Hydrological Cycle Rain and rivers The Hydrosphere Rain and rivers OUTLINE 1
Generalizations (non-political conservatism) Conservative (not affected) and Non-Conservative (affected) Ions Distinction: whether or not ion concentrations in H2O are affected by changes in ph T P (and pe) at relatively low concentration Works well for natural waters Example Ions and complexes Conservative ions: High solubility salts (fully dissociated) Constant ratios between each other and vs salinity Na + K + Ca 2+ Mg 2+ Cl - SO 4 NO 3 - Non-conservative ions: H + and OH - and ions that dissociate with them; gases, nutrients (the rest) high solubility: low solubility: HCO - 3 CO 3 B(OH) - 4 HS - NH 4+ H 3 SiO - 4 phosphate species many organic anions 2
What was alkalinity again? Alkalinity Ability to neutralize acid Total Alkalinity includes carbonate alkalinity + alkalinity from major non-conservative ions: [Alk] = [HCO 3 ] + 2[CO 3 2 ] + [OH ] + [B(OH) 4 ] + [H 3 SiO 4 ] + [HS - ] + [H 2 PO 4 ] + 2[HPO 4 2 ] - [H + ] For charge balance (+ vs ): What was eq again? Seq cations = S eq anions Charge balance equation in terms of conservative-ness : Seq cations = S eq anions Adding types and rearranging... Seq conservative cations - Seq conservative anions = Seq non-conservative anions -Seq non-conservative cations = alkalinity So: Alk =Seq conservative cations - Seq conservative anions So non-intuitively, Total Alkalinity is conservative: independent of ph, pressure or temperature, although the concentrations of the individual species are not independent 3
Rain Starting point composition for water in a given watershed Rivers and ground water compositions reflect weathering and biological processes (+anthropogenic) Rain Why does rain form? atmosphere becomes supersaturated in water vapor at some temperature & pressure Need to nucleate drops on things like dust in the air 4
Surface Water Chemistry changes from rain to river: SiO 2 & Ca increase why? weathering K = low why? clays HCO 3- high from CO 2 dissolution increase other ions in rain proportions Rain composition links to its origin The mostly marine ions are: Cl - = Na + >Mg 2+ The mostly terrigenous ions are: K + > Ca 2+ > SO 4 > NO 3 = NH 4+, Al +3 = SiO 2 (aq) Al 3+ or SiO 2 (aq) indicate continental origin Al 3+ /X, SiO 2 /Y complicated, so not used quantitatively 5
Tracking marine contributions to rain All major ions in ocean conservative (except Ca): what do you expect their ratios to look like? How do I use that to look at water origin/path? Ratios should be ~same ÞUse common Na + or Cl - to quantify marine contribution ÞThen move on to other ions compared to these GG325 L17, F213 Compare other ions to Cl Compare excesses / deficits vs. marine ratios: v how much was added? v what do terrigenous particulate sources look like? v any solubility reactions involved? v anthropogenic sources of Cl? [ion]/[cl - ] (sea water ratio) x [Cl - ] (in weight units) = [ion] expected from seawater ÞCompare [ion] with [ion] expected from seawater 6
Clear Cl gradient away from coastline Not many sources for Cl besides ocean Na + distribution is more complicated from what? GG325 L17, F213 Na + /Cl - rain vs. Na+ /Cl - seawater shows "excess" Na everywhere Excesses from dust/soils/clays adding Na + to marine ratio Cl - is low inland, makes ratio sensitive inland GG325 L17, F213 7
[Ca 2+ ] map derives mostly from CaCO 3 and CaSO 4 dissolution Where would CaCO 3 be dissolved, how about CaSO 4? Lo Hi Hi Lo GG325 L17, F213 Calcium in US rain Evaluating non-marine Ca by comparing Ca content, rain ph and SO 4. v CaCO 3 dissolution neutralizes rain acidity, raising ph. v CaSO 4 dissolution does not affect ph. Look at these and tell me why: Acid K a2 = 1.2 x 1-2 = (SO K a14 * H+ ) / HSO K - a2 4 sulfuric vs acid (H 2 SO 4 ) 1. x 1 3 1.2 x 1-2 carbonic acid (H 2 CO 3 ) 4.5 x 1-7 4.7 x 1 K -11 a2 = 4.7 x 1-11 = (CO 3 * H+ ) / HCO - 3 Which one reacts more H +? Tell source of Ca with high [Ca 2+ ] and basic ph (CaCO 3 ) CaSO 4 particles add Ca to rain without CO 3 : ph is not shifted as [Ca 2+ ] increases along with [SO 4 ]. 8
Rain summary: Rain = H2O "starting" composition of a particular watershed Distinguish marine, local terrigenous and anthropogenic components Example from the Amazon Basin: Concentrations of all rain components drop with distance from the coast, reflecting rainout of marine particulates as storm clouds move inland. Terrigenous components such as SO 4 and Ca 2+ increase at various points further inland, dominated by local effects, perturbed by human activities GG325 L17, F213 Rivers Rivers integrated effects over a watershed of rain vs. ground (rock/soil) Rivers transport material in related suspended and dissolved forms. 9
Dissolved load in rivers What affects river TDS (dissolved solids) chemistry? v inorganic reactions v biological processes v water sources (rain, ground water, lakes) v climate (temperature) v weathering v ion solubility Suspended load reflects: v watershed relief (river gradient) v watershed area (sq km) v rock type v climate (temperature) Suspended load in rivers Mostly made up of v Weathering resistant minerals v Low solubility elements v Organic particulates 1
TABLE 5.1 Major Rivers that Flow to the Sea, Listed in Order of Discharge River Water (km 3 /yr) Dissolved Solids (Tg/yr) Suspended Solids (Tg/yr) Dissolved/ Suspended ratio Drainage Area (1 6 km 2 ) 1. Amazon 63 275 12.23 6.15 2. Zaire (Congo) 125 Lots 41 Lots of 43.95 Lots of 3.82 of dissolved sediment 3. Orinoco 11 water 32 load 15.21.99 4. Yangtze (Chiang) 9 247 478.53 1.94 5. Brahmaputra 63 61 54.11.58 6. Mississippi 58 125 21 (4).6 3.27 7. Yenisei 56 68 13 5.2 2.58 8. Lena 525 49 18 2.7 2.49 9. Mekong 47 57 16.36.79 1. Ganges 45 75 52.14.975 11. St. Lawrence 447 45 4 11.3 1.3 Not much sediment Tg = 1 6 tons = 1 12 g; Source: Berner and Berner, Global Environment, 1996 Suspended load variations around the globe Where s the most? 11
9/27/17 Human effects on sediment load v increased erosion due to agriculture, deforestation v decreased load transport due to dams, bank stabilization v increased surface runoff due to urbanization Load from here? https://www.meted.ucar.edu/ http://remaingreen.weebly.com/the-downside-to-deforestation.html Sources of major ions in river water Table 5.11 Sources of Major Elements in World River water (in Percent Actual Concentrations) source: Berner and Berner, Global Environment (1996) Element Ca C (HCO3-) Na Cl S (sulfate) Mg K SiO2 (aq) Atmos. Cyclic Salt Carbonates.1 65 <<1 61c 8 13 2d 2 36 1 <<1 Weathering Silicates 18 37c 22 54 87 99+ Evaporitesa 8 42 57 22d <<1 5 Pollutionb 9 2 28 3 54 8 7 a. also includes NaCl from shales and thermal springs b. values from Meybeck (1979) except sulfate, which is based on a calculation given in the text c. for carbonates, 34% from calcite and doliomite and 27% from soil CO 2; for silicates, all 37% from soil CO2; thus, total HCO3- from soil (atmospheric) CO2 = 64% (see also Table 5.13) d. other sources of river sulfate: natural biogenic emissions to atmosphere delivered to land, 3%; volcanism, 8%; pyrite weathering, 11% Pollution calculated as the part not explained by Weathering or Salt 12