摘要:

We describe the sources and routing of the Amazon River flood wave through a 2000‐km reach of the main channel, between São Paulo de Olivença and Obidos, Brazil. The damped hydrograph of the main stem reflects the large drainage basin area, the 3‐month phase lag in peak flows between the north and south draining tributaries due to seasonal differences in precipitation, and the large volume of water stored on the floodplain. We examined several aspects of the valley floor hydrology that are important for biogeochemistry. These include volumes of water storage in the channel and the floodplain and the rates of transfer between these two storage elements at various seasons and in each segment of the valley. We estimate that up to 30% of the water in the main stem is derived from water that has passed through the floodplain. To predict the discharge at any cross section within the study reach, we used the Muskingum formula to predict the hydrograph at downriver cross sections from a known hydrograph at upstream cross‐sections and inputs and outputs along each reach. The model was calibrated using three years of data and was successfully tested against an additional six years of data. With this model it is possible to interpolate discharges for unsampled times an

ISSN:0886-6236    

DOI:10.1029/GB003i003p00191

年代:1989

数据来源: WILEY

摘要:

The distribution of methane in an ombrotrophic bog was examined by extracting the gas from different depths, using evacuated bottles and sampling tubes. Methane was extracted during 75 min, from 60 cm, 90 cm and 120 cm depths at 25 stations in a 24 meter‐square area. The amount of methane extracted varied widely between samples, and this variation was greater within each depth than between the different depths. Approximately two and a half times as much methane was found at 90 cm and 120 cm depths as at 60 cm. The amount of methane from sites more than 60 cm below the surface can be correlated with the methane microbially produced from peat from the same site during laboratory incubations. Much less methane could be extracted from near‐surface peat than from deeper levels, but laboratory incubations of peat from this level produced 10‐fold more methane. Our results show that there is a considerable amount of methane trapped below 50 cm depth within an ombrotrophic bog, which we calculate in the bog studied to be 1.7 Gg. We suggest this entrapped methane reduces the hydraulic conductivity in the lower layers of the peat by blocking the soil pore spaces and preventing fluid movement; this in turn generates an elevated water table allowing the formation of a raised bog. We further suggest that if this peat is disturbed by mining or farming, the entrapped methane could be released into the atmosphere and add to the atmospheric pollution by greenhouse

ISSN:0886-6236    

DOI:10.1029/GB003i003p00205

年代:1989

数据来源: WILEY

摘要:

In an attempt to create a scenario for the cause of the glacial to interglacial CO2change recorded in air trapped in polar ice, we call on an increase in the alkalinity of polar surface waters. In this way we circumvent a major deficiency of the polar nutrient scenarios of Sarmiento and Toggweiler (1984), Siegenthaler and Wenk (1984) and Knox and McElroy (1984). Namely, our scenario does not require a drop in the nutrient content of polar surface waters in conformity with the demonstration by Boyle (1988a, b) that the cadmium content of planktonic foraminifera from polar regions did not decrease from late glacial to Holocene time. The rise in alkalinity required by our model is a natural consequence of the demise, during glacial time, of North Atlantic Deep Water as a major force in ocean circulation and of the nutrient maximum deepening of Boyle (1988b). Rather than being original, our hypothesis builds on the concept basic to the polar nutrient hypotheses, namely that the CO2partial pressure in polar waters controls that for both the atmosphere and warm surface ocean. It also requires the alkalinity increase in surface waters produced by Boyle's nutrient deepening.

ISSN:0886-6236    

DOI:10.1029/GB003i003p00215

年代:1989

数据来源: WILEY

摘要:

A coupled water balance and water transport model (WBM / WTM) was constructed as part of a larger study of global biogeochemistry. The WBM / WTM provides critical hydrologic information to models of terrestrial primary production, organic matter decay, riverine nutrient flux and trace gas exchanges with the troposphere. Specifically, it creates high‐resolution data sets for monthly soil moisture, evapotranspiration, runoff, river discharge and floodplain inundation. As a first step toward eventual global coverage, the WBM / WTM was applied to South America, represented by more than 5700 1/2° (latitude / longitude) grid cells. The WBM transforms spatially complex data on long‐term climate, vegetation, soils and topography into predictions of soil moisture (SM), evapotranspiration (ET) and runoff (RO). For South America, field capacity in soils ranged from 27 to 582 mm of water, and computed values for mean annual SM, ET and RO were 284 mm, 1059 mm/yr and 619 mm/yr, respectively. There were large differences regionally and over the year. The transport model uses WBM‐derived runoff, information on fluvial topology, linear transfer through river channels and a simple representation of floodplain inundation to generate monthly discharge estimates for any cell within a simulated catchment. The WTM successfully determined the timing and magnitude of discharge at selected locations within the Amazon / Tocantins basin. It also demonstrated the importance of floodplain inundation in defining flow regime on the mainstem Amazon. Estimated mean annual discharge was 207,000 m3/s for the Amazon River and 17,000 m3/s for the Tocantins. In these basins, 45% of the incident precipitation emerges as river flow; 55% is lost to ET. The model described in this paper will be expanded to include the dynamics of carbon, major nutrients and sediments. It will serve as a semimechanistic tool to quantify the transport of materials from the landscape to the world's oceans. Such a capability becomes increasingly important as we seek to understand the impacts of climate and land use change on major river systems of the

ISSN:0886-6236    

DOI:10.1029/GB003i003p00241

年代:1989

数据来源: WILEY

摘要:

The 1982‐1983 El Niño event perturbed the otherwise steady growth in atmospheric CO2due to fossil fuel combustion. Compared to the recent average growth rate in atmospheric CO2of about 1.5 ppm per year, the growth rate in late 1982 fell to about zero. During this strong El Niño event, additional sinks for atmospheric CO2operated. By late 1983, the growth rate rebounded to above average, indicating the presence of new sources. To a large extent, the relative roles of the possible actors have eluded us. In this study, box models of the ocean‐atmosphere carbon cycle are used to isolate and estimate the effects of the collapse and return of the upwelling in the equatorial Pacific during an El Niño. The models capture the major trends during the El Niño for sea surface temperature, nutrients, and ΔpCO2. The drop in ΔpCO2in the normally strong source of the equatorial Pacific can account for a partial amount (probably less than 30%) of the decrease in the growth rate in atmospheric CO2centered around late 1982. The recovery to normal equatorial conditions plays an even smaller and nearly negligible role in any growth rate overshoot later in El Niño. Changes in the higher‐latitude oceans and disequilibrium in the terrestrial cycle of photosynthesis and respiration continue as major potential agents behind the

ISSN:0886-6236    

DOI:10.1029/GB003i003p00267

年代:1989

数据来源: WILEY

摘要:

The importance of seasonal cycles of N2O flux from tropical ecosystems and the possibility that tropical deforestation could contribute to the ongoing global increase in N2O concentrations were assessed by measuring N2O flux from forest, cleared land, and pasture over an annual cycle in the central Amazon. A pasture that had been converted from tropical forest had threefold greater annual N2O flux than a paired forest site; similar results were obtained in spot measurements in other pastures. If these results are general, such tropical pastures represent a globally significant source of increased N2O.

ISSN:0886-6236    

DOI:10.1029/GB003i003p00281

年代:1989

数据来源: WILEY