Global Biogeochemical Cycles
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Intra‐annual variability of organic carbon concentrations in running waters: Drivers along a climatic gradient Abstract Trends in surface water dissolved organic carbon (DOC) concentrations have received considerable scientific interest during recent decades. However, intra‐annual DOC variability is often orders of magnitude larger than long‐term trends. Unraveling the controls on intra‐annual DOC dynamics holds the key to a better understanding of long‐term changes and their ecological significance. We quantified and characterized intra‐annual DOC variability and compared it with long‐term DOC trends in 136 streams and rivers, varying in size and geographical characteristics, across a 1400 km latitudinal gradient during 2000–2010. Discharge, temperature, and month of the year were the most significant predictors of intra‐annual DOC variability in a majority of the running waters. Relationships between DOC, discharge, and temperature were, however, different along a mean annual temperature (MAT) gradient. Running waters with low MAT generally displayed positive DOC‐discharge correlations whereas the relationships in sites with higher MAT were more variable. This reflected contrasting relationships between temperature and discharge with discharge positively correlated with temperature in cold areas, while it was negatively correlated with temperature in catchments with higher MAT. Sites where flow, temperature, and month were poorly related to intra‐annual DOC dynamics were large catchments or sites with extensive upstream lake cover. DOC trends were generally much smaller than intra‐annual DOC variability and did not show any north‐south gradient. Our findings suggest that DOC in running waters could respond to a changing climate in ways not predictable, or even discernible, from extrapolation of recent interannual trends.
Global Biogeochemical Cycles - Tập 28 Số 4 - Trang 451-464 - 2014
Environmental control of leaf area production: Implications for vegetation and land‐surface modeling Leaf surface area per unit ground cover (leaf area index, LAI) is one of the major controls on plant productivity and biospheric feedbacks on atmospheric energy and water exchanges. Nearly all vegetation and land‐surface models include parameterizations of LAI, however not much research currently focuses on the validation of simulated responses of LAI to environmental change. The objective of our research was to quantitatively review the plant science literature to extract information on the response of LAI to variations in soil moisture, soil fertility and atmospheric CO2 . Our synthesis confirms that LAI is likely co‐limited by a number of resources, including water, nitrogen and light. Atmospheric CO2 influences LAI in much the same manner as other plant resources. When CO2 supply is strongly limiting to gross primary production (i.e., at relatively low CO2 concentrations), LAI is strongly correlated with CO2 , whereas when CO2 is abundant, LAI sensitivity to CO2 dramatically decreases. Such a nonlinear relationship between leaf area production and atmospheric CO2 may introduce a potential bias for global change modeling, particularly in the simulation of low‐density vegetation that has the potential to significantly increase canopy size without inducing self‐shading.
Global Biogeochemical Cycles - Tập 17 Số 1 - 2003
Farming the planet: 2. Geographic distribution of crop areas, yields, physiological types, and net primary production in the year 2000 Croplands cover ∼15 million km2 of the planet and provide the bulk of the food and fiber essential to human well‐being. Most global land cover data sets from satellites group croplands into just a few categories, thereby excluding information that is critical for answering key questions ranging from biodiversity conservation to food security to biogeochemical cycling. Information about agricultural land use practices like crop selection, yield, and fertilizer use is even more limited. Here we present land use data sets created by combining national, state, and county level census statistics with a recently updated global data set of croplands on a 5 min by 5 min (∼10 km by 10 km) latitude‐longitude grid. The resulting land use data sets depict circa the year 2000 the area (harvested) and yield of 175 distinct crops of the world. We aggregate these individual crop maps to produce novel maps of 11 major crop groups, crop net primary production, and four physiologically based crop types: annuals/perennials, herbaceous/shrubs/trees, C3 /C4 , and leguminous/nonleguminous.
Global Biogeochemical Cycles - Tập 22 Số 1 - 2008
A global high‐resolution emission inventory for ammonia A global emissions inventory for ammonia (NH3 ) has been compiled for the main known sources on a 1° × 1° grid, suitable for input to global atmospheric models. The estimated global emission for 1990 is about 54 Tg N yr−1 . The major sources identified include excreta from domestic animals (21.6 Tg N yr−1 ) and wild animals (0.1 Tg N yr−1 ), use of synthetic N fertilizers (9.0 Tg N yr−1 ), oceans (8.2 Tg N yr−1 ), biomass burning (5.9 Tg N yr−1 ), crops (3.6 Tg N yr−1 ), human population and pets (2.6 Tg N yr−1 ), soils under natural vegetation (2.4 Tg N yr−1 ), industrial processes (0.2 Tg N yr−1 ), and fossil fuels (0.1 Tg N yr−1 ). About half of the global emission comes from Asia, and about 70% is related to food production. The regions with highest emission rates are located in Europe, the Indian subcontinent, and China, reflecting the patterns of animal densities and type and intensity of synthetic fertilizer use. The overall uncertainty in the global emission estimate is 25%, while the uncertainty in regional emissions is much greater. As the global human population will show considerable growth in the coming decades, food production and associated NH3 emissions are likely to increase as well.
Global Biogeochemical Cycles - Tập 11 Số 4 - Trang 561-587 - 1997
Estimation of global NH<sub>3</sub>volatilization loss from synthetic fertilizers and animal manure applied to arable lands and grasslands One of the main causes of the low efficiency in nitrogen (N) use by crops is the volatilization of ammonia (NH3 ) from fertilizers. Information taken from 1667 NH3 volatilization measurements documented in 148 research papers was summarized to assess the influence on NH3 volatilization of crop type, fertilizer type, and rate and mode of application and temperature, as well as soil organic carbon, texture, pH, CEC, measurement technique, and measurement location. The data set was summarized in three ways: (1) by calculating means for each of the factors mentioned, in which findings from each research paper were weighted equally; (2) by calculating weighted median values corrected for unbalanced features of the collected data; and (3) by developing a summary model using linear regression based on weighted median values for NH3 volatilization and by calculating global NH3 volatilization losses from fertilizer application using 0.5° resolution data on land use and soils. The calculated median NH3 loss from global application of synthetic N fertilizers (78 million tons N per year) and animal manure (33 million tons N per year) amount to 14% (10–19%) and 23% (19–29%), respectively. In developing countries, because of high temperatures and the widespread use of urea, ammonium sulfate, and ammonium bicarbonate, estimated NH3 volatilization loss from synthetic fertilizers amounts to 18%, and in industrialized countries it amounts to 7%. The estimated NH3 loss from animal manure is 21% in industrialized and 26% in developing countries.
Global Biogeochemical Cycles - Tập 16 Số 2 - 2002
Exploring global nitrogen and phosphorus flows in urban wastes during the twentieth century Abstract This paper presents a global model‐based country‐scale quantification of urban N and P mass flows from humans, animals, and industries and their waste N and P discharges to surface water and urban waste recycling in agriculture. Agricultural recycling was practiced commonly in early twentieth century Europe, Asia, and North America. During the twentieth century, global urban discharge to surface water increased ~3.5‐fold to 7.7 Tg yr‐1 for N and ~4.5‐fold to 1.0 Tg yr‐1 for P; the major part of this increase occurred between 1950 and 2000. Between 1900 and ~1940, industrial N and P flows dominated global surface water N and P loadings from urban areas; since ~1940, human wastes are the major source of urban nutrient discharge to both surface water and agricultural recycling. During the period 1900–2000, total global recycling of urban nutrients in agriculture increased from 0.4 to 0.6 Tg N yr‐1 and from 0.07 to 0.08 Tg P yr‐1 . A large number of factors (the major ones related to food consumption, urban population, sewer connection, and industrial emissions) contribute to the uncertainty of −18% to +42% for N and −21% to +45% for P around the calculated surface water loading estimate for 2000.
Global Biogeochemical Cycles - Tập 27 Số 3 - Trang 836-846 - 2013
Source and transport of terrigenous organic matter in the upper Yukon River: Evidence from isotope (δ<sup>13</sup>C, Δ<sup>14</sup>C, and δ<sup>15</sup>N) composition of dissolved, colloidal, and particulate phases Natural organic matter was collected from the upper Yukon River and size fractionated into the <1 kDa low‐molecular‐weight dissolved (LMW‐DOC), colloidal (COC, 1 kDa to 0.45 μm) and particulate organic carbon (POC, >0.45 μm) phases for characterization of elemental (C and N) and isotopic (13 C, 14 C and 15 N) composition to examine their sources and transport. Concentrations of total organic carbon (TOC) decreased from 3010 μM in mid‐May to 608 μM in September, accompanying an increase in river water δ18 O from the snowmelt to summer and early fall. COC was the predominant OC species, comprising, on average, 63 ± 8% of the TOC, with 23 ± 5% partitioned in the LMW‐DOC and 14 ± 5% in the POC fraction. Annual riverine export flux to the ocean was 2.02 × 1012 g‐C for TOC, 7.66 × 1010 g‐N for total organic nitrogen (TON), and 3.53 × 1012 g‐C for dissolved inorganic carbon (DIC), respectively. The C/N molar ratios were distinctly different between colloidal organic matter (COM, 46 ± 3) and particulate organic matter (POM, 15 ± 1.4). Similar δ13 C values were found for LMW‐DOM (−27.9 ± 0.5‰), COM (−27.4 ± 0.2‰), and POM (−26.2 ± 0.7‰), although there was a general increase with increasing size, suggesting a common terrigenous organic source. In contrast, distinct Δ14 C values were found for LMW‐DOC (−155 to +91‰), COC (40 to 140‰), and POC (−467 to −253‰) with a decreasing trend from snowmelt to ice‐open season, suggesting that turnover pathways and transport mechanisms vary with organic matter size fractions. The high abundance of COC and its contemporary 14 C ages points to a predominant source from modern terrestrial primary production, likely from the leaching/decomposition of fresh plant litter in the upper soil horizon. The predominately old POC (average 3698 ± 902 years B.P.), in contrast, was largely derived from riverbank erosion and melting of permafrost. These results imply that ice‐opening Yukon River flows are dominated by snowmelt (low δ18 O) with high DOC (high Δ14 C) but low DIC and Si(OH)4 concentrations, whereas late summer flows contain more products of permafrost or ice melt and rain (high δ18 O), with low DOC (low Δ14 C) but high DIC and Si(OH)4 concentrations. A warming climate with a deeper permafrost active layer in the Yukon River watershed would enhance the mobilization and export of old terrestrial OC, but largely in the particulate form into the Bering Sea and Arctic Ocean.
Global Biogeochemical Cycles - Tập 20 Số 2 - 2006
Solute Production and Transport Processes in Chinese Monsoonal Rivers: Implications for Global Climate Change Abstract The negative feedback between chemical weathering and climate is hypothesized to act as an important control on modulating atmospheric CO2 over geologic timescales, affecting the evolution of Earth's climate over the history of Earth. Here, we investigated solute production processes by analyzing concentration‐discharge, denoted here as concentration‐runoff (C ‐q ), relationships of Chinese monsoonal rivers, through both the empirical power law relationship and a recently developed Solute Production Model. We found that solute concentrations were highly modulated by hydrologic conditions which shifted the Damköhler number, Da , the ratio of fluid transit time versus the time required to reach equilibrium. Additionally, the among‐catchment behavior of HCO3 − responding to changing runoff was correlated with the average Da of each catchment. Rivers with high average Da induced high maximum weathering fluxes, while the maximum weathering potential was primarily controlled by the Damköhler coefficient (Dw , m/yr), the reactivity of the material in the weathering zone over a given length scale, among the catchments in this study. Globally, HCO3 − behaviors and weathering characteristics are highly influenced by carbonate bedrock distributions and abundance. In addition, Chinese monsoonal rivers have higher weathering fluxes, weathering potential, and climate‐weathering feedback sensitivity (4.4%/°C) than most other global rivers. Our work disclosed the mechanisms that link runoff, lithology, and weathering fluxes in monsoonal rivers and analyzed the controlling factors on solute dynamics on global scale, which can be implemented in exploring the chemical weathering processes under ongoing global climate change.
Global Biogeochemical Cycles - Tập 34 Số 9 - 2020
Peatland responses to varying interannual moisture conditions as measured by automatic CO<sub>2</sub> chambers Net ecosystem CO2 exchange (NEE) was measured from June 2000 through October 2001 by 10 automatic chambers at a peatland in southeastern New Hampshire. The high temporal frequency of this sampling method permitted detailed examination of NEE as it varied daily and seasonally. Summer of 2001 was significantly drier than the 30‐year average, while summer of 2000 was wetter than normal. Although NEE varied spatially across the peatland with differences in plant species composition and biomass, maximum CO2 uptake was 30–40% larger in the drier summer in evergreen and deciduous shrub communities but the same or lower in sedge sites. Ecosystem respiration rates were 13–84% larger in the drier summer depending on plant growth form with water table and temperature as strong predictors. Ecosystem respiration was also correlated with maximum ecosystem productivity and foliar biomass suggesting that plant processes, water table, and temperature are tightly linked in their control of respiratory losses. The ratio between maximum productivity and respiration declined for evergreen shrub and sedge sites between the wet and dry summer, but increased in deciduous shrub sites. A drier climate may reduce the CO2 sink function of peatlands for some growth forms and increase it for others, suggesting that ecosystem carbon and climate models should account for differences in growth form responses to climate change. It also implies that plant functional types respond on short timescales to changes in moisture, and that the transition from sedges to shrubs could occur rapidly in peatlands under a drier and warmer climate.
Global Biogeochemical Cycles - Tập 17 Số 2 - 2003
Cycling of dissolved rare earth elements in Chesapeake Bay The measurement of dissolved rare earth elements (REE) in the surface waters, water column of anoxic basins, and pore waters in Chesapeake Bay has provided new insights to the biogeochemistry and estuarine chemistry of REE. All dissolved REE from the riverine source show large‐scale removal in the lower salinity zone (0‐10‰). The shale‐normalized pattern of dissolved Susquehanna River water is opposite in form to that of surface sediments in the Bay. The former is enriched in heavy REE (HREE) while the latter are enriched in light REE (LREE). Neither component has a flat pattern normally assumed for river‐ transported REE to the ocean. The dissolved LREE (i.e., La, Ce, Nd, Sm, and Eu) are enriched 3 to 9 times) in the oxygen‐depleted deep waters over their concentrations in the oxic surface waters. In contrast, HREE (Er, Yb, and Lu) are slightly depleted. All REE concentrations in the two surface (0‐2 cm) pore waters are greatly enriched (8‐17 times; 43 times for Ce) relative to oxygen‐depleted bottom waters and have relative abundances opposite to those of their sediments. While Ce has a positive anomaly in the pore waters, negative anomalies exist in the oxygen‐depleted bottom waters. The REE are participating in a set of complex biogeochemical cycles within the water column and surface sediments. Fractionation of REE during these cycles leads to the preferential enrichment of LREE in the seasonally oxygen‐depleted bottom waters. It is proposed that this fractionation is coupled to redox cycles of Mn and Fe and the interaction of dissolved REE with suspended particles and surficial sediments.
Global Biogeochemical Cycles - Tập 2 Số 2 - Trang 157-176 - 1988
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