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At least 73 records · Page 4Linked to original sources
USGS2003

Modeling radium and radon transport through soil and vegetation

A one-dimensional flow and transport model was developed to describe the movement of two fluid phases, gas and water, within a porous medium and the transport of 226Ra and 222Rn within and between these two phases. Included in this model is the vegetative uptake of water and aqueous 226Ra and 222Rn that can be extracted from the soil via the transpiration stream. The mathematical model is formulated through a set of phase balance equations and a set of species balance equations. Mass exchange, sink terms and the dependence of physical properties upon phase composition couple the two sets of equations. Numerical solution of each set, with iteration between the sets, is carried out leading to a set-iterative compositional model. The Petrov-Galerkin finite element approach is used to allow for upstream weighting if required for a given simulation. Mass lumping improves solution convergence and stability behavior. The resulting numerical model was applied to four problems and was found to produce accurate, mass conservative solutions when compared to published experimental and numerical results and theoretical column experiments. Preliminary results suggest that the model can be used as an investigative tool to determine the feasibility of phytoremediating radium and radon-contaminated soil. ?? 2003 Elsevier Science B.V. All rights reserved.

Journal of Contaminant Hydrology↗
USGS2019

Understanding conservation decisions of agriculture producers

Most land in the United States (US) is privately owned and used for agriculture. To address the effect of agriculture on wildlife, conservation professionals and organizations need to understand the land use decisions made by farmers and ranchers. We developed a tool for categorizing farmers and ranchers by their conservation land use values (LUVs) to understand how those values affect their land use motivations and resultant decisions. We defined land as the whole natural environment including soil, water, plants, fish, and wildlife. We used principal axis factoring and reliability analysis to identify statements representing human-centered values and nature-centered values of farmers and ranchers. We tested the validity of the combined statements with a survey of South Dakota’s private landowners (N = 4,000, [Jan through May 2016]) resulting in the LUV scale. Crossing the average scores on the human-centered and nature-centered statements identified 4 LUV types: humans first (20%), nature first (29%), interconnected (29%), and disconnected (22%). Analysis of variance and chi-square tests showed that, compared to the humans first and disconnected LUV types, the nature first and interconnected LUV types reported significantly greater importance of the following: most categories of types of wildlife in their land use decisions; conservation-related motivations for participating in a United States Farm Bill Conservation Program; conservation-related motivations for land use decisions; and participation in conservation-related behaviors. Conservation professionals and organizations may use the LUV scale to better understand landowners’ land use decisions to evaluate and inform conservation policy, programs, messaging, and improve conservation outcomes.

Journal of Wildlife Management↗
USGS1991

Selenium mobility and distribution in irrigated and nonirrigated alluvial soils

Dissolution and leaching of soil salts by irrigation water is a primary source of Se to shallow groundwater in the western San Joaquin Valley, California. In this study, the mobility and distribution of selenite and selenate in soils with different irrigation and drainage histories was evaluated using sorption experiments and an advection-dispersion model. The sorption studies showed that selenate (15–12400 µg Se L −1 ) is not adsorbed to soil, whereas selenite (10–5000 µg Se L −1 ) is rapidly adsorbed. The time lag between adsorption and desorption of selenite is considerable, indicating a dependence of reaction rate on reaction direction (hysteresis). Selenite adsorption and desorption isotherms were different, and both were described with the Freundlich equation. Model results and chemical analyses of extracts from the soil samples showed that selenite is resistant to leaching and therefore can represent a potential long-term source of Se to groundwater. In contrast, selenate behaves as a conservative constituent under alkaline and oxidized conditions and is easily leached from soil.

Soil Science Society of America Journal↗
USGS2005

Bioeconomic analysis of selected conservation practices on soil erosion and freshwater fisheries

Farmers can generate environmental benefits (improved water quality and fisheries and wildlife habitat), but they may not be able to quantify them. Furthermore, farmers may reduce their incomes from managing lands to produce these positive externalities but receive little monetary compensation in return. This study simulated the relationship between agricultural practices, water quality, fish responses to suspended sediment and farm income within two small watersheds, one of a cool water stream and one of a warm water stream. Using the Agricultural Drainage and Pesticide Transport (ADAPT) model, this study related best management practices (BMPs) to calculated instream suspended sediment concentrations by estimating sediment delivery, runoff, base flow, and streambank erosion to quantify the effects of suspended sediment exposure on fish communities. By implementing selected BMPs in each watershed, annual net farm income declined $18,000 to $28,000 (1 to 3 percent) from previous levels. “Lethal” fish events from suspended sediments in the cool water watershed decreased by 60 percent as conservation tillage and riparian buffers increased. Despite reducing suspended sediments by 25 percent, BMPs in the warm water watershed did not reduce the negative response of the fisheries. Differences in responses (physical and biological) between watersheds highlight potential gains in economic efficiency by targeting BMPs or by offering performance based “green payments.”

Journal of the American Water Resources Associatio↗
USGS2022

Challenges in linking soil health to edge-of-field water quality across the Great Lakes basin

To better understand agricultural nutrient losses, we evaluated relationships between management (e.g., manure and tillage), soil health measurements, and resulting edge-of-field (EOF) surface water quality. This work was conducted before or early into conservation implementation at 14 Great Lakes Restoration Initiative EOF sites spanning Wisconsin, Michigan, Indiana, Ohio, and New York. Analyses of site characteristics (hydroclimate, management, catchment properties) along with 3 yr of soil health measurements (chemical, biological, and physical properties) showed EOF-nutrient export depended on both site and soil properties. A pattern emerged whereby sites not receiving manure and sites with manure defined opposite ends of several gradients for soil and water data. Sites receiving manure had increased microbial activity, organic matter (3.2 vs. 2.7%), and soil test phosphorus (P) (2.8 times more) relative to sites without manure. Suspended sediments (SS), total P (TP), and total nitrogen (TN) in EOF surface runoff varied over three to five orders. Multivariate analysis among sites showed covariant linkages between soil nutrients, soil C, microbial properties, and nutrients in EOF water. There were positive univariate relationships between water-extractable soil P and annual EOF-water concentrations and yields of orthophosphate, TP, TN, and SS ( p < .01). Some soil physical properties (e.g., bulk density and infiltration) also covaried among sites but were not consistently related to runoff index or water yield variables. Given the observed among-site variability, we were not able to isolate desirable soil health signals on EOF surface water quality.

Journal of Environmental Quality↗
USGS2019

Modeling δ18O as an early indicator of regime shift arising from salinity stress in coastal vegetation

In many important coastal habitats, a combination of increasing soil salinization due to sea level rise, reduced precipitation and storm surges may induce regime shift from salinity-intolerant glycophytic vegetation to salinity-tolerant halophytic species. Early detection of regime shift due to salinity stress in vegetation may facilitate conservation efforts. It has been shown that the 18 O value of water in the xylem of trees can be used as a surrogate for salinity in the rooting zone of plants. Coupling measured δ 18 O values in the tree xylem with simulated δ 18 O values in trees and salinity in the vadose zone can be used to investigate competitive responses of glycophytic versus halophytic trees. MANTRA-O18 simulations suggest that the impacts of salinization on diminishing the resilience of salinity-intolerant trees can be detected up to 25 years before the glycophytic trees are threatened with regime shift to halophytic species. This early detection provides critical lead time and valuable information and insights useful for planning adaptation strategy to mitigate against the adverse impacts of sea level rise and climate change.

Hydrogeology Journal↗
USGS2026

Development of a SWAT+ model to improve conservation practice efficacy for protecting stream health in karst pasturelands

Placing appropriate conservation practices in critical source areas of pollutants can benefit stream health in karst environments susceptible to agricultural pollution. Watershed models, such as the Soil and Water Assessment Tool+ (SWAT+), can optimize both practice selection and placement across the landscape, but to our knowledge no studies have tested this model in karst pasturelands. Our goal was to understand pollutant dynamics in pasturelands with karst topography in southwest Virginia, United States. We built a SWAT+ model to predict streamflow and pollutant loads for four watersheds. SWAT+ predicted that streamflow estimates were most affected by setting the available water capacity to zero and increasing the hydraulic conductivity of the soil, revealing that water, and associated pollutants, move primarily through subsurface pathways. Predicted sediment yield was negatively associated with agricultural land cover and was strongly influenced by channel erodibility—indicating that the predominant sediment source may be streambanks. Therefore, practices that stabilize stream banks (e.g., fencing cattle out of streams) may be most effective at reducing sediment loads. The model unsatisfactorily predicted total nitrogen and total phosphorus loads. The utility of SWAT+ for cattle grazing operations in karst regions could be improved by more accurately representing the effects of cattle grazing on streambank erosion and the dynamic subsurface movement of pollutants.

Virginia↗
USGS2002

Rangeland health attributes and indicators for qualitative assessment

Panels of experts from the Society for Range Management and the National Research Council proposed that status of rangeland ecosystems could be ascertained by evaluating an ecological site's potential to conserve soil resources and by a series of indicators for ecosystem processes and site stability. Using these recommendations as a starting point, we developed a rapid, qualitative method for assessing a moment-in-time status of rangelands. Evaluators rate 17 indicators to assess 3 ecosystem attributes (soil and site stability, hydrologic function, and biotic integrity) for a given location. Indicators include rills, water flow patterns, pedestals and terracettes, bare ground, gullies, wind scour and depositional areas, litter movement, soil resistance to erosion, soil surface loss or degradation, plant composition relative to infiltration, soil compaction, plant functional/structural groups, plant mortality, litter amount, annual production, invasive plants, and reproductive capability. In this paper, we detail the development and evolution of the technique and introduce a modified ecological reference worksheet that documents the expected presence and amount of each indicator on the ecological site. In addition, we review the intended applications for this technique and clarify the differences between assessment and monitoring that lead us to recommend this technique be used for moment-in-time assessments and not be used for temporal monitoring of rangeland status. Lastly, we propose a mechanism for adapting and modifying this technique to reflect improvements in understanding of ecosystem processes. We support the need for quantitative measures for monitoring rangeland health and propose some measures that we believe may address some of the 17 indicators.

Journal of Range Management↗
USGS2016

Effectiveness of vegetation buffers surrounding playa wetlands at contaminant and sediment amelioration

Playa wetlands, the dominant hydrological feature of the semi-arid U.S. High Plains providing critical ecosystem services, are being lost and degraded due to anthropogenic alterations of the short-grass prairie landscape. The primary process contributing to the loss of playas is filling of the wetland through accumulation of soil eroded and transported by precipitation from surrounding cultivated watersheds. We evaluated effectiveness of vegetative buffers surrounding playas in removing metals, nutrients, and dissolved/suspended sediments from precipitation runoff. Storm water runoff was collected at 10-m intervals in three buffer types (native grass, fallow cropland, and Conservation Reserve Program). Buffer type differed in plant composition, but not in maximum percent removal of contaminants. Within the initial 60 m from a cultivated field, vegetation buffers of all types removed >50% of all measured contaminants, including 83% of total suspended solids (TSS) and 58% of total dissolved solids (TDS). Buffers removed an average of 70% of P and 78% of N to reduce nutrients entering the playa. Mean maximum percent removal for metals ranged from 56% of Na to 87% of Cr. Maximum removal was typically at 50 m of buffer width. Measures of TSS were correlated with all measures of metals and nutrients except for N, which was correlated with TDS. Any buffer type with >80% vegetation cover and 30–60 m in width would maximize contaminant removal from precipitation runoff while ensuring that playas would continue to function hydrologically to provide ecosystem services. Watershed management to minimize erosion and creations of vegetation buffers could be economical and effective conservation tools for playa wetlands.

Journal of Environmental Management↗
USGS2007

Biogeochemical effects of global change on U.S. National Parks

Federal parks and other public lands have unique mandates and rules regulating their use and conservation. Because of variation in their response to local, regional, and global-scale disturbance, development of mitigation strategies requires substantial research in the context of long-term inventory and monitoring. In 1982, the National Park Service began long-term, watershed-level studies in a series of national parks. The objective was to provide a more comprehensive database against which the effects of global change and other issues could be quantified. A subset of five sites in North Carolina, Texas, Washington, Michigan, and Alaska, is examined here. During the last 50 years, temperatures have declined at the southern sites and increased at the northern sites with the greatest increase in Alaska. Only the most southern site has shown an increase in precipitation amount. The net effect of these trends, especially for the most northern and southern sites, would likely be an increase in the growing season and especially the time soil processes could continue without moisture or temperature limitations. During the last 18 years, there were few trends in atmospheric ion inputs. The most evident was the decline in SO 4 2 deposition. There were no significant relationships between ion input and stream water output. This finding suggests other factors as modification of precipitation or canopy throughfall by soil processes, hydrologic flow path, and snowmelt rates are major processes regulating stream water chemical outputs.

Alaska, Michigan, North Carolina, Texas, Washingto↗
USGS2019

Assessment of site-specific agricultural Best Management Practices in the Upper East River watershed, Wisconsin, using a field-scale SWAT model

The Great Lakes “Priority Watershed” effort targeted the Upper East River watershed, a 116.5 km2 tributary watershed to Green Bay in Wisconsin, to reduce sediment and nutrients entering Green Bay. A Soil and Water Assessment Tool (SWAT) model was created to determine the effectiveness of Best Management Practices (BMPs) derived from the U.S. Department of Agriculture-Natural Resources Conservation Service National Conservation Planning (NCP) Database. The model was calibrated at the monthly timestep for flow, sediment, dissolved reactive phosphorus (DRP), total phosphorus (TP), and total nitrogen (TN). Field- and watershed-scale sediment and nutrient reductions were calculated due to the implementation of 74 BMP combinations on dairy and cash grain rotations. Modeling results indicated that when multiple BMPs are placed on a field, especially those that included filter strips and grassed waterways, generally reduced sediment and nutrient loads more than a single BMP implementation. The most effective in-field practice at reducing DRP and TP on dairy fields was a combination of 5 different BMPs: cover crops, crop rotation, nutrient management plan, reduced tillage, and a filter strip. Conservation cover was the most effective practice at reducing sediment and nutrient yields. Sediment and nutrient loads decreased at the watershed scale as the quantity and coverage of BMPs increased. When all contracted NCP BMPs were simulated at the watershed scale, sediment loads were reduced 2%, while TP, DRP, TN and nitrate loads were reduced 20%, 9%, 24%, and 17%, respectively. Modeling scenarios indicated that as the number and area of BMPs were increased, sediment and nutrient load reductions were also increased.

Wisconsin↗
USGS2013

Temporal and spatial variability of groundwater recharge on Jeju Island, Korea

Estimates of groundwater recharge spatial and temporal variability are essential inputs to groundwater flow models that are used to test groundwater availability under different management and climate conditions. In this study, a soil water balance analysis was conducted to estimate groundwater recharge on the island of Jeju, Korea, for baseline, drought, and climate-land use change scenarios. The Soil Water Balance (SWB) computer code was used to compute groundwater recharge and other water balance components at a daily time step using a 100 m grid cell size for an 18-year baseline scenario (1992–2009). A 10-year drought scenario was selected from historical precipitation trends (1961–2009), while the climate-land use change scenario was developed using late 21st century climate projections and a change in urban land use. Mean annual recharge under the baseline, drought, and climate-land use scenarios was estimated at 884, 591, and 788 mm, respectively. Under the baseline scenario, mean annual recharge was within the range of previous estimates (825–959 mm) and only slightly lower than the mean of 902 mm. As a fraction of mean annual rainfall, mean annual recharge was computed as only 42% and less than previous estimates of 44–48%. The maximum historical reported annual pumping rate of 241 × 10 6 m 3 equates to 15% of baseline recharge, which is within the range of 14–16% computed from earlier studies. The model does not include a mechanism to account for additional sources of groundwater recharge, such as fog drip, irrigation, and artificial recharge, and may also overestimate evapotranspiration losses. Consequently, the results presented in this study represent a conservative estimate of total recharge.

Jeju↗
USGS2021

Uncertainty in critical source area predictions from watershed-scale hydrologic models

Watershed-scale hydrologic models are frequently used to inform conservation and restoration efforts by identifying critical source areas (CSAs; alternatively 'hotspots'), defined as areas that export relatively greater quantities of nutrients and sediment. The CSAs can then be prioritized or ‘targeted’ for conservation and restoration to ensure efficient use of limited resources. However, CSA simulations from watershed-scale hydrologic models may be uncertain and it is critical that the extent and implications of this uncertainty be conveyed to stakeholders and decision makers. We used an ensemble of four independently developed Soil and Water Assessment Tool (SWAT) models and a SPAtially Referenced Regression On Watershed attributes (SPARROW) model to simulate CSA locations for flow, phosphorus, nitrogen, and sediment within the ~17,000-km 2 Maumee River watershed at the HUC-12 scale. We then assessed uncertainty in CSA simulations determined as the variation in CSA locations across the models. Our application of an ensemble of models - differing with respect to inputs, structure, and parameterization - facilitated an improved accounting of CSA prediction uncertainty. We found that the models agreed on the location of a subset of CSAs, and that these locations may be targeted with relative confidence. However, models more often disagreed on CSA locations. On average, only 16%–46% of HUC-12 subwatersheds simulated as a CSA by one model were also simulated as a CSA by a different model. Our work shows that simulated CSA locations are highly uncertain and may vary substantially across models. Hence, while models may be useful in informing conservation and restoration planning, their application to identify CSA locations would benefit from comprehensive uncertainty analyses to avoid inefficient use of limited resources.

Ohio↗
USGS2023

Incorporating temperature into seepage loss estimates for a large unlined irrigation canal

Quantifying seepage losses from unlined irrigation canals is necessary to improve water use and conservation. The use of heat as a tracer is widely used in quantifying seepage rates across the sediment–water interface. In this study, field observations and two-dimensional numerical models were used to simulate seepage losses during the 2018 and 2019 irrigation season in the Truckee Canal system. Nineteen transects were instrumented with temperature probes and stage recording devices for inverse modeling to derive seepage flux and volumetric losses over the 39 km length of canal. The numerical models for each transect were calibrated and validated using the two-year dataset. Soil zones and observation data were used in each numerical model to help guide calibration of vertical and lateral heat and fluid fluxes. Model simulations were used to derive multivariable regression equations that consider stage, temperature, and hydraulic gradient. The results demonstrate the value of long-term datasets that illustrate the seasonality of groundwater levels, siltation, stage, and temperature on seepage rates. Seepage rates estimated by the numerical models range from 0.16 to 4.6 m 3 /d m −1 . Total annual volumetric losses estimated for 2018 and 2019 were 1.6 × 10 -2 to 1.2 × 10 -2 km 3 , respectively. The seepage losses estimated by this study account for 32 % to 41 % of the inflow volumes. Regression models were able to reproduce seepage time-series simulated by the numerical models reasonably well. In arid environments, water diverted into irrigation canals may be influenced by seasonal variations in temperature sufficient to influence the water accounting of conveyed surface flows.

Nevada↗
USGS2021

Conservation implications of spatiotemporal variation in the terrestrial ecology of Western spadefoots

Conservation of species reliant on ephemeral resources can be especially challenging in the face of a changing climate. Western spadefoots ( Spea hammondii ) are small burrowing anurans that breed in ephemeral pools, but adults spend the majority of their lives underground in adjacent terrestrial habitat. Western spadefoots are of conservation concern throughout their range because of habitat loss, but little is known about the activity patterns and ecology of their terrestrial life stage. We conducted a radio-telemetry study of adult western spadefoots at 2 sites in southern California, USA, from December 2018 to November 2019 to characterize their survival, behavior, and movements from breeding through aestivation to refine conservation and management for the species. Western spadefoot survival varied seasonally, with risk of mortality higher in the active season than during aestivation. The probability of movement between successive observations was higher during the winter and spring and when atmospheric moisture was high and soil water content at 10-cm depth was low. The amount of rain between observations had the strongest effect on the probability of movement between observations; for every 20 mm of rainfall between observations, western spadefoots were 2.4 times more likely to move. When movements occurred, movement rates were highest when both relative humidity and soil water content at 10-cm depth were high. The conditions under which western spadefoots were likely active on the surface, likely to have moved, and moved at the highest rates are conditions that reduce the risk of desiccation of surface-active spadefoots. Western spadefoot home range areas varied between study sites and were mostly <1 ha, although 1 individual's home range area was >6 ha. Western spadefoots rapidly dispersed from the breeding pools, and asymptotic distances from the breeding pool were generally reached by June. The asymptotic distance from the breeding pool varied between sites, with the 95th percentile of the posterior predictive distribution reaching 486 m at 1 site and 187 m at the other. Western spadefoots did not select most habitat components disproportionately to their availability, but at Crystal Cove State Park, they avoided most evaluated vegetation types (graminoids, forbs, and shrubs). Spatial variation was evident in most evaluated western spadefoot behaviors; context-dependent behavior suggests that site-specific management is likely necessary for western spadefoots. Furthermore, comparison with an earlier study of western spadefoots at Crystal Cove State Park indicated substantial temporal variation in western spadefoot behavior. Therefore, basing management decisions on short-term studies might fail to meet conservation objectives. Better understanding the influences of spatial context and climatic variation on western spadefoot behavior will improve conservation efforts for this species.

California↗
USGS2023

Machine-learning model to delineate sub-surface agricultural drainage from satellite imagery

Knowing subsurface drainage (tile-drain) extent is integral to understanding how landscapes respond to precipitation events and subsequent days of drying, as well as how soil characteristics and land management influence stream response. Consequently, a time series of tile-drain extent would inform one aspect of land management that complicates our ability to explain streamflow and water-quality as a function of climate variability or conservation management. We trained a UNet machine-learning model, a convolutional neural network designed to highlight objects of interest within an image, to delineate tile-drain networks in panchromatic satellite imagery without additional data on soils, topography, or historical tile-drain extent. This was done by training the model to match the accuracy of human experts manually tracing the surface representation of tile drains in satellite imagery. Our approach began with a library of images that were used to train and quantify the accuracy of the model, with model performance tested on imagery from two areas that were not used to train the model. Satellite imagery included acquisition dates from 2008 to 2020. Training imagery was from agricultural areas within the US Great Lakes basin. Validation imagery was from the upper Maumee River, tributary to western Lake Erie, and an Indiana, Ohio-River headwater tributary. Our analysis of the satellite imagery paired with meteorological and soil data found that during spring, a combination of relatively high solar radiation, intermediate soil-water content and bare fields enabled the best model performance. Each area of interest was heavily tile-drained, where better understanding the movement of water, nutrients, and sediment from fields to downstream water bodies is key to managing harmful algal blooms and hypoxia. The trained UNet model successfully identified tile drains visible in the validation imagery with an accuracy of 93%–96% and balanced accuracy of 52%–54%, similar to performance for training data (95% and 63%, respectively). Model performance will benefit from ongoing contributions to the training library.

Indiana, Michigan, Ohio, Wisconsin↗
USGS2009

Assessment of water quality trends in the Minnesota River using non-parametric and parametric methods

Excessive loading of sediment and nutrients to rivers is a major problem in many parts of the United States. In this study, we tested the non-parametric Seasonal Kendall (SEAKEN) trend model and the parametric USGS Quality of Water trend program (QWTREND) to quantify trends in water quality of the Minnesota River at Fort Snelling from 1976 to 2003. Both methods indicated decreasing trends in flow-adjusted concentrations of total suspended solids (TSS), total phosphorus (TP), and orthophosphorus (OP) and a generally increasing trend in flow-adjusted nitrate plus nitrite-nitrogen (NO 3 -N) concentration. The SEAKEN results were strongly influenced by the length of the record as well as extreme years (dry or wet) earlier in the record. The QWTREND results, though influenced somewhat by the same factors, were more stable. The magnitudes of trends between the two methods were somewhat different and appeared to be associated with conceptual differences between the flow-adjustment processes used and with data processing methods. The decreasing trends in TSS, TP, and OP concentrations are likely related to conservation measures implemented in the basin. However, dilution effects from wet climate or additional tile drainage cannot be ruled out. The increasing trend in NO 3 -N concentrations was likely due to increased drainage in the basin. Since the Minnesota River is the main source of sediments to the Mississippi River, this study also addressed the rapid filling of Lake Pepin on the Mississippi River and found the likely cause to be increased flow due to recent wet climate in the region. Copyright ?? 2009 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved.

Journal of Environmental Quality↗
USGS2014

Controls of vegetation structure and net primary production in restored grasslands

1. Vegetation structure and net primary production (NPP) are fundamental properties of ecosystems. Understanding how restoration practices following disturbance interact with environmental factors to control these properties can provide insight on how ecosystems recover and guide management efforts. 2. We assessed the relative contribution of environmental and restoration factors in controlling vegetation structure, above- and below-ground investment in production across a chronosequence of semiarid Conservation Reserve Program (CRP) fields recovering from dryland wheat cropping relative to undisturbed grassland. Importantly, we determined the role of plant diversity and how seeding either native or introduced perennial grasses influenced the recovery of vegetation properties. 3. Plant basal cover increased with field age and was highest in CRP fields seeded with native perennial grasses. In contrast, fields seeded with introduced perennial grasses had tall-growing plants with relatively low basal cover. These vegetation structural characteristics interacted with precipitation, but not soil characteristics, to influence above-ground NPP (ANPP). Fields enrolled in the CRP program for >7 years supported twice as much ANPP as undisturbed shortgrass steppe in the first wet year of the study, but all CRP fields converged on a common low amount of ANPP in the following dry year and invested less than half as much as the shortgrass steppe in below-ground biomass. 4. ANPP in CRP fields seeded with native perennial grasses for more than 7 years was positively related to species richness, whereas ANPP in CRP fields seeded with introduced perennial grasses were controlled more by dominant species. 5. Synthesis and applications. Seeding with introduced, instead of native, perennial grasses had a strong direct influence on vegetation structure, including species richness, which indirectly affected NPP through time. However, the effects of restoring either native or introduced grasses on NPP were secondary to low water availability. Therefore, restoration strategies that maximize basal cover and below-ground biomass, which promote water acquisition, may lead to high resilience in semiarid and arid regions.

Colorado↗