Environmental Risks of Pesticides Versus Genetic Engineering for Agricultural Pest Control

Despite the application of 2.5 million tons ofpesticides worldwide, more than 40% of all potentialfood production is lost to insect, weed, and plantpathogen pests prior to harvest. After harvest, anadditional 20% of food is lost to another group ofpests. The use of pesticides for pest control resultsin an estimated 26 million human poisonings, with220,000 fatalities, annually worldwide. In the UnitedStates, the environmental and public health costs forthe recommended use of pesticides total approximately$9 billion/yr. Thus, there is a need for alternativenon-chemical pest controls, and genetic engineering(biotechnology) might help with this need. Diseaseand insect pest resistance to various pests has beenslowly bred into crops for the past 12,000 years;current techniques in biotechnology now offeropportunities to further and more rapidly improve thenon-chemical control of disease and insect pests ofcrops. However, relying on a single factor, like theBacillus thuringiensis toxin that has beeninserted into corn and a few other crops for insectcontrol, leads to various environmental problems,including insect resistance and, in some cases, athreat to beneficial biological control insects andendangered insect species. A major environmental andeconomic cost associated with genetic engineeringapplications in agriculture relates to the use ofherbicide resistant crops (HRC). In general, HRCtechnology results in increased herbicide use but noincrease in crop yields. The heavy use of herbicidesin HRC technology pollutes the environment and canlead to weed control costs for farmers that may be2-fold greater than standard weed control costs. Therefore, pest control with both pesticides andbiotechnology can be improved for effective, safe,economical pest control.     

Human–Carnivore Coexistence on Communal Land Bordering the Greater Kruger Area,South Africa

The aim of this study was to assess the potential for coexistence between rural people (living adjacent to a protected area) and predators (from the same area) ranging onto communal land. Ninety members of local communities bordering Manyeleti Game Reserve, which is contiguous with Kruger National Park, South Africa were interviewed. Respondents expressed diverging attitudes toward predators, which were more favorable among participants with higher education. Negative views were particularly due to fear of human and livestock losses, especially to lions, Panthera leo. Lions were thought to be the most abundant predator both within and outside the reserve. Lions were also the best known predator and were most often held responsible for killing livestock. Despite these livestock losses and a lack of conservation education, most participants voiced favorable opinions about large carnivore conservation, as predators were considered an integral part of the respondents’ natural heritage. Thanks to this cultural tolerance and also because of a largely accepted management policy regarding predator control, large carnivores and people can coexist in the vicinity of Kruger National Park.     

Effects of Bioengineered Streambank Stabilization on Bank Habitat and Macroinvertebrates in Urban Streams

Non-structural streambank stabilization, or bioengineering, is a common stream restoration practice used to slow streambank erosion, but its ecological effects have rarely been assessed. We surveyed bank habitat and sampled bank macroinvertebrates at four bioengineered sites, an unrestored site, and a comparatively less-impacted reference site in the urban Peachtree-Nancy Creek catchment in Atlanta, GA, USA. The amount of organic bank habitat (wood and roots) was much higher at the reference site and three of the bioengineered sites than at the unrestored site or the other bioengineered site, where a very different bioengineering technique was used (“joint planting”). At all sites, we saw a high abundance of pollution-tolerant taxa, especially chironomids and oligochaetes, and a low richness and diversity of the bank macroinvertebrate community. Total biomass, insect biomass, and non-chironomid insect biomass were highest at the reference site and two of the bioengineered sites (p < 0.05). Higher biomass and abundance were found on organic habitats (wood and roots) versus inorganic habitats (mud, sand, and rock) across all sites. Percent organic bank habitat at each site proved to be strongly positively correlated with many factors, including taxon richness, total biomass, and shredder biomass. These results suggest that bioengineered bank stabilization can have positive effects on bank habitat and macroinvertebrate communities in urban streams, but it cannot completely mitigate the impacts of urbanization.     

EFFECTS OF CROPPING SYSTEMS ON NO3-N LOSSES TO TILE DRAIN1

Abstract: Diverse cropping systems can have significant impacts on nutrient losses through tile drain systems and to surface water bodies (rivers and streams). Increased transport of nitrogen to water bodies can reduce dissolved oxygen and enrich the supply of nutrients, resulting in hypoxic zones. With the objective of reducing the transport of nutrients from agricultural watersheds, long term studies (1990 to 1998) were conducted in Iowa to investigate the impact of tillage, crop rotation, and N-management practices on NO₃-N leaching losses to tile drain water. Results of these studies indicated that continuous corn production systems required higher input of nitrogen fertilizers and resulted in significantly higher NO₃-N leaching losses compared to rotated corn in plots either fertilized with manure or urea ammonium nitrate. Also, rotated corn gave higher corn yields, 8 megagrams per hectare (Mg/ha) versus 6 Mg/ha, than continuous corn. The higher N application rates resulted in increased NO₃-N concentrations in tile water. A strip cropping system with alfalfa lowered NO₃-N concentrations in tile water to less than 10 mg/l. These studies indicated that better land use practices can reduce NO₃-N leaching losses to surface and ground water systems and will help in mitigating environmental concerns of the production agriculture.     

The potential importance of nut removal by rodents from Australian macadamia orchards

Extensive crop damage due to rodents, predominantly the black rat (Rattus rattus) is a major concern to both the Hawaiian and Australian macadamia industries. Within Australian systems, indicated the importance of adjacent non-crop habitats in the damage process with damage being directly related to the size and temporal stability of these habitats. It was also suggested that the current estimates of crop loss might be underestimates as R. rattus may remove nuts into adjacent non-crop habitats, however, the economic significance of nut removal was not investigated. This study has determined that the crop loss due to nut removal is equivalent to the crop loss due to in-crop feeding within the first row of the orchard, with nuts being removed and consumed under the cover provided by weedy adjacent habitats. Previous studies (White et al.,1997; Horskins et al.,1998; White et al.,1998) investigating the impact of rodents on crop damage have ignored the nut removal component of the damage process and hence rodents have a far greater impact on the Australian macadamia industry than previously suggested. This study also indicates that the cost-benefit of habitat manipulation as a rodent management strategy is much greater than that suggested by . Habitat manipulation is not only a cost-effective means of damage control but is also sustainable, having none of the potentially adverse public health and environmental effects of continual rodenticide use.     

Assessing vulnerability to invasion by nonnative plant species at multiple spatial scales

Basic information on where nonnative plant species have successfully invaded is lacking. We assessed the vulnerability of 22 vegetation types (25 sets of four plots in nine study areas) to nonnative plant invasions in the north–central United States. In general, habitats with high native species richness were more heavily invaded than species-poor habitats, low-elevation areas were more invaded than high-elevation areas, and riparian zones were more invaded than nearby upland sites. For the 100 1000-m² plots (across all vegetation types), 50% of the variation in nonnative species richness was explained by longitude, latitude, native plant species richness, soil total percentage nitrogen, and mean maximum July temperature (n = 100 plots; P < 0.001). At the vegetation-type scale (n = 25 sets of four 1000-m² plots/type), 64% of the variation in nonnative species richness was explained by native plant species richness, elevation, and October to June precipitation (P < 0.001). The foliar cover of nonnative species (log) was strongly positively correlated with the nonnative species richness at the plot scale (r = 0.77, P < 0.001) and vegetation-type scale (r = 0.83, P < 0.001). We concluded that, at the vegetation-type and regional scales in the north–central United States, (1) vegetation types rich in native species are often highly vulnerable to invasion by nonnative plant species; (2) where several nonnative species become established, nonnative species cover can substantially increase; (3) the attributes that maintain high native plant species richness (high light, water, nitrogen, and temperatures) also help maintain nonnative plant species richness; and (4) more care must be taken to preserve native species diversity in highly vulnerable habitats.     

Thinning Pine Plantations to Reestablish Oak Openings Species in Northwestern Ohio

Globally the area in forest plantations is rising by 2% annually, increasing the importance of plantations for production of human goods and services and for ecological functions such as carbon storage and biodiversity conservation. Specifically in the Great Lakes states and provinces of Midwestern North America, thousands of hectares of pine plantations were established in the early and mid-1900s to revegetate abandoned agricultural fields that had replaced mixed-species forests and oak–prairie ecosystems. Plantation establishment also was intended to bolster the timber base. Management priorities have shifted, with many resource managers currently seeking to manage existing plantations for promoting mixed-species ecosystems. The purpose of this study was to assess plant succession and the reestablishment of oak savanna and prairie species after thinning 14 plantations of Pinus resinosa and strobus in northwestern Ohio, USA. Thinning reduced tree basal area by an average of 75%. Plant communities were sampled on 0.05-ha plots one and 3 years after thinning and compared to 10 unthinned control plantations. By 3 years after thinning, thinned plots contained 2–3 times more species and 14 times more plant cover than control plots. The species composition of colonizing plants was most strongly correlated with residual pine basal area and soil variables related to drainage (e.g., sand concentration, available water capacity). Although plant composition was dominated by widespread colonizers such as Erechtites hieraciifolia, the coefficient of conservatism (indicative of species of more intact, undisturbed communities) significantly increased on thinned plots from year 1 to 3. This finding, coupled with the presence of four rare, state-listed Ohio species whose eight plot occurrences all were on thinned plots, suggests that plant composition is moving towards species typifying more high-quality savanna and prairie habitats.     

Biological Responses to Contrasting Hydrology in Backwaters of Upper Mississippi River Navigation Pool 25

Water level management in Mississippi River Pool 25 differentially influences off-channel habitats in the mid-pool and lower pool. Hydrologic models indicate lower pool off-channel habitats dry with greater frequency and duration compared to similar habitats at mid-pool. We examined the influence of this contrasting hydrology on substrate characteristics, organic matter, macroinvertebrate, and fish communities in off-channel habitats during 2001–2003. Benthic organic matter standing stocks were stable in mid-pool habitats but lower pool values were variable because of annual differences in moist-soil vegetation production. Generally, small-bodied and multivoltine invertebrate taxa had high community biomass and dominated lower pool habitats, whereas longer-lived and large-bodied taxa were more abundant and had higher community biomass in mid-pool habitats having longer hydroperiods. Fish communities were dominated by cyprinids in both habitats, and mid-pool habitats tended to be higher in overall species richness. Unique fish taxa were collected in each pool, with primarily rheophilic forms in mid-pool habitats and limnophilic forms in lower pool habitats. Results indicate that contrasting hydrology associated with a mid-pool control point directly and indirectly influences biological communities in off-channel habitats. Further, management regimes that promote hydrologic diversity in off-channel habitats may enhance biological diversity at larger spatial and temporal scales.     

Weed seed viability in composted beef cattle feedlot manure

Manure composting has gained increased acceptance by the beef cattle (Bos taurus) feedlot industry in southern Alberta, Canada. Unlike fresh manure, compost is often promoted as being "weed-free." Studies were conducted with five weed species in 1997 and thirteen in 1999 to examine the effect of feedlot manure composting on weed seed viability. Weed seeds were buried in open-air compost windrows and recovered at various times during the thermophilic phase of composting. Windrow temperature and water contents were also measured. Germinability was zero for all composted weed seeds at all sampling times in 1997. However, some seeds remained viable (positive tetrazolium test denoting respiration) on Day 70. In 1999, only one of the thirteen species retained germinability on Day 21 and only two species had respiring seeds on Day 42. Time-viability relationships during composting were defined by exponential decay models. Lethal temperatures to eliminate viability was species-dependent. In 1999, four weed species were killed in the initial 7 d of composting at a lethal temperature of 39 degrees C while temperatures of > 60 degrees C were required for two species. Regression analysis on weed seed viability versus windrow temperature resulted in significant R2 values, which showed that only 17 to 29% of the variation in viability was accounted for by temperature. The lack of definitive relationships between temperature and weed seed viability demonstrated that factors other than temperature may play a role in eliminating weed seeds during composting.     

The Impacts of Human Visitation on Mussel Bed Communities Along the California Coast: Are Regulatory Marine Reserves Effective in Protecting These Communities?

Rocky intertidal habitats frequently are used by humans for recreational, educational, and subsistence-harvesting purposes, with intertidal populations damaged by visitation activities such as extraction, trampling, and handling. California Marine Managed Areas, particularly regulatory marine reserves (MRs), were established to provide legal protection and enhancement of coastal resources and include prohibitions on harvesting intertidal populations. However, the effectiveness of MRs is unclear as enforcement of no-take laws is weak and no regulations protect intertidal species from other detrimental visitor impacts such as trampling. The goal of this study was two-fold: (1) to determine impacts from human visitation on California mussel populations (Mytilus californianus) and mussel bed community diversity; and (2) to investigate the effectiveness of regulatory MRs in reducing visitor impacts on these populations. Surveys of mussel populations and bed-associated diversity were compared: (1) at sites subjected to either high or low levels of human use, and (2) at sites either unprotected or with regulatory protection banning collecting. At sites subjected to higher levels of human visitation, mussel populations were significantly lower than low-use sites. Comparisons of mussel populations inside and outside of regulatory MRs revealed no consistent pattern suggesting that California no-take regulatory reserves may have limited effectiveness in protecting mussel communities. In areas where many people visit intertidal habitats for purposes other than collecting, many organisms will be affected by trampling, turning of rocks, and handling. In these cases, effective protection of rocky intertidal communities requires an approach that goes beyond the singular focus on collecting to reduce the full suite of impacts.     

NUTRIENT CONTENT OF CROP CANOPY THROUGHFALL PRECIPITATION IN EASTERN SOUTH DAKOTA1

ABSTRACT: Nutrient contents of canopy throughfall precipitation (TFP) from fertilized and unfertilized crops were analyzed and compared to determine the importance of fertilization on this source of nutrients in runoff. Continuous barley, corn, oats, rye, and wheat plots, that had been unfertilized since 1941 and divided and half fertilized since 1959, were studied. TFP soluble PO₄, total PO₄, and soluble K amounts were usually larger from fertilized plots in comparison to unfertilized ones but the differences usually were not significant. NH₄-N and NO₃-N may have been adsorbed from precipitation by corn canopies.     

The Contribution of Headwater Streams to Biodiversity in River Networks1

Abstract: The diversity of life in headwater streams (intermittent, first and second order) contributes to the biodiversity of a river system and its riparian network. Small streams differ widely in physical, chemical, and biotic attributes, thus providing habitats for a range of unique species. Headwater species include permanent residents as well as migrants that travel to headwaters at particular seasons or life stages. Movement by migrants links headwaters with downstream and terrestrial ecosystems, as do exports such as emerging and drifting insects. We review the diversity of taxa dependent on headwaters. Exemplifying this diversity are three unmapped headwaters that support over 290 taxa. Even intermittent streams may support rich and distinctive biological communities, in part because of the predictability of dry periods. The influence of headwaters on downstream systems emerges from their attributes that meet unique habitat requirements of residents and migrants by: offering a refuge from temperature and flow extremes, competitors, predators, and introduced species; serving as a source of colonists; providing spawning sites and rearing areas; being a rich source of food; and creating migration corridors throughout the landscape. Degradation and loss of headwaters and their connectivity to ecosystems downstream threaten the biological integrity of entire river networks.     

Practitioner Insights into Weed Management on California’s Rangelands and Natural Areas

Working rangelands and natural areas span diverse ecosystems and face both ecological and economic threats from weed invasion. Restoration practitioners and land managers hold a voluminous cache of place-based weed management experience and knowledge that has largely been untapped by the research community. We surveyed 260 California rangeland managers and restoration practitioners to investigate invasive and weedy species of concern, land management goals, perceived effectiveness of existing practices (i.e., prescribed fire, grazing, herbicide use, and seeding), and barriers to practice implementation. Respondents identified 196 problematic plants, with yellow starthistle (Centaurea solstitialis L.) and medusahead (Elymus caput-medusae L.) most commonly listed. Reported adoption and effectiveness of weed management practices varied regionally, but the most highly rated practice in general was herbicide use; however, respondents identified considerable challenges including nontarget effects, cost, and public perception. Livestock forage production was the most commonly reported management goals (64% of respondents), and 25% of respondents were interested in additional information on using grazing to manage invasive and weedy species; however, 19% of respondents who had used grazing for weed management did not perceive it to be an effective tool. Across management practices, we also found common barriers to implementation, including operational barriers (e.g., permitting, water availability), potential adverse impacts, actual effectiveness, and public perception. Land manager and practitioner identified commonalities of primary weeds, management goals, perceived practice effectiveness, and implementation barriers across diverse bioregions highlight major needs that could be immediately addressed through management–science partnerships across the state’s expansive rangelands and natural areas.     

Conservation of biodiversity within Canadian agricultural landscapes: Integrating habitat for wildlife

Industrialized agriculture currently substitutes many of the ecological functions of soil micro-organisms, macroinvertebrates, wild plants, and vertebrate animals with high cost inputs of pesticides and fertilizers. Enhanced biological diversity potentially offers agricultural producers a means of reducing the cost of their production. Conservation of biodiversity in agricultural landscapes may be greatly enhanced by the adoption of certain crop management practices, such as reduced pesticide usage or measures to prevent soil erosion. Still, the vast monocultures comprising the crop area in many Canadian agricultural landscapes are often of limited conservation value, thus the inclusion of appropriate wildlife habitat in and around arable lands is a fundamental prerequisite for the integration of wild species within agricultural landscapes. This review of current literature considers the potential for non-crop areas within agricultural landscapes to be reservoirs of agronomically beneficial organisms including plants, invertebrates, and vertebrate species. Non-crop habitats adjacent to crop land have been identified as significant for the maintenance of plant species diversity, for the conservation of beneficial pollinating and predatory insects, and as essential habitat for birds. A key component for enhancement of biodiversity is the reintroduction of landscape heterogeneity by (1) protection and enhancement of key non-crop areas, (2) smaller fields and farms, and (3) a greater mixture of crops, through rotation, intercropping and regional diversification. The benefits of increased biodiversity within arable lands are reviewed for various species groups. In the Canadian context, any serious attempt to derive significant agronomic benefit from increased biodiversity will require considerable changes in the agricultural programs and policies which shape mainstream industrialized agriculture. The problems of crop depredation by vertebrate species, weed and insect competition, which still represent significant impediments to the creation and proper management of wildlife habitat, are also discussed.     

Small mammal abundance and habitat relationships on deciduous forested sites with different susceptibility to gypsy moth defoliation

Small mammals are important predators of gypsy moths (Lymantria dispar L.), which are major defoliators of deciduous forests in the northeastern United States. Abundance and habitat relationships of small mammals were studied during summers 1984 and 1985 on forested sites at Moshannon and Rothrock state forests in two physiographic regions of Pennsylvania (Allegheny High Plateaus Province and Valley and Ridge Province, respectively) that varied in potential susceptibility to defoliation. The white-footed mouse (Peromyscus leucopus), which is a major vertebrate predator of gypsy moths, was the most common small mammal on all sites. Of the four common species, northern short-tailed shrews (Blarina brevicauda), southern red-backed voles (Clethrionomys gapperi), and white-footed mice were more abundant at Moshannon compared to Rothrock State Forest, but masked shrews (Sorex cinereus) were more abundant at Rothrock. Elevation was a major factor affecting abundance and distribution of small mammals. Because of the greater abundance of small mammals and more suitable physiographic features at Moshannon compared to Rothrock State Forest, small mammals may be more effective as predators on gypsy moths in the Allegheny High Plateaus than the Valley and Ridge Province of Pennsylvania.     

Nitrous oxide emissions from corn-soybean systems in the midwest

Soil N2O emissions from three corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] systems in central Iowa were measured from the spring of 2003 through February 2005. The three managements systems evaluated were full-width tillage (fall chisel plow, spring disk), no-till, and no-till with a rye (Secale cereale L. 'Rymin') winter cover crop. Four replicate plots of each treatment were established within each crop of the rotation and both crops were present in each of the two growing seasons. Nitrous oxide fluxes were measured weekly during the periods of April through October, biweekly during March and November, and monthly in December, January, and February. Two polyvinyl chloride rings (30-cm diameter) were installed in each plot (in and between plant rows) and were used to support soil chambers during the gas flux measurements. Flux measurements were performed by placing vented chambers on the rings and collecting gas samples 0, 15, 30, and 45 min following chamber deployment. Nitrous oxide fluxes were computed from the change in N2O concentration with time, after accounting for diffusional constraints. We observed no significant tillage or cover crop effects on N2O flux in either year. In 2003 mean N2O fluxes were 2.7, 2.2, and 2.3 kg N2O-N ha(-1) yr(-1) from the soybean plots under chisel plow, no-till, and no-till + cover crop, respectively. Emissions from the chisel plow, no-till, and no-till + cover crop plots planted to corn averaged 10.2, 7.9, and 7.6 kg N2O-N ha(-1) yr(-1), respectively. In 2004 fluxes from both crops were higher than in 2003, but fluxes did not differ among the management systems. Fluxes from the corn plots were significantly higher than from the soybean plots in both years. Comparison of our results with estimates calculated using the Intergovernmental Panel on Climate Change default emission factor of 0.0125 indicate that the estimated fluxes underestimate measured emissions by a factor of 3 at our sites.     

Ethanol fuels: Energy security,economics, and the environment

Problems of fuel ethanol production have been the subject of numerous reports, including this analysis. The conclusions are that ethanol: does not improve U.S. energy security; is uneconomical; is not a renewable energy source; and increases environmental degradation. Ethanol production is wasteful of energy resources and does not increase energy security. Considerably more energy, much of it high- grade fossil fuels, is required to produce ethanol than is available in the energy output. About 72% more energy is used to produce a gallon of ethanol than the energy in a gallon of ethanol. Ethanol production from corn is not renewable energy. Its production uses more non- renewable fossil energy resources in growing the corn and in the fermentation/distillation process than is produced as ethanol energy. Ethanol produced from corn and other food crops is also an unreliable and therefore a non-secure source of energy, because of the likelihood of uncontrollable climatic fluctuations, particularly droughts which reduce crop yields. The expected priority for corn and other food crops would be for food and feed. Increasing ethanol production would increase degradation of agricultural land and water and pollute the environment. In U.S. corn production, soil erodes some 18- times faster than soil is reformed, and, where irrigated, corn production mines water faster than recharge of aquifers. Increasing the cost of food and diverting human food resources to the costly and inefficient production of ethanol fuel raise major ethical questions. These occur at a time when more food is needed to meet the basic needs of a rapidly growing world population.     

Paleozoological Data Suggest Euroamerican Settlement Did Not Displace Ursids and North American Elk from Lowlands to Highlands

The hypothesis that Euroamerican settlement displaced some populations of large mammal taxa from lowland plains habitats to previously unoccupied highland mountain habitats was commonly believed in the late nineteenth and early twentieth centuries. By the middle twentieth century biologists had come to favor the hypothesis that Euroamerican colonization resulted in the extirpation of populations of large mammal in lowland habitats and those taxa survived in pre-existing relict populations in the highlands. Why modern biologists changed their minds is unclear. There is no historical evidence that unequivocally favors one hypothesis over the other. The low-elevation Columbia Basin of eastern Washington state in the northwestern United States is surrounded by forested mountains. The majority of historical records (1850 AD or younger) of black bear (Ursus americanus), brown bear (Ursus arctos), and North American elk (Cervus elaphus) occur in mountainous, coniferous forest habitats. Paleozoological records of these taxa ≤ 10,000 year old and >160 year old in both highland and lowland habitats suggest the displacement hypothesis does not apply to ursids and elk in this area. These taxa seem to have been more or less ubiquitous in the area prior to Euroamerican colonization (ca. 1850 AD), and were extirpated from lowland habitats after colonization. Recent colonization of lowland shrub-steppe habitats by elk in particular, although historically unprecedented, must be categorized as recolonization rather than an invasion. Whether a species is classified as indigenous or nonindigenous may influence management activities focused on that species. The paleozoological record indicates ursids and elk are indigenous to the highland forest habitats of eastern Washington.     

Water Quality Assessment of Large‐scale Bioenergy Cropping Scenarios for the Upper Mississippi and Ohio‐Tennessee River Basins

The Upper Mississippi River Basin and Ohio‐Tennessee River Basin comprise the majority of the United States Corn Belt region, resulting in degraded Mississippi River and Gulf of Mexico water quality. To address the water quality implications of increased biofuel production, biofuel scenarios were tested with a Soil and Water Assessment Tool (SWAT) model revision featuring improved biofuel crop representation. Scenarios included corn stover removal and the inclusion of two perennial bioenergy crops, switchgrass and Miscanthus, grown on marginal lands (slopes >2% and erosion rates >2 t/ha) and nonmarginal lands. The SWAT model estimates show water quality is not very sensitive to stover removal. The perennial bioenergy crops reduce simulated sediment, nitrogen (N), and phosphorus (P) yields by up to 60%. Simulated sediment and P reductions in marginal lands were generally twice that occurring in the nonmarginal lands. The highest unit area reductions of N occurred in the less sloping tile‐drained lands. Productivity showed corn grain yield was independent from stover removal, while yields of the two perennial bioenergy crops were similar in the marginal and nonmarginal lands. The results suggest planning for biofuel production in the Corn Belt could include the removal of stover in productive corn areas, and the planting of perennial bioenergy crops in marginal land and in low‐sloped tile‐drained areas characterized by high N pollution. Editor's note : This paper is part of the featured series on SWAT Applications for Emerging Hydrologic and Water Quality Challenges. See the February 2017 issue for the introduction and background to the series.     

Enzyme-based resource allocated decomposition and landscape heterogeneity in the Florida Everglades

Enzyme catalyzed reactions are generally considered the rate-limiting step in organic matter degradation and may be significantly influenced by the structure and composition of plant communities. Changes in these rates have the potential to effect long-term peat accumulation and influence the topography of a wetland ecosystem. To determine habitat influences on enzyme activities, we examined slough and sawgrass plots within enriched and reference phosphorus (P) sites in the Everglades. Assays were performed for the enzymes involved in carbon (C), nitrogen (N), and P cycling and lignin depolymerization. Enzyme activities were normalized and analyzed in terms of a resource allocation strategy. Plant composition was found to significantly alter the allocation of enzymatic resources due to varying substrate complexities. Potential decomposition in the slough was less influenced by lignin than in the sawgrass habitats. Additionally, an index relating hydrolytic and oxidative enzymes was significantly greater in the slough habitats, whereas C/N ratios were significantly lower. These indices suggest more favorable decomposition conditions and thus slower peat accretion within the slough communities, which may contribute to the development of elevation differences within the sawgrass ridge and slough topography of the Everglades.