Propagating uplift controls on high-elevation, low-relief landscape formation in the southeast Tibetan Plateau

High-elevation, low-relief surfaces are widespread in many mountain belts. However, the origin of these surfaces has long been debated. In particular, the southeast Tibetan Plateau has extensive low-relief surfaces perched above deep valleys and in the headwaters of three of the world’s largest rivers (Salween, Mekong, and Yangtze Rivers). Various geologic data and geodynamic models show that many mountain belts grow first to a certain height and then laterally in an outward propagation sequence. By translating this information into a kinematic propagating uplift function in a landscape evolution model, we propose that the high-elevation, low-relief surfaces in the southeast Tibetan Plateau are simply a consequence of mountain growth and do not require a special process to form. The propagating uplift forms an elongated river network geometry with broad high-elevation, low-relief headwaters and interfluves that persist for tens of millions of years, consistent with the observed geochronology. We suggest that the low-relief interfluves can be long-lived because they lack the drainage networks necessary to keep pace with the rapid incision of the large main-stem rivers. The propagating uplift also produces spatial and temporal exhumation patterns and river profile morphologies that match observations. Our modeling therefore reconciles geomorphic observations with geodynamic models of uplift of the southeast Tibetan Plateau, and it provides a simple mechanism to explain the low-relief surfaces observed in several mountain belts on Earth.

Supplemental Material: Propagating uplift controls on high-elevation, low-relief landscape formation in the southeast Tibetan Plateau

Landscape evolution model, model setup, and propagating uplift used in this study, river profile morphology analyses, and resulting data.

Supplemental Material: Propagating uplift controls on high-elevation, low-relief landscape formation in the southeast Tibetan Plateau

Landscape evolution model, model setup, and propagating uplift used in this study, river profile morphology analyses, and resulting data.

Perennial grasses as means to improve land productivity in the semi-desert of the Caspian Sea region

Объектом исследований являлись посевы многолетних трав 15- и 18-летнего возраста в Западно-Казахстанской (Казахстан) и Волгоградской областях соответственно и режимы выпадения атмосферных осадков по полупустынной зоне за 22 года. Атмосферные осадки и характер их выпадения в полупустынной зоне определяют продуктивность пашни. Поэтому структура сельскохозяйственных угодий и посевов служит основным механизмом формирования экологически сбалансированных агролесоландшафтов. Продуктивность сельскохозяйственных угодий повышается при увеличении удельного веса посевных площадей кормовых культур, в т.ч. многолетних трав, за счёт проведения культуртехнических работ. Осеннее чизелевание дернины и азотные подкормки обеспечивают долголетие (15–20 лет) и высокую продуктивность (2,6–2,8 т/га сена) многолетних трав при рентабельности 88–122%. В целом в полупустынной зоне под многолетние травы выделяется лишь 5,8% обрабатываемой пашни. Проблема рационального землепользования успешно решается предприятиями Палласовского муниципального района на площади 124,1 тыс. га. В структуре пашни под многолетние травы отводится 22,2%, под зерновые и технические — 55,3% и под чистые пары — 21,5%. Сложившаяся структура пашни обеспечивает потребность в кормах 28,3 тыс. голов крупного рогатого скота, 153,5 тыс. голов овец, а также поголовья других сельскохозяйственных животных в личных подворьях населения. Кормовая база единственных в зоне племенных репродукторов опирается на значительные площади посева многолетних трав в сравнении с прочими районами. Производственные показатели Палласовского района свидетельствуют, что в полупустынной зоне увеличение удельного веса площадей многолетних трав в структуре посева обеспечивает устойчивое развитие мясного животноводства. Fifteen- and sixteen-years old perennial grasses were analyzed in the West Kazakhstan (Kazakhstan) and Volgograd regions, respectively. Precipitation rates for 22 years were evaluated in the semi-desert. Precipitations are the main factor determining field productivity in the semi-desert. Therefore, sowing system has a significant impact on mechanisms of sustainable landscape formation. Wide cultivation of forage crops, particularly perennial grasses, positively affects field productivity due to the introduction of various cultural practices. Subsoil plowing and nitrogen fertilization in autumn have positive impact on plant longevity (15–20 years) and productivity (2.6–2.8 t ha-1 of hay) providing economic efficiency of 88–122%. In the semi-desert perennial grasses occupy only 5.8% of farm lands. Sustainable land cultivation is performed on 124.1 thousand ha area by the organizations of the Pallasovskiy district. Sowing system includes 22.2% of perennial grasses, 55.3% of grain and industrial crops and 21.5% of clean fallow. Such system is able to provide 28.3 thousand heads of cattle, 153.5 thousand heads of sheep as well as other livestock on private farms with forage. Forage resources for pedigree breeding stock depend significantly on total cultivation area of perennial grasses in the district. It was shown that wider cultivation of perennial grasses had positive effect on beef farming in the semi-desert of the Pallasovskiy district.

Ionomic Responses of Local Plant Species to Natural Edaphic Mineral Variations

Leaf ionome indicates plant phylogenetic evolution and responses to environmental stress, which is a critical influential factor to the structure of species populations in local edaphic sites. However, little is known about leaf ionomic responses of local plant species to natural edaphic mineral variations. In the present study, all plant species and soil samples from a total of 80 soil sites in Shiozuka Highland were collected for multi-elemental analysis. Ioniomic data of species were used for statistical analysis, representing 24 species and 10 families. Specific preferences to ionomic accumulation in plants were obviously affected by the phylogeny, whereas edaphic impacts were also strong but limited within the phylogenetic preset. Correlations among elements resulted from not only elemental synergy and competition but also the adaptive evolution to withstand environmental stresses. Furthermore, ionomic differences of plant families were mainly derived from non-essential elements. The majority of variations in leaf ionome is undoubtedly regulated by evolutionary factors, but externalities, especially environmental stresses also have an important regulating function for landscape formation, determining that the contributions of each factor to ionomic variations of plant species for adaptation to environmental stress provides a new insight for further research on ionomic responses of ecological speciation to environmental perturbations and their corresponding adaptive evolutions.

A new hypothesis for the origin of Amazonian Dark Earths

Amazonian Dark Earths (ADEs) are unusually fertile soils characterised by elevated concentrations of microscopic charcoal particles, which confer their distinctive colouration. Frequent occurrences of pre-Columbian artefacts at ADE sites led to their ubiquitous classification as Anthrosols (soils of anthropic origin). However, it remains unclear how indigenous peoples created areas of high fertility in one of the most nutrient-impoverished environments on Earth. Here, we report new data from a well-studied ADE site in the Brazilian Amazon, which compel us to reconsider its anthropic origin. The amounts of phosphorus and calcium—two of the least abundant macronutrients in the region—are orders of magnitude higher in ADE profiles than in the surrounding soil. The elevated levels of phosphorus and calcium, which are often interpreted as evidence of human activity at other sites, correlate spatially with trace elements that indicate exogenous mineral sources rather than in situ deposition. Stable isotope ratios of neodymium, strontium, and radiocarbon activity of microcharcoal particles also indicate exogenous inputs from alluvial deposition of carbon and mineral elements to ADE profiles, beginning several thousands of years before the earliest evidence of soil management for plant cultivation in the region. Our data suggest that indigenous peoples harnessed natural processes of landscape formation, which led to the unique properties of ADEs, but were not responsible for their genesis. If corroborated elsewhere, this hypothesis would transform our understanding of human influence in Amazonia, opening new frontiers for the sustainable use of tropical landscapes going forward.

Sediment redistribution beneath the terminus of an advancing glacier, Taku Glacier (T'aakú Kwáan Sít'i), Alaska

The recently-advancing Taku Glacier is excavating subglacial sediments at high rates over multi-decadal timescales. However, sediment redistribution over shorter timescales remains unquantified. We use a variety of methods to study subglacial and proglacial sediment redistribution on decadal, seasonal, and daily timescales to gain insight into sub- and proglacial landscape formation. Both excavation and deposition were observed from 2003 to 2015 (2.8 ± 0.9 m a−1 to +2.9 ± 0.9 m a−1). The observed patterns imply that a subglacial conduit has occupied the same site over the past decade. Outwash fans on the subaerial end moraine experience fluvial sediment reworking almost year-round, with net sediment gain in winter and net sediment loss in summer, and an overall mass gain between 2005 and 2015. We estimate that tens of meters of sediment still underlie the glacier terminus, sediments which can be remobilized during future activity. However, imminent retreat from the proglacial moraine will limit its sediment supply, leaving the moraine vulnerable to erosion by bordering rivers. Retreat into an over-deepened basin will leave the glacier vulnerable to increased frontal ablation and accelerating retreat.