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Journal of Paleolimnology 7: 157-161, 1992. 9 1992 Kluwer Academic Publishers. Printed in Belgium. 157. Note. A simple, inexpensive piston corer for ...
Journal of Paleolimnology 7: 157-161, 1992. 9 1992 Kluwer Academic Publishers. Printed in Belgium.

157

Note

A simple, inexpensive piston corer for collecting undisturbed sediment/water interface profiles Millard M. Fisher 1, Mark Brenner 2 & K. R. Reddy 3 1"3Soii and Water Science Department, University of Florida, Gainesville, FL 32611 USA; 2Department of Fisheries and Aquaculture, University of Florida, 7922 N W 71st Street, Gainesville, FL 32606 USA Received 16 March 1992; accepted 30 June 1992

Key words: coring device, paleolimnology, sediments

Introduction

Paleolimnological techniques are invaluable for assessing recent environmental changes, especially in circumstances where long-term ecological data are unavailable. Paleoecological reconstructions rely on multiple lines of stratigraphic evidence that may require measurement of numerous sediment properties, including density, percent dry weight, organic matter and nutrient content, mineralogy, inorganic chemistry, pigments, pollen, animal and algal microfossils, and radionuclide activities (i.e. 2l~ and 137Cs). A large-volume sediment/water interface corer that is capable of retrieving substantial amounts of mud is required to provide sufficient material for multiple analyses. Several corers are commercially available (e.g. KB T M and Davis-Doyle samplers), but may be prohibitively expensive, capable of recovering only small volumes of sediment, or required only in deep water. Some investigators have developed new corers to meet specific needs (Ali, 1984; Cooper et al., 1991). We designed a simple sediment/water interface corer similar to the apparatus developed by Brown (1956). Our large-volume piston corer (38.3 cm 3 c m - 1) takes sediment profiles up to about 1 m long and has been used to take hundreds of cores in shallow ( < 10 m) lakes. The modified Brown sampler has many advantages: 1)it is inexpensive, costing less than

US $100 to build, 2) the piston possesses a vacuum breaker that permits piston removal without sediment disturbance, allowing transport of intact cores, 3)the corer requires no metal machining and can be constructed with standard power tools, 4)parts are available through local hardware stores, scientific supply companies and plastics retailers, 5) the clear, polycarbonate core barrel allows inspection of the retrieved section prior to extrusion, 6)cores can be extruded vertically into a tray, permitting stratigraphic collection of unconsolidated surface deposits, and 7) the basic design can be easily modified to meet special needs. In this paper we provide instructions for the assembly and use of the corer. Part dimensions are generally given in inches to be consistent with inventory listings of most US hardware and plastics dealers.

Construction of the piston corer

The core barrel (Fig. la) is a clear, unbreakable polycarbonate (Lexan | tube with a 3" (7.62 cm) outer diameter (OD) and 23/4" (6.99 cm) inner diameter (ID). The 1/8" (0.32 cm) wall thickness resists bending during the coring operation. A 4-ft tube (122 cm) is capable of taking cores about 90 cm long, but longer tubes can be used. Core barrels should be marked in 1-cm increments using an indelible ink marker or a diamond-tipped

158 1~ S~mp]er

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Fig. 1. a. Exploded view of core sampler showing component

parts: A-1/s" or 1/16" coated piston cable; B-11/2" PVC female pipe thread bushing; C - ll/z " PVC coring rod; D - 11/2" PVC male pipe thread bushing; E-11/2 " PVC female pipe thread bushing; F - 11)" x 3" PVC reducing bushing; G - Y PVC coupling; H - 6"-long, 3" ID section of PVC pipe; I - 5 "-long X 3 / 1 6 " - d i a m e t e r stainless steel bolt and wing nut; J - 3" (OD), l/s"-wall polycarbonate core tube; K - p i s t o n assembly. Fig. 1 b. Plan view of the 11/2" x 3 PVC reducing bushing

(part F in Fig. la), showing the location of 1/4"-diameterholes that accommodate the piston cable and permit filling of the core tube with water. Fig. 1 c. Detail of piston assembly showing component parts:

L-1/8" or x/16" coated piston cable; M-ferrule or cable clamp; N - b r a s s snap or swivel clip; O-5"-long, t/;,. diameter eye bolt; P - 1/4" nut and plate washer; Q - # 131/2 sanded rubber stoppers; R - 1/4" wing nut and plate washer; S-rubber serum bottle stopper; T - 1 5 - c m long, 3/8" OD polyethylene tubing.

etching tool. Acrylic tubes are cheaper and can be substituted, but may crack or break. The coring head consists of four schedule 40 PVC parts: a 15-cm length of 3" ID pipe, a coupling for 3" ID pipe, a reduction bushing for stepping down from 3" ID to 11/2" ID, and a 11/2" pipe thread bushing with female threads (Fig. la). Prior to assembling the coring head, drill two 1/4"-diameter holes on opposite sides of the 11/2"

opening in the reduction bushing (Fig. lb). One hole accommodates the piston cable, and water enters the core barrel through the other hole. Use PVC cement to secure the parts of the coring head together (parts E-H in Fig. 1a). When the PVC glue is dry, slide the polycarbonate core barrel into the coring head as far. as it will go. With the core barrel inserted securely into the coring head, use a long drill bit to drill a 1/4"diameter hole all the way through the coring head and core barrel. The hole should be positioned about 1" below the PVC coupling and about 31/2 " above where the polycarbonate core barrel enters the coring head (Fig. la). Slide a 4"-long, 3/16"diameter stainless steel bolt through the holes, and secure the coring head and core barrel with a wing nut. The bolt serves to secure the core barrel to the coring head and acts as a 'stop' for the piston at the end of a coring drive. Coring rods are made of 5-foot lengths of 11/2" ID schedule 40 PVC pipe. Each length of pipe possesses a male-threaded coupling at one end and a female threaded coupling at the other end (Fig. la). Attach pipe thread couplings to the rod ends with PVC cement. Drill several 1/4"diameter holes just above the male coupling on the rod that connects to the coring head (Fig. la). These holes facilitate rapid filling of the core barrel with water. Use 1/16" or 1/8" plastic-coated cable for piston attachment. Rope or braided cord should not be used because they stretch. A brass snap or swivel clip can be permanently attached to the end of the cable with aluminum or nickel ferrules and a crimping tool. Alternatively, the brass snap may be temporarily fixed to the piston wire using a cable clamp. The cable and rods can be marked in 10-cm increments to measure water depth and length of drive during coring. The piston is made from two # 131/2 rubber stoppers. Stoppers are first modified by 'turning' them on a belt sander which reduces the diameter of the larger end, and provides a flat surface for contact with the core tube walls (Fig. lc). Hold stoppers in a gloved hand and turn them slowly so that rubber is removed uniformly. Wet the stopper and check its fit in the core tube period-

159 ically. Stop sanding when the sanded end of the stopper can just be forced into the core tube. When both stoppers are sanded, place one on top of the other with their small-diameter ends together and bore a 1/4"-diameter hole through the center of both. Next, place a nut and plate washer on the top of the piston and insert a 5"-long, 1/4"-diameter stainless steel eye bolt through the washers and stoppers (Fig. lc). It may be necessary to turn the eye bolt as it is inserted into the piston, but a tight fit is recommended. When the eye bolt is seated, place a plate washer over the lower end of the bolt and attach a wing nut. Tighten the wing nut gently against the lower washer. At this point the piston diameter should be checked again for fit in the core tube. First, lubricate the piston by dipping it in water. If the fit is excessively tight, it can be sanded some more, but be careful not to remove too much rubber. Use the wing nut to adjust the fit of the piston in the core tube. Bore a second, 3/s"-diameter hole through both rubber stoppers. The hole should run parallel to the eye bolt and be located between the edge of the plate washer and the edge of the piston (Fig. lc). Insert a 15-cm length of 3/8"-OD, polyethylene tubing through the hole in the piston until it is flush with the base of the bottom stopper. This will leave about 8 cm of tubing protruding from the top of the piston. Cover the the top of the tubing with a tight-fitting, rubber serum bottle stopper. The tube and bottle stopper serve as a vacuum breaker to facilitate piston removal prior to core extrusion. Several additional # 131/2 stoppers can be sanded down for use as extruder pistons. Drill holes through the centers of each extruder piston. Place plate washers on either side of the piston, insert an eye bolt and attach a wing nut so that the fit of the extruder pistons in the core tube can be adjusted. Core tubes can be plugged with unmodified #131/2 stoppers to transport intact cores. Operation of the piston corer The first step in a successful coring operation is proper anchoring of the coring platform over the

core site. When the platform is securely anchored, measure the water depth at the coring location to within + 10 cm. Accurate measurement of the water depth is necessary to determine the depth at which the coring drive must start, and to guarantee that an undisturbed sediment/water interface will be recovered. Assemble the corer by first screwing one length of coring rod into the coring head. Next, thread the end of the cable without the brass snap up through one of the 1/4" holes in the coting head. Pull nearly the entire length of cable through, leaving about 1.5 m of cable emerging from the bottom of the coring head. At this point it is wise to recheck the fit of the wet piston in the core tube, and adjust it if necessary. Next, feed the brass snap end of the cable down through the polycarbonate core barrel and push the top of the core barrel up into the coring head. Slide the 3/16"-diameter bolt through the coring head and core barrel and secure them together with the wing nut. At this point, the end of the cable with the brass snap should extend about 30 cm from the bottom of the core barrel. Attach the piston to the end of the cable by clipping the brass snap to the piston eye bolt. Pull up gently on the cable where it emerges from the top of the coring head, and guide the piston into the base of the core barrel. Push the piston into the corer until the bottom of the piston is flush with the base of the core barrel, and take up any slack in the cable. The other end of the cable can be tied off to the platform as a safety precaution. Hold the cable tightly against the core rod, and lower the assembly over the side of the coring platform. Place the core barrel in the water in a near-horizontal position ( < 3 0 ~ and push the coring head under the lake surface to fill the core barrel with water. A shallow angle prevents water pressure from driving the piston up into the airfilled core barrel. When the corer is filled with water, check that the piston is still positioned at the base of the core barrel, and bring the assembly to a vertical position. Hold the cable firmly against the core rod and lower the assembly to a position where it is convenient for your coting partner to attach another length of coring rod. Run the cable

160 tightly along the new section of rod and lower the assembly until it is necessary to add another section of coring rod. Note that it may be difficult to work with PVC fittings under freezing conditions. Continue adding sections of PVC rod until the bottom of the corer is ~ 2 0 cm above the lake bottom, but take care not to disturb the sediment surface. Make sure that there is sufficient coring rod above the water surface to make a complete drive (i.e. 1.5 m). Next, anchor the cable so that it will remain stationary during the coring drive. Keep slack out of the cable, but do not pull on the cable excessively as this will draw the piston up into the core barrel. The cable can be secured with vice grips that have had their jaws covered in several wraps of duct tape. Clamp the cable tightly and hold the vice grips against the edge of the coring platform. Push straight down on the rods with a single, firm, steady thrust. The drive will terminate when the bolt that secures the core barrel comes down on the piston or when impenetrable sediments are reached. To retrieve the core, grab the cable below the level where it is clamped with the vice grips and hold the cable tightly against the coring rods. Release the vice grips and pull up on the assembly, making sure to hold the cable tightly against the core rods. This prevents slipping of the cable and retreat of the stopper down the core barrel. The coring assistant should remove core rods during the retrieval process. Remove all coring rods except the one attached to the coring head. When the bottom of the core barrel is about 20 cm below the water surface, a # 131/2 rubber stopper should be inserted into the bottom of the core barrel. The choice of plug is determined by whether the core is to be extruded immediately in the field, or returned to the laboratory. Still holding the cable tightly against the remaining coring rod, lift the assembly onto the coring platform and set it on the deck in a vertical position. The assistant can help with this procedure by lifting the bottom of the core barrel and making certain that the plug in the bottom of the tube stays put. With the assembly safely on deck, examine the core carefully to make sure that the drive did not begin too deep and that the sediment/water interface was

obtained (i.e. there should be at least 10 cm of water between the base of the piston and the top of the mud). Note that a sufficiently long section has been recovered, and that the core is intact. To disassemble the corer, unscrew the wing nut on the bolt that secures the core tube to the coring head. Pull the bolt and remove the coring rod and coring head. Lay the rod/coting head assembly on deck, being careful to feed the cable through the coring head while setting it down. If the drive was incomplete and there is water above the piston, it should be removed by siphoning. Next, make sure that the plug in the bottom of the core barrel is firmly secured. If the core is to be transported to the lab intact, insert and duct tape a # 131/2 rubber stopper in the bottom of the core barrel. Next, remove the serum bottle stopper on the polyethylene tubing, thereby breaking the vacuum behind the piston. In the event of an incomplete drive, it may be necessary to use a piece of wire with a loop on the end to remove the serum bottle stopper. Pull up on the piston cable slowly. Air will enter the core barrel through the polyethylene tube, but if the procedure is done slowly, it will not disturb the sediment surface. Remove the piston from the core tube. Extrusion methods vary according to specific sampling needs. We mount a sampling tray on top of the core barrel and extrude sediments upward, into the tray. The tray is handy for sampling topmost, unconsolidated deposits. It consists of a 12-cm length of 3" PVC pipe inserted through the center and glued to a 20 cm • 20 cm, 3/16" thick PVC sheet with 2-cm walls. Samples are transferred from the tray to storage containers via a small opening in the corner of the tray. Alternatively, a 3" PVC pipe can be inserted through a plastic food storage container, and fixed in place with silicone sealer. We allow about 4 cm of the 3" pipe to protrude above the surface of the tray. Prior to mounting the tray, run two wraps of duct tape around the top of the core barrel to plug the holes that were drilled to enable fastening of the core tube to the coring head. Next, slip the tray over the core barrel until the 3" PVC pipe of the sampling tray is flush with the top of the core barrel. The lower section of the PVC pipe in the

161 sampling tray can be taped to the core barrel. A piece of PVC or metal pipe driven into the ground serves as an extruder rod. The core barrel can be set over the extruder rod and the extruder piston can be driven upward by gentle downward pressure on the core barrel. Push up on the extruder piston until the sediment surface is flush with the top of the core barrel. Thereafter, stratigraphic sediment slices can be collected in the tray by pushing upward on the extruder piston. Sampling intervals are measured by noting the travel distance of the extruder piston through the marked core barrel. Recent advances in paleolimnology have stimulated paleoecological research designed to evaluate human-induced changes in lakes and their watersheds. This has necessitated the development or modification of corers designed to collect sediment/water interface profiles (e.g. Renberg, 1988; Glew, 1991). We developed an inexpensive, 'lowtech' piston sampler for the express purpose of retrieving long, undisturbed, large-volume, sediment/water interface cores from shallow lakes. The simple design enables individuals with an interest in recent sediments to construct their own coring apparatus.

Acknowledgements This work was supported in part by contracts from the St. Johns River Water Management District, Palatka, FL, and the South Florida Water Management District, West Palm Beach, FL. We thank Drs. Mary Collins, Paula Gale, Ed Phlips, Michael Binford, John Stool and anonymous reviewers for helpful comments.

References Ali, A., 1984. A simple and efficient sediment corer for shallow lakes. J. Envir. Qual. 13: 63-66. Brown, S. R., 1956. A piston sampler for surface sediments of lake deposits. Ecology 37:611-613. Cooper, C. M., F. R. Schiebe & J. C. Ritchie, 1991. An inexpensive sampler for obtaining bulk sediment cores. Envir. Geol. War. Sci. 18: 115-117. Glew, J. R., 1991. Miniature gravity corer for recovering short sediment cores. J. Paleolim. 5: 285-287. Renberg, I., 1991. The HON-Kajak sediment corer. J. Paleolim. 6: 167-170.