Maryna Strokal

Increasing eutrophication in the coastal seas of China from 1970 to 2050.

We analyzed the potential for eutrophication in major seas around China: the Bohai Gulf, Yellow Sea and South China Sea. We model the riverine inputs of nitrogen (N), phosphorus (P) and silica (Si) to coastal seas from 1970 to 2050. Between 1970 and 2000 dissolved N and P inputs to the three seas increased by a factor of 2-5. In contrast, inputs of particulate N and P and dissolved Si, decreased due to damming of rivers. Between 2000 and 2050, the total N and P inputs increase further by 30-200%. Sewage is the dominant source of dissolved N and P in the Bohai Gulf, while agriculture is the primary source in the other seas. In the future, the ratios of Si to N and P decrease, which increases the risk of harmful algal blooms. Sewage treatment may reduce this risk in the Bohai Gulf, and agricultural management in the other seas.

Alarming nutrient pollution of Chinese rivers as a result of agricultural transitions

Transitions in Chinese agriculture resulted in industrial animal production systems, disconnected from crop production. We analyzed side-effects of these transitions on total dissolved nitrogen (TDN) and phosphorus (TDP) inputs to rivers. In 2000, when transitions were ongoing, 30%–70% of the manure was directly discharged to rivers (range for sub-basins). Before the transition (1970) this was only 5%. Meanwhile, animal numbers more than doubled. As a result, TDN and TDP inputs to rivers increased 2- to 45-fold (range for sub-basins) during 1970–2000. Direct manure discharge accounts for over two-thirds of nutrients in the northern rivers and for 20%–95% of nutrients in the central and southern rivers. Environmental concern is growing in China. However, in the future, direct manure inputs may increase. Animal production is the largest cause of aquatic eutrophication. Our study is a warning signal and an urgent call for action to recycle animal manure in arable farming.

Nitrogen and phosphorus inputs to the Black Sea in 1970–2050

Increased nitrogen (N) and phosphorus (P) inputs are major causes of eutrophication in the coastal waters of the Black Sea. The objective of this study is to analyze the past and future trends in river export of nitrogen and phosphorus to the coastal waters of the Black Sea and to assess the associated potential for coastal eutrophication. The Global NEWS-2 (Nutrient Export from WaterSheds) model was used for this purpose. Currently, most eutrophication occurs in the North Black Sea and the Azov Sea. In the future, however, this may change. We analyzed trends up to 2050 on the basis of the Millennium Ecosystem Assessment (MEA) scenarios. The results indicate that nutrient loads in rivers draining into the North Black Sea and the Azov Sea may decrease in the coming decades as a result of agricultural trends and environmental policy. However, in these scenarios, the targets of the Black Sea Convention are not met. In the South Black Sea, there is currently little eutrophication. But this may change because of increases in nutrient inputs from sewage in the future.

The increasing impact of food production on nutrient export by rivers to the Bay of Bengal 1970-2050

The objective of this study is to assess the impact of food production on river export of nutrients to the coastal waters of the Bay of Bengal in the past (1970 and 2000) and the future (2030 and 2050), and the associated potential for coastal eutrophication. We model nutrient export from land to sea, using the Global NEWS (Nutrient Export from WaterSheds) approach. We calculate increases in river export of N and P over time. Agricultural sources account for about 70-80% of the N and P in rivers. The coastal eutrophication potential is high in the Bay. In 2000, nutrient discharge from about 85% of the basin area of the Bay drains into coastal seas contributes to the risk of coastal eutrophication. By 2050, this may be 96%. We also present an alternative scenario in which N and P inputs to the Bay are 20-35% lower than in the baseline.

The MARINA model (Model to Assess River Inputs of Nutrients to seAs): Model description and results for China

Chinese agriculture has been developing fast towards industrial food production systems that discharge nutrient-rich wastewater into rivers. As a result, nutrient export by rivers has been increasing, resulting in coastal water pollution. We developed a Model to Assess River Inputs of Nutrients to seAs (MARINA) for China. The MARINA Nutrient Model quantifies river export of nutrients by source at the sub-basin scale as a function of human activities on land. MARINA is a downscaled version for China of the Global NEWS-2 (Nutrient Export from WaterSheds) model with an improved approach for nutrient losses from animal production and population. We use the model to quantify dissolved inorganic and organic nitrogen (N) and phosphorus (P) export by six large rivers draining into the Bohai Gulf (Yellow, Hai, Liao), Yellow Sea (Yangtze, Huai) and South China Sea (Pearl) in 1970, 2000 and 2050. We addressed uncertainties in the MARINA Nutrient model. Between 1970 and 2000 river export of dissolved N and P increased by a factor of 2-8 depending on sea and nutrient form. Thus, the risk for coastal eutrophication increased. Direct losses of manure to rivers contribute to 60-78% of nutrient inputs to the Bohai Gulf and 20-74% of nutrient inputs to the other seas in 2000. Sewage is an important source of dissolved inorganic P, and synthetic fertilizers of dissolved inorganic N. Over half of the nutrients exported by the Yangtze and Pearl rivers originated from human activities in downstream and middlestream sub-basins. The Yellow River exported up to 70% of dissolved inorganic N and P from downstream sub-basins and of dissolved organic N and P from middlestream sub-basins. Rivers draining into the Bohai Gulf are drier, and thus transport fewer nutrients. For the future we calculate further increases in river export of nutrients. The MARINA Nutrient model quantifies the main sources of coastal water pollution for sub-basins. This information can contribute to formulation of effective management options to reduce nutrient pollution of Chinese seas in the future.

Reducing future nutrient inputs to the Black Sea.

Rivers export increasing amounts of dissolved inorganic (DIN, DIP) and organic (DON, DOP) nitrogen and phosphorus to the Black Sea causing coastal eutrophication. The aim of this study is to explore future trends in river export of these nutrients to the sea through a sensitivity analysis. We used the Global NEWS (Nutrient Export from WaterSheds) model to this end. We calculated that between 2000 and 2050 nutrient inputs to the Black Sea may increase or decrease, depending on the assumed environmental management. We analyzed the effects of agricultural and sewage management on nutrient inputs to the sea in 2050 relative to two Millennium Ecosystem Assessment (MEA) scenarios, Global Orchestration (GO) and Adaptive Mosaic (AM). In these baselines, total N and P inputs to the Black Sea decrease between 2000 and 2050, but not for all rivers and nutrient forms. Our results indicate that it is possible to reduce nutrient inputs to the sea further between 2000 and 2050 in particular for dissolved inorganic N and P and for many river basins, but not for all. For scenarios assuming combined agricultural and sewage management dissolved inorganic N and P inputs to the Black Sea are reduced by up to two-thirds between 2000 and 2050 and dissolved organic N and P inputs by one-third. River export of DIN is mainly affected by agricultural management and that of DIP by sewage management. On the other hand, in scenarios assuming increased fertilizer use for, for instance bioenergy crops, nutrient inputs to the sea increase. An increase in DIP inputs by southern rivers seems difficult to avoid because of the increasing number of people connected to sewage systems.

Reactive nitrogen losses from China's food system for the shared socioeconomic pathways (SSPs)

Food production in China has been changing fast as a result of socio-economic development. This resulted in an increased use of nitrogen (N) in food production, and also to increased reactive nitrogen (Nr) losses to the environment, causing nitrogen pollution. Our study is the first to quantify future Nr losses from Chinas food system for the Shared Socio-economic Pathways (SSPs). We show that Nr losses differ largely among SSPs. We first qualitatively described the five SSP storylines for China with a focus on food production and consumption. Next, we interpreted these SSP scenarios quantitatively for 2030 and 2050, using the NUFER (NUtrient Flows in Food chains, Environment and Resources use) model to project the Nr losses from Chinas food system. The results indicate that Nr losses from future food system in China are relatively low for SSP1 and SSP2, and relatively high for SSP3 and SSP4. In SSP5 Nr losses from Chinas food system are projected to be slightly lower than the level of today.

Human waste : An underestimated source of nutrient pollution in coastal seas of Bangladesh, India and Pakistan

Many people practice open defecation in south Asia. As a result, lot of human waste containing nutrients such as nitrogen (N) and phosphorus (P) enter rivers. Rivers transport these nutrients to coastal waters, resulting in marine pollution. This source of nutrient pollution is, however, ignored in many nutrient models. We quantify nutrient export by large rivers to coastal seas of Bangladesh, India and Pakistan, and the associated eutrophication potential in 2000 and 2050. Our new estimates for N and P inputs from human waste are one to two orders of magnitude higher than earlier model calculations. This leads to higher river export of nutrients to coastal seas, increasing the risk of coastal eutrophication potential (ICEP). The newly calculated future ICEP, for instance, Godavori river is 3 times higher than according to earlier studies. Our modeling approach is simple and transparent and can easily be applied to other data-poor basins.

Hotspots for Nitrogen and Phosphorus Losses from Food Production in China: A County-Scale Analysis

Food production in China results in large losses of nitrogen (N) and phosphorus (P) to the environment. Our objective is to identify hotspots for N and P losses to the environment from food production in China at the county scale. To do this, we used the NUFER (Nutrient flows in Food chains, Environment and Resources use) model. Between 1990 and 2012, the hotspot area expanded by a factor of 3 for N, and 24 for P. In 2012 most hotspots were found in the North China Plain. Hotspots covered less than 10% of the Chinese land area, but contributed by more than half to N and P losses to the environment. Direct discharge of animal manure to rivers was an important cause of N and P losses. Food production was found to be more intensive in hotspots than in other counties. Synthetic fertilizer use and animal numbers in hotspots were a factor of 4–5 higher than in other counties in 2012. Also the number of people working in food production and the incomes of farmers are higher in hotspots than in other counties. This study concludes with suggestions for region-specific pollution control technologies for food production in China.