Freshwater Ecology & Management
H1: Introduction to Limnology & freshwater
1.1: Intro
Limnology = study of inland waters, AKA following watertypes:
• Freshwater (zoetwater)
• Brackish (brak)
• Saline (zout)
Example: lakes, reservoirs, rivers, streams, wetlands, & groundwater
Freshwater ecology is part of limnology that focusses on freshwater ecosystems. => Freshwater systems vary, from
deep, permanent lakes in well-watered northern temperate zones to shallow, temporary, ponds. Their dynamics
depend on climate, catchment conditions & degree of disturbance.
Freshwater ecosystems are integrated land – water systems linking drainage basin, atmosphere, & biotic
communities through energy flux (sunlight → producers → consumers → decomposers) & nutrient cycling.
2 Flowtypes:
• Lentic = standing water (stilstaand, such as lakes & ponds)
• Lotic = flowing water (stromend, such as river & streams)
Hutchinson & Löffler 1956 made classification based on mixing regimes, which is determined by thermal stratification
(= layering).
4 thermal lake types:
• Oligotrophic = nutrient-poor, clear, oxygen-rich, low productivity.
• Mesotrophic = intermediate productivity.
• Eutrophic = nutrient-rich, algal blooms, oxygen depletion.
• Hypereutrophic/Polymictic = extreme nutrient enrichment & frequent mixing.
=> Process of eutrophication can occur naturally with age or be caused by human inputs of
nutrients.
In nature there are many temporary shallow/smaller systems, that can be made by wind, animal activity, or human-
made. These shallow systems have close interactions between organisms, water & sediments
Climate-Zone differences in food-web trophic structure, which highlight
regional variability & caution against broad generalizations:
• Temperate => Clear trophic structure is seen, which is dominated by
algivorous invertebrates & zooplankton = strong bottom-up control
(AKA nutrient limitation).
• Subtropical & Tropical => More productive & biodiverse foodweb with
lots of interactions, resulting in no clear trophic structure. Tends to be
dominated by omnivorous, planktivorous fish & shrimps = strong top-
down control (AKA predation).
1.1.1: Humans & Freshwater
Human activities now profoundly alter freshwater systems through urbanization, industrialization, agriculture,
deforestation, warming, elevated CO₂, altered hydrology, salinization, pollution, eutrophication, & invasive species.
=> Such pressures mean that human influences can no longer be considered secondary in freshwater ecology.
C Dynamics in Peatlands
• Natural peatlands => Act as C sinks, because water & anoxic conditions in peatland soil slow down
decomposition process of dead plant material, which remains stored as C.
, • Drained peatlands => Act as C sources, because drainage
channel avoids accumulation of water & aerobic
decomposition begins. Oxygen exposure accelerates
microbial decay & CO₂ emissions.
=> This shift reinforces positive climate feedbacks, as more CO₂
leads to further warming & decomposition. Also deforestation &
peat drainage together increase both C release & sediment
delivery to lakes.
Understanding such feedbacks requires research across biological levels (individual to ecosystem) & spatial–temporal
scales. Long-term, whole-system, & comparative studies are essential to capture ecosystem complexity & function.
Many studies today are small scale & short time period.
Example: Changes in dynamics of lake-sediment system with time scale reveal:
• Long-term (centuries) trends driven by climate, land use, & deforestation.
• Seasonal–annual (years) variability linked to weather, nutrient loading,
decomposition & productivity.
• Short-term (day) oscillations comes from phytoplankton blooms,
resuspension, or benthic feeding.
Ecosystem Functions & Services provided by Freshwater ecosystems:
• Functions = C sequestration, nutrient retention, hydrological balance
• Services = water supply, food, recreation, health regulation
Forests help with water infiltration, retention, & soil stabilization.
Transpiration from trees reduces surface runoff & mitigates flooding. In
forested areas, after high intensity storm of short duration, there is reduced
peak discharge in streamflow.
Urbanization & deforestation increase river flushing, sediment loads, &
nutrient runoff. High intensity storm of short duration will be shortly followed
by pronounced peak streamflow discharge
1.2: Global water distribution
Earth is blue planet, but water is critical global issue due to its uneven distribution & limited
freshwater availability. Water covers about 71% of Earth’s surface, of this:
• 97% = stored in oceans (≈1.4 billion km³).
• 3% = freshwater:
o ≈79% = glaciers & polar ice.
o ≈29% = groundwater.
o ≈1% = accessible surface freshwater (52% in lakes ≈125,000 km³, 1% in rivers, 8% water
vapor, 38% is soil moisture, …).
Freshwater environments include both lentic & lotic systems. There are millions of
lakes worldwide, yet majority of systems are small & shallow, but ecologically vital.
• Wetlands => found in boreal forests, subarctic zones, & equatorial regions.
• Large freshwater lakes (>100 km²) => found around 40–50° latitude in both
hemispheres & near Equator.
,Ca 117 million lakes larger than 0.002 km². Only ca 20 lakes are considered very large or deep.
• 3 lakes are deeper than 1,000m = Lake Baikal, Lake Tanganyika, &
Caspian Sea.
• Lake Baikal contains ca 20% of world’s unfrozen freshwater.
• Great Laurentian Lakes in North America
o are largest continuous body of freshwater on Earth.
o contain ca 21% of world’s surface freshwater.
• Lake Victoria is relatively shallow (mean depth ≈ 40m) but can be
considered largest lake by surface area by criteria of surface vs. volume.
• Caspian Sea is largest inland water basin by surface & volume.
Some definitions:
• Sea = waterbody connected to the ocean => Caspian Sea is historical misnomer, as it’s an inland lake.
• Pond = waterbody with surface area <8 ha (often <5 ha).
1.3: Lake types and formation
1.3.1: Lake types
On continental scale, lake & reservoir types are classified according to their hydrological regimes (= balance between
inflow, precipitation, evaporation & outflow). => values expressed as % of total freshwater.
1) Exorheic or Open-Basin Lakes = have outflow channels that connect to rivers or ocean, allowing continuous water
exchange. Characteristics:
• Experience low surface evaporation due to regular outflow.
• Are found in areas where precipitation > evaporation => Humid or
temperate regions with adequate precipitation.
• Water usually fresh because dissolved salts are flushed out of system.
, 2) Endorheic or Closed-Basin Lakes = no outflow channels, so no surface & subsurface
drainage exits basin. Characteristics:
• Water loss occurs through evaporation.
• Progressive accumulation of salts, resulting in saline or hypersaline waters.
• Common in arid & semi-arid regions (Central Asia, Middle East, & parts of Africa).
Examples: stress on Endorheic System
• Colorado River basin (Western North America) faces overextraction & salinization.
• Ogallala Aquifer (Wisconsin to Texas) projected to dry up this century due to unsustainable groundwater use.
Example: Aral Sea AKA “Lake That Cotton Absorbed” => Endorheic
water body between northern Kazakhstan & southern Uzbekistan
along historic Silk Road & was once 4th-largest lake in world
(≈68,000 km²). In 1930s here was large-scale agricultural
intensification led to rerouting of Amu Darya & Syr Darya rivers
for cotton irrigation. Furthermore, inefficient canal systems
caused severe water loss. Between 1960 & 2000, cotton
production doubled, while lake’s inflow & surface area collapsed.
Impacts:
• Environmental
o Groundwater salinity reached 6 g·L⁻¹ => 6x higher than WHO safety threshold.
o Volume of Aral Sea decreased & salinity rose from 10 to 370 g·L⁻¹,
o Frequent dust & sandstorms lift up ca 43 million tons of contaminated material annually from exposed
seabed.
• Social Impacts => By 2000, only 32% of residents had access to safe drinking water.
• Pollution & Human Health:
o Fertilizers & chlorinated pesticides (such as DDT, DDE) used contaminated soil & surface waters.
o Mining runoff introduced heavy metals (copper, nickel & lead) to Amu Darya river.
o Persistent organic pollutants such as PCBs, PCDDs, & PCDFs are found in fish, livestock products, & local
vegetables (such as carrots, onions).
o Elevated concentrations of hexachlorocyclohexane (HCH) detected in most samples, posing long-term
toxicological & public health risks.
3) Transitional Lakes = alternate between open & closed conditions depending on climatic variability.
• During wet periods => Inflow increases & salinity decreases = open-basin lakes.
• During dry periods => inflow declines & evaporation dominates, raising salinity
= closed system.
=> These systems are sensitive to climate change & regional water management,
thus good indicators.
1.3.2: Formation, age & origin
Lakes vary widely in age, depth, & origin.
• Majority of lakes are geologically young, formed only 6,000–15,000 years
ago after last Ice Age => Most lakes are formed by glacial processes (ice
movement & retreat), that’s why most are young…
• Coastal lakes are even more recent, appearing as sea levels stabilized
~6,000 years ago.
• Ancient lakes are rare (typically 2–20 million years old), often deep & of tectonic or volcanic origin. Example:
such as Baikal, Tanganyika, Malawi, Biwa
• Many modern systems are biotic or man-made, & shallow or small in scale.
H1: Introduction to Limnology & freshwater
1.1: Intro
Limnology = study of inland waters, AKA following watertypes:
• Freshwater (zoetwater)
• Brackish (brak)
• Saline (zout)
Example: lakes, reservoirs, rivers, streams, wetlands, & groundwater
Freshwater ecology is part of limnology that focusses on freshwater ecosystems. => Freshwater systems vary, from
deep, permanent lakes in well-watered northern temperate zones to shallow, temporary, ponds. Their dynamics
depend on climate, catchment conditions & degree of disturbance.
Freshwater ecosystems are integrated land – water systems linking drainage basin, atmosphere, & biotic
communities through energy flux (sunlight → producers → consumers → decomposers) & nutrient cycling.
2 Flowtypes:
• Lentic = standing water (stilstaand, such as lakes & ponds)
• Lotic = flowing water (stromend, such as river & streams)
Hutchinson & Löffler 1956 made classification based on mixing regimes, which is determined by thermal stratification
(= layering).
4 thermal lake types:
• Oligotrophic = nutrient-poor, clear, oxygen-rich, low productivity.
• Mesotrophic = intermediate productivity.
• Eutrophic = nutrient-rich, algal blooms, oxygen depletion.
• Hypereutrophic/Polymictic = extreme nutrient enrichment & frequent mixing.
=> Process of eutrophication can occur naturally with age or be caused by human inputs of
nutrients.
In nature there are many temporary shallow/smaller systems, that can be made by wind, animal activity, or human-
made. These shallow systems have close interactions between organisms, water & sediments
Climate-Zone differences in food-web trophic structure, which highlight
regional variability & caution against broad generalizations:
• Temperate => Clear trophic structure is seen, which is dominated by
algivorous invertebrates & zooplankton = strong bottom-up control
(AKA nutrient limitation).
• Subtropical & Tropical => More productive & biodiverse foodweb with
lots of interactions, resulting in no clear trophic structure. Tends to be
dominated by omnivorous, planktivorous fish & shrimps = strong top-
down control (AKA predation).
1.1.1: Humans & Freshwater
Human activities now profoundly alter freshwater systems through urbanization, industrialization, agriculture,
deforestation, warming, elevated CO₂, altered hydrology, salinization, pollution, eutrophication, & invasive species.
=> Such pressures mean that human influences can no longer be considered secondary in freshwater ecology.
C Dynamics in Peatlands
• Natural peatlands => Act as C sinks, because water & anoxic conditions in peatland soil slow down
decomposition process of dead plant material, which remains stored as C.
, • Drained peatlands => Act as C sources, because drainage
channel avoids accumulation of water & aerobic
decomposition begins. Oxygen exposure accelerates
microbial decay & CO₂ emissions.
=> This shift reinforces positive climate feedbacks, as more CO₂
leads to further warming & decomposition. Also deforestation &
peat drainage together increase both C release & sediment
delivery to lakes.
Understanding such feedbacks requires research across biological levels (individual to ecosystem) & spatial–temporal
scales. Long-term, whole-system, & comparative studies are essential to capture ecosystem complexity & function.
Many studies today are small scale & short time period.
Example: Changes in dynamics of lake-sediment system with time scale reveal:
• Long-term (centuries) trends driven by climate, land use, & deforestation.
• Seasonal–annual (years) variability linked to weather, nutrient loading,
decomposition & productivity.
• Short-term (day) oscillations comes from phytoplankton blooms,
resuspension, or benthic feeding.
Ecosystem Functions & Services provided by Freshwater ecosystems:
• Functions = C sequestration, nutrient retention, hydrological balance
• Services = water supply, food, recreation, health regulation
Forests help with water infiltration, retention, & soil stabilization.
Transpiration from trees reduces surface runoff & mitigates flooding. In
forested areas, after high intensity storm of short duration, there is reduced
peak discharge in streamflow.
Urbanization & deforestation increase river flushing, sediment loads, &
nutrient runoff. High intensity storm of short duration will be shortly followed
by pronounced peak streamflow discharge
1.2: Global water distribution
Earth is blue planet, but water is critical global issue due to its uneven distribution & limited
freshwater availability. Water covers about 71% of Earth’s surface, of this:
• 97% = stored in oceans (≈1.4 billion km³).
• 3% = freshwater:
o ≈79% = glaciers & polar ice.
o ≈29% = groundwater.
o ≈1% = accessible surface freshwater (52% in lakes ≈125,000 km³, 1% in rivers, 8% water
vapor, 38% is soil moisture, …).
Freshwater environments include both lentic & lotic systems. There are millions of
lakes worldwide, yet majority of systems are small & shallow, but ecologically vital.
• Wetlands => found in boreal forests, subarctic zones, & equatorial regions.
• Large freshwater lakes (>100 km²) => found around 40–50° latitude in both
hemispheres & near Equator.
,Ca 117 million lakes larger than 0.002 km². Only ca 20 lakes are considered very large or deep.
• 3 lakes are deeper than 1,000m = Lake Baikal, Lake Tanganyika, &
Caspian Sea.
• Lake Baikal contains ca 20% of world’s unfrozen freshwater.
• Great Laurentian Lakes in North America
o are largest continuous body of freshwater on Earth.
o contain ca 21% of world’s surface freshwater.
• Lake Victoria is relatively shallow (mean depth ≈ 40m) but can be
considered largest lake by surface area by criteria of surface vs. volume.
• Caspian Sea is largest inland water basin by surface & volume.
Some definitions:
• Sea = waterbody connected to the ocean => Caspian Sea is historical misnomer, as it’s an inland lake.
• Pond = waterbody with surface area <8 ha (often <5 ha).
1.3: Lake types and formation
1.3.1: Lake types
On continental scale, lake & reservoir types are classified according to their hydrological regimes (= balance between
inflow, precipitation, evaporation & outflow). => values expressed as % of total freshwater.
1) Exorheic or Open-Basin Lakes = have outflow channels that connect to rivers or ocean, allowing continuous water
exchange. Characteristics:
• Experience low surface evaporation due to regular outflow.
• Are found in areas where precipitation > evaporation => Humid or
temperate regions with adequate precipitation.
• Water usually fresh because dissolved salts are flushed out of system.
, 2) Endorheic or Closed-Basin Lakes = no outflow channels, so no surface & subsurface
drainage exits basin. Characteristics:
• Water loss occurs through evaporation.
• Progressive accumulation of salts, resulting in saline or hypersaline waters.
• Common in arid & semi-arid regions (Central Asia, Middle East, & parts of Africa).
Examples: stress on Endorheic System
• Colorado River basin (Western North America) faces overextraction & salinization.
• Ogallala Aquifer (Wisconsin to Texas) projected to dry up this century due to unsustainable groundwater use.
Example: Aral Sea AKA “Lake That Cotton Absorbed” => Endorheic
water body between northern Kazakhstan & southern Uzbekistan
along historic Silk Road & was once 4th-largest lake in world
(≈68,000 km²). In 1930s here was large-scale agricultural
intensification led to rerouting of Amu Darya & Syr Darya rivers
for cotton irrigation. Furthermore, inefficient canal systems
caused severe water loss. Between 1960 & 2000, cotton
production doubled, while lake’s inflow & surface area collapsed.
Impacts:
• Environmental
o Groundwater salinity reached 6 g·L⁻¹ => 6x higher than WHO safety threshold.
o Volume of Aral Sea decreased & salinity rose from 10 to 370 g·L⁻¹,
o Frequent dust & sandstorms lift up ca 43 million tons of contaminated material annually from exposed
seabed.
• Social Impacts => By 2000, only 32% of residents had access to safe drinking water.
• Pollution & Human Health:
o Fertilizers & chlorinated pesticides (such as DDT, DDE) used contaminated soil & surface waters.
o Mining runoff introduced heavy metals (copper, nickel & lead) to Amu Darya river.
o Persistent organic pollutants such as PCBs, PCDDs, & PCDFs are found in fish, livestock products, & local
vegetables (such as carrots, onions).
o Elevated concentrations of hexachlorocyclohexane (HCH) detected in most samples, posing long-term
toxicological & public health risks.
3) Transitional Lakes = alternate between open & closed conditions depending on climatic variability.
• During wet periods => Inflow increases & salinity decreases = open-basin lakes.
• During dry periods => inflow declines & evaporation dominates, raising salinity
= closed system.
=> These systems are sensitive to climate change & regional water management,
thus good indicators.
1.3.2: Formation, age & origin
Lakes vary widely in age, depth, & origin.
• Majority of lakes are geologically young, formed only 6,000–15,000 years
ago after last Ice Age => Most lakes are formed by glacial processes (ice
movement & retreat), that’s why most are young…
• Coastal lakes are even more recent, appearing as sea levels stabilized
~6,000 years ago.
• Ancient lakes are rare (typically 2–20 million years old), often deep & of tectonic or volcanic origin. Example:
such as Baikal, Tanganyika, Malawi, Biwa
• Many modern systems are biotic or man-made, & shallow or small in scale.
