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Melynda K. May. PATTERN and PROCESS of HEADWARD EROSION in SALT MARSH TIDAL CREEKS

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Melynda K. May. PATTERN and PROCESS of HEADWARD EROSION in SALT MARSH TIDAL CREEKS Melynda K. May. PATTERN AND PROCESS OF HEADWARD EROSION IN SALT MARSH TIDAL CREEKS. (Under the direction of Mark M. Brinson) Department of Biology. December 2002. Under conditions of rising sea level and low sedimentation rates, tidal creeks erode headward. I described the physical, soil, and vegetation characteristics from tidal creek channels to the upland boundary of marshes. Based on the variability in this pattern, I identified three tidal creek classes that were statistically verified using discriminant function analysis. Creek class appears to be determined by the presence and thickness of an organic rich layer in the marsh. Creeks eroding into thick organic rich deposits were classified as strong wasting terrace (ST) creeks. ST creeks were generally found in marshes with poor drainage due to the low slope of the marsh surface. The low slope may have allowed water to pond on the surface of the marsh creating the persistent anoxic conditions needed to accumulate organic matter. ST creeks probably erode headward at a relatively high rate. Creeks eroding into thin organic rich deposits were classified as weak wasting terrace (WT) creeks, and were generally found in marshes with an intermediate slope and likely an intermediate drainage regime. WT creeks probably erode headward at an intermediate rate. Creeks eroding into marshes with no organic rich deposits were classified as no wasting terrace (NT) creeks. NT creeks were generally found in marshes with relatively good drainage due to the high slope of the marsh surface. NT creeks probably erode headward at a relatively slow rate. Slope appears to be the master variable in control of the pattern and process of headwater erosion. I also suggest an explanation that resolves the dual observations of high 2 sedimentation rates near tidal creeks and the erosion (lengthening and widening) of tidal creeks. 3 PATTERN AND PROCESS OF HEADWARD EROSION IN SALT MARSH TIDAL CREEKS A Thesis Presented to The Faculty of the Department of Biology East Carolina University In Partial Fulfillment Of the Requirements for the Degree Masters of Science in Biology by Melynda K. May December 2002 4 PATTERN AND PROCESS OF HEADWARD EROSION IN SALT MARSH TIDAL CREEKS by Melynda K. May APPROVED BY: DIRECTOR OF THESIS __________________________________________________ Mark M. Brinson, Ph.D. COMMITTEE MEMBER _________________________________________________ Robert R. Christian, Ph.D. COMMITTEE MEMBER _________________________________________________ Claudia L. Jolls, Ph.D. COMMITTEE MEMBER _________________________________________________ Kevin F. O’Brien, Ph.D. CHAIR OF THE DEPARTMENT OF BIOLOGY ______________________________ Ronald J. Newton, Ph.D. DEAN OF THE GRADUATE SCHOOL _____________________________________ Thomas L. Feldbush, Ph.D. 5 Acknowledgments I would like to thank Dr. Brinson for guiding this project, but also for obligating me to work independently on it. I would also like to thank him for spending so much time editing the final product. Thanks to my other committee members Dr. Bob Christian, Dr. Claudia Jolls, and especially Dr. Kevin O’Brien who spent many hours helping me with my statistics. Jon Sellars helped in the field and spent many an evening discussing salt marsh ecology with me, even though it had nothing to do with sea beach amaranth or GIS, and most importantly protected my sanity throughout this project. Philip Smith instructed me in the use of GPS equipment, spent many hours in the field with me, and did all the post processing of the GPS points. Jennifer Jones, Mark Keusenkothen, and Jon Sellars helped me process and collect soil cores. Jon Sellars, Dan Kroes, Mark Keusenkothen, Chris Bason, Jessi O’Neal, Ed Scanlan, Carol Phillips, Sandy Morris, Kevin Miller, Greg Meyer, Steve Roberts, and Oussama Saleh have made the last three years a lot of fun. Thanks to Jimmy McCutchan for giving me my first job in the environmental sciences, and for being such a patient and attentive teacher. Last but not least I thank my family, Jeff, Judie, and David May. This work was made possible with funding from the National Science Foundation, the ECU Department of Biology, and the cooperation of the Nature Conservancy. 6 Table of Contents List of Figures…………………………………………………………….……..………..vi List of Tables…………………………………………………………………………….vii 1. Introduction……..……………………………………………………….………..……1 2. Methods…….….………………………………………………………….……………8 2.1. Site Description….………………………….........…….…………………………..8 2.2. Creek Zones…………………..………..….........………………………..…..…...10 2.3. Creek Classes……………………….…….........…………………...………...….14 2.4. Sampling Location and Methods………….........…………………..…………….18 2.4.1. Elevation and Slope……….……..............…………………………….…19 2.4.2. Holes and vegetation……………………............………...………………20 2.4.3. Soil Collection and Analysis…………............……..…………………….21 2.5. Repeat Sample Plots………..………………….........……………………………23 2.6. Remote Sensing……………………..………………….........…………………...24 2.7. Data Analysis……………………..………………….…........………….………..24 3. Results…………………………………………………...……………………………27 3.1. Physical Characteristics………..…………………….........……………..……….27 3.2. Soil Organic Matter.………………..……………….….........……………………34 3.3. Sediment Holes………………..……………………….........……………………39 3.4. Analysis of Hole Dynamics…..…..…………………….........…………………...44 3.5. Vegetation Characteristics…………..……………….........……………………...46 7 3.6. Species Composition……...…………..……………..........………………………50 3.7. Discriminate Function Analysis………..…………..........………………………..52 3.8. Summary of Results……..………………………….........……………………….47 4. Discussion…………...………………………………………………………………..57 4.1. Geographic Position and the Effects of Slope in Determining Creek Class………………………………….……………………………............57 4.2. A Comparison of Transgression Among Creek Classes……...………….........….58 4.3. Sediment Dynamics of Tidal Creeks………..………………….……….........…..64 4.4. Inferring the Rate of Headward Erosion……………………………….........……65 4.5. Conclusion…………...………………………….…...……………….........……..68 Literature Cited……...…………….....…………………………………………………..70 Appendix A. Mann-Whitney U Post Hoc Tests Across Creek Zones……......……..…..78 Appendix B. Mann-Whitney U Post Hoc Tests Across Creek Classes..………....……..81 Appendix C. Latitude and Longitude Coordinates for all Sites…………………....……84 Appendix D. Physical Data………………………………………………………….......85 Appendix E. Hole Data………………………………………….………………..…....100 Appendix F. Vegetation Data………………………………………………….…........109 Appendix G. Soil Data……………………………………………………………....…130 8 List of Figures 2.1. Study sites located in the VCR LTER, Eastern Shore, Virginia…………………….9 2.2. Aerial diagram of creek classes and placement of transect legs 1 and 2……….…..11 2.3. Photo of the basin, transition, and front terrace zones in a strong wasting terrace creek……………….………………..……………………….….....13 2.4. Diagram of vegetation and soil characteristics for each of the creek classes….…...15 3.1. Average physical data across creek classes and zones………...……………..…….28 3.2. Average soil data across creek classes and zones…………...……………………...35 3.3. Average hole data across creek classes and zones……...…………………………..40 3.4. Average vegetation data across creek classes and zones…………….……..………48 3.5. Scatter plot of 23 tidal creek for discriminant functions one and two..…………….53 9 List of Tables 3.1. Summary of the averages for physical, soil, hole, and vegetation characteristics for all of the creek zones and classes…………….…………………30 3.2. Krukal-Wallace results comparing zones within each creek class…….…………...31 3.3. Kruskal-Wallace results comparing creek classes in each zone……….…………...33 3.4. Hole density (mm) measurements over time……..………………….……………..45 3.5. Repeated measures ANOVA, Greenhouse-Geisser test comparing hole diameter over time in three creek classes…………………………………………..47 3.6. Percent frequency of vascular plant occurrences at 23 tidal creeks sites, and elevation above mean sea level for selected species..…………………...51 1. Introduction Tidal creeks play an important role in the hydrodynamics of tidal salt marshes by increasing drainage and flooding in their zone of hydrologic influence. Plant communities occur in distinct zones in salt marshes, and the location of these zones is determined by a variety of factors including distance from a tidal creek and frequency of flooding, salinity, redox, biotic interactions between plants, and physical disturbance (Adams 1963, Bertness and Ellison 1987, Bertness 1991, Pennings and Callaway 1992, Bertness and Hacker 1994, Hacker and Bertness 1995, Brewer et al. 1999). However, Sanderson et al. (2001) found that they could accurately predict the spatial distribution of 10 marsh species based on the distance from a tidal creek, and the stream order and length of that tidal creek. This suggests that tidal creeks play a primary role in determining the zonation of salt marsh plant communities. Near tidal creeks, marshes are flooded more frequently, and this zone is vegetated by tall form Spartina alterniflora Liosel.in US Atlantic Coast salt marshes (Radford et al. 1968). Farther from the tidal creek, short form S. alterniflora vegetates the marsh surface, and at greater distances other halophytes such as Spartina patens (Aiton) Muhl. and Distichlis spicata Greene can also be found (Radford et al. 1968). As tidal creeks migrate headward in response to rising sea level, the vegetation that characterizes these zones migrates inland in a process known as ecosystem state change (Hayden et al. 1991, Hayden et al. 1995, Brinson et al. 1995, Scheffer et al. 2001).
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