**3. Management issues for large river floodplains lake ecosystems**

At least four major disturbancing factors have been identified for alteration of ecosystem processes of the large river floodplains lakes worldwide. Resource managers are increasingly concerned about management issues of river regulation, land use activity, introduction of exotic species and rapid climate warming which have been considered to make significant impacts on large river floodplains lake ecosystem processes worldwide in recent decades.

#### **3.1 River regulation**

Water abstraction, diversion and regulations are one of critical management issues of floodplains lake ecosystems of river basins. Naturally occurring physical structures strongly support biodiversity of lakes. Natural flows are important for succession of food web structure and dynamics (Fig. 2). Physical structures enhance water quality, energy budget and flow regime of rivers. Improved water quality maintains the health of floodplain lakes. Interaction between channel morphology and river discharge in up-streams is important for structure and function of the downstream river ecosystems (Bunn & Arthington, 2002). For example, braided river channels in arid and semi-arid climates are characterised by a network of constantly shifting low sinuosity water courses while meandering river channels are influenced by channel width and depth with steady discharge (Johnston et al., 1997). The alteration of these river channels influences morphology consequently the habitat of a wide range of biota in the reaches which are significant source of energy transfer across the food web. For example, fish of the Orinoco River use the main channel primarily for migration and dispersal depends largely on floodplains for growth and subsistence (Lewis et al., 2000). Diversity and length of the food chains increase in natural flow regimes of many large river systems (Maddock et al., 2004). However, construction of dams, weirs and irrigation channels can have substantial implications for physical structures and riparian ecosystems (Walker, 1985). Such consequences can be immediate and obvious or gradual and subtle depending on the nature of regulation and the occurrence, diversity and composition of biota (Power et al., 1996).

Management Strategies for Large River Floodplain Lakes Undergoing Rapid Environmental Changes 333

332 International Perspectives on Global Environmental Change

(RCC), flood pulse and riverine productivity (RPM) models, where most of these models were tested in North America, Europe and Australia for understanding ecosystem processes of the large river systems (Vannote et al., 1980; Naiman et al., 1987; Junk et al., 1989; Thorpe & Delong, 1994). The case studies on critical management issues of rapid environmental changes of the large river basins were collated from various continents including the Yangtze River System, Asia (Yang et al., 2007; Chen et al., 2011), the Mississippi River System, North America (Wren et al., 2008), the Orinco, Salado and the Paraguay River Systems, South America (Lundberg et al., 1987; Claps et al., 2009), Orange-Vaal River System, South Africa (Ashton et al., 1986), Erbo River System, Europe (Gallardo et al., 2007) and the Murray Darling River System, Australia (Humphries et al., 1999; King et al., 2003). Following the identification of critical management issues of the large river systems, prevailing conditions of biotic assemblages in changes in large river floodplain lakes were reviewed from the case studies of Europe, North America and Australia (Fisher et al., 2000; Lewis et al., 2000). Then a comprehensive review was undertaken on the use of microcrustaceans to understand the complex ecosystem processes and configure effective management strategies when they are exposed to a range of external disturbances including

climate change over temporal and spatial scales.

recent decades.

**3.1 River regulation** 

**3. Management issues for large river floodplains lake ecosystems** 

At least four major disturbancing factors have been identified for alteration of ecosystem processes of the large river floodplains lakes worldwide. Resource managers are increasingly concerned about management issues of river regulation, land use activity, introduction of exotic species and rapid climate warming which have been considered to make significant impacts on large river floodplains lake ecosystem processes worldwide in

Water abstraction, diversion and regulations are one of critical management issues of floodplains lake ecosystems of river basins. Naturally occurring physical structures strongly support biodiversity of lakes. Natural flows are important for succession of food web structure and dynamics (Fig. 2). Physical structures enhance water quality, energy budget and flow regime of rivers. Improved water quality maintains the health of floodplain lakes. Interaction between channel morphology and river discharge in up-streams is important for structure and function of the downstream river ecosystems (Bunn & Arthington, 2002). For example, braided river channels in arid and semi-arid climates are characterised by a network of constantly shifting low sinuosity water courses while meandering river channels are influenced by channel width and depth with steady discharge (Johnston et al., 1997). The alteration of these river channels influences morphology consequently the habitat of a wide range of biota in the reaches which are significant source of energy transfer across the food web. For example, fish of the Orinoco River use the main channel primarily for migration and dispersal depends largely on floodplains for growth and subsistence (Lewis et al., 2000). Diversity and length of the food chains increase in natural flow regimes of many large river systems (Maddock et al., 2004). However, construction of dams, weirs and irrigation channels can have substantial implications for physical structures and riparian ecosystems (Walker, 1985). Such consequences can be immediate and obvious or gradual and subtle depending on the nature of

regulation and the occurrence, diversity and composition of biota (Power et al., 1996).

Fig. 2. Free flowing rivers consist of series of rapids and slow flowing stretches. Rapids are important for succession of food web structure and dynamics. Naturally occurring physical structures enhance water quality, energy budget and flow regime of the river. Improved water quality maintains the health of riverine floodplain lake ecosystems. In impounded rivers, rapids have been removed by erected dams. Dams can have direct implications on hydrology reducing the downstream flow variation. Dams hinder the upstream migration of biota, alter thermal environment, nutrient movement and sediment loading and predatorprey interaction in downstream food webs (adapted after Nilsson & Berggren, 2000).

Regulation of the Murray River, Australia over the past 50 years has resulted in considerable implications for ecosystem structure and functions. For example, construction of dams in the Murray River has reduced downstream flows as well as obstructed upstream migration of biota including thermal environment, nutrient movement and sediment loading and predator-prey interactions (Gehrke & Harris, 2000). Since flooding generates biogeochemical processes, the major impact of dams is the interruption of the exchange of energy between river and riparian zone during flood events (Sam et al., 2000). Low flows events are critical for lowland fish assemblages and plant community structure (Capon, 2003). Increased water residence time increases crustacean biomass (Humphries et al., 1999). However, alternation of natural low flow patterns can influence diadromous fish populations which utilize crustaceans as their major diet. Fish species such as Murray cod (*Maccullochella peelii peelii*) and silver perch (*Bidyanus bidyanus)* which do not require special flood events in the Murray River Australia is able to utilize low-flows events for spawning (King et al., 2003. However, the growth of larvae of Murray cod (*M. peelii peelii)* is significantly influenced by construction of dams and irrigation channels across the MDB. Larvae are consistently stranding in the dam when drifting (Koehn & Harrington, 2005). In contrast, recruitment of other fish species requires floodplain inundation and increased water volume (King et al., 2003).

Alteration of riparian vegetation can influence nutrient sources of wetland biota. Composition and diversity of naturally occurring riparian forests such as river red gum trees (*Eucalyptus camaldulensis*) in MDB have declined as a result of river regulation (Robertson et al., 2001). For example, stable isotope ratios of oxygen reveal that river red gum (*E. camaldulensis*) forests are efficient for utilizing water at varying salinity gradients (Mensforth et al., 1994) through reduced transpiration rates (Costelloe et al., 2008). However, continued low flows occur as a result of a rise in ground water salinity. Absence of natural floods influences recharge of naturally occurring groundwater salinity levels and will have detrimental effects on floodplains riparian biota (Jolly et al., 2001). Die back in

Management Strategies for Large River

Floodplain Lakes Undergoing Rapid Environmental Changes 335

Continuous use of nitrogen and phosphorous as fertilizers in agriculture and urban landscapes lead to leaking of mobile inorganic nitrate ions in the system (Turner et al. 2003). As a result of algal blooms and low dissolved oxygen at nutrient rich environment, wetland ecosystem health has reduced substantially. Widespread release of phosphorous into the Yangtze River floodplain lakes over the past decades, for example, has caused a regime shift, where a transformation has occurred in large number of lakes with macrophyte dominated states to algal dominated states (Yang et al., 2007). Although some disturbances are beneficial to habitat heterogeneity and species, the lack of disturbance events have negative impacts on these lakes. For example, the Oxbow Lake of the Middle Erbo River (Spain) and Bottle Bend Lagoon of the Murray River (Australia) are reported to have undergone increased salinisation and eutrophication followed by a loss of biodiversity as a

Land use activity has also exacerbated the release of a range of toxic substances in large river floodplain lakes. Trace metals (e.g., Hg, Pb, Zn), persistent organic pollutants (POPs), and organometallic compounds are detrimental for ecosystem health. Polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), polychlorinated dibenzo-pdioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) as well as many other organochlorine pesticides (e.g. DDTs; taxophene) and brominated flame retardants (BFRs; including polybrominated diphenyl ethers (PBDEs) can be lethal for wetland biota if their concentration is high in the system. The organometallic compound, such as methylmercury (MeHg) is the most toxic compound (Leung et al., 2007). Following the industrial revolution in Europe (1800 AD), wetland contamination by organochlorine compounds increased substantially. The DDT concentrations for example in lake sediments were the highest during the 1950s. Boating activity in floodplain lakes has influenced substantially for estuarine biota in the large river mouths as well as mollusc communities in freshwater environments due to increased organometallic toxicity (US-EPA, 2003). Methylmercury, for example although present in a small concentration (0.1-5.0 percent) of total mercury, it represents 90-100% in invertebrates and fish. Increased POPs, PCBs and PAHs toxicity can cause endocrine disruption in fish and crustaceans (Matthiessen & Johnson, 2007). The tributyl tin (TBT) can cause reproductive failure in *Daphnia* at 400 ng L-1 and 380 ng L-1 TBT levels (Brooke et al., 1986). Macrophyte density in lowland shallow river floodplain wetlands in the UK substantially reduced in the sixties as a result of recreational boating

Introduction of exotic flora and fauna is another significant management issue of the large river floodplain lake ecosystems worldwide. Displacement of habitats and subsequent extinction of native populations are reported as some of the foremost impacts of introduced species in many large river floodplain lakes. River basins of the Northern Hemisphere inhabit the highest number of non-native fish species (Leprieur et al., 2008). More than 50% of the biota of the Hudson River in the USA comprises introduced species mostly from Europe where 10% of those populations have significant ecological impacts on native populations (Nilsson & Berggren, 2000). Human activities are blamed to facilitate the establishment of non-native species by disturbing natural landscapes and by increasing propagule pressures on native populations (Leprieur et al., 2008; Simões et

result of land use change (Lamontagne et al. 2006; Gallardo et al., 2007).

followed by TBT pollution (Sayer et al., 2006).

**3.3 Introduction of exotic species** 

al., 2009).

river red gum (*E. camaldulensis*) communities can occur at electrical conductivity as high as 40dSm-1 (Mensforth et al., 1994). Substantial buffering of catchment soils as a result of river regulation and subsequent release of sulphur in floodplains following the European settlements has influenced on diatom communities in the Lower Murray River (Gell et al., 2007). Irrigation of soils with low permeability is also causing saline groundwater to rise. Salt accumulates in the top soil as water continues to evaporate. Partial drying of previously inundated floodplains reduce nutrient availability such as total nitrogen (TN) and total phosphorous (TP) in the system causing negative effects on ecosystem functioning (Baldwin & Mitchell, 2000). Irrigation dams in the previously fertile Indus River floodplain (Pakistan) are also reported to have caused a massive salinity problem. Extensive abstraction of water from the Amu Dar'ya and Syr Dar'ya, the two largest tributaries of the Aral Sea has caused 80% reduction of the water volume in the Aral Sea within the last four decades resulting in a four-fold increase in salinity concentrations of the floodplain lake consequently limiting ecosystem structure and functions (Aladin & Plotnikov, 1993).

#### **3.2 Land use**

Increased land use activity across the catchment of the large river system is other significant management issue. Ecological attributes of large river floodplain lakes have been constantly modified by industrial and cultural developments. Modern farming practices have made implications for physical and hydrological features of floodplain wetlands including the changes in water quality and sediment processes. Wren et al. (2008) reported that the sediment accumulation rates of the Sky Lake in the Mississippi River system, USA has increased to 50-folds following the clearing of forests began by humans in 300 years ago. In natural flood pulse concept, river floodplains are regularly flooded and dried (Bayley, 1995). Catchment organic matter generated across spatial and temporal scales is transported to river floodplains. A high turnover rate of organic matter and nutrients are predicted to occur as a result of natural flood events. During flood events, nutrients dissolve with flood waters consequently accelerating primary production. However, under dry conditions, decomposition processes of floodplain lakes would increase relative to production. Intensification of land use including waste disposal, agriculture, grazing and forest clearance in catchments all have considerable implications for natural flood pulse events (Jansen & Robertson, 2001).

Large river floodplain wetlands are species rich habitats which connect distant ecosystem not only through the migration of river biota but also from the transport of water, sediments, nutrients and contaminants (Sparks, 1995; Fisher et al., 2000, Chen et al., 2011). The integrity of floodplain lakes, which is maintained by hydrological dynamics, biological productivity and river connectivity are significantly impeded by land use activity. Alteration in riparian vegetation in particular is detrimental for changes in species diversity and ecosystem functioning of floodplain lakes. For example, alteration of the natural riparian vegetation by humans has modified the ecosystem processes of the wetlands and its catchments across the Sacromento, USA. Modification of wetland landscape has already been noticed as a result of cultivation, soil erosion and sedimentation to down-streams and in many cases loss of productivity has also occurred (Alpert et al., 1999).

Application of nitrogen and phosphorous has increased for agriculture across the large river basins worldwide. An alteration in global nitrogen cycle has occurred in recent years by widespread use of N-fixing crops, fertilizers, habitat change and burning of fossil fuels.

river red gum (*E. camaldulensis*) communities can occur at electrical conductivity as high as 40dSm-1 (Mensforth et al., 1994). Substantial buffering of catchment soils as a result of river regulation and subsequent release of sulphur in floodplains following the European settlements has influenced on diatom communities in the Lower Murray River (Gell et al., 2007). Irrigation of soils with low permeability is also causing saline groundwater to rise. Salt accumulates in the top soil as water continues to evaporate. Partial drying of previously inundated floodplains reduce nutrient availability such as total nitrogen (TN) and total phosphorous (TP) in the system causing negative effects on ecosystem functioning (Baldwin & Mitchell, 2000). Irrigation dams in the previously fertile Indus River floodplain (Pakistan) are also reported to have caused a massive salinity problem. Extensive abstraction of water from the Amu Dar'ya and Syr Dar'ya, the two largest tributaries of the Aral Sea has caused 80% reduction of the water volume in the Aral Sea within the last four decades resulting in a four-fold increase in salinity concentrations of the floodplain lake consequently limiting

Increased land use activity across the catchment of the large river system is other significant management issue. Ecological attributes of large river floodplain lakes have been constantly modified by industrial and cultural developments. Modern farming practices have made implications for physical and hydrological features of floodplain wetlands including the changes in water quality and sediment processes. Wren et al. (2008) reported that the sediment accumulation rates of the Sky Lake in the Mississippi River system, USA has increased to 50-folds following the clearing of forests began by humans in 300 years ago. In natural flood pulse concept, river floodplains are regularly flooded and dried (Bayley, 1995). Catchment organic matter generated across spatial and temporal scales is transported to river floodplains. A high turnover rate of organic matter and nutrients are predicted to occur as a result of natural flood events. During flood events, nutrients dissolve with flood waters consequently accelerating primary production. However, under dry conditions, decomposition processes of floodplain lakes would increase relative to production. Intensification of land use including waste disposal, agriculture, grazing and forest clearance in catchments all have considerable implications for natural flood pulse events

Large river floodplain wetlands are species rich habitats which connect distant ecosystem not only through the migration of river biota but also from the transport of water, sediments, nutrients and contaminants (Sparks, 1995; Fisher et al., 2000, Chen et al., 2011). The integrity of floodplain lakes, which is maintained by hydrological dynamics, biological productivity and river connectivity are significantly impeded by land use activity. Alteration in riparian vegetation in particular is detrimental for changes in species diversity and ecosystem functioning of floodplain lakes. For example, alteration of the natural riparian vegetation by humans has modified the ecosystem processes of the wetlands and its catchments across the Sacromento, USA. Modification of wetland landscape has already been noticed as a result of cultivation, soil erosion and sedimentation to down-streams and

Application of nitrogen and phosphorous has increased for agriculture across the large river basins worldwide. An alteration in global nitrogen cycle has occurred in recent years by widespread use of N-fixing crops, fertilizers, habitat change and burning of fossil fuels.

in many cases loss of productivity has also occurred (Alpert et al., 1999).

ecosystem structure and functions (Aladin & Plotnikov, 1993).

**3.2 Land use** 

(Jansen & Robertson, 2001).

Continuous use of nitrogen and phosphorous as fertilizers in agriculture and urban landscapes lead to leaking of mobile inorganic nitrate ions in the system (Turner et al. 2003). As a result of algal blooms and low dissolved oxygen at nutrient rich environment, wetland ecosystem health has reduced substantially. Widespread release of phosphorous into the Yangtze River floodplain lakes over the past decades, for example, has caused a regime shift, where a transformation has occurred in large number of lakes with macrophyte dominated states to algal dominated states (Yang et al., 2007). Although some disturbances are beneficial to habitat heterogeneity and species, the lack of disturbance events have negative impacts on these lakes. For example, the Oxbow Lake of the Middle Erbo River (Spain) and Bottle Bend Lagoon of the Murray River (Australia) are reported to have undergone increased salinisation and eutrophication followed by a loss of biodiversity as a result of land use change (Lamontagne et al. 2006; Gallardo et al., 2007).

Land use activity has also exacerbated the release of a range of toxic substances in large river floodplain lakes. Trace metals (e.g., Hg, Pb, Zn), persistent organic pollutants (POPs), and organometallic compounds are detrimental for ecosystem health. Polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), polychlorinated dibenzo-pdioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) as well as many other organochlorine pesticides (e.g. DDTs; taxophene) and brominated flame retardants (BFRs; including polybrominated diphenyl ethers (PBDEs) can be lethal for wetland biota if their concentration is high in the system. The organometallic compound, such as methylmercury (MeHg) is the most toxic compound (Leung et al., 2007). Following the industrial revolution in Europe (1800 AD), wetland contamination by organochlorine compounds increased substantially. The DDT concentrations for example in lake sediments were the highest during the 1950s. Boating activity in floodplain lakes has influenced substantially for estuarine biota in the large river mouths as well as mollusc communities in freshwater environments due to increased organometallic toxicity (US-EPA, 2003). Methylmercury, for example although present in a small concentration (0.1-5.0 percent) of total mercury, it represents 90-100% in invertebrates and fish. Increased POPs, PCBs and PAHs toxicity can cause endocrine disruption in fish and crustaceans (Matthiessen & Johnson, 2007). The tributyl tin (TBT) can cause reproductive failure in *Daphnia* at 400 ng L-1 and 380 ng L-1 TBT levels (Brooke et al., 1986). Macrophyte density in lowland shallow river floodplain wetlands in the UK substantially reduced in the sixties as a result of recreational boating followed by TBT pollution (Sayer et al., 2006).

#### **3.3 Introduction of exotic species**

Introduction of exotic flora and fauna is another significant management issue of the large river floodplain lake ecosystems worldwide. Displacement of habitats and subsequent extinction of native populations are reported as some of the foremost impacts of introduced species in many large river floodplain lakes. River basins of the Northern Hemisphere inhabit the highest number of non-native fish species (Leprieur et al., 2008). More than 50% of the biota of the Hudson River in the USA comprises introduced species mostly from Europe where 10% of those populations have significant ecological impacts on native populations (Nilsson & Berggren, 2000). Human activities are blamed to facilitate the establishment of non-native species by disturbing natural landscapes and by increasing propagule pressures on native populations (Leprieur et al., 2008; Simões et al., 2009).

Management Strategies for Large River

energy balance in the system (Dunlop & Brown, 2008).

2003).

ecosystems.

**floodplain lakes** 

Floodplain Lakes Undergoing Rapid Environmental Changes 337

fish populations such as golden perch (*Macquaria ambigua ambigua*) are significantly altered

Climate change influences nutrient concentrations in floodplain lakes (Spink et al., 1998). Elementary nitrogen level and biogeochemical cycles in sediments can vary with climate warming (Catalan et al., 2002). In drought phase, sulphur stored in the upper areas of the littoral zone can re-oxidise causing lakes and river floodplains in down-streams to re-acidify (e.g., Yan et al., 1996; Dillion & Lazerte, 1992). Rising temperature, longer dry spells and runoff distribution in the MDB for example have intensified vegetation patterning and concentration of dryland salinity in recent decade (Hughes, 2003). When soil with rich sulphides (or 'black ooze') characteristic of dark and soft are disturbed and oxygenated, they react rapidly resulting in environmental hazards floodplains systems (Lamontagne et al.,

Climate warming can influence growth and reproduction as well as phenology of wetlands biota directly (Hughes, 2003). Increased concentration of atmospheric CO2 intensifies photosynthetic processes of riparian trees. The leaf stomatal conductance of these trees decreases and the plant-water use efficiency increases in elevated CO2. However, productivity of plant biomass at high level of CO2 is short-lasted resulting in changes in

Whist we have identified some key management issues of the large river floodplains lake ecosystems, the next step is to find appropriate solutions for these problems. There are a range of management options available, our aim is however, how we can understand and best interpret the ecosystem processes of the floodplain lakes that are exposed to anthropogenic and climatic variability and can guide resource mangers using the best management strategy. Understanding of changes in assemblages and diversity of wetlands biota, particularly micro-crustaceans along temporal and spatial scales is one of potential tools that provides prevailing conditions of changing large river floodplains lake

**4. Prevailing conditions of biotic assemblages in changing large river** 

The structure of micro- and macro- invertebrate communities is dependent on factors such as water quality (e.g. nutrients salinity, pH), food resources and habitat availability. Oligotrophic (low nutrient) conditions may limit primary production, thereby limiting a key food resource (i.e. phytoplankton) for some functional groups of invertebrates (Jeppesen et al., 2000). Eutrophic (high nutrient) conditions, high temperature and stable (e.g. stratified and poorly mixed) water bodies may favour key phytoplankton groups (i.e. cyanobacteria) that are a poor quality food resources for micro-invertebrates (Jeppesen et al., 2000). Furthermore, some functional groups of invertebrates feed exclusively on either phytoplankton or macrophytes. Consequently, shifts between macrophyte and phytoplankton dominated states will lead to shifts in the composition of micro- and macroinvertebrate communities (Jeppesen et al., 2002). Changes in water column salinity may also substantially influence the composition of the micro-and macro-invertebrate community due to differences in species-specific salinity tolerances. Furthermore, it is considered highly likely that changes in soil salinity (Brock et al., 2005) or soil pH (Hall & Baldwin, 2006) may severely impact the viability of invertebrate seed banks within wetland/floodplain soils. It is also recognised that the viability of invertebrate seed banks decreases with time (Nielsen

as a result of climate-induced low flow events in the MDB (Humphries et al., 1999).

Large river floodplain lakes are increasingly sensitive to biological invasion. The extended river networks often have recurrent disturbances and enhanced invasion (Elvira, 1995; Mills et al., 1996). Dispersal of seeds and eggs are rapid at landscape level through river channel networks. Disturbance regime and floodplain productivity also enhance invasion (Chapin III et al., 2000). Non-native species once introduced in large river systems can spread rapidly (Koehn, 2004). Favouring wide ranging climates, flexible in habitat selection and increased physiological adaptation are characteristic features of non-native species for a successful colonisation in a new environment (Mooney & Cleland, 2001). Whilst the impacts of invasion on native populations has been increasing, what condition is necessary for invasion, the way the invasion progresses through space and time and the properties of invasive biota is yet to be understood fully. Under regulated environments these patterns have become pronounced, and the nature of the invading species in susceptible habitats is also becoming unpredictable (Bunn & Arthington, 2002). For example, water regulation in one of the South African large river systems (Orange-Vaal River System) has stabilized the natural flow regimes favouring the alien aquatic vegetation (e.g. *Myriophyllum* sp, *Azolla* sp) consequently reducing the water movement, light penetration and oxygenation followed by displacing the native vegetation bed (Ashton at al., 1986). Introduced fish species such as European perch (*Perca fluviatilis*) and common carp (*Cyprinus carpio*) in the Murray River Australia have successfully established populations following the European arrival causing retarded growth and development of native fish populations (Koehn, 2004). Some endemic species including Macquarie perch (*Macquaria australasica*) Murray hardyhead (*Craterocephalus fluviatilis*) and Murray cod (*M. peelii peelii*) have become critically endangered or vulnerable in recent decades (Hutchison & Armstrong, 1993).

#### **3.4 Climate change**

Rapid rate of climate warming in recent decades has become one of important management issues of large river floodplain lake ecosystems. Climate change can cause floodplain lakes ecosystems through a variety of ways such as alteration of flood events, channel morphology, nutrient dynamics and growth and reproduction of wetland and riparian biota.

Floods are essential for nutrient dynamics, primary and secondary production and growth and development of native plant and animals (Harris & Gehrke, 1993). Regular inundation provides water for riparian vegetation and continuation of ecosystem processes (Nilsson & Berggren, 2000). Runoff with organic rich nutrients create potential for the establishment of a new community. Recovery of riparian catchments after flood or drought is rapid and the diversity and abundance of flora and fauna increase substantially within a short period (Jenkins & Boulton, 2003). However, climate warming reduces annual inflows and runoff volume of the large river systems. Climate change also alters river channels, erosion, nutrient and sediment transports influencing terrestrial vegetation, soil moisture and evapotranspiration processes in large river floodplains lakes (Palmer et al., 2008). Holocene records of floodplains in the USA show that magnitude of floods is intense in arid regions resulting in channel widening which often have sparse riparian vegetation (Carpenter et al., 1992). In Murray River, a rise of 1 C in recent decades is predicted to have caused approximately 15% reduction in the annual flows (Cai & Cowan, 2008). Since 1950s, the MDB has experienced warming of around 0.8 C with declining rainfall as low as 10 mm per decade resulting in degraded water quality across the region. Important flood-cued native

Large river floodplain lakes are increasingly sensitive to biological invasion. The extended river networks often have recurrent disturbances and enhanced invasion (Elvira, 1995; Mills et al., 1996). Dispersal of seeds and eggs are rapid at landscape level through river channel networks. Disturbance regime and floodplain productivity also enhance invasion (Chapin III et al., 2000). Non-native species once introduced in large river systems can spread rapidly (Koehn, 2004). Favouring wide ranging climates, flexible in habitat selection and increased physiological adaptation are characteristic features of non-native species for a successful colonisation in a new environment (Mooney & Cleland, 2001). Whilst the impacts of invasion on native populations has been increasing, what condition is necessary for invasion, the way the invasion progresses through space and time and the properties of invasive biota is yet to be understood fully. Under regulated environments these patterns have become pronounced, and the nature of the invading species in susceptible habitats is also becoming unpredictable (Bunn & Arthington, 2002). For example, water regulation in one of the South African large river systems (Orange-Vaal River System) has stabilized the natural flow regimes favouring the alien aquatic vegetation (e.g. *Myriophyllum* sp, *Azolla* sp) consequently reducing the water movement, light penetration and oxygenation followed by displacing the native vegetation bed (Ashton at al., 1986). Introduced fish species such as European perch (*Perca fluviatilis*) and common carp (*Cyprinus carpio*) in the Murray River Australia have successfully established populations following the European arrival causing retarded growth and development of native fish populations (Koehn, 2004). Some endemic species including Macquarie perch (*Macquaria australasica*) Murray hardyhead (*Craterocephalus fluviatilis*) and Murray cod (*M. peelii peelii*) have become critically

endangered or vulnerable in recent decades (Hutchison & Armstrong, 1993).

Rapid rate of climate warming in recent decades has become one of important management issues of large river floodplain lake ecosystems. Climate change can cause floodplain lakes ecosystems through a variety of ways such as alteration of flood events, channel morphology, nutrient dynamics and growth and reproduction of wetland and riparian

Floods are essential for nutrient dynamics, primary and secondary production and growth and development of native plant and animals (Harris & Gehrke, 1993). Regular inundation provides water for riparian vegetation and continuation of ecosystem processes (Nilsson & Berggren, 2000). Runoff with organic rich nutrients create potential for the establishment of a new community. Recovery of riparian catchments after flood or drought is rapid and the diversity and abundance of flora and fauna increase substantially within a short period (Jenkins & Boulton, 2003). However, climate warming reduces annual inflows and runoff volume of the large river systems. Climate change also alters river channels, erosion, nutrient and sediment transports influencing terrestrial vegetation, soil moisture and evapotranspiration processes in large river floodplains lakes (Palmer et al., 2008). Holocene records of floodplains in the USA show that magnitude of floods is intense in arid regions resulting in channel widening which often have sparse riparian vegetation (Carpenter et al., 1992). In Murray River, a rise of 1 C in recent decades is predicted to have caused approximately 15% reduction in the annual flows (Cai & Cowan, 2008). Since 1950s, the MDB has experienced warming of around 0.8 C with declining rainfall as low as 10 mm per decade resulting in degraded water quality across the region. Important flood-cued native

**3.4 Climate change** 

biota.

fish populations such as golden perch (*Macquaria ambigua ambigua*) are significantly altered as a result of climate-induced low flow events in the MDB (Humphries et al., 1999).

Climate change influences nutrient concentrations in floodplain lakes (Spink et al., 1998). Elementary nitrogen level and biogeochemical cycles in sediments can vary with climate warming (Catalan et al., 2002). In drought phase, sulphur stored in the upper areas of the littoral zone can re-oxidise causing lakes and river floodplains in down-streams to re-acidify (e.g., Yan et al., 1996; Dillion & Lazerte, 1992). Rising temperature, longer dry spells and runoff distribution in the MDB for example have intensified vegetation patterning and concentration of dryland salinity in recent decade (Hughes, 2003). When soil with rich sulphides (or 'black ooze') characteristic of dark and soft are disturbed and oxygenated, they react rapidly resulting in environmental hazards floodplains systems (Lamontagne et al., 2003).

Climate warming can influence growth and reproduction as well as phenology of wetlands biota directly (Hughes, 2003). Increased concentration of atmospheric CO2 intensifies photosynthetic processes of riparian trees. The leaf stomatal conductance of these trees decreases and the plant-water use efficiency increases in elevated CO2. However, productivity of plant biomass at high level of CO2 is short-lasted resulting in changes in energy balance in the system (Dunlop & Brown, 2008).

Whist we have identified some key management issues of the large river floodplains lake ecosystems, the next step is to find appropriate solutions for these problems. There are a range of management options available, our aim is however, how we can understand and best interpret the ecosystem processes of the floodplain lakes that are exposed to anthropogenic and climatic variability and can guide resource mangers using the best management strategy. Understanding of changes in assemblages and diversity of wetlands biota, particularly micro-crustaceans along temporal and spatial scales is one of potential tools that provides prevailing conditions of changing large river floodplains lake ecosystems.

### **4. Prevailing conditions of biotic assemblages in changing large river floodplain lakes**

The structure of micro- and macro- invertebrate communities is dependent on factors such as water quality (e.g. nutrients salinity, pH), food resources and habitat availability. Oligotrophic (low nutrient) conditions may limit primary production, thereby limiting a key food resource (i.e. phytoplankton) for some functional groups of invertebrates (Jeppesen et al., 2000). Eutrophic (high nutrient) conditions, high temperature and stable (e.g. stratified and poorly mixed) water bodies may favour key phytoplankton groups (i.e. cyanobacteria) that are a poor quality food resources for micro-invertebrates (Jeppesen et al., 2000). Furthermore, some functional groups of invertebrates feed exclusively on either phytoplankton or macrophytes. Consequently, shifts between macrophyte and phytoplankton dominated states will lead to shifts in the composition of micro- and macroinvertebrate communities (Jeppesen et al., 2002). Changes in water column salinity may also substantially influence the composition of the micro-and macro-invertebrate community due to differences in species-specific salinity tolerances. Furthermore, it is considered highly likely that changes in soil salinity (Brock et al., 2005) or soil pH (Hall & Baldwin, 2006) may severely impact the viability of invertebrate seed banks within wetland/floodplain soils. It is also recognised that the viability of invertebrate seed banks decreases with time (Nielsen

Management Strategies for Large River

functioning section of the river (Fisher et al., 2000).

**ecosystems: Role of micro-crustaceans** 

**5.1 Management of food web** 

mid-summer (Pease et al., 2006).

Floodplain Lakes Undergoing Rapid Environmental Changes 339

As a result, water quality of the adjacent wetlands will change following the flood inundation, consequently diversifying the biotic and abiotic assemblages across the wetland (Lewis et al., 2000). For example, in Missouri River floodplain wetlands, alteration of river corridor is reported to have reduced flood pulses significantly. As a result of the absence of flood pulses, micro-crustaceans such as copepod and *Bosmina* showed a strong sensitivity to basic habitat characteristics during and after the flood events within the naturally

A comprehensive understanding of the large river floodplains lake ecosystems can only help configure effective management strategies. Information regarding diversity and assemblages of micro-crustaceans across temporal and spatial scales is useful for understanding degraded floodplains lake ecosystems and water quality. Changes in assemblages of micro-crustaceans at particular time can provide disturbances caused by external forces such as climate change, invasive species and anthropogenic release of

Assemblage structure of micro-crustaceans such as cladoceran zooplankton across temporal and spatial scales of large river floodplains lakes can help resource managers for understanding the drivers of ecosystem changes and configuring a range of management strategies. Below how the information obtained from micro-crustaceans are useful to

Understanding of temporal and spatial changes in diversity, composition and abundances of micro-crustacean assemblages are useful for sustainable ecosystem management in large river floodplain lakes. Seasonal production of autochthonous carbon (algae, macrophytes) and inputs derived from the riparian catchments help functioning of floodplains lake ecosystems (Thorpe & Delong, 1994; Lewis et al., 2000). The carbon derived from the riparian system is assimilated by micro-invertebrates supporting the higher trophic levels in food web. However, the degree of energy assimilation by micro-crustaceans in lacustrine food web is less understood. The physical transport of materials to biological transformation to carbon in floodplains lakes varies substantially due to alteration of river flows (Walker et al., 1995). Micro-crustaceans serve as an important role during energy transfer across the trophic levels. For example, in an arid river, Rio Grande (New Mexico, USA), recruitment of some fish occurred during high flows (spring), whereas other fish recruited during lowflows (late summer). Micro-habitats with low current velocity and high temperature were vital nursery grounds for the Rio Grande fishes. Stable isotope analyses of carbon revealed that the Rio Grande fish larvae would obtain carbon predominately from algal production in early summer, but would use organic carbon derived from emergent macrophytes when river discharge would decrease in mid-summer. The shift in carbon assimilation was facilitated by micro-invertebrates that reduced edible algae switching to macrophytes in

Some species of cladocerans have responded to flood events in the Orinoco River floodplain lakes in Venezuela by showing a varying birth, death and population rates (Twombly & Lewis, 1989). In these floodplain lakes, birth rates increase at a time of flood inundation

nutrients into the systems and help resource mangers to mitigate these problems.

**5. Configuring management strategies of large river floodplain lake** 

manage floodplains lake ecosystem is comprehensively discussed.

et al., 2007). Long (i.e. >10 years) dry periods may exceed the viability period, severely compromising the invertebrate community that will hatch from soil seed banks during subsequent floods (Williams, 1985).

However, the variety of conditions among floodplains lake biota at any given time is largely dependent on system processes of the river basin. Abundance and diversity of microcrustaceans can change with the initial condition of the basin morphometry, where setpoints are determined by flood inundation (Fig. 3). The ecosystem of large river floodplain lakes adjacent to the large river is primarily influenced by its position, how far the lake is situated from the river, and how long the inundation is lasted for (Lewis et al., 2000).

Fig. 3. Causes of the variation in the assemblages of wetland biota including microcrustaceans, and abiotic composition amongst large river floodplain lakes. Setpoint at the time of inundation (upper diagram) is determined by position of adjacent lakes distributed within the c. 600 km of the floodplain; setpoint following the inundation (lower diagram) is determined by basin morphology (adapted after Lewis et al., 2000).

et al., 2007). Long (i.e. >10 years) dry periods may exceed the viability period, severely compromising the invertebrate community that will hatch from soil seed banks during

However, the variety of conditions among floodplains lake biota at any given time is largely dependent on system processes of the river basin. Abundance and diversity of microcrustaceans can change with the initial condition of the basin morphometry, where setpoints are determined by flood inundation (Fig. 3). The ecosystem of large river floodplain lakes adjacent to the large river is primarily influenced by its position, how far the lake is situated from the river, and how long the inundation is lasted for (Lewis et al., 2000).

Fig. 3. Causes of the variation in the assemblages of wetland biota including microcrustaceans, and abiotic composition amongst large river floodplain lakes. Setpoint at the time of inundation (upper diagram) is determined by position of adjacent lakes distributed within the c. 600 km of the floodplain; setpoint following the inundation (lower diagram) is

determined by basin morphology (adapted after Lewis et al., 2000).

subsequent floods (Williams, 1985).

As a result, water quality of the adjacent wetlands will change following the flood inundation, consequently diversifying the biotic and abiotic assemblages across the wetland (Lewis et al., 2000). For example, in Missouri River floodplain wetlands, alteration of river corridor is reported to have reduced flood pulses significantly. As a result of the absence of flood pulses, micro-crustaceans such as copepod and *Bosmina* showed a strong sensitivity to basic habitat characteristics during and after the flood events within the naturally functioning section of the river (Fisher et al., 2000).

A comprehensive understanding of the large river floodplains lake ecosystems can only help configure effective management strategies. Information regarding diversity and assemblages of micro-crustaceans across temporal and spatial scales is useful for understanding degraded floodplains lake ecosystems and water quality. Changes in assemblages of micro-crustaceans at particular time can provide disturbances caused by external forces such as climate change, invasive species and anthropogenic release of nutrients into the systems and help resource mangers to mitigate these problems.

### **5. Configuring management strategies of large river floodplain lake ecosystems: Role of micro-crustaceans**

Assemblage structure of micro-crustaceans such as cladoceran zooplankton across temporal and spatial scales of large river floodplains lakes can help resource managers for understanding the drivers of ecosystem changes and configuring a range of management strategies. Below how the information obtained from micro-crustaceans are useful to manage floodplains lake ecosystem is comprehensively discussed.

#### **5.1 Management of food web**

Understanding of temporal and spatial changes in diversity, composition and abundances of micro-crustacean assemblages are useful for sustainable ecosystem management in large river floodplain lakes. Seasonal production of autochthonous carbon (algae, macrophytes) and inputs derived from the riparian catchments help functioning of floodplains lake ecosystems (Thorpe & Delong, 1994; Lewis et al., 2000). The carbon derived from the riparian system is assimilated by micro-invertebrates supporting the higher trophic levels in food web. However, the degree of energy assimilation by micro-crustaceans in lacustrine food web is less understood. The physical transport of materials to biological transformation to carbon in floodplains lakes varies substantially due to alteration of river flows (Walker et al., 1995). Micro-crustaceans serve as an important role during energy transfer across the trophic levels. For example, in an arid river, Rio Grande (New Mexico, USA), recruitment of some fish occurred during high flows (spring), whereas other fish recruited during lowflows (late summer). Micro-habitats with low current velocity and high temperature were vital nursery grounds for the Rio Grande fishes. Stable isotope analyses of carbon revealed that the Rio Grande fish larvae would obtain carbon predominately from algal production in early summer, but would use organic carbon derived from emergent macrophytes when river discharge would decrease in mid-summer. The shift in carbon assimilation was facilitated by micro-invertebrates that reduced edible algae switching to macrophytes in mid-summer (Pease et al., 2006).

Some species of cladocerans have responded to flood events in the Orinoco River floodplain lakes in Venezuela by showing a varying birth, death and population rates (Twombly & Lewis, 1989). In these floodplain lakes, birth rates increase at a time of flood inundation

Management Strategies for Large River

**Riparian vegetation/littoral macrophytes** 

**Increased C and N production** 

**Increased growth of benthic zooplankton/micro-crustaceans** 

**Less erosion/increased water clarity** 

**Increased trophic levels/ fish populations** 

**Strong food web structure and dynamics** 

**5.2.1 Phosphorous (P) and nitrogen (N) management** 

Box 1.

(Turner & Rabalais, 2003).

Floodplain Lakes Undergoing Rapid Environmental Changes 341

system was a result of land use intensification following the European arrival. An increased grazing pressure by zooplankton on large algae resulted in increased smaller phytoplankton populations in the Michigan River wetland (Turner & Rabalais, 2003). By keeping a constant zooplankton:phytoplankton (Zp:Ph) ratio in off-shore zone has helped resource managers to maintain clear water quality of the Michigan River wetland system in recent decades

> **Box 1 Natural river system Regulated river system**

Phosphorous compounds are measured as total phosphorous (TP) and soluble reactive phosphorous (SRP) and nitrogen is measured as total nitrogen (TN), ammonia (NH3+), nitrate (NO3-) and nitrite (NO2). Understanding the dynamics of P and N is essential whilst managing water quality. In shallow enriched lakes internal cycling of P can result in highly variable TP concentrations, often a strong seasonal variation occurs as well as this can usually be high in the summer when P is released from the sediment under anoxic conditions. Nitrogen concentrations however in summer are low in shallow temperate lakes due to an increased assimilation by algae. The high algal biomass leads to oxygen depletion and loss of biodiversity and fish mortality. Understanding of the environmental

**Dieback of littoral zone** 

**No C and N balance /Increased salinization** 

**Decreased growth and reproduction of littoral zooplankton/micro-crustaceans** 

**Increased erosion and turbidity** 

**Decreased trophic levels/less fish populations** 

**Weak food web structure and dynamics** 

while mortality increases when fish and invertebrate predations are high (Twombly & Lewis, 1989). In a lowland river system, fish can have size selective predation leading to small sized zooplankton dominating the system, consequently the preservation of the small-sized zooplankton such as *Bosmina* in the system. Mean size of cladoceran mandibles, remains of *Daphnia:Bosmina* ratios and the length of the carapaces and mucros of *Bosmina* can infer past fish assemblages in floodplain lakes and help understanding any changes in food web over time (Kattel, 2011). The cladocerans display morphological variability (cyclomorphosis) in food web. Vertebrate predation pressure on *Bosmina*, for example can result in variation in size of the mucro (Hann et al., 1994). In temperate arid Australia, *Daphnia carinata* show a cyclomorphic behaviour with seasonal changes in body size. Increase in *D. carinata* size indicates a low seasonal water temperature and can help infer the condition of the microhabitat climates for growth and reproduction of these animals (Mitchell, 1978).

Prolonged drought can lead to cessation of crustacean populations and functioning of floodplain ecosystems. Intensity of floodplain drying also increases changes in algal composition and diversity intensifying the top-down predation and competition (Schneider & Frost, 1996). However, the dry-wet cycles in floodplains recharge the system contributing to the emergence of endangered species of micro-crustaceans through regeneration of egg banks (Boulton & Loyid, 1992). The ephippia of cladocerans in floodplain lakes are viable for several decades. Hatching of resting eggs through genetically advanced technology can help restoring endemic populations (Jeppesen et al., 2000). For example, *Daphnia* ephippia as old as 40 years derived from a lake in South Australia is reported to have been able to hatch in the laboratory environment (Barry et al., 2005). Recently Jeppesen et al. (2002) have successfully reconstructed the catch per unit effort (CPUE) of the planktivorous fish inferred by *Daphnia* ephippia size in a European lake. In the Murray Darling River, the patterns of micro-crustacean distribution and ecosystem processes have been altered by alteration of littoral vegetation and zooplankton egg banks (Jenkins & Boulton, 2007). Unlike in natural condition, where riparian vegetation and littoral macrophyte communities are intact, C and N production is cyclical in nature promoting the growth of littoral macrophytes and microcrustaceans stabilizing food web structure and dynamics through improvement of the water quality (Box 1), the dieback of littoral vegetation in impounded rivers can alter entire ecological processes including the C and N balances followed by increased salinisation in the region. Zooplankton to phytoplankton ratios serves as a good indicator for grazing intensity of fish and provides the insight for food web structure and dynamics of floodplain lakes (Jeppesen et al., 2001).

#### **5.2 Management of water quality**

Micro-crustaceans are used for assessing water quality of the large river floodplain lakes extensively (Gannon & Stemberger, 1978). These organisms are classified according to their preferences for nutrient enrichments (e.g. eutrophic, mesotrophic or oligotrophic), chemistry (e.g. alkaline, acidic or saline) in water. Phophorous (P) and nitrogen (N) are two key nutrients significant for wetland ecosystems. Phosphorous is commonly the growth limiting nutrient in freshwaters exerting a strong control on species composition and primary productivity. Nitrogen can also be a limiting or colimiting nutrient with phosphorous. Anthropogenic influences especially from sewage effluences and agricultural fertilizers can enrich P and N concentrations substantially reducing the water quality (Boucherle & Züllig, 1983). For example, dramatic rise of nitrate concentrations in the Michigan River wetland system was a result of land use intensification following the European arrival. An increased grazing pressure by zooplankton on large algae resulted in increased smaller phytoplankton populations in the Michigan River wetland (Turner & Rabalais, 2003). By keeping a constant zooplankton:phytoplankton (Zp:Ph) ratio in off-shore zone has helped resource managers to maintain clear water quality of the Michigan River wetland system in recent decades (Turner & Rabalais, 2003).

Box 1.

340 International Perspectives on Global Environmental Change

while mortality increases when fish and invertebrate predations are high (Twombly & Lewis, 1989). In a lowland river system, fish can have size selective predation leading to small sized zooplankton dominating the system, consequently the preservation of the small-sized zooplankton such as *Bosmina* in the system. Mean size of cladoceran mandibles, remains of *Daphnia:Bosmina* ratios and the length of the carapaces and mucros of *Bosmina* can infer past fish assemblages in floodplain lakes and help understanding any changes in food web over time (Kattel, 2011). The cladocerans display morphological variability (cyclomorphosis) in food web. Vertebrate predation pressure on *Bosmina*, for example can result in variation in size of the mucro (Hann et al., 1994). In temperate arid Australia, *Daphnia carinata* show a cyclomorphic behaviour with seasonal changes in body size. Increase in *D. carinata* size indicates a low seasonal water temperature and can help infer the condition of the micro-

Prolonged drought can lead to cessation of crustacean populations and functioning of floodplain ecosystems. Intensity of floodplain drying also increases changes in algal composition and diversity intensifying the top-down predation and competition (Schneider & Frost, 1996). However, the dry-wet cycles in floodplains recharge the system contributing to the emergence of endangered species of micro-crustaceans through regeneration of egg banks (Boulton & Loyid, 1992). The ephippia of cladocerans in floodplain lakes are viable for several decades. Hatching of resting eggs through genetically advanced technology can help restoring endemic populations (Jeppesen et al., 2000). For example, *Daphnia* ephippia as old as 40 years derived from a lake in South Australia is reported to have been able to hatch in the laboratory environment (Barry et al., 2005). Recently Jeppesen et al. (2002) have successfully reconstructed the catch per unit effort (CPUE) of the planktivorous fish inferred by *Daphnia* ephippia size in a European lake. In the Murray Darling River, the patterns of micro-crustacean distribution and ecosystem processes have been altered by alteration of littoral vegetation and zooplankton egg banks (Jenkins & Boulton, 2007). Unlike in natural condition, where riparian vegetation and littoral macrophyte communities are intact, C and N production is cyclical in nature promoting the growth of littoral macrophytes and microcrustaceans stabilizing food web structure and dynamics through improvement of the water quality (Box 1), the dieback of littoral vegetation in impounded rivers can alter entire ecological processes including the C and N balances followed by increased salinisation in the region. Zooplankton to phytoplankton ratios serves as a good indicator for grazing intensity of fish and provides the insight for food web structure and dynamics of floodplain

Micro-crustaceans are used for assessing water quality of the large river floodplain lakes extensively (Gannon & Stemberger, 1978). These organisms are classified according to their preferences for nutrient enrichments (e.g. eutrophic, mesotrophic or oligotrophic), chemistry (e.g. alkaline, acidic or saline) in water. Phophorous (P) and nitrogen (N) are two key nutrients significant for wetland ecosystems. Phosphorous is commonly the growth limiting nutrient in freshwaters exerting a strong control on species composition and primary productivity. Nitrogen can also be a limiting or colimiting nutrient with phosphorous. Anthropogenic influences especially from sewage effluences and agricultural fertilizers can enrich P and N concentrations substantially reducing the water quality (Boucherle & Züllig, 1983). For example, dramatic rise of nitrate concentrations in the Michigan River wetland

habitat climates for growth and reproduction of these animals (Mitchell, 1978).

lakes (Jeppesen et al., 2001).

**5.2 Management of water quality** 
