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Freshwater Microbiology - Biodiversity And Dynamic Interactions Of Microorganisms In The Aquatic Environment

Contents


1 Microbial diversity and freshwater ecosystems 1
1.1 General introduction 1
1.1.1 The aquatic existence 1
1.1.2 The global water supply – limnology and oceanography 1
1.1.3 Freshwater systems: some terms and definitions 3
1.1.4 The biology of freshwater microorganisms 4
A. BIOLOGICAL DIVERSITY IN THE FRESHWATER ENVIRONMENT 4
1.2 Biodiversity of microorganisms 4
1.2.1 Domains of life 4
1.2.2 Size range 6
1.2.3 Autotrophs and heterotrophs 7
1.2.4 Planktonic and benthic microorganisms 10
1.2.5 Metabolically active and inactive states 11
1.2.6 Evolutionary strategies: r-selected and K-selected organisms 12
1.3 Biodiversity in ecosystems, communities, and species populations 15
1.3.1 Main ecosystems 15
1.3.2 Diversity within subsidiary communities 16
1.3.3 Biodiversity within single-species populations 16

B. ECOSYSTEMS 17
1.4 The biofilm community: a small-scale freshwater ecosystem 18
1.4.1 Interactions between microorganisms 19
1.4.2 Biomass formation and transfer 20
1.4.3 Maintenance of the internal environment 20
1.4.4 Interactions with the external environment 21
1.5 The pelagic ecosystem: a large-scale unit within the lake environment 21
1.5.1 Interactions between organisms 21
1.5.2 Trophic connections and biomass transfer 23
1.5.3 Maintenance of the internal environment 28
1.5.4 Interactions with the external environment 28
1.6 Homeostasis and ecosystem stability 29
1.6.1 Stress factors 30
1.6.2 General theoretical predictions: the community response 30
1.6.3 Observed stress responses: from molecules to communities 31

1.6.4 Assessment of ecosystem stability 31
1.6.5 Ecosystem stability and community structure 32
1.6.6 Biological response signatures 34
C. FOOD WEBS IN LENTIC AND LOTIC SYSTEMS 34
1.7 Pelagic food webs 34
CASE STUDY 1.1 MICROBIAL FOOD WEB ASSOCIATED WITH AN ALGAL BLOOM 34
CASE STUDY 1.2 GENERAL FOOD WEB IN THE WATER COLUMN OF LAKE BAIKAL (RUSSIA) 36
1.8 Communities and food webs of running waters 40
1.8.1 Allochthonous carbon: dissolved and particulate matter in river systems 40
1.8.2 Pelagic and benthic communities 42
1.8.3 The microbial food web 43
2 Freshwater environments: the influence of physico-chemical
conditions on microbial communities 47
A. INTRODUCTION 47
2.1 The aquatic medium: water, dissolved and particulate components 47
2.1.1 Particulate matter 47
2.1.2 Aquatic matrix 48
2.2 Freshwater environments 52
B. LAKES 53
2.3 Lake morphology and hydrology 53
2.3.1 Lake morphology 53
2.3.2 Lake hydrology and the surrounding terrestrial environment 57
2.4 Lakes as isolated environments 60
2.4.1 Isolated development 60
2.4.2 Lake Baikal: an ancient lake with a diverse and unique fauna and flora 60
2.5 Climatic influences on lakes 62
2.5.1 Temperate lakes – seasonal variations and lake stratification 63
2.5.2 Biological significance of stratification 65
2.5.3 Tropical lakes 66
2.5.4 Polar and sub-polar lakes 67
C. WETLANDS 68
2.6 General characteristics 68
2.6.1 Wetland diversity and global scale 68
2.6.2 Unifying features of wetlands 68
2.6.3 The role of wetlands in energy and material flow 69
2.7 Wetland habitats and communities 69
2.8 Case studies on wetland areas 70
CASE STUDY 2.1 TRˇ EBONˇ BASIN BIOSPHERE RESERVE 71
D. STREAMS AND RIVERS 72
2.9 Comparison of lotic and lentic systems 72
2.10 River flow and the benthic community 73
2.10.1 Flow characteristics of lotic systems 73
2.10.2 Influence of water flow on benthic microorganisms 75
2.11 River hydrology 78
E. ESTUARIES 79
2.12 River inflow: water mixing, estuarine productivity, and eutrophication of coastal areas 80

2.12.1 Mixing of fresh and saltwaters 80
2.12.2 High productivity of estuarine systems 81
2.12.3 Eutrophication of surrounding coastal areas 82
2.13 Habitats and communities 82
2.13.1 Pelagic zone 82
2.13.2 Sediments and mudflats 82
F. ADVERSE AND EXTREME CONDITIONS IN FRESHWATER ENVIRONMENTS 84
2.14 Adverse conditions as part of the environmental continuum 85
2.14.1 Variations in oxygen concentration 85
2.14.2 Nutrient availability 85
2.14.3 Solar radiation 86
2.15 Extreme environmental conditions 86
2.15.1 Temperature 86
2.15.2 pH 89
2.15.3 Conditions of low water availability: saline environments 91
2.15.4 Conditions of low water availability: ice and snow environments 92
2.15.5 Variations in hydrostatic pressure 93
2.15.6 Organic and inorganic pollution 93
2.16 A potentially extreme microenvironment: the air–water surface 95
2.16.1 Chemical composition of the surface microlayer 95
2.16.2 Physical processes and transformations in the surface biofilm 96
2.16.3 Microbial community at the air–water interface 98
2.17 Microbial communities of snow and ice: life in the frozen state 99
2.17.1 Snow and ice as an extreme environment 99
2.17.2 Requirement for water in the liquid state 99
2.17.3 Snow ecosystems 99
2.17.4 The physical properties of snow 100
2.17.5 Snow and ice microorganisms 102
3 Algae: the major microbial biomass in freshwater systems 105
A. TAXONOMIC AND MOLECULAR CHARACTERIZATION 107
3.1 Major taxonomic divisions of freshwater algae 107
3.1.1 Microscopical appearance, motility and ecological features 107
3.1.2 Biochemical and cytological characteristics 110
3.1.3 General summary of the different groups 112
3.2 Algal species: taxonomy and intraspecific variation 114
3.2.1 Taxonomy of algal species 114
3.2.2 Chemical diversity within species – enzyme analysis, molecular groups,
and elemental composition 115
3.3 Molecular analysis 116
3.3.1 Molecular characterization and identification of algae 116
3.3.2 Investigation of gene function in freshwater algae 119
B. SIZE, SHAPE, AND SURFACE MUCILAGE 123
3.4 Phytoplankton size and shape 123
3.4.1 Cell counts and biovolume 123
3.4.2 From picoplankton to macroplankton 123
3.4.3 Biological significance of size and shape 124
3.4.4 Variation in size and shape within phytoplankton populations 128
3.5 Mucilaginous and non-mucilaginous algae 130
3.5.1 Chemical composition of mucilage 131

3.5.2 Role of mucilage in phytoplankton activities 131
3.5.3 Environmental impact and biogeochemical cycles 133
C. ACTIVITIES WITHIN THE FRESHWATER ENVIRONMENT 133
3.6 Benthic algae: interactions with planktonic algae and ecological significance 133
3.6.1 Planktonic and benthic algae 133
3.6.2 Lake periphyton 136
3.6.3 Benthic algae in flowing waters 138
3.6.4 Ecological role of benthic algae 138
3.7 Temporal activities of freshwater algae 139
3.7.1 Short-term changes: molecular and cellular processes 140
3.7.2 Medium-term changes: algal succession 142
3.7.3 Long-term changes: variations over a number of years 146
3.8 Phytoplankton distribution within the water column 148
CASE STUDY 3.1 VERTICAL ZONATION OF PHYTOPLANKTON IN A STRATIFIED LAKE 148
3.8.1 Active migration of algae 149
3.8.2 Passive movement of algae within the water column 156
3.9 Freshwater algae and nutrient status of the environment 157
3.9.1 Phytoplankton species composition and lake nutrient status 157
3.9.2 Nutrient status of river environments – effect on benthic algal biofilms 160
D. STRATEGIES FOR SURVIVAL 161
3.10 Strategies for survival: the planktonic environment 161
3.10.1 Meroplanktonic algae 162
3.10.2 Strategies for unstable and stable environments: r-selected and K-selected algae 164
3.11 Heterotrophic nutrition in freshwater algae 165
3.11.1 Organotrophy 167
3.11.2 Phagotrophy 168
3.12 Survival in snow and ice: adaptations of cryophilic algae 171
3.12.1 Major groups of cryophilic algae 171
3.12.2 Life cycles of snow algae 173
3.12.3 Physiological adaptations of snow algae 174
E. BIODIVERSITY IN THE ALGAL COMMUNITY 177
3.13 Variety of freshwater algae: indices of species diversity 177
3.13.1 The paradox of phytoplankton diversity 177
3.13.2 Biodiversity indices 178
3.13.3 Numerical comparison of phytoplankton populations 179
3.13.4 Biodiversity and ecosystem function 180
4 Competition for light 181
4.1 The light environment 182
4.1.1 Physical properties of light: terms and units of measurement 182
4.1.2 Light thresholds for biological activities 183
4.1.3 Light under water: refraction, absorption, and scattering 184
4.1.4 Light energy conversion: from lake surface to algal biomass 186
4.2 Photosynthetic processes in the freshwater environment 188
4.2.1 Light and dark reactions 188
4.2.2 Photosynthetic microorganisms 189
4.2.3 Measurement of photosynthesis 189
4.2.4 Photosynthetic response to varying light intensity 190
4.3 Light as a growth resource 192
4.3.1 Strategies for light uptake and utilization 192
4.3.2 Light–photosynthetic response in different algae 193

4.3.3 Conservation of energy 194
4.3.4 Diversity in small molecular weight solutes and osmoregulation 195
4.4 Algal growth and productivity 196
4.4.1 Primary production: concepts and terms 196
4.4.2 Primary production and algal biomass 197
4.4.3 Field measurements of primary productivity 197
4.5 Photosynthetic bacteria 199
4.5.1 Major groups 200
4.5.2 Photosynthetic pigments 200
4.5.3 Bacterial primary productivity 201
4.6 Photoadaptation: responses of aquatic algae to limited supplies of light energy 202
4.6.1 Different aspects of light limitation 203
4.6.2 Variable light intensity: light-responsive gene expression 204
4.6.3 Photosynthetic responses to low light intensity 205
4.6.4 Spectral composition of light: changes in pigment composition 209
4.7 Carbon uptake and excretion by algal cells 210
4.7.1 Changes in environmental CO2 and pH 210
4.7.2 Excretion of dissolved organic carbon by phytoplankton cells 211
4.8 Competition for light and carbon dioxide between algae and higher plants 215
4.8.1 The balance between algae and macrophytes in different aquatic environments 215
CASE STUDY 4.1 COMPETITION BETWEEN ALGAE AND MACROPHYTES IN SHALLOW
LAKES OF THE TRˇEBONˇ WETLANDS 216
4.8.2 Physiological and environmental adaptations in the competition between
algae and macrophytes 218
4.9 Damaging effects of high levels of solar radiation: photoinhibition 221
4.9.1 Specific mechanisms of photoinhibition 221
4.9.2 General effects of photoinhibition 224
4.9.3 Strategies for the avoidance of photoinhibition 225
4.9.4 Photoinhibition and cell size 227
4.9.5 Lack of photoinhibition in benthic communities 228
4.9.6 Photoinhibition in extreme high-light environments 228
4.10 Periodic effects of light on seasonal and diurnal activities of freshwater biota 230
4.10.1 Seasonal periodicity 230
4.10.2 Diurnal changes 231
4.10.3 Circadian rhythms in blue-green algae 232
4.10.4 Circadian rhythms in dinoflagellates 234
5 Inorganic nutrients: uptake and cycling in freshwater systems 235
5.1 Chemical composition of natural waters 235
5.1.1 Soluble inorganic matter in lakes and rivers 235
5.1.2 Aerial deposition of nutrients 237
5.1.3 Nutrient inflow from terrestrial sources 237
5.1.4 Chemical requirements and composition of freshwater biota 238
CASE STUDY 5.1 ELEMENTAL COMPOSITION OF CERATIUM HIRUNDINELLA 240
5.1.5 Nutrient availability and cycling in aquatic systems 243
5.2 Nutrient uptake and growth kinetics 246
5.2.1 Empirical models for algal nutrient kinetics 246
5.2.2 Competition and growth in the aquatic environment 248
5.2.3 Nutrient availability and water movement 250
5.2.4 Acute nutrient deprivation as an environmental stress factor 251
A. NITROGEN 251
5.3 Biological availability of nitrogen in freshwater environments 251
5.3.1 Soluble nitrogenous compounds 251

5.4 The nitrogen cycle 254
5.4.1 Nitrate entry and uptake (soluble inorganic to insoluble organic nitrogen) 254
5.4.2 Complex organic nitrogen (biomass) transformations
(successive states of insoluble organic nitrogen) 255
5.4.3 Remineralization (insoluble organic to soluble inorganic nitrogen) 255
5.4.4 Nitrification/denitrification (oxidation/reduction of soluble inorganic compounds) 255
5.5 Uptake of nitrate and ammonium ions by algae 257
5.5.1 Biochemical processes 257
5.5.2 Species variations in nitrate uptake 258
5.5.3 Environmental regulation of nitrate assimilation 258
5.5.4 Nitrogen uptake, CO2 assimilation, and photosynthesis 259
5.6 Nitrogen fixation 260
5.6.1 Ecological significance of nitrogen fixation 260
5.6.2 The nitrogenase enzyme and strategies of fixation 260
5.6.3 Heterocysts: nitrogen fixation by colonial blue-green algae 261
5.6.4 Diurnal control of nitrogen fixation: unicellular blue-green algae 262
5.6.5 Anaerobic environment: nitrogen-fixing bacteria 263
B. PHOSPHORUS 265
5.7 Occurrence and biological availability of phosphorus 265
5.7.1 Phosphorus availability and limitation 265
5.7.2 The phosphorus cycle 266
5.8 Adaptations of freshwater microorganisms to low phosphorus concentrations 269
5.8.1 Kinetics of phosphorus uptake 269
5.8.2 Luxury consumption of phosphate 269
5.8.3 Secretion of alkaline phosphatase 271
C. SILICON: A WIDELY-AVAILABLE ELEMENT OF LIMITED
METABOLIC IMPORTANCE 272
5.9 The silicon cycle 272
5.10 Silicon and diatoms 274
5.10.1 Si uptake and phytoplankton succession 274
5.10.2 Si uptake and cell-wall formation 275
D. TRACE ELEMENTS 279
5.11 Biological role of trace elements 280
5.11.1 Environmental uptake of trace elements 280
5.11.2 Stimulation of growth in aquatic environments 281
5.11.3 Importance of trace metals in the culture of aquatic algae 281
5.11.4 Biochemical roles of trace elements 282
5.12 Cycling of iron and other trace metals in the aquatic environment 283
5.12.1 The iron cycle 283
5.12.2 The manganese cycle 286
6 Bacteria: the main heterotrophic microorganisms in freshwater systems 287
A. GENERAL DIVERSITY WITHIN THE ENVIRONMENT 287
6.1. General diversity, habitat preferences, and ecological significance of freshwater bacteria 287
6.1.1 General diversity 287
6.1.2 Habitat preferences 288
6.1.3 Environmental significance of freshwater bacteria 290
6.2 Taxonomic, biochemical, and molecular characterization of freshwater bacteria 291
6.2.1 Species identification 291

6.2.2 Genetic markers: detection of particular strains in the aquatic environment 292
6.2.3 Biochemical characterization of bacterial communities 293
CASE STUDY 6.1 CHANGES IN BACTERIAL COMMUNITY FUNCTION AND COMPOSITION AS
A RESPONSE TO VARIATIONS IN THE SUPPLY OF DISSOLVED ORGANIC MATERIAL (DOM) 293
B. GENETIC INTERACTIONS 294
6.3 Genetic diversity 294
6.3.1 Chromosomal and accessory DNA 294
6.3.2 The ecological importance of gene transfer in freshwater systems 295
6.3.3 Total genetic diversity: the ‘community genome’ 296
6.4 Mechanisms for gene transfer in freshwater systems 297
6.4.1 Transformation: uptake of exogenous DNA 297
6.4.2 Transduction: gene transfer between bacteria via bacteriophages 300
6.4.3 Conjugation: transfer of plasmid DNA by direct cell contact 300
6.5 Evidence for gene transfer in the aquatic environment 300
6.5.1 Retrospective analysis 300
CASE STUDY 6.2 PLASMID-BORNE RESISTANCE IN AQUATIC BACTERIA 301
6.5.2 Laboratory (in vitro) studies on plasmid transfer 301
CASE STUDY 6.3 PLASMID TRANSFER IN PSEUDOMONAS AERUGINOSA 302
6.5.3 Field (in situ) studies on bacterial gene transfer 303
C. METABOLIC ACTIVITIES 304
6.6 Metabolic diversity of freshwater bacteria 304
6.6.1 Key metabolic parameters 304
6.6.2 CO2 fixation 304
6.6.3 Breakdown of organic matter in aerobic and anaerobic environments 305
6.6.4 Bacterial adaptations to low-nutrient environments 310
6.7 Photosynthetic bacteria 312
6.7.1 General characteristics 312
6.7.2 Motility 312
6.7.3 Ecology 314
6.8 Bacteria and inorganic cycles 314
6.8.1 Bacterial metabolism and the sulphur cycle 315
D. BACTERIAL POPULATIONS AND PRODUCTIVITY 316
6.9 Bacterial populations 316
6.9.1 Techniques for counting bacterial populations 316
6.9.2 Biological significance of total and viable counts 317
6.10 Bacterial productivity 318
6.10.1 Measurement of productivity 318
6.10.2 Regulation of bacterial populations and biomass 319
6.10.3 Primary and secondary productivity: correlation between bacterial and algal populations 320
6.10.4 Primary and secondary productivity: the role of dissolved organic carbon 321
6.10.5 Bacterial productivity and aquatic food webs 323
E. BACTERIAL COMMUNITIES IN THE LOTIC ENVIRONMENT 324
6.11 Bacterial Biofilms 324
6.11.1 The development of biofilms 324
6.11.2 Dynamic interactions in the establishment of biofilms: the role of bacterial co-aggregation 326
CASE STUDY 6.4 SPECIFIC RECOGNITION AND ADHESION AMONGST AQUATIC BIOFILM BACTERIA 326
F. BACTERIAL INTERACTIONS WITH PHYTOPLANKTON 328
6.12 Interactions between phytoplankton and planktonic bacteria 328
6.12.1 Competition for inorganic nutrients 328
6.12.2 Antagonistic interactions between bacteria and algae 329

6.13 Epiphytic associations of bacteria with phytoplankton 332
6.13.1 Bacteria within the phycosphere 333
6.13.2 Observation and enumeration of epiphytic bacteria 334
6.13.3 Specific associations between bacteria and blue-green algae 336
7 Viruses: major parasites in the freshwater environment 339
7.1 Viruses as freshwater biota 339
7.1.1 General role in the freshwater environment 339
7.1.2 Major groups and taxonomy of freshwater viruses 340
7.2 The virus life cycle: intracellular and free viral states 340
7.2.1 Significance of the lysogenic state 341
7.3 Detection and quantitation of freshwater viruses 342
7.3.1 Free particulate viruses 342
7.3.2 Infected host cells 345
7.4 The growth and control of viral populations 345
7.4.1 Virus productivity 345
7.4.2 Regulation of viral abundance 346
7.5 Control of host populations by aquatic viruses: impact on the microbial food web 349
7.5.1 Metabolic effects of viruses: reduction of algal primary productivity 349
7.5.2 Destruction of algal and bacterial populations 350
7.5.3 Viruses and the microbial loop 350
7.6 Cyanophages: viruses of blue-green algae 351
7.6.1 Classification and taxonomic characteristics 351
7.6.2 Infection of host cells 352
7.7 Phycoviruses: parasites of eukaryote algae 354
7.7.1 General characteristics 354
7.7.2 Host cell infection 356
CASE STUDY 7.1 THE INFECTIVE LIFE CYCLE OF CHLOROVIRUS 356
7.7.3 Ecological impact of phycoviruses 359
7.8 Virus infection of freshwater bacteria 360
7.8.1 General role of bacteriophages in the biology of freshwater bacteria 360
7.8.2 Bacteriophages in pelagic and benthic systems 360
7.8.3 Occurrence of free bacteriophages in aquatic systems 361
7.8.4 Incidence of bacterial infection 361
7.8.5 Temperate/virulent phage equilibrium and bacterial survival 363
7.8.6 Bacteriophage control of planktonic bacterial populations 365
CASE STUDY 7.2 VIRAL LYSIS OF BACTERIA IN A EUTROPHIC LAKE 365
7.8.7 Transduction: bacteriophage-mediated gene transfer between freshwater bacteria 367
CASE STUDY 7.3 TRANSDUCTION OF PLASMID AND CHROMOSOMAL DNA IN
PSEUDOMONAS AERUGINOSA 368
8 Fungi and fungal-like organisms: aquatic biota with a mycelial growth form 371
A. ACTINOMYCETES, OOMYCETES, AND TRUE FUNGI 371
8.1 Fungi and fungal-like organisms: the mycelial growth habit 371
8.2 Actinomycetes 372
8.2.1 Taxonomic characteristics 372
8.2.2 Habitat 373
8.2.3 Nutrition 374
8.2.4 Competition with other microorganisms 374
8.3 Oomycetes 374
8.3.1 Oomycetes and true fungi 375

8.3.2 Taxonomic diversity 376
8.4 True fungi 377
8.4.1 Old and new terminology 377
8.4.2 Taxonomic diversity within the true fungi 378
B. FUNGI AS SAPROPHYTES AND PARASITES 381
8.5 Saprophytic activity of fungi 381
8.5.1 Colonization, growth, and fungal succession 382
8.5.2 Breakdown of leaf litter 383
8.5.3 Saprophytic fungi – chytrids and deuteromycetes 386
8.6 Parasitic activities of aquatic fungi 388
8.6.1 Parasitic and predatory deuteromycetes: fungi that attack small animals 388
8.6.2 Parasitic chytrids: highly specialized parasites of freshwater organisms 389
8.7 Fungal epidemics in the control of phytoplankton populations 392
8.7.1 Ecological significance 392
CASE STUDY 8.1 CHYTRID INFECTION OF THE ASTERIONELLA DURING AN
AUTUMN DIATOM BLOOM 392
8.7.2 Net effect of infected and non-infected host cells 394
8.7.3 Factors affecting the development of fungal infection 395
9 Grazing activities in the freshwater environment: the role of
protozoa and invertebrates 401
A. PROTOZOA 401
9.1 Introduction 401
9.1.1 Relative importance of protozoans, rotifers, and crustaceans in pelagic communities 401
9.1.2 Ecological role of protozoa 402
9.2 Protozoa, algae, and indeterminate groups 402
9.3 Taxonomic diversity of protozoa in the freshwater environment 403
9.3.1 Ciliates 403
9.3.2 Flagellate protozoa 407
9.3.3 Amoeboid protozoa 409
9.4 Ecological impact of protozoa: the pelagic environment 412
9.4.1 Positioning within the water column 412
9.4.2 Trophic interactions in the water column 413
9.5 Heterotrophic nanoflagellates: an integral component of planktonic communities 413
9.5.1 Enumeration of nanoflagellate populations in aquatic samples 414
9.5.2 Taxonomic composition of HNF communities 415
9.5.3 Abundance and control of flagellate populations 415
9.5.4 Nanoflagellate grazing rates and control of bacterial populations 416
9.5.5 Co-distribution of bacteria and protozoa within the water column 418
9.6 Ecological impact of protozoa: the benthic environment 419
9.6.1 Benthic microenvironments 419
9.6.2 Seasonal changes 421
9.6.3 Organic pollution 421
9.6.4 Sewage-treatment plants: activated sludge 422
B. GRAZING OF MICROBIAL POPULATIONS BY ZOOPLANKTON 423
9.7 General features of zooplankton: rotifers, cladocerans and copepods 423
9.7.1 Morphology and size 423
9.7.2 Reproduction and generation times 426
9.7.3 Predation of zooplankton 426
9.8 Grazing activity and prey selection 427
9.8.1 Seasonal succession in zooplankton feeding 427

9.8.2 Method of feeding 429
9.8.3 Selection of food by zooplankton 429
9.9 Grazing rates of zooplankton 432
9.9.1 Measurement 432
9.9.2 Factors affecting grazing rates 433
9.9.3 Diurnal variations in grazing activity 434
9.10 Effects of algal toxins on zooplankton 435
9.11 Biomass relationships between phytoplankton and zooplankton populations 437
9.11.1 Control of zooplankton populations 437
9.11.2 Biomass transfer 437
C. GRAZING OF BENTHIC MICROORGANISMS 438
9.12 Comparison of pelagic and benthic systems 438
9.13 Role of invertebrates in consuming river microorganisms 440
9.13.1 Grazing of periphyton biomass 440
9.13.2 Effects of grazing on periphyton community structure 441
10 Eutrophication: the microbial response to high nutrient levels 443
A. ORIGINS OF EUTROPHICATION 444
10.1 Nutrient status of freshwater environments: from oligotrophic to eutrophic systems 444
10.1.1 Eutrophic and oligotrophic lakes: definition of terms 444
10.1.2 Determinants of trophic status: location, morphology and hydrology 445
10.1.3 Artificial eutrophication: the impact of human activities 446
10.1.4 Eutrophication of rivers and streams 446
B. ECOLOGICAL EFFECTS OF EUTROPHICATION IN STANDING WATERS 448
10.2 General biological changes 448
10.2.1 The progression from oligotrophic to eutrophic waters 448
10.2.2 Effects of eutrophication on the water column of stratified lakes 452
10.2.3 Major changes in ecological balance: the breakdown of homeostasis 452
10.3 Biological assessment of water quality 453
10.3.1 Algal indicator groups 453
CASE STUDY 10.1 USING THE A/C (ARAPHID PENNATE/CENTRIC) DIATOM RATIO TO ASSESS
EUTROPHICATION IN LAKE TAHOE (USA) 454
10.3.2 Indices of species diversity 455
10.4 Problems with intentional eutrophication: destabilization of fishpond ecosystems 455
10.4.1 Promotion of high productivity in fishponds 455
10.4.2 Destabilization and restoration of the ecosystem 456
C. THE GROWTH AND IMPACT OF ALGAL BLOOMS 457
10.5 Algal blooms and eutrophication 457
10.6 Formation of colonial blue-green algal blooms 459
10.6.1 General requirements for bloom formation 459
10.6.2 Competition with other algae 459
CASE STUDY 10.2 USE OF ENCLOSURE EXPERIMENTS TO STUDY FACTORS AFFECTING
BLUE-GREEN DOMINANCE 461
10.7 Environmental effects of blue-green blooms 461
10.7.1 General environmental changes 461
10.7.2 Specific effects on water quality 462
10.7.3 Production of toxins 462

D. CONTROL OF BLUE-GREEN ALGAE 464
10.8 Strategies for the control of blue-green algae 464
10.8.1 Nutrient limitation (bottom-up control) 465
CASE STUDY 10.3 RESTORATION OF WATER QUALITY IN LAKE WASHINGTON, NORTH WEST USA 466
10.8.2 Direct eradication 466
10.8.3 Top-down control of blue-green algae: the use of biomanipulation 467
CASE STUDY 10.4 TOP-DOWN AND BOTTOM-UP CONTROL OF ALGAL POPULATIONS IN
THE BROADS WETLAND AREA (UK) 467
10.9 Biological control of blue-green algae 471
10.9.1 Biological control agents 472
10.9.2 Protocol for the development of biological control agents 474
CASE STUDY 10.5 POTENTIAL PROTOZOON CONTROL AGENTS 475
10.9.3 Application of plant litter to control blue-green algae 475
10.10 Strategies for the control of blue-green algae in different water bodies 477
10.10.1 Integrated management policy 477
CASE STUDY 10.6 ENVIRONMENTAL MONITORING AT HOLLINGWORTH LAKE,
GREATER MANCHESTER (UK) 479
10.10.2 Specific remedial measures in different freshwater systems 481


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