2024 Water Quality Initiative UpdateFEBRUARY 2024
The Stillwater Rosebud Water Quality Initiative (SRWQI) began in September 2020 and has completed 40 months of stream monitoring in the Stillwater River and Rosebud Creek watersheds. We’ve been sampling for Total Suspended Solids (TSS), Total Nitrogen (TN), Nitrite+Nitrate Nitrogen (NO2+NO3-N) and Total Phosphorous (TP). Field parameters are measured with a Hanna field water quality meter. We’ve also measured the flow rate of Butcher Creek at Highway 78 near Absarokee, and of it’s two tributaries east of Roscoe. Two monitoring locations were modified in October 2022, dropping two sites on upper Butcher Creek tributaries east of Roscoe, and adding two on the Stillwater River, one at the Moraine fishing access site below Nye and the other at Fireman’s Point near Columbus. With three sites on the Stillwater River, we’ve been accumulating basic water quality data on the entire main stem. The backstory of this change, however, actually has to do with Butcher Creek. The Butcher Creek Backstory The SRWQI initially gave some emphasis to Butcher Creek due to the abundance of historical data collected on it, in the 1960’s by the US Geological Survey, and in the 1990’s by Stillwater Conservation District, NRCS and DEQ. These agencies in the 1990’s, in cooperation with landowners, made large investments in monitoring water quality and on-farm cost sharing projects to reduce the sediment and nutrient loads to Butcher Creek, the lower Rosebud and Stillwater rivers. After taking a deep dive into all the stream flow and water quality data on Butcher Creek it appears that Butcher Creek in recent years is having a significantly smaller water quality impact than it did historically. We crunched some numbers and created some charts to inform you, so please take your seats and read on. Rockin' & Rollin' in the 60’s If you can remember that there was a USGS streamflow gaging station on Butcher Creek from September 1960 through September 1962, you are likely a resident super senior. In fact, there was, located just upstream of the current Highway 78 bridge near the Rockin J. This station logged the flow every day for two years before being abandoned. In Figure 1 below, we plotted the daily flow recorded by this gage with our own monthly flow measurements near the same location just downstream of the bridge. We normalized the two-year time scale to start with October 1 as day #1 to allow overplotting the 1960’s with the 2020’s. Notice that starting June 1 of both years (day #243 and #608 respectively) our flows measured since 2020 are mostly much lower than those measured by USGS. It’s also relevant to note that our region was in a drought in 1960 and most of 1961, returning to normal and wetter conditions by 1962 (NOAA, 2024). This means that the higher flows of Butcher Creek measured throughout 1960-62 were not predominately caused by wet weather, but by irrigation water carriage and return flows. Getting into Garth Brooks and Monitoring in the 90’s If you were sipping on a Crystal Pepsi and listening to Garth Brooks on your pickup radio as you turned up the Butcher Creek road in the 1990’s, you might have spied someone wading the creek taking some kind of measurement. A team of scientists from the SCS (now NRCS), the DHES (now DEQ) and the SCD (same old Stillwater Conservation District), with the help of our local landowners, spent eight years collecting flow and water quality information on Butcher Creek. The goal was to understand the extent and causes of non-point source degradation of Butcher Creek from runoff and irrigation return flows sufficiently to develop on the ground solutions. We dug out those old files from the depths of the SCD office and extracted 67 flow measurements made from 1991 through 1995, mostly in the growing seasons. We again normalized the time scale to day-numbers, in this case with January 1 as #1. Figure 2 shows the 1990s flow measurements by year between April and October in colored lines. Our SRWQI project made 26 flow measurements between September 2020 and October 2022 which are plotted as individual points (black squares). The 2020 – 2022 flow measurements are mostly on the lower end or less than those made in the 1990s. Thanks to the thorough science developed in the 1990s studies, we can also compare the suspended sediment load carried by Butcher Creek. The state SCS office at that time (D.Jones, 1993) used 15 paired flow and suspended sediment concentrations collected on Butcher Creek near the mouth to calculate an estimate of the total sediment load for the 1992 April-September period. We duplicated the same procedure using 14 paired flow and suspended sediment values from 2021 and 2022. Figure 3 is a bar chart showing the calculated total sediment loads in tons transported by Butcher Creek for April – September 1992, 2021 and 2022. The same data allows us to compare the average suspended sediment concentrations and average stream flow rates for Butcher Creek near the mouth in Figure 4. Average sediment concentrations are shown in orange and average stream flow rates in blue for each of the years. Good scientific assessments often lead us to new questions, and so we can ask why the sediment load of recent years appears to be much less than that documented in the 1990’s studies. Keep in mind that stream flow and sediment transport can vary greatly from year to year, and these data, while reliable, are snapshots in time. Subject to all appropriate limitations, we hypothesize that because recent growing season flow rates of Butcher are significantly less than historical, there is less erosion and sediment transport in the watershed. Lower flow rates, especially lower peak flows, may have allowed for the Butcher Creek channel and banks to better stabilize and revegetate. Some landowners have suggested that farm consolidation and changes in irrigation practices are likely reasons for these observations. We plan to continue our evaluation as more data become available, and we welcome the public’s thoughts and observations. Stillwater Valley Watershed Council Coordinator, Lindsey Clark, stressed that the data collected by this project is of an educational and non-regulatory nature, intended to provide basic indicators of stream health to inform the residents of the Stillwater Valley and protect all the uses we make of our streams for this generation and those to come. |