Net Anthropogenic Nitrogen Inputs Research Articles

Unraveling safe boundaries for net anthropogenic nitrogen inputs: A case study focusing on village scale

The estimation of safe nitrogen (N) boundaries at the village scale is a powerful complement to planetary boundaries and can be used to propose more targeted regional measures. In this paper, net anthropogenic N inputs (NANI) of the village scale is assembled with the depiction of the internal flow of N. The village-scale NANI was estimated for the case area, Liyang, Taihu Basin, eastern China. The safe NANI boundary of the village scale was defined with the help of the N use efficiency (NUE) conceptual framework. The results showed that chemical fertilizer N application played a decisive role in NANI of the village unit. The upper limit of NANI in village planting system was more sensitive to the response of NUE, so the safe NANI boundary at the village scale referring to the above upper limit was determined as Noutput = Ninput – 327.24 kg ha−1 yr−1. Additionally, by using scenario analysis, it was found that village units with high NUE could put in more N according to the safe NANI boundary. In turn, higher NANI can be achieved by increasing NUE. The results, which take into account the difference of villages, are informative for village scale diversity N management.

Spatiotemporal distribution and controlling factors on ammonium in waters in the central Yangtze River Basin, China

High levels of ammonium in water can compromise the ecological environment and be harmful to human beings. It is of great significance to understand the source and controlling factors of ammonium in waters. However, the distribution and controlling factors on ammonium in the central Yangtze River Basin have been rarely reported. The results showed that 6.58% of the surface water (SW) exceeded the China national guideline of category III for NH4+-N (i.e., 1.0 mg/L) and 30.19% of the groundwater (GW) exceeded the China national guideline of category III for NH4+-N (i.e., 0.5 mg/L). Notably, the ammonium concentrations of the plain area in the middle were much higher, which reached to the highest value at the junction of the Yangtze River and Dongting Lake. Nitrogen in SW may originate from manure but more nitrogen sources in GW. The net anthropogenic nitrogen input (NANI) can provide enough organic nitrogen for the mineralization. NH4+-N in SW was more affected by fertilizer nitrogen and feed nitrogen input but more affected by agricultural nitrogen fixation in GW. Agricultural and industrial activities controlled NH4+-N in SW and GW by increasing nitrogen input and changing hydrological conditions. In general, this research exposed the controlling of different types of factors on ammonium in waters, providing a guidance for the water pollution prevention in study area.

Hierarchical Spatially Varying Coefficient Process Regression for Modeling Net Anthropogenic Nitrogen Inputs (NANI) from the Watershed of the Yangtze River, China

The increasing discharge of nitrogen nutrients into watersheds calls for assessing and predicting nitrogen inputs, as an important basis for formulating management strategies. The traditional net anthropogenic nitrogen inputs (NANI) budgeting model relies on 45 predictor variables, for which data are sourced from local or national statistical yearbooks. The large number of predictor variables involved makes NANI accounting difficult, and the missingness of data reduces its accuracy. This study aimed to build a prediction model for NANI based on as few predictor variables as possible. We built a prediction model based on the last 30 years of NANI data from the watershed of the Yangtze River in China, with readily available and complete socio-economic predictor variables (per gross domestic product, population density) through a hierarchical spatially varying coefficient process model (HSVC), which exploits underlying spatial associations within 11 sub-basins and the spatially varying impacts of predictor variables to improve the accuracy of NANI prediction. The results showed that the hierarchical spatially varying coefficient model performed better than the Gaussian process model (GP) and the spatio-temporal dynamic linear model (DLM). The predicted NANIs within the entire catchment of the Yangtze River in 2025 and in 2030 were 11,522.87 kg N km−2 to 12,760.65 kg N km−2, respectively, showing an obvious increasing trend. Nitrogen fertilizer application was predicted to be 5755.1 kg N km−2 in 2025, which was the most significant source of NANI. In addition, the point prediction and 95% interval prediction of NANI in the watershed of the Yangtze River for 2025 and 2030 were also provided. Our approach provides a simple and easy-to-use method for NANI prediction.

Effect of Agricultural Structure Adjustment on Spatio-Temporal Patterns of Net Anthropogenic Nitrogen Inputs in the Pearl River Basin from 1990 to 2019

Worldwide urbanization has brought dramatic changes in agricultural structures, as well as serious agricultural non-point source pollutions of nitrogen and phosphorus. However, understanding the effect of agricultural structure adjustment on net anthropogenic nitrogen inputs (NANI) has been still limited. In this paper, statistical data from the agricultural statistical Yearbook, the National Economic and Social Development Statistical Bulletin were collected from 1990 to 2019 in the Pearl River Basin, China, and used to analyze the spatial and temporal patterns of NANI and its influencing factors. The results indicated that the agricultural structure adjustment has significantly influenced the spatial and temporal patterns of NANI in the last 30 years in the Pearl River Basin. The NANI decreased from 1990 to 2019, and had a spatial pattern of higher values in the upstream areas and lower in the downstream areas. In terms of the nitrogen input sources of NANI, in the economically developed regions downstream, nitrogen inputs are dominated by food/feed nitrogen, which accounted for an average of 49.6% of total nitrogen inputs. In upstream areas with relatively low economic development, fertilizer nitrogen accounted for an average of 54.9% of total nitrogen inputs. A novel nitrogen input source index of NANI, namely the ratio of agricultural nitrogen inputs to non-agricultural nitrogen inputs of NANI(ASNA), was also proposed to characterize the impact of the agricultural industry restructuring on NANI changes over time. Similar to the characteristics of NANI from 1990 to 2019, the ASNA showed a decreasing trend in the study area. Moreover, agricultural variables (agricultural land area, nitrogen fertilizer consumption and livestock farming density) tended to contribute less to the explained ASNA variances, while the contributions of the non-agricultural factors (population density and non-agricultural GDP) increased from 1990 to 2019. This indicated that the contribution of nitrogen inputs from agricultural sources to the NANI decreased while the contribution of nitrogen inputs from non-agricultural sources increased, with the shifts of agricultural sectors to the secondary and tertiary sectors in the Pearl River Basin. Our findings also suggest that differently regional targeting should be considered for the nitrogen pollution management in the Pearl River Basin, which focuses on the nitrogen pollution management of non-agricultural sources in the downstream areas, and but highlights agricultural nitrogen pollution management in the upstream areas.

Influence of nitrogen inputs, dam construction and landscape patterns on riverine nitrogen exports in the Yangtze River basin during 1980–2015

A quantitative understanding of different N sources and the factors controlling riverine N fluxes is critical for optimizing water pollution control strategies. However, the lack of a comprehensive understanding of N pollution legacy effects and human alteration of landscapes (e.g., dam construction and land use/land cover) hinders development of efficient N management strategies. This study integrated long-term (1980–2015) net anthropogenic nitrogen inputs (NANI) and different forms of N exports, hydroclimate data, dam construction and landscape metrics to elucidate N sources and the factors controlling N fluxes in the Yangtze River basin (YRB). Over the 36-year study period, annual NANI in the YRB increased from 4166 to 8571 kg N km−2 yr−1. Riverine concentrations of total nitrogen (TN), dissolved inorganic nitrogen (DIN) and dissolved organic nitrogen (DON) increased ∼ 3-fold, ∼3-fold and ∼ 36-fold during 1980–2015, respectively, whereas riverine particulate nitrogen (PN) decreased by ∼ 90 %. Such long-term riverine N export dynamics were driven by elevated NANI, landscape configuration change and dam construction activities. Inclusion of these variables in multiple linear regression models explained 91 %, 83 % and 96 % of the annual variability in riverine DIN, DON and PN fluxes, respectively. Estimated riverine TN flux from sum of predicted DIN, DON and PN fluxes showed high agreement with measured values (R2 = 0.92, Nash–Sutcliffe coefficients = 0.91), indicating strong efficacy for the developed regression models. Separation of annual riverine N exports into current year NANI versus legacy source contributions indicated that legacy sources contributed ∼ 49 % (26–82 %), 51 % (<1–78 %), 95 % (87–98 %) and 56 % (36–86 %) of riverine DIN, DON, PN and TN exports, respectively. The release of legacy N from the landscape is associated with increases in dam construction, urban density, and the number of small area farm operations between 1980 and 2015. This study highlights the potential of aggregating multiple historical N input datasets, along with changes in land use and river regulation to model long-term riverine N export dynamics. The results of the study provide a foundation for developing integrated watershed N management strategies that address both current and legacy N pollution.

Net Anthropogenic Nitrogen Input and Its Relationship with Riverine Nitrogen Flux in a Typical Irrigated Area of China Based on an Improved NANI Budgeting Model

Excessive nitrogen (N) inputs from human activities in the watershed have resulted in water quality deterioration and other biological hazards. It is therefore critical to fully understand the anthropogenic N inputs and their potential impacts on regional water quality. In this study, a modified net anthropogenic nitrogen input (NANI) budgeting model considering the irrigation N input was developed and applied to investigate spatial–temporal variations of anthropogenic N inputs and their relationship with riverine N flux from 2005 to 2019 in a semi-arid irrigated watershed, Ulansuhai Nur watershed (UNW), China. The results showed that the annual average anthropogenic N inputs reached 14,048.0 kg N km−2 yr−1 without a significant temporal change trend. Chemical N fertilizer was the major contributor for watershed NANI and accounted for 75.3% of total NANI. Hotspots for N inputs were located in the central part of the watershed. In this study, watershed NANI does not have a significant regression relationship with riverine N export during the study period. Riverine N export showed an obvious decreased trend, which mainly was attributed to human activities. In addition, approximately 1.92% of NANI was delivered into the water body. Additionally, the N inputs into the watershed by the irrigation water accounted for 9.9% of total NANI. This study not only expands the application range of the NANI model in irrigated watersheds, but also provides useful information for watershed N management strategies.

The Characteristics of Net Anthropogenic Nitrogen and Phosphorus Inputs (NANI/NAPI) and TN/TP Export Fluxes in the Guangdong Section of the Pearl River (Zhujiang) Basin

Human activities have greatly influenced the inputs and cycling pathways of nitrogen (N) and phosphorus (P), causing dramatic environmental problems in the Pearl River Basin. In this study, the characteristics of net anthropogenic nitrogen and phosphorus inputs (NANI/NAPI) were analyzed in the Guangdong section of the Pearl River Basin from 2016 to 2020. NANI showed a very slight decrease trend from (1.51 ± 0.09) × 104 to (1.36 ± 0.08) × 104 kg·N·km−2·yr−1, while the average intensity of NAPI was 3.8 × 103 kg·P·km−2·yr−1. Both NANI and NAPI intensities were at high levels, resulting in the serious deterioration of water quality in the Pearl River Basin. Fertilizer input was the most important component for the intensities of NANI and NAPI, accounting for 38–42% and 53–56%. However, in the Pearl River Delta, the major components of NANI and NAPI were the human and animal consumption (food/feed) inputs and non-food net phosphorus input. The input of NANI and NAPI should be controlled for different areas, based on the differing driving forces, to alleviate the deterioration of water quality. This study of NANI and NAPI in the Pearl River Basin is one of the important prerequisites for clarifying the input and water quality, providing support for further effective control of nitrogen and phosphorus pollution in the Pearl River.

Changes in net anthropogenic nitrogen and phosphorus inputs in the Yangtze River Economic Belt, China (1999–2018)

Since the industrial revolution, excess inputs of nitrogen (N) and phosphorus (P) from human activities have been the main threat of deterioration to water environmental quality. In this study, to understand the variation characteristics, evolutionary pattern, composition structure, and main influencing factors on net anthropogenic nitrogen inputs (NANI) and net anthropogenic phosphorus inputs (NAPI) in the Yangtze River Economic Belt, 20 years of data from 1999 to 2018 at the general, provincial and city scales were analyzed. The results showed that NANI and NAPI in the Yangtze River Economic Belt increased and then decreased from 1999 to 2007 and from 2008 to 2018, with average values of 7189.26 kg N km−2 yr−1 and 2169.31 kg P·km−2 yr−1. Fertilizer application constituted the largest source of contributions to NANI and NAPI, with average contribution rates of 66.31 % and 68.20 %. The spatial pattern of NANI and NAPI exhibited a decreasing trend from east to west and from north to south. Western Jiangsu, eastern Anhui, central Hubei, and western Sichuan were high-risk areas. The contribution rates of human activity factors were ranked as economic factors > land-use factors > social factors, and changes in economic factors contributed the most to changes in NANI and NAPI, with averages of 70.50 % and 70.10 %. The Yangtze River Economic Belt has crossed the Environmental Kuznets Curve (EKC) inflection point for the N/P input load and has entered the coordinated development stage of economic growth and environmental improvement. The city scale can effectively identify and optimize the control area compared with the provincial scale, and the proportions of the administrative areas for NANI and NAPI at different targets decreased by 4.11 % (5.20 %), 7.52 % (11.95 %), and 9.79 % (17.29 %), respectively.

Spatiotemporal differences in riverine nitrogen and phosphorus fluxes and associated drivers across China from 1980 to 2018

Increases in nutrient loadings to waterways over the past four decades have led to widespread eutrophication and water quality impairments across China. Understanding the spatial, interannual and long-term variations in nutrient loadings and associated drivers at the national scale is crucial for developing effective nutrient reduction strategies. However, the controls on, and spatiotemporal variations in, nutrient fluxes remain a problem from both an academic and management perspective. This study provides spatially extensive and temporally contiguous estimates of changes in riverine total nitrogen (TN), ammonia nitrogen (NH3–N) and total phosphorus (TP) fluxes for continental area of China based on machine learning stack models and empirical modeling over the period from 1980 to 2018. Results reveal considerable spatial, interannual and long-term variability in annual TN, NH3–N and TP fluxes, with spatial variations in average TN and NH3–N fluxes primarily driven by net anthropogenic nitrogen inputs. Interannual variability is dominated by precipitation across continental areas of China. Spatial variability in the estimated average annual TP flux in the undeveloped western and the developed middle east regions of China are primarily controlled by net anthropogenic phosphorus inputs and precipitation, respectively. We found that TN, NH3–N and TP fluxes increased from 1980 to 2018 in watersheds in East China; the national mean annual TN, NH3–N and TP fluxes increased before 2015 and decreased after 2015. This study illustrates the important role of precipitation and temperature variability in controlling the spatial, interannual and long-term variability of nutrient fluxes, and indicates that the influence of the meteorological conditions on annual loadings is needed when designing watershed nutrient reduction or management strategies.

Spatio-temporal variation of net anthropogenic nitrogen inputs (NANI) from 1991 to 2019 and its impacts analysis from parameters in Northwest China

At present, excessive nutrient inputs caused by human activities have resulted in environmental problems such as agricultural non-point source pollution and water eutrophication. The Net Anthropogenic Nitrogen Inputs (NANI) model can be used to estimate the nitrogen (N) inputs to a region that are related to human activities. To explore the net nitrogen input of human activities in the main grain-producing areas of Northwestern China, the county-level statistical data for the Ningxia province and NANI model parameters were collected, the spatio-temporal distribution characteristics of NANI were analyzed and the uncertainty and sensitivity of the parameters for each component of NANI were quantitatively studied. The results showed that: (1) The average value of NANI in Ningxia from 1991 to 2019 was 7752 kg N km−2 yr−1. Over the study period, the inputs first showed an overall increase, followed by a decrease, and then tended to stabilize. Fertilizer N application was the main contributing factor, accounting for 55.6%. The high value of NANI in Ningxia was mainly concentrated in the Yellow River Diversion Irrigation Area. (2) The 95% confidence interval of NANI obtained by the Monte Carlo approach was compared with the results from common parameters in existing literature. The simulation results varied from −6.4% to 27.4% under the influence of the changing parameters. Net food and animal feed imports were the most uncertain input components affected by parameters, the variation range was −20.7%–77%. (3) The parameters of inputs that accounted for higher proportions of the NANI were more sensitive than the inputs with lower contributions. The sensitivity indexes of the parameters contained in the fertilizer N applications were higher than those of net food and animal feed imports and agricultural N-fixation. This study quantified the uncertainty and sensitivity of parameters in the process of NANI simulation and provides a reference for global peers in the application and selection of parameters to obtain more accurate simulation results.

Evaluation of net anthropogenic nitrogen inputs in the Three Gorges Reservoir Area

Excessive nitrogen input caused by human activities is an important factor threatening regional water security and economic development. In this study, net anthropogenic nitrogen input has offered an advantage in evaluating nitrogen input’s temporal and spatial variation in the Three Gorges Reservoir Area in 2006–2019. Component characteristics like sensitivity and proportional contribution of net anthropogenic nitrogen input in the time trend were assessed using a mathematical differential equation multivariate function principle for the first time. Then, redundancy analysis quantitatively analysed the distribution and interpretation of districts’ socio-economic and environmental impact factors on net anthropogenic nitrogen input. The results showed high net anthropogenic nitrogen input levels in the Three Gorges Reservoir Area in 2006–2019 with significant temporal and spatial variations (one-way ANOVA, p < 0.01), the mean value of net anthropogenic nitrogen input in the Three Gorges Reservoir Area was 12399.35 kg·km−2·a−1. Net anthropogenic nitrogen input in Xingshan (4907.45 kg·km−2·a−1) was the smallest, and that in Fuling (24005.10 kg·km−2·a−1) was the largest. The spatial distribution characteristics were high at two ends, they were low in the middle of the Three Gorges Reservoir Area. Even though the proportion of nitrogen fertiliser with the largest input source of net anthropogenic nitrogen input, accounted for 48%–53%, the main methods to reduce net anthropogenic nitrogen input also reduced the nitrogen fertilisers’ input in the Three Gorges Reservoir Area. Subsequently, since the atmospheric nitrogen deposition proportion was generally increasing, we focused on controlling the emission of the atmospheric nitrogen in the future. Districts had different net anthropogenic nitrogen input compositions, revealing the analysis of districts was necessary. Additionally, the sensitive coefficients of the nitrogen fixation and nitrogen of crop production were the largest, accounting for 1.09 and 0.98, which indicated that biological nitrogen fixation is the most sensitive factor in adjusting the agricultural structure that can quickly affect net anthropogenic nitrogen input in the Three Gorges Reservoir Area. Similarly, results showed that the sensitive coefficient and proportional contributions changed with districts and presented different characteristics. Therefore, the transformation from the reservoir to the region can serve as a more accurate management strategy. Moreover, the distribution of net anthropogenic nitrogen input in the districts was highly and significantly correlated with sowing area (p < 0.01), making it significantly and negatively correlated with the forest coverage rate. This result indicated that while the agricultural structure was the most sensitive factor affecting net anthropogenic nitrogen input, accurate nitrogen input management could be realised on a district scale. Therefore, we consider analyses of district component characteristics and impact factors important in providing decision support for the accurate and effective regional control of nitrogen input management.

Management implications of spatial-temporal variations of net anthropogenic nitrogen inputs (NANI) in the Yellow River Basin.

It is an important content of environment management to accurately identify the time change and spatial distribution of net anthropogenic nitrogen inputs (NANI) in the river basin. In order to develop a unified management and diverse control strategy that fits the characteristics of the basin, this study establishes the NANI-S model combining the NANI model with the spatial autocorrelation analysis method, which is a quantification-analysis-control process, and takes the 70 prefecture-cities in the Yellow River Basin (YRB) as the study area. The result shows that (1) the NANI of YRB increased first and then decreased with an average NANI value of 6787.59kg/(km2·a), showing that the overall N pollution situation of the YRB shows a trend of improvement in nitrogen (N) fertilizer input as the main source, and the average contribution rate was 47.45%. (2) There were obvious spatial differences in the NANI in the YRB because the global Moran's I fluctuated between 0.67 and 0.78. Cities with high NANI clustered in the middle and lower reaches, while low NANI clustered in the upper reaches. (3) Improving fertilizer utilization rate and industrial and domestic sewage treatment capacity was the key point of N control. Based on the results, practical policy recommendations for water pollution management were constructed, which provides a scientific basis for pollution prevention and high-quality development in the basin. In addition, this analysis method can also be applied to other basin N management studies.

Spatio-temporal characteristics and determinants of anthropogenic nitrogen and phosphorus inputs in an ecologically fragile karst basin: Environmental responses and management strategies

Excessive nitrogen and phosphorus inputs to land and subsequent export to water via runoff leads to aquatic ecosystem deterioration. The WRB is the world’s largest karst basin which is characterized by a fragile ecosystemcoupling with high population pressure, and the transformation of intensive agriculture. Quantifying different sources of pollution in karst regions is challenging due to the complexity of landscape topography and geology coupled with high transmissivity and connectivity of subsurface hydrological systems. This results in large uncertainty associated with nitrogen (N) and phosphorus (P) flow pathways. This combination of factors contributes to the WRB being a high priority for quantitatively understanding the contribution of regional nutrient inputs and those of other major water quality determinants. Here we applied the latest statistical data (2000–2018) andsimple quasi-mass-balance methods of net anthropogenic nitrogen and phosphorus inputs (NANI and NAPI) to estimate spatio-temporal heterogeneity of N and P inputs. The results show that while NANI and NAPI are first decreasing, this is followed by an increasing trend during 2000–2018, with average values of 11262.06 ± 2732 kg N km− 2 yr−1 and 2653.91 ± 863 kg P km−2 yr−1 respectively. High N and P concentrations in the river drainage network are related to the spatial distribution of excessive inputs of N and P. Rapid urbanization, livestock farming and the conflicts between economic development and lagged-environmental management are the main reasons for the incremental regional N and P inputs. Management decisions on nutrient pollution in karst regions need careful consideration to reduce ecological impacts and contamination of karst aquifers. This study provides new insight for policy and decision making in the WRB, highlighting policy options for managing nutrient inputs and providing recommendations for closing the science-policy divide.

Trends of the response-relationship between net anthropogenic nitrogen and phosphorus inputs (NANI/NAPI) and TN/TP export fluxes in Raohe basin, China

The intensification of anthropogenic nitrogen (N) and phosphorus (P) inputs profoundly affects water environmental quality. Hence it is pivotal to clarify the response relationship between riverine TN/TP export and anthropogenic N/P inputs to provide strategies guidance in N/P management. Based on the variation of net anthropogenic N and P inputs (NANI/NAPI) in the Raohe basin from 1990 to 2018, we constructed the response relationship between NANI/NAPI and total nitrogen and phosphorus (TN/TP) export fluxes in the riverine, which successfully predicted N and P export at the basin scale management. We found N export ratio (ratio of TN export to NANI) increased with slight fluctuation and was mainly affected by the combined effects of Nfer (fertilizer N inputs) and Ndep (atmospheric N deposition) etc., while the decrease of P export ratio (ratio of TP export to NAPI) was mainly due to intensive retention effect of the soil and sediment induced by anthropogenic influence to P transportation process. These results indicate that the downstream aquatic systems take a high risk of increasing N load pressure and the basin systems suffer a danger from rising P load pressure. Therefore, it is recommended to concentrate more on downstream aquatic systems during the N management strategy implementation and pay closer attention to the whereabouts of P in the basin system.

Estimating Virtual Nitrogen Inputs to Integrated U.S. Corn Ethanol and Animal Food Systems.

To accurately assess contributions of human activities to nitrogen (N) cycle disruption, we must consider how systems such as food and renewable fuel production are connected. N impacts of food and biofuel systems have been studied separately, but links between them have not been sufficiently considered. Since 2002, corn ethanol production in the United States has increased sixfold, and ethanol coproducts' roles in animal diets have increased similarly. In this study, we estimated virtual N in ethanol fuel and animal products using the commodity-specific Net Anthropogenic Nitrogen Inputs (CSNANI) model, which uses national corn ethanol, crop, and animal production data to estimate animal diets and the corresponding virtual N inputs to agricultural commodities. Virtual N attributable to ethanol fuel was 30 to 35 g N per liter of ethanol. As ethanol coproduct inclusion in animal diets increased from 1997 to 2012, N per kilogram of beef protein decreased by 19% and N per kilogram of milk protein decreased by 13%. With allocation of virtual N between ethanol and ethanol feed coproducts, the virtual N of both ethanol fuel and products from animals consuming ethanol coproducts is reduced relative to estimates from studies that do not consider the connection between these systems.

Changes in net anthropogenic nitrogen input in the watershed region of Zhanjiang Bay in south China from 1978 to 2018

Due to the intensive human activities and rapid economic development during the past few decades, the anthropogenic sourced nitrogen (N) input into coastal waters has increased dramatically. In this study, the net anthropogenic nitrogen input (NANI), including the deposition of atmospheric N, the application of N fertiliser, the fixation of biological N, and the net N inputs from food and feed, into the Zhanjiang Bay watershed from 1978 to 2018 were estimated using statistical data, and the driving forces were analysed using the Logarithmic Mean Divisia Index (LMDI) factor decomposition approach. The results show that the NANI dramatically increased from 5269 to 20 639 kg N km−2. The cause of this increase was related to high input from N fertilisers and the net food and feed N input (with average contributions of 56.45% and 41.42%, respectively), which was accompanied by rapid economic development in Zhanjiang Bay. The output from the LMDI illustrates that the cause of the changes in the NANI was a shift in the dietary structure instead of an increase in the human population, which suggests that the impact of human population on the increase in the NANI using simple relational analysis may be overestimated. Remarkably, we found that the N from aquatic protein and animal protein comprised a significant proportion of the total N consumption in this coastal city, which differs from previous studies of inland cities. This is likely due to the fact that aquaculture is significantly developed in this coastal city.

Net anthropogenic nitrogen and phosphorus inputs in the Yangtze River economic belt: spatiotemporal dynamics, attribution analysis, and diversity management

Excess production of nitrogen (N) and phosphorus (P) by human activities poses a severe threat to water quality. Therefore, quantitative evaluations of regional nutrient inputs and contributions from the main driving factors are necessary. This study aims to identify the spatiotemporal heterogeneity of the net anthropogenic N and P inputs (NANI and NAPI) in China’s Yangtze River economic belt and explore the environmental effects, influencing factors, and diversity management through the NANI and NAPI model and statistical models. The results reveal that (1) NANI and NAPI first increase and then decrease during 2000–2017, with average values of 7,292 kg N km−2 yr−1 and 2,306 kg P km−2 yr−1, respectively; (2) the spatial variation of NANI and NAPI exhibits a decreasing trend from east to west and north to south, which is strongly related to the distribution of urban agglomerations and land-use patterns; (3) the higher net anthropogenic inputs of N and P are associated with the higher N and P concentrations in rivers and lakes, which show the spatial pattern of a banded distribution and local concentration; and (4) changes in economic factors contribute the most to the changes in NANI and NAPI, with average contributions of 74.1% and 74.3%, respectively, followed by land-use factors, with average values of 19.5% and 19.3%, respectively; social factors are less impactful to changes in NANI and NAPI (6.4% for each). Based on results, a nutrient diversity management mechanism was constructed, which provides a scientific reference for regional environmental protection and policy formulation.

Spatiotemporal Dynamics of Nitrogen Budgets under Anthropogenic Activities in Metropolitan Areas

The rapid growth of metropolitan regions is closely associated with high nitrogen (N) flows, which is known as the most important reason for widespread water pollution. It is, therefore, crucial to explore the spatiotemporal patterns of N budgets under intensive human activity. In this study, we estimated the long-term (2000–2015) N budgets by integrating the net anthropogenic nitrogen input (NANI) and the export coefficient model (ECM) in the Yangtze River Delta Urban Agglomeration (YRDUA), a typical metropolitan area with strong human disturbances. The results revealed that the NANI decreased by 10% from 2000 to 2015, while N exports showed a 6% increase. Hotspots for N budgets were found in the northeastern areas, where cropland and construction land were dominant. The linear regression showed a close relationship between the NANI and N export, and about 18% of the NANI was exported into the river system. By revealing the critical sources and drivers of N budgets over time, our work aimed to provide effective information for regional policy on nitrogen management. Future strategies, such as improving the fertilizer efficiency, optimizing the land use pattern, and controlling the population density, are necessary in order to address the environmental challenge concerns of excessive N.

Influences of the landscape pattern on riverine nitrogen exports derived from legacy sources in subtropical agricultural catchments

Changes in the landscape pattern can disturb legacy nitrogen (N) release by influencing hydrological and biogeochemical processes; thus, understanding the effects of landscape patterns on riverine N exports from legacy sources is critical for preparing water quality improvement strategies. In this study, an empirical statistical model that incorporates the net anthropogenic nitrogen input (NANI), runoff coefficient, and residential land area percentage was used to quantify the contribution of legacy sources to annual riverine ammonium nitrogen (NH4+–N), nitrate nitrogen (NO3−–N), and total nitrogen (TN) exports in eight adjacent agricultural catchments in subtropical southern China. The results indicated that annual riverine NH4+–N, NO3−–N, and TN exports from legacy sources ranged from 0.36–1.03, 3.09–4.89, and 3.94–6.79 kg ha−1 year−1, respectively, during the 2012–2017 period. Redundancy analysis (RDA) was used to analyze the interactions between legacy N release and landscape metrics at both the landscape and class levels. The RDA results suggested that higher dispersion, lower shape complexity, and greater heterogeneity in landscape patches can enhance the release of legacy N at the landscape level. In agricultural and residential areas, higher release of legacy N was associated with patches that are unfragmented and have a low shape complexity, whereas in woodland areas, the opposite was true. These analyses provide scientific support for preparing legacy N control strategies from the perspective of landscape ecology.

Net anthropogenic nitrogen and phosphorus inputs in Pearl River Delta region (2008–2016)

Excess inputs of nitrogen (N) and phosphorus (P) are the main contributors of aquatic environmental deterioration. Due to the agricultural and industrial activities in the rapidly urbanized basin, the anthropogenic N and P cycle are significantly different from other regions. In this study, we took the Pearl River Delta as an example and introduced the budget list of N and P in the five survey years, including the net anthropogenic N inputs (NANI) and net anthropogenic P inputs (NAPI). The results revealed that the intensities of NANI and NAPI in this area increased from 2008 to 2010 and then decreased after 2010. The peak values were 21001 kg N km−2yr−1 and 4515 kg P km−2yr−1 for the intensities of NNAI and NAPI, respectively, while the lowest values decreased to 19186 kg N km−2yr−1 and 4103 kg P km−2yr−1 in 2016. The most important contribution of NANI and NAPI sources in this area were net N and P inputs for human food and animal feed with an average contribution of 61.41% and 76.83%, which indicated that large amounts of N and P were introduced into the environment through the food system. This study expanded the knowledge on regional environmental management from human dietary consumption, human life consumption, animal consumption and fertilizer consumption. Its reuse will be put into practice by understanding the driving factors of N and P inputs in each region of the basin, combining the urbanization characteristics.