Scientific Investigations Report
2008-5018 PDF (3.2 MB)

Abstract

The Middle Fork of the Saline River has many qualities that have been recognized by State and Federal agencies. The Middle Fork provides habitat for several rare aquatic species and is part of a larger stream system (the Upper Saline River) that is known for relatively high levels of species richness and relatively high numbers of species of concern. 

Water-quality samples were collected and streamflow was measured by the U.S. Geological Survey at three sites in the Middle Fork Basin between October 2003 and October 2006.  The Arkansas Department of Environmental Quality collected discrete synoptic water-quality samples from eight sites between January 2004 and October 2006.  The Arkansas Department of Environmental Quality also sampled fish (September-October 2003) and benthic macroinvertebrate communities (September 2003-December 2005) at five sites. 

Streamflow varied annually among the three streamflow sites from October 2003 to October 2006.  The mean annual streamflow for Brushy Creek near Jessieville (MFS06) was 0.72 cubic meters per second for water years 2004-2006.  The Middle Fork below Jessieville (MFS05) had a mean annual streamflow of 1.11 cubic meters per second for water years 2004-2006.  The Middle Fork near Owensville (MFS02), the most downstream site, had a mean annual streamflow of 3.01 cubic meters per second.  The greatest streamflows at the three sites generally occurred in the winter and spring and the least in the summer. 

Nutrient dynamics in the Middle Fork are controlled by activities in the basin and processes that occur in the stream.  Point sources and nonpoint sources of nutrients occur in the Middle Fork Basin that could affect the water-quality.  Nitrogen and phosphorus concentrations generally were greatest in Mill Creek (MFS04E) and in the Middle Fork immediately downstream from the confluence with Mill Creek (MFS04) with decreasing concentrations at sites farther downstream in Middle Fork.  The site in Mill Creek is located downstream from a wastewater-treatment plant discharge and concentrations at sites farther downstream probably had lesser concentrations because of dilution effects and from algal uptake.  Nutrient concentrations generally were significantly greater during high-flow conditions compared to base-flow conditions.

Flow-weighted nutrient concentrations were computed for the three streamflow sites and were compared to 82 relatively undeveloped sites identified across the Nation, to the Alum Fork of the Saline River near Reform, Arkansas, and to the Illinois River south of Siloam Springs, Arkansas, a site influenced by numerous point and nonpoint sources of nutrients.  Annual flow-weighted nutrient concentrations for MFS06, MFS05, and MFS02 were greater than relatively undeveloped sites, but were substantially less than the Illinois River south of Siloam Springs.

Fecal indicator bacteria concentrations were slightly greater at MFS06 and MFS05 compared to concentrations at MFS02 for October 2003 to October 2006.  MFS05 had the greatest E.coli concentrations and MFS06 had the greatest fecal coliform concentrations.  Overall, fecal indicator bacteria concentrations were significantly greater for samples collected during high-flow conditions compared to samples collected during low-flow conditions at all three sites.

Suspended-sediment concentrations did not vary significantly among MFS06, MFS05, and MFS02 for all the samples collected from October 2003 to October 2006. Suspended-sediment concentrations were significantly greater in samples collected during high-flow conditions compared to samples collected during base-flow conditions.  Synoptic samples indicated varied total suspended-solids distributions from upstream to downstream in the Middle Fork between January 2004 and October 2006.  Overall, total suspended-solids values were the greatest at site MFS02 and decreased at sites upstream and downstream. 

Turbidity measured when water-quality samples were collected showed little variation between MFS06, MFS05, and MFS02.  The State standard primary value (10 nephelometric turbidity units) was exceeded in 9 samples collected from MFS06, 11 samples at MFS05, and 12 samples from MFS02.  The State standard stormflow value (18 nephelometric turbidity units) was exceeded in 5 samples collected from MFS06, 7 samples at MFS05, and 10 samples from MFS02.  Turbidity data varied from upstream to downstream at the eight synoptic sites in the Middle Fork Basin from January 2004 to October 2006, similar to the patterns of the total suspended-solids data. 

Dissolved-oxygen concentrations at MFS02 demonstrated seasonal changes from October 2003 to October 2006.  Dissolved-oxygen concentrations generally were greater in the winter and spring compared to the summer and fall.  The dissolved-oxygen concentrations at MFS02 were less than 6 milligrams per liter during 189 days from October 2003 to October 2006, mainly in the summer and fall.

Synoptic samples were analyzed for 19 different trace metals.  Several of the metals generally had concentrations near or below the laboratory reporting level.  Concentrations of boron, copper, and zinc had the greatest concentrations in Mill Creek, at the site below the wastewater-treatment discharge (site MFS04E), compared to the other sites in the Middle Fork from January 2004 to October 2006.

Continuously measured turbidity and streamflow data were compared to total phosphorus, fecal indicator bacteria, and suspended-sediment concentrations at site MFS02 to potentially provide continuous estimates of these constituents.  Total phosphorus, fecal indicator bacteria, and suspended-sediment concentrations had relatively fair correlations with turbidity and streamflow at higher turbidity and streamflows, but were poorly correlated at lower turbidities and streamflow. 

Biological samples (benthic macroinvertebrate and fish communities) were collected and habitat variables were measured at various times between September 2003 and October 2005 at five sites.  Physical habitat variables were measured at each site to assess biological or ecological integrity. 

Although there was some variation of total habitat scores among sites, and temporally, the habitats at all sites during all seasons uniformly were classified as suboptimal.  Scores for sediment deposition, embeddedness, and velocity/depth regime variability (all of which could be affected by excess sediment) generally were lower than scores for other habitat variables.  

Several biological metrics associated with Middle Fork Basin sites varied in a reasonably consistent manner.  These metrics and the communities they represent could be affected by water quality or other habitat factors.  Habitats (all of which were classified as suboptimal habitats as measured by total habitat scores) did not vary substantially among sites or in a way that suggests that physical habitat is the major factor causing the biological community differences among these sites; nonetheless, degraded habitats could be having a detrimental but similar effect on all sites.  However, several biological metrics varied at Middle Fork Basin sites in a way that is similar to the variation in many of the water-quality variables—elevated or depressed at the Mill Creek site (relative to the site upstream from Mill Creek) and then returning to or approaching values associated with the site upstream from Mill Creek.  Values for Middle Fork Basin sites for most metrics that were compared to values for least disturbed Ouachita Mountains streams were similar to the values for the least disturbed sites.

Implications for rural landowners, suburban landowners, government entities, and natural-resource managers include that water quality, habitat, and aquatic biological communities in the Middle Fork Basin are the result of the interaction of several factors.  In addition, although data indicate that macroinvertebrate and fish communities are somewhat affected by water-quality degradation, these effects are greatest near the Mill Creek wastewater-treatment plant and communities farther downstream are similar to communities upstream from Mill Creek or to communities from relatively undisturbed sites. 

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Version 1.0

Posted May 2008

• Report PDF (3.2 MB)