Geology Reports⌕ Search

SEARCH · Geology Reports

Results for “Plant and Soil”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 379 records · Page 21Linked to original sources
USGS2018

Fungal loop transfer of nitrogen depends on biocrust constituents and nitrogen form

Besides performing multiple ecosystem services individually and collectively, biocrust constituents may also create biological networks connecting spatially and temporally distinct processes. In the fungal loop hypothesis rainfall variability allows fungi to act as conduits and reservoirs, translocating resources between soils and host plants. To evaluate the extent to which biocrust species composition and nitrogen (N) form influence loops, we created a minor, localized rainfall event containing 15 NH 4 + and 15 NO 3 − . We then measured the resulting δ 15 N in the surrounding dry cyanobacteria- and lichen-dominated crusts and grass, Achnatherum hymenoides , after 24 h. We also estimated the biomass of fungal constituents using quantitative PCR and characterized fungal communities by sequencing the 18S rRNA gene. We found evidence for the initiation of fungal loops in cyanobacteria-dominated crusts where 15 N, from 15 NH 4 + , moved 40 mm h −1 in biocrust soils with the δ 15 N of crusts decreasing as the radial distance from the water addition increased (linear mixed effects model (LMEM)): R 2 = 0.67, F 2,12 = 11, P = 0.002). In cyanobacteria crusts, δ 15 N, from 15 NH 4 + , was diluted as Ascomycota biomass increased (LMEM: R 2 = 0.63, F 2,8 = 6.8, P = 0.02), Ascomycota accounted for 82 % (±2.8) of all fungal sequences, and one order, Pleosporales, comprised 66 % (±6.9) of Ascomycota. The seeming lack of loops in moss-dominated crusts may stem from the relatively large moss biomass effectively absorbing and holding N from our minor wet deposition event. The substantial movement of 15 NH 4 + may indicate a fungal preference for the reduced N form during amino acid transformation and translocation. We found a marginally significant enrichment of δ 15 N in A. hymenoides leaves but only in cyanobacteria biocrusts translocating 15 N, offering evidence of links between biocrust constituents and higher plants. Our results suggest that minor rainfall events may initiate fungal loops potentially allowing constituents, like dark septate Pleosporales, to rapidly translocate N from NH 4 + over NO 3 − through biocrust networks.

Biogeosciences↗
USGS2016

Low soil moisture during hot periods drives apparent negative temperature sensitivity of soil respiration in a dryland ecosystem: A multi-model comparison

Arid and semiarid ecosystems (drylands) may dominate the trajectory of biosphere-to-atmosphere carbon (C) exchange, and understanding dryland CO 2 efflux is important for C cycling at the global-scale. However, unknowns remain regarding how temperature and moisture interact to regulate dryland soil respiration ( R s ), while ‘islands of fertility’ in drylands create spatially heterogeneous R s . At a site in southeastern Utah, USA we added or removed litter (0–650 % of control) in plots associated with either shrubs or biological soil crust-dominated interspaces between vascular plants. We measured R s , soil temperature (T s ), and water content (θ) repeatedly from October 2013 to November 2014. R s was highest following rain in late summer at T s ~30 °C, and lowest mid-summer at T s > 40 °C, resulting in apparent negative temperature sensitivity of R s at high temperatures, and positive temperature sensitivity at low-moderate temperatures. We used Bayesian statistical methods to compare models capturing a range of hypothesized relationships between T s , θ, and R s . The best model indicates that apparent negative temperature sensitivity of R s at high T s reflects the control of water content, not high temperatures. Modeled Q 10 ranged from 2.7 to 1.4 between 5 and 45 °C. Litter addition had no effect on Q 10 or reference respiration ( R ref = R s at 20 °C and optimum θ) beneath shrubs, and little effect on R ref in interspaces, yet R ref was 1.5 times higher beneath shrubs than in interspaces. Altogether, these results suggest reduced R s often observed at high T s in drylands is dominated by the control of θ, and, on shorter-timescales, variable litter inputs exert minimal control over R s .

Biogeochemistry↗
USGS2020

Photosynthetic and respiratory acclimation of understory shrubs in response to in situ experimental warming of a wet tropical forest

Despite the importance of tropical forests to global carbon balance, our understanding of how tropical plant physiology will respond to climate warming is limited. In addition, the contribution of tropical forest understories to global carbon cycling is predicted to increase with rising temperatures, however, in situ warming studies of tropical forest plants to date focus only on upper canopies. We present results of an in situ field-scale +4°C understory infrared warming experiment in Puerto Rico (Tropical Responses to Altered Climate Experiment; TRACE). We investigated gas exchange responses of two common understory shrubs, Psychotria brachiata and Piper glabrescens , after exposure to 4 and 8 months warming. We assessed physiological acclimation in two ways: (1) by comparing plot-level physiological responses in heated versus control treatments before and after warming, and (2) by examining physiological responses of individual plants to variation in environmental drivers across all plots, seasons, and treatments. P. brachiata has the capacity to up-regulate (i.e., acclimate) photosynthesis through broadened thermal niche and up-regulation of photosynthetic temperature optimum ( T opt ) with warmer temperatures. P. glabrescens , however, did not upregulate any photosynthetic parameter, but rather experienced declines in the rate of photosynthesis at the optimum temperature ( A opt ), corresponding with lower stomatal conductance under warmer daily temperatures. Contrary to expectation, neither species showed strong evidence for respiratory acclimation. P. brachiata down-regulated basal respiration with warmer daily temperatures during the drier winter months only. P. glabrescens showed no evidence of respiratory acclimation. Unexpectedly, soil moisture, was the strongest environmental driver of daily physiological temperature responses, not vegetation temperature. T opt increased, while photosynthesis and basal respiration declined as soils dried, suggesting that drier conditions negatively affected carbon uptake for both species. Overall, P. brachiata , an early successional shrub, showed higher acclimation potential to daily temperature variations, potentially mitigating negative effects of chronic warming. The negative photosynthetic response to warming experienced by P. glabrescens , a mid-successional shrub, suggests that this species may not be able to as successfully tolerate future, warmer temperatures. These results highlight the importance of considering species when assessing climate change and relay the importance of soil moisture on plant function in large-scale warming experiments.

Puerto Rico↗
USGS2021

Seasonal impoundment alters patterns of tidal wetland plant diversity across spatial scales

Understanding patterns of biodiversity is a key goal of ecology and is especially pressing in the current human‐caused biodiversity crisis. In wetland ecosystems, human impacts are centered around hydrologic manipulation including the common practice of wetland diking and impoundment. Constraining how wetland management influences plant biodiversity patterns across spatial scales will provide information on how best to modify actions to preserve biodiversity and ecosystem function in managed wetlands. Here, we compare patterns of plant diversity and species presence, abundance, and community composition at several spatial scales among tidal wetlands along an estuarine salinity gradient and managed wetlands that were formerly tidal. Managed impounded wetlands had decreased alpha and gamma diversity of rare species, with less than 60% of the species richness found in tidal brackish wetlands at several spatial scales. There was little change in the overall pattern of alpha, beta, and gamma diversity for common species in impounded wetlands; however, dominant tidal brackish species, primarily perennial rhizomatous graminoids, were replaced with management target plants and non‐native annual grasses in impounded wetlands. This species replacement led to over 60% of impounded sites being classified as containing novel plant assemblages. An additional 25% of impounded sites were classified as containing tidal saline plant assemblages, suggesting potential soil salinization. Along the estuarine gradient, patchiness and codominance of common plant species drove high diversity and turnover in tidal brackish wetlands, while it remains unclear whether tidal fresh or brackish wetlands maximize rare plant diversity. With reduced species richness, altered functional dominants, and novel or saline assemblages, impounded brackish wetlands may require careful water management to balance native plant biodiversity, associated ecosystem processes, and waterfowl requirements.

California↗
USGS1962

Biogeochemistry of vanadium

Vanadium is known to occur in soils as vanadates of copper, zinc, lead, uranium, ferric iron, manganese, calcium, and potassium. Vanadium replaces aluminum in clays and occurs in porphyrin complexes in bituminous sediments. Small amounts of vanadium are stimulating to plants; large amounts are toxic. Ten to 20 ppm vanadium in nutrient solution is commonly harmful to plants, but larger amounts can be tolerated by specific legumes, which use vanadium in the nitrogen-fixation process. Old wood in vegetation contains more vanadium than young wood, and roots contain the greatest accumulations. Herbs are more efficient accumulators of vanadium than trees and shrubs. Allium and some species of Astragalus, Castilleja, and Chrysothamnus are shown to be accumulators of vanadium. The vanadium content of plants rooted in highly calcic soils is very low, and that of plants rooted in seleniferous soils is high. Outdoor plot experiments verify a decrease in the presence of selenium. The absorption and translocation of vanadium by several plant species was found to be in direct ratio to that of selenium. Plant species that absorb large amounts of calcium are most tolerant of high-vanadium soils as the vanadium is precipitated in the root. Vanadium occurs in all animals and is accumulated in large amounts by Ascidians and by Holothuroidians. Vanadium is probably essential to vertebrates. Vanadium has been shown to decrease dental caries in animals and children. Vanadium inhibits the biosynthesis of cholesterol in both animals and man. Seleniferous areas in the western conterminous United States may support vegetation that contains large amounts of vanadium. Many areas of this country on the other hand may be nutritionally deficient in vanadium.

Open-File Report↗
USGS2020

Soil water availability shapes species richness in mid-latitude shrub steppe plant communities

Questions Ecological communities are controlled by multiple, interacting abiotic and biotic factors that influence the distribution, abundance, and diversity of species. These processes jointly determine resource availability, resource competition, and ultimately species richness. For many terrestrial ecosystems in dryland climates, soil water availability is the most frequent limiting resource for plant species. We used field sampling coupled with process‐based soil water balance modeling to explore the relative importance of multiple macroclimatic, ecohydrological, and biotic variables on plant species and functional type richness at the landscape scale in dryland plant communities. Location Dryland plant communities dominated by big sagebrush ( Artemisia tridentata ) that span climatic and elevational gradients in Wyoming, USA. Methods We quantified species richness at 1,000 m 2 and used multiple regression to determine whether mean climatic conditions, multiple metrics of soil moisture from a soil water balance model (SOILWAT2), soil physical and chemical properties, and shrub stand structure (biotic) variables were related to species and functional type richness. Results Species richness varied between 16 and 54 across sites. We found that species and functional type richness were related to both macroclimate and ecohydrology, but ecohydrology explained slightly more variation than climate. Biotic variables were always secondary to macroclimate and ecohydrology in our models. Variance partitioning revealed that large portions of variability in species (~54%), forb (~47%), and grass (~40%) richness were explained by ecohydrological variables. Conclusions Our results highlight the importance of the spatial and temporal distribution of soil water for dryland plant species richness and suggest that documenting the ways in which climate, vegetation, and soil properties interact to determine soil water availability is critical for understanding biodiversity patterns in dryland plant communities. This work has relevance for other mid‐latitude, shrub‐dominated dryland plant communities where soil water availability strongly influences ecosystem structure and function.

Wyoming↗
USGS2009

Weathering of the New Albany Shale, Kentucky: II. Redistribution of minor and trace elements

During weathering, elements enriched in black shale are dispersed in the environment by aqueous and mechanical transport. Here a unique evaluation of the differential release, transport, and fate of Fe and 15 trace elements during progressive weathering of the Devonian New Albany Shale in Kentucky is presented. Results of chemical analyses along a weathering profile (unweathered through progressively weathered shale to soil) describe the chemically distinct pathways of the trace elements and the rate that elements are transferred into the broader, local environment. Trace elements enriched in the unweathered shale are in massive or framboidal pyrite, minor sphalerite, CuS and NiS phases, organic matter and clay minerals. These phases are subject to varying degrees and rates of alteration along the profile. Cadmium, Co, Mn, Ni, and Zn are removed from weathered shale during sulfide-mineral oxidation and transported primarily in aqueous solution. The aqueous fluxes for these trace elements range from 0.1 g/ha/a (Cd) to 44 g/ha/a (Mn). When hydrologic and climatic conditions are favorable, solutions seep to surface exposures, evaporate, and form Fe-sulfate efflorescent salts rich in these elements. Elements that remain dissolved in the low pH (<4) streams and groundwater draining New Albany Shale watersheds become fixed by reactions that increase pH. Neutralization of the weathering solution in local streams results in elements being adsorbed and precipitated onto sediment surfaces, resulting in trace element anomalies. Other elements are strongly adsorbed or structurally bound to solid phases during weathering. Copper and U initially are concentrated in weathering solutions, but become fixed to modern plant litter in soil formed on New Albany Shale. Molybdenum, Pb, Sb, and Se are released from sulfide minerals and organic matter by oxidation and accumulate in Fe-oxyhydroxide clay coatings that concentrate in surface soil during illuviation. Chromium, Ti, and V are strongly correlated with clay abundance and considered to be in the structure of illitic clay. Illite undergoes minimal alteration during weathering and is concentrated during illuvial processes. Arsenic concentration increases across the weathering profile and is associated with the succession of secondary Fe(III) minerals that form with progressive weathering. Detrital fluxes of particle-bound trace elements range from 0.1 g/ha/a (Sb) to 8 g/ha/a (Mo). Although many of the elements are concentrated in the stream sediments, changes in pH and redox conditions along the sediment transport path could facilitate their release for aqueous transport.

Applied Geochemistry↗
USGS2015

Do shrubs reduce the adverse effects of grazing on soil properties?

Increases in the density of woody plants are a global phenomenon in drylands, and large aggregations of shrubs, in particular, are regarded as being indicative of dysfunctional ecosystems. There is increasing evidence that overgrazing by livestock reduces ecosystem functions in shrublands, but that shrubs may buffer the negative effects of increasing grazing. We examined changes in water infiltration and nutrient concentrations in soils under shrubs and in their interspaces in shrublands in eastern Australia that varied in the intensity of livestock grazing. We used structural equation modelling to test whether shrubs might reduce the negative effects of overgrazing on infiltration and soil carbon and nitrogen (henceforth &lsquo;soil nutrients&rsquo;). Soils under shrubs and subject to low levels of grazing were more stable and had greater levels of soil nutrients. Shrubs had a direct positive effect on soil nutrients; but, grazing negatively affected nutrients by increasing soil bulk density. Structural equation modelling showed that shrubs had a direct positive effect on water flow under ponded conditions but also enhanced water flow, indirectly, through increased litter cover. Any positive effects of shrubs on water flow under low levels of grazing waned at high levels of grazing. Our results indicate that shrubs may reduce the adverse effects of grazing on soil properties. Specifically, shrubs could restrict access to livestock and therefore protect soils and plants beneath their canopies. Low levels of grazing are likely to ensure the retention of soil water and soil carbon and nitrogen in shrubland soils.

Cobar↗
USGS2011

Sources, fate, and transport of nitrogen and phosphorus in the Chesapeake Bay watershed: An empirical model

Spatially Referenced Regression on Watershed Attributes (SPARROW) was used to provide empirical estimates of the sources, fate, and transport of total nitrogen (TN) and total phosphorus (TP) in the Chesapeake Bay watershed, and the mean annual TN and TP flux to the bay and in each of 80,579 nontidal tributary stream reaches. Restoration efforts in recent decades have been insufficient to meet established standards for water quality and ecological conditions in Chesapeake Bay. The bay watershed includes 166,000 square kilometers of mixed land uses, multiple nutrient sources, and variable hydrogeologic, soil, and weather conditions, and bay restoration is complicated by the multitude of nutrient sources and complex interacting factors affecting the occurrence, fate, and transport of nitrogen and phosphorus from source areas to streams and the estuary. Effective and efficient nutrient management at the regional scale in support of Chesapeake Bay restoration requires a comprehensive understanding of the sources, fate, and transport of nitrogen and phosphorus in the watershed, which is only available through regional models. The current models, Chesapeake Bay nutrient SPARROW models, version 4 (CBTN_v4 and CBTP_v4), were constructed at a finer spatial resolution than previous SPARROW models for the Chesapeake Bay watershed (versions 1, 2, and 3), and include an updated timeframe and modified sources and other explantory terms. Chesapeake Bay receives an estimated 1.32 x 10 8 kilograms (132,000 metric tons) of nitrogen and 9.74 x 10 6 kilograms (9,740 metric tons) of phosphorus annually from its watershed, mainly through its two largest tributaries, the Susquehanna and Potomac Rivers. Significant (α=0.10) sources of nutrients to streams in the watershed include fertilizer and manure applications in agricultural areas, undifferentiated urban activities, point sources, atmospheric deposition and direct fixation by crops (for nitrogen), and mineral sources (for phosphorus). Agriculture (primarily fertilizer applications and crop fixation) contributes more than half of the nitrogen delivered from the watershed to the bay; phosphorus contributions are more mixed, and fairly evenly distributed among agricultural (fertilizer and manure applications) and urban (including point) sources. Natural mineral dissolution contributes approximately 14 percent of the phosphorus flux from the watershed to the Chesapeake Bay. Empirical estimates of average yields from different source areas and of the portion of selected applications delivered to streams agree closely with previously reported values in the literature. Nutrient fate and transport through the Chesapeake Bay watershed to the bay reflect the diferent physical and chemical properties of nitrogen and phosphorus compounds. Groundwater is an important pathway for nitrogen transport (as nitrate), and TN flux is greatest in areas with greater groundwater flow and in areas of the Piedmont underlain by carbonate rocks. TN flux decreases with increasing vegetative growth (likely indicative of plant uptake) and soil available water capacity (likely indicative of reducing conditions). Phosphorus transport to streams, conversely, is greatest in areas most likely to generate overland runoff and related erosion, including those with less permeable and more erodible soils and greater precipitation. Phosphorus transport also is greater in the Coastal Plain than in other areas, possibly due to saturation of soils with historical phosphorus applications. Both nitrogen and phosphorus are lost within watershed impoundments (lakes, ponds, or reservoirs), and nitrogen is also lost significantly along flowing reaches, particularly in small streams and in larger streams in warmer areas.

Chesapeake Bay↗
USGS2024

Spatial differences in soil nutrients along a hydrographic gradient on floodplains in Dongting Lake

The spatial heterogeneity of soil nutrients is crucial for the water bird and whole floodplain wetland ecosystem in large lakes, and it is influenced by the dramatic water level changes and sedimentation progress in West Dongting Lake (WDL). Soil samples were collected at various soil depths along the Yuan River and Li River that feed into WDL. The concentrations of soil total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), and soil grain size were tested. The stoichiometric ratios of C, N, P, and the mean value of soil grain size ( Mz ) were calculated. The differences of soil TOC, TN, TP and the stoichiometric ratio at different sites and soil depths were compared. Linear regression was used to explore the relationships of Mz and nutrient concentrations, and relationships between TOC, TN, and TP. Redundancy analysis was used to explore the relationship between soil nutrients, heavy metal concentrations, and plant community diversity. The results showed that the distributions of soil TOC, TN, and TP concentrations differed across regions in west Dongting Lake along the Yuan and Li Rivers. Total organic carbon concentration differed at different sedimentation depths. Soil grain size showed negative effect with soil TOC, TN, and TP concentrations in this region. Plant community diversity correlated positively with soil TOC and negatively with Hg. West Dongting Lake was N limited despite the high wet deposition of N. It could potentially be attributed to the insufficient presence of aerobic environments for microbes during intermittent flooding of the floodplain, coupled with feeble mineralization. This study can provide valuable insights for the conservation of water bird habitats and wetland ecosystems.

West Dongting Lake↗
USGS1981

Biological and economic impact of stream alteration in the Virginia Piedmont

A 31 month (September 1974 - March 1977) study was conducted on warmwater streams located in the Roanoke Creek watershed of the Piedmont Region of Virginia. The purpose of the study was to determine the effects of stream channelization on the aquatic/riparian wildlife resource and agricultural land-use patterns associated with the altered streams. Three streams, which were channelized 3, 6, and 10 years prior to initiation of the study, and teo unaltered streams, were selected as representative streams for the study. Recently channelized streams lacked overstory cover but has an abundance of herbaceous and small woody plany cover, Conversely, control streams had significantly larger percentages of trees over 46 m tall. Plant species diversity, foliage height diversity, and evenness diversity increased as age since channelization increased. No major differences in water quality parameters were found for either channelized or control streams, although channelized streams had greater deposits of sand and lesser amount of rock, rubble, and gravel. These changes in substrate composition did not significantly modify actual stream flow rates. Fish species composition and species diversity among channelized and unchannelized streams were only slightly different, with most of the differences probably attributable to strays from adjacent habitats, However, evenness diversity for fish communities was lower in channelized streams. The benthic population showed greater changes than did the fish populations with an increase in Chironominae tolerant of unstable sand substrates in channelized streams. Evenness diversity of benthic populations was also higher and showed more consistency in the control stream than in channelized streams. Evenness diversity of benthic communities in control stream averaged between 0.5 to 0.6 and was quite consistent; whereas, the average in the two youngest channelized streams was 0.3 to 0.4. These data seem to indicate decreased stability of the biota in altered streams. In general, benthic macroinvertabrate and fish community parameters collected from channelized streams located 1200 m below a reservoir were either comparable to, or intermediate between, upstream (unchannelized) and reservoir tailwater values. The shallow surface discharge impoundments associated with channelized streams appeared to have a highly localized impact on the downstream benthic marcoinvertabrate and fish communities. During winter, bird species diversity (BSD) among channelized stream sites was not significantly different. During the breeding season, species richness (number of breeding species) and BSD increased with age since channelization. Breeding bird densities were 6.2 pairs/ha in the most recent (3 yr) channelized site and 13.3 pairs/ha on the control streams. Bird diversity and density, particularly for Parulids (warblers), during the breeding season were reduced significantly by removal of tree and shrub layers along channelized streams. No significant differences were found among study sites for either total number of small mammals or their species diversity indices; although, there was a trend toward increasing diversity as age since channelization increased. Smaller differences in species diversity values for small mammals on channelized sites than for birds suggests that small mammal populations require less time for recovery following channelization than avian communities. When streams are channelized: 1) vegetation should be removed from only one side of the stream, with minimal disturbance of top-soil; followed by plantings of herbaceous and woody vegetation, 2) hedgrow plantings should be maintained between agricultural fields and the stream for bank stabilization, 3) dead snags and large trees should be left for birds, 4) all channelization projects should be designed according to the most recent guidelines recommended by the SCS and other resources agencies. In 1958, the Roanoke County Watershed Work Plan projected annual costs of the structured measures (mainly reservoirs and downstream channelization) to be $79,897 and the average annual monetary benefits to be $111,103. With this favorable benefit/cost ration of 1.4, work began in 1960. In 1970, the annual capital cost was 60,780 and operations/maintenance costs were 10,402, or a total annual project cost of $71, 182. High and low values of annual benefits from agricultural income, water supply, recreation, and non-agricultural flood damage were determined for 1970 and compared to annual project cost. The benefit/cost ratio obtained was between 0.25 and 0.58, considerably lower than the 1.4 estimate of the 1958. work plan. This unsatisfactory ratio for the project was due mainly to the failure of the project to encourage large scale cropping of bottomland area. Future projects should be planned with 1) a greater recognition of constraints on farm operator behavior which affect land use change, 2) conservative projection for land use changes in area where agriculture ids in overall decline, 3) increased use of sensitivity analysis to examine the consequences for project economic justification of alternative land use change projections.

Virginia↗
USGS2018

STEPWAT2: An individual‐based model for exploring the impact of climate and disturbance on dryland plant communities

The combination of climate change and altered disturbance regimes is directly and indirectly affecting plant communities by mediating competitive interactions, resulting in shifts in species composition and abundance. Dryland plant communities, defined by low soil water availability and highly variable climatic regimes, are particularly vulnerable to climatic changes that exceed their historical range of variability. Individual‐based simulation models can be important tools to quantify the impacts of climate change, altered disturbance regimes, and their interaction on demographic and community‐level responses because they represent competitive interactions between individuals and individual responses to fluctuating environmental conditions. Here, we introduce STEPWAT2, an individual plant‐based simulation model for exploring the joint influence of climate change and disturbance regimes on dryland ecohydrology and plant community composition. STEPWAT2 utilizes a process‐based soil water model (SOILWAT2) to simulate available soil water in multiple soil layers, which plant individuals compete for based on the temporal matching of water and active root distributions with depth. This representation of resource utilization makes STEPWAT2 particularly useful for understanding how changes in soil moisture and altered disturbance regimes will concurrently impact demographic and community‐level responses in drylands. Our goals are threefold: (1) to describe the core modules and functions within STEPWAT2 (model description), (2) to validate STEPWAT2 model output using field data from big sagebrush plant communities (model validation), and (3) to highlight the usefulness of STEPWAT2 as a modeling framework for examining the impacts of climate change and disturbance regimes on dryland plant communities under future conditions (model application). To address goals 2 and 3, we focus on 15 sites that span the spatial extent of big sagebrush plant communities in the western United States. For goal 3, we quantify how climate change, fire, and grazing can interact to influence plant functional type biomass and composition. We use big sagebrush‐dominated plant communities to demonstrate the functionality of STEPWAT2, as these communities are among the most widespread dryland ecosystems in North America.

Ecosphere↗
USGS1998

Metal concentrations in aquatic macrophytes as influenced by soil and acidification

Bioavailability of metals to aquatic plants is dependent on many factors including ambient metal concentration, pH of soil or water, concentration of ligands, competition with other metals for binding sites, and mode of exposure. Plants may be exposed to metals through water, air, or soil, depending on growth form. This paper examines the influence of soil type under two regimens of water acidification on metal uptake by four species of aquatic macrophytes: smartweed (Polygonum sagittatum), burreed (Sparganium americanum), pondweed (Potamogeton diversifolius), and bladderwort (Utricularia vulgaris) in constructed, experimentally acidified wetlands. Soil types consisted of a comparatively high-metal clay or a lower-metal sandy loam. Each pond was either acidified to pH ca. 4.85.3 or allowed to remain circumneutral. Metal concentrations tended to be higher in the submerged bladderwort and pondweed than in the emergent burreed and smartweed. Soils were important to plant metal concentrations in all species, but especially in the emergents. Acidification influenced plant concentrations of some metals and was especially important in the submerged pondweed. Bioaccumulation of metals occurred for Mn, B, Sr, Ba, and Zn, compared to soil concentrations.

Water, Air, & Soil Pollution↗
USGS2020

Quantifying drought’s influence on moist soil seed vegetation in California’s Central Valley through remote sensing

Across the Central Valley of California, millions of wintering waterfowl rely on moist soil seed (MSS) plants that grow in managed seasonal wetlands as a critical source of food. Estimates of MSS plant production are used to set waterfowl habitat targets yet this information is not well known. We created the first Central Valley-wide time series maps of MSS plant distributions and productivity. We found that MSS plant seed yield declined in critical drought years, which corresponded with reduced water delivery to managed wetlands. Our results provide improved food resource estimates and information to help managers prioritize actions as water supply becomes more uncertain with climate change.

California↗
USGS2018

Flood effects on soil thermal regimes in contrasting cold‐desert river floodplains (Yampa and Green rivers, Colorado)

Heat transfer theory suggests that floodplain soils in dryland riverine ecosystems can be cooled by hyporheic flows generated during spring floods. I compared soil temperature cycles and associated hydrologic factors on a free‐flowing river to those on a river where flows and surface water temperatures are now regulated. Spring surface water temperatures were comparable on the 2 rivers, as was apparent diffusivity of the soil under mature Populus fremontii in a year when severe drought produced similar soil moisture regimes. Over 9 years of monitoring, mean annual maximum soil temperature was higher on the regulated river than on the free‐flowing river (10 cm depth: 33 vs. 23 °C; 40 cm depth: 30 vs. 20°C, respectively), and sinusoidal models of the annual temperature cycle at each depth indicated higher means and greater amplitudes on the regulated river. The annual maximum soil temperature was inversely related to peak flood discharge on the free‐flowing river but not on the regulated river. Temporal shifts in the lag between diel cycles at 40 and 10 cm depths—an index of soil thermal diffusivity—suggested that the capillary fringe is strongly involved in heat exchange. An increase in the lag during some water table declines suggested that shallow soils may undergo flood‐induced evaporative cooling. Hyporheic recharge can be an ecologically important determinant of growing‐season soil temperatures at plant rooting depth in dryland river floodplains. Reductions in spring flood magnitude due to river regulation, water abstraction, or climate change can increase these temperatures and thereby alter ecosystem structure and functioning.

Colorado↗
USGS2014

Phytoremediation of a petroleum-hydrocarbon contaminated shallow aquifer in Elizabeth City, North Carolina, USA

A former bulk fuel terminal in North Carolina is a groundwater phytoremediation demonstration site where 3,250 hybrid poplars, willows, and pine trees were planted from 2006 to 2008 over approximately 579,000 L of residual gasoline, diesel, and jet fuel. Since 2011, the groundwater altitude is lower in the area with trees than outside the planted area. Soil-gas analyses showed a 95 percent mass loss for total petroleum hydrocarbons (TPH) and a 99 percent mass loss for benzene, toluene, ethylbenzene, and xylenes (BTEX). BTEX and methyl tert-butyl ether concentrations have decreased in groundwater. Interpolations of free-phase, fuel product gauging data show reduced thicknesses across the site and pooling of fuel product where poplar biomass is greatest. Isolated clusters of tree mortalities have persisted in areas with high TPH and BTEX mass. Toxicity assays showed impaired water use for willows and poplars exposed to the site's fuel product, but Populus survival was higher than the willows or pines on-site, even in a noncontaminated control area. All four Populus clones survived well at the site.

North Carolina↗
USGS1998

Choosing indicators of natural resource condition: A case study in Arches National Park, Utah, USA

Heavy visitor use in many areas of the world have necessitated development of ways to assess visitation impacts. Arches National Park recently completed a Visitor Experience and Resource Protection (VERP) plan. Integral to this plan was developing a method to identify biological indicators that would both measure visitor impacts and response to management actions. The process used in Arches for indicator selection is outlined here as a model applicable to many areas facing similar challenges. The steps were: (1) Vegetation types most used by visitors were identified. Impacted and unimpacted areas in these types were sampled, comparing vegetation and soil factors. (2) Variables found to differ significantly between compared sites were used as potential indicators. (3) Site-specific criteria for indicators were developed, and potential indicators evaluated using these criteria. (4) Chosen indicators were further researched for ecological relevancy. (5) Final indicators were chosen, field tested, and monitoring sites designated. In Arches, indicators were chosen for monitoring annually (soil crust index, soil compaction, number of used social trails and soil aggregate stability) and every five years (vegetation cover and frequency; ground cover; soil chemistry; and plant tissue chemistry).

Environmental Management↗
USGS2012

Nitrogen limitation, 15 N tracer retention, and growth response in intact and Bromus tectorum -invaded Artemisia tridentata ssp. wyomingensis communities

Annual grass invasion into shrub-dominated ecosystems is associated with changes in nutrient cycling that may alter nitrogen (N) limitation and retention. Carbon (C) applications that reduce plant-available N have been suggested to give native perennial vegetation a competitive advantage over exotic annual grasses, but plant community and N retention responses to C addition remain poorly understood in these ecosystems. The main objectives of this study were to (1) evaluate the degree of N limitation of plant biomass in intact versus B. tectorum -invaded sagebrush communities, (2) determine if plant N limitation patterns are reflected in the strength of tracer 15 N retention over two growing seasons, and (3) assess if the strength of plant N limitation predicts the efficacy of carbon additions intended to reduce soil N availability and plant growth. Labile C additions reduced biomass of exotic annual species; however, growth of native A. tridentata shrubs also declined. Exotic annual and native perennial plant communities had divergent responses to added N, with B. tectorum displaying greater ability to use added N to rapidly increase aboveground biomass, and native perennials increasing their tissue N concentration but showing little growth response. Few differences in N pools between the annual and native communities were detected. In contrast to expectations, however, more 15 N was retained over two growing seasons in the invaded annual grass than in the native shrub community. Our data suggest that N cycling in converted exotic annual grasslands of the northern Intermountain West, USA, may retain N more strongly than previously thought.

Arizona;California;Colorado;Idaho;Nevada;Oregon;Ut↗