Evaluation of changes to the quality of riparian forest buffers in the Susquehanna River Watershed Karen Stretton Geoenvironmental Research Paper M.S. Candidate Department of Geography and Earth Science Shippensburg University of Pennsylvania 1 Table of Contents Abstract p. 3 I. Introduction p. 3 II. Literature Review p. 4-9 A. Definition of riparian buffer B. Functions of riparian forests C. Buffer design D. Geospatial technology and riparian buffers E. Urbanization and riparian buffers in the CBW III. Study Area p. 9-10 IV. Purpose and Scope p. 10 V. Methodology p. 11-16 A. Land cover mapping methods B. Stream data C. Stream buffering methods VI. Results p. 16-20 VII. Discussion p. 20 VIII. Works Cited p. 22-24 IX. Appendix p. 24-30 Figures and Tables Figure 1. Flow of water through a riparian buffer p. 5 Figure 2. Three zone design of riparian buffers p. 8 Figure 3. Map of study area p. 10 Table 1. Reclassification scheme for land cover data p. 13 Table 2. Reclassification scheme for Omernik ecoregions p. 13 Figure 4. Map of 30 meter buffer quality values in 2006 p. 17 Table 3. Statistics on riparian health values p. 18 Figure 5. Map of changes in buffer quality, 1984 to 2006 p. 19 Table 4. Table of changes to buffer quality in Cumberland p. 20 County between 1984 and 2006 2 Abstract This research assesses changes to the quality of riparian buffers between 1984 and 2006 at the scale of subwatersheds of the Susquehanna River Basin (SRB). The methodology follows the Natural Lands Trust SmartConservationTM program. Geographic Information Systems (GIS) is used to incorporate land cover and stream order data to determine the quality of existing buffers as healthy riparian ecosystems. Thirty, 60 and 90 meter buffers are assessed on both sides of the water body. The analysis shows that there were minimal changes to buffer quality between 1984 and 2006. Additionally, buffer quality does not vary significantly between buffer widths. I. Introduction Riparian buffers have become an accepted way to mitigate the effects of agricultural and urban land uses on stream health. The reestablishment and protection of riparian buffers in the Chesapeake Bay Watershed (CBW) are important components of the initiative to restore the health of the Chesapeake Bay. In 2008, approximately 60 percent of the streams in the CBW had forested buffers (Sprague et al, 2006) The United States Geological Survey (USGS) estimates that 0.5 percent of buffers were cleared between 1996 and 2005 due to urbanization (Chesapeake Bay Program, 2008). Riparian buffers are especially important in the Susquehanna River Basin (SRB), which drains over 40 percent of the CBW and provides approximately half of the freshwater in the Bay (Horton, 2003). Healthier riparian ecosystems along tributaries to the Bay would have improved capabilities to reduce nutrient and sediment pollution, and consequently lead to an input of higher quality water into the Bay. The goal of this research is to provide an assessment of changes to the quality of riparian buffers between 1984 and 2006 at the scale of subwatersheds of the SRB. The assessment will be based on the SmartConservationTM methodology devised by the Natural Lands Trust that incorporates land cover and stream order to determine the quality of existing buffers as healthy riparian ecosystems. Thirty, 60 and 90 meter buffers will be assessed on both sides of streams. 3 II. Literature Review A. Definition of riparian buffer Due to the complexity of riparian systems, there are countless possible variations to the definition of riparian buffer. Critical components of the definition include the characteristics of being linear but with no definite boundaries, adjacent to and upgradient from water, and acting as a transition zone between aquatic and non-aquatic environments. The Chesapeake Bay Riparian Handbook provides the concise definition of “an area maintained in permanent vegetation and managed to reduce the impacts of adjacent land use” (Palone, 1998, p. 1-10). For the purpose of this study, riparian buffers will include a zone on both sides of a water body. B. Functions of riparian forests Riparian forests provide critical functions that contribute to the health of hydrologic systems. Riparian forests comprise approximately five percent of the total land cover in the CBW, but have a much larger role in maintaining healthy riparian systems (Sprague et al, 2006). Although the environmental benefit of riparian buffers varies based on site characteristics, there are several primary functions that all buffers perform to some extent. One critical function of riparian buffers is slowing the velocity of surface runoff, which promotes the filtration of nutrient and sediment pollutants (Wagner, 2008). Early studies concluded that both grass and forest buffers were effective at removing sediments and nitrates, but were less effective at removing dissolved phosphates (Daniels and Gilliam, 1996; Lowrance et al, 1997). Figure 1 depicts a typical flow of water containing a nutrient and sediment load through a riparian buffer. Roberts and Prince (2010) performed research 4 Figure 1. Flow of water through a riparian buffer, including nutrient removal processes . Source: Sprague et al, p.58 that specifically linked land cover in riparian buffers ranging from 31 to 1000 meters in the CBW to reductions of nutrient runoff to the Bay. Another important function of riparian buffers deals with the enhanced storage capacity for floodwater (Wagner, 2008). A third function of riparian buffers is to create valuable habitat for the transition between aquatic and non-aquatic ecosystems. Healthy riparian ecosystems have been correlated with better stream water quality. In subwatersheds of the CBW in Montgomery County, Maryland, the amount of tree cover in riparian buffers was found to be the second most significant predictor of stream health. Only percent impervious surface area in the watershed had a bigger impact on water quality. In this study, the Index of Biotic Integrity (IBI), a common water quality index, was used to evaluate the diversity of fish and macro-invertebrate species. Data on temperature, dissolved oxygen concentration, and pH were also utilized (Snyder et al, 2005). Another study at the scale of the entire CBW found that tree cover within 30 meter riparian buffer zones was the second most important indicator of stream health, with impervious area in the watershed again being the primary indicator (Goetz et al, 2004). Research based in a southern Alabama 5 watershed also found that stream water quality was impacted by riparian vegetation and land use within a 30 meter buffer (Sawyer et al, 2004). It is noteworthy that riparian functions are generally studied in established buffers. Research on buffer restoration in the CBW in northern Virginia emphasizes the slow results of buffer restoration. A four year study of new riparian buffers showed an average improvement in IBI, but positive water quality results were not present at all study locations (Teels et al, 2006). Stream order is considered an important factor in the effectiveness of buffers, with lower stream orders considered more beneficial because of the higher amount of interaction between the water and the riparian land (Palone, 1998; Meyer et al, 2003). Stream order is a hierarchical means to classify stream networks. The Strahler method is a common way to determine stream order based on the number of tributaries that feed into a particular stream; therefore, stream order tends to increase when progressing downstream. All headwater streams are classified as first order. When two streams of the same order intersect, they become the next highest order (Kang and Lin, 2009). It’s estimated that first and second order streams represent 75 percent or higher of the total stream length in the United States (Meyer et al, 2003). Kang and Lin (2009) performed an analysis on riparian buffer zones in the East Mahantango Creek Watershed in east- central Pennsylvania, a CBW subwatershed, which examined differences in soil and landscape distribution for streams of different orders. Lower soil depth and available water capacity were found in first and second order streams, when compared to buffers of comparable widths in third through fifth order streams. C. Buffer design The width of a riparian buffer is a primary factor in determining its effectiveness. It is a basic assumption that a wider buffer tends to be more effective. Research on the Spring Creek 6 Watershed in central Pennsylvania, a subwatershed of the CBW, provides an example of how narrow grass buffers of only three to four meters reduced suspended sediment loading (Carline, 2007). However a 30 meter buffer on both sides of the water body is a generally accepted standard in the United States (Goetz, 2006). The United States Environmental Protection Agency (EPA) found that buffers over 50 meters are more reliable at removing substantial amounts of nitrogen (Mayer et al, 2005). It is also noteworthy that either fixed or variable width buffers underestimate the importance of areas further from the stream in improving water quality. These buffers that emphasize proximity to the stream can miss the complexity of local hydrology, which is strongly impacted by soil and geology (Qiu, 2009). One hundred meter buffers are considered at the wide range of buffer size (Mayer et al, 2005). This project will assess 30, 60 and 90 meter buffers on both sides of waterways. Thirty meter buffers were selected because it’s the minimum width that can be analyzed with Landsat data and also because it’s a standard minimum size. The 90 meter buffer was chosen because it’s approximately the maximum buffer size incorporated into land use policy at the state and federal level (Mayer et al, 2005). The 60 meter buffer size was selected because it’s the midpoint between 30 and 90.