Using Benthic Macroinvertebrates and GIS to Assess and Manage Watershed Health of the

Colorado River Basin


By Jennifer Thompson




Monitoring aquatic communities and more specifically, benthic macroinvertebrate  populations of rivers, lakes, and streams, is a common practice implemented by local, state and federal authorities to help assess and monitor the health of waterbodies.  Aquatic benthic macroinvertebrates are bottom-dwelling (“benthic”) organisms, living and foraging for food on the substratum of a waterbody.  A majority of benthic macroinvertebrates are aquatic insects, and can be easily seen with the unaided eye (“macro”).  The diversity, type, and abundance of these organisms are thought to be a reflection of water quality and the local hydrology of a waterbody.  The use of GIS to spatially represent monitoring locations and bug and water quality data with the power of  overlaying watersheds and other variables (e.g. land use) can reveal subtle relationships that can be used to help local land managers identify areas of concern, focus monitoring and remediation strategies, and understand critical links between the hydrology and biology.


As part of the Clean Water Act Section 303(d) each state is required to monitor and assess their state’s surface waters and report water quality with regard to their findings in a report to the U.S. Environmental Protection Agency (EPA) every two years.  The Texas Commission on Environmental Quality (TCEQ) keeps track of these data for the State of Texas in the Texas Regulatory Activities and Compliance System (TRACS) database. 




Using surface water quality and macroinvertebrate data, in addition to multiple shape files provided by the USGS, this study will focus on the watershed health of the Colorado River Basin (shown here as region 14).   


This project will attempt to meet the following objectives:

·        Provide a spatial representation of monitoring sites and data; create a comprehensive geodatabase

·        Provide a temporal representation of data collected from 1995-2004

·        Learn about state criteria, screen and water quality standards, and how the Colorado River Basin measures in comparison



Upon starting this project, I quickly came to realize the rudimentary nature of the State’s data collection systems into multiple databases, and thus the need to develop a user-friendly way to view and relate spatial and temporal representations of biological and water quality information.  Therefore, the goals of the project were pared to adapt to this situation and were focused to meet a more immediate objective, as to what would a comprehensive biological database look like. 




Currently, the State’s water quality and biological data is available online at:    



The current form of data files available for viewing/downloading for one category of data, e.g. surface water quality, consist of two files; an event and result file, in which the two files must be joined to form one relational database to obtain all data related to one sample event.  Furthermore, all meta data associated with the result and event file is also stored in separate files.  Using Microsoft Access, I made relational databases of bug and water quality data, specific to the parameters I chose, and imported them into ArcCatalog to form one geodatabase.  The geodatabase consisted of both biological (benthic macroinvertebrate data) and surface water quality data from 1995-2004.   


In addition to building and importing the relational databases created in Microsoft Access into ArcGIS to form one geodatabase, several layers and coverages were also imported to create the foundation for making the basemaps.  Hydrologic Cataloging Unit (HUC) files for water resource region 12 and EPA river reach files for region 12 were downloaded, converted to shape files, and used for providing the spatial context for the basemaps.  These files can be downloaded from:



Monitoring locations were assigned by importing the latitude/longitude locations (in decimal degrees) into Arc Catalog and ArcMap, and assigning XY data using ‘Tools’. 


To evaluate the “health” of the Colorado River Basin, I calculated an Index of Biological Integrity (IBI) “score” for each sampling event based on the results downloaded from the State’s database. The formula for calculating this score can be found in “Guidance for Assessing Texas Surface and Finished Drinking Water Quality Data, 2004” available from TCEQ’s website.  I then spatially represented these scores for the sampling events and compared the result to what it is expected for these waters based on the Texas Surface Water Quality Standards (TSWCS, TCEQ Rules Chapter 307).





There is not enough available data to determine the health of the Colorado River Basin using benthic macroinvertebrate data from the State’s TRACS database.  Of only 67 available entries from the period of time 1995-2004, only twenty-one events had a complete dataset to calculate IBI’s.  Of the twenty-one entries, 8 sampling events received a score of “Exceptional”; seven “High”; six “Intermediate”; and none received the lowest narrative score,  “Limited”.


Due to the few monitoring locations and infrequent sampling events associated with them, temporal representations did not show any real relevance.  Furthermore, utilities such as Tracking Analyst were thus not applicable.




The current form of retrieving information from the State’s website and evaluating the health of Colorado River Basin using biological integrity indices is inadequate.  First of all, there is a lack of data within the database according to what is required by the State’s guidelines and rules (see State’s Surface Water Quality Monitoring Program’s sampling schedule as outlined in the Guidance for Assessing Texas Surface and Finished Drinking Water Quality Data, 2004 document).  Likely, the lack of data in the database is under review due to current actions of the agency and review committees.  Until this is resolved, an evaluation such as this is not very valuable.  Furthermore, of the 67 datasets that were available, only 21 had complete datasets to calculate IBI’s.  The State has two sets of scoring criteria for calculating IBI’s, and they are dependent on the type of method used in sample collection.  The scoring criteria applied in this evaluation was based on the kick sample method of collection, or also known as Rapid Bioassessment Protocol (RBP).  This scoring criteria best fit most of the datasets and tends to be more conservative of the two, and thus was chosen. (The other scoring criteria are based on the Surber sampler method of bug collection.)  However, a significant number of incomplete datasets were missing a common scoring category associated with both sampling methods and scoring tables.  It is possible that some of these datasets employed a different sampling protocol or targeted a specific study using different criteria than that for the calculation of IBI’s based on the Guidance and Assessment manual as previously mentioned.  Thus, the need to develop or stick with one method and/or biological index for evaluating streams and water bodies statewide is apparent and can not be stressed enough.  Benthic macroinvertebrates have shown to be powerful indicators of the state or our waterbodies, and the need for consistency across the state could not be more emphasized.  Thus, the modified objective of this project, then becomes, “What would a biological geodatabase look like?”


As a start, I wanted to see and verify the utility and power of GIS in using surface and biological data to assess watershed health.  I decided to spatially and temporally represent an extensive dataset of bug data from the City of Austin, Texas.  With over 1,000 data points of benthic macroinvertebrates only and over 24,000 water quality data from 1993-2003, the City of Austin (COA) has a very extensive dataset to work with.  In addition to adhering to State requirements, the COA collects much more additional information upon time of sampling (e.g. flow) and has developed more powerful indices, in addition to that used by the State, and consistently monitors designated sites routinely.  Specifically, the COA has developed the Ecological Integrity Index (EII), which is a composite of six sub-indices:  water quality, sediment quality, contact recreation, habitat quality, and aquatic life (Herrington, 2003).  (Benthic macroinvertebrates fall under the aquatic life use score).  A score is assigned for each EII site or subwatershed.  Scores range from 0-100 (very bad to excellent). 


Using shape files of central Texas counties and subwatersheds within the COA jurisdiction, provided by the City of Austin, the following maps were produced:







Figure 1.  EII Benthic Macroinvertebrate Scores, City of Austin, Austin, Texas.





Figure 2.  Total EII Watershed Scores, City of Austin, Austin, Texas.



At a first glance, when spatially represented, the benthic macroinvertebrate/aquatic life use scores and total EII scores for each watershed generally appear to correspond quite well with what one might expect.  Following closely along the Colorado River to the center of Travis County lays the City of Austin.  As one moves from the center to the east, spanning more highly dense, urban areas, bug and EII scores are much lower than southwest of the City.  Areas to the south and west into Hays County are much less developed and represent good to excellent scores (total EII score) and fair to excellent benthic macroinvertebrate scores. 


Importance and Future Work


The power of GIS to spatially and visually relate the results of such monitoring programs can be used by watershed managers to identify areas of concern, focus monitoring efforts, and track the success of remediation efforts.  The COA in particular uses these results to prioritize subwatersheds for addressing Capitol Improvement Projects (CIP’s), monitoring programs, and planning in general.


Future work should include linear referencing all monitoring locations in a watershed, whereby field staff and information managers could query specific sites and identify exactly their location for either site visits or for more in depth statistical analyses.  Additionally, incorporating and linear referencing flow gaging stations, either USGS or agency dependent (e.g. FEWS for COA), along with consistent, routine biological and habitat assessments could ultimately help to reveal subtle links between the hydrology and biology.  In Central Texas, determining minimum instream flows to maintain biological communities for waterbodies is a very hard answer to get at.  Perhaps linking these two types of data (hydrological and biological) with the utilities provided in GIS and ArcHydro may help to provide some insight into these questions.  Furthermore, water quality data important to benthic macroinvertebrates (e.g. temperature, conductivity, total suspended solids (TSS), nitrate as N, dissolved oxygen) and specific physical habitat quality data (instream cover, depth, substrate, flow velocity, river and stream channel characteristics) should all be fields within the biological geodatabase.


In summary, streams and rivers harbor extremely complex and dynamic ecosystems that provide our communities with clean water, energy, fish and other recreational activities.  Rivers also provide freshwater to the bays and estuaries along the coast, providing important nutrients and freshwater to coastal nurseries.  To understand what parameters are most important to these communities, it is important from a biological perspective to not only calculate indices and spatially represent water quality data, but to incorporate more detailed physical habitat quality parameters into biological geodatabases and to be able to track and monitor their changes as well.  With a comprehensive database, one could use GIS to interpolate IBI’s and habitat characteristics as one moves downstream.  Furthermore, applying land use coverages may help to explain if and how urbanization is affecting local streams and waterbodies.  Finally, it should be apparent that much more data collection is necessary (especially habitat data), and on a more routine basis to build a comprehensive geodatabase and use the applications of GIS and ArcHydro to assess and mange the health local and state water bodies.





Herrington, Chris.  2003.  Changes in Environmental Integrity Index values (1996-2002). 

   City of Austin, Environmental Resources Division, Watershed Protection and    

   Development Review, City of Austin, Texas.


Texas Commission on Environmental Quality (TCEQ).  2003.  Guidance for Assessing

   Texas Surface and Finished Drinking Water Quality Data, 2004. 


TCEQ.  2000.  Texas Administrative Code, Chapter 307:  Texas Surface Water Quality