njun Jia

Changes in water and sediment exchange between the Changjiang River and Poyang Lake under natural and anthropogenic conditions, China

To study the fluvial interaction between Changjiang River and Poyang Lake, we analyze the observed changes of riverine flux of the mid-upstream of Changjiang River catchment, the five river systems of Poyang Lake and Poyang Lake basin. Inter-annual and seasonal variations of the water discharge and sediment exchange processes between Changjiang River and Poyang Lake are systematically explored to determine the influence of climate change as well as human impact (especially the Three Gorges Dam (TGD)). Results indicate that climate variation for the Changjiang catchment and Poyang Lake watershed is the main factor determining the changes of water exchanges between Changjiang River and Poyang Lake. However, human activities (including the emplacement of the TGD) accelerated this rate of change. Relative to previous years (1956-1989), the water discharge outflow from Poyang Lake during the dry season towards the Changjiang catchment increased by 8.98 km(3)y(-1) during 2003-2010. Evidently, the water discharge flowing into Poyang Lake during late April-late May decreased. As a consequence, water storage of Poyang Lake significantly reduced during late April-late May, resulting in frequent spring droughts after 2003. The freshwater flux of Changjiang River towards Poyang Lake is less during the flood season as well, significantly lowering the magnitude and frequency of the backflow of the Changjiang River during 2003-2010. Human activities, especially the emplacement and operation of the TGD and sand mining at Poyang Lake impose a major impact on the variation of sediment exchange between Changjiang main river and Poyang Lake. On average, sediments from Changjiang River deposited in Poyang Lake before 2000. After 2000, Changjiang River no longer supplied sediment to Poyang Lake. As a consequence, the sediment load of Changjiang River entering the sea increasingly exists of sediments from Lake Poyang during 2003-2010. As a result, Poyang Lake converted from a depositional to an erosional system, with a gross sediment loss of 120.19 Mty(-1) during 2001-2010, including sand mining.

Sediment dynamic processes of the Yuehu inlet system, Shandong Peninsula, China

In order to investigate the sediment dynamic behavior of the Yuehu, a small inlet system characterized by abundant sediment supply and rapid sediment infilling, measurements and sampling were undertaken to obtain data sets of tidal water levels, current velocities, suspended sediment concentrations, grain size parameters, deposition rates and organic carbon contents. Sediment budget and the time-velocity asymmetry patterns of the inlet system were analyzed. The results show that the deposition rates are relatively high within the tidal basin. The total sediment flux cannot be balanced by the input from the open sea, the aerosol and biological production; rather, the material from land (which has been intensified by agricultural activities over the past several decades) represents a major component for the balance. Thus, the denudation rate must be reduced to protect the Yuehu as a natural reserve. Furthermore, it is found from the present study that the Yuehu inlet system exhibits all of the four time-velocity asymmetry patterns with varied frequencies of occurrence, compared with the two asymmetry patterns identified for larger inlet systems; such phenomena are partly due to the adjustment of entrance channel geometry. This behavior may be representative of the small tidal inlets at their late stage of morphological evolution and, therefore, may be utilized to prolong the lifespan of small inlet systems

A numerical investigation of freshwater and sediment discharge variations of Poyang Lake catchment, China over the last 1000 years

The Poyang Lake catchment, an important sub-catchment of Changjiang, experienced ‘Little Ice Age’ (LIA) and accelerating intensity of human activities during the last 1000 years. As such, the area and time period serve as a perfect case to study the variations in water and sediment discharge under combined natural and anthropogenic impact. Simulation results of the model HydroTrend indicate that the annual average cumulative water discharge of the five rivers entering Poyang Lake over the last 1000 years is 103.65 ± 1.80 km3, and climate change is the dominating factor determining water discharge variations over time. Influenced by the LIA (AD 1451–1850), the total water discharge of the five rivers was reduced by 10%. Sediment load discharging into Poyang Lake by the five rivers was only 9.21 ± 0.43 Mt yr−1 between AD 1000 and 1700, when the anthropogenic impact on the landscape was still low. However, with the human activities accelerating during the past 300 years, the sediment load entering Poyang Lake underwent a drastic change. Because of intensified soil loss, the total sediment load entering Poyang Lake during AD 1800–1950 increased by 58.7%, compared with AD 1000–1700. After AD 1950, the sediment load variation is mainly reflected by the combined impact of dam emplacement and soil erosion. As sediment interception by dams continuously increased over time, the total sediment load entering Poyang Lake during AD 1990–2000 is only 60.9% of that of the highest riverine sediment flux during AD 1951–1980, which is almost equal to that of the lowest level during AD 1000–1700. The sediment load of many rivers in the world exhibited similar variation trends as that of Poyang Lake under combined impact of climate change and human activities. Better understanding the mechanisms of these variation trends is helpful to analyzing the formation and evolution of an estuary-shelf sedimentary system over the Holocene.

Coastal Embayment Long-Term Erosion/Siltation Associated with P-A Relationships: A Case Study from Jiaozhou Bay, China

Abstract Liu, Y.; Wang, Y.P.; Li, Y.; Gao, J.; Jia, J.; Xia, X., and Gao, S., 2012. Coastal embayment long-term erosion/siltation associated with P-A relationships: A case study from Jiaozhou Bay, China. The sedimentary environment of a large coastal embayment, Jiaozhou Bay, eastern China, in terms of erosion/siltation, has been assessed on the basis of seabed bathymetry and coastline data sets from sea charts (1936–2002) and Landsat-5 TM images (1986–2011). Nine types of sedimentary environment are identified according to the sedimentation rate. The results indicate that slow siltation was generally present from 1936 to 1963, with exceptions of some patchy, slightly eroding areas within the embayment. Transformation to a slow erosion pattern occurred in the main channels over the central embayment in 1963, and such a situation continued until 1982. Subsequently, since 1986, most of the coastlines extended toward the sea at a rate of 101–102 m y−1; this was mainly attributable to human activities, including reclamation over the NW tidal-flat and harbour construction along the east and south coastlines. Using the same data set, patterns of changes in tidal prism and deposition rate within the entrance channel were established. An equivalent friction coefficient (K) is proposed to evaluate the P-A relationship of the large tidal inlets in Jiaozhou Bay. The K value increases gradually over time, indicating a trend toward stable equilibrium in Jiaozhou Bay. This coefficient can be used to examine the status of morphological stability and equilibrium of coastal embayments.

Developing a Cost-Effective Methodology to Manage Fecal Coliform Loading in Shellfish Harvesting Areas of Upper Chesapeake Bay, Maryland

There are more than 75 shellfish harvesting areas in the upper Chesapeake Bay of Maryland that are impaired due to elevated bacterial levels. A comprehensive plan must be established to support the management of bacterial sources in the drainage areas of these waterbodies 1) to protect water quality for public health, 2) to identify potential pollutant sources in the watershed, and 3) to establish the assimilative capacity of the waterbody. Traditionally, a linked watershed and receiving waters modeling approach has been used for estimating assimilative capacity of the waterbodies and developing pollutant load reductions. However, the horizontal scales of these impaired areas vary from a few kilometers to more than 100 kilometers, while the required assessment period to demonstrate the attainment of the water quality standard is 3 to 5 years, requiring long-term observation data and model simulations. Therefore, application of this traditional approach is not feasible for these many areas due to the requirements of large modeling efforts to simulate both the watershed processes and instream fecal coliform concentrations for long-term simulation. To address this challenge, the Virginia Institute of Marine Science and the Maryland Department of the Environment have worked together to develop a cost-effective methodology to achieve these goals. The key element of our approach is to use inverse modeling to estimate fecal coliform loads from the watershed and to establish the assimilative capacity for the waterbody. The inverse modeling approach can be invoked by either the tidal prism model or 3D transport models; it is thus applicable to the large range of spatial scales encountered. By integrating, modeling results with GIS-based source analysis and bacteria source tracking results, potential fecal coliform sources can be identified. With the use of an inverse modeling approach, accurate loads estimation can be achieved while watershed modeling is not available. A case study of the inverse modeling approach for Marylands Choptank River is presented here to demonstrate the feasibility of simulating the fecal coliform distribution in the tidal river and the capability of using the system to support management needs.

On the sediment age estimated by 210Pb dating: probably misleading “prolonging” and multiple-factor-caused “loss”

The radionuclide 210Pb is suitable for century-scale dating and has been used to calculate the sedimentation rate in a variety of environments. However, two common ways to apply 210Pb dating techniques may give misleading results. One is “prolonging of age”, i.e., using the calculated sedimentation rate to date back to 200 or 300 years. This practice must be treated with caution because the 210Pb dating techniques do not guarantee direct dating for ages much older than 100 years. Another is “loss of age”, i.e., the calculated time span between the topmost layer and the 210Pb background layer in cores is less than 100 years when an apparent sedimentation rate is used in the calculation. Here, we propose that based on the principle of 210Pb dating, the upper limit of age suitable for direct 210Pb dating is between 110 and 155 years. The “prolonging” application is acceptable only if the sedimentary environment in the past several hundred years was stable and the sedimentation rate was generally constant, and verification with independent evidence (such as historical records or biomarker methodology) is needed. Furthermore, after analyzing many published and collected data, we found four possible reasons for the “loss of age”. First, the compaction effect of sediment should be corrected in laboratory analysis or else the calculated age will be underestimated. Second, the accuracy and uncertainty of 210Pb activity measurement affect the judgment of the background. To be cautious, researchers are apt to choose a background activity with a younger age. Third, use of a slightly smaller value of supported 210Pb activity in a calculation will lead to considerable underestimation of the time span. Finally, later-stage erosion and migration are common for sedimentation, which lead to loss of sedimentary records and are often reflected as a “loss of age” in cores. We believe that proper use of 210Pb dating data may provide helpful information on our understanding of sediment records and recent environmental changes.

Assessing the vulnerability of changing coasts, Hainan Island, China

Knowledge of coastline changes and vulnerability is of great importance to local government departments that are responsible for the management and development of coastal zones. To study the nature of change and vulnerability along the coasts of the Hainan Island, we collected a large number of sediment samples through the last few years, and reconstructed the changes of the coastline by combining the data of sediment grain-size analysis and the nautical charts/TM RS imaginary. Contrary to being almost free from erosion (as expected from the findings that the coastlines are in a relatively stable state), four major cities in Hainan (i.e., Haikou, Wenchang, Sanya and Changjiang) turned out to be suffered from a moderate coastal vulnerability primarily because of the large populations that impose considerable pressure on the coastlines. Thus, the assessment methodology utilized in this study, including both anthropogenic and natural factors, serves as a useful tool to obtain a comprehensive understanding of coastline vulnerability for local government, in terms of coastal management and adaptation.