|
Tales of Stream Monitoring Fun
|
|
|
Friends of Accotink Creek and Friends of Lake Accotink Park hold biological stream monitoring workdays four times per year. |
|
 Familiar face? Could this be the same crayfish we saw in September? |
December 14 2024 Stream Monitoring: The weather was sunny and more than seasonably cold, with temperatures starting below freezing and rising to about 35. The cold made conditions tough at the examination table. A thin glaze of ice formed on the surface of the net and a few icicles hung along the edges. For spotting invertebrates on the collection net, we usually rely on looking for movement. However, the chilled invertebrates were mostly motionless, having turned into "bugsicles" in the crisp air. We volunteers could sympathize, finding it nearly as hard to move our freezing fingers. Our catch today was had a fairly good mix of species, with higher than usual numbers of species less commonly seen here, such as Hellgrammites, Mayflies, and Riffle beetle larvae. Despite that, the catch was dominated by aquatic worms and Netspinner caddisflies, species that are tolerant of impaired waters. We caught one crayfish today, an uncommon species at this site. It was so similar in size and appearance to the one we caught in September that it may well have been the same individual. If it is the same crayfish, it appears to have lost it's left claw and is regrowing a new one. Accotink Creek achieved a numeric stream health score of 4, down in the unacceptable range. Sediment caused by excessive runoff from paved surfaces is the major factor reducing invertebrate populations and impairing the health of streams in our region. See the tabulated results here.
Paved surfaces are the nemesis of Accotink Creek's benthic invertebrate population. Take advantage of financial incentives to become part of the solution with Conservation Assistance.
|
|
Our region has been in drought conditions for weeks, so we were not surprised to find the stream level low. Still there was sufficient flow that we had no difficulty setting out our collection nets. Temperatures were mild, in the low 70's. The dry conditions for much of the year may have contributed to the high percentage of beetle larvae in our catch. At 25.22%, it is the highest percentage we have ever achieved here. Beetles are less tolerant of impaired water than some other species, so their higher numbers are encouraging. With a 2-point boost from the beetles, our monitoring today produced a stream health score of 6, above our usual average, but still outside the acceptable threshold of eight on the 0 - 12 scale. See the tabulated results here. |
Captured crayfish considers escape options. |
|
June 8, 2024 Stream Monitoring: It was a splendid day for monitoring, with sunny skies and temperatures in the low 70's. Perhaps people were diverted to other activities by the fine weather, for only three volunteers showed up. We were fortunate to catch the full quota of over 200 invertebrates with just one net today, making this the third June in a row we've had that bit of luck. Our catch today was 82% Netspinner caddisflies, a species tolerant of impaired water, and the one we catch most often (though usually no quite so many). We caught a single caddisfly which was not a Netspinner, and a single Riffle beetle larva, just as we did last June. These are species which require better quality water than Accotin Creek can generally offer. One unusual catch was a Mayfly, probably of the genus Caenis. Bulky, squat, and slow moving, unlike the more diminutive and gracile mayfly larvae we have occasionally encountered before, we had to seek more expert guidance to make a positive identification. Accotink Creek achieved a stream health score of 5, outside the acceptable range on the scale of 0 to 12. See the tabulated results here. |
 This invertebrate was first thought to be a mayfly, then a damselfly, then a mayfly again. |
 The ones that got away - mayfly and damselfly larvae were found after the session. |
We had a crew of 20 volunteers today. The weather was favorable, sunny and calm, with temperatures rising to 48 degrees. Accotink Creek was a bit after rain two days before, but otherwise. We set the maximum of 4 nets, but didn't manage to collect the minimum of 200 invertebrates for a valid score. Sometimes the quantity of invertebrates just seems to be a matter of luck. Our catch today was overwhelmingly dominated by aquatic worms, the creature most tolerant of water quality impairment. Accotink Creek received a poor numeric stream health score of 4 on a scale of 0 to twelve, typical of the scores over the years at this site. (The score was unofficial due to the count of invertebrates being under 200.) See the tabulated results here. After we had packed up, one volunteer looking around in the creek made two lucky finds - a mayfly, which we seldom see at this site, and a damselfly, which we have never caught in our nets here.
Paved surfaces are the nemesis of Accotink Creek's benthic invertebrate population. All the runoff during rainstorms pours down storm drains and shoots into the creek, scouring away the banks and smothering stream life in fine sediment. At least we can say the sediment-generating activities of the I-66 project have finally come to a halt. Take advantage of financial incentives to become part of the solution with Conservation Assistance.
|
 A row of rescued mussels |
January 13 & 14, 2024 Mussel Rescue: On the evening of January 9th the USGS stream gauge on Accotink Creek in Wakefield Park briefly went over 2000 cubic feet per second, crossing the threshold at which freshwater mussels are pushed out of the streambed and stranded on the gravel bars. Once the water receded, four volunteers set out to search. We located 92 mussels and returned them to safety in deeper water. It was gratifying to see how many were juveniles, indicating the population is healthy enough to continue reproducing. The smallest was 1.5 inches long vs. the largest about 6 inches. We found individuals of each of the three mussel species living in Accotink Creek, the Eastern Elliptio (Elliptio complanata), the Eastern Floater (Pygandon cataracta), and the Paper Pondshell (Utterbackia imbecillus. See the rest of the mussel rescue photos here. Read about our 2015 freshwater mussel biological survey. Learn more about freshwater mussels.
|
|
Accotink Creek Creatures
A lament for aquatic invertebrates penned
GET YOUR BRAIN WET!
Plan now to volunteer again with others to preserve our oceans and waterways Back to our main Monitoring Page
|
