Science of Water : Concepts and Applications

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Environmental Biomonitoring, Sampling, and Testing 267 All these tests have one thing in common—they all depend on measuring orthophosphate. The total orthophosphate test measures the orthophosphate that is already present in the sample. The others measure that which is already present and that which is formed when the other forms of phosphorus are converted to orthophosphate by digestion. Monitoring phosphorus involves two basic steps: 1. Collecting a water sample 2. Analyzing it in the fi eld or lab for one of the types of phosphorus described above Sampling and Equipment Considerations Sample containers made of either some form of plastic or Pyrex ® glass are acceptable to the USEPA. Because phosphorus molecules have a tendency to “absorb” (attach) to the inside surface of sample containers, if containers are to be reused, they must be acid-washed to remove absorbed phosphorus. The container must be able to withstand repeated contact with hydrochloric acid. Plastic containers, either high-density polyethylene or polypropylene, might be preferable to glass from a practical standpoint because they are better able to withstand breakage. Some programs use disposable, sterile, plastic Whirl-pak bags. The size of the container depends on the sample amount needed for the phosphorus analysis method chosen, and the amount needed for other analyses to be performed. All containers that will hold water samples or come into contact with reagents used in the orthophosphate test must be dedicated. They should not be used for other tests, to eliminate the possibility that reagents containing phosphorus will contaminate the labware. All labware should be acid-washed. The only form of phosphorus this text recommends for fi eld analysis is total orthophosphate, which uses the ascorbic acid method on an untreated sample. Analysis of any of the other forms requires adding potentially hazardous reagents, heating the sample to boiling, and requires too much time and too much equipment to be practical. In addition, analysis for other forms of phosphorus is prone to errors and inaccuracies in fi eld situations. Pretreatment and analysis for these other forms should be handled in a laboratory. Ascorbic Acid Method for Determining Orthophosphate In the ascorbic acid method, a combined liquid or prepackaged powder reagent consisting of sulfuric acid, potassium antimonyl tartrate, ammonium molybdate, and ascorbic acid (or comparable compounds) is added to either 50 or 25 mL of the water sample. This colors the sample blue in direct proportion to the amount of orthophosphate in the sample. Absorbence or transmittance is then measured after 10 min, but before 30 min, using a color comparator with a scale in milligrams per liter that increases with the increase in color hue, or an electronic meter that measures the amount of light absorbed or transmitted at a wavelength of 700–880 nm (again, depending on the manufacturer’s directions). A color comparator may be useful for identifying heavily polluted sites with high concentrations (>0.1 mg/L). However, matching the color of a treated sample to a comparator can be very subjective, especially at low concentrations, and lead to variable results. A fi eld spectrophotometer or colorimeter with a 2.5-cm light path and an infrared photocell (set for a wavelength of 700–880 nm) is recommended for accurate determination of low concentrations (between 0.2 and 0.02 mg/L). Use of a meter requires that a prepared known standard concentration be analyzed ahead of time to convert the absorbence readings of a stream sample to milligrams per liter, or that the meter reads directly in milligrams per liter. For information on how to prepare standard concentrations and on how to collect and analyze samples, refer to Standard Methods and USEPA, 1991 (Method 365.2). Nitrates Measurement As mentioned, nitrates are a form of nitrogen found in several different forms in terrestrial and aquatic ecosystems. These forms of nitrogen include ammonia (NH 3 ), nitrates (NO 3 ), and nitrites
268 The Science of Water: Concepts and Applications (NO 2 ). Nitrates are essential plant nutrients, but excess amounts can cause signifi cant water quality problems. Together with phosphorus, nitrates in excess amounts can accelerate eutrophication, causing dramatic increases in aquatic plant growth and changes in the types of plants and animals that live in the stream. This, in turn, affects DO, temperature, and other indicators. Excess nitrates can cause hypoxia (low levels of DO) and can become toxic to warm-blooded animals at higher concentrations (10 mg/L or higher) under certain conditions. The natural level of ammonia or nitrate in surface water is typically low (
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Second Edition THE SCIENCE OF WATER
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Cover Image: Falling Spring at Fall
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Contents Preface ..................
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Contents ix Velocity Head .........
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Contents xi Specifi c Conductance .
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Contents xiii (5) Beetles (Order: C
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Contents xv Chlorine Residual Testi
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Contents xvii Water Filtration Calc
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To the Reader In reading this text,
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1 Introduction When color photograp
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Introduction 3 On second look, we s
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Introduction 5 As mentioned earlier
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Introduction 7 This scream of lost
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Introduction 9 Metcalf & Eddy, Inc.
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12 The Science of Water: Concepts a
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3 Water Hydraulics Anyone who has t
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Water Hydraulics 47 Another relatio
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Water Hydraulics 49 • • 1 ft 3
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Water Hydraulics 51 √ Important P
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Water Hydraulics 53 FIGURE 3.4 Thru
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Water Hydraulics 55 Example 3.8 Pro
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Water Hydraulics 57 FIGURE 3.6 Lami
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Water Hydraulics 59 With regard to
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Water Hydraulics 61 or hydraulic gr
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Water Hydraulics 63 E 1 smaller fl
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Water Hydraulics 65 √ Note: In de
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Water Hydraulics 67 • Cone of dep
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Water Hydraulics 69 • • • •
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Water Hydraulics 71 The Darcy-Weisb
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Water Hydraulics 73 Of course, pipe
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Water Hydraulics 75 In this section
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Water Hydraulics 77 Slope (S) The s
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Water Hydraulics 79 and important c
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Water Hydraulics 81 and the depth o
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Water Hydraulics 83 TYPES OF DIFFER
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Water Hydraulics 85 √ Important P
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Water Hydraulics 87 Meter backpress
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Water Hydraulics 89 VELOCITY FLOWME
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Water Hydraulics 91 The positive-di
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Water Hydraulics 93 Solution: 1200g
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Water Hydraulics 95 Water and Waste
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100 The Science of Water: Concepts
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6 Water Ecology The subject of man
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Water Ecology 157 The environment i
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Water Ecology 159 FIGURE 6.2 Notone
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Water Ecology 161 H 2 O O 2 FIGURE
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Water Ecology 163 FeS FIGURE 6.6 Th
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Water Ecology 165 Algae FIGURE 6.8
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Water Ecology 167 2. Likewise, biom
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Water Ecology 169 Population densit
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Water Ecology 171 succession can be
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Water Ecology 173 dark winter month
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Water Ecology 175 In rain events wh
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Water Ecology 177 long profi le, cr
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Water Ecology 179 THE FLOODPLAIN A
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Water Ecology 181 It is important t
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Water Ecology 183 Specifi c Adaptat
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Water Ecology 185 serve to indicate
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Water Ecology 187 UNITS OF ORGANIZA
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Water Ecology 189 FIGURE 6.20 Stone
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Water Ecology 191 FIGURE 6.22 Midge
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Water Ecology 193 FIGURE 6.25 Riffl
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Water Ecology 195 They push their m
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Water Ecology 197 FIGURE 6.32 Damse
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Water Ecology 199 Darwin, C., 1998.
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10 Water Treatment Calculations Gup
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Water Treatment Calculations 327 We
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Water Treatment Calculations 383 g
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