Polder Area Research Articles

Landscape Character and Management Zones in Polder Landscapes: A Case Study of the Dongting Lake Area

Polder landscapes, as a representative of lowland agriculture landscapes, possess diverse natural and cultural values. However, polder landscapes are facing multiple challenges arising from economic and climate changes, including increasing flood threats and the fragmentation of landscape patterns. These issues have severely threatened the safety and regional characteristics of the polder landscape. Therefore, this study aims to preserve the regional characteristics of polder landscapes while promoting the sustainable development of lowland environments, and the objective is to provide a foundation and baseline for the management and planning of polder landscapes. In this study, the Dongting Lake Area (DLA) was selected as a representative case of polder landscapes. To identify the landscape character and delineate the landscape management zones, this study employed the Landscape Character Assessment (LCA) method in conjunction with a polder typology method at two scales. As a result, the polder landscape types were identified and visualized at two different scales. At the Lake Scale, a comprehensive identification method for polder unit types and polder landscape regions was established, achieving a stepwise transition from polder areas to polder clusters and ultimately to individual polder units. At the Local Scale, an integrative analysis of landscape character diversity (LCD) and land construction suitability (LCS) was employed to establish five landscape management zones for polder landscapes, thereby realizing a balance between the conservation of polder landscape diversity with the sustainable development of wetland environments. This study contributes a set of cross-scale ideas and methods for identifying landscape characters and delineating management zones in polder landscapes, which could be expanded to other lowland agricultural landscapes.

Health Risk of Heavy Metals in Drinking Water Sources of Water-Carrying Lakes Affected by Retreating Polder: A Case Study of Luoma Lake

Heavy metal pollution is a critical issue affecting the safety of drinking water sources. However, the impact of human activities on heavy metal risk levels in water-carrying lakes remains unclear. This study aims to explore the risk mechanisms of heavy metals in Luoma Lake, an important water-carrying lake for the South-to-North Water Diversion Project. We explored the spatial and temporal differences in the distribution of heavy metals in Lake Luoma using methods such as the heavy metal pollution index (HPI) and assessed the risk variations using a health assessment model. The results indicated that heavy metal concentrations in water-carrying lakes generally decreased during the dry season, with Mn and Zn levels decreasing by 89.3% and 56.2%, respectively. The comprehensive score of HPI decreased by 13.16% following the retreating polder compared to the control area (Non-retreating polder area). Furthermore, the HPI at the drinking water intake was lower, which is closely associated with the elevated dissolved oxygen (DO) and oxidation–reduction potential (ORP) resulting from water diversion. The annual average health risk across the entire lake was not significant, with higher levels observed in the control area. The annual non-carcinogenic risk levels of Mn, Ni, Cu, Zn, and Pb range from 10−13 to 10−9, which are considered negligible risk levels. Notably, the carcinogenic risk posed by arsenic (As) through the drinking pathway reached 10−5 a−1, exceeding the maximum levels recommended by certain organizations. These findings provide a critical foundation for managing heavy metals in water-carrying drinking water sources.

Flood Modeling in a Composite System Consisting of River Channels, Flood Storage Areas, Floodplain Areas, Polder Areas, and Flood-Control-Protected Areas

The Linhuaigang flood control project (LFCP), situated on the Huaihe River, China, uses the river channels upstream of the LFCP, together with the hinterland areas outside the channels, to retain and store fluvial floodwaters that exceed the downstream channel’s discharge capacity. The hinterland areas are split into seven flood storage areas, three floodplain areas, eight polder areas, and three flood-control-protected areas, and they are connected to the river in various ways. A coupled hydrodynamic model was established to simulate the hydrodynamic and water volume exchange between the river channels and the hinterland areas. The flood storage area, under the control of a flood diversion sluice, was simulated with a 2D hydrodynamic model, and the inflow process initiated by the flood diversion sluice was simulated as a control structure. The polder area was generalized as a reservoir that would be filled in several hours once put into use because of its small size. The uncontrolled inflow process between the flood-control-protected areas and the channel was simulated by means of a dam break model, which could simulate levee breaching. The flooding within the flood-control-protected area, which represents a vast space, was simulated with a 2D hydrodynamic model. The floodplain area was laterally connected to the river channel along the river levee. The difference between the simulated and the measured flood peak water stage did not exceed 0.2 m in 2003 and 2007, indicating that the accuracy of the model was relatively high. In the scenario of a design flood with a return period of 100 years, the flood storage areas and the LFCP were used in the following order: Mengwa, Qiujiahu, Nanrunduan, Shouxihu, Jiangtanghu, Chengxihu, Chengdonghu, and the LFCP. When the Huaihe River encounters a flood with a return period of 1000 years that exceeds the design standard, the highest water stage upstream of the LFCP and Zhengyangguan shall not exceed 29.30 m and 27.96 m after the use of all the flood storage areas, floodplain areas, and flood-control-protected areas. The results of this research can provide technical support for the flood risk management of the LFCP.

Cash crop farmers’ perceptions of, and adaptation to climate change: A preliminary study of Black Bush Polder, Guyana

Farmers Black Bush Polder, Guyana, have been experiencing changes in weather variability and climate parameters as well as the impacts of those changes on their livelihoods. Understanding farmers’ perception of climate change and their adaptation strategies is crucial to assisting with efforts for developing suitable intervention strategies to combat the effects of climate variability and climate change. In this non-experimental research engaging fifty (50) randomly selected farmers the aim was to: (1) examine how cash crop farmers in Black Bush Polder perceived the effects of climate change; (2) identify adaptation strategies used by farmers in combating the effects of climate change; (3) identify the factors that influence the adaptation strategies chosen by farmers; (4) identify perceived barriers in the implementation of adaptation measures; and (5) make recommendations in light of the difficulties encountered by farmers. A self-administered structured questionnaire survey was used to collect primary data and the responses to the items using a modified Likert scale. Descriptive statistics, and Pearson Correlation Coefficient were used to analyze the data. The results showed that there was variation in both temperature and rainfall in the Black Bush Polder Area. Overall, farmers had a general perception that these variations had an impact on their farming activities as well as on their choice of adaptation measures. Key recommendations made were: planting improved, or more resistant varieties of crops, changing planting times as dictated by rainfall, collection of water in furrows near plants, utilizing drip irrigation systems and techniques for preparing crop beds, and using of shade houses and greenhouses to lessen the effects of climate change.

Investigating Flood Characteristics and Mitigation Measures in Plain-Type River-Connected Lakes: A Case Study of Poyang Lake

The flow of plain-type river-connected lakes is affected by both upstream and downstream rivers, and the hydrological conditions are very complex. Poyang Lake, situated in Jiangxi Province, is the largest river-connected lake in the Yangtze River Basin. Its unique geographical features and complex hydrological conditions have made it a heavy disaster area and a frequent area of floods since ancient times. As typical mitigation measures of Poyang Lake, semi-restoration polder areas and flood storage and detention areas play a crucial role in the flood control of Poyang Lake. Taking Poyang Lake as an example, this article studies the flood characteristics of Poyang Lake based on the measured hydrological data. Furthermore, by using the weir (gate) outflow formula to construct the hydraulic model of semi-restoration polder areas and DHI MIKE to construct the hydrodynamic model of Kangshan flood storage and detention area, the flood diversion capacity of the two, and the flood diversion effect under the super-historical flood in 2020 are analyzed. The results show that compared with the non-use of mitigation measures, the maximum cumulative reduction in Xingzi water level can be reduced by 0.68 m and 0.48 m when semi-restoration polder areas and Kangshan flood storage and detention areas are used alone. Finally, the article puts forward some thoughts and suggestions on the flood control of Poyang Lake. The research results can offer some reference to the flood risk management of plain-type river-connected lakes.

Evaluating the Benefits of Flood Warnings in the Management of an Urban Flood-Prone Polder Area

Polders are low-lying areas located in deltas, surrounded by embankments to prevent flooding (river or tidal floods). They rely on pumping systems to remove water from the inner rivers (artificial rivers inside the polder area) to the outer rivers, especially during storms. Urbanized polders are especially vulnerable to pluvial flooding if the drainage, storage, and pumping capacity of the polder is inadequate. In this paper, a Monte Carlo (MC) framework is proposed to evaluate the benefits of rainfall threshold-based flood warnings when mitigating pluvial flooding in an urban flood-prone polder area based on 24 h forecasts. The framework computes metrics that give the potential waterlogging duration, maximum inundated area, and pump operation costs by considering the full range of potential storms. The benefits of flood warnings are evaluated by comparing the values of these metrics across different scenarios: the no-warning, perfect, deterministic, and probabilistic forecast scenarios. Probabilistic forecasts are represented using the concept of “predictive uncertainty” (PU). A polder area located in Nanjing was chosen for the case study. The results show a trade-off between the metrics that represent the waterlogging and the pumping costs, and that probabilistic forecasts of rainfall can considerably enhance these metrics. The results can be used to design a rainfall threshold-based flood early warning system (FEWS) for a polder area and/or evaluate its benefits.

Pendampingan Budidaya Sayuran Lokal Khas Rawa di Pekarangan dalam Upaya Peningkatan Keberagaman Konsumsi Pangan Masyarakat di Polder Alabio

The supply of nutritious food through a variety of food consumption is very important in reducing stunting prevalence. Some areas of Hulu Sungai Utara (HSU) Regency are the alabio polder area with high cases of stunting children and unproductive swamp land conditions when flooded with rainwater. This service activity provides a solution in utilizing home yards as a place to cultivate local swamp vegetables that have high nutrition, namely water spinach and water mimosa. The activities carried out include planning, which is done by direct observation and coordination with related stakeholders, then educating about the importance of consuming nutritious vegetables. Training and mentoring were given to 25 residents, the majority of whom were farming mothers. Evaluation was carried out by giving a questionnaire to participants regarding the sustainability of the activity. This activity was able to increase the knowledge and skills of the community in cultivating plants in the yard. The application of semi-hydroponic cultivation techniques of typical swamp vegetables has helped the community in providing vegetables when swamp rice fields are flooded in the rainy season and cannot be planted. Evaluation results showed that 88% of participants were enthusiastic about implementing the training in their daily lives because it suited their needs.

Growth and production of superior rice varieties in freshwater swampland at the Alabio Polder, Hulu Sungai Utara

The freshwater swampland is one alternative as a source of food production in Indonesia because it is quite fertile and vast about 25.20 million ha. Several limitations of this area includes unpredictable water regime, floods in the rainy season, and drought in the dry season. The objective of this study is to evaluate new high yielding varieties and planting system in the freshwater swampland. The experiments were carried out in the freshwater swampland of the Alabio polder area, Teluk Cati Village, Hulu Sungai Utara Regency covering an area of 5 ha, in the dry season in 2013 and 2014. In 2013 there were two kinds of treatment: planting system (2:1 and 4:1) and varieties (Ciherang, Inpari-1, Inpari-17, and Inpari-19). In 2014, the treatment were varities (Ciherang, Inpari-1, Inpari-17 and Inpari-30) and planted by jajar legowo planting 4:1. The treatments were implemented by randomized block design with 10 replication. This study indicates that high-yielding varieties can increase rice productivity and farmer income. Rice productivity in the two growing seasons ranges from 4.46 to 7.12 t ha−1 dry grain. The study concluded that at freshwater swampland, jajar legowo (2:1 and 4:1) was not significantly different. The new superior varieties of rice like Inpari-1, Inpari-17 dan Inpari-30 can increase the productivity and income of farmers at Teluk Cati Village. In 2013 n 2014, the yield of inpari varieties (1, 17, 19, 30) were higher than ciherang, average yield 5,91 t/ha. Rice farming on freshwater swampland is profitable (RC−1 3.09 and 2.78) and feasible (BC−1 2.09 and 1.78).

Pemodelan Rain-On-Grid Untuk Kasus Banjir pada Polder Pluit, Jakarta

Jakarta flood occurs almost every year, one of the reasons is the rapid development of its urban areas. Generally, Jakarta is categorized as a flat area, of which some locations are lower than the mean sea level, for example Pluit Polder area, thus being prone to flood. In this study, the rain-on-grid modeling with HEC-RAS software is carried out to determine the parts of the Pluit Polder that are still inundated so that better mitigation strategies can be achieved. The modeling results show that there are still inundated areas around the Pluit Polder ranging from 0.25 m to 2.75 m.

Temporal Variations in Chemical Proprieties of Waterbodies within Coastal Polders: Forecast Modeling for Optimizing Water Management Decisions

In polder-type land, water dynamics are heavily influenced by the artificial maintenance of water levels. Polders are low-lying areas of land that have been reclaimed from the sea or from freshwater bodies and are protected from flooding by dikes or other types of flood-protection structures. The water regime in polders is typically managed using a system of canals, pumps, and sluices to control the flow of water in and out of the area. In this study, the temporal changes in water salinity in the polder-type agricultural floodplain within the Neretva River Delta (NRD), Croatia, were analyzed by applying multivariate statistics and forecast modelling. The main aim of the study was to test the model that can be used in practice to forecast, primarily, water suitability for irrigation in a coastal low-lying agricultural catchment. The specific aim of this study was to use hydrochemistry data series to explain processes in water salinity dynamics and to test the model which may provide accurate salinity prediction, or finally select the conditions in which the model can be applied. We considered the accuracy of the model, and it was validated using independent data sets. To describe different patterns of chemical changes in different water classes due to their complex hydrological connectivity, multivariate statistics (PCA) were coupled with time-series analysis and Vector Autoregression (VAR) model forecasting. The multivariate statistics applied here did not indicate a clear connection between water salinity of the surface-water bodies and groundwater. The lack of correlation lies in the complex hydrological dynamics and interconnectivity of the water bodies highly affected by the artificial maintenance of the groundwater level within the polder area, as well as interventions in the temporal release of freshwater into the drainage canal network. Not all individual water classes contributed equally to the dominant patterns of ionic species identified by PCA. Apparently, land use and agricultural management practices in the different polders lead to uneven water chemistry and the predominant contributions of specific ions, especially nutrients. After applying the Granger causality test to reveal the causal information and explain hidden relationships among the variables, only two surface-water and two groundwater monitoring locations displayed a strong causal relationship between water electrical conductivity (ECw) as an effect and sea level as a possible cause. The developed models can be used to evaluate and emphasize the unique characteristics and phenomena of low-lying land and to communicate their importance and influence to management authorities and agricultural producers in managing and planning irrigation management in the wider Mediterranean area.

Reconstruction of Recharge and Discharge Pattern in the Polder Drainage Canal Network

Rainfed agriculture is dependent on rainfall and runoff patterns, especially in lowland areas that rely on pumping operation to remove excess water from the drainage network. Polder areas are extremely vulnerable to saltwater intrusion and subsequent soil salinization driven by rising sea levels and accelerated by climate change. The aim of this paper is to reconstruct the recharge and discharge pattern in the Vidrice polder, a drainage canal network within the Neretva River Delta agroecosystem used to collect the surface and subsurface runoff from the agricultural land and saltwater infiltration through the aquifer. Water regime data are collected over an 18-month period of real-time monitoring at 15 min intervals on three stations along the primary drainage canal and one station at the secondary canal. Analysis of water level flashiness in the Vidrice polder using the Richards-Baker flashiness index (R-Bindex) indicates that daily pumping of water infiltrated in the canal network is sub-optimal: discharge fluctuates significantly more than recharge, by 46% on average, resulting in unnecessary lowering of the water level in the drainage network. The results show that the correlation between the intensive rainfall events (>10 mm/day) and the recharge rates can be used to modify the daily pumping operation and maintain high freshwater levels in the canal network to increase the resistance to infiltration and reduce saltwater intrusion into the polder.

Dune Erosion at the German Baltic Coast—Investigation and Analysis of a Large-Scale Field Experiment Compared to Life Dunes

A large part of the Baltic Sea coastline in the north-eastern provinces of Germany (Mecklenburg-Vorpommern and Schleswig-Holstein) is protected by coastal protection dunes, which are constructed and maintained to preserve a quasi-natural beach environment. The latest IPCC report predicts a significant sea level rise even in the Baltic, together with an increase in storm surges within the next decades. Sand dune constructions are particularly affected by these developments, in close connection to the increasing problems of sediment mining for beach nourishment and dune maintenance. In the BMBF research project PADO (Processes and Implications of Dune Breaching at the German Baltic Sea Coast), scientists from Rostock University and RWTH Aachen University investigated together with various partners how constructed sand dunes would fail during a storm surge, focusing on the erosion and the initiation and development of a breach. Therefore, a large-scale field experiment was installed at the beach of Rostock-Warnemünde, which was instrumented and surveyed in high resolution during the storm surge in November 2018, leading to the collapse of the dune, using innovative measurement systems, including terrestrial laser scanning and photogrammetry. The measurements were used to run a numerical model (XBeach) to simulate dune breaching for three different sections of existing sand dunes at the coast of Mecklenburg-Vorpommern. Additional investigations were made to analyse the filling and emptying of the polder areas behind the coastal protection dunes and the consequences of the floods with respect to saltwater intrusion. In this paper, the field experiment and the results from measurements and simulations are compared to one of the real reference dunes, and the transfer of results to a dune breach incident near Rostock in 2019 is discussed.

The Water Budget Myth and Its Recharge Controversy: Linear vs. Nonlinear Models.

The water budget myth, which is the idea that safe pumping must not exceed the initial recharge, gave rise to a controversy about the role of recharge in assessing the sustainability of groundwater development. To refute the concept of safe yield, a simplified water budget equation is used, which equals the total pumping rate to the sum of capture and storage change. Since initial recharge and discharge are canceled out from this equation, it is concluded that sustainable pumping has nothing to do with recharge. Investigating the assumptions underlying this equation, it is seen that it expresses the superposition principle, which implicitly assumes the groundwater reservoir can be depleted indefinitely and boundary conditions are an infinite source of water. To evaluate sustainability, however, the limits of the aquifer system must be examined accurately. Theoretically, this can only be accomplished applying nonlinear models, in which case setting up the simplified water budget equation is impossible without knowing the initial conditions. Hence, excluding recharge when assessing sustainable pumping may not be done inconsiderately, which is illustrated by two examples. An analytical solution, developed by Ernst in 1971 to simulate flow to a well in a polder area with a nonlinear function for drainage, even shows that it is not necessarily a misconception to assume the cone of depression stops expanding when the pumping rate is balanced by the infiltration rate.

Mapping water table depths in wetlands and polder areas by probability sampling

• The map can serve as a benchmark in model validation. • The map provides input for risk analyses. • Only verified model assumptions were used. • Accuracy and resolution fit to use in regional water management. Information on water table depth (WTD) in polder areas and wetlands is important in, for example, estimating emissions of greenhouse gases, assessing the agricultural and ecological potential, and flood risk management. The seasonal variation of WTDs is summarized with averages of the yearly highest (shallowest) and lowest (deepest) water tables (MHW and MLW). These characteristics show short-distance variations within the fields in polder areas, which cannot be mapped using geostatistical interpolation techniques or physical modelling against reasonable costs or with acceptable accuracy. The within-field variations depend on soil type and water management. MHW and MLW were determined from auger hole measurements of WTDs at locations being selected following stratified simple random sampling in subareas classified by soil type and water management. Within these subareas, a further classification was made on the basis of distance to ditches. For each subarea spatial distribution functions of MHW and MLW were made, taking censored observations into account. Uncertainty was quantified by 10,000 bootstrap realisations of the spatial distribution functions. From these realisations maps depicting summary statistics for the spatial distribution of WTD-characteristics within the subareas were derived, as well as a map with probabilities of exceedance of a critical level that can serve as input for risk analysis.

Glass eel (Anguilla anguilla L. 1758) feeding behaviour during upstream migration in an artificial waterway

The transition from marine to fresh water is a challenging task for juvenile eels. This critical step in the early eels' life is preceded by a metamorphosis from the oceanic larval to the continental glass eel stage, requiring major energy-demanding morphological, physiological and behavioural modifications during which time these animals do not feed. The success of the glass eels' inland migration after metamorphosis will largely depend on remaining energy levels, which can be supplemented only by resuming food uptake. Although it is crucial for their survival and the maintenance of the population, the feeding behaviour of glass eels is still an understudied aspect of the eels' complex life cycle. Many uncertainties about the phenology, diet, potential prey preferences and their relation with migration modus (migratory vs. sedentary) still remain. In this study, the authors analysed the stomach and gut contents of 458 European glass eels (Anguilla anguilla L. 1758) captured in a drainage canal connecting a small mesotidal estuary with an adjacent polder area during the spring migration seasons of 2016 and 2017. They demonstrated that although glass eels started feeding briefly upon arrival in the estuary, food uptake for early arrivals was restricted to a minority that sparsely feed on detritus and some worm-like benthic invertebrates. Along the season, food uptake intensified eventually engaging all glass eels and their dietary palette diversified including a wide array of planktonic and benthic organisms. Crustacean plankton (mainly cyclopoid copepods) was an important part of the glass eel diet, whereas benthic oligochaetes were less abundant as food source in spite of their high presence in the sediments. No clear differences in feeding behaviour could be observed between migratory and sedentary glass eels. This study showed that glass eels can use highly artificial and dynamic drainage canals as feeding ground during their critical marine/freshwater transition. This outcome is also a plea to improve the accessibility of alternative (unnatural) migration routes between the ocean and suitable freshwater growth habitats for the European eel.

Optimizing aeration pattern to improve nitrogen treatment performance of ditch wetlands in polder areas around Chaohu Lake, China

Ditch wetlands in polders are planned to attenuate the nitrogen load from paddy fields, mainly resulting in eutrophication of Chaohu Lake, China. The nitrogen treatment performance of ditch wetlands is poor because of the low dissolved oxygen (DO) concentration observed in field. Aeration is often used to improve both DO concentration and nitrogen treatment performance, but aeration pattern needs to be optimized for better treatment performance. A dynamic model was constructed to explore the nitrogen transformation with the DO effect. The simulation results show that through an optimal aeration pattern, the treatment performance of total nitrogen (TN) increased from 3.9% to 23.9% when TN was dominated by ammonium and organic nitrogen (NH4 + ON). The optimal aeration pattern was that the ratio of aeration time to non-aeration time was approximately 1:1, and the aeration cycle period was equal to the experimental period (10 d). The essence of aeration is to ensure that the mass of nitrogen nitrified from NH4 is denitrified, which means that the rate of nitrification is close to that of denitrification. The concentration ratio of (NH4 + ON)/NO3 was a reasonable indicator to determine the aeration time for various composition of TN. Finally, guidelines for drainage water recycling within polders from the point of DO are provided to achieve the objective of nitrogen load reduction in polders.

Climate risk perceptions and perceived yield loss increases agricultural technology adoption in the polder areas of Bangladesh

The effects of climate change are likely to increase the frequency of flood, drought, and salinity events in the coastal areas of Bangladesh, posing many challenges for agrarian communities. Sustainable intensification in the form of improved agricultural management practices and new technologies may help farmers cope with stress and adapt to changing conditions. In this study, we explore how climate change perceptions of agricultural risk affect adaptation to climate change through technology adoption in a unique landscape: the polders of Bangladesh. In 2016, a survey was conducted in 1003 households living on these artificial, leveed islands facing the Bay of Bengal. We analyzed the responses from polder residents to construct a climate risk index which quantifies climate risk perception in this highly vulnerable agrarian landscape. We analyzed how polder demographics influence their perceptions about climatic change using seemingly unrelated regression (SUR). Further, by using three bivariate probit regression models, we estimated how the perception of climate risk drives the differential adoption of new agricultural technologies. Our findings show that farmers perceive polder agriculture as highly vulnerable to four environmental change factors: flooding, drought, salinity, and pest infestation. The SUR model suggests that farmer demographics, community group memberships, and access to different inputs and services strongly influence climatic risk perceptions. Findings also suggest that polder farmers with higher risk perceptions have a higher propensity to adopt both chemical and mechanical adaptation strategies. Cost, however, limits the ability of farmers to adopt improved technologies, suggesting an opportunity for institution-led approaches.

Data fusion of geotechnical and geophysical data for three-dimensional subsoil schematisations

Subsoil schematisations are a paramount activity for the execution of infrastructure earthworks. Currently, subsoil schematisations are laborious, and mostly based on correlation and interpolation of available geotechnical and geophysical in-situ data. Geotechnical in-situ testing tends to be accurate but merely provides local information, while geophysical investigations are often performed to image the subsurface, and provide valuable insight for areas. Yet, there is not always a clear way to reflect geophysical properties to soil schematisation. This paper presents a data fusion methodology to perform subsoil schematisation and parametrisation. This methodology makes use of available geotechnical, geological and geophysical data sets, and combines them by means of machine learning algorithms (Neural Networks and Random Forest). The data fusion method is applied on two case studies. The first case study concerns a large area of a flood defence line, and the second case study concerns a small polder area next to a dike. The accuracy of the data fusion algorithm is assessed by comparing its results against a validation data set, that has not been exposed to the data fusion algorithm. The performance of the two algorithms and of the parameters that govern each algorithm is discussed. The results show that both Neural Networks and Random Forest are suitable to perform subsoil schematisations. The analyses show that the Random Forest leads to a lower error on the validation data set. However, Random Forest fails to predict the occurrence of thin clay layers in the second case study, while Neural Networks are successful at it. The data fusion methodology shows the potential to enhance the subsoil schematisation procedure, by increasing the schematisation spatial resolution.

Pollution and Release Characteristics of Nitrogen, Phosphorus and Organic Carbon in Pond Sediments in a Typical Polder Area of the Lake Taihu Basin

There is currently a lack of knowledge on the release characteristics of nutrients from artificial pond sediments in polder areas, resulting in problems in future management of such environments, including converting polders to lakes. In this study, sediment samples were taken from a fish pond and a lotus pond in a typical polder area of the Lake Taihu Basin in China. The total nitrogen (TN, 1760–1810 mg/kg), total phosphorus (TP, 1370–1463 mg/kg) and total organic carbon (TOC, 10.1–21.2 g/kg) contents were significantly higher than those found in sediments from the adjacent aquatic system, which indicates that the legacy of agricultural activities has had an obvious cumulative effect on pond sediment nutrients. The release behavior of TN, TP and TOC varied significantly, not only under disturbed and static conditions, but also from sediments sampled at different ponds and depths. During the disturbing condition, there were continuous releases of carbon and nutrients in the lotus pond sediments, while the fish pond sediments showed a higher release at the beginning. Under static release conditions, the release of TP in the surface and bottom sediments of the fish pond increased first, then decreased and stabilized within 24 h, while the release of the lotus pond showed a slow upward trend. Despite the lower concentration of nutrients and TOC, the lotus pond sediment showed a higher release rate. The results suggested that it is necessary to adopt different strategies for different types of ponds in the project of returning polders to lakes; it is especially important to pay attention to the release of nutrients from the bottom sediments of lotus ponds in the project management.

Mapping Water Table Depths in Wetlands and Polder Areas by Probability Sampling

Mapping Water Table Depths in Wetlands and Polder Areas by Probability Sampling