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USGS1998

The environmental occurrence of herbicides: The importance of degradates in ground water

Numerous studies are being conducted to investigate the occurrence, fate, and effects on human health and the environment from the extensive worldwide use of herbicides to control weeds. Few studies, however, are considering the degradates of these herbicides in their investigations. Our study of herbicides in aquifers across Iowa found herbicide degradates to be prevalent in ground water, being detected in about 75% of the wells sampled. With the exception of atrazine, the frequencies of detection in ground water for a given herbicide increased multifold when its degradates were considered. Furthermore, a majority of the measured concentration for a given herbicide was in the form of its degradates—even for a relatively persistent compound such as atrazine. For this study, degradates comprised from 60 to over 99% of a herbicide's measured concentration. Because herbicide degradates can have similar acute and chronic toxicity as their parent compounds, these compounds have environmental significance as well as providing a more complete understanding of the fate and transport of a given herbicide. Thus, it is essential that degradates are included in any type of herbicide investigation.

Iowa↗

USGS2020

Associational effects of plant ontogeny on damage by a specialist insect herbivore

Intraspecific variation in plant traits is a major cause of variation in herbivore feeding and performance. Plant defensive traits change as a plant grows, such that ontogeny may account for a substantial portion of intraspecific trait variation. We tested how the ontogenic stage of an individual plant, of an individual in the context of its neighboring plants, and of a patch of plants with mixed or uniform stages affect plant–herbivore interactions. To do this, we conducted an experimental study of the interactions between Lepidium draba , a perennial brassicaceous weed, and Plutella xylostella , a common herbivore of L. draba . We found that L. draba foliar glucosinolates, secondary metabolites often implicated in defense, decreased in concentration with plant age. In single-stage patches, herbivores performed similarly on L. draba plants of different ages. Furthermore, we found no difference in the cumulative performance of herbivores reared on mixed- or even-staged patches of L. draba . However, in mixed-stage patches, the damage experienced by a focal plant depended on the stage of neighboring plants, suggesting a preference hierarchy of the herbivore among plant stages. In our study, the amount of herbivory depended on the ontogenic neighborhood in which the plant grew. However, from the herbivore’s perspective, variation in plant ontogenic stage was unimportant to its success in terms of feeding rate and final weight.

Oecologia↗

USGS2008

A plastid gene phylogeny of the non-photosynthetic parasitic Orobanche (Orobanchaceae) and related genera

The phylogenetic relationships of the non-photosynthetic Orobanche sensu lato (Orobanchaceae), which includes some of the economically most important parasitic weeds, remain insufficiently understood and controversial. This concerns both the phylogenetic relationships within the genus, in particular its monophyly or lack thereof, and the relationships to other holoparasitic genera such as Cistanche or Conopholis. Here we present the first comprehensive phylogenetic study of this group based on a region from the plastid genome (rps2 gene). Although substitution rates appear to be elevated compared to the photosynthetic members of Orobanchaceae, relationships among the major lineages Cistanche, Conopholis plus Epifagus, Boschniakia rossica (Cham. & Schltdl.) B. Fedtsch., B. himalaica Hook. f. & Thomson, B. hookeri Walp. plus B. strobilacea A. Gray, and Orobanche s. l. remain unresolved. Resolution within Orobanche, however, is much better. In agreement with morphological, cytological and other molecular phylogenetic evidence, five lineages, corresponding to the four traditionally recognised sections (Gymnocaulis, Myzorrhiza, Orobanche, Trionychon) and O. latisquama Reut. ex Boiss. (of sect. Orobanche), can be distinguished. A combined analysis of plastid rps2 and nuclear ITS sequences of the holoparasitic genera results in more resolved and better supported trees, although the relationships among Orobanche s. l., Cistanche, and the clade including the remaining genera is unresolved. Therefore, rps2 is a marker from the plastid genome that is well-suited to be used in combination with other already established nuclear markers for resolving generic relationships of Orobanche and related genera. ?? 2008 The Botanical Society of Japan and Springer.

Journal of Plant Research↗

USGS2020

Combined effects of biological control of an invasive shrub and fluvial processes on riparian vegetation dynamics

Plant community responses to biocontrol of invasive plants are understudied, despite the strong influence of the composition of replacement vegetation on ecosystem functions and services. We studied the vegetation response to a folivore beetle ( Diorhabda genus, Coleoptera) that has been introduced along southwestern US river valleys to control the invasion of non-native shrubs in the genus Tamarix (Tamaricaceae). We collected detailed plant compositional and environmental data during four different surveys over 7 years (2010–2017), including two surveys prior to when substantial beetle-induced dieback occurred in summer 2012, along the lower Virgin River, Nevada. The study river was of special interest because it is one of only a few largely unregulated rivers in the region, and a large flood of 40-year return period occurred between the first and second surveys, allowing us to study the combined effects of fluvial processes, which typically drive riparian plant community assembly, and biocontrol. Vegetation trajectories differed as a function of the dominant geomorphological process. Tamarix cover declined an average of 75% and was replaced by the native shrub Pluchea sericea as the new dominant species in the floodplain, especially where sediment deposition predominated. Following deposition, and especially erosion, opportunistic native herbs, Tamarix seedlings, and noxious weeds colonized the understory layer but did not increase in cover over time. Stands of the native shrub Salix exigua , a desirable replacement species following Tamarix control, only increased slightly and remained subordinate in the floodplain. Overall, our results showed that, by successfully controlling the target non-native plant, a biocontrol agent can substantially modify the replacement plant communities in a riparian system, but that fluvial processes also strongly influence the resulting communities.

Arizona, Nevada, Utah↗

USGS2016

Changing agricultural practices: Potential consequences to aquatic organisms

Agricultural practices pose threats to biotic diversity in freshwater systems with increasing use of glyphosate-based herbicides for weed control and animal waste for soil amendment becoming common in many regions. Over the past two decades, these particular agricultural trends have corresponded with marked declines in populations of fish and mussel species in the Upper Conasauga River watershed in Georgia/Tennessee, USA. To investigate the potential role of agriculture in the population declines, surface waters and sediments throughout the basin were tested for toxicity and analyzed for glyphosate, metals, nutrients, and steroid hormones. Assessments of chronic toxicity with Ceriodaphnia dubia and Hyalella azteca indicated that few water or sediment samples were harmful and metal concentrations were generally below impairment levels. Glyphosate was not observed in surface waters, although its primary degradation product, aminomethyl phosphonic acid (AMPA), was detected in 77% of the samples (mean = 509 μg/L, n = 99) and one or both compounds were measured in most sediment samples. Waterborne AMPA concentrations supported an inference that surfactants associated with glyphosate may be present at levels sufficient to affect early life stages of mussels. Nutrient enrichment of surface waters was widespread with nitrate (mean = 0.7 mg NO 3 -N/L, n = 179) and phosphorus (mean = 275 μg/L, n = 179) exceeding levels associated with eutrophication. Hormone concentrations in sediments were often above those shown to cause endocrine disruption in fish and appear to reflect the widespread application of poultry litter and manure. Observed species declines may be at least partially due to hormones, although excess nutrients and herbicide surfactants may also be implicated.

Environmental Monitoring and Assessment↗

USGS2016

The origin of shallow lakes in the Khorezm Province, Uzbekistan, and the history of pesticide use around these lakes

The economy of the Khorezm Province in Uzbekistan relies on the large-scale agricultural production of cotton. To sustain their staple crop, water from the Amu Darya is diverted for irrigation through canal systems constructed during the early to mid-twentieth century when this region was part of the Soviet Union. These diversions severely reduce river flow to the Aral Sea. The Province has >400 small shallow (<3 m deep) lakes that may have originated because of this intensive irrigation. Sediment cores were collected from 12 lakes to elucidate their origin because this knowledge is critical to understanding water use in Khorezm. Core chronological data indicate that the majority of the lakes investigated are less than 150 years old, which supports a recent origin of the lakes. The thickness of lacustrine sediments in the cores analyzed ranged from 20 to 60 cm in all but two of the lakes, indicating a relatively slow sedimentation rate and a relatively short-term history for the lakes. Hydrologic changes in the lakes are evident from loss on ignition and pollen analyses of a subset of the lake cores. The data indicate that the lakes have transitioned from a dry, saline, arid landscape during pre-lake conditions (low organic carbon content) and low pollen concentrations (in the basal sediments) to the current freshwater lakes (high organic content), with abundant freshwater pollen taxa over the last 50–70 years. Sediments at the base of the cores contain pollen taxa dominated by Chenopodiaceae and Tamarix , indicating that the vegetation growing nearby was tolerant to arid saline conditions. The near surface sediments of the cores are dominated by Typha/Sparganium , which indicate freshwater conditions. Increases in pollen of weeds and crop plants indicate an intensification of agricultural activities since the 1950s in the watersheds of the lakes analyzed. Pesticide profiles of DDT (dichlorodiphenyltrichloroethane) and its degradates and γ-HCH (gamma-hexachlorocyclohexane), which were used during the Soviet era, show peak concentrations in the top 10 cm of some of the cores, where estimated ages of the sediments (1950–1990) are associated with peak pesticide use during the Soviet era. These data indicate that the lakes are relatively young (mostly <150 years old) and that without irrigation and canal inputs from the Amu Darya, the lakes would not exist as freshwater lakes.

Khorezm Province↗

USGS2022

Herbivory changes biomass allocation but does not induce resistance among clones of an invasive plant

Inducible responses to herbivores can be either localized or spread systemically throughout a plant. The ways in which clonal plants integrate their response to herbivores among clonal ramets is not well understood. Yet, this is important to understand the impacts that herbivores may have on clonal plants. We conducted a factorial split-plot greenhouse experiment to determine whether resistance is induced among ramets and how biomass allocation changes among ramets following herbivore damage to one of them. We manipulated the presence of two herbivores, Pieris rapae and Trichoplusia ni, and the root connection of ramets of the clonal invasive weed, Lepidium draba . We found local inducible resistance on the ramet where an herbivore fed, but not in neighboring ramets. Biomass allocation shifted in response to herbivores. Feeding by the generalist caterpillar T. ni resulted in a greater belowground biomass relative to shoot biomass in the local plant, but only when the clonal connection was intact. In contrast, herbivores had little impact on the root mass fraction of neighboring ramets. Herbivory to the local ramet increased the regrowth of neighboring ramets that lacked clonal connection, a trend that was driven by the specialist herbivore P. rapae . Herbivores did not induce systemic resistance among ramets of L. draba , but herbivores, especially the specialist, did alter how neighboring ramets regrow after grazing or mowing. Our observations suggest that individual ramets have fairly autonomous responses to herbivores, and that coordination among ramets, when present, may happen via signals that do not depend on root connections.

Arthropod-Plant Interactions↗

USGS2010

Climate warming-induced intensification of the hydrologic cycle: A review of the published record and assessment of the potential impacts on agriculture

Climate warming is expected to intensify and accelerate the global hydrologic cycle resulting in increases in evaporation, evapotranspiration (ET), atmospheric water-vapor content, and precipitation. The strength of the hydrologic response, or sensitivity of the response for a given degree of warming, is a critical outstanding question in climatology and hydrology. In this review chapter, I examine the published record of trends in various components of the hydrologic cycle and associated variables to assess observed hydrologic responses to warming during the period of observational records. Global and regional trends in evaporation, ET, and atmospheric water-vapor content and several large river basin water-balance studies support an ongoing intensification of the hydrologic cycle. Global trends in precipitation, runoff, and soil moisture are more uncertain than the trends in the variables noted above, in part because of high spatial and temporal variability. Trends in associated variables, such as systematic changes in ocean salinity, the length of the growing season, and the rate of precipitation recycling are generally consistent with intensification of the hydrologic cycle. The evidence for an increase in the frequency, intensity, or duration of extreme-weather events like hurricanes is mixed and remains uncertain. The largest potential impacts to agricultural systems depend greatly on the responses of hydrologic variables that are the most uncertain; for example, intensity and duration of heavy rainfall events; frequency, intensity, and duration of major storms and droughts; and rates of erosion. Impacts on agriculture will depend greatly on how insects, diseases, weeds, nutrient cycling, effectiveness of agrichemicals, and heat stress are affected by an intensification of the hydrologic cycle.

Advances in Agronomy↗

USGS2025

Multi-sensor proximal remote sensing for cover crop biomass estimation at high and moderate spatial resolutions

Cover crops play a critical role in providing agroecological services such as improving soil health, reducing erosion and nitrogen loss, and suppressing weeds, which are closely tied to their performance such as accumulated biomass. This study evaluated the Active Canopy Sensor (ACS) -214, an active proximal sensing device equipped with its own light-emitting red and near-infrared spectral reflectance sensors, a time-of-flight laser, and an ultrasonic sensor, for estimating winter cover crop biomass across 13 U.S. states from 2020 to 2024. We assessed 11 species from three functional groups – grasses ( n = 797), legumes ( n = 264), and brassicas ( n = 181) – using Random Forest (RF) models and four cross-validation strategies. The ACS-214 showed moderate to strong prediction accuracy for grasses ( R 2 = 0.51 – 0.64) and legumes ( R 2 = 0.44 – 0.76), though performance declined in leave-one-region-out analyses ( R 2 = 0.06 – 0.46), indicating limited spatial generalizability. Brassica models had low prediction accuracy for all models ( R 2 < 0.30), likely due to flowering and patchy growth. Biomass prediction breakpoints were observed at ∼3000 kg ha −1 for legumes and ∼4000 kg ha −1 for grasses. We also evaluated the effectiveness of using ACS-214 data to train Sentinel-2 satellite imagery for estimating grass cover crop biomass using withheld, out of bag data from 2023 to 2024. Sentinel-2 RF models trained with ACS-214 data showed good agreement with field-sampled ( R 2 = 0.58 – 0.61) and ACS-214-estimated biomass ( R 2 = 0.70). While Sentinel-2 offers scalability, the ACS-214 enables finer-resolution biomass mapping and better accounts for within-field variability, making it an effective tool for localized management and monitoring. These findings support the integration of proximal and satellite sensing approaches to enhance cover crop biomass estimation and agroecological assessment.

Alabama, Florida, Indiana, Iowa, Kansas, Maryland,↗

USGS2021

Chronic exposure to glyphosate in Florida manatee

Florida manatees depend on freshwater environments as a source of drinking water and as warm-water refuges. These freshwater environments are in direct contact with human activities were glyphosate-based herbicides are being used. Glyphosate is the most used herbicide worldwide and it is intensively used in Florida as a sugarcane ripener and to control invasive aquatic plants. The objective of the present study was to determine the concentration of glyphosate and its breakdown product, aminomethylphosphonic acid (AMPA), in Florida manatee plasma and assess their exposure to manatees seeking a warm-water refuge in Crystal River (west central Florida), and in South Florida. We analyzed glyphosate’s and AMPA’s concentrations in Florida manatee plasma (n = 105) collected during 2009–2019 using HPLC-MS/MS. We sampled eight Florida water bodies between 2019 and 2020, three times a year: before, during and after the sugarcane harvest using grab samples and molecular imprinted passive Polar Organic Chemical Integrative Samplers (MIP-POCIS). Glyphosate was present in 55.8% of the sampled Florida manatees’ plasma. The concentration of glyphosate has significantly increased in Florida manatee samples from 2009 until 2019. Glyphosate and AMPA were ubiquitous in water bodies. The concentration of glyphosate and AMPA was higher in South Florida than in Crystal River, particularly before and during the sugarcane harvest when Florida manatees depend on warm water refuges. Based on our results, Florida manatees were chronically exposed to glyphosate and AMPA, during and beyond the glyphosate applications to sugarcane, possibly associated with multiple uses of glyphosate-based herbicides for other crops or to control aquatic weeds. This chronic exposure in Florida water bodies may have consequences for Florida manatees’ immune and renal systems which may further be compounded by other environmental exposures such as red tide or cold stress.

Florida↗

USGS2024

Season of grazing interacts with soil texture, selecting for associations of biocrust morphogroups

Livestock grazing, a widespread land use in semi-arid systems, is often placed in opposition to the perpetuation of biological soil crusts (“biocrusts”: lichens, mosses, and algal crusts including cyanobacteria) that live on the soil surface and provide ecosystem functions. The composition of biocrusts and vascular plants varies with climate, soils, and disturbance. In general, ruderal mosses and light algal crusts make up greater proportions of biocrusts in the presence of disturbance, although morphogroups of biocrusts respond differently to various disturbances. It is unknown if there are scenarios under which grazing can occur and ruderal components of biocrust could be maintained. We examine the hypothesis that soil surface texture-moisture interactions influence the ability of biocrusts to withstand trampling, reasoning that finer-textured soils are firmer (therefore serving as a better substrate for biocrusts) when dry and that coarser-textured are firmer when wet. We test these relationships within Birds of Prey, National Conservation Area (Boise, Idaho, USA). Results demonstrate two associations of biocrusts, dependent on season of grazing: one dominated by light algal crusts and lichens that frequently occurs with wet season grazing, and a second dominated by tall mosses and cup lichens that frequently occurs with dry season grazing. High cover of the invasive annual grass, Bromus tectorum (L.) was observed on sites with coarse-textured soils, and high sand content, that are grazed at relatively high intensities, creating unstable surfaces, and likely putting biocrusts at greater susceptibility to trampling. Results suggest that livestock management that accounts for soil texture and moisture could be used to maintain cover of ruderal biocrusts on fine-textured soils, that are grazed in the dry season, at low intensity. We discuss our findings in the context of managing for species of interest. Our findings are timely as varying the season of grazing is increasingly discussed as a means of favoring desirable native perennial grasses. Although ruderal morphogroups of biocrusts are not interpreted as having equivalent ecosystem functions compared to intact biocrusts, their contributions to soil stability, fertility, hydrology, and weed abatement could increase if they were more intentionally targeted by management.

Geoderma↗

USGS2020

Post-fire management-scale trials of bacterial soil amendment MB906 show inconsistent control of invasive annual grasses

Rangeland managers need tools to control invasive annual grasses, particularly following wildfire. We assessed responses of native and invasive/exotic grasses to the MB906 soil amendment containing live cultures of a purportedly weed-suppressive strain of the bacterium Pseudomonas fluorescens (“WSB”). MB906 was applied alone and in combination with the pre-emergent herbicide imazapic on >3000 ha across three sagebrush-steppe landscapes burned several months prior. Replicate plots of each treatment type were established and plant cover was measured in the following three years. Cover of invasive-annual grasses (“IAG”) was not responsive to MB906 when all IAG species were considered (“IAG-All”). However, MB906 led to a 54% reduction in the IAG's that were previously reported to be controlled by WSB (“IAG-Target”) in the second year following application (IAG-Target = cheatgrass, Bromus tectorum and medusahead, Taeniatherum caput-medusae; IAG-All also includes Vulpia myuros and Bromus arvensis ). MB906 reduced the effectiveness of co-applied imazapic: Imazapic alone reduced IAG-All by 83% and 68% in years 1 and 2, respectively, while imazapic+MB906 reduced IAG-All by 48% and 38% in years 1 and 2, respectively, across all landscapes, and a similar response pattern was observed for IAG-Target. Perennial grass cover was unaffected by the treatments except where it increased 4-fold in response to imazapic applied at a high rate (0.140 kg a.i. ha −1 ) in one of the landscapes. Tank mixing MB906 and herbicide may have lessened the biological activity of the herbicide by altering the pH or mineral content of the spray solution or by direct metabolism of the herbicide by the bacteria. These results do not provide strong support for MB906 as a tool for annual grass control, though they suggest further investigation may be warranted.

Rangeland Ecology and Management↗

USGS2020

Energy development and production in the Great Plains: Implications and restoration opportunities

Energy is an integral part of society. The major US energy sources of fossil fuels (coal, oil, natural gas); biofuels (ethanol); and wind are concentrated in grassland ecosystems of the Great Plains. As energy demand continues to increase, mounting pressures will be placed on North American grassland systems. In this review, we present the ecological effects of energy development and production on grassland systems. We then identify opportunities to mitigate these effects during the planning, construction, and production phases by using informed methodology and improved technology. Primary effects during energy development include small- and large-scale soil disturbance and vegetation removal as small patches of grasslands are used to host oil or gas wells, wind turbine pads, associated roadways, and pipelines or through the conversion of large grassland areas to biofuel croplands. Direct habitat loss or habitat fragmentation can affect wildlife directly through increased mortality or indirectly through reduction in habitat quantity and quality. During energy production, air and water quality can be affected through regular emissions or unplanned spills. Energy development can also affect the economy and health of local communities. During planning, energy development and production effects can be reduced by carefully considering effects on grasslands during siting and even by selecting different energy source types. During construction, effects on soil and plant systems can be minimized by eliminating weed populations before disturbance, salvaging and stockpiling topsoil for future revegetation, and harvesting native local seed for postsite restoration. During energy production operations, noise and road traffic reduction plans and atmospheric monitoring will enable more informed mitigation measures. Continued research on energy development effects and mitigation measures is necessary to establish best management practices beneficial to grassland health while providing needed energy for the United States.

Colorado, Illinois, Indiana, Iowa, Kansas, Minneso↗

USGS2025

Costs of land treatments on public lands in the western United States

Public land managers often conduct rehabilitation and restoration actions to achieve desired conditions or specific natural resource objectives. These “land treatments” include a variety of techniques, such as biomass removal or manipulation, seeding, and herbicide application. Limited information exists on the costs of conducting many common types of land treatments, but such information can be paired with treatment effectiveness data to prioritize application of limited resources where they may have the greatest benefit and improve efficiency. Here, we investigated cost information recorded in the Land Treatment Digital Library, a catalog of legacy land treatment information on public lands managed by the U.S. Department of the Interior's Bureau of Land Management. Based on 1,701 treatment records across eleven western U.S. states, we developed empirical per-acre cost estimates for representative land treatments in eight categories: three seeding categories (aerial seeding, drill seeding, and seedling planting), prescribed burning, soil disturbance, soil stabilization, vegetation disturbance, and weed control. We evaluated spatio-temporal factors that may be associated with variation in treatment costs and found strong evidence for nonlinear decreases in per-acre costs as treatment areas increased and that per-acre treatment costs have increased in real terms in recent decades. We also found evidence that per-acre costs for drill seeding, prescribed burns, and soil stabilization increased with the average slope of the terrain of a treated area and that per-acre costs for prescribed burns, seedling planting, and soil stabilization were influenced by distance to urban areas or major roads. These results can inform planning, prioritization, and assessment of common land treatments on public lands in the western United States, in particular supporting greater consideration of costs and cost effectiveness.

Rangeland Ecology & Management↗

USGS2006

Urban contributions of glyphosate and its degradate AMPA to streams in the United States

Glyphosate is the most widely used herbicide in the world, being routinely applied to control weeds in both agricultural and urban settings. Microbial degradation of glyphosate produces aminomethyl phosphonic acid (AMPA). The high polarity and water-solubility of glyphosate and AMPA has, until recently, made their analysis in water samples problematic. Thus, compared to other herbicides (e.g. atrazine) there are relatively few studies on the environmental occurrence of glyphosate and AMPA. In 2002, treated effluent samples were collected from 10 wastewater treatment plants (WWTPs) to study the occurrence of glyphosate and AMPA. Stream samples were collected upstream and downstream of the 10 WWTPs. Two reference streams were also sampled. The results document the apparent contribution of WWTP effluent to stream concentrations of glyphosate and AMPA, with roughly a two-fold increase in their frequencies of detection between stream samples collected upstream and those collected downstream of the WWTPs. Thus, urban use of glyphosate contributes to glyphosate and AMPA concentrations in streams in the United States. Overall, AMPA was detected much more frequently (67.5%) compared to glyphosate (17.5%).

Science of the Total Environment↗

USGS2020

Influence of land use and region on glyphosate and aminomethylphosphonic acid in streams in the USA

Glyphosate is the most widely used herbicide in the United States for agricultural and non-agricultural weed control. Many studies demonstrate possible effects of glyphosate and its degradate AMPA on human and ecological health. Although glyphosate is thought to have limited mobility in soil, it is found year-round in many rivers and streams throughout the world in both agricultural and developed environments. It is vitally important to continue to increase the knowledge base of glyphosate use, distribution, transport, and impacts on human health and the environment. Here we show that glyphosate and AMPA are found in nearly all of 70 streams throughout the United States at concentrations far below human health or ecological benchmarks, with less occurrence in the Northeast and that undeveloped land, classified as such by land use near the sampling station, has lower concentrations compared to other types of land. Results also show that sites with large watersheds tend to have more AMPA than glyphosate and the opposite is true for small watersheds. Travel times and opportunity for glyphosate to degrade to AMPA and for reservoirs of AMPA to grow are greater in large watersheds. Factors that promoted quick movement of glyphosate to streams, such as subsurface tile or storm drains, sewers, overland flow from developed landscapes, and arid landscapes were associated with sites that had greater concentrations of glyphosate compared to AMPA. These results contribute contemporary information and generalized interpretations adding to the knowledge base of the fate of glyphosate on a national scale and provide a springboard for further exploration of technical processes controlling transport to streams.

Science of the Total Environment↗

USGS2024

Common use herbicides increase wetland greenhouse gas emissions

Wetlands play a disproportionate role in the global climate as major sources and sinks of greenhouse gases. Herbicides are the most heavily used agrochemicals and are frequently detected in aquatic ecosystems, with glyphosate and 2,4-Dichlorophenoxyacetic acid (2,4-D), representing the two most commonly used worldwide. In recent years, these herbicides are being used in mixtures to combat herbicide-tolerant noxious weeds. While it is well documented that herbicide use for agriculture is expected to increase, their indirect effects on wetland greenhouse gas dynamics are virtually unknown. To fill this knowledge gap, we conducted a factorial microcosm experiment using low, medium, and high concentrations of glyphosate or 2,4-D, individually and in combination to investigate their effects on wetland methane, carbon dioxide, and nitrous oxide fluxes. We predicted that mixed herbicide treatments would have a synergistic effect on greenhouse gases compared to individual herbicides. Our results showed that carbon dioxide flux rates and cumulative emissions significantly increased from both individual and mixed herbicide treatments, whereas methane and nitrous oxide dynamics were less affected. This study suggests that extensive use of glyphosate and 2,4-D may increase carbon dioxide emissions from wetlands, which could have implications for climate change.

Science of the Total Environment↗

USGS2002

Practical application of disease resistance: A brook trout fishery selected for resistance to furunculosis

Selection is unwittingly influenced by nuances of fish culturists and adaptation of fish to intensive culture within artificial environments. When pathogens are present, susceptible individuals may be selectively eliminated from a population, accounting for inter-specific and intra-specific differences in susceptibility to disease. Biologists often intensify such selection to enhance resistance. Particularly important to this discourse is the selective breeding program initiated by the New York State Department of Environmental Conservation (Rome, NY, USA) to produce brown trout ( Salmo salar ) and brook trout ( Salvelinus fontinalis ) that are resistant to Aeromonas salmonicida . This program, specifically as it relates to brook trout, is reviewed throughout the current manuscript. In addition, we present a comparison between the performance of the Rome strain of brook trout to that of the Owhi strain of brook trout during a 17-month production cycle at the Ed Weed Fish Culture Station (Grand Isle, VT, USA) and after stocking into Vermont waters. The Owhi strain is used in recreational fisheries because it has good post-stocking survival, but these fish are sensitive to furunculosis. Our data indicated that the Rome strain had a food conversion rate of 1.3 that was slightly less than the 1.1 conversion rate of the Owhi brook trout. The growth rate measured as Monthly Temperature Units per inch (MTU/in.) among Rome brook trout (24.9 MTU/in.) was better than the Owhi brook trout (29.5 MTU/in.). Both the average length (23.6 cm) and weight (159.7 g) of individual Rome brook trout were superior to those of the Owhi strain (20.4 cm and 78.2 g, respectively). Just prior to stocking, survival within the hatchery was 84% among the Rome trout, but only 51% among the Owhi brook trout and mortality was attributed to a persistent epizootic of furunculosis. Microbiological assays indicated that the prevalence of A. salmonicida in dermal mucus attained equivalent levels within both strains of fish at different phases of the production cycle. The level of systemic infection, however, was regulated to a much greater extent by the Rome strain of brook trout throughout production. Our results indicated that the Rome brook trout strain satisfies management objectives for establishing an effective recreational brook trout fishery. Use of this strain also reduces management issues that complicate production when A. salmonicida is enzootic.

Vermont↗