Use of Resident Macroinvertebrates to Monitor the Improvement of a Restored First Order Stream
Although often ignored due to their small size and seeming lack of economic importance, headwater streams have a high ecological importance to watersheds. Although restoration efforts on both streams and rivers have increased in recent years, monitoring on smaller successful and unsuccessful restoration strategies. The purpose of this study is to use macroinvertebrate bioassessment protocols to monitor and gauge the success of a restoration on a flood impaired headwater stream, Smith's Run, within a highly urban watershed. Kick net sampling was used to collect macroinvertebrate samples (100 individuals) and water quality testing was done in April 2006 and March 2007, before and after a stream restoration, at the Schuylkill Center for Environmental Education, Philadelphia PA. Sample sites were chosen according to spatial relationship to restoration. Water quality was compared to national Environmental Protection Agency (EPA) standards for freshwater systems. Quality and diversity of macroinvertebrate collections were assessed using a Cumulative Biodiversity Index and a Shannon Diversity Index, respectively. Collected data was compared amongst sites and to a similar stream system presently in excellent ecological condition. While water quality remained stable between testing sessions, changes were observed in macroinvertebrate populations. Restoration and downstream sites showed improvement in species diversity and quality of observed species with the downstream site showing significant improvement when compared to the unrestored upstream site. Our initial results indicate that commonly applied restoration techniques may have a significant localized impact in restoring diversity to resident macroinvertebrate populations within flood damaged headwater streams. The monitoring of Smith's Run will continue as the restored riparian buffer establishes itself and further restoration take place at the site.
Due to their small size, relative abundance, lack of fish species, and lack of importance for industry, headwater, or first-order streams, are often seen as unimportant which has contributed to both their deterioration and destruction (Meyer and Wallace 2001). These misconceptions ignore the varied and significant roles both first-order streams and their assorted wildlife play within watersheds. Although each individual first-order stream contributes only a small fraction of the total water within a watershed, combined these streams dominate watershed systems, contributing upwards of 73% of stream miles to a given watershed (Leopold et al. 1964) and providing significant amounts of water to upstream rivers (Meyer and Wallace 2001). Beyond hydrological importance, headwater streams also serve as refuges for aquatic life in disturbed higher order streams and rivers (Doppelt et al. 1993). Moreover, their relative isolation makes them perfect habitats for rare and unique species (Muchow and Richardson 2000).
Due to the relative small size, the ubiquity, and the connected nature of headwater streams within terrestrial habitats, the important ecological roles headwater streams and their resident life play within watersheds are under unique threats from human development. Destruction of riparian corridors, mining practices, groundwater depletion, flow alterations, and excessive nutrient input are just a few of many destructive anthropogenic or human caused processes that have not only degraded headwater streams but have also made aquatic freshwater species far more threatened than terrestrial species (Ricciardi and Rasmussen 1999). This is especially true for watersheds with diverse catchments, such as the Schuylkill River Watershed in Pennsylvania which includes urban, suburban, and rural areas. Suburbanization and urbanization has caused severe impairments and damage to the Schuylkill River Watershed with over 33 percent of its stream miles impaired (SAN 2002). One of its most significant impairments is storm-mediated over-sedimentation responsible for approximately 39 percent of its impaired stream miles. This is directly attributable to the degradation of riparian corridors (the plant life surrounding a given stream) and the removal of soil and plants in favor of paved surfaces. During rain events, these actions dramatically increase flooding into lotic or freshwater aquatic systems increasing the influx of land sediments (PWA 2004).
Preserving and restoring impaired headwater streams is important due to the direct impact such systems have on higher order streams and rivers. Headwater streams and their resident species, such as macroinvertebrates, serve as sinks and processors of organic and inorganic matter regulating the flow of detritus and sediment into higher order systems (Meyer and Wallace 2001). This is important as this processed organic matter or fine particulate organic matter (FPOM) may serve as a food source for downstream reaches, and at high levels, can increase water turbidity negatively affecting downstream primary production (Vannote 1980). Excess sediment input from small streams to large rivers can reduce the depth of downstream river beds negatively impacting industry. Headwater streams also help to reduce the number and severity of downstream flooding events by retaining water longer than terrestrial habitats (Meyer and Wallace 2001).
Within the United States, stream/river restoration projects have become more prevalent with an estimated 15 Billion USD spent in the past 20 years on various restoration projects (Bernhardt et al. 2005). The National River Restoration Synthesis Service in its efforts to capture data on stream restoration projects has collected data from over 37,000 separate projects (Bernhardt et al. 2005). The most frequently reported project intents were riparian management, water quality management, bank stabilization, in-stream habitat improvement, and aesthetic improvement, respectively (NRRSS). While some restoration projects are extensive in scope with equally extensive funding sources, such as projects on the Kissimmee River, FL or the Grand Canyon, AZ, the majority of stream restoration projects have more limited goals, seeking to restore less than 2 km of stream length and having budgets under 50,000 USD (Bernhardt et al. 2005). Bernhardt et al (2005) found that these smaller scale restoration projects were far more likely to lack monitoring. This creates a significant difficulty for planners of future restoration projects as vital information goes un-disseminated on both successful and unsuccessful restoration strategies resulting in both the loss of time in the restoration of critically damaged systems and a significant loss of capital.
Limited financial and human resources for such small scale restorations represents a significant challenge for monitoring the ecological impact of restoration practices on impaired lotic systems. Measurements of water chemistry while relatively inexpensive are time sensitive and only accurate for that moment in time. For lotic systems impaired by flood-mediated sedimentation, the measured reduction of sedimentation after a restoration is dependent on accurate tracking of rain events, the ability to visit the restoration site precisely at the moment of storm events, and accurate calculation of sediment particle size during rain events. Not only do these research requirements place a serious impediment to such studies, but also the results of such research ignores what should be an essential objective for any restoration, the restoring of biological processes within lotic systems. This suggests the need for a biological measure of such restored systems. Periphyton (in-stream microscopic plants), fish, and benthic macroinvertebrates survey are all methods used federally and within states to biologically assess the health and ecological function of lotic systems (Barbour et al 1999). Among these, macroinvertebrates are the easiest to apply.
Benthic macroinvertebrates are aquatic insects, worms and crustaceans most often found in the substrate of streams. They are vital to lotic systems as essential members of detrital foodwebs by processing organic matter and serving as food for both aquatic life, such as fish (Barbour et al. 1999), and terrestrial life, such as birds (Gray 1993).
They are ideal for use in bioassessment due to their ubiquity in stream systems and their relative large size (Barbour et al. 1999). Macroinvertebrate taxa show differing tolerance to habitat conditions including stream acidity (Dangles 2002), allochthonous (organic matter from outside an aquatic system) input (Negishi 2002), temperature, chemistry, and riffle (Quinn et al 1997). Even more importantly, macroinvertebrate communities also show differential responses to disturbances such as flood events (Lepori and Hjerdt 2006; Death and Zimmerman 2005), with high levels of disturbance negatively affecting taxa number and diversity.
Here we examine Smith's Run, a first-order stream within the Schuylkill River Watershed, severely degraded by flooding events in 2004. We conducted water quality testing and macroinvertebrate surveys before and after a summer 2006 restoration to determine the success of the applied restoration techniques in rehabilitating this first-order stream.
MATERIALS AND METHODSSite Description
Smith's Run is a first order stream, which originates on the property of the Schuylkill Center for Environmental Education (SCEE) in Philadelphia, Pennsylvania 19128 (40o03' N 75o15'W) and flows into the Schuylkill River (Figure 1). Smith's Run is one of the last two remaining intact first order streams in Philadelphia, PA both of which originate at the SCEE (Crockett 2006).
First established in 1965, the SCEE now owns a 137.6 hectare property maintained as a nature preserve and environmental education center that is accessible to the general public. The riparian buffer surrounding Smith's Run is a secondary temperate deciduous forest with a native overstory dominated by White Ash (Fraxinus americana), Tulip Poplar (Lirodendroan tulipfera) and Black Gum (Nyssa sylvatica). Although the understory contains a mix of both native and non-native species, it is dominated by non-natives, such as Japanese stilt grass (Microstegium vimineum), Japanese honeysuckle (Lonicera japonica), and oriental bittersweet (Lindera benzoin). An over-population of white-tailed deer (Odocoileus virginianus) estimated to have a density of 154 ind km-2 impacts understory plants through over-browsing (Bower et al. 2006). With population densities of 89 ind m-2, Asian earthworms (Amynthas hilgendorfi and agrestis) have also severely impacted vegetation by altering upper soil horizons, consuming leaf litter and altering soil pH (Bower et al. 2006).Restoration
In August and September of 2004, the Philadelphia area experienced two severe storm events. On the 1st of August 2004, the SCEE experienced a 25 year storm event totaling 12.8 centimeters of precipitation in approximately 9 hrs (NOAA 2008). The remnants of Hurricane Jeanne in late September 2004 resulted in a historic 200 year storm event with an additional 26.4 centimeters of precipitation in less than 24 hours (NOAA 2008). The subsequent flooding from these two storm events severely degraded the stream, as seen in Figure 2a. The banks were scoured; and the riffle experienced heavy siltation. Rain mediated erosion at the site was estimated to be 1.5-3 cubic meters per year (Lawn and Williams 2004).
In the summer of 2006, SCEE in collaboration with Philadelphia University and Delaware Riverkeeper initiated a restoration project. The project was funded by a National Fish Wildlife Foundation-Delaware Estuary Grant (#2005-0002-013). The goal was to restore 304.8 total linear meters of the worst affected parts of the stream and riparian buffer. The project directly modified 42.7 linear meters of the streambank by regrading the bank to a more stable (1:2 or 1:3) slope. Large woody debris which contributed to the scouring and erosion of Smith's Run was also removed. Stabilization of graded slopes used 100% degradable coir-based erosion control fabric. In addition, 11 herbaceous, two graminoid, five shrubs and 15 tree species native to Southeastern Pennsylvania and adapted to flooding events were planted along the streambank for further stabilization (Table 1). A bridge and trail destroyed by the storms was rebuilt for light foot traffic (Figure 2b).
After the restoration, Smith's Run had a maximum depth of less than eight centimeters. The riffle consisted of a range of rock sizes from a diameter of a few centimeters to approximately 20 centimeters. The rocks sat on a stream bed consisting of fine sediment. The width of the riffle was approximately a meter. The stream's depth excludes it from a stable fish population, but it did have in-stream cover for small organisms, such as macroinvetebrates. Smith Run's flow pattern was dominated by two patterns: slow/shallow and fast/shallow (Delaware River Basin Commission 2005).Pre/Post Restoration Sampling Methodology
Smith's Run stream quality was assessed three months before restoration and eight months after restoration. Chemical testing and bioassessment of Smith's Run were conducted at three sites along Smith's Run. Sites were selected according to orientation to the 42.7 linear meters of Smith's Run which had its streambank regraded. The restoration site was located at 40.0546°N 75.2489°W (Figure 1). The next site was located approximately 100 meters upstream at 40.0549°N 75.2477° (Figure 1). The final site was located approximately 200 meters downstream at 40.0537°N 75.2488° (Figure 1).Macroinvertebrate Sampling and Analysis
The macroinvertebrate survey was done using a Stream Quality Assessment Technique (Sutherland 2006; Deutsch, et al 1996). Sampling was done at all sites by starting downstream and working upstream. Kick net sampling, a sampling technique employed by positioning a net downstream and disturbing a one square meter area upstream with one's foot or manually removing organisms from rocks was employed to dislodge macroinvertebrates into a dip net. The macroinvertebrate samples from each location were combined into a single homogeneous sample of at least 100 organisms. Organisms were then carefully removed from debris, sorted into families, counted on the site and then returned to stream.
Following the protocol of Deutsch et al 1996, a biodiversity index of macroinvertebrate families was calculated. Macroinvertebrate samples were placed into one of three categories in relation to their water pollution sensitivity: 1) poor, 2) wide ranging, or 3) excellent. A weighted index of the number of families was calculated by multiplying the number of families in each category by the numerical value of its category, and adding together each value. In addition to this index value, Shannon Diversity Indices, a logarithmic calculation which accounts for both diversity and evenness within a given population, was used to compare diversity among all sites (Shannon 1948).
For comparison with the three Smith's Run survey sites, Shannon Diversity Index and Deutsch biodiversity Index were calculated from a Pennsylvania Department of Environmental Protection (PA DEP 2002) survey of Crum Creek's West Branch. Crum Creek's West Branch is another first order stream within the Delaware River basin, which was determined to have reached "exceptional value" by the PA DEP in 2002 and has been used as a reference stream in other PA DEP surveys.Water Chemistry Sampling and Analysis
Chlorine, Chloride, Nitrate-n, Dissolved Oxygen, Phosphate, pH, and Fluorine tests were all done at all sites before and after with Water Quality Educator and Monitoring Code 5870 (LaMotte Company, Chestertown Maryland). Water chemistry data was then compared to both US Environmental Protection Agency standards for freshwater streams published in 1986 and 1988 and water chemistry data from Crum Creek WB (EPA 1986 and 1988; DEP 2000).
Taxa counts before the restoration were highest at the upstream site with counts at the restoration site somewhat lower and the downstream site lower still. After restoration taxa counts were highest at the downstream site, somewhat lower at the restoration site, and lowest at the upstream site (Table 2).
Prior to restoration the Cumulative Biodiversity Index (CBI) at all SCEE sites were below that of Crum Creek (WB) (Figure 3). After restoration, the Cumulative Biodiversity Index (CBI) at the Restoration increased to the same value as Crum Creek (WB), while the Downstream site exceeded the Crum Creek value. However, the CBI value of the Upstream site remained relatively unchanged.
Comparison between Downstream and Upstream sample sites, showed a significant improvement in the CBI of the Downstream site relative to the Upstream site (chi-squared p=0.0196). Similar comparison between Upstream and Restoration sample sites showed a less statistically significant improvement (chi-squared p=0.22).
Similarly, the Shannon Diversity index at all sites was below that of Crum Creek (WB) before restoration. After restoration, this diversity metric increased at restoration and downstream sites (Figure 4).
Chi-squared analysis of the Shannon Diversity Index values among the three sample sites showed no significant improvement between downstream and upstream sites or restoration and upstream sites.Smith's Run Water Quality
For a healthy freshwater system, there was no measurable change in water chemistry from before to after restoration (Table 3).
For urban watersheds, impervious cover, land covered by roads, parking lots and other surfaces which prevent water infiltration into soil, is among the most significant indicators of stream degradation (Schueler 1998). Impervious cover disturbs watershed hydrology by enhancing storm-water related habitat destruction and increasing inputs of pollution into stream systems (Schuylkill Watershed Conservation Plan 2001). Smith's Run exists in an area with the highest percentage of impervious cover in the Schuylkill River Watershed with percentages between 20 and 70 percent (SWCP 2001).
Flood mediated disturbance is the most common type of disturbance in lotic systems (Leopold et al 1964), and the impact of this form of disturbance is only enhanced by anthropogenic activities, such as the destruction of riparian corridor habitat (Meyer and Wallace 2001) and increased impervious cover. The impact of flood mediated disturbance tends to limit macroinvertebrate biodiversity by filtering out those taxa that don't have the required traits to deal with flooding events (Poff 1997). Moreover, disturbance tends to increase numerical dominance among resistant taxa (Death and Zimmerman 2005). Pratt et al found that urban storm-water runoff disrupts macroinvertebrate populations even after the passage of flooding events (1981). Gresens et al found that urban stormwater runoff disrupts macroinvertebrate resident populations by increasing the percentage of tolerant organisms (2007).
Although our study lacked direct measures of in-stream sedimentation, our results closely follow these trends. Pre-restoration, all sites suffered from a high degree of domination by their most abundant taxon with the downstream site being the most dramatically affected (Table 2).
We expected that the two main methods of restoration used at Smith's Run, stream bank stabilization and riparian buffer rehabilitation, would result in improved in-stream habitat and reduced biological disturbance at the restoration and downstream sites, as they were the only sites of those examined that would be directly impacted by the restoration methods employed.
This improved habitat was expected to increase both macroinvertebrate richness and evenness at both sites, and as expected both richness and evenness increased at both the restoration and downstream sites.
Our results clearly indicate that the restoration and downstream sites have much improved macroinvertebrate communities after restoration than before restoration. Macroinvertebrate taxa richness improved with the downstream site gaining seven more macroinvertbrate and restoration site gaining two taxa as shown in Table 2. Moreover, both restoration and downstream sites showed significantly less dominance from their most abundant taxon. Although it is notable that the upstream site also showed reduced dominance, taxa increases were seen in pollution tolerant taxa, chironimidae and oligochaetae, while the other sites had increases in more sensitive taxa (Table 2).
The change in cumulative biodiversity index values from pre to post restoration was also significant. As shown in Figure 3, restoration and downstream sites improved from fair to good and from poor to excellent, respectively. Although the site upstream from the restoration had a fall from 15 to 12 in its quantitative cumulative biodiversity value, this represented only a small change, as the upstream site maintained an overall qualitative value of good.
As shown in Figure 4, both downstream and restoration sites had measurable increases in their Shannon Diversity index values from pre to post restoration assessments with approximate increases of 0.7 and 0.4 respectively. The upstream site, again predicted to be unaffected by the downstream streambank restoration, showed only a small increase in its Shannon Diversity Index value from pre to post restoration assessments. Less than a year from the actual restoration, these changes were not statistically remarkable. Yet these changes do indicate the continued recovery of the stream system in terms of macroinvertebrate evenness, reduced dominance from the most common taxa and increased diversity.
Combined the improvements in the Cumulative Biodiversity Index and Shannon Diversity index values at the restoration and downstream sites from pre to post restoration and the relative stability of both of these metrics at the upstream site, indicate a causal link between the restoration and improved macroinvertebrate populations.
Furthermore, chemical testing both before and after the restoration did not indicate significant improvements in water quality at any site (Table 3). In fact, for the measurements taken, the water quality at Smith's Run both before and after restoration qualified as a system in excellent condition. This was expected as the restoration was in large part designed to stabilize Smith's Run stream banks and reduce sedimentation, not to impact in-stream water chemistry. This suggests the macroinvertebrate improvement observed was due to reduced disturbance from sedimentation.
By disrupting the normal stream bed habitat for macroinvertebrates, sedimentation can become a major impairment of lotic systems (Lepori and Hjerdt 2006). In a previous study involving dam removal within the Schuylkill River Watershed, it was found that releasing the sediment within a dam's catchment had the affect of significantly reducing downstream macroinvertebrate densities (Thompson et al 2005). Although other macroinvertebrate metrics were not significantly affected in this study, it is important to note that the dam removal project was done on a fourth order stream not a first order stream. For a much smaller first order stream with small macroinvertebrate populations, drops in macroinvertebrate density could easily impact other macroinvertebrate metrics, such as taxa richness.
Our results although mixed, do indicate that the restoration resulted in not only in improved aesthetics but also the improved ecological function of Smith's Run. Results from other flooding disturbed lotic systems indicate that with continued geomorphic stability, further monitoring of Smith's Run will show continued improvements in macroinvertebrate metrics.
With comparisons to a more thoroughly studied lotic system such as Crum Creek's West Branch, we also demonstrate not only the effectiveness of the restoration techniques applied to Smith's Run but also the ability to effectively monitor other such small stream systems using a relatively inexpensive bioassessment protocol.
Currently, the Schuylkill Center for Environmental Education has received an additional grant from the National Fish and Wildlife Fund along with other supplemental funds for the continued restoration of the riparian buffer of Smith's Run. In addition, monitoring efforts have continued along all three sample locations on Smith's Run for further study of its ecological restoration.
We would like to extend our thanks to all who donated both their time and finances to accomplish the restoration of this important ecological and educational resource. We would also like to thank the Staff of the Schuylkill Center and the student volunteers from Philadelphia University who made the monitoring of this restoration project possible. Also, special thanks should be extended to the National Fish and Wildlife Foundation for their continued support of this project.
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