Future projections of river nutrient export to the global coastal ocean show persisting nitrogen and phosphorus distortion

Nitrogen (N) and phosphorus (P) from anthropogenic sources are needed to produce food for the growing world population. As a result, these nutrients can be found in nearly every water body across the globe. Not only nutrient loading is important but also the molar ratio and its deviation from the “natural” Redfield ratio. Here we show that rivers, which have more than 50% anthropogenic sources and at the same time elevated N:P ratios (> 25) contributed 36% to the total global N export to coastal waters in 2015. The five Shared Socioeconomic Pathways (SSP) were used in combination with the Representative Concentration Pathways climate scenarios to project river nutrient loadings for 2050. Future nutrient export is projected to decline in high-income countries (with N:P ratios exceeding Redfield). In Brazil, India and China, however, a decline of N:P is only the case in a scenario oriented toward sustainable development (SSP1). The human-dominated river N and P export with elevated N:P ratios will increase in all SSPs, except in SSP1 where it stabilizes. Integrated strategies for both N and P considering all relevant trade-offs and societal sectors are urgently needed to reduce the nutrient pressure on surface waters

Effects of Nitrogen Emissions on Fish Species Richness across the World’s Freshwater Ecoregions

The increasing application of synthetic fertilizer has tripled nitrogen (N) inputs over the 20th century. N enrichment decreases water quality and threatens aquatic species such as fish through eutrophication and toxicity. However, the impacts of N on freshwater ecosystems are typically neglected in life cycle assessment (LCA). Due to the variety of environmental conditions and species compositions, the response of species to N emissions differs among ecoregions, requiring a regionalized effect assessment. Our study tackled this issue by establishing regionalized species sensitivity distributions (SSDs) of freshwater fish against N concentrations for 367 ecoregions and 48 combinations of realms and major habitat types globally. Subsequently, effect factors (EFs) were derived for LCA to assess the effects of N on fish species richness at a 0.5 degree × 0.5 degree resolution. Results show good SSD fits for all of the ecoregions that contain sufficient data and similar patterns for average and marginal EFs. The SSDs highlight strong effects on species richness due to high N concentrations in the tropical zone and the vulnerability of cold regions. Our study revealed the regional differences in sensitivities of freshwater ecosystems against N content in great spatial detail and can be used to assess more precisely and comprehensively nutrient-induced impacts in LCA

Harmful Algal Blooms in Chinese Coastal Waters Will Persist Due to Perturbed Nutrient Ratios

The three large marine ecosystems (LMEs) bordering China (Yellow Sea/Bohai Sea, East China Sea, and South China Sea) have received excess nitrogen (N) and phosphorus (P) in the past decades with detrimental consequences for ecosystem functioning, such as increased productivity, loss of biodiversity, and proliferation of harmful algal blooms (HABs). N loading increased much faster than that of P. Here, we show that HABs in the three LMEs started to proliferate after the N:P molar ratio exceeded the threshold value of 25 in the 1980s. The mismatch of N and P inputs is not only related to differences in loads but also inherent to the differences in their biogeochemical cycles which more efficiently filter P than N in land- and waterscapes. Future Shared Socioeconomic Pathways show that high N:P ratios will persist for decades to come, even worsening in a future oriented toward sustainability, and indicate that HABs may be a persisting problem in China’s coastal waters. While efforts in agricultural systems are governed by the agronomic crop requirements and are not easy to manage with respect to N:P ratios, the separate collection of urine in urban and rural areas could contribute to decreases in both total nutrient loads and N:P ratios

Efficiency of phosphorus resource use in Africa as defined by soil chemistry and the impact on crop production

By 2050 the global population will be 9.7 billion, placing an unprecedented burden on the world’s soils to produce extremely high food yields. Phosphorus (P) is crucial to plant growth and mineral fertilizer is added to soil to maintain P concentrations, however this is a finite resource, thus efficient use is critical. Plants primarily uptake P from a labile (available) P pool and not from the stable solid phase; transfer between these pools limits bioavailability. Transfer is controlled by soil properties which vary between soil types. The dynamic phosphorus pool simulator (DPPS) quantifies crop production and soil P relationships by utilising the transfer. This approach effectively models crop uptake from soil inputs, but it does not quantify the efficiency use. This study incorporates geochemical techniques within DPPS to quantify the efficiency of fertilizer-P use based on soil chemistry

Aquatic risks from human pharmaceuticals - Modelling temporal trends of carbamazepine and ciprofloxacin at the global scale

Despite the worldwide presence of pharmaceuticals in the aquatic environment, a comprehensive picture of their aquatic risk (AR) at the global scale has not yet been produced. Here, we present a procedure to estimate ARs of human pharmaceuticals at a freshwater ecoregion level. First, we predicted country- and year-specific per capita consumption with a regression model. Second, we calculated spatially explicit freshwater concentrations via a combination of mass balance models, addressing the pharmaceutical's fate in respectively humans, wastewater treatment plants and the environment. Finally, we divided the freshwater concentrations at the level of individual freshwater ecoregions with the regulatory limit value derived from toxicity tests to come to an ecoregion-specific AR. We applied our procedure to model time-trends (1995-2015) of ARs of carbamazepine and ciprofloxacin, two widely detected and regulatory relevant human use pharmaceuticals. Our analysis of carbamazepine and ciprofloxacin showed that ARs, due to exposure to these human pharmaceuticals, typically increased 10-20 fold over the last 20 years. Risks due to carbamazepine exposure were still typically low for the time period assessed (AR < 0.1), although some more densely populated and/or arid ecoregions showed higher ARs (up to 1.1). Risks for ciprofloxacin were found to be much higher with ARs larger than 1 for 223 out of 449 freshwater ecoregions in 2015. Comparison with measured concentrations in ten river basins showed that carbamazepine concentrations were predicted well. Concentrations of ciprofloxacin, measured in four river basins, were, however, generally underestimated by our model with one to two orders of magnitude. We conclude that our procedure provides a good starting point to evaluate ARs of a wide range of human pharmaceuticals at the global scale

Anthropogenic Biomes: 10,000 BCE to 2015 CE

Human populations and their use of land have reshaped landscapes for thousands of years, creating the anthropogenic biomes (anthromes) that now cover most of the terrestrial biosphere. Here we introduce the first global reconstruction and mapping of anthromes and their changes across the 12,000-year interval from 10,000 BCE to 2015 CE; the Anthromes 12K dataset. Anthromes were mapped using gridded global estimates of human population density and land use from the History of the Global Environment database (HYDE version 3.2) by a classification procedure similar to that used for prior anthrome maps. Anthromes 12K maps generally agreed with prior anthrome maps for the same time periods, though significant differences were observed, including a substantial reduction in Rangelands anthromes in 2000 CE but with increases before that time. Differences between maps resulted largely from improvements in HYDE’s representation of land use, including pastures and rangelands, compared with the HYDE 3.1 input data used in prior anthromes maps. The larger extent of early land use in Anthromes 12K also agrees more closely with empirical assessments than prior anthrome maps; the result of an evidence-based paradigm shift in characterizing the history of Earth’s transformation through land use, from a mostly recent large-scale conversion of uninhabited wildlands, to a long-term trend of increasingly intensive transformation and use of already inhabited and used landscapes. The spatial history of anthropogenic changes depicted in Anthromes 12K remain to be validated, especially for earlier time periods. Nevertheless, Anthromes 12K is a major advance over all prior anthrome datasets and provides a new platform for assessing the long-term environmental consequences of human transformation of the terrestrial biosphere

Anthropogenic Biomes: 10,000 BCE to 2015 CE

Human populations and their use of land have reshaped landscapes for thousands of years, creating the anthropogenic biomes (anthromes) that now cover most of the terrestrial biosphere. Here we introduce the first global reconstruction and mapping of anthromes and their changes across the 12,000-year interval from 10,000 BCE to 2015 CE; the Anthromes 12K dataset. Anthromes were mapped using gridded global estimates of human population density and land use from the History of the Global Environment database (HYDE version 3.2) by a classification procedure similar to that used for prior anthrome maps. Anthromes 12K maps generally agreed with prior anthrome maps for the same time periods, though significant differences were observed, including a substantial reduction in Rangelands anthromes in 2000 CE but with increases before that time. Differences between maps resulted largely from improvements in HYDE’s representation of land use, including pastures and rangelands, compared with the HYDE 3.1 input data used in prior anthromes maps. The larger extent of early land use in Anthromes 12K also agrees more closely with empirical assessments than prior anthrome maps; the result of an evidence-based paradigm shift in characterizing the history of Earth’s transformation through land use, from a mostly recent large-scale conversion of uninhabited wildlands, to a long-term trend of increasingly intensive transformation and use of already inhabited and used landscapes. The spatial history of anthropogenic changes depicted in Anthromes 12K remain to be validated, especially for earlier time periods. Nevertheless, Anthromes 12K is a major advance over all prior anthrome datasets and provides a new platform for assessing the long-term environmental consequences of human transformation of the terrestrial biosphere

Aquaculture Production is a Large, Spatially Concentrated Source of Nutrients in Chinese Freshwater and Coastal Seas

As Chinese aquaculture production accounts for over half of the global aquaculture production and has increased by 50% since 2006, there is growing concern about eutrophication caused by aquaculture in China. This paper presents a model-based estimate of nutrient flows in China's aquaculture system during 2006-2017 using provincial scale data, to spatially distribute nutrient loads with a 0.5° resolution. The results indicate that with the increase in fish and shellfish production from 30 to 47 million tonnes (Mt) during 2006-2017, the nitrogen (N) release increased from 1.3 to 2.1 Mt/year and that of phosphorus (P) from 0.14 to 0.23 Mt/year. Nutrient release from freshwater aquaculture was concentrated in Guangdong, Jiangsu, and Hubei, and that from mariculture in Shandong, Fujian, and Guangdong. Aquaculture is an important strongly concentrated nutrient source in both freshwater and marine environments. Its nutrient release is >20% of total nutrient inputs to freshwater environments in some provinces, and nutrients from mariculture are comparable to river nutrient export to Chinese coastal seas. Aquaculture production and nutrient excretions are now comparable to those of livestock production systems in China and need to be accounted for when analyzing causes of eutrophication and harmful algal blooms and possible mitigation strategies

Forms and subannual variability of nitrogen and phosphorus loading to global river networks over the 20th century

Nitrogen (N) and phosphorus (P) play a major role in the biogeochemical functioning of aquatic systems. N and P transfer to surface freshwaters has amplified during the 20th century, which has led to widespread eutrophication problems. The contribution of different sources, natural and anthropogenic, to total N and P loading to river networks has recently been estimated yearly using the Integrated Model to Assess the Global Environment - Global Nutrient Model (IMAGE-GNM). However, eutrophic events generally result from a combination of physicochemical conditions governed by hydrological dynamics and the availability of specific nutrient forms that vary at subyearly timescales. In the present study, we define for each simulated nutrient source: i) its speciation, and ii) its subannual temporal pattern. Thereby, we simulate the monthly loads of different N (ammonium, nitrate + nitrite, and organic N) and P forms (dissolved and particulate inorganic P, and organic P) to global river networks over the whole 20th century at a half-degree spatial resolution. Results indicate that, together with an increase in the delivery of all nutrient forms to global rivers, the proportion of inorganic forms in total N and P inputs has risen from 30 to 43% and from 56 to 65%, respectively. The high loads originating from fertilized agricultural lands and the increasing proportion of sewage inputs have led to a greater proportion of DIN forms (ammonium and nitrate), that are usually more bioavailable. Soil loss from agricultural lands, which delivers large amounts of particle-bound inorganic P to surface freshwaters, has become the dominant P source, which is likely to lead to an increased accumulation of legacy P in slow flowing areas (e.g., lakes and reservoirs). While the TN:TP ratio of the loads has remained quite stable, the DIN:DIP molar ratio, which is likely to affect algal development the most, has increased from 18 to 27 globally. Human activities have also affected the timing of nutrient delivery to surface freshwaters. Increasing wastewater emissions in growing urban areas induces constant local pressure on the quality of aquatic systems by delivering generally highly bioavailable nutrient forms, even in periods of low runoff

Forms and subannual variability of nitrogen and phosphorus loading to global river networks over the 20th century

Nitrogen (N) and phosphorus (P) play a major role in the biogeochemical functioning of aquatic systems. N and P transfer to surface freshwaters has amplified during the 20th century, which has led to widespread eutrophication problems. The contribution of different sources, natural and anthropogenic, to total N and P loading to river networks has recently been estimated yearly using the Integrated Model to Assess the Global Environment - Global Nutrient Model (IMAGE-GNM). However, eutrophic events generally result from a combination of physicochemical conditions governed by hydrological dynamics and the availability of specific nutrient forms that vary at subyearly timescales. In the present study, we define for each simulated nutrient source: i) its speciation, and ii) its subannual temporal pattern. Thereby, we simulate the monthly loads of different N (ammonium, nitrate + nitrite, and organic N) and P forms (dissolved and particulate inorganic P, and organic P) to global river networks over the whole 20th century at a half-degree spatial resolution. Results indicate that, together with an increase in the delivery of all nutrient forms to global rivers, the proportion of inorganic forms in total N and P inputs has risen from 30 to 43% and from 56 to 65%, respectively. The high loads originating from fertilized agricultural lands and the increasing proportion of sewage inputs have led to a greater proportion of DIN forms (ammonium and nitrate), that are usually more bioavailable. Soil loss from agricultural lands, which delivers large amounts of particle-bound inorganic P to surface freshwaters, has become the dominant P source, which is likely to lead to an increased accumulation of legacy P in slow flowing areas (e.g., lakes and reservoirs). While the TN:TP ratio of the loads has remained quite stable, the DIN:DIP molar ratio, which is likely to affect algal development the most, has increased from 18 to 27 globally. Human activities have also affected the timing of nutrient delivery to surface freshwaters. Increasing wastewater emissions in growing urban areas induces constant local pressure on the quality of aquatic systems by delivering generally highly bioavailable nutrient forms, even in periods of low runoff