Streamwater. 1) Dissolved 2) Dissolved 3) Suspended and dissolved 4) Dissolved 5) 1) Dissolved

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1 Streamwater 1) Dissolved 2) Dissolved 3) Suspended and dissolved 4) Dissolved 5) 1) Dissolved TDS (Total dissolved solids) = sum of all. A general indicator of. Pass through 2 micrometer filter Much regional variation [TABLE 4.2] TDS of ~100 mg/l is world average [= 0.1 grams per 1000 grams water = 0.1 ppt, 100 ppm] TDS of <500 mg/l is drinking water standard for U.S. [0.5 ppt] Lower Colorado: TDS > 800 mg/l [0.8 ppt] Levels above 1000 mg/l can cause How to measure TDS? electrical conductance of water due to dissolved ions. 1

2 Salinity (effectively same as TDS in freshwater) Hardness = In U.S. used as synonym for alkalinity FW < 0.5 ppt Ocean ave. = 35 ppt Alkalinity. HCO 3, CO 3, OH units: mg/l (ppm) CaCO 3, or meq/l Alkalinity often used as surrogate for stream fertility production of crustaceans (gammarids, crayfish) and fish often higher with Ca 2+ concentrations; aquatic insect production sensitive. Fig. 4.6 shows salmonid production across an alkalinity gradient. alkalinity limits production variation at alkalinity What other environmental factors correlated with high alkalinity? Sources of? Why is streamwater than rainwater? [FIG. 4.1] * * Contact with minerals in soil Weathering of rock (limestone)» high in Ca 2+, Mg 2+, HCO 3» granite, slate, sand (SiO 2 ) (long contact with soil/rock) 2

3 Effects Fig. 4.7 shows effects of road salt on water salinity (Cl ) along ruralurban gradient. natural [Cl ] Note these concentrations are just for Cl ; total TDS would be much. 2) Dissolved (N,P,C,Si) N P Humans export N and P to oceans globally Fig. 13.3: N and P vary with Forest to agriculture gradient Human inputs NO 3 in PO 4 in NO 3 in 3

4 3) Suspended and dissolved organic matter Seston, including plankton, organic detritus, and inorganic material. important food for Dissolved Organic Material (DOM), includes leachates from living organisms and soils, and decaying detritus important food for 4) dissolved : O 2, CO 2 O 2, CO 2 Factors controlling concentration [TABLE 4.1] (altitude) For example, at 5 C» sea level, 100% O2 saturation is 12.5 mg/l» 3200 m altitude, 100% saturation is 8.6 mg/l What biological processes regulate O2 and CO2 concentrations? Concentration in atmosphere at sea level O 2 = 21% CO 2 = 0.03% (ratio of atmospheric O 2 to CO 2 = 700) Supersaturation occurs when water has oxygen concentration exceeding 100% of solubility How would concentration of O 2 and CO 2 be different in groundwater? How would organic pollution affect the dissolved oxygen in a stream? 4

5 What is ph and what controls it? What is it? Negative log 10 of [H + ] If [H + ] = mol/l, ph = Why is it important? (~4.5 to ~9.5) Natural gradients in ph Fig. 4.8: Sampling across streams in acidic regions of southern England ph of various liquids, rain, and lakes microarthropods macroarthropods Main point? Fewer species adapted to ph. Biological effects of excessive [H + ] Loss of body and failure to acquire Damage to (fish gills, mayfly gills) and Leaching of toxic from soils into streams (Fig. 4.9) Examples (from text): Invertebrates: species composition changes along ph gradient in Swiss streams Fish: Brook trout decline while blacknose dace and sculpin can be eliminated by ph in northeastern US 5

6 Sources of Acidity Natural Acidification (noncalcareous soils) [see equations] (dissolved organic material from wetlands, etc.) Anthropogenic acidification Addition of, in acid rain What makes streams (and lakes) vulnerable to acidification? Figure 16. Regions of sensitivity to acid rain in the United States. Also shown are the isopleths of the ph of precipitation; for example, all of the eastern U.S. currently has an average ph of rainfall between 4 5, where "neutral" rainwater has a ph of ~6. What is the ph of distilled water? ph = _ = log 10 [ ] #1: H 2 O H + + OH Why is ph of pure rain only? #2: H 2 O + CO 2 H 2 CO 3 HCO 3 + H + forms and dissociates into weak acid. How much more acidic than neutral? [10 7 / = ] = 25 Why is acid rain << ph? Strong acids disassociate in water H 2 SO 4 2H + + SO 4 HNO 3 H + + NO 3 But most streams! 6

7 What makes water acidic? addition of H + what are sources? (e.g., carbonic acid (Eqn #2)) from atmosphere, groundwater #2: H 2 O + CO 2 H 2 CO 3 HCO 3 + H + What makes water more (ph > _)? addition of OH what are sources? Reactions of water with (HCO 3 ) and (CO 3 ) ions #4: HCO 3 + H 2 O H 2 CO 3 + OH #5: CO 3 + H 2 O HCO 3 + OH Where does and come from???!! (groundwater contact with, ( ) a source of HCO 3 ) Only 3 forms of their relative proportions depends on ph. CO 2 HCO 3 CO 3 Most streams in ph range of, and HCO 3 dominates. If H + added to stream, neutralized by OH formed from reaction of water with HCO 3 (Eqn #3) or with CO 3 (Eqn #4) and ph. Adding enough H + can use up OH provided by CO 3 or HCO 3 and ph, eventually producing dissolved CO 2. #2: H 2 O + CO 2 H 2 CO 3 HCO 3 + H + 7

8 Bicarbonate Buffering System Streams with alkalinity (HCO 3 or CO 3 ) can hold a lot of H + without notable change in ph. #3: H 2 O + CO 2 H 2 CO 3 HCO 3 + H + CO 3 + H + How does Acid Rain + Stream Water =? OH neutralizes H + and more OH forms immediately from reaction of CO 3 or HCO 3 with water! ph until supply of CO 3 or HCO 3 is exhausted most streams Why are some streams more susceptible? (CaCO 3 is source of HCO 3 ) (humans) A carbonate(d) twist (Eqn #6) (from rain) reacts with in soil: H 2 CO 3 + CaCO 3 Ca HCO 3 Calcium ion reacts with abundant HCO 3 in stream to form Calcium bicarbonate: #6: Ca HCO 3 Ca(HCO 3 ) 2 CaCO 3 +H 2 O + CO 2 can precipitate out of stream water under what conditions? Removing drives the equation to the right. How can be removed?? 8

9 In hard waters: removed in two ways: 1) Biological activity Shoreline (mostly lakes) Chara (skunk weed) Removes and becomes encrusted with What happens at? #6: Ca HCO 3 Ca(HCO 3 ) 2 CaCO 3 +H 2 O + CO 2 2) Physicalchemical processes where excess dissolved vented e.g., Travertine terraces (e.g., Mammoth Hot Springs, Yellowstone) in subterranean water degasses upon contact with atmosphere #6: Ca HCO 3 Ca(HCO 3 ) 2 CaCO 3 +H 2 O + CO 2 What would happen in stream below a dam if water rich in calcium bicarbonate were released from the hypolimnion of a deep reservoir during summer stratification? Hint: Deep reservoir water is 9

10 Synopsis: CO 2 dissolves into surface water to HCO 3 and CO 3 enter through Controls on ph? 1) buffering reactions of 2) amount of and derived from rock weathering (produces OH ) 3) buffering reactions also influenced by,, but we re not concerned with that here Bicarbonate Buffering System deceptively simple Wetzel: in alkaline, hard water lakes, often twice the content of Ca 2+ and HCO 3 found than predicted on the basis of chemical equilibria. 10