1、Designation: D 4132 82 (Reapproved 2004)Standard Practice forSampling Phytoplankton with Conical Tow Nets1This standard is issued under the fixed designation D 4132; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers the procedures for obtaining quali-tative samples of a phytoplankton community by use of conicaltow n
3、ets. Nets will not retain all phytoplankton taxa; forexample, nannoplankton and ultraplankton generally will passthrough a net.1.2 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish a
4、ppro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Summary of Practice2.1 The net is attached to a tow line and towed at the surfaceor at a greater depth using a cable depressor. After a specifieddistance or period of time, the net is r
5、etrieved and the capturedphytoplankton are removed from the net. The phytoplanktonmay be preserved as dictated by the objective of the study.3. Significance and Use3.1 The advantages of conical tow nets are as follows:3.1.1 They are relatively inexpensive, easy to construct, andhighly versatile in a
6、 variety of surface waters.3.1.2 They can be used from a small powered boat with aminimum of auxiliary equipment.3.1.3 They provide a simple means by which to collectqualitative samples of macro- and micro-plankton.3.1.4 They can be adapted with a flowmeter to collectsemiquantitative samples of macr
7、o- and micro-plankton.3.2 The disadvantages of conical tow nets are as follows:3.2.1 They are effective only where drawn through a stratumof water having considerable thickness. They are not suitablefor collecting samples from a small or restricted region.3.2.2 They are not suitable for collections
8、in very shallowwater.3.2.3 They collect only qualitative samples, or semiquanti-tative samples when used with a flowmeter.3.2.4 Clogging of the net by extraneous materials, such asfloating vascular plants or debris can cause erroneous results.3.2.5 If discrete depths are sampled using a horizontal t
9、ow,the sample can be contaminated with organisms from otherdepths during the deployment and retrieval of the samples.3.3 There are several special considerations that shall beobserved when using conical tow nets. They are as follows:3.3.1 The conical net samplers are designed to be towed atspeeds le
10、ss than 3 knots; however, greater speeds have beenused for the larger nets with a concomitant increase in capture.3.3.2 Although there is a tendency to use the smallest meshsize available, there is the liability of small mesh sizes reducingthe collection efficiency and increasing equipment failureth
11、rough tearing.3.3.3 If discrete depth samples are required, an opening andclosing net device should be installed on the sampler.3.3.4 The nets should be washed frequently and inspectedfor pin-size holes, tears, net deterioration, and other anomalies.3.3.5 Following use, wet nets should be suspended
12、fulllength in air and in subdued light and allowed to dry.4. Procedure4.1 According to Heron,2the material used in sampling netsshould have the following properties: “The meshes should besquare and the mesh aperture uniform. The material of thestrands should be stiff enough to resist bending or stre
13、tching,but flexible enough to allow self-cleaning action. The nature ofthe weave should prevent the meshes from distorting diago-nally. The porosity should not change when the net is immersedin water. The gauze should resist clogging and allow completeremoval of material after use. The material of t
14、he strand shouldnot abrade easily. It should resist degradation by sunlight andby chemicals used in cleaning.”4.2 For many years, the standard mesh opening used inphytoplankton net was the standard silk size No. 25 having anaperture of 64 m. Depending upon the study objective, alarger mesh opening (
15、for example, 80 m) can be used. A meshopening smaller than 64 m can be used, but it is doubtfulwhether the additional cost and slower operation are justified.4.3 A conical tow net (Fig. 1a) typically is composed of asingle hoop, a towing bridle, a cone-shaped net, and acollecting container. The size
16、 of the net can vary considerably;however, the mouth diameter to length ratio should be greater1This practice is under the jurisdiction of ASTM Committee E47 on BiologicalEffects and Environmental Fate and is the direct responsibility of SubcommitteeE47.01 on Aquatic Assessment and Toxicology.Curren
17、t edition approved April 1, 2004. Published April 2004. Originallyapproved in 1982. Last previous edition approved in 1998 as D 4132 82 (1998).2Heron, A. C., “Plankton Gauze,” In: UNESCO, Zooplankton Sampling,UNESCO Press, Paris, France, 1968, pp. 1925.1Copyright ASTM International, 100 Barr Harbor
18、Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.than 1:5 to ensure a high filtration efficiency. The net generallyis attached to a tow line and towed at the surface or at a greaterdepth using a cable depressor. The precise depth of towing isdifficult to determine because a slight
19、 change in the movementof a boat will cause the depth of the net to vary. Under steadyforward movement, the depth (D) of tow can be determined asfollows:D 5 L cos a (1)where:L = length of the tow line from the surface of the waterto the sampler, andcos a = cosine of the cable angle.The duration of t
20、ow should be determined experimentally, andwill be dependent upon the density of phytoplankton, depth oftow, size of net, and speed of forward movement.4.4 Conical tow nets are of several, but similar, designs. Thesimple tow net sampler described above contains a single hoop.A Wisconsin net sampler
21、(Fig. 1b) consists of three majorparts: an upper section in the form of a short inverted truncatedcone consisting of light-weight canvas or sailcloth, a middlesection in the form of an elongated cone and consisting of thefiltration material, and a detachable plankton bucket. A hoop islocated at the
22、mouth of the net and another at the junction ofthe canvas and filtration material. The latter hoop is the largerof the two. The Wisconsin net sampler generally is used formaking vertical tows, whereas the simple tow net sampler isused for making horizontal tows.4.5 A Birge closing net sampler (Fig.
23、1c) is constructed sothat it can be lowered into the water to a selected position,made to function from that point by drawing it through thewater, closed by means of a messenger at the conclusion of thehaul, and the catch brought to the surface without furtheradditions to the sample.3It is used for
24、both vertical andhorizontal towing. The sampler consists of two truncated conesconnected at their bases. The inlet cone is made of light-weightcanvas or sailcloth. The other cone consists of the filtrationmaterial. A plankton bucket is affixed at the narrow end of thefiltering cone. The sampler cont
25、ains two hoops situated similarto those of the Wisconsin net sampler. The towing bridleconsists of three cords that are equidistantly placed andextending from the mouth hoop. The main draw line is attachedto a brass ring at the bottom of the canvas sleeve. At the otherend is located the tripping mec
26、hanism.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such righ
27、ts, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional
28、standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM
29、Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the abovea
30、ddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).3Welch, P. S., Limnological Methods, McGraw-Hill Book Co., New York, NY,1948, 381 pp.FIG. 1 Plankton Nets (a) Conical Tow Net (b) Wisconsin Net Sampler (c) Birge Closing Net Sampler (Illustration by J. W. Steiner andW. G. Hester, U.S. Geological Survey, Doraville, GA)D 4132 82 (2004)2
