Evaluating the Effects of Aquaculture Wastewater Irrigation with Fertilizer Reduction on Greenhouse Tomato Production,Economic Benefits and Soil Nitrogen Characteristics

The utilization of aquaculture wastewater as irrigation is an effective way to recycle and reuse water and nitrogen fertilizer resources because it contains numerous nutrients.However,it is still unclear that the pattern of substituting aquaculture wastewater irrigation for fertilizer supplementing is conducive to improving the soil nitrogen status,fruit yield and water-fertilizer use efficiency for tomato production.In this context,the experiment was intended to establish the appropriate irrigation regime of aquaculture wastewater in tomato production for freshwater replacement and fertilizer reduction to ensure good yields.Pot experiments were conducted with treatments as farmers accustomed to irrigation and fertilization used as control(CK),1.75 L aquaculture wastewater with base fertilizer(W1),2 L aquaculture wastewater with base fertilizer;and 2.25 L aquaculture wastewater with base fertilizer(W3).We examined the effects of aquaculture wastewater irrigation on soil nitrogen distribution,Nrelated hydrolases,tomato yield,and economic benefits.The results showed that the control treatment had the highest N input,about 24.68%higher than the W3 treatment,while the yield was only about 7.81%higher than W3.This indicated that the overuse of chemical fertilizer was present in the current tomato production.Although the reduction of fertilizer in aquaculture wastewater irrigation caused a decrease in tomato production,this economic loss can be compensated by cost savings in the wastewater disposal.Among aquaculture wastewater treatments,the W3 treatment had the highest overall benefit,achieving 62.63%freshwater savings,37.50%fertilizer input reduction,and an economic return of approximately 19,466 Yuan per hectare higher than the control.Additionally,increasing the irrigation volume of aquaculture wastewater could provide more available nutrients to the soil,which were more prevalent in the form of organic nitrogen.The lower soil nitrate reductase activities(NR)under aquaculture wastewater treatments after harvesting also proved that this pattern was beneficial to reduce soil nitrate nitrogen residues.Overall,the results demonstrate that aquaculture wastewater irrigation alleviates the soil nitrate residues,improves nutrient availability,and results in more economic returns with water and fertilizer conservation for the greenhouse production of tomatoes.

Soil Microbial Characteristics Under Long-Term Heavy Metal Stress:A Case Study in Zhangshi Wastewater Irrigation Area,Shenyang

Soil samples were collected from Zhangshi Wastewater Irrigation Area in the suburb of Shenyang City,China,an area with a 30-year irrigation history with heavy metal-containing wastewater.The chemical properties and microbial characteristics of the soils were examined to evaluate the present situation of heavy metal pollution and to assess the soil microbial characteristics under long-term heavy metal stress.In light of the National Environmental Quality Standards of China,the soil in the test area was heavily polluted by Cd and to a lesser degree by Zn and Cu,even though wastewater irrigation ceased in 1993.Soil metabolic quotient (qCO_2) had a significant positive correlation,while soil microbial quotient (qM) had a negative correlation with content of soil heavy metals.Soil microbial biomass carbon (MBC) had significantly negative correlation with Cd,but soil substrate-induced respiration (SIR),dehydrogenase activity (DHA),cellulase activity, and culturable microbial populations had no persistent correlations with soil heavy metal content.Soil nutrients,except for phosphorous,showed positive effects on soil microbial characteristics,which to a certain degree obscured the adverse effects of soil heavy metals.Soil Cd contributed more to the soil microbial characteristics,but qM and qCO_2 were more sensitive and showed persistent responses to heavy metals stress.It could be concluded that qM and qCO_2 can be used as bioindicators of heavy metal pollution in soils.

Wastewater irrigation and crop yield:A meta-analysis

Although wastewater irrigation in agriculture could be a potential adaptation to water scarcity, its effect on crop yield varies in the literature, making it difficult to evaluate its role in global food security comprehensively. Using agronomic experiment data from 62 studies between 1987 and 2021, we employ a meta-analysis to analyze the factors contributing to the heterogeneous effects of wastewater irrigation on crop yield. Our findings can be summarized as(1) the mean yield growth effect of wastewater irrigation is 19.7%;(2) domestic and breeding wastewater irrigation could significantly increase crop yield, while industrial wastewater has a negative effect although not significant;(3) high nutrients concentration of domestic wastewater is significantly positively correlated with crop yield;(4) agronomic experiment designs in terms of field experiment, experiment times, and fertilizer use could contribute to the divergent crop yield effects across the studies;(5) there is a publication bias of the research results between the English and Chinese literature;(6) the literature mainly sheds light on the short-run effect, and the long-run impact shall be an important research question in the future.

Nitrogen Removal in Wastewater Irrigation Systems and Its Influence on Groundwater Pollution

The experiment included ten soil columns and field investigation in 1 - 2 year duration. Data on the columns continuously flooded with waste water indicated that when total input of NH4-N reached to above 70% of the NH4-N adsorption capacity in soil the breakthrough would appear in the output . Adequate removal of nitrogen from the waste water would require at least 170 cm deep groundwater table . Fine textured soil would promote denitrification . The columns simulating discontinuous waste water irrigation indicated that denitrification existed only in the partial microenvironment of reduction .Groundwater table depth had no strong influence on nitrogen removal . The investigation in field revealed that the groundwater recharged with waste water was not polluted by nitrogen when the aeration profile was in finer textures owing to the combined contribution of nitrification and denitrification .

Approaches to municipal wastewater irrigation and environmental protection

To reuse the water and nutrient resources from ecological point of view the goals, criteria and constraint conditions of the scientifically municipal wastewater irrigation are discussed as well as the practice in major municipal wastewater irrigation areas in China is introduced, of which particularly the effects of municipal water irrigation mixing with oil refinery wastewater on the agricultural ecosystem are studied and described. It has been revealed that benzo(a)pyrene in various parts of paddy crop is attributed to air pollution, water-soil pollution and biosynthesis of plant. Of exogenous contributions of benzo(a)pyrene in paddy shoot system under natural condition, the dominant factor is the air pollution, whereas the water-soil factor is considered to be secondary. Therefore, it is mostly urgent to control the air pollution source of benzo(a)pyrene, to which the edible parts of various green plants are exposed directly.

Effects of compound microbial inoculant treated wastewater irrigation on soil nutrients and enzyme activities

Wastewater treated by compound microbial inoculant(CMI)in agricultural irrigation can enrich soil fertility and decompose the possible pollutants.In this study,a greenhouse experiment using tomato as the model crop was performed to investigate the effects of treated wastewater irrigation on soil nutrients and enzymes.For this purpose,certain parameters were measured,including soil total nitrogen(N),nitrate N,total phosphorus(P),available potassium(K)and the activities of the enzymes urease,acid phosphatase and catalase in soils irrigated with fresh water,wastewater and CMI-treated wastewater under three amount of irrigation water.The results showed that irrigation with both treated and untreated wastewater significantly increased soil total N,total P,and available K,however the treated wastewater showed higher effects on soil enrichment,especially on available K.The activity of soil urease and acid phosphatase reached highest with treated wastewater irrigation,whereas wastewater irrigation increased the activity of catalase obviously.Soil enzyme and nutrient with fresh water irrigation decreased with increasing water amount;the content of soil urease,nitrate-nitrogen,total N and total P in treated wastewater and wastewater irrigation rose with increasing water amount,but the highest activity of acid phosphatase and the lowest activity of catalase were found in medium irrigation water amount.Under the condition of tomato cultivation,total N,nitrate N and total P were closely correlated with soil urease and catalase;there were significant positive correlation among soil urease,catalase,total N,nitrate N and total P;there existed significantly positive correlation between acid phosphatase and all measured soil nutrient indexes.The results suggested that irrigation with CMI-treated wastewater is a security and effective strategy to agricultural land management.

Soil properties and habitats determine the response of bacterial communities to agricultural wastewater irrigation

Increasing temperatures and variability of precipitation events due to climate change will lead in the future to higher irrigation demands in agroecosystems.However,the use of secondary treated wasterwater(TWW)could have consequences for the receiving soil environment and its resident microbial communities.The objective of this study was to characterize the importance of soil properties and habitats to the response of soil bacteria and archaea to irrigation with TWW.Two agricultural soils with contrasting textures(loamy sand or silt loam)and,for each,three variants differing in soil organic carbon and nitrogen,as generated by long-term fertilization,were analyzed.For each of these six soils,prokaryotic communities from two habitats,i.e.,root-free bulk soil and the rhizosphere of developing cucumber plants in the greenhouse,were characterized.Communities were analyzed by the quantity and diversity of their polymerase chain reaction(PCR)-amplified 16S rRNA genes.To account for TWW-associated nutrient effects,potable water(PW)served as a control.Amplicon sequence analysis showed that prokaryotic communities mainly consisted of bacteria(99.8%).Upon irrigation,regardless of the water quality,prokaryotic diversity declined,p H increased,and no bacterial growth was detected in bulk soil.In contrast,the growth of cucumbers was stimulated by TWW,indicating that plants were the main beneficiaries.Moreover,strong responses were seen in the rhizosphere,suggesting an indirect effect of TWW by altered rhizodepositions.The main bacterial responders to TWW were Proteobacteria,Bacteroidetes,Actinobacteria,and Planctomycetes.Changes in bacterial communities due to TWW were less pronounced in all variants of the silt loam,indicating the importance of clay and soil organic carbon for buffering effects of TWW on soil bacterial communities.Hence,soil organic carbon and soil texture are important parameters that need to be considered when applying TWW in agriculture.

Evaluation of Spatial and Vertical Variability of Nitrogen and Phosphorus in Sewage-Irrigated Soil in Tongliao, China

The reuse of wastewater for the irrigation of farmlands is gaining popularity, and the nutrient leaching associated with wastewater irrigation is becoming a matter of concern. The variability of nitrogen and phosphorus frac- tions in wastewater-irrigated soil was investigated in both horizontal and vertical directions in Kongjiaxiang, Tongliao, Inner Mongolia, China. The results showed that wastewater irrigation resulted in the concentrations of available N and P being 40.36% and 66.49% higher, respectively, than those with groundwater irrigation. Different forms of N and P exhibited significantly different distribution pattems. Higher concentrations of NO~ and total available N, as well as of those of Ca-P and total available P were observed near wastewater irrigation channels. Ca-P has a spatial distribu- tion pattern similar to that of available P. The concentrations of NO3 and NH4 were the highest in top soil and de- creased with depth. The complex interactions between nitrate leaching and nitrogen transformation processes （e.g., nitrification, denitrification, and mineralization） determined the vertical profile of NO3. The significant amount of NH~ loss inhibited its deep seepage. The Ca-bound compound contained more P than other inorganic fractions as a result of high Ca levels throughout the soil profile. The differences in the concentrations of Ca-bound P at different depths could be due to the upward flux or translocation of Ca from subsurface to surface soil and the sequestration of P.

Chemically Induced Bioremediation of Heavy MetalContaminated Sewage-irrigated Soils in Tianjin Municipality

Festuca arundinacea L.was planted in sewage-irrigated soils from the sewage irrigation regions of Tianjin.Different concentrations of nitrilotriacetic acid（NTA）and sodium dodecylsulphate（SDS）were applied in bioremediation of Cd,Cu and Zn in sewage irrigation regions.According to the results,under the treatment of 15 mmol/kg NTA＋1 mmol/kg SDS,the concentrations of Cd and Zn reached the highest in shoots of F.arundinacea,which were 3.03 and 9.28 times over that in control,respectively;the concentrations of Cd and Zn in roots of F.arundinacea displayed the same trend as shoots.The combined addition of surfactant SDS and chelator NTA significantly increased Cd concentration in F.arundinacea,but the effect was not significant on Cu enrichment.Considering comprehensively the biomass,bioaccumulation effect and economic cost,it is economical and effective to remediate heavy metal-contaminated sewage-irrigated soils with 5mmol/kg NTA＋1 mmol/kg SDS or 10 mmol/kg NTA＋1 mmol/kg SDS.

Health risk assessment of heavy metals in soils and vegetables from wastewater irrigated area,Beijing-Tianjin city cluster,China

The possible health risks of heavy metals contamination to local population through food chain were evaluated in Beijing and Tianjin city cluster, China, where have a long history of sewage irrigation. The transfer factors （TF） for heavy metals from soil to vegetables for six elements including Cu, Zn, Pb, Cr, As and Cd were calculated and the pollution load indexes （PLI） were also assessed. Results indicate that only Cd exceeded the maximum acceptable limit in these sites. So far, the heavy metal concentrations in soils and vegetables were all below the permissible limits set by the Ministry of Environmental Protection of China and World Health Organization. The transfer factors of six heavy metals showed the trend as Cd 〉 Zn 〉 Cu 〉 Pb 〉 As 〉 Cr, which were dependent on the vegetable species. The estimated dietary intakes of Cu, Zn, Pb, Cr, As and Cd were far below the tolerable limits and the target hazard quotient （THQ） values were less than 1, which suggested that the health risks of heavy metals exposure through consuming vegetables were generally assumed to be safe.

Transfer and migration of polycyclic aromatic hydrocarbons in soil irrigated with long-term wastewater

In order to investigate the transfer and migration behavior of polycyclic aromatic hydrocarbons(PAHs)in soil with long-term wastewater irrigation,Groundwater Ubiquity Score(GUS)and fugacity method were respectively used to assess the potential entry into the groundwater and transfer capacity of PAHs.The results of assessment using GUS show that there is significant correlation between the GUS and organic carbon sorption coefficient(KOC)for PAHs and a simple assessment method with KOC was referred to evaluate contamination of groundwater.Applying fugacity method,evaluation results of transfer and migration of PAHs in soil suggest that the PAHs accumulation in the soil through long-term wastewater irrigation could be re-volatilized as secondary emission sources to atmosphere for the Low Molecular Weight(LMW)PAHs,in contrast to High Molecular Weight(HMW)PAHs for which the soil remains a sink that could absorb more PAHs.The net volatilisation flux was 0.39 g/d in upland and 0.32 g/d in paddy for LMW Nap(Naphthalene),and 0.97×10^(-3)g/d in upland and 0.37×10^(-3)g/d in paddy for LMW Phe(Phenanthrene).The net deposition was 0.72×10^(-4)g/d in upland and 0.10×10^(-3)g/d in paddy for HMW Fla(Fluoranthene),and 0.22×10^(-4)g/d in upland and 0.20×10^(-4)g/d in paddy for HMW Bap(Benzo[a]pyrene).Sensitivities of the model estimates to input parameters were tested,and the sensitivity coefficient was defined for the test.The most influential parameters were the volumes of the air,water,and organic carbon fractions in soil and the thickness of the soil.

Characterization of contamination, source and degradation of petroleum between upland and paddy fields based on geochemical characteristics and phospholipid fatty acids

To evaluate contamination caused by petroleum, surface soil samples were collected from both upland and paddy fields along the irrigation canals in the Hunpu wastewater irrigation region in northeast China. N-alkanes, terpanes, steranes, and phospholipid fatty acids （PLFA） in the surface soil samples were analyzed. The aliphatic hydrocarbon concentration was highest in the samples obtained from the upland field near an operational oil well; it was lowest at I-3P where wastewater irrigation promoted the downward movement of hydrocarbons. The Hunpu region was found contaminated by heavy petroleum from oxic lacustrine fresh water or marine deltaic source rocks. Geochemical parameters also indicated significantly heavier contamination and degradation in the upland fields compared with the paddy fields. Principal component analysis based on PLFA showed various microbial communities between petroleum contaminated upland and paddy fields. Gram-negative bacteria indicated by 15：0, 3OH 12：0, and 16：1（9） were significantly higher in the paddy fields, whereas Gram-positive bacteria indicated by i16：0 and 18：1（9）c were significantly higher in the upland fields （p 〈 0.05）. These PLFAs were related to petroleum contamination. Poly-unsaturated PLFA （18：2ω6, 9; indicative of hydrocarbon- degrading bacteria and fungi） was also significantly elevated in the upland fields. This paper recommends more sensitive indicators of contamination and degradation of petroleum in soil. The results also provide guidelines on soil pollution control and remediation in the Hunpu region and other similar regions.