Streams
Open systems, constant input of water and nutrients
Precipitation flows into streams via 2 routes:– Overland flow through surface runoff– Infiltrating soil surface, then flowing
underground and into streams as groundwater
Stream Classification
Based on flow– Permanent: constant above-ground flow
year-round
– Intermittent/Ephemeral: flow aboveground for parts of the year, not all (temporal)
– Interrupted: flow aboveground for parts of the stream, not all (spatial)
Stream Classification
Based on order– 1st: no streams
flowing into it
– 2nd: two 1st-order streams joining
– 3rd: two 2nd-order streams joining
Physical features– Channel shape and pattern
• Changes with age
– Pools and riffles• Velocities, microclimate differ
Rivers “age”– Young: little meanders, small floodplain,
fast velocity, “V” cross-sectional profile– Mature: many meanders, slower velocity,
oxbows form, “U” profile
Watershed
The area that a stream drains, a.k.a, drainage basin, or catchment area
UNDERC area is near continental divide between Great Lakes drainage basin and Mississippi River basin
Water flows downhill– Upstream– Downstream
River Continuum Hypothesis
Predictable structure of river (physical features, dominant organisms) from upstream “headwaters” to downstream high-order stream
Headwaters/upstream:– Riffles/rapids predominant – Heavily shaded by riparian vegetation– Energy imported—allochthonous material– High diversity of benthic fauna
Downstream– Pools of slow water dominant– Only banks shaded by riparian vegetation– Autochthonous input
Lakes
May be created by a variety of geologic and climatic events:– Movement of tectonic plates– Volcanic eruptions– Landslides– Glaciation
Lake Zonation
Littoral zone: shallow (<2 m deep) margin characterized by rooted vegetation
Limnetic zone: characterized by open water
Profundal: beneath limnetic, extends to lake bed
Benthic: actual lake bed
Vegetation Zonation
Shrub & Trees
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Open waterphytoplankton
Lake Stratification
Different zones or layers due to water temperature and water density– Epilimnion: layer closest to surface of water;
warmed by the sun, least dense
– Metalimnion: “middle” layer with thermocline; transitional layer
– Hypolimnion: deepest layer, generally coldest; sunlight does not penetrate
Seasonal Changes
Summer:Warm temperatures,
long daysObvious vertical
stratification– Epilimnion saturated
with oxygen– Hypolimnion anoxic
Fall:Air temperatures cool, surface water cools
fastest and sinks to the bottom
Complete lake turnover– Lake no longer stratified
Lake eventually becomes a uniform 4ºC
Winter:Surface water cooler
than rest of lake water
Ice prevents mixing
Winter stratification, 0ºC at surface, 4ºC at bottom
Spring:Ice melts, water surface hits 4ºC and
again begins to sink
Spring turnover, process repeats itself
Nutrients
Temperature not the only stratified element of a lake– Oxygen: highest concentration near
surface (photosynthesis)– Nitrogen: NO3
- at surface, NH4+ at benthos
– Sulfur: SO4 at surface, H2S at benthos– Iron: Fe+3 at surface, Fe+2 at benthos
Marsh (Eutrophic)Bog (Dystrophic)
OligotrophicLake
Mesotrophic to Eutrophic Lake
Terrestrial
Sphagnum
Wetlands: technical definitionVegetation
– presence of “hydrophytic” (water-loving, flood-tolerant) plants
Soils– presence of “hydric” (flooded, reduced) soils
Hydrology– water table at or near the surface for part of the
growing season
Wetland history
Historically, wetlands have been drained to:– Provide land for agricultural purposes– Reduce the incidence of mosquito-borne
diseases, like malaria, yellow fever
Wetlands now recognized as having commercial, aesthetic, and ecological value
Why are wetlands important?
• Storm and floodwater storage
• Improved water quality: filtration
• Rare or endangered plants and animals
• Waterfowl nursery grounds
• Migration stop-overs
Bogs• Acidic (pH < 4.1)• Nutrient-poor soils• Ombrotrophic:
precipitation-fed system• Dominant vegetation:
Sphagnum moss, Vaccinium (cranberries and blueberries), and other low-lying species
• Slightly less acidic (pH 4.1-6.0)
• Soil more nutrient-rich• Minerotrophic:
groundwater-fed system• Dominant vegetation:
sedges, rushes, and grasses
Fens
Long LakeLong Lake
Peter LakePeter Lake
Paul LakePaul Lake
Nutrients added/Nutrients added/No PiscivoresNo Piscivores
Nutrients added/Nutrients added/PiscivoresPiscivores
No Piscivores
Piscivores
Recent Work
Trophic cascade work continues
Invasive species (crayfish)
Nutrient cycling in wetlands
Artificial streams
Plant and animal surveys of wetlands
Pitcher plant microcosms
Comparisons of tropical versus temperate stream function
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