Published in Soil Sci. Soc. Am. J. 68:705-708 (2004).
© 2004 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
DIVISION S-10—NOTES
A NEW IDEA IN MARSH CORING
THE WEDGE
Patrick W. Inglett*,a,
Eric Viollierb,
Alakendra N. Roychoudhuryc and
Philippe Van Cappellend
a Dep. of Soil and Water Science, University of Florida, Gainesville, FL 32611-0510
b Géochimie des Eeaux, University of Paris 7, 75721 Paris, France
c Dep. of Geological Sciences, University of Cape Town, Rondebosch, Cape Town, 7700, South Africa
d Faculty of Earth Sciences, Utrecht University, 3508 TA Utrecht, The Netherlands
* Corresponding author (pwi{at}mail.ifas.ufl.edu).
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ABSTRACT
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Standard coring techniques are often ineffective in the unconsolidated and vegetated soils and sediments of marsh environments. In this paper, a novel coring device is presented that minimizes the problems of compaction, core plugging, and root disturbance to allow the collection of intact 35+ cm cores from densely vegetated marsh areas. The simple concept uses a sharpened main body and cover plate that are inserted sequentially to obtain a wedge-shaped soil or sediment slice. In a typical application, the corer is transferred to the field laboratory where sectioning can occur. Removal of the cover plate exposes a large surface area of soil or sediment for visual inspection and sampling. The advantages of the wedge corer design are described in relation to its use in a Spartina alterniflora salt marsh.
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INTRODUCTION
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SALT MARSH STUDIES frequently require the collection of undisturbed soil and sediment samples. Often, particular interest is placed on the depth distributions of various parameters (e.g., solid-phase chemistry, organism counts, bulk density, root distributions, fossil occurrence, stratigraphy, pedological features, etc.). Traditionally, small-diameter tube or barrel coring methods have been utilized for their simplicity and convenience, however, these methods can result in the errors of sediment compaction, thinning, and bypassing in highly porous marsh soils and sediments (Blomqvist, 1991; Morton and White, 1997). Also, as observed by the authors, the presence of roots (e.g., those of Spartina alterniflora) can result in further disturbance to the core profile even when using sharpened core tubes. For these reasons, traditional tube coring techniques are often ineffective in retrieving consistently long, undisturbed soil or sediment cores in densely vegetated marsh areas.
One improvement on the round-barreled corer design is the square-type coring system, often reported in the literature as "can" (e.g., Howard and Frey, 1975; Lim and Je, 1998) or "box" corers (e.g., Bradley and Morris, 1990; Craswell and Castillo, 1979). These devices are typically constructed of sharpened thin sheet steel or plexiglas to facilitate entry into the sediment. Often, box-type corers consist of two parts that are inserted sequentially to reduce friction between the corer and the soil or sediment being sampled. Such designs can successfully minimize core compaction and root interference, and can even allow rapid inspection of the core with the removable side panel (Craswell and Castillo, 1979). However, because these designs utilize an open-bottomed tube or box, there is no convenient method for retrieval of the core sample. In most cases, core retrieval occurs by excavating the entire coring device. Thus, the destructive "digging out" process limits the use of these corers to situations of one-time or very infrequent sampling or, in the case of routine measurements, constant changes in sampling site locations.
During a study of salt marsh geochemistry, we found the existing coring methods to be inadequate. Therefore we developed a coring device, which utilizes the benefits of small diameter tube corers (size and weight) and square corers (minimal compaction and removable side) while still allowing non-destructive removal of undisturbed marsh cores. The concept of this new coring device is similar to that of most box-type, two-part coring systems having a three-sided main body and a removable cover plate inserted into a groove track in the main body. The new design differs from previous devices in that the cover plate is inserted not parallel, but at an angle to the main body. Thus, when the cover plate is fully inserted, it joins the rear plate of the main body at the bottom completely enclosing the core sample. The resulting core has the shape of a rectangular wedge, wide at the top tapering to a point at depth. Because of its shape, we call the device the wedge corer (Fig. 1
and 3).
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Fig. 1. Wedge corer schematic. When fully assembled, the cover plate should slide easily into the groove tracks on the side plates of the main body. To facilitate entry into the soil and sediment, lower edges of all components are sharpened.
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Construction Details
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The following are the design details used in the construction of the wedge corer device being presented. Although the exact dimensions of the wedge corer components are provided here, the design of the device can easily be manipulated to suit the depth, width, and volume requirements of any particular study.
The basic design of the wedge corer consists of four components: the back plate, the cover plate, and two side plates (Fig. 2)
. All parts of the wedge corer should be stainless steel (e.g., 304 alloy series) to resist corrosion. The back plate and cover plates are both constructed from 3.18 mm (0.125'') thickness stainless steel sheet stock (Fig. 2a). The main body of the wedge corer is formed by welding the two side plates to the back plate (Fig. 1, 2a). These welds should be stainless steel and ground smooth to allow clean sectioning of the core sample and to prevent dragging of sediment during corer insertion. Precise machining of the side plate groove and accurate positioning of the side plates is essential to obtain a working tolerance for the removable cover plate feature.
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Fig. 2. Wedge corer construction components: cover and back plates. The points of side plate attachment to the back plate are denoted by ‘X’s. Detail of wedge corer component side plate. Please note, as they are mirror images, only one of the two required side plates is pictured.
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Following assembly of the main body, the cover plate can be inserted into the groove track created by the opposing side plates (Fig. 1). During use, the cover plate is held in place by pins inserted through holes drilled into the outer edge of each side plate to mate with two tubes welded to the face of the cover plate (Fig. 1, 2a). Incremental holes along the length of the side plates allow the precise lowering of the cover plate during core sectioning (Fig. 2b). In this study, the holes were spaced at 1-cm spacing to yield consistent, depth-incremented samples of sufficient volume for chemical and microbiological analyses. Also, the upper edge of the cover plate is bent forward to create a lip for convenient handling of the cover plate (Fig. 2a). To assist entry of the device into the sediment as well as facilitate the cutting of plant roots, all insertion points (i.e., the bottom of the back and cover plates, and the side plate front and lower edges) are sharpened (Fig. 1). A rectangular cutout has also been placed in the upper portion of the back plate serving as a handle for core retrieval.
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Operation
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Typical operation of the wedge corer begins with insertion of the main body (cover plate removed) into the sediment to be sampled (Fig. 3)
. Following insertion, the cover plate is fully inserted into the groove track on the main body. The retaining pins are inserted to hold the cover plate in place, and the entire core-containing assembly is withdrawn from the sediment using the cutout handle on the back plate of the main body.
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Fig. 3. Wedge corer operation. (1) The main body is inserted, (2) the cover plate is inserted into the groove track, (3) retaining pins are inserted to hold the cover plate in place, and (4) the core-containing assembly is removed.
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Because the wedge corer main body consists of only three sides of thin sharpened steel, insertion is easily accomplished by hand in fine-grained sediments. Occasionally, additional effort was necessary when using the wedge corer in coarse-grained, sandy soils, and especially in more clastic sediments where insertion can be completely prevented. Similarly, the cover plate slides easily into the groove of the main body when used in fine-grained sediments, but requires additional (though not extreme) pressure in sandy soils and sediment conditions where sand can clog the groove track. Also, the main body back plate and cover plate are constructed of sufficiently thick steel to resist flexing during the insertion procedure. During our use of the wedge corer, we very rarely encountered problems due to misalignment of the cover plate and side plate grooves.
Because the wedge corer (as described here) encloses a relatively thin soil or sediment slice, retrieval of the device from the soil or sediment surface is typical of small to medium diameter (5–10 cm) tube corers. Adhesion of the soil to the device does occur creating a vacuum, particularly in fine grained soils or sediments, however, digging out was never required using the wedge corer. Depending on the intended use of the core, the wedge corer may be taken to a field laboratory for removal of the cover plate and core sectioning, or the cover plate may be removed for immediate onsite inspection of the core. Removal of the cover plate can be hindered when coring very fine-grained soils and sediments, which tend to adhere to the smooth metal surface. In these situations, we found that light tapping with a hammer was sufficient to free the mechanism. Core sectioning is easily accomplished by positioning the corer horizontally on a table, sliding the cover plate incrementally down the core (using the locking pins and side plate holes), and removing each exposed sediment slice using a sharpened wide-blade instrument (e.g., putty knife). If desired, the core may also be sectioned under anaerobic conditions by placing the wedge corer inside a glove bag. Caution must be exercised when horizontally sectioning loose, flocculent, or sandy sediments, which tend to form slurries when agitated.
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Design Advantages
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The wedge corer was field tested during a study of salt marsh geochemistry and microbiology conducted on Sapelo Island, GA (USA) (Roychoudhury, 1999; Lowe et al., 2000). During that study, core samples were needed for detailed analyses of solid phase geochemical and microbiological parameters. These samples consisted of a wide variety of soil and sediment types including fine- and coarse-grained, unvegetated creek channel sediments, fine-grained creek bank soils with occasional tall Spartina roots and rhizomes, and fine- to coarse-grained soils with very dense short Spartina roots and rhizomes. Initially, we attempted to use sharpened small to medium diameter (5–10 cm) coring tubes, however, these designs were plagued with problems of compaction and root disturbance. For this reason, we developed the wedge corer, and its effectiveness in this study quickly became evident.
One advantage of the wedge corer is that for its small size, it has the ability to obtain deep, relatively undisturbed core samples approaching 50 cm in depth with only minimal compaction (approximately 2–5%) (Fig. 4)
. In contrast, it was observed that diameters of 10 cm (>4 inches) are required of barrel or tube devices to achieve similar cores of this depth at these sites. These large diameter cores are cumbersome and often require destructive digging out to retrieve the sample. Another obvious benefit of the wedge corer design is the exposure of a large surface area of the soil and sediment profile following removal of the cover plate (Fig. 4). This large exposed surface area permits the rapid inspection of core condition and pedological features, and allows subsampling of core microsites (e.g., root rhizospheres, shell pockets, etc.). This feature is virtually impossible using traditional solid barrel corers where complete removal of the sediment sample is required before subsampling. Inspection of cores obtained from Sapelo Island reveal the wedge corer's ability to preserve soil and sediment features (e.g., crab burrows) and cleanly cut plant roots with minor disturbance to the core profile (Fig. 4). Also, site destruction was minimal using the wedge corer, leaving only the void of the obtained core slice. Such voids closed quickly, and thus, seasonal sampling within a 1.0-m radius became feasible during the course of the study.
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Fig. 4. Photograph showing wedge corer sample following removal of the cover plate. Note the wide exposed core face, presence of cleanly cut Spartina alterniflora roots, and preserved organism burrows.
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Conclusions
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The wedge corer improves on previous marsh coring techniques by minimizing the problems of sediment compaction and root disturbance while still allowing non-site destructive removal of core samples. The wedge corer design is simple to operate and consistently yields intact marsh cores of >35 cm. Additionally, the wedge corer design offers benefits of microzone and burrow preservation, as well as the exposure of a large surface area of the core profile, thus allowing the ability to rapidly and conveniently inspect and subsample the core. These benefits, combined with the depth of sampling and ease of operation, offer the potential for the wedge corer to enhance salt marsh studies requiring undisturbed sediment samples.
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NOTES
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Florida Agricultural Experiment Station Journal Series No. R-09007.
Received for publication August 8, 2002.
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REFERENCES
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- Blomqvist, S. 1991. Quantitative sampling of soft-bottom sediments: Problems and solutions. Mar. Ecol. Prog. Ser. 72:295–304.
- Bradley, P.M., and J.T. Morris. 1990. Physical characteristics of salt marsh sediments: Ecological implications. Mar. Ecol. Prog. Ser. 61:245–252.
- Craswell, E.T., and E.G. Castillo. 1979. A convenient device for taking large, undisturbed samples of paddy soil. Int. Rice Res. Newsl. 4:22.
- Howard, J.D., and R.W. Frey. 1975. Estuaries of the Georgia coast, USA: Sedimentology and Biology. I. Introduction. Senckenbergiana Marit. 7:1–31.
- Lim, H., and J. Je. 1998. Macrobenthic communities on the macro-tidal flats of Taebudo and Tando in the west coast of Korea. Ocean Res. 20:121–130.
- Lowe, K.L., T.J. DiChristina, A.N. Roychoudhury, and P. van Cappellen. 2000. Microbiological and geochemical characterization of microbial Fe(III) reduction in salt marsh sediments. Geomicrobiol. J. 17:163–178.
- Morton, R.A., and W.A. White. 1997. Characteristics of and corrections for core shortening in unconsolidated sediments. J. Coast. Res. 13:761–769.
- Roychoudhury, A.N. 1999. Biogeochemical dynamics in aquatic sediments; novel laboratory and field-based approaches. Ph.D. Thesis, Georgia Institute of Technology, Atlanta, GA.
TOP
ABSTRACT
INTRODUCTION
