Showing papers by "Peter A. Raymond published in 2008"
TL;DR: An unprecedented high-temporal-resolution, 100-year data set from the Mississippi River is introduced and it is shown that the large increase in bicarbonate flux that has occurred over the past 50 years is clearly anthropogenically driven.
Abstract: The flow of dissolved inorganic carbon from rivers to the oceans is an important net flux connecting the terrestrial and marine carbon reservoirs. Now a remarkable 100-year record of bicarbonate determinations, made at water treatment plants in the towns of Carrollton and Algiers, has been used as a basis for a study of Mississippi River water and carbon fluxes. Previous work revealed a significant increase the amount of dissolved inorganic carbon, mostly bicarbonate, exported by the Mississippi to the ocean over the past 50 years, but the cause for the increase remained uncertain. The Carrollton/Algiers data, together with sub-watershed and precipitation data, point to a mainly anthropogenic origin — increased bicarbonate discharge from agricultural watersheds that was not balanced by a rise in precipitation. A high temporal resolution, 100-year data set from the Mississippi River is coupled with sub-watershed and precipitation data to reveal that a ∼40 percent increase in flux of bicarbonate that has occurred over the last 50 years is clearly anthropogenically driven. This is caused by an increase in discharge from agricultural watersheds not balanced by a rise in precipitation. It is suggested that land use change and management are arguably more important than changes in climate and carbon dioxide fertilization. The water and dissolved inorganic carbon exported by rivers are important net fluxes that connect terrestrial and oceanic water and carbon reservoirs1. For most rivers, the majority of dissolved inorganic carbon is in the form of bicarbonate. The riverine bicarbonate flux originates mainly from the dissolution of rock minerals by soil water carbon dioxide, a process called chemical weathering, which controls the buffering capacity and mineral content of receiving streams and rivers2. Here we introduce an unprecedented high-temporal-resolution, 100-year data set from the Mississippi River and couple it with sub-watershed and precipitation data to reveal that the large increase in bicarbonate flux that has occurred over the past 50 years (ref. 3) is clearly anthropogenically driven. We show that the increase in bicarbonate and water fluxes is caused mainly by an increase in discharge from agricultural watersheds that has not been balanced by a rise in precipitation, which is also relevant to nutrient and pesticide fluxes to the Gulf of Mexico. These findings demonstrate that alterations in chemical weathering are relevant to improving contemporary biogeochemical budgets. Furthermore, land use change and management were arguably more important than changes in climate and plant CO2 fertilization to increases in riverine water and carbon export from this large region over the past 50 years.
462 citations
TL;DR: In this article, the authors show that there is substantial seasonal variability in the lability of DOC transported by Alaskan rivers to the Arctic Ocean: little DOC is lost during incubations of samples collected during summer, but substantial losses (20-40%) occur during incubation of sample collected during the spring freshet when the majority of the annual DOC flux occurs.
Abstract: [1] Arctic rivers transport huge quantities of dissolved organic carbon (DOC) to the Arctic Ocean. The prevailing paradigm is that DOC in arctic rivers is refractory and therefore of little significance for the biogeochemistry of the Arctic Ocean. We show that there is substantial seasonal variability in the lability of DOC transported by Alaskan rivers to the Arctic Ocean: little DOC is lost during incubations of samples collected during summer, but substantial losses (20–40%) occur during incubations of samples collected during the spring freshet when the majority of the annual DOC flux occurs. We speculate that restricting sampling to summer may have biased past studies. If so, then fluvial inputs of DOC to the Arctic Ocean may have a much larger influence on coastal ocean biogeochemistry than previously realized, and reconsideration of the role of terrigenous DOC on carbon, microbial, and food-web dynamics on the arctic shelf will be warranted.
328 citations
TL;DR: Cooper et al. as mentioned in this paper used coordinated collections between 2003 and 2006 that were temporally distributed to capture linked seasonal dynamics of river flow and tracer values, showing significant variation in the contributions each river makes to the Arctic Ocean.
Abstract: dissolved organic carbon (DOC), dissolved barium and total alkalinity from the six largest Arctic rivers: the Ob’, Yenisey, Lena, Kolyma, Yukon and Mackenzie These data, which can be used to trace runoff, are based upon coordinated collections between 2003 and 2006 that were temporally distributed to capture linked seasonal dynamics of river flow and tracer values Individual samples indicate significant variation in the contributions each river makes to the Arctic Ocean Use of these new flow-weighted estimates should reduce uncertainties in the analysis of freshwater transport and fate in the upper Arctic Ocean, including the links to North Atlantic thermohaline circulation, as well as regional water mass analysis Additional improvements should also be possible for assessing the mineralization rate of the globally significant flux of terrigenous DOC contributed to the Arctic Ocean by these major rivers Citation: Cooper, L W, J W McClelland, R M Holmes, P A Raymond, J J Gibson, C K Guay, and B J Peterson (2008), Flow-weighted values of runoff tracers (d 18 O, DOC, Ba, alkalinity) from the six largest Arctic rivers, Geophys Res Lett, 35, L18606, doi:101029/2008GL035007
229 citations
University of Texas at Austin1, Woods Hole Research Center2, Marine Biological Laboratory3, Texas A&M University4, United States Geological Survey5, University of Maryland Center for Environmental Science6, University of Victoria7, Shirshov Institute of Oceanology8, Yale University9, State Hydrological Institute10
TL;DR: The Pan-Arctic River Transport of Nutrients, Organic Matter, and Suspended Sediments ( PARTNERS) project was initiated in 2002 to help remedy this deficit, and an extraordinary data set has emerged over the past few years as a result of the effort.
Abstract: More than 10% of all continental runoff flows into the Arctic Ocean. This runoff is a dominant feature of the Arctic Ocean with respect to water column structure and circulation. Yet understanding of the chemical characteristics of runoff from the pan-Arctic watershed is surprisingly limited. The Pan- Arctic River Transport of Nutrients, Organic Matter, and Suspended Sediments ( PARTNERS) project was initiated in 2002 to help remedy this deficit, and an extraordinary data set has emerged over the past few years as a result of the effort. This data set is publicly available through the Cooperative Arctic Data and Information Service (CADIS) of the Arctic Observing Network (AON). Details about data access are provided below.
75 citations
TL;DR: In this paper, the relative importance of sources and control mechanisms on NO3 export from five forested watersheds in the Connecticut River watershed was determined by combining isotopic data obtained using the denitrifier method, with chemical and hydrologic measurements.
Abstract: Nitrogen from atmospheric deposition serves as the dominant source of new nitrogen to forested ecosystems in the northeastern U.S. By combining isotopic data obtained using the denitrifier method, with chemical and hydrologic measurements we determined the relative importance of sources and control mechanisms on nitrate (NO3−) export from five forested watersheds in the Connecticut River watershed. Microbially produced NO3− was the dominant source (82–100%) of NO3− to the sampled streams as indicated by the δ15N and δ18O of NO3−. Seasonal variations in the δ18O–NO3− in streamwater are controlled by shifting hydrologic and temperature affects on biotic processing, resulting in a relative increase in unprocessed NO3− export during winter months. Mass balance estimates find that the unprocessed atmospherically derived NO3− stream flux represents less than 3% of the atmospherically delivered wet NO3− flux to the region. This suggests that despite chronically elevated nitrogen deposition these forests are not nitrogen saturated and are retaining, removing, and reprocessing the vast majority of NO3− delivered to them throughout the year. These results confirm previous work within Northeastern U.S. forests and extend observations to watersheds not dominated by a snow-melt driven hydrology. In contrast to previous work, unprocessed atmospherically derived NO3− export is associated with the period of high recharge and low biotic activity as opposed to spring snowmelt and other large runoff events.
59 citations