Simulation,quantification and comparison of in-channel and floodplain sediment processes in a lowland area – A case study of the Upper Stör catchment in northern Germany

Erosion and sedimentation processes within the channel and on the floodplain are indicative of catchment hydrodynamic procedures, as well as the associated nutrient and contaminant transportation. In this paper, we linked the SWAT model with the hydraulic HEC-RAS model to set up a sediment model for 10 river sections in the Upper Stör catchment and simulated the sediment processes from 2001 to 2010. Based on the HEC-RAS output, quantification and comparison of channelized and floodplain sediment processes were conducted. The results indicate that (1) with an average sedimentation depth of 2.85 cm, the deposition process dominated the Upper Stör catchment at the decadal time scale, and the land use/cover condition resulted in differences in sedimentation amounts between different sub-catchments, and (2) the mean deposition rates were 1.75 g/m²/d in the channel and 1.69 g/m²/d on the floodplain, and the floodplain deposition accounted for only 1% of the total sedimentation amount. This observation was mainly caused by the stream power distribution in the channel and on the floodplain. (3) The granularity of the channelized sedimentation was determined by the altitude of the river section, while the granularity of the floodplain sedimentation was positively correlated with the stream power of the flood. The D50s of the channelized and floodplain sediments were 0.92 mm and 0.16 mm, respectively, while the D90 of the sediment was 4.2 mm in the channel and 0.32 mm on the floodplain. Despite the higher uncertainty of the sediment simulation, the results yielded by the combination of the HEC-RAS and SWAT models are comparable to the traditional radioactive dating, sediment trapping or combined model methods used in similar and nearby catchments.     

Partitioning of water resources among plants of a lowland tropical forest

Source water used by plants of several species in a semi-evergreen lowland tropical forest on Barro Colorado Island, Panama, was assessed by comparing the relative abundance of deuterium, D, versus hydrogen, H (stable hydrogen isotope composition, D) in xylem sap and in soil water at different depths, during the dry season of 1992. Ecological correlates of source water were examined by comparing xylem water D values with leaf phenology, leaf water status determined with a pressure chamber, and rates of water use determined as mass flow of sap using the stem heat balance method. Soil water D values decreased sharply to 30 cm, then remained relatively constant with increasing depth. Average D values were-13, for 0–30 cm depth and-36.7 for 30–100 cm depth. Soil water D values were negatively associated with soil water content and soil water potential. Concurrent analyses of xylem water revealed a high degree of partitioning of water resources among species of this tropical forest. Xylem water D of deciduous trees (average=-25.3±1.4) was higher than that of evergreen trees (average=-36.3±3.5), indicating that evergreen species had access to the more abundant soil water at greater depth than deciduous species. In evergreen shade-tolerant and high-light requiring shrubs and small trees, D of xylem water was negatively correlated with transpiration rate and leaf water potential indicating that species using deeper, more abundant water resources had both higher rates of water use and more favorable leaf water status.     

Concentration of iron and manganese in rice plants as influenced by hexachlorocyclohexane applied to soil

Summary Application of a granular formulation of hexachlorocyclohexane (HCH) to the potted soil at flooding decreased the concentration of iron and. to some extent, manganese in rice plants, especially at concentrations above 3 ppm active ingredient (a.i.) Likewise, HCH, applied to rice fields at transplanting (several days after submergence) caused a significant decrease in the concentration of iron, and not manganese, in the rice plant but only at concentrations above 12.5 kg a.i./ha despite high levels of reduced iron in the soil. Inhibition of iron reduction by HCH was more pronounced when applied at flooding than at several days after flooding.     

氢醌和双氰胺对种稻土壤N2O和CH4排放的影响

通过盆栽试验,研究了脲酶抑制剂氢醌（ＨＱ）、硝化抑制剂双氰胺（ＤＣＤ）及二者的组合（ＨＱ＋ＤＣＤ）对种稻土壤Ｎ２Ｏ和ＣＨ４排放的影响．结果表明,在未施麦秸粉时,所有施抑制剂的处理均较单施尿素的能显著减少水稻生长期供试土壤Ｎ２Ｏ和ＣＨ４的排放．特别是ＨＱ＋ＤＣＤ处理,其Ｎ２Ｏ和ＣＨ４排放总量分别约为对照的１／３和１／２．而在施麦秸粉后,该处理的Ｎ２Ｏ排放总量为对照的１／２,但ＣＨ４排放总量却较少差别．不论是Ｎ２Ｏ还是ＣＨ４的排放总量,施麦秸粉的都比未施的高出１倍和更多．因此,单从土壤源温室气体排放的角度看,将未腐熟的有机物料与尿素共施,并不是一种适宜的施肥制度．供试土壤的Ｎ２Ｏ排放通量,与水稻植株的ＮＯ－３Ｎ含量和土表水层中的矿质Ｎ量分别呈显著的指数正相关和线性正相关;ＣＨ４的排放通量则与水稻植株的生长量和土表水层中的矿质Ｎ量呈显著的线性负相关．在Ｎ２Ｏ与ＣＨ４的排放间,未施麦秸粉时存在着定量的相互消长关系;施麦秸粉后,虽同样存在所述关系,但难以定量化．     

Landscape diversity patterns and endemism of Araceae in Ecuador

Araceae is one of the largest herb families in tropical America, but its patterns of diversity and endemism are poorly known. We used predictive distribution modelling in GIS to study Araceae richness on a landscape scale in Ecuador. Modelling was based on georeferenced herbarium collections with humidity and mean annual temperature as climatic variables. Variation partitioning using multiple regression showed that humidity and altitude were main factors in explaining Araceae diversity patterns. Endemism was less well explained by present climatic factors. Unlike common diversity patterns of herbs or epiphytes, Araceae richness was highest in the eastern (Amazon) lowland rain forest with a secondary centre on the Andean foothills of northwestern Ecuador. The peak in endemism was on the western slopes of the Andes, corresponding to areas that have been severely affected by human activities and deforestation. Eastern lowland (Amazonian) forests were poor in endemic Araceae.     

Lentic water quality characterization using macroinvertebrates as bioindicators: An adapted BMWP index

Water quality in lowland lentic system was evaluated through the use of aquatic macroinvertebrates as bioindicators, and their relationship with basic physicochemical factors was considered; thus, two biotopes were established for identifying both groups of macroinvertebrates, one being the population associated with macrophytes (AM) and the other being benthic (B). As a result, 46 families of macroinvertebrates were collected, with Hydrobiidae, Chironomidae, Thiaridae and Polymitarcyidae being the most abundant in the system. In addition, families with high tolerance to extreme conditions, such as Ceratopogonidae, Chironomidae and Syrphidae, were found, as well as some families with low tolerance to these conditions, such as Caenidae and Leptoceridae. The first biotope presented 7.189 individuals (50.42%) and the second 7.056 (49.5%), for a total of 14.259 individuals. Biotope AM presented 100% of the richness, while biotope B was significantly less rich, with 15 families, which represent 32,06%. In order to evaluate the families found in the lowland lentic system, their distribution in the ranges of variation of the physicochemical factors and tolerance levels was taken into account. As a consequence, a new score table was established, where this system obtained a total score of 207 with an average of 166 per sampling station, suggesting signs of contamination. Finally, these results allow an adaptation of the BMWP (Biological Monitoring Working Party) index to be proposed, including the lowland lentic systems.     

Distance‐dependent effects of soil‐derived biota on seedling survival of the tropical tree legume Ormosia semicastrata

Question: How do seed germination and subsequent seedling survival of O. semicastrata (Hance forma litchiifolia How) vary with respect to distance from parent trees and conspecific density in different types of tropical forest? Are there effects of soil biota on O. semicastrata that systematically depend on distance from parent trees and conspecific density? Do soil pathogens differently affect survival of O. semicastrata in different types of tropical forest? Location: Tropical lowland rain forest and tropical montane rain forest in Jianfengling National Nature Reserve, Hainan Island, China. Methods: Individual adult O. semicastrata trees were selected in lowland rain forest and montane rain forest. Soil was collected at a distance of 0‐5 m or 15‐20 m from the parent tree. Soil samples from each distance were combined into a bulk sample. Half of the soil sample was sterilized by autoclaving. Surface‐sterilized seeds were then added to the soil material in shade‐houses at both forests. Results: Germination of O. semicastrata seeds at low‐ or high‐seed density was barely affected by the sterilization procedure. In both forests, seedlings grown in non‐sterilized soil collected close to parent trees had significantly higher mortality compared to those in sterilized soil. In contrast, seedling survival with soil collected far from parent trees was not affected by the soil sterilization procedure. Conclusions: Host‐specific pathogens concentrated in the soil around parent trees may regulate community structure of tropical trees at the stage of seedling development.     

Habitat niche partitioning by 16 species of Myristicaceae in Amazonian Ecuador

The distribution and spatial pattern of plants in tropical forests have important implications for how species interact with each other and their environments. In this article we use a large-scale permanent census plot to address if the coexistence of 16 co-occurring species of Myristicaceae is aided by topographic and light gradient niche partitioning. We used a second order spatial pattern analysis based on Ripley’s K function to describe species’ distributions and associations among species, and a torus translation procedure to test for associations with three topographically defined habitats. A majority of species displayed spatial aggregation and over half had one or more significant habitat associations. Four species were associated with the ridge habitat, four species with slope habitat, and two with valley habitat. Seven other species showed no habitat association. Within each habitat group, species exhibited a variety of distributions in relation to light availability. However, habitat associations were largely unexplained by differential rates of mortality, growth or recruitment over a 5-year interval. We conclude that although in principle partitioning of the topographic and light environments may double or treble the number of species able to coexist, there is no evidence that partitioning of physical habitats can explain the coexistence of all 16 of these closely related species.     

Dispersal and colonisation of plants in lowland streams: success rates and bottlenecks

Plant dispersal and colonisation, including rates of dispersal, retention, colonisation and survival of dispersed propagules (shoots and seeds), were studied in a 300-m stream reach in a macrophyte-rich lowland stream during one growing season. Relationships between colonisation processes and simple flow parameters were tested. Each fortnight during a growing season, the number of dispersed plant propagules and the number of new and lost plant colonisations since the last sampling day were recorded. The retention of dispersing shoots was tested on two occasions during the growing season by releasing plant shoots and subsequently re-collecting the retained shoots in the study reach. The main bottleneck for plant colonisation in macrophyte-rich lowland streams is the primary colonisation (development of attached roots in the sediment from vegetative propagules or seedlings) of retained shoots and seeds, due in part to low retention success (1% of the dispersed shoots per 100-m reach) and to unsuccessful colonisation of retained shoots (3.4% of retained shoots colonised). The number of drifting shoots and seeds per day during the growing season were 650–6,950 and 2,970–62,780, respectively, and caused no constraint to colonisation. The survival rate of primary colonists was high with 80% surviving during the first growing season and about 50% surviving the first winter. There was no relationship between number of drifting shoots and flow, but the number of drifting seeds increased with flow. The number of colonisations between two consecutive sampling days correlated to the extent of low flow in the period. The loss rate of colonisations correlated to high flow events, but was low overall. My study strongly indicates that the number of propagules is not a constraint to colonisation in macrophyte-rich lowland streams. Rather, I conclude that primary colonisation is the main constraint to regaining vegetation in lowland streams in general and in vegetation-free rehabilitated streams in particular. Therefore, if plant colonisation is a target for stream rehabilitation, it is important to enhance retention and colonisation of propagules by creating areas of low flow and by providing physical obstacles to work as retention agents in the stream. Handling editor: L. M. Bini