ASTM_D_4132_-_82_2012.pdf

Designation:D413282(Reapproved 2012)Standard Practice forSampling Phytoplankton with Conical Tow Nets1This standard is issued under the fixed designation D4132;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()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 nets.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 appro-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 retrieved 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 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 macro-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 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 tow,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 less 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 failurethrough 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 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 stretching,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 the 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(for example,80 m)can be used.Ameshopening smaller than 64 m can be used,but it is doubtfulwhether the additional cost and slower operation are justified.1This practice is under the jurisdiction of ASTM Committee D19 on Water andis the direct responsibility of Subcommittee D19.24 on Water Microbiology.Current edition approved Sept.1,2012.Published November 2012.Originallyapproved in 1982.Last previous edition approved in 2004 as D4132 82(2004).DOI:10.1520/D4132-82R12.2Heron,A.C.,“Plankton Gauze,”In:UNESCO,Zooplankton Sampling,UNESCO Press,Paris,France,1968,pp.1925.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 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 of the net can vary considerably;howev