The streamflow trend in Tangwang River basin in northeast China and its difference response to climate and land use change in sub-basins

In this study, the hydro-climatic trends (1964–2006) of Tangwang River basin (TRB) were examined using the Kendall’s test. Moreover, the impacts of climate variability and land use change on streamflow in each sub-basin were assessed using the Soil and Water Assessment Tools (SWAT) model. The results indicated that annual mean flow and peak flow showed insignificant decreasing trends (?0.14 m³ s^?1 year^?1, 1 %; ?8.67 m³ s^?1 year^?1, 40 %), while annual low flow exhibited a slightly increasing trend (0.02 m³ s^?1 year^?1, 11 %). Correspondingly, the annual precipitation for the entire basin decreased by 0.02 mm year^?2, while the annual means of daily mean, maximum and minimum temperature increased significantly by 0.07, 0.10 and 0.02 °C year^?1, respectively. On the other hand, with the implementation of “Natural Forest Protection Project” and “Grain for Green Project”, the forests in TRB totally increased by 744.5 km² (4.00 %) from 1980 to 2000. Meanwhile, the grasslands and the farmlands decreased by 378.0 km² (?1.98 %) and 311.9 km² (?1.63 %), respectively. Overall, land use changes played a more important role for the streamflow reduction than climate change for SUB1, SUB2 and SUB3, in which the primary conversions were from grassland, farmland and bare land to forests. Conversely, in SUB4, the influence of climate variability was predominant. The results obtained could be a reference for water resources planning and management under changing environment.     

Carbon dynamics of temperate grassland ecosystems in China from 1951 to 2007: an analysis with a process-based biogeochemistry model

Grasslands account for 40 % of the Chinese land area. About 80 % of the total grasslands are in the northern temperate zone. These grassland ecosystems provide goods and services to the local people and play an important role in the global carbon cycle. Remote sensing and ecosystem modeling approaches have been used to quantify the carbon budget of these grasslands. However, the intensive site measurements and meteorological data acquired in these ecosystems in the last few decades have not been adequately used to improve ecosystem model capabilities, in turn, better quantify their carbon budget. In this study an effort was made to examine the carbon budget and its spatial–temporal variation of the temperate grasslands in China from 1951 to 2007 using a process-based biogeochemistry model. It was found that the regional grasslands acted as a small carbon sink at 11.25 g C m^?2 year^?1 in the study area of 64.96 million hectares with a high inter-annual variability ranging from ?124 to 122.7 g C m^?2 year^?1 during the study period. As a result, the temperate grasslands sequestered about 410 Tg C in their vegetation and soils during the study period. The carbon sink occurred in typical steppe in central Inner Mongolia within the 300–400 mm rainfall zone and forest steppe in central and western China. By contrast, forest steppe in northeastern China mainly acted as a carbon source. Three major ecosystem types of forest steppe, typical steppe and desert steppe account for 54, 34, and 12 % of the total sink (7.3 Tg C year^?1) during 1951–2007, respectively. Soil moisture and evapotranspiration had a dominant effect on carbon budget in the typical steppe and the forest steppe while both water conditions and nitrogen mineralization rate were the major factors in the desert steppe. At a decadal scale, the air temperature significantly increased by 0.4 °C and annual precipitation insignificantly decreased by 0.2 mm; the regional carbon sink increased by 2.2 Tg C per decade during the period 1951–2007. However, further sensitivity analysis suggests that the sink of temperate grasslands will be reduced if the climate gets warmer and drier during this century since the increasing net primary production does not keep up with the increase of heterotrophic respiration.     

Submarine Groundwater Discharge as a Source of Dissolved Inorganic Nitrogen and Phosphorus to Coastal Ponds of Southern Rhode Island

Measurements of groundwater-dissolved inorganic nitrogen (nitrate?+?nitrite?+?ammonia) and phosphate concentrations were combined with recent, radium-based, submarine groundwater discharge (SGD) fluxes and prior estimates of SGD determined from Darcy’s Law, a hydrologic model, and total recharge to yield corresponding SGD nutrient fluxes to Ninigret, Point Judith, Quonochontaug, and Winnapaug ponds, located in southern Rhode Island. Results range from 80 to279 mmol N m^?2 year^?1 and 4 to 15 mmol P m^?2 year^?1 for Ninigret, 48 to 265 mmol N m^?2 year^?1 and 4 to 23 mmol P m^?2 year^?1 for Point Judith, 31 to 62 mmol N m^?2 year^?1 and 1 to 2 mmol P m^?2 y^?1 for Quonochontaug, and 668 to 1,586 mmol N m^?2 year^?1 and 29 to 70 mmol P m^?2 year^?1 for Winnapaug ponds, respectively. On a daily basis, the SGD supply of dissolved inorganic nitrogen and phosphorus is estimated to represent ～1–6 % of the total amount of these nutrients in surface waters of Ninigret, Point Judith, and Quonochontaug ponds and up to 84 and 17 % for Winnapaug, respectively, which may reflect a greater SGD nutrient supply to this pond because of the proximity of fertilized golf courses. With regard to the total external input of these essential nutrients, SGD represents 29–45 % of dissolved inorganic nitrogen input to Ninigret, Point Judith, and Quonochontaug ponds and as much as 93 % for Winnapaug pond. For phosphorus, the contribution from SGD represents 59–85 % of the total external input for Ninigret, Point Judith, and Quonochontaug ponds and essentially all of the phosphorus input to Winnapaug pond. Estimated rates of primary productivity potentially supported by the average supply of dissolved inorganic nitrogen from SGD range from 10 g C m^?2 year^?1 for Ninigret, 13 g C m^?2 year^?1 for Point Judith, 4 g C m^?2 year^?1 for Quonochontaug, and as high as 84 g C m^?2 y^?1 for Winnapaug pond. The imputed SGD-derived rates of primary productivity represent 4–9 % of water column primary production for Ninigret, Point Judith, and Quonochontaug ponds, and 74 % for Winnapaug pond, a result that is reasonably comparable to several other coastal environments where estimates of SGD nutrient supply have been reported. The implication is that SGD represents an ecologically significant source of dissolved nutrients to the coastal salt ponds of southern Rhode Island and, by inference, other coastal systems.     

Seasonal and Inter-annual Patterns in Primary Production,Respiration, and Net Ecosystem Metabolism in Three Estuaries in the Northeast Gulf of Mexico

Measurements of primary production and respiration provide fundamental information about the trophic status of aquatic ecosystems, yet such measurements are logistically difficult and expensive to sustain as part of long-term monitoring programs. However, ecosystem metabolism parameters can be inferred from high frequency water quality data collections using autonomous logging instruments. For this study, we analyzed such time series datasets from three Gulf of Mexico estuaries: Grand Bay, MS; Weeks Bay, AL; and Apalachicola Bay, FL. Data were acquired from NOAA's National Estuarine Research Reserve System Wide Monitoring Program and used to calculate gross primary production (GPP), ecosystem respiration (ER), and net ecosystem metabolism (NEM) using Odum's open water method. The three systems represent a diversity of estuaries typical of the Gulf of Mexico region, varying by as much as two orders of magnitude in key physical characteristics, such as estuarine area, watershed area, freshwater flow, and nutrient loading. In all three systems, GPP and ER displayed strong seasonality, peaking in summer and being lowest during winter. Peak rates of GPP and ER exceeded 200 mmol O₂?m^?2 day^?1 in all three estuaries. To our knowledge, this is the first study examining long-term trends in rates of GPP, ER, and NEM in estuaries. Variability in metabolism tended to be small among sites within each estuary. Nitrogen loading was highest in Weeks Bay, almost two times greater than that in Apalachicola Bay and 35 times greater than to Grand Bay. These differences in nitrogen loading were reflected in average annual GPP rates, which ranged from 825 g C m^?2 year^?1 in Weeks Bay to 401 g C m^?2 year^?1 for Apalachicola Bay and 377 g C m^?2 year^?1 in Grand Bay. Despite the strong inter-annual patterns in freshwater flow and salinity, variability in metabolic rates was low, perhaps reflecting shifts in the relative importance of benthic and phytoplankton productivity, during different flow regimes. The advantage of the open water method is that it uses readily available and cost-effective sonde monitoring technology to estimate these fundamental estuarine processes, thus providing a potential means for examining long-term trends in net carbon balance. It also provides a historical benchmark for comparison to ongoing and future monitoring focused on documenting the effect of human activities on the coastal zone.     

Roles of climate changes and human interventions in land degradation: a case study by net primary productivity analysis in China’s Shiyanghe Basin

The Thornthwaite Memorial, Synthetic, and Carnegie Ames Stanford Approach (CASA) models, with inputs from SPOT-VGT-S10 NDVI data, meteorological data (precipitation, temperature, solar radiation), and land use data were used to estimate the values of net primary productivity (NPP) from 1999 to 2007 in China’s Shiyanghe Basin. The human appropriation of NPP, which represents the difference between potential NPP predicted using the climatic models and actual NPP calculated using the CASA model, served as the indicator of human intervention in the evolution of productivity of the land. Analysis showed that 78.9% (~9,172 km²) of the degradation occurring in the Shiyanghe Basin was caused by human activities versus 15.0% (~1,752 km²) that was caused by climatic factors, whereas 16.9% (~6,404.5 km²) of the vegetation restoration resulted from human activities versus 49.7% (~18,881 km²) that resulted from climate changes. Human activity played a key role in vegetation restoration in the central areas of the basin and in determining land degradation in the southwestern and northeastern areas. In addition, climate significantly controlled the vegetation restoration in the southwestern and northeastern areas and controlled land degradation in the central area.     

Integration of geospatial technologies with RUSLE for analysis of land use/cover change impact on soil erosion: case study in Rib watershed,north-western highland Ethiopia

In recent times, soil erosion interlocked with land use and land cover (LULC) changes has become one of the most important environmental issues in developing countries. Evaluation of this complex interaction between LULC change and soil erosion is indispensable in land use planning and conservation works. This paper analysed the impact of LULC change on soil erosion in the north-western highland Ethiopia over the period 1986–2016. Rib watershed, the area with dynamic LULC change and severe soil erosion problem, was selected as a case study site. Integrated approach that combined geospatial technologies with revised universal soil loss equation model was utilized to evaluate the spatio-temporal dynamics of soil loss over the study period. Pixel-based overlay of soil erosion intensity maps with LULC maps was carried out to understand the change in soil loss due to LULC change. Results showed that the annual soil loss in the study area varied from 0 to 236.5 t ha^?1 year^?1 (tons per hectare per year) in 1986 and 0–807 t ha^?1 year^?1 in 2016. The average annual soil loss for the entire watershed was estimated about 40 t ha^?1 year^?1 in 1986 comparing with 68 t ha^?1 year^?1 in 2016, a formidable increase. Soil erosion potential that was estimated to exceed the average soil loss tolerance level increased from 34.5% in 1986 to 66.8% in 2016. Expansion of agricultural land at the expense of grassland and shrubland was the most detrimental factor for severe soil erosion in the watershed. The most noticeable change in soil erosion intensity was observed from cropland with mean annual soil loss amount increased to 41.38 t ha^?1 year^?1 in 2016 from 26.60 in 1986. Moreover, the most successive erosion problems were detected in eastern, south-eastern and northern parts of the watershed. Therefore, the results of this study can help identify the soil erosion hot spots and conservation priority areas at local and regional levels.     

Sedimentation and Organic Carbon Burial in the Yangtze River and Hudson River Estuaries: Implications for the Global Carbon Budget

One of the most important challenges in global climate change research is balancing the carbon budget within the global carbon cycle. Carbon burial in sediments at the land–ocean interface has been difficult to quantify and model because it represents non-steady-state boundary conditions that are also affected by human activities. In this study, we document carbon burial rates in the Yangtze River (1.6–4.9 × 10¹² gC year^?1) and Hudson River (1.8–3.6 × 10¹⁰ gC year^?1) estuaries and integrate our results with carbon burial rates determined by others in the world’s 25 largest river-estuarine systems (6–11 × 10¹³ gC year^?1). Our results indicate that carbon burial in estuaries, bays, coves, lagoons, mud flats, marshes, mangroves, and other highly productive or protected low-energy areas at the land–ocean interface along the entirety of the world’s coastlines may serve as an unrecognized sink within the global carbon budget.     

Role of early warning systems for sustainable agriculture in Iran

Drought is a complex phenomenon in meteorology and can affect agriculture. Its impacts vary greatly since they depend not only on the magnitude, timing, duration, and frequency of rainfall deficits but also on the differing responses of various plants to water stress. The essence of good drought management is to use this range of responses to the best advantage. Iran is one of the world’s largest and most productive suppliers of food and fiber. The objective of this study was, therefore, to gather and analyze standardized information on the Role of Early Warning Systems for Sustainable Agriculture for cereals and leguminous and industrial crops in Iran environmental zones. Annual average rainfall (mm year^?1) and ET_O (mm year^?1) are 76.56 and 3001, respectively, in stations with very dry climate; 195.41 and 2249, respectively, in stations with dry climate; 343.9 and 1351, respectively, in stations with semi-dry climate; 583.8 and 1153, respectively, in stations with semi-humid climate; and 1272 and 949, respectively, in stations with humid climate. The maximum and minimum of annual average rainfall happened in Rasht (1337 mm year^?1) and Zabol (57 mm year^?1) stations, and the maximum and minimum for annual average ET_O happened in Chabahar (3909.15 mm year^?1) and Anzali harbor (890.6 mm year^?1), respectively. Therefore, 13.63 % of stations have suitable conditions for crop productions and 86.37 % are in critical conditions.     

Decadal Change in Sediment Community Oxygen Consumption in the Abyssal Northeast Pacific

Long time-series studies are critical to assessing impacts of climate change on the marine carbon cycle. A 27-year time-series study in the abyssal northeast Pacific (Sta. M, 4000 m depth) has provided the first concurrent measurements of sinking particulate organic carbon supply (POC flux) and remineralization by the benthic community. Sediment community oxygen consumption (SCOC), an estimate of organic carbon remineralization, was measured in situ over daily to interannual periods with four different instruments. Daily averages of SCOC ranged from a low of 5.0 mg C m^?2 day^?1 in February 1991 to a high of 31.0 mg C m^?2 day^?1 in June 2012. POC flux estimated from sediment trap collections at 600 and 50 m above bottom ranged from 0.3 mg C m^?2 day^?1 in October 2013 to 32.0 mg C m^?2 day^?1 in June 2011. Monthly averages of SCOC and POC flux correlated significantly with no time lag. Over the long time series, yearly average POC flux accounted for 63 % of the estimated carbon demand of the benthic community. Long time-series studies of sediment community processes, particularly SCOC, have shown similar fluctuations with the flux of POC reaching the abyssal seafloor. SCOC quickly responds to changes in food supply and tracks POC flux. Yet, SCOC consistently exceeds POC flux as measured by sediment traps alone. The shortfall of ~37 % could be explained by sediment trap sampling artifacts over decadal scales including undersampling of large sinking particles. High-resolution measurements of SCOC are critical to developing a realistic carbon cycle model for the open ocean. Such input is essential to evaluate the impact of climate change on the oceanic carbon cycle, and the long-term influences on the sedimentation record.     

Evaluation of methane generation rate and potential from selected landfills in Malaysia

Methane emissions and oxidation were measured during the wet and dry seasons at the Air Hitam, Jeram, and Sungai Sedu landfills in Malaysia. The resulting levels of methane emissions and oxidation were then modeled using the Inter-governmental Panel on Climate Change 1996 first order decay (FOD) model to obtain methane generation rate and potential values. Emissions measurements were performed using a fabricated static flux chamber. A combination of gas concentrations in soil profiles and surface methane and carbon dioxide emissions at four monitoring locations in each landfill was used to estimate the methane oxidation capacity. The methane potential value was 151.7 m³ t^?1 for the Air Hitam and Jeram sanitary landfills and 75.9 m³ t^?1 for the Sungai Sedu open dumping landfill. The methane generation rate value of the Jeram and Air Hitam sanitary landfills during the wet season was 0.136 year^?1, while that of Jeram during the dry season was 0.072 year^?1. The methane generation rate values of the Sungai Sedu open dumping landfill during the wet and dry seasons were 0.008 and 0.0049 year^?1, respectively. The observed values of methane generation rate and potential assist to accurately estimate total methane emissions from Malaysian landfills using the Inter-governmental Panel on Climate Change FOD model.     

Assessment of soil erosion risk using SWAT model

Soil erosion is one of the most serious land degradation problems and the primary environmental issue in Mediterranean regions. Estimation of soil erosion loss in these regions is often difficult due to the complex interplay of many factors such as climate, land uses, topography, and human activities. The purpose of this study is to apply the Soil and Water Assessment Tool (SWAT) model to predict surface runoff generation patterns and soil erosion hazard and to prioritize most degraded sub-catchment in order to adopt the appropriate management intervention. The study area is the Sarrath river catchment (1,491 km²), north of Tunisia. Based on the estimated soil loss rates, the catchment was divided into four priority categories for conservation intervention. Results showed that a larger part of the watershed (90 %) fell under low and moderate soil erosion risk and only 10 % of the watershed was vulnerable to soil erosion with an estimated sediment loss exceeding 10 t?ha^?1?year^?1. Results indicated that spatial differences in erosion rates within the Sarrath catchment are mainly caused by differences in land cover type and gradient slope. Application of the SWAT model demonstrated that the model provides a useful tool to predict surface runoff and soil erosion hazard and can successfully be used for prioritization of vulnerable areas over semi-arid catchments.     

Responses of typical grasslands in a semi-arid basin on the Qinghai-Tibetan Plateau to climate change and disturbances

Alpine grassland ecosystems on the Qinghai-Tibetan Plateau (QTP) are vulnerable to climate change and anthropogenic disturbances, which may have significant effects on the QTP’s carbon budgets. In this study, vegetation and soil characteristics were compared among alpine grassland ecosystems in a semi-arid basin on the northeast ridge of the QTP (1) among alpine swamp meadow, meadow, steppe meadow and steppe soils, which represent the direction of succession under climate-warming conditions, and (2) among alpine, degraded and tilled meadow soils to investigate the effects of human disturbance. The results showed that (1) if the alpine grassland ecosystems succeed in this direction, climate warming will cause a loss of carbon, and (2) tilling activity also results in carbon loss. Therefore, these results indicate that anthropogenic disturbance regimes that change more rapidly than climate may exert a more profound influence on carbon dynamics and balance. However, the plots that were set in the present study represented only part of the basin due to road accessibility. Relationships between leaf area index (biomass and soil carbon) and fractional vegetation cover × vegetation height from this study are fairly good, which can be applied at regional scale to estimate carbon pools. In combination with detailed information of grassland types, climate and human activities, the effects of climate change and disturbances can be estimated using remote sensing datasets.     

An assessment of human versus climatic impacts on large-sized basin erosion: the case of the upper Yangtze River

Riverine sediment load, a reflection of basin erosion and sediment yield, is influenced by both climatic and human factors. Complex interaction between various factors within a basin dampens and counteracts the forces that drive sediment variations. The gross human impact index and the index estimation method have both been proposed to reflect the impacts of human activities on soil erosion and sediment yield. Sediment load and daily rainfall data from 1955 to 2010 in the upper Yangtze basin, and in the Wu, Jialing, Min and Jinsha subbasins, were collected to assess the human versus climatic impacts on sediment yield. From 1955 to 2010, the average annual runoff in the study area was 428.2 billion m³, and the average annual suspended sediment load was approximately 0.43 billion t. There was a critical point in 1984, 1985, 1991, 1993 and 1999 when the sediment load decreased in the Wu, Jialing, upper Yangtze, Min and Jinsha river, respectively. The annual regional rainfall erosivities in the upper Yangtze basin in most years ranged between 2,500 and 3,500 MJ mm hm^?2 h^?1 year^?1 and fluctuated around 3,000 MJ mm hm^?2 h^?1 year^?1 with a small coefficient of variation of 0.11. In the Jinsha subbasin, the index indicated that increasing rainfall erosivity could not account for the reduction in riverine sediment load and that anthropogenic erosion-control measures played a key role. The index values for the Min, Jialing and Wu subbasins ranged from 76 to 97 % and for the upper Yangtze basin is 95 %, demonstrating the joint effects of precipitation and human activities in all basins, with erosion-controlling measures playing a major role in sediment load reduction.     

Effect of nitrogen addition on soil organic carbon in freshwater marsh of Northeast China

Increased nitrogen (N) input to ecosystems could alter soil organic carbon (C) dynamics, but the effect still remains uncertain. To better understand the effect of N addition on soil organic C in wetland ecosystems, a field experiment was conducted in a seasonally inundated freshwater marsh, the Sanjiang Plain, Northeast China. In this study, litter production, soil total organic C (TOC) concentration, microbial biomass C (MBC), organic C mineralization, metabolic quotient (qCO₂) and mineralization quotient (qmC) in 0–15 cm depth were investigated after four consecutive years of N addition at four rates (CK, 0 g N m^?2 year^?1; low, 6 g N m^?2 year^?1; moderate, 12 g N m^?2 year^?1; high, 24 g N m^?2 year^?1). Four-year N addition increased litter production, and decreased soil organic C mineralization. In addition, soil TOC concentration and MBC generally increased at low and moderate N addition levels, but declined at high N addition level, whereas soil qCO₂ and qmC showed a reverse trend. These results suggest that short-term N addition alters soil organic C dynamics in seasonally inundated freshwater marshes of Northeast China, and the effects vary with N fertilization rates.     

The Declining Role of Organic Matter in New England Salt Marshes

The Northeast USA is experiencing severe impacts of a changing climate, including increased winter temperatures and accelerated relative sea level rise (RSLR). The sediment-poor, organic-rich nature of many Southern New England salt marshes makes them particularly vulnerable to these changes. In order to assess how marsh accretion has changed over time, we returned to Narragansett Bay, RI where salt marsh vertical accretion rates were documented almost 30 years ago. Using radionuclide tracers (²¹⁰Pb and ¹³⁷Cs), we observe no significant change in overall accretion rates (0.27–0.69 cm year^?1) compared to historical averages (0.24–0.60 cm year^?1), but we document a shift in how these marshes maintain elevation. Organic matter now plays a smaller role in contributing to vertical accretion across all study sites, declining by 22 % on average. We attribute this reduction to potentially higher decomposition rates fueled by higher water temperature. Inorganic matter also contributes less to accretion (declining by 44 % on average at marshes located more internal to the estuary), likely due to diminishing sediment supply in this region. With organic and inorganic solids accounting for less of the total accretion, several of the marshes are experiencing symptoms of swelling, with water and porespace contributing more towards accretion compared to historical values. Accretion rates (0.27–0.45 cm year^?1) at these organic-rich (>40 % sediment organic matter) marshes are predominantly lower than the current (30 years) rate of RSLR (0.41?±?0.07 cm year^?1). These results, combined with the increased rate of RSLR and the hardened shorelines inhibiting landward migration, call into question the long-term survivability of these marshes.     

Carbon dioxide fluxes over a temperate meadow in eastern Inner Mongolia,China

Understanding the carbon dynamics in grassland is essential to precisely estimate global atmospheric carbon budget in response to climatic change. Eddy flux measurements were carried out during 2011 and 2012 to characterize seasonal and annual variability of carbon exchanges above a temperate meadow in eastern Inner Mongolia, China. The CO₂ flux showed obvious diurnal variations and the monthly mean amplitudes of diurnal course followed June/July > August > May > September. The daily maximum NEE reached up to ?8.0 and ?7.7 g C m^?2 for 2011 and 2012, respectively. CO₂ uptake was mainly from May to August, with seasonal peaks of ?16.0 g C m^?2 day^?1 in both two years. Gross primary production (GPP) and ecosystem respiration (Re) were ?1,084.5, 987.1 g C m^?2 year^?1 in 2011, and ?1,123.3, 1,040.2 g C m^?2 year^?1 in 2012, respectively. The meadow acted as a stable carbon sink, with integrated net ecosystem exchange (NEE) of ?97.4 and ?83.1 g C m^?2 year^?1 for 2011 and 2012, respectively. Compared with 2011, the ecosystem assimilated more carbon and meanwhile respired even more, leading to a less carbon sequestration in 2012. PAR and leaf area index (LAI) dominated the seasonal variations in NEE, with PAR explaining 61–69 % of the variance in NEE as LAI maintaining the plateau during June to July. Harvest significantly decreased ecosystem carbon uptake. The interannual variability in GPP and Re resulted primarily from the variations in temperature and its effect on biomass growth.     

Geospatial assessment of soil erosion intensity and sediment yield: a case study of Potohar Region,Pakistan

Estimation of spatial extent of soil erosion, one of the most serious forms of land degradation, is critical because soil erosion has serious implications on soil fertility, water ecosystem, crop productivity and landscape beauty. The primary objective of the current study was to assess and map the soil erosion intensity and sedimentation yield of Potohar region of Pakistan. Potohar is the rainfed region with truncated and complex topography lying at the top of the Indus Basin, the world’s largest irrigation networks of canals and barrages. Spatially explicit Revised Universal Soil Loss Equation (RUSLE) Model integrated with Remote Sensing-GIS techniques was used for detecting/mapping of erosion prone areas and quantification of soil losses. The results show that the Potohar region is highly susceptible to soil erosion with an average annual soil loss of 19 tons ha^?1 year^?1 of which the maximum erosion (70–208 tons ha^?1 year^?1) was near the river channels and hilly areas. The sediment yield due to the erosion is as high as 148 tons ha^?1 year^?1 with an average of 4.3 tons ha^?1 year^?1. It was found that 2.06% of the total area falls under severe soil erosion, 13.34% under high erosion, 15.35% under moderate soil erosion while 69.25% of the area lies in the low (tolerable) soil erosion. Chakwal and Jhelum districts of the region are seriously affected by erosion owing to their topography and soil properties. The information generated in this study is a step forward towards proper planning and implementation of strategies to control the erosion and for protection of natural resources. It is, hence, necessary that suitable water harvesting structures be made to control water to prevent soil erosion and provision of water in the lean season in this region. Tree plantation and other erosion control practices such as strip cropping can also minimize soil erosion in this region.     

Understanding the Cyclicity of Chemical Weathering and Associated CO<Subscript>2</Subscript> Consumption in the Brahmaputra River Basin (India): The Role of Major Rivers in Climate Change Mitigation Perspective

Weathering of rocks that regulate the water chemistry of the river has been used to evaluate the CO₂ consumption rate which exerts a strong influence on the global climate. The foremost objective of the present research is to estimate the chemical weathering rate (CWR) of the continental water in the entire stretch of Brahmaputra River from upstream to downstream and their associated CO₂ consumption rate. To establish the link between the rapid chemical weathering and thereby enhance CO₂ drawdown from the atmosphere, the major ion composition of the Brahmaputra River that drains the Himalaya has been obtained. Major ion chemistry of the Brahmaputra River was resolved on samples collected from nine locations in pre-monsoon, monsoon and post-monsoon seasons for two cycles: cycle I (2011–2012) and cycle II (2013–2014). The physico-chemical parameters of water samples were analysed by employing standard methods. The Brahmaputra River was characterized by alkalinity, high concentration of Ca²⁺ and HCO₃ ^? along with significant temporal variation in major ion composition. In general, it was found that water chemistry of the river was mainly controlled by rock weathering with minor contributions from atmospheric and anthropogenic sources. The effective CO₂ pressure (log\({{\text{P}}_{{\text{C}}{{\text{O}}_{\text{2}}}}}\)) for pre-monsoon, monsoon and post-monsoon has been estimated. The question of rates of chemical weathering (carbonate and silicate) was addressed by using TDS and run-off (mm year^?1). It has been found that the extent of CWR is directly dependent on the CO₂ consumption rate which may be further evaluated from the perspective of climate change mitigation The average annual CO₂ consumption rate of the Brahmaputra River due to silicate and carbonate weathering was found to be 0.52 (×10⁶ mol Km^?2 year^?1) and 0.55 (×10⁶ mol Km^?2 year^?1) for cycle I and 0.49 (×10⁶ mol Km^?2 year^?1) and 0.52 (×10⁶ mol Km^?2 year^?1) for cycle II, respectively, which were significantly higher than that of other Himalayan rivers. Estimation of CWR of the Brahmaputra River indicates that carbonate weathering largely dominates the water chemistry of the Brahmaputra River.     

Dynamics of carbon fluxes with responses to vegetation,meteorological and terrain factors in the south-eastern Tibetan Plateau

Tibetan Plateau (TP) is the highest and most extensive plateau in the world and has been known as the roof of the world, and it is sensitive to climate change. The researches of CO₂ fluxes (F _C) in the TP region play a significant role in understanding regional and global carbon balance and climate change. Eddy covariance flux measurements were conducted at three sites of south-eastern TP comprising Dali (DL, cropland ecosystem), LinZhi (LZ, alpine meadow ecosystem) and Wenjiang (WJ, cropland ecosystem); amongst those DL and LZ are located in plateau region, while WJ is in plain region. Dynamics of F _C and influences of vegetation, meteorological (air temperature, photosynthetically active radiation, soil temperature and soil water content) and terrain factors (altitude) were analysed on the basis of data taken during 2008. The results showed that, in the cool sub-season (March, April, October and December), carbon sink appeared even in December with fluxes of (?0.021 to ?0.05) mg CO₂ m^?2 s^?1 and carbon source only in October (0.03 ± 0.0048) mg CO₂ m^?2 s^?1 in DL and WJ site. In LZ site, carbon sink was observed in April: (?0.036 ± 0.0023) mg CO₂ m^?2 s^?1 and carbon sources in December and March (0.008–0.010 mg CO₂ m^?2 s^?1). In the hot sub-season (May–August), carbon source was observed only in May with (0.011 ± 0.0022), (0.104 ± 0.0029) and (0.036 ± 0.0017) fluxes in LZ, DL and WJ site, respectively, while carbon sinks with (?0.021 ± 0.0041), (?0.213 ± 0.0007) and (?0.110 ± 0.0015) mg CO₂ m^?2 s^?1 fluxes in LZ, DL, and WJ, respectively. Comparing with plain region (WJ), carbon sinks in plateau region (DL and LZ) lasted for a longer time, and the absorption sum was large and up to (–357.718 ± 0.0054) and (?371.111 ± 0.0039) g C m^?2 year^?1, respectively. The LZ site had the weakest carbon sink with (?178.547 ± 0.0070) g C m^?2 year^?1. Multivariate analysis of covariance showed that altitude (AL) as an independent factor explained 39.5 % of F _C (P < 0.026). F _C had a quadratic relationship with Normalized difference vegetation index (NDVI) (R ² ranges from 0.485 to 0.640 for three sites), an exponential relationship with soil temperature at 5-cm depth (ST ₅) at night time and a quadratic relationship with air temperature (T _a) at day time. Path analysis indicated that photosynthetically active radiation (PAR), sensible heat fluxes (H) and other factors all had direct or indirect effects on F _C in all of the three tested sites around the south-eastern TP.     

Influences of climate change and human activities on Tarim River runoffs in China over the past half century

The changes in annual runoff of the three original rivers and the mainstream of Tarim River were analyzed by the non-parametric tests based on the hydrologic data during the period of 50 years. Using hydrologic data, meteorological data and the fitted equation, the impacts of climate change and human activities on annual runoff of the mainstream were assessed. Based on the analysis, the following conclusions can be drawn: (1) headstream runoff has increased in the past 50 years, and has sharply jumped after 1990; (2) mainstream runoff decreased progressively in the past 50 years, which indicated that interference from human activities was the main cause for the decreasing runoff. This had greater negative influence than positive influence, which caused the mainstream average runoff to decrease by 5.4 × 10⁸ m³ from 1990 to 2008 as compared to 1957–2008; (3) if human activities remained at pre-1990 levels, climate change alone would have caused the runoff of mainstream of Tarim River to increase by 5.4 × 10⁸ m³ annually in the past 20 years; (4) if the climate had remained at pre-1990 conditions, human activities alone would have caused the runoff of mainstream of Tarim River to increase by 5.4 × 10⁸ m³ annually over the past 20 years. However, mainstream average runoff was 42.6 × 10⁸ m³ from 1990 to 2008 with the negative effects of human activities masked by the larger, positive effect of climate changes. The results in this paper provide a scientific basis for conservation strategies, sustainable management, and ecological restoration of the Tarim River Basin.