Natural Resource Conservation- Aquatic Envs: Ecosystems - Wetlands

River Continuum Concept (RCC)

Ecological concept describing streams/rivers as continuously changing ecosystems, where physical, chemical, and biological conditions change along a longitudinal gradient (from headwaters to mouth)

• Rivers are a single integrated system- upstream shapes downstream

Stream Order

Headwaters (1st) → Larger Rivers (7+)

• Headwaters

• Mid-reach Streams

• Large Rivers

Key Rule:

• Only two streams of the same order merging moves up one order

Headwaters

Heterotrophic, allochthonous (dense canopy), shredders dominant organisms (what they break goes downstreams)

• Orders 1-3

Mid-reach Streams

Medium rivers, generally open canopies, algae and aquatic plants (primary productivity happening), autotrophic, autochthonous, grazers/scrapers are dominant organisms

• Orders 4-6

Large Rivers

Deep, high turbidity, input from wetlands and floodplains, not much plant growth, heterotrophic, allochthonous, collector gathers and filters are dominant organisms

• Orders 7+

Each Stream Order is Influenced by:

• Conditions (canopy cover, turbidity)

• Primary Production (P/R)- amount of energy produced to the amount of energy used

• Energy Source

• Dominant Organisms

Autotrophic

Primary production greater than respiration (produce more than consuming)

• P/R > 1

Heterotrophic

Respiration is greater than primary production (use more than producing)

• P/R < 1

Autochthonous

Organic matter is produced within the river/stream itself

• Mainly algae and plants

Allochthonous

Organic matter is originating from outside the stream

• Leaf litter, animals drowning

Dominant Organisms (functional feeding group)- 5 invert groups:

• Shredders

• Grazers/Scrapers

• Collector Gatherers

• Collector Filterers

• Predatory

Shredders

Breaking down organic material into smaller parts

Grazers/Scrapers

Getting algae and microbes off of surfaces in stream/riverbed

Collector Gatherers

Getting material from sediment

Collector Filterers

Getting material from flowing water

Predatory

Catching live macroinvert prey

Flow Regimes and Hydrological Connectivity

Impacted by:

• Magnitude- volume of water discharged

• Frequency- how often flood/low flows occur

• Timing- seasonal pattern of flows

• Duration- length of high/low flow events

• Rate of Change- speed or rise and fall

• Human Alterations- influence all 5 components

  • Dams, tile drainage, and impervious surfaces

High vs Low Flow

• High Flow- carves out channels, promotes erosion and deposition, allows for diverse habitats to be maintained, creates heterogeneous landscape

  • Bad when it happens too often

  • Flashy is too much

• Low Flow- concentrates organisms, changes temp, often seasonal and gives biological cues to animals in the system

Thermal Stratification

Separation of lakes into distinct horizontal layers based on temperature and density differences

• Occurs in temperate lakes > 10m in depth

• Water density is temperature-dependent

  • Densest at 4℃

Epilimnion

Uniformly warm, well-mixed, high O₂, light penetrates and photosynthesis can occur

Metalimnion

Barrier between top and bottom layer

Thermocline

Rapid drop in temp every meter you go down 

• Generally drop 1℃ every 1 meter down

Hypolimnion

Uniformly cold (4℃), isolated, low O₂, sunlight cannot penetrate, 

• Metalimnion prevents mixing, quickly leading to hypoxic and anoxic zones

Seasonal Turnover

Epilimnion cools, becomes denser, and sinks to bottom, causing mixing the mixing of layers

• Dimictic lake- turnover happens twice a year (spring and fall)

• Generally good but depends on lakes conditions

• Critical for oxygenation of bottom layer

• Internal Loading

Internal Loading

Release of P when oxygen depleted in hypolimnion

• When oxygen is high, iron is bound to P so P is bound up in sediment 

• When oxygen is low, organisms in sediment use iron, turning it into a form that cannot bind P so P becomes available to aquatic system

  • Leads to algal blooms

  • Ex. Lake Erie Dead Zone

Lake Trophic State Classification

3 Variables Measured:

• Total phosphorus concentration

• Chlorophyll-a concentration- proxy for algal biomass

• Secchi disk depth- shows water transparency

Lakes Slowly Age Through 4 Classifications

• Oligotrophic

• Mesotrophic

• Eutrophic

• Hypereutrophic

Ex. Lake Erie

• Eastern Basin- mesotrophic

• Western Basin- eutrophic

Oligotrophic

Low nutrients, high clarity, cold, deep

• TSI 0-40

Mesotrophic

Moderate nutrients and clarity

• TSI 40-50

Eutrophic

High nutrients, algal blooms, low O₂ bottom

• TSI 50-70

Hypereutrophic

Excessive nutrients, dense HABs (harmful algal blooms), odor, fish kills

• Even all nutrient input stopped, still will be loaded for long time

• Hard to recover from this state

• TSI 70+

Wetlands

Areas inundated/saturated by surface or groundwater at a frequency and duration that supports vegetation adapted for life in saturated soil conditions

Key Characteristics of Wetlands

• Hydric Soils

• Hydrophytic Vegetation

• Wetland Hydrology

Hydric Soils

Anaerobic (oxygen depleted) soils formed under prolonged water conditions, 

• Very distinct, not super firm

• Take a long time to form

Hydrophytic Vegetation

Plants have morphological or physiological adaptations that allow them to survive in water logged conditions

• Ex. Stilt Root- above ground part of root allows for oxygen transfer, provide support/stabilization

Wetland Hydrology

Water present for enough time to cause soil inundation/saturation

• Dictates development of hydric soils and hydrophytic vegetation 

• Basically, have to be able to tell it is regularly flooded

Wetland Types

• Marshes

• Swamps

• Bogs/Fens

• Saline Wetlands/Estuaries

• Others- prairie potholes, vernal pools, riparian wetlands

Marshes

Periodically or constantly flooded, dominated by herbaceous soft-stemmed plants, can be fresh of salt water

Swamps

Periodically or constantly flooded, dominated by woody plants (trees), can be in tropical areas

• Mangroves

Bogs/Fens

Dominated by moss and decaying plant matter, peat accumulating, generally found in boreal zones

Saline Wetlands/Estuaries

Freshwater meets and mixes with the saltwater sea, creates brackish water

• Tidal flats, salt marshes, mangroves, etc.

Wetland Function

Among the most productive systems on Earth

• Water Quality Improvement

• Flood Attenuation

• Carbon Sequestration

• Wildlife Habitat

Wetland Water Quality Improvement

All wetland plants settle nutrients and allows for denitrification (remove nitrogen from the system), also sequester phosphorus, important for removing nutrients and preventing overload

Wetland Flood Attenuation

Increases groundwater recharge and base flow, allowing continued flow in streams during times of little rain, returns water more slowly which reduces flooding

Carbon Sequestration

Carbon sink when healthy

• When drained, C released back into the atmosphere

Wildlife Habitat

• Biodiversity hotspots

• Habitat for birds and fish

• Distributed globally

Wetland Threats

Threatened worldwide

• Drainage- 35% in world’s lost since 1970s

  • Michigan lost 40%, Ohio lost 90%