What is a Watershed? http://www.wbtownship.org What is a Watershed? E DIVID A surface water designation The area that flows into a distinct drainage
stream, river, creek, pond Separated from other watershed by ridge-top boundaries divides DIVID E WATERSHE D
http://www.wbtownship.org HUC Watersheds: Major Watersheds Hydrologic Unit Codes http://water.usgs.gov/GIS/regions.html
Reynolds Creek Experimental Watershed Attribute to USDA-ARS.gov Watershed (Ecosystem) Services Regulation of climate Provision of shade and shelter
Prevention of soil erosion Maintenance of soil fertility Maintenance of soil health Maintenance of healthy waterways Water filtration Regulation of river flows and groundwater levels Ecosystem Services Project T.OKeefe(flickr)
Watershed Functions Hydrological Functions Water capture Water storage Water release Ecological Functions Provide diverse sites for biogeochemical reactions Provide habitat for plants and
animals Brian Crawford geo.lsa.umich.edu Capitalpress.com How Does Grazing Affect Watershed Services and Functions? Forage Utilization
J. Peterson Biodiversity Control weeds/invasive species Introduce weeds/invasive species Management Actions Creating water storage Prescribed fire
K. Launchbaugh The Hydrologic Cycle Water is classified as: Surface water or overland flow in a watershed context Underground water rangeland focus is on aquifers & recharge zones
K. Launchbaugh Fate of Water in Hydrologic Cycle Hydrology and Erosion by T. Thurow http://cnrit.tamu.edu/rlem/textbook/Chapter6.htm Fate of Water in Hydrologic Cycle
Hydrology and Erosion by T. Thurow http://cnrit.tamu.edu/rlem/textbook/Chapter6.htm Water Capture Precipitation - accumulation of water vapor forming rain drops, snow, or hail. Interception - precipitation that strikes objects such as vegetation, litter, or rocks and may eventually enter soil... but not necessarily. Infiltration water moving into the soil Percolation water moving through the soil
Capture is dependent on: Vegetation Soil Landcover Storm intensity
ecomerge.blogspot.com Infilitration Infiltration rate - water passing through the soil surface per unit of time. Thurow et al. 1986. Hydrologic characteristics of vegetation types as affected by livestock grazing systems, Edwards Plateau, Texas. Journal of Range Manage. 39:505-509. Infiltration
Depends on soil structure: Aggregation = soil particles held together in clusters Porosity = the amount of pores in the soil; creates air space in soils http://cnrit.tamu.edu/rlem/textbook/Chapter6.htm Effect of Vegetation on Water Transit Vegetation type: Oak Motte, Bunchgrass, Sodgrass, Bare ground (10 cm rainfall in 30 minutes)
Thurow, et al. 1986. Hydrologic characteristics of vegetation types as affected by livestock grazing systems, Edwards Plateau, Texas. Journal of Range Manage. 39:505-509. Effect of Vegetation on Water Transit Litter accumulation - slows runoff and decreases droplet impact Biomass differences - affects runoff, interception, and droplet impact Soil organic matter - increases water holding capacity of soil and increases infiltration
nceas.uscb.edu Effect of Fire on Runoff on Range Runoff after prescribed burn w/RO shows average of areas that had runoff (n=5) and removes areas without runoff (n=3) Runoff on sagebrush-steppe in SE Idaho Reynolds Creek Watershed
Moffet et al. 2007. Modeling soil erosion on steep sagebrush rangeland before and after prescribed fire. Catena. 71(2):218-228. Water Storage Surface Detention Water held in micro-relief formed by topography, vegetation growth, and accumulated litter. Is affected by micro-relief, slope, soil texture, soil structure, and soil depth. Water Table Upper surface of the ground water (saturated zone) can be above the ground surface e.g. streams, ponds, lakes. Aquifer Large volume of water underground on the top of an impermeable
layer of soil or bedrock Recharge Water added to the water table or aquifer Constructed water storage Reservoirs Water Release Runoff Surface runoff - water not entering soil, moving into streams or wetlands. Interflow - water below the surfacing moving horizontally. Can create springs and seeps.
Water Release Evapo-transpiration - combined effect of transpiration and evaporation Transpiration - plants lose water as part of respiration and cooling Evaporation - loss of water by heat. Vegetation tends to reduce evaporation through shade and reduce wind at soil surface. However, loss from evaporation on leaves often outweighs reduced evaporation from shade and reduced wind.
Water Release Deep Drainage Deep Drainage loss of water below the root zone Low bulk density because of trampling can decrease deep drainage Any factor that decreases infiltration
will likely decrease deep drainage http://ga.water.usgs.gov/edu/watercyclesummary.html Impacts on Runoff and Infiltration Water Inflow - generally little affect of grazing management on precipitation patterns Overgrazing could ... biomass & litter ... albedo ... convection precipitation events Overgrazing could ... air-borne bacteria ... water droplet
formation... precipitation Interception Grasses = 10-20% interception Deciduous trees & shrubs = 25-50% interception (when leaves are on) Evergreen trees = 50 - 100% (for example essentially no rain may hit the ground under a full juniper tree. A.Kabir(flickr)
M.Fathe All (flickr) T.Martin(flickr) Fire and Grazing at the Watershed Level Wildfires Must Consider: Appropriate rest period following fire Invasive plants livestock can control or introduce weeds Seed bed preparation hoof action can break up hydrophobic soils
Erosion potential is high following fire Prescribed Burning K. Launchbaugh Infiltration Depends on how grazing affects: Aggregate soil stability Soil bulk density or compaction Standing crop/litter biomass
Turner. 1971. Soil and Grazing Influences on a Salt-Desert Shrub Range in Western Colorado. Journal of Range Management. 24:31-37 Trampling Effects Herd Effect or Hoof Action
Compacts soil and/or breaks up soil aggregation at surface Effect depends on soil type, grazing intensity, climatic condition, etc. May enhance seed germination - Incorporates seeds into soils Disturb biotic (or cryptogamic) crust on soil Can increase infiltration in some area But, usually decreases infiltration and increases erosion. http://www.soilcrust.org/
Surface detention Depends on grazing intensity & soil moisture: Can _____surface detention and micro-relief at moderate grazing intensities At very heavy intensities on dry soils trampling can _____ micro-relief K.Launchbaugh Trampling Effects
Type conversion from herbaceous to woody = affects interception & infiltration Effect of Stocking Rate Effect depends on veg. type Ungrazed areas generally have higher infiltration rates than grazed plots Moderate and light grazing intensities have similar infiltration rates Only excessive grazing influences infiltration Heavily grazed areas cause reduction in infiltration
rates http://cnrit.tamu.edu/rlem/textbook/Chapter6.htm Human Needs, Desires, and Influences Clean water supply Food Recreation Wildlife viewing
Conclusions What happens at the top of the watershed affects the bottom of the watershed Many ecosystem functions and services are provided by watersheds Proper grazing management is critical to maintain these functions and services Interception Infiltration Recharge The watershed is a complicated area with many interactions
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