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Part IV. Biological Treatment of Wastewater Irwin Pages Orin Pages Part V. Biological Treatment and Aquifer Recharge Part VI. Implementation of Alternatives Acknowledgments Pages Index Pages General note: By using the comment function on degruyter. A respectful treatment of one another is important to us. Full-time 41 Contract 3 Part-time 3 Temporary 2 Commission 1. Experience Level. Forgot to save your resume? Use for to create your resume on Indeed and apply to jobs quicker.

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Indeed may be compensated by these employers, helping keep Indeed free for jobseekers. Indeed ranks Job Ads based on a combination of employer bids and relevance, such as your search terms and other activity on Indeed. For more information, see the Indeed Privacy Policy. Senior Water Pollution Control Operator. Environmental Chemist I. Collects and analyzes samples from municipal water and water pollution control systems for laboratory analyses and process control in accordance with Federal….

Stantec reviews. Sawyer Only sewered population known. Application of lime to the water or mud reduces the amount of soluble phosphorus released. Acidification of previously alkalized mud will, upon agitation, increase the amount of phosphorus entering solution. In an aquarium experiment, circulation of the water above phosphorus-rich mud, with the aid of air bubbles, in- creased the phosphorus in solution.

Zicker et al. Dredging deepens an area within a lake and can be beneficial if the in- creased depth is sufficient to prevent growth of larger nuisance plants. Dredging uncovers yet another soil strata that will contain phosphorus in some quantity. The newly dredged area im- mediately begins to receive organic fallout from waters above, and forms a new interface at which nutrient exchange is substantial. Sediments dis- turbed during a dredging operation liberate nutrients at a rate more rapid than sediments left undisturbed and all of these factors must be consid- ered when recommending dredging for nutrient remosal.

Based entirely on nutrient considerations, dredging can be advantageous only when it re- moves sediments that contain a higher concentration of nutrients than the interface likely to be formed by fallout. Gerbil and Skoog in laboratory insestigations determined that 5 units of nitrogen plus 0. Allen found that to obtain arty appreciable increase it was necessary to supplement the sewage with nitrogen as well as carbon. Saner studied the southeastern Wisconsin lakes and concluded that a 0.

Nitrogen appears to be the more critical factor limiting algal production in natural waters Ger- loft and Skoog. Sawyer discussed factors that influence the de ebopment of nuisance algal growths in lakes. The surface area is important since the accumulations of algae along the shoreline of a large lake under a given set of wind conditions could easily be much larger than on a small lake.

The shape of the lake determines to some degree the amount of fertilizing matter the lake can assimilate with- out algal nuisances since prevailing winds blowing along a long axis will concentrate the algal production from a large water mass into a relatively small area. The most offensive conditions develop during periods of very mild breezes that tend to skim the floating algae and push them toward shore.

Shallow lakes, too, respond differently from deep stratified lakes in which the deeper waters are sealed off by a thermocline. In stratified waters, only the nutrients confined to the epilimnion are available except during those brief periods when complete circulation occurs. In some tropical and highly eutrophic temperate lakes. Evidence from the addi- tion of fertilizers to fish ponds and from what is known about the eutro- phication of lakes by sewage supports the view that phosphorus plays a major role in production.

The lower limit of optimum range of phosphorus concentration var- ies from about 0. Low phosphorus concentrations may, therefore, like low nitrogen concentrations, exert a selective limiting influence on a phytoplankton population.

Learning Outcomes for Study Session 7

The nitrogen concentration determines to a large extent the amount of chlorophyll formed. Nitrogen concentrations beyond the opti- mum range inhibit the formation of chlorophyll in green algae. Strickland stated that the limiting phosphorus concentration in some cultures has been found to be less than S pg 1. The problem is complicated because auxiliary compounds may affect the availability of phosphate to a plant cell.

The question is sometimes asked, how much algae can be grown from a given amount of phosphorus? Thus, assuming optimum growth conditions and maximum phosphate uti- lization, the maximum algal crop that could be grown from 1 pound of phosphorus would be 1, pounds of wet algae under laboratory condi- tions or pounds of wet algae under field conditions. Considering a phosphorus P content of 0. Those waters now contain- ing less phosphorus should not be degraded Mackenthun, Ade- quate phosphorus controls must now be directed toward treatment of nu- trient point sources and to wastewater diversion around the lake or dilution within the lake, where feasible.

Micronutrients It is generally conceded that abundant major nutrients in the form of available nitrogen and phosphorus are an important and a necessary com- ponent of an environment in which excessive aquatic growths arise. Algae, however, are influenced by many and varied factors.

Vitamins, trace metals, hormones and auxins, extracellular metabolites, autointoxicants, viruses, and predation and grazing by aquatic animals are factors that stimulate or reduce algal growths. Some of these may be of equal impor- tance to the major nutrients in influencing nuisance algal bloom produc- tion. Harder, in , is credited with first connecting growth inhibiting substances with algae. As early as These papers gave rise to a common belief that a plant can create its self-destruction through the production of growth inhibiting substances that it cannot tolerate but which may, in turn, stimulate other growths.

Natural waters contain these active agents that are secreted and excreted by freshwater algae. The toxicity of these agents to other algae and bacteria and to fish varies constantly and is not well understood in the natural aquatic environment. It has been postulat- ed that algae secrete not just one substance but several, some antibiotic, others stimulating.

Thus, sequences of algal blooms may be expected to occur under conditions of a nutrient supply f at in excess of critical values. This role is presently neither clearly defined nor understood. It does seem clear that the constant progression of the geologic clock cannot be substantially altered. The old-swimmin-hole lingers on in local folklore.

Recent- ly defiled waters can be improved substantially, however, by reducing or removing the varying causes of algal productivity. By placing all known algal population influencing factors in their proper perspective and by in- tensifying investigative efforts directed towards the interrelationships of factors most likely to effect population controls, knowledge and nuisance reducing efforts will be enhanced. Eyster divided the elements requircd by green plants into ma- cronutrients and micronutrients. Macronutricnts include carbon, hydro- gen, oxygen, nitrogen.

Micronu- trients include iron, manganese, copper. Manganese is one of the key elements in photosynthesis and man- ganese-deficient cells have a reduced level of photosynthesis and a reduc- tion in chlorophyll. Iron is associated with nitrogen metabolism. Anion confirmed that chloride is a coenzyme of photosynthesis specifi- cally concerned with oxygen evolution. Vanadium and zinc appear to be involved in photosynthesis.

Calcium and boron are involved in nitrogen fixation. Molybdenum is necessary for nitrate utilization and nitrogen fixa- tion. Cobalt is associated with the nutritional functions of vitamin B Fitzgerald discussed the sequences of algal blooms that occur under conditions of nutrient supply in sewage stabilization ponds far in excess of those found in natural lakes.

He also reviews some of the fac- tors other than nutrition that might influence the algal population. These factors include grazing and the production of inhibiting extracellular pro- ducts. It is pointed out that there is evidence that an inverse relationship frequently exists between the density of phytoplankton and zooplankton. In situations where the algae are so abundant that their control may be required by chemical means, it appears that animal predation or attacks by micro-organisms are not enough to cause a shift in the dominant spe- cies.

Once the dominant species is eliminated, however, other species in- crease in numbers and become dominant. Factors thought to contribute to species dominance include secreted or excreted inhibiting extracellular products Rice, When the water is renewed slowly, this phenomenon does not occur because the extracellular products are constantly removed.

Also, when one species of algae pre- dominates in standing water, other species appear only sporadically and the number of bacterial species decreases. Of 1 54 algal species.

Water Pollution: Effects, Prevention, and Climatic Impact

Those blue-green algae not requiring B 12 employ it readily as a cobalt source; since cobalt is generally scarse in water, even organisms not requiring B 12 may compete for it. A great part of the vitamins in freshwaters and in the littoral zone of the sea can be assumed to come from any soil run-off especially during the spring floods. Muds are anoth- er source of vitamins. A third source is the vitamins present as solutes in water.

Vitamins are synthesized by several organisms. Burkholder studied the production of B vitamins by bacteria isolated from waters and muds from Long Island Sound and found that 27 percent of these gave off vitamins B 12 , 50 percent gave off biotin, 60 percent thiamine, and 11 percent nicotinic acid. Sixty-five per- cent of the actinomycetes studied were found by Burton and Lockhead to produce vitamin B 1 1. Robbins et al. Toxic Substances Many pesticides and heavy metals are toxic to aquatic life in low con- centrations.

Many studies have related these toxici ies to specific orga- nisms and to specific dilution waters. The toxicity of a particular substance is dependent to a large extent on other water quality characteristics asso- ciated with the toxicant. In many instances it is necessary to determine through bioassay the toxicity to fish or other aquatic organisms by testing the particular ef- fluent discharged with the particular water quality that receives the dis- charge.

Objectives B. Investigation I. Study Planning 2. Data Collection 3. Sample and Data Analyses C. Reporting 1. Data Organization and Display 2. Interpretation 3. Report Writing a. Introduction b. Summary c. Conclusions d. Recommendations e. Predictions f. Area Description g.

Water Uses h. Waste Sources Effects on Water Ouality j. Appendix D. Demonstrations Objectives Careful thought should be given to the development of study objectives. Studs objectives should be realistically oriented to the numbers. Ultimately as the study progresses and it concluded, its success and accomplishments will be judged on the satisfaction, or degree of satisfaction, of the objectives stated at the instigation of the project. Study objectives become extremely important tools to guide and control subsequent investigation, to delineate avenues of approach towards prob- lem solving, and eventually to judge success.

Planning A field investigation encompasses three equally important areas of ac- tivity: study planning. Study planning involves a myriad of details. First, maps of the waterway in question must be secured and points of access noted. Mobile chemical ana mlcrob4ologlcal laboratones receiving samples near river bank. Development of stream mileages necessitates that the maps be accurate and of suitable scale. During the reconnaissance survey a judg- ment is reached on the potential effects on water quality of individual waste sources, the reach or reaches of waterway that are of potentially greatest concern in the particular investigation, and possible sampling sites and actual points of access.

A judgment should be reached on the advan- tages and disadvantages of sampling the entire waterway by boat as op- posed to a cartop or trailered boat that is lowered into the water from several points of access along the waterway. Perhaps answers to the prob- lem can be satisfactorily obtained by sampling the stream while wading and, should this be the case, much time, effort, and expence could be saved in so doing.

Observations should be made at various points of ac- cess on stream width, depth if ascertainable, nature and type of stream bed, relative flow, as well as any other morphometric features that would seem to contribute towards a better organized sampling procedure when samples are collected. It is extremely important to know where boats and other equipment may be lowered into the waterway and possible difficul- ties that may be encountered when this is done.

It is equally important to ascertain that proportion of the samples that may be collected by wading or by some means other than by boat. Observations should be made that may later relate to the use of such gear as conventional biological sam- pling dredges. During the reconnaissance survey contacts can be made with lo- cal officials or local investigators who may be encouraged to participate in some manner with the investigation.

Arrangements should be made with land owners to cross private lands at times when samples are to be col- lected from the waterway. Water samples for chemical analyses should be collected from access points along the waterway during the reconnaissance survey to ascertain the relative magnitude of pollution at various points, and to aid in the judgment of selecting sampling stations. Concurrently the aquatic orga- nisms that can be observed qualitatively on rocks and other submerged objects should be noted and recorded for similar use. Following the completion of a reconnaissance survey, and subject to modification or change during the course of the field sampling, decisions can be made on the following: I.

Types of samples necessary to point to a solution to the problem i. Periodicity of sampling and approximate collection time for a spe- cific sample type and 4. Approximate number of samples necessary to complete the study. A field investigation of a problem that demands the services of a biolo- gist or the collection of biological samples should be investigated also by the chemist, the microbiologist, the sanitary engineer, and perhaps a rep- resentative of another pertinent discipline.

Thus, the points that are discussed herein are related specifically to the bi- ologist but can be used with appropriate modifications for associated dis- ciplines. Indeed, biological data will serve to complement chemical, physi- cal, and other data in the process of formulating a solution to.. The next aspect of study planning involves, logically, the carrying out of details that are necessary to initiate the process of data collection. De- cisions must be made on methods of sample handling, sample preserva- tion, and transportation of samples to a base laboratory. In the conduct of biological investigations these decisions are often not complex.

Samples are placed in appropraite sample containers, usually preserved with a so- lution of formaldehyde and transported to a base laboratory either at the completion of the field study or at intervals by commercial transportation. The number of samples expected to be collected during an investigation will determine the relative number of sample collection containers that must be made ready for the study. Sampling equipment, data cards, note- books and all of the necessary paraphernalia associated with the collec- tion.

A part of the study planning involves the making of travel arrange- ments, room accommodations, transportation of samples and equipment both to and from the sampling area, and arragements for such items as outboard motor gasoline, cartons for shipping collected samples, and ice for sample preservative, if this is a necessary consideration. Adequate survey planning can save so much time and expense during the field study that it is worthwhile to make a list of judgments that are necessary during this planning stage.

By checking this list one can reduce the possibility of oversight that otherwise would be a cause of frustration at a later time. In addition, a preliminary survey of pertinent literature is of extreme importance. A thorough study of the most complete maps of the study area will facilitate both organizational planning and initial field in- vestigation. Station Selection Preliminary to the collection of a sample, the investigator must firmly establish the location of sampling stations.

Station selection varies with the physical features of the waterway and this discussion will relate to streams, lakes, reservoirs, and estuaries. Biological sampling stations for the stream environment should be rou- tinely located close to or at those sampling stations selected for chemical 49 Figure Laboratory analyses being conducted inside mobile laboratory. Sampling stations should be located upstream and downstream from suspected pollution sources, and from major tributary streams, and at appropriate intervals throughout the stream reach under investigation.

The upstream stations should depict conditions unaffected by a pollution source or tributary. The nearest downstream station to the pollution source or tributary should be so located that it leaves no doubt that conditions depicted by the sample can be related to the cause of any environmental change. The minimum number of downstream stations from this point should be located in the most severe area of the zone of active decomposition, downstream in an area depicting less severe condi- tions within this zone, near the upstream reach of the zone of recovery, near the downstream reach of the recovery zone, and in the downstream reach that first shows no effect from the suspected pollution source.

Pre- cise station location will depend on the flow, the strength, volume and type of pollution entering at the source, and the entrance of additional sources of pollution to complicate the stream recovery picture. When wa- ter in tributary streams is found to be polluted or to influence water quali- ty in the primary stream, these streams should be similarly investigated.

A stream usually is composed of riffles and pools. These areas will vary in depth. Because the biologist seeks to determine changes that occur in water qual- ity as depicted by aquatic organisms and to relate these changes to particular sources, he must compare observations at a particular station with observations and findings from an upstream station, as well as a sta- tion within the stream reach that is unaffected by a suspected source. To accomplish this an effort should be made to collect samples from habitat types that are morphometrically similar. Riffle samples should be com- pared with riffle samples and pool samples compared with pool samples.

Both should be studied where feasible. To determine the extent of each major environmental change produced by pollution, the biological investi- gator may need to choose a number of stations in addition to those select- ed for routine chemical or bacteriological sampling. Plankton samples are collected usually at one point within the study station, most commonly at midstream I to 2 feet below the surface.

Sam- ples for bottom associated organisms should be collected at a number of points on a transsection line between the stream banks. Optimally, these samples should be collected at a minimum of 5 points across the stream mid and two quarter points and at near zero water level with banks ; more than one sample may. Realistically the objectives of a particular survey and the number of stations at which bottom fauna are collected may dictate the number of samples from a particular station.

Attached growths are sampled wherever they occur. The effluent of a natural lake will usual- ly give a better than average composite of the epilimnionic waters of the lake. The discharge from a reservoir penstock located below the thermoc- line, however, will not give a representative sample of the productive zone of the reservoir but shows water quality in a portion of the hypolimnion instead. A study would be indicated to show the effect of the low-level discharge on the receiving waters.

Within the lake or reservoir, a number of sampling sites may be chosen depending on the problem under investigation and the conditions to be studied. An investigation of the kinds and relative abundance of aquatic vegetation would naturally be limited to the littoral area. A mapping of aquatic plants often proves useful for future comparisons. Fish sampling Figure Diagram of a natural lake basin showing suggested sampling sites. Samples taken from points on transaction lines on a periodic or seasonal basis are valuable to determine vertical water characteristics and the benthic standing crop.

The use of transections in sampling a lake bottom is of particular val- ue because there are changes in depth and because benthos concentration zones usually occur. Unless sampling is done systematically and at rela- tively close intervals along transections, especially those that extend across the zone between the weed beds and the upper extent of the hypolimnion, concentration zones may be missed entirely or inadequately represented. Maximum benthic productivity may occur in the profundal region. Be- cause depth is an important factor in the distribution of bottom orga- nisms, productivity is often compared on the basis of samples collected from similar depth zones.

Collections from a transection will sample all depth zones, and a sufficient number of samples must be taken to make the data meaningful. A circular lake basin should be sampled from several transections ex- tending from shore to the deepest point of the basin. A long narrow basin is suitable for regularly spaced parallel transects that cross the basin per- pendicular to the shore, beginning near the inlet and ending near the out- let.

A large bay should he bisected by a transection originating near shore and extending to the lake proper. There are definite advantages in sampling the benthic population in winter beneath the ice cover in lakes.

Samples can be collected at definite, spaced intervals on a transection, and the exact location of sampling points can be determined. Also, collections are at a time of peak benthic population when emerging insects do not alter the benthic population. Transactions also aid in sampling the palnkton population. Because of the number of analyses necessary to appraise the plankton popula- tion. Because of significant population variation, plankton samples must be taken vertically at periodic depths. Reservoirs are usually long and narrow water bodies with the widest portions occuring downstream.

They are particularly suitable for the placement of imaginary transection lines that extend perpendicularly from one shore to the opposite shore. Sampling stations can be conveniently lo- cated on these transections.

The Three Types of Water Pollution | Sciencing

In addition water use return waters or areas designated for water use removals should be sampled. The selection of sampling stations in estuaries combines the aspects of stream sampling with those of the more static lake environment. Diagram of a long, narrow reservoir showing suggested sampling stations. Thus, the flow characteristics of the water mass are extremely important in order to define water quality and prognosticate effects of waste discharges on it.

The flowing water por- tion of an estuarine study should be attacked in a manner similar to that described for the stream environment. Sampling stations within the true estuary can be profitably developed along transection lines that either cross the estuary, more or less perpendicularly from one shore to another, or that extend out of the estuary in two or more directions from a sus- pected point source of pollution.


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Whenever possible, samples should be collected from areas that represent the estuarine habitat unaffected by pollution, as well as areas that depict environmental changes produced by it. Sampling Periodicity Weekly collecuons. In special studies, samples are often collected daily or even periodically during a hour day to assess these changes.

During the non-growing season, monthly samples of these constituents should be adequate except where otherwise indicated by the objecives of the stud. A reconnaissance and mapping of the aquatic veg- etation should be done during maximum vegetation growth, usually in midsummer. Insect representatives of the bottom organism community emerge from the water as adults periodically throughout the warm weather period; time of emergence depends on the species involved.

Life histories of these or- ganisms tend to overlap so that at no time is there a dearth of these orga- nisms within the bottom associated community. Bottom fauna should be sampled during the annual seasons; the standing crop will be highest. Because of the report deadline or limited personnel available, the theo- ry and practice of station location and sampling periodicity may not be the same.

The objectives of a study may be met by investigating only bot- tom fauna and attached organisms in a stream, and these on only one oc- casion. Much can be learned from this minimal effort. The investigator should keep in mind that water quality effects from organic wastes will likely be at their worst during the warm weather low-flow period. When streams become covered with ice in northern climes during winter, anoth- er period with severe conditions of existence for bottom fauna occurs in late winter.


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The zone of active decomposition resulting from an organic waste source will be transferred a considerable distance downstream under ice cover. Because these organisms are carried by the currents, a given sample is representative of water quality at some point upstream rather than at the place of sampling. Data and Saniple Collection The collection of data and samples from a particular station involves making a number of scientific observations, flow measurements on streams, inlets and outlets to standing bodies of water such as lakes and reservoirs, suspected municipal and industrial waste sources, and water use drawoff and return points, which can be correlated with sampling dates, are of utmost importance.

Such data permit a calculation of the amounts of particular water quality constituents passing a point at a given time, and estimates can be made from these data on daily, monthly, or annual contributions. Rainfall may be a contributing factor to investigations con- cerning major aquatic plant nutrients and should be sampled to determine annual contributing amounts of nitrogen and phosphorus. A house-to- house survey of the area draining to a watercourse may be indicated to determine types of waste treatment and to project potential impact of wastes that are discharged to or reach the watercourse.

The types and amounts of fertilizers applied to lands within the drainage basin, as well as the period of the year when fertilizers arc applied. Groundwater may be a factor and should be sampled from appropriate adjacent wells for those constituents of importance. On approaching a stream station a number of observations must be made that will later be considered in interpreting the biological findings.

Observations are made on water depth; presence of riffles and pools; stream width; flow characteristics; bank cover; presence of slime growths. Organisms associated with the stream bed are studied most often in the biological evaluation of water quality. These organisms are valuable to relate water quality because they are not equipped to move great distances through their own efforts and, thus, remain at fixed points to indicate wa- ter quality. Because the life history of many of these organisms extends through 1 year or longer, their presence or absence is indicative of water quality within the past.

Bottom associated orga- nisms are relatively easy to capture with conventional sampling equipment and the amount of time and effort devoted to their capture and interpreta- tion is not as great as that required for other segments of the aquatic community. Specifically, where would I expect to find these creatures? What is the appropriate gear with which to capture them? A close search of the respective areas should be made noting and collect- ing qualitatively the various types of organisms.

A commercial mesh sieve is a handy exploratory tool. The qualitative search for benthos should involve the collection of or- ganisms from rocks, plants, submerged twigs or debris, or leaves of over- hanging trees that become submerged and waterlogged. It is often conven- ient to scrape and wash organisms from these materials into a bucket or tub partially filled with water and then to pass this water through the sieve to concentrate and retain the organisms.

The collected sample may be preserved for organism sorting and identification later. The investigator should search until he is certain that he has collected the majority of spe- cies that can tolerate the particular environment. Gravel F. Sand F. Clay F. Field Collection Card for Benthic Samples. Cards can be carried in a field notebook; they may be filed after field and laboratory use. The backside of the card may be ruled to itemize the organisms observed in the laboratory examination of the collected sample.

Qualitative sampling determines the variety of species occupying a reach of a waterway. Samples may be taken by any method that will cap- ture representatives of the species present. Collections from such sam- plings indicate changes in the environment, but they generally do not ac- curately reflect the degree of change.

Mayflies, for example, may be reduced in the stream because of adverse conditions from to 1 per square foot, whereas sludgeworms may increase from 1 to 14, per square foot. Qualitative data would indicate the presence of both species, but might not necessarily delineate the change in predominance from mayflies to sludgeworms. The basic principal in qualitative sampling is to collect as many differ- ent kinds of animals as practical.

A minimum of 30 minutes and a maximum of an hour is a convenient range in which to establish this limit. A number of tools readily obtained in any community are valuable in this type of sampling: a. Pocket-knives are excellent tools to remove animals from crevices in rocks, to peel bark from decaying logs thus exposing animals, and to slip under animals to lift and transfer them to sample containers.

Common garden rakes are valuable to retrieve rocks, brush, logs and aquatic vegetation for inspection. Fine-meshed dip-nets are good devices for sweeping animals from vegetation or out from under over-hanging rock ledges. Buckets are handy to quickly receive rocks and debris, thus prevent- ing escape of the swift running animals. Sheet polyethyelene, 6 x 6 feet, can be spread on the stream bank and substrate materials placed upon it.

As the materials begin to dry the animals will abandon their hiding places and can be seen readily as they migrate across the sheet seeking water. Standard Series No. The entire qualitative sam- ple can also be screened to standardize the organism sizes taken at various sampling sites. Any other tools, such as forceps, scalpels, shovels, and forks are le- gitimate devices and can prove their merit in individual situations.

Following these general observations, the investigator collects appropri- ate quantitative samples of the various kinds of organisms present in the aquatic area. He makes certain that: 1 The sampling area selected is representative of stream conditions, and 2 the sample is representative of and contains those forms predominant in the area and encountered during the qualitative search.

Bottom samples in lakes usually may be collected with an Ekman dredge. The Ekman dredge Ekman. When open. To close the dredge. The hinged top of the box may he equipped with a perma- nent mesh screen to prevent loss of organisms if the samples sinks into mud deeper than its own height. The sampler is especially adapted for use iii soft, finely divided mud and muck; it does not function properly on sand bottoms or hard substrates. The Ekman can also be mounted on a pipe for shallow stream sampling and tripped by a thrust-through rod.

The Petersen dredge Petersen. It is widely used to sample hard bottoms such as sand. It is an iron. By means of a rope. As tension is eased on the rope, the mechanism holding the jaws apart is released. As the rope is again made taut, a sam- ple is secured. The operator controls the dredge by maintaining tension on the rope until the dredge is placed. This is helpful in sampling gravel or rubble, as the operator can determine through sound and touch the type of bottom and by carefully manipulating the dredge, can secure a better sample than would otherwise be possible.

Biological collecting equipment. From left, Kemmerer sampler, Ekman dredge, U. Standard No. The orange-peel dredge, is a multij awed, round dredge with a canvas closure serving as a portion of the sample compartment. Its sampling area is a function of depth of penetration and this area must be calibrated, usually with the volume of sediment contents. It has received wide use in marine waters and in the Great Lakes, where it has advantages over other tools for sampling sandy sub- strates.

The ponar dredge is receiving increased use in deep lakes. In appearance it is similar to a Petersen dredge but it has side-plates and a screen on the top of the sam- ple compartment. The Smith-McIntyre dredge has the heavy steel construction of the Pe- tersen, but its jaws are closed by strong coil springs. Its principal advan- tage is its stability or operator control in rough waters. Its bulk and heavy weight requires operation from large boats equipped with a powered winch. Their efficient use requires dense animal populations.

Corer design varies from hand- pushed tubes to explosive driven and automatic surfacing models. The Phieger type is the most widely used corer in water quality studies. It is a gravity corer, relying on its weight near lbs. A core of this length is adequate for most physical, chemical or fossil examination to de- lineate recent environmental changes. Its operation may be restricted to the vegetation, or mud-water interface sediment may be included. Drift nets may be suspended in flowing waters to capture invertebrates that have migrated into the water mass from the bottom substrates and are temporarily being transported by currents.

Their principal uses have been to study migratory movements and to evaluate sublethal toxicants, especially insecticides, on the fauna. Before toxicants become lethal the animals are weakened and cannot maintain their benthic position and thus are swept away by the currents and carried into the nets. As of now no single style of net has been standardized among investigators. It is recom- mended that these nets be designed with a 1 x 1 foot upstream opening, with U.