No abstract

No abstract

The discrepancy between estimates of net terrestrial CO2 emissions derived from (1) inverse modeling of the ocean/atmosphere system and (2) modeling of land use change, better known as the "missing" CO2 sink, suggests that some changing environmental factor, such as CO2, anthropogenic N emissions, or climate, has fertilized terrestrial ecosystems. To address this question, we herein describe and apply GLOCO, a global carbon cycle model. GLOCO's ocean submodel combines a box diffusion model with representations of chemical equilibria and biological processes to simulate the distributions and cycling of inorganic and organic carbon, phosphate, and alkalinity. The terrestrial submodel divides the biosphere into seven natural biomes with dynamic carbon and nitrogen cycling in both vegetation and soils. Anthropogenic influences on the functioning of the carbon and nitrogen cycles, such as fossil fuel combustion, forestry, and agricultural development, are also incorporated in the model. Our analysis confirms previous suggestions that because temperate and boreal forests are N limited, CO2 fertilization of these forests is less than predicted by short-term CO2 response factors. Modeling of temperate/boreal forest fertilization by anthropogenic N deposition suggests that CO2 is initially sequestered at a C:N ratio of --100, rather than the steady state value for the ecosystem of-30. If N deposition is to account for the 40-70% of the fertilization of the terrestrial biosphere not explainable by CO2 fertilization and temperature increases, then we estimate that 26-30 Tg N yr-1 of anthropogenic deposition in the temperate and boreal zones would be required. Recent anthropogenic NOx and NH3 deposition fluxes at northern temperate latitudes have been estimated to be 20-28 Tg N yr-1. Thus fertilization by anthropogenic N emissions likely constitutes a significant portion of the missing CO2 sink. HUDSON ET AL.' MODELING THE GLOBAL CARBON CYCLE Z•tC + AOc + Z•Bc = I EFossil fuel dt or expressed in terms of rates of change d/dt dAc dOc dBc • + + -EFossil fuel dt dt dt (la) (lb) The rate of change in atmospheric CO2 is the best quantified term in the mass balance at 3.2_+0.2 Pg C yr 4 for the period 1980-1989 [Keeling, 1990]. Fossil fuel emissions are also well quantified at 5.4_+0.5 Pg C yr-• for the same period [Marland, 1990; Marland and Rotty, 1984]. The change in carbon storage in the oceans, assumed to arise primarily from increased absorption of atmospheric CO2, can be modeled by &convolution of the atmospheric CO2 record (reconstructing oceanic uptake using models and historical atmospheric CO2 partial pressure Pco2). By considering the results of a number of such studies, Siegenthaler and Sarmiento [1993] argue that the perturbation in oceanic uptake (~dOc/dt) is 2.0_+0.6 Pg C yr-• for the 1980s. Analysis of measured surface ocean Pco2 values and the distributions, sources, and sinks of atmospheric CO2 using an atmospheric transport model lead Tans et al. [1990] to suggest that the perturbation in oceanic uptake was les...

No abstract

No abstract

No abstract

No abstract

Past approaches for evaluating the effects of organic acids on the acid-base characteristics of surface waters have typically treated them solely as weak acids. Analysis of data collected by the Adirondack Lakes Survey Corporation (ALSC) from 1469 lakes throughout the Adirondack region shows that this approach is not valid. While the data indicate that natural organics contain a continuum of acid functional groups, many of which display weak acid characteristics, a significant fraction of the organic acid is strong (PKa < 3). Dissolved organic carbon (DOC) contributes 4.5-5 t•eq/mg DOC of strong acid to solution. The associated anions make a negative contribution to Gran acid-neutralizing capacity (ANC). Because organic anions can produce negative Gran ANC values, the common practice of considering negative values of Gran ANC evidence of acidification solely by mineral acids is not valid. The strength of organic acids also influences the observed deviation between Gran ANC values and ANC values calculated as the difference between base cation and mineral acid anion concentrations(Ca -CA). Ninety percent of the deviation is due to the presence of strong organics while the remaining 10% is due to DOC-induced curvature in the F1 Gran function. Organic acids can also strongly influence p H. Their largest effects were found in the 0-50/xeq/L Gran ANC range where they depressed pH by up to 1.5 units. In addition, a method for predicting changes in pH in response to changes in mineral acidity, DOC, or both without having to rely on inferred thermodynamic constants and the uncertainties associated with them has been developed. Using the predictive method, the response of representative lakes from four sensitive lake classes to a 15-/aeq/L decrease in mineral acidity ranged from +0.17 to +0.38 pH units. If concurrent increases in DOC are considered, the pH changes would be even smaller. 1989]. A briefsummary is provided below. The ALSC survey provides an extremely comprehensive overview of the current status of water chemistry and fish communities in Adirondack lakes. The lakes sampled are distributed within the five major watersheds originating in the Adirondack ecological zone: Lake Champlain, Oswegatchie-Black, St. Lawrence-Raquette, Upper Hudson, and Mohawk-Hudson. The ecological zone is defined as the area generally lying within the 305-m (1000 feet) elevation contour surrounding the Adirondack uplands and mountain region. It covers approximately 2.6 million ha (10,000 square miles); 2759 individual lakes and ponds greater than 0.2 ha in size {more than 99,000 ha of lake area) have been identified on U.S. Geological Survey (USGS) 15-minute and 7.5-minute maps within the zone boundary [Colquhoun et al., 1984]. The ALSC surveyed 1469 or 53% of these waters. Water samples from each of the ALSC lakes were collected for chemical analysis twice during the study; once during the spring (April-June) or fall (September-October) biological survey, and once during the midsummer chemistry survey (July and August). During the bio...