EEB Papers - Robert Howarth

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https://hdl.handle.net/1813/60806

Professor Howarth is the David R. Atkinson Professor of Ecology & Evolutionary Biology in the Department of Ecology and Evolutionary Biology at Cornell University. He is a biogeochemist and ecosystem scientist, an active research scientist who also enjoys teaching and is deeply involved in the environmental management and policy communities in the State, nationally, and internationally. His training was in oceanography, and much of his research still focuses on coastal marine ecosystems. However, he also works on freshwater systems (both rivers and lakes) and on large river basins.

Professor Howarth's research laboratory works broadly on human alteration of element cycles (particularly nutrients) in coastal marine ecosystems and in the watersheds that feed them. He also works on the environmental consequences of energy systems, particularly from oil and gas development and from biofuels, emphasizing water quality and greenhouse gas emissions. Specific current topics of study include:

The biogeochemical feedbacks which may either aggravate or partially ameliorate eutrophication that occurs in seagrass-dominated systems as nutrient loads increase;
The influences of climate change, land use, and management practices on the export of nutrients and sediment from large river basins;
The importance of dry deposition of nitrogen gases from the atmosphere (particularly in the near proximity of vehicle emissions) as a source of nutrient pollution to coastal waters;
The environmental consequences of biofuels;
The greenhouse gas footprint of natural gas extracted from shale formations such as the Marcellus shale.

A more complete and current listing of Prof. Howarth's work and scholarly output can be found on his EEB Department web page and the Howarth & Marino Lab web site, or through the links below.

Google Scholar Page

ResearchGate Profile Page

ORCID ID: https://orcid.org/0000-0001-9531-4288

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Now showing 1 - 10 of 24

Anthropogenic phosphorus inputs to a river basin and their impacts on riverine phosphorus fluxes along its upstream-downstream continuum
Zhang, W.S.; Swaney, D. P.; Hong, B.; Howarth, R. W. (Wiley, 2017-12-23)
The increasing trend in riverine phosphorus (P) loads resulting from anthropogenic inputs has gained wide attention because of the well-known role of P in eutrophication. So far, however, there is still limited scientific understanding of anthropogenic P inputs and their impacts on riverine flux in river reaches along the upstream-to-downstream continuum. Here we investigated P budgets in a series of nested watersheds draining into Hongze Lake of China and developed an empirical function to describe the relationship between anthropogenic inputs and riverine P fluxes. Our results indicated that there are obvious gradients regarding P budgets in response to changes in human activities. Fertilizer application and food and feed P import was always the dominant source of P inputs in all sections, followed by nonfood P. Further interpretation using the model revealed the processes of P loading to the lake. About 2%–9% of anthropogenic P inputs are transported from the various sections into the corresponding tributaries of the river systems, depending upon local precipitation rates. Of this amount, around 41%–95% is delivered to the main stem of the Huai River after in-stream attenuation in its tributaries. Ultimately, 55%–86% of the P loads delivered to different locations of the main stem are transported into the receiving lake of the downstream, due to additional losses in the main stem. An integrated P management strategy that considers the gradients of P loss along the upstream-to-downstream continuum is required to assess and optimize P management to protect the region's freshwater resource.
Human health effects of a changing global nitrogen cycle
Townsend, A. R.; Howarth, R. W.; Bazzaz, F. A.; Booth, M. S.; Cleveland, C. C.; Collinge, S. K.; Dobson, A. P.; Epstein, P. R.; Holland, E. A.; Keeney, D. R.; Mallin, M. A.; Rogers, C. A.; Wayne, P.; Wolfe, A. H. (Wiley, 2003-06-01)
Changes to the global nitrogen cycle affect human health well beyond the associated benefits of increased food production. Many intensively fertilized crops become animal feed, helping to create disparities in world food distribution and leading to unbalanced diets, even in wealthy nations. Excessive air- and water-borne nitrogen are linked to respiratory ailments, cardiac disease, and several cancers. Ecological feedbacks to excess nitrogen can inhibit crop growth, increase allergenic pollen production, and potentially affect the dynamics of several vector-borne diseases, including West Nile virus, malaria, and cholera. These and other examples suggest that our increasing production and use of fixed nitrogen poses a growing public health risk.
Sulfur and carbon isotopes as tracers of salt-marsh organic matter flow
Peterson, B.J.; Howarth, R. W.; Garritt, R.H. (Wiley, 1986-08-01)
Stable isotopes of sulfur and carbon were used to trace the dominant flows of organic matter from producers to macroconsumers in Great Sippewissett Salt Marsh on Cape Cod. Spartina alterniflora and sulfur-oxidizing bacteria assimilate isotopically light sulfides produced via sulfate reduction, and this light sulfur was detected in consumers. In contrast, phytoplankton and upland plants assimilate isotopically heavier SO4 2- with little or no fractionation. A dual-isotope approach using both delta 13C and delta 14S showed that Ilyanassa obsoleta and Fundulus heteroclitus depend very heavily on Spartina detritus, while filter feeders such as Crassostrea virginica and Geukensia demissa depend on a mixture of plankton and Spartina detritus. Spartina detritus and plankton were both much more important as organic matter derived from terrestrial inputs.
Toward a better understanding and quantification of methane emissions from shale gas development
Caulton, D.R.; Shepson, P. B.; Santoro, R.L.; Sparks, J.P.; Howarth, R. W.; Ingraffea, A.; Camaliza, M.O.; Sweeney, C.; Karion, A.; Davis, K.J.; Stirm, B.H.; Montzka, S.A.; Miller, B. (National Academy of Sciences, 2014-04-29)
The identification and quantification of methane emissions from natural gas production has become increasingly important owing to the increase in the natural gas component of the energy sector. An instrumented aircraft platform was used to identify large sources of methane and quantify emission rates in southwestern PA in June 2012. A large regional flux, 2.0-14 g CH4 s-1 km-2, was quantified for a ?2,800-km2 area, which did not differ statistically from a bottom-up inventory, 2.3-4.6 g CH4 s-1 km-2. Large emissions averaging 34 g CH 4/s per well were observed from seven well pads determined to be in the drilling phase, 2 to 3 orders of magnitude greater than US Environmental Protection Agency estimates for this operational phase. The emissions from these well pads, representing ?1% of the total number of wells, account for 4-30% of the observed regional flux. More work is needed to determine all of the sources of methane emissions from natural gas production, to ascertain why these emissions occur and to evaluate their climate and atmospheric chemistry impacts.
Human alteration of the global nitrogen cycle: Causes and consequences
Vitousek, P.M.; Aber, J.; Bayley, S. E.; Howarth, R. W.; Likens, G. E.; Matson, P. A.; Schindler, D. W.; Schlesinger, W. H.; Tilman, G. D. (Wiley, 1997-08-01)
Nitrogen is a key element controlling the species composition, diversity, dynamics, and functioning of many terrestrial, freshwater, and marine ecosystems. Many of the original plant species living in these ecosystems are adapted to, and function optimally in, soils and solutions with low levels of available nitrogen. The growth and dynamics of herbivore populations, and ultimately those of their predators, also are affected by N. Agriculture, combustion of fossil fuels, and other human activities have altered the global cycle of N substantially, generally increasing both the availability and the mobility of N over large regions of Earth. The mobility of N means that while most deliberate applications of N occur locally, their influence spreads regionally and even globally. Moreover, many of the mobile forms of N themselves have environmental consequences. Although most nitrogen inputs serve human needs such as agricultural production, their environmental consequences are serious and long term. Based on our review of available scientific evidence, we are certain that human alterations of the nitrogen cycle have: approximately doubled the rate of nitrogen input into the terrestrial nitrogen cycle, with these rates still increasing; increased concentrations of the potent greenhouse gas N2O globally, and increased concentrations of other oxides of nitrogen that drive the formation of photochemical smog over large regions of Earth; caused losses of soil nutrients, such as calcium and potassium, that are essential for the long?term maintenance of soil fertility; contributed substantially to the acidification of soils, streams, and lakes in several regions; and greatly increased the transfer of nitrogen through rivers to estuaries and coastal oceans. In addition, based on our review of available scientific evidence we are confident that human alterations of the nitrogen cycle have: increased the quantity of organic carbon stored within terrestrial ecosystems; accelerated losses of biological diversity, especially losses of plants adapted to efficient use of nitrogen, and losses of the animals and microorganisms that depend on them; and caused changes in the composition and functioning of estuarine and nearshore ecosystems, and contributed to long?term declines in coastal marine fisheries.
Nutrient limitation of phytoplankton growth in Vineyard Sound and Oyster Pond, Falmouth, Massachusetts
Weber, C. F.; Barron, S.; Marino, R. M.; Howarth, R. W.; Tomasky, G.; Davidson, E. A. (University of Chicago Press, 2002-10)
Intensive agriculture represents a recent extension of green roof technology. Perceived ecosystem services provided by rooftop farming include stormwater management and the production of affordable and nutritious vegetables for local consumption. However, intensive agriculture can increase nutrient loads to surface water, yet there is little empirical data from full-scale operational rooftop farms. This study reports the N balance and N management efficiency of the Brooklyn Grange Navy Yard Farm, a 0.61-ha farm atop an 11-story building in New York City USA. We monitored atmospheric N deposition, soil N concentration, N output by harvest, N leaching from soil, and drainage N output, in addition to estimating net N mineralization and the N load to sewers during the combined sewer overflows. We found that the annual drainage N output was 1,100% of the atmospheric bulk N deposition, and was 540% of the estimated total atmospheric N deposition, which makes the Brooklyn Grange a net N source in the urban environment. Annual N leaching from soil was 97% of fertilizer N input, and the efficiency of N management can be lower than in conventional vegetable production. For the Brooklyn Grange to integrate stormwater management and intensive agriculture, it will be important to use soil with greater water holding capacity within the range of readily available water, and to recycle drainage. This case study shows how the intensification of agriculture on rooftops should be managed for both the yield and quality of crops and to reduce N loss to storm drains, which affects aquatic ecosystems and water quality.
Nitrogen biogeochemistry of an urban rooftop farm
Harada, Y.; Whitlow, T.H.; Templer, P.H.; Howarth, R. W.; Walter, M.T.; Bassuk, N.L.; Russell-Anelli, J.H. (Frontiers Media S.A., 2018-10-11)
Intensive agriculture represents a recent extension of green roof technology. Perceived ecosystem services provided by rooftop farming include stormwater management and the production of affordable and nutritious vegetables for local consumption. However, intensive agriculture can increase nutrient loads to surface water, yet there is little empirical data from full-scale operational rooftop farms. This study reports the N balance and N management efficiency of the Brooklyn Grange Navy Yard Farm, a 0.61-ha farm atop an 11-story building in New York City USA. We monitored atmospheric N deposition, soil N concentration, N output by harvest, N leaching from soil, and drainage N output, in addition to estimating net N mineralization and the N load to sewers during the combined sewer overflows. We found that the annual drainage N output was 1,100% of the atmospheric bulk N deposition, and was 540% of the estimated total atmospheric N deposition, which makes the Brooklyn Grange a net N source in the urban environment. Annual N leaching from soil was 97% of fertilizer N input, and the efficiency of N management can be lower than in conventional vegetable production. For the Brooklyn Grange to integrate stormwater management and intensive agriculture, it will be important to use soil with greater water holding capacity within the range of readily available water, and to recycle drainage. This case study shows how the intensification of agriculture on rooftops should be managed for both the yield and quality of crops and to reduce N loss to storm drains, which affects aquatic ecosystems and water quality.
A century of legacy phosphorus dynamics in a large drainage basin
McCrackin, M. L.; Muller-Karulis, B.; Gustafsson, B. G.; Howarth, R. W.; Humborg, C.; Svanbäck, A.; Swaney, D. P. (Wiley, 2018-06-27)
There is growing evidence that the release of phosphorus (P) from “legacy” stores can frustrate efforts to reduce P loading to surface water from sources such as agriculture and human sewage. Less is known, however, about the magnitude and residence times of these legacy pools. Here we constructed a budget of net anthropogenic P inputs to the Baltic Sea drainage basin and developed a three-parameter, two-box model to describe the movement of anthropogenic P though temporary (mobile) and long-term (stable) storage pools. Phosphorus entered the sea as direct coastal effluent discharge and via rapid transport and slow, legacy pathways. The model reproduced past waterborne P loads and suggested an ~30-year residence time in the mobile pool. Between 1900 and 2013, 17 and 27 Mt P has accumulated in the mobile and stable pools, respectively. Phosphorus inputs to the sea have halved since the 1980s due to improvements in coastal sewage treatment and reductions associated with the rapid transport pathway. After decades of accumulation, the system appears to have shifted to a depletion phase; absent further reductions in net anthropogenic P input, future waterborne loads could decrease. Presently, losses from the mobile pool contribute nearly half of P loads, suggesting that it will be difficult to achieve substantial near-term reductions. However, there is still potential to make progress toward eutrophication management goals by addressing rapid transport pathways, such as overland flow, as well as mobile stores, such as cropland with large soil-P reserves.
Inputs of sediment and carbon to an estuarine ecosystem: Influence of land use
Howarth, R. W.; Fruci, J.R.; Sherman, D.M. (Wiley, 1991-02-01)
Estuaries and coastal marine ecosystems receive large inputs of nutrients, organic carbon, and sediments from non—point—source runoff from terrestrial ecosystems. In the tidal, freshwater Hudson River estuary, such inputs are the major sources of organic carbon, driving ecosystem metabolism, and thus strongly influencing dissolved oxygen concentrations. We used a watershed simulation model (GWLF) to examine the controls on inputs of organic carbon and sediment to this estuary. The model provides estimates of water discharge, sediment inputs, and organic carbon inputs that agree reasonably well with independent estimates of these fluxes. Even though the watershed for the Hudson River estuary is dominated by forests, the model predicts that both sediment and organic carbon inputs come overwhelmingly from urban and suburban areas and from agricultural fields. Thus changes in land use within the Hudson River basin may be expected to altering inputs to the estuary, thereby altering its metabolism. Precipitation is important in controlling carbon fluxes to the estuary, and so climate change can be expected to alter estuarine metabolism. However, the day—to—day and seasonal patterns of precipitation appear more important than annual mean precipitation in controlling organic carbon fluxes.
Coupled biogeochemical cycles: eutrophication and hypoxia in temperate estuaries and coastal marine ecosystems
Howarth, R. W.; Chan, F.; Conley, D. J.; Garnier, J.; Doney, S. C.; Marino, R. M.; Billen, G. (Wiley, 2011-02-01)
Nutrient fluxes to coastal areas have risen in recent decades, leading to widespread hypoxia and other ecological damage, particularly from nitrogen (N). Several factors make N more limiting in estuaries and coastal waters than in lakes: desorption (release) of phosphorus (P) bound to clay as salinity increases, lack of planktonic N fixation in most coastal ecosystems, and flux of relatively P-rich, N-poor waters from coastal oceans into estuaries. During eutrophication, biogeochemical feedbacks further increase the supply of N and P, but decrease availability of silica - conditions that can favor the formation and persistence of harmful algal blooms. Given sufficient N inputs, estuaries and coastal marine ecosystems can be driven to P limitation. This switch contributes to greater far-field N pollution; that is, the N moves further and contributes to eutrophication at greater distances. The physical oceanography (extent of stratification, residence time, and so forth) of coastal systems determines their sensitivity to hypoxia, and recent changes in physics have made some ecosystems more sensitive to hypoxia. Coastal hypoxia contributes to ocean acidification, which harms calcifying organisms such as mollusks and some crustaceans.

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