Floodplain Management Session 12 Biology Effects of human disturbances on rivers and floodplains Prepared by Susan Bol

1. Floodplain Management Session 12BiologyEffects of human disturbances on rivers and floodplainsPrepared by Susan Bolton, PhD, PE

2. Effects of human disturbances Objectives: 12.1 Identify changes in land cover/land use in watersheds and learn how to assess these changes as they relate to river and floodplain ecology 12.2 Identify changes of concern in aquatic and floodplain communities due to changes in land use and land cover. 12.3 Identify additional sources of threats to floodplain and river ecology

3. Landscape controls Physiography Climate Gross reach morphology Habitat Forming Processes Solar energy and Organic input Regime Nutrient Inputs Sediment and Hydrologic Regime Stream Morphology and Conditions Habitat complexes and conditions e.g., pools, riffles, temperature, etc. Biodiversity Species assemblages Land use/cover and vegetation Modified from Roni et al. 2002.

4. Land use and land cover • Land use is technically the way humans employ the land and its resources • Land cover is the physical state of the land surface and originally referred to vegetation (e.g., forest, grass) • Land cover also included soils and water information (e.g., soil types, wetlands, streams) • Land cover now includes human structures such as pavement and buildings

5. Land cover/use information • Annual National Resource Inventory by the USDA-NRCS • 8 categories • Cropland, pastureland, grassland, forest land, other rural land, developed land, water bodies and land in conversion from cropland to vegetated land (CRP- conservation reserve program) • Other agencies may use different categories

6. Land cover/use information • Ohio uses a number of subdivisions of the 8 USDA categories when data are available http://www.dnr.state.oh.us/htdocs/realm/ resanalysis/lumain.html#definitions • Other agencies may use different categories

7. Watershed Assessment • Watershed assessment is a crucial first • step in determining the current and • potential condition of a watershed. • Identify historic and current habitat types • What is/were their size and distribution over • the watershed? • How do the habitats relate to current or historic • distributions of species?

8. Watershed Assessment • Identify current and historical habitat distributions in the watershed • Use air photos, old maps, General Land Office surveys, etc. • Relate current and potential habitat to species distribution • Identify habitat forming processes and any changes to their rates, frequency, magnitude or duration

9. Watershed AssessmentHabitat forming processes • Sediment regime • Hydrologic regime • Nutrient inputs • Solar energy/light inputs • Organic matter inputs

10. Watershed assessment methodsHabitat forming processes • Sediment regime • Quantify landslides and estimate sediment budgets • Assign landslide hazard ratings to roads and hillslopes • Map surface erosion areas such as unpaved roads, bare areas, construction zones

11. Watershed assessment methodsHabitat forming processes • Hydrologic regime • Analyze flow records for changes in peak flows, flow durations, base flows, etc. • Assess connectivity changes in watershed, e.g. dams, diversions, levees, impervious area

12. Watershed assessment methodsHabitat forming processes • Nutrient input regime • Assess background inorganic inputs based on geologic and soils maps • Assess inputs from anthropogenic sources such as:

13. Watershed assessment methodsHabitat forming processes • Solar energy/light regime • Assess current and historical shade/canopy conditions in stream and floodplain • Assess current and historic turbidity levels in streams

14. Watershed assessment methodsHabitat forming processes • Organic matter input regime • Assess riparian and floodplain forest/vegetation conditions • Identify current and historic fire return patterns

15. Watershed Assessmentfinal steps • Identify which processes have been altered by changes in the watershed condition and the origin of the alterations. • Identify the effects of the changes on stream ecology and decide whether to try and correct the changes.

16. Objective: 12.2 Identify changes of concern in aquatic and floodplain communities due to changes in land use and land cover.

17. Characteristics of disturbances • Frequency – number of times an event or disturbance occurs over a fixed time period, referred to more accurately as probability (e.g. probability of a flood of a given magnitude over some time period) • Duration – The time span over which the disturbance occurs (e.g., flooded time period) • Magnitude – this size of the disturbance, this may refer to the quantity of the disturbance (e.g., rainfall) or the area covered (e.g., acres burned) • These concepts are evident in engineering design in the form of design limits (e.g., the use of ‘depth-duration-intensity’ charts for precipitation used for designing runoff storage)

18. Changes of concern • Alter ecosystem structure and function such that recovery from the disturbance is threatened • Loss of watershed process or structure that persists beyond normal cyclical change (i.e., disturbances are more frequent, larger or of longer duration than expected)

19. Effects of human disturbances on rivers and floodplains Changes of concern generally permanently alter habitat forming processes

20. Examples of changes of concern • Changes in efficiency and pathways of nutrient cycling • Alteration or cessation of vegetation successional sequences • Pronounced changes in species diversity • Increased incidence of diseases • Abnormal population fluctuations • Permanent shifts in energy sources • Shifts in water temperature, light, and suspended sediment

21. Human caused disturbances • Agriculture • Timber harvest • Mining • Urbanization • Introduction of exotic species • Harvesting of fish and wildlife

22. Human caused disturbances • Agriculture

23. Human caused disturbances • Timber harvest

24. Human caused disturbances • Mining M. Kondolf

25. Human caused disturbances • Urbanization

26. Human caused disturbances • Introduction of exotic species Whirling disease in trout Sea lamprey and trout damage Water hyacinth

27. Human caused disturbances • Harvesting of fish and wildlife

28. Land Use and Vegetation The landscape control factor on which humans have the most influence • Mining: extent of vegetation alteration depends on type of mining • Forestry: tree removal and replacement over time • Urbanization: tree removal and replacement with grass and impervious surfaces • Agriculture: tree removal and replacement with pasture or crops, often non-perennial

29. Common effects of human alterations to the landscape • Vegetation removal or alteration • Changes in soil characteristics (compaction, paving, roads and ditches) • Changes in water and sediment storage (dams, retention ponds, stormwater) • Changes affect the connectivity of the watershed by altering flow paths and flow timing

30. Potential effects of human alterations to the landscape • Changes in vegetation on streams and floodplains affects • Light and energy inputs to the aquatic ecosystem • Organic matter inputs to the aquatic ecosystem • Sediment inputs to the aquatic ecosystem • Changes in light and flow pathways can alter water temperature • Changes in organic matter can alter habitat complexity and food webs • Changes in sediment production, transport and storage affects channel morphology, and substrate habitat

31. How can streamflow be described in a way that has ecological meaning?

32. Flow characterization • Magnitude - how much? • Frequency - how often? • Timing - when? • Duration - how long? • Rate of change – how fast?

33. Indicator of Hydrologic Alteration Model • The IHA was developed by The Nature Conservancy • Model available free from TNC web site • Used to assess extent of change in streamflow from a dam or diversion • Need pre- and post- disturbance flow data

34. Ecological importance of hydrologic indices • Skewness (mean daily flow/median daily flow) describes daily flow conditions for aquatic taxa and may be especially important below dams with variable releases compared to natural flows

35. Ecological importance of hydrologic indices • Coefficient of variation of mean monthly flows in natural systems may indicate the importance of high and low flows for the distribution and propagation of riparian vegetation seeds and riparian vegetation density

36. Ecological importance of hydrologic indices • A flood duration measurement (e.g. monthly flow equaled or exceeded 95% of the time divided by mean monthly flow) can be important for determining the ability of floodplains to sustain a diverse riparian forest in snowmelt driven stream

37. Ecological importance of hydrologic indices • Indicators of flashiness (e.g. the coefficient of variation of the number of flows that exceed the 75th percentile of daily values) or the variability in changes of flow reversals (e.g. the coefficient of variation of the number of negative and positive changes in water level from one day to the next) may help identify the persistence of native and non-native stream organisms in intermittent streams

38. Ecological importance of hydrologic indices • For more examples and more information see (Olden and Poff 2003) and other references cited within

39. Objectives: 12.3 Identify sources of threats to floodplain and river ecology

40. Threats to Aquatic Species • Aquatic species at higher risk of extinction in the U.S. than terrestrial species • < 20% of terrestrial vertebrates are classified as at risk • Estimates range from 35% to 70% of aquatic species at risk

41. Sources of major threats • Habitat destruction and fragmentation • Pollution • Exotic species

42. River habitat destruction and fragmentation • Dams, diversions and channelization disrupt the 4 dimensions of the river ecosystem, especially the lateral and longitudinal connectivity of rivers

43. Brooks1988

44. Effects of dams • Cold bottom release water can threaten native warm-water species • Riparian vegetation survival and reproduction is affected by floods or the lack thereof • Sediment and nutrient retention behind dams affects food webs, energy flow and nutrient cycling below dams

45. Pollution • In 1994, EPA identified siltation/sediment as the leading cause of water quality impairment • > 70% from agricultural practices • 15% from municipal point sources • 11% from urban runoff and sewer discharge • Other sources include resource extraction, industrial point sources and silviculture

46. Pollution • Nutrient enhancement the second leading cause of water quality impairment • 45% comes from agricultural practices • 42% comes from municipal land use • Other sources of pollution include pathogens, pesticides, and organic enrichment which can lead to low dissolved oxygen levels

47. Exotic Species • Changes in floodplain vegetation can affect evapotranspiration rates, stream bank stability, food and nesting sites for animals, stream shade and organic inputs to streams • Changes in aquatic species can alter food webs and nutrient and energy transfers in the stream

48. Homework- Prepare for discussion at start of next session • What are the major land use/land cover categories in your watershed? • Are there any aquatic or riparian species at risk in your watershed? If so, what are the reasons for their imperiled status? • Write a short essay on how sediment, hydrologic, nutrient, organic and solar energy/light regimes have changed since the pre-development state of your watershed.