Noel Urban - Academia.edu (original) (raw)

Papers by Noel Urban

Journal of Great Lakes Research, 2004

Biogeochemistry, Mar 1, 1989

The mass balance and internal cycle of sulfur within a small forested,Sphagnum bog in northern Mi... more The mass balance and internal cycle of sulfur within a small forested,Sphagnum bog in northern Minnesota are presented here based on a 4-year record of hydrologic inputs and outputs (precipitation, throughfall, streamflow, upland runoff) and a 3-year measurement of plant growth and sulfur uptake. Concentrations and accumulation rates of inorganic and organic sulfur species were measured in porewater. The bog

Journal of Geophysical Research, 2005

Canadian Journal of Fisheries and Aquatic Sciences, Sep 1, 1993

Laboratory microcosms were used to investigate rates of S movement into and out of sediments and ... more Laboratory microcosms were used to investigate rates of S movement into and out of sediments and factors affecting its net retention and speciation. Rates of sulfate reduction, calculated from movement of 35S into and out of the sediments, were much higher than net rates of sulfate movement into the sediments. Results suggested that high rates of sulfide oxidation accompanied high rates of sulfate reduction; net flux across the interface depended on the balance between these two processes. Both pyrite and acid-volatile sulfides were dynamic pools undergoing rapid formation and oxidation. Measurement of S in fulvic acid, humic acid, and humin fractions revealed differences between organic S formed by algae and that resulting from sulfate reduction and subsequent reactions in sediments; sulfate esters formed by algae were hydrolyzed in hot acid to a greater extent than sulfate esters formed within the sediments. The organic S species also reflected the extent of oxygenation of the overlying water; low oxygen in overlying water resulted in a high sulfate ester content in the humic acid fraction. Addition of Fe to sediments did not cause increased S retention, but did lead to greater formation of pyrite relative to iron monosulfides.

AGU Spring Meeting Abstracts, May 1, 2005

ABSTRACT With the aim of understanding particle dynamics in the slope-profundal region in coastal... more ABSTRACT With the aim of understanding particle dynamics in the slope-profundal region in coastal areas of the Great Lakes and the particulate organic carbon availability to benthic organisms, sediment cores were taken along three transects in the nearshore region of Lake Superior. Inventories of 137Cs and excess 210Pb and focusing factors (based on both isotopes) were calculated for 28 cores. 7Be was only found in the fluff layer of the sediments at most sites, but its presence in deep-water sites attests to the rapidity of sedimentation. The 210Pb-derived focusing factors ranged from 0.04 to 2.3 with mean and median values of 0.36 and 0.15, respectively. The study region is thus categorized as a temporary deposition zone. A 2-dimensional steady-state nested-box model was developed and applied to individual transects with the 210Pb inventories as model input. Model output included isotope residence times and cross-margin fluxes of sediments and isotopes. The time scale for the particles focusing from the shelf zone to the profundal zone of the transect was on the order of 10 years. The predicted residence times also indicate the existence of local enrichment zones for both isotopes and sediments as well as depletion zones along each transect. The results suggest that food availability may explain the observed Diporeia distributions along the transects. High ratios of 137Cs:210Pb were interpreted to indicate longshore transport by the Keweenaw Current and the general counter-clockwise circulation in the lake. This circulation entrains older sediments into the nearshore zone where they remain for periods of 10-30 years.

2014 AGU Fall Meeting, Dec 18, 2014

A Research Agenda for Environmental Management, 2019

This chapter examines a transdisciplinary (TD) research project that included space for stakehold... more This chapter examines a transdisciplinary (TD) research project that included space for stakeholder and decision maker participation. The project, funded by the National Science Foundation, focused on the atmospheric transport of compounds (such as mercury and PCBs) responsible for fish consumption advisories in the Great Lakes region and the systems of governance in place to address this concern. The TD research question pursued in this project, which was “when will it be safe for people in the Great Lakes region to consume as much fish as desired?”, emerged out of a workshop held with community partners soon after the project began. The various challenges that emerged in the framing and execution of this interdisciplinary project and in the execution of its TD component are considered here, along with the value of having natural science and social science researchers collaborate with community partners

Studies at the Marcell Experimental Forest (MEF) have measured the pools, cycling, and transport ... more Studies at the Marcell Experimental Forest (MEF) have measured the pools, cycling, and transport of a variety of elements in both the upland and peat-land components of the landscape. Peatlands are important zones of element retention and biogeochemical reactions that greatly influence the chemistry

Aerosol filter samples were collected daily during summer 2013, at the Pico Mountain Observatory ... more Aerosol filter samples were collected daily during summer 2013, at the Pico Mountain Observatory (PMO, 38.47°N, 28.40°W, 2,225 m a.s.l.), Azores Islands. PMO monitors free troposphere air and aerosols transported from neighboring continents; North America has the most frequent influence due to predominantly westerly winds in mid-latitude regions, while aerosols from Europe and Africa are sampled occasionally. The residence time during long-range transport in the atmosphere has a critical impact on aerosol chemical and physical properties, and it can be estimated by measuring activities of radionuclides attached to aerosols. 210Pb (t1/2 = 22.1 years) and 210Po (t1/2 = 138 days) are daughter nuclides in the decay chain of 222Rn, an inert gas species produced throughout the Earth\u27s crust and emitted into the atmosphere. Due to different rates of decay, the activity ratio of 210Po to 210Pb can be used to estimate atmospheric residence times of the carrier aerosols. 210Po activity counting of 58 samples was conducted to investigate aerosol residence times in this study. 210Po activity was measured twice serially for each aerosol sample to predict the initial activity of 210Po on the sampling date and the activity of very slowly decaying 210Pb. Aerosol ages calculated by the activity ratio of 210Po to 210Pb were compared with air tracer ages simulated using the FLEXible PARTicle dispersion model (FLEXPART) and studied together with aerosol particle physical properties. The activity of terrestrial radionuclides per unit of aerosol mass can also reveal source information of the aerosols. FLEXPART backward trajectories will be used to verify correlations between source regions and activity of radionuclides in aerosols. In previous research related to long-range atmospheric transport to PMO, FLEXPART has proven to be reliable in identifying upwind source regions

Advances in Chemistry, 1994

Page 1. 10 Retention of Sulfur in Lake Sediments NR Urban Lake Research Laboratory, Swiss Federal... more Page 1. 10 Retention of Sulfur in Lake Sediments NR Urban Lake Research Laboratory, Swiss Federal Institute for Water Resources and Water Pollution Control (EAWAG/ETH), CH-6047 Kastanienbaum, Switzerland Measurements ...

Environmental Science: Processes & Impacts, 2018

The effect of policy on fish mercury levels varies spatially, even within the Great Lakes Basin.

Environmental science. Processes & impacts, Jan 29, 2018

A geographic enigma is that present-day atmospheric deposition of mercury in the Upper Peninsula ... more A geographic enigma is that present-day atmospheric deposition of mercury in the Upper Peninsula of Michigan is low (48%) and that regional industrial emissions have declined substantially (ca. 81% reduction) relative to downstate. Mercury levels should be declining. However, state (MDEQ) surveys of rivers and lakes revealed elevated total mercury (THg) in Upper Peninsula waters and sediment relative to downstate. Moreover, Western Upper Peninsula (WUP) fish possess higher methyl mercury (MeHg) levels than Northern Lower Peninsula (NLP) fish. A contributing explanation for elevated THg loading is that a century ago the Upper Peninsula was a major industrial region, centered on mining. Many regional ores (silver, copper, zinc, massive sulfides) contain mercury in part per million concentrations. Copper smelters and iron furnace-taconite operations broadcast mercury almost continuously for 140 years, whereas mills discharged tailings and old mine shafts leaked contaminated water. We s...

Effects of Atmospheric Pollutants on Forests, Wetlands and Agricultural Ecosystems, 1987

Wetlands include ecosystems on predominantly inorganic sediments and those that accumulate organi... more Wetlands include ecosystems on predominantly inorganic sediments and those that accumulate organic peat. Peat-accumulating ecosystems cover about 460 Mha — approximately 3% of the Earth’s land surface — and contain about 150 Gt of carbon — a value that may be compared with an estimate of 560 Gt of carbon in the Earth’s non-marine biomass. On the whole, these ecosystems are not of great economic importance, although they are locally exploited for agriculture (drained fens, cranberry bogs), forestry, and mining of peat. They do, however, have substantial effects on the chemistry of the water that runs from them to streams and lakes. Damage to peat-forming ecosystems is likely to be quickly reflected in water quality and possibly in the ability to act as absorbents of aerial pollutants. In spite of the actual and potential importance of peat-accumulating ecosystems, the money spent on assessing the consequences of damaging them by aerial pollution is probably less than 1% of that spent for a similar purpose on forests or on agriculture. This is short-sighted.