Assessment of soil erosion in a tropical mountain river basin of the southern Western Ghats,India using RUSLE and GIS

Revised Universal Soil Loss Equation(RUSLE) model coupled with transport limited sediment delivery(TLSD) function was used to predict the longtime average annual soil loss, and to identify the critical erosion-/deposition-prone areas in a tropical mountain river basin, viz., Muthirapuzha River Basin(MRB; area=271.75 km~2), in the southern Western Ghats, India. Mean gross soil erosion in MRB is 14.36 t ha~(-1) yr~(-1), whereas mean net soil erosion(i.e., gross erosion-deposition) is only 3.60 t ha~(-1) yr~(-1)(i.e., roughly 25% of the gross erosion). Majority of the basin area(~86%) experiences only slight erosion(5 t ha~(-1) yr~(-1)), and nearly 3% of the area functions as depositional environment for the eroded sediments(e.g., the terraces of stream reaches, the gentle plains as well as the foot slopes of the plateau scarps and the terrain with concordant summits). Although mean gross soil erosion rates in the natural vegetation belts are relatively higher, compared to agriculture, settlement/built-up areas and tea plantation, the sediment transport efficiency in agricultural areas and tea plantation is significantly high,reflecting the role of human activities on accelerated soil erosion. In MRB, on a mean basis, 0.42 t of soil organic carbon(SOC) content is being eroded per hectare annually, and SOC loss from the 4th order subbasins shows considerable differences, mainly due to the spatial variability in the gross soil erosion rates among the sub-basins. The quantitative results, on soil erosion and deposition, modelled using RUSLE and TLSD, are expected to be beneficial while formulating comprehensive land management strategies for reducing the extent of soil degradation in tropical mountain river basins.     

准噶尔盆地吉木萨尔凹陷梧桐沟组层序地层划分

准噶尔盆地吉木萨尔凹陷二叠系梧桐沟组作为一套重要的储集岩,具有良好的油气成藏前景,但对其层序划分及地层沉积样式的认识一直存在争议。在构造背景分析的基础上,结合岩芯、测井及地震资料,对研究区梧桐沟组层序地层划分及地层沉积样式研究表明,梧桐沟组沉积时期构造强度较弱,地形较为平缓,地层在全区稳定分布;中晚二叠世盆地发生造山运动,吉木萨尔凹陷东南边缘区域经过构造抬升,上部地层遭受不同程度的剥蚀,形成了现今"底平顶削"的地层样式。以凹陷中部少数地层保存较全的井的地层叠加样式分析为基础,通过井-震结合识别不同类型界面,特别是最大湖泛面,建立了区域层序地层格架,即梧桐沟组为一个完整的长期基准面旋回(三级层序),并在其内部识别出5个中期旋回。梧桐沟组地层在不同的层序发育时期表现出不同的旋回叠加样式:下段沉积时期,即最大湖泛面以下,随着可容纳空间的增大,地层表现为明显的退积叠加样式;上段沉积时期,即最大湖泛面以上,随着可容纳空间的减小,地层表现为明显的进积叠加样式,符合沉积物体积分配原理。     

Geoarchaeological evidence on a Late Bronze Age earthquake,Ohrid Basin (North Macedonia)

Geoarchaeological investigations on the northeastern shore of Lake Ohrid revealed 3.5 m thick deepwater lacustrine sediments overlying terrestrial vegetation macrofossils, worked wood and abundant potsherds dated to the Late Bronze Age (LBA). Distinct contact of deepwater sediment with the sub-aerial weathered limestone bedrock point to a sudden increase in lake level. According to radiocarbon data, catastrophic flooding occurred shortly after 1214 yr bc. Because the area is located in a highly active seismic zone, we propose that this event was caused by tectonically induced, metre-scale coseismic subsidence related to faults bordering the Ohrid alluvial plain. Moreover, this event coincides well with a dramatic switch in the habitation and settlement strategy in the region. More important, however, is the finding that the age of the proposed massive tectonic event and change in habitation lies within the interval of the proposed ‘earthquake storm’ in the eastern Mediterranean dated to 1225–1175 bc. As the Ohrid-Korça zone belongs to the same tectonic province, a relationship between the abovementioned earthquakes and the proposed event can be expected. This research therefore might provide the first direct evidence of a large-scale earthquake event linkable to the LBA collapse of Europe's first urban civilisation in the Aegean.     

闽西南地区块状硫化物矿床的喷流-沉积成矿作用

通过对闽西南地区石炭纪—早二叠世主要块状硫化物矿床的区域成矿背景、贮矿层位特征以及矿石矿物成分、结构构造,硫同位素地球化学特征、成矿温度等分析研究,指出该地区石炭纪—早二叠世块状硫化物矿床的形成多与海底火山活动有关,贮矿层中伴有典型的喷流沉积岩—硅质岩,并提出闽西南地区块状硫化物矿床存在海底喷流-沉积成矿作用的新认识。     

Onshore sandbar migration at Tairua Beach (New Zealand): Numerical simulations and field measurements

We observed the onshore migration (3.5 m/day) of a nearshore sandbar at Tairua Beach, New Zealand during 4 days of low-energy wave conditions. The morphological observations, together with concurrent measurements of waves and suspended sediment concentrations, were used to test a coupled, wave-averaged, cross-shore model. Because of the coarse bed material and the relatively low-energy conditions, the contribution of the suspended transport to the total transport was predicted and observed to be negligible. The model predicted the bar to move onshore because of the feedback between near-bed wave skewness, bedload, and the sandbar under weakly to non-breaking conditions at high tide. The predicted bathymetric evolution contrasts, however, with the observations that the bar migrated onshore predominantly at low tide. Also, the model flattened the bar, while in the observations the sandbar retained its steep landward-facing flank. A comparison between available observations and numerical simulations suggests that onshore propagating surf zone bores in very shallow water (< 0.25 m) may have been responsible for most of the observed bar behaviour. These processes are missing from the applied model and, given that the observed conditions can be considered typical of very shallow sandbars, highlight a priority for further field study and model development. The possibility that the excess water transported by the bores across the bar was channelled alongshore to near-by rip-channels further implies that traditional cross-shore measures to judge the applicability of a cross-shore morphodynamic model may be misleading.     

Profiling Planctomycetales diversity with reference to anammox‐related bacteria in a South China Sea,deep‐sea sediment

A systematic assessment of Planctomycetales diversity in a South China Sea, deep‐sea sediment (1657 m) was conducted using the 16S rRNA gene analysis approach. PCR amplification of the samples from seven sediment layers (0.1, 1, 3, 5, 7, 9 and 11 m below the surface sediment) using the primer set Pla‐46‐F/1392‐R showed that the Planctomycetales existed within a limited range of sediment depths (≤ 5 m), and had a decreasing trend in diversity with increasing depth. The majority of the retrieved Pla‐46‐F/1392‐R sequences belonged to Pirellula‐related Planctomycetales, and two sequences retrieved from the 0.1‐m layer (GenBank accession numbers: DQ996944 and DQ996945 ) shared the same anammox‐related signature oligonucleotides and were closely related to commonly recognized anammox organisms. To identify new anammox‐related biomarkers, three primer sets were designed for amplifying the fragments of hydroxylamine oxidoreductase and S‐adenosylmethionine radical enzyme genes, but no related sequences were found. Our multiple 16S rRNA gene primer sets (Journal of Rapid Methods and Automation in Microbiology, 2008, in press) revealed even an higher diversity of Planctomycetales in the 0.1‐m layer of the sediment, especially at genus level. Our data profiled the distribution pattern of Planctomycetales diversity along sediment depths, and provided molecular evidence for the existence of anammox‐related bacteria in a new location, which broadens our understanding of Planctomycetales diversity in deep sea sediments.     

Spatial changes in a macrozoobenthic community along environmental gradients in a shallow brackish lagoon facing Sendai Bay, Japan

The spatial distribution, abundance, and assemblage structure of macrozoobenthos were examined at 45 stations in a brackish lagoon (Idoura Lagoon, Japan) to examine the animal–environmental relations in estuarine soft-bottom habitats. We found a total of 23 taxa; the polychaetes Heteromastus sp., Hediste spp., and Prionospio japonica and the isopod Cyathura muromiensis numerically dominated the community. Cluster analysis and one-way analysis of similarity (ANOSIM) identified seven groups of stations that had significantly different macrozoobenthic communities; these were subsequently consolidated into five habitat groups according to their association with environmental characteristics. Canonical correspondence analysis (CCA) showed that salinity, silt-clay content, and the oxidation–reduction potential (ORP) of the sediment strongly affected the macrozoobenthos distribution pattern in the lagoon, whereas other factors (e.g., relative elevation of the habitat and sediment organic content) had much weaker effects. Similarity percentages (SIMPER) procedures indicated that the polychaete Notomastus sp. and the bivalve Macoma contabulata were specific to habitats with low salinity and reduced mud, whereas the bivalve Nuttallia olivacea was specific to sandy bottoms. Heteromastus sp. and Hediste spp. achieved their highest densities in rather oxidized sediments. The acid-volatile sulfide (AVS) content in the sediment was suggested as another possible factor affecting macrozoobenthic density. Our results clearly demonstrate that macrozoobenthic assemblages in estuarine soft-bottoms have high spatial heterogeneity on a small scale (e.g., hundreds of meters) related to physical and chemical environmental changes. Our data also suggested the importance of sediment redox condition (e.g., ORP and AVS content) and sediment grain size as structuring factors in estuarine soft-bottom communities as well as the salinity in the habitat.     

Detecting environmental change in estuaries: Nutrient and heavy metal distributions in sediment cores in estuaries from the Gulf of Finland,Baltic Sea

Historical sediment nutrient concentrations and heavy metal distributions were studied in four estuaries in the Gulf of Finland, Baltic Sea to examine the response of these estuaries to temporal changes in human activities. Cores were collected using a 1-m Mackereth corer and dated using ²¹⁰Pb and ¹³⁷Cs. The cores were analyzed for total carbon (TC), total nitrogen (TN), total phosphorus (TP), organic phosphorus (OP), inorganic phosphorus (IP), biogenic silica (BSi), loss-on-ignition (LOI), Cu, Zn, Al, Fe, Mn, K, Ca, Mg and Na. Principal component analysis (PCA) was used to summarize the trends in the chemical variables and to compare the trends at the different sites. Applying the 1986 ¹³⁷Cs date as a reference point, ²¹⁰Pb chronologies were constructed for the sites using either the CRS model or a composite model (using both CIC and CRS). Significant increases were observed in sedimentation rates, TP and TN concentrations in all of the cores. Copper showed clear increases from 1850 towards present at all sites. Furthermore, redundancy analysis (RDA) was used to correlate environmental variables (catchment land use, catchment size, estuary surface area, depth and lake percentage) to sediment geochemistry. Based on redundancy analysis (RDA), the percentage of agriculture in the catchment was the most important factor affecting the sediment accumulation rate. Urban land-use types and industry correlate well with sediment Cu and Ca concentrations. Forest areas were related to high sediment BSi concentrations. Catchment land use was the most significant factor affecting sediment geochemical composition and sediment accumulation rates in these coastal embayments. Our results demonstrate that the coastal estuaries of the Gulf of Finland respond to the increased nutrient loading with the increased sedimentation and nutrient accumulation rates.     

Temporal and spatial changes of dunes in the Changjiang (Yangtze) estuary,China

The response of subaqueous dunes to the variation of riverine sediment supply in an estuary is rarely reported. Five sets of field measurements of bed sediments and topography were made in the Changjiang estuary, China during dry and flood seasons for the past 9 years. Results show that dunes were mainly three-dimensional (3D) during flood seasons and two-dimensional (2D) dunes during dry seasons. Dunes were also much larger in flood seasons. Dunes mainly occurred within the main channels of the estuary although they extended 11.7 km seaward of their normal extent in the South Channel during dry seasons from 2002 to 2006. This extension of the dune field is likely due to a sharp decline of sediment discharge caused by large reservoirs such as Three Gorges.     

Lagrangian measurements and modelling of fluid advection in the inner surf and swash zones

New laboratory and field data are presented on fluid advection into the swash zone. The data illustrate the region of the inner surf zone from which sediment can be directly advected into the swash zone during a single uprush, which is termed the advection length. Experiments were conducted by particle tracking in a Lagrangian reference frame, and were performed for monochromatic breaking waves, solitary bores, non-breaking solitary waves and field conditions. The advection length is normalised by the run-up length to give an advection ratio, A, and different advection ratios are identified on the basis of the experimental data. The data show that fluid enters the swash zone from a region of the inner surf zone that can extend a distance seaward of the bore collapse location that is approximately equal to half of the run-up length. This region is about eight times wider than the region predicted by the classical swash solution of Shen and Meyer [Shen, M.C., Meyer, R.E., 1963. Climb of a bore on a beach. Part 3. Runup. Journal of Fluid Mechanics 16, 113–125], as illustrated by Pritchard and Hogg [Pritchard, D., Hogg, A.J., 2005. On the transport of suspended sediment by a swash event on a plane beach. Coastal Engineering 52, 1–23]. Measured advection ratios for periodic waves show no significant trend with Iribarren number, consistent with self-similarity in typical swash flows. The data are compared to recent characteristic solutions of the non-linear shallow water wave (NLSW) equations and both finite difference and finite volume solutions of the NLSW equations.