Special Sessions
Sponsored by the Geomorphology Specialty Group
Association of American Geographers 103rd Annual Meeting
San Francisco, California, April 17-21.

Human Impacts on Watershed Processes 4 - Ecological Aspects

Paper Session 4401
Friday, 4/20/07, from 2:00 PM - 3:40 PM

Sponsorship(s):

Geomorphology Specialty Group
Water Resources Specialty Group
Spatial Analysis and Modeling Specialty Group

Organizer(s):

John Faustini - Oregon State University
Shixiong Hu - East Stroudsburg University

Chair(s):

John Faustini - Oregon State University

Abstract(s):

• 2:00 PM Author(s):
  *Luc Claessens - University of Connecticut
  Christina Tague - University of California Santa Barbara
  

  Abstract Title: Hydro-Ecological Linkages in Nitrogen Export from Urbanizing Watersheds.

  
  

  We investigate the role of small streams in controlling nitrogen export from an urbanizing watershed, Baisman Run, located within the Baltimore LTER program. From extensive field experiments and hydro-ecological modeling, we demonstrate that small streams play an important but complex role in controlling nitrogen export from this urbanizing watershed. In-stream nitrogen processing is strongly controlled by both stream size and stream flow conditions. In addition, spatial and temporal variability in nitrogen concentrations throughout the stream network complicates the interpretation of experimentally derived uptakes. We will present a variety of results from nutrient addition experiments, synoptic sampling, long-term nutrient budgets, and stable isotopic sampling. In addition we will present results from hydro-ecological modeling investigations, including the development of a simple geomorphic-based model of nitrate loss, and its application using Lidar-derived stream characteristics.

  Keywords: hydrology, ecology, urbanization, watershed, nitrogen

  
  
• 2:20 PM Author(s):
  *Shixiong Hu - East Stroudsburg University
  Jerilyn Jewett-Smith - East Stroudsburg University
  

  Abstract Title: Study on Environmental Controlling Factors for Spread of Invasive Riparian Plants in the Paradise Watershed, PA.

  
  

  Paradise Watershed, a small northeastern Pennsylvania system with an area of 44.5 square miles, is experiencing the spread of invasive plants in the river corridor. This change in the riparian vegetation is displacing indigenous species and has the potential to impair biodiversity. For effective management of the invasive plants, knowledge about the general patterns and controlling factors of spread in the riparian corridor is needed. Using GPS and hand-held GIS units, an inventory of invasive species, including Japanese knotweed (Polygonum cuspidatum), stilt grass (Microstegium vimineum), Japanese barberry ( Berberis thunbergii) and multiflora rose (Rosa multiflora), has been built through field investigation. Major environmental factors for the spread of invasive plants have been identified with the Geostatistical Analyst extension in ARC GIS and SPSS software. A statistical relationship between the distribution of invasive plants and the controlling factors has been established to examine the relative contribution of each factor. The preliminary results show that the distance to roads, flood plain, light, temperature, soil nutrients, bridge existences and high stream flow are major controlling factors for the hot spots of invasive plants in the river corridors. These factors account for about 75% of the distribution and abundance pattern in invasive riparian plants.

  Keywords: Spread of Invasive Plant, Northeast PA, Environmental Controlling Factors, and biodiversity

  
  
• 2:40 PM Author(s):
  Nicole M Czarnomski - Oregon State University
  David M Dreher - Oregon State University
  *Julia Jones - Oregon State University
  Frederick J Swanson - US Forest Service Pacific Northwest Research Station
  

  Abstract Title: Landscape-scale dynamics of wood in stream networks of the western Cascades, Oregon.

  
  

  This study develops a network and patchwork dynamics approach to predict wood in a stream network in order to understand wood dynamics in river networks and address riparian reserve design for managed forest landscapes. We examined the effect of four factors on wood sources and transport: (1) forest harvest, removal of wood from streams, and creation of young forest plantations; (2) roads adjacent to or crossing the stream; (3) debris flows in tributary channels; and (4) capacity of the stream to transport wood by fluvial processes (i.e. floods). Wood volumes and numbers of pieces were surveyed along 25 km of 3rd- through 5th-order stream reaches in summer 2002 in a steep forested basin in western Oregon, and related to land use (forest harvest and roads) and fluvial geomorphic processes (debris flows and floods) recorded over the period 1948- 2002. Wood patterns reflect 50-year legacies of land use practices, especially the conversion of old-growth forest to young forest near the stream, and the construction of roads alongside, or crossing, streams. In channels with low fluvial transport wood depletion was localized adjacent to harvest patches, but wood reductions were extensive in channels with high fluvial transport, or where debris flows have entered the mainstem. The configuration of harvest patches, road networks, and stream networks provide a landscape-scale basis to explain and predict patterns of wood in streams, and hence, the effectiveness of riparian reserves for sustaining wood in streams.

  Keywords: legacies of clearcutting, riparian buffers, roads

  
  
• 3:00 PM Author(s):
  *Jerry D. Davis - San Francisco State University
  

  Abstract Title: Biogeomorphic Riparian Assessment and Salmonid Habitat Enhancement in a Suburban Landscape: San Pedro Creek Watershed.

  
  

  San Pedro Creek is a perennial stream in a 2070-ha basin in Pacifica, California, a suburb south of San Francisco, which provides a degraded but still viable habitat for threatened anadromous steelhead (Oncorhynchus mykiss). The watershed, home to approximately 17,000 Pacificans, is approximately 33% built out with low to moderate density housing and services; most of the undeveloped land is protected as county, state, or federal land. The two largest subwatersheds - that drained by the culverted North Fork (614 ha) and that of the relatively undeveloped Middle and South forks (total 624 ha) ? exhibit expected contrasts in storm-flow time of concentration and sediment yield, related to contrasts in impervious surface area. Stream channel bed and bank materials and morphology reflect a history of 200+ years of agriculture (channelization and relict water diversion structures) and 50+ years of basin and stream-side suburbanization (impervious surface expansion and armoring with concrete, riprap, and gabions), with concomitant downcutting and bank erosion. Up to 4.5 m of vertical degradation below bridge culverts has created barriers to steelhead migration. Biogeomorphic analysis of bed and bank materials, sediment systems, channel morphometry, and related salmonid habitat elements has guided ongoing restoration projects aimed at reversing degradation and enhancing habitat.

  Keywords: biogeomorphology, watershed assessment, salmonid habitat, suburbanization

  
  

Session Description: Human impacts are pervasive across the modern landscape. Land use, resource extraction, and other human activities alter vegetation cover and species distributions; alter surface topography and disrupt soil layers; move large quantities of rock, soil and other materials; re-route surface and subsurface water flows; and directly or indirectly introduce large quantities of chemicals across the landscape, among other impacts. These many impacts affect key watershed processes even in relatively remote areas, altering the routing and delivery of water, sediment, organic matter, and dissolved chemicals to rivers and streams and in turn altering channel and floodplain morphology, aquatic habitat quality, and riparian ecosystem structure and function. Because humans depend upon watersheds for water supply, recreation, and many ecosystem services, understanding and management of human impacts on watershed processes is profoundly important to human societies. This series of sessions explores human impacts to hydrogeomorphic, biogeochemical, and ecological systems and processes in watersheds in a range of environments. Primary focus areas include (1) mountain watersheds; (2) geochemistry, water quality, and nutrients; (3) watershed management, particularly with respect to streamflow and fluvial processes in urbanizing landscapes; and (4) ecological impacts and processes.