Soil seed flora, germination and regeneration pattern of woody species in an Acacia woodland of the Rift Valley in Ethiopia

The objectives of this study were to determine the composition, density and spatial distribution of the soil seed bank of woody species, as well as their regeneration pattern in two different land use systems, controlled (ranch) and open grazing, in an Acacia woodland of the Rift Valley in Ethiopia. We also compared the species composition of the soil seed bank and the above-ground vegetation to find out if differences exist in the soil seed bank and advance regeneration between the two land use systems. The germination requirements of seeds of the woody species were also investigated under laboratory conditions. Acacia senegal, Acacia seyal, Acacia tortilis, Dichrostacys cinerea and Balanites aegyptiaca were encountered in the above-ground vegetation in both systems. Seeds of only A. tortilis (90±32 seeds m⁻²) from the ranch, and A. senegal (5±3 seeds m⁻²) and A. tortilis (72±34 seeds m⁻²) from the open system were found in the soil seed bank along transects with patchy horizontal pattern. The two systems were not significantly different in density of soil seed banks of A. senegal andA. tortilis . Jaccard's similarity index showed that only a few woody species were common in the soil seed flora and above ground vegetation. However, all of the species accumulated seeds (58±43–331±130 seeds m⁻²) in/on the soil under the canopy. Very large numbers of seeds of A. tortilis (19382±9722 seeds m⁻²) and D. cinerea (1278±494 seeds m⁻²) were also found in barns. Most of the seeds recovered from the soil samples (60–80%) were found in the litter layer. Acid and mechanical scarification improved legume germination (36–99% and 60–99%, respectively) over boiling water (0–48%). Treatment means differed significantly for all the legumes (p<0·001) but not for Balanites. Height and diameter class distribution of regeneration of A. tortilis and D. cinerea in both systems and A. senegal in the open system had a negative exponential correlation (r_s=−0·5, −0·25 and −0·86, respectively). A. seyal and B. aegyptiaca showed poor regeneration. Horizontal distribution of advance regeneration of all the species was patchy. Advance regeneration of A. seyal, A. tortilis and B. aegyptiaca were not significantly different, while that of A. senegal and D. cinerea were significantly different between the two systems. Poor representation of species in the soil seed bank along transects and in the different height and diameter classes may be attributed to the low density of mature trees as well as the mode and strategy of seed dispersal. Ungulate and wind dispersed species (e.g. A. senegal, A. tortilis and D. cinerea) were highly favoured. Patchiness in the distribution of seeds and advance regeneration was also a result of endozoochory. Dispersal of non-ungulate dispersed seeds (A. senegal, A. seyal and B. aegyptiaca) was restricted to the canopy zone. Piles of seeds ofA. tortilis and D. cinerea that were found in barns were a result of consumption of their pods by cattle. High concentration of seeds in the litter layer may be due to low soil disturbance and larger size of seeds. The height and diameter class distribution of A. senegal (in the open system), A. tortilis and D. cinerea also indicated that the species have good regeneration. Results from the germination tests indicated that seeds of the legumes require pre-sowing treatments to give a rapid, uniform and improved germination. Intervention through artificial regeneration should be employed to improve the density and regeneration capacity of those species with hampered regeneration at both systems.     

Effects of indole-3-acetic acid and zinc on the growth, osmotic potential and soluble carbon and nitrogen components of soybean plants growing under water deficit

Three-week old soybean (Glycine max) plants were subjected to a factorial combination of four regimes of soil matric water potential (ψ_m=−0·03, −0·5, −1·0 and −1·5 MPa), two levels of supplementary Zn (O and 20 mgl⁻¹) and two levels of foliar IAA application (O and 10 mgl⁻¹). Under control conditions (no Zn, no IAA), increasing soil drying progressively retarded shoot and root growth (length and dry mass production), reduced leaf relative water content (RWC) and decreased the contents of chlorophyll (Chl) and shoot soluble sugars (SS), but increased soluble sugar content of roots and lowered osmotic water potential of shoots and roots (osmotic adjustment). Total free amino acid (TAA) content increased in shoots but decreased in roots whereas contents of soluble proteins (SP) decreased in shoots and roots. The effect of water stress was statistically significant (p<0·05) and had a major effect (as indicated by η²values) on leaf RWC, shoot and root dry masses and osmotic potential. Supplementary Zn improved root growth at all levels of stress and shoot growth under severe stress. Improvement of growth was positively correlated with the internal tissue Zn concentrations (r=0·91 and 0·86 for shoot and 0·94 and 0·82 for root length and dry mass respectively). Exogenous IAA raised (p<0·05) RWC, Chl, DM (slightly), root SS, and SP, whereas shoot TAA was lowered. Effects on root TAA and shoot SS were more complex: they were lowered at zero stress and raised under severe stress. IAA and Zn in combination had additive effects on Chl, growth and osmotic potential, but their combined effects on SP and TAA were more complex. It is concluded that the treatment of soybean plants grown under conditions of low soil water potentials and Zn deficiency with Zn and IAA solutions counteracted the deleterious effects of stress, especially at high stress levels, and helped stressed plants to grow successfully under these adverse unfavourable conditions.     

Groundwater Balance and Safe Yield of the coastal aquifer system in NEastern Korinthia, Greece

The northern coastal part of Korinthia prefecture can be characterized as an agrotourism center that has grown and urbanized rapidly. The area is formed of recent unconsolidated material consisting of sands, pebbles, breccias and fine clay to silty sand deposits. These deposits host the main aquifer system of the area, which depends on groundwater as a water resource. Groundwater is the main source for irrigation in the area. A total water volume of 29.2×10⁶–34.3×10⁶ m³ yr⁻¹ was estimated to recharge the aquifer system from direct infiltration of rainfall, streambed infiltration, irrigation return, artificial recharge via flood irrigation and lateral subsurface inflows. The present annual abstraction ranges between 39.2×10⁶ and 44.6×10⁶ m³ yr⁻¹. Groundwater abstraction in dry years exceeds renewable freshwater resources by more than 38%. Approximately 79% of the total abstraction is consumed for agriculture supply. Water balance in the coastal aquifer system is in disequilibrium; a deficit, which ranges from 4.9×10⁶ to 15.4×10⁶ m³ yr⁻¹ exists. The safe yield of the coastal aquifer system has been estimated at 37.1×10⁶ m³ yr⁻¹ for normal hydrological year and 32×10⁶ m³ yr⁻¹ for severely dry hydrological year. The total abstraction is greater than the recharge and the safe yield of the aquifer. The aquifer system has shown signs of depletion, seawater intrusion and quality contamination. The integrated water resources management, securing water in the future, should include measures that augment groundwater budget in the coastal aquifer of the study area.     

Invasion of the noxious weed Nicotiana glauca R. Graham after an episodic flooding event in the arid zone of Australia

During November 1997, an extreme rainfall event caused flooding in the Olary Creek and created a terminal lake within mallee vegetation on Nagaela Station, far western New South Wales. To assess the effect of this rare event on native flora, six 25×25 m² grazing exclusion plots were established on flooded (4), and un-flooded control (2) areas. We investigated (i) the distribution of Nicotiana glauca in relation to the 1997 flooding event (ii) the variation in density of N. glauca soil-stored seed between soil in control and exclosure plots (iii) the allelopathic effects of N. glauca on germination of Lactuca sativa seeds. Analysis of N. glauca stem sections revealed a maximum of five growth rings, confirming an origin following the 1997 flood event. At a September 1998 assessment, no N. glauca were found across flooded and control plots. In October 2000 N. glauca occurred at densities of 24 and 12 N. glauca seedlings ha⁻¹ in the flooded unfenced and fenced plots respectively. No N. glauca individuals were recorded either from control fenced or unfenced plots. The soil-stored seed study revealed that larger numbers of N. glauca seeds were recovered from the flooded open plot (1936±968) than in flooded fenced plots (856±428.12) but none was found in the control plots. Leachates obtained from dry leaves and twigs had a significantly greater negative impact (p>0.001) on germination of L. sativa seeds than leachates obtained from fresh leaves and bark. This study showed that the density of N. glauca is high in areas where grazing had eliminated competition from native shrubs and grasses. N. glauca is potentially a serious weed along the Olary Creek and ephemeral lake boundaries. Management strategies such as reducing grazing pressure from native and introduced animals and/or effective eradication programs should be adopted, to minimize further infestation.     

Groundwater resources and quality in northeastern Jordan: safe yield and sustainability

Over-abstraction of groundwater is one concern of the Badia Research and Development Programme. The upper aquifer of the Azraq basin forms the largest resource of good-quality water, but current abstraction exceeds both average recharge and the safe yield of the aquifer, which is over-exploited. Although there has been no deterioration in water quality and only minor drawdown, the springs at Azraq have dried up, with severe, undesirable environmental impacts. Total abstraction of 20 × 10⁶ m³ yr⁻¹ appears to be sustainable and would allow some springflow, but this leaves a shortfall of 40 × 10⁶ m³ yr⁻¹ for domestic supply and agriculture.     

Germination of Callitris seeds in relation to temperature, water stress, priming, and hydration–dehydration cycles

The effects of temperature, water stress, hydration–dehydration cycles and seed priming on the germination of Callitris verrucosa and Callitris preissii, two Australian semi-arid coniferous tree species, were investigated. Optimum germination occurred at 18°C, with a minimum germination time of 8–9 days for both species. At this temperature, germination was inhibited at osmotic potentials lower than −1·0 MPa, but the capacity to germinate at low osmotic stress increased as the temperature decreased. Seed priming and hydration–dehydration cycles did not reduce seed viability, and Callitris seeds appear to retain the physiological changes induced by short-term hydration, as the time to the onset of germination was decreased to about 3 days. The capacity of Callitris seeds for incremental germination is likely to increase overall germination success in a low rainfall environment.     

Seeds dispersed in dung of insectivores and herbivores in semi-arid southern Africa

We investigated the incidence of endozoochory in the semi-arid South African Karoo shrubland and Kalahari savanna by dissecting and germinating seed from dung samples from a wide range of wild mammals and domestic livestock. Intact seeds occurred at a mean density of 1575 seeds kg⁻¹in livestock air-dried dung and 3613 seeds kg⁻¹in air-dried dung of indigenous animals. Seedlings emerged from dung at an average density of 153 kg⁻¹air-dry dung. Seeds of Aizoaceae, Mesembryanthemaceae, Chenopodiaceae and Poaceae were abundant in the dung of wild and domestic herbivores as well as such ant- and termite-eating insectivores as aardvark (Orycteropus afer) and bat-eared fox (Otocyon megalotis). Seeds of fleshy-fruited shrubs occurred in dung of browsing herbivores and the bat-eared fox. Five non-indigenous weeds were found in the dung samples. Although the floras of the Kalahari and Karoo are considered to be largely wind and water-dispersed, endozoochory is a primary or secondary dispersal mechanism in many plant families and for many plant life-forms. Animals dispersed seeds of many species characteristic of fertile and disturbed habitats. In Mesembryanthemaceae, a family in which seeds are primarily dispersed very short distances by raindrops, endozoochory enables occasional long-distance dispersal.     

Responses of photosynthesis and water relations to rainfall in the desert shrub creosote bush (Larrea tridentata) as influenced by municipal biosolids

Responses of photosynthesis (P_n), stomatal conductance (g_s), pre-dawn leaf water potential (Ψ_lp) and leaf water content (ω_l) of creosote bush to 10 rainfall events in the Chihuahuan Desert were investigated. Infiltration of rainwater was manipulated by applying municipal biosolids. The responses of P_nand water relation parameters to rainfall (>10 mm) were mainly dependent upon drought severity: (1) following a moderate drought, P_n, g_s, Ψ_lpand ω_lrecovered to corresponding values of irrigated plants within 2 days after a 23-mm rainfall; (2) Ψ_lpand g_sresponded to a 15-mm rainfall within 2 days, following a 25-day drought, whereas responses of P_nand ω_lwere delayed for several days; (3) responses of P_n, g_s, Ψ_lpand ω_lto a 14·7-mm rainfall were all delayed for several weeks following a 110-day drought, but the delay was longer in P_n, g_sand ω_lthan in Ψ_lp. Creosote bush responded to small rainfall events (approximately 6 to 8 mm) with an increase in Ψ_lp, but without noticeable changes in g_sand P_n, suggesting a strong stomatal control of water loss even though xylem embolism was reduced. Biosolids applied at high rates (3·4 and 9 kgm⁻²) decreased the soil water by 2 to 4 mm following rainfall events, and this in turn delayed and decreased the responses of P_nand water relation parameters to rainfall.P_nand g_swere linearly related to ω_land exponentially related to Ψ_lp. With the generally coincidental responses of P_nor g_sand ω_lto rainfall, we concluded that the responses of P_nand g_sto rainfall were dependent on leaf rehydration which resulted from restored hydraulic conductance following drought.     

Reproductive and recruitment traits as indicators of the invasive potential of Kalanchoe daigremontiana (Crassulaceae) and Stapelia gigantea (Apocynaceae) in a Neotropical arid zone

Populations of two ornamental exotic species, Kalanchoe daigremontiana and Stapelia gigantea, have been recently detected inside a protected area containing arid ecosystems in Venezuela. We indirectly tested their invasive potential by characterizing their reproductive biology and recruitment patterns and comparing our estimates against Baker's Law and reproductive profiles reported for invasive plants. K. daigremontiana is autogamous, produces >16,000 seeds per plant and also reproduces clonally. Despite low seed viability (17.9%) and germination rates (11.9%), seeds were present in the seed bank. Plantlets of asexual origin showed high survival (75–100%) compared to seedlings of sexual origin (10%). S. gigantea is self-incompatible, xenogamous and produces close to 1500 seeds per m² of plant tissue. Seed viability (77%) and germination rates (62%) were high, but this species is not represented in the seed bank. It has a vegetative growth. A combination of reproductive and recruitment attributes, which match those considered in Baker's Law and others reported for invasive plants, confer K. daigremontiana and S. gigantea the potential to invade Neotropical arid zones; the former mainly through selfing and production of numerous asexual plantlets, and the latter through an association with a locally abundant pollinator and production of wind dispersed seeds.     

Ground-water quality of the Nile west bank related to soil characteristics and geological setting

The objective of this study is to outline how the ground-water quality is affected by geological factors, soil characteristics and subsurface structure. The results of 25 ground-water samples, and 30 soil samples of which 10 soil samples analysed chemically provide the basis of this study. Procedures to interpret water quality data are based on a combined use of the traditional graphical methods, ratios of Na⁺/Cl⁻and Ca²⁺/Mg²⁺, multivariate geostatistical methods and computation of the saturation indices (SI) of minerals. The results of soil analyses show that the grain size ranges from very coarse sand to clayey loams, and from well sorted and extremely poorly sorted. The soil salinity increases in old alluvial plains and decreases in the dissected wadis of limestone plateaux, while vertical distribution decreases with depth. It is found that the ground-water is supersaturated with respect to calcite and dolomite, and undersaturated with respect to gypsum. Calculated values of P_CO2for the ground-water samples range from 2×10⁻⁴to 7×10⁻³with a mean value of 3×10⁻³(atm.). This indicates that the ground-water becomes charged with CO₂during infiltration processes.     

Chemical weathering and CO2 consumption in the Xijiang River basin, South China

Monthly samples of riverine water were collected and analyzed for the concentrations of major ions (Ca²⁺, Mg²⁺, K⁺, Na⁺, HCO₃⁻, SO₄²⁻, Cl⁻, NO₃⁻), dissolved silicon, and total dissolved solids (TDS) at Wuzhou hydrological station located between the middle and lower reaches of the Xijiang River (XJR) from March 2005 to April 2006. More frequent sampling and analysis were carried out during the catastrophic flooding in June 2005. Stoichiometric analysis was applied for tracing sources of major ions and estimating CO₂ consumption from the chemical weathering of rocks. The results demonstrate that the chemical weathering of carbonate and silicate rocks within the drainage basin is the main source of the dissolved chemical substances in the XJR. Some 81.20% of the riverine cations originated from the chemical weathering processes induced by carbonic acid, 11.32% by sulfuric acid, and the other 7.48% from the dissolution of gypsum and precipitates of sea salts within the drainage basin. The CO₂ flux consumed by the rock chemical weathering within the XJR basin is 2.37 × 10¹¹ mol y^− 1, of which 0.64 × 10¹¹ mol y^− 1 results from silicate rock chemical weathering, and 1.73 × 10¹¹ mol y^− 1 results from carbonate rock chemical weathering. The CO₂ consumption comprises 0.38 × 10¹¹ mol during the 9-d catastrophic flooding. The CO₂ consumption from rock chemical weathering in humid subtropical zones regulates atmospheric CO₂ level and constitutes a significant part of the global carbon budget. The carbon sink potential of rock chemical weathering processes in the humid subtropical zones deserves extra attention.     

Seed germination of five Helianthemum species: Effect of temperature and presowing treatments

The germination behaviour of five Helianthemum species (H. almeriense, H. appeninum, H. cinereum, H. hirtum, H. squamatum) has been studied under controlled conditions. Constant 15, 20 or 25 °C and alternating 25/15 °C temperature regimes and 16/8 h light/dark photoperiod conditions were used. Presowing treatments applied were manual scarification, boiling water, hot water, dry heat and sulphuric acid. Germination values recorded were final germination percentage and germination rate expressed as days to reach 50% of the final germination percentage (T₅₀). Incubation temperature had no significant effect on final germination percentage for untreated seeds of the five Helianthemum species. However, variation due to temperature was significant for scarified seeds, with the lowest germination percentage attained at 25 °C. In all Helianthemum species studied, the highest germination percentages were obtained by manual scarification of seeds. Germination rate of scarified seeds decreased as germination temperature increased. The different presowing treatments investigated allowed some germination in some species, but none were any better than manual scarification. The high germination among most species studied, following mechanical rupture of the seed coat, shows that the mechanism of dormancy lies in the seed coat. The physical dormancy caused by impermeable seed-coat appears to be the main reason of poor germination of untreated seeds of Helianthemum species studied.     

Thermoregulation, water balance and plasma constituents in Sudanese desert sheep: responses to diet and solar radiation

The responses of desert rams to diet composition (concentrate vs. lucerne hay) in unshaded and shaded environments were investigated. The rectal temperature was higher (p < 0·01) with the concentrate diet but only in the afternoon, whereas the respiration rate was higher (p < 0·01) with the concentrate diet in unshaded and shaded environments during both morning and afternoon. Dry matter intake (DMI) was higher (p < 0·05) with the concentrate diet, while the ratio of water intake to DMI was higher (p < 0·01) with lucerne hay. Water gain through preformed and metabolic avenues and water loss through faeces and evaporative avenues were higher (p < 0·01) with the concentrate diet. With both diets, water turnover rate was higher (p < 0·05) in the unshaded environment. Feeding lucerne hay increased plasma total protein (p < 0·01) and albumin (p < 0·05) in unshaded and shaded environments. Plasma urea was higher (p < 0·01) with the concentrate diet. Plasma glucose level and plasma osmalality were higher (p < 0.01) and level of free fatty acids was lower (p < 0·01) with the concentrate diet in both thermal environments. Plasma cholesterol level was higher (p < 0·05) with the concentrate diet in the shaded environment, but lower (p < 0·05) in the unshaded environment. With lucerne hay, plasma cholesterol level remained the same in both environments.     

Seed reserves in the central Monte Desert, Argentina: implications for granivory

It has been suggested that lower rates of granivory in South American warm deserts compared to their North American counterparts arose from a reduction of seed reserves in the former owing to the extinction of argyrolagid marsupials. We measured seed reserves in two habitats of the central Monte Desert in an attempt to detect such seed decline, but to no avail. After moderate rainfall, maximum seed standing crops reached 16,000 and 23,000 seeds m⁻²in shrublands and open forests, respectively. Under the canopy of trees and shrubs there were 19,000 and 37,000 seeds m⁻²; whereas in exposed areas there werec. 10,000 seeds m⁻²in both habitats. Seed banks in other South American semi-arid areas showed similar values. Total grass seeds as well as those presumably preferred by ants also seem to be similar in both continents. Hence, granivory in South America, as has been already reported for Australia, is lower than in North America in spite of the great similarity of seed bank sizes. Moreover, argyrolagids were unlikely seed-hoarding granivores, therefore some other reason than argyrolagid extinction should be sought to explain the lack of specialized seed-eating mammals, and the smaller overall seed consumption rates in South American deserts.     

Germination of Denmoza rhodacantha (Salm-Dyck) Britton & Rose (Cactaceae)

The germination response of Denmoza rhodacantha (Salm-Dyck) Britton & Rose to seed scarification and different calcium concentrations was analysed. Both scarified and unscarified seeds were treated with two different calcium concentrations (1.74 or 6.36 meq l⁻¹ calcium sulfate in distilled water). All treatments were conducted under a constant temperature (30 °C), and a photoperiodic regime of 12 h light and 12 h dark. Germination was initiated significantly sooner (3.6 days), and the rate of final germination was significantly higher (90.8%), for scarified seeds treated with a solution of 6.36 meq l⁻¹ Ca compared with all other treatments (9.0–11.4 days and 3.6–6.8%, respectively). There were no significant differences among the treatments for the time in which 50% of final germination occurred (6.9–13.6 days). The results suggest that both factors, scarification and calcium concentration, favor germination of Denmoza seeds.     

Seed germination responses of Periploca sepium Bunge, a dominant shrub in the Loess hilly regions of China

Experiments were conducted to determine the effects of temperature, light, osmotic stress, hydration-dehydration regime and stress relief on the seed germination of Periploca sepium Bunge (Chinese silk vine Asclepiadaceae), which is a native shrub in the Loess Plateau of Northwest China. Freshly harvested seeds germinated equally well in both light and darkness. Seeds germinated under all of tested temperature regimes, and much faster when temperature was maintained at 30, 35, and 30/20, 30/25, 35/25, 35/30 °C range, with more than 90% of seeds germinating within 2 days. Moderate osmotic stress did not inhibit germination at any tested temperature. At 30 °C, seed germination was not affected significantly above −0.8 MPa. The hydration-dehydration pretreatment showed none side effects on P. sepium seeds and the seeds germinated more rapidly as soon as optimal water condition was restored. These results show the advantages of P. sepium, which is a competitive and widespread shrub in dry areas, and provide useful information for vegetation restoration in these drought-prone regions.     

Effect of rhizobia inoculation on the seed (herbage) production of mungbean (Phaseolus aureusRoxb.) grown at Uzbekistan

In field trials conducted at Uzbekistan, inoculation of mungbean (Phaseolus aureusRoxb.) with commercial strain CIAM1901 ofBradyrhizobiumsp. (Phaseolus) increased (on average for two cultivars) the herbage mass by 46·6±6·0%, seed mass by 39·2 ± 3·6%, mass of 1000 seeds by 16·0 ± 0·8%, nitrogen content in seeds by 58·3 ± 8·9%, starch content in seeds by 30·0 ± 5·5% and number of nodules by 254%. Inoculation with this strain produced the same herbage (seed) mass as NH₄NO₃application (120 kg ha⁻¹of N), while the combined treatment of rhizobia and 60 kg ha⁻¹of N produced significantly higher yields than rhizobia inoculation alone or application of 120 kg ha⁻¹of N. The rhizobia strain M11 was isolated from Uzbekistan soils and significantly exceeded the commercial strain CIAM1901 in its influence on herbage mass by 3·9–10·6%. Two-factor analysis of variance demonstrated that the herbage mass and number of nodules are controlled mainly by the rhizobia strain genotypes, while seed yield, number of pods, mass of 1000 seeds and N and starch content in seeds are influenced by the plant cultivar genotypes.     

Flux and fate of Yangtze River sediment delivered to the East China Sea

Numerous cores and dating show the Yangtze River has accumulated about 1.16 × 10¹² t sediment in its delta plain and proximal subaqueous delta during Holocene. High-resolution seismic profiling and coring in the southern East China Sea during 2003 and 2004 cruises has revealed an elongated ( 800 km) distal subaqueous mud wedge extending from the Yangtze River mouth southward off the Zhejiang and Fujian coasts into the Taiwan Strait. Overlying what appears to be a transgressive sand layer, this distal clinoform thins offshore, from  40 m thickness between the 20 and 30 m water depth to < 1–2 m between 60 and 90 m water depth, corresponding to an across shelf distance of less than 100 km. Total volume of this distal mud wedge is about 4.5 × 10¹¹ m³, equivalent to  5.4 × 10¹¹ t of sediment. Most of the sediment in this mud wedge comes from the Yangtze River, with some input presumably coming from local smaller rivers. Thus, the total Yangtze-derived sediments accumulated in its deltaic system and East China Sea inner shelf have amounted to about 1.7 × 10¹² t. Preliminary analyses suggest this longshore and across-shelf transported clinoform mainly formed in the past 7000 yrs after postglacial sea level reached its mid-Holocene highstand, and after re-intensification of the Chinese longshore current system. Sedimentation accumulation apparently increased around 2000 yrs BP, reflecting the evolution of the Yangtze estuary and increased land erosion due to human activities, such as farming and deforestation. The southward-flowing China Coastal Current, the northward-flowing Taiwan Warm Current, and the Kuroshio Current appear to have played critical roles in transporting and trapping most of Yangtze-derived materials in the inner shelf, and hence preventing the sediment escape into the deep ocean.     

Long-term bed load transport rate based on aerial-photo and ground penetrating radar surveys of fan-delta growth, Coast Mountains, British Columbia

Sequential aerial photography, sonar bathymetry, ground-penetrating radar (GPR), and sediment sampling and analysis provide the basis for calculating the volumetric and mass rate of progradation of the delta of Fitzsimmons Creek, a steep, high-energy, debris-flow-dominated channel draining about 100 km² of the southern Coast Mountains of British Columbia. Fitzsimmons Creek is typical of small mountain rivers in the region. GPR imaging is used to define the pre-depositional morphology of the receiving basin, a technique that improves the accuracy of the volumetric survey. The 52-year record (1947–1999) of progradation yielded an average annual volumetric transport rate of 1.00±0.16×10⁴ m³ year⁻¹ for bed load, corresponding to a mass transport rate of 1.60±0.28×10⁴ Mg year⁻¹. Bed load yields are consistent with those obtained in hydrogeomorphically similar basins in the region and elsewhere. Decade-based annual rates, which vary from 0.64±0.11×10⁴ to 2.85±0.38×10⁴ Mg year⁻¹, provide poor estimates of the 52-year average. Indeed, the 52-year record may also not be long enough to fully integrate the significant fluctuations in the sediment efflux from Fitzsimmons Creek. The methodology proposed in this paper can be transferred to other comparable mountain environments worldwide.     

Plant water relations of thornscrub shrub species, north-eastern Mexico

As an approach to understand how diurnal and seasonal plant water potentials (Ψ) are related to soil water-content and evaporative demand components, the responses of six thornscrub shrubs species (Havardia pallens, Acacia rigidula, Eysenhardtia texana, Diospyros texana, Randia rhagocarpa, and Bernardia myricaefolia) of the north-eastern region of Mexico to drought stress were investigated during the course of 1 year. All study species showed the typical diurnal pattern of variation in Ψ. That is, Ψ decreased gradually from predawn (Ψ_pd) maximal values to reach minima at midday (Ψ_md) and began to recover in the late afternoon. On a diurnal basis and with adequate soil water-content (>0.20 kg kg⁻¹), diurnal Ψ values differed among shrub species and were negatively and significantly (p<0.001) correlated with air temperature (r=−0.741 to −0.883) and vapor pressure deficit (r=−0.750 to −0.817); in contrast, a positive and significant (p<0.001) relationship was found to exist with relative humidity (r=0.758–0.842). On a seasonal basis, during the wettest period (soil water-content>0.20 kg kg⁻¹), higher Ψ_pd (−0.10 MPa) and Ψ_md (−1.16 MPa) values were observed in R. rhagocarpa, whereas lower figures (−0.26 and −2.73 MPa, respectively) were detected in A. rigidula. On the other hand, during the driest period (soil water-content<0.15 kg kg⁻¹), Ψ_pd and Ψ_md values were below −7.3 MPa; i.e. when shrubs species faced severe water deficit. Soil water-content at different soil layers, monthly mean relative humidity and monthly precipitation were significantly correlated with both Ψ_pd (r=0.538–0.953; p<0.01) and Ψ_md (r=0.431–0.906; p<0.05). Average soil water-content in the 0–50 cm soil depth profile explained between 70% and 87% of the variation in Ψ_pd. Results have shown that when gravimetric soil water-content values were above 0.15 kg kg⁻¹, Ψ_pd values were high and constant; below this threshold value, Ψ declined gradually. Among all shrub species, A. rigidula appeared to be the most drought tolerant of the six species since during dry periods it tends to sustain significantly higher Ψ_pd in relation to B. myricaefolia. The remaining species showed an intermediate pattern. It is concluded that the ability of shrub species to cope with drought stress depends on the pattern of water uptake and the extent to control water loss through the transpirational flux.