In my last blog post, I talked about the research that I have been doing this summer; however, I did not get around to talking about the results. Over the past 2 months, I have been comparing fish habitat amongst 3 study sites: Last Chance, the Flat Rock, and the Buffalo River. At each site, I conducted a qualitative site analysis as well as a quantitative macrophyte cover estimate. At each study site, I also conducted a QHEI (qualitative habitat evaluation index) developed by the Ohio EPA. Last Chance received a score of 68, Flat Rock a 65, and the Buffalo River a 73.5. While these scores are all fairly similar, their differences were a result of substrate and riparian zones. The Buffalo River had a wide variety of substrates ranging from boulders all the way to silt and muck. Last Chance consisted primarily of boulder and cobble whereas the Flat Rock reach consisted primarily of gravel and sand. The Buffalo River interacted with its riparian zone and flood plain whereas the Last Chance and Flat Rock reaches were mostly confined and had very little interaction with their riparian zones. These scores are all relatively similar; however, because last Chance is known for its great fishery, I would have predicted it to score the highest of the 3 study sites. While the QHEI is a great way to gain a general understanding of the river and its habitat, they have no statistical power due to the fact that they are all visual estimates. QHEI scores have no confidence intervals or error bars. The macrophyte cover estimates done in this study on the other hand are much more exact and will have statistical significance.
The results of the macrophyte cover estimates were much more in line with my original hypothesis. Last Chance had an average macrophyte cover of 65.1875%, the Flat Rock reach had an average macrophyte cover of 48.26168%, and the Buffalo River had an average macrophyte cover of 52.07627%. After running a statistical test to determine the significance of these results, we determined that there was no real statistically significant difference between the Flat Rock reach and the Buffalo River; however, there was a statistically significant difference between the Last Chance reach and the Buffalo River as well as the Last Chance reach and the Flat Rock reach.
Between my two sampling dates of July 13th and July 20th, we received multiple reports of large quantities of uprooted macrophytes floating down the river through Harriman State Park. These reports actually coincided with my data, which shows an overall decrease in macrophyte cover.
This graph shows macrophyte cover by date. The black line shows the median percent cover.
This graph shows a significant decrease in macrophyte cover at the Last Chance sampling site.
This dramatic decrease in percent macrophyte cover in Last Chance could be a result of the macrophytes growing too large for the velocity of the river. Because the substrate here consists primarily of boulder and cobble, the macrophyte roots do not have much to hold on to. As the plants grow larger, they essentially act like parachutes in the water of the river, thus potentially uprooting them.
After viewing the data, it is very clear that there is a significant difference in habitat amongst the three sites. It is also evident that macrophyte growth is essential for maintaining a quality trout fishery. Despite the Flat Rock reach and the Buffalo River having the ideal substrate for macrophyte growth, the two sites have very little macrophyte cover. We know that the substrate is not limiting macrophyte growth in the Flat Rock reach or the Buffalo River so we are wondering what this cause could be. My prediction is that the macrophytes in these two reaches are suffering from nutrient limitation. The Flat Rock reach used to hold large quantities of large trout in the 70s and early 80s; however, the homes in this region switched from septic tanks to a sewer system in the early 80s, which could have resulted in a decrease in nitrogen and phosphorous levels in the water thus limiting macrophyte growth. In order to fully understand the differences in these macrophyte cover percentages, we must look into nutrient differences amongst these sites. By fully understanding the upper river region (the Flat Rock reach), the Mack’s Inn sewage treatment plant could potentially be used for its treated sewage full of nitrogen and phosphorous to boost macrophyte growth and hopefully bring in an abundance of large fish. My supervisor, Jack McLaren, is conducting his doctoral research on water quality in the Upper Henry’s Fork region and will be including this in his work.