A wet and wild spring
On April 20, teams of HRWC volunteers poured from our office and explored the Huron Watershed in search of aquatic insects, snails, clams, and crustaceans. The data that these volunteers collect enables HRWC to keep a finger on the pulse of the Huron River and it’s tributaries; to understand where streams are degrading and where they are getting better.
This year’s event was marked by very high water, just like our Spring Roundup in 2011. And just like in 2011, data interpretation has been difficult. The data collected from a River Roundup are meant to show overall conditions across the watershed and be comparable to past year’s data in order to tell us how things are changing over time. In flooded conditions, the stream systems are not comparable to past years, often because the volunteers are forced to sample in an unusual manner (like standing on the bank and reaching into the swollen river rather than entering it).
QAPPs are useful- yes, seriously!
HRWC follows a quality assurance project plan (QAPP) to make sure that we deal with the issue of bad samples in a consistent manner.
From the QAPP:
“The resulting measures of Total Insect Taxa for each site will be compared to the median from the site’s whole data record and there should be a relative percent difference of less than 40%. The same comparison will be made for Total Abundance (for all taxa).
Sample results that exceed these standards will be noted as “outliers” and examined to determine if the results are likely due to sampling error or a true environmental variation. If sampling error is determined or if the environmental variation is not reflective of normal conditions (ie extreme flooding), the data point shall be removed from the data record.”
13 samples were removed from the official data record for failing to meet these requirements. The rejected samples had on average total abundances 50% less than the median of past results, and coincidentally 50% less insect diversity than the median of past results. (We would expect these two numbers to be related but it is strange that they are exactly the same).
2 samples were at new sites where past data didn’t exist to test results against the QAPP
requirements, but volunteer descriptions make it plain that the sites could not be sampled properly. These samples were also rejected.
27 samples were accepted. For all accepted samples, total abundance was down 20%, and insect diversity was only down 14% from the median of past results. This amount of variation is normal even in unflooded conditions.
You can see all the results in the Spring 2013 River Roundup Report.
Current Watershed Health
In a nutshell, the health of the watershed as judged by our macroinvertebrate sampling is holding steady. Of the 59 sites that we monitor to judge this, 28 sites have had no statistically significant changes over time, and 6 sites are too new to make this judgment.
13 sites are declining, and these include locations on Chilson Creek, Davis Creek, east branch of Fleming Creek, the Huron River at Flat Rock, Norton Creek, and South Ore Creek. It should be pointed out, as it was after the 2012 Fall Roundup, that the majority (though not all) of the declining sites are in Livingston County.
12 sites are improving, including Boyden Creek, Horseshoe Creek, the main and west branches of Fleming Creek, Huron Creek, the Huron River in Ann Arbor and Ypsilanti, and several places on Mill Creek. The majority (though not all) of the improving sites are in Washtenaw County.
The rejected samples aren’t thrown away. They are placed into a separate database and flagged with the reason for their exclusion. Such data may prove useful in the future- for example, quantifying the effect of high flows on macroinvertebrate populations… as a way at getting at how climate change could be changing our watershed.
Let’s hope for a drier fall- but if it is wet and flooded again- we know how to deal with it!