Gully Area Research Articles

Resource-environmental cost of grain production in the gully areas of Loess Plateau.

Resource-environmental cost of grain production in the gully areas of Loess Plateau.

Long-term Soil Organic Carbon and Crop Yield Dynamics on Cropland in Hilly and Gully Areas of Loess Plateau

Long-term Soil Organic Carbon and Crop Yield Dynamics on Cropland in Hilly and Gully Areas of Loess Plateau

Surface and subsurface flow effect on permanent gully formation and upland erosion near Lake Tana in the northern highlands of Ethiopia

Abstract. Gully formation in the Ethiopian Highlands has been identified as a major source of sediment in water bodies, and results in sever land degradation. Loss of soil from gully erosion reduces agricultural productivity and grazing land availability, and is one of the major causes of reservoir siltation in the Nile Basin. This study was conducted in the 523 ha Debre-Mawi watershed south of Bahir Dar, Ethiopia, where gullies are actively forming in the landscape. Historic gully development in a section of the Debre-Mawi watershed was estimated with semi structured farmer interviews, remotely sensed imagery, and measurements of current gully volumes. Gully formation was assessed by instrumenting the gully and surrounding area to measure water table levels and soil physical properties. Gully formation began in the late 1980's following the removal of indigenous vegetation, leading to an increase in surface and subsurface runoff from the hillsides. A comparison of the gully area, estimated from a 0.58 m resolution QuickBird image, with the current gully area mapped with a GPS, indicated that the total eroded area of the gully increased from 0.65 ha in 2005 to 1.0 ha in 2007 and 1.43 ha in 2008. The gully erosion rate, calculated from cross-sectional transect measurements, between 2007 and 2008 was 530 t ha−1 yr−1 in the 17.4 ha area contributing to the gully, equivalent to over 4 cm soil loss over the contributing area. As a comparison, we also measured rill and interrill erosion rates in a nearby section of the watershed, gully erosion rates were approximately 20 times the measured rill and interrill rates. Depths to the water table measured with piezometers showed that in the actively eroding sections of the gully the water table was above the gully bottom and, in stable gully sections the water table was below the gully bottom during the rainy season. The elevated water table appears to facilitate the slumping of gully walls, which causes the gully to widen and to migrate up the hillside.

Geomorphology and GIS analysis for mapping gully erosion susceptibility in the Turbolo stream catchment (Northern Calabria, Italy)

This work summarizes the results of a geomorphological and bivariate statistical approach to gully erosion susceptibility mapping in the Turbolo stream catchment (northern Calabria, Italy). An inventory map of gully erosion landforms of the area has been obtained by detailed field survey and air photograph interpretation. Lithology, land use, slope, aspect, plan curvature, stream power index, topographical wetness index and length-slope factor were assumed as gully erosion predisposing factors. In order to estimate and validate gully erosion susceptibility, the mapped gully areas were divided in two groups using a random partitions strategy. One group (training set) was used to prepare the susceptibility map, using a bivariate statistical analysis (Information Value method) in GIS environment, while the second group (validation set) to validate the susceptibility map, using the success and prediction rate curves. The validation results showed satisfactory agreement between the susceptibility map and the existing data on gully areas locations; therefore, over 88% of the gullies of the validation set are correctly classified falling in high and very high susceptibility areas. The susceptibility map, produced using a methodology that is easy to apply and to update, represents a useful tool for sustainable planning, conservation and protection of land from gully processes. Therefore, this methodology can be used to assess gully erosion susceptibility in other areas of Calabria, as well as in other regions, especially in the Mediterranean area, that have similar morphoclimatic features and sensitivity to concentrated erosion.

Spatial variability and distribution of soil nutrients in a catchment of the Loess Plateau in China

Inappropriate land use is one of the main reasons for soil erosion and nutrient loss in the hilly loess area of the Liudaogou catchment of the Loess Plateau, a typical topography area of hills and gullies. Good management practices, such as the nutrient variability for the different land uses (woodland, grassland, shrub land, farmland, and gully), would help the farmers. One study of the use of Geographic Information System (GIS) spatial analysis and geostatistic analysis was carried out in the catchment. The results showed that the trend of the content of clay and silt in the different soil ranks was: farmland < grassland < shrub land < gully soil. The sandy soil contained fewer nutrients than did the other soils. The farmland contains fewer total phosphorus (TP) and . The spatial dependence of the total nitrogen (TN) and the organic matter (OM) in the sandy soil is strong, but is only moderate in the other types of land use except for OM in farmland. The spatial dependence of TP in the different types of land use patterns is strong too, except in woodland, and the dependence of TP is moderate in grassland. The spatial dependence of and is not strong, especially in woodland, shrub land, and farmland. The dependence of is weak in grassland, gully, and farmland. In the catchment scale, the degree of spatial dependence (GD) is moderate for soil nutrients especially for TN and , but the different nutrients were modelled in different stationary models. The spatial variability of OM, TP, and was modelled by a Gaussian model, and the spatial variability of TN and was modelled by an exponential equation. The nutrients’ distribution in the catchment has been mapped by GIS. From the results, it was seen that annual grass played an important role in the conservation and improvement of soil quality in the Loess Plateau. In addition, the farmland should be given more fertilizer.

Gully erosion, land use and topographical thresholds during the last 60 years in a small rangeland catchment in SW Spain

AbstractGully erosion plays an important role in degradation processes of Mediterranean environments. In this paper aerial orthophotographs were used for (i) analysing the evolution of a valley bottom gully and its relation with land use and vegetation cover, (ii) exploring the role of land use and vegetation cover on the coefficients of the equation S = aA −b (where S is slope at the headcut and A is drainage area), which is based on the topographical threshold concept and is commonly used to predict gully initiation. The study was carried out in a small catchment (99·5 ha) located in the southwest of the Iberian Peninsula. Gullies and headcuts were mapped together with land use and vegetation cover using aerial photographs for the years 1945, 1956, 1989, 1998, 2002 and 2006, which had to be digitized and orthorectified in advance. The results showed an increase of the area affected by gullying from 695 m2 in 1945–1009 m2 in 2006, reaching a maximum of 1560 m2 in 1956. Gullying was closely related with land use, especially with the amount of cultivated areas within the catchment and also with grazing intensity. No clear relationship was found between the evolution of the gullied area and rainfall amounts. Finally, the values of the exponent b obtained for different headcuts and different dates (close to 0·4) were similar to those proposed by other authors for gully erosion caused by Hortonian overland flow in semiarid environments. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Factors affecting species diversity of plant communities and the restoration process in the loess area of China

The Loess Plateau of China is a special region that has suffered from soil erosion and water loss for a long time. Ecological restoration is an urgent task for this region. This study aims to characterize the variation in the vegetation restoration process on the abandoned croplands in the loess area. A series of quadrats were set up in different restoration stages in the Yancun watershed, Shanxi Province, an area of typical loess hills and gullies. Species and environmental data were recorded in each quadrat. Multivariate analysis and indices for species richness, diversity and evenness were used in the analysis. A series of plant community stages with different composition, structure and environments were identified by clustering analysis (UPGMA). These communities included three main restoration stages, grassland stage, scrubland stage and forest stage, and nine sub-stages, i.e. nine associations. Canonical correspondence analysis (CCA) showed that time since abandonment was the key factor for the restoration process, and the first CCA axis was effectively a time gradient. Elevation, soil type, slope and aspect were also important in the restoration process in the loess area. Species richness and diversity increased, and evenness decreased in the restoration process. The variation of species richness and diversity significantly correlated with time since abandonment, elevation and soil type. Time since abandonment is most important to the restoration process and species diversity is the main indicator of community changes in restoration in the Loess Plateau. For effective management, abandoned lands should be kept from disturbance.

Topographic thresholds in gully development on the hillslopes of communal areas in Ngqushwa Local Municipality, Eastern Cape, South Africa

The relationships between the spatial distribution of gully erosion and topographic thresholds in the form of slope angle, position and configuration, as well as land use change in the form of abandoned lands were examined in several affected catchments of the Eastern Cape Province, South Africa. Land use and permanent gullies were mapped, digitized from orthophoto maps in Arc/info 3.5.2 GIS and converted to shapefiles using ArcView 3.2 GIS. Relationships between the mapped phenomena and topographic variables were sought using a Digital Elevation Model (DEM) in Idrisi Kilimanjaro GIS. A comparison between areas with a high potential for gullying and actual gully erosion was made using the Stream Power Index ( SPI) as a surrogate for critical flow shear stress. Field surveys were also conducted to assess the present condition of the gullied sites as well as to validate DEM derivations. Seventy five percent of the gullied area was noted to lie on abandoned lands. A predominance of gullying in concave bottom lands was also identified. The SPI values highlighted a distinct preferential topographic zone for gully location. A conceptual model depicting the interaction between land use and topographic parameters to induce gully erosion was developed. This should assist local authorities to develop a policy regarding management of abandoned lands.

Gully development in the Moldavian Plateau of Romania

Gully erosion has been recognized as an important environmental threat in the Moldavian Plateau of Eastern Romania. The main objective of this study was to define the process-based gully development by providing quantitative information from long-term field measurements in small catchments. Three main areas of monitoring gullies were explored: aerial photographs of flights in 1960 and 1970, classical leveling and repeated survey through a particular close stakes grid after 1980. The Caesium-137 technique has been used effectively in the areas of deposition of gully sediments to obtain reliable information on dating specific levels of sediments and to provide chronological measures of gully development. Most of the discontinuous gullies exhibit both proper gullying, mainly if not exclusively by gully head advance, and aggradation of the gully basin floor. Results indicated that the mean gully head retreat was 0.92 m year − 1 and the mean areal gully growth was 17.0 m 2 year − 1 . Both values indicate a slow erosion rate for this area. The average annual regime of gullying is pulsatory, one that is best described by great fluctuations. Conventional measurements on sedimentation over the period 1987–1997 indicate a higher rate of aggradation in the upper half of the gully floor. Information on the Caesium-137 depth profile was used to provide estimates of a mean sedimentation rate of 4.4 cm year − 1 over the period 1963–1996 and 2.5 cm year − 1 after 1986 for the short successive discontinuous gullies. A new classification of the discontinuous gullies based on two criteria, respectively, the field patterns and the rate of aggradation within the gully basin floor was established. For continuous gullies, linear gully head retreat, areal gully growth and eroded material rates were quantified for three periods (1961–1970, 1971–1980 and 1981–1990). Results indicate that gully erosion has decreased since 1960. This gullying decline is due to the rainfall distribution, and the increased influence of soil conservation practices. The mean gully head retreat of 12.5 m year − 1 between 1961–1990 was accompanied by a mean areal gully growth of 366.8 m 2 year − 1 and a mean erosion rate of 4168 t year − 1 . As with discontinuous gullies, continuous gullies showed pulsatory development. The critical period for gullying over 1981–1996 covers 4 months from Mid March to Mid July in an area with mean annual precipitation around 500 mm. Another main finding of this 16-year stationary monitoring was that 57% of the total gullying occurred during the cold season, with the remainder during the warm season. Of the total gully growth, 66% results from only four years (1981, 1988, 1991 and 1996), when a greater amount of precipitation fell.

Development and controlling factors of gullies and gully complexes, East Coast, New Zealand

AbstractSequential aerial photographs of a small headwater catchment in the Waiapu basin, East Coast Region, North Island, New Zealand, were interpreted to measure and analyse temporal changes in active area of gullies and gully complexes for a longer time span (1939–2003) and with higher temporal resolution compared to previous studies. We focus on the conditions leading to the development of gullies and gully complexes under pasture and forest by using topographic thresholds (slope–area relationships) of catchments for the initiation of gullies and gully complexes. In addition, the influence of two different lithologies as well as the occurrence of major rainfall events was related to gully activity.Twenty gullies and four gully complexes (occupying 62·5 ha or 12·5 per cent of the catchment area) occurred in the study catchment between 1939 and 2003. However, the majority of these were not active at all of the dates studied. Gullies developed in the sandstone‐dominated Tapuwaeroa Formation tended to attain their maximum size by 1957 with a mean catchment area of 2·1 ha. Gullies developed in mudstone of the Whangai Formation attained their maximum size in 1939 with a mean catchment area of 4·31 ha. Exceptions are gullies which developed into mass movement deposits or into an earth flow deposit as well as gullies developed under indigenous forest. Topographic threshold values for gullies under pasture and indigenous forest show that values for gullies under forest plot far above the threshold line of gullies under pasture, indicating that the topographical threshold for gully development under forest is higher compared to under pasture. A threshold value of 9·4 ha in catchment area is needed for the development of gully complexes under pasture, all located in the Whangai Formation and with the same orientation as the strike of the mudstones. Gully‐complex area and dominance of mass‐movement erosion increased with larger catchment area. A decreasing distance to the threshold line for gullies under pasture indicates a later development for gully complexes. No gully complexes developed under indigenous forest, indicating that the threshold value for gully‐complex development is higher than for gully complexes under pasture and was not reached in the study area.A model of shifting topographical threshold for gully development for a given catchment is developed which depends on land use. When a catchment has an indigenous forest cover the topographical threshold is very high. After conversion to pasture, threshold values decrease drastically. With the invasion of scrub, the threshold slowly increases and returns to a similar level to that under indigenous forest after reforestation.Development of gullies and gully complexes is a highly dynamic phenomenon, and phases of expansion and inactivity indicate that models describing only unidirectional advancing stages without periods of inactivity are not suitable. Therefore, this study adds more phases to models of gully and gully‐complex development in the East Coast Region. The threshold line for gully initiation under pasture and a value of 9·4 ha in catchment area for gully‐complex initiation permits one to predict which catchments, under similar environmental settings, develop gullies and gully complexes on a physical basis. This enables land managers to implement sustainable land‐use strategies to reduce erosion rates of gullies and gully complexes. Copyright © 2006 John Wiley &amp; Sons, Ltd.

CONCENTRATED FLOW BREAKTHROUGHS MOVING THROUGH SILVICULTURAL STREAMSIDE MANAGEMENT ZONES: SOUTHEASTERN PIEDMONT, USA1

ABSTRACT: Geomorphic characteristics and spatial frequency of ephemeral concentrated flow paths entering streamside management zones (SMZs) were evaluated to determine the efficiency of best management practices (BMPs) in preventing concentrated overland flow and associated sediment from reaching stream channels. Specifically, SMZs of 30 recently clearcut and site prepared commercial forestry units in the Georgia Piedmont were surveyed to find two types of locations: those where flow and/or sediment from the adjacent silvicultural site entered and moved through SMZs into stream channels (breakthroughs), and those where either flow and/or sediment entered SMZs without reaching stream channels or where no overland flow entered SMZs (successes). A total of 187 breakthroughs were identified on 3,773 total acres. On average, sites featured one breakthrough for every 20 acres of clearcut or site prepared area. The average hydrologic contributing area to a breakthrough was 1 acre. The percentage of the total clearcut or site prepared area contributing to breakthroughs was 5 percent. Approximately 50 percent of all breakthroughs occurred in areas of convergence (swales) and gullies, while 25 percent of all breakthroughs occurred where runoff from roads or skid trails was concentrated. Breakthroughs tended to occur in areas with large contributing area, low litter cover, and steep slopes. However, individually these variables did not differentiate well between breakthroughs and successes. The variables that discriminated best between successes and failures were the product of contributing area and percent bare ground, and the same variable multiplied by average slope. Fourteen percent of the breakthroughs traveled more than 100 feet through SMZs before reaching streams. Results imply that reduction of bare ground, better dispersal of road runoff, introduction of hydraulic resistance to likely flow paths, and targeted extensions of SMZ width may be warranted in improving BMPs on Piedmont forests.

Geomorphological and Geoecological Controls and Processes Following Gully Development in Alpine Mires, Lesotho

Despite the international reputation of Lesotho’s severely eroded landscape, there have been no previous quantitative accounts of soil erosion processes and associated consequences from the alpine belt. This paper examines sedimentological, geomorphological, and geoecological controls and processes following gully development within alpine mires in eastern Lesotho. Contemporary gully extension is controlled by exposure to various sedimentary sequences, by gully sidewall crack development, and by topographic aspect. Significant vertical gully denudation rates of 8 cm (mineral sediment) to 13 cm (peat) were recorded over an 18-mo period. During a 5-d field experiment in July 1999, the continuously frozen south-facing gully walls recorded considerable horizontal movement of peat blocks (avg. = 19.8 mm/5 d), whereas needle ice–induced horizontal particle movement rates on north-facing walls averaged 10.2 mm/5 d. Soil moisture transect data show a pronounced reduction in surface soil moisture toward and between the gullied areas of a mire. The percentage of moisture loss toward midwinter was found to be greater between the gullies (47.4%) than in the adjoining zones, where moisture loss averaged 33.6%. Similarly, vegetation transects indicate a reduction in vegetation cover at the drier and more intensely burrowed (by Otomys, or “ice rats”) zones close to the gullies. Invasive dwarf Karroid shrubs (e.g., Chrysocoma ciliata) are now establishing themselves alongside gullies, burrowed sites, and fringe areas of mires. We found that dryland plant invasions around grazing posts and heavily grazed areas on the slopes subsequently spread along alpine hydrological systems, particularly where gully erosion has created a suitable habitat.

Characteristics and controlling factors of old gullies under forest in a temperate humid climate: a case study from the Meerdaal Forest (Central Belgium)

In many forests of Northwestern Europe old gullies can be found, but few studies have reported their genesis and characteristics. This study investigates these old gullies under forest in the large case-study area of Meerdaal Forest, in the Central Belgian loess belt. The objectives are (1) to determine the spatial distribution of these gullies, (2) to measure their morphological and topographical characteristics and (3) to reconstruct the factors that led to their development. In the 1329-ha study area, 252 channel-like incisions were mapped. Different types of incisions could be distinguished. Besides small and large gullies, many incisions were sunken lanes or road gullies. These road gullies are aligned along north–south oriented lines, whereas the concentration of old gullies is strongly related to the distribution of archaeological sites. Out of the 252 mapped incisions, 43 large gullies and 21 representative road gullies were selected for detailed morphological and topographical measurements. The characteristics of these two types of incisions were compared with ephemeral gullies formed under nearby cropland. Significant differences in morphology between the three types could be demonstrated. Ephemeral gullies under cropland and large gullies under forest differ significantly in all measured parameters, except bottom width. Both the old gullies and road gullies under forest have a significantly larger cross section and total eroded volume compared with the ephemeral gullies observed under cropland. This indicates that once formed, the old gullies were not ploughed in nor were they filled by sediment originating in their drainage areas, because of limited sediment production. Comparing topographical characteristics (i.e. slope at the gully head and runoff contributing area) of forest gullies and ephemeral gullies that formed under cropland yields important indications about their formation. The larger sedimentation slope of forest gullies, compared with ephemeral gullies and road gullies, suggests that the forest gullies incised on vegetated slopes as a consequence of runoff from the adjacent plateau, where the forest cover was disturbed. For the old gullies under forest, no relation between slope at the gully head and runoff contributing area is observed, probably because most gullies occur on very steep slopes. When simulating arable land-use in the study area, zones where ephemeral gullies are expected to develop can be predicted using published topographical threshold relationships. Comparing the zones where ephemeral gullies are predicted with the position of old gullies under forest leads to the conclusion that gully incision was most probably not triggered by extreme rainfall events and that they are not of periglacial origin. The observed gully pattern can best be explained by local, anthropogenically determined land-use changes.

A study on responses of soil erosion and sediment yield to closing cultivation on sloping land in a small catchment using 137Cs technique in the Rolling Loess Plateau, China

By comparison of volumes and 137Cs contents of the deposited sediments before and after 1993, changes of specific sediment yields and relative sediment contributions from the gully area and from the inter gully area after closing cultivation on the later area on a small catchment of Zhaojia Gully, in the Rolling Loess Plateau, are analyzed in this paper. Closing cultivation in a large scale has not resulted in decrease but increase of specific sediment yield of the catchment, in sharp decrease of the sediment yield and the relative sediment contribution of the inter-gully area, and in increase of the sediment yield and the contribution of the gully area, for a short term. The mean specific sediment yield of 29650 t km−2 a−1 of 1994–1996 in the catchment was 2.2 times the average value of 13413 t km−2 a−1 for a long term. The specific sediment yield of the inter-gully area decreased from the 14335 t km−2 a−1 in 1994 to 7034 t km−2 a−1 in 1995 and 3517 t km−2 a−1 in 1996, while the yield of the gully area varied between 44944 and 62136 t km−2 a−1 during the period of 1994–1996 which was much greater than the value of 21118 t km−2 a−1 before 1993. The relative sediment contribution from the inter-gully area decreased from 23% in 1994 to 15% in 1995 and 6% in 1996, while the contribution from the gully area increased from 77% in 1994 to 85% in 1995 and 94% in 1996. It is suggested that compacting of ploughed soils resulted in increasing of the erosion resistance but in decreasing of the precipitation infiltration, therefore, the soil erosion reduced but the runoff amount increased on the inter-gully area. Increase of delivering runoff from the inter-gully area to the gully area should result in activeness of gully erosion and mass movements, consequently, in increase of the total sediment yield from the catchment.

Paraglacial modification of slope form

The morphological consequences of paraglacial modification of valley-side drift slopes are investigated at six sites in Norway. Here, paraglacial slope adjustment operates primarily through the development of gully systems, whereby glacigenic sediment is stripped from the upper drift slope and redeposited in debris cones downslope. This results in an overall lowering of average gradient by up to 4·5° along gully axes. In general, slope profile adjustment appears to be characterized by a convergence of slope profiles towards an ‘equilibrium form’ with an upper rectilinear slope gradient at 29°± 4° and a range of concavities of approximately 0·0 to 0·4. After initial rapid incision, further gully deepening is limited, but gullies become progressively wider as sidewall gradients decline to c. 25°, after which parallel retreat appears to predominate. The final form of mature paraglacial gully systems consists of an upper bedrock-floored source area, a mid-slope area of broad gullies whose sidewalls rest at stable, moderate gradients, and a lower slope zone where gullies discharge onto the surfaces of debris cones and fans. Some gullies appear to have attained this final form and have stabilized following exhaustion of readily entrainable sediment within decades of gully initiation. At most sites, paraglacial activity has transformed steep drift-mantled valley sides into gullied slopes where an average of c. 2–3 m of surface lowering has taken place. At the most active sites, these average amounts imply minimum erosion rates averaging c. 90 mm a−1 since gully initiation, which highlights the extreme rapidity of paraglacial erosion of deglaciated drift-mantled slopes. Copyright © 1999 John Wiley & Sons, Ltd.

USE OF RESERVOIR DEPOSITS AND CAESIUM-137 MEASUREMENTS TO INVESTIGATE THE EROSIONAL RESPONSE OF A SMALL DRAINAGE BASIN IN THE ROLLING LOESS PLATEAU REGION OF CHINA

This paper reports the results of an investigation of the erosional response of the 3.86 km(2) Zhaojia Gully catchment in the rolling loess plateau region of Zichan County, Shaanxi Province, China . In the absence of direct measurements , information derived from reservoir deposits and from caesium - 137 measurements on both the catchment soils and reservoir deposits was used to obtain a retrospective assessment of the longer-term (ca. 30 year) erosional response of the catchment and of the relative contributions of the rolling plateau surface and the gully areas to the sediment output from the basin . Net erosion rates on cultivated land occupying the gentle crest slopes and steeper lower slopes of the rolling plateau and the steep gully slopes were estimated to be 4500 t km(-2) year(-1), 8584 t km(-2) year(-1) and 15851 t km(-2) year(-1) respectively. Estimates of annual sediment yield from the study catchment based on analysis of sediment deposits year in the two sediment-trap reservoirs ranged between 4627 and 32472 t km(-2) year(-1). Almost all the sediment transported from the catchment was contributed by 2-4 large floods each year. Measurements of the caesium - 137 content of recent sediment deposits in a sediment-trap reservoir allowed the relative contributions of the total sediment yield derived from the rolling plateau and gully areas of the catchment to be estimated at 23 and 77 per cent, respectively. Analysis of the sediment deposits dating from 1973-1977 in another sediment trap reservoir allowed individual flood event couplets to be identified and indicated that the sediment associated with the first one or two floods in a season, when the soils of the plateau area were relatively dry, was derived primarily from the gully areas. The cultivated soils of the rolling plateau contributed an increased proportion of the total sediment yield during the latter stages of the flood season when the soils were wetter, and surface runoff and erosion were more widespread. Based on analysis of the caesium - 137 content of the sediment deposited in this sediment-trap reservoir , the relative contributions of sediment from the rolling plateau and gully areas over the period 1973-1977 were estimated to be 21 and 79 per cent, respectively. The results obtained demonstrate the potential for using caesium - 137 measurements and analysis of reservoir deposits to document the erosional response of a drainage basin . (C) 1997 by John Wiley & Sons, Ltd.

Legislation & Regulation

Water scarcity seriously hinders the sustainable development of the fruit tree–crops intercropping system in the Loess Gully Area of western Shanxi. The combination of mulch measures and appropriate irrigation would help to maintain soil moisture and improve crop yield and water use efficiency (WUE). This study investigated the combined effects of mulch and irrigation on soil water and root distribution, yield, and water use of an apple–soybean intercropping system. A three-year field trial was performed with two factors: two types of mulch, namely straw mulch (M1), and plastic mulch (M2), and three levels of maximum irrigation (55%, 70%, or 85% of field capacity [Fc]), which were designated W1, W2, and W3, respectively. Three groups of non-irrigation controls i.e., CK0 (no mulch), CK1 (straw mulch), and CK2 (plastic mulch) were also included. These results indicated that the soil water contents (SWC) in each treatment initially decreased and then increased with increasing distance from the tree, whereas it increased gradually with depth. The SWCs in various sampling points under straw mulch was generally higher than under plastic mulch. The root length density (RLD) of apple tree decreased with increasing distance from the tree in the horizontal direction, while the opposite trend was observed for soybean. The RLD of both apple tree and soybean in the soil layer (0–60 cm) under plastic mulch was higher than that under straw mulch, and increased with increased irrigation level. The underground interspecific competition intensity index (UICII) of the apple–soybean intercropping system under straw mulch was higher than that under plastic mulch, and increased with the increased irrigation amount. Water consumption, soybean yield, and WUE under plastic mulch were significantly higher than under straw mulch. The results of this study suggested that the combination of plastic mulch and irrigation water supplied at 70–85% Fc could effectively increase the yield and WUE of the apple–soybean intercropping system.

Paleoseismicity of the Wellington ‐ Hutt Valley Segment of the Wellington Fault, North Island, New Zealand

Abstract The Wellington Fault is one of the major active right‐lateral strike‐slip faults of the southern North Island and represents a significant seismic hazard to the greater Wellington region. Trench excavations across the fault in the Long Gully/Karori Reservoir area and near Kaitoke, along with Quaternary stratigraphic and soil studies at Te Mania, indicate that the most recent surface rupture event along the southern portion of the Wellington Fault was 300–450 cal B .P. (calendar years before A.D. 1950) and the next oldest event was 670–830 cal B.P. The elapsed time between these two events is 220–530 years. Based on the previously reported 6.0–7.6 mm/yr, long‐term (c. 140 ka), average, horizontal slip rate calculated at Emerald Hill, and the 3.2–4.7 m single‐event offsets (the five most recent events) measured at Te Marua, the average recurrence interval for this portion of the Wellington Fault is 420–780 years. At the Long Gully trench site, two stream channels are laterally displaced by c. 50 m. Displacement has resulted in the ponding of the streams behind an uphill‐facing bedrock scarp. The ponding began about 10 ka, as inferred from the age of the oldest organic material exposed in the trench excavations. The average lateral slip rate in the Long Gully area is thus c. 5 mm/yr. Recent surface fault movements at Long Gully, Te Mania, and Kaitoke have similar timings, suggesting that the 75 km long section of the Wellington Fault extending from Cook Strait to Kaitoke comprises a single fault‐rupture segment: the Wellington ‐ Hutt Valley Segment.

A Miocene Gilbert-type fan-delta from a volcanically influenced lacustrine basin, Rusinga Island, Lake Victoria, Kenya

A lacustrine, volcanically influenced fan-delta is recognized in the Kulu Formation of the Miocene Rusinga Group in western Kenya. In the Nyamsingula Gully area on Rusinga Island in Lake Victoria, mapped lithologic units include the classic topset, foreset (mega-foreset) and bottomset structure of a Gilbert-type delta. A distinctive mega-breccia unit of colluvial origin interfingers laterally with the delta deposits and consists of pyroclastic and sedimentary rock fragments derived from underlying and laterally adjacent strata. The breccia formed from the bevelling of a fault escarpment, from which the fan-delta also originated. Away from the fan-delta axis, slumping of fault-scarp colluvium into the lake produced matrix-supported debris flows that are interbedded with lacustrine shales. In the topset beds of the delta, clasts of a distinctive melilitite–nephelinite tuff of airfall origin can be identified and traced down a palaeoslope through laterally adjacent units from the original bedded tuff, into the mega-breccia unit, and finally into debris-flow deposits in the foreset and bottomset beds. During resedimentation the tuff behaved in a brittle fashion due to quick cementation as a result of its water soluble, ultra-alkaline composition. The Kulu Formation is a distinctive facies that interfingers with the lowermost Hiwegi Formation. Both formations are part of the Rusinga Group. The bulk of the Rusinga Group, excluding the Kulu Formation, represents braidplains and alluvial aprons that flanked the Miocene volcano of Kisingiri. The braidplain and alluvial apron deposits have primary dips away from the volcano and were derived from material erupted and eroded from the volcano. The Kulu Formation, in contrast, was deposited in two small, elongate lacustrine basins separated by a small horst (approximately 5 km long and 2–3 km wide), from which the deposits were largely derived. The fan-delta systems prograded symmetrically away from the horst margins, into the adjoining lacustrine basins. The long dimensions of the horst and lake basins roughly parallel the local slope of the Kisingiri volcano, and therefore deposition in the Kulu Formation was perpendicular to deposition of the other Rusinga Group formations in the vicinity

Use of caesium‐137 measurements to investigate erosion and sediment sources within a small drainage basin in the loess plateau of China

AbstractThe contributions of sediment from different geomorpholigical units within a small basin in the Loess Plateau have been determined using caesium‐137 as a tracer. The mean caesium‐137 content of sediment originating from the hill area, where sheet and rill erosion are predominant, was 3–37 Bq kg‐1, whereas no caesium‐137 was detected in the sediment originating from the gully area where gullying and gravitational erosion are predominant. The mean caesium‐137 content of sediment from two flood deposits was 0–23 Bq kg‐1 and 0–89 Bq kg‐1. The relative contribution from the hill area in the two floods was 7 per cent and 26 per cent, whilst that from the gully area was 93 per cent and 74 per cent.