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Ecological Functions of Headwaters Streams and Riparian Zones

Ecological Functions of Headwaters Streams and Riparian Zones. Dr. James D. Gregory Department of Forestry North Carolina State University. Hydrologic Functions. Processes related to water at the earth’s surface Rainfall input to the surface Infiltration into the soil

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Ecological Functions of Headwaters Streams and Riparian Zones

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  1. Ecological Functions of Headwaters Streams and Riparian Zones Dr. James D. Gregory Department of Forestry North Carolina State University

  2. Hydrologic Functions • Processes related to water at the earth’s surface • Rainfall input to the surface • Infiltration into the soil • Storage and movement of water in the soil • Runoff to streams • Transport of sediment and dissolved constituents in runoff

  3. Headwaters Stream • Refers to the first order and second order streams of a watershed without regard to location in the watershed or their classification as intermittent or perennial.

  4. Riparian Zone • Riparian zone - land area transitional between terrestrial and aquatic ecosystems in which the ecological functions of the land are influenced by proximity to water and the ecological functions of the water are influenced by proximity to land. Zone of transfer between the land and a water body.

  5. Think Stream Corridor • Stream and the riparian zone are components of an integral ecosystem • Considering nonpoint source pollutant inputs, the water quality of major tributaries and rivers is influenced mainly by the hydrologic and ecologic functions of headwaters stream corridors.

  6. Hydrologic Role of Headwaters Streams • Most of the land area of the humid US drains to them • Headwaters streams are bordered by a major portion of the total length of riparian zones • Headwaters streams are the piping network for transport of pollutants from the land to rivers and estuaries

  7. Stream Order Number of Stream Segments Total Stream Length, miles Area Drained, % of Watershed 1 20 16.1 73 2 5 3.1 12 3 2 2.1 9 4 1 1.1 6 Total 28 22.4 100 Stream Network Parameters

  8. Stormflow Accounts for Most of Pollutant Transport to Streams ! • All erosion and sediment transport to streams – most of that on an annual basis occurs during the few largest storm events • Potential pollutants are flushed from the soil and transported to streams • Microorganisms • Soluble inorganic compounds • Soluble organic compounds from organic matter decomposition • Anthropogenic toxics

  9. Ecological Role of Riparian Zones Effects on Stream Water Quality

  10. Source Area for Streamflow • Natural forested ecosystems – subsurface flow to riparian zone, discharge from upstream - ephemeral streams!!!! • Agricultural ecosystems – greater proportion of stormflow is overland flow, ephemeral streams in fields • Suburban & urban – overland flow is dominant, pipe or ditch flow through the riparian zone

  11. Removal of Dissolved Nutrients from Runoff • Maximal removal occurs with subsurface flow • Phosphorus – most is adsorbed to sediment • Nitrogen – most removal occurs in soil that has combination of aerobic and anaerobic zones • Aerobic – NH4 to NO3 • Anaerobic – NO3 to N2

  12. Sediment Removal from Overland Flow • Infiltration to convert overland flow to interflow • High surface roughness (litter, large woody debris, ground level vegetation) - slows velocity of overland flow, promotes sedimentation

  13. Tall, Deep Rooted Woody Vegetation • Root systems help maintain channel stability and limit rates of bank erosion • Contributes litter (fine organic matter) to stream food chain – key component of food chain in headwaters streams • Contributes coarse woody debris – structure in stream, contributes to habitat diversity and quality • Shading riparian zone soil and the stream to maintain the natural stream temperature regime

  14. Ecological Role of Headwaters Stream Channels • Biological and chemical processes remove nutrients from streamflow • Exported organic matter contributes to food chain support downstream • Main source of water to the major streams and rivers - high quality water or polluted water

  15. Timber Harvesting Impacts • Soil hydrologic functions • Riparian zones • Stream channels

  16. Functional Widths of Riparian Zones • Remove nutrients from subsurface flow: 50-100 ft. • Remove sediment from dispersed overland flow: 50-100 ft. • Organic matter input to the stream – width greater than tallest trees • Shade – • Stream channel stabilization – trees within 15-25 ft. of the stream

  17. Soil Hydrologic Functions Reduced infiltration capacity and reduced soil water storage capacity Results from – compaction, loss of macropore space Conversion of subsurface flow to overland flow Increased runoff – increased potential for elevated nutrients and sediment in runoff that reaches streams All these effects also result in reduced productivity

  18. Stream Corridors • Reduced capacity of the riparian zone functions • Negative impacts on stream functions • Increased inputs of sediment and nutrients • Reduced input of fine organic matter • Increased runoff – possibly increased rate of channel erosion • Alteration/degradation of the biotic elements of the stream • Reduced water quality

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