Stream Ecology

1. Stream Ecology R. Christian Jones June 2008 Tidal Potomac Teacher Training Workshop

2. Fate of Precipitation in a Watershed • Interception • Depression Storage • Infiltration • Surface Runoff • Interflow • Groundwater • Stormflow • Baseflow

3. Baseflow • Streams continue to flow even when rainfall is not occuring or has not occurred in the past few days • The flow not directly associated with at storm is called baseflow • It derives from groundwater and part of the throughflow which takes a long time to reach the stream

4. Stormflow • Surface runoff and near surface throughflow result in rapid increases in streamflow following a storm • This is called stormflow

5. Storm Hydrograph • A storm hydrograph shows the response stream discharge (Q) to a single storm • Basin lag is the time between the peak of precipitation and the peak of runoff • Stormflow/storm runoff is the surface runoff directly attributable to the storm

6. Watershed size influences the response time and flashiness of the hydrograph Characteristics of Stream & River Flow Large Watershed Small Watershed

7. Stream Ordering System • We can define where we are at in the longitudinal drainage network by determining stream orders • The rules for stream ordering are fairly simple: • Headwater streams are order 1 • Stream order increases by 1 when two stream of the same order come together.

8. Stream Food Webs • Sources of Organic Matter • Autochthonous: production occuring within stream system (ex. Algae, macrophytes) • Allochthonous: production occuring elsewhere and being imported into the stream system (ex. Terrestrial leaves)

9. Stream Food Webs • Types of Organic Matter by Size • CPOM: coarse particulate organic matter • (>1mm) • [whole leaves, large leaf fragments] • FPOM: fine particulate organic matter • (<1mm, >0.45 um) • [fine leaf fragments] • DOM: dissolved organic matter • (<0.45 um) • [sugars, amino acids, etc.]

10. Longitudinal Changes – Reach Scale • Longitudinal changes are also observed at shorter scales than the entire river length • We call this shorter scale the “reach” scale • One example of reach scale changes is the pool-riffle pattern found in many streams draining areas with medium gradient like our area • Riffle is an area of rapid flow over coarse substrate (rocks) whereas the pool is a slower flowing stretch with finer substrate

11. Stream Food Webs • Types of Consumers • By food type • Herbivores: feed on living primary producers • Detritivores: feed on dead organic matter and associated microbes

12. Stream Food Webs • Types of Consumers • By feeding mode • Scrapers: obtain food by rasping or scraping it from rocks (dominantly herbivores) • Shredders: ingest detrital material torn or shredded from large pieces (ex. Leaves) • Filter collectors: ingest FPOM collected by filtration, usually from flowing water, often found in riffles • Deposit collectors: ingest FPOM collected from deposits, often found in pools • Predators: ingest other animals

13. Stream Food Web - Overview

14. River Continuum Concept • Stream food web changes in an orderly and predictable way as stream order increases

15. Erosive High current velocity Larger substrate particles (cobble) Often shallower “riffles” ---- “runs” Depositional Low current velocity Smaller substrate particles (clay, silt) Often deeper “pools” ---- “backwaters” Stream Habitats

16. Consumers - Taxa • Turbellarians • Flatworms • Generally carnivores on other small invertebrates • Nematodes • “round worms” • Very small: herbivores and carnivores

17. Consumers - Taxa • Annelid worms • Oligochaetes • Aquatic earthworms • Deposit feeders • Very common • Hirudinea • Leeches • Carnivores, Detritivores

18. Consumers - Taxa • Molluscs • Snails • Mobile • scrapers • Bivalves • sessile • Filter collectors

19. Consumers - Taxa • Crustaceans (arthropods) • Crayfish • Detritivores • Large, may be found in urban streams • Amphipods • Detritivores • Medium sized • May be important, esp below cow activity & in alkaline waters

20. Consumers - Taxa • Insect Life Cycles • Complete Metamorphosis • Growth and development phases separate • Egg  Larvae  Pupa  Adult • Incomplete Metamorphosis • Growth and development phases combined • Egg  Nymph  Adult

21. Consumers - Taxa • Insects (arthropods) • Plecoptera • “stoneflies” • Shredders or predators • “clean water” • Nymph aquatic • Ephemeroptera • “mayflies” • Scrapers or collectors • “clean water” • Nymph aquatic

22. Consumers - Taxa • Insects (arthropods) • Trichoptera • “caddisflies” • Filter collectors and scrapers • Many spin nets • Mostly clean water • Larvae and Pupae aquatic

23. Consumers - Taxa • Insects (arthropods) • Coleoptera • “beetles” • Predators or collectors • Mostly clean water • Megaloptera • “hellgrammites” • Predators • Mostly clean water

24. Consumers - Taxa • Insects (arthropods) • Diptera • “two-winged flies” • Includes a wide diversity of feeding types and tolerances • Chironomids (“midges”) are a very ubiquitous group • Larva and pupa aquatic

25. Adaptation to Flowing Water • Life Cycles are often adaptive • Many aquatic insects are aerial as adults to facilitate dispersal and crossbreeding • Some species concentrate their growth phases in periods of favorable conditions (moderate temp, plenty of water and food) and revert to dormant stages (eggs, pupae) during other stages

26. Adaptation to Flowing Water • Feeding mechanisms: • Scrapers: radula in snails, mayfly nymphs use bristles • Filtering mechanisms: • Fringes of hairs on mouthparts and legs • Caddisfly Nets • Blackfly

27. Adaptation to Flowing Water • Anchoring • Flattening of bodies to stay in boundary layer • Suckers, hooks, silky secretions • Ballast

28. Comparative Energy Flow in Streams • Bear Brook • Wooded second order stream in New England • Dominated by allochthonous inputs from forest canopy directly and from upstream

29. Comparative Energy Flow in Streams • New Hope Creek, NC • Third order stream with more open canopy, but still allochthonous material is more important

30. Large Rivers • In large rivers, interactions between main river channel and floodplain become increasingly important • Length>2000 km, Order>7

31. Large Rivers • Channel is deep and turbid • Substrate is fine and in constant motion • Upstream food supplies are of poor quality, best compounds have already been utilized • Many backwaters and side channels with slower flow • Flood plain inundation is relatively predictable so aquatic communities can adapt to this as a resource

32. Large Rivers • Single large pulse inundates the entire flood plain • Land-water interface (littoral) is pushed to the edge of the floodplain • As year proceeds, the moving littoral (ATTZ) slowly edges back toward the channel margin • ATTZ-aquatic-terrestrial transition zone

33. Large Rivers • Habitats within the floodplain: • Backwaters • Lakes • Wetlands

34. River brings Plant nutrients (N&P), organic particulates, inorganic particles from upstream N&P  fuel high production Particulates  build up flood plain, carry P Flood plain contributes Fresher CPOM, FPOM, DOM than upstream sources Nursery ground for many invertebrate prey organisms Many larger predator animals enter flood plain to feed Large Rivers – Exchanges of Materials