Land Use Land Cover Change Governing Watershed Nitrogen Threshold And Stream Water QualityEPA Grant Number: R832449
Title: Land Use Land Cover Change Governing Watershed Nitrogen Threshold And Stream Water Quality
Investigators: McGlynn, Brian , Gardner, Kristin , Patten, Duncan T. , Schmitz, Denine , Shanley, James
Institution: Montana State University
EPA Project Officer: Hiscock, Michael
Project Period: September 1, 2005 through August 31, 2007 (Extended to August 31, 2009)
Project Amount: $293,397
RFA: Exploratory Research: Understanding Ecological Thresholds In Aquatic Systems Through Retrospective Analysis (2004) RFA Text | Recipients Lists
Research Category: Ecosystems , Water , Aquatic Ecosystems
This study will quantify the impact of recreational and exurban development on streamwater quality in a characteristic mountain west watershed. It will be the first study to integrate terrain analysis and spatial variability of land use land cover change (LULCC) to improve model quantification of past and future nitrogen thresholds and nitrogen saturation status of sub-watersheds. Our study site is the Big Sky resort community in southwestern Montana, which is characteristic of early stage resort development in mountainous regions.
We will use a time series of historical water quality, biological, and land use land cover data from the West Fork of the Gallatin River and its tributaries to investigate the interconnections among ecological thresholds, hydrological and biogeochemical processes, and resort development. We will reconstruct the trajectory of LULC from satellite and aerial photos (dating back to the 1940’s), water quality in Big Sky watersheds using baseline data from a 1970’s National Science Foundaton RANN study (Research Applied to National Needs) and more recent multi-site streamwater sampling from government agencies, environmental consultants, and non-profit agencies. We strengthen the observations of nitrogen thresholds and the spatial variability of nitrogen status across the drainage by conducting a synoptic sampling to identify key controlling processes of nitrogen export. Identifying the controlling processes will be fundamental to modeling historical thresholds exceeded and to predict future water quality thresholds. Existing land use impact studies on water quality typically fail to incorporate critical topographical and topological drivers that regulate nitrate transport to streams. We will address this shortcoming by applying a framework that integrates terrain analysis with LULC found in the upslope contributing areas of historical monitoring locations and synoptic sampling sites to model nitrate concentrations. The relationships between LULC, watershed characteristics, and synoptic nitrate export will be used to create a continuous time series of nitrate concentration across the West Fork sub-watersheds. By comparison to nitrate saturation stage concepts developed by Aber et al., 1989, we will determine when nitrogen thresholds were crossed in driving the ecosystem to leak increased nitrate to the stream.
We will identify LULC thresholds governing nitrogen export in developing mountain watersheds. We will improve methods to quantify impacts of LULCC on water quality by accounting for topographical characteristics and spatial distribution of LULC. Finally, we will provide a tool and methodology for land managers to detect nitrogen thresholds in mountainous watersheds and predict streamwater nitrate export risk to help guide low-impact development and minimize water quality degradation of our nation’s headwaters.