealed the highest removal rates with bluegreen algae and a phytoplankton size fraction of 2–19 μm (R _e?>?90%, Mann–Whitney U?=?64.5–74.0, p?<?0.01), the dominant fractions in the reservoir. Our biomanipulation technique may provide a key tool for efficient management and restoration of eutrophied reservoirs.     

Nutrient Loss Following Phragmites australis Removal in Controlled Soil Mesocosms

Mechanisms to remove Common reed (Phragmites australis) typically include a combination of herbicide applications and mechanical cutting or plowing of the soil. The objective of this study was to remove P. australis by various mechanisms and measure the subsequent short-term release of nutrients via simulated rain events. Three rain events of similar duration and intensity were conducted on a control subset and three treatments (above and belowground biomass removal, herbicide application, and basal cut) of soil mesocosms (n?=?6) that were designed to export excess water as either surface runoff or leachate through the soil profile. The dominant pathway for soluble reactive phosphorus (p?<?0.001) and ammonium (p?<?0.001) export were surface runoff while nitrate (p?<?0.001) was leached through the soil profile. More nitrate was exported in the vegetation removal treatments (i.e., biomass removal, herbicide, and basal cut) than the control (p?<?0.001) while more soluble reactive phosphorus was exported in the herbicide and basal cut treatment compared to the control (p?=?0.010). In regards to ammonium, a higher export was observed in the herbicide treatment compared to the control, biomass removal, and basal cut treatments (p?<?0.001). We attribute the higher amount of ammonium export in the herbicide treatment to the fact that the glyphosate herbicide used was in an isopropylamine salt form. After examining pre- and postmanipulation soil cores, there was a larger decrease in extractable ammonium in the control and all treatments compared to soil extractable nitrate, which displayed a smaller decrease and in some treatments actually increased during the course of the experiment. Ultimately, in this study, we observed a strong potential for nitrogen biogeochemistry to occur and the removal of vegetation-enhanced nutrient export.     

Surfactants in the Sea Surface Microlayer,Underlying Water and Atmospheric Particles of Tropical Coastal Ecosystems

This study aims to determine the composition of surfactants in the sea surface microlayer (SML), underlying water (ULW) and atmospheric particles (AP). Surfactants were determined colorimetrically as methylene blue active substances (MBAS) and disulphine blue active substances (DBAS) for anionic and cationic surfactants, respectively. The concentration of dissolved inorganic nutrients (DIN) in ULW was determined so as to indicate the influence of ULW to the surfactants in SML. The results showed that the concentration of MBAS and DBAS in SML at both stations ranged between 0.05 and 0.31 μmol L^?1, and between 0.19 and 0.59 μmol L^?1, respectively. Surfactants in ULW influence the concentration of surfactants in SML (r?=?0.65, p?<?0.01, n?=?36). The station influenced by anthropogenic sources showed a higher concentration of surfactants in ULW, SML and AP. This finding suggests fine mode atmospheric particles (FMAP) are the main carrier for anionic surfactants as MBAS in the coastal ecosystem. Anionic surfactants as MBAS were found as better indicator of anthropogenic sources than cationic ones.     

Spatial and vertical variations in the soil organic carbon concentration and its controlling factors in boreal wetlands in the Greater Khingan Mountains,China

Purpose

Wetlands have a critical impact on the global carbon cycle. This study aims to investigate the spatial and vertical distribution of the soil organic carbon concentration (SOCc), to identify the differences of SOCc among swamps, marshes, bogs, and fens at a regional scale, and finally to examine the main environmental factors impacting SOCc at different depth intervals within different wetland types located in the Greater Khingan Mountains (GKM).

Materials and methods

A total of 218 soil samples were collected. SOCc was determined by the combustion-oxidation method. To analyze the impacts of wetland type, soil type, mean annual precipitation (MAP), mean annual temperature (MAT), evapotranspiration (ET), elevation (EL), and slope (SL) on SOCc, statistical analysis methods were executed, including ANOVA with the Duncan test, Pearson correlations analysis, and the stepwise multiple regressions analysis.

Results and discussion

The mean values of SOCc in the 0–30, 30–60, and 60–100-cm intervals were 130.4, 64.2, and 32.6 g kg^?1, respectively. The wetland type played an important role in the pattern of SOCc in terms of significant differences (p?<?0.05) among the different wetland types in the 0–60-cm depth. However, significant differences were not found among different soil types. In terms of the wetland type, the highest SOCc was found in bogs (p?<?0.05), probably due to the higher MAP and lower MAT. The increased MAP (R²?=?0.1369, p?<?0.01) and decreased MAT (R²?=?0.1225, p?<?0.01) had positive associations on the wetland SOCc. ET (R²?=?0.2809, p?<?0.01), MAP (R²?=?0.2025, p?<?0.01), and EL (R²?=?0.0484, p?<?0.05) were positively correlated with marsh SOCc. Moreover, MAP was positively correlated with the bog SOCc (R²?=?0.1296, p?<?0.01). For vertical patterns, SOCc was higher in the 0–30-cm interval and decreased with depth. The impacts of environmental factors on SOCc decreased with depth for each wetland type. Models were developed to document the relations between the SOCc of marshes and fens and corresponding environmental factors.

Conclusions

Wetland types largely differed in the soil carbon pools in the GKM of China. The relative importance of environmental factors was different for the SOCc values of various wetland types. To minimize carbon loss into the atmosphere, more protections are required for wetlands, especially in the 0–30-cm depth interval because it contains higher SOCc values and is more vulnerable and less stable than those in the deeper layers.

     

Seasonal Variations of Ten Metals in Highway Runoff and their Partition between Dissolved and Particulate Matter

Knowledge of differentiation of pollutants in urban runoff between dissolved and particulate matter is of great concern for a successful design of a water treatment process. Seasonal variations in pollutant load are of equal importance. Ten metals (Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn), as dissolved and particulate bound, was studied in the runoff from a major urban highway during a winter season and its following summer. Studded tyres and winter salting were expected to have an impact on the runoff water quality. The dissolved part of Al, Cd, Co, Cr, Mn and Ni was significantly higher in winter in comparison with summer (p?<?0.01). For Fe, however, the dissolved part was lower during winter. No significant difference was found for Cu, Pb and Zn between the two seasons. The mass concentration (mg kg^?1) for all metals was significantly higher over the summer except for Al and Co, which showed a higher mass concentration during the winter. The concentration of selected metals vs. total suspended solids (TSS) showed a linear relationship (r ²?>?0.95) during winter runoff events except for Cd. A good correlation (r ²?>?0.90) was also found for the summer period for Al, Cu, Fe, Mn, Ni and Zn. It is suggested that the metal pollutant load during winter could be assessed indirectly by measurement of TSS.     

How Effective is Reduced Tillage–Cover Crop Management in Reducing N2O Fluxes from Arable Crop Soils?

Field management is expected to influence nitrous oxide (N₂O) production from arable cropping systems through effects on soil physics and biology. Measurements of N₂O flux were carried out on a weekly basis from April 2008 to August 2009 for a spring sown barley crop at Oak Park Research Centre, Carlow, Ireland. The soil was a free draining sandy loam typical of the majority of cereal growing land in Ireland. The aims of this study were to investigate the suitability of combining reduced tillage and a mustard cover crop (RT?CCC) to mitigate nitrous oxide emissions from arable soils and to validate the DeNitrification?CDeComposition (DNDC) model version (v. 9.2) for estimating N₂O emissions. In addition, the model was used to simulate N₂O emissions for two sets of future climate scenarios (period 2021?C2060). Field results showed that although the daily emissions were significantly higher for RT?CCC on two occasions (p?<?0.05), no significant effect (p?>?0.05) on the cumulative N₂O flux, compared with the CT treatment, was found. DNDC was validated using N₂O data collected from this study in combination with previously collected data and shown to be suitable for estimating N₂O emissions (r ²?=?0.70), water-filled pore space (WFPS) (r ²?=?0.58) and soil temperature (r ²?=?0.87) from this field. The relative deviations of the simulated to the measured N₂O values with the 140?kg N ha^?1 fertiliser application rate were ?36?% for RT?CCC and ?19?% for CT. Root mean square error values were 0.014 and 0.007?kg N₂O?CN ha^?1 day^?1, respectively, indicating a reasonable fit. Future cumulative N₂O fluxes and total denitrification were predicted to increase under the RT?CCC management for all future climate projections, whilst predictions were inconsistent under the CT. Our study suggests that the use of RT?CCC as an alternative farm management system for spring barley, if the sole objective is to reduce N₂O emissions, may not be successful.     

Distribution characteristics of iron,carbon, nitrogen and phosphorus in the surface soils of different land use types near Xingkai Lake

Purpose

The purpose of this study was to research the differences in iron, phosphorus, nitrogen and organic matter contents at two soil depths in areas with different land use types in the Xingkai Lake National Nature Reserve and to determine the causes of those differences. Additionally, this study sought to analyse the correlations between the contents of different nutrients and to determine the reasons for those correlations.

Materials and methods

Five typical land use types, namely, lakeshore sandy land, grassland, forestland, dryland and wetland, were selected in the Xingkai Lake National Nature Reserve. The contents of amorphous iron (Fe_o), complexed iron (Fe_p), dithionite-extractable iron (Fe_d), total iron (TFe), total phosphorus (TP), total nitrogen (TN) and organic matter (OM) were measured in these soils at two depths: 0–5 cm (soil depth 1) and 5–10 cm (soil depth 2).

Results and discussion

For soil depth 1 and soil depth 2, the land use type had no significant effect on the element contents. For the entire soil depth range (0–10 cm), the land use type had the most significant impact on the TP content (p?<?0.01). Furthermore, soil depth had a significant effect on the contents of Fe_o (p?<?0.01), TP (p?<?0.01) and OM (p?<?0.05). Overall, the element content at soil depth 2 was higher than that at soil depth 1. The interaction between land use type and soil depth significantly influenced the contents of TN and OM (p?<?0.05). The contents of TN and OM in the lakeshore sandy land and dryland were high, and the contents of TN and OM were highly positively correlated (r?=?0.90652, p?<?0.01).

Conclusions

Different land use types caused different degrees of disturbance in the soil, resulting in differences in the element contents in the soils. The differences in the distribution of soil element contents in the topsoil were the result of important natural and human factors.