A preliminary study of near-stream vegetative cover and in-stream biological integrity in the lower Fox River, Illinois.
 
Thomas. N. Kompare
 Center for Biodiversity
Illinois Natural History Survey
Champaign, Illinois USA
 
 
ABSTRACT
 
   I completed an analysis of near-stream vegetative cover on all streams of the lower Fox River (below Yorkville, Illinois) that appear in the 1:100,000 USGS Digital Line Graph data.  These streams are divided into three groups according to Biological Streams Characterization (BSC) designation (Bertrand et al. 1993).  BSC designated A and B streams in one group, BSC C streams in another, and undesignated streams in a third.  There are no D or E designated streams in the lower Fox River watershed. BSC designations was the basis for division because they reflect relative aquatic ecosystem health. Most third and higher order streams were included in the BSC study and given a BSC designation. Most first and second order streams were not part of the BSC study, therefore, make up the majority of the undesginated group.

    According to the GIS analysis, a trend occurs in these data.  As the quality of the stream decreases, there is an increase in row crop near-stream cover and a decrease in upland and bottomland woods near-stream cover.  This seems to indicate there is a correlation between near-stream cover and stream quality.  There is probably not an cause/effect relationship.  Near-stream vegetative cover is one of several factors that shape stream quality (Bertrand et al.  1993; Page 1991).

 

INTRODUCTION

    Illinois streams are directly and indirectly affected by human alteration of surrounding lands (Larimore and Bayley 1996). When natural vegetation is replaced with urban and agricultural uses, physical and biological relationships with adjacent streams are altered, resulting in degradation of habitat and negative impacts on stream biota (Karr and Schlosser 1978; Schlosser 1991). Within Illinois, 83.2% of its total area is now covered by urban or agricultural land (Luman et al. 1996).

    A natural vegetated riparian zone is important to the biological integrity of streams (Naiman 1992; Sweeney 1992). Riparian vegetation has many functions critical to the natural stream ecosystem (Karr and Schlosser 1978). Leaf litter provides food for many species of invertebrate shredders (Cummins et al. 1989). Woody debris from near-stream vegetation provides cover for aquatic organisms and alters the physical structure of the stream (Karr and Schlosser 1978). Trees directly at the stream's bank provide shade from the direct rays of the sun. This allows stream temperatures to moderate during the artificial low flow periods of summer (Barton et al. 1985; Smith 1971). Riparian vegetation also filters sediments from overland flow, this reduces the amount of sediment and sedment-transported chemicals in the stream (Dillaha et al. 1989; Daniels and Gilliam 1996).

    Several studies used maps or Geographic Information Systems (GIS) to relate land cover to in-stream biotic integrity. Steedman (1988) reports biotic integrity of Ontario streams was related to the proportion of stream length with riparian forest. Omernick et al. (1981) found that nitrate and phosphorous levels in streams were related to total watershed land use, but not to near-stream land use. Osborne and Wiley (1988) used the buffer-overlay method in a GIS to report that riparian land use nearest to the stream most closely relates to in-stream nutrient concentrations.

    This study examined the relationships between near-stream vegetative cover and in-stream biotic integrity. I used the lower Fox River watershed (below Yorkville, Illinois) as my study site. I used the Biological Streams Characterization Report (Bertrand et al. 1993) as my measure of biotic integrity. I used the Land Cover of Illinois GIS data (Luman et al 1996) as my measure of land cover.
 

METHODS

Study Site

    The Fox River watershed below Yorkville, Illinois, is located just west-southwest of the Chicago urban fringe. This 775.32 mi2 (496,205 acre) watershed is mainly agricultural. Corn and soybeans are the dominant rotational crops with a small minority of other crops. There are small-sized farm communities scattered throughout the study area. Wooded areas are found mainly in riparian areas of medium the large sized streams. This study area is typical of what the land cover of the Grand Prairie Division of Illinois (Schwegman, 1973) has become.

Land Cover

    I used the GIS program ArcInfo 7.0.4 in a UNIX networked environment for this study. All streams within this study site that appear on the USGS 1:100,000 scale Digital Line Graph Series (DLG) data were examined for its near-stream land cover characteristics. A buffer of 100 meters each side of the streams acted as the "cookie cutter" to clip out near-stream land cover data from the Land Cover of Illinois data. A buffer of this size allows for spatial location error inherent in both of these data sets.

Biotic Integrity

    The measure of biotic integrity used in this study is from Bertrand et al. (1993) Biological Streams Characterization Report. This Report grades Illinois streams A (Excellent) to E (Very Poor) based on the index of biotic integrity found in Karr et al. (1986). All graded streams in this study site have grades A (excellent), B (good), or C (fair). This study site is rather unique in Illinois due to the fact that it has no D (poor) or E (very poor) graded streams. Only one stream, Buck Creek (LaSalle County, Illinois), was graded as an A stream by the BSC. One stream is not a significant sample to run a comparative study, therefore, A and B graded streams were grouped together in the analysis. BSC C graded streams made up the second group of this study. The vast majority of the first and second order stream lengths were not assessed in the BSC project and have no biotic integrity grade. These streams were classified into a third group.

    These ungraded streams are historically structurally different than BSC graded streams due to differing stream orders. Forest cover on first and second order streams may never have reached the levels of larger ordered streams.  The narrowness of their runs may not have posed a major firebreak that wider streams did.  Narrow streams may have acted only as as intermittent firebreaks, and may have had savanna where forest would have occurred in conjunction with well-defined firebreaks (Bowles et al.  1994). Comparing these narrow, ungraded streams to BSC graded streams by land cover characteristics may not be valid. They are included in this study for completeness.

    I divided the buffered land cover data by stream segment and grouped it into its corresponding biotic integrity group. I grouped all of the BSC A and B near-stream land cover data, the BSC C near-stream data, and all of the remaining (ungraded) near-stream land cover data.

RESULTS

    According to the GIS analysis, a trend occurs in these data.  As the quality of the stream decreases, there is an increase in row crop near-stream cover and a decrease in upland and bottomland woods near-stream.  This seems to indicate there is a correlation between near-stream cover and stream quality.  There is probably not an cause/effect relationship.  Near-stream vegetative cover is one of several factors that shape stream quality (Bertrand et al.  1993; Page 1990).

The results of this preliminary analysis are show in the table below:
 
 

Streams and Corresponding Land cover
Near-stream cover BSC A+B BSC C Ungraded All Streambanks Entire Watershed
High Density Built-up 0.4% 0.2% 0.2% 0.2% 0.4%
Medium Density Built-up 0.4% 0.1% 0.2% 0.2% 0.3%
Low Density Built-up 0.1% 0.2% 0.3% 0.2% 0.5%
Urban Grasslands 1.8% 1.3% 2.0% 1.8% 1.5%
Row Crops 18.3% 30.4% 55.4% 46.2% 73.5%
Small Grains 0.7% 1.0% 1.0% 1.0% 1.0%
Rural Grasslands 25.6% 34.0% 28.7% 29.1% 17.2%
Upland Woods 29.4% 19.7% 8.5% 13.2% 3.4%
Open Canopy Woods 3.0% 2.8% <0.1% 2.5% 0.7%
Coniferous Woods 0.0% <0.1% <0.1% <0.1% <0.1%
Bottomland Woods 19.0% 9.6% 1.0% 4.9% 0.7%
Shallow Marsh 1.3% 0.4% 0.4% 0.5% 0.2%
Deep Marsh <0.1% <0.1% <0.1% <0.1% <0.1%
Barren Lands <0.1% 0.0% <0.1% <0.1% <0.1%
 

SUMMARY

    The significance of these results are that they indicate a need for a more detailed analysis of the relationship between biotic integrity and land cover. Future directions this preliminary study might lead are:
 

    Since vegetation cover is only one of several factors that influence stream quality and biotic integrity, any future vegetative cover analyses should collaborate with other studies of factors that influence the biotic integrity of Illinois streams. This will allow for a more holistic view of biotic integrity.

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