The Impacts of Introduced Fish and Aquatic Macrophytes on the Ecology and Fishery Potential of Lake Victoria, Kenya

*Job O. Omweno, Reuben Omondi, Fredrick M. Ondemo and Argwings Omondi*

## **Abstract**

Fish have been deliberately introduced into new ecosystems as a management tool, to argument overfished native stocks, to occupy vacant niches, and to create lucrative commercial fisheries. Lake Victoria has witnessed successful introductions of predatory Nile perch, *Lates niloticus* and four Tilapiine species (including Nile tilapia, *Oreochromis niloticus, Tilapia zilii*, and *Oreochromis leucostictus*). These introductions have negatively and positively impacted the fishery potential and ecology of native fisheries in the lake. The predation of native species by the voracious Nile perch has contributed to decimation and virtual disappearance of over 300 species of Haplochromines. In addition, competition for feeding and breeding areas and interspecific hybridization between exotic *O. niloticus* and the native Tilapiines have also yielded undesirable results such as disappearance of native *Oreochromis esculentus*. The most successful invasive plant introductions have been water hyacinth, *Eichhornia crassipes*, Nile cabbage, *Pistia stratiotes*, and dense waterweed, *Egeria densa*. Proliferation of water hyacinth has led to increased shading and turbidity. The introduced species have manifested more pronounced deleterious effects on the native fisheries and their ecology in Lake Victoria. Therefore, future introductions of new species should be based on sound scientific research in order to minimize their unprecedented impacts in the new ecosystems.

**Keywords:** introduced species, aquatic ecosystem, macrophytes, ecology, fishery, Lake Victoria

## **1. Introduction**

Lake Victoria, located in the eastern part of Africa, is one of the largest tropical freshwater lakes in the world. It supports a rich ecosystem and plays a vital role in the economies and livelihoods of the riparian countries, including Kenya [1]. Over the years, however, the introduction of non-native fish species and aquatic macrophytes

has had significant impacts on the ecology and fishery potential of Lake Victoria [1, 2]. Species introductions have been used as a fishery management tool globally. This has occurred through intentional and accidental introductions across biogeographic and ecological boundaries [1]. Over 237 species have been introduced in more than 140 countries globally, out of which the African continent has recorded 147 introductions [1]. Kenya has recorded a total 14 fishery introductions. With a total of six fishery introductions, Lake Victoria is the second leading ecosystem in fishery introductions after Lake Naivasha. Currently, the commercial fishery of Lake Victoria (with an annual fishery output of approximately one million tons) is dominated by two non-native species, Nile perch *Lates niloticus*, Nile tilapia *Oreochromis niloticus*, and the native Silver cyprinid *Rastrineobola argentea* [2]. Before the decline and disappearance of native species, Lake Victoria had a diverse multi-species fishery dominated by native Tilapiines, *Oreochromis esculentus*, *Oreochromis leucosticus, Oreochromis variabilis*, the African lungfish, more than species of haplochromines [3]. Some species like the African carp, *Labeo victorianus,* however, declined long before the introduction of exotic tilapia and predatory Nile perch due to overfishing and habitat degradation [3]. Other factors contributing to fishery changes in Lake Victoria are nutrient pollution and massive wetland degradation that led to eutrophication. However, remarkable changes in fish biodiversity occurred after the introduction of Nile perch and exotic Tilapiines such as Nile tilapia (*O. niloticus*) whose ecological impact has been widely manifested [3, 4].

The introduction of non-native fish species, particularly the Nile Perch (*Lates niloticus*), in the 1950s, aimed to enhance fisheries and boost economic development in the region. While the introduction initially resulted in a boom in the fishery industry, it has led to numerous ecological consequences. The Nile Perch, a voracious predator, caused a decline in native fish species, leading to a loss of biodiversity and disruption of the natural food web [5]. Several endemic cichlid species, which were crucial for maintaining the ecological balance, have been pushed to the brink of extinction. In addition to the introduction of non-native fish, Lake Victoria has also been invaded by aquatic macrophytes, primarily the Water Hyacinth (*Eichhornia crassipes*). The rapid proliferation of these invasive plants has had severe ecological and socioeconomic implications [6]. Water Hyacinth forms dense mats on the lake's surface, reducing oxygen levels in the water, and blocking sunlight from reaching submerged vegetation. This, in turn, negatively impacts native aquatic plants and leads to the decline of fish populations, as they lose vital habitats and food sources. The impacts of introduced fish and aquatic macrophytes on the fishery potential of Lake Victoria are substantial [7, 8]. Furthermore, the presence of Water Hyacinth has posed significant challenges to fishing activities. The dense mats of this invasive plant clog fishing gear, impede navigation, and hinder access to fishing grounds. Fishermen have to spend more time and effort clearing the waterways, reducing their fishing productivity [9]. Consequently, the overall fishery potential of Lake Victoria has been compromised, leading to economic losses and food security concerns for the surrounding communities. The introduction of non-native fish species, such as the Nile Perch, and the invasion of aquatic macrophytes, particularly Water Hyacinth, have had profound impacts on the ecology and fishery potential of Lake Victoria in Kenya. Efforts to mitigate these impacts and restore the ecological balance of the lake are crucial for ensuring the sustainable use of Lake Victoria's resources and the well-being of the surrounding communities [8, 10]. Comprehensively, based on a systematic literature review, the main objective of this chapter was to explore and determine the impacts of introduced fish and aquatic macrophytes on the ecology and fishery potential of Lake Victoria.

*The Impacts of Introduced Fish and Aquatic Macrophytes on the Ecology and Fishery Potential… DOI: http://dx.doi.org/10.5772/intechopen.112388*

## **2. Introduced fish species and their impacts on the ecology and fishery potential of Lake Victoria**

Lake Victoria is known for its diverse fish species and its significance as a vital fishery resource. The lake is home to numerous native and introduced fish species, each having its own impacts on the lake's ecology and fishery potential [5]. One of the most notable native fish species in Lake Victoria is the Nile perch (*Lates niloticus*). Another important native fish species in the lake is the dagaa (*Rastrineobola argentea*), also known as the silver cyprinid [11]. Dagaa are small pelagic fish that form a critical part of the fishery in Lake Victoria. They are an important food source for humans and are also used as bait for larger fish species. The population dynamics of dagaa are closely linked to the ecological conditions of the lake, such as water quality and the availability of food resources [10, 11]. These introductions have been driven by the desire to diversify fisheries and provide alternative fishing opportunities. However, the presence of non-native fish species can have both positive and negative impacts on the ecosystem. While they may enhance fishery potential by providing new fishing opportunities, they can also compete with native species for resources and potentially disrupt the ecological balance of the lake [2, 5]. Overall, the diverse fish species in Lake Victoria, including both native and introduced species, have complex interactions with the lake's ecology and fishery potential. Understanding these interactions is crucial for sustainable management practices and maintaining the long-term health and productivity of the lake's fishery resources [12].

### **2.1 The Nile perch, Lates niloticus**

The introduction of Nile Perch (*Lates niloticus*) to Lake Victoria has had significant impacts on the ecology and fishery potential of the lake. Originally introduced in the 1950s to enhance fisheries and promote economic development, the unintended consequences of this introduction have had far-reaching effects on the ecosystem [4, 5]. One of the most notable impacts of the Nile Perch introduction is the decline in native fish species. As a voracious predator, the Nile Perch feeds on a wide range of fish, including many endemic species that were once abundant in Lake Victoria. This predation pressure has led to a significant reduction in the populations of these native fish, some of which are now critically endangered or have even become extinct. The decline of these species not only disrupts the ecological balance of the lake but also poses a threat to the cultural and biodiversity values associated with them [4]. Furthermore, the introduction of Nile Perch has caused a disruption in the natural food web of Lake Victoria. Native fish species played essential roles in the ecosystem as both predators and prey. Their feeding habits helped control populations of smaller fish and maintained a balance in the lake's biodiversity. With the decline of these native species, the natural food web has been altered, leading to cascading effects on other organisms. This disruption can result in changes in nutrient cycling, phytoplankton dynamics, and overall ecosystem health [6]. The ecological impacts of Nile Perch introduction extend beyond the decline of native fish species. The feeding habits and behavior of the Nile Perch have also affected other aspects of the ecosystem. For instance, Nile Perch feed heavily on zooplankton, which are crucial for controlling algae populations. The reduction in zooplankton abundance due to predation by Nile Perch has resulted in increased algal blooms, leading to eutrophication and a decline in water quality. This has negative implications for other organisms, including fish

and aquatic plants, which rely on clean and well-oxygenated water for survival [13]. In addition to the ecological consequences, the introduction of Nile Perch has had mixed effects on the fishery potential of Lake Victoria. Initially, the introduction resulted in a boom in the fishery industry. The Nile Perch grew rapidly and provided a valuable commercial catch, attracting fishing activities and generating economic benefits for local communities. The export of Nile Perch fillets became a significant source of foreign exchange for the riparian countries [14]. However, over time, the fishery potential of Lake Victoria has faced challenges. The high demand for Nile Perch has led to unsustainable fishing practices, including overfishing and the use of destructive fishing methods. This has put pressure on Nile Perch populations and led to a decline in their abundance. As a result, fish catches have become less predictable, and the fishing industry has become less reliable as a source of income and livelihood for local communities [7]. Furthermore, the dominance of the Nile Perch in the fishery has resulted in a loss of diversity in catch composition. Traditional fish species, which were once abundant and provided food security for local communities, have been overshadowed by the Nile Perch. This has raised concerns about the resilience and long-term sustainability of the fishery, as the overreliance on a single species increases vulnerability to disease outbreaks, environmental changes, and market fluctuations [7, 15, 16]. Other species severely impacted upon by the Nile perch invasion and predation are three catfishes (*Clarias gariepinus*, *Synodontis* spp., and *Schilbe altinialis*) and the African Lungfish (*Protopterus aethiopicus*) [6, 7, 17]. The introduction of Nile Perch to Lake Victoria has had profound impacts on the ecology and fishery potential of the lake. The decline of native fish species, disruption of the natural food web, and alteration of the ecosystem dynamics have altered the ecological balance and biodiversity of the lake. The fishery industry initially benefited from the introduction but is now facing challenges due to overfishing, loss of diversity, and market uncertainties. Balancing the conservation of native species, sustainable fishing practices, and the economic needs of local communities is essential [17, 18].

## **2.2 Introduced Tilapiines**

The introduction of Tilapiines, particularly the Nile tilapia (*Oreochromis niloticus*) and the Nile tilapia hybrids, to Lake Victoria has had significant impacts on the ecology and fishery potential of the lake. In the 1920s*, Oreochromis variabilis* and *O. esculentus* were the main native Tilapiines contributing to the commercial fishery of Lake Victoria. Tilapiines were introduced to Lake Victoria in the 1950s as an additional fishery resource and to provide alternative fishing opportunities [15]. The Nile tilapia, in particular, was known for its adaptability, fast growth, and tolerance to a wide range of environmental conditions. However, the unintended consequences of this introduction have had profound effects on the lake's ecosystem. However, the native tilapia fisheries declined because the species could not stand high levels of overexploitation. As a result, Haplochromines and Silver cyprinid *Rastrineobola argentea* became the main target species. Research has also shown that the introduced stocks of *Tilapia zilli* have contributed to proliferation of free-floating macrophytes such as *Pistia stratiotes* [16]. According to Outa et al. [15], the total haplochromine catches of 650,000 tons accounted for 80% of the total lake catches in 1967. It also prompted the introduction of *L. niloticus* and *O. niloticus* which increased the lake's fish catches fivefold. However due to its advanced competitive strategies, Nile tilapia outcompeted the endemic Tilapiines *O. esculentus* and *O. variabilis* resulting to their

## *The Impacts of Introduced Fish and Aquatic Macrophytes on the Ecology and Fishery Potential… DOI: http://dx.doi.org/10.5772/intechopen.112388*

displacement and total disappearance from the lake [8]. As a result of these disappearances, the Nile perch became the main target species in the lake fishery and fishing pressure using illegal gears was meted on the species. The decline of Nile perch populations in Lake Victoria has reportedly contributed to the recovery of some of the cichlids that initially disappeared as a result of its invasion [6]. Nevertheless, the *O. niloticus* contributed to increases in fish landings from the lake providing affordable and quality animal protein sources to the riparian communities [19].

Another notable impact of introduced Tilapiines is the alteration of the trophic structure of the lake. Tilapiines are generalist feeders that consume a variety of food sources, including plankton, algae, and detritus. Their feeding habits and high reproductive rates have resulted in increased competition for resources with native fish species. This has led to changes in the relative abundance and distribution of different fish populations, potentially displacing or reducing the numbers of native species [19, 20]. Moreover, the introduction of Tilapiines has led to changes in the lake's nutrient dynamics. Tilapiines are efficient grazers of algae, and their feeding activities can reduce algal biomass. While this may initially seem beneficial in controlling algal blooms, it can also have unintended consequences. Algae play a vital role in the lake's food web, serving as a food source for zooplankton, which, in turn, are consumed by other fish species. The reduction in algal biomass due to Tilapiine grazing can disrupt the balance of the food web and impact the availability of food for other organisms, potentially leading to cascading effects throughout the ecosystem [17]. Additionally, the introduction of Tilapiines has had mixed effects on the fishery potential of Lake Victoria. Initially, the introduction provided new opportunities for fishing and contributed to the expansion of the fishery industry. Tilapiines, particularly the Nile tilapia hybrids, are known for their fast growth and high reproductive rates, which made them an attractive target for commercial fishing. The increased availability of Tilapiines led to economic benefits for fishing communities and contributed to local livelihoods [6].

However, the proliferation of Tilapiines has also posed challenges to the fishery. The high reproductive capacity and aggressive behavior of Tilapiines have led to overpopulation and increased competition for resources. This has resulted in slower growth rates and smaller sizes of individual fish, reducing their market value. Moreover, the dominance of Tilapiines in the fishery has resulted in a loss of diversity in catch composition, as other native species are overshadowed and less targeted [16]. This raises concerns about the resilience and long-term sustainability of the fishery, as it becomes more vulnerable to environmental changes and disease outbreaks. The ecological and socioeconomic impacts of introduced Tilapiines highlight the need for careful management and conservation strategies in Lake Victoria [6, 7]. Efforts are being made to balance the conservation of native fish species, the control of invasive Tilapiines, and the sustainable use of the lake's resources. These include implementing fishing regulations, promoting sustainable fishing practices, and conducting research on the impacts of Tilapiine populations [21]. Therefore, the introduction of Tilapiines, particularly the Nile tilapia and its hybrids, to Lake Victoria has had significant impacts on the lake's ecology and fishery potential. The alteration of the trophic structure, changes in nutrient dynamics, and challenges to the fishery industry are among the consequences of this introduction. Balancing the conservation of native species, management of invasive Tilapiines, and sustainable fishing practices are crucial for ensuring the long-term health and productivity of Lake Victoria's ecosystem and the well-being of local communities [10].

## **3. Introduced aquatic macrophytes species and their impacts on the ecology and fishery potential of Lake Victoria**

Macrophytes are aquatic plants that play a significant role in the ecology and fishery potential of Lake Victoria, the largest tropical lake in Africa. These plants, which include both native and invasive species, have diverse impacts on the lake's ecosystem. Native macrophytes in Lake Victoria, such as various species of submerged plants, floating plants, and emergent plants, provide important ecological functions. They serve as habitats and spawning grounds for fish, provide food sources, and contribute to the overall biodiversity of the lake [10]. Submerged plants, for instance, offer shelter for small fish and provide areas for the attachment of algae and other organisms. Floating plants, like water lilies, create sheltered areas for young fish, while emergent plants, such as papyrus, form dense stands along the lake's shoreline, offering nesting sites for birds and other wildlife [22]. However, the presence of invasive macrophytes, notably water hyacinth (*Eichhornia crassipes*), has had significant impacts on the ecology and fishery potential of Lake Victoria. Water hyacinth, originally introduced as an ornamental plant, has rapidly spread across the lake, forming dense mats that cover large areas of the water surface. These mats block sunlight, hampering the growth of submerged plants and leading to reduced oxygen levels in the water. The reduced oxygen levels can cause fish kills and negatively impact other aquatic organisms [23]. Additionally, the mats impede water flow, disrupt navigation, and reduce available habitat for fish and other wildlife, affecting fishery activities. Managing the presence of invasive macrophytes and promoting the growth and conservation of native macrophytes are essential for maintaining the ecological balance and fishery potential of Lake Victoria [24].

## **3.1 Water hyacinth (***Eichhornia crassipes***)**

Water hyacinth (*Eichhornia crassipes*) is an invasive macrophyte species that has become a major ecological and economic concern in Lake Victoria, the largest tropical lake in Africa. Originally introduced as an ornamental plant, water hyacinth has rapidly spread across the lake, forming dense mats that cover large areas of the water surface. Water hyacinth (*Eichhornia crassipes*) is a free-floating macrophyte that established in the lake due to nutrient influxes [16]. Water hyacinth was reportedly introduced to Lake Victoria from the Ugandan sector through the mouth of River Kagera [25]. Water hyacinth's ability to reproduce rapidly and form dense mats has contributed to its status as an invasive species in Lake Victoria. The plant's floating nature allows it to easily spread across the water surface, aided by wind, water currents, and human activities. The absence of natural predators and competitors in the lake has further facilitated its uncontrolled growth. Water hyacinth thrives in eutrophic conditions, taking advantage of high nutrient levels resulting from agricultural runoff and untreated sewage discharge [20]. The proliferation of water hyacinth has had severe ecological consequences in Lake Victoria. The dense mats of water hyacinth block sunlight, reducing photosynthesis and oxygen levels in the water. This inhibits the growth of submerged aquatic plants and disrupts the balance of the lake's ecosystem. The reduced oxygen levels also lead to fish kills and negatively impact other aquatic organisms [10]. Additionally, water hyacinth alters the physical structure of the lake by impeding water flow, hindering navigation, and reducing the available habitat for fish and other wildlife. The mats create stagnant water pockets, which promote the breeding of disease-carrying mosquitoes,

## *The Impacts of Introduced Fish and Aquatic Macrophytes on the Ecology and Fishery Potential… DOI: http://dx.doi.org/10.5772/intechopen.112388*

increasing the risk of malaria and other waterborne diseases among the human population living near the lake [22].

Lake Victoria is renowned for its vibrant fisheries, providing a source of livelihood for millions of people. However, water hyacinth has severely impacted the fishery potential of the lake. The dense mats of the plant reduce access to fishing grounds, making it difficult for fishers to cast their nets or use traditional fishing gear [23]. As a result, fish catches have significantly declined, leading to economic losses and food insecurity. The plant's dense growth also alters the food web dynamics in the lake. Water hyacinth outcompetes and displaces native aquatic plants, which serve as important habitats and food sources for fish. The reduction in the availability of suitable spawning grounds and food for young fish hampers their survival and growth [10, 26]. Consequently, fish populations, particularly those that rely on submerged vegetation, have declined. Water hyacinth also reduces fishing pressure in the intensively infested areas by blocking the movement of fishing crafts and deployment of the fishing gear. The weed has contributed to reduced primary productivity of the lake due to shading of phytoplankton by water hyacinth mats. In addition, the water hyacinth mats also restrict wind action on surface waters preventing the exchange of oxygen across the air-water interface [25]. They also deplete dissolved oxygen from the water column through the microbial breakdown of decomposing plant remains [16]. This creates anoxic conditions that cause deleterious effects to aquatic organisms and can lead to massive fish mortalities [17]. In addition, this range falls below the lethal limit of 2 mg l−1 that is detrimental to fish survival and can often cause massive fish mortalities [27]. Studies have shown that *Lates niloticus* and *Rastrineobola argentea* mainly occur in the oxygenated open waters because they are sensitive to low DO levels of less than 5 mg l−1 [8]. This excludes *L. niloticus* and *R. argentea* from areas covered by water hyacinth mats that have reportedly recorded low DO levels ranging from 1.32 to 3.68 mg l−1 [28]. In addition, the proliferation of water hyacinth has led to the recovery of hypoxia tolerant native fish species as catfishes, *haplochromines*, *Protopterus aethiopicus,* and *O. niloticus* that find refugia from predation beneath water hyacinth mats [7, 16]. According to Meerhoff et al. [12, 25], the abundance and diversity of fish species in Lake Victoria were higher in submerged vegetation, followed by water hyacinth and unvegetated littoral sites. The marked differences in fish diversities between open waters and water hyacinth infested areas can be attributed to exclusion of *L. niloticus* which preys upon most native species as well as food, shelter, and refugia provided to the fishes by water hyacinth mats [12]. Several methods (biological, chemical, and mechanical) have been used by the three riparian countries to control the weed with very little success. It has been suggested that reducing nutrient loads through influent rivers can curtail the proliferation of the water hyacinth within the lake [7, 12, 16]. Numerous strategies have been implemented to mitigate the impacts of water hyacinth in Lake Victoria. These include manual and mechanical removal, biological control using weevils (Neochetina spp.), and the development of eco-friendly technologies for harvesting and processing the plant. These efforts aim to control the spread of water hyacinth, restore ecological balance, and revive the fishery potential of the lake [12].

#### **3.2 Dense waterweed (***Egeria densa* **Planchon)**

Like water hyacinth, Dense waterweed, *Egeria densa* is endemic to warm tropical and temperate lakes in South America [18]. The plant belongs to family Hydrocharitaceae of submerged monocotyledonous perennial aquatic plants (**Figure 1**). Little has been documented about the ecology of these plant in Lake Victoria. Nevertheless, the plant has been observed to grow in the shallow inshore areas of the Kenyan sector, forming dense and thick mats with intertwining stems, and rooted 1–2 m below the water surface [21]. Furthermore, the plant persists as fragments that drift in the water column, which are propagated into thick and extensive marts that cover large and expansive areas of the water column [9, 18, 21]. This helps to absorb nutrients locked in the substrate, making them available to biota. The plant is successfully propagated in a submerged environment due to its physiological adaptations related to its metabolism [29].

These traits enable the plant to photosynthesize under low CO2 concentration, non-optimal water temperatures, and different nutrient concentrations of water and sediments that affect plant metabolism and ultimately community structure and distribution of the plants [21, 30, 31]. For instance, *Egeria densa*, exhibits the C4 pathway and utilizes bicarbonates HCO3 − in waters with low CO2 levels, can tolerate high phosphorous levels, but is susceptible to iron deficiency. Despite being able to thrive in turbid environments [10, 30], the plant has been displaced, having low populations in areas covered by dense marts of Water Hyacinth.

Note: The presence of large populations of *E. densa* decreases water turbulence and resuspension of sediments, which increases the amount of light available in the water column. By sequestering nutrients from sediments, *E. densa* reduces phytoplankton biomass and increases zooplankton abundance and distribution by providing refugia against their predation (**Figure 2**). However, in the long-term plants may result in the increase in sediment height [9].

As a dominant species in the nutrient dynamics, *E. densa* frequently influences phytoplankton biomass by shading phytoplankton in the water column, and can provide refugia to zooplankton and fish escaping predation [22, 23, 32, 33]. Given its tendency to acquire nutrients from the water column, *E. densa* can reduce nutrient availability for phytoplankton. The highly invasive nature of Egeria results in the weed outcompeting and displacing native underwater vegetation such as floating pondweed and ribbon weed [24, 34, 35].

**Figure 1.** *Photograph of Egeria densa (Planchon) [9].*

*The Impacts of Introduced Fish and Aquatic Macrophytes on the Ecology and Fishery Potential… DOI: http://dx.doi.org/10.5772/intechopen.112388*

**Figure 2.** *Egeria densa as an ecosystem engineer.*

## **4. The aftermath of species introductions**

The decline and virtual disappearance of native fisheries in Lake Victoria can be attributed to overexploitation, destructive fishing, and introduction of nonnative species [26]. The major cyprinids, *Labeobarbus altianialis*, and African carp *Labeo victorianus*, are currently redlisted among the critically endangered species by IUCN [36]. *Labeo victorianus* is a potamodromous fish that migrates from the lake to the major influent streams and tributaries such as Sondu, Kuja, and Mara during the rainy season to spawn in the floodplains [36]. According to Balirwa et al. [7], the contribution of *L. altanialis* to fish landings from Lake Victoria declined from 8173 tons in the 1980s to 152 tons in the late 1990s and early 2000. Before the establishment *L. niloticus* as a top predator, the catfishes *Bagrus docmak*, *Clarias gariepinus,* and *Schilbe intermedius* were the apex predators in the lake [15]. While *B. docmak* disappeared completely, *C. gariepinus* and *S. intermedius* were not greatly affected by this ecological change. Although S. *intermedius* can partly occupy open waters, it has been the main target species of the gill net fishery in the inshore areas, resulting to its decline over the years. On the other hand, the population of *C. gariepinus* is replenished by continuous recruitment of juveniles from major influent rivers. Populations of the African lungfish *Protopterus aethiopicus* in Lake Victoria have also reported a remarkable decline in the past, for instance, from 0.3 to 0.07 tons between 1986 and 1990 [37]. This could be attributed to loss of refugia caused by wetland conversion, and decreased recruitment, due to harvesting of the nest-guarding male lungfish [11]. Other possible reasons for this decline could be predation by the voracious Nile perch, declining food resources and habitat alteration [11, 37].

## **5. Conclusion and recommendations**

In Lake Victoria, introduction of non-native cichlids such as Lates niloticus, *Oreochromis niloticus*, *Tilapia zilii*, and *Oreochromis leucosticus* had negative and positive impacts on the fishery potential and the ecology of the lake. These include interspecific competition among the introduced and native Tilapiines, hybridization of native tilapia by *O. niloticus*. The most remarkable change observed in Lake Victoria fisheries is the decline and total disappearance of endemic Tilapiines *Oreochromis esculentus* and *O. variabilis*, some catfishes (*Xenoclarias eupogon*), several species of Haplochromines and the cyprinids *Labeo victorianus* and *Labeobarbus altinialis*. This has significantly reduced the lake biodiversity, and prompted the introduction of non-native species such as *Lates niloticus* and four non-native Tilapiines including *O. niloticus* into the lake. There is a need to assess current fishery management strategies and formulate new ones based on sound scientific research, which can be implemented in order to prevent loss of biodiversity. On the other hand, some introduced species have led to increase in fish landings as well as utilization of unoccupied niches. Successful establishment and infestation of water hyacinth, *Eichhornia crassipes* outcompeted Nile cabbage, *Pistia stratiotes and* dense waterweed *Egelia densa* resulting to shading, increased turbidity, and reduced dissolved oxygen levels. This has been a major factor contributing to dwindling trends in *L. niloticus* and *R. argentea* fisheries in the lake. However, proliferation of the macrophyte has recently contributed to reemergence of some native species such as catfishes, haplochromines, *O. niloticus,* and the African lungfish *P. aethiopicus*. Future introductions should be based on sound scientific research in order to minimize the effects of introduced species on native species in the new ecosystems.

*The Impacts of Introduced Fish and Aquatic Macrophytes on the Ecology and Fishery Potential… DOI: http://dx.doi.org/10.5772/intechopen.112388*

## **Author details**

Job O. Omweno1,2\*, Reuben Omondi2 , Fredrick M. Ondemo1,2 and Argwings Omondi2,3

1 Department of Agriculture, Livestock, Fisheries, Cooperative Development and Irrigation, Kisii County Government, Kisii, Kenya

2 Department of Environment, Natural Resources and Aquatic Sciences, Kisii University, Kisii, Kenya

3 Department of Agriculture and Environmental Science, Sigalagala National Polytechnic, Kakamega, Kenya

\*Address all correspondence to: omwenojob@gmail.com

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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## **Chapter 9**

## Dynamic Limnology between Movements and Management

*Maximilien Bernier*

## **Abstract**

The subject matter of this chapter revolves around the intersection of hydrodynamics in French lakes with the economic development of their respective territories. The aim is to understand the interactions between the dynamics of these lakes and territorial actors operating within these limnic areas. Each party is subjected to different management approaches, yet none of them take advantage of lake movements. These management strategies are organized based on the specific limnological mechanisms of each lake, including their temporal and spatial characteristics, as well as the risks they pose to human activities integrated into these lake ecosystems. This chapter will specifically focus on unused water and sediment movements as means to interact with local management practices. These phenomena serve as a foundation upon which all actors surrounding these lakes can rely to guide the protective measures implemented for their activities. This chapter aims to provide scientific insights to support decision-making for the actors operating in proximity to these lakes.

**Keywords:** hydrodynamics, lakes, limnology, management, movements

## **1. Introduction**

During the inception of limnology, François-Alphonse Forel introduced the concept that human beings are not merely part of lake's ecosystem. Through their activities, humans have the capacity to interact significantly with a lake and impact its ability to provide ecosystem services [1]. From a legal perspective, French lakes, including those in Europe, are theoretically required to be managed in the same manner. However, the reality is different. Despite the fact that management approaches are heavily influenced by scientific knowledge, each manager operates according to their individual needs and challenges. Every entity present along the shores of these lakes contributes to human influence on their respective areas of interest.

From a management perspective, the administrative structuring of water resources in France is guided by a range of directives, including the Water Framework Directive (WFD-2000), Water Development and Management Master Plans, and municipal decrees. The overarching objective is to achieve a state of "good condition," which theoretically considers societal entities inhabiting the managed territory and their expectations. However, practical implementation deviates from this ideal. Despite aspirations for a systemic approach, the prevailing framework is characterized by

rigidity, relying on naturalistic indicators while neglecting a diverse range of actors utilizing these aquatic environments, particularly for recreational purposes. Today, the number of stakeholders surrounding the lakes has diversified significantly and is still gradually increasing. Within the federation of municipalities of the Great Lakes, a multitude of sectors are represented, including military, oil, tourism, associations, regulatory authorities, and administrative entities. Consequently, the primacy of exclusively studying the dynamics of lakes as a reference for management indicators becomes increasingly questionable. Significant dynamic phenomena, such as flooding, water level fluctuations, navigation, erosion, or conservation of fauna and flora, come into play and shape management considerations. It is thus pertinent to explore dynamic behaviors of these lakes. Limnology facilitates a territorial approach that encompasses all relevant stakeholders integrating them into a comprehensive societal system. This approach considers the spatial and temporal dimensions, encompassing both natural and anthropogenic aspects. It involves establishing linkages between the environmental dynamics of biocenosis, biotope, and the socio-cultural practices imposed by human activities in relation to lakes.

In an approach to limnological geography [2], which places lakes at the centre of societal-environmental interactions across various spatial and temporal scales, the employ of dynamic limnology will use, in this chapter. This discipline seeks to understand the physical dynamics exerted by a lake within its own boundaries or towards its immediate surroundings. This dynamic perspective completes physical and biocenosis approach usually prefer to study water bodies to assist in management strategies in the face of global change. This study of lake dynamics (movements of water and sediments) was born with the creation of limnological sciences by F.-A. Forel, first studied the dynamics of the formation of Lake Geneva (Léman, in French), including geomorphological aspects and the appearance of "seiches" (variations in water level within the same lake) [3]. More recent researchers have furthered these investigations to enhance the quantification and mapping of lake physics at various scales [4]. We have opted for the dynamic approach due to its historical neglect in these limnic territories [5], especially by managers. The multitude of spatial approaches employed in contemporary limnology adds complexity to discerning the roles of different actors in lake management, without assigning undue importance to any perspective. To address this complexity and translate it into a diagnosis that prioritize specific parameters, our focus is on diagnosing water and sediment movements.

Our objective here is to produce a comprehensive diagnosis of the dynamic mechanisms occurring within these lakes to enhance their consideration by managers. By creating a diagnosis rooted in dynamic phenomena applied to specific territories, we aim to provide novel and readily applicable data on lake behaviours that can be easily understood by stakeholders and inform future management strategies. To achieve this, we will generate new cartographic data at the scale of the specific lake under study, irrespective of its characteristics, within the federation of municipalities of the Great Lakes located in the Landes, New-Aquitaine, France.

## **2. Methods**

In order to develop a chapter that offers practical perspectives to managers, we will study the hydrodynamic processes of lakes using methodologies that can be easily replicated.

## **2.1 Presentation of studied lakes**

The sites examined in this chapter concern two lakes situated in the federation of municipalities of the Great Lakes (**Figure 1**), within the Department of Landes, in

**Figure 1.** *Localization map.*

the region of New Aquitaine (France). This study follows on from a French thesis that explores the following question: Can water movements and their effects on differentiated sediment deposits in lakes and ponds contribute to the maintenance of economic activities in their territory?

Most lakes along the Aquitaine coast are geographically separated from the Atlantic Ocean by coastal dune barriers. The formation and development of these water bodies are closely intertwined with the history of the dunes themselves. By examining the periods of mobility of the dune belts, it has been possible to determine the specific characteristics and evolution of these lakes. The available data indicate that these bodies of water originally existed as lagoons wide open to the ocean until around 1000 BC [6]. Subsequently, these lagoons progressively became obstructed due to the accumulation of sand transported by longshore drift and finally closed definitively in Gallo-Roman era.

These lakes within the federation of municipalities of the Great Lakes are commonly referred to as ponds of Parentis-Biscarrosse and Cazaux-Sanguinet in France. Historically, these study sites were neglected in favor of their proximity to the nearby ocean, leading to their derogatory classification as "ponds" at the time. However, according to Laurent Touchart's definition, these water bodies qualify as lakes. Locally, they are now recognized and referred to as lakes, which is technically accurate considering that their average depth exceeds six metres, as defined by the Ramsar Convention of 1971. Additionally, they cover an area exceeding 200 ha, which meets the criteria set forth by E. Jedicke for defining a lake. Therefore, in this chapter, we will refer to them as lakes. Studied lakes collectively encompass over 9340 ha, with a total volume of 750 million liters. More specifically, Lake Parentis-Biscarrosse holds an estimated volume of 250 million liters, while Lake Cazaux-Sanguinet is estimated to contain 500 million liters [7].

Parentis-Biscarrosse and Cazaux-Sanguinet lakes are located in the extreme northwest of the Landes department, close to the border with Gironde (a French department a little further north) and below Arcachon basin. These two natural lakes can be reached in around an hour's drive from Bordeaux. Lake Parentis-Biscarrosse is slightly smaller and situated a little further south than Lake Cazaux-Sanguinet. It covers an area of approximately 3540 ha at an altitude of 19 m above sea level, with a maximum depth of 20.5 m. Lake Cazaux-Sanguinet, on the other hand, covers an area of around 5600 ha, at an altitude of 20 m above sea level, with a maximum depth of 23 m [7].

These lakes also share the characteristic of being shared by different communes. Lake Parentis-Biscarrosse is located in the municipalities of Parentis-en-Born, Biscarrosse, Gastes and Sainte-Eulalie-en-Born. Its counterpart is spread across the communes of Biscarrosse, Sanguinet and Cazaux, which come under the jurisdiction of the Gironde town of La Teste-de-Buch.

To move beyond the confines of limnology solely for naturalistic or physicochemical purposes, we have incorporated dynamics (**Figure 2**) of these "lentic" features to address their economic and societal significance. This diagnostic approach considers the criteria mentioned above.

Methodologies employed in this study encompass a combination of surveys and field observations, complemented using Geographic Information Systems (GIS).

#### **2.2 Bathymetries**

Lakes exist within basins, and when examining their dynamics, bathymetry emerges as a fundamental approach for initial investigations. The Adour-Garonne *Dynamic Limnology between Movements and Management DOI: http://dx.doi.org/10.5772/intechopen.112632*

#### **Figure 2.** *Illustration of lake dynamics interest.*

**Figure 3.** *Sediment movement's process.*

water agency conducted bathymetric surveys of lakes under study in 2014, and we will leverage their existing data. Additionally, bathymetric information was supplemented with a Digital Terrain Model generated by the French National Geographical Institute (IGN). By utilizing pre-existing data available throughout French territory, this diagnostic approach can be replicated on other water bodies (**Figure 3**).

• Data formatting: a dataset was prepared involving the processing of approximately 37,000 points for each of these lakes.


This initial methodological approach enables us to understand dynamics of lake beds, as well as the water levels and volumetric characteristics of the water bodies studied.

## **2.3 Water movements on surface**

Following the examination of lake depressions where certain movements occur, our attention will shift to movements generated by winds. The study of wind patterns serves to augment the previous analysis by elucidating the formation of waves on the lake surface. The investigation of these wind patterns (**Figure 4**) is conducted through the utilization of two distinct yet complementary methodologies.


This secondary methodological approach allows for the acquisition of findings regarding the dynamics of the lake banks or beds and the effects of wave-induced water actions on lake surfaces.

*Dynamic Limnology between Movements and Management DOI: http://dx.doi.org/10.5772/intechopen.112632*

**Figure 4.** *Water movement process on lake's surface.*

## **2.4 Water movements inside lakes**

The movements taking place inside lakes are commonly called currents. Apparently, lakes are even less calm than we think. These currents are not visible to the naked eye but can be easily identified if we pay attention to the evolution of bathymetry, fish location or invasive plants.

The use of an acoustic Doppler current meter coupled with mapping software makes it possible to visualise currents by spatialising their dynamic cells within lakes. Their visualizations depend on whether the current metre is in a fixed station or if it moves on the water's surface. In a fixed station, the device is fixed on a support that is immersed at a predefined point upstream. Its aim is then to go from the lake bottom to the surface. On the other hand, the other device will be guided by our boat and will detect lake currents from the surface to the bottom. To detect the direction of the currents will be used by a compass linked to the device is calibrated directly in real-time by the device in a fixed station. In the mobile position, the compass must be calibrated before any measurement is taken.


This third methodological approach enables the acquisition of results pertaining to the internal dynamics of lakes and directions of water flux.

These three methodological parts presented the dynamics that we seek to comprehend through a concise diagnosis of water and sediment movements. However, it is important to acknowledge that these dynamics do not exist in isolation from human interactions. Further societal investigations will soon complement this dynamic diagnosis of water bodies.

## **3. Results**

To address societal concerns related to phenomena such as floods, water quality issues, erosion, and sedimentation, we will employ dynamic limnology and utilize the methodologies to assess the impacts in these two lakes with similar genesis.

#### **3.1 Bathymetries**

The bathymetric analysis of these lakes was conducted using GIS. Generated maps provide visual representations of submerged topography and features within the lakes. Through this data acquisition, updated volume calculations for lakes were obtained. Newly determined volumes exhibit a variation of approximately 5% compared to previous measurements, even for lakes with identical altimetry, as exemplified by Lake Parentis-Biscarrosse in **Figure 5**.

Nevertheless, these bathymetric analyses of these lakes revealed irregularities that correspond to archeological findings in certain instances, and potential archeological discoveries in others. The lake basins were subsequently incorporated into a digital model, facilitating adjustments to water levels to address the various concerns related to buildings and utility network infrastructures.

Water level projections (**Figure 6**) have been established based on historical records of significant flooding or low-water periods, with the aim of comparing them with water management practices regulated by the lake's altitude. The aim is to assess the need for better management of water levels.

This baseline data will then be used to analyze changes in sediment dynamics linked to the anthropization of the lake's banks.

*Dynamic Limnology between Movements and Management DOI: http://dx.doi.org/10.5772/intechopen.112632*

**Figure 5.** *Water movement process inside lakes.*

**Figure 6.** *Pixel-based bathymetry analysis and volume of lake parentis-Biscarrosse.*

## **3.2 Water movements on surface**

To study the relationship between wind and waves, we implemented the calculation method proposed by Håkanson and Jansson [9] to determine fetches. To carry out this approach, we selected points of interest in order to recreate fetch diagrams

for each wind direction based on the wind rose data from MétéoFrance. Maximum fetches lengths were extracted, while the remaining values were weighted according to the frequency of the corresponding winds. The data obtained can be used to identify beaches subject to erosion due to wind-induced wave action.

The evaluation of fetches makes it possible to obtain theoretical values for the waves that reach the coast. This information helps managers to understand wave phenomena in their limnic territory. Moreover, these theoretical waves can be observed daily by anyone looking to enjoy the view from these lakes.

The analysis of lake dynamics related to wind-induced water movements has produced some interesting results, described in an article written jointly by Pascal Bartout, Laurent Touchart and myself [10]. The obtained data are presented in the form of graphs and maps (**Figures 7** and **8**). Maps highlight the most exposed coasts, characterized by sectorial winds, which correspond to the eroded zones (illustrated in dark blue in **Figure 9**). Erosion can be understood through accompanying graphs that provide insights into the impacting wave characteristics. Conversely, areas that have experienced minimal wind exposition on these maps exhibit visible sediment accumulation (illustrated by light blue zones in **Figure 9**).

As revealed by the image captured prior to the 2022 summer season (**Figure 10**), the southern coast of Lake Cazaux-Sanguinet exhibits significant erosion, indicated by the dark blue color (**Figure 9**). As a result, this beach, previously used by tourists, is now closed to the public for safety reasons. These phenomena could have been anticipated and dealt with by implementing local policies aimed at reducing these risks. By identifying areas with a high potential for erosion, managers of the federation of

**Figure 7.** *Issues highlighted by GIS visualization.*

## *Dynamic Limnology between Movements and Management DOI: http://dx.doi.org/10.5772/intechopen.112632*

**Figure 8.**

*Wave graphs according to fetches.*

#### **Figure 9.**

*Wind exposure maps by lake (weighted on the left for lake parentis-Biscarrosse and maximum on the right for lake Cazaux-Sanguinet).*

municipalities of the Great Lakes can use these results to prevent risks and forecast the costs of environmental works to maintain uses. This study is, therefore, essential for lake managers to better manage and safeguard these lake environments.

Furthermore, it is noteworthy that invasive exotic plants, Lagarosiphon Major and Egeria Densa, present in these lakes exhibit a tendency to avoid areas characterized by intense winds and waves. These plants have a greater propensity to acclimatize themselves in protected areas from winds and waves. Additional factors and conditions play a role in the colonization of specific sectors by these plants, as it will be explored in the subsequent section.

#### **3.3 Water movements inside lakes**

Internal movements of lakes are commonly referred to as currents. Although not very visible, these currents manifest in the form of lake-specific cells moving in different directions and at speeds ranging from almost zero to several metres per second. This section highlights the results related to the correct interpretation of these currents in lake environments.

## *3.3.1 Water movements directions inside lakes*

Movements internal to the lakes are specific because of their directions. These currents must be detected thanks to currents metre in lakes that identify water moving in cells. Different directions and highs from few centimeters to some tens are remarkable. This section highlights the results related to the correct interpretation of these current directions in lake environments.

*Dynamic Limnology between Movements and Management DOI: http://dx.doi.org/10.5772/intechopen.112632*

Cells can be identified by depth. Thanks to this representation by transects and georeferencing on GIS software, it is possible to map it.

With current data, we obtain significant values and representations with speeds associated (**Figure 11**). This makes it possible to have a global visualization of what happens in the lakes at a time T. This particularity allows us today to confirm that lakes are not simple basins filled with water and where water circulates from upstream to downstream, or tributaries to outfalls. In fact, we can follow tributaries from their entrance into lakes to the outfall. It appeared in **Figure 12** with purple water column next to the coasts. Entrance currents followed runs along the coast like an oceanic littoral drift [11], marking a new frontier that invasive plants do not overtake. Moreover, the rest is still moving as we can see a lot of different directions of water inside lakes (**Figure 13**).

Direction data is easily correlated thanks to date and time parameter with winds of the sector, easily identifiable thanks to a wind rose from MeteoFrance. Currents directions correspond to those of the winds and waves produced. Their directions seem to be affected by prevailing winds only on the first 20 cm (**Figure 14**).

**Figure 11.** *One of currents map possible.*

**Figure 12.** *Data directions untreated.*

**Figure 13.** *Frontier between lake and invasive plants.*

#### **Figure 14.**

*Wind rose of the directions from currents.*

Wind rose of currents in one point, taken from Parentis-Biscarrosse Lake gives evidence directions exiting inside lake and extracting from a current metre. Directions are oscillating inside water column, all day long but also any day (**Figure 15**).

Moreover, these directions on a step of 10 cm is significant to distinguish all movements inside the lakes despite the gales visible in **Figures 16** and **17**. A limit imposed by currents metre to constate that lakes are not calm and sleeping described in the literature.

**Figure 15.** *Currents direction.*

**Figure 16.** *Transect of speeds.*

## *3.3.2 Water movements speeds inside lakes*

Each current reveals a significant speed in cells detected by a current metre. Currents identified by the different measurement campaigns have speeds ranging from nearly 0.01 m per second to more than 4 m per second according to the wind (**Figure 17**).

As the previous figure shows speeds cells of currents, during a day without wind, in red, a tributary of Parentis-Biscarrosse that affects the entirety of the water column. The rest of the lake contains a lot of speeds in blocks that could be considered as a new typology of lake zonation.

Contrary to currents direction and homogeneity in changing, current speeds show irregularities because of gales.

With this graphic, the average speed is the same during all the period of measurement. Parentis-Biscarrosse Lake appears to be in a dynamic equilibrium situation at around a speed of 0.5 m per second, a speed corresponding to the value in metre per second of the largest tributary of the lake. Measurements over the month of June 2022 confirm this average balance at around 0.5 m per second average in this lake. Measurements on the lake, of similar genesis, Cazaux-Sanguinet, will they be able to confirm this hypothesis arises from the interpretation of the results of the lake of Parentis-Biscarrosse?

**Figure 17.** *Currents speeds graphic.*

Nevertheless, balance is here of several increases in the average speed in connection with gales exceeding 60 km per hour, over the few days of measurements.

Therefore, a concise assessment of water body dynamics can be achieved utilizing open-source GIS software, requiring no specialized equipment other than for current measurements. The outcomes generated through these distinct methodologies serve as a bridge between local stakeholders and the lakes, facilitating the guidance and planning of actions on these limnic territories.

## **4. Discussions**

These lakes seem to be full of vitality. Are they alive? And just as blood circulates in the human body, water circulates in the lakes, and in an almost random way but under the main effect of winds or rivers.

With these results, the findings obtained enable actors and managers of these lakes to comprehend most phenomena that impact their limnic territories. They can perceive these lakes or ponds as living systems, dependent on various mechanisms that require monitoring to ensure their proper functioning. Armed with this knowledge, each stakeholder can establish guidelines for the preservation of their activities. By analyzing dynamic movements of water and sediments within these water bodies, action plans can be devised to combat invasive plants and safeguard banks

and infrastructure. An improved understanding of these dynamics facilitates the anticipation of water body evolution. Based on this information, what measures will the stakeholders in these limnic territories undertake next?

That section on currents brings here, a lot of future evolution. Movement inside lakes are manifold but useful to manager of this lake. These currents can guide jobs for lake as new zonation to advantage some part rather than other?

Currents are permanent, but their direction is not dependable. Could these currents help human being to energetic transition?

This concise chapter awaits further completion with available information pertaining to the subject of these water bodies. It will soon be augmented with comprehensive lake data.

## **5. Conclusion**

This chapter presents a significant advancement in the integration of dynamic limnology by providing a diagnostic approach based on lake movements. It highlights the previously underemphasized dynamic aspects of water bodies, which have not received sufficient attention from managers due to the predominant focus on biocenosis. The inclusion of spatial criteria for dynamics now allows for a comprehensive consideration of the entire system, including human interactions, within the limnic territory. Through these studies, various lake users who previously overlooked the significance of movements occurring within these water bodies can now better comprehend the intricacies of the environment in which they operate. The understanding of erosion, sediment deposition, floods, invasive plant development, and other issues can be improved by incorporating dynamic criteria related to water and sediment movements. This dynamic perspective facilitates the creation of decisionsupport maps for stakeholders in their respective limnic areas. At the scale of water bodies, focusing on dynamics raises questions about the future evolution of these aquatic environments. Indeed, dynamic characteristics of a water body can vary from one region to another, as observed in these two lakes of similar origin and shape in the northern region of Landes, France. Therefore, this diagnostic approach warrants consideration for every water body due to its ease of implementation. It offers valuable insights and enhances management practices by facilitating a deeper understanding of these complex environments through the lens of lake dynamics.

## **Acknowledgements**

The thanks for this chapter go directly to the federation of municipalities of the Great Lakes (in the Landes, France) and all users or managers of these lakes. Of course, I thank university of Orleans, my thesis directors, and university Mont Blanc – Savoy to that opportunity to study misunderstood lakes movements with materials and knowledges.

*Science of Lakes – Multidisciplinary Approach*

## **Author details**

Maximilien Bernier EA 1210 CEDETE – Laboratory of Geography, University of Orleans, France

\*Address all correspondence to: maximilien.bernier@etu.univ-orleans.fr

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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[4] Choffel Q, Touchart L, Bartout P, Al DM. Le centre thermique, nouvel outil de compréhension du bilan thermique et de l'évolution spatio-temporelle de la température d'un étang? norois. 2018;**246**:57-73

[5] Bartout P, Touchart L. Le territoire limnique, une alternative à la gouvernance des plans d'eau par masses d'eau? vertigo. 2017;**17**:3. Disponible sur: http://journals.openedition.org/ vertigo/18692

[6] Grousset F. Chapitre 2 : Du climat du passé au climat du futur. In: Le Treut H. Les impacts du changement climatique en Aquitaine. Presses Universitaires de Bordeaux; 2013. pp. 41-60. Disponible sur: http://books.openedition.org/ pub/621

[7] Moreira S, Laplace-Treyture C, Eon M, Jan G. Rapport d'activité du suivi scientifique des plans d'eau de Carcans-Hourtin. Lacanau: Cazaux-Sanguinet et Parentis- Biscarrosse; 2015. p. 106

[8] Papon P, Maleval V, Nedjaï R. Le bilan sédimentaire en lac : l'influence de la course du vent sur l'érosion (Lake sedimentary balance : the fetch influence on the erosion). bagf. 2005;**82**(2):213-223 [9] Håkanson L, Jansson M. Principles of Lake Sedimentology; 2002. p. 316

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Section 3
