Changes In Microtopography Research Articles

Soil micro-topography change detection at hillslopes in fragile Mediterranean landscapes

Measuring soil surface changes at field scale can be an important tool to analyse sediment connectivity and may contribute to a better understanding of processes causing soil detachment and transport. Recent technological and algorithmic developments in high resolution topography measurement techniques enable to capture field plots with high spatial resolution and at varying temporal frequencies using UAV photogrammetry (SfM+MVS) and/or terrestrial LiDAR devices. In this study, three large areas of interest (600–2400m2) in Andalusia, Spain, are investigated during an observation period of 2years. Field campaigns were conducted immediately before and after single intense precipitation events in spring and autumn to capture surface changes caused by torrential rainfall. Accuracies and resolution achieved are below 8.5 and 10mm, respectively. An approach is used to utilise UAV and TLS point cloud data in a synergetic manner considering surface properties and data acquisition schemes. Besides the calculation of DEMs of difference to measure height changes, isotropic and anisotropic roughness is calculated to measure its influence on across- and along-slope runoff formation. On the one hand, detected surface changes reveal that the estimation of soil erosion is not possible using HiRT methods alone due to processes such as compaction, consolidation, swelling and shrinkage. Surface height shifts due to non-erosive processes amount to 26mm. On the other hand, the HiRT measurement of these processes with large area coverage enables the detection of spatio-temporally variable micro-topographic changes, not seen before, e.g. plant and soil type influenced circular patterns and rill attenuation as well as re-appearance of former soil tillage tracks due to varying soil bulk densities.

Evapotranspiration across plant types and geomorphological units in polygonal Arctic tundra

Coastal tundra ecosystems are relatively flat, and yet display large spatial variability in ecosystem traits. The microtopographical differences in polygonal geomorphology produce heterogeneity in permafrost depth, soil temperature, soil moisture, soil geochemistry, and plant distribution. Few measurements have been made, however, of how water fluxes vary across polygonal tundra plant types, limiting our ability to understand and model these ecosystems. Our objective was to investigate how plant distribution and geomorphological location affect actual evapotranspiration (ET). These effects are especially critical in light of the rapid change polygonal tundra systems are experiencing with Arctic warming. At a field site near Barrow, Alaska, USA, we investigated the relationships between ET and plant cover in 2014 and 2015. ET was measured at a range of spatial and temporal scales using: (1) An eddy covariance flux tower for continuous landscape-scale monitoring; (2) An automated clear surface chamber over dry vegetation in a fixed location for continuous plot-scale monitoring; and (3) Manual measurements with a clear portable chamber in approximately 60 locations across the landscape. We found that variation in environmental conditions and plant community composition, driven by microtopographical features, has significant influence on ET. Among plant types, ET from moss-covered and inundated areas was more than twice that from other plant types. ET from troughs and low polygonal centers was significantly higher than from high polygonal centers. ET varied seasonally, with peak fluxes of 0.14mmh−1 in July. Despite 24 hours of daylight in summer, diurnal fluctuations in incoming solar radiation and plant processes produced a diurnal cycle in ET. Combining the patterns we observed with projections for the impact of permafrost degradation on polygonal structure suggests that microtopographic changes associated with permafrost thaw have the potential to alter tundra ecosystem ET.

Hydrodynamic effects of macrophyte microtopography: spatial consequences of interspecific benthic transitions

Rhizophytic green algae of the genus Caulerpa are potential competitors with seagrass-dominated habitats. At Cadiz Bay Natural Park, Caulerpa prolifera and the seagrass Cymodocea nodosa co-occur in overlapping patches, which may be considered as transition zones. In these zones, changes in microtopography are stepped because patches of C. prolifera normally occur at 5 to 10 cm above the adjacent C. nodosa patches. We hypothesized that hydrodynamics influenced by this microtopography may foster sedimentation on the C. nodosa side, which in turn would facilitate the spreading of C. prolifera. To test this hypothesis, an experiment simulating the flow between both species was conducted in a race-track flume tank, allowing us to study the influence of unidirectional free stream velocity (low velocity, LV = 0.065 m s-1, vs. high velocity, HV = 0.14 m s-1) and microtopography (flat bottom, FB, vs. stepped bottom, SB) on shear stress (τ), turbulent kinetic energy above the canopy (TKEabove) and volumetric flow rate through the canopy (Qc). Under our experimental conditions, comparison of τ-values with theoretical thresholds revealed sedimentation scenarios. However, at HV, the probability of sedimentation was higher in C. nodosa than in C. prolifera patches. Moreover, Qc was higher within C. nodosa canopies than within C. prolifera, ensuring a higher source of sediment with potential to be trapped within the canopy. Although we found no species-specific differences in TKEabove values, they increased with HV increasing the vertical mixing. Overall, conditions for sedimentation seemed more facilitated in C. nodosa than in C. prolifera in SB only under HV conditions.

Application of Digital Elevation Model (DEM) for description of soil microtopography changes in laboratory experiments

Abstract In the study we evaluated spatial and quantitative changes in soil surface microtopography to describe water erosion process under simulated rain with use of a non-contact optical 3D scanner. The experiment was conducted in two variants: with and without drainage layer. Two clay soils collected from farmlands from the catchment of lake Zgorzała (Warsaw) were investigated. Six tests of simulated rain were applied, with 55 mm·h−1. The surface roughness and microrelief were determined immediately after every 10 min of rainfall simulation by 3D scanner. The volume of surface and underground runoff as well as soil moisture were measured. The surface points coordinates obtained while scanning were interpolated using natural neighbour method and GIS software to generate Digital Elevation Models (DEM) with a 0.5 mm resolution. Two DEM-derived surface roughness indices: Random Roughness (RR) and Terrain Ruggedness Index (TRI) were used for microrelief description. Calculated values of both roughness factors have decreased with time under the influence of rainfall in all analyzed variants. During the sprinkling the moisture of all samples had been growing rapidly from air-dry state reaching values close to the maximum water capacity (37–48% vol.) in 20–30 min. Simultaneously the intensity of surface runoff was increasing and cumulative runoff value was: 17–35% for variants with drainage and 72–83% for the variants without drainage, relative to cumulative rainfall. The observed soil surface elevation changes were associated with aggregates decomposition, erosion and sedimentation, and above all, with a compaction of the soil, which was considered to be a dominant factor hindering the assessment of the erosion intensity of the of the scanned surface.

Insight into sediment transport processes on saline rangeland hillslopes using three‐dimensional soil microtopography changes

AbstractIn arid and semi‐arid rangeland environments, an accurate understanding of runoff generation and sediment transport processes is key to developing effective management actions and addressing ecosystem response to changes. Yet, many primary processes (namely sheet and splash and concentrated flow erosion, as well as deposition) are still poorly understood due to a historic lack of measurement techniques capable of parsing total soil loss into these primary processes. Current knowledge gaps can be addressed by combining traditional erosion and runoff measurement techniques with image‐based three‐dimensional (3D) soil surface reconstructions. In this study, data (hydrology, erosion and high‐resolution surface microtopography changes) from rainfall simulation experiments on 24 plots in saline rangelands communities of the Upper Colorado River Basin were used to improve understanding on various sediment transport processes. A series of surface change metrics were developed to quantify and characterize various erosion and transport processes (e.g. plot‐wide versus concentrated flow detachment and deposition) and were related to hydrology and biotic and abiotic land surface characteristics. In general, erosivity controlled detachment and transport processes while factors modulating surface roughness such as vegetation controlled deposition. The extent of the channel network was a positive function of slope, discharge and vegetation. Vegetation may deflect runoff in many flow paths but promoted deposition. From a management perspective, this study suggests that effective runoff soil and salt load reduction strategies should aim to promote deposition of transported sediments rather than reducing detachment which might not be feasible in these resource‐limited environments. Copyright © 2016 John Wiley & Sons, Ltd.

Performance of the Rangeland Hydrology and Erosion Model for runoff and erosion assessment on a semiarid reclaimed construction site

The ability to assess the impact of management actions on soil and water resources is crucial to sustainable land management. The Rangeland Hydrology and Erosion Model (RHEM) was developed as an assessment and decision support tool for resource management agencies and has been used to estimate soil erosion at national, regional, and local scales for both disturbed and undisturbed rangeland soil and vegetation conditions. In this paper, runoff, sediment, and microtopography data were collected during a series of rainfall simulation experiments aimed at evaluating the effectiveness of revegetation on a shrub-dominated post-construction hillslope where the soil has had time to reconsolidate. RHEM9s input parameters are simple to collect and consist of soil texture, slope configuration, and canopy and ground cover. Experimental results showed that a mix of the shrub species rabbitbrush (<i>Chrysothamnus nauseosus</i>) and the invasive annual grass cheatgrass (<i>Bromus tectorum</i>) were more effective at reducing runoff and soil loss than rabbitbrush alone. Plots with more than 45% of residue cover produced as much as 2.1 times less runoff and 16 times less sediments than those with less than 15% of litter. Microtopographic changes information allowed partitioning the erosion process into diffuse and concentrated flow processes. Analysis of this 3D data highlighted the central role of concentrated flow erosion in sediment delivery on rangeland hillslopes. RHEM9s performance as expressed by the coefficient of determination, <i>R</i>², and the Nash-Stucliffe Efficiency (NSE) was <i>R</i>² = 0.84 and NSE = 0.27 for runoff and <i>R</i>² = 0.81 and NSE = 0.26 for sediments. This study demonstrates that RHEM can be effectively used by land managers and project managers to estimate soil erosion as a function of precipitation event on construction sites that have been revegetated to rangeland plant communities.

Spatial and temporal variation of the soil moisture regime along a hillslope segment and a small mountain catchment

Relationship between spatial patterns of soil moisture pressure head, soil depth and topography is important to understand factors controlling the dynamics of infiltrated rainwater into the soil matrix. We analysed the spatial and temporal variability of soil moisture pressure head in a small catchment (0.2 ha) and along a heavily instrumented hillslope transect (25 m long) within a roaded catchment in the Fudoji experimental watershed, Shiga, Japan. We monitored these variations at different depths on 51 observation nodes on both sites. The pressure head measurements on the hillslope segment located within the roaded catchment revealed the importance of topography and geomorphic processes in dictating the propagation of the soil water pressure head. Geomorphic process strongly contributed to the variability in soil depth and soil vertical profiles of the upper, middle and lower parts of the hillslope segment. Similarly, results from systematically installed observation nodes on the small catchment shows a spatially organised soil moisture variation with depth in a relatively flat segment of the planar topographic unit. The changes in micro-topography and soil depth highly dictate the routing of infiltrated water to downslope sections and thus the amount of water stored in the soil profiles.

Erosion processes in black marl soils at the millimetre scale: preliminary insights from an analogous model

Abstract. To investigate the millimetre-scale surface processes caused by natural rainfall, an undisturbed sample of badlands soil (1 m long, 0.5 m wide and 0.15 m thick) was carefully extracted. The sample is composed of black marl soil from a badlands area of the Draix Observatory (SE France). After extraction, the undisturbed sample was placed at the same slope angle (45°) as its original orientation and was then monitored for several processes via a terrestrial laser scanner (TLS) with millimetre-scale accuracy and resolution. This experiment identified several surface processes interpreted as micro-landslides, swelling of the black marl material and lateral expansion that closed desiccation cracks. These micro-processes illustrate the complexity of the surface micro-topography changes that control erosion and infiltration rates over time.

Source of error and uncertainty in sheet erosion rates estimated from dendrogeomorphology

AbstractDendrogeomorphology has been used since the 1960s to estimate sheet erosion rates. To date, most efforts have focused on accurately determining the first year of root exposure. However, an adequate methodological approach that takes into consideration the microtopography of the ground surface when estimating sheet erosion rates using dendrogeomorphology has not been proposed. In this study, terrestrial laser scanning (TLS) was used for the first time to examine how changes in microtopography determine the level of certainty in estimates. To this end, highly accurate TLS‐based digital elevation models representing exposed roots and their immediate vicinity were analysed using geographic information system tools. The results indicate that erosion rates calculated using the standard dendrogeomorphic method have been underestimated by up to 29% because the method does not take into account changes to the microtopography caused by the axial and radial pressure of the roots. Another source of uncertainty, which we estimate to be 50%, was also found and is the result of changes in the ground surface microtopography caused by variations in soil roughness. These findings do not invalidate the usefulness of dendrogeomorphology for assessing soil erosion, although they do show the need for correct characterization of the microtopography to guarantee reliability. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Soil physical properties of selected soil series in relation to compaction and erosion on farmers’ fields at Abeokuta, southwestern Nigeria

This study evaluated physical properties of selected soil series and their implications on the soil compaction and erosion in Abeokuta, southwestern Nigeria. Daily rainfall data (1999–2007) were collected to estimate the rainfall erosivity. Seven soil series (Iwo, Iseyin, Ekiti, Jago, Okemesi, Apomu, and Egbeda) were sampled from 0–15, 15–30, and 30–50 cm depths for particle size distribution, organic carbon, pH, upper plastic limit, and compactibility (Proctor test). Microtopographical changes along and across toposequences of two farmers’ fields cleared mechanically and manually, respectively, were monitored using the erosion pin method. Mean annual erosivity (EI30) was high (7646 MJ mm ha−1 hr−1). Particle size, organic carbon, and pH were similar (p ≥ 0.05), while upper plastic moisture was ≤ 2% among different soil series. Soil-moisture density curves indicated a maximum bulk density of 1.77–1.99 g cm−3 for a moisture range of 7.6–14%; while the soils were prone to compaction at low moisture content. Microtopographic changes were found between –2 and 0 cm and –8 and –2 cm on mechanically and manually cleared farmland, respectively. Spatial dependence showed that the soil erosion could be predicted within 5–8 m distance. To avoid erosion and compaction, soil water content should be less than 7.6% before the introduction of mechanical tillage.

Quantifying soil surface change in degraded drylands: Shrub encroachment and effects of fire and vegetation removal in a desert grassland

Woody plant encroachment, a worldwide phenomenon, is a major driver of land degradation in desert grasslands. Woody plant encroachment by shrub functional types ultimately leads to the formation of a patchy landscape with fertile shrub patches interspaced with nutrient‐depleted bare soil patches. This is considered to be an irreversible process of land and soil degradation. Recent studies have indicated that in the early stages of shrub encroachment, when there is sufficient herbaceous connectivity, fires (prescribed or natural) might provide some reversibility to the shrub encroachment process by negatively affecting shrub demography and homogenizing soil resources across patches within weeks to months after burning. A comprehensive understanding of longer term changes in microtopography and spatial patterning of soil properties following fire in shrub‐encroached grasslands is desirable. Here, we investigate the changes in microtopography with LiDAR (light detection and ranging), vegetation recovery, and spatial pattering of soil properties in replicated burned, clipped, and control areas in a shrub‐grass transition zone in the northern Chihuahuan Desert four years after prescribed fire or clipping. Results indicate a greater homogeneity in soil, microtopography, and vegetation patterning on burned relative to clipped and control treatments. Findings provide further evidence that disturbance by prescribed fire may allow for reversal of the shrub encroachment process, if the event occurs in the early stages of the vegetation shift. Improved understanding of longer‐term effects of fire and associated changes in soil patterning can inform the use and role of fire in the context of changing disturbance regimes and climate.

On Influence of Change in Anodic Surface Micro-Topography on Electric Current Field in Electrochemical Finishing

In processing of electrochemical finishing (ECF), electrochemical dissolution makes anodic surface micro-topography change. To identify the influence of the change on the distribution of electric-current field between electrodes, mathematical model describing the distribution of the electric-current field along the profile of the anodic surface micro-topography was established. The results of simulations and experiments show that the variation in the anodic surface micro-topography makes the distribution density of the electric-current uniform, and the sharp or peak-like micro-topography is in favour of improving the finishing ability of ECF.

Effect of fire on solute release from organic horizons under larch forest in Central Siberian permafrost terrain

To evaluate the effects of forest fire and post-fire stand recovery on the organic layer chemistry and solute release within mound and trough microrelief elements (termed earth hummock microtopography) that mainly distribute permafrost affected area, we chose five fire plots (larch forests burned in 1951, 1981, 1990, 1994 and 2005) paired with adjacent control plots in mature larch forests in Central Siberian permafrost terrain. We determined total carbon, nitrogen and ash content in solid organic soils, and analyzed total carbon, nitrogen, bases and major anions in water extracts. There was a significant correlation between water-extracted organic carbon (WEOC) and total carbon (kg m −2) in area basis, implying that the quantity of total carbon was a major factor in WEOC production. WEOC correlated negatively with pH, indicating strong control by organic horizons (organic solute leaching) on soil acidity and base cation dynamics. The sum of water extractable base cations was also correlated significantly to total carbon, indicating that cations can be released through organic matter decomposition. Organic horizons in troughs in burned plots released greater amounts of Ca, Mg and K than those in mounds, probably due to greater content of organic matter as a cation source. Anions including nitrate and phosphate and WEOC also accumulated in trough depressions, due probably to organic matter degradation. The contrasting distribution of solutes between mounds and troughs in burned plots seems to be controlled by organic horizon development via changes in microtopography after forest fires.

Invasive plants and plant diversity as affected by groundwater depth and microtopography in the Great Basin

ABSTRACTWe evaluated invasive exotic weeds and plant species diversity in relation to depth to groundwater (DTW) and microtopography in areas with DTW from 0·3–4 m in Owens Valley, California. Transects dominated by common plant species of the area were read at 1‐cm intervals, and species cover was obtained at different scales: 1‐m transect portions (microsites), whole transects (68 m average length), and the whole study area. Species richness and the Shannon–Wiener diversity index were obtained in microsites. DTW and microtopographical variation (soil‐surface relative elevations) were jointly measured along the vegetation transects. Found in 34% of the sampled transects, the annual Bassia hyssopifolia was the most common exotic weed of the area. Its cover in the whole study area was only 0·9%, but it was the second most dominant species (19% cover) in microsites. B. hyssopifolia coexisted mainly with herbaceous species, typically in places with shallow groundwater (average &lt;1·5 m) and microtopographical depressions. However, B. hyssopifolia cover was not affected by variations in DTW or relative elevation. In contrast, B. hyssopifolia cover was negatively associated with perennial cover and species richness. Species diversity (Shannon–Wiener) slightly decreased with the increase in DTW but not with changes in microtopography. In contrast, species richness clearly varied with the identity of the dominant species in microsites. Our study suggests that the variation in community‐intrinsic factors such as competition and diversity may play a greater role in the growth of invasive plants than the variation in physical factors such as groundwater and microtopography. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Role of microtopography in rainfall‐runoff partitioning: An analysis using idealized geometry

Microtopography, consisting of small‐scale excursions in the elevation of the land surface on millimeter to centimeter scales, is ubiquitous on hillslopes, but its effects are rarely incorporated into hydrological analyses of rainfall‐runoff partitioning. To progress toward a hydrological theory that accounts for microtopography, two research questions are considered: (1) Does microtopography change the partitioning of rainfall into runoff and infiltration compared to a background case that lacks these small‐scale excursions? and (2) how do soil, mean slope, storm properties, and microtopographic geometric attributes influence this partitioning? To address these questions, a simplified one‐dimensional hillslope with uniform sinusoidal microtopography is considered, and several rainfall‐runoff scenarios are examined with a numerical model. The results indicate that for a range of realistic conditions, microtopography increases the proportion of rainfall infiltrating by 20–200% relative to an equivalent “background state” in which microtopography is absent. Additional theoretical development addressing issues of connectivity and improved representations of flow hydraulics over microtopographic surfaces are needed to refine these estimates and extend them to less idealized conditions. If confirmed, the results suggest that microtopography may have a significant impact on streamflow generation, plant water availability and the co‐evolution of geomorphic, hydrological and ecological systems, with important implications for land management, especially in arid ecosystems.

Reconstruction of subgrid‐scale topographic variability and its effect upon the spatial structure of three‐dimensional river flow

A new approach to describing the associated topography at different scales in computational fluid dynamic applications to gravel bed rivers was developed. Surveyed topographic data were interpolated, using geostatistical methods, into different spatial discretizations, and grain‐size data were used with fractal methods to reconstruct the microtopography at scales finer than the measurement (subgrid) scale. The combination of both scales of topography was then used to construct the spatial discretization of a three‐dimensional finite volume Computational Fluid Dynamics (CFD) scheme where the topography was included using a mass flux scaling approach. The method was applied and tested on a 15 m stretch of Solfatara Creek, Wyoming, United States, using spatially distributed elevation and grain‐size data. Model runs were undertaken for each topography using a steady state solution. This paper evaluates the impact of the model spatial discretization and additional reconstructed‐variability upon the spatial structure of predicted three‐dimensional flow. The paper shows how microtopography modifies the spatial structure of predicted flow at scales finer than measurement scale in terms of variability whereas the characteristic scale of predicted flow is determined by the CFD scale. Changes in microtopography modify the predicted mean velocity value by 3.6% for a mesh resolution of 5 cm whereas a change in the computational scale modifies model results by 60%. The paper also points out how the spatial variability of predicted velocities is determined by the topographic complexity at different scales of the input topographic model.

The Impacts of Micro-Topographic Changes on Mangroves in the Lower Reaches of the Benin River, Niger Delta

The Impacts of Micro-Topographic Changes on Mangroves in the Lower Reaches of the Benin River, Niger Delta

Development and Application of Digital Elevation Model Rectification Method in Monitoring Soil Microtopography Changes During Rainfall

The soil microtopography has a great impact on soil-water interactions during rainfall. The objectives of this study were to develop methods to rectify the digital elevation model (DEM) generated by the automated digital photogrammetry system and to apply these methods in monitoring the changes in soil microtopography during rainfall. Two rectification methods were used in order to detect and eliminate the DEM errors. The first method was the reference surface method (RSM), which was developed as a part of this study to detect the DEM errors prior to interpolation. The second was the parametric statistical method (PSM), which was used to detect and rectify the DEM errors after interpolation. The DEMs accuracy was assessed using the difference between the measured and photogrammetrically estimated checkpoints coordinate and elevation (x, y and z, respectively) values. The root mean square error (RMSE) in x-direction, y-direction and z-direction of the checkpoints were 2.08, 2.59 and 1.96 mm, respectively. The changes on the soil surface were assessed using three roughness indices. The soil surface random roughness (RR), the limited elevation difference (LD) and the limited slope (LS) indices decreased with the time. The automated digital photogrammetric system with the rectification methods accurately generated three dimensional (3D) visions of the soil microtopography during rainfall. It gives a new insight for monitoring the changes of soil microtopography and the effects on soil-water interaction processes.

Calcium adsorption and changes of the surface microtopography of cyanobacteria studied by AFM, CFM, and TEM with respect to biogenic calcite nucleation

We investigated calcium interactions with the surface of individual living cells of the freshwater cyanobacterium Synechococcus leopoliensis PCC 7942 under illumination and calcite supersaturation, with respect to calcium carbonate nucleation on the cell surface. Immobilized living cells were scanned by Atomic Force Microscopy (AFM) with conventional and chemically modified tips which were coated with carboxylic groups, so‐called Chemical Force Microscopy (CFM). Calcium adsorption was heterogeneous and altered the surface charge of the cells. This was confirmed by bulk measurements of the zeta‐potential at different Ca2+ concentrations and compared to measurements made with other bivalent cations (Mg2+, Sr2+, Ba2+). Zeta‐potential increased rapidly (&lt;2 min) from −46.9 mV in calcium‐free solution to +0.8 mV in 22 mmol L−1 CaCl2 solution, using a 1.5 mmol L−1 NaHCO3 solution as background electrolyte in both cases. This was followed by the slow (several hours) formation of nonmineralized protuberances at the cell surface. These changes in the microtopography did not show obvious spatial relationship to surface charge or Ca2+ adsorption. The formation of the protuberances was reversible when Ca2+ was removed from the circumfluent solution. Ca2+ adsorption to the cell surface was faster than calcium‐induced changes in the surface microtopography and much faster than calcite nucleation on the cell surface which was observed on a fraction of the cells in previous bulk experiments under similar supersaturation.

Do vehicle track disturbances affect the productivity of soil‐growing lichens in a fog desert?

Summary 1The re-establishment of soil-crust lichens following disturbances may be enhanced or discouraged by human-altered microtopographies. This research asks whether such microtopographic changes alter microclimates significantly, and whether changes affect metabolically active periods of recolonizing lichens. 2In the fog-driven Namib Desert, the water relations of five lichen species were investigated and photosynthetic activity (PSII) was assessed via chlorophyll a fluorescence under natural and altered conditions, based on measured microclimates in vehicular disturbances. 3Surface temperatures in vehicle tracks were significantly higher than controls by up to 2 °C. Fog deposition was significantly lower in tracks, and evaporation rates were higher. 4Foliose and fruticose lichens retained fog moisture for long periods, and carried out PSII at low relative moisture contents. Desiccation rates of lichens were estimated to increase by 36% in tracks, which reduces PSII durations by as much as 50% in the critical hours following sunrise. Lecidella crystallina was least affected due to a pre-existing low water-holding capacity. Extreme temperatures (>45 °C) halted PSII in certain species. 5These results illustrate the importance of temperature–moisture ratios on desert soil surfaces. Reduced periods of photosynthesis caused by human-induced microtopographic changes, as predicted here, may have important ecological implications by reducing productivity in lichen communities.