183 research outputs found
Ecohydrological implications of aeolian processes in drylands
No full textAeolian processes, the erosion transport and deposition of soil particles by wind, are dominant geomorphological processes in many drylands, and important feedbacks are known to exist among aeolian, hydrological, and vegetation dynamics (Field et al. 2010; Ravi et al. 2011). The wind, a natural geomorphic agent, has been active as an erosive agent throughout geological times in many parts of the world. Outstanding examples are the extensive loess deposits along the Huanghe River (Yellow River) in China and along the Missouri and Mississippi rivers in the United States. Climatic changes and anthropogenic activities can greatly accelerate soil erosion by wind with implications for soil and vegetation degradation (Kok et al. 2012; Webb and Pierre 2018; Nauman et al. 2018). For instance, in the 1930s, a decreased precipitation coupled with intensive agricultural activities caused a dramatic increase in wind erosion in the Great Plains of the United States, resulting in the so-called Dust Bowl. Wind erosion can be activated also by land-use change. An example is provided by the Mu Us region in North China with an annual precipitation of 400 mm, which was once a grassland partially covered with forest, yet now is one of the major sources of dust in the world as a result of overgrazing and agricultural practices (Wang et al. 2005; Miao et al. 2016)
COMBINED LAND USE OF SOLAR INFRASTRUCTURE AND AGRICULTURE FOR SOCIOECONOMIC AND ENVIRONMENTAL CO-BENEFITS IN THE TROPICS
No full textSolar photovoltaic (PV) generation has been gaining popularity as low carbon energy technology in the face of the global climate change. However, conventional utility-scale PV requires large swaths of land to be occupied for decades which prevents the land from producing food or performing vital ecosystem services. Co-location of PV with crop cultivation is an emerging strategy for mitigating the land use of PV. In order to optimize this strategy, the impact of the plant growth-related soil properties need to be quantified. To this end, the first portion of the thesis investigated the impacts on the soil properties in a re-vegetated solar PV facility in Boulder, Colorado, which was the oldest vegetation-PV co-location site in the world. The second portion of the thesis uses a life cycle analysis (LCA) approach to test the feasibility of co-location of model crop cultivation and solar PV electricity generation in rural Indonesia, and it is the first study to use the LCA study of the co-located solar in the tropics. The first approach revealed that the soil hydrology, grain size distribution, and total carbon and nitrogen are significantly altered from their original state by the construction and presence of photovoltaic arrays, and that those properties had not been restored to their pre-construction levels despite the fact that ten years had passed since re-vegetation of the PV array. The persistence of the altered soil properties meant that the designs regarding re-vegetation or co-location of PV with crops would have to be considered at the beginning of the construction of the PV to minimize the impact on the soil and the existing vegetation. Furthermore, soil moisture was the highest in the soil underneath the western edge of the PV panels, where the western tilt of the PV panel had concentrated the rainfall. The heterogeneity in soil hydrology created by the panels could be manipulated to benefit the growth of vegetation within the PV array. The LCA approach revealed that a hectare of PV arrays with full module density would carbon offsets against diesel electricity generation and the grid, and that the annual supply of electricity from the PV could satisfy the demand of a typical rural Indonesian village several times over. However, the high capital expenditure of solar mean that co-location with full PV module density would not be economically feasible, even with the income stream from the co-located crop cultivation. In order to reduce the capital expenditure, the PV module density for co-location was reduced to half. The combination of reduced capital expenditure and the income stream from the crop made the co-located land use significantly less costly. Additionally, the rural electrification would be able to provide secondary socioeconomic benefits such as avoidance of health costs through operation of public health infrastructures, increased standard of living, and secondary income opportunities from processing of raw materials. However, better subsidies for renewables, specialized loan structures for small-scale renewable systems, and a culture of co-operation between small landholders would need to be implemented before the co-located system becomes affordable to the inhabitants in rural Indonesian villages.Geolog
MONITORING STORMWATER INFILTRATION IN A VACANT LOT COMPARING TIME-LAPSE ELECTROMAGNETIC INDUCTION AND ELECTRICAL RESISTIVITY TOMOGRAPHY
No full textVacant lots in cities and surrounding urban areas can potentially be used for stormwater management because they are pervious. However, the extent to which vacant lots provide pervious cover to increase infiltration and reduce stormflow is poorly understood. The goal of this study was to develop faster methods for monitoring stormwater infiltration to improve characterization of heterogeneous urban systems. Geophysical techniques are capable of mapping and characterizing subsurface materials, but are often limited by time and sensitivity constraints. In this study, the infiltration characteristics of a vacant lot created by the demolition of a house was characterized using a series of modeling, field and lab experiments. Site characterization under background conditions with an EM Profiler was used to map zones of different fill materials. Three zones were identified in the study site: grass area, driveway area, and a former house area. Transient soil moisture conditions were monitored during irrigation tests using two geophysical methods (electrical resistivity tomography [ERT] and electromagnetic induction [EM]) to evaluate method sensitivity and differences between the three zones. ERT proved more sensitive than EM profiling at detecting changes in the three zones. Soil moisture changes in the driveway area were particularly difficult to detect using EM. The EM Profiler showed a reduction rather than increase in conductivity at the start of irrigation and storms, which was attributed to flushing of high conductivity pore fluids by dilute irrigation or rain water. This explanation was supported using Archie’s Law to model the response of apparent conductivity under highly conductive pore fluid conditions. The EM Profiler was also used under natural precipitation conditions to quickly monitor areas too large for the ERT to reasonably survey. The results suggested that EM instrument drift needs to be corrected to make the method more sensitive. It was difficult to detect differences in hydrologic characterization between areas of the vacant lot using traditional soil point measurements because of the inherent spatial variability. The most useful point measurement was soil moisture loggers. Data from soil moisture loggers was used to parameterize the model; in addition, the soil moisture loggers showed a slow drying period. By combining the EM Profiler method with soil moisture data and applying corrections for drift, some improvement in sensitivity might be achieved. Quantitative characterization of fill material was shown by ERT, which detected more heterogeneous infiltration in the area of the former house than in the grass area.Geolog
Concentration of Suspended Solids and Nutrients in Overland Flow in Suburban Philadelphia Watersheds
No full textSuburban Philadelphia is a densely populated region with a history of urbanization and waterway channelization. Situated within the Delaware River watershed, 70% of the region’s stream segments are impaired, primarily due to excess sediment and nutrients. To improve water quality, the Upstream Suburban Philadelphia Cluster of the Delaware River Watershed Initiative (DRWI) established focus areas within the region for targeted implementation of stormwater control measures and community outreach about stormwater management. The focus areas consisted of upstream headwaters to four streams flowing into the Delaware River. The objective of this study was to determine sediment and nutrient concentrations in first flush overland flow (OLF) in three of the DRWI focus areas. Seven sites were selected for collection of OLF, stream, and rain samples. A total of 228 samples from 24 sample locations across 17 storms were collected from the Pennypack Creek, Jenkintown Creek, and Sandy Run watersheds. Samples were analyzed for nitrate (N), total dissolved phosphorous (TDP), total phosphorous (TP), suspended sediment concentration (SSC), and chloride (Cl), and results were compared to catchment metrics including area and land cover. OLF samples showed a wider variability of sediment, chloride, and nutrient concentrations than stream samples, and the stormwater quality varied between catchments with different land cover composition. Higher N correlated with increased road coverage and landscaping applications in vegetated areas. Lower TDP was linked to increased tree canopy, while higher TP was linked to smaller lot sizes. In the stream samples, higher SSC was linked to increased road coverage and smaller building sizes, and higher Cl was linked to nearby impervious surfaces. SSC was often reduced in the OLF samples after flowing downhill or through vegetated patches. Two bioretention basins were sampled at the inlet and outlet. Both basins experienced a decrease in SSC and N at the outlets, showed marginal to poor efficiency for TDP and TP removal, and provided an increase in Cl in outlet. A review of all collected data suggests that land cover and human activity in these watersheds are greater drivers of stormwater quality than rainfall and weather patterns. The data presented in this report has implications for stormwater control. First, this study provides an understanding of local heterogeneities in the distribution of nutrients, sediment, and chloride in stormwater runoff from seemingly similar watersheds in terms of land use. Second, the presented data can be used in projects and models at the headwater scale and the micro-catchment scale to improve planning and monitoring.Geolog
Using Geophysics and Terrestrial LiDAR to Assess Stormwater Parameters in Vacant Lots in Philadelphia
No full textManaging stormwater volume and quality has become an important issue in urban hydrology. Impervious cover associated with urbanization increases surface runoff volumes and degrades the water quality of urban streams and rivers. Cities with combined stormwater and sewer lines such as Philadelphia, have been tasked with decreasing runoff volumes to help reduce combined sewer overflows and improve the water quality of local waterways. The Philadelphia Water Department uses the Environmental Protection Agency’s Storm Water Management Model (SWMM) to predict runoff and evaluate if proposed stormwater infrastructure will reduce overflows. This study focused on the hydrogeological properties of grassy areas on and near Temple University’s main campus in north Philadelphia. The dataset includes terrestrial LiDAR, ground penetrating radar, soil moisture sensor, surface compaction, and double ring and mini disk infiltrometer measurements. These data were used to establish what controls infiltration rates in the area and also provide input parameters for a SWMM model. A terrestrial LiDAR scan of the Berks St. site, a grassy vacant lot located just east of Temple’s campus was used to generate a high-resolution digital elevation model. This elevation model was used to calculate the depression storage parameter, partition subcatchments in the SWMM model, and calculate a topographic wetness index (TWI). The TWI is a microtopography-based predictor of where runoff will collect and infiltrate. The TWI assumes a homogeneous infiltration rate and that runoff is routed by topography. This TWI was compared with soil moisture sensor measurements to determine if the microtopographic index could predict the majority of change in soil moisture at the field site. To determine if accounting for buried debris helped strengthen the TWI, GPR was used to map the extent and depth of subsurface objects. The results indicate that the TWI and GPR data could not predict where runoff would accumulate and then infiltrate because the TWI’s assumptions were not met. Measurements made with a double ring infiltrometer indicate that infiltration rates at the site were both high and heterogeneous (40 to 1060 mm/hr), allowing precipitation to infiltrate into the subsurface rather than become runoff, minimizing the influence of microtopography. Co-located surface compaction and double ring infiltrometer measurements at sites on and nearby Temple’s campus showed a negative correlation between surface compaction and infiltration rate (R2 = 0.67). Compacted areas on campus had lower infiltration rates and exhibited depression storage and runoff during rain events. Less compacted areas off campus had higher infiltration rates and exhibited no depression storage or runoff. The results of this study showed variance in surface compaction caused grassy areas around Temple’s campus respond differently to rain events. The results not only provided field-based parameter values for a SWMM model, but shows that compaction’s influence on infiltration should be considered when constructing a SWMM model. Runoff volumes in SWMM may be underestimated if compacted grassy areas are modeled with high infiltration rates.Geolog
Fault-Controlled Damage and Permeability at the Brady Geothermal System, Nevada, U.S.A.
No full textIdentifying and locating permeable zones in geothermal fields is a critical step in determining reservoir potential and realizing energy production. Despite a general association with active faults, geothermal systems typically display heterogeneously distributed permeability that makes locating successful wells difficult. Faults are associated with complex distributions of secondary fractures, with variable attitude, fracture density, and connectivity – all of which can influence permeability. Simulations of the local stress state due to slip on a detailed model of the fault system at Brady Geothermal Field, NV, supported by models of key idealized fault geometries, are used to test the relationship between both productive wells or hydrothermal features and failed wells with stress states that promote or suppress fracture. These simulations show that hydrothermal features are generally associated with portions of faults best oriented to slip in the stress state measured at Brady. Critically, regions of enhanced coulomb stress (S_c^((max))) and reduced least compressive principal stress (σ3) that promote fractures occur at narrow, extensional relays and at intersections between faults; at Brady such locations correlate with the locations of production wells and hydrothermal surface manifestations. Despite this positive correlation, several of these structures do not host evidence of hydrothermal flow due to a lack of persistence along the dip of the fault necessary to connect to the heat source at depth. In contrast, regions of reduced S_c^((max)) and enhanced σ3 correspond to volumes that lie near the interior of faults, including at bends and at contractional relays. These locations are generally associated with failed wells; however, major production wells occur at a clear bend in a large fault at Brady. This may reflect the origin of the bend as breached relay and warrants further investigation.Geolog
Determining the ability of terrestrial time-lapse microgravity surveying on a glacier to find summer mass balance using gravitational modeling
No full textMass loss of alpine glaciers presently account for about half of the cryospheric contribution to the global sea-level rise. Mass balance of alpine glaciers has predominantly been monitored by; (1) glaciological and hydrological methods, and (2) satellite gravimetric methods using data from NASA’s Gravity Recovery and Climate Experiment (GRACE) satellite mission. However, the former can be logistically costly and have large extrapolation errors: measurements taken at monthly temporal scales are expensive and have a spatial resolution of roughly one kilometer. The latter provides monthly mass-balance estimates of aggregates of alpine glaciers, although the spatial resolution (~300 km) is far too coarse for assessing individual glaciers’ mass balance. Ground-based, time-lapse microgravity measurements can potentially overcome some of the disadvantages of the glaciological, hydrological, and satellite gravitational methods for assessing mass changes and their spatial distribution on a single glacier. Gravity models were utilized to predict the gravity signals of the summer-time mass balance, changes in the seasonal snow cover outside of the glacier, and the vertical gravity gradient (VGG) needed for the free-air correction on Wolverine Glacier, AK. The modeled gravity signal of the summer-time mass balance (average of -0.237 mGal) is more than an order of magnitude larger than the uncertainty of conventional relative gravimeters (±0.007 mGal). Therefore, modeling predict that the time-lapse gravitational method could detect the summer-time mass balance on Wolverine Glacier. The seasonal snow effect was shown to have the greatest influence (~ -0.15 mGal) on the outer 100 m boundary of the glacier and minimal effect (~ -0.02 mGal) towards the center, both larger than the uncertainty of relative gravimeters. The VGG has a positive deviation, about -0.1 to -0.2 mGal/m, from the normal VGG (-0.309 mGal/m). Thus, seasonal snow effect and VGG need to be correctly accounted for when processing gravity measurements to derive the residual gravity signal of the glacier mass balance. Accurate measurements of elevation changes, seasonal snow depth, and the VGG should be performed in future gravity surveys of glaciers.Geolog
Quantifying Post-Fire Aeolian Sediment Transport Using Rare Earth Element Tracers
No full textGrasslands provide fundamental ecosystem services in many arid and semi-arid regions of the world, but are experiencing rapid increases in fire activity making them highly susceptible to post-fire accelerated soil erosion by wind. A quantitative assessment that integrates fire-wind erosion feedbacks is therefore needed to account for vegetation change, soil biogeochemical cycling, air quality, and landscape evolution. We investigated the applicability of a novel tracer technique – the use of multiple rare earth elements (REE) - to quantify aeolian soil erosion and to identify sources and sinks of wind-blown sediments in a burned and unburned shrub-grass transition zone in the Chihuahuan desert, NM, USA. Results indicate that the horizontal mass flux of wind-borne sediment increased approximately three times following the fire. The REE-tracer analysis of aeolian sediments shows that an average 88% of the horizontal mass flux in the control area was derived from bare microsites, whereas at the burned site it was derived from shrub and bare microsites, 42% and 39% respectively. The vegetated microsites, which were predominantly sinks of aeolian sediments in the unburned areas, became sediment sources following the fire. The burned areas exhibited a spatial homogenization of sediment tracers, highlighting a potential negative feedback on landscape heterogeneity induced by shrub encroachment into grasslands. Though fires are known to increase aeolian sediment transport, accompanying changes in the sources and sinks of wind-borne sediments likely influence biogeochemical cycling and land degradation dynamics. Our experiment demonstrated that REEs can be used as reliable tracers for field-scale aeolian studies.GeologyAccompanied by one compressed .zip file: MET_Tower_Data.zi
EVALUATION OF LAND, SOIL, WATER, AND VEGETATION-RELATED ECOSYSTEM SERVICES AND TRADEOFFS AT UTILITY-SCALE SOLAR PHOTOVOLTAIC FACILITIES
No full textSolar photovoltaics are a low-emission electricity source, but utility-scale development of ground-mounted PV may displace natural or agricultural land and compromise the land’s ability to provide ecosystem services. Co-locating solar photovoltaics with vegetation (sometimes referred to as “agrivoltaics”) could provide a sustainable solution to meet growing food and energy demands while minimizing the land-use impacts of solar energy. Pilot-scale experiments and modeling studies have shown potential for microclimatic alterations by the solar photovoltaics (PV) and the soil-vegetation components of a co-located system to benefit each other. One predicted co-benefit is cooling of PV modules caused by diversion of sensible heat to latent heat for evapotranspiration in the understory vegetation during the growing season. Field experiments that validate the theorized co-benefits within a utility-scale co-located system are less common. Since a large percentage of current and future land use conversions for utility-scale solar energy developments are estimated to occur on farmlands, validation of co-benefits in utility-scale co-located systems are critical for determining the outcome of co-location in a wide range of physical conditions and optimizing the system design for the environmental co-benefits. In the first study of its kind and scale, three years (2019 – 2021) of microclimate and soil data at three vegetated utility-scale solar plants in Minnesota were tied to the power output data from the corresponding period to examine the influence of ground cover on the PV performance and that of the arrays on the underlying soil and vegetation. Soil moisture, soil temperature, air temperature, relative humidity, wind direction/speed were recorded at a 15-minute interval at three treatments: PV arrays with a vegetated ground cover (“veg PV”), PV arrays with a bare ground cover (“bare PV”), and a nearby open space with the same vegetation as that in veg PV (control). Solar irradiance and cumulative precipitation were also recorded in the control. While air temperature and relative humidity were not significantly different between the veg PV and the bare PV, soil moisture was lowest in the bare PV treatment and comparable between the veg PV and the control. Soil moisture also varied spatially along the transect perpendicular to the array, though the spatial distribution was not consistent between the treatments and different facilities. Soil temperature was the lowest in the veg PV and the highest in the control, implying that the partial shade from the solar array keeps the underlying soils cooler. Cooler soil temperature in PV arrays could be a buffer for plants during periods of drought, which implies that co-located systems could be implemented in ecosystem restoration projects for climate resilience.
In addition to the microclimate variables, panel temperature was also recorded at veg PV and bare PV treatments and electricity generation data from the corresponding treatments during the study period was provided by the operators of the facilities. Neither vegetation-driven panel cooling nor the increased power output was observed in the veg PV: the bare PV had higher output and panel temperatures than the veg PV in the early mornings, which may imply that the observed difference in output may be due to shading of the panels in the veg PV treatment by the co-located vegetation. The differential of total daily production (bare PV – veg PV) was positive on most days, though the mode in a frequency distribution of the differential was centered around a very small positive value. The lack of panel-cooling in the veg PV was determined to be due to the short rainfall interval (1-2 days) during the study period. Because of the frequent rainfalls, evaporation in the bare PV treatment and evapotranspiration process in the veg PV treatment remained in an energy-limited stage, and the water would evaporate more rapidly from the bare soil that is more exposed to sunlight and wind. In a drier environment with infrequent rainfalls, evaporation and evapotranspiration would be moisture-limited most of the times, and plants may be able to transpire water from deeper in the soil over a longer period of time to cool the overlying panels, given enough irrigation. The lack of panel cooling in our field sites implies that such environmental co-benefits are likely to be climate dependent, which indicates the need for further study of the influence of the vegetation on the PV operation and vice-versa at large-scale solar facilities in varying climate zones.
Soil samples were also collected for grain size analysis using laser diffraction and nutrient analysis using standard combustion methods. In the sandy soils at the Chisago facility, the bare PV treatment had significantly less clay portion than the veg PV treatment and the control. On the other hand, the clay percentages did not significantly differ among the three treatments in the other two facilities with higher background clay contents (Atwater and Eastwood). The loss in total carbon, nitrogen, and soil cations was also the most pronounced in the bare PV in a facility with the sandy soil. Maintenance of vegetation or re-vegetation while minimizing land grading may protect the soil’s ability to store carbon and nutrients, and that effect may be magnified in coarse-textured soils or ones whose carbon and nutrient storage capacity is otherwise compromised. Overall, the field investigation found that the occurrence of some of the environmental co-benefits of co-locating PV with vegetation depended on the climate and soil, prompting a need for case-by-case consideration of these variables to identify which of the co-benefits will be achievable.
Extensive solar PV development to meet energy demand and decarbonize the energy grid will significantly impact the landscape. Co-location offers an opportunity to mitigate the potential negative impacts of utility-scale solar energy, while still meeting sustainable development goals. A system dynamics model is developed to compare the regional land occupation, water usage, carbon emissions, and change in soil carbon storage resulting from solar development using two different development strategies: traditional, in which the land is graded and vegetation is removed, and co-location, in which land grading is minimized and the soil is re-vegetated with native vegetation. The model is applied in two water-sensitive semi-arid regions with high technical potential for solar energy where agriculture is an important element of the local economy. First, Rajasthan, India is undergoing rapid expansion of solar PV to address the growing energy demand while meeting sustainable energy development goals in a developing economy. The results show that at the current growth rate of solar energy in Rajasthan, solar energy will grow to more than 500 GW by 2070 and will occupy a land area equivalent to 20% to 95% of the unused land suitable for solar. Second, the Central Valley of California has a mature power system in a mature economy seeking to decarbonize. The results show that the overall capacity of California’s solar energy in 2070 will be less than a fifth of Rajasthan’s and occupy at most 10% of California’s unused land suitable for solar. Consequently, soil carbon loss due to future solar capacity additions under conventional development strategy will be similarly smaller in California than in Rajasthan. Together, the results show that the opportunity for the mitigation of the negative impacts of energy development may be greater in younger economies with a developing grid network.Geoscienc
Spatial Analysis of Post-Fire Sediment Redistribution Using Rare Earth Element Tracers
No full textMany grasslands in arid and semi-arid regions are undergoing rapid changes in vegetation, including encroachment of woody plants and invasive grasses, which can alter the rates and patterns of fire and sediment transport in these landscapes. We investigated the spatial distribution of sediments at the scale of vegetated microsites for three years following a prescribed fire using a multiple rare earth element (REE) tracer-based approach in a shrub-grass transition zone in the northern Chihuahuan desert (New Mexico, USA). To this end, we applied REE tracers – holmium, europium, and ytterbium on shrub, grass, and bare microsites, respectively in March 2016. Soil samples were collected from both burned and control (not burned) sites before (March) and after (June) the annual windy season, from 2016 through 2018. Results indicate that although the horizontal mass flux (HMF) of wind-borne sediment increased approximately threefold in the first windy season following the fire, and the HMF of both plots were not significantly different after three windy seasons. Comparing REE concentrations in sediments from both plots over the three years and three annual windy seasons, we observed a post-fire shift in source and sink dynamics of sediments. The tracer analysis of wind-borne sediments indicated that the source of the HMF in the burned site was mostly derived from shrub microsites following the fire, whereas the bare microsites were the major contributors for aeolian sediment in control areas. The shift in sources and sinks, and the spatial homogenization of REEs indicate that the removal of shrub vegetation resulted in sediment redistribution to the bare microsites even three years after the prescribed fire. The findings of this study will improve our understanding of post-fire geomorphic processes at a microsite scale in a grassland ecosystem undergoing land degradation induced by shrub encroachment.Geolog
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