Headlines: Water temperatures through the Ranch have been on the warm side. Temperature has climbed above 71˚F for a couple of hours each day over the last week. However, daily maximum temperatures have not been deadly for rainbow trout, and only a few daily averages have been at the lowest levels that would stress fish. This is the same pattern we saw in both 2015 and 2016, when streamflows were about 800 cfs higher than current flows. Thus, releasing additional water from IP dam does not result in significantly cooler summertime water temperatures, but we do know that increasing flow out of Island Park Dam decreases water clarity and will reduce winter flows, which reduces survival of juvenile trout next winter and hence recruitment of 2-year old fish into the population in 2019.
This fall HFF initiated a new water-quality monitoring study designed to answer the following question: How far downstream of Island Park Dam (IP Dam) do high turbidity levels persist? I introduced this study in my blog post made on September 9, 2016. Please find details of the background and motivation for this study, as well as a map of the sampling sites, in the previous blog post. The current blog post summarizes what we found during our 2016 data collection season.
On Wednesday, September 7th HFF initiated an exciting addition to our water-sampling program designed to answer the following question: How far downstream of Island Park dam do high turbidity levels persist? These results will be important for predicting which reaches of the river will be most affected, and to what extent, during periods of high sediment delivery from Island Park reservoir.
Brief background: There are three genera and many species of cyanobacteria; only a handful of these produce a toxin harmful to mammals. Blue-green algae (or BGA) is the common name for cyanobacteria, which is a single-celled bacteria that photosynthesizes and is neither an algae nor a plant. All plants, algae, and cyanobacteria use chlorophyll A, a pigment used to capture light for photosynthesis. In addition to chlorophyll A, freshwater cyanobacteria also utilize phycocyanin for photosynthesis, which is a bluish pigment that gives them their color.
During our regular water-quality monitoring last week, we observed that recent turbidity levels are above average in all reaches of the river, except below Island Park Dam, and the highest observed turbidity last week is higher than any observed turbidity below Island Park Dam since we started regular water-quality monitoring there in the summer of 2013. The highest turbidity levels we observed last week were in the Warm River-to-Ashton Reservoir reach (18 NTU) and at Pinehaven (9 NTU).
Oxygen content in the water is critical to fish in the same way oxygen in the air is critical for us. The way we measure oxygen content for fish is milligrams per liter (mg/L) of dissolved oxygen, or DO. Habitat requirements, such as average DO requirements, are useful in our research and monitoring programs for interpreting our data and designing management actions.
What is meant by average dissolved oxygen requirements?
I recently created two figures to accompany the quick reference poster of water quality on the Henry’s Fork that was featured in our blog post on October 30th. These figures illustrate the optimal, sub-optimal, stressful, and lethal temperature ranges for Brown Trout (Salmo trutta) and Rainbow Trout (Oncorhynchus mykiss).
To support our water quality monitoring efforts, we have a new quick reference poster in the office! For now, the poster displays the recent, daily range of dissolved oxygen (averaged over the previous 4 days) and the weekly average temperature from our sampling/sonde sites. We have seven sites that we capture data from; I download data from 3 of the sondes one week, then retrieve data from the remaining 4 sondes the following week. Therefore half of the displayed data are from the previous week, and the other half of the site data are two weeks old.