In addition to enhancing agricultural productivity, synthetic nitrogen (N) and phosphorous (P) fertilizer application in croplands dramatically alters global nutrient budget, water quality, ...greenhouse gas balance, and their feedback to the climate system. However, due to the lack of geospatial fertilizer input data, current Earth system and land surface modeling studies have to ignore or use oversimplified data (e.g., static, spatially uniform fertilizer use) to characterize agricultural N and P input over decadal or century-long periods. In this study, we therefore develop global time series gridded data of annual synthetic N and P fertilizer use rate in agricultural lands, matched with HYDE 3.2 historical land use maps, at a resolution of 0.5° × 0.5° latitude–longitude during 1961–2013. Our data indicate N and P fertilizer use rates on per unit cropland area increased by approximately 8 times and 3 times, respectively, since the year 1961 when IFA (International Fertilizer Industry Association) and FAO (Food and Agricultural Organization) surveys of country-level fertilizer input became available. Considering cropland expansion, the increase in total fertilizer consumption is even larger. Hotspots of agricultural N fertilizer application shifted from the US and western Europe in the 1960s to eastern Asia in the early 21st century. P fertilizer input shows a similar pattern with an additional current hotspot in Brazil. We found a global increase in fertilizer N ∕ P ratio by 0.8 g N g−1 P per decade (p < 0.05) during 1961–2013, which may have an important global implication for human impacts on agroecosystem functions in the long run. Our data can serve as one of critical input drivers for regional and global models to assess the impacts of nutrient enrichment on climate system, water resources, food security, etc. Datasets available at doi:10.1594/PANGAEA.863323.
Aim: Land use and land cover changes (LCLUC) are among the most important driving forces that alter terrestrial ecosystem functions and their feedbacks to climate systems, but reliable, spatially ...explicit datasets over century-long periods are still lacking for fine-scale earth system modeling. We aimed to combine multiple data sources and reconstruct long-term land use history in the continental U.S., examining cropland expansion and abandonment since 1850. Location: Conterminous U.S. Time period: 1850 to 2016. Major taxa studied: Cropland. Methods: Cropland density maps, displaying the distribution and percentage of cultivated land each year (excluding summer idle/fallow, cropland pasture), were reconstructed by harmonizing multiple sources of inventory data and high-resolution satellite images. The cropland data are freely available to the public. Results: In total, national cropland expansion was 104 million hectares (Mha) from 1850 to 2016 and peaked at about 127 Mha in 1920. Forests and shrublands were the dominant land cover types that croplands were converted from during 1850 to 1880, which may be primarily attributed to agriculture development in the northeast U.S. Croplands began to expand into grasslands from 1870 onwards and the encroached area dramatically increased, mainly due to cultivation development in the Great Plain and midwestern areas. In comparison, the area of abandoned cropland in the U.S. was 65 Mha during the study period. We found cropland abandonment mostly occurred in the central and southeast U.S., while cropland expansion was centered upon the midwestern states, central California, and the Mississippi Alluvial Plain. Main conclusions: Nationally, cultivated lands shifted from the eastern to midwestern U.S. during the study period, contributing to the increasingly important role of the Midwest in the rise of food and biofuel production, enhanced greenhouse gas (GHG) emissions, and high nitrogen loads into the Gulf of Mexico. Our cropland database is essential for modeling assessments of LCLUC impacts, crop production estimation and socioeconomic analysis.
A wide variety of studies have revealed a substantial increase in nitrogen (N) deposition in China, but the lack of spatially-explicit time-series N deposition data set has long hindered us from ...assessing the impacts of atmospheric N input on ecosystem services. In this study, we combined site-level monitoring, gridded precipitation data and atmospheric transport modeling results to generate annual N bulk deposition data in China with a spatial resolution of 10 km × 10 km and a time span from 1961 to 2008. It shows that national average N deposition rate had large interannual variation, and it increased by 59%, from 12.64 kg N ha−1 yr−1 in the 1960s to 20.07 kg N ha−1 yr−1 in the recent decade, with the most rapid increase centered in the southeastern China that is already N-enriched. Large spatial variation as well as dry deposition input has to be taken into account when estimating the amount of N deposited onto land surface of China. The spatial and temporal information on N deposition derived from this study could be used by ecosystem, hydrological, and climate modeling as well as by policy makers for assessing the impacts of nitrogen enrichment on regional climate, water resources, and biogeochemical cycles.
•Gridded N deposition data in China during 1961–2008 was developed in this study.•China's N deposition is found to increase by 59%, to 20.07 kg N ha−1 yr−1 in the 2000s.•Spatial heterogeneity ought to be considered in estimating China's N deposition.
Increasing reactive nitrogen (N) input has been recognized as one of the important factors influencing climate system through affecting the uptake and emission of greenhouse gases (GHG). However, the ...magnitude and spatiotemporal variations of N‐induced GHG fluxes at regional and global scales remain far from certain. Here we selected China as an example, and used a coupled biogeochemical model in conjunction with spatially explicit data sets (including climate, atmospheric CO2, O3, N deposition, land use, and land cover changes, and N fertilizer application) to simulate the concurrent impacts of increasing atmospheric and fertilized N inputs on balance of three major GHGs (CO2, CH4, and N2O). Our simulations showed that these two N enrichment sources in China decreased global warming potential (GWP) through stimulating CO2 sink and suppressing CH4 emission. However, direct N2O emission was estimated to offset 39% of N‐induced carbon (C) benefit, with a net GWP of three GHGs averaging −376.3 ± 146.4 Tg CO2 eq yr−1 (the standard deviation is interannual variability of GWP) during 2000–2008. The chemical N fertilizer uses were estimated to increase GWP by 45.6 ± 34.3 Tg CO2 eq yr−1 in the same period, and C sink was offset by 136%. The largest C sink offset ratio due to increasing N input was found in Southeast and Central mainland of China, where rapid industrial development and intensively managed crop system are located. Although exposed to the rapidly increasing N deposition, most of the natural vegetation covers were still showing decreasing GWP. However, due to extensive overuse of N fertilizer, China's cropland was found to show the least negative GWP, or even positive GWP in recent decade. From both scientific and policy perspectives, it is essential to incorporate multiple GHGs into a coupled biogeochemical framework for fully assessing N impacts on climate changes.
Abstract
Carbon budget accounting relies heavily on Food and Agriculture Organization land-use data reported by governments. Here we develop a new land-use and cover-change database for China, ...finding that differing historical survey methods biased China’s reported data causing large errors in Food and Agriculture Organization databases. Land ecosystem model simulations driven with the new data reveal a strong carbon sink of 8.9 ± 0.8 Pg carbon from 1980 to 2019 in China, which was not captured in Food and Agriculture Organization data-based estimations due to biased land-use and cover-change signals. The land-use and cover-change in China, characterized by a rapid forest expansion from 1980 to 2019, contributed to nearly 44% of the national terrestrial carbon sink. In contrast, climate changes (22.3%), increasing nitrogen deposition (12.9%), and rising carbon dioxide (8.1%) are less important contributors. This indicates that previous studies have greatly underestimated the impact of land-use and cover-change on the terrestrial carbon balance of China. This study underlines the importance of reliable land-use and cover-change databases in global carbon budget accounting.
Our understanding and quantification of global soil nitrous oxide (N2O) emissions and the underlying processes remain largely uncertain. Here, we assessed the effects of multiple anthropogenic and ...natural factors, including nitrogen fertilizer (N) application, atmospheric N deposition, manure N application, land cover change, climate change, and rising atmospheric CO2 concentration, on global soil N2O emissions for the period 1861–2016 using a standard simulation protocol with seven process‐based terrestrial biosphere models. Results suggest global soil N2O emissions have increased from 6.3 ± 1.1 Tg N2O‐N/year in the preindustrial period (the 1860s) to 10.0 ± 2.0 Tg N2O‐N/year in the recent decade (2007–2016). Cropland soil emissions increased from 0.3 Tg N2O‐N/year to 3.3 Tg N2O‐N/year over the same period, accounting for 82% of the total increase. Regionally, China, South Asia, and Southeast Asia underwent rapid increases in cropland N2O emissions since the 1970s. However, US cropland N2O emissions had been relatively flat in magnitude since the 1980s, and EU cropland N2O emissions appear to have decreased by 14%. Soil N2O emissions from predominantly natural ecosystems accounted for 67% of the global soil emissions in the recent decade but showed only a relatively small increase of 0.7 ± 0.5 Tg N2O‐N/year (11%) since the 1860s. In the recent decade, N fertilizer application, N deposition, manure N application, and climate change contributed 54%, 26%, 15%, and 24%, respectively, to the total increase. Rising atmospheric CO2 concentration reduced soil N2O emissions by 10% through the enhanced plant N uptake, while land cover change played a minor role. Our estimation here does not account for indirect emissions from soils and the directed emissions from excreta of grazing livestock. To address uncertainties in estimating regional and global soil N2O emissions, this study recommends several critical strategies for improving the process‐based simulations.
The ensemble of terrestrial biosphere models indicates that global soil N2O emissions have increased from 6.3 ± 1.1 Tg N2O‐N/year in the preindustrial period (the 1860s) to 10.0 ± 2.0 Tg N2O‐N/year in the recent decade (2007–2016). Cropland soil emissions increased from 0.3 Tg N2O‐N/year to 3.3 Tg N2O‐N/year over the same period, accounting for 82% of the total increase, among which 54% attributes to nitrogen fertilizer application. Regionally, China, South Asia, and Southeast Asia underwent rapid increases in cropland N2O emissions since the 1970s. However, European cropland N2O emissions appear to have decreased by 14%.
Drought can affect the structure, composition and function of terrestrial ecosystems, yet drought impacts and post-drought recovery potentials of different land cover types have not been extensively ...studied at a global scale. We evaluated drought impacts on gross primary productivity (GPP), evapotranspiration (ET), and water use efficiency (WUE) of different global terrestrial ecosystems, as well as the drought-resilience of each ecosystem type during the period of 2000 to 2011. Using GPP as biome vitality indicator against drought stress, we developed a model to examine ecosystem resilience represented by the length of recovery days (LRD). LRD presented an evident gradient of high (>60 days) in mid-latitude region and low (<60 days) in low (tropical area) and high (boreal area) latitude regions. As average GPP increased, the LRD showed a significantly decreasing trend, indicating readiness to recover after drought, across various land cover types (R2 = 0.68, p < 0.0001). Moreover, zonal analysis revealed that the most dramatic reduction of the drought-induced GPP was found in the mid-latitude region of the Northern Hemisphere (48% reduction), followed by the low-latitude region of the Southern Hemisphere (13% reduction). In contrast, a slightly enhanced GPP (10%) was evident in the tropical region under drought impact. Additionally, the highest drought-induced reduction of ET was found in the Mediterranean area, followed by Africa. Water use efficiency, however, showed a pattern of decreasing in the Northern Hemisphere and increasing in the Southern Hemisphere. Drought induced reductions of WUE ranged from 0.96% to 27.67% in most of the land cover types, while the increases of WUE found in Evergreen Broadleaf Forest and savanna were about 7.09% and 9.88%, respectively. These increases of GPP and WUE detected during drought periods could either be due to water-stress induced responses or data uncertainties, which require further investigation.
Given the importance of the potential positive feedback between methane (CH4) emissions and climate change, it is critical to accurately estimate the magnitude and spatiotemporal patterns of CH4 ...emissions from global rice fields and better understand the underlying determinants governing the emissions. Here we used a coupled biogeochemical model in combination with satellite‐derived contemporary inundation area to quantify the magnitude and spatiotemporal variation of CH4 emissions from global rice fields and attribute the environmental controls of CH4 emissions during 1901–2010. Our study estimated that CH4 emissions from global rice fields varied from 18.3 ± 0.1 Tg CH4/yr (Avg. ±1 SD) under intermittent irrigation to 38.8 ± 1.0 Tg CH4/yr under continuous flooding in the 2000s, indicating that the magnitude of CH4 emissions from global rice fields is largely dependent on different water schemes. Over the past 110 years, our simulated results showed that global CH4 emissions from rice cultivation increased by 85%. The expansion of rice fields was the dominant factor for the increasing trends of CH4 emissions, followed by elevated CO2 concentration, and nitrogen fertilizer use. On the contrary, climate variability had reduced the cumulative CH4 emissions for most of the years over the study period. Our results imply that CH4 emissions from global rice fields could be reduced through optimizing irrigation practices. Therefore, the future magnitude of CH4 emissions from rice fields will be determined by the human demand for rice production as well as the implementation of optimized water management practices.
Key Points
Methane emissions from global rice fields in the 2000s varied from 18.3 to 38.8 Tg CH4/yr depending on different water schemes
Expansion of rice cultivation was the key factor causing CH4 emission increase in the past century
Intermittent irrigation could reduce half CH4 emission comparing with continuous flooding
The effects of global change on ecosystem productivity and water resources in the southern United States (SUS), a traditionally ‘water-rich’ region and the ‘timber basket’ of the country, are not ...well quantified. We carried out several simulation experiments to quantify ecosystem net primary productivity (NPP), evapotranspiration (ET) and water use efficiency (WUE) (i.e., NPP/ET) in the SUS by employing an integrated process-based ecosystem model (Dynamic Land Ecosystem Model, DLEM). The results indicated that the average ET in the SUS was 710
mm during 1895–2007. As a whole, the annual ET increased and decreased slightly during the first and second half of the study period, respectively. The mean regional total NPP was 1.18
Pg
C/yr (525.2
g
C/m
2/yr) during 1895–2007. NPP increased consistently from 1895 to 2007 with a rate of 2.5
Tg
C/yr or 1.10
g
C/m
2/yr, representing a 27% increase. The average WUE was about 0.71
g
C/kg
H
2O and increased about 25% from 1895 to 2007. The rather stable ET might explain the resulting increase in WUE. The average WUE of different biomes followed an order of: forest (0.93
g
C/kg
H
2O)
>
wetland (0.75
g
C/kg
H
2O)
>
grassland (0.58
g
C/kg
H
2O)
>
cropland (0.54
g
C/kg
H
2O)
>
shrubland (0.45
g
C/kg
H
2O). WUE of cropland increased the fastest (by 30%), followed by shrubland (17%) and grassland (9%), while WUE of forest and wetland changed little from the period of 1895–1950 to the period of 1951–2007. NPP, ET and WUE showed substantial inter-annual and spatial variability, which was induced by the non-uniform distribution patterns and change rates of environmental factors across the SUS. We concluded that an accurate projection of the regional impact of climate change on carbon and water resources must consider the spatial variability of ecosystem water use efficiency across biomes as well as the interactions among all stresses, especially land-use and land-cover change and climate.
Although the hypoxia formation in the Gulf of Mexico is predominantly driven by increased riverine nitrogen (N) export from the Mississippi-Atchafalaya River basin, it remains unclear how ...hydroclimate extremes affect downstream N loads. Using a process-based hydro-ecological model, we reveal that over 60% of the land area of the Basin has experienced increasing extreme precipitation since 2000, and this area yields over 80% of N leaching loss across the region. Despite occurring in ~9 days year
−1
, extreme precipitation events contribute ~1/3 of annual precipitation, and ~1/3 of total N yield on average. Both USGS monitoring and our modeling estimates demonstrate an approximately 30% higher annual N load in the years with extreme river flow than the long-term median. Our model suggests that N load could be reduced by up to 16% merely by modifying fertilizer application timing but increasing contribution of extreme precipitation is shown to diminish this potential.
Over the past 40 years, precipitation extremes have become more important for delivering N to the Gulf of Mexico, according to simulations with a hydro-ecological model. This is likely to diminish the effectiveness of alternative N use practices
PDF
