Atmospheric Nitrogen And Phosphorus Deposition In Nanjing And Effects Of Simulated Nitrogen Deposition On Gaseous Emissions Of Soils

Since industrial revolution, human activities have accelerated the wordwide atmospheric nitrogen (N) and phosphorus (P) deposition. Atmospheric deposition is an important part of biogeochemical cycles of N and P, and directly affects the nutrients input to various natural ecosystems, the nutrients balance in agricultural ecosystem, and water quality. This study was carried out in Nanjing area of China to observe the atmospheric N and P deposition over a four-year period. The primary objectives were to compare the different observation methods, to quantify the N and P deposition fluxes, to identify the N compositions and sources using the 515NH4+-N and δ15NO3--N in bulk deposition and the two end-mixing member model at three observation sites, and to assess the effects of N deposition on gaseous emissions from agricultural and forest soils.The study included four experiments as follows:① The effect of three different methods including dry deposition to water (DW) and land (DD) surfaces, along with wet deposition (Wet) on the fluxes and composition of atmospheric N and P deposition and their dynamic variation were investigated in suburban of Nanjing from 2009 to 2011.② Three different sites (SB:suburban site, RU:rice-upland crop site, VC:vegetable crop site) in Nanjinga area were selected to quantify the fluxes and composition of bulk and wet deposition of N and P and their temporal and spatial variations from 2010 to 2012. ③ The natural abundances of 8 NH4+-N and δ15NO3--N in bulk deposition were observed, and the sources of NH4+-N and NO3--N in bulk deposition and their contributions of different N sources were determined via the two end-mixing member model at these three sites during 2010-2012. ④ A simulated N deposition experiment was established to explore the effects of N deposition and biochar addition on N2O, NH3 and CO2 emissions and their dynamics from agricultural and forest soils. The simulated experiment was subjected to six N deposition events every two months over one-year period, and N was applied at rates of 0(N0),60(N60) and 120(N120) kg N hm-2a-1 with (30 t hm-2) or without (0 t hm-2) biochar addition.The main results are listed as follows:(1) The dry deposition of NH4+-N, NO3--N and TP to both water (DW) and land (DD) surfaces, and wet deposition (Wet), were simultaneously monitored from 2009 to 2011 in Nanjing. Results showed that dry deposition of NH4+-N, NO3--N and TP deposition were 7.5 kg N hm-2 a-1,6.3 kg N hm-2 a-1, and 1.9 kg P hm-2 a-1, respectively by the DW method; dry deposition of NH4+-N, NO3--N and TP deposition were 2.2 kg N hm-2 a-1,4.9 kg N hm-2 a-1, and 0.4 kg P hm-2 a-1, respectively by the DD method. There were significant differences between DW and DD methods. The deposition of NH4+-N, NO3--N and TP by the DD-method were approximately 29%,78% and 21%, respectively, of the deposition by the DW method, suggesting that the DW and DD methods should be simultaneously employed for separately simulating N deposition into aquatic and terrestrial ecosystems in a watershed area.The wet deposition of total phosphorus (TP) and inorganic N (NH4+-N and NO3--N) amounted to 1.1 kg P hm-2 a-1 and 28.7 kg N hm-2a-1, respectively, where NH4+-N contributed 43% to inorganic N. In water ecosystem, the total deposition (dry plus wet deposition) of NH4+-N, NO3--N and TP were 19.8 kg N hm-2a-1,22.7 kg N hm-2 a-1 and 3.0 kg P hm-2 a-1, respectively, in which dry deposition observed by the DW method contributed 38%,28% and 63%, respectively to the total deposition. In terrestrial ecosystem, the total deposition (dry plus wet deposition) of NH4+-N, NO3--N and TP were 14.5 kg N hm-2a-1,21.3 kg N hm-2a-1 and 1.5 kg P hm-2 a-1, in which dry deposition observed by the DD method contributed 15%,23% and 27%, respectively to the total deposition. Thus, the dry deposition of N and P in terrestrial ecosystems should be taken into account. Moreover, both DW+Wet and DD+Wet methods should be simultaneously employed to measure atmospheric N and P deposition in a watershed area with both aquatic and terrestrial ecosystems.(2) We analyzed the bulk (wet plus partly dry deposition) and wet deposition of inorganic N and TP at SB, RU and VC sites in Nanjing area from 2010 to 2012. Results showed that bulk deposition fluxes of inorganic N and TP averaged 54.82 kg N hm"2 a-1 (with 69.7% in the form of NH4+-N) and 1.82 kg P hm-2 a-1, respectively; and the bulk depositon of NH4+-N was 34.97,36.87 and 42.8 kg N hm-2a-1 at SB, RU and VC sites, respectively, which mostly occurred in summer and largely affected by regional activities and rainfall. Wet deposition fluxes of inorganic N and TP, being 25.65 kg N hm-2 a-1 and 1.29 kg P hm-2 a-1, respectively, were much lower than their bulk deposition fluxes, suggesting the potential contribution of N and P from the dry deposition.(3) We analyzed the δ15NH4+-N and δ15NO3--N in the bulk deposition at SB, RU and VC sites in Nanjing area from 2010 to 2012. Results showed that the values of δ15NH4+-N in bulk deposition ranged from -12.85%o to +14.47%o with obviously seasonal variations due to crop fertilization and temperature change in Nanjing across three sites. The values of δ15NO3--N in bulk deposition ranged from -9.31‰ to +15.67‰ and mostly above on 0‰. Based on the ratio of NH4+-N/NO3--N and the δ15N values of NH4+-N and NO3--N in combination with model results, chemical fertilizer and animal manure sources contributed to 53.6% and 46.4%, respectively for NH4+-N deposition; fossil fuel and soil emissions sources contributed to NO3--N deposition by 75.1% and 24.9%, respectively. Thus, it is highlighted the major contributions of animal manure and fossil fuel to N deposition.(4) There were significant differences in the effects of N deposition and biochar addition on the emissions of N2O, NH3 and CO2 from agricultural and forest soils. For the agricultural soil, compared to without N treatments, the cumulative amounts of N2O emissions were 8.89 kg N hm-2a-1 and 13.64kg N hm-2a-1 from N60 and N120 treatments, increased by 29.8% and 99.1%(p<0.05), respectively. Similarily, the amounts of NH3 volatilization were 2.82 kg N hm-2 a-1 and 4.05 kg N hm-2 a-1, increased by 33.6% and 91.9%(p<0.05) from N60 and N120 treatments. For the forest soil, the amounts of N2O cumulative emissions were 9.02 kg N hm-2 a-1 and 15.82 kg N hm-2a-1, increased by 141.2% and 323.0% (p<0.05) from N60 and N120 treatments, respectively, compared to without N treatments. The amounts of NH3 volatilization were 3.42 kg N hm-2 a-1 and 3.84 kg N hm-2a-1, increased by 39.0% and 56.1%(p<0.05). Though no effect was found on CO2 fluxes, adding N significantly increased cumulative N2O and NH3 emissions from agricultural and forest soils, suggesting that the sources of soil N2O and NH3 would be further strengthed with increasing atmospheric N deposition.Biochar amendment significantly (p<0.05) decreased cumulative N2O emissions by 20.2% and 25.5% from agricultural and forest soils, respectively. Following biochar addition, increased CO2 emissions slightly by 7.2% and NH3 volatilization obviously by 21.0% in the agricultural soil were observed, whereas significantly decreased CO2 emissions by 31.5% and NH3 volatilization by 22.5% in the forest soil were determined. Under the increasing N deposition conditions, biochar amendment could effectively depresse N2O, NH3 and CO2 emissions in the forest soil, indicating that biochar addition to soils may provide a potential tool for climate change mitigation in response to atmospheric N deposition. However, biochar amendment can significantly migiate N2O emission in the agricultural soil, but promote CO2 and NH3 emissions. Thus, whether biochar served as a potential tool to migiate the effect of N deposition should be further researched.Thus, the methods of DW+Wet and DD+Wet should be adopted simultaneously to monitor atmospheric N and P deposition in watershed region, which represent the amounts of atmospheric deposition into water and terrestrial ecosystems, respectively. Note that the contribution of the dry deposition to total deposition is important. More attentions should be paied on the increasing contributions of animal manures and fossil fuel to atmospheric deposition and the effects of N deposition on N2O and NH3 emissions from various soils. Under the increasing N deposition conditions, whether biochar can act as a potential tool to migiate the N deposition effect warrants further investigation.