2004 Sun River Watershed
Water Quality Monitoring Project
Overview/Preface
The Sun River Watershed consists of 1.4 million acres located in North Central Montana. The river starts along the eastern Rocky Mountain Front and flows for 97.4 miles to the Missouri River at Great Falls , Montana . The watershed land use is diversified, of which 35% is cropland, 35% forested, 28% rangeland, and 2% urban. Cropland consists of both irrigated and dryland, 75% of which is in a dryland small grain cropping system.
The Montana 1996 and 2000 303(d) list for the Sun planning area includes the entire Sun River, Muddy Creek, lower Ford Creek, Gibson Reservoir, Willow Creek Reservoir and Freezout Lake. The types of impairments include sediment, nutrients, thermal modification, organic enrichment/DO, pH, salinity/TDS/chlorides, habitat alteration, and flow alteration. Probable causes for these impairments are agriculture and hydromodification that cause water bodies to only partially support beneficial uses of fisheries, aquatic life, swimming, and recreation. Portions of the Sun River and its tributaries are also non-supporting of some beneficial uses. Besides the water bodies listed on the state’s 303d list, there are other Sun River tributaries that are of concern for their contribution to the basin’s water quality impairments. The Sun River is also a tributary of the Missouri River , with significant water quality impacts at and below the city of Great Falls .
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Allan Rollo and Kim Hershberger |
Project Goal
The Sun River Watershed TMDL and water quality plan are close to completion and will list current watershed conditions, along with targets and areas of responsibilities. Yet, there are no provisions for an effective monitoring program. Without a monitoring program it is difficult to determine success of improvement efforts. It is also difficult to determine direction of future efforts.
In an effort to address these issues, the Sun River Watershed Group contracted with Montana State University Extension to perform water quality sampling, data compilation, and analysis at key sites within the Sun River Watershed.
One goal of the project reported here was to review and summarize existing water quality and quantity data. Different agencies and entities have taken flow and water quality measurements throughout the years. While having a large data set on a particular watershed is good, this data provides little value in either assessment or design of management, unless all the data is aggregated and transformed so that it is in a consistent format, easily assessable and sufficiently understandable to support decision-making.
Another objective of this project was to define existing water quality conditions.
By assessing historic and current water quality conditions, this project attempted to address the following issues:
- What are baseline conditions in the Sun River and major tributaries?
- What would constitute an effective long-term monitoring program in the Sun River?
Approach
A total of 24 sampling sites were selected to monitor flow and water quality in 2004. Figure 1 shows the approximate locations of these sampling sites. On-site water quality data and water samples for subsequent laboratory analysis were collected once a month, from April through September. The following parameters were measured on-site along with associated flow volumes: salinity, water temperature, dissolved oxygen, conductivity, pH, and sediment. On-site measurements were made on grab samples collected within channel. These measurements, with the exception of sediment, were made using the Horiba meter. Sediment was measured using a Hach turbidity meter with units reported in NTUs (nephelometric turbidity units). In addition to these measurements, at 13 of these sites (identified by Montana Department of Environmental Quality), water samples were collected and sent to Energy Laboratories for subsequent analyses - nitrate + nitrite nitrogen, total kjeldahl nitrogen, total phosphorous, and total suspended sediment (TSS).
Observations and Measurements
Phosphorus
Figure 2 shows phosphorus levels measured over a range of 27 years at each of the stations. There is a lot of exceedence of the 0.03 mg/L threshold (level for prevention of nuisance and algae growth noted in the administrative rules of Montana), indicated by the dotted red line. The largest contributors of phosphorus in the Sun River system, excluding outliers, are found in Muddy Creek (Muddy Creek at Vaughn and Muddy Creek at Cordova). This is predictable, as Muddy Creek is a documented source of significant sediment loads (Browning et al., forthcoming, 2005). Phosphorus data from the Sun River at Ulm Bridge sampling site also are quite elevated. This is likely to be directly related to Muddy Creek, as the confluence of Muddy Creek with Sun River is just upstream from this station. Mill Coulee, Adobe Creek, Duck Creek, and Simms Creek all exhibit phosphorus levels significantly higher than the acceptable standard. This figure shows that tributaries are contributors of phosphorus to this river system. It is also noteworthy that few phosphorus levels exceed the 0.03 mg/L standard in Sun River samples upstream of the confluence with Simms Creek. The data suggest that ambient (naturally occurring) baseline phosphorus concentrations (without influence of anthropogenic inputs) in the Sun River ranges from <0.01 to approximately 0.03 mg/L.
Nitrogen
Like phosphorus, too much nitrogen can result in eutrophication. Two types of nitrogen measurements had been made over the years in this river system. Those are nitrate + nitrite nitrogen and total kjeldahl nitrogen (TKN). Figure 3 shows the nitrate + nitrite levels at each sampling site. The two values greater than 10 mg/L (human health standard) are found in Muddy Creek at Gordon and Vaughn. With the exception of the Muddy Creek stations and Mill Coulee, which doesn’t exceed 4 mg/L, nitrate + nitrite concentrations are less than 2 mg/L in the Sun River and tributaries.
The TKN analysis quantifies organic nitrogen, and when combined with inorganic nitrogen (NH4, NO3, NO2), the result is the total nitrogen. There are no standards for TKN in Montana, although there is a standard for total nitrogen. Available data range from 1977 to present. With many of these samples, the lab reporting limit for TKN was 0.5 mg/L. As such, these samples could not be depicted in graphic form. Thus, any samples with TKN levels less than 0.5 mg/L were not included. 104 of the total 184 samples, or 56% of the samples, were less than 0.5 mg/L. Figure 4 shows that the highest TKN levels are found in Muddy Creek at Vaughn, Mill Coulee, Adobe Creek, and Sun River at Fort Shaw.
When nitrate + nitrite nitrogen levels are compared to TKN levels, it is apparent that nitrate + nitrite levels are the significant contributor to total N. This suggests that a large percent of nitrogen found in the Sun River is contributed by groundwater sources since the generally recognized avenue of nitrate mobility is through leaching to groundwater, and groundwater is assumed to be a contributing source to baseflow in the Sun River and its’ tributaries.
pH
The acceptable range for pH, according to Montana standards, is from 6.5 – 9. Figure 5 shows the pH values for the individual stations, broken down into three groups – Sun River, Sun River tributaries, and Muddy Creek. Almost every station had pH values recorded greater than 9. pH in the Sun River and tributaries, including Muddy Creek and its’ tributaries, are within the same range. An analysis of the pH data showed that values less than 8 most often occurred in June and July. pH values greater than 9 were most often measured in September, October, and November. The higher pH values are likely due to lower flows when irrigation waters are shut off.
Conductivity
Figure 6 shows the conductivity levels recorded at the individual stations. The two red dotted lines on this figure represent risk thresholds for potential irrigation problems, as set forth by Ayers and Westcott (1985). Only one value in this dataset is greater than 3 mS/cm and that is found at Adobe Creek at upper end/middle. Both of the sampling locations on Adobe Creek appear to have some of the higher conductivity concentrations. Duck Creek also is a moderate risk with conductivity values close to 2 mS/cm. Sampling stations at the upper end of the Sun River – Augusta, FSID, Simms, and Fort Shaw have the lowest conductivity values and most likely reflect non-anthropogenically impacted baseline conductivity levels.
Total Suspended Solids (TSS)
Figure 7 depicts the TSS levels at each of the individual stations within the Sun River Monitoring project and in order along the river. The largest sediment values are found upstream of the confluence with Muddy Creek and are a reflection of sediment entering the Sun River via Duck Creek. The EPA does not provide a standard for TSS. Yet, in the upcoming Sun River TMDL document, Montana DEQ has provided target thresholds/values for the Sun River watershed, broken down into sections. One of the reaches begins at the Highway 287 Bridge (where the Sun River at Augusta monitoring site is located) and ends at Muddy Creek. The target TSS level set is less than 10 mg/L at discharges under 200 cfs.
The Lower Sun River is characterized in the Sun River TMDL document as the Sun River from the confluence of Muddy Creek to the rivers’ mouth. The target set for this reach is that the 75 th percentile of suspended sediment data collected in this reach is 42 mg/L. This threshold was determined based on the assumption that the sediment concentration above Muddy Creek should be mimicked below Muddy Creek confluence. The highest values in this reach are at the Sun River at Ulm Bridge. These higher values are probably more a reflection of the TSS levels in Muddy Creek, a tributary just upstream from the monitoring station.
The TMDL also set threshold for Muddy Creek at Vaughn. The target value of total annual sediment load for Muddy Creek at Vaughn is 29,959 tons per year and is based on meeting flow targets.
Dissolved Oxygen (DO)
Figure 8 gives some insight into dissolved oxygen concentrations at each of the individual monitoring stations. A red dotted line is drawn at 5 mg/L, which is considered the minimum DO level for early life stages for warm water streams in Montana. 3 mg/L is the minimum DO level for other life stages. Only 1 –2% of the data values are below 5 mg/L. Only the Sun River at Great Falls and Sun River at Sun River stations have DO values recorded less than 5 mg/L. Most stations have at least one value less than 8 mg/L. The lowest DO values are found in the Sun River proper. DO progressively decreases moving downstream from SR at Simms to SR at Fort Shaw to Sun River at Sun River to Sun River at Great Falls. Several circumstances potentially contribute to depressed or low DO levels. Return flow back into the stream will likely elevate water temperature, and decrease DO. As stream flow (velocity) decreases and streambed width increases, more opportunity for warming occurs. Increased sediment and nutrient enrichment may also contribute to lowered DO.
There are some fish species in the Sun River that would necessitate cold water standards for DO. These standards are a minimum of 8 mg/L for early life, and 4 mg/L for other life stages. Eighty percent of Sun River Project data samples would meet the 8 mg/L minimum standard. DO levels seem to be in excellent condition in the Sun River.
Summary
This study included monitoring of water quality at 24 locations within the Sun River watershed during the 2004 and compiling, organizing, and summarizing all available data collected for those stations during the pasted 20+ years.
Some conclusions, ideas, and recommendations:
- Discharges from Muddy Creek alter all of the water quality parameters of the Sun River measured in this study. The Sun River at Ulm Bridge monitoring station shows the influence of Muddy Creek. The elevation of water quality parameters resulting from Muddy Creek discharges decreases in the stretch of river between Ulm Bridge and Great Falls gauging stations.
- Water quality conditions were the best at the Sun River at Augusta station.
- Elk Creek contributes excellent water quality to the Sun River.
- Phosphorus levels within Mill Coulee, Adobe Creek, and Duck Creek are elevated relative to background phosphorus levels in the Sun River. Tributaries of the Sun River are the source of elevated phosphorus concentrations within the Sun River. The Sun River at FSID monitoring site accurately reflects the background phosphorus levels upstream of FSID. Thus, it would be possible to eliminate phosphorus sampling at Elk Creek and Sun River at Augusta.
- With regard to nitrate + nitrite nitrogen levels, the Sun River behaves by itself with no significant change from Augusta down to Fort Shaw. Unless there are significant changes in land use or discharges from new sources, a single nitrate + nitrite sample taken at the Sun River at Fort Shaw site should be significant to quantify nitrate + nitrite - nitrogen levels upstream. Nitrate + Nitrite - N levels at Muddy Creek at Gordon and Vaughn are essentially the same. Therefore, it would not be necessary to take samples at both of these sites. A sample at the Muddy Creek at Vaughn site would be ideal, as one could get an accurate sample of nitrate + nitrite nitrogen entering the Sun River. Two different sampling strategies could be applied – reduce the frequency of sampling, or collect samples from fewer sites.
- In the TKN dataset, there are three stations that have levels elevated above the rest of the stations – Muddy Creek at Vaughn, Mill Coulee, and Adobe Creek at Fort Shaw. When sampling, it is pertinent to concentrate on the problem areas. Unless a change is suspected, a bare bones monitoring program may only need to include sampling at these three sites.
- pH runs between 7.8 and 9. The pH pattern is consistent throughout the river, and therefore it is probably only necessary to measure in the Sun River proper. Yearly samples may only need to include one in a low flow period (September/October/November) and one in a high flow period (June/July).
- Simms Creek, Adobe Creek, and Duck Creek have elevated conductivities and are important to keep monitoring. A conductivity measurement at Mill Coulee and Muddy Creek at Power would give you the approximate conductivities for Muddy Creek at Cordova, Muddy Creek at Power, Tank Coulee, Spring Coulee, MC#3, MC#2, and MC#1. Another option would be to take a measurement at the bottom end of the river ( Sun River at Great Falls) and then manage the tributaries, as the tributaries are where elevated conductivities are found.
- Overall, DO levels within the Sun River and tributaries do not appear to be overly compromised. DO within MC#1, Tank Coulee, Spring Coulee, MC#2, MC#3, MC at Power, MC at Cordova, and MC at Vaughn is the same. A single measurement at MC at Vaughn would suffice in the place of measuring at all of these stations. Key sampling spots are the stations located in the Sun River proper.
- It is probably not necessary to monitor water quality in the tributaries of Muddy Creek. The Muddy Creek at Vaughn sampling site reflects the water quality within these tributaries. In almost all cases the water quality parameter measured at Vaughn was greater than in the tributaries. Likewise, measuring water quality at Gordon is probably not necessary as the Vaughn station reflects what is happening at Vaughn.
- There are sewage treatment plants discharging into the Sun River in the communities of Vaughn and Sun Prairie and a small plant near Vaughn. Also, there are several old septic tanks that drain in the Sun River, all of which are located on the lower Sun River. There is not sufficient data/information at present to make informed decisions regarding the effects this may have on the nutrient levels in the Sun River. Some monitoring of this situation would be advisable to determine the degree of concern these discharges are to the Sun River.
- Some sort of monitoring plan, whether extensive or small, should be in place in the Sun River watershed. Continual monitoring will be key to ensuring that water quality does not deteriorate and to document improvements within the watershed.
- In the event that revised management practices are put into place or significant changes in land use practices evolve, a well-defined monitoring program should be put in place to assess qualitative and quantitative impacts of these changes. The data organized and presented here will serve as an acceptable baseline for comparison purposes.
