Lecture 26: STREAMS & RIVERS

Transcription

1 Lecture 26: STREAMS & RIVERS

2

3 LENTIC & LOTIC DIFFERENCES Lentic systems Lakes & ponds Standing water (stable) Organic material - within Lotic systems Streams & rivers Flowing water (dynamic) Organic material - outside 1. Physical 2. Chemical 3. Biological

4 Generally speaking, LOTIC SYSTEMS Stream narrower, shallower, clearer, cooler River wider, deeper, murkier, warmer Primary function - move water and solids (energy) Watershed area drained by a network of surface and groundwater flow into a waterway

5 1. PHYSICAL EFFECTS Flowing water erodes along its path: Solvent Hydraulic action dislodges materials Abrasion tumbling materials As a river meanders, it carves out some areas, deposits on other areas

6 1. PHYSICAL EFFECTS

7 STREAM HABITATS Pool - deeper area, slower moving water Riffle - more shallow, faster moving water Run - area in between, smooth flowing water

8

9 Previous habitats all within the main channel but lotic systems also have a floodplain Delineated by topography and flooding severity

10 Hyporheic zone saturated area below the stream; often connected to groundwater Kalff 2002

11 Riparian zone - transitional area between the aquatic system and adjacent land

12 RIPARIAN ZONE What is its importance? In many places, where has it gone?

13 2. CHEMICAL EFFECTS No epilimnion or hypolimnion (stratification):! No vertical gradients as in lakes! Large diel fluctuations in temperature (<DO) Instead, have longitudinal gradients:! Upstream impacts downstream In large systems, may have vertical light gradient - Mississippi River Influenced by watershed geology and land-use:! Point (direct) and non-point (runoff)

14 3. BIOLOGICAL EFFECTS: Advantages: FLOW! Food/nutrients may come to you (drift)! Typically sufficient dissolved oxygen! Dispersal of young Disadvantages:! May be washed downstream! Energy expenses Benthic processes dominate over planktonic

15 3. BIOLOGICAL EFFECTS: FLOW To survive, stream organisms need to balance getting enough food (nutrients) while avoiding predators and/or being washed downstream. Adaptations?

16 3. BIOLOGICAL EFFECTS: ORGANIC MATERIAL Autochthonous - originating within the system: Benthic algae: more important than phytoplankton Periphyton - algae, bacteria, protists and fungi that grow attached to submerged surfaces Macrophytes: Submerged Emergent Allochthonous - originating externally to the system

17 Coarse particles (CPOM)! Leaves, woody debris Fine particles (FPOM)! Partly decomposed litter, pollen, etc. Dissolved (DOM)! Nutrients from fresh, deciduous leaves! Soil particles, broken down materials Invertebrates

18 CPOM Shredders:! Stoneflies, crayfish, sowbugs FPOM Collectors:! Some mayflies/caddisflies, black flies, mussels (filter) DOM Bacteria, fungus, - phytes Periphyton Grazers/scrapers:! Snails, beetles, some mayflies/caddisflies Predators: Invertebrates (dragonflies) & vertebrates (fish) Trout: In summer, diet is up to 80% terrestrial invertebrates If excluded, shift to benthic invertebrates Nakan, Miyaksa, & Kuhara Ecology 80:

19 Primarily the same issues at a bigger scale Dominated by pool habitat Some shift from alloc- to auto- chtonous

20 Erode, transport, bury, channelize, etc. Export / deposit large quantities of organic material into floodplain! Enrich floodplain soils, enhance production Return of nutrients after flood recedes! Entrain fresh detritus from floodplain into river = augments food chains

21 Extremely valuable: Reduce downstream floods (energy release) Replenish ground water Filter silt, nutrients, & chemical contaminants Provide habitat (fish spawning & nursery) Communities dependent on seasonal inundation with unique producers and consumers " Flood pulse concept : annual, predictable

22 Natural process for rivers: Build natural levees Transfer of water & nutrients Artificial levees:

23 Definition - classification of a stream relative to its position in the hierarchy of its tributaries - branching complexity (tree) First order - headwaters, no tributaries (twigs) Second order - confluence of two first order streams (branches) New order - only when two streams of the same order converge Final order flows into a larger river or the ocean (trunk)

24 STREAM ORDER First and second orders: 80-90% of all streams Largest river systems: Mississippi 10 th order Amazon 12 th order

25

26 2 nd Order Mountain stream 5 th Order Piedmont stream Characteristics? Food web? Alloc- vs. auto- chthonous material? 8 th Order Piedmont-Coastal river

27

28

29

30 Useful concept, but always exceptions

31