Wednesday, April 4, 2012

Wissahickon Wetland

Killdeer (Charadrius vociferus) See end of post.

I am adjunct faculty at a local university this term, teaching undergraduates about ecological restoration.  Most of the class time consists of lectures, but on Thursday, April 29, we visited a wetland restoration project.

This project lies on the floodplain of Sandy Run, the largest tributary of Wissahickon Creek, which is itself a tributary of the Schuylkill River in southeastern Pennsylvania.  Like all of the streams around Philadelphia, the Wissahickon and its tributaries are heavily urbanized and very "flashy" (i.e., they have low baseflow between precipitation events because groundwater recharge is limited by the imperious surfaces in the watershed, and they become roaring torrents after storms because so much water runs directly off the pavement and rooftops and into the streams).

The Wissahickon Valley Watershed Association received a $40,000 grant to convert a perennially soggy softball field adjacent to Sandy Run into a wetland.
The original plan for the project called for the creation of a seasonally flooded wetland that would dry out between storms.  But, once excavation got underway, the planners found that the groundwater level was higher than they had anticipated, so the basin was perennially flooded.  Instead of a seasonal wetland, they created an emergent marsh.
Emergent marshes aren't "bad" but, because they hold water all the time, they allow for the colonization of fish, which are amphibian predators.  Thus, the habitat is not as desirable for amphibians as a seasonal wetland would be.  In a second phase of the project, the planners "got it right," and created shallower depressions above the water table that only hold water after storms.

Between the created wetland and Sandy Run lies a mostly wooded riparian zone.  Floods have deposited gravel and sand from the stream into a low dike adjacent to the stream channel, and that berm has been colonized by scrubby box elders and sycamores.  The floodplain as been invaded by the non-native invasive buttercup, lesser celandine (Ranunculus ficaria), and by pernicious purple loosestrife (Lythrum salicaria).  As part of the wetland restoration project, the planners also planted trees on the floodplain to augment the riparian buffer that had developed naturally.
All of the trees have to be caged to protect them from deer damage.  Bob Adams, Director of Stewardship for the Watershed Association, showed the students how the cages are subject to damage from floods and how they snag debris washed downstream during storms.

And, the Killdeer...

As the field trip was winding down, I heard the distinct call of a Killdeer, but didn't give it much more than passing notice.  Then, I saw a group of students gazing down at the ground, captivated by something.  When I went to investigate, I discovered a Killdeer sitting on the ground, and I was able to get within three feet of the bird, which didn't move a muscle.

Floods associated with Hurricane Irene and Tropical Storm Lee late last summer had washed gravel off a parking lot and deposited it in a think layer adjacent to the wetland restoration project.  It provided perfect nesting habitat for the Killdeer, which wasn't about to be moved off her territory.  I despair for the bird's success, though; the site is very near a very busy road, and people use the trail through the wetland for recreation and to walk their dogs.


John "By Stargoose And Hanglands" said...

Nice to see the Killdeer if only in a photo. A few turn up on this side of the ocean from time to time and cause excitement among birders. Our Little Ringed Plovers are similarly reckless in their choice of nest site, sometimes nesting near working quarries.

Scott said...

I think I could easily have stepped on the bird if I didn't know it was there, John--it just wouldn't budge.

packrat said...

An interesting and informative field trip, Scott.

packrat said...


Forgot to mention that I responded to your questions on my blog the otherday. No need to publish this comment.

Scott said...

Packrat: I'm glad you enjoyed my account of a short walk in the spring woods here at the restored wetland. And, I always check your blog to see if you've answered my (seemingly endless) questions--you always do!