Article

Global Nutrient Export from WaterSheds 2 (NEWS 2): Model Development and Implementation

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Abstract

Global NEWS is a global, spatially explicit, multi-element and multi-form model of nutrient exports by rivers. Here we present NEWS 2, the new version of Global NEWS developed as part of a Millennium Ecosystem Assessment scenario implementation from hindcast (1970) to contemporary (2000) and future scenario trajectories (2030 & 2050). We provide a detailed model description and present an overview of enhancements to input datasets, emphasizing an integrated view of nutrient form sub-models and contrasts with previous NEWS models (NEWS 1). An important difference with NEWS 1 is our unified model framework (multi-element, multi-form) that facilitates detailed watershed comparisons regionally and by element or form. NEWS 2 performs approximately as well as NEWS 1 while incorporating previously uncharacterized factors. Although contemporary global river export estimates for dissolved inorganic nitrogen (DIN) and particulates show notable reductions, they are within the range of previous studies; global exports for other nutrient forms are comparable to NEWS 1. NEWS 2 can be used as an effective tool to examine the impact of polices to reduce coastal eutrophication at regional to global scales. Continued enhancements will focus on the incorporation of other forms and sub-basin spatial variability in drivers and retention processes.

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... Another important modification to the OCMIP2 formulation is the inclusion of riverine inputs of phosphorus and carbon, and sedimentary burial fluxes to balance these inputs in steady-state. The riverine inputs of DIP, DOP, POP, DOC, and POC are prescribed following the second phase of the Global Nutrient Export from Watersheds (NEWS2) model (Mayorga et al., 2010). The riverine DIC flux is computed using the GEMS-GLORI database (Meybeck & Ragu, 2012) as described by Kwon et al. (2021). ...
... The global riverine P and C sources are placed into the surface grid cells adjacent to river mouths. With total phosphorus and carbon fluxes of 7.6 TgP/yr and 0.61 PgC/yr (Mayorga et al., 2010;Meybeck & Ragu, 2012), the riverine inputs represent only ∼1% of the global ocean export fluxes of POP. Therefore, the impact of riverine inputs on our estimates is likely to be small. ...
... The global database for alkalinity and dissolved inorganic carbon are from Lauvset et al. (2016) and available at http://cdiac.ornl.gov/oceans/GLODAPv2/. The riverine nutrients and organic carbon flux data are from Mayorga et al. (2010) and available at http://staff.washington.edu/emiliom/globalnews/GlobalNEWS-2ModeledExports_RH2000-version1.0.1.zip. The riverine inorganic carbon flux data are from Meybeck and Ragu (2012) and available at https://doi.org/10.1594/PANGAEA.804574. ...
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The stoichiometric carbon to phosphorus ratios (rC:P) in suspended particulate organic matter (POM) are generally inversely correlated with surface phosphate (PO4) concentration. However, it is uncertain if previously suggested relationships between rC:P and PO4 are appropriate for the vertical export flux of organic matter. Using a global steady‐state inverse ocean biogeochemistry model and annual‐mean observed tracers, we estimate optimal parameters for both linear and power law representations of rP:C (= 1/rC:P), and find rP:C = (0.0066 ± 0.0018) × [PO4] + (0.0053 ± 0.0010) and rP:C = (0.0112 ± 0.0018) × [PO4](0.36±0.07), respectively, where [PO4] is in μM. Both parameterizations allow us to fit global tracer observations equally well, but the power law model implies an up to 50% larger uptake rC:P in oligotrophic gyres. For both formulations, the POM export rC:P from the euphotic zone is nearly equal to the uptake rC:P, while the dissolved organic matter export rC:P is up to two times larger than the uptake rC:P. Although weakly constrained, our model suggests that in eutrophic regions the vertical organic P fluxes are attenuated faster with depth than the organic C fluxes. By contrast, in oligotrophic regions there are no discernible differences between the organic P and C flux‐attenuation profiles. As a result, the large spatial range of rC:P spanning 50–200 at the base of the euphotic zone is diminished to 110–160 at 2000 m depth. In oligotrophic regions at 150–500 m depths, our estimated export rC:P values are significantly lower than those measured with sediment traps, implying a potentially large modulation of export rC:P by migrating zooplankton within the twilight zone.
... This number of sub-basins is larger than in earlier studies. For example, Mayorga et al. (2010) focused on around 6000 basins. In our study, large basins are split into sub-basins (details are in Strokal et al., 2021a). ...
... Spatial variabilities in river pollution hotspots are comparable with other studies van Vliet et al., 2019;Mayorga et al., 2010;Vermeulen et al., 2019). For example, our river pollution hotspots in many sub-basins of Asia, South America, and Africa coincide with existing studies Vermeulen et al., 2019). ...
... Generally, river pollution hotspots (Fig. 5) are calculated for subbasins that also receive high manure inputs (Fig. 3). This is in line with other studies (e.g., Beusen et al., 2015;Mayorga et al., 2010;Bouwman et al., 2009). Studies show that areas with higher runoff generally receive more pollutants (Yang and Toor, 2018;Chen et al., 2018), which is also shown in our study for sub-basins. ...
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Livestock production is often a source of multiple pollutants in rivers. However, current assessments of water pollution seldomly take a multi-pollutant perspective, while this is essential for improving water quality. This study quantifies inputs of multiple pollutants to rivers from livestock production worldwide, by animal types and spatially explicit. We focus on nitrogen (N), phosphorus (P), and Cryptosporidium (pathogen). We developed the MARINA-Global-L (Model to Assess River Inputs of pollutaNts to seAs for Livetsock) model for 10,226 sub-basins and eleven livestock species. Global inputs to land from livestock are around 94 Tg N, 19 Tg P, and 2.9 × 10²¹ oocysts from Cryptosporidium in 2010. Over 57% of these amounts are from grazed animals. Asia, South America, and Africa account for over 68% of these amounts on land. The inputs to rivers are around 22 Tg Total Dissolved Nitrogen (TDN), 1.8 Tg Total Dissolved P (TDP), and 1.3 × 10²¹ oocysts in 2010. Cattle, pigs, and chickens are responsible for 74-88% of these pollutants in rivers. One-fourth of the global sub-basins can be considered pollution hotspots and contribute 71-95% to the TDN, TDP, and oocysts in rivers. Our study could contribute to effective manure management for individual livestock species in sub-basins to reduce multiple pollutants in rivers.
... Nutrient models exist to quantify nutrient pollution in water systems and their sources. Examples are the Global NEWS-2 (Nutrient Export from Watersheds) model on the basin scale (Mayorga et al., 2010), the family of the MARINA (Model to Assess River Inputs of Nutrients to seAs) models on the sub-basin scale for China (Strokal et al., 2016a;Wang et al., 2020b) and the IMAGE-GNM (Global Nutrient Model) model on a 0.5 • grid scale for the world (Beusen et al., 2015;Liu et al., 2018). The MARINA model for China accounts for direct discharges of animal manure, which is ignored in many other existing nutrient models. ...
... The following paragraphs explain how L F is calculated (details are in S1.2, SI). D F and FQrem are modified based on the approach of the Global NEWS-2 (Mayorga et al., 2010) and MARINA 1.0 and 2.0 models (Strokal et al., 2016a;Wang et al., 2020b) and explained in the S1.2 in SI. ...
... IMAGE-GNM (Beusen et al., 2015)). Our model is an intermediate, with a largely processed based approach and only a few calibrated parameters, in line with the earlier versions of the MARINA model and Global NEWS (Mayorga et al., 2010;Strokal et al., 2016a). A fully calibrated model at the scale of China is not preferred, because of lack of data. ...
Article
Nutrient pollution is a widespread problem in rivers in China. Managing nutrient pollution requires better knowledge of in-stream processes governing the surface water quality. As current nutrient models for China mainly focus on river export of nutrients to seas, in-stream surface water quality and their contributing sources and processes are, therefore not well understood. This requires accounting for combined effects of nutrient inputs to rivers from produced waste, biochemistry of different forms of nutrients and their transport by river network. Moreover, improvements can be made in evaluating the model performance of large-scale nutrient models based on water quality measurements in China (using the surface water quality classes from 1 to 6). The objective of this study is to quantify the spatial variation in in-stream water quality for nutrients, and associated sources, for water quality classes in China. Our new Model to Assess River Inputs of Nutrients to seAs (MARINA 3.0) for in-stream water quality distinguishes different nutrient forms including dissolved inorganic (DIN, DIP) and organic (DON, DOP) nitrogen and phosphorus and was applied for the year 2012. Our model simulations compare reasonably well with measurements across 155 river sections. Results show that between 12% and 66% of the streams are highly polluted (exceeding water quality class 3) and depending on nutrient form. Diffuse sources dominate in 76% of the streams for DIN. Point sources such as direct discharges of animal manure dominate in 46%–59% of the streams for DON, DIP and DOP. The dominant sources vary considerably between rivers and nutrient forms. This indicates the need account for nutrient forms in models and national monitoring programs. Our model results could support effective management to reduce nutrient pollution in China.
... et al., 2019;Schindler, 2006;Vollenweider, 1971). The study of Cosme and Hauschild (2017) estimated CFs for N in 66 large marine ecosystems (LMEs) and their corresponding watershed based on the global Nutrient Export from WaterSheds (NEWS) 2 model (Mayorga et al., 2010). However, a gridscale FF model for freshwater N is not available globally. ...
... N fate in soil and freshwater depends on its input, transport, and removal processes (Mayorga et al., 2010;Seitzinger et al., 2005). At any location on land, N is imported from applications, depositions, erosion, and fixation, and further transported to the freshwater. ...
... This research builds on previous studies, and it provides FFs of inland N emitted both from the soil and directly to freshwater. Previous research of Cosme et al. (2018) extracted hydrological parameters from the Global NEWS 2 model (Mayorga et al., 2010), in which the residence time was also used to estimate denitrification, and constructed a FF model for the global coast. Cosme et al. (2018) Cosme et al. (2018); Payen et al. (2021) also identified hotspots in the Ganges River and the Hudson Bay, while these are not hotspots according to our FFs or the ones of Cosme et al. (2018). ...
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Excessive nitrogen (N) use in agriculture, industry, and household waste leads to widespread N release throughout the environment, causing eutrophication in both freshwater and coastal areas. To better understand N-induced eutrophication and other N-use-related environmental impacts at the local scale, improvements in the spatial resolution of life cycle impact assessment measures are required. Here, we present a method to estimate gridded fate factors (FFs) at a half-degree resolution based on the Integrated Model to Assess the Global Environment-Global Nutrient Model to provide eutrophication indicators for global N-related manufacture, trade, and consumption in life cycle assessment. Across global freshwater systems, our cumulative FFs have a 5th percentile of 0.9 days and a 95th percentile of 184.0 days. Aggregated FFs for administrative units range from 0.3 days to 211.9 days. The hotspots of cumulative FFs are mainly distributed upstream of large reservoirs or lakes. On a global level, advection is the dominant process controlling the FF (69.7% of areas), followed by retention (29.0%), and water consumption (1.3%). N retention dominates in advection-favoring, high-discharge regions due to the high residence times, while water consumption tends to dominate water-scarce zones. The results demonstrate the importance of gridded information to assess eutrophication impacts, as it characterizes N emissions from anthropogenic sources at high spatial resolution in comparison to basin- or country-level assessments. Introducing soil–freshwater N fate complements existing P-related fates to improve global assessments of eutrophication. This article met the requirements for a Gold–Gold Badge JIE data openness badge described at http://jie.click/badges
... The conversion between different spatial scales is important for bridging the data demand of modeling and statistics or survey results for various nutrient sources (Beusen et al., 2015;Chen et al., 2019b). Common methods are averaging or convergence based on land use, which inevitably ignores local differences at smaller scales (Boumans et al., 2015;Mayorga et al., 2010). For example, Gross Domestic Production (GDP) and protein intake per capita have been applied to calculate human nutrient emission factors, and the disparity between rural and urban living standards has not been well represented (Strokal et al., 2016a;Wang et al., 2019b). ...
... The actual production coefficients and reuse ratio of rural domestic wastewater obtained from the Second National Pollution Source Survey of China were used in this study. In contrast to the existing models (Global NEWS-2 and IMAGE-GNM) (Beusen et al., 2015;Mayorga et al., 2010), the survey parameters and simple treatments at the county scale are more accurate in quantifying rural domestic nutrient production. Simple treatment refers to the harmless removal of nutrients by toilets, septic tanks, and other sanitation facilities (Cheng et al., 2018;Li et al., 2021). ...
Article
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A high-resolution nutrient emission inventory can provide reliable and accurate identification of priority control areas, which is crucial for efficient decisions on water quality restoration. However, the inventories widely used in large-scale modeling are usually based on provincial inputs, which induce the challenges of lacking localized parameters and missing localized characteristic when provincial scale inputs are converted to finer scales with the down-scale methods. Based on elaborate investigations and statistical data at the county scale with multi-scale data conversion, the China Emission Inventory of Nutrients (CEIN) was developed with a spatial resolution of a 0.1 • grid and sub-basin scales. The Yangtze River Basin was used as a case study to illustrate the potential applications of CEIN. The emissions of total nitrogen (TN) and total phosphorus (TP) of Yangtze River Basin is 0.43 Mt and 0.04 Mt for point sources, 11.09 Mt and 4.64 Mt for diffuse sources in 2017. The hotspot analysis for 2606 sub-basins indicated that cropland is the key source of nutrient emissions, accounting for 58.88% and 79.15% of TN and TP, respectively. Industrial sewage and freshwater aquaculture accounted for 27.39% (TN) and 21.98% (TP) of the point sources, which is substantial due to their direct discharge into surface waters. The current results also reveal that, in contrast to CEIN, the previously used common emission factors based on GDP per capita produced considerable overestimations of 2.37 and 2.65 times the actual TN and TP emissions, respectively. Additional advantages of the CEIN have been demonstrated in identifying priority control areas more accurately with reduced bias and quantifying the effects of policies at much smaller scales. For example, the CEIN helps to distinguish hotspots, which was neglected when identifying sources at the level-III sub-basin scale, and indicates that the management of fractional areas (TN: 16.97%; TP: 13.44%) provides the highest nutrient emissions control (TN: 44.34%; TP: 48.65%) for the entire basin. The evaluation of China's toilet revolution policy demonstrates that achieving equitable access to safe sanitation has resulted in a reduction of 7240 t of TN and 833 t of TP, which is extremely critical for rural water quality and health.
... Managing wastewater, particularly for non-sewered systems, has been a cornerstone of public health intervention around the world [22,23], and human sewage is known to contribute substantially to anthropogenic N inputs [24][25][26][27][28]. But the solution space for wastewater treatment can look very different for mitigating excess N input versus pathogen risk. ...
... Existing models that estimate nitrogen inputs or pathogen inputs to surface water from human sewage suffer from limitations. Global nutrient river export models that account for human sewage rely on coarse-grained (0.5 by 0.5 degree) input data, focus primarily on the largest watersheds, are limited to assessing input from sewered systems [25][26][27][28][29][34][35][36][37][38], and generally do not propagate inputs into coastal waters (instead focusing on watershed impacts). Yet, over 60% percent of the planet's population lack sewage connections (instead using open defecation, pit latrines, or septic tanks) [39], the vast majority (>99%) of the global coastline is not adjacent to the mouth of the largest watersheds [3], and coastal ecosystems are known to be sensitive to N inputs. ...
Article
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Coastal marine ecosystems face a host of pressures from both offshore and land-based human activity. Research on terrestrial threats to coastal ecosystems has primarily focused on agricultural runoff, specifically showcasing how fertilizers and livestock waste create coastal eutrophication, harmful algae blooms, or hypoxic or anoxic zones. These impacts not only harm coastal species and ecosystems but also impact human health and economic activities. Few studies have assessed impacts of human wastewater on coastal ecosystems and community health. As such, we lack a comprehensive, fine-resolution, global assessment of human sewage inputs that captures both pathogens and nutrient flows to coastal waters and the potential impacts on coastal ecosystems. To address this gap, we use a new high-resolution geospatial model to measure and map nitrogen (N) and pathogen—fecal indicator organisms (FIO)—inputs from human sewage for ~135,000 watersheds globally. Because solutions depend on the source, we separate nitrogen and pathogen inputs from sewer, septic, and direct inputs. Our model indicates that wastewater adds 6.2Tg nitrogen into coastal waters, which is approximately 40% of total nitrogen from agriculture. Of total wastewater N, 63% (3.9Tg N) comes from sewered systems, 5% (0.3Tg N) from septic, and 32% (2.0Tg N) from direct input. We find that just 25 watersheds contribute nearly half of all wastewater N, but wastewater impacts most coastlines globally, with sewered, septic, and untreated wastewater inputs varying greatly across watersheds and by country. Importantly, model results find that 58% of coral and 88% of seagrass beds are exposed to wastewater N input. Across watersheds, N and FIO inputs are generally correlated. However, our model identifies important fine-grained spatial heterogeneity that highlight potential tradeoffs and synergies essential for management actions. Reducing impacts of nitrogen and pathogens on coastal ecosystems requires a greater focus on where wastewater inputs vary across the planet. Researchers and practitioners can also overlay these global, high resolution, wastewater input maps with maps describing the distribution of habitats and species, including humans, to determine the where the impacts of wastewater pressures are highest. This will help prioritize conservation efforts.Without such information, coastal ecosystems and the human communities that depend on them will remain imperiled.
... This model provides spatially explicit fate factors describing N emissions to soil, freshwater, and marine systems. The CFs are derived from the NEWS2 model (Mayorga et al. 2010), which provides inland soil and freshwater fate for dissolved inorganic N at a watershed scale. In the Cosme et al. work, the residence time of N in the receiving marine systems is modeled as a function of advection and denitrification. ...
... • freshwater eutrophication due to P emissions to freshwater (Helmes et al. 2012), with a 0.5° × 0.5° grid cell resolution • marine eutrophication in large marine ecosystems (LMEs) due to nitrogen emissions to LMEs, inland freshwater, or inland soil (Cosme et al. 2017a), with an emission resolution of NEWS2 hydrological basins (Mayorga et al. 2010), and an impact resolution of LMEs (Sherman 2001). A large marine ecosystem is a region of ocean 200,000 km 2 or greater, including coastal areas from river basins and estuaries, ...
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PurposePrior versions of the Tool for Reduction and Assessment of Chemical and other environmental Impacts (TRACI) have recognized the need for spatial variability when characterizing eutrophication. However, the method’s underlying environmental models had not been updated to reflect the latest science. This new research provides the ability to differentiate locations with a high level of detail within the USA and provides global values at the country level.Methods In previous research (Morelli et al. 2018), the authors reviewed a broad range of domain-specific models and life cycle assessment methods for characterization of eutrophication and ranked these by levels of importance to the field and readiness for further development. The current research is rooted in the decision outcome of Morelli et al. (2018) to separate freshwater and marine eutrophication to allow for the most tailored characterization of each category individually. The current research also assumes that freshwater systems are limited by phosphorus and marine systems are limited by nitrogen. Using a combination of spatial modeling methods for soil, air, and water, we calculate midpoint characterization factors for freshwater and marine eutrophication categories and evaluate the results through a US-based case application.Results and discussionMaps of the nutrient inventories, characterization factors, and overall impacts of the case application illustrate the spatial variation and patterns in the results. The importance of variation in geographic location is demonstrated using nutrient-based activity likelihood categories of agricultural (rural fertilizer), non-agricultural (urban fertilizer), and general (human waste processing). Proximity to large bodies of water, as well as individual hydraulic residence times, was shown to affect the comparative values of characterization factors across the USA.Conclusions In this paper, we have calculated and applied finely resolved freshwater and marine eutrophication characterization factors for the USA and country-level factors for the rest of the globe. Additional research is needed to provide similarly resolved characterization factors for the entire globe, which would require expansion of publicly available data and further development of applicable fate and transport models. Further scientific advances may also be considered as computing capabilities become more sophisticated and widely accessible.
... Using the best combination of retention models for geographical zones (Supplementary Table S2), we simulated the global export to coastal waters of N and P are 30.5 and 5.8 Tg P yr −1 . For the global N export, our estimation is lower than those of NEWS-2 (45 Tg N yr −1 , Mayorga et al., 2010) and IMAGE-GNM (37 Tg N yr −1 , Beusen et al., 2016). The combination of retention models for various zones can better represent the realistic retention and results in a lower global export that is closer to observations. ...
... The combination of retention models for various zones can better represent the realistic retention and results in a lower global export that is closer to observations. For P, our estimation falls between the global export of NEWS-2 (9 Tg P yr −1 , Mayorga et al., 2010) and IMAGE-GNM (4 Tg P yr −1 , Beusen et al., 2016). Moreover, the best combination of P retention models avoids the bias caused by Wollheim et al. (2006) to predict zero P loads in the high-retention regions. ...
Article
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Against the backdrop of increasing agricultural production, population, and freshwater/coastal eutrophication, studies are aiming to understand the behavior of nitrogen (N) and phosphorus (P) in the global freshwater system. Global nutrient models are typically used to quantify the nutrient amount and content in freshwater systems across different river orders and catchments. Such models typically use empirically derived nutrient retention equations for predicting nutrient fate, and these equations may be derived using data from a specific region or environment or for a specific context. Here we used IMAGE-GNM, a spatially explicit nutrient model at a half-degree resolution, to examine the performance of several well-known empirical equations by comparing the respective model outcomes with observed data on a global scale. The results show that (1) globally, the empirical retention equations work better for predicting N fate than P fate; (2) hydraulic drivers are the most important factor affecting the residual of total N and P concentrations, compared with the functional forms and the coefficients in the empirical equations. This study can aid in assessing the variability and accuracy of various retention equations from regional to global scales, and thus further strengthen our understanding of global eutrophication.
... estimate the lateral carbon export by rivers to the coast minus the imports from rivers entering in each country (for relevant cases), including DOC, POC and DIC of atmospheric origin. Estimates of DOC, POC and DIC are obtained from the Global NEWS model(Mayorga et al., 2010), with a correction based onResplandy et al. (2018) so that the global total exported to the coastal ocean is 2.86 PgCO 2 yr −1 (0.78 PgC yr −1 ). perform a correction to the Global NEWS estimates to remove the contribution of lithogenic carbon, using the methodology ofCiais et al. (2021). ...
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Accurate accounting of emissions and removals of CO2 is critical for the planning and verification of emission reduction targets in support of the Paris Agreement. Here, we present a pilot dataset of country-specific net carbon exchange (NCE; fossil plus terrestrial ecosystem fluxes) and terrestrial carbon stock changes aimed at informing countries’ carbon budgets. These estimates are based on "top-down" NCE outputs from the v10 Orbiting Carbon Observatory (OCO-2) modeling intercomparison project (MIP), wherein an ensemble of inverse modeling groups conducted standardized experiments assimilating OCO-2 column-averaged dry-air mole fraction (XCO2) retrievals (ACOS v10), in situ CO2 measurements, or combinations of these data. The v10 OCO-2 MIP NCE estimates are combined with "bottom-up" estimates of fossil fuel emissions and lateral carbon fluxes to estimate changes in terrestrial carbon stocks, which are impacted by anthropogenic and natural drivers. These flux and stock change estimates are reported annually (2015–2020) as both a global 1° × 1° gridded dataset and as a country-level dataset. Across the v10 OCO-2 MIP experiments, we obtain increases in the ensemble median terrestrial carbon stocks of 3.29–4.58 PgCO2 yr-1 (0.90–1.25 PgC yr-1). This is a result of broad increases in terrestrial carbon stocks across the northern extratropics, while the tropics generally have stock losses but with considerable regional variability and differences between v10 OCO-2 MIP experiments. We discuss the state of the science for tracking emissions and removals using top-down methods, including current limitations and future developments towards top-down monitoring and verification systems.
... Biogeochemical riverine inputs, when included, primarily rely on external river export models, including the Integrated Model to Assess the Global Environment-Global Nutrient Model (IMAGE-GNM) (Beusen et al., 2015(Beusen et al., , 2016, the Global Nutrient Export from Watersheds (NEWS) model (Seitzinger et al., 2005;Mayorga et al., 2010), and the Global Erosion Model (GEM) (Ludwig and Probst, 1996). ...
Article
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Climate change may impact ocean ecosystems through a number of mechanisms, including shifts in primary productivity or plankton community structure, ocean acidification, and deoxygenation. These processes can be simulated with global Earth system models (ESMs), which are increasingly being used in the context of fisheries management and other living marine resource (LMR) applications. However, projections of LMR-relevant metrics such as net primary production can vary widely between ESMs, even under identical climate scenarios. Therefore, the use of ESM should be accompanied by an understanding of the structural differences in the biogeochemical sub-models within ESMs that may give rise to these differences. This review article provides a brief overview of some of the most prominent differences among the most recent generation of ESM and how they are relevant to LMR application.
... In addition to the models for determining the efficient application of fertilizers, the determination of the phosphorus transported from cropfields to waterbodies provides key information for determining what areas are more vulnerable to nutrient pollution, and in turn to define the areas where the phosphorus supply must be more severely controlled and more resources should be directed to control its accumulation and release. Different phosphorus fate and transport models have been proposed in the literature, including but not limited to Spatially Referenced Regression on Watershed Attributes (SPARROW) (Smith et al., 1997), Nutrient Export from Watersheds 2 (NEWS 2) (Mayorga et al., 2010), Soil and Water Assessment Tool (SWAT) (Arnold et al., 1998), and Erosion Productivity Impact Calculator (EPIC) (Sharpley, 1990). These models have the potential of being integrated into wider frameworks in order to perform integrated analysis of phosphorus fluxes in a certain area, and different applications of these models have been explored for determining significant contributors to phosphorus releases at watershed level under uncertainty (Kim et al., 2017), as well as the contribution of nutrient flows from croplands, weather patterns and other environmental factors in the occurrence of harmful algal blooms (HABs) and the mitigating effect of implementing phosphorus recovery processes (Hu et al., 2019). ...
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The intensification of agricultural systems has increased the food production efficiency, increasing the productivity while the production costs are reduced. Although these factors are key to global food security in a context of continued human population growth, the use of intensive agricultural techniques results in different environmental issues. Mitigating these negative impacts is a requirement for adopting sustainable food production systems. Notably, nutrient pollution is one of the main environmental issues associated with both livestock and crop production. These activities result in different point and non-point source releases of phosphorus, which eventually reach surface and ground waterbodies. This might result in the accumulation of phosphorus over time, contributing to the eutrophication of water ecosystems, and the development of harmful algal bloom (HABs) episodes. The releases of nutrients from agricultural activities can be abated through different management strategies, including the implementation of nutrient recovery techniques at livestock facilities, embracing precision fertilization methods, and developing integrated crop-livestock systems for achieving circular food production systems. In this work, we describe opportunities for Process System Engineering (PSE) to address the development of phosphorus management techniques for mitigating phosphorus pollution from agricultural systems balancing trade-offs between recovery cost and environmental impact mitigation. These techniques integrate the spatial analysis of nutrient pollution from agriculture using geographical information systems (GIS) with the assessment and the selection of phosphorus management techniques combining techno-economic analysis (TEA) and environmental metrics through multi-criteria decision analysis (MCDA) frameworks, and use mathematical programming for the conceptual design of integrated crop-livestock systems.
... Phytoplankton growth is controlled by nutrients, light availability and water temperature. In the version of the model we used, river supply to the ocean of all elements apart from dissolved inorganic carbon and alkalinity is taken from the GLOBAL-NEWS2 datasets 76 and does not vary from one simulation to another. Model parameterizations are detailed in a previous report 6 . ...
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Although the role of Earth’s orbital variations in driving global climate cycles has long been recognized, their effect on evolution is hitherto unknown. The fossil remains of coccolithophores, a key calcifying phytoplankton group, enable a detailed assessment of the effect of cyclic orbital-scale climate changes on evolution because of their abundance in marine sediments and the preservation of their morphological adaptation to the changing environment1,2. Evolutionary genetic analyses have linked broad changes in Pleistocene fossil coccolith morphology to species radiation events³. Here, using high-resolution coccolith data, we show that during the last 2.8 million years the morphological evolution of coccolithophores was forced by Earth’s orbital eccentricity with rhythms of around 100,000 years and 405,000 years—a distinct spectral signature to that of coeval global climate cycles⁴. Simulations with an Earth System Model⁵ coupled with an ocean biogeochemical model⁶ show a strong eccentricity modulation of the seasonal cycle, which we suggest directly affects the diversity of ecological niches that occur over the annual cycle in the tropical ocean. Reduced seasonality in surface ocean conditions favours species with mid-size coccoliths, increasing coccolith carbonate export and burial; whereas enhanced seasonality favours a larger range of coccolith sizes and reduced carbonate export. We posit that eccentricity pacing of phytoplankton evolution contributed to the strong 405,000-year cyclicity that is seen in global carbon cycle records.
... Physical process-based models e.g., SWAT, AGNPS, HSPF can simulate nutrient cycling and pathways with high accuracy but require numerous parameters in the fitting process (Arhonditsis et al., 2007;Hashemi et al., 2016;Ding et al., 2010;Mayorga et al., 2010;Singh et al., 2005). Furthermore, in karst basins, the complex subsurface system is comprised of karst pipelines, caves and fissures, which can facilitate the leakage of surface water to groundwater resulting in high uncertainty with respect to unknown nutrient flow pathways (Song et al., 2019;Fiorillo et al., 2015;Jiang et al., 2014). ...
Article
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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 ecosystem coupling 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) and simple 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.
... Our results are also important from a water resources management perspective because they may contribute to global nutrient exportation models in larger watersheds (Kroeze et al., 2012). In general, such models usually focus on non-point pollution sources such as urban and agriculture runoff influencing retention and transport of nutrients along river networks (but see Mayorga et al., 2010). However, studies have indicated that point sources (e.g., WWTPs effluents) may also be a relevant driver of nutrient availability and quality impairment in rivers (Carey and Migliaccio, 2009;Hutchins et al., 2018). ...
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Riparian areas are recognized for their buffering capacity regarding phosphorus and nitrogen from agricultural and urban runoff. However, their role in attenuating nutrient loads of rivers receiving point source nutrient inputs (e.g., from wastewater treatment plants, WWTPs) is still little understood. Here, we investigated whether ammonium (NH4-N), nitrate (NO3-N), and soluble reactive phosphorus (SRP) retention were influenced by the riparian land use in three Brazilian rivers receiving WWTP effluents. We hypothesized that nutrient attenuation would be potentially influenced by the hydrological connectivity between the main channel and riparian areas with native vegetation. We estimated retention from longitudinal patterns of dilution-corrected nutrient concentrations below the WWTPs. We assessed nutrient retention during periods with high (i.e., the wet) and low connectivity (i.e., the dry season). Relationships between non-conservative (nutrients) and conservative (chloride) solutes in both seasons were used to identify potential changes in the river chemistry due to the hydrological connectivity with the riparian areas. We also evaluated the relationship between net uptake velocities (Vf-net) and the accumulated percent native vegetation cover in the 100-m buffer using linear regressions, comparing the response for each nutrient between seasons with Analysis of Covariance. Slopes of regressions between nutrients and chloride significantly differed between seasons for NO3-N and SRP but not for NH4-N. The relationships between Vf-net and accumulated native vegetation in the riparian buffer presented steeper slopes for SRP in the wet than in the dry season. No significant relationships between NO3-N Vf-net and native vegetation cover were observed in either season. In contrast, increases in V f-net with increasing vegetation cover were observed for NH4-N in the dry season. In periods with expected higher connectivity, NO3-N and SRP concentrations tended to be lower relative to chloride concentrations, with a potential effect of native vegetation in the riparian area on SRP retention. Our results suggest that seasonal connectivity between nutrient-rich river water and riparian areas is likely to induce changes in the predominant nutrient transformation processes, thereby favoring either nutrient retention or export in such rivers.
... However, they should capture the broad effect of climate on chemical weathering rates (Phillips & Cowling, 2019; and the effect of runoff on flowpath and dilution . Importantly, agricultural, urban, and atmospheric pollution were not considered here and could be key determinants of constituents such as nitrogen (Bouwman et al., 2009;Mayorga et al., 2010), particularly in the southern and central NPCTR where watersheds have more human population, industry, and agriculture . Human-alteration of watersheds may also play a changing role in determining spatial patterns of streamflow and DOC dynamics (e.g., Lajtha & Jones, 2018). ...
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Watershed classification has long been a key tool in the hydrological sciences, but few studies have been extended to biogeochemistry. We developed a combined hydro-biogeochemical classification for watersheds draining to the coastal margin of the Northeast Pacific coastal temperate rainforest (1,443,062 km2), including 2,695 small coastal rivers (SCR) and 10 large continental watersheds. We used cluster analysis to group SCR watersheds into 12 types, based on watershed properties. The most important variables for distinguishing SCR watershed types were evapotranspiration, slope, snowfall, and total precipitation. We used both streamflow and dissolved organic carbon (DOC) measurements from rivers (n = 104 and 90 watersheds respectively) to validate the classification. Watershed types corresponded with broad differences in streamflow regime, mean annual runoff, DOC seasonality, and mean DOC concentration. These links between watershed type and river conditions enabled the first region-wide empirical characterization of river hydro-biogeochemistry at the land-sea margin, spanning extensive ungauged and unsampled areas. We found very high annual runoff (mean > 3000 mm, n = 10) in three watershed types totaling 59,024 km2 and ranging from heavily glacierized mountain watersheds with high flow in summer to a rain-fed mountain watershed type with high flow in fall-winter. DOC hotspots (mean > 4 mg L-1, n = 14) were found in three other watershed types (48,557 km2) with perhumid rainforest climates and less-mountainous topography. We described four patterns of DOC seasonality linked to watershed hydrology, with fall-flushing being widespread. Hydro-biogeochemical watershed classification may be useful for other complex regions with sparse observation networks.
... One of the main challenges for global water quality modeling is the lack of spatial consistency in datasets for model inputs, especially in regions where data are insufficient for a detailed assessment Kroeze et al., 2016). Due to the limited information on global wastewater, all published global water quality models until now (e.g., GLOBAL-FATE, Global NEWS, WorldQual, GlowPa, and IMAGE-GNM) quantify the load of wastewater into the river system using population density and national sanitation statistics as proxies (e.g., Font et al., 2019;Strokal et al., 2019;Mayorga et al., 2010;Van Drecht et al., 2009;Williams et al., 2012;Beusen et al., 2015;Hofstra et al., 2013). More specifically, calculations are typically based on the fractions of population connected to sewage systems per country. ...
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The main objective of wastewater treatment plants (WWTPs) is to remove pathogens, nutrients, organics, and other pollutants from wastewater. After these contaminants are partially or fully removed through physical, biological, and/or chemical processes, the treated effluents are discharged into receiving waterbodies. However, since WWTPs cannot remove all contaminants, especially those of emerging concern, they inevitably represent concentrated point sources of residual contaminant loads into surface waters. To understand the severity and extent of the impact of treated-wastewater discharges from such facilities into rivers and lakes, as well as to identify opportunities of improved management, detailed information about WWTPs is required, including (1) their explicit geospatial locations to identify the waterbodies affected and (2) individual plant characteristics such as the population served, flow rate of effluents, and level of treatment of processed wastewater. These characteristics are especially important for contaminant fate models that are designed to assess the distribution of substances that are not typically included in environmental monitoring programs. Although there are several regional datasets that provide information on WWTP locations and characteristics, data are still lacking at a global scale, especially in developing countries. Here we introduce a spatially explicit global database, termed HydroWASTE, containing 58 502 WWTPs and their characteristics. This database was developed by combining national and regional datasets with auxiliary information to derive or complete missing WWTP characteristics, including the number of people served. A high-resolution river network with streamflow estimates was used to georeference WWTP outfall locations and calculate each plant's dilution factor (i.e., the ratio of the natural discharge of the receiving waterbody to the WWTP effluent discharge). The utility of this information was demonstrated in an assessment of the distribution of treated wastewater at a global scale. Results show that 1 200 000 km of the global river network receives wastewater input from upstream WWTPs, of which more than 90 000 km is downstream of WWTPs that offer only primary treatment. Wastewater ratios originating from WWTPs exceed 10 % in over 72 000 km of rivers, mostly in areas of high population densities in Europe, the USA, China, India, and South Africa. In addition, 2533 plants show a dilution factor of less than 10, which represents a common threshold for environmental concern. HydroWASTE can be accessed at https://doi.org/10.6084/m9.figshare.14847786.v1 (Ehalt Macedo et al., 2021).
... Initial conditions for the ocean biogeochemistry were set in agreement with the OMIP-BGC protocols (Orr et al., 2017) and forcing fields for nitrogen deposition and atmospheric carbon dioxide were fixed to the year 1,850 reference values. Climatological river loads were set using estimates from Mayorga et al. (2010). This component was spun up for 300 years in offline mode forced by dynamical fields obtained from the first 10 years of the CMCC-CM2-SR5 piControl simulation (Lovato & Peano, 2020). ...
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This article introduces the second generation CMCC Earth System Model (CMCC‐ESM2) that extends a number of marine and terrestrial biogeochemical processes with respect to its CMIP5 predecessor. In particular, land biogeochemistry was extended to a wider set of carbon pools and plant functional types, along with a prognostic representation of the nitrogen cycle. The marine ecosystem representation was reshaped toward an intermediate complexity of lower trophic level interactions, including an interactive benthic compartment and a new formulation of heterotrophic bacterial population. Details are provided on the model setup and implementation for the different experiments performed as contribution to the sixth phase of the Coupled Model Intercomparison Project. CMCC‐ESM2 shows an equilibrium climate sensitivity of 3.57°C and a transient climate response of 1.97°C which are close to the CMIP5 and CMIP6 multi‐model averages. The evaluation of the coupled climate‐carbon response in the historical period against available observational datasets show a consistent representation of both physical and biogeochemical quantities. However, the land carbon sink is found to be weaker than the current global carbon estimates and the simulated marine primary production is slightly below the satellite‐based average over recent decades. Future projections coherently show a prominent global warming over the northern hemisphere with intensified precipitations at high latitudes. The expected ranges of variability for oceanic pH and oxygen, as well as land carbon and nitrogen soil storage, compare favorably with those assessed from other CMIP6 models.
... Riverine nutrient (N, P, Si, and Fe), dissolved inorganic carbon, alkalinity, and DOM fluxes are supplied to the CESM2 ocean model from a data set, which includes nutrient loading estimates from GlobalNEWS (Mayorga et al., 2010) and the Integrated Model to Assess the Global Environment-Global Nutrient Model (IMAGE-GNM) (Beusen et al., 2015(Beusen et al., , 2016. Nutrient inputs are provided for dissolved inorganic nitrogen (DIN), phosphorus (DIP), Si and Fe, as well as dissolved organic nitrogen and phosphorus. ...
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The Marine Biogeochemistry Library (MARBL) is a prognostic ocean biogeochemistry model that simulates marine ecosystem dynamics and the coupled cycles of carbon, nitrogen, phosphorus, iron, silicon, and oxygen. MARBL is a component of the Community Earth System Model (CESM); it supports flexible ecosystem configuration of multiple phytoplankton and zooplankton functional types; it is also portable, designed to interface with multiple ocean circulation models. Here, we present scientific documentation of MARBL, describe its configuration in CESM2 experiments included in the Coupled Model Intercomparison Project version 6 (CMIP6), and evaluate its performance against a number of observational data sets. The model simulates present‐day air‐sea CO2 flux and many aspects of the carbon cycle in good agreement with observations. However, the simulated integrated uptake of anthropogenic CO2 is weak, which we link to poor thermocline ventilation, a feature evident in simulated chlorofluorocarbon distributions. This also contributes to larger‐than‐observed oxygen minimum zones. Moreover, radiocarbon distributions show that the simulated circulation in the deep North Pacific is extremely sluggish, yielding extensive oxygen depletion and nutrient trapping at depth. Surface macronutrient biases are generally positive at low latitudes and negative at high latitudes. CESM2 simulates globally integrated net primary production (NPP) of 48 Pg C yr⁻¹ and particulate export flux at 100 m of 7.1 Pg C yr⁻¹. The impacts of climate change include an increase in globally integrated NPP, but substantial declines in the North Atlantic. Particulate export is projected to decline globally, attributable to decreasing export efficiency associated with changes in phytoplankton community composition.
... These fluxes determine the carbon budget of the aquatic coastal margin ecosystems, and we recommend that they should also be considered "blue carbon". River C fluxes at the river mouth into estuaries can be estimated from dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and particulate organic carbon (POC) concentration data for the rivers involved and the associated river flow rates (Ludwig et al., 1998;Mayorga et al., 2010;Dai et al., 2012). Few RECCAP2 regions ( Fig. 1) receive C from rivers entering their territory. ...
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Regional land carbon budgets provide insights into the spatial distribution of the land uptake of atmospheric carbon dioxide and can be used to evaluate carbon cycle models and to define baselines for land-based additional mitigation efforts. The scientific community has been involved in providing observation-based estimates of regional carbon budgets either by downscaling atmospheric CO2 observations into surface fluxes with atmospheric inversions, by using inventories of carbon stock changes in terrestrial ecosystems, by upscaling local field observations such as flux towers with gridded climate and remote sensing fields, or by integrating data-driven or process-oriented terrestrial carbon cycle models. The first coordinated attempt to collect regional carbon budgets for nine regions covering the entire globe in the RECCAP-1 project has delivered estimates for the decade 2000–2009, but these budgets were not comparable between regions due to different definitions and component fluxes being reported or omitted. The recent recognition of lateral fluxes of carbon by human activities and rivers that connect CO2 uptake in one area with its release in another also requires better definitions and protocols to reach harmonized regional budgets that can be summed up to a globe scale and compared with the atmospheric CO2 growth rate and inversion results. In this study, using the international initiative RECCAP-2 coordinated by the Global Carbon Project, which aims to be an update to regional carbon budgets over the last 2 decades based on observations for 10 regions covering the globe with a better harmonization than the precursor project, we provide recommendations for using atmospheric inversion results to match bottom-up carbon accounting and models, and we define the different component fluxes of the net land atmosphere carbon exchange that should be reported by each research group in charge of each region. Special attention is given to lateral fluxes, inland water fluxes, and land use fluxes.
... Another platform for the potential upscaling of denitrification studies is modeling studies. Nitrogen processing models such as Global NEWS (Mayorga et al., 2010) and nutrient loading models such as PCLake+ (Janssen et al., 2019) and VEMALA (Huttunen et al., 2016), often include denitrification as a nitrogen conversion term. Moreover, other ecosystem models such as the MyLake-Sediment model (Markelov et al., 2019) and the terrestrial NEMIS model (Hénault & Germon, 2000), even use (derivatives of) Q10-values to describe the temperature sensitivity of denitrification. ...
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Freshwater denitrification removes a considerable amount of nitrogen from inland waters, which are under pressure from eutrophication and warming. However, incomplete denitrification can lead to the formation of N2O, a potent greenhouse gas, which can amplify climatic warming. Although temperature effects on denitrification are well studied in individual habitats and experiments, global patterns in temperature‐responses of denitrification and N2O emissions remain to be elucidated. Here, we investigated the temperature sensitivity (Q10) of denitrification and N2O emissions in freshwater ecosystems worldwide, using a meta‐analytic approach. To this end, Q10 values from in‐situ and temperature manipulation studies were related to environmental nutrient conditions, O2, pH, sediment organic matter (SOM), and geographic location. Temperature sensitivity of denitrification displayed a strong positive correlation with environmental nitrogen concentrations, pH and O2. Significant correlations with SOM and SOM:N ratios were observed as well, but the direction of the effect differed between in‐situ and temperature manipulation studies. Surprisingly, temperature sensitivity of N2O emissions did not correlate with pH, SOM, nutrient or O2 conditions. Temperature sensitivity of the ratio between N2O emission and NO3⁻ concentration (adapted EF5 values) was 6.6 times higher in Australia and New Zealand compared to other geographic regions. As global temperatures and nitrogen deposition in freshwater ecosystems are expected to increase over the coming decades, our results suggest enhanced future denitrification, which may present a natural way to balance eutrophication. The observed temperature sensitivity of N2O emission factors, however, may indicate enhanced denitrification‐derived N2O emissions from freshwater ecosystems in a future warmer world.
... For this study, we updated the scheme employed to compute the river supply of nutrients and other elements because the palaeogeography was significantly different from that of the present day 56 . In the original version, the delivery of elements is fixed, and the model uses results from the Global Erosion Model 57 for dissolved inorganic carbon and alkalinity or GLOBAL-NEWS2 datasets 58 for other elements. Here, the riverine nutrient input to the ocean was calculated as the simulated model runoff multiplied by the riverine concentration for each element. ...
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The drivers of the evolution of the South Asian Monsoon remain widely debated. An intensification of monsoonal rainfall recorded in terrestrial and marine sediment archives from the earliest Miocene (23–20 million years ago (Ma)) is generally attributed to Himalayan uplift. However, Indian Ocean palaeorecords place the onset of a strong monsoon around 13 Ma, linked to strengthening of the southwesterly winds of the Somali Jet that also force Arabian Sea upwelling. Here we reconcile these divergent records using Earth system model simulations to evaluate the interactions between palaeogeography and ocean–atmosphere dynamics. We show that factors forcing the South Asian Monsoon circulation versus rainfall are decoupled and diachronous. Himalayan and Tibetan Plateau topography predominantly controlled early Miocene rainfall patterns, with limited impact on ocean–atmosphere circulation. The uplift of the East African and Middle Eastern topography played a pivotal role in the establishment of the modern Somali Jet structure above the western Indian Ocean, while strong upwelling initiated as a direct consequence of the emergence of the Arabian Peninsula and the onset of modern-like atmospheric circulation. Our results emphasize that although elevated rainfall seasonality was probably a persistent feature since the India–Asia collision in the Paleogene, modern-like monsoonal atmospheric circulation only emerged in the late Neogene. A modern-like South Asian Monsoon only appeared when East African and Middle Eastern uplift led to the establishment of the Somali Jet around 13 million years ago, according to Earth system modelling using a range of regional palaeogeographies.
... Tropical coastal waters are often considered nutrient-poor because shelf seas exchange large volumes of water with adjacent nutrient-poor open oceans (Brunskill, 2010). However, they also receive more than half of the global river input of freshwater, nutrients, and dissolved organic matter (Dai et al., 2012;Jennerjahn, 2012;Mayorga et al., 2010). Nutrient concentrations and ratios delivered by tropical rivers can be different from temperate regions: for example, tropical rivers typically have higher dissolved silicon concentrations (Jennerjahn et al., 2006). ...
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Coastal tropical waters are experiencing rapid increases in anthropogenic pressures, yet coastal biogeochemical dynamics in the tropics are poorly studied. We present a multi-year biogeochemical time series from the Singapore Strait in Southeast Asia's Sunda Shelf Sea. Despite being highly urbanised and a major shipping port, the strait harbours numerous biologically diverse habitats and is a valuable system for understanding how tropical marine ecosystems respond to anthropogenic pressures. We observed strong seasonality driven by the semi-annual reversal of ocean currents: dissolved inorganic nitrogen (DIN) and phosphorus varied from ≤0.05 μmol l⁻¹ during the intermonsoons to ≥4 μmol l⁻¹ and ≥0.25 μmol l⁻¹, respectively, during the southwest monsoon. Si(OH)4 exceeded DIN year-round. Based on nutrient concentrations, their relationships to salinity and coloured dissolved organic matter, and the isotopic composition of NOx⁻, we infer that terrestrial input from peatlands is the main nutrient source. This input delivered dissolved organic carbon (DOC) and nitrogen, but was notably depleted in dissolved organic phosphorus. In contrast, particulate organic matter showed little seasonality, and the δ¹³C of particulate organic carbon (−21.0 ± 1.5‰) is consistent with a primarily autochthonous origin. The seasonal pattern of the diel changes in dissolved O2 suggests that light availability controls primary productivity more than nutrient concentrations. However, diel changes in pH were greater during the southwest monsoon, when remineralisation of terrestrial DOC lowers the seawater buffer capacity. We conclude that terrestrial input results in mesotrophic conditions, and that the strait might undergo further eutrophication if nutrient inputs increase during seasons when light availability is high. Moreover, the remineralisation of terrestrial DOC within the Sunda Shelf may enhance future ocean acidification.
... We estimated the lateral carbon export by rivers minus the imports from rivers entering each country, including dissolved organic carbon, particulate organic carbon, and dissolved inorganic carbon of atmospheric origin distinguished from that of lithogenic origin, by using the data and methodology described by . Data are from Mayorga et al. (2010) and Hartmann et al. (2009) and follow the approach of proposed for large regions but here with new data at a national scale. Over a country that only exports river carbon, the amount of carbon exported is equivalent to an atmospheric CO 2 sink, denoted as F rivers tot as in Eq. (1), thus ignoring burial, which is a small term. ...
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In support of the global stocktake of the Paris Agreement on climate change, this study presents a comprehensive framework to process the results of an ensemble of atmospheric inversions in order to make their net ecosystem exchange (NEE) carbon dioxide (CO2) flux suitable for evaluating national greenhouse gas inventories (NGHGIs) submitted by countries to the United Nations Framework Convention on Climate Change (UNFCCC). From inversions we also deduced anthropogenic methane (CH4) emissions regrouped into fossil and agriculture and waste emissions, as well as anthropogenic nitrous oxide (N2O) emissions. To compare inversion results with national reports, we compiled a new global harmonized database of emissions and removals from periodical UNFCCC inventories by Annex I countries, and from sporadic and less detailed emissions reports by non-Annex I countries, given by national communications and biennial update reports. No gap filling was applied. The method to reconcile inversions with inventories is applied to selected large countries covering ∼90 % of the global land carbon uptake for CO2 and top emitters of CH4 and N2O. Our method uses results from an ensemble of global inversions produced by the Global Carbon Project for the three greenhouse gases, with ancillary data. We examine the role of CO2 fluxes caused by lateral transfer processes from rivers and from trade in crop and wood products and the role of carbon uptake in unmanaged lands, both not accounted for by NGHGIs. Here we show that, despite a large spread across the inversions, the median of available inversion models points to a larger terrestrial carbon sink than inventories over temperate countries or groups of countries of the Northern Hemisphere like Russia, Canada and the European Union. For CH4, we find good consistency between the inversions assimilating only data from the global in situ network and those using satellite CH4 retrievals and a tendency for inversions to diagnose higher CH4 emission estimates than reported by NGHGIs. In particular, oil- and gas-extracting countries in central Asia and the Persian Gulf region tend to systematically report lower emissions compared to those estimated by inversions. For N2O, inversions tend to produce higher anthropogenic emissions than inventories for tropical countries, even when attempting to consider only managed land emissions. In the inventories of many non-Annex I countries, this can be tentatively attributed to a lack of reporting indirect N2O emissions from atmospheric deposition and from leaching to rivers, to the existence of natural sources intertwined with managed lands, or to an underestimation of N2O emission factors for direct agricultural soil emissions. Inversions provide insights into seasonal and interannual greenhouse gas fluxes anomalies, e.g., during extreme events such as drought or abnormal fire episodes, whereas inventory methods are established to estimate trends and multi-annual changes. As a much denser sampling of atmospheric CO2 and CH4 concentrations by different satellites coordinated into a global constellation is expected in the coming years, the methodology proposed here to compare inversion results with inventory reports (e.g., NGHGIs) could be applied regularly for monitoring the effectiveness of mitigation policy and progress by countries to meet the objective of their pledges. The dataset constructed by this study is publicly available at https://doi.org/10.5281/zenodo.5089799 (Deng et al., 2021).
... Our treatment of freshwater runoff along the coastal zone, and from the Greenland and Antarctic Ice Sheets, is coarsely represented and does not capture IAV (Fekete et al., 2002). Furthermore, we do not include biogeochemical runoff (i.e., DIC and nutrients, Mayorga et al., 2010), which may be critical for accurate simulation of Arctic Ocean biogeochemistry (Le Fouest et al., 2013Fouest et al., , 2015. Future efforts should incorporate time-varying, point-source global freshwater (Feng et al., 2021) and biogeochemical runoff (Resplandy et al., 2018) to improve the simulated ocean sink in coastal (Chen et al., 2013) and high-latitude regions (Hopwood et al., 2018(Hopwood et al., , 2020Wadham et al., 2019). ...
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The inventory and variability of oceanic dissolved inorganic carbon (DIC) is driven by the interplay of physical, chemical, and biological processes. Quantifying the spatiotemporal variability of these drivers is crucial for a mechanistic understanding of the ocean carbon sink and its future trajectory. Here, we use the Estimating the Circulation and Climate of the Ocean‐Darwin ocean biogeochemistry state estimate to generate a global‐ocean, data‐constrained DIC budget and investigate how spatial and seasonal‐to‐interannual variability in three‐dimensional circulation, air‐sea CO2 flux, and biological processes have modulated the ocean sink for 1995–2018. Our results demonstrate substantial compensation between budget terms, resulting in distinct upper‐ocean carbon regimes. For example, boundary current regions have strong contributions from vertical diffusion while equatorial regions exhibit compensation between upwelling and biological processes. When integrated across the full ocean depth, the 24‐year DIC mass increase of 64 Pg C (2.7 Pg C year⁻¹) primarily tracks the anthropogenic CO2 growth rate, with biological processes providing a small contribution of 2% (1.4 Pg C). In the upper 100 m, which stores roughly 13% (8.1 Pg C) of the global increase, we find that circulation provides the largest DIC gain (6.3 Pg C year⁻¹) and biological processes are the largest loss (8.6 Pg C year⁻¹). Interannual variability is dominated by vertical advection in equatorial regions, with the 1997–1998 El Niño‐Southern Oscillation causing the largest year‐to‐year change in upper‐ocean DIC (2.1 Pg C). Our results provide a novel, data‐constrained framework for an improved mechanistic understanding of natural and anthropogenic perturbations to the ocean sink.
... For this study, we updated the scheme employed to compute the river supply of nutrients and other elements because the palaeogeography was significantly different from that of the present day 56 . In the original version, the delivery of elements is fixed, and the model uses results from the Global Erosion Model 57 for dissolved inorganic carbon and alkalinity or GLOBAL-NEWS2 datasets 58 for other elements. Here, the riverine nutrient input to the ocean was calculated as the simulated model runoff multiplied by the riverine concentration for each element. ...
Article
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In the modern northern Indian Ocean, biological productivity is intimately linked to near-surface oceanographic dynamics forced by the South Asian, or Indian, monsoon. In the late Pleistocene, this strong seasonal signal is transferred to the sedimentary record in the form of strong variance in the precession band (19–23 kyr), because precession dominates low-latitude insolation variations and drives seasonal contrast in oceanographic conditions. In addition, internal climate system feedbacks (e.g. ice-sheet albedo, carbon cycle, topography) play a key role in monsoon variability. Little is known about orbital-scale monsoon variability in the pre-Pleistocene, when atmospheric CO2 levels and global temperatures were higher. In addition, many questions remain open regarding the timing of the initiation and intensification of the South Asian monsoon during the Miocene, an interval of significant global climate change that culminated in bipolar glaciation. Here, we present new high-resolution (
... Then, we calculated the sub-basin-specific water discharges by subtracting the upstream discharges if needed. 9 Actual water discharges for 2010 are calculated using the ratio of Q nat and Q act from Mayorga et al. (2010) and natural water discharges from the VIC hydrological model (see above). For 2050, actual water discharges are calculated using population growth. ...
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The Black Sea receives increasing amounts of microplastics from rivers. In this study, we explore options to reduce future river export of microplastics to the Black Sea. We develop five scenarios with different reduction options and implement them to a Model to Assess River Inputs of pollutaNts to seA (MARINA-Global) for 107 sub-basins. Today, European rivers draining into the Black Sea export over half of the total microplastics. In 2050, Asian rivers draining into the sea will be responsible for 34–46% of microplastic pollution. Implemented advanced treatment will reduce point-source pollution. Reduced consumption or more collection of plastics will reduce 40% of microplastics in the sea by 2050. In the optimistic future, sea pollution is 84% lower than today when the abovementioned reduction options are combined. Reduction options affect the share of pollution sources. Our insights could support environmental policies for a zero pollution future of the Black Sea.
... We estimated the lateral carbon export by rivers minus the imports from rivers entering in each country, 255 including dissolved organic carbon, particulate organic carbon and dissolved inorganic carbon of atmospheric origin distinguished from lithogenic, by using the data and methodology described by Ciais et al. (2020b). Data are from Mayorga et al. (2010) and Hartmann et al. (2009) and follow the approach of Ciais et al. (2020a, b) proposed for large regions, but here with new data at national scale. Over a country that only exports river carbon, the amount of carbon exported is equivalent to an atmospheric CO2 sink, denoted as as in eq. ...
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In support of the Global Stocktake of the Paris Agreement on Climate change, this study presents a comprehensive framework to process the results of atmospheric inversions in order to make them suitable for evaluating UNFCCC national inventories of land-use carbon dioxide (CO2) emissions and removals, corresponding to the Land Use, Land Use Change and Forestry and waste sectors. We also deduced anthropogenic methane (CH4) emissions regrouped into fossil and agriculture and waste emissions, and anthropogenic nitrous oxide (N2O) emissions from inversions. To compare inversions with national reports, we compiled a new global harmonized database of national emissions and removals from periodical UNFCCC inventories by Annex I countries, and from sporadic and less detailed emissions reports by Non-Annex I countries, given by National Communications and Biennial Update Reports. The method to reconcile inversions with inventories is applied to selected large countries covering 78 % of the global land carbon uptake for CO2, as well as emissions and removals in the land use, land use change and forestry sector, and top-emitters of CH4 and N2O. Our method uses results from an ensemble of global inversions produced by the Global Carbon Project for the three greenhouse gases, with ancillary data. We examine the role of CO2 fluxes caused by lateral transfer processes from rivers and from trade in crop and wood products, and the role of carbon uptake in unmanaged lands, both not accounted for by the rules of inventories. Here we show that, despite a large spread across the inversions, the median of available inversion models points to a larger terrestrial carbon sink than inventories over temperate countries or groups of countries of the Northern Hemisphere like Russia, Canada and the European Union. For CH4, we find good consistency between the inversions assimilating only data from the global in-situ network and those using satellite CH4 retrievals, and a tendency for inversions to diagnose higher CH4 emissions estimates than reported by inventories. In particular, oil and gas extracting countries in Central Asia and the Persian Gulf region tend to systematically report lower emissions compared to those estimated by inversions. For N2O, inversions tend to produce higher anthropogenic emissions than inventories for tropical countries, even when attempting to consider only managed land emissions. In the inventories of many non-Annex I countries, this can be tentatively attributed to either a lack of reporting indirect N2O emissions from atmospheric deposition and from leaching to rivers, or to the existence of natural sources intertwined with managed lands, or to an under-estimation of N2O emission factors for direct agricultural soil emissions. The advantage of inversions is that they provide insights on seasonal and interannual greenhouse gas fluxes anomalies, e.g. during extreme events such as drought or abnormal fire episodes, whereas inventory methods are established to estimate trends and multi-annual changes. As a much denser sampling of atmospheric CO2 and CH4 concentrations by different satellites coordinated into a global constellation is expected in the coming years, the methodology proposed here to compare inversion results with inventory reports could be applied regularly for monitoring the effectiveness of mitigation policy and progress by countries to meet the objective of their pledges.
... Increased riverine nutrients and TA loads affect coastal carbon cycling by enhanced biological uptake and changes in seawater buffering capacity, which are rarely represented in current GOBMs that assume constant present-day riverine loads of both carbon and nutrients. Lacroix et al. (2020) estimated that present-day global riverine nutrients loads have increased relative to preindustrial times by 8-197%, 37-144%, and 115-141% for phosphorus, nitrogen, and silicate, respectively (Beusen et al. 2009(Beusen et al. , 2016Frings et al. 2016;Mayorga et al. 2010). Changes in TA are less well constrained, although Goll et al. (2014) suggested an increase of ca. ...
Article
This review examines the current understanding of the global coastal ocean carbon cycle and provides a new quantitative synthesis of air-sea CO2 exchange. This reanalysis yields an estimate for the globally integrated coastal ocean CO2 flux of −0.25 ± 0.05 Pg C year−1, with polar and subpolar regions accounting for most of the CO2 removal (>90%). A framework that classifies river-dominated ocean margin (RiOMar) and ocean-dominated margin (OceMar) systems is used to conceptualize coastal carbon cycle processes. The carbon dynamics in three contrasting case study regions, the Baltic Sea, the Mid-Atlantic Bight, and the South China Sea, are compared in terms of the spatio-temporal variability of surface pCO2. Ocean carbon models that range from box models to three-dimensional coupled circulation-biogeochemical models are reviewed in terms of the ability to simulate key processes and project future changes in different continental shelf regions. Common unresolved challenges remain for implementation of these models across RiOMar and OceMar systems. The long-term trends in coastal ocean carbon fluxes for different coastal systems under anthropogenic stress that are emerging in observations and numerical simulations are highlighted. Knowledge gaps in projecting future perturbations associated with before and after net-zero CO2 emissions in the context of concurrent changes in the land-ocean-atmosphere coupled system pose a key challenge. Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 50 is May 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... River runoff affects only salinity. Nutrient loads from the rivers are derived from the modelled dataset, GlobalNEWS (Mayorga et al., 2010;Seitzinger et al., 2010), which include nitrate, phosphate and silicate. Nutrient loads were scaled by the TRIP runoff volume resulting in monthly climatology loads. ...
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ECOSMO II is a fully coupled bio-physical model of 3d-hydrodynamics with an intermediate complexity N(utrient) P(hytoplankton) Z(ooplankton) D(etritus) type biology including sediment-water column exchange processes originally formulated for the North Sea and Baltic Sea. Here we present an updated version of the model incorporating chlorophyll a as a prognostic state variable: ECOSMO II(CHL). The version presented here is online coupled to the HYCOM ocean model. The model is intended to be used for regional configurations for the North Atlantic and the Arctic incorporating coarse to high spatial resolutions for hind-casting and operational purposes. We provide the full descriptions of the changes in ECOSMO II(CHL) from ECOSMO II and provide the evaluation for the inorganic nutrients and chlorophyll variables, present the modeled biogeochemistry of the Nordic Seas and the Artic and experiments on various parameterization sets as use cases targeting chlorophyll a dynamics. The model evaluations demonstrated that the simulations are consistent with the large-scale climatological nutrient settings, and are capable of representing regional and seasonal changes. The Norwegian and Barents Seas primary production show distinct seasonal patterns with a pronounced spring bloom dominated by diatoms and low biomass during winter months. The Norwegian Sea annual primary production is around double that of the Barents Sea while also having an earlier spring bloom. The parameterization experiments showed that the representation of open ocean chlorophyll a benefits from using higher phytoplankton growth and zooplankton grazing rates with less photosynthesis efficiency compared to the original implementation of ECOSMO II, which was valid for the North Sea and the Baltic Sea representing coastal domains. Thus, for open ocean modeling studies, we suggest the use of the parameterization sets presented in this study.
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Tropical coastal waters are highly dynamic and amongst the most biogeochemically active zones in the ocean. This review compares nitrogen (N) and phosphorus (P) cycles in temperate and tropical coastal waters. We review the literature to identify major similarities and differences between these two regions, specifically with regards to the impact of environmental factors (temperature, sunlight), riverine inputs, groundwater, lateral fluxes, atmospheric deposition, nitrogen fixation, organic nutrient cycling, primary production, respiration, sedimentary burial, denitrification and anammox. Overall, there are some similarities but also key differences in nutrient cycling, with differences relating mainly to temperature, sunlight, and precipitation amounts and patterns. We conclude that due to the differences in biogeochemical processes, we cannot directly apply cause and effect relationships and models from temperate systems in tropical coastal waters. Our review also highlights the considerable gaps in knowledge of the biogeochemical processes of tropical coastal waters compared with temperate systems. Given the ecological and societal importance of tropical coastal waters, we hope that highlighting the differences and similarities to temperate systems as well as the existing gaps, will inspire further studies on their biogeochemical processes. Such knowledge will be essential to better understand and forecast impacts on tropical coastal nutrient cycling at local, regional, and global scales.
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The vital role of terrestrial biogeochemical cycles in influencing global climate change is explored by modelling groups internationally through land surface models (LSMs) coupled to atmospheric and oceanic components within Earth system models (ESMs). The sixth phase of the Coupled Model Intercomparison Project (CMIP6) provided an opportunity to compare ESM output by providing common forcings and experimental protocols. Despite these common experimental protocols, a variety of terrestrial biogeochemical cycle validation approaches were adopted by CMIP6 participants, leading to ambiguous model performance assessment and uncertainty attribution across ESMs. In this review we summarize current methods of terrestrial biogeochemical cycle validation utilized by CMIP6 participants and concurrent community model comparison studies. We focus on variables including the dimensions of evaluations, observation-based reference datasets, and metrics of model performance. To ensure objective and thorough validations for the seventh phase of CMIP (CMIP7), we recommend the use of a standard validation protocol employing a broad suite of certainty-weighted observation-based reference datasets, targeted model performance metrics, and comparisons across a range of spatiotemporal scales.
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A common notion is that negative feedbacks stabilize the natural marine nitrogen inventory. Recent modeling studies have shown, however, some potential for localized positive feedbacks leading to substantial nitrogen losses in regions where nitrogen fixation and denitrification occur in proximity to each other. Here we include dissolved nitrogen from river discharge in a global 3-D ocean biogeochemistry model and study the effects on near-coastal and remote-open-ocean biogeochemistry. We find that at a steady state the biogeochemical feedbacks in the marine nitrogen cycle, nitrogen input from biological N2 fixation, and nitrogen loss via denitrification mostly compensate for the imposed yearly addition of 22.8 to 45.6 Tg of riverine nitrogen and limit the impact on global marine productivity to
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Significant research on surface water pollution modelling has been carried out over diverse landscapes has sought to explain the sources, transport, and surface water pollution. To date, surface water pollution studies have focused on nutrients, plastics, and chemicals. Consequently, the current review aims to identify and synthesise peer-reviewed literature about integrated contaminants modelling in surface water. Thus, highlighting that modelling potentially multiple sources of a pollutant from the surface water has remained a thought-provoking topic. Studies differed significantly in terms of the type of model application and procedures for reporting findings, making it challenging to separate clear trends and patterns. Accordingly, most studies agree that pollutants such as plastics and agrochemicals can have adverse consequences on surface water quality; these coincide with difficulties in modelling pollutant transport. Consequently, no regional or global estimates are available for the water pollution burden of flood-related pollution, considering the demonstrable modelling techniques, the significance of the concurrent impacts of surface water pollution by contaminants. Multi-pollutant approaches to modelling the potential sources of pollution and encourage protective behaviour are essential. Mainstreaming freshwater pollution concerns into planning strategies will also be needed to lessen anthropological contribution to surface water pollution. While the implementation of these models is constrained by lack of adequate field data, the model output must be analysed within the model inputs' uncertainty, data limitations and methodologically established surface water modelling principles from the literature.
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Global rivers and streams are important carbon transport pathways from land to the ocean. However, few studies have quantified terrigenous carbon dynamics in river ecosystems and its variations due to climate change and anthropogenic perturbations. Therefore, our study analysed fluvial particulate organic carbon (POC) and developed a processed‐based model (TRIPLEX‐HYDRA) to simulate the production, transport, and removal (i.e., deposition, degradation, dam retention) processes of fluvial POC along the land‐ocean aquatic continuum (LOAC). Based on our results, approximately 0.29 Pg of POC is exported from land to the ocean through rivers each year. More specifically, we found that rivers at low latitudes (30°S–30°N, 0.18 Pg yr‐1) and high northern latitudes (60°N–90°N, 0.05 Pg yr‐1) had higher POC fluxes compared to rivers in other regions. This high POC flux is related to strong erosion rates and high soil organic carbon storage. Additionally, our model simulation revealed that total POC flux from global river has not significantly changed from 1983 to 2015, but display markedly decreased or increased trend at regional scale. These regional variations in POC export are affected by climate warming and dam construction. Moreover, approximately 0.46 Pg of POC is deposited or trapped by dams along the LOAC system, which plays a vital role in the global river carbon budget. Although some limitations and uncertainties remain, this study establishes a theoretical and methodological basis for quantifying riverine POC dynamics in the LOAC system.
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The supply of particulate organic carbon (POC) associated with terrigenous solids transported to the ocean by rivers plays a significant role in the global carbon cycle. To advance our understanding of the source, transport, and fate of fluvial POC from regional to global scales, databases of riverine POC are needed, including elemental and isotope composition data from contrasted river basins in terms of geomorphology, lithology, climate, and anthropogenic pressure. Here, we present a new, open-access, georeferenced, global database called Modern River Archives of Particulate Organic Carbon (MOREPOC) version 1.0, featuring data on POC in suspended particulate matter (SPM) collected at 231 locations across 118 major river systems. This database includes 3,424 SPM data entries, among which 2,943 with POC content, 3,260 with stable carbon isotope (δ13C) values, 2,018 with radiocarbon activity (Δ14C) values, 1,838 with total nitrogen content, and 309 with aluminum-to-silicon mass ratios (Al / Si). The MOREPOC database aims at being used by the Earth System community to build comprehensive and quantitative models for the mobilization, alteration, and fate of terrestrial POC. The database is made available on the Zenodo repository in machine-readable formats as data table and GIS shapefile at https://doi.org/10.5281/zenodo.6541925 (Ke et al., 2022).
Chapter
With the abundance of observations and advancement in modeling, temperate regions allow for a comprehensive comparison of the data-driven and process-based methods of carbon budget estimation. This chapter presents a review of the latest methodologies for carbon budget and component flux estimation, and the key components in the temperate carbon budget, such as forest regrowth, and summarizes uncertainties in the current carbon budget of temperate ecosystems that the research community needs to resolve. Lastly, we describe the key progress made in the carbon budget assessment in past decades, and how it should be further advanced to be useful for policy decision-making.
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Riverine transport of nutrients and carbon from inland waters to the coastal and finally the open ocean alters marine primary production (PP) and carbon (C) uptake, not only regionally but also globally. So far, this contribution is represented in the state-of-the-art Earth system models with limited effort. Here we assess changes in marine PP and C uptake projected under the Representative Concentration Pathway 4.5 climate scenario using the Norwegian Earth system model, with four riverine configurations: deactivated, fixed at a contemporary level, coupled to simulated freshwater runoff, and following four plausible future scenarios. The inclusion of riverine nutrients and carbon improves the modelled contemporary spatial distribution relative to observations, especially on the continental margins (5.4 % reduction in root mean square error [RMSE] for PP) and in the North Atlantic region (7.4 % reduction in RMSE for C uptake). Riverine nutrient inputs alleviate nutrient limitation, especially under future warmer conditions as stratification increases, and thus lessen the projected future decline in PP by up to 0.6 PgC yr−1 (27.3 %) globally depending on the riverine configuration. The projected C uptake is enhanced along continental margins where increased PP, due to riverine nutrient inputs, dominates over the CO2 outgassing owing to riverine organic matter inputs. Conversely, where the riverine organic matter inputs dominate over the nutrient inputs, the projected C uptake is reduced. The large range of the riverine input across our four riverine configurations does not transfer to a large uncertainty of the projected global PP and ocean C uptake, suggesting that transient riverine inputs are more important for high-resolution regional studies such as in the North Atlantic and along the continental margins.
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Rivers play an important role in the global carbon (C) cycle. However, it remains unknown how long-term river C fluxes change because of climate, land-use, and other environmental changes. Here, we investigated the spatiotemporal variations in global freshwater C cycling in the 20th century using the mechanistic IMAGE-Dynamic Global Nutrient Model extended with the Dynamic In-Stream Chemistry Carbon module (DISC-CARBON) that couples river basin hydrology, environmental conditions, and C delivery with C flows from headwaters to mouths. The results show heterogeneous spatial distribution of dissolved inorganic carbon (DIC) concentrations in global inland waters with the lowest concentrations in the tropics and highest concentrations in the Arctic and semiarid and arid regions. Dissolved organic carbon (DOC) concentrations are less than 10 mg C/L in most global inland waters and are generally high in high-latitude basins. Increasing global C inputs, burial, and CO2 emissions reported in the literature are confirmed by DISC-CARBON. Global river C export to oceans has been stable around 0.9 Pg yr–1. The long-term changes and spatial patterns of concentrations and fluxes of different C forms in the global river network unfold the combined influence of the lithology, climate, and hydrology of river basins, terrestrial and biological C sources, in-stream C transformations, and human interferences such as damming.
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The spatiotemporal characteristics and sources identification of agricultural nitrogen (N) and phosphorus (P) emissions to the gulf are rarely reported in tropical regions of China, mainly due to the lack of local reliable data and quantitative tools for spatiotemporal changes. In this study, we constructed a high-resolution NUFER (NUtrient Flow in food chains, Environment and Resources use) model based on geology, meteorology, land use data, statistical data, and field investigation to quantify the spatiotemporal characteristics and sources of N and P emissions. Bamen Bay (BMB), a bay with a mangrove national wetland Park in the Hainan Island, China, was chosen as a case study. The results showed that agricultural N emission to water in 2018 increased fivefold compared to 1990. Leaching was the main method of agricultural N emission and was mainly distributed in farms in the west and north. The contribution of N emission from crop system to water increased 20.3% in 28 years. Poultry and fruits have contributed the most to N output, and the trend is continuing. P emission to water increased sevenfold compared 1990. The contribution of P emission from animal system to water increased from 86.8% in 1990 to 90.1% in 2018 due to low removal rate of livestock manure. P emission was mainly via direct discharge of manure, mainly distributed in livestock breeding sites near the bay. Poultry has consistently contributed the most to P output in 28 years, accounting for 49.1% in 2018. Fertilizers and fodder were the largest sources of N and P. The average N and P loss rates of BMB were 5.32 t km² yr⁻¹ and 0.26 t km² yr⁻¹. The future agricultural transformation is essential, and it is necessary to reduce the application of N fertilizer and increase the removal rate of livestock manure. These results can provide reference for other typical agricultural pollution bays in exploring the spatiotemporal characteristics of N and P emissions to water and the identification of agricultural sources.
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Anthropogenic activities have led to widespread contamination with mercury (Hg), a potent neurotoxin that bioaccumulates through food webs. Recent models estimated that, presently, 200 to 600 t of Hg is sequestered annually in deep-sea sediments, approximately doubling since industrialization. However, most studies did not extend to the hadal zone (6,000- to 11,000-m depth), the deepest ocean realm. Here, we report on measurements of Hg and related parameters in sediment cores from four trench regions (1,560 to 10,840 m), showing that the world’s deepest ocean realm is accumulating Hg at remarkably high rates (depth-integrated minimum–maximum: 24 to 220 μg ⋅ m−2 ⋅ y−1) greater than the global deep-sea average by a factor of up to 400, with most Hg in these trenches being derived from the surface ocean. Furthermore, vertical profiles of Hg concentrations in trench cores show notable increasing trends from pre-1900 [average 51 ± 14 (1σ) ng ⋅ g−1] to post-1950 (81 ± 32 ng ⋅ g−1). This increase cannot be explained by changes in the delivery rate of organic carbon alone but also need increasing Hg delivery from anthropogenic sources. This evidence, along with recent findings on the high abundance of methylmercury in hadal biota [R. Sun et al., Nat. Commun. 11, 3389 (2020); J. D. Blum et al., Proc. Natl. Acad. Sci. U. S. A. 117, 29292–29298 (2020)], leads us to propose that hadal trenches are a large marine sink for Hg and may play an important role in the regulation of the global biogeochemical cycle of Hg.
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The Arctic coastal margin receives a disproportionately large fraction of the global river discharge. The bio-geochemistry of the river water as it empties into the marine environment reflects inputs and processes that occur as the water travels from its headwaters. Climate-induced changes to Arctic vegetation and permafrost melt may impact river chemistry. Understanding the impact of river nutrients on coastal marine production, and how this may change in the future, are important for resource managers and community members who monitor and rely on coastal food resources. Using the Energy Exascale Earth System Model we explore the impact of timing and river nutrient concentrations on primary production in each coastal Arctic region and then assess how this influences secondary production and particle fluxes supporting the benthic food web. Our results indicate that while the concentration of Arctic river nitrogen can have a significant impact on annual average nitrogen and primary production in the coastal Arctic, with production increases of up to 20% in the river influenced interior Seas, the timing of the river nutrient inputs into the marine environment appears less important. Bloom timing and partitioning between small and large phytoplankton were minimally impacted by both river nutrient concentration and timing, suggesting that in general, coastal Arctic ecosystem dynamics will continue to be primarily driven by light availability, rather than nutrients. Under a doubling river nutrient scenario, the percentage increase in the POC flux to the benthos on river influenced Arctic coastal shelves was 2-4 times the percentage increase in primary production, suggesting changes to the river nutrient concentration has the potential to modify the Arctic food web structure and dynamics. Generally, the nutrient-induced changes to primary production were smaller than changes previously simulated in response to ice reduction and temperature increase. However, in the Laptev Sea, the production increase resulting from a doubling of river nutrients exceeded the production increase simulated with an atmospheric warming scenario. Dissolved organic carbon is presently poorly represented in the model so its impact on production is hard to simulate. Applying established relationships between modeled DOC, total DOC, and light absorption we illustrate that DOC could play a very important role in modulating production. Our findings highlight the importance of developing more realistic river nutrient and discharge forcing for Earth System Models such that their impact on the critical Arctic coastal domain can be more adequately resolved.
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Recent research has shown that inland water – including rivers, lakes, and groundwater – may play some role in carbon cycling, although the extent of its contribution has remained uncertain due to the limited amount of reliable data available. To evaluate global changes in the carbon cycle due to anthropogenic factors, such as application of fertilizer and manure, in major rivers including 130 tidal estuaries over an 18-year period (1998-2015), the present study used an advanced process-based model derived by coupling a process-based National Integrated Catchment-based Eco-hydrology (NICE) model with various biogeochemical cycle models (NICE-BGC). Generally, total nitrogen and phosphorus transports in overland flow were found to increase. In contrast, total suspended sediment in overland flow decreased in some regions because the vegetation was able to expand to cover the ground, resulting in less erosion. NICE-BGC simulated the difference in carbon budget in major rivers with and without nutrient application. Generally, CO2 degassing across the water-air interface decreased and particulate organic carbon (POC) increased in most rivers through variations in carbon budget, where excess nutrients might stimulate gross primary production of carbon-rich algal biomass. The simulated result also showed that the estuarine carbon cycle was sensitive to intense anthropogenic disturbances reflected by nutrient load, seawater temperature, increases in sea level, and ocean acidification. Extension of previous studies only by categorizing MARgins and CATchments Segmentation (MARCATS) segment numbers showed that the estimated total CO2 flux from the world’s estuaries was 0.14 Pg C/yr. Generally, the simulation showed that incorporation of the nutrient cycle into the terrestrial-aquatic-estuarine continuum improved estimates of net land flux and carbon budget in inland waters, thus emphasizing that the effect of estuarine inland water should be explicitly included in the global carbon model to minimize the range of uncertainty. This article is protected by copyright. All rights reserved.
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Karst watersheds accommodate high landscape complexity and are influenced by both human-induced and natural activity, which affects the formation and process of runoff, sediment connectivity and contaminant transport and alters natural hydrological and nutrient cycling. However, physical monitoring stations are costly and labor-intensive, which has confined the assessment of water quality impairments on spatial scale. The geographical characteristics of catchments are potential influencing factors of water quality, often overlooked in previous studies of highly heterogeneous karst landscape. To solve this problem, we developed a machining learning method and applied Extreme Gradient Boosting (XGBoost) to predict the spatial distribution of water quality in the world's most ecologically fragile karst watershed. We used the Shapley Addition interpretation (SHAP) to explain the potential determinants. Before this process, we first used the water quality damage index (WQI-DET) to evaluate the water quality impairment status and determined that CODMn, TN and TP were causing river water quality impairments in the WRB. Second, we selected 46 watershed features based on the three key processes (sources-mobilization-transport) which affect the temporal and spatial variation of river pollutants to predict water quality in unmonitored reaches and decipher the potential determinants of river impairments. The predicting range of CODMn spanned from 1.39 mg/L to 17.40 mg/L. The predictions of TP and TN ranged from 0.02 to 1.31 mg/L and 0.25–5.72 mg/L, respectively. In general, the XGBoost model performs well in predicting the concentration of water quality in the WRB. SHAP explained that pollutant levels may be driven by three factors: anthropogenic sources (agricultural pollution inputs), fragile soils (low organic carbon content and high soil permeability to water flow), and pollutant transport mechanisms (TWI, carbonate rocks). Our study provides key data to support decision-making for water quality restoration projects in the WRB and information to help bridge the science:policy gap.
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Carbon storage by the ocean and by the land is usually quantified separately, and does not fully take into account the land-to-ocean transport of carbon through inland waters, estuaries, tidal wetlands and continental shelf waters—the ‘land-to-ocean aquatic continuum’ (LOAC). Here we assess LOAC carbon cycling before the industrial period and perturbed by direct human interventions, including climate change. In our view of the global carbon cycle, the traditional ‘long-range loop’, which carries carbon from terrestrial ecosystems to the open ocean through rivers, is reinforced by two ‘short-range loops’ that carry carbon from terrestrial ecosystems to inland waters and from tidal wetlands to the open ocean. Using a mass-balance approach, we find that the pre-industrial uptake of atmospheric carbon dioxide by terrestrial ecosystems transferred to the ocean and outgassed back to the atmosphere amounts to 0.65 ± 0.30 petagrams of carbon per year (±2 sigma). Humans have accelerated the cycling of carbon between terrestrial ecosystems, inland waters and the atmosphere, and decreased the uptake of atmospheric carbon dioxide from tidal wetlands and submerged vegetation. Ignoring these changing LOAC carbon fluxes results in an overestimation of carbon storage in terrestrial ecosystems by 0.6 ± 0.4 petagrams of carbon per year, and an underestimation of sedimentary and oceanic carbon storage. We identify knowledge gaps that are key to reduce uncertainties in future assessments of LOAC fluxes. An assessment of the land-to-ocean cycling of carbon through inland waters, estuaries, tidal wetlands and continental shelf waters provides a perspective on the global carbon cycle and identifies key knowledge gaps.
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Deep-sea sponges inhabit multiple areas of the deep North Atlantic at depths below 250 m. Living in the deep ocean, where environmental properties below the permanent thermocline generally change slowly, they may not easily acclimatize to abrupt changes in the environment. Until now consistent monitoring timeseries of the environment at deep sea sponge habitats are missing. Therefore, long-term simulation with coupled bio-physical models can shed light on the changes in environmental conditions sponges are exposed to. To investigate the variability of North Atlantic sponge habitats for the past half century, the deep-sea conditions have been simulated with a 67-year model hindcast from 1948 to 2014. The hindcast was generated using the ocean general circulation model HYCOM, coupled to the biogeochemical model ECOSMO. The model was validated at known sponge habitats with available observations of hydrography and nutrients from the deep ocean to evaluate the biases, errors, and drift in the model. Knowing the biases and uncertainties we proceed to study the longer-term (monthly to multi-decadal) environmental variability at selected sponge habitats in the North Atlantic and Arctic Ocean. On these timescales, these deep sponge habitats generally exhibit small variability in the water-mass properties. Three of the sponge habitats, the Flemish Cap, East Greenland Shelf and North Norwegian Shelf, had fluctuations of temperature and salinity in 4–6 year periods that indicate the dominance of different water masses during these periods. The fourth sponge habitat, the Reykjanes Ridge, showed a gradual warming of about 0.4°C over the simulation period. The flux of organic matter to the sea floor had a large interannual variability, that, compared to the 67-year mean, was larger than the variability of primary production in the surface waters. Lateral circulation is therefore likely an important control mechanism for the influx of organic material to the sponge habitats. Simulated oxygen varies interannually by less than 1.5 ml/l and none of the sponge habitats studied had oxygen concentrations below hypoxic levels. The present study establishes a baseline for the recent past deep conditions that future changes in deep sea conditions from observations and climate models can be evaluated against.
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ECOSMO II is a fully coupled bio-physical model of 3D hydrodynamics with an intermediate-complexity NPZD (nutrient, phytoplankton, zooplankton, detritus) type biology including sediment-water column exchange processes originally formulated for the North Sea and Baltic Sea. Here we present an updated version of the model incorporating chlorophyll a as a prognostic state variable: ECOSMO II(CHL). The version presented here is online coupled to the HYCOM ocean model. The model is intended to be used for regional configurations for the North Atlantic and the Arctic incorporating coarse to high spatial resolutions for hind-casting and operational purposes. We provide the full descriptions of the changes in ECOSMO II(CHL) from ECOSMO II and provide the evaluation for the inorganic nutrients and chlorophyll a variables, present the modelled biogeochemistry of the Nordic Seas and the Arctic, and experiment on various parameterization sets as use cases targeting chlorophyll a dynamics. We document the performance of each parameter set objectively analysing the experiments against in situ, satellite and climatology data. The model evaluations for each experiment demonstrated that the simulations are consistent with the large-scale climatological nutrient setting and are capable of representing regional and seasonal changes. Explicitly resolving chlorophyll a allows for more dynamic seasonal and vertical variations in phytoplankton biomass to chlorophyll a ratio and improves model chlorophyll a performance near the surface. Through experimenting with the model performance, we document the general biogeochemisty of the Nordic Seas and the Arctic. The Norwegian and Barents seas primary production show distinct seasonal patterns with a pronounced spring bloom dominated by diatoms and low biomass during winter months. The Norwegian Sea annual primary production is around double that of the Barents Sea while also having an earlier spring bloom.
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Humic substances, a component of terrestrial dissolved organic matter (tDOM), contribute to dissolved organic matter (DOM) and chromophoric DOM (CDOM) in coastal waters, and have significant impacts on biogeochemistry. There are concerns in recent years over browning effects in surface waters, due to increasing tDOM inputs, and their negative impacts on aquatic ecosystems, but relatively little work has been published on estuaries and coastal waters. Photodegradation could be a significant sink for tDOM in coastal environments, but the rates and efficiencies are poorly constrained. We conducted large-scale DOM photodegradation experiments in mesocosms amended with humic substances and nutrients in the Gulf of Finland to investigate the potential of photochemistry to remove added tDOM and the interactions of DOM photochemistry with eutrophication. The added tDOM was photodegraded rapidly, as CDOM absorption decreased and spectral slopes increased with increasing photons absorbed in laboratory experiments. The in situ DOM optical properties became similar amongst the control, humic-, and humic+nutrients-amended mesocosm samples towards the end of the amendment experiment, indicating degradation of the excess CDOM/DOM through processes including photodegradation. Nutrient additions didn't significantly influence the effects of added humic substances on CDOM optical property changes, but induced changes in DOM removal.
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We developed a simple model that related NO3 export to point-source N loading and nonpoint source N loads from chemical fertilizers and NO(y) deposition and tested it at the global scale using data from 35 large rivers with a global distribution. The model explained well (r2 > 0.8) the nearly 1000-fold variation in NO3 export from different regions of the world. The model suggests that human activity is the dominant control of NO3 export even though less than 20 of the 100 Tg N yr-1 added to land in fertilizer and NO(y) deposition is at present exported from rivers as NO3. Watershed export to rivers may increase in the future due to either increased loads to the watershed or decreased watershed retention. Simple models, coupled with continued measurements of NO3 in rivers, will be of use in interpreting these regional changes.
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Global nitrogen (N) budgets for intensive agricultural systems were compiled for a 0.5 by 0.5 degree resolution. These budgets include N inputs (N fertilizer, animal manure, biological N fixation and atmospheric N deposition) and outputs (N removal from the field in harvested crops and grass and grass consumption by grazing animals, ammonia volatilization, denitrification and leaching). Data for the historical years 1970 and 1995 and a projection for 2030 were used to study changes in the recovery of N and the different loss terms for intensive agricultural systems. The results indicate that the overall system N recovery and fertilizer use efficiency slowly increased in the industrialized countries between 1970 and 1995, the values for developing countries have decreased in the same period. For the coming three decades our results indicate a rapid increase in both the industrialized and developing countries. High values of > 80% for fertilizer use efficiency may be related to surface N balance deficits, implying a depletion of soil N and loss of soil fertility. The projected intensification in most developing countries will cause a gradual shift from deficits to surpluses in the coming decades. The projected fast growth of crop and livestock production, and intensification and associated increase in fertilizer inputs will cause a major increase in the surface N balance surplus in the coming three decades. This implies increasing losses of N compounds to air (ammonia, nitrous oxide and nitric oxide), and groundwater and surface water (nitrate).
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Renewable fresh water comprises a tiny fraction of the global water pool but is the foundation for life in terrestrial and freshwater ecosystems. The benefits to humans of renewable fresh water include water for drinking, irrigation, and industrial uses, for production of fish and waterfowl, and for such instream uses as recreation, transportation, and waste disposal. In the coming century, climate change and a growing imbalance among freshwater supply, consumption, and population will alter the water cycle dramatically. Many regions of the world are already limited by the amount and quality of available water. In the next 30 yr alone, accessible runoff is unlikely to increase more than 10%, but the earth's population is projected to rise by approximately one-third. Unless the efficiency of water use rises, this imbalance will reduce freshwater ecosystem services, increase the number of aquatic species facing extinction, and further fragment wetlands, rivers, deltas, and estuaries. Based on the scientific evidence currently available, we conclude that: (1) over half of accessible freshwater runoff globally is already appropriated for human use; (2) more than 1 x 10(9) people currently lack access to clean drinking water and almost 3 x 10(9) people lack basic sanitation services; (3) because the human population will grow faster than increases in the amount of accessible fresh water, per capita availability of fresh water will decrease in the coming century; (4) climate change will cause a general intensification of the earth's hydrological cycle in the next 100 yr, with generally increased precipitation, evapotranspiration, and occurrence of storms, and significant changes in biogeochemical processes influencing water quality; (5) at least 90% of total water discharge from U.S. rivers is strongly affected by channel fragmentation from dams, reservoirs, interbasin diversions, and irrigation; and (6) globally, 20% of freshwater fish species are threatened or extinct, and freshwater species make up 47% of all animals federally endangered in the United States. The growing demands on freshwater resources create an urgent need to link research with improved water management. Better monitoring, assessment, and forecasting of water resources will help to allocate water more efficiently among competing needs, Currently in the United States, at least six federal departments and 20 agencies share responsibilities for various aspects of the hydrologic cycle. Coordination by a single panel with members drawn from each department, or by a central agency, would acknowledge the diverse pressures on freshwater systems and could lead to the development of a well-coordinated national plan.
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This paper presents a multiple linear regression model developed for describing global river export of sediments (suspended solids, TSS) to coastal seas, and approaches for estimating organic carbon, nitrogen, and phosphorous transported as particulate matter (POC, PN, and PP) associated with sediments. The model, with river-basin spatial scale and a 1-year temporal scale, is based on five factors with a significant influence on TSS yields (the extent of marginal grassland and wetland rice, Fournier precipitation, Fournier slope, and lithology), and accounts for sediment trapping in reservoirs. The model generates predictions within a factor of 4 for 80% of the 124 rivers in the data set. It is a robust model which was cross-validated by using training and validation sets of data, and validated against independent data. In addition, Monte Carlo simulations were used to deal with uncertainties in the model coefficients for the five model factors. The global river export of TSS calculated thus is 19 Pg yr−1 with a 95% confidence interval of 11–27 Pg yr−1 when accounting for sediment trapping in regulated rivers. Associated POC, PN, and PP export is 197 Tg yr−1 (as C), 30 Tg yr−1 (N), and 9 Tg yr−1 (P), respectively. The global sediment trapping included in these estimates is 13%. Most particulate nutrients are transported by rivers to the Pacific (∼37% of global particulate nutrient export), Atlantic (28–29%), and Indian (∼20%) oceans, and the major source regions are Asia (∼50% of global particulate nutrient export), South America (∼20%), and Africa (12%).
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Regulation of rivers by damming as well as eutrophication in river basins has substantially reduced dissolved silicon (DSI) loads to the Black Sea and the Baltic Sea. Whereas removal of N and P in lakes and reservoirs can be compensated for by anthropogenic inputs in the drainage basins, no such compensation occurs for DSI. The resulting changes in the nutrient composition (DSI:N:P ratio) of river discharges seem to be responsible for dramatic shifts in phytoplankton species composition in the Black Sea. In the Baltic Sea, DSI concentrations and the DSI:N ratio have been decreasing since the end of the 1960s, and there are indications that the proportion of diatoms in the spring bloom has decreased while flagellates have increased. The effects on coastal biogeochemical cycles and food web structure observed in the Black Sea and the Baltic Sea may be far reaching, because it appears that the reductions in DSi delivery by rivers are probably occurring worldwide with the ever increasing construction of dams for flow regulation.
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Most modern estimates of dissolved nitrogen and phosphorus delivery to the ocean use Meybeck's estimates from approximately 30 large rivers. We have derived an extended database of approximately 165 sites with nutrient loads. For both dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP), the logarithmic yields (log [load/area]) can be parameterized as functions of log (population density) and log (runoff/area) (R2 for DIN and DIP approximately 0.6). Landscape production of DIN and DIP is largely assimilated. Even though DIN and DIP follow substantially different biogeochemical cycles, loading for DIN and DIP is tightly coupled (R2 for log DIN versus log DIP approximately 0.8), with a constant loading ratio of about 18:1. Estimates of DIN and DIP fluxes are distributed globally around the world coastlines by using basin population density and runoff at 0.5° increments of latitude and longitude. We estimate that total loads for the 1990s are about three times Meybeck's estimates for the 1970s.