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The Peace River is a critical water source in southwest Florida, United States. The watershed contains many phosphate mines that decrease water safety. Whether phosphate mining leads to a reduction in surface runoff and affects water quality in the Peace River Basin has been a highly controversial subject. Thus, the environmental impacts of phosphate mining in the Peace River were assessed. The Soil and Water Assessment Tool (SWAT) model is a widely used physical-mechanism-based distributed hydrological model that uses spatial distribution data, such as topography, soil, land use, and weather, to predict water, sediment, nutrient, pesticide, and fecal bacteria production. Based on a SWAT model, runoff, total nitrogen (TN) load, and total phosphorus (TP) load at the outlet of the Peace River Basin from 2001 to 2018 were investigated. The applicability of the four uncertainty methods in the hydrological simulation of the basin was assessed. The runoff at five stations in a specified mining area was simulated to analyze the impact of human-dominated land use changes caused by phosphate mining on the water environment. The results for the pre- and post-mining periods showed that the land use transfer in the study area experienced large fluctuations and that the land use change had a significant impact on the runoff (the outlet site decreased by 44.14%), indicating that phosphate mining has a significant effect on reducing runoff in the basin. An analysis of three scenarios (pre-mining [s1], post-mining [s2], and reclamation [s3]) showed that during s1–s2–s3, the change in mining land area is large (increased by 142.86%) and that TN and TP loads increased, indicating that human activities mainly affect the water environment through phosphate mining. This is mainly because a large amount of wastewater containing high concentrations of inorganic chemicals, which is produced in the process of phosphate mining and processing, overflows directly or from the sedimentation tank into the river. In summary, the simulation results showed that the changes in runoff and pollutants were attributed to phosphate rock mining. Therefore, strengthening the management of phosphate mining and adopting effective protection measures is of substantial significance for the effective protection of water resources. By analyzing the measured data, this study can help people understand more actual situations and further evaluate the impact of phosphate mining activities on the water environment. The simulation results can also be used to predict the future trend of runoff and water quality in the Peace River Basin and provide a decision-making basis for government management departments to issue water resource protection measures. [ABSTRACT FROM AUTHOR]

Maintaining sufficient farmland to ensure food security and a strong rural economy is crucial for China. At the national as well as regional levels, we compared the quality of the land converted from and to farmland during the period 1986-2005, thus quantifying the change in farmland quality directly attributable to land-use conversion. Specifically, we compared land cover maps compiled for the initial and final years of the study period at a 1:250,000 scale by institutes of the Chinese Academy of Sciences, and combined this with national land quality assessment data compiled at the beginning of the period. Comparison of the land cover maps revealed that over the 20-year period 12·9 Mha of farmland were converted to other land uses and 14·0 Mha of new farmland were brought under cultivation. Large net increases in farmland area occurred in Heilongjiang, Jilin, Liaoning, Xinjiang, and Inner Mongolia, together contributing 3·5 Mha of the net increase in farmland area. Several developed provinces, e.g. Beijing (−21·20%), Shanghai (−15·81%), Zhejiang (−9·85%), Guangdong (−7·79%), and Tianjin (−6·35%), experienced rapid farmland decreases. Although there was a net increase in farmland, the most suitable and productive farmland decreased by 1·8% while low-quality farmland increased by 1·4%. Thus, focusing solely on maintaining the total farmland area did not prevent overall loss of a substantial amount of high-quality farmland. Farmland protection policies should therefore take into account both farmland quantity and quality. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Knowledge about the annual and seasonal patterns of organic and inorganic carbon (C) exports from the major rivers of the world to the coastal ocean is essential for our understanding and potential management of the global C budget so as to limit anthropogenic modification of global climate. Unfortunately our predictive understanding of what controls the timing, magnitude, and quality of C export is still rudimentary. Here we use a process-based coupled hydrologic/ecosystem biogeochemistry model (the Dynamic Land Ecosystem Model) to examine how climate variability and extreme events, changing land use, and atmospheric chemistry have affected the annual and seasonal patterns of C exports from the Mississippi River basin to the Gulf of Mexico. Our process-based simulations estimate that the average annual exports of dissolved organic C (DOC), particulate organic C (POC), and dissolved inorganic C (DIC) in the 2000s were 2.6 ± 0.4 Tg C yr−1, 3.4 ± 0.3 Tg C yr−1, and 18.8 ± 3.4 Tg C yr−1, respectively. Although land use change was the most important agent of change in C export over the past century, climate variability and extreme events (such as flooding and drought) were primarily responsible for seasonal and interannual variations in C export from the basin. The maximum seasonal export of DIC occurred in summer while for DOC and POC the maximum occurred in winter. Relative to the 10 year average (2001-2010), our modeling analysis indicates that the years of maximal and minimal C export cooccurred with wet and dry years (2008: 32% above average and 2006: 32% below average). Given Intergovernmental Panel on Climate Change-predicted changes in climate variability and the severity of rain events and droughts of wet and dry years for the remainder of the 21st century, our modeling results suggest major changes in the riverine link between the terrestrial and oceanic realms, which are likely to have a major impact on C delivery to the coastal ocean. [ABSTRACT FROM AUTHOR]

The North American east coast (NAEC) region experienced significant climate and land-use changes in the past century. To explore how these changes have affected land water cycling, the Dynamic Land Ecosystem Model (DLEM 2.0) was used to investigate the spatial and temporal variability of runoff and river discharge during 1901-2010 in the study area. Annual runoff over the NAEC was 420 ± 61 mm/yr (average ± standard deviation). Runoff increased in parts of the northern NAEC but decreased in some areas of the southern NAEC. Annual freshwater discharge from the study area was 378 ± 61 km3/yr (average ± standard deviation). Factorial simulation experiments suggested that climate change and variability explained 97.5% of the interannual variability of runoff and also resulted in the opposite changes in runoff in northern and southern regions of the NAEC. Land-use change reduced runoff by 5-22 mm/yr from 1931 to 2010, but the impacts were divergent over the Piedmont region and Coastal Plain areas of the southern NAEC. Land-use change impacts were more significant at local and watershed spatial scales rather than at regional scales. Different responses of runoff to changing climate and land-use should be noted in future water resource management. Hydrological impacts of afforestation and deforestation as well as urbanization should also be noted by land-use policy makers. [ABSTRACT FROM AUTHOR]

Chen, J.; Pan, D.; Mao, Z.; Chen, N.; Zhao, J., and Liu, M., 2014. Land-cover reconstruction and change analysis using multisource remotely sensed imageries in Zhoushan Islands since 1970. Islands are hotspot areas with intensive interactions between land and ocean, and they are also the most vulnerable places to human activities and environmental change. As the frontier zone of oceanic economic development, coastal regions of China have undergone enhanced changes in land-cover change during recent decades. This study was conducted to investigate how land cover in Zhoushan Island and its surrounding islands, which are typical islands of China, has changed since the economic reform by using multisource remotely sensed imageries. The earliest land cover in 1970, 1976, and 1980 was interpreted and digitalized from CORONA and KH-9 photographs, respectively. For the period of 1986−2000, TM (Thematic Mapper) and ETM (Enhanced Thematic Mapper) imageries were classified to build land-cover maps with the supervised classification method. The most recent land-cover data in 2006 and 2011 were generated by inventory land-use vector map and SPOT5 imageries. The reconstructed land-cover time series indicate that Zhoushan Islands have involved substantial land-cover change since 1970. The arable land has changed into built-up types, mainly, and rate of change reached its peak in 2000, while the spatial distribution of transition was not uniform. Nevertheless, water bodies and woodlands have been well preserved during the past 40 years. During the urbanization process, the tidal zone of these islands shrank sharply, and some of them turned to built-up land-cover directly. [ABSTRACT FROM AUTHOR]

Summary: Little is known about how the terrestrial hydrological cycle responds to multiple environmental changes at large spatial scale and over long time period. Here, we applied a well calibrated and verified ecosystem model (the Dynamic Land Ecosystem Model, DLEM), in conjunction with newly developed data sets of multiple environmental factors including land use change, climate variability, elevated atmospheric carbon dioxide (CO2), nitrogen deposition, ozone pollution, and nitrogen fertilizer application, to characterize the spatial and temporal patterns of evapotranspiration (ET) and runoff in eastern China during 1961–2005 and further quantified the relative contributions of multiple environmental factors to these patterns at both basin and regional scales. The simulation results indicated that annual ET in the study area had a significantly increasing trend from 1961 to 2005. Yet there were no significant changing trends for estimated runoff and net water balance (precipitation minus ET). Substantial spatial heterogeneities in ET and runoff were observed. Annual ET increased in all basins except Yellow River Basin. Runoff increased in the southern part of the study area (including Pearl River and the Southeast basin), but decreased in northern part of the study area, particularly in Haihe and Huaihe river basins. Factorial analysis showed that climate change was the dominant factor responsible for the interannual variations in ET and runoff in the past 45years. Land use change (including land conversions and land management practices) yielded minor effects on the interannual variations in ET and runoff but caused relatively large effects over long-term period. For the accumulated change in ET at basin scale, climate change was the dominant factor in the basins of Song-Liao, Pearl River, while land use change contributed the most in the basin of Haihe, Huaihe, and Yellow River. Climate change was the dominant factor controlling runoff change in all basins except Huaihe and Yangtze River basins. Our simulated results imply that it is important to quantify relative roles of natural and anthropogenic disturbances on water fluxes for maintaining water sustainability in a changing climate. [Copyright &y& Elsevier]

Abstract: There are large discrepancies among estimates of the cropland area in China due to the lack of reliable data. In this study, we used Landsat TM/ETM data at a spatial resolution of 30 m to reconstruct spatial and temporal patterns of cropland across China for the time period of 1990–2000. Our estimate has indicated that total cropland area in China in 2000 was 141.1 million hectares (ha), including 35.6 million ha paddy land and 105.5 million ha dry farming land. The distribution of cropland is uneven across the regions of China. The North-East region of China shows more cropland area per capita than the South-East and North regions of China. During 1990–2000, cropland increased by 2.79 million ha, including 0.25 million ha of paddy land and 2.53 million ha of dry farming land. The North-East and North-West regions of China gained cropland area, while the North and South-East regions showed a loss of cropland area. Urbanization accounted for more than half of the transformation from cropland to other land uses, and the increase in cropland was primarily due to reclamation of grassland and deforestation. Most of the lost cropland had good quality with high productivity, but most gained cropland was poor quality land with less suitability for crop production. The globalization as well as changing environment in China is affecting land-use change. Coordinating the conflict between environmental conservation and land demands for food will continue to be a primary challenge for China in the future. [Copyright &y& Elsevier]

• Extreme summer flood affects NO 3 – dynamics differently in river and Lake systems. • NO 3 – and δ15N–NO 3 – rose from headwaters to agricultural and residential river zones. • Flood-driven soil erosion and fertilizers dominated NO 3 – sources in Xin'an River. • Sewage in tributaries, treatment plant overflow impact Lake Qiandao during flooding. • Lake Qiandao remains affected by non-point source pollution during dry seasons. Nitrate (NO 3 −) pollution poses a global aquatic threat, promoting eutrophication and endangering human health. Large floods can swiftly drive significant nitrogen load into rivers and downstream water bodies, nevertheless, precisely quantifying NO 3 − sources in watersheds with complex land use patterns remains challenging. In June 2020, heavy and persistent rainfall triggered severe floods across southeastern China, causing Lake Qiandao, the largest reservoir in this region, to reach its highest recorded level. This study investigated NO 3 − sources and transformations within the Xin'an River-Lake Qiandao system, particularly focusing on the impact of the catastrophic summer flooding event. Through extensive sampling, we identified a distinct nitrogen concentration gradient: from the pristine Xin'an River source, characterized by 95 % forest cover and consistently low nitrogen levels for the initial 125 km, to a gradual rise as the river traversed human-impacted regions, culminating in peak concentrations within residential and agricultural areas. Isotopic analysis identified a general upward trend in nitrate stable isotope (δ15N–NO 3 –) associated with the expansion of agricultural and urban lands. Mean values of δ15N–NO 3 – gradually increased from headwaters and forest-dominant catchments (+2.88 ‰) to agricultural regions (+6.64 ‰) and residential areas (+7.10 ‰). A Bayesian modeling identified that during the flood season, soil erosion and chemical fertilizers were the primary contributors, collectively accounting for 74 % of NO 3 − sources in the Xin'an River. However, accumulated sewage in tributaries and the overflow of sewage from treatment plants, exacerbated by the flood, significantly impacted Lake Qiandao, particularly in densely populated urban areas, contributing 53 % of the total NO 3 − input. Additionally, NO 3 − levels and isotopic values in Lake Qiandao were influenced by a mixture of sources and nitrogen cycling processes, including nitrification and algae assimilation following the flood event. In contrast, during baseflow conditions, the contribution of domestic sewage and livestock wastewaters increased to 41 % in the upper river, while Lake Qiandao remained affected by non-point source pollution, with soil erosion and chemical fertilizers contributing 58 % to the total nitrogen pollution. This study sheds light on the complex dynamics of NO 3 − dynamics within river–reservoir systems, particularly in the context of extreme flooding, emphasizing the critical need for comprehensive water quality management strategies along the entire watershed. [ABSTRACT FROM AUTHOR]