By Jeffrey Manner, Student
University of Pennsylvania
March 19, 2020
Born from waters that emerge from gneiss* and schist** bedrock, White Clay Creek (WCC) flows through the Piedmont Upland Province of Southeastern Pennsylvania. Winding its way south through the rolling hills of Southern Chester County, the stream meanders through forests, farmlands, and urban centers, all of which influence its characteristics. WCC’s main stem originates from three headwater sources, the West, Middle, and East Branches, that merge into one before crossing into Delaware. The main stem passes through Newark and ends at its confluence with the Christiana River near Wilmington.
In Northern Delaware, more than 600,000 residents rely on a water supply drawn from the Christiana River Watershed, and for residents of Newark, the bulk of that water comes from White Clay Creek. Its waters support biologically diverse aquatic communities that at times have struggled to adapt to anthropogenic disturbances. Federal laws have been enacted to improve waterway health, protect aquatic ecosystems, and safeguard America’s drinking water. However, to better protect rivers and streams from pollution and degradation, conservation efforts must also be implemented at local and regional scales along the entire length of waterways, including their headwaters.
Each year, tens of millions of dollars are spent on river restoration projects throughout the United States . In Chester County, the Stroud Water Research Center (SWRC) has been conducting riparian reforestation and river restoration projects along sections of White Clay Creek and other watersheds since 1967. The Stroud Center’s campus is located near Avondale, PA, and sits on the banks of the East Branch of White Clay Creek in an area that was previously deforested for agricultural purposes. Extensive and long-running research and reforestation projects have been undertaken along the East Branch of WCC in an area called the Long-Term Research in Environmental Biology (LTREB) section. The efficacy of these projects has been researched by SWRC scientists for the past 52 years and continues with my own independent research project conducted over the past two semesters.
The clearing of trees and other vegetation along river networks (riparian deforestation) can cause dramatic shifts in aquatic ecosystems. Reductions in water quality, habitat complexity, and food availability following riparian deforestation can greatly affect resident species[4,5]. Changes in thermal regimes, geomorphological structure, food-web dynamics, and competition affect fish movement in and between habitats . A better understanding of the factors affecting fish movement following anthropogenic disturbance can help guide river restoration and conservation projects in the future.
During Fall 2019, I began a quest to understand the effects of these conservation efforts on fish species in the East Branch of WCC. Using historical data and mark-and-recapture surveys, I examined population dynamics and fish movement between three different habitat types associated with SWRC’s reforestation project.
Today, the LTREB section of WCC consists of three different stream reaches: old-growth forest, restoration, and meadow . The meadow and restoration reaches were previously cleared and utilized for cattle grazing. Reforestation efforts have transformed once barren pasturelands back into a forest along the restoration reach. The meadow has been kept clear of all trees to simulate continued agricultural use and is bordered to the south by cornfields. Each reach type is associated with different biotic and abiotic conditions that influence the aquatic environment. Thus, the effects of riparian deforestation and restoration on fish movement can be researched among these three different aquatic habitats.
Research has been conducted through mark-and-recapture surveys using electrofishing techniques. Block nets are set in-stream to restrict fish movement along 100-meter (m) stretches, which are further divided into 20-m sections. Fish are then removed from each 20-m section using backpack electroshocking units and hand nets. Electrofishing stuns the fish as an electrical current is sent from an anode attached to the end of a hand-held pole towards a cathode that trails behind the operator. Stunned fish float belly up and can be scooped into hand nets. Captured fish are placed in aerated buckets until all measurements and markings are finished.
During the initial marking period, all fish are weighed and measured, and fish over 50 millimeters are tagged. In this study, we utilized visual implant elastomer (VIE) tags which consist of a subdermal injection of a pliable biocompatible fluorescent material that is injected in the dermis just beneath the scale . The color and location of the tags can be alternated to create unique individual identifiers using a numerical coding system. This allows us to identify fish in sequential electrofishing surveys. After an entire 100-m stretch has been completed, all fish are returned to their original 20-m section.
Recapture sampling consists of all original 100-m sections plus another 100-m up and downstream from the original locations. Marked fish provide data on growth rates and movement. For this study, tagging was done in September of 2019, with recapture sampling conducted in late November 2019 and February 2020. Preliminary results show an upstream bias; however, this could also be attributed to seasonal movement or a preference for wooded habitat. The single most predictive variable among movement was species type. Species with larger average size ranges had the most and furthest recorded movements. Within these larger species, size did not appear to be a determinant factor. Additional data analysis is currently in progress to predict whether there is a preference for specific habitat.
With interest in the conservation and protection of our waterways comes the opportunity to study the effects of restoration projects on resident species. Among the most consequential influences on fish populations caused by habitat, change are alterations to water quality, food-webs, and spawning habitat [4, 8]. Anyone of these factors can cause fish to move in or from their home range. A better understanding of the effects of habitat degradation and restoration on fish species can help to guide future projects. This study provides a starting point for assessing fish movement in White Clay Creek and a basis for future studies in this watershed as restoration projects continue.
*Gneiss is formed by high temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks.
**Schist is a medium-grade metamorphic rock formed from mudstone or shale.
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. Stroud Water Research Center (SWRC). 2010. LTREB: Trajectory for the recovery of stream ecosystem structure and function during reforestation. NSF grant proposal. SWRC files. Avondale (PA).
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Jeff Manner is a senior at the University of Pennsylvania pursuing a double major in biology and environmental science. He holds an Associate in Science in mathematics and natural science from Delaware County Community College. He has spent two summers interning at the Stroud Water Research Center in the fluvial geomorphology lab and is currently conducting independent undergraduate research with their fisheries department. Jeff found a passion for rivers and aquatic life while growing up in Michigan and subsequentially spending his twenties in the Rocky Mountains.