Average Annual Flux Research Articles

Characterizing spatiotemporal dynamics of anthropogenic heat fluxes: A 20-year case study in Beijing–Tianjin–Hebei region in China

Rapid urbanization, which is closely related to economic growth, human health, and micro-climate, has resulted in a considerable amount of anthropogenic heat emissions. The lack of estimation data on long-term anthropogenic heat emissions is a great concern in climate and urban flux research. This study estimated the annual average anthropogenic heat fluxes (AHFs) in Beijing–Tianjin–Hebei region in China between 1995 and 2015 on the basis of multisource remote sensing images and ancillary data. Anthropogenic heat emissions from different sources (e.g., industries, buildings, transportation, and human metabolism) were also estimated to analyze the composition of AHFs. The spatiotemporal dynamics of long-term AHFs with high spatial resolution (500 m) were estimated by using a refined AHF model and then analyzed using trend and standard deviation ellipse analyses. Results showed that values in the region increased significantly from 0.15 W· m−2 in 1995 to 1.46 W· m−2 in 2015. Heat emissions from industries, transportation, buildings, and human metabolism accounted for 64.1%, 17.0%, 15.5%, and 3.4% of the total anthropogenic heat emissions, respectively. Industrial energy consumption was the dominant contributor to the anthropogenic heat emissions in the region. During this period, industrial heat emissions presented an unstable variation but showed a growing trend overall. Heat emissions from buildings increased steadily. Spatial distribution was extended with an increasing tendency of the difference between the maximum and the minimum and was generally dominated by the northeast–southwest directional pattern. The spatiotemporal distribution patterns and trends of AHFs could provide vital support on management decision in city planning and environmental monitoring.

Spatiotemporal evolution of carbon sequestration of limestone weathering in China

Carbonate carbon sequestration (CS) can aid in solving the problem of terrestrial residual carbon sinks and imbalances in the global carbon budget. Thus, complete understanding of the magnitude, spatiotemporal distribution, and evolution of this sequestration is highly desirable. On the basis of random forest regression and maximal potential dissolution model for carbonate, we estimated the CS of typical carbonate weathering in China from 2000 to 2014, that is, the sequestration of limestone weathering, using long-term ecologic, meteorological, hydrological raster data, and monitored data from 44 watersheds in China and surrounding regions. We extended our analyses by systematically exploring the spatiotemporal pattern and evolution trend of the flux and total sequestration. High levels of ionic activity coefficients of Ca2+ and HCO 3 − in limestone regions were observed to be mainly distributed in Northern and Northwestern China with a clear gradient from northwest to southeast. With a contrary spatial pattern, the annual average CS flux (CSF) of limestone weathering in China was estimated to be 4.28 t C km−2 yr−1, with high values mainly in the karst zones in Southeastern China. The mean CSF in different latitudes showed that Southern China (south of 28.14°N) was the region with the largest interannual fluctuation of flux and CSF increases as latitude decreases. The mean CSF in subtropical and tropical (TR) regions was the maximum of all major climate types, and for the frigid (F), mid-temperate (MTE), warm temperate (WTE), and temperate (TE) major climates; the CSF in the desert (D) subdivided climate was the minimum of these climates. By contrast, the values in grassland (G) and broad-leaved forest subdivided climate were the maximum. The pixel-based trend analysis indicated that the CSF of limestone weathering in China was slightly increasing in the period 2000–2014 with a rate of 0.036 t C km−2 yr−1. Furthermore, the annual total CS was estimated to be 7.07 Tg carbon per year (Tg C yr−1) with high levels in 2002, 2008, and 2010, and the minimum appeared in 2011 with a slightly increasing trend of the total CS being observed with a rate of 0.06 Tg C yr−1. Tibet Autonomous Region was the administrative division with the largest total CS of limestone weathering (1.20 Tg C yr−1) in China, and karst zones in Southeastern China had the largest total CS (4.95 Tg C yr−1) which accounts for 70.01% of that in the three divided karst regions. On the basis of the diversity of rock chemical weathering carbon cycle mechanisms of different carbonate rock types, we estimated that the total CS of carbonate weathering in China may reach 11.37 Tg C yr−1 (the sink was approximately 5.02 t C km−2 yr−1), which amounts to 16.20% of the total biomass CS in China, furthermore, the CSF of carbonate weathering in China can reach 6.54 t C km−2 yr−1 if excluding the interference of the negative runoff. This finding indicates that CS of carbonate weathering is an indispensable part of China’s terrestrial carbon sink system. The research pattern of this study was important for further improving the accuracy of the estimation for the global carbonate weathering carbon sink.

Assessment of the wave energy resource in the South China Sea

Assessments of wave energy resources form the basis of plans for developing and using wave energy, and provide guidance about where to site wave power stations and how to design wave energy convertors. Various indexes, including the spatial and temporal distributions of wave energy fluxes, the occurrence of the effective significant wave height, monthly and seasonal variability and the frequency of high sea states, were calculated from the recent 37-year European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis of wave field data. The results showed that areas with abundant and stable exploitable wave energy in the South China Sea were mainly between the Luzon Strait and the southeast of the Indo-China Peninsula, where the annual average wave energy fluxes ranged from 10 to 18 kW/m and the monthly and seasonal variability indexes were less than 2·2 and 1·6, respectively. The wave energy was found to be poor in some coastal areas of the Beibu Gulf, the Gulf of Thailand and the Sulu Sea. In the areas where wave energy was abundant, high sea states occurred frequently, meaning that it was relatively difficult to use the energy. Therefore, the wave energy resources and the frequency of high sea states need to be considered when choosing sites for wave energy farms.

Characterization of Wave Energy Potential for the Baltic Sea with Focus on the Swedish Exclusive Economic Zone

In this study, a third-generation wave model is used to examine the wave power resource for the Baltic Sea region at an unprecedented one-kilometer-scale resolution for the years 1998 to 2013. Special focus is given to the evaluation and description of wave field characteristics for the Swedish Exclusive Economic Zone (SEEZ). It is carried out to provide a more detailed assessment of the potential of waves as a renewable energy resource for the region. The wave energy potential is largely controlled by the distance from the coast and the fetch associated with the prevailing dominant wave direction. The ice cover is also shown to significantly influence the wave power resource, especially in the most northern basins of the SEEZ. For the areas in focus here, the potential annual average wave energy flux reaches 45 MWh/m/year in the two sub-basins with the highest wave energies, but local variations are up to 65 MWh/m/year. The assessment provides the basis for a further detailed identification of potential sites for wave energy converters. An outlook is given for additional aspects studied within a broad multi-disciplinary project to assess the conditions for offshore wave energy conversion within the SEEZ.

Characterizing Spatiotemporal Dynamics of CH₄ Fluxes from Rice Paddies of Cold Region in Heilongjiang Province under Climate Change.

Paddy fields have become a major global anthropogenic CH4 emission source, and climate change affects CH4 emissions from paddy ecosystems by changing crop growth and the soil environment. It has been recognized that Heilongjiang Province has become an important source of CH4 emission due to its dramatically increased rice planting area, while less attention has been paid to characterize the effects of climate change on the spatiotemporal dynamics of CH4 fluxes. In this study, we used the calibrated and validated Long Ashton Research Station Weather Generator (LARS-WG) model and DeNitrification-DeComposition (DNDC) model to simulate historical and future CH4 fluxes under RCP 4.5 and RCP 8.5 of four global climate models (GCMs) in Heilongjiang Province. During 1960–2015, the average CH4 fluxes and climatic tendencies were 145.56 kg C/ha and 11.88 kg C/ha/(10a), respectively. Spatially, the CH4 fluxes showed a decreasing trend from west to east, and the climatic tendencies in the northern and western parts were higher. During 2021–2080, the annual average CH4 fluxes under RCP 4.5 and RCP 8.5 were predicted to be 213.46 kg C/ha and 252.19 kg C/ha, respectively, and their spatial distributions were similar to the historical distribution. The average climatic tendencies were 13.40 kg C/ha/(10a) and 29.86 kg C/ha/(10a), respectively, which decreased from west to east. The simulation scenario analysis showed that atmospheric CO2 concentration and temperature affected CH4 fluxes by changing soil organic carbon (SOC) content and plant biomass. This study indicated that a paddy ecosystem in a cold region is an important part of China’s greenhouse gas emission inventory in future scenarios.

Effects of afforestation on soil nitrous oxide emissions in a subtropical montane agricultural landscape: A 3-year field experiment

Afforestation, through the conversion of upland cropland to forest, is of great significance to land use change in montane (hilly) agricultural landscapes worldwide. Such afforestation is implemented to improve soil and water conservation and facilitate terrestrial carbon sequestration. However, particularly for subtropical and tropical regions, the effects of afforestation on soil N2O emissions have not been well investigated. Therefore, a three-year field experiment was conducted to simultaneously monitor N2O emissions from three paired sites of afforestation with cypress (Cypressus funebris) and adjacent cropland under a wheat-maize rotation system. The experiment was carried out in a subtropical montane agricultural landscape in southwest China. In both forest and cropland ecosystems, the N2O emissions exhibited a pronounced spatial and temporal variability. These variations in N2O emissions can be well explained by the spatiotemporal dynamics of environmental variables, such as soil temperature, WFPS, soil NH4+ or NO3− availability, because these environmental variables correlated significantly with the N2O emissions across different experimental sites and years. The average annual N2O fluxes were 2.69 kg N ha-1 for cropland and 0.13 kg N ha-1 for afforestation. It is noteworthy that the annual N2O fluxes for afforestation found in the present study constitute one of the lowest recorded N2O fluxes for unfertilized forest ecosystems globally. Overall, across all experimental sites and years, afforestation with cypress (Cypressus funebris) stands significantly decreased N2O fluxes by over twenty times relative to the adjacent cropland. This outcome suggests that afforestation could be an effective mitigation strategy for soil N2O emissions in a subtropical montane agricultural landscape.

Sources and dry deposition of carbonaceous aerosols over the coastal East China Sea: Implications for anthropogenic pollutant pathways and deposition

75 paired TSP and PM2.5 samples were collected over four seasons on Huaniao Island (HNI), an island that lies downwind of continental pollutants emitted from mainland China to the East China Sea (ECS). These samples were analyzed for organic carbon (OC) and elemental carbon (EC), with a special focus on char-EC (char) and soot-EC (soot), to understand their sources, and the scale and extent of pollution and dry deposition over the coastal ECS. The results showed that char concentrations in PM2.5 and TSP averaged from 0.13 to 1.01 and 0.31–1.44 μg m−3; while for soot, they were from 0.03 to 0.21 and 0.16–0.56 μg m−3, respectively. 69.0% of the char and 36.4% of the soot were present in PM2.5. The char showed apparent seasonal variations, with highest concentrations in winter and lowest in summer; while soot displayed maximum concentrations in fall and minimum in summer. The char/soot ratios in PM2.5 averaged from 3.29 to 17.22; while for TSP, they were from 1.20 to 7.07. Both of the ratios in PM2.5 and TSP were highest in winter and lowest in fall. Comparisons of seasonal variations in OC/EC and char/soot ratios confirmed that char/soot may be a more effective indicator of carbonaceous aerosol source identification than OC/EC. Annual average atmospheric dry deposition fluxes of OC and EC into ECS were estimated to be 229 and 107 μg m−2 d−1, respectively, and their deposition fluxes significantly increased during episodes. It was estimated that the loadings of OC + EC and EC accounted for 1.3% and 4.1% of the total organic carbon and EC in ECS surface sediments, respectively, implying a relatively small contribution of OC and EC dry deposition to organic carbon burial. This finding also indicates a possibly more important contribution of wet deposition to organic carbon burial in sediments of ECS, and this factor should be considered for future study.

First Assessment of Inorganic Nitrogen Deposition Budget Following the Impoundment of a Subtropical Hydroelectric Reservoir (Nam Theun 2, Lao PDR)

AbstractWith around 490 km2 at full level of operation, the Nam Theun 2 Reservoir (NT2R) is one of the largest hydroreservoir in Southeast Asia. This study presents a first estimation of the atmospheric inorganic nitrogen deposition into the NT2R based on a 2‐year monitoring (June 2010 to July 2012) including gas concentrations and precipitation. Dry deposition fluxes are estimated by the inferential method using, on the one hand, surface measurements of gas concentrations (NO2, HNO3, NH3) from passive samplers and, on the other hand, modeled exchange rates. Wet deposition fluxes are calculated from NH4+ and NO3− concentrations determined in samples of rain from an automatic precipitation collector. The average nitrogen deposition flux is estimated at 1.26 ± 0.14 kgN·ha−1·year−1 from dry processes and 5.01 ± 0.92 kgN·ha−1·year−1 from wet ones, that is, an average annual total nitrogen flux of 6.27 ± 1.06 kgN·ha−1·year−1 deposited at the NT2R with 80% from wet deposition. Before impoundment, the mean N flux has been estimated at 3.42 ± 1.88 kgN·ha−1·year−1 for dry deposition and 5.01 ± 2.12 kgN·ha−1·year−1 for wet deposition, or a total N deposition flux of 8.43 ± 4.01 kgN·ha−1·year−1 over the studied area dominated by forests with little agriculture soil and water surfaces. Thus, the total N deposition over the studied area has been reduced of 26% (or 63% for dry deposition) following the reservoir impoundment based on our working hypothesis.

An Integrated Methodology to Analyze the Total Nitrogen Accumulation in a Drinking Water Reservoir Based on the SWAT Model Driven by CMADS: A Case Study of the Biliuhe Reservoir in Northeast China

Human activities, especially dam construction, have changed the nutrient cycle process at the basin scale. Reservoirs often act as a sink in the basin and more nutrients are retained due to sedimentation, which induces the eutrophication of the surface water system. This paper proposes an integrated methodology to analyze the total nitrogen (TN) accumulation in a drinking water reservoir, based on the soil and water assessment tool (SWAT) model driven by the China Meteorological Assimilation Driving Datasets for the SWAT model (CMADS). The results show that the CMADS could be applied to drive the SWAT model in Northeast China. The dynamic process of TN accumulation indicates that the distribution of TN inputted into the reservoir fluctuated with the dry and wet seasons from 2009–2016, which was mainly governed by the amount of runoff. The annual average TN input and output fluxes of the Biliuhe reservoir were 274.41 × 104 kg and 217.14 × 104 kg, which meant that 19.76% of the TN input accumulated in the reservoir. Higher TN accumulation in the reservoir did not correspond to a higher TN load, due to the influence of flood discharge and the water supply. Interestingly, a higher TN accumulation efficiency was observed in normal hydrological years, because the water source reservoir always stores most of the water input for future multiple uses but rarely discharges surplus water. The non-point sources from fertilizer and atmospheric deposition and soils constituted the highest proportion of the TN input, accounting for 35.15%, 30.15%, and 27.72% of the average input. The DBWD (Dahuofang reservoir to Biliuhe reservoir water diversion) project diverted 32.03 × 104 kg year−1 TN to the Biliuhe reservoir in 2015–2016, accounting for 14.05% of the total annual input. The discharge output and the BDWD (Biliuhe reservoir to Dalian city water diversion) project output accounted for 48.75% and 47.74%, respectively. The effects of inter-basin water diversion projects should be of great concern in drinking water source water system management. There was a rising trend of TN level in the Biliuhe reservoir, which increases the eutrophication risk of the aquatic ecosystem. The TN accumulated in the sediment contributed to a large proportion of the TN accumulated in the reservoir. In addition to decreasing the non-point source nitrogen input from the upper basin, discharging anoxic waters and sediment with a high nitrogen concentration through the bottom hole of the dam could alleviate the nitrogen pollution in the Biliuhe reservoir.

On the Contribution of the Eddy Transport to the Annual Mean Heat Budget of the Upper Layer in the North Atlantic

According to Ocean Re-Analysis System 3 (ORA-S3) data, all components of the annual mean heat budget of the upper quasi-homogeneous ocean layer (UQL) in the North Atlantic for the period of 1959–2011 have been calculated and errors of these estimates have been determined. It has been shown that the contribution of the horizontal eddy diffusivity (estimated as a residual term of the UQL heat balance equation) to changes in the UQL annual mean temperature is significantly overestimated. This takes place mainly due to neglecting the covariances of seasonal fluctuations of current velocity vector components and UQL temperature gradients in calculations carried out with the use of annual average values. These covariances play an important role in the annual mean heat budget in some regions of the North Atlantic, especially in tropical latitudes. Changes in the annual average UQL temperature in the central and eastern parts of the North Atlantic are significantly affected by errors related to an inaccuracy of estimates of annual average heat fluxes on the ocean surface. The maximum contribution of the horizontal eddy diffusivity to the interannual variability of the UQL temperature is observed in the northwestern part of the North Atlantic and the region of the Subpolar Gyre.

Investigating reservoir sedimentation and its implications to watershed sediment yield: The case of two small dams in data‐scarce upper Blue Nile Basin, Ethiopia

AbstractBathymetric and sedimentation surveys were conducted with a sonar‐based depth gauge system in two small reservoirs (Selamko and Shina) in the data‐scarce upper Blue Nile Basin, Ethiopia. Bathymetric survey data were merged within geographic information system (GIS) software to provide detailed visualization and analyses of current depths. Preimpoundment topographic information was obtained from dam owners and designers. Bathymetric differencing was used to investigate and quantify the distribution and estimate volumes of deposited sediment, long‐term average annual sediment fluxes and remaining water storage capacity. Calculated long‐term average sediment accumulation rates were used to estimate remaining lifetimes of each reservoir. Results from the depth sonar surveys and GIS analyses suggest a projected lifetime of ~7 years for Shina Reservoir, compared to a projected lifetime of ~22 years for Selamko Reservoir. It also indicated the annual average sedimentation rate for both reservoirs was greater than the global average of one per cent (1.67% for Shina Reservoir; 2.295% for Selamko Reservoir). The specific sediment yield (SSY) is relatively larger for both watersheds (2,499 and 4,333.6 t km−2 year−1 for Shina and Selamko, respectively) indicating the watersheds are degraded by any global standard. The Revised Universal Soil Loss Equation (RUSLE) model‐generated erosion magnitude was only slightly larger from the watersheds of both reservoirs, compared to the bathymetric estimates. These data and analyses also provide a baseline relevant to understanding sedimentation processes and are necessary for developing long‐term management plans for these reservoirs and their watersheds.

Estimation of Available Wave Energy in the Barents Sea

The purpose of this research is to estimate the energy potential of the Barents Sea based on numerical modeling of the wave energy over a long period of time from 1979 to 2010. Using the WaveWatchIII wave model, the wave energy flux in the open part and in the coastal zone of the Barents Sea has been calculated. The calculations are based on the data of the NCEP/CFSR reanalysis with spatial resolution of 0.3°. The calculations were performed on a unstructured grid, which has high spatial resolution at the shore (200–500 m). The long-term average annual significant wave height1 varies from 1.5–2.0 m for the open part of the Barents Sea to 1.0–1.5 m in the coastal zone of Murmansk oblast. The long-term average annual wave energy flux varies from 15–20 kW/m for the open part of the Barents Sea to 5–10 kW/m in the coastal zone of Murmansk region. The probability of exceedance of wave energy of more than 1 kW/m is 80–90% for the open part of the sea and 70–75% at the northeastern coast of the Rybachy Peninsula. To the east and west of the peninsula, this figure decreases significantly. Near the village of Teriberka, the probability of exceedance of the wave energy is 65–70%. The probability of exceedance of energy of more than 5 kW/m is 50–60% in the open sea and it does not exceed 35% in the coastal zone. The average probability of exceedance of the wave energy is subject to seasonal fluctuations. Thus, in the coastal zone, the probability of exceedance of energy of 1 kW/m is approximately 90% in the winter months and it does not exceed 50% in summer. The obtained results can be applied to designing a wave power station in the Barents Sea.

Seasonal and Spatial Variation of Nitrogen Oxide Fluxes from Human-Disturbance Coastal Wetland in the Yellow River Estuary

Anthropogenic activities strongly affect greenhouse gases emissions in coastal wetland. In situ field study was conducted to explore the effects of anthropogenic activities on the N2O emissions, used static, manual stainless steel chambers in four seriously disturbed coastal wetlands (west side of the seawall, WSS; oil field existed, OF; Spartina alterniflora coastal marsh, SCM; and aquaculture pond, ACP) in the Yellow River estuary. Results showed that N2O emissions showed significant seasonal variation (p < 0.05). The maximum values were found in August at WSS and ACP, in December and April at SCM and OF, while minimal values were observed in April, February, October, and August, respectively. The annual average N2O fluxes from WSS, OF, SCM, and ACP were 13.24, 9.83, 8.11 and 2.70 μg N2O m−2 h−1, and the variance analysis results showed that the difference between WSS and ACP reached significant level (p < 0.05). For each month, significant differences were observed between WSS and ACP during June, December and February, WSS and SCM during October, and SCM and ACP during December (p < 0.05). Basing on previous natural wetland measurements, we found that seawall construction and S. alterniflora invasion significantly affected the N2O fluxes in the Yellow River estuary, especially seawall construction which accelerated N2O emissions due to its block of seawater migration, resulting in changes of soil physicochemical properties. Pearson correction analysis showed that significant correlations were observed between N2O emissions and electrical conductivity at WSS and OF, while other environmental factors (temperature, water content, total carbon, total nitrogen, C/N ratio) had no significant effect, which indicated that electrical conductivity was the most important factor that affected N2O emissions in these sampling sites. Our results suggested that there could be considerable changes of N2O emissions as a response of artificial disturbance, particularly seawall construction.

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

Atmospheric concentrations of nitrous oxide (N2O) have increased over the last 150 years due to human activities. Soils are important source of N2O where its production is largely regulated by biological processes. Nitrogen (N) deposition can alter the processes of autotrophic nitrification and denitrification, thus affecting the rate and direction of the soil N2O exchange with the atmosphere. It is obvious that atmospheric N deposition has influenced a dry alpine meadow in the Qinghai–Tibetan Plateau (QTP). Therefore, we investigated the effects of N deposition on the annual N2O emissions in an alpine meadow of the QTP. The N2O flux was measured for 2 years using static chambers and gas chromatography methods at four treatments (N0, background level; N7, add 7 kg N ha−1 yr−1; N20, add 20 kg N ha−1 yr−1; N40, add 40 kg N ha−1 yr−1). We found that high N deposition increased the N2O flux, not only in the growing season but also in winter and the spring thaw period. The average annual N2O fluxes at N0 and N40 plots were 3.1 and 6.1 μg m−2 h−1, respectively. Compared with N0, the average annual N2O fluxes increased at N7, N20, and N40 plots by 13.7%, 47.6%, and 98.7%, respectively, the N2O fluxes in N40 plots increased by 113.6%, 41.6%, and 78.7% during the growing season, winter and spring thaw period, respectively. The emission of N2O during the growing season, winter and spring thaw period accounted for 63.2%, 29.9% and 6.9% of annual total emission of N2O, respectively. The N2O flux correlated significantly with air temperature, soil temperature, soil water content, total nitrogen, total organic carbon, and soil NH4+–N content in the alpine meadow.

Role of Scirpus mariqueter on Methane Emission from an Intertidal Saltmarsh of Yangtze Estuary

The role of wetland plant (Scirpus mariqueter) on methane (CH4) emissions from a subtropical tidal saltmarsh of Yangtze estuary was investigated over a year. Monthly CH4 flux and pore-water CH4 concentration were characterized using static closed chamber technique and pore-water extraction. Measured chamber CH4 fluxes indicated that saltmarsh of the Yangtze estuary acted as a net source of atmospheric CH4 with annual average flux of 24.0 mgCH4·m−2·day−1. The maximum chamber CH4 flux was in August (91.2 mgCH4·m−2·day−1), whereas the minimum was observed in March (2.30 mgCH4·m−2·day−1). Calculated diffusion CH4 fluxes were generally less than 6% of the chamber fluxes. Significant correlations were observed between the chamber CH4 flux and rhizospheric pore-water CH4 concentration (11–15 cm: p &lt; 0.05, R = 0.732; 16–20 cm: p &lt; 0.05, R = 0.777). In addition, chamber CH4 fluxes from July to September constituted more than 80% of the total annual emission and were closely correlated with aboveground biomass yield of S. mariqueter. The results indicated that S. mariqueter transportation was the dominant CH4 emission pathway and it provided an efficient route for the belowground CH4 to escape into the atmosphere while avoiding oxidation, leading to CH4 emissions.

Sediment Flux of Particulate Organic Phosphorus in the Open Black Sea

The interannual variation of the monthly average (weighted average) concentrations of particulate organic phosphorus (PPOM) in the photosynthetic layer, oxycline, redox zone, and H2S zone in the open Black Sea is estimated based on long-term observation data. The suspension sedimentation rates from the studied layers are assessed using model calculations and published data. The annual variation of PPOM sediment fluxes from the photosynthetic layer, oxycline, redox zone, and upper H2S zone to the anaerobic zone of the sea and the correspondingly annual average values are estimated for the first time. A regular decrease in the PPOM annual average flux with depth in the upper active layer is demonstrated. A correlation between the annual average values of PPOM sediment flux from the photosynthetic layer and ascending phosphate flux to this layer is shown, which suggests their balance in the open sea. The results are discussed in terms of the phosphorus biogeochemical cycle and the concept of new and regenerative primary production in the open Black Sea.

Satellite estimation of coastal pCO2 and air-sea flux of carbon dioxide in the northern Gulf of Mexico

Satellite approaches for estimation of the partial pressure of CO2 (pCO2) and air-sea flux of CO2 in coastal regions offer the potential to reduce uncertainties in coastal carbon budgets and improve understanding of spatial and temporal patterns and the factors influencing them. We used satellite-derived products in combination with an extensive data set of ship-based observations to develop an unprecedented multi-year time-series of pCO2 and air-sea flux of CO2 in the northern Gulf of Mexico for the period 2006–2010. A regression tree algorithm was used to relate satellite-derived products for chlorophyll, sea surface temperature, and dissolved and detrital organic matter to ship observations of pCO2. The resulting relationship had an r2 of 0.827 and a prediction error of 31.7μatm pCO2 (root mean-squared error of the relationship was 28.8μatm). Using a wind speed and gas exchange relationship along with satellite winds, estimates of air-sea flux of CO2 were derived yielding an average annual flux over the period 2006–2010 of −0.8 to −1.5 (annual mean=−1.1±0.3) molCm−2y−1, where the negative value indicates net ocean uptake. The estimated total annual CO2 flux for the study region was −4.3+1.1TgCy−1. Relationships of satellite-derived pCO2 with salinity were consistent with shipboard observations and exhibited a concave relationship with low values at mid- and low salinities attributed to strong biological drawdown of CO2 in the high productivity river-mixing zone. The time-series of satellite-derived pCO2 was characterized by a seasonal pattern with values lower during winter and spring, low to intermediate values during fall, and higher and more variable values during summer. These findings were similar to simulations from a coupled physical-biogeochemical model. A seasonal pattern was also evident in the air-sea flux of CO2 with generally more negative fluxes (i.e., ocean uptake) during winter and spring, and positive fluxes during summer months with fall being a period of transition. Interannual variations in annual means of both air-sea flux of CO2 and DIN loading were significant, with higher DIN loading coinciding in some cases with more negative air-sea flux of CO2 (i.e., net ocean uptake). Spatial patterns of pCO2 reflected regional environmental forcing including effects of river discharge, wind forcing, and shelf-slope circulation. Our study also illustrates the utility of satellite extrapolation for highlighting areas that may contribute significantly to regional signals and for guiding prioritization of locations for acquiring further observations. The approach should be readily applicable to other regions given adequate availability of in situ observations for algorithm development.

A three-year experiment of annual methane and nitrous oxide emissions from the subtropical permanently flooded rice paddy fields of China: Emission factor, temperature sensitivity and fertilizer nitrogen effect

Annual CH4 and N2O emissions from these rice production systems that accounts for over 10% of national rice cultivation of China are rarely reported. To improve understanding of greenhouse gas emissions from croplands in China, we measured methane (CH4) and nitrous oxide (N2O) emissions from the subtropical permanently flooded rice paddy fields through a 3-year field experiment that utilized three nitrogen fertilizer application rates (0 [N0], 150 [N150] and 250 [N250] kg N ha−1) in southwestern China. Results showed that seasonal patterns of CH4 and N2O emissions were consistent with temporal weather patterns. The average annual cumulative CH4 fluxes were in the range of 794 to 883 kg CH4-C ha−1 yr−1 and N2O fluxes ranged from 1.61 to 3.10 kg N2O-N ha−1 yr−1 across the experimental treatments. The Q10 values (soil temperature sensitivity coefficient) of CH4 and N2O emissions were 2.72–3.67 and 3.32–6.05, respectively, for the three treatments. Inconsistent with our hypothesis, the nitrogen fertilizer application did not increase seasonal and annual N2O emissions over three years, compared to the control. Thus, the annual direct N2O emission factors (EFd) averaged 0.07%, which was substantially lower than the IPCC default value of 0.30% for rice paddy fields. Nitrogen fertilizer application significantly decreased the mean seasonal global warming potential (GWP) and yield-scaled GWP for the rice season, whereas this was not true on an annual basis if fallow season was also considered. Since CH4 emission was the major contributor to total GWP, it is necessary to propose mitigation options, which could include draining the floodwater layer and introducing upland crops during the fallow season. However, it will be challenging to reduce N2O emissions and retain soil organic carbon if the floodwater layer is drained and upland crops are introduced during the fallow season.

Mercury Release Flux and Its Influencing Factors Under Four Typical Vegetation Covers at Jinyun Mountain, Chongqing

In order to reveal the characteristics of mercury release flux and exchange across the soil/atmosphere interface under different vegetation cover types, four of these types (evergreen broad-leaved forest, bamboo forest, shrub, and grassland) were chosen as research samples at Jinyun Mountain National Nature Reserve, Chongqing, Continuous monitoring of the different vegetation covers, soil/atmosphere interface, and mercury release flux was conducted, at the same time as the effects of environmental factors were also considered. Results show that the annual average Hg emission flux for the four kinds of forest cover have obvious differences. The overall emission performance of Hg is ranked as:bamboo forest[17.77 ng·(m2·h)-1] > grassland[17.58 ng·(m2·h)-1] > shrubbery[16.87 ng·(m2·h)-1] > evergreen broad-leaved forest[14.32 ng·(m2·h)-1]. There are obviously seasonal differences between Hg emission and the four kinds of forested stands in Jinyun mountain and there are significant differences among the different forests. These differences mainly reflect that emissions in the warm season are higher than in the cold season. There is also an obvious diurnal variation of soil mercury release flux from different forested stands in Jinyun Mountain. Meteorological factors of light intensity, air temperature, soil temperature, and relative humidity also effects the soil/air interface meaning that mercury flux is not the same across land cover types. Temperature is the main factor affecting evergreen broad-leaved forest, shrub forests, and bamboo forests. Light intensity is the main influencing factor for grasslands.

Distribution and migration of 239+240Pu in abiotic components of the Black Sea ecosystems during the post-Chernobyl period

Distribution of 239,240Pu in abiotic components (water and bottom sediment) of the Black Sea ecosystems was studied during the post-Chernobyl period at different offshore and near-shore locations. The trends of these radionuclides accumulation by sediments were analyzed. The spatial-temporal changes in the 239,240Pu distribution as well as effective half-life for these radionuclides in the Black Sea surface water in deep-sea area are presented. The estimations of the average annual removal fluxes of the 239,240Pu into the bottom sediments were obtained. The Black Sea sediments were characterized by a higher 239,240Pu concentration factor (Cf ≈ n·104–n·106) and radiocapacity factor (F(239,240Pu) was about 99.9% on the shelf, 94.5–99.1% on deep-sea basin for silty and 94.6–98.9% on the shelf for sandy bottom sediments) as compared with Cf and F for 137Cs and 90Sr. Silty bottom sediments play the role of 239,240Pu main depot in the Black Sea ecosystem. The studied radioecological characteristics of Pu allowed us to define the type of plutonium biogeochemical behavior in the Black Sea as a pedotropic one. The results of this complex radioecological monitoring of 239+240Pu contamination in the Black Sea and their analysis makes it possible to understand the plutonium redistribution pathways which will enable to carry out the tracing of its migration within the ecosystems.