River Sediment Load Research Articles

Different controls on sedimentary organic carbon in the Bohai Sea: River mouth relocation, turbidity and eutrophication

Abstract The extractable lipids and bulk organic geochemical parameters in three sediment cores (M-1, M-3 and M-7) from southern, central and northern Bohai Sea were analyzed in order to reconstruct environmental changes since 1900. The C/N ratio and multiple biomarkers (e.g., C27 + C29 + C31 n-alkanes, C24 + C26 + C28 n-alkanols, branched versus isoprenoid tetraether index) suggest more terrigenous organic carbon (OC) inputs in southern Bohai Sea. The abrupt changes of biomarker indicators in core M-1 are generally synchronous with the Yellow River mouth relocation events (e.g., 1964, 1976 and 1996), suggesting the distance to the river mouth being an important factor for sedimentary OC dispersal in the southern Bohai Sea. However, in cores M-3 and M-7, terrigenous biomarkers (i.e., BIT) show a long-term declining trend, consistent with a continuous reduction of the Yellow River sediment load, whereas marine biomarkers such as cholesterol, brassicasterol and dinosterol dramatically increased post-1980, apparently related to human-induced eutrophication in the Bohai Sea. Our study suggests different controlling factors on sedimentary OC distribution in the southern (high turbidity) and other parts (less turbidity) of the Bohai Sea, which should be considered for interpretation of paleoenvironments and biogeochemical processes in the river dominated margins that are hotspots of the global carbon cycling.

Impact of Normalization and Input on ARMAX-ANN Model Performance in Suspended Sediment Load Prediction

The suspended sediment load in rivers is an important parameter in watershed planning and management. Since daily suspended sediment time series contain linear and nonlinear components, existing prediction models are associated with limitations. Therefore, this study introduces a new hybrid model comprising two commonly used stochastic and nonlinear models. The sediment load is first modeled by an autoregressive-moving average with exogenous terms (ARMAX) model. Subsequently, the ARMAX residuals are modeled with an artificial neural network (ANN). For this purpose, discharge (Q) and sediment (S) are considered as model input parameters. Three modeling scenarios are defined to investigate the impact of data normalization on the hybrid model. The exponential and Box-Cox transformation methods are combined into a new data normalization method called mixed transformation. The performance of these methods is then compared. In addition, the impact of the type and number of input combinations on ARMAX-ANN model accuracy is evaluated. To this end, 12 input combinations and 1331 ARMAX and ANN models are verified. The ARMAX model inputs include S, Q and the white noise disturbance term (e), while the ANN model inputs include the ARMAX model results and residuals. Moreover, the hybrid model’s accuracy is compared with the ARMAX and ANN models.

Agricultural land use doubled sediment loads in western China’s rivers

Abstract Land use changes, such as deforestation and agricultural expansion, increase soil erosion on the scale of hillslopes and small drainage basins. However, the effects of these changes on the sediment load in rivers is poorly quantified, with a few studies scattered globally, and only 10 data points in the world’s most populous nation, China. At 20 different sites in western China, we compare contemporary fluvial sediment yield data collected daily over 4 to 26 years between 1945 and 1987 (median = 19 years) to long-term measures of sediment generation based on new isotopic measurements of in situ 10Be (beryllium-10) in river sediments. We find that median sediment yield at these sites exceeds background sediment generation rates by a factor of two (from 0.13 to 5.79 times, median 1.85 times) and that contemporary sediment yield is statistically significantly different from long-term sediment generation rates (p

State-shifting at the edge of resilience: River suspended sediment responses to land use change and extreme storms

The interaction of climate, geomorphology, and land use dictates catchment sediment production and associated river sediment loads. Accordingly, the resilience of catchments to disturbances can be assessed with suspended sediment regimes. This case study in the hill country of the lower North Island of New Zealand was a decade-long examination of the short- and long-term effects of an extreme storm event on sediment supply and exhaustion in the Oroua and Pohangina catchments, two catchments that have experienced intense land use changes and frequent broad-scale landslides. Indicators of Hydrologic Alteration, a program developed to characterize hydrologic regimes, was used to analyze daily suspended sediment records over a period of a decade in order to characterize sediment regimes of the Oroua and Pohangina. An aggregated data set of sediment-bearing events for the period of record was analyzed to examine the suspended sediment response of individual storms relative to runoff magnitudes. The findings of this study demonstrate that large storms that generate extreme landsliding and flooding have the ability to produce enough sediment to temporarily convert catchments from a supply-limited state to a transport-limited state. Landsliding and thus sediment supply was disproportionately high in locations where livestock grazing occurred on steep hillslopes. The timing and intensity of previous storms, or the antecedent catchment condition, was also shown to influence the response of the catchments. In both catchments, suspended sediment loads were elevated for a period of ~4years following the landslide-generating February 2004 storm. The methods and findings we present are useful for assessing the resilience of catchments exposed to frequent disturbances such as land use changes and landslides.

Assessing natural and anthropogenic influences on water discharge and sediment load in the Yangtze River, China

The water discharge and sediment load of rivers are changing substantially under the impacts of climate change and human activities, becoming a hot issue in hydro-environmental research. In this study, the water discharge and sediment load in the mainstream and seven tributaries of the Yangtze River were investigated by using long-term hydro-meteorological data from 1953 to 2013. The non-parametric Mann-Kendall test and double mass curve (DMC) were used to detect trends and abrupt change-points in water discharge and sediment load and to quantify the effects of climate change and human activities on water discharge and sediment load. The results are as follows: (1) the water discharge showed a non-significant decreasing trend at most stations except Hukou station. Among these, water discharge at Dongting Lake and the Min River basin shows a significant decreasing trend with average rates of −13.93×108m3/year and −1.8×108m3/year (P<0.05), respectively. However, the sediment load exhibited a significant decreasing trend in all tributaries of the Yangtze River. (2) No significant abrupt change-points were detected in the time series of water discharge for all hydrological stations. In contrast, significant abrupt change-points were detected in sediment load, most of these changes appeared in the late 1980s. (3) The water discharge was mainly influenced by precipitation in the Yangtze River basin, whereas sediment load was mainly affected by climate change and human activities; the relative contribution ratios of human activities were above 70% for the Yangtze River. (4) The decrease of sediment load has directly impacted the lower Yangtze River and the delta region. These results will provide a reference for better resource management in the Yangtze River Basin.

Influence of Ecological Technology Measures on the Annual Sediment Load of the Wuding River

Abstract: The influence of ecological technology measures on the annual sediment loads of rivers complies with the principles of statistics. In this paper, the annual sediment load of the Wuding River is taken as the dependent variable and the rainfall, rainstorms during the flood period of the Wuding River and areas of ecological technology measures are taken as the independent variables to analyze the influence of ecological technology measures on the annual sediment load of the Wuding River during the years 1956 to 2007. This research uses a stepwise regression method. The result shows that 1) the non-linear regression equation composed of three independent variables including 7–8 monthly rainfalls along the Wuding River, areas of ecological technology measures and maximum daily rainfall along the Wuding River has been calculated and set up; the correlation coefficient is R2=0.857 and the significance level is α=0.001. 2) R2=0.717 is adjusted and the regression equation reveals a change of annual sedim...

Predicting improved optical water quality in rivers resulting from soil conservation actions on land

Deforestation in New Zealand has led to increased soil erosion and sediment loads in rivers. Increased suspended fine sediment in water reduces visual clarity for humans and aquatic animals and reduces penetration of photosynthetically available radiation to aquatic plants. To mitigate fine-sediment impacts in rivers, catchment-wide approaches to reducing soil erosion are required. Targeting soil conservation for reducing sediment loads in rivers is possible through existing models; however, relationships between sediment loads and sediment-related attributes of water that affect both ecology and human uses of water are poorly understood. We present methods for relating sediment loads to sediment concentration, visual clarity, and euphotic depth. The methods require upwards of twenty concurrent samples of sediment concentration, visual clarity, and euphotic depth at a river site where discharge is measured continuously. The sediment-related attributes are related to sediment concentration through regressions. When sediment loads are reduced by soil conservation action, percentiles of sediment concentration are necessarily reduced, and the corresponding percentiles of visual clarity and euphotic depth are increased. The approach is demonstrated on the Wairua River in the Northland region of New Zealand. For this river we show that visual clarity would increase relatively by approximately 1.4 times the relative reduction of sediment load. Median visual clarity would increase from 0.75m to 1.25m (making the river more often suitable for swimming) after a sediment load reduction of 50% associated with widespread soil conservation on pastoral land. Likewise euphotic depth would increase relatively by approximately 0.7 times the relative reduction of sediment load, and the median euphotic depth would increase from 1.5m to 2.0m with a 50% sediment load reduction.

Recent morphological changes of the Yellow River (Huanghe) submerged delta: Causes and environmental implications

The Yellow River (Huanghe) submerged delta (YRSD) has been under the threat of erosion and retreat during the Anthropocene due to dramatic climatic and anthropogenic changes in the Yellow River basin. The analysis of field data shows that over the period of 1977–2005, the changes in climate (decrease in precipitation and increase in air temperature) and human interventions (increase in water diversion projects) throughout the watershed have resulted in the sharp reductions of river flow and sediment discharges into the Bohai Sea. Consequently, over the decadal timescale, morphological evolution of the YRSD has gone through three stages: i.e. rapid accumulation (5.77×108m3/year) in 1977–1985, moderate accumulation (3.80×108m3/year) in 1986–1995 and slow accumulation (0.91×108m3/year) in 1996–2005. Climatic change within the catchment characterized by the rapid increase of air temperature contributed significantly to the transitions from the rapid accumulation to the moderate accumulation, and to the subsequent slow accumulation. The decadal morphological changes of the YRSD also show peculiar deposition/erosion characteristics over the medium timescale under river input reduction. Within the three decades, the patterns of the main sedimentary body exhibit irregular ellipses with the long axis parallel to the −5 or −10m isobaths and short axis perpendicular to the isobaths. The depocentres of the YRSD are located between the −10 and −15m isobaths close to the respective river mouths, with a high vertical accretion rate of ~1.20m/year. The time series data of annual volumetric change of the YRSD and river sediment load from 1977 to 2005 further demonstrate significant linear positive relationships between deltaic geomorphic change and fluvial input over shorter timescales (annual and 3-year). The critical sediment discharges for maintaining the deposition/erosion equilibrium state of the YRSD over the annual and 3-year timescales are found to be 1.79×108t/year and 1.29×108t/year, respectively. The analysis from the latest hydrological data (2006–2015) suggests that over the decadal timescale, the evolution state of the YRSD currently has transitioned from constructive to destructive due to the weakened fluvial input. Moreover, there exists a close quantitative link between the progradation of the Yellow River subaerial delta (YRAD) and the YRSD over the five-year timescale, indicating that every 1×108m3/year increase of the YRSD's yearly volumetric change will result in a 3.28km2/year increase of the YRAD's yearly land-accretion area, and the YRAD will reach the extension/retreat balance state when yearly morphological change of the YRSD is at 0.73×108m3/year.

Using check dam deposits to investigate recent changes in sediment yield in the Loess Plateau, China

Check dams are one of the most important engineering measures for controlling soil and water loss from watersheds and can play a key role in reducing sediment loads in rivers. In addition, the associated sediment deposits can in some circumstances provide a valuable source of information on changing rates of sediment production from the upstream watershed through time. A sediment profile with a depth of 11.325m was examined within the deposits associated with a check dam at the outlet of the Nianyangou catchment, in the northern Loess Plateau, China, with a drainage area of 0.181km2. The profile contained evidence of a total of 75 clearly identifiable flood event couplets, which corresponded to storm events occurring during the period 1960–1990. The variability of the grain size composition (clay content) of the sediment and its 137Cs activity and organic matter (SOM) content down the profile was used to identify individual flood event couplets and the record of event rainfall (particularly extreme storm events) was used to establish a chronology for the individual flood event couplets. Based on the reservoir capacity curve and information on couplet thickness and sediment bulk density, the sediment yield associated with each flood couplet has been calculated. Using these data, annual sediment yields were estimated to range between zero in 1965 to 9750t in 1984. The period from 1960 to 1990 was divided into three distinct phases based on evidence for changing rates of sediment production within the watershed above the check dam provided by a double mass plot of cumulative sediment yield versus cumulative precipitation. These phases represent the periods: 1960 to 1964, 1965 to 1983 and 1984 to 1990, which were characterized by mean annual specific sediment yields of 26,220tkm−2year−1, 5590tkm−2year−1 and 19,130tkm−2year−1, respectively. This study is seen as demonstrating the potential for using the sediment deposits associated with check dams to obtain retrospective assessments of changes in sediment yield in repose to land use change and the implementation of soil conservation and sediment control measures.

Ensemble Wavelet-Support Vector Machine Approach for Prediction of Suspended Sediment Load Using Hydrometeorological Data

Explicit prediction of the suspended sediment loads in rivers or streams is very crucial for sustainable water resources and environmental systems. Suspended sediments are a governing factor for the design and operation of hydraulic structures, like canals, diversions and dams. In recent decades, to model hydrological phenomena which are complex in nature the machine learning models are used commonly. In the present study, support vector machine (SVM) with wavelet transform (WASVM) has been employed for prediction of daily suspended sediment load (SL) for two south Indian watersheds (Marol and Muneru) using hydrometeorological data. A 40-year daily observed data (1972–2011) have been used for the analysis, where past SL, streamflow (Q), and rainfall (R) data were used as the model inputs, and SL was the model output. Using conventional correlation coefficient analysis between input and output variables, the best input of WASVM model was identified. The reliability of SVM and WASVM models were evaluated on the basis of different performance criteria, i.e., coefficient of determination (R2), root mean square error (RMSE), normalized mean square error (NMSE), and Nash-Sutcliffe coefficient (NS). Initially, 1-day ahead SL prediction was performed using the best WASVM model. The results showed that, 1-day predictions were very precise, showing a close agreement with the observed SL data (R2=0.94, NS=0.94 for the Marol watershed, and R2=0.77, NS=0.77 for the Muneru watershed) in the testing period. The same WASVM model was then used for the prediction of SL for the higher lead periods. The NMSE value for the Marol watershed was found as low as 0.06 for 1-day ahead prediction, and increases subsequently as 0.29, 0.46, and 0.70 for 3-, 6-, and 9-day higher leads, respectively. Likewise, for the Muneru watershed, the NMSE value was found as low as 0.21 for 1-day ahead prediction, and increases subsequently as 0.42, 0.53, and 0.68 for 3-, 6-, and 9-day higher leads, respectively. Further, the model was evaluated on the basis of its capability of predicting peak SL and cumulative SL for 1- to 6-day leads. The statistical analysis shows that the developed WASVM model can predict the target value successfully up to a 6-day lead and is not suitable for higher lead specifically in the selected watersheds having similar hydroclimatic conditions like the ones selected in this study. Predictions by the WASVM model were found significantly superior to the ones obtained by the conventional SVM model. The results revealed that the WASVM model provides a very good accuracy in predicting SL and can be used as an effective forecasting tool for hydrological applications.

Total organic carbon fluxes of the Red River system (Vietnam)

AbstractRiverine transport of organic carbon from terrestrial ecosystems to the oceans plays an important role in the global carbon cycle. The Red River is located in Southeast Asia where river discharge, sediment loads and fluxes of elements (carbon, nitrogen and phosphorus) associated with suspended solids have been dramatically altered over past decades as a result of reservoir impoundment and land use, population, and climate change. Dissolved organic carbon (DOC) and particulate organic carbon (POC) concentrations were measured monthly at four stations of the Red River system from January 2008 to December 2010. The results reveal that POC changed synchronically with total suspended solids (TSS) concentration and with the river discharge, whereas no clear trend was observed for DOC concentration. The mean value of total organic carbon (TOC = DOC + POC) flux in the delta of the Red River was 31.5 × 1013 ± 4.0 × 1013 MgC.yr−1 (range 27.9–35.8 × 1013 MgC.yr−1 which leads to a specific TOC flux of 2012 ± 255 kgC.km−2.yr−1 during this 2008–2010 period. About 80% of the TOC flux was transferred to the estuary during the rainy season as a consequence of the higher river water discharge. The high mean value of the POC:Chl‐a ratio (1585 ± 870 mgC.mgChl‐a−1) and the moderate C:N ratio (7.3 ± 0.1) in the water column system suggest that organic carbon in the Red River system is mainly derived from erosion and soil leaching in the basin. The effect of two new dam impoundments in the Red River was also observable with lower TOC fluxes in 2010 compared with 2008. Copyright © 2017 John Wiley &amp; Sons, Ltd.

A combined use of acoustic and optical devices to investigate suspended sediment in rivers

The use of acoustic and optic devices has become more and more common for estimating suspended sediment loads in rivers. The echo intensity levels (EIL) recorded by means of an Acoustic Doppler Current Profiler (ADCP) have been applied in different methods, which provided relationships between scattering particles features derived from samples (i.e., concentration and grain size) and corresponding backscattering strength and sound attenuation. At the same time, the laser diffraction was applied by an in-stream sampler (LISST-SL) to measure suspended sediment concentration and the corresponding particle size distribution (PSD). These two techniques exhibited different limitations in terms of the measured range of concentration, sensitivity to a certain spectrum of particle sizes, and instruments deploy feasibility especially in large rivers, in a way that the use of sampled PSD by LISST-SL to validate ADCP methods may not be trivial. The aim of this study was to combine the vertical profiling of EIL by an ADCP with results from LISST-SL, eventually demonstrating the possibility of using moving ADCP measurements to detect different suspended matters along a Danube River section characterized by a small tributary junction. At the same time, this work elucidates optical to acoustic method deviations that hinders an actual validation of ADCP methods based on LISST-SL rather than with physical samplings.

Assessment of minimum variance unbiased estimator and beta coefficient methods to improve the accuracy of sediment rating curve estimation

Because of the requirement to just one input data, the basic sediment rating curve (SRC) method is the most recognised method for the study of river sediment load. Beside its advantages, this method suffers from low accuracy, especially for upper limit of sediment load values which is leading to the reduction of its reliability. In this study, sediment data recorded in four hydrometry station located in Gorgan Gulf basin are used to investigate and compare the accuracy of minimum variance unbiased estimator (MVUE) and beta coefficient as two correction methods. Visual criterion and two goodness of fit tests, namely mean square error (MSE) and model efficiency (ME) were applied to compare the results of SRC estimations. Visual and goodness of fit tests showed both correction methods particularly beta coefficient method improve the SRC estimation especially for upper limit of river sediment load in three of the four understudy stations.

Widening the scope: linking coastal sedimentation with watershed dynamics in Java, Indonesia

Watershed processes and their effects on coasts are shaped by numerous interacting natural and societal factors. The knowledge of these factors and processes is often limited. This makes the field prone to politicisations with debates, research, and interventions being confined to a few selected factors. Debates on the causes of high river sediment loads and coastal sedimentation in Java have focussed on rainfed agriculture on peasants’ private lands, while other drivers have been neglected. This has undermined the effectiveness of watershed management. This paper links the sedimentation of the Segara Anakan lagoon on Java’s south coast with landscape characteristics and transformations in its catchment. Three-fourths of the lagoon have silted up since 1857/60. This is the result of a much broader range of drivers than commonly assumed to date. In addition to rainfed agriculture on peasants’ private lands, these drivers include coffee cultivation, timber extraction, plantation development, and in-migration in the late nineteenth and early twentieth century; erosion on contested state forest and plantation lands; state forest management practices; slope cuts to enlarge agricultural fields; agriculture in riparian zones; erosion from roads, trails, and settlements; river channel and floodplain modifications; and volcanic eruptions. The choice and expectations of societal responses aimed at reducing river sediment loads and coastal sedimentation hence need to be reconsidered, and related debates and research agendas must be broadened.

Magnetic susceptibility as a simple tracer for fluvial sediment source ascription during storm events

Sediment tracing using a single tracer, low frequency magnetic susceptibility (Xlf), was used to apportion suspended sediment to geologically defined source areas and to interpret sediment source changes during flood events in the degraded catchment of the Vuvu River, a headwater tributary of the Mzimbubu River, South Africa. The method was tested as a simple tool for use by catchment managers concerned with controlling erosion. The geology of the 58 km2 catchment comprises two distinct formations: basalt in the upper catchment with a characteristically high magnetic susceptibility and shales with a low magnetic susceptibility in the lower catchment. Application of an unmixing model incorporating a Monte Carlo uncertainty analysis showed that Xlf provided a means to assign the proportion of each geological province contributing to the river's sediment load. Grab water samples were collected at ten-minute intervals during flood events for subsequent analysis of suspended sediment concentration and the magnetic susceptibility of the filtered sediment. Two floods are presented in detail, the first represents a significant event at the start of the wet season (max. discharge 32 m3 s−1); the second was a smaller flood (max discharge 14 m3 s−1) that occurred a month later. Suspended sediment concentrations during the twelve monitored events showed a characteristic decline over the wet season. The main source of suspended sediment was shown to be from the mudstones in the lower catchment, which contributed 86% of the total measured load. The sediment dynamics during the two floods monitored in detail were quite different from each other. In the first the sediment concentration was high (11 g L−1), peaking after the flood peak. The Xlf value increased during the event, indicating that contribution to the sediment load from basalt in the upper catchment increased during the recession limb. In the second, smaller flood the sediment peak (6 g L−1) coincided with the flood peak. Low Xlf values indicated that mudstones in the lower catchment soils dominated the sediment load throughout the entire event. Sediment tracing using a single property (Xlf) was thus used effectively to study changing sediment sources both between and during a flood event in a catchment with strongly contrasting magnetic signatures in different areas. The results support the use of magnetic susceptibility as a simple and cheap tool to determine sediment provenance that can be used to guide catchment restoration in similar environments.

Fluvial fluxes from the Magdalena River into Cartagena Bay, Caribbean Colombia: Trends, future scenarios, and connections with upstream human impacts

Fluxes of continental runoff and sediments as well as downstream deposition of eroded soils have severely altered the structure and function of fluvial and deltaic-estuarine ecosystems. The Magdalena River, the main contributor of continental fluxes into the Caribbean Sea, delivers important amounts of water and sediments into Cartagena Bay, a major estuarine system in northern Colombia. Until now, trends in fluvial fluxes into the bay, as well as the relationship between these tendencies in fluvial inputs and associated upstream changes in the Magdalena catchment, have not been studied. Here we explore the interannual trends of water discharge and sediment load flowing from the Magdalena River-Canal del Dique system into Cartagena Bay during the last three decades, forecast future scenarios of fluxes into the bay, and discuss possible connections between observed trends in fluvial inputs and trends in human intervention in the Magdalena River basin. Significant upward trends in annual runoff and sediment load during the mid-1980s, 1990s, and post-2000 are observed in the Magdalena and in the Canal del Dique flowing into Cartagena Bay. During the last decade, Magdalena streamflow and sediment load experienced increases of 24% and 33%, respectively, compared to the pre-2000year period. Meanwhile, the Canal del Dique witnessed increases in water discharge and sediment load of 28% and 48%, respectively. During 26y of monitoring, the Canal del Dique has discharged ~177Mt of sediment to the coastal zone, of which 52Mt was discharged into Cartagena Bay. Currently, the Canal drains 6.5% and transports 5.1% of the Magdalena water discharge and sediment load. By 2020, water discharge and sediment flux from the Canal del Dique flowing to the coastal zone will witness increments of ~164% and 260%, respectively. Consequently, sediment fluxes into Cartagena Bay will witness increments as high as 8.2Mty−1 or 317%. Further analyses of upstream sediment load series for 21 tributary systems of the main Magdalena during the 2005–2010 period reveal that six tributaries, representing 55% of the analyzed Magdalena basin area, have witnessed increasing trends in sediment load, raising the river's sediment load by 44Mty−1. Overall, trends in sediment load of the Magdalena and the Canal del Dique during the last three decades are in close agreement with the observed trends in human induced upstream erosion. The last decade has witnessed even stronger increments in fluvial fluxes to Cartagena Bay. Our results emphasize the importance of the catchment-coast linkage in order to predict future changes of fluvial fluxes into Caribbean estuarine systems.

Suspended sediment projections in Apalachicola Bay in response to altered river flow and sediment loads under climate change and sea level rise

AbstractSuspended sediments, or total suspended solids (TSS), are an important factor for oyster habitat. While high concentrations of suspended sediments can cause a reduction of oyster density, some level of suspended sediment is required to supply oysters with necessary nutrients. In this study, characteristics of TSS variations in response to sea level rise (SLR) at two oyster reefs in Apalachicola Bay are investigated by coupled estuarine hydrodynamic and sediment transport modeling. A storm event in 1993 and a year‐long period in 2010 under recent sea level conditions are selected as the baseline conditions. Scenarios of river flow and sediment loads under SLR and climate change are obtained by downscaled global climate modeling. Compared to the baseline conditions, simulations of TSS indicate that predicted SLR yields a substantial decrease in TSS near the two oyster reefs. However, TSS levels differed at the two study locations. TSS changes by SLR revealed minimal impact on oyster habitat at the Dry Bar site (to the west of the mouth of the Apalachicola River) but are projected to have a significant impact at the Cat Point site (to the east of the Apalachicola River). At Cat Point, because SLR causes the increase of salt water intrusion from the Gulf through a large tidal inlet (East Pass), maximum sediment concentration is near zero for 0.2‐m SLR and equal to zero for 0.5‐ and 1.2‐m SLR. Therefore, SLR may result in a substantial loss of nutrients from suspended sediment in the oyster reef at Cat Point.

Managing road transport in a world of changing climate and land use

Natural hazards of river flooding, erosion, landslides and high sediment loads in streams and rivers continue to pose a significant threat to the management of infrastructure, particularly road transport, in most parts of the world. In Asia and Africa, especially, these hazards are considered to be on the increase in response to climate and land use-related factors. Recent studies in Africa and especially Ethiopia lead to the conclusion that complex and poorly understood interactions between geology, climate change and land use change have given rise to increased levels of damage and disruption to transport infrastructure. The prognosis for the future is that these trends will continue and perhaps accelerate. Current policies tend to focus on the ‘proofing’ of infrastructure against future climate change, possibly without due regard to other factors that may be more important in the short–medium term. This is possibly counterproductive in situations where existing and future risks are determined more by geohazard uncertainty and design deficiencies, and the sometimes overriding effects of land use change and land management practices.

A meta‐analysis of soil salinization effects on nitrogen pools, cycles and fluxes in coastal ecosystems

Salinity intrusion caused by land subsidence resulting from increasing groundwater abstraction, decreasing river sediment loads and increasing sea level because of climate change has caused widespread soil salinization in coastal ecosystems. Soil salinization may greatly alter nitrogen (N) cycling in coastal ecosystems. However, a comprehensive understanding of the effects of soil salinization on ecosystem N pools, cycling processes and fluxes is not available for coastal ecosystems. Therefore, we compiled data from 551 observations from 21 peer-reviewed papers and conducted a meta-analysis of experimental soil salinization effects on 19 variables related to N pools, cycling processes and fluxes in coastal ecosystems. Our results showed that the effects of soil salinization varied across different ecosystem types and salinity levels. Soil salinization increased plant N content (18%), soil NH4+ (12%) and soil total N (210%), although it decreased soil NO3- (2%) and soil microbial biomass N (74%). Increasing soil salinity stimulated soil N2 O fluxes as well as hydrological NH4+ and NO2- fluxes more than threefold, although it decreased the hydrological dissolved organic nitrogen (DON) flux (59%). Soil salinization also increased the net N mineralization by 70%, although salinization effects were not observed on the net nitrification, denitrification and dissimilatory nitrate reduction to ammonium in this meta-analysis. Overall, this meta-analysis improves our understanding of the responses of ecosystem N cycling to soil salinization, identifies knowledge gaps and highlights the urgent need for studies on the effects of soil salinization on coastal agro-ecosystem and microbial N immobilization. Additional increases in knowledge are critical for designing sustainable adaptation measures to the predicted intrusion of salinity intrusion so that the productivity of coastal agro-ecosystems can be maintained or improved and the N losses and pollution of the natural environment can be minimized.

Human impact on erosion patterns and sediment transport in the Yangtze River

Sediment load in rivers is an indicator of erosional processes in the upstream river catchments. Understanding the origin and composition of the sediment load can help to assess the influence of natural processes and human activities on erosion. Tectonic uplift, precipitation and run-off, hill slopes and vegetation can influence erosion in natural systems. Agriculture and deforestation are expected to increase the sediment yield, but dams and reservoirs can trap much of this sediment before it reaches the ocean. Here, we use major element composition and 40Ar/39Ar ages of detrital muscovites to constrain the sediment contribution of various tributaries to sedimentation in the Yangtze delta. The sediment contribution calculated from muscovite data was compared with that estimated from current sediment load data from gauging stations. Muscovite data show that the main contributor to the Yangtze delta sands is the Min River, while the current sediment load suggests that the Jinsha and Jialing rivers are the most important current contributors to delta sediments. We suggest that this difference reflects an “old” and “young” erosion pattern, respectively as medium grained muscovite could be transported much slower than suspended sediment load in the complex river-lake systems of the Yangtze River basin. These two different erosion patterns likely reflect enhanced human activity (deforestation, cultivation, and mining) that increasingly overwhelmed long-time natural factors controls on erosion since ~1900calyears B.P.