How Rivers Export Plastic: Insights from Three Contrasting Global Systems

As part of the Reactive Chlorine Emissions Inventory, a global model of chemical processes in the marine boundary layer (MBL), Marine Aerosol and Gas Phase Interactions (MAGPI), was developed to calculate direct monthly production of HCl and ClNO2 from sea salt dechlorination on a 2.8 × 2.8 latitude‐longitude grid. Sea salt mass and size distributions and associated surface exchange fluxes were calculated using the Canadian General Circulation Model; integrated annual production of sea salt Cl− was 1785 Tg Cl yr−1. Corresponding distributions of gas‐phase HNO3, SO2, N2O5, H2O2, O3, H2SO4 and NH3 were calculated using different global chemical transport models in which sea salt reactions were not considered. A chemical scheme was developed to estimate the monthly mean steady‐state phase partitioning of product and reactant species at each grid point. Average annual gridded fluxes of HCl and ClNO2 varied spatially from 1 to 300 mg Cl m−2 yr−1 and from 1 to 8 mg Cl m−2 yr−1, respectively. Maxima occurred in polluted coastal regions of the North Atlantic, the western North Pacific and the Mediterranean where up to 20% of the total Cl and 80% of the sub‐micron Cl volatilized. In remote oceanic regions, available acidity was insufficient to titrate all sea salt alkalinity, thus, significant HCl was not produced via acid displacement. However, in these regions virtually all HNO3 was scavenged by sea salt. The integrated annual global fluxes for HCl and ClNO2 were 7.6 Tg Cl yr−1 and 0.06 Tg Cl yr−1, respectively; virtually all in the Northern Hemisphere. Largest HCl and ClNO2 fluxes occur in northern hemisphere winter due to high sea salt loading and elevated HNO3, SO2 and N2O5 concentrations. 70% of the HCl dechlorination occurs on particles between 0.75 μm and 4 μm radius; ClNO2 volatilized from slightly larger particles. The aerosol pH of each particle size bin equilibrates towards the same value once the alkalinity has been titrated.

CH4 and CO2 are important greenhouse gases, playing a very important role in greenhouse effect. In order to estimate the current situation of source and sink of main greenhouse gases in Baiyangdian wetland and evaluate the influences of wetland system to the greenhouse effect of North China, static closed chamber-gas chromatogram method was adopted to study the space-time variation characteristics of N2O, CH4, and CO2 emission fluxes in Baiyangdian wetland. The analysis results indicate: the lake wetland which was abundant in organic matters and nutritive salt was an important greenhouse gases emission source. During one year of observation, it was found out that the fluxes of N2O, CH4, and CO2 of Baiyangdian wetland posses a very high time variability, with the range of variation being-0.08~0.33 mg·m-2·h-1, -5.40~328.65 mg·m-2·h-1 and -814.06~2934.93 mg·m-2·h-1. The emission fluxes of N2O, CH4, and CO2 reaches to maximum in summer, respectively being 62.09%, 92.15% and 87.04% of the annual total emission flux, The lakeside was a core area of N2O, CH4 emission, with annual average emission flux respectively reaching up to 0.11 mg·m-2·h-1 and 40.86 mg·m-2·h-1. Although the main emission area of CO2 was land, the emission flux of lakeside, with annual average emission flux being 692.35 mg·m-2·h-1, was also very high, ranking only second to land, the lakeside area of Baiyangdian wetland was only 12.60% of the whole lake wetland area, but the emission loads of N2O, CH4, and CO2 were respectively 26.51%, 43.96% and 23.76% of the total emission load, which explains that the lakeside was leading the greenhouse gases emission of Baiyangdian wetland.

Nitrogen deposition induced significant increase of N2O emissions in an dry alpine meadow on the central Qinghai–Tibetan Plateau

Based on multi-source observation data, such as lidar ceilometer, aircraft AMDAR, and conventional sites, combined with numerical simulation (CAMx-PSAT), this study took the typical cities of the Beijing-Tianjin-Hebei region-Beijing (BJ) urban area and suburbs (Miyun) and Shijiazhuang (SJZ) urban area and suburbs (Pingshan) as the case study areas. The differences in boundary layer height between urban areas and suburbs (ΔPBLH), surface PM2.5 mass concentration (ΔSurf_PM2.5), vertical PM2.5 mass concentration (ΔVert_PM2.5), and transmission flux intensity and height distribution characteristics were analyzed. The results showed:due to factors such as anthropogenic heat sources, short-wave radiation, and thermal turbulence, the annual average planetary boundary layer height in urban areas was 8%-29% higher than that in the suburbs, and in different seasons, the monthly average planetary boundary layer height in urban areas was 2% (April in SJZ)-47% (July in BJ) higher than that in the suburbs. Due to the combined effects of anthropogenic emissions, inversions, and atmospheric turbulence, the annual averageρ(PM2.5) in urban areas between 0-1260 m was higher than that in suburbs by 0.1 (SJZ)-29.7 (BJ) μg·m-3 and decreased with the increase in height. The annual average total net flux intensity in urban areas was much greater than that in suburbs, with outflows in urban areas and inflows in suburbs; due to the urban low pressure and the suburban high pressure, suburban thermal circulation was formed. The annual average total net flux intensity in BJ (44.77 t·d-1) was greater than that in SJZ (34.44 t·d-1). Affected by wind speed and PM2.5 mass concentration, between 0-1260 m, the fluxes in urban areas and suburbs and surrounding areas showed an obvious trend of increasing net flux intensity with the increase in height above the ground. Furthermore, the transmission exchange between urban areas and suburbs and surrounding areas in January and April had the most obvious impact on the environment. The intensity of the maximum net flux in the lower urban areas and the suburbs in different seasons was significantly different, and the difference between the two was 2.23-4.48 times; however, the height characteristic difference in the intensity of the maximum net flux was small, mainly located at 611-1260 m.

A screening model-based study of transport fluxes and fate of airborne mercury deposited onto catchment areas

The rapid increase in the concentration of greenhouse gases in our atmosphere has led to significant changes in global climate. Methane is second to carbon dioxide in terms of its contribution to global warming. The wetlands serve as a major natural source of methane. Orissa State, located on the east coast of India, has a number of natural wetlands. Three representative wetlands: Chilka – the largest semi-saline lake of Asia, Anshupa – a land-locked fresh water lake and Gahirmatha – a tidal flood plain of Bhitara Kanika region that has sprawling mangrove vegetation (extension of the Sunderbans of the Gangetic delta) were chosen for intensive monitoring of water and sediment quality, along with methane flux over a period of three years during 1997–2000. The average seasonal methane fluxes were integrated to arrive at the annual flux from each wetland category. Finally, those results were extended to other natural wetlands of Orissa to arrive at the average annual methane flux of Orissa State. This is useful in calculating the total budget of greenhouse gases of India.

Fluxes of nutrients from the tropical River Hooghly at the land–ocean boundary of Sundarbans, NE Coast of Bay of Bengal, India

A stochastic flood generator and calibrated sediment transport formulae were used to assess the decadal impact of major river rehabilitation strategies on two fraction bed material sediment flux and net storage, first‐order indicators of aquatic riverine habitat, in a large river system. Model boundary conditions were modified to reflect the implementation of three major river rehabilitation strategies being considered in the Sacramento River Valley: gravel augmentation, setting back of levees, and flow alteration. Fifty 30‐year model simulations were used to compute probabilities of the response in sediment flux and net storage to these strategies. Total annual average bed material sediment flux estimates were made at six gauged river cross sections, and ∼60 km reach‐scale sediment budgets were evaluated between them. Gravel augmentation to improve spawning habitat induced gravel accumulation locally and/or downstream, depending on the added mixture. Levee setbacks to recreate the river corridor reduced flow stages for most flows and hence lowered sediment flux. Flow alteration to mimic natural flow regimes systematically decreased total annual average flux, suggesting that high‐magnitude low‐frequency transport events do not affect long‐term trends in bed material flux. The results indicate that each rehabilitation strategy reduces sediment transport in its target reaches and modulates imbalances in total annual bed material sediment budgets at the reach scale. Additional risk analysis is necessary to identify extreme conditions associated with variable hydrology that could affect rehabilitation over decades. Sensitivity analysis suggests that sorting of bed material sediment is the most important determinant of modeled transport and storage patterns.

Quantitative assessment of plastic waste in rubber plantations through modelling approach

Quantifying plastic pollution on surface water is essential to understand and mitigate the impact of plastic pollution to the environment. Current monitoring methods such as visual counting are labor intensive. This limits the feasibility of scaling to long‐term monitoring at multiple locations. We present an automated method for monitoring plastic pollution that overcomes this limitation. Floating macroplastics are detected from images of the water surface using deep learning. We perform an experimental evaluation of our method using images from bridge‐mounted cameras at five different river locations across Jakarta, Indonesia. The four main results of the experimental evaluation are as follows. First, we realize a method that obtains a reliable estimate of plastic density (68.7% precision). Our monitoring method successfully distinguishes plastics from environmental elements, such as water surface reflection and organic waste. Second, when trained on one location, the method generalizes well to new locations with relatively similar conditions without retraining (≈50% average precision). Third, generalization to new locations with considerably different conditions can be boosted by retraining on only 50 objects of the new location (improving precision from ≈20% to ≈42%). Fourth, our method matches visual counting methods and detects ≈35% more plastics, even more so during periods of plastic transport rates of above 10 items per meter per minute. Taken together, these results demonstrate that our method is a promising way of monitoring plastic pollution. By extending the variety of the data set the monitoring method can be readily applied at a larger scale.

The net mass flux from the stratosphere to the troposphere can be computed from the heating rate along the 380 K isentropic surface and the time rate of change of the mass of the lowermost stratosphere (the region between the tropopause and the 380 K isentrope) following Appenzeller et al. [1996]. Given this net mass flux and the cross‐tropopause diabatic mass flux, the residual adiabatic mass flux across the tropopause can also be estimated. These fluxes have been computed using meteorological fields from a free‐running general circulation model (the finite volume general circulation model) and two assimilated data sets, finite volume data assimilation system (FVDAS), and UK Met Office (UKMO). All of the calculations agree that the annual average net mass flux for the Northern Hemisphere is about 1010 kg/s. There is less agreement on the Southern Hemisphere flux that might be half as large. For all three data sets the adiabatic mass flux is from the upper troposphere into the lowermost stratosphere. This adiabatic flux into the lowermost stratosphere is roughly 5 times larger than the diabatic mass flux into the stratosphere across the tropical tropopause. For the FVDAS the midlatitude tropopause diabatic flux is smaller than UKMO, apparently due to a systematically colder, higher FVDAS tropopause. Both data assimilation systems have a warmer, lower midlatitude tropopause compared to radiosondes, so the mass flux estimates can be considered upper bounds. Finally, we note that the difference in the diabatic mass fluxes between the two assimilated meteorological analyses is much larger than the interannual variability in either.

Abstract. The Canadian Arctic Archipelago (CAA) serves as both a source and a sink for sea ice from the Arctic Ocean, while also exporting sea ice into Baffin Bay. We use observations from Sentinel-1, RADARSAT-2, the RADARSAT Constellation Mission (RCM), and CryoSat-2, together with the Canadian Ice Service ice charts, to quantify sea ice transport and replenishment across and within the CAA from 2016 to 2022. We also provide the first estimates of the ice area and volume flux within the CAA from the Queen Elizabeth Islands to Parry Channel, which spans the central region of the Northwest Passage shipping route. Results indicate that the CAA primarily exports ice to the Arctic Ocean and Baffin Bay, with an average annual (October to September) ice area flux of 137 ± 72 × 103 km2 and a volume flux of 58 ± 68 km3. The CAA contributes a larger area but smaller volume of ice downstream to the North Atlantic than what is delivered via Nares Strait. The average annual ice area flux from the Queen Elizabeth Islands to Parry Channel was 27 ± 10 × 103 km2 and the volume flux was 34 ± 12 km3, with a majority occurring through Byam Martin Channel, which is directly above the central region of Northwest Passage. Over our study period, annual multi-year ice (MYI) replenishment within the CAA was resilient, with an average of 14 ± 38 × 103 km2 imported from the Arctic Ocean and an average of 56 ± 36 × 103 km2 of first-year ice (FYI) retained following the melt season. The considerable ice flux to Parry Channel, together with sustained MYI replenishment, emphasizes the continued risk that sea ice poses to practical utilization of key shipping routes in the CAA, including the Northwest Passage.

We present helium 3 (3He) and dissolved oxygen (DO) distributions in the upper waters of the central Weddell Sea obtained from samples collected during the Winter Weddell Sea Project (WWSP, July to September 1986), and the Antarctic Zone Flux Experiment (ANZFLUX, July to August 1994). The data are discussed in terms of apparent entrainment rates of Weddell Deep Water (WDW) into the Winter Mixed Layer (WML) and the associated apparent heat flux. The fraction of WDW in the WML derived from the 3He excess (Δδ3He) and DO deficit in the mixed layer increases with latitude and reaches 10–20% at 68°S. The corresponding apparent heat flux during the winter entrainment period is 14 ± 4 W m−2, and the apparent annual heat flux is 6 ± 4 W m−2. Significantly larger heat fluxes (winter ocean heat flux of 25 W m−2; average annual heat flux of 15 W m−2) are observed near Maud Rise and in the region southwest of the rise in features that are associated with a Taylor column that apparently forms over the seamount. The entrainment rates and heat fluxes obtained from a one‐dimensional numerical model exceed those calculated from the WDW fraction in the WML by about a factor of two, mainly because of the effect of gas exchange through leads on the mass balance of 3He and DO in the WML. The best agreement between model calculations performed for 62.5°S, 65°S, and 67.5°S and observations is achieved for entrainment rates of 25–35 m yr−1, 30–40 m yr−1, and 35–45 m yr−1, respectively. Daily entrainment rates are practically identical (0.28–0.39 m d−1) for the three latitudes. Corresponding simulated heat fluxes for the winter entrainment period and the annual average are 36–50 W m−2 and 10–17 W m−2, respectively. Extrapolation of the annual average heat flux to the seasonally ice‐covered Weddell Sea yields a value of 0.04–0.07 PW.

The Land2Sea database contains data on the sizes of 1519 exorheic river drainage basins (79% of the exorheic land area), annual suspended sediment fluxes (593 rivers, 63% of the exorheic land area), and water discharges (1272 rivers, 76% of the exorheic land area) that have been compiled from a variety of sources. The database extends earlier compilations, such as GEMS/GLORI. The river basins are grouped into 19 large‐scale drainage regions to investigate the regional variability in freshwater and sediment fluxes to various ocean basins. The annual suspended sediment flux to the coastal ocean (∼18.5 × 109 tons) is dominated by east Asia (6.1 × 109 tons); Arabia, India, and southeast Asia (4.3 × 109 tons); and eastern South America (2.4 × 109 tons). Small topical islands of Oceania support the highest annual sediment fluxes per drainage area (∼9650 t km−2 a−1). Annual freshwater discharge to the coastal ocean (∼38,857 km3) is dominated by runoff from eastern South America (11,199 km3); east Asia (7114 km3); and Arabia, India, and southeast Asia (4384 km3). The empirical data agree well with results from global models (ART and BQART) that have been trained on a subset of the data compiled here.

CO2 emissions from subtropical arable soils of China