Quantifying the Spatiotemporal Variation of Evapotranspiration of Different Land Cover Types and the Contribution of Its Associated Factors in the Xiliao River Plain

Evapotranspiration (ET) is a vital constituent of the hydrologic cycle. Researching changes in ET is necessary for understanding variability in the hydrologic cycle. Although some studies have clarified the changes and influencing factors of ET on a regional or global scale, these variables are still unclear for different land cover types due to the range of possible water evaporation mechanisms and conditions. In this study, we first investigated spatiotemporal trends of ET in different land cover types in the Xiliao River Plain from 2000 to 2019. The correlation between meteorological, NDVI, groundwater depth, and topographic factors and ET was compared through spatial superposition analysis. We then applied the ridge regression model to calculate the contribution rate of each influencing factor to ET for different land cover types. The results revealed that ET in the Xiliao River Plain has shown a continuously increasing trend, most significantly in cropland (CRO). The correlation between ET and influencing factors differed considerably for different land cover types, even showing an opposite result between regions with and without vegetation. Only precipitation (PRCP) and NDVI had a positive impact on ET in all land cover types. In addition, we found that vegetation can deepen the limited depth of land absorbing groundwater, and the influence of topographic conditions may be mainly reflected in the water condition difference caused by surface runoff. The ridge regression model eliminates multicollinearity among influencing factors; R2 in all land cover types was over 0.6, indicating that it could be used to effectively quantify the contribution of various influencing factors to ET. According to the results of our model calculations, NDVI had the greatest impact on ET in grass (GRA), cropland (CRO), paddy (PAD), forest (FOR), and swamp (SWA), while PRCP was the main influencing factor in bare land (BAR) and sand (SAN). These findings imply that we should apply targeted measures for water resources management in different land cover types. This study emphasizes the importance of comprehensively considering differences among various hydrologic cycles according to land cover type in order to assess the contributions of influencing factors to ET.

Optimized Main Ditch Water Control for Agriculture in Northern Huaihe River Plain, Anhui Province, China, Using MODFLOW Groundwater Table Simulations

Controlled drainage by regulating the groundwater level in open ditches is necessary to ensure the normal growth of crops in Northern Huaihe River Plain, China. The groundwater model MODFLOW was calibrated and validated in a representative area, and was then conducted to simulate the groundwater under different main drainage ditch water depth control schemes during the growth period of corn and wheat. Then the scenario with highest water depth (Scenario 20) from 1989 to 2019 was simulated, and the annual cumulative drought and waterlogging intensity (ACDWI) were analyzed in each decade and in different hydrological years. The results showed that the study area was dominated by drought stress. The lowest level of drought stress was achieved under Scenario 20. The frequency of drought gradually decreased from north to south in the study area. Moreover, the ACDWI decreased with increase of precipitation during 1989 to 2019. The results indicated that it was important to store water during the dry season, while it is also necessary to control the drainage in the rainy season to drain excess water on time. The results suggested that the water depth of the main drainage ditch should be regulated by zoning and by season to alleviate crop drought and waterlogging.

Sediment Load Concentration and Resultant Channel Planform in the Lower Gandak Plain

Erosion, transportation and deposition by running water are closely related and these works are performed in association and not in isolation. One cannot be performed without others. These works are determined on other factors like topography, geology, structure and composition of rocks, slope, amount of water availability and its characteristics, climate etc. Huge catchment area of the Gandak River is lying in the Himalayan mountainous region. This region is receiving good amount of rainfall concentrated in four months of monsoonal period June to September (JJAS). This period has also high temperatures leading to large amount of glacial ice melt. Hence, enormous water is drained off the mountain steep slope. The Himalaya is very young and has fragile rocks and ecosystem. Anthropogenic activities in those areas are primary cause, apart from natural weathering, for generation of more and more shattered materials which are brought by running water downstream much easily. Therefore, highly sediment concentrated water brings large quantity of loads. It is deposited in suitable conditions along its paths in the plain and with flood water. It results the formation of flood plain. According to the erosion and deposition, different types of major and minor features are formed. In other words, water and sediment determine the layout of the plain appearance. In this background, it is attempted to (i) study sediment concentration in discharged water and (ii) illustrate the channel planform of the Gandak River in the plain. To achieve these aims, secondary data has been collected and analyzed. It is expected that this study will help in executing an integrated development plan for the flood affected area of Lower Gandak River Plain. Keywords: sediment load, channel bars, channel planform, meandering, braiding, slope/gradient and channel cutoff.

Timescales and thermal evolution of large silicic magma reservoirs during an ignimbrite flare-up: perspectives from zircon

Four voluminous ignimbrites (150–500 km3) erupted in rapid succession at 27 Ma in the central San Juan caldera cluster, Colorado. To reconstruct the timescales and thermal evolution of these magma reservoirs, we used zircon ID-TIMS U–Pb geochronology, zircon LA-ICP-MS geochemistry, thermal modeling, and zircon age and crystallization modeling. Zircon geochronology reveals dispersed zircon age spectra in all ignimbrites, with decreasing age dispersion through time that we term a ‘chimney sweeping’ event. Zircon whole-grain age modeling suggests that 2σ zircon age spans represent approximately one-quarter of total zircon crystallization timescales due to the averaging effect of whole-grain, individual zircon ages, resulting in zircon crystallization timescales of 0.8–2.7 m.y. Thermal and zircon crystallization modeling combined with Ti-in-zircon temperatures indicates that magma reservoirs were built over millions of years at relatively low magmatic vertical accretion rates (VARs) of 2–5 × 10–3 m y−1 (2–5 × 10–6 km3 y−1 km−2), and we suggest that such low VARs were characteristic of the assembly of the greater San Juan magmatic body. Though we cannot unequivocally discern between dispersed zircon age spectra caused by inheritance (xenocrystic or antecrystic) versus prolonged crystallization from the same magma reservoir (autocrystic), our findings suggest that long-term magma input at relatively low VARs produced thermally mature upper crustal magma reservoirs resulting in protracted zircon crystallization timescales. Compiling all U–Pb ID-TIMS zircon ages of large ignimbrites, we interpret the longer timescales of subduction-related ignimbrites as a result of longer term, lower flux magmatism, and the shorter timescales of Snake River Plain ignimbrites as a result of shorter term, higher flux magmatism.

Major reorganization of the Snake River modulated by passage of the Yellowstone Hotspot

The details and mechanisms for Neogene river reorganization in the U.S. Pacific Northwest and northern Rocky Mountains have been debated for over a century with key implications for how tectonic and volcanic systems modulate topographic development. To evaluate paleo-drainage networks, we produced an expansive data set and provenance analysis of detrital zircon U-Pb ages from Miocene to Pleistocene fluvial strata along proposed proto-Snake and Columbia River pathways. Statistical comparisons of Miocene-Pliocene detrital zircon spectra do not support previously hypothesized drainage routes of the Snake River. We use detrital zircon unmixing models to test prior Snake River routes against a newly hypothesized route, in which the Snake River circumnavigated the northern Rocky Mountains and entered the Columbia Basin from the northeast prior to incision of Hells Canyon. Our proposed ancestral Snake River route best matches detrital zircon age spectra throughout the region. Furthermore, this northerly Snake River route satisfies and provides context for shifts in the sedimentology and fish faunal assemblages of the western Snake River Plain and Columbia Basin through Miocene−Pliocene time. We posit that eastward migration of the Yellowstone Hotspot and its effect on thermally induced buoyancy and topographic uplift, coupled with volcanic densification of the eastern Snake River Plain lithosphere, are the primary mechanisms for drainage reorganization and that the eastern and western Snake River Plain were isolated from one another until the early Pliocene. Following this basin integration, the substantial increase in drainage area to the western Snake River Plain likely overtopped a bedrock threshold that previously contained Lake Idaho, which led to incision of Hells Canyon and establishment of the modern Snake and Columbia River drainage network.

Supplemental Material: Linking exhumation, paleo-relief, and rift formation to magmatic processes in the western Snake River Plain, Idaho, using apatite (U-Th)/He thermochronology

Table S1: Calculations of footwall exhumation and basin extension magnitudes in the western Snake River Plain. Figure S1: Figure illustrating regions of high-elevation, low-relief topography in the southern Idaho batholith.

Supplemental Material: Linking exhumation, paleo-relief, and rift formation to magmatic processes in the western Snake River Plain, Idaho, using apatite (U-Th)/He thermochronology

Table S1: Calculations of footwall exhumation and basin extension magnitudes in the western Snake River Plain. Figure S1: Figure illustrating regions of high-elevation, low-relief topography in the southern Idaho batholith.

Removal of the Northern Paleo-Teton Range along the Yellowstone Hotspot Track

Classically held mechanisms for removing mountain topography (e.g., erosion and gravitational collapse) require 10-100 Myr or more to completely remove tectonically generated relief. Here, we propose that mountain ranges can be completely and rapidly (<2 Myr) removed by a migrating hotspot. In western North America, multiple mountain ranges, including the Teton Range, terminate at the boundary with the relatively low relief track of the Yellowstone hotspot. This abrupt transition leads to a previously untested hypothesis that preexisting mountainous topography along the track has been erased. We integrate thermochronologic data collected from the footwall of the Teton fault with flexural-kinematic modeling and length-displacement scaling to show that the paleo-Teton fault and associated Teton Range was much longer (min. original length 190-210 km) than the present topographic expression of the range front (~65 km) and extended across the modern-day Yellowstone hotspot track. These analyses also indicate that the majority of fault displacement (min. 11.4-12.6 km) and the associated footwall mountain range growth had accumulated prior to Yellowstone encroachment at ~2 Ma, leading us to interpret that eastward migration of the Yellowstone hotspot relative to stable North America led to removal of the paleo-Teton mountain topography via posteruptive collapse of the range following multiple supercaldera (VEI 8) eruptions from 2.0 Ma to 600 ka and/or an isostatic collapse response, similar to ranges north of the Snake River plain. While this extremely rapid removal of mountain ranges and adjoining basins is probably relatively infrequent in the geologic record, it has important implications for continental physiography and topography over very short time spans.

Late Glacial and Holocene buried black soils in Emilia (northern Italy): genetic and paleoenvironmental insights

Purpose The existence of black horizons (BHs) is often highlighted in European soils, and in the Po River plain of northern Italy. Nevertheless, BH chronological frameworks and genetic models are still debated. The present study investigated the genesis of BHs in the eastern Po Plain where they are buried at various depths. Materials and methods Soil sequences were investigated with a multidisciplinary approach integrating geomorphologic, stratigraphic, pedologic, geochemical, isotopic, palynological, and radiometric analyses. Results and discussion The formation of the studied BHs was scattered over time from the Last Glacial Maximum to at least the middle Holocene. The new data indicate that BHs developed when the landscape was dominated by coniferous forest during conditions that were totally different from the current pedoclimatic setting. The recurrent presence of black particles indicates that this vegetation cover was systematically affected by fire episodes that induced soil degradation and mineralization processes of the original organic compounds, thus contributing to darkening of the upper soil horizons. Conclusions BH formation clearly coincided with cold time lapses. Evidence for repeated fire events (natural or human-induced?) provides insights for the controversial debate on early anthropogenic impacts on the environment.

Supplemental Material: Major reorganization of the Snake River modulated by passage of the Yellowstone Hotspot

Figure S1: Detrital zircon age spectra from modern rivers.; Figure S2: Detrital zircon age spectra from fluvial and lacustrine sandstones; Figure S3: Shepard plots from Multi-Dimensional scaling (MDS) analysis comparing distance and disparity for four metrics of detrital zircon similarity; Figure S4: DZmix results for three hypothesized river networks; Figure S5: SRP sample location map and detrital unmixing results; Table S1: Modern and ancestral river detrital zircon sample locations, ages, and references; Table S2: U-Pb zircon age results for new modern and ancestral river sands; Table S3: Intercomparison results between modern and ancestral river sediments; Table S4: Best-fit DZmix results estimating the relative contribution of hypothesized sources to measured detrital zircon age spectra of ancestral river sands; Table S5: Best-fit DZMix results that estimate the relative contribution of Snake River Plain tributaries to Miocene-Pliocene Lake Idaho strata.