Papers by Gregory McIsaac
The Scientific World Journal, 2001
The Midwest has large riverine exports of nitrogen (N), with the largest flux per unit area to th... more The Midwest has large riverine exports of nitrogen (N), with the largest flux per unit area to the Mississippi River system coming from Iowa and Illinois. We used historic and current data to estimate N inputs, outputs, and transformations for Illinois where human activity (principally agriculture and associated landscape drainage) have had a dominant impact. Presently, ~800,000 Mg of N is added each year as fertilizer and another 420,000 Mg is biologically fixed, primarily by soybean (Glycine max L. Merr.). These annual inputs are greater than exports in grain, which results in surplus N throughout the landscape. Rivers within the state export approximately 50% of this surplus N, mostly as nitrate, and the remainder appears to be denitrified or temporarily incorporated into the soil organic matter pool. The magnitude of N losses for 1880, 1910, 1950, and 1990 are compared. Initial cultivation of the prairies released large quantities of N (~500,000 Mg N year-1), and resulted in riverine N transport during the late 19th century that appears to have been on the same order of magnitude as contemporary N losses. Riverine flux was estimated to have been at a minimum in about 1950, due to diminished net mineralization and low fertilizer inputs. Residual fertilizer N from corn (Zea mays L.), biological N fixed by soybean, short-circuiting of soil water through artificial drainage, and decreased croppingsystem diversity appear to be the primary sources for current N export.
Journal of Professional Issues in Engineering Education and Practice, 1998
Journal of Environmental Quality
ABSTRACT
Transactions of the ASAE, 1992
Unit Stream Power (USP) and the associated Yang (1973) sediment transport equations were compared... more Unit Stream Power (USP) and the associated Yang (1973) sediment transport equations were compared to soil detachment rates and sediment concentrations in runoff from eroding soils. Although USP was significantly correlated with rill detachment rates, potential energy dissipation rate per unit rill area was a better predictor of soil detachment rates. The Yang (1973) equations estimated sediment concentrations within a factor of 10 of the observed concentrations, if the median soil aggregate diameter was within the range of diameters used by Yang to estimate the equation parameters. When median aggregate sizes were less than 0.15 mm, the lower limit of Yang's (1973) calibration range, the equations tended to produce unrealistically large estimates of sediment concentration. KEYWORDS.
and some corrective measures have been implemented. The longer term history may provide an unders... more and some corrective measures have been implemented. The longer term history may provide an understanding of the context within which local sustainable resource management efforts must operate to move the larger system closer to sustainability. Great Lakes Region Prehistory After the Recent Glaciation The topography of the Great Lakes region was formed by repeated cycles of glacial advance and retreat over the last million years. The most recent glaciers reached its maximum extent about 20,000 years ago and extended south of the Basin. There is evidence of human activity in the region that is 13,000 years old (Walters and Stafford , 2007). At that time, glaciers and tundra covered the northern portions of the Great Lakes Basin. Between 10,000 and 12,000 years ago, 35 genera of large mammals went extinct in North America, including mastodons, mammoths and horses. The causes of this extinction event are uncertain, but may include climate change, extraterrestrial impact, and human hunting pressure (Faith and Surovell , 2009).
and some corrective measures have been implemented. The longer term history may provide an unders... more and some corrective measures have been implemented. The longer term history may provide an understanding of the context within which local sustainable resource management efforts must operate to move the larger system closer to sustainability. Great Lakes Region Prehistory After the Recent Glaciation The topography of the Great Lakes region was formed by repeated cycles of glacial advance and retreat over the last million years. The most recent glaciers reached its maximum extent about 20,000 years ago and extended south of the Basin. There is evidence of human activity in the region that is 13,000 years old (Walters and Stafford , 2007). At that time, glaciers and tundra covered the northern portions of the Great Lakes Basin. Between 10,000 and 12,000 years ago, 35 genera of large mammals went extinct in North America, including mastodons, mammoths and horses. The causes of this extinction event are uncertain, but may include climate change, extraterrestrial impact, and human hunting pressure (Faith and Surovell , 2009).
Aquacultural Engineering, 2020
Abstract The denitrifying woodchip bioreactor is designed to remediate nitrate-rich water, includ... more Abstract The denitrifying woodchip bioreactor is designed to remediate nitrate-rich water, including those produced from aquaculture effluents. Reuse of treated bioreactor outflows in recirculating aquaculture would offer considerable water savings and valuable alkalinity recuperation. However, such bioreactors may leach detrimental wood-bound contaminants, preventing outflow reuse. To determine water reuse potential, woodchip media from two hardwood species (white ash, Fraxinus americana; Norway maple, Acer platanoides) were evaluated for 206 d under a range of operating conditions (start-up, steady-state, reducing conditions, and drying-rewetting cycles) for a spectrum of potentially harmful dissolved contaminants. Aerated outflows also were evaluated for acute and chronic toxicity to the biologically sensitive invertebrate Ceriodaphnia dubia. Dissolved metal leaching subsided within the first few weeks of operation, though initial concentrations of copper and zinc were detected at concentrations of concern. Elevated concentrations of tannins-lignin and total ammonia nitrogen were detected throughout the study and were influenced by operational phase. Acute toxicity was not generally detected, though chronic toxicity was observed during drying-rewetting cycles in the maple outflows. The measured toxicity was not correlated with water chemistry, indicating an additive effect of several toxicants. Overall, significant differences in outflow water quality between ash and maple wood species were negligible. Results indicated that bioreactor outflows may be applicable for aquacultural reuse, though reusing outflows immediately following start-up or restarting after a dry period would not be recommended.
Transactions of the ASAE, 1990
Simulated rainfall was applied to a Tama silt loam soil under six tillage treatments, two crops (... more Simulated rainfall was applied to a Tama silt loam soil under six tillage treatments, two crops (com and soybeans), two crop stages (at planting and one month later), and two row orientations (on the contour and up-and-down the slope, UD). Runoff was greatest from UD moldboard plowed plots and least from plots which had been chisel plowed immediately prior to planting and from no-till plots following soybeans. Non-linear regression models, using plot slope, percent residue and canopy cover as independent variables, accounted for 84% of the variation in average sediment concentration from the UD treatments, but only 62% of the variation in average sediment concentration from the contour treatments. Under steady runoff conditions, 76% of the log of the sediment concentration from either row orientation was accounted for by equations which included either measured runoff velocity or unit stream power calculated from measured runoff velocity. INTRODUCTION E stimates of average annual soil erosion in the U.S. Corn Belt have exceeded estimates of top soil formation rates on 38% of the cropland (National Research Council, 1986). The greatest erosion rates appear to be associated with steeply sloping land. Major Land Resource Area 108 covers 6 million ha in Illinois and Iowa, which have an average erosion rate of 19 Mg/ha. This area includes 1 million ha with slopes between 6% and 12% which have an average annual erosion rate of 42 Mg/ha (Pierce et al., 1984). While these estimates are based on the best available methodologies, there is a need to improve soil erosion estimation (Soil Conservation Service, 1987) as well as identify socially acceptable land use practices which reduce erosion. Tillage practices which leave crop residues on the soil surface appear to be gaining farmer acceptance, possibly due to reduced machinery, labor and fuel costs (Crosson, 1981; Doster et al., 1983). Reduced soil erosion from tillage systems which leave crop residue on the soil surface has been demonstrated by Laflen et al. (1980), Laflen and
Aquacultural Engineering, 2019
Abstract Recirculating aquaculture systems (RAS) facilities subject to point-source effluent regu... more Abstract Recirculating aquaculture systems (RAS) facilities subject to point-source effluent regulations need to implement cost-effective N remediation for their wastewater outflows. Relatively low-cost denitrifying “woodchip” bioreactors can effectively remove N from aquaculture effluents for at least one year, but questions remain about bioreactor lifespan for aquacultural wastewaters. Four pilot-scale bioreactors (L × W × D; 3.8 × 0.76 × 0.76 m), two with a conventional single distribution inflow manifold and two with an experimental multiple-header, feed-forward distribution manifold, were operated over 784 d to observe second-year N removal performance and to determine if the manifold design can influence bioreactor effectiveness. The study also quantified performance metrics for chemical oxygen demand, total suspended solids, and phosphorus. Manifold style did not have notable impact on bioreactor performance when treating wastewater under the facilities’ normal operating conditions, but the multiple distribution style demonstrated an 11 % increase in nitrate and 12 % increase in total suspended solids removal efficiency over the single distribution manifold toward the end of the study when bioreactors treated higher strength wastewater. Additionally, bioreactor performance in both manifold designs decreased from an average of 92 % total suspended solids removal efficiency under normal operating conditions to
Journal of Environmental Management, 2018
Nutrients in drainage waters from the Upper Mississippi River Basin states have been a well-docum... more Nutrients in drainage waters from the Upper Mississippi River Basin states have been a well-documented contributor to the Gulf of Mexico hypoxic zone for decades, and in response, twelve states have developed strategies to address this issue, with Iowa, Minnesota, and Illinois performing rigorous science assessments which estimated nitrogen and phosphorus reduction effectiveness for numerous agricultural non-point source conservation practices. The practices identified in these strategies were compared to identify areas of consensus and discord on nutrient load reduction potentials. Additionally, each practice was assessed for (1) the suitability to stack or be layered with other practices (stackability), (2) the ability to track implementation within a state or regionally (trackability), and (3) the level of production system change required to implement the practice. Overall, there was general consensus among the state strategies in the nutrient load reduction effectiveness of most practices with the exception of cover crops (10%-31% nitrogen reduction) and bioreactors (13%-43% nitrogen reduction). The most effective water quality-improvement practices (i.e., land-use change practices) required relatively more production system changes to agronomic management and were the most trackable (scores: 5, 1-5 scale), although they were also less stackable with other practices (scores: 1 to 1.8; 1-5 scale) and were the least cost effective on a unit area basis (generally $15 to $964 per ha). The most cost effective practices tended to be highly stackable (e.g., nitrogen management: (−)$49 per ha and stackability of 4.7), which indicated that stacking a variety of practices may be the most cost effective use of conservation dollars. The practices that were most difficult to track had relatively lower nitrogen loss reduction effectiveness, but these practices were less costly to implement and required relatively less production system change to agronomic management, two factors of importance to many producers.
Encyclopedia of Soil Science, Third Edition, 2016
Journal of Environmental Quality, 2016
The Illinois River is a major contributor of nitrate-N to the Mississippi River and the Gulf of M... more The Illinois River is a major contributor of nitrate-N to the Mississippi River and the Gulf of Mexico, where nitrate is a leading cause of summertime benthic hypoxia. Corn-soybean production on tile-drained land is a leading source of nitrate-N in this river system, in addition to municipal wastewater discharge. We calculated annual nitrate-N loads in the Illinois River at Valley City from 1976 to 2014 by linear interpolation. Although there was not a significant trend in annual loads during the entire study period, there was a significant downward trend in flow-weighted nitrate-N concentration after 1990 despite high concentrations in 2013 after the 2012 drought. Multivariate regression analysis revealed a statistically significant association between annual flow-weighted nitrate-N concentration and cumulative residual agricultural N inputs to the watershed during a 6-yr window. This suggests that declines in flow-weighted nitrate-N concentration may reflect increasing N use efficiency in agriculture and a depletion of legacy N stored in the watershed. The watershed appears to have transitioned from a state of stationarity in nitrate concentration to nonstationarity. The average annual nitrate-N load at Valley City from 2010 to 2014 was 10% less than the 1980-1996 average load, indicating recent progress toward Illinois' nutrient loss reduction milestone of 15% reduction by 2025 and ultimate target of 45% reduction.
Current Sustainable/Renewable Energy Reports, 2014
The Energy Independence and Security Act (EISA) mandated an increase in the production of liquid ... more The Energy Independence and Security Act (EISA) mandated an increase in the production of liquid fuels from renewable sources, including corn, soybeans, and perennial crops. Expanded corn production poses a risk to water quality, and expanded production of perennial crops for cellulosic ethanol may have positive effects on water quality as well as positive or negative impacts on water quantity. Nitrate contamination from corn production is greatest in regions with subsurface drainage systems. Sediment and phosphorus contamination are more likely to come from sloping soils. The risks to water quality can be reduced by conservation practices, such as planting winter cover crops, but the costs of implementing these practices represent a barrier to adoption when there is little or no benefit to the farm owner or operator. The magnitude of these impacts appears to be highly variable and there is a need for more empirical work to improve simulation models to quantify the impacts in different physiographic settings and at a range of scales.
Environmental science & technology, Jan 8, 2015
Implementing public policies often involves navigating an array of choices that have economic and... more Implementing public policies often involves navigating an array of choices that have economic and environmental consequences that are difficult to quantify given the complexity of multiple system interactions. Implementing the mandate for cellulosic biofuel production in the Renewable Fuel Standard (RFS), and reducing hypoxia in the northern Gulf of Mexico by reducing riverine nitrate-N loads represent two such cases that overlap in the Mississippi River Basin. To quantify the consequences of these interactions, we developed a system of systems (SoS) model that incorporates interdependencies among the various subsystems, including biofuel refineries, transportation, agriculture, water resources and crop/ethanol markets. The model allows examination of the impact of nitrate-N load limits on the biofuel production system as a whole, including land use change and infrastructure needs. The synergies of crop choice (first versus second generation biofuel crops), infrastructure developmen...
Humans have more than doubled the rate at which nitrogen enters the terrestrial biosphere due to ... more Humans have more than doubled the rate at which nitrogen enters the terrestrial biosphere due to agricultural land expansion, fossil fuel burning and fertilizer application (Galloway et al., 2004) Water quality degradation associated with nitrogen leaching is an important environmental issue worldwide (Davis and Koop, 2006) To data, very few national to global scale studies exist (Dumont et al., 2005) and estimates of nitrogen leaching is still insufficient (Seitzinger et al., 2005
Advances in Agroecology, 2001
FarmCommunity Entrepreneurial Partnerships in the Midwest Cornelia Butler Flora, Gregory McIsaac... more FarmCommunity Entrepreneurial Partnerships in the Midwest Cornelia Butler Flora, Gregory McIsaac, Stephen Gasteyer, and Margaret Kroma CONTENTS Introduction................................. .................... 115 Rural Communities................................................ 117 Production Skills........... ...
Uploads
Papers by Gregory McIsaac