Historical Erosion Research Articles

Shifting sands: The influence of coral reefs on shoreline erosion from short-term storm protection to long-term disequilibrium

Climate change is exacerbating shoreline erosion and flooding, posing significant risks to coastal communities. Although traditional coastal defenses such as seawalls, dykes, and breakwaters offer protection from these hazards, their high environmental and economic costs are driving interest in cost-competitive nature-based solutions. Coral reef restoration is a nature-based solution that may be particularly apt to mitigate tropical coastal flooding and shoreline erosion while providing benefits to local tourism, fisheries, and nature. However, the novelty of this field requires studies demonstrating the benefits of reefs for coastal protection. While the flood protection benefits of reefs have been well-documented, their effects on shoreline erosion are comparatively less understood. Here, we investigate the effects of coral reefs on shoreline erosion by comparing tropical beach responses at short and long timescales, as well as identifying important reef structural features influencing coastal erosion rates. Our analyses leveraged two key datasets created in this study: the first derived from a literature review on short-term shoreline erosion due to storm events, and another compiling >80 years of long-term erosion rates, bathymetry, habitat, and wave energy for the Hawaiian Islands of Kauaʻi, Oʻahu, and Maui. Our analyses reveal three key findings regarding the effects of reefs on shoreline erosion. Firstly, we find evidence for the role of reefs in mitigating shoreline erosion during storm events, with coral reef-protected beaches experiencing 97 % less beach volume loss than unprotected beaches. Secondly, a linear regression analysis demonstrates that coral reef structure and wave energy are important predictors of long-term shoreline erosion rates, explaining 34 % of the variation across the Hawaiian Islands. Consistent with prior research, we find beaches protected by coral reefs with shallow reef crests, wide reef flats, calmer offshore conditions, and positioned farther from the shore exhibit lower erosion rates than others. Finally, when comparing historical erosion rates of protected and unprotected beaches in Hawai'i, we find a seemingly incongruous pattern where coral reef-protected beaches eroded up to 2x faster than beaches without reefs. While the cause of the enhanced erosion is yet to be fully understood, a combination of coral reef structural degradation and sea-level rise is likely shifting the equilibrium profiles of reef-protected beaches inshore. These results emphasize the role of coral reefs in reducing coastal erosion during storm events while revealing contrasting erosion patterns over long timescales. Future studies would ideally broaden the scope to include various regions, utilize advanced sediment transport models, and undertake field experiments to deepen our understanding of coral reef-coupled shoreline dynamics.

Toprak Kayıp Modellerinin Somali İçin Değerlendirilmesi

Soil erosion stands as a significant environmental concern impacting both agricultural productivity and natural ecosystems across various regions worldwide. The soil losses attributed to erosion exacerbate concerns about food security and land degradation in Somalia, a country already grappling with numerous socio-economic challenges. This study aims to evaluate the erosion risk in Somalia by examining potential techniques that offer valuable insights for sustainable land management and resource planning. Emphasizing the utilization of remote sensing data, geographic information system (GIS) techniques, and hydrological modeling, the research highlights the exploration of erosion risk factors and their spatial distribution nationwide. Topographic data, soil properties, land use and land cover data, precipitation models, and vegetation indices could be employed to identify erosion-prone areas and sensitive points in Somalia. Furthermore, analyzing historical erosion data can aid in calibrating and validating predictive models. Continuous monitoring of sensitive areas over the years is recommended, considering the role of human activities such as ongoing deforestation, poor agricultural practices, and excessive grazing, which contribute to escalating erosion risks on Somali lands. Decision-makers should focus on methodologies that can be utilized to implement efficient erosion management techniques ensuring environmental sustainability across Somalia.

Variability in terrestrial characteristics and erosion rates on the Alaskan Beaufort Sea coast

Arctic coastal environments are eroding and rapidly changing. A lack of pan-Arctic observations limits our ability to understand controls on coastal erosion rates across the entire Arctic region. Here, we capitalize on an abundance of geospatial and remotely sensed data, in addition to model output, from the North Slope of Alaska to identify relationships between historical erosion rates and landscape characteristics to guide future modeling and observational efforts across the Arctic. Using existing datasets from the Alaska Beaufort Sea coast and a hierarchical clustering algorithm, we developed a set of 16 coastal typologies that captures the defining characteristics of environments susceptible to coastal erosion. Relationships between landscape characteristics and historical erosion rates show that no single variable alone is a good predictor of erosion rates. Variability in erosion rate decreases with increasing coastal elevation, but erosion rate magnitudes are highest for intermediate elevations. Areas along the Alaskan Beaufort Sea coast (ABSC) protected by barrier islands showed a three times lower erosion rate on average, suggesting that barrier islands are critical to maintaining mainland shore position. Finally, typologies with the highest erosion rates are not broadly representative of the ABSC and are generally associated with low elevation, north- to northeast-facing shorelines, a peaty pebbly silty lithology, and glaciomarine deposits with high ice content. All else being equal, warmer permafrost is also associated with higher erosion rates, suggesting that warming permafrost temperatures may contribute to higher future erosion rates on permafrost coasts. The suite of typologies can be used to guide future modeling and observational efforts by quantifying the distribution of coastlines with specific landscape characteristics and erosion rates.

Coast Change: Understanding Sensitivity to Beach Loss for Coastal Tourism in the Colombian Caribbean

Beach and sun tourism in the Colombian Caribbean is an extremely important activity that leads to social practices that generate recreational and economic activities directly impacting the environment. The research focuses on assessing the sensitivity to the loss of beaches as tourist resources in four locations within the Colombian Caribbean (Santa Verónica, Salinas del Rey, Bocatocino, and Las Arenas). The sensitivity indicator was developed using GIS to process variables such as the width of the usable beach, the presence of dunes, and rates of coastal erosion spanning from 2003 to 2019. Additionally, anthropic occupation was examined through satellite images. The results allowed for identifying vulnerability indices and recognizing the critical role of dunes in beach preservation. The study revealed that the analyzed beaches exhibited varying degrees of sensitivity. Notably, historical erosion rates and dunes were the most influential variables affecting sensitivity. In conclusion, understanding the sensitivity state concerning the loss of beach areas as tourist resources helps delineate stable sectors and those more susceptible to erosion processes. This knowledge proves invaluable in prioritizing the design and implementation of protective measures in areas requiring urgent attention.

Precipitation as a key control on erosion rates in the tectonically inactive northeastern Sonoran Desert, central Arizona, USA

ABSTRACT Langbein and Schumm (1958) connected precipitation to erosion in a right-skewed curve used in earth science textbooks for over six decades, where denudation increases with precipitation on the arid/semiarid limb and decreases in humid regions. Development of the catchment-averaged 10Be denudation method a quarter-century ago led geomorphologists to evaluate this hypothesis using data not influenced by the Anthropocene, with mixed findings. The Sonoran Desert in Arizona, USA, is optimal for investigating the longstanding hypothesis of increased erosion from arid to semiarid climates due to: (i) the modern orographic effect aligning elevated precipitation with altitude, mirroring Neotoma packrat midden paleoecology research for the Holocene and late Pleistocene; (ii) the region has been tectonically quiet for the residence times of analyzed 10Be ranging from ca. 8,000-110,000 years. Our significant finding echoes Langbein and Schumm's work, revealing heightened erosion along an elevation-precipitation gradient from arid to semiarid conditions. Notably, the significance of precipitation-elevation contrasts with the absence of significant correlation between 10Be denudation and attributes like slope, drainage area, relief, or landform type (e.g., alluvial fan, pediment, mountain watershed). Modern faunalturbation, increasing along this gradient, exposes more ground to rainsplash and overland flow at higher elevations, adding complexity to these results. Further insights unveil that (i) catchments in areas with substantial Quaternary base level reduction imitate tectonic effects, tripling 10Be denudation rates; (ii) basaltic boulders and cobbles yield an armoring influence; (iii) historical erosion acceleration due to urbanization and wildfires insignificantly affects 10Be denudation rates in the Sonoran Desert; and (iv) minute desert catchments yield anomalous erosion rates.

Beach rebuilding period buffers Indiana beach erosion in Lake Michigan

Recent high-water levels in the Laurentian Great Lakes caused widespread shoreline damage to beaches, homes, and coastal infrastructure. To quantify these shoreline changes and place them in historical context, shoreline imagery was analyzed to determine the magnitude, rates, and spatial variability of shoreline changes along the Indiana shoreline of Lake Michigan. The analysis shows that over the recent period of water level increase from 2013 to 2020, during which the water level rose nearly 2 m, the median shoreline recession along the Indiana coastline was 58 m and the median recession slope was 35:1 (shoreline recession : water level change). This magnitude of shoreline change is comparable to that experienced in other water level increase periods, 1965–1973 and 1990–1998. This recent shoreline recession was highly variable spatially, but not strongly correlated with shoreline type or position relative to littoral barriers. In spite of the widespread recent shoreline changes, the 2020 shoreline was generally more lakeward than previous high-water shorelines examined, with the exception of historical erosion zones downdrift of littoral barriers. Analysis of water level records and available wave hindcasts for the coastline suggest that while large, the erosion associated with the recent water level increase was tempered by a prolonged beach rebuilding period of low water levels and waves that resulted in an accreted shoreline that largely buffered the erosion associated with the water level increase. These results suggest that recent Indiana erosion could have been substantially worse had it not been preceded by the beach rebuilding period.

Unprecedented Historical Erosion of US Gulf Coast: A Consequence of Accelerated Sea‐Level Rise?

AbstractMost of the US Gulf Coast is composed of barrier islands, peninsulas, chenier plains, and mainland beaches that are the main line of defense for wetlands, estuaries, and urban and industrial centers from rising sea level and severe storms. These wave‐dominated shorelines are currently experiencing widespread erosion. Using newly acquired and existing results from 13 sites spanning south Florida to south Texas, we compare shoreline migration rates during the late Holocene (∼−4000 to 1850 CE) with historical changes since the mid‐19th century. The records show an overall trend of seaward growth during the late Holocene followed by landward migration or a decrease in the rate of growth during historical time. Diminishing offshore sand supply, human alteration of rivers and coastal sand transport, and severe storms have contributed to this change in shoreline trajectory, but their influence has been mostly limited in extent. The most likely cause of this reversal from coastal stability and growth to widespread shoreline retreat is the dramatic historical increase in the rate of sea‐level rise over the past century.

Mapping the impacts of coastal erosion on the heritage assets of Ynys Enlli (Bardsey Island), North Wales, UK

Coastal erosion and sea level rise has become a significant threat to coastal heritage due to climate change. Management bodies are monitoring the risks posed by undertaking studies, ranging from Rapid Coastal Zone Assessments to much larger government and research council funded studies. These studies have incorporated varying techniques and datasets such as environmental sampling, LiDAR, GPS, and UAV surveys. However, these approaches rarely combine study of historic shoreline change with physical susceptibility modeling. This paper presents a combined methodology, utilizing LiDAR and survey data collected by the Climate, Heritage, Environments of Reefs, Islands and Headlands (CHERISH) project, along with historic mapping and aerial photography to produce a risk assessment for the heritage assets located on Ynys Enlli (Bardsey Island), North Wales. By constructing an Historic Erosion Model and an Erosion Susceptibility Model using ESRI’s ArcGIS 10.5.1. with the DSAS Plugin and combining them with the LiDAR-derived spatial extents of archaeological features on the island, this project has shown that using both methodologies alongside each other can create a more complete overview of coastal environment change for the creation of vulnerability indexes.

Dilemmas of resistance: How concerns for cultural aspects of identity shape and constrain resistance among minority groups

ABSTRACT A major theme in social psychological models of collective action is that shared social identity is a critical foundation for resistance and collective action. In this review, we suggest that this foundational role of social identity can be double edged for many minority groups because material disadvantage is often coupled with the historical erosion of key aspects of ingroup culture and identity. Focusing on the role of ingroup language in Welsh national identity and history in relation to African identity, we present an integrative review of our research on five different dilemmas of resistance that can arise when perceived threats to socio-cultural aspects identity sit alongside threats to the material position (in terms of status and power) of the group. We conclude that the central role of social identity in collective action and resistance can itself present challenges for groups whose core sense of who they are has been eroded..

A Study on Traditional Villages and Towns in Lintan County, Gannan Prefecture

The human history of Lintan County in Gannan Tibetan Autonomous Prefecture can be traced back to 4000 years ago. It has undergone the historical erosion of the Neolithic Age, Xia and Zhou, Tang, Northern Song, and Ming dynasties, and is also a fusion zone of Tuyuhun King, Tubo King, and Han ethnic culture, forming a traditional culture with local characteristics. In Gannan Prefecture, there is a relatively special type of culture mainly composed of Han, Hui, and Tibetan culture. Through field research, the author visited the traditional conservation villages and towns in Lintan County, and preliminarily constructed the characteristics of the area from its characteristics (site selection, layout, form, etc.) and the characteristics of traditional building construction (courtyard composition, residential functions). The reasons for its formation, including military defense, agricultural natural resources, and watershed traffic arteries and other factors, were analyzed.

Height Estimation of Soil Erosion in Olive Groves Using a Time-of-Flight Sensor

The olive groves’ relevance has historically been ingrained in Mediterranean cultures. Spain stands out as a leading producer worldwide, where olive trees are extensively grown in the Andalusian region. However, despite the importance of this strategic agricultural sector, cultivation through the years has given rise to various crop management practices that have led to disruptive erosion processes. The objective is to measure land erosion in over 100-year-old olive groves considering the 3D reconstructed recent relief of olive tree mounds. A time-of-flight depth sensor, namely, Kinect v2, was employed to 3D model the target areas, i.e., trunk and exposed roots, to determine the height as a surrogate of the difference between the historical and recent relief. In three plots in southern Spain, the height of relic tree mounds was measured in olive trees at the upper and bottom parts to determine soil profile truncation. The results were compared and validated with manual measurements (ground truth values). Olive trees were grouped into high, moderate, and low slope gradient classes. The results showed, in all cases, high consistency in the correlation equations (Pearson’s coefficients over 0.95) between the estimated values in the models and the actual values measured in the olive trees. Consequently, these excellent results indicate the potential of this low-budget system for the study of historical erosion. Notably, the Kinect v2 can generate 3D reconstructions of tree mounds at microtopographic scales in outdoor situations that would be challenging for other depth cameras under variable lighting conditions, as found outdoors.

River dynamics - a geospatial analysis of Jamuna (Brahmaputra) River in Bangladesh during 1973-2019 using Landsat satellite remote sensing data and GIS.

The present study is designed to illuminate the dynamics of the Jamuna River in Bangladesh for 46years, from 1973 to 2019. About 240km of the Jamuna River course was assessed using remote sensing and GIS. Landsat remote sensing imageries were processed, and bank lines were extracted and analysed using GIS. The main objective of the study was to understand the pattern of bed movement of the Jamuna River. The river dynamics were assessed based on bank erosion, accretion, bank line shifts, channel width, and river course and confluence shift. Area vulnerable to erosion was assessed using historical erosion rate and trend analysis. The result revealed that the river area increased by about 48% over 46years. The total eroded area was about 1038 km2, with 35.40% more erosion on the left bank than on the right. Due to higher erosion than deposition, the river widened. The average width of the river increased by about 56.40% during the period. The average rate of shifting was higher on the left bank than on the right, indicating the eastward movement of the river. Impact analysis showed that overall, a total of 822 km2 and 390 km2 of croplands and settlements were eroded during the period 1973-2019. The width of the confluence at the Padma River junction decreased by about 28%. The straight shift of the confluence was 9.27km towards the southeast. The vulnerable area assessment anticipated that there would be more erosion on the left bank than on the right, and that Kurigram, Tangail and Jamalpur are the districts most susceptible to future left bank erosion. And, the lower reach of the right bank of the Padma River is at high vulnerable to erosion at the confluence. The methods and analysis adopted in this study can be applied to any other braided river to monitor the dynamics of the river and to formulate an action plan to protect the river from erosion.

Fingerprinting historical tributary contributions to floodplain sediment using bulk geochemistry

Sediment deposition on floodplains is essential for the development and maintenance of riparian ecosystems. Upstream erosion is known to influence downstream floodplain construction, but linking these disparate processes is challenging, especially over large spatial and temporal scales. Sediment fingerprinting is thus a robust tool to establish process linkages between downstream floodplain development and sediment production in distal headwater basins. Here we use sediment geochemistry to connect historical erosion in several tributaries of the Yampa River in Colorado and Wyoming, USA, to the construction of downstream floodplains on which extensive cottonwood forests established. Using a combination of conventional techniques and the relatively novel machine-learning random forest algorithm, we build multiple fingerprints of diagnostic geochemical tracers that are then input into a Bayesian mixing model to apportion provenance of floodplain sediment. Sediment samples for provenance analysis were collected from an excavated floodplain in Deerlodge Park on the Yampa River at the rooting surface of the surrounding cottonwood forest and dominantly comprised of very fine (4Φ) sand. Fingerprinting analysis of the 4Φ fraction of collected floodplain sink (n = 38) and tributary source (n = 218) samples revealed floodplain sediment to be dominantly sourced from the tributaries of Muddy Creek (45 ± 4%) and Sand Wash (42 ± 6%). Dendrochronology results moreover indicate the Deerlodge floodplain sediment was deposited in ∼1912, which falls squarely within the time (1880–1940) these tributaries were actively eroding. Taken together, study results indicate a demonstrable link between historical tributary erosion and downstream floodplain construction and concomitant forest establishment. Our findings suggest processes operating in tributary watersheds play an important role in the dynamics of large rivers and emphasize both the need for holistic, collaborative management of sediment as an essential resource and the potential to utilize sediment fingerprinting to inform and direct river ecosystem management.

Rates of Historical Anthropogenic Soil Erosion in the Midwestern United States

AbstractErosion degrades soils, reduces crop yields, and diminishes ecosystem services. The total amount of soil that has been eroded since the initiation of farming is unknown in most agricultural landscapes, which hinders assessment of soil erosion trends. In the Midwestern U.S., erosion has caused native prairie remnants to become perched above surrounding farmland, providing an opportunity to measure historical soil erosion rates. We use high‐resolution topographic surveys conducted across erosional escarpments at the boundary between 20 prairies and adjacent agricultural fields and show the median reduction in soil thickness ranges from 0.04 to 0.69 m, corresponding to erosion rates of 0.2–4.3 mm year−1, with a median value of 1.9 mm year−1. We used an association between the measured reduction in soil thickness and topographic curvature to predict regional soil erosion integrated since the beginning of farming to the present. We estimate a median historical erosion rate of 1.8 ± 1.2 mm year−1, which is nearly double the rate considered tolerable by the U.S. Department of Agriculture (USDA). Current soil loss predictions from the USDA National Resources Inventory (NRI) and the Daily Erosion Project (DEP) are lower than our historically averaged erosion rate by a factor of 3 and 8, respectively. We suggest that the NRI and the DEP underpredict soil loss rates because they do not include tillage erosion, a process shown to be important throughout the Midwestern U.S. Our findings indicate that further implementation of conservation practices is needed to reduce the high centennial‐averaged soil erosion rates that we measure to sustainable levels.

Asynchronized erosion effects due to climate and human activities on the central Chinese Loess Plateau during the Anthropocene and its implications for future soil and water management

AbstractVariations and regional differences in land surface processes during the Anthropocene have directly impacted local economic development and social stability. Nevertheless, little is known about the historical erosion effects and human–environment interactions at annual and decadal scales on the central Chinese Loess Plateau (CLP) over the past 200 years, when human activities and annual sediment discharge both reached historical peaks. Located in the northcentral hilly–gully and southcentral plateau–gully regions, respectively, the Jingbian and Heshui landslide‐dammed reservoirs were ideal settings to reconstruct the erosion flux and precipitation over A.D. 1850–2000 due to vertical stacking of interannual couplets. During this period, the mean annual specific sediment yield reached 1.17 × 104 t/(km2 a) in the Jingbian catchment (precipitation threshold of 30 mm), while it reached 1.13 × 104 t/(km2 a) in the Heshui catchment (precipitation threshold of 40 mm) according to sediment yield with frustum and extrapolation of historical precipitation. Interannual El Niño–Southern Oscillation (ENSO) events were deemed a primary climatic factor inducing soil erosion over the central CLP. This should remind decision‐makers that it is necessary to prevent large‐scale floods and severe erosion before future ENSO events. Changes in population, policies, and human activities also affected land surface processes on the central CLP during 1850–2000. In addition, the results revealed that abandoned farmlands in the southcentral regions with 600 mm and more precipitation had a strong ecological resilience, while this was weak in the northcentral drier region. These findings imply that future ecological restoration of the central CLP should consider the ecological resilience of farmlands that have been recently abandoned due to urbanization. These novel results provide new insights into regional soil and water management under China's development agenda of ‘Ecological Conservation and High‐quality Development of the Yellow River Basin’.

Determining the drivers and rates of soil erosion on the Loess Plateau since 1901

Attributing soil erosion to land management and climatic drivers is important for global policy development to protect soils. The Chinese Loess Plateau is one of the most eroded areas in the world. However, there has been limited assessment of historic spatial changes in erosion rates on the Loess Plateau and the major contributors driving these spatial changes. In this study, the Revised Universal Soil Loss Equation was empirically validated and employed to assess spatially distributed historical erosion rates on the Loess Plateau from 1901 to 2016. A double mass curve attribution technique was then used to investigate the impact of land management and climatic drivers on the Loess Plateau. Decadal average erosion rates and the total area with intensive erosion (>5000 t km−2 yr−1) experienced a sharp increase from the 1930s to 1970s, followed by a decline to an historic low between the 1980s and 2000s. Mean erosion rates for the 2000s were 54.3% less than those of the 1970s. However, a recent increase in erosion rates was observed between 2010 and 2016. Land management change was the dominant driver of historical erosion rate changes before 2010. Extensive deforestation and farming, driven by population increase, were responsible for intensifying erosion between the 1930s and 1970s, while policy-driven conservation schemes and revegetation led to reduction thereafter. However, the recent increase in erosion between 2010 and 2016 was mainly driven by extreme rainfall events, a major concern given climate change projections. Advanced erosion control strategies are therefore required as part of integrated catchment management that both maintain water supplies for human use during dry periods while reducing erosion during storm events.

Estimate of decadal‐scale riverbed deformation and bed‐load sediment transport during flood events in the lowermost Mississippi River

AbstractRiverbed changes are important to applications in engineering in the environment, such as navigation, salt‐water intrusion and habitat quality. This study employed decadal hydrographic data over the past 50 years (1963–2013), as well as daily water stages and discharges to outline the long‐term channel morphological changes and bed‐load sediments deposited by floods in the lowermost Mississippi River (LMR). To generate accurate bathymetric digital elevation models (DEMs), we interpolated the hydrographic survey in a channel‐centred coordinate system by employing ordinary kriging with anisotropy. Riverbed deformations were estimated by subtracting the elevations between DEMs at two different times to generate a series of DoDs (DEM of difference). The results from DoDs exhibit temporal riverbed change patterns and also reveal net degradation after the completion of the Old River Control Structure in 1963, except for the period 1992–2004. Spatially, over 32% of the total area experienced continuous erosion, with only 0.4% having continuous aggradation. Historical erosion over the past 50 years could be removing the alluvial veneer in sections of the river, and exposing more non‐alluvial sediments, particularly between river kilometre RK 230 and RK 40. Our analysis also shows that riverbed deformation patterns are mainly controlled by flood events, backwater effects, as well as the drawdown effect near the Bonnet Carré spillway. In this study, we also examine whether the LMR traps bed‐load sediment under flood conditions. The probability distribution estimated by Monte Carlo simulation suggests only low amounts of bed‐load sediments are deposited on the channel bed during floods. Spatially, the short‐term bed‐load erosion/deposition pattern roughly matches the decadal‐scale riverbed deformation estimated from DoDs. Moreover, this study finds that the trends between the thalweg changes and riverbed deformation are similar, suggesting that both of these patterns are controlled by the same factors.

Hydrogeomorphology as a Tool in the Evolutionary Analysis of the Dynamic Landscape—Application to Larrodrigo, Salamanca, Spain

Evolutionary analysis of the fluvial landscape provides relevant inputs for the environmental management of a territory, in such a way that the understanding of the dynamics of fluvial spaces becomes a preponderant factor in the definition of protection and management strategies. Although the development of geographic information systems is a step forward in the study of the landscape, it is necessary to establish methodological frameworks that make remote sensing techniques available at multiple spatio-temporal scales, especially in basins with high levels of intervention. In the present study, we develop a methodology for the analysis of the fluvial landscape development in the last century of a highly modified water body, through the detailed study of hydrogeomorphic elements, using remote sensing techniques including high-density surface data (LiDAR) and historical aerial imageries; when supported by fieldwork, these allow for the identification of the sequence of sedimentation–erosion zones, differentiating in detail the zones denominated as areas of current erosion, accretion zones, and historical erosion zones. An application of the methodology was carried out in the Larrodrigo stream, located in Salamanca, Spain.

Sediment‐ecological connectivity in a large river network

AbstractSediment eroded from the headwaters of a large basin strongly influences channels and ecosystems far downstream, but the connection is often difficult to trace. Disturbance‐dependent riparian trees are thought to rely primarily on floods for formation of the sand bars necessary for seedling establishment, but pulses of sediment should also promote formation of such features. In order to expand understanding of the role of sediment connectivity in governing ecological processes, here we explore the hypothesis that cottonwood forest along the Green and Yampa Rivers in Utah and Colorado are dominated by trees established a century ago during a period of extensive channel migration caused by significant headwater erosion. Analysis of historical documents and aerial photographs suggests that three key tributaries of the Yampa River underwent significant historical erosion from roughly 1880 to 1940. Average width and depth of tributaries with defined arroyos increased two to six times from historical surveys, resulting in the export of ~30 million metric tons of sediment, sizably increasing the sediment load and channel migration rate of the Yampa and Green Rivers. Establishment of major portions of several downstream cottonwood forests occurred during this period of historical erosion, increased sediment loads, and heightened channel migration rates, and the area of forest dating to that time is much greater than can be explained by high flows alone. Viewed collectively, our findings suggest tributary erosion played a vital role in successful downstream forest establishment, a link we contend is best illustrated through a sediment‐ecological connectivity framework. Broadly, this framework facilitates consideration of linkages between morphological and ecological processes at the watershed‐scale. Development and utilization of a watershed‐scale sediment‐ecological connectivity perspective highlights the value of sediment as a critical ecological resource to be managed jointly with flow to ensure the maintenance of vital riverine ecosystems.

Spatial decoupling of legacy phosphorus in cropland: Soil erosion and deposition as a mechanism for storage

Agricultural production continues to be implicated as one cause of eutrophication of water courses and water bodies in many agro-ecosystems. The generally-held consensus is that soil erosion by water is a major mechanism for loss of phosphorus (P) to adjacent water bodies and down-stream reservoirs from crop and grazing lands. Nonetheless, it does not explain the whole story of the fate of P losses applied to soils. This study assessed the spatial distribution of P as a consequence of historical erosion and redistribution of soil in an agricultural field in the Lake Erie basin in southern Ontario. Combining stratified random sampling with geospatial analysis of landscape position, plant-available (Olsen) P concentrations and stocks were measured and compared to other soil properties and related to soil erosion and redistribution. Toe-slope and foot-slope positions had two to three times the Olsen P stocks compared to summit landscape positions (mean of 52 +/- 9 kg P ha−1 and 47 +/- 9 kg P ha−1 versus 20 +/- 2 kg P ha-1, respectively) which was attributed to both water and tillage erosion. Burial of P beneath the plowing depth showed that the toe-slopes had over two to three times more Olsen P stocks below 25 cm depth compared to all other landscape positions. Olsen P stocks were significantly related (R2 = 0.50; p < 0.001) to soil organic carbon (SOC) stocks which was a consequence of historical soil erosion and redistribution in the field. The fate of legacy P in soils may be dependent upon the history of erosion and redistribution resulting in deposition of P in toe-slope and foot-slope positions in an agricultural landscape.