Implications of Channelization and Sedimentation on Bottomland Hardwood Ecosystems Aaron Pierce, Ph.D. Louisiana State University Hydrology • Single most important factor affecting wetland function • Influence plant structure, composition, invert communities and wildlife Hydroperiod • Seasonal pattern of water level in a wetland • Defines the rise and fall of a wetlands surface and subsurface water levels 1 Wetland Hydroperiod Seasonal pattern of water level in a wetland. Hydrologic Signature Hydrograph Depth Ground Time Surface 3 Components: 1) Flood duration: Average or total amount of time standing (6 COE Zones) water exists during a flood event. 2) Flood frequency: Average number of times a wetland has standing water per year. 3) Flood depth: Depth of aboveground standing water. Hydroperiod Variability • General patterns over long-term but highly unpredictable within and among years • Natural variability is essential to maintain system productivity Flood Pulse Concept • Lateral connectivity of a river and its floodplain is critical for productivity of river, forests, and its organisms • Life-cycles of floodplain plants and animals and many floodplain functions (e.g., sediment retention) are linked to flooding patterns 2 Dynamic Hydrology of Hardwood Bottomlands Day 1 Day 5 Natural hydroperiod is characterized by stochastic and ephemeral flooding events Unaltered Systems Geomorphology • Floodplains are formed from the erosion and deposition of sediment • Patterns and rates of erosion and deposition are critical forces affecting wildlife Where is natural scouring and and fish habitat deposition occurring? 3 Sedimentation • Provides sediment retention, improves water quality, replenishes nutrients, and creates new areas for colonization by wetland plants Point bar deposition – within stream channel • creates ridge and swale topography • temporary storage of sediment Vertical Accretion – deposition in the floodplain • results from overbank flooding • forms the primary floodplain soils • rates and textures are highly variable Overbank Sedimentation • Deposition rates typically <1 cm/yr • Most deposition occurs near the stream channel • Depressional areas can also receive high rates of deposition Geomorphology and Vegetation Black Gum White Oak Live Oak Loblolly Pine Water Hickory Overcup Oak Hickories Overcup Oak Green Ash Water Oak Red Maple Cow Oak River Birch Green Ash Cherrybark Oak Black Willow Water Elm Sweetgum Cottonwood Water Tupelo Willow Oak Baldcypress High Ridge Low Flats Back- Ridge High swamp Low Ridge Ridge Levee Oxbow Stream Channel First Bottom Second Bottom From Conner 1994 4 Activities Impacting Wetlands •Dams •Highways • Irrigation • Levees • Oilfield Canals • Channelization Reasons for Channelization • Mainly for agricultural purpose to remove water from land for cultivation Channelization • Straightens, shortens, and steepens stream channels • Increases stream velocity and stream power • Facilitates transport of sand to the river system • Impacts hydrology and geomorphology 5 Hydrologic Impacts • Alters timing, depth, duration, and frequency of flooding • Disconnects rivers from the floodplain • Can cause excessive ponding at confluences Geomorphic Impacts • Excessive sediment deposition, increased overbank flooding, increased water table, degrade bottomland systems Hatchie River • Headwaters are in Upper East Gulf of Mexico Coastal Plain • Drains into MS River • Longest unchannelized stretch of river in LMAV 6 Hatchie River • Supports 100 species of fish, 250 species of birds, 50 species of mammals, 35 species of mussels, and numerous herps • Globally rare Hatchie River burrowing crayfish • TNC "Last Great Place" list http://www.hatchie.com/index.html BLH Forests • Structurally diverse • Highly productive • Important timber resource and provides important wildlife and fisheries habitat Economic Value • Over $3.6 billion generated by timber industry in West TN in 1997 • BLH are an important component of regional and state economy 7 BLH Losses Arkansas Arkansas Tennessee Tennessee Mississippi Mississippi Louisiana Louisiana System Alterations • Extensive channelization of over 90% of the tributaries • Altered hydrology caused rapid geomorphic adjustment Root of the Problem • Geology – Source of the sand • Past and Present Land Use – expose the sand Thin Fertile Loess Layer with Underlying Sand 8 Gully Erosion Channel Erosion Jeffers Creek 9 Bed Load Transport Fine Silts and Clays Coarse Sand Valley Plugs • Occur where sediment (sand) laden waters slow in velocity • Debris jams and intersections of tributaries and rivers are common locations • Completely plugs the channel • During subsequent flows, the plug enlarges upstream as additional sand is deposited 10 Valley Plug Unaltered Tributary Valley Plug Formation Bear Creek Channel Profile Distance upstream from VP and Channel Depth 0.4 Filled at Valley Plug 0 01234567899 VP -0.4 50m 100m (m) 150m 200m 250m -0.8 -1.2 Full channel depth at 250 m -1.6 (m) Possible Impacts • Increases in the water table height • Shift in floodplain plant species composition • Homogenizes aquatic habitats • Alters flood frequency Hickory Creek – valley plug 11 Overbank Flooding Excessive Deposition Sand Splay Telephone Pole Effect Sanding of Timber • Kills standing timber • Alters tree species composition •Buries productive soils 12 Ponding of Timber • Increased water table and accelerated natural levee development encourage permanent ponding of timber Abandoned Channel • Reduced flooding and sedimentation leading to a shift in species composition Shoal Sites • Shoal sites may be impacted in similar ways as valley plug sites but to a lesser Tributary extent Intersection • Channel filling influences overbank flooding and the water table • Crevasse splays cause excessive deposition in the floodplain 13 Location of Study Streams Control Study Site Sampling Design Upstream Tributary 50m 200m = plots sampled for Downstream sediment deposition Valley Plug Study Site Sampling Design Downstream Abandoned Channel 200m = Valley Plug = plots sampled for sediment deposition 50m Upstream 14 Feldspar Clay Sediment Pads Excessive Sand Deposition 0.78 meters Early Spring Fall • Dendrogeomorphic approach to measure sedimentation • Provides a long- term average of sedimentation Relate age with depth to root collar (tree base) 15 Mean Annual Deposition 2002-2004 Valley Plug Sites (4): A 6.0 • Mean = 5.46 cm/yr •SE = 0.44 4.5 Shoal Sites (2): 10X • Mean = 0.57 3.0 Deposition •SE = 0.24 1.5 Control Sites (4): Annual Deposition (cm) B B • Mean = 0.46 cm/yr 0.0 •SE = .05 Valley plug Shoal Control Geomorphic Feature Maximum Annual Sediment Deposition Rates (cm/yr) Valley Plug Sites 80 70 60 50 N 40 R R T , A A r e , , e k p r s 30 v e e i a t N L m iv i R a i T t S r o w R 20 n l u r o S e o f r o e l h t s t e k c s s e c a n Deposition Range (cm/yr) Deposition 10 i a o e R l C M C W B 0 Heimann & Hupp & McInyre & Hupp & Kleiss Pierce & Pierce & Roell 2000 Brazemore Naney Morris 1996 King 2004 King 2004 40X 1993 1991 1990 Study <2 cm per year Deposition Texture Types 100% 90% 80% 70% Larger 60% Sediment 50% at VP 40% and 30% Shoals! of Plots Percentage 20% 10% 0% Valley Plug Shoal Meander % Sand % Silt/Sand % Silt 16 Deposition at Valley Plugs by Location 14 11 Where does 7 deposition occur? 4 Annual Deposition (cm) 0 1234 1 = upstream of vp, 2 = at vp, 3 = downstream of vp, 4 = control Dendrogeomorphic Analysis 8 Why?? 7 valley plug 6 control 5 4 Greatest 3 Sedimentation with Youngest 2 Mean Deposition in cm/yr Trees 1 0 1840 1860 1880 1900 1920 1940 1960 1980 2000 Year of Tree Germination Spatial Trends Deposition In direction at Control of channel Site and in depressions Low Deposition (<0.5 cm/yr) Prediction Map 0 120 240 Meters Contours 0 - 0.19 cm/yr 0.20 - 0.47 cm/yr 17 Spatial Trends Perpendicular to channel Deposition at Valley Plug High Deposition (>1 cm/yr) Prediction Map 0 110 220 Meters Contours 0 - 0.76 cm/yr 5.80 - 11.19 cm/yr 11.20 – 41.55 cm/yr 0.77 - 1.52 cm/yr 1.52 – 5.79 cm/yr Summary • Deposition is 10 times greater at valley plug sites than at control and shoal sites • Significant differences in deposition types among soil types • Valley plugs are progressing upstream, impacting new areas • Valley plugs change the spatial dynamics of sedimentation Future Work • Investigate linkages between excessive sedimentation and changes in surface and subsurface hydrological regimes • Determine implications of excessive sedimentation, surface and subsurface hydrology on succession of BLH forests 18 Maximum Flood Depth and Total Duration of Flooding Initial Findings 250 VP Sites Drier!!! 200 Why? 150 100 50 0 Bear vp Hickory vp Jeffers vp Marshall Spring Hatchie GVL Maximum Flooding Depth (cm) Total Duration of Flooding (days) Abundance of Tree Species Control SiteInitial Findings Valley Plug Site Cypress, Oaks Maple Maple, Willow, Sweetgum Oak Elm Ash Cypress-Tupelo Willow-Birch Sweetgum Hickory Sycamore-Cottonwood Others Differences in Species Evenness! Acknowledgements • Funding provided Special Thanks : by the U.S. Fish Dr. Cliff Hupp and Wildlife Service and the U.S.D.A. – Dr. Tim Diehl CSREES: Initiative The Nature Conservancy for Future Agriculture and Food Systems. Field Crew: Justin Nolte, Eric Sawyers, Chuck Yoest, Nick Wirwa, B.J. Wilson, Wes Cochran, Jimmy Fox, Jeff Roberson, and Nick Winstead 19 Questions? Photograph by Byron Jorjorian 20.