Canal Dredging Research Articles

Tình hình đào, vét kênh rạch ở tây nam kỳ thời thuộc pháp (1867-1945)

Vietnamese society during the French colonial period (1867 - 1945) was marked by the French colonization of three provinces in the western region of Cochinchina, turning this land in particular and Cochinchina in general into a colony of France. At that time, Southwest Vietnam still had many deserted areas, interlaced rivers and canals, which were not convenient for exploitation. However, the Southwest region will bring great benefits in terms of rice, seafood, etc. if it is invested. Therefore, the French colonialists boldly invested in irrigation and drainage in the Southwest region in various forms such as: dredging the old canals, digging a number of great canals, etc. to serve economic, political and military purposes for France. Therefore, the irrigation and canal system in the Southwest region had many changes during this period. Residents’ mobility became easier, the trade between regions becomes favorable, that has contributed to the economic and social transformation of the Southwest region. However, within the scope of this article, we mainly refer to the digging and dredging of canals in the southwestern region of the French colonial period; thereby drawing some comments on the characteristics of the canal system in the Southwest of Vietnam during this period.

EDTA Combined with C-Pilot Files and Microultrasound for Root Canal Calcification: Dredging Effect and Safety Analysis.

Objective This paper discussed the dredging effect and safety of ethylenediaminetetraacetic acid (EDTA) combined with C-pilot files and microultrasound (mUS) on root canal calcification. Methods From October 2021 to January 2022, 132 patients with calcified root canals treated in our hospital were selected as the research subjects. Among them, 64 cases who received EDTA combined with C-pilot Files and mUS plus ultrasonic instruments to dredge calcified root canals were regarded as the research group (RG), and another 68 cases given ultrasonic instruments plus C-pilot files were regarded as the control group (CG). The root canal dredging time was recorded, and the dredging success rate and total success rate of different tooth positions and calcification sites were compared between groups. The clinical efficacy was assessed 6 months after treatment. Pain severity was evaluated by the Pain Intensity Numerical Rating Scale (PI-NRS) before (T0), during (T1), and after treatment (T2). Finally, the incidence of adverse reactions within one week after treatment was counted. Results RG was observed with statistically higher success rates of root canal dredging in different tooth positions and calcified sites than CG (P < 0.05). Besides, the total effective rate of treatment was 92.19% in RG, which was also higher compared with CG, while the root canal dredging time in RG was shorter than that in CG (P < 0.05). Increased NRS scores were found in both groups at T1, and the score in RG was significantly lower compared with that in CG. At T2, both groups showed a lower PI-NRS score than T1 but higher than T0, and the score at T2 was also lower in RG as compared to CG (P < 0.05). Moreover, the reduced incidence of adverse reactions were observed in RG compared with CG (P < 0.05). Conclusions EDTA combined with C-pilot files and mUS can effectively improve the dredging success rate of root canals obstructed by calcification, shorten the dredging time, and improve patient comfort, which is an effective method for clinical dredging of calcification obstructed root canals.

Limiting burrowing activity and overland dispersal of the invasive alien red swamp crayfish Procambarus clarkii by sophisticated design of watercourses

Invasive alien crayfish species pose major ecological and hydrological risks globally. The red swamp crayfish (Procambarus clarkii) is one of the most widespread crayfish species worldwide. Its impacts arise from burrowing activities and lead to mobilization of soil nutrients, water safety risks by instability of dikes and erosion of banks. Increased sediment load demands additional dredging of drainage ditches and canals to ensure their water discharge capacity. Sustainable methods for limiting burrowing in banks and dispersal behaviour of crayfish were not yet available. Therefore, a field study was performed to determine whether the number of burrows and overland movement of crayfish were related to a particular bank type. Burrows were counted in three watercourses during a water-level decline. The number of burrows was significantly lower in natural banks than in non-natural and semi-natural banks. The construction of natural-like banks along watercourses may significantly reduce sediment load, erosion and the collapse of banks by burrowing activities of crayfish. An inclination experiment mimicking various types of terrestrial dispersal barriers elucidated that steepness, soil type and vegetation structure of small embankments near watercourses were significant factors for manipulating overland movement of crayfish. Crayfish were taken out of the water for this purpose and placed on small experimental embankments varying in slope and types of vegetation. The lowest frequencies of upward movement were recorded at inclinations of 20° and 30° on bare sandy soil and short and species-poor grassland substrates. This implies that crayfish crawling out of the water will return to the watercourse when encountering such a dispersal barrier. Therefore, a sophisticated design of embankments along watercourses can be a tool to reduce colonization risk of nearby located, hydrologically isolated water bodies with high nature values.

Impact of Flash Floods On Agri-based Livelihoods In Sylhet Haor Basin

Bangladesh is most vulnerable to natural disasters and climate change. Over the past few decades, flash floods have frequently affected the livelihood of people in the Sylhet Haor Basin. This study highlights the causes of increased flash floods, their impact on farming practices and livelihoods, and possible solutions to flash flood risk in the Sylhet Haor Basin. Data were collected using a pre-tested structured questionnaire from randomly selected 298 Haor farmers in high and moderately vulnerable flash flood zones across the Haor region during November 2021 and April 2022. In moderately vulnerable areas, the lack of rivers and canal dredging was the main factor contributing to flash flood deterioration. Index scores and ranks revealed that flash floods most severely affect the primary production sector (agriculture) and threaten the lives and livelihoods of the local populace in high- and moderately flood-prone areas. After the severe flash flood, farmers were forced to turn to other occupations instead of agriculture for their livelihood. To reduce the impact of flash floods on particular features or entire wetlands, most farmers preferred the construction of embankments over sandbags, concrete or stone dams, submergible embankments, and rubber dams. For flash flood risk management, farmers in high- and moderately flash flood-vulnerable areas emphasize the construction of higher dams and embankments and the installation of more flood barriers (dams/embankments). The concerned flash flood management agencies could incorporate the key findings of this study while formulating risk mitigation strategies for the Sylhet Haor Basin. Ann. Bangladesh Agric. (2022) 26 (1) : 61-73

Sentinel-2 Reveals Abrupt Increment of Total Suspended Matter While Ever Given Ship Blocked the Suez Canal

The blockage of the Suez Canal, one of the world’s key trade routes, by a giant container ship in March 2021 was in the spotlight of news media worldwide, mainly because of its economic impacts. In this study, we look at this event from an environmental perspective by analyzing the impact of the artificial barrier made by the ship over the channel and of operations like dredging on the concentration of total suspended matter (TSM). In this context, multitemporal Sentinel-2 images are used to study short-term variations of TSM within a time window spanning before, during, and after the blockage event. A well-established neural network-based processor called Case 2 Regional CoastColour (C2RCC) is employed to derive remote sensing reflectance (Rrs) and then TSM concentrations from Sentinel-2 imagery. The results indicate that the stuck ship acted as an artificial barrier leading to very different TSM conditions north and south of the canal. Furthermore, the blockage of the Suez Canal and subsequent dredging caused an abrupt increment (+400%) in the concentration of TSM moving north from the ship’s location. We also identified a very high contrast between the TSM concentration in the north and south of the vessel during the blockage event.

Exploring Vietnamese cereal smallholders’ perceptions and adaptations to temperature and precipitation variability: implications for adaptation strategies

ABSTRACT In order to foster the adoption of temperature and precipitation variability (TPV) adapting practices by smallholders, it is essential to comprehend their views of TPV. However, few empirical studies have investigated how smallholders perceive TPV in Vietnam. This study investigates smallholders’ attitudes towards TPV and their adapting practices in South Central Vietnam. A random sampling strategy was used to select 250 cereal smallholders for interviews and a structured questionnaire was developed to collect data. Descriptive and bivariate analyses were used. The study results show that smallholders had experienced TPV. They perceived that TPV have increased farming losses, labour costs in cereal fields, the costs of pest/weed control, the costs of water management, and the application rate of chemical inputs. The smallholders were adopting traditional adapting methods to reduce unexpected impacts of TPV on their cereal-based farming systems. Key adapting methods identified include: (1) dredging and restoration of irrigation canals; (2) planting of drought resistant cereal varieties; (3) usage of wells and water pumps for irrigation; and (4) early planting. A statistically significant relationship, existing between the cereal smallholders’ perceptions of TPV and their education level (Pearson = 0.152, p = 0.016), income (Pearson = 0.108, p = 0.088), farm size (Pearson = 0.196; p = 0.002), gender (Eta = 0.184, p = 0.004), agricultural practices (Eta = 0.246, p = 0.000), information and communication technology own (Eta = 0.151, p = 0.017), training participation (Eta = 0.235, p = 0.000), and community-based organisation participation (Eta = 0.147, p = 0.020).

Life Cycle of Oil and Gas Fields in the Mississippi River Delta: A Review

Oil and gas (O&amp;G) activity has been pervasive in the Mississippi River Delta (MRD). Here we review the life cycle of O&amp;G fields in the MRD focusing on the production history and resulting environmental impacts and show how cumulative impacts affect coastal ecosystems. Individual fields can last 40–60 years and most wells are in the final stages of production. Production increased rapidly reaching a peak around 1970 and then declined. Produced water lagged O&amp;G and was generally higher during declining O&amp;G production, making up about 70% of total liquids. Much of the wetland loss in the delta is associated with O&amp;G activities. These have contributed in three major ways to wetland loss including alteration of surface hydrology, induced subsidence due to fluids removal and fault activation, and toxic stress due to spilled oil and produced water. Changes in surface hydrology are related to canal dredging and spoil placement. As canal density increases, the density of natural channels decreases. Interconnected canal networks often lead to saltwater intrusion. Spoil banks block natural overland flow affecting exchange of water, sediments, chemicals, and organisms. Lower wetland productivity and reduced sediment input leads to enhanced surficial subsidence. Spoil banks are not permanent but subside and compact over time and many spoil banks no longer have subaerial expression. Fluid withdrawal from O&amp;G formations leads to induced subsidence and fault activation. Formation pore pressure decreases, which lowers the lateral confining stress acting in the formation due to poroelastic coupling between pore pressure and stress. This promotes normal faulting in an extensional geological environment like the MRD, which causes surface subsidence in the vicinity of the faults. Induced reservoir compaction results in a reduction of reservoir thickness. Induced subsidence occurs in two phases especially when production rate is high. The first phase is compaction of the reservoir itself while the second phase is caused by a slow drainage of pore pressure in bounding shales that induces time-delayed subsidence associated with shale compaction. This second phase can continue for decades, even after most O&amp;G has been produced, resulting in subsidence over much of an oil field that can be greater than surface subsidence due to altered hydrology. Produced water is water brought to the surface during O&amp;G extraction and an estimated 2 million barrels per day were discharged into Louisiana coastal wetlands and waters from nearly 700 sites. This water is a mixture of either liquid or gaseous hydrocarbons, high salinity (up to 300 ppt) water, dissolved and suspended solids such as sand or silt, and injected fluids and additives associated with exploration and production activities and it is toxic to many estuarine organisms including vegetation and fauna. Spilled oil has lethal and sub-lethal effects on a wide range of estuarine organisms. The cumulative effect of alterations in surface hydrology, induced subsidence, and toxins interact such that overall impacts are enhanced. Restoration of coastal wetlands degraded by O&amp;G activities should be informed by these impacts.

Breeding Ecology of the Endangered Black-Bellied Tern (Sterna acuticauda) in Eastern India and Implications for Conservation

The global population of Black-bellied Tern (Sterna acuticauda) is declining, and insufficient information is available on its breeding ecology. The aim of this study was to record its breeding ecology and factors affecting breeding success along the Mahanadi River in Odisha, eastern India. Breeding was observed during January-April 2018, with peak activity in March. Among 24 nests recorded on seven sandy islands, only 11 nests successfully produced chicks. Factors affecting survival of nests were flooding due to anthropogenic changes in water levels (54%), predation (31%), and trampling (15%). Dredging of canals that use water from the river is recommended to reduce fluctuations in water levels. Targeted long-term studies along the entire length of the Mahanadi River and other large rivers can aid in identifying other breeding sites and ongoing threats to this rare and endangered species. Outreach in communities near breeding sites and recruiting of local residents as nest guardians can also help in protection of nesting sites.

Calcium chloride washing of calcareous sediment from a freshwater canal: effect on the removal of potentially toxic elements and water aggregate stability

Canal dredging and shaping produce considerable amounts of sediments whose reuse on- and off-site depends on their pollution level. This study explores the potential of a calcium chloride washing to remove potentially toxic elements (PTEs) from a freshly dredged calcareous sediment and to affect the aggregate stability of the washed sediment. The ability of 0.5-M CaCl2 washing to restore the sediment samples polluted with Cu and Zn dredged from a freshwater canal was assessed. The distribution of the two metals among the sediment geochemical phases, the potential availability to plants (DTPA), and the water aggregate stability of particles were evaluated on the washed samples and compared to control. In the most polluted sample (~200 and 500 mg kg−1 of Cu and Zn, respectively), the washing decreased the amount of Cu by 26%, mainly in the sulfide/organic fraction, and of Zn by 10%, mainly in carbonates. A decrease in the dispersivity of clay fraction was observed due to the well-known effect of Ca2+ ions on flocculation of colloidal clay particles. At large scale, the aggregates formed by the interaction between large particles and flocculated clay showed lower water stability with respect to the control, thus suggesting the need to improve the physical properties of the treated material. Noteworthy, after 1 year of dry storage from washing, the average percentage of potentially bioavailable (DTPA) Cu and Zn (23 and 13% of pseudo-total amount, respectively) dropped with respect to the control (40 and 19%) and a concomitant carbonate increase (+33%) was observed. The CaCl2 washing is a promising method to reduce Cu and, to a minor extent, Zn in wet calcareous sediments dredged from freshwater canals. However, there is still room for improvement. The PTE fractions remaining in carbonates and organic component of washed sediment clearly indicate the potential of combining mild acidic pH values with calcium chloride in the washing to enhance the PTE removal.

Survival under anthropogenic impact: the response of dragonflies (Odonata), beetles (Coleoptera) and caddisflies (Trichoptera) to environmental disturbances in a two-way industrial canal system (central Poland).

Ecological metrics and assemblages of three orders of aquatic insects (Odonata, Coleoptera and Trichoptera—OCT) in an industrial canal system affected by dredging were studied. Five sites (a river as a control site and canals) along the Vistula River in Central Poland were sampled during six sampling periods (2011 and 2013). Canonical correspondence analyses (CCA) was used to assess the influence of environmental variables on the distribution of 54 insect species in the following system of habitats—a river feeding the canals, river-fed inlet canals and outlet canals with cooling waters. Additionally, before and after control impact (BACI) was used to test for the impact of canal dredging in 2011 on the insect response metrics. Non-metric multidimensional scaling analysis differentiated insect assemblages of the three habitats and similarity percentage (SIMPER) indicated the species most responsible for the faunistic dissimilarities. Temperature was found to be a key factor governing the presence of insects in the outlet canals with cooling water. CCAs revealed that electrolytic conductivity (EC) and salinity had the greatest influence on the OCT fauna in the river and the inlet canals, whilst it was the dissolved oxygen and the level of development of aquatic plants that proved most important in the outlet canals. Modified ANOVAs showed that dredging significantly affected the mean species richness and the dominance in the canals. The changes in OCT species composition were highly informative. The comparison between tolerance patterns of the OCT orders against the five parameters (temperature, EC, total dissolved solids (TDS), pH and current) revealed that caddisflies are the most sensitive group, followed by Coleoptera while Odonata proved the most resistant. Dragonflies have the greatest potential to serve as bioindicators of industrially heated waters. The OCT fauna responded specifically to different environmental factors and stressors, it is strongly recommended to track the responses on different levels, not only metrics, but above all, species.

Long-term monitoring of the endemicRana latastei: suggestions for after-LIFE management

AbstractWe monitored egg clutch numbers of a population of the endemic Italian agile frogRana latasteiin a Site of Community Interest in northern Italy (SCI IT 209000) during 1997–2017 with the aim of assessing the long-term variation in its abundance. We walked along the banks of canals and small ponds (n = 22) 1–3 times per week between early February and mid-April each year to detect egg clutches. The relationships between the start of the breeding season, yearly egg mass counts, rate of yearly change in the number of recorded egg masses and 15 climatic and environmental variables were assessed by multiple regression. The first deposition of eggs occurred progressively later in the year throughout the study period and mean air temperature during the breeding season decreased over this period. Agile frogs showed high deposition site-fidelity. Despite large variations in the number of egg clutches detected from year to year, the population size remained stable in the long term. Peaks in the number of egg clutches occurred 2 years after the dredging of canals, carried out every 4–6 years to improve water availability, starting in 2004 as part of a LIFE Nature Project. This was the only predictor of the number of egg clutches deposited, suggesting that periodical management is needed to support the agile frog population. Our results reinforce the need for multi-year monitoring to determine both the long-term success of habitat restoration projects and the status of residual populations.

Propensity for erosion and deposition in a deltaic wetland complex: Implications for river management and coastal restoration

The Mississippi River Delta is one of the most rapidly changing area on Earth, with large areas experiencing land loss and smaller areas experiencing loss. While some of the drivers of these changes are well known (high rates of relative sea level rise, reduced sediment inputs, canal dredging), debate exists about other drivers. One area that has received substantial attention is the role of, “river diversions,” areas where sediments and water are diverted from the Mississippi River into degrading wetlands with the hope of reinitiating deltaic land building processes. Some authors have argued that diversions lead to reduced shear strengths of wetland soils that make them more vulnerable to storm driven erosion, while other authors have argued that sediments from river diversions will develop stable land. This study examined this controversy in the Cubits Gap Subdelta, an analogue for a large (>1420m3s−1) river diversion by testing the hypothesis that areas of land gain, and/or resilience to erosion occurred in areas that actively received river sediments and as a result had mineral rich soils with high shear strength. To accomplish this, a Normalized Difference Water Index (NDWI) was developed for Landsat-7 Enhanced Thematic Mapper (ETM+) and Landsat-8 Operational Land Imager (OLI) images. The NDWI was calculated from (Blue−SWIR)/(Blue+SWIR), where SWIR is the shorter wavelength, and yielded land/water boundary maps with 30m resolution. Results indicate that land gain occurred predominantly in the riverside section of this subdelta where sediments were imported from Mississippi River crevasses and/or dredging. Land loss typically occurred in the distal regions of the subdelta, which had lower levels of sediment supply and greater wave exposure. Sediment geotechnical analyses revealed land loss pixels generally correlated sediments with to high organic contents (9.0±1.9%), water contents (54.8±3.7%) and salinity (6.5±2.0PSU), with low shear strengths (5.7±0.8kNm−2) and low bulk density (0.6±0.8g cm−3), whereas land gain pixels generally correlate with low organic content (3.9±0.6%), water content (38.1±4.2%) high shear strength (10.9±4.1kNm−2) and bulk density (1.00±0.1gcm−3). This study suggests plans to restore the region by partially diverting the flow of the Mississippi River will be most successful if they carry high loads of sediment, and that concerns about the integrity of fresh marsh may be unwarranted if those marshes are sediment rich.

Physiological performance and growth of Viburnum tinus L. on phytoremediated sediments for plant nursing purpose

Sediments are fundamental resources for productive activities like plant nursing, which are also likely to be responsible of their loss. In contrast, other activities like the dredging of canals and waterways involve the extraction and continuous accumulation of sediments. Most dredged sediments are polluted, and need to be stocked and transported to landfills, with extremely high costs for transport and management. To address these problems, a low-cost remediation methodology was previously developed to decontaminate sediments which were tested for use in plant nursery field plantations located in Pistoia (Italy). The phytoremediated sediments were mixed in percentages of 33% and 50% with alluvial soil, which itself was used as control. We studied the characteristics of these mixtures, and the physiological response and growth of Viburnum tinus L. grown on each substrate, as well as its corresponding root ball. Substrates with sediments showed quick water infiltration and no waterlogging, in sharp contrast to what was observed in autumn in the control. Despite a rainy summer, V. tinus demonstrated a good acclimation to the different substrates, showing the lowest leaf water potentials in mixed substrates and no signs of stress. No differences in leaf carbon assimilation or transpiration were observed among substrates, while in late August plants grown on substrates with sediments showed a higher performance index for energy conservation from photons absorbed by PSII to the reduction of intersystem electron acceptors. In the 50% mixture, there was also an enhancement of electron transport from PSII to PSI. Moreover, no differences in growth and biomass were found. Plants in all substrates showed some thin-root mortality, likely due to the persistent rainfall, though a higher number of plants with dead roots was observed in control. Thanks to the dense and fibrous root apparatus of V. tinus, the mixture with 33% sediments produced satisfactory results even for the root ball, resulting in less deformation and a lower breakage percentage.

Performance of a pilot showcase of different wetland systems in an urban setting in Singapore.

The Alexandra Wetlands, part of PUB's Active, Beautiful, Clean Waters (ABC Waters) Programme, showcase a surface flow wetland, an aquatic pond and a sub-surface flow wetland on a 200 m deck built over an urban drainage canal. Water from the canal is pumped to a sedimentation basin, before flowing in parallel to the three wetlands. Water quality monitoring was carried out monthly from April 2011 to December 2012. The order of removal efficiency is sub-surface flow (81.3%) >aquatic pond (58.5%) >surface flow (50.7%) for total suspended solids (TSS); sub-surface (44.9%) >surface flow (31.9%) >aquatic pond (22.0%) for total nitrogen (TN); and surface flow (56.7%) >aquatic pond (39.8%) >sub-surface flow (5.4%) for total phosphorus (TP). All three wetlands achieved the Singapore stormwater treatment objectives (STO) for TP removal, but only the sub-surface flow wetland met the STO for TSS, and none met the STO for TN. Challenges in achieving satisfactory performance include inconsistent feed water quality, undesirable behaviour such as fishing, release of pets and feeding of animals in the wetlands, and canal dredging during part of the monitoring period. As a pilot showcase, the Alexandra Wetlands provide useful lessons for implementing multi-objective wetlands in an urban setting.

Land surface dynamics and environmental challenges of the Niger Delta, Africa: Remote sensing-based analyses spanning three decades (1986–2013)

The Niger Delta, the largest river delta on the African continent, is one of the most densely populated river deltas globally and hosts the world's third largest mangrove forest. It is a major biodiversity hot spot of our planet. At the same time the delta is home to Africa's largest oil reserves and responsible for a skyrocketing GDP development of Nigeria since the 1970s. Nigeria ranks 13th among all oil producing countries, but oil exploitation also brought with it severe environmental degradation, leading to the delta's nomination for a place on the top 10 list of the “World's Worst Polluted Places Report” in 2013. Despite the outstanding importance of the region for Nigeria, Africa, and the international community most studies published focus mainly on topics of geology, geochemistry, and environmental toxicology. Studies employing earth observation satellite data to assess Niger Delta dynamics are rare. This paper aims at contributing to an overview of Niger Delta geography and environmental threats and challenges, as well as to an understanding of Niger Delta land surface dynamics from 1986 to 2013. Covering the complete delta, we present results of land cover change analyses, results of an assessment of coastline dynamics, as well as the manifestation of oil exploitation activity as expressed via oil access canal dredging and gas flaring, monitored within the 27 year time span investigated.

Effective management for acidic pollution in the canal network of the Mekong Delta of Vietnam: A modeling approach

Acidic pollution can cause severe environmental consequences annually in coastal areas overlain with acid sulfate soils (ASS). A water quality model was used as an analytical tool for exploring the effects of water management options and other interventions on acidic pollution and salinity in Bac Lieu, a coastal province of the Mekong Delta. Fifty eight percent of the provincial area is covered by ASS, and more than three-fourths (approximately 175,000 ha) are used for brackish-water shrimp culture. Simulations of acid water propagation in the canal network indicate that the combination of opening the two main sluices along the East Sea of the study area at high tide for one day every week in May and June and widening the canals that connect these sluices to the West Sea allows for adequate saline water intake and minimizes the acidic pollution in the study area. On the other hand, canal dredging in the freshwater ASS area should be done properly as it can create severe acidic pollution.

Current Status of Sludge Collection, Transportation and Treatment in Ho Chi Minh City

In the process of construction and development, Ho Chi Minh City is discharging about six types of sludge: 1) sludge from urban wastewater drainage systems; 2) sludge from industrial wastewater drainage system; 3) sludge from the canal dredging activities periodically; 4) sludge from septic tanks; 5) sludge from the water treatment station/plant; 6) sludge from the construction sites. Sludge’s components are very different among types of sludge, sludge from the sewer network and canal dredging contain mainly sand and soil (70% - 90% dry weight), while the sludge from the wastewater/water treatment station/plant and from septic tanks contain mainly biodegradable organic substances (55% - 80% dry weight). The concentrations of all above-mentioned sludge (except sludge from the hazardous industrial wastewater treatment plant) are lower than toxic threshold. The volume of total sludge is about 3000 - 4000 m3/day (5000 - 6000 tons/day), excepting the amount of sludge generated from the water treatment plant (which is collected and treated separately). Sludge from wastewater treatment plants and septic tanks is collected, transported and recycled to become organic fertilizer. The other types of sludge are collected, transported, and disposed at the “unknown” locations, even though they have different values for use.

Tracing anthropogenically driven groundwater discharge into a coastal lagoon from southern Brazil

Summary We investigated the distribution of naturally occurring geochemical tracers ( 222 Rn, 223 Ra, 224 Ra, 226 Ra, CH 4 , δ 18 O, and δ 2 H) in the water column and adjacent groundwater of Mangueira Lagoon as proxies of groundwater discharge. Mangueira Lagoon is a large (90 km long), shallow (∼4–5 m deep), fresh, and non-tidal coastal lagoon in southern Brazil surrounded by extensively irrigated rice plantations and numerous irrigation canals. We hypothesized that the annual, intense irrigation for rice agriculture creates extreme conditions that seasonally change groundwater discharge patterns in the adjacent lagoon. We further supposed that dredging of irrigation canals alters groundwater fluxes. While the activities of 222 Rn in shallow groundwater were 2–3 orders of magnitude higher than in surface water, CH 4 and radium isotopes were only ∼1 order of magnitude higher. Therefore, 222 Rn appears to be the preferred groundwater tracer in this system. Radon concentrations and conductivities were dramatically higher near the pump house of rice irrigation canals, consistent with a groundwater source. Modeling of radon inventories accounting for total inputs (groundwater advection, diffusion from sediments, and decay of 226 Ra) and losses (atmospheric evasion, horizontal mixing and decay) indicated that groundwater advection rates in the irrigation canals (∼25 cm/d) are over 2 orders of magnitude higher than along the shoreline (∼0.1 cm/d). Nearly 75% of the total area of the canals is found in the southern half of the lagoon, where groundwater inputs seem to be higher as also indicated by methane and stable isotope trends. In spite of the relatively small area of the canals, we estimate that they contribute nearly 70% of the total (∼57,000 m 3 /d) groundwater input into the entire Mangueira Lagoon. We suggest that the dredging of these canals cut through aquitards which previously restricted upward advection from the underlying permeable strata. The irrigation channels may therefore represent an important but previously overlooked source of nutrients and other dissolved chemicals derived from agricultural practices into the lagoon.

Coastal Exploitation, Land Loss, and Hurricanes: A Recipe for Disaster

Southern Louisiana occupies a dynamic landscape, marked by coastal wetlands interrupted by both natural and human‐made levees, and vulnerable to both the Mississippi and Atchafalaya rivers and major storms coming off the Gulf of Mexico. It is also a region into which, for centuries, exiled and threatened populations have moved and found refuge. Systematic and dramatic changes along the entire reach of the Mississippi River coupled with activities within the region's wetlands such as levee construction, canal dredging, and petroleum extraction have contributed to both pollution and extensive coastal land loss. In this article, I discuss the recent hurricanes in light of the relationship between Louisiana and the rest of the United States and the environmental and community degradation that has occurred along the coast. I focus on petroleum development, the most recent and extensive natural resource to shape southern Louisiana's wealth and economy.

Arsenic in soils and plants of woodland regenerated on an arsenic-contaminated substrate: A sustainable natural remediation?

Plant As accumulation at three As-polluted sites where spontaneous re-vegetation has taken place is examined. Each site had a different source of soil As (coal fly ash, LeBlanc process waste, canal dredging). Plant analysis indicates that soil-plant As transfer is poor at each site. Any mobile As is retained in root tissues, with little transfer to shoots. Bryophytes, pteridophytes, herbaceous and woody plants sampled at each site predominantly showed As concentrations of <3 mg kg(-1) dry wt, whilst total soil As ranged between 50 and 220 mg kg(-1) dry wt. Risk associated with food chain transfer at these sites is low when compared to other routes such as direct ingestion/inhalation of As-contaminated particulates re-entrained from an unvegetated or unstable substrate.