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 2 - Geochemistry, Water Quality and Nutrients

Paper Session 4201
Friday, 4/20/07, from 10:00 AM - 11:40 AM

Sponsorship(s):

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

Organizer(s):

Shixiong Hu - East Stroudsburg University
Yong Q Tian - University of Massachusetts - Boston

Chair(s):

Shixiong Hu - East Stroudsburg University

Abstract(s):

• 10:00 AM Author(s):
  *Christopher J. Woltemade - Shippensburg University
  Jinnieth J. Woodward - SUNY - College of Environmental Science and Forestry
  

  Abstract Title: Hydrology and Nitrate Removal in a Restored Spring-fed Wetland, Pennsylvania.

  
  

  In 2001 the 1.04-ha Hornbaker wetland in south-central Pennsylvania was restored by blocking an artificial drainage ditch to increase water storage and hydraulic retention time (HRT). A primary goal was to diminish downstream delivery of nitrate that enters the wetland from a limestone spring, its main source of inflow. Wetland inflow and outflow were monitored weekly for two years (2004 - 2006) to assess nitrate flux, water temperature, pH, and specific conductivity. In Year 2 spring discharge was measured weekly to allow calculation of nitrate loads and the hydraulic retention time. Surface runoff was confirmed to be a small fraction of wetland inflow via rainfall-runoff modeling with TR-55. The full data set (n = 102) was screened to remove 13 weeks in which spring discharge constituted less than 85% of total inflows due to high precipitation and runoff. Over two years (n = 89), mean nitrate-nitrogen concentrations were 7.89 mg/l in inflow and 3.68 mg/l in outflow, with a mean nitrate removal of 4.19 mg/ l. During Year 2 (n = 47) the wetland removed an average of 2.32 kg N/day, 65% of the load. Univariate analysis shows that nitrate removal was significantly correlated with HRT, water temperature, and the concentration of nitrate in inflow. Nitrate removal was significantly greater during the growing season (5.36 mg/l, 64%) than during the non-growing season (3.23 mg/l, 43%). Multivariate regression analysis shows that about 27% of the variance in nitrate removal is accounted for by HRT and water temperature (n = 47).

  Keywords: wetlands, restoration, nutrients, nitrogen, agriculture, Pennsylvania

  
  
• 10:20 AM Author(s):
  *Yong Q Tian - University of Massachusetts - Boston
  

  Abstract Title: Spatial and temporal modeling the fate and transport of dissolved organic carbon (DOC) from landscapes to coastal waters.

  
  

  Marine dissolved organic carbon (DOC) is one of the largest reservoirs of organic carbon (about 680 gigatons) at the Earth’s surface. However, the dynamics of carbon cycle at the land-sea interface are not well understood due to complex mixing processes, multiple sources of organic carbon, high biogeochemical reactivity in estuaries, and a lack of the high temporal and spatial resolution data needed to assess these fluxes at a global scale during times of rapid (decadal) changes in source and transport mechanisms. This presentation introduces an integrative modeling approach to quantify the sources and transport mechanisms of DOC in the coastal oceans. Dissolved organic matter (DOM) in seawater is one of the largest reactive reservoirs of carbon on earth. The fraction of the DOM that absorbs light is called chromophoric or colored dissolved organic matter (CDOM). Under certain conditions, CDOM can be used as an indicator for DOC concentration. This paper discusses two study results: 1) in situ measurements of freshwater CDOM endmember variability due to watershed and rainfall properties and seasonal cycling; and 2.) use a GIS approach to develop a predictive model of CDOM sources from terrestrial watersheds and groundtruth the predictive model in watersheds of various sizes.

  Keywords: colored dissolved organic matters

  
  
• 10:40 AM Author(s):
  *Mark S. Johnson - University of British Columbia
  Johannes Lehamann - Cornell University
  

  Abstract Title: Decadal Dynamics in Watershed Loadings in a Mixed-Land Use Watershed.

  
  

  Stream water loadings of nutrients and pollutants to water bodies integrate internal and external processes that vary in both space and time. While land cover dynamics can be assessed remotely, changes in land use practices within a land cover class can be difficult to ascertain. Here we explore nitrate and alkalinity fluxes for 1972-2005 from the Fall Creek watershed, a 326 km2 mixed-land use catchment in western New York. Annual watershed loadings were computed for each year and normalized by dividing loading fluxes of water quality constituents by annual discharge. Normalized loadings for both nitrate and alkalinity increased during the 1970s and 1980s, peaking in the early 1990s. Both nitrate and alkalinity fluxes then decreased from 1992 through 2005. In this paper, we explore the driving factors for these trends by looking at internal factors such as changes in land use/land cover, dynamics in agricultural production and fertilizer use, and external factors such as atmospheric deposition. Decreases in agricultural acreage within the watershed during the 1990s is detected in remotely sensed data as well as through farm-level data complied by the USDA. This change appears to be replaced by regenerating forest cover. The implications for these findings on downstream water quality and carbon cycle dynamics are also discussed.

  Keywords: land use/land cover change, watershed biogeochemistry

  
  
• 11:00 AM Author(s):
  *Gwenda J Schlomer - Missouri State University
  Robert T Pavlowsky - Missouri State University
  Scott A Lecce - East Carolina University
  

  Abstract Title: Using geochemical and sedimentological trends to identify pre- and post- settlement boundaries in floodplain deposits of the North Carolina Piedmont.

  
  

  The environmental history of a watershed can be preserved in vertically accreted floodplain deposits, offering the potential to reconstruct major disturbances to the fluvial system. Human settlement and land clearing tend to increase sedimentation rates on valley floors, particularly during forest to agriculture conversion. Mining pollution tracers are useful to date historical floodplain units and study watershed-scale patterns of sedimentation. The upper Dutch Buffalo Watershed (253 km2) in the North Carolina Piedmont was first introduced to mining activities in 1842 by the Gold Hill Mining District located near the headwaters. Mercury released during gold ore processing, along with a well-documented mining history, enables the dating of overbank units during the mining period (1842-1915). The geochemical and sedimentological response of the basin during the pre-mining period, however, is largely unknown due to the lack of a geochemical mining signal. This study will address using geochemical and physical properties of pre/post settlement overbank units to characterize pre-mining floodplain deposits. Floodplain sediment cores were collected along three cross-valley transects downstream of the mining district in the upper, middle and lower reaches of the watershed and analyzed for 32 elements and physical properties including organic matter, pH, grain size, and color. Preliminary results indicate that geochemical profiles are sensitive to subtle changes in land use. Pre-settlement deposits are indicated by the presence of buried Ahorizons and/or shifts in elemental ratios and other physical properties. This will improve on understanding the history of channel and floodplain changes caused by anthropogenic processes on the North Carolina Piedmont.

  Keywords: fluvial geomorphology, sedimentation, geochemistry, Piedmont

  
  
• 11:20 AM Author(s):
  *Dan Royall - UNC-Greensboro
  Anita Henderson - UNC-Greensboro
  Zhi-Jun Liu - UNC-Greensboro
  

  Abstract Title: Downstream Reduction of Urban Influence on Channel Processes: a Case Study.

  
  

  The impacts of urbanization on the fluvial system, water resources, and aquatic biota are of increasing global concern. Locally, within more populous portions of the US, the most rapidly urbanizing areas face potential land and water resource conflicts with neighboring urban centers. How far downstream do urban influences extend? The answers to this question apparently vary widely with environmental and geographical specifics. In this study, we consider the case of fully urbanized headwaters exiting into rural landscape. The headwaters of North Buffalo Creek lie entirely within the urbanized area of Greensboro, NC (population 230,000) in the Appalachian Piedmont province. The stream exits abruptly into rural landscape at the city’s eastern margin, and its watershed begins to acquire a growing proportion of pervious surface area with downstream distance. The purpose of this paper is to document the nature of the resulting transition in stream hydrology and form for North Buffalo Creek. Indices of urban streamflow regime (e.g., days exceeding mean annual discharge; TQmean) suggest substantial urban influence after more than 5 km down-valley distance (~ 45% rural). Channel cross-section area switches from general conformity with published urban regional curves to greater rural curve similitude soon after exiting the urbanized area (~ 15% rural). Both physical effects and choice of urban streamflow regime indices can account for the apparent difference in location at which rural dominance is reached.

  Keywords: urban stream, hydrology, channel form, North Carolina

  
  

Session Description: This session will cover the recent development of human impact on geochemical processes, movement of nutrients and water quality issues in watershed.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.