Effectiveness of reforestation in erosion mitigation and implications for future sediment yields,East Coast catchments,New Zealand: A review

This paper argues that reforestation of unstable and degraded parts of the East Coast region, predominantly with exotic pines, has successfully stabilised existing erosion forms and prevented the initiation of new ones. Effectiveness is often assessed by capturing erosion scars on aerial photography taken before and after reforestation and any change in scar size is measured in a geographic information system (GIS). Combined with forest age data, modelled reforestation scenarios indicate that sediment generation from earth flows and shallow landslides would be negligible within eight to 10 years after planting, and if all remaining gullies were to be reforested before 2020, sediment yield could halve by 2030 and remain constant thereafter. In a similar time frame, the risk to infrastructure by sedimentation and flooding would likely decrease.     

The response of soil erosion and sediment export to land-use change in four areas of Europe: The importance of landscape pattern

The response of erosion and sediment export to past land-use change has been studied in four agricultural areas of Europe. Three of these areas were subject to land abandonment or de-intensification and one to intensification of land-use practices. Erosion and sediment yield were modeled using the WaTEM/SEDEM model, which combines the RUSLE equation with a sediment routing algorithm. Spatial relationships between the RUSLE C-factor (i.e. land-use) and other erosion and sediment export-determining factors (slope, soil erodibility and distance to rivers) were investigated, as these account for non-linearity in the response of erosion and sediment export to land-use change.Erosion and sediment export have decreased enormously in the de-intensified areas, but slightly increased in the intensively cultivated area. The spatial pattern of land-use change in relation to other erosion and sediment export-determining factors appears to have a large impact on the response of soil erosion and sediment export to land-use change. That the drivers of abandonment of arable land and erosion coincide indicates that de-intensification leads to a more favourable landscape pattern with respect to reduction of erosion and sediment export. This mechanism applies not only within the study areas, but also among the European study areas where the process of intensification of some areas and de-intensification of others might result in an overall decrease of erosion and sediment yield through time.     

Wind erosion from military training lands in the Mojave Desert, California, U.S.A.

Military training activities reduce vegetation cover, disturb crusts, and degrade soil aggregates, making the land more vulnerable to wind erosion. The objective of this study was to quantify wind erosion rates for typical conditions at the Marine Corps Air Ground Combat Center, Twentynine Palms, CA, U.S.A. Five Big Spring Number Eight (BSNE) sampler stations were installed at each of five sites. Each BSNE station consisted of five BSNE samplers with the lowest sampler at 0·05 m and the highest sampler at 1·0 m above the soil surface. Once a month, sediment was collected from the samplers for analysis. Occurrence of saltating soil aggregates was recorded every hour using Sensits, one at each site. The site with the most erosion had a sediment discharge of 311 kg m⁻¹ over a period of 17 months. Other sites eroded much less because of significant rock cover or the presence of a crust. Hourly sediment discharge was estimated combining hourly Sensit count and monthly sediment discharge measured using BSNE samplers. More simultaneously measured data are needed to better characterize the relationship between these two and reconstruct a detailed time-series of wind erosion. This measured time-series can then be used for comparison with simulation results from process-based wind erosion models such as the Wind Erosion Prediction System (WEPS), once it has been adapted to the unique aspects of military lands.     

Using 137Cs and 210Pbex to investigate the soil erosion and accumulation moduli on the southern margin of the Hunshandake Sandy Land in Inner Mongolia

Wind-driven soil erosion results in land degradation, desertification, atmospheric dust, and sandstorms. The Hunshandake Sandy Land, an important part of the Two Barriers and Three Belts project, plays important roles in preventing desert and sandy land expansion and in maintaining local sustainability. Hence, assessing soil erosion and soil accumulation moduli and analyzing the dynamic changes are valuable. In this paper, Zhenglan Banner, located on the southern margin of the Hunshandake Sandy Land, was selected as the study area. The soil erosion and accumulation moduli were estimated using the ¹³⁷Cs and ²¹⁰Pb_ex composite tracing technique, and the dynamics of soil erosion and soil accumulation were analyzed during two periods. The results are as follows: (1) the regional ¹³⁷Cs reference inventory was 2123.5±163.94 Bq/m ², and the regional ²¹⁰Pb_ex reference inventory was 8112±1787.62 Bq/m ². (2) Based on the ¹³⁷Cs isotope tracing analysis, the erosion moduli ranged from -483.99 to 740.31 t·km ^-2·a ^-1. Based on the ²¹⁰Pb_ex isotope tracing analysis, the erosion moduli ranged from -441.53 to 797.98 t·km ^-2·a ^-1. (3) Compared with the earliest 50 years, the subsequent 50 years exhibited lower soil erosion moduli and accumulation moduli. Therefore, the activities of local sand dunes weakened, and the quality of the local ecological environment improved. The multi-isotope composite tracing technique combining the tracers ¹³⁷Cs and ²¹⁰Pb_ex has potential for similar soil erosion studies in arid or semiarid regions around the world.     

内蒙古浑善达克沙地南缘 137Cs、 210Pbex复合示踪研究

土壤风蚀是导致土地退化、荒漠化以及大气扬尘、风沙天气的重要原因。内蒙古浑善达克沙地南缘是国家主体功能区规划确定的“两屏三带”的重要部分,科学估算本地区土壤风蚀强度及其变化,是地区生态安全和生态建设成效评估的重要内容。选择浑善达克沙地南缘的正蓝旗为研究区,运用 ¹³⁷Cs、 ²¹⁰Pb_ex复合示踪技术,对研究区土壤侵蚀速率及其变化进行了分析。结果表明：① 研究区内 ¹³⁷Cs本底值为2123.5±163.94 Bq·m ^-2, ²¹⁰Pb_ex本底值为8112±1787.62 Bq·m ^-2。② 基于 ¹³⁷Cs同位素示踪分析,研究区侵蚀模数为-483.99~740.31 t·km ^-2·a ^-1;基于 ²¹⁰Pb_ex同位素示踪分析,研究区侵蚀模数为-441.53~797.98 t·km ^-2·a ^-1。③ 与20世纪20-70年代相比,20世纪70年代以来土壤侵蚀与堆积速率明显降低,研究区风沙活动明显减弱,区域生态环境质量得到改善。综合 ¹³⁷Cs和 ²¹⁰Pb_ex的多同位素复合示踪技术在干旱、半干旱地区土壤侵蚀研究中具有较大的潜力。     

Historical rates of sediment and nutrient accumulation in marshes of the Upper St. Johns River Basin, Florida, U.S.A.

We used 210Pb-dated sediment cores from wetlands and Blue Cypress Lake, in the Upper St. Johns River Basin (USJRB), Florida, USA, to measure historical accumulation rates of bulk sediment, total carbon (C), total nitrogen (N), and total phosphorus (P). Marsh cores displayed similar stratigraphies with respect to physical properties and nutrient content. Wetland sediments typically contained > 900 mg organic matter (OM) g^–1 dry mass, > 500 mg C g^–1, and 30–40 mg N g^–1. OM, C, and N concentrations were slightly lower in uppermost sediments of most cores, but displayed no strong stratigraphic trends. Total P concentrations were relatively low in bottommost deposits (0.01–0.11 mg g^–1), but ranged from 0.38–2.67 mg g^–1 in surface sediments. The mean sediment accretion rate in the marsh since ~ 1900, 0.33 ± 0.05 cm yr^–1, was calculated from ten ²¹⁰Pb-dated cores. All sites displayed increases in accumulation rates of bulk sediment, C, N, and P since the early part of the 20th century. These trends are attributed to recent hydrologic modifications in the basin combined with high nutrient loading from agricultural, residential, and urban sources.     

广东惠州黄洞水库沉积物特征及其反映的近50年土壤侵蚀意义

在广东省东南部惠州市的黄洞水库中取得沉积物柱芯,对其样品做了²¹⁰Pb 和¹³⁷Cs 比活度分析、粒度分析和孢粉及炭屑分析,并收集了这一水库邻近气象站的降水数据,计算了1960 年以来的年降水量、夏季（6-9 月） 降水量和24 小时暴雨量。利用上述²¹⁰Pb和¹³⁷Cs比活度分析结果建立了沉积物剖面的年代框架,结合孢粉浓度、炭屑浓度与降水量计算结果,对沉积剖面的粒度变化做出了解译,并初步推测1960-2009 年间水库所在流域的土壤侵蚀变化情况及其原因。研究表明,在该亚热带丘陵地区植被覆盖度较高的自然条件下,侵蚀作用对降水量波动和植被（尤其是乔木、灌木等木本植物） 覆盖度变化的响应十分灵敏,水库沉积物的粒度变化在一定程度上可以反映流域内土壤侵蚀相对强度的变化。     

输沙量、侵蚀量与泥沙输移比的流域尺度关系——以赣江流域为例

输沙量、侵蚀量与泥沙输移比的流域尺度转换研究是当前流域侵蚀产沙研究领域的前沿课题,旨在通过尺度转换理论将坡面小区试验研究成果转换到流域的更大范围。以赣江流域实测输沙量和计算侵蚀量与泥沙输移比数据为基础,探讨了该流域3个变量的流域尺度关系,进而研究分析了3个变量尺度转换的可能性。3个变量与流域面积的关系散点图和相关方程都反映了这3者与流域面积不存在明显的相关关系,相悖于前人反比关系的结论。文章还阐述了流域面积的内涵及输沙量、侵蚀量和输移比的影响因素与流域面积的关系,发现3个变量的影响因素与流域面积不存在尺度效应。由此推断在赣江流域输沙量、侵蚀量和泥沙输移比实现尺度转换存在的可能性不大。这一研究结论是否成立或是否具有普遍性意义还有待于更多流域的研究成果来进一步证实。     

The influence of rainfall and land use patterns on soil erosion in multi-scale watersheds: A case study in the hilly and gully area on the Loess Plateau,China

Soil erosion has become a major global environmental problem and is particularly acute on the Loess Plateau (LP), China. It is therefore highly important to control this process in order to improve ecosystems, protect ecological security, and maintain the harmonious relationship between humans and nature. We compared the effects of rainfall and land use (LU) patterns on soil erosion in different LP watersheds in this study in order to augment and improve soil erosion models. As most research on this theme has so far been focused on individual study areas, limited analyses of rainfall and LU patterns on soil erosion within different- scale watersheds has so far been performed, a discrepancy which might influence the simulation accuracies of soil erosion models. We therefore developed rainfall and LU pattern indices in this study using the soil erosion evaluation index as a reference and applied them to predict the extent of this process in different-scale watersheds, an approach which is likely to play a crucial role in enabling the comprehensive management of this phenomenon as well as the optimized design of LU patterns. The areas considered in this study included the Qingjian, Fenchuan, Yanhe, and Dali river watersheds. Results showed that the rainfall erosivity factor (R) tended to increase in these areas from 2006 to 2012, while the vegetation cover and management factor (C) tended to decrease. Results showed that as watershed area increased, the effect of rainfall pattern on soil erosion gradually decreased while patterns in LU trended in the opposite direction, as the relative proportion of woodland decreased and the different forms of steep slope vegetation cover became more homogenous. As watershed area increased, loose soil and craggy terrain properties led to additional gravitational erosion and enhanced the effects of both soil and topography.     

The effects of land use on runoff and soil nutrient losses in a gully catchment of the hilly areas: implications for erosion control

Serious soil erosion is one of the major issues threatening sustainable land use in semiarid areas, especially in the Loess Plateau of China. Understanding the effects of land use on soil and water loss is important for sustainable land use strategy. Two sub-catchments: catchment A (CA) and catchment B (CB) with distinct land uses were selected to measure soil moisture, runoff and soil nutrient loss in Da Nangou catchment of the Loess Plateau of China. The effects of land use patterns on runoff and nutrient losses were analyzed based on soil moisture pattern by kriging and soil nutrients using multiple regression model. The results indicated that there were significant differences in runoff yield and soil nutrient losses between the two sub-catchments. With similar land uses, the CA produced an average sediment yield of 49 kg ha-1 and 22.27 kg ha-1 during two storm events. Meanwhile, there was almost no runoff in the CB with dissimilar land uses during the same events. Buffer zones should be established to re-absorb runoff and to trap sediments in catchment with similar land use structure such as the CA. Moreover, land use management strategy aiming to increase the infiltration threshold of hydrological response units could decrease the frequency of runoff occurrence on a slope and catchment scale.     

黄土丘陵小流域土地利用格局对径流与土壤养分流失的影响--土壤侵蚀控制的意义

Serious soil erosion is one of the major issues threatening sustainable land use in semiarid areas, especially in the Loess Plateau of China. Understanding the effects of land use on soil and water loss is important for sustainable land use strategy. Two sub-catchments: catchment A (CA) and catchment B (CB) with distinct land uses were selected to measure soil moisture, runoff and soil nutrient loss in Da Nangou catchment of the Loess Plateau of China. The effects of land use patterns on runoff and nutrient losses were analyzed based on soil moisture pattern by kriging and soil nutrients using multiple regression model. The results indicated that there were significant differences in runoff yield and soil nutrient losses between the two sub-catchments. With similar land uses, the CA produced an average sediment yield of 49 kg ha-1 and 22.27 kg ha-1 during two storm events.Meanwhile, there was almost no runoff in the CB with dissimilar land uses during the same events.Buffer zones should be established to re-absorb runoff and to trap sediments in catchment with similar land use structure such as the CA. Moreover, land use management strategy aiming to increase the infiltration threshold of hydrological response units could decrease the frequency of runoff occurrence on a slope and catchment scale.     

A record of vegetation dynamics and lake level changes from Lake Emakat,northern Tanzania,during the last c. 1200 years

Analyses of down-core variations in pollen and charcoal in two short cores of lake sediment and wood samples taken from the in situ remains of Nuxia congesta from Lake Emakat, a hydrologically-closed volcanic crater lake occupying the Empakaai Crater in northern Tanzania, have generated evidence of past vegetation change and lake level fluctuations. Eight AMS radiocarbon (¹⁴C) dates on bulk samples of lake sediment provide a chronological framework for the two cores and indicate that the sediment record analysed incorporates the last c. 1200 years. The in situ remains of a Nuxia congesta tree, now standing in deep water, were dated with three additional AMS ¹⁴C dates, suggesting tree growth within the interval ∼1500–1670 AD. Down-core variations in pollen from terrestrial taxa, particularly the montane forest trees Hagenia abyssinica and Nuxia congesta, indicate a broad period of generally more arid conditions in the catchment to c. 1200 AD and at a prolonged period between c. 1420 and 1680 AD. Variations in pollen from plants in lake margin vegetation indicate low lake levels, presumably as a result of reduced effective precipitation, contemporary with indications of relatively dry conditions mentioned above, but also during the late 18th and the late 19th centuries. The presence of charcoal throughout both cores indicates the frequent occurrence of vegetation fires. An increase in burning, evident in the charcoal data and dated to the early to mid second millennium AD, could relate to an expansion of human population levels and agricultural activity in the region.     

Patterns, rates and possible causes of saltmarsh erosion in the Greater Thames area (UK)

The estuary-dominated coast of the Greater Thames in England has experienced rapid lateral erosion and internal dissection of saltmarshes. This paper provides an overview of saltmarsh development in this area, and re-examines the role of environmental and human forcing factors. It draws on documentary evidence, including historical maps, survey data and time-series data of forcing factors. Lateral marsh retreat began in the 19th century in the Medway and Blackwater Estuaries, followed by other estuaries in the Greater Thames region at the beginning of the 20th century. The outer estuaries and the wider parts of the inner estuaries especially have experienced erosion. Erosion has been modest in wave-sheltered areas, e.g., the Colne and the inner Crouch. In the 1960s and, more widely, the 1970s, a phase of rapid erosion took place, with erosion rates of up to ca. 16 ha year⁻¹ per site, notably along the open coast of Dengie and Foulness, and in the Blackwater and Thames Estuaries. At all sites, vertical sediment accretion was well able to keep up with sea level rise over the past century. Evidence indicates that there may have been several causes for the erosion of saltmarshes. These are notably land claim and embankment construction (increasing the tidal range and current velocities) and a continuous rise of, especially, high and extreme water levels. The latest episode of rapid erosion in the 1970s is largely attributed to changes in the wind/wave climate. For example, erosion at wave-exposed sites coincided with a peak in high magnitude waves combined with a high incidence of southeasterly waves. The study shows that many factors, including natural forcing factors and human activities, have to be taken into account when explaining saltmarsh development.     

The Interaction of Religion,Political Ideology,and Concern About Climate Change in the United States

Political ideology and religion are considered important influences on attitudes about climate change, as many people rely on ideological and religious cues to help shape attitudes about this highly complex, uncertain, and politicized issue. While many scholars have studied the impacts of political orientation and religious affiliation independently, few have studied whether and how they interact in shaping concern about climate change. This article uses a large sample study to examine the impact of religious tradition on two indicators of concern about climate change within categories of political ideology. This study shows that religious affiliation moderates the impact of ideology, and that these interaction effects vary across religious traditions. Perhaps most significantly, this study reveals that religious affiliation is most influential on political liberals but has very little impact on conservatives. This holds significant implications for the way we understand the relationship between religion and environmental attitudes.     

Soil erosion assessment tools from point to regional scales—the role of geomorphologists in land management research and implementation

Geomorphological research has played an important role in the development and implementation of soil erosion assessment tools. Because policy and management approaches include the use of soil erosion assessment tools, soil erosion research directly affects the public in terms of providing information on natural hazards and human impacts, and also as the basis for regulatory policy on land management. For example, soil loss calculations and geomorphological expertise are used to support soil conservation planning, both through agricultural legislation that defines maximum tolerable soil loss rates, and through federal and local legislation that requires soil erosion controls on many construction sites.To be useful for decision makers, soil erosion models must have simple data requirements, must consider spatial and temporal variability in hydrological and soil erosion processes, and must be applicable to a variety of regions with minimum calibration. The growing use of erosion models and Geographic Information Systems (GIS) in local to regional scale soil and water conservation raises concerns about how models are used. This has prompted interest in methods to assess how models function at management scales and with the types of data that are commonly available to users. A case study of a GIS-based soil erosion assessment tool using the process-based Water Erosion Prediction Project (WEPP) shows that using commonly available data rather than research grade data can have (predictably) a significant impact on model results. If model results are then used in management decisions, it is critical to assess whether the scale and direction of variation in results will affect management and policy decisions. Geomorphologists provide unique perspectives on soil erosion and can continue to affect policy through soil erosion research. This research should focus on fundamental processes, but equally important is continued development and evaluation of models that are matched to real world data availability, geomorphic settings, and information needs.     

The evidence for paraglacial sedimentation and its temporal scale in the deglacierizing basin of Small River Glacier, Canada

Spatially sampled suspended sediment data from extra-channel surfaces of different ages during rainfall events were used to infer the timescale of landscape adjustment to Little Ice Age (LIA) deglacierization at Small River Glacier, Canada. Surface ages were determined by aerial photograph interpretation. Turbidimeters were installed in three ephemeral channels on “young,” “mature” and “old” surfaces; and their response to rainfall events of different magnitudes recorded. Results showed “young” ice proximal surfaces exposed since 1977 were increasingly vulnerable to mobilization during rainfall events. A suspended sediment response from “old” surfaces exposed since 1910 was recorded for only three events with 5- and 30-year return periods. The intensity and duration of rainfall events therefore had to increase in magnitude to mobilize sediment on surfaces of increasing maturity. Hysteresis in the channel suspended sediment response further confirmed the dependence of surface response on rainfall event magnitude. The rapid temporal decline in surface response indicated that surface armoring or sediment exhaustion is stabilizing surfaces within decades of exposure from the LIA maximum (ca. 1910) at Small River Glacier. However, further perturbation, for example by glacial advance or extreme climatic events, would likely modify the pattern of suspended sediment yields by changing terrain surface mobilization thresholds and reconfiguring channel sediment stores. We therefore suggest that it is difficult to determine when “paraglacial sedimentation” ceases to influence suspended sediment yields, and therefore significantly limiting the usefulness of the term to describe the period of suspended sediment yield adjustment following deglacierization.     

The role of soil erosion and fluvial processes in the post-fallout redistribution of Chernobyl-derived caesium-137: a case study of the Lapki catchment, Central Russia

The central area of the Russian Plain received substantial amounts Cs-137 fallout as a result of the Chernobyl accident in 1986, with inventories exceeding 40 kBq m⁻² in many of the areas close to Chernobyl. Concern over the longer-term fate of this contamination has focused attention on the need to predict the post-fallout redistribution of the radiocaesium and, thus, future changes in the spatial distribution of contamination in the landscape. Since radiocaesium reaching the land surface as fallout is rapidly and strongly adsorbed by soil and sediment particles, any attempt to predict its post-fallout redistribution must focus on erosion and sediment delivery processes and must rely heavily on a knowledge of the geomorphological processes involved. This paper reports a detailed investigation of post-fallout Cs-137 redistribution in the 2.18-km² Lapki catchment in the Middle-Russian Upland, which has required consideration of soil erosion processes, sediment delivery pathways, sediment delivery ratios and sediment sinks. The time elapsed since the Chernobyl accident is currently insufficient to result in significant reduction of Cs-137 inventories in eroding areas, but areas of deposition on both the lower slopes and on the balka sides and bottoms are already marked by significant increases in Cs-137 inventories. The results obtained emphasise that any attempt to develop meaningful predictions of the longer-term redistribution of Chernobyl-derived Cs-137 fallout within the Russian Plain must be based on a sound and detailed understanding of the linkage between the slopes and the balka systems and the fate of sediment entering the balka systems.     

The role of channel and floodplain storage in the suspended sediment budget of the River Ouse, Yorkshire, UK

This study attempts to quantify the amount of fine-grained (ca. < 150 μm) sediment stored on the floodplains and on the channel bed of the non-tidal sections of the main channels in the catchment of the River Ouse (3315 km²) and of one of its tributaries, the River Waarfe (818 km²), in Yorkshire, UK. Caesium-137 analyses of floodplain sediment cores were used to quantify the amount of Iloodplain deposition as a result of overbank flooding during the last ca. 40 years. A combination of bulk and sectioned cores were collected along transects perpendicular to the channel at 26 sites throughout the study basins. In general, rates of overbank sedimentation decrease with distance from the channel. The average values for individual transects range between 0.010 and 0.554 g cm⁻² year⁻¹. Floodplain storage along the main channels of the Ouse and Wharfe basins accounts for 60645 and 10325 t year⁻¹, respectively, and represents a net loss from the system. The amount of fine-grained sediment stored on the channel bed was estimated by a survey undertaken in August 1996, during which the fine material deposited on the bed was resuspended and its mass estimated at 16 locations. The average values for the individual locations range between 0.017 and 0.924 g cm⁻² and tend to increase downstream. The total channel bed storage at the time of sampling in 1996 was estimated to be 16076 and 1866 t for the Ouse and Wharfe basins, respectively. It is assumed that channel bed storage is seasonal and that no net loss to the system occurs at the annual timescale. Floodplain storage for the Ouse and Wharfe basins represents 39 and 49%, and channel bed storage equals 10 and 9%, respectively, of the annual suspended sediment load (1995–1996) delivered to the channel system. These results have important implications for the routing of fine-grained sediment and sediment-associated contaminants in drainage basins, and for the interpretation of downstream sediment yields in terms of upstream sediment mobilisation.     

Coastal resilience and late Holocene tidal inlet history: The evolution of Dungeness Foreland and the Romney Marsh depositional complex (U.K.)

Dungeness Foreland is a large sand and gravel barrier located in the eastern English Channel that during the last 5000 years has demonstrated remarkable geomorphological resilience in accommodating changes in relative sea-level, storm magnitude and frequency, variations in sediment supply as well as significant changes in back-barrier sedimentation. In this paper we develop a new palaeogeographic model for this depositional complex using a large dataset of recently acquired litho-, bio- and chrono-stratigraphic data. Our analysis shows how, over the last 2000 years, three large tidal inlets have influenced the pattern of back-barrier inundation and sedimentation, and controlled the stability and evolution of the barrier by determining the location of cross-shore sediment and water exchange, thereby moderating sediment supply and its distribution. The sheer size of the foreland has contributed in part to its resilience, with an abundant supply of sediment always available for ready redistribution. A second reason for the landform's resilience is the repeated ability of the tidal inlets to narrow and then close, effectively healing successive breaches by back-barrier sedimentation and ebb- and/or flood-tidal delta development. Humans emerge as key agents of change, especially through the process of reclamation which from the Saxon period onwards has modified the back-barrier tidal prism and promoted repeated episodes of fine-grained sedimentation and channel/inlet infill and closure. Our palaeogeographic reconstructions show that large barriers such as Dungeness Foreland can survive repeated “catastrophic” breaches, especially where tidal inlets are able to assist the recovery process by raising the elevation of the back-barrier area by intertidal sedimentation. This research leads us to reflect on the concept of “coastal resilience” which, we conclude, means little without a clearly defined spatial and temporal framework. At a macro-scale, the structure as a whole entered a phase of recycling and rapid progradation in response to changing sediment budget and coastal dynamics about 2000 years ago. However, at smaller spatial and temporal scales, barrier inlet dynamics have been associated with the initiation, stabilisation and breakdown of individual beaches and complexes of beaches. We therefore envisage multiple scales of “resilience” operating simultaneously across the complex, responding to different forcing agents with particular magnitudes and frequencies.     

Evaluating the mobility of137Cs,239+240Pu and210Pb from their distributions in laminated lake sediments

Post-depositional mobility of¹³⁷Cs,^239+240Pu and²¹⁰Pb was assessed in six small lake basins by comparing sedimentary nuclide profiles with their known fallout history. Laminae couplets, when present, were determined to be varves because the¹³⁷Cs and^239+240Pu 1963 fallout peaks are present in laminae couplets corresponding to years 1962–1964. There is no evidence of mobility of²¹⁰Pb, because 1) mass accumulation rates based on²¹⁰Pb agree with those based on¹³⁷Cs and^239+240Pu peak depths and with those based on varve counts, and 2)²¹⁰Pb ages agree with varve ages. Significant mobility of¹³⁷Cs is evident from the penetration of¹³⁷Cs to depths 15–20 cm deeper than^239+240Pu. Deep penetration of¹³⁷Cs in spite of a sharp gradient below the peak is interpreted by a numerical model to suggest that¹³⁷Cs is present in two distinct forms in these sediments, 67–82% as an immobile form and 18–33% reversibly adsorbed with a K _d of approximately 5000. The profiles can be interpreted equally well assuming a small portionof the total¹³⁷Cs was present as an extremely mobile phase (K _d 5000) in the months to years following peak fallout, slowly becoming more strongly adsorbed. High NH ₄ ⁺ concentrations in porewaters may enhance diffusion of the mobile form of¹³⁷Cs, but not of the immobile form of¹³⁷Cs that defines the sharp gradient. Mobility of¹³⁷Cs is likely also enhanced by the low clay content and the high porosity of these sediments. Thus the first detection of¹³⁷Cs in the sediments cannot automatically be assumed to correspond to a date of 1952 (initial testing of thermonuclear weapons), although the depth of the peak can be assumed to correspond to 1963 (the year of maximum fallout from testing of thermonuclear weapons).^239+240Pu is a more reliable sediment chronometer than¹³⁷Cs because it is significantly less mobile.This is the sixth of a series of papers to be published by this journal following the 20 ^th anniversary of the first application of²¹⁰Pb dating of lake sediments. Dr P.G. Appleby is guest editing this series.