Average Concentrations Of Total Nitrogen Research Articles

Characteristics of Carbon and Nitrogen in the Downstream Columnar Sediment of Maozhou River, Shenzhen

Based on the determinations of total nitrogen (TN), organic matter (OM), carbon-nitrogen ratio (C/N), δ15 N, and δ13 C on 12 sediment cores, the distribution characteristics and the sources of nitrogen and organic matter were analyzed in sediments from the lower reaches and main tributaries of the Maozhou River. The results showed that the average concentrations of total nitrogen (TN) and organic matter (OM) were 1815.37 mg·kg-1 and 22 401.68 mg·kg-1, respectively, in the Maozhou River sediments, which were higher than in TaihuLake and ChaohuLake. The levels of TN and OM in the study area were high and varied greatly with the increase of depth. The δ15 N content in the sediments of the MaozhouRiver downstream ranged from 2.20 ‰ to 32.78 ‰, while the δ13 C content ranged from -27.53 ‰ to -21.95 ‰. The average concentrations of δ15 N and δ13 C were 6.78 ‰ and -25.41 ‰. Moreover, the C/N ratio ranged from 0.49 to -18.23. The δ13 C varied slightly with the increase of depth, while δ15 N and C/N varied greatly. A source analysis in the study area indicated that C3 plants and chemical fertilizer were the main sources in the surface sediments (0-40 cm) downstream of the Maozhou River. Furthermore, algae were the main sources of organic matter in the deep sediments downstream of the Maozhou River and in tributary sediments of the Shajing River. Nitrogen in the surface sediments (0-40 cm) downstream of the Maozhou River mainly comes from inorganic fertilizer and soil organic nitrogen, while nitrogen in the Maozhou River deep sediments and Shajing River sediments mainly come from soil erosion and soil organic nitrogen.

Characteristics of Nitrogen Loss through Surface-Subsurface Flow on Red Soil Slopes of Southeast China

Soil nitrogen (N) loss related to surface flow and subsurface flow (including interflow and groundwater flow) from slope lands is a global issue. A lysimetric experiment with three types of land cover (grass cover, GC; litter cover, LC; and bare land, BL) were carried out on a red soil slope land in southeast China. Total Nitrogen (TN) loss through surface flow, interflow and groundwater flow was observed under 28 natural precipitation events from 2015 to 2016. TN concentrations from subsurface flow on BL and LC plots were, on average, 2.7–8.2 and 1.5–4.4 times greater than TN concentrations from surface flow, respectively; the average concentration of TN from subsurface flow on GC was about 36–56% of that recorded from surface flow. Surface flow, interflow and groundwater flow contributed 0–15, 2–9 and 76–96%, respectively, of loss load of TN. Compared with BL, GC and LC intercepted 83–86% of TN loss through surface runoff; GC intercepted 95% of TN loss through subsurface flow while TN loss through subsurface flow on LC is 2.3 times larger than that on BL. In conclusion, subsurface flow especially groundwater flow is the dominant hydrological rout for N loss that is usually underestimated. Grass cover has the high retention of N runoff loss while litter mulch will increase N leaching loss. These findings provide scientific support to control N runoff loss from the red soil slope lands by using suitable vegetation cover and mulching techniques.

Evaluation of leachate dissolved organic nitrogen discharge effect on wastewater effluent quality

Nitrogen is limited more and more frequently in wastewater treatment plant (WWTP) effluents because of the concern of causing eutrophication in discharge waters. Twelve leachates from eight landfills in Florida and California were characterized for total nitrogen (TN) and dissolved organic nitrogen (DON). The average concentration of TN and DON in leachate was approximately 1146mg/L and 40mg/L, respectively. Solid-phase extraction was used to fractionate the DON based on hydrophobic (recalcitrant fraction) and hydrophilic (bioavailable fraction) chemical properties. The average leachate concentrations of bioavailable (bDON) and recalcitrant (rDON) DON were 16.5mg/L and 18.4mg/L, respectively. The rDON fraction was positively correlated, but with a low R2, with total leachate apparent color dissolved UV254, chemical oxygen demand (COD), and humic acid (R2 equals 0.38, 0.49, and 0.40, respectively). The hydrophobic fraction of DON (rDON) was highly colored. This fraction was also associated with over 60% of the total leachate COD. Multiple leachate and wastewater co-treatment simulations were carried out to assess the effects of leachate on total nitrogen wastewater effluent quality using removals for four WWTPs under different scenarios. The calculated pass through of DON suggests that leachate could contribute to significant amounts of nitrogen discharged to aquatic systems.

Spatio-Temporal Distribution of Total Nitrogen and Phosphorus in Dianshan Lake, China: The External Loading and Self-Purification Capability

In this article, long-term data, statistical analysis, and spatial interpolation method were applied to the analyses of the spatial and temporal changes of total nitrogen (TN) and total phosphorus (TP) in Dianshan Lake. We also estimated the self-purification capability of TN and TP in Dianshan Lake. The results showed that interannual variability of the average concentration of TN in Dianshan Lake changed significantly, showing a characteristic increase before a decline, and the average concentration of TN showed an obvious downward trend, especially after 2007. Interannual variability of the average concentration of TP in Dianshan Lake fluctuated, and the average concentration of TP showed a downward trend after 2007. The seasonal variations of TN and TP in Dianshan Lake were similar. Higher TN concentration occurred in winter and spring, while higher TP concentration appeared in summer, autumn, and winter. The spatial distribution of TN and TP in Dianshan Lake were similar, showing a characteristic which decreased from north to south and west to east. The highest TN and TP values were mainly distributed in the inlet monitoring sites, while the lowest TP values were distributed in the outlet monitoring sites. The self-purification capability of TN and TP were about 2289.97 t/yr and 112.16 t/yr, which suggested a deterioration of natural water quality. Our research showed that Dianshan Lake was highly eutrophic and that water quality showed a substantial improvement from 1996 to 2015.

Long term (1997-2014) spatial and temporal variations in nitrogen in Dongting Lake, China.

In order to protect the water quality of Dongting Lake, it is significant to find out its nitrogen pollution characteristics. Using long-term monthly to seasonally data (1997–2014), we investigated the spatial and temporal variations in nitrogen in Dongting Lake, the second largest freshwater lake in China. The average concentrations of total nitrogen (TN) in the eastern, southern, and western parts of the lake were 1.77, 1.56, and 1.35 mg/L, respectively, in 2014. TN pollution was generally worse in the southern area than in the western area. Concentrations showed temporal variation, and were significantly higher during the dry season than during the wet season. Based on the concentration and growth rate of TN, three different stages were identified in the long term lake data, from 1997 to 2002, from 2003 to 2008, and from 2009 to 2014, during which the concentrations and the growth rate ranged from 1.09–1.51 mg/L and 22.09%-40.03%, 1.05–1.57 mg/L and -9.05%-7.74%, and 1.68–2.02 mg/L and 57.99%-60.41%, respectively. The main controls on the lake water TN concentrations were the quality and quantity of the lake inflows, spatial and temporal variations in hydrodynamic conditions within the lake (flow velocity, flow direction), and point and nonpoint inputs from human activities. Diffuse nutrient losses from agricultural land are a significant contributor. As a priority, the local government should aim to control the pollutant inputs from upstream and non-point nutrient losses from land.

Vertical Distribution and Pollution Risk Assessment of Nitrogen, Phosphorus, and Organic Matter in Sediment of Inflowing Rivers of Erhai Lake Estuarine Wetland in Wet and Dry Seasons

The estuarine wetland of Luoshijiang River, which flows into Erhai Lake in Yunnan province, was regarded as the typical research object. Sediment samples in the estuarine wetland of Luoshijiang River were collected by the cylindrical sediment sampler and the samples were from surface layer (0-10cm), middle layer (10-30 cm), and bottom layer (30-60 cm). The vertical distribution of total nitrogen, total phosphorus, and total organic material in dry and rainy season was analyzed and contamination risk assessment of sediment was accomplished. The results showed that: ① In dry season, average concentrations of total nitrogen in sediment on surface, middle and bottom layer at estuarine wetland of Luoshijiang River were respectively 1.734, 1.453 and 1.255 g·kg-1, the average concentrations of total phosphorus were respectively 1.085, 1.034 and 0.992 g·kg-1, the average concentrations of organic material were respectively 59.051, 47.730 and 42.133 g·kg-1. In rainy season, average concentrations of total nitrogen in sediment on surface, middle and bottom layer at estuarine wetland of Luoshijiang River were respectively 1.147, 0.948 and 0.895 g·kg-1, the average concentrations of total phosphorus were respectively 0.599, 0.523 and 0.519 g·kg-1, the average concentrations of organic material were respectively 53.098, 46.897 and 43.395 g·kg-1. ② Single factor pollution index, organic nitrogen and organic index assessment were used to evaluate the contamination level of sediment, the assessment results showed that: In dry season, the contamination level of nitrogen and phosphorus in sediment was on severe level, organic material contamination was on medium level. In rainy season, the contamination levels of ON and OI were medium, and that of PI was mild. Generally, the contamination levels of nitrogen, phosphorus and organic material in sediment tendency were as follows: dry season>rainy season, and the pollution index of each layer followed the sequence of surface layer > middle layer > bottom layer, and the most extraordinary contamination of them on surface layer was uncovered whatever the season was. ③ Pollution origin of estuarine wetland of Luoshijiang River in dry and wet season had great differences, it was mainly the exogenous source in dry season, but it was the internal source in wet season; The potential risk of release of nutrient salt of sediment in dry season was higher than the wet, and the risk in the surface layer was the highest.

A coupled system of half-nitritation and ANAMMOX for mature landfill leachate nitrogen removal

ABSTRACTA coupled system of membrane bioreactor-nitritation (MBR-nitritation) and up-flow anaerobic sludge blanket-anaerobic ammonium oxidation (UASB-ANAMMOX) was employed to treat mature landfill leachate containing high ammonia nitrogen and low C/N. MBR-nitritation was successfully realized for undiluted mature landfill leachate with initial concentrations of 900–1500 mg/L and 2000–4000 mg/L chemical oxygen demand. The effluent concentration and the accumulation efficiency were 889 mg/L and 97% at 125 d, respectively. Half-nitritation was quickly realized by adjustment of hydraulic retention time and dissolved oxygen (DO), and a low DO control strategy could allow long-term stable operation. The UASB-ANAMMOX system showed high effective nitrogen removal at a low concentration of mature landfill leachate. The nitrogen removal efficiency was inhibited at excessive influent substrate concentration and the nitrogen removal efficiency of the system decreased as the concentration of mature landfill leachate increased. The MBR-nitritation and UASB-ANAMMOX processes were coupled for mature landfill leachate treatment and together resulted in high effective nitrogen removal. The effluent average total nitrogen concentration and removal efficiency values were 176 mg/L and 83%, respectively. However, the average nitrogen removal load decreased from 2.16 to 0.77 g/(L d) at higher concentrations of mature landfill leachate.

Mainstream partial nitritation and anammox: long-term process stability and effluent quality at low temperatures

The implementation of autotrophic anaerobic ammonium oxidation processes for the removal of nitrogen from municipal wastewater (known as “mainstream anammox”) bears the potential to bring wastewater treatment plants close to energy autarky. The aim of the present work was to assess the long-term stability of partial nitritation/anammox (PN/A) processes operating at low temperatures and their reliability in meeting nitrogen concentrations in the range of typical discharge limits below 2 mgNH4-N·L−1 and 10 mgNtot·L−1. Two main 12-L sequencing batch reactors were operated in parallel for PN/A on aerobically pre-treated municipal wastewater (21 ± 5 mgNH4-N·L−1 and residual 69 ± 19 mgCODtot·L−1) for more than one year, including over 5 months at 15 °C. The two systems consisted of a moving bed biofilm reactor (MBBR) and a hybrid MBBR (H-MBBR) with flocculent biomass. Operation at limiting oxygen concentrations (0.15–0.18 mgO2·L−1) allowed stable suppression of the activity of nitrite-oxidizing bacteria at 15 °C with a production of nitrate over ammonium consumed as low as 16% in the MBBR. Promising nitrogen removal rates of 20–40 mgN·L−1·d−1 were maintained at hydraulic retention times of 14 h. Stable ammonium and total nitrogen removal efficiencies over 90% and 70% respectively were achieved. Both reactors reached average concentrations of total nitrogen below 10 mgN·L−1 in their effluents, even down to 6 mgN·L−1 for the MBBR, with an ammonium concentration of 2 mgN·L−1 (set as operational threshold to stop aeration). Furthermore, the two PN/A systems performed almost identically with respect to the biological removal of organic micropollutants and, importantly, to a similar extent as conventional treatments. A sudden temperature drop to 11 °C resulted in significant suppression of anammox activity, although this was rapidly recovered after the temperature was increased back to 15 °C. Analyses of 16S rRNA gene-targeted amplicon sequencing revealed that the anammox guild of the bacterial communities of the two systems was composed of the genus “Candidatus Brocadia”. The potential of PN/A systems to compete with conventional treatments for biological nutrients removal both in terms of removal rates and overall effluent quality was proven.

Spatial and temporal variations in non-point source losses of nitrogen and phosphorus in a small agricultural catchment in the Three Gorges Region.

Losses of agricultural pollutants from small catchments are a major issue for water quality in the Three Gorges Region. Solutions are urgently needed. However, before pollutant losses can be controlled, information about spatial and temporal variations in pollutant losses is needed. The study was carried out in the Wangjiagou catchment, a small agricultural catchment in Fuling District, Chongqing, and the data about non-point source losses of nitrogen and phosphorus was collected here. Water samples were collected daily by an automatic water sampler at the outlets of two subcatchments from 2012 to 2014. Also, samples of surface runoff from 28 sampling sites distributed through the subcatchments were collected during 12 rainfall events in 2014. A range of water quality variables were analyzed for all samples and were used to demonstrate the variation in non-point losses of nitrogen and phosphorus over a range of temporal and spatial scales and in different types of rainfall in the catchment. Results showed that there was a significant linear correlation between the mass concentrations of total nitrogen (TN) and nitrate (NO3-N) in surface runoff and that the relationship was maintained with changes in time. Concentrations of TN and NO3-N peaked after fertilizer was applied to crops in spring and autumn; concentrations decreased rapidly after the peak values in spring but declined slowly in autumn. N and P concentrations fluctuated more and showed a greater degree of dispersion during the spring crop cultivation period than those in autumn. Concentrations of TN and NO3-N in surface runoff were significantly and positively correlated with the proportion of the area that was planted with corn and mustard tubers, but were negatively correlated with the proportion of the area taken up with rice and mulberry plantations. The average concentrations of TN and NO3-N in surface runoff reached the highest level from the sampling points at the bottom of the land used for corn only, but lowest in rice fields. Slope gradient had a significant positive correlation with TN’s and total phosphorus (TP)’s concentration losses. Concentrations of TN, NO3-N, and total phosphorus were significantly correlated with rainfall. Peak concentrations of ammoniacal nitrogen occurred during the fertilizer application period in spring and autumn. Different structures of land use types had a significant influence on the concentration losses of nitrogen and phosphorus; thus, using a reasonable way to adjust land use structure and spatial arrangement of whole catchment was an effective solution to control non-point source pollution of the Three Gorges Region.

Impact of nutrient losses from agricultural lands on nutrient stocks in Dianshan Lake in Shanghai, China

The water quality of Dianshan Lake in Shanghai Municipality, China, is impacted by nutrient losses from agricultural lands around the lake. In this study, nine types of agricultural land use were monitored in 2010 and 2011, and a correlation analysis between nutrient losses from agricultural non-point sources (NPS) and nutrient stocks in the lake was conducted over monthly and seasonal time periods. The results indicate that the monthly average concentration of total nitrogen (TN) ranged from 1.41 to 7.34 mg/L in 2010 and from 1.52 to 5.90 mg/L in 2011, while the monthly average concentration of total phosphorous (TP) ranged from 0.11 to 0.26 mg/L in 2010 and from 0.13 to 0.30 mg/L in 2011. The annual loss of TN from agricultural NPS was 195.55 tons in 2010 and 208.40 tons in 2011. The cultivation of water oat made the largest contribution to the loss of TN. The annual loss of TP was 44.58 tons in 2010 and 48.12 tons in 2011, and multi-vegetable cultivation made the largest contribution to the loss of TP. The results of correlation analysis show that the monthly stocks of TN and TP in the lake have a positive correlation with the monthly losses of TN and TP from agricultural NPS. According to the seasonal data, the stocks of TN and TP in the lake both have a much stronger correlation with the losses of TN and TP from agricultural NPS in summer than in other seasons. Agricultural NPS pollution control should be the main focus for the water resource conservation in this area.

Nitrogen distribution and diffusive fluxes in sediment interstitial water of Poyang Lake

The concentration and distribution characteristics of nitrogen in the sediment interstitial water from the Poyang Lake were determined. Diffusive fluxes of nitrogen between interstitial water and overlying water were estimated. The results showed that the average concentration of total nitrogen and nitrate nitrogen in surface sediment interstitial water of Poyang Lake were 1.29 and 0.76 mg/L. Total nitrogen existed mainly in the form of nitrate nitrogen, which amounted to 45.38–73.54 % of the total nitrogen. The spatial distribution characteristics of total nitrogen and nitrate nitrogen concentration in surface sediment interstitial water are similar, and the contents of total nitrogen and nitrate nitrogen do not show significant spatial variation at all sampling sites. The profiles of nitrogen were characterized by sharp gradients near the sediment–water interface. The contents of nitrogen increased with degree of depth at first and then decreased with degree of depth. The concentrations of nitrogen in surface sediment interstitial water were much higher than that in the overlying water at most sites, indicating that nitrogen tended to release from sediment to water. The average diffusive fluxes of total nitrogen and nitrate nitrogen at the sediment–water interface were 0.87 and 0.86 mg/m2 day, respectively.

Nitrogen distribution and ammonia release from the overlying water and sediments of Poyang Lake, China

Poyang Lake is the largest freshwater lake in China and is one of the two largest lakes connected with the Yangtze River. It is an overflow lake which absorbs and releases water seasonally. To evaluate the geochemical cycling of nitrogen (N) in Poyang Lake, the spatial distributions of ammonia nitrogen (NH4 +–N), nitrate nitrogen (NO3 −–N) and total nitrogen (TN) in sediments and overlying water were measured. The experimental results showed that the average concentrations of TN in the sediment samples, surface water, and bottom water samples from Poyang Lake were 1,107.375 mg kg−1, 1.998 and 2.237 mg L−1, respectively. The highest concentrations of TN were measured in the water and sediment obtained from the river tail region south of Poyang Lake, with decreasing pattern from south to north affected by the river input. The contribution of TN to the internal load played an important role on N distribution in the overlying water. The vertical distribution of TN in sediment cores of Poyang Lake showed a decreasing trend with depth. The NH4 +–N content in sediment cores initially decreased with depth and then increased slowly. The NO3 −–N content in sediment cores exhibited an inverse trend compared with that of NH4 +–N due to the influence of nitrification and denitrification processes. Release kinetic experiments of NH4 +–N demonstrated that the maximum NH4 +–N release rate occurred within first 5 min and reached 90–94 % of the maximum value within 0–10 min.

Temperature influence on nitrogen removal in a hybrid constructed wetland system in Northern Italy

The objective of this research was to investigate the efficiency and seasonal performance of a full-scale hybrid constructed wetland system (HCW) in reducing total nitrogen (TN), ammonia nitrogen (NH4-N) and nitrate nitrogen (NO3-N). HCW with a total area of about 130m2 and hydraulic load of 2m3/day was composed of three subsurface flow vertical systems (VF), working in parallel and one horizontal (HF) connected in series. The system was loaded daily with synthetic wastewater having an average concentration of TN of 250mg/L (about 125mg/L of NH4-N and 125mg/L of NO3-N). Water samples were collected and analyzed from May to July 2011 and from January 2012 to July 2012. Variations were observed in nutrient removal performance related to temperature.During the whole monitoring period median reduction efficiency (RE) in the HCW was TN 95%, NH4-N 95% and NO3-N 93%, although three sub-periods characterized by different performances have been observed. During the first period (from May to July 2011) the RE was positive for the three nitrogen forms considered, whereas from January to the end of March 2012 the RE was lower, particularly for TN and NO3-N. From April 2012, when the temperature rose above 14.8°C, there was an increase in the performance that reached the 2011 values.Internal production of NO3-N was observed, mainly in the VF systems between January and March 2012. The median removals of mass pollutants per m2 of HCW per day were TN 3.1g/m2/d, NH4-N 1.5g/m2/d, NO3-N 1.5g/m2/d. Segmented regression analysis identified a breakpoint at 14.2°C for wastewater temperature that caused variations in TN and NO3-N concentration reduction performances. According to this approach the abatement was always positively correlated with temperature, but different regression slopes were obtained below and above the breakpoint. In particular, with lower temperature the abatement of NO3-N and TN increased by 1.7 and 2.0% per °C of temperature increase; with temperature higher than 14.2°C the increase in abatement due to increased temperature was sharper, especially for NO3-N.

Characteristics of nitrogen loading and its influencing factors in several typical agricultural watersheds of subtropical China.

Increasingly, the characteristics of nitrogen (N) loading have been recognized to be critical for the maintenance and restoration of water quality in agricultural watersheds, in response to the spread of water eutrophication. This paper estimates N loading and investigates its influencing factors in ten small watersheds variously dominated by forest and agricultural land use types in the subtropics of China, over an observation period of 23-29 months. The results indicate that the average concentrations of total nitrogen (TN), NH4 (+)-N, and NO3 (-)-N were 0.83, 0.07, and 0.46 mg N L(-1) in the forest watersheds and 1.49-5.16, 0.21-3.23, and 0.99-1.30 mg N L(-1) in the agricultural watersheds, respectively. Such concentrations exceed the national criteria for nutrient pollution in surface waters considerably, suggesting severe stream pollution in the studied agricultural watersheds. The average annual TN loadings (ANL) were estimated to be 1,640.8 kg N km(-2) year(-1) in the agricultural watersheds, 63.3-86.1 % of which was composed of dissolved inorganic N (DIN; comprising NO3 (-)-N and NH4 (+)-N). The watershed with intensive livestock production (i.e., the maximum livestock density of 2.66 animal units (AU) ha(-1)) exhibited the highest ANL (2,928.7 kg N km(-2) year(-1)) related to N loss with effluent discharge. The results of correlation and principle component analysis suggest that livestock production was the dominant influencing factor for the TN and NH4 (+)-N loadings and that the percentages of cropland in watersheds can significantly increase the NO3 (-)-N loading in agricultural watersheds. Therefore, to restore and maintain water quality, animal production regulations and more careful planning of land use are necessary in the agricultural watersheds of subtropical China.

The content of nitrogen compounds in the Wel river in the light of the Nitrates Directive

In this paper, the results of the research are presented on the content and transformation of nitrogen compounds in the Wel River (the largest tributary of the Drwęca River). The catchment area of the studied river is predominantly agriculturally developed. Along the river course, 6 sample collection sites were selected, situated in places with different land development of the drainage basin. The average concentration of total nitrogen in the water of the Wel River amounted to 1.807 mg/dm3, mineral nitrogen - 0.557 mg/dm3 and organic nitrogen - 1.250 mg/dm3. The organic form of nitrogen dominated at all sites (the average content for the whole river amounted to 69%). Nitrate nitrogen dominated in the pool of mineral nitrogen. The lowest concentrations of nitrates were being recorded at lakeland sites, whereas the highest - at two terminal sites situated within the lower reaches of the river, where the drainage basin has a typically agricultural character.

Dynamic characteristics of nutrients and causal analysis in eutrofic reservoir: a case study of Shibianyu reservoir

Eutrofication and the resulting proliferation of phytoplankton have become a serious problem of reservoirs around the world. In order to make effective algae control measures through reducing concentrations of nutrients, in this study both the dynamic characteristics of nutrients and its source were investigated in Shibianyu reservoir located in north-western of China. The results showed that a 2.8 mg/L of annual average total nitrogen concentration in Shibianyu reservoir was observed, which exceeded the source water quality standard during whole monitoring years, and the maximum concentration reached 5.1 mg/L in spring. Moreover, it was observed that there is high total phosphorus concentration during the mixing period in winter or the heavy rainfall period. The hypolimnion became anoxic during the stratified period to increase the release of nutrients from the sediments. The nutrients of upper water increased rapidly when stratification disappeared because the high concentrations of pollutants in the bottom water were carried into the upper water. The continuous heavy rains led to significant increase of nitrogen and phosphorus in summer because a large number of sediment was flushed into reservoir. The excess nutrients promoted algae to multiply. Intense cyanobacterial blooms have been observed in Shibianyu reservoir. It is premise to improve water quality in Shibianyu reservoir that the infusion of nutrient must reduce during rainstorm period. Inhibition of endogenous pollutants release would be the key to control and improve the water quality in Shibianyu reservoir.

Restoration of a subtropical eutrophic shallow lake in China: effects on nutrient concentrations and biological communities

While numerous reports exist on the results of lake restoration initiatives in temperate regions, only a few exist from subtropical lakes. We present results of the lake restoration of shallow, subtropical Lake Wuli, China, conducted between 1999 and 2010. After restoration, annual average concentrations of total nitrogen, total phosphorus (TP), and chlorophyll a and the chemical oxygen demand declined significantly, though summer TP remained high. Suspended solids increased significantly over the years, whereas transparency decreased, though not significantly so. The contribution of cryptophytes to total phytoplankton biomass decreased, while the proportion of cyanobacteria, especially potentially N2-fixing species, increased. Rotifers were superseded by crustaceans as the dominant taxon of the zooplankton community. Enhanced abundance of Daphnia spp., appearance of Leptodora kindti, and increased biomass ratios of zooplankton to phytoplankton, calanoids to cyclopoids, and nauplii to copepods in the post-restoration period indicate reduced fish predation and stronger top-down control of phytoplankton. However, the increase in non-algal turbidity, probably caused by the higher biomass of benthivorous fish, apparently prevented the re-establishment of submerged macrophyte communities. We conclude that removal of fish, particularly benthivorous species, will further improve water quality in this and other subtropical shallow lakes.

Nitrogen removal from wastewater plant secondary effluent in a compound natural treatment system

A method for removal of low concentrations of nitrogen in the secondary effluent from a wastewater plant was evaluated. The method can be summarized as follows: Primary Subsurface Vertical Flow Wetland (PSVFW)→Submerged Macrophyte Oxidation Ponds (SMOPs)→Secondary Subsurface Vertical Flow Wetland (SSVFW). Pilot experiments were conducted to assess the efficiency of total nitrogen (TN) removal from secondary effluent from the Chengjiang Wastewater Treatment Plant, China. At a total hydraulic retention time (HRT) of 21.38 days and a hydraulic loading (HL) of 0.024m3m−2d−1, the average TN concentration in the influent decreased from 6.60mgL−1 in the influent to 0.87mgL−1 in the effluent, thus meeting the Class-III surface water standards. PSVFW mediated the ammonification of organic nitrogen (ORG-N) and the nitrification of NH3-N (ammonia), resulting in a TN reduction of 7.58%. In the SMOPs, the concentration of NH3-N was further reduced, and most NO3−-N (nitrate nitrogen) was denitrified under aerobic conditions, resulting in a 63.18% TN reduction. In the SSVFW, the concentrations of the remaining NO3−-N and ORG-N declined even further so that the whole process accounted for an 86.82% TN removal efficiency relative to the influent TN concentrations.

The extent that natural lakes in the United States of America have been changed by cultural eutrophication

We used paleolimnological data for 240 lakes from the U.S. Environmental Protection Agency's (USEPA) 2007 National Lakes Assessment to estimate the extent that natural lakes in the coterminous United States have been changed by anthropogenic activities. In order to detect cultural eutrophication, we analyzed data on diatom‐inferred concentrations of total nitrogen (TN), total phosphorus (TP), specific conductance (SC), and pH as determined from lake sediments from the tops and bottoms of sediment cores from 240 natural lakes where the bottom of the core was judged to represent conditions prior to European settlement. We found no statistically significant increases in the average concentrations of TN, while TP decreased by 14% in this population of lakes since the time of European settlement. We also analyzed data from 48 reference lakes used by the USEPA to determine the relative condition of the sample lakes. Paired t‐tests showed the TN concentrations were not significantly different between the two time periods (p > 5%), while the average TP concentrations had significantly decreased by 26% since presettlement times (p < 5%). There were statistically significant increases in SC (17%) and pH (0.05 pH units). There were no statistically significant differences between the changes in TP, TN, SC, and pH in the 240 sample lakes and the changes in the 48 reference lakes. The proportions of lakes categorized as oligotrophic, mesotrophic, eutrophic, and hypereutrophic for the presettlement time period were not significantly different from the proportions found in 2007.

Effects of Incorporation of Nano-carbon into Slow-released Fertilizer on Rice Yield and Nitrogen Loss in Surface Water of Paddy Soil

The use of slow-released fertilizer has become a new trend to save fertilizer consumption and to minimize environmental pollution. Duo to its high surface energy and chemical activity, the application domain of nanomaterials has significantly expanded with the development of nanotechnology in conjunction with biotechnology in various fields, such as water purification, wastewater treatment, environmental remediation, food processing and packaging, industrial and household purposes, medicine and in smart sensor development. However, use in agriculture, especially for plant production, is an under-explored area in the research community. In this work, nano-carbon was incorporated into slow-released fertilizer and the influence on rice yield and nitrogen loss in surface water of paddy soil was conducted by field experiment. The experiment was a randomized block design with five treatments and three replications, the control (CK), Jingzhengda slow-released fertilizer (JSCU, N 42%), Jingzhengda slow-released fertilizer and nano-carbon (JSCU+C), Stanley slow-released compound fertilizer (SSRF, N-P2O5-K2O=20:9:11), Stanley slow-released compound fertilizer and nano-carbon (SSRF+C), respectively. The results indicated that the total nitrogen concentration in surface water of paddy soil increased rapidly at the 2nd day after fertilization and decreased gradually after that in all treatments. Compare to JSCU, sampling at different times after fertilization, the total nitrogen concentration in surface water of paddy soil under JSCU+C treatment was declined in the range of 19.1%-46.8%, the average was 31.0%, and the time of nitrogen runoff loss due to rainfall was shorten 2.2 day. For SSCU+C treatment, the average total nitrogen concentration was decreased by 29.8% and the time of nitrogen runoff loss was shorten 1.8 day. The rice grain yield and nitrogen use efficiency were increased significantly after applying slow-released fertilizer added nano-carbon. The rice grain yield and nitrogen use efficiency under JSRU+C and SSRF+C treatments were 11650.5 kg/hm2, 21.4 kg/kg N and 11201.0 kg/hm2, 18.4 kg/kg N, respectively, increased by 11.3%, 7.9 kg/kg N compared with JSRU and 5.6% and 4.4 kg/kg N compared with SSRF. The rate of saving nitrogen was 10.1% and 5.1% for JSCU+C and SSRF+C, respectively. These results suggest that it is possible that the nano-carbon is used as coating material for slow-released fertilizer and incorporation of nano-carbon into slow-released fertilizer is benefit for reducing water pollution, especially JSCU+C.