Linking Watershed Characteristics with Flow Regime and Geomorphic Context to Diagnose Water Quality Impairment at Multiple Spatiotemporal ScalesEPA Grant Number: R831367
Title: Linking Watershed Characteristics with Flow Regime and Geomorphic Context to Diagnose Water Quality Impairment at Multiple Spatiotemporal Scales
Investigators: Poff, N. LeRoy , Bledsoe, Brian P. , Dean, Denis , Ramirez, Jorge A.
Current Investigators: Poff, N. LeRoy , Bledsoe, Brian P. , Dean, Denis
Institution: Colorado State University
EPA Project Officer: Hiscock, Michael
Project Period: November 1, 2003 through October 31, 2007
Project Amount: $897,798
RFA: Development of Watershed Classification Systems for Diagnosis of Biological Impairment in Watersheds and Their Receiving Water Bodies (2003) RFA Text | Recipients Lists
Research Category: Water and Watersheds , Water
Overall, this study will be the first to quantitatively link water quantity with water quality at a national scale, using EMAP data to establish quantitative linkages. It will also be the first to explicitly include stream geomorphology in a network context to improve model predictions of water quality impairment. The study will specifically explore how extreme events, especially antecedent low flow conditions, may regulate the deposition of fine sediments and influence associated biological responses.
Existing watershed classifications for water quality impairment are of limited utility because they fail to incorporate critical environmental drivers that regulate ecological processes. We will address this shortcoming by developing a framework for integrating streamflow regime and geomorphic context along with watershed and land use metrics into classifications of water quality impairment. Using existing EMAP / R-EMAP data, we will focus on two important measures of water quality impairment - biological condition (algae, invertebrates, fish) and fine sediment deposition - and construct and test a hierarchical classification applicable at regional to national scales.
We will define watersheds of EMAP stream sites in terms land coverage (using GIS databases), flow regime (using actual USGS gauge data and modeling synthetic time series for ungauged sites), and multi-scale geomorphic context (using spatially-explicit GIS modeling combined with DEMs and EMAP field data). With these multiscale variables, we will classify water quality impairment at EMAP sites. This classification will reveal the integrated relationships between flow regime, watershed and land use metrics, and geomorphic context in regulating important indicators of water quality, and thereby advance scientific understanding needed for better watershed management.
Hydrologic alteration is increasingly recognized as a major source of water quality degradation, and we will take the results from the above-described research and develop a national classification of hydrologic impairment. By focusing on the "sensitive" flow metrics from our EMAP analysis, we will characterize flow regimes at thousands of existing USGS streamflow gauges nationwide in terms that directly relate to water quality impairment (as determined from the prior EMAP analysis). Stream flows across the US will be classified in terms of both sensitive flow metrics (associated with water quality impairment) and departure from regional "reference" conditions. Reference streams will comprise those showing minimal flow alteration (e.g., those in the USGS Sentinel Gauge network), and we will use hydrologic modeling to estimate departure from the unimpaired condition for non-reference streams. This classification will potentially help identify sensitive regions where water quality impairment is most likely and/or where biomonitoring programs might suffer from relatively large uncertainty in detecting water quality impairment (due either to inherent hydrologic variability or to hydrologic modification). We will also compare this classification against other, existing national ecohydrologic classifications to examine their utility in predicting indicators of water quality impairment.
Finally, we will conduct a field project in the Colorado mountains to rigorously test the validity of our inferences based on EMAP and USGS data. By selecting sites across a gradient of stream diversion and stratifying by geomorphic factors, we will be able to hold land use constant and quantify the effect of antecedent flows on fine sediment deposition and the interactive effect of siltation and flow alteration on biological impairment. Extensive anthropogenic alteration of natural stream flows in pristine headwater streams in Colorado affords a unique opportunity to validate broader scale inferences based on snapshot EMAP data. This study will be complement and extend ongoing efforts in the State of Colorado to define sediment and associated biological impairment in streams.