CONTAMINATION IN AQUATIC ECOSYSTEMS
A healthy aquatic ecosystem is defined in such a way that human activities do not disturb the natural functioning (e.g., nutrient cycling) nor appreciably modify the system structural design (e.g., species composition). An unhealthy aquatic ecosystem, on the other hand, is defined with imbalanced occurred to the natural state due to anthropogenic impacts, either physical (e.g., streaming in abnormal hot water), chemical (e.g., applying toxic wastes at a concentrations where species suffer from harms or damages), or biological (e.g., supporting non-native species invasion).
The aquatic environment as a whole is a very complex system which is the seat of some chemicals, physical and biological reactions, and this system is closely related to all the other systems or compartments (Westrich & Förstner, 2007). Because of the water cycle, aquatic ecosystems are likely to be contaminated by accidental or chronic pollutions. Excess of natural products and many human-made molecules are therefore expected to pollute aquatic ecosystems. Nutrients and contaminants transport via inland waters in polluted aquatic systems have been receiving increasing attention because these inland waters are the central support, the backbone of continuum linkage between land and sea waters. In this hydraulic system of watersheds, the wetlands are playing an essential role as buffer zones for wastewater mitigation (Billen & Garnier, 2007; Le et al., 2010).
Long regarded as a passive conduit between land and ocean, inland water systems are significantly more complex and influential than previously believed (Böhlke et al., 2009). They do not only transport materials from land to sea, but they internally store sediments and liquid influents, support the food web of the aquatic environment and bring the water cleaning regulation for human needs. Wilson and Carpenter (1999) claimed that continental aquatic systems are in the middle of a tightly linked network of interests, regarding economy, politics, and environment, which can be proved by the numerous uses that human civilization harness from these systems. In contrast, those relying on the water source suffer from various contaminants (mineral, inorganic, and organic) during these uses.
Sources of pollution of the aquatic environment
As a sink for pollutants in the aquatic environment, the water-sediment interface, known to be one of the most vulnerable (Devault et al., 2009) receiving a hefty source of pollution from agricultural practices and metropolis areas. The accumulation of contaminants, such as nutrients, metals, or a persistent toxic organic compound (PCBs) in the water-sediment interface at levels that are not rapidly lethal may result in long-term, subtle effects to the biota by direct uptake or through the food web.
ECOLOGICAL ENGINEERING AND ECOSYSTEM RESTORATION
Ecological engineering is an emerging part of the environmental sciences integrating ecology and engineering knowledge and concerned with the design, monitoring, and construction of new sustainable ecosystems, which benefit of both human and nature well-being (Mitsch & Jørgensen, 2004). It is also the practice of fitting environmental technology with ecosystems self-design for maximum performance (Odum & Odum, 2003), with the aim at (1) conserving and (2) restoring ecological systems, (3) modifying ecological systems to increase the quantity, quality, and sustainability of particular services they provide, or (4) building new ecological systems that would provide natural services. Those task without ecological engineering would otherwise be provided through more conventional engineering based on non-renewable resources with high energy and economic costs (Barot et al., 2012). Thus, the objective of ecological engineering is to better understand the natural functioning of the ecosystem, to better favor their resiliences, and to seek solutions of bioremediation. In other words, ecological engineering plays a significant role in a sustainable society by providing benefits for humankind without destroying the ecological balance (Mitsch & Jørgensen, 2004). These approaches are seeking for solving environmental questions that are not only useful for our human well-being but also for aquatic systems conservation. Finding new solutions based on natural functions of ecosystems for climate change mitigation, pollution removal of ecosystems and others majors issues of environment has been recently generalized as an innovative concept of Nature-based solutions (NBS) (Eggermont et al., 2015; Maes & Jacobs, 2017). Even though environmental management tools are now more and more numerous and complex, they include the simultaneous application of environmental technology, cleaner technology, environmental legislation, ecological engineering, and ecosystem restoration (Fig.I.2). Likewise, realizing nature-based solutions requires political, economic, and scientific challenges to be tackled (Maes & Jacobs, 2017). Ecological innovation such as ecological engineering is a key to designing nature-based solutions which effectively contribute to sustainable economic growth (Maes & Jacobs, 2017).
WETLAND AS FOCUSING SITES FOR ECOLOGICAL ENGINEERING
Wetlands are known for their provisioning of ecosystem services and thus have great potential to be used as nature-based solutions to address a variety of environmental, social and economic challenges (Thorslund et al., 2017).
Ecological engineering strategies may be based on one or more of the following classes described by Mitsch & Jørgensen (Table I.2, 2004). Those strategies that are particularly suitable for wetland restoration are classes (1) and (2) below:
(1) Ecosystems services are used to reduce or solve a pollution problem that otherwise would be (more) harmful to other ecosystems. A typical example is the use of natural wetlands for wastewater treatment.
Natural wetlands are well known for their ability to remove sediments, nutrients, and other contaminants from water. They have been used as convenient wastewater discharge sites treatments (Ballantine et al., 2017; Hu et al., 2017; Kadlec & Wallace, 2009; Zedler & Kercher, 2005).
(2) Ecosystems are imitated or copied to reduce or solve a pollution problem, leading to constructed ecosystems. Examples are artificial fishponds and constructed wetlands for treating wastewater or diffuse pollution sources.
Wetlands construction to treat various wastewaters has been accelerating around the world since 1985 (Kadlec & Wallace, 2009) and successfully applied for decades as a sustainable wastewater management option worldwide (Wang et al., 2017). Constructed wetlands for water treatment are complex, integrated systems of water, plants, animals, microorganisms, and the environment (EPA, 2016). The use of natural wetlands for wastewater treatment has recently became limited due to being protected by Federal law, while constructed wetlands provide a relatively simple and inexpensive solution for controlling many water pollution problems without detrimentally affecting natural wetlands resources (Kadlec & Wallace, 2009). Creating and restoring constructed wetlands is a typical example of imitating or copying an existing ecosystem by creating or restoring one that mimics field patterns of the ecosystem to solve a pollution problem (Mitsch & Gosselink et al., 2000).
(3) The recovery of ecosystems after significant disturbances. Examples are coal mine reclamation and restoration of lakes, estuaries, and rivers.
(4) The use of ecosystems for the benefit of humanity without destroying the ecological balance (i.e., the utilization of ecosystems on an ecologically sound basis). Typical examples are the use of integrated agriculture and development of organic agriculture; this type of ecological engineering finds wide application in the ecological management of renewable resources.
Tubificid worms – a typical example of bioturbation in aquatic systems
Among the benthic invertebrate community that inhabits the freshwater wetland, the oligochaetes are the organism among the most resistant to chemical perturbations. It is widely known that Tubificid Oligochaeta (ITIS – Integrated Taxonomic Information System), is at the source of bioturbation processes that are related to conveying biotransport of sediment in the majority of the freshwater deposit sediment with fine granulometric (McCall & Fisher, 1980). Tubificids are described as small (vertically) burrowing worms (which are often about 2-5 cm long and roughly 1 mm in diameter), living in the sediment-water environments. They have located vertically in the surface muddy sediments with a head-down orientation so that they are feeding at depth in the sediment and are continuously egesting its fecal pellets at the surface of the sediment. With large densities of tubificids in aquatic sediment, they are generating the conveyor belt phenomena. During their activities, they consume and dispose sediment particles from the bottom layers to the superficial sediment layers (Cunningham et al., 1999) in a typical conveying process with related bioadvection of the surrounding sediment. Bioadvection is a process with the similarity of the natural sedimentation but with higher rates of sediment burial due to the tubificids that defecate at the sediment surface so that the surface sediment in buried under deposition of large quantities of fecal pellets. This bioadvection is a downward advection of the water-sediment interface under the influence of large densities of the tubificid population, as head-down deposit feeders. This biotransport modifies the distribution of fine particles that increases in the surface layer where fecal pellets accumulate (Ciutat et al., 2006).
Influence of bioturbation on the fate of aquatic pollutants
Bioturbation and related biotransports may significantly influence the physicochemical properties of sediment (Mermillod-Blondin et al., 2001, 2002, 2003, 2004; Pigneret et al., 2006), and the contaminant incorporation into the sediment (Delmotte et al., 2007; Devault et al., 2009). In most cases, bioturbation effects on the physical, chemical, and biological properties of sediment-water result in increased mineralization rate of organic matters in marine sediment (Gerino et al., 1998). By changing the ratio between sediment and water, bioturbation also possibly modify the vertical distribution of pollutants in the sediment column (Anschutz et al., 2012; Ciutat et al., 2007, 2006; Delmotte et al., 2007; Gerino et al., 2014; Hoang et al., 2018; Hölker et al., 2015; Kristensen et al., 2012; Teal, Parker, & Solan, 2013). Bioturbation, generated by invertebrates’ benthic activities, therefore is controlling the fluxes of organic matter and nutrients through water-sediment interface, and the contaminant incorporation into the sediment.
The redistribution of the sediment particles due to bioturbation could lead to a change in its grain size in different sediment layers. The bioturbation activity can modify the vertical granulometric distribution of the sediment. Other conveyors organisms are responsible for a granulo-reclassification of particles: they ingest the finest particles at depth and reject the fecal pellets on the surface, resulting in a depletion of fine particles in depth and enrichment in the surface layers. This is the case of the polychaetes Arenicola marina (Rasmussen et al., 2000) and Naineris laevigata in the marine environment; tubificids in freshwater (McCall & Fisher, 1980; Ciutat et al., 2006); and earthworms in the terrestrial environment. Fecal pellets produced by conveyor organisms are often agglomerated by mucus, generating larger particles that increase the porosity of this layer of fecal pellets and, together, the fluxes through the interface by simple diffusion. It is important to emphasize that these fecal pellets contain a relatively high proportion of low-density organic matter. Also, the balls are not bonded together, thus reducing the compactness and cohesively compared to the non- bioturbated sediment, depending on the type of bottom (sandy or muddy) considered. This layer of fecal pellets is systematically more abundant in water, which will facilitate its resuspension by currents or other organisms (McCall & Fisher, 1980; Rhoads & Young, 1970). Downward transport of the surface sediment results from the accumulation of fecal pellets at the sediment surface, simultaneously with sediment depression in deeper layers due to sediment ingestion by the worm feeding (Anschutz et al., 2012; Ciutat et al., 2006). Consequently, bioturbation creates two distinct layers in the bioturbated sediment: a top layer corresponding to the fecal pellets accumulation from ingested anoxic sediment, and a bottom layer of with increasing particle size (Anschutz et al., 2012).
Table of contents :
PART I. BIBLIOGRAPHY SYNTHESIS
I.A. AQUATIC CONTAMINATION BY METALS AND PESTICIDES
I.A.1 AQUATIC ECOSYSTEM
I.A.2. CONTAMINATION IN AQUATIC ECOSYSTEMS
I.B. ECOLOGICAL ENGINEERING AS SOURCE OF NATURAL ATTENUATION PROCESSES FOR AQUATIC SYSTEMS
I.B.1. ECOLOGICAL ENGINEERING AND ECOSYSTEM RESTORATION
I.B.2. WETLAND AS FOCUSING SITES FOR ECOLOGICAL ENGINEERING
I.B.5. COMBINED EFFECTS OF BIOTURBATION AND PHYTOREMEDIATION AS A BIOLOGICAL PROCESS FOR POLLUTANTS REMOVAL IN AQUATIC SYSTEMS
PART II. METHODOLOGY
II. A. MICROCOSM STRUCTURE AND EXPERIMENTAL DESIGN
II. A.1 SAMPLING SITE AND PROCESSING OF SEDIMENT AND PLANTS
II. A.2 EXPERIMENTAL DESIGNS
II. A.3 ECOLOGICAL ENGINERING TOOLS USED
II.B. METHODOLOGICAL TOOLS
II.B.1 CORING SEDIMENT AND SAMPLING OF INTERSTITIAL WATERS AND SEDIMENT PARTICLE
II.B.2 BIOTURBATION ACTIVITY MEASUREMENTS
II.B.3 CADMIUM MEASUREMENT
II.B.4. PHYSICOCHEMICAL VARIABLES OF SEDIMENT AT THE END OF THE EXPERIMENTS
II.B.5. ATRAZINE AND ITS METABOLITES MEASUREMENTS
II.B.6. CALCULATIONS AND DATA TREATMENTS
II. C. ASSESSMENT THE EFFICIENCY OF THE COMBINED BIOREMEDIATION TOOLS BY USING TOXICOLOGICAL BIOASSAY
II.C.1. MICROALGAE STRAIN AND CULTIVATION.
II.C.3. DETERMINATION OF CHLORELLA GROWTH CURVE FROM DIFFERENT GENERATIONS
II.C.4. CHLORELLA TEST WITH PURE ATRAZINE SOLUTION.
II.C.5. APPLICATION ON SAMPLES FROM EXPERIMENTAL MICROCOSMS.
PART III. RESULTS AND DISCUSSION
CHAPTER III.A. INFLUENCE OF COMBINED BIOTURBATION AND PHYTOREMEDIATION ON CONSERVATIVE POLLUTANT (CADMIUM AS AN EXAMPLE) IN AQUATIC SEDIMENT
III.A.1. BIOTURBATION EFFECT ON T. LATIFOLA’S BIOACCUMULATION RATES
III.A.2. EFFECTS OF TUBIFICID WORMS AND T. LATIFOLIA PLANT ON CADMIUM
MASS BALANCE AND FLUXES
III.A.3. TOXICITY OF CADMIUM AND THE POSSIBILITY TO APPLY THE BIOTURBATION AS A BIOREMEDIATION STRATEGY
CHAPTER III.B. INFLUENCE OF COMBINED BIOTURBATION AND PHYTOREMEDIATION ON A MICRO-ORGANIC POLLUTANT: ATRAZINE
CHAPTER III.C. COMPARISON OF BIOREMEDIATION EFFECTS ON TWO DIFFERENT TYPES OF POLLUTANTS
III.C.1. TRANSPORT AND BIOAVAILABILITY OF POLLUTANTS EXAMPLES OF
CADMIUM AND ATRAZINE
III.C.2. COMPARISON OF BIOREMEDIATION OF WATER AND SEDIMENT TOXICITY BETWEEN NON-CONSERVATIVE AND CONSERVATIVE POLLUTANTS
PART IV. CONCLUSIONS AND PERSPECTIVES