Alluvial Valley Research Articles

Anti-plane responses of acceleration by a shallow hill next to an alluvial valley

This study proposed a hybrid method combining finite element method (FEM) and a wave function based on the Lamb series in conjunction with modified transfinite interpolation for use in examining surface accelerations on a semi-elliptical hill subjected to shear horizontal (SH) waves of various dimensionless frequencies (η) at various incident angles (θ). The case topography included a semi-elliptical hill of fixed height adjacent to a semi-elliptical alluvial valley of variable depth (EHAV). Differences in site effects between EHAV and a single semi-elliptical hill (or a semi-elliptical alluvial valley) were investigated as a function of the modified transmissibility (TR). Variations in TR associated with η clearly revealed the resonance frequencies (RFs), associated with an elevated probability of landslides. Our simulation results revealed a larger number of RFs form in hills adjacent to AV than in isolated hill. This study proposes a systematic approach for the analysis of site effects of EHAV, focusing on the identification of potential landslides due to seismic waves excitation.

A Recent Taxonomic Study of the Fish from the Jinam River in Dima Hasao Biodiversity Hotspot Region of Assam (India)

Abstract The Jinam River habitats inventory revealed the presence of alluvial valley, cascades, riffle-pools, boulders, cobbles, and gravel as types of substrata. The limnological parameters portrayed average values of air and water temperature, turbidity, pH, dissolved oxygen, free carbon di-oxide, total alkalinity, and conductivity. This recent pioneering study on the fish of the Jinam River in the Dima Hasao District of Assam revealed the presence of 18 species belonging to 15 genera, five families, and three orders, which are reported for the first time through this paper. Worth highlighting is the abundance of Barilius bendelisis and Devario aequipinnatus, and the fewer numbers of Chanda nama, these warranting proper management and conservation of the fish for this river.

VARIABILIDADE ESPACIAL DA UMIDADE E CONDUTIVIDADE ELÉTRICA DO SOLO EM VALE ALUVIAL UTILIZANDO TÉCNICAS GEOFÍSICAS

Os métodos de indução eletromagnética na agricultura de precisão possuem alto potencial em aplicações voltadas para estudos da variabilidade espacial da salinidade e umidade do solo. O objetivo deste trabalho foi verificar o desempenho do EM38® em vale aluvial no semiárido para fins de aplicação de agricultura de precisão, e avaliar a dinâmica e dependência espacial da umidade e da condutividade elétrica em diferentes profundidades do solo. A área de estudo está localizada no município de Parnamirim, Pernambuco, no Campus Avançado de Agricultura Irrigada de Parnamirim da Universidade Federal Rural de Pernambuco. Duas malhas regulares foram adotadas, uma de 10 x 10 m para amostragem de condutividade elétrica aparente do solo (CEa) estimada com o aparelho EM38® e outra de 20 x 10 m para amostragem de solo, para determinação da umidade, salinidade, silte e argila nas camadas de 0-0,3 m, 0,3-0,6 m e 0,6-0,9 m. Informações diretas e indiretas foram utilizadas nas análises geoestatísticas, construção de semivariogramas e krigagem de mapas. O Grau de Dependência Espacial dos atributos avaliados variou entre forte e moderado. Maior umidade na camada mais profunda do solo foi constatada, as maiores CEa foram encontradas na camada 0,3-0,6 m. O EM38® mostrou-se eficiente na estimativa da condutividade elétrica do solo, e possibilitou a validação de modelo de regressão previamente calibrado na mesma área, em período com restrição hídrica no solo.

Two-dimensional scattering of plane waves by irregularities in a multi-layered transversely isotropic saturated half-space

Wave scattering of plane waves by irregularities in a transversely isotropic (TI) saturated half-space has been rarely studied. Based on Biot's theory, this paper used an indirect boundary element method (IBEM) to solve the two-dimensional (2D) wave scattering of incident plane qP1- and qSV-waves by irregularities in a layered TI saturated half-space. 2D dynamic Green's functions for uniformly distributed loads as well as pore pressure acting on internal inclined line in a layered TI saturated half-space are derived. The method was verified by comparing with two published results for isotropic medium. The canyon, partially filled alluvial valley and fully filled alluvial valley with trapezoidal cross-section are covered in numerical calculations. Results show that the dynamic responses of the three types of irregularities are significantly different. The peak surface displacement amplitude of the fully filled alluvial valley case is up to approximately twice as much as that of the canyon case. The influences of TI property on the three irregularities are apparent, and the soft sedimentary material is more sensitive to TI property. Besides, the ground motion of the local irregularities strongly affected by the incident angle and frequency of plane wave.

Simulation of the spatially correlated multiple-station earthquake ground motions of the coupled alluvial valley-hill terrain

Based on both the boundary element and spectral representation methods, an effective simulation method for multiple-station spatially correlated ground motions on both bedrock and surface is developed, incorporating the spectral density function, coherence function, and site transfer function that consider the wave scattering effect. The accuracy and feasibility of the present method is validated by a typical numerical example. Our results indicate that at the coupled alluvial valley-hill terrain, the presence of the mountain enlarges the ground motion of the alluvial valley significantly; the existence of alluvial valley enlarges the ground motion at the ridge of the mountain to some extent and weakens the ground motion at the top of the mountain. The local site conditions significantly affect the multipoint spatially correlated earthquake ground motions. It is necessary to use spatially varying ground motions with the rational consideration of local site effects as input during the seismic analysis of long-span structures

Spatial regionalisation of morphometric characteristics of mini watershed of Northern Foreland of Peninsular India

The morphometric (geomorphic) parameters are reconnaissance tools used to analyse and evaluate the different aspects of a river basin (watershed) such as lithological characteristics, geomorphic landforms, and hydrological behaviour. In this study, a recurrent drought-affected Barua watershed of Tons river basin has been selected for detailed analysis of spatial regionalisation of morphometric characteristics. This mini watershed has been studied using topographic maps (1:50,000 scale), satellite images (CARTOSAT DEM of 1″ or ~ 32-m resolution), extensive field surveys, and generated isopleth maps of morphometric parameters in GIS environment using ArcGIS 10.2.2. The areal parameters indicate elongated shape of the basin, hilly region, and moderate-to-steeper ground slope. More than 85% of the area have gentle-to-moderate slope (2–10°); steep slope found along the escarpment of the Bhander Plateau; more than half of the area has above 30 m of basin relief. Hypsometric integral (HI) is 0.47, and the shape of hypsometric curve is sigmoidal; it indicate equilibrium stage of the watershed. The correlation matrix enables that the correlation coefficient between drainage attributes (as drainage density, stream frequency, and drainage texture) are reflecting very strong positive correlation and ranges from 0.83 to 0.91, and the basin relief showing very strong positive correlation with dissection index (0.99), moderately positive correlation with average slope and ruggedness number. The HI and length of overland flow (Lo) are show weak correlation with the other variables. It means the high drainage density, stream frequency, and drainage texture are associated with moderately hilly region, less permeable rock, and high run-off, giving less time for infiltration. Hence, hilly and rocky surfaces of the region are identified as poor groundwater-potential zones, while the areas of alluvial valley plain are characterised as better groundwater-potential zones.

Identification of Groundwater Potential Zones Using Analytical Hierarchy Process (AHP) and GIS-Remote Sensing Integration, the Case of Golina River Basin, Northern Ethiopia

Groundwater is the main source of water both for domestic and irrigation purposes in the study area, Golina basin. The Golina basin is located in the North Wollo Administration, Amhara regional state, Northern Ethiopia. The study area has a surface area of 916.77 km 2 and is a semi-arid environment with an annual mean precipitation of 913 mm/year. Because of its presumed groundwater potential, the area has recently received significant attention from the regional and federal governments as well as investors. As a result, 81wells have been drilled for groundwater extraction mainly for irrigation purposes. About 182 springs and hand-dug wells have been developed for domestic purposes. However, little has been done to know the overall groundwater potential, the groundwater potential zonation and the sustainability of the current and planned groundwater extraction in the basin. Thus, the main objective of this work is to delineate groundwater potential zones of the area using an integrated method of AHP, GIS, and Remote sensing. A total of 10 thematic layers are used for the groundwater potential zone assessment. Based on the AHP method, the priority of the thematic layers with their weight are as follows: geology (0.22), geomorphologic landform (0.22), lineament density (0.17), slope (0.12), drainage density (0.09), soil (0.07), land use land cover (0.04), precipitation (0.04), normalized difference vegetation index (NDVI) (0.02) and topographic wetness index (TWI) (0.02). The groundwater potential zones of the area are computed using raster calculator in spatial analyst tool in GIS software and divided into five classes as very poor, poor, moderate, good and very good with area coverage of 93 km 2 (10%), 265km 2 (29%), 175 km 2 (19%), 221 km 2 (24%) and 162 km 2 (18%) of the total area, respectively. The result is validated using the existing spring, hand-dug wells and borehole yields. Accordingly, the high yield boreholes are drilled and concentrated in very good groundwater potential zones whereas the low yield springs are developed in the very poor. Out of 263 water points 74, 72, 48, 59 and 10 water points are located in very good, good, moderated, poor and very poor groundwater potential zones, respectively. Mainly the very good groundwater potential fall in the alluvial deposit, plain and valley landforms, very low slope (flat), high lineament density, low drainage density, coarse soil textures, and water body and cultivated lands with high precipitation, NDVI and TWI. The result of this study can be used for the planning of new groundwater-based projects and the expansion of the existing irrigation project in the basin. DOI: https://doi.org/10.23953/cloud.ijarsg.460

Evaluation of complex site effects through experimental methods and numerical modelling: The case history of Arquata del Tronto, central Italy

This work deals with the experimental and numerical evaluation of the local seismic response of Arquata del Tronto area (Marche Region, central Italy), severely struck by the Mw 6.0 August 24th, 2016 earthquake. Arquata main village rises on elongated WNW-ESE-trending ridge of the central Apennines thrust-belt (central Italy), at elevations about 170 m higher than the underlying alluvial valleys where Borgo and San Francesco hamlets are built on. Despite their proximity (less than 500 m), Arquata del Tronto, Borgo and San Francesco reported a different damage distribution after the August 2016 mainshock, suggesting that the seismic response of the area may be controlled by site effects. In order to explore this hypothesis, we evaluated the 2D numerical local seismic response along four representative geological cross-sections passing through Arquata del Tronto, San Francesco and Borgo. Additional 1D analyses were carried out at strategic points along the cross-sections in order to explore the 2D physical phenomena governing the local response. The satisfactory agreement between numerical amplification functions in linear range and experimental amplification functions obtained by the Generalized Inversion Technique (GIT) applied to a large number of aftershocks confirms the substantial reliability of the subsoil models. Numerical analyses representative of the 2016 mainshock were carried out and processed in terms of peak and key ground motion parameters. A comparison with the damage induced by the 2016 mainshock was finally undertaken substantially justifying the observed pattern. This study provides general implications about site response and seismic microzonation in sites characterized by similar complex geological and morphological settings.

Assessment of the Dnieper Alluvial Riverbed Stability Affected by Intervention Discharge Downstream of Kaniv Dam

Along the middle reaches of the Dnieper River in central Ukraine, braided riverbeds with many islands have developed in alluvial valleys. In the 1970s, six dams were commissioned, and respective monitoring infrastructure was installed. Riverbanks and valley floors composed of unconsolidated material have much lower bank strengths and are susceptible to fluvial erosion and bank collapse, particularly during the release of high flow volumes from hydropower dams. The regulation of the Dnieper River along a cascade of storage reservoirs caused significant changes in its active river channel and hydrological regime. In order to estimate channel stability downstream of the Kaniv reservoir, we conducted an analysis of the hydraulic conditions in terms of changes in flow velocity and propagation of waves caused by intervention water discharges from the Kaniv Hydroelectric Power Plant (HPP). In this paper, we assess the hydromorphological parameters of the studied river reach as well as the characteristics of the related erosion and deposition zones. Therefore, a monitoring framework for channel processes (MCP) downstream of the Kaniv HPP was installed. The analysis of the intervention discharge parameters was conducted based on measurements from July 2015. Channel stability was expressed by the following factors: Lohtin’s number (L), Makkaveev’s (Kc) factor of stability, and a complex index of stability (Mx) by Grishanin. This study shows that the velocity of artificial wave propagation may reach a speed of up to 74.4 km·h−1. The wave propagates for a distance of approx. 45 km within 65 min at a mean velocity of 37.4 km·h−1. The L, Kc, and Mx indicators used in this work showed that when water discharge increased (e.g., during typical peak-capacity operation), the channel becomes unstable and sediments are subject to erosion processes. The riverbed stability indicators clearly illustrate that an increase in parameter values is not dependent on the distance to the dam. The results are valuable for sustainable sediment management at catchment scale and hence, directly applicable in water management.

Dynamic response of an alluvial valley consists of three types of soil

Dynamic response of an alluvial valley consisting of three different types of soil was studied. In the two-dimensional model, the alluvial valley was assumed to have half-cylindrical shape. The alluvial valley contained three different types of soil with different shapes. The valley was surrounded by a half-space. All of the soil types and the half-space were assumed to be isotropic, homogeneous and linear elastic. The half-space was excited by simple harmonic SH-waves radiated from a strike-slip fault. The fault was assumed to have circular-arc shape in the mathematical model. The governing equations were solved by using wave function expansion method where boundary conditions were relatively simple. In the regions where boundary conditions were more complex, finite difference method was employed. Consequently, the wave propagation problem was solved semi-analytically. The obtained numerical results showed that surface displacement amplitudes are significantly affected by the material properties of the different soil types of the alluvial valley. It was also observed that the shapes of the soil types in the alluvial valley played a considerable role in surface displacements.

Determining Anti-plane responses of a semi-circular alluvial valley embedded in a single layered half-space

This paper proposes a modified hybrid computational method, comprising finite element method and a Lamb series for a single layered half-space, to derive displacement amplitude (|uyjAV|) in a field that includes a semi-circular alluvial valley (SCAV) embedded within a single layered half-space subjected to shear horizontal (SH) waves. Variations in |uyjAV| associated with depth (from the free surface through the SCAV and layered medium to the half-space) and site effects were also examined under various incident angles (θ2) and dimensionless frequencies (ζ). Our analytical solutions, based on a theoretical model of the single layered half-space, revealed the thickness effects and the resonance frequencies (RFs) under various θ2, due to a soft layered medium. We compared the resulting |uyjAV| value with those of an SCAV embedded in a half-space (i.e., |uyjav|) and theoretical solutions based on a single layered half-space (i.e., |uyjf|) under RFs with various θ2. We discovered that due to the embedding of an SCAV in the single layered half-space, the thickness effects created by that space were a major contributor to site effects. The response amplitudes at the free surface were also magnified by the enlargement effect of the SCAV. Additional numerical simulations were conducted to obtain responses of |uyjAV| under ζ ranging from 0.01 to 2.0. These results support our discovery that thickness effects dominate the site effects. This paper provides a valuable reference to further our understanding of site effects associated with surface irregularities in the single layered half-space.

Groundwater recharge from an oxbow lake‐wetland system in the Mississippi Alluvial Plain

AbstractThe Mississippi River Valley Alluvial Aquifer ranks among the most overdrafted aquifers in the United States due to intensive irrigation. Concern over declining water levels has increased focus on understanding the sources of recharge. Numerous oxbow lakes overlie the aquifer that are often considered hydraulically disconnected from the groundwater system due to fine‐grained bottom sediments. In the current study, groundwater levels in and around a 445‐ha oxbow lake‐wetland in Mississippi were monitored for a 2‐year period that included an unusually long low‐water condition in the lake (>17 months), followed by a high‐water event lasting over 4 months before returning to earlier low‐water levels. The high‐water pulse (>4 m rise) provided a unique opportunity to track the impact in the underlying alluvial aquifer. During low‐water conditions, groundwater flowed westward beneath the lake. Following the lake rise, groundwater beneath and near the perimeter responded as quickly as the same day, with more delayed responses moving away from the lake. Within 2 months, a groundwater mound formed near the centre of the oxbow (>3 m increase), with a reversal in the local hydraulic gradient towards the east. Flow returned to a westward gradient when the lake level dropped back below 0.3 m. Analysis of precipitation and nearby river stage could not account for the observed behavior. Recharge to the aquifer is attributed to rising water levels spreading over point bar deposits and into the surrounding forested wetlands where preferential flow pathways are likely to exist due to buried and decomposing tree remains. An earlier study in the wetland demonstrated an increasing redox potential in isolated zones, consistent with the existence of preferential flow pathways through the bottom sediments (Lahiri & Davidson, 2020). Retaining high‐water levels in oxbow lakes could be a relatively low‐cost water management practice for enhancing aquifer recharge.

Improving the performance of extensive livestock farming in marshes and alluvial valleys

Les agriculteurs, en particulier les eleveurs pratiquant l’elevage extensif, sont les premiers gestionnaires des zones humides de marais et de vallees alluviales. Leur activite est capable de valoriser ces espaces tout en etant garante du maintien de leurs fonctionnalites et de la biodiversite. Ces elevages doivent s’adapter et axer leur developpement sur la specificite de ces zones humides en coherence avec des objectifs economiques et environnementaux. Actuellement, il n’existe que tres peu d’etudes constitutives de references pour ces territoires sensibles. Ce projet propose de fournir aux eleveurs des cles d’amelioration de leur systeme d’exploitation. Cela passe par la caracterisation des systemes d’un point de vue sociologique, technico-economique, agro-ecologique et sanitaire.

Use of Landsat 8 OLI Images to Assess Groundwater Potential Areas in the Bamun Plateau: Cameroon Volcanic Line (CVL)

The problem of groundwater supply in the Bamun plateau situated in the Cameroon Volcanic Line exists and no proper solution has been found so far. This investigation intends to find the suitable groundwater potential zones by overlaying the geomorphologic map, lineament map, lineament density map and lithological map, using visual interpretation of Landsat imagery. The results reveal that about 1921 structural elements, ranging in size, from 30 m to 5.845 km with an average length of 671 m in the field. The total length of the mapped lineaments is approximately 1289 km. The most important lineament (5.845 km length) diagonally crosses the study area in the direction NNE-SSW. In addition to this trend, all others are smaller than 14 km. More than 92% of lineaments are less than 5 km in size and only 1.3% of them are larger than 10 km. Small lineaments are thus the most numerous. According to their directions, the lineaments listed are grouped into 18 directional classes of 10-degree intervals. The rosette of their directions highlights the preferred directions NE-SW, N-S, E-W, NNE-SSW and ENE-WSW. Most of the lineaments clusters in the central part of the area are N20° - 30°E and N60° - 70°E trending lineaments. In this study, the NE-SW trend dominates the structural trend followed by NW-SE and N-S. This can be an indication of the directions of groundwater movement in the area. Alluvial plain and valley have moderate to very good groundwater potential that occurs all over the study area. Porosity of the volcanic rocks varies greatly, but it is everywhere more porous than the underlying, unweathered bedrock. There are essentially three classes (low, average and high) of groundwater potential zones. Hight potential zones are observed around the localities of the Khogham, Mbatpit and Mbam massifs on the one hand and Manswen, Njikwop, Mfelap, Foumban, Njindare, Nkoundem and Ngwen jigoumbe localities on the other hand. About 13% of the area has good groundwater potential around the mountains while 58% is moderately good which corresponds to high to moderate lineament densities situated at average altitude 1200 m and about 31% of the area has poor groundwater potential corresponding to low lineament density areas. Moreover, this work has helped develop a detailed lineament map that can be used for mining and hydrological prospecting campaigns.

Use of Landsat 8 OLI Images to Assess Groundwater Potential Areas in the Bamun Plateau: Cameroon Volcanic Line (CVL)

The problem of groundwater supply in the Bamun plateau situated in the Cameroon Volcanic Line exists and no proper solution has been found so far. This investigation intends to find the suitable groundwater potential zones by overlaying the geomorphologic map, lineament map, lineament density map and lithological map, using visual interpretation of Landsat imagery. The results reveal that about 1921 structural elements, ranging in size, from 30 m to 5.845 km with an average length of 671 m in the field. The total length of the mapped lineaments is approximately 1289 km. The most important lineament (5.845 km length) diagonally crosses the study area in the direction NNE-SSW. In addition to this trend, all others are smaller than 14 km. More than 92% of lineaments are less than 5 km in size and only 1.3% of them are larger than 10 km. Small lineaments are thus the most numerous. According to their directions, the lineaments listed are grouped into 18 directional classes of 10-degree intervals. The rosette of their directions highlights the preferred directions NE-SW, N-S, E-W, NNE-SSW and ENE-WSW. Most of the lineaments clusters in the central part of the area are N20° - 30°E and N60° - 70°E trending lineaments. In this study, the NE-SW trend dominates the structural trend followed by NW-SE and N-S. This can be an indication of the directions of groundwater movement in the area. Alluvial plain and valley have moderate to very good groundwater potential that occurs all over the study area. Porosity of the volcanic rocks varies greatly, but it is everywhere more porous than the underlying, unweathered bedrock. There are essentially three classes (low, average and high) of groundwater potential zones. Hight potential zones are observed around the localities of the Khogham, Mbatpit and Mbam massifs on the one hand and Manswen, Njikwop, Mfelap, Foumban, Njindaré, Nkoundem and Ngwen jigoumbé localities on the other hand. About 13% of the area has good groundwater potential around the mountains while 58% is moderately good which corresponds to high to moderate lineament densities situated at average altitude 1200 m and about 31% of the area has poor groundwater potential corresponding to low lineament density areas. Moreover, this work has helped develop a detailed lineament map that can be used for mining and hydrological prospecting campaigns.

Developing sensor‐based irrigation scheduling that maximizes soybean grain yield, irrigation water use efficiency, and returns above irrigation costs

AbstractAgricultural withdrawal from the Mississippi River Valley Alluvial aquifer (MRVAA) exceeds its recharge rate, causing groundwater declines and cones of depression across the midsouthern United States. This research was conducted to determine whether sensor‐based irrigation scheduling of soybean [Glycine max (L.) Merr.] could improve yield and profitability while minimizing consumptive water use. The effects of season‐long soil water potential (SWP) threshold (−50 and −85 centibar [cbar]) on consumptive water use and on agronomic and economic parameters were compared with scheduling irrigations as a function of growth stage (VN–R2, R3–R4, and R5–R6.5) and SWP threshold (−50, −85, and −125 cbar) on a Dundee silty clay loam (fine‐silty, mixed, active, thermic Typic Endoaqualfs) near Stoneville, MS, from 2015 through 2017. Decreasing the season‐long SWP threshold for soybean from −50 to −85 cbar reduced consumptive water use 49% while having no adverse effect on yield, returns above irrigation costs, or irrigation water use efficiency (IWUE). Adjusting the irrigation threshold as a function of growth stage did not improve yield or returns above irrigation costs. Our data indicate that maintaining a season‐long irrigation threshold of −85 cbars optimizes yield, returns above irrigation costs, and IWUE efficiency while reducing withdrawal for soybean irrigation from the MRVAA up to 49% relative to the −50 cbar producer standard.

Impacts of sediment connectivity on Holocene alluvial records across a Mediterranean basin (Guadalentín River, SE-Spain)

Two contiguous alluvial valleys (Maria and Guadalupe sectors) of the upper Guadalentín River (SE Spain) show distinct Holocene alluvial architecture (cut-and-fill, nested and stepped fill terraces), revealing a strong control of valley morphology and bedrock barriers on sediment delivery, storage and preservation. The headwater valley (Maria sector) preserves four morphosedimentary alluvial units corresponding to two palaeogeographic stages. Morphosedimentary unit (MSU1), the most extensive, is a major depositional valley infill dominated by sand and silt texture, showing three stratigraphic sets dated 9000–8500, 5300–4800, 4000–3000 cal BP. This vertically stacked alluvial accumulation occurs upstream of a narrow bedrock channel, that limited sediment connectivity with the downstream Guadalupe sector. Between 3000 and 2350 cal BP, a 15-m deep incision on MSU1 occurred, and subsequent cut-and-fill cycles generated three alluvial terraces dated at 2350–1900 cal BP (MSU2), 1800–700 cal BP (MSU3), and post-400 years (MSU4). In the downstream valley (Guadalupe sector), six flights of alluvial terraces (MSUg1 to MSUg6) were formed by episodic aggradation and quasi-continuous incision, in response to baselevel changes of the lower Guadalentín River during the Holocene. Alluvial chronologies in these two contiguous valleys show out-of-phase sedimentation periods under low connectivity conditions (9–3 ka), and in-phase cut-and-fill cycles after valley re-connection (post-3.0 ka). The late Holocene alluvial activity periods also coincide with morpho-stratigraphic data from the lower Guadalentín, indicating that fluvial connectivity throughout the catchment was only completed in the late Holocene.

Geospatial DSS for Maintaining Agricultural Diversions under Environmental Flow Requirements

AbstractCompeting demands for scarce water supplies in irrigated alluvial valleys can lead to conflicts between disparate uses, resulting in an increased risk of restrictions on agricultural divers...

Determining the optimum irrigation schedule in furrow‐irrigated cotton using soil moisture sensors

The Mississippi River Valley Alluvial Aquifer is declining at a rapid rate due to withdrawal for agricultural irrigation. This research was conducted to develop a sensor‐based irrigation threshold for cotton that maximizes net returns and irrigation water use efficiency. Earn 1 CEU in Soil & Water Management by reading this article and taking the quiz at www.certifiedcropadviser.org/education/classroom/classes/727.

Late glacial aster prairie at the Aubrey Clovis site, North Texas, USA

Pollen analysis of pond and spring deposits at the Aubrey Clovis site in North Texas provides a 1300-year record of late glacial grassland vegetation from 17,200 to 15,900 cal years BP. Forty-six pollen taxa are identified in the well-preserved assemblages. The late glacial pollen record at the Aubrey site represents three environments: upland, riparian, and lacustrine-wetland. The pond-related sediments are dominated by 80% Poaceae pollen, an unusually high amount in pollen records; the spring tufa sediments are dominated by Cyperaceae. Cattail (Typha latifolia) and other wetland plants, including green algae Botryococcus, Pediastrum, and Chara were present. The riparian habitat of the wide late glacial alluvial valley had alder (Alnus), willow (Salix), cottonwood (Populus), and water elm (Planera aquatica). The upland vegetation was a treeless grassland with comparatively high amounts of Asteraceae-type pollen; it is therefore called the aster prairie. Quercus, Juniperus, Carya, Ulmus, Ambrosia, and Chenopodiaceae pollen are much less abundant than found in modern grassland pollen records. Small amounts of Artemisia, Pinus, and Picea pollen are present, a consequence of long-distance transport. Regional late glacial cool-wet climate produced moist prairie soils. The Cross Timbers oak forest that occurs near the site today had not yet formed. Dissimilarity analysis of the pollen data shows that the late glacial aster prairie has no analog with modern shortgrass, mixed-grass, or tallgrass prairies. In contrast, a favorable analog exists with fossil pollen data from a lower zone at Patschke Bog, central Texas, and Muscotah Marsh, northeastern Kansas, indicating that a grassland characterized by high amounts of Asteraceae pollen formed a unique late glacial vegetation type in the region, earlier in Texas and later in Kansas. Because of its chronology and location in the eastern Great Plains, the late glacial aster prairie may be ancestral to the modern tallgrass prairie.