LAKE ECOLOGY

1. LAKE ECOLOGY Unit 1: Module 2/3 Part 5 - Major Ions and NutrientsJanuary 2004

2. Modules 2/3 overview • Goal – Provide a practical introduction to limnology • Time required – Two weeks of lecture (6 lectures) and 2 laboratories • Extensions – Additional material could be used to expand to 3 weeks. We realize that there are far more slides than can possibly be used in two weeks and some topics are covered in more depth than others. Teachers are expected to view them all and use what best suits their purposes.

3. Modules 2/3 outline • Introduction • Major groups of organisms; metabolism • Basins and morphometry • Spatial and temporal variability – basic physical and chemical patchiness (habitats) • Major ions and nutrients • Management – eutrophication and water quality

4. 5. Water chemistry: Gases, major ions & nutrients

5. 5. Water chemistry: Gases, major ions & nutrients • Gases • Oxygen (O2) • Carbon dioxide (CO2) • Nitrogen (N2) • Hydrogen sulfide (H2S) • Major ions (anions and cations) • Nutrients (phosphorus and nitrogen)

6. Water chemistry: gases • What are the ecologically most important gases ? • O2 • CO2 • N2 • H2S

7. Gas solubility • The maximum amount of gas that can be dissolved in water (100% saturation) is determined by temperature, dissolved ion concentration, and elevation • solubility decreases with temperature “warm beer goes flat” • solubility decreases with higher dissolved ion content (TDS, EC25, salinity) “DO saturation is lower in saltwater than freshwater (for the same temperature, solids “drive out” gases)

8. Water chemistry: O2 • ~ 21% of air • Very soluble (DO) • Highly reactive and concentration is dynamic • Involved in metabolic energy transfers (PPr & Rn) • Major regulator of metabolism (oxic-anoxic) • Aerobes (fish) vs anaerobes (no-fish, no zoops) • Types of fish • Salmonids = high DO (also coldwater because of DO) • Sunfish, carp, catfish = low DO (also warmwater)

9. O2 variability • Diel (24 hr) variation due to ____________? • Seasonal variation due to _____________ ?

10. Major sources of O2 • Sources • Photosynthesis (phytoplankton, periphyton, macrophytes) • Air from wind mixing • Inflows • tributaries may have higher or lower DO • groundwater may have higher or lower DO • Diffusion (epilimnion to hypolimnion and vice versa)

11. Major sinks of O2 • Sinks • Respiration • bacteria, plants, animals; water and sediments • Diffusion to sediment respiration • Outflow (tributary or groundwater)

12. Gases: wind mixing from storms • Oxygen from a storm – How many mixing “events” can you find for Halsteds Bay in Lake Minnetonka, MN in this 1 year record?

13. Gases: seasonal wind mixing • Oxygen varies seasonally and the entire water column lake may be fully saturated at certain times. How often did this happen in Ice Lake, MN in this 5+ year record?

14. O2: Human significance • Not a direct threat to humans • Directly affects fish physiology and habitat • Indirectly affects fish and other organisms via toxicants associated with anoxia: • H2S • NH4+ (converts to NH4OH and NH3 above ~pH 9) • Indirectly affects domestic water supply • H2S (taste and odor) • Solubilizes Fe (staining) • Indirectly affects reservoir turbines • Via H2S corrosion and pitting (even stainless steel) • Via regulation of P-release from sediments (mediated via Fe(OH)3 adsorption)

15. Gases: N2 • ~ 78% of air • Concentrations in water usually saturated because it is nearly inert • Supersaturation (>100 %) can occur in reservoir tailwaters from high turbulence • May be toxic to fish (they get “the bends) • N2 -fixing bacteria and cyanobacteria (blue-green “algae”) convert it to bio-available NH4+ • Denitrifying heterotrophic bacteria convert NO3- to N2and/orN2O under anoxic conditions

16. Gases: CO2 • Only about 0.035% of air (~ 350 ppm) • Concentration in H2O higher than expected based on low atmospheric partial pressure because of its high solubility How long does your soda pop fizz after shaking it?

17. CO2 reactions in water • <1% is hydrated to form carbonic acid: CO2 + H2O H2CO3 • Some of the carbonic acid dissociates into bicarbonate and hydrogen ions which lowers the pH: H2CO3 HCO-3 + H + • As the pH rises, bicarbonate increases to 100% at a pH of 8.3. Above this, it declines by dissociating into carbonate: HCO-3 CO3-2 + H+

18. H2CO3 HCO3 CO3 Fraction of carbon species pH Inorganic - C equilibria Note – 100% CO2 for pH< ~ 4.5; 100% bicarbonate for pH ~ 8 and 100% carbonate for pH > ~12

19. Inorganic - C: Major sources and sinks Sources: • Atmospheric CO2 (invasion) • Respiration and other aerobic and anaerobic decomposition pathways in the water and sediments • Groundwater from soil decomposition products • Groundwater from volcanic seeps Sinks: • pH dependent conversions to bicarbonate and carbonate • Precipitation of CaCO3 and MgCO3 at high pH • Photosynthesis

20. CO2 supersaturation – killer Lake Nyos • In 1986, a tremendous explosion of CO2 from Lake Nyos, in Cameroon, West Africa, killed >1700 people and livestock up to 25 km away. • Dissolved CO2 seeps from volcanic springs beneath the lake and is trapped in deep water by hydrostatic pressure. Nearby Lake Manoun is similar in nature • Although unconfirmed, a landslide probably triggered the gas release Visit http://www.biology.lsa.umich.edu/~gwk/research/nyos.html and http://perso.wanadoo.fr/mhalb/nyos/index.htm for detailed information

21. www.saddleback.cc.ca.us/faculty/thuntley/ms20/seawaterprops2/sld013.htmwww.saddleback.cc.ca.us/faculty/thuntley/ms20/seawaterprops2/sld013.htm Soda pop chemistry

22. CO2 and the inorganic carbon system • Carbon dioxide diffuses from the atmosphere into water bodies and can then be incorporated into plant and animal tissue • It is also recycled within the water with some being tied up in sediments and some ultimately diffusing back into the atmosphere • Fixed carbon also enter the water as “allocthonous” particulate and dissolved material

23. CO2 and the inorganic carbon system - 2 • Alkalinity, acid neutralizing capacity (ANC), acidity, carbon dioxide (CO2), pH, total inorganic carbon, and hardness are all related and are part of the inorganic carbon complex

24. CO2 chemistry: Alkalinity • Alkalinity – the ability of water to neutralize acid; a measure of buffering capacity or acid neutralizing capacity (ANC) • Total Alkalinity (AlkT) = [HCO3-] + 2[CO32-] +[OH-] - [H+] • Typically measured by titration with a strong acid. The units are in mg CaCO3/L for reasons relevant to drinking water treatment (details in Module 9) • Can be used to estimate the DIC (dissolved inorganic carbon) concentration if the [OH-] • Conversely, direct measurements of DIC by infrared analysis or gas chromatography, together with pH and the carbon fractionation schematic can be used to estimate alkalinity (* see slide notes)

25. Alkalinity and water treatment • Advanced wastewater treatment (domestic sewage) • Phosphorus nutrient removal by adding lime (Ca(OH) 2) or calcium carbonate (CaCO3) • As pH increases >9, marl precipitates adsorbed PO4-3 • Settle and filter the effluent to obtain 90-95% removal • Used for particle (TSS) removal also • Drinking water treatment • For TSS removal prior to disinfection • Acid-rain mitigation to whole lakes • Lime or limestone added as powdered slurry to increase impacted lake pH • Also broadcast aerially to alkalize entire watersheds

26. CO2 chemistry: Hardness • Hardness - the total concentration of multi-valent (i.e. >2) cations • Ca+2 + Mg+2 + Fe +3 (when oxic) + Mn+2 (when oxic); all other multivalent cations are typically considered to be negligible • Sources- • Minerals such as limestone (Ca and Mg) and gypsum (Ca) • Water softeners and other water treatment processes such as reverse osmosis and ion exchange • Evaporation can increase hardness concentration • Drinking water effects (no real health effects) • Soap scums and water spots on glasses and tableware • Deposits (scaling) can cause clogging problems in pipes, boilers and cooling towers

27. SiO2 < 1 Water chemistry – Major ions Note: plant nutrients such as nitrate, ammonium and phosphate that can cause algae and weed overgrowth usually occur at 10’s or 100’s of parts-per-billion and along with other essential micronutrients usually represent <1% of the actual amount of cations or anions present in the water

28. Major ion concentrations - freshwater

29. Nutrients – phosphorus • Essential for plant growth • Usually the most limiting nutrient in lakes • Derives from phosphatic rock – abiotic, unlike nitrogen • No gas phase, but can come from atmosphere as fugitive dust • Adsorbs to soils • Naturally immobile unless soil is eroded or excess fertilizer is applied • Phosphorus moves with sediments

30. Nutrients – phosphorus • Not toxic • Algae have physical adaptations to acquire phosphorus • High affinity (low k) • APA • Storage • Luxury uptake • Single redox state • Phosphorus cycle is closely linked to the iron (Fe) cycle

31. Phosphorus – basic properties • No redox or respiration reactions directly involved (organisms are not generating energy from P chemistry) • PO4–3 highly adsorptive to cationic sites (Al+3, Fe+3, Ca+2) • Concentration strongly affected by iron redox reactions • Ferric (+3) – insoluble floc • Ferrous (+2) – soluble, unless it reacts with sulfide, causing FeS to precipitate

32. Phosphorus levels in the environment • Major factors affecting phosphorus levels, cycling, and impacts on water quality include: • Soil properties • Land use and disturbance • Transport associated with runoff

33. Where does phosphorus come from?

34. Phosphorus – external sources • Nonpoint sources • Watershed discharge from tributaries • Atmospheric deposition • Point sources • Wastewater • Industrial discharges

35. Phosphorus – nonpoint sources • Watershed discharges from tributaries • Strongly tied to erosion (land use management) • Stormwater runoff (urban and rural) • Agricultural and feedlot runoff • On-site domestic sewage (failing septic systems) • Sanitary sewer ex-filtration (leaky sewer lines) • Atmospheric deposition • Often an issue in more pristine areas • Arises from dust, soil particles, waterfowl

36. Phosphorus – point sources • Wastewater • Municipal treated wastewater • Combined sewer overflows (CSOs) • Sanitary sewer overflows (SSOs) • Industrial discharges

37. Phosphorus – internal sources • Mixing from anoxic bottom waters with high phosphate levels is closely tied to iron redox reactions • O2 > 1 mg/L – Insoluble ferric (+3) salts form that precipitate and settle out, adsorbing PO4-3 • O2 < 1 mg/L (anoxic) – ferric ion reduced to soluble ferrous ion (Fe+2) – allowing sediment phosphate to diffuse up into the water • Wind mixing (storms and fall de-stratification) can re-inject high P water to the surface, causing algal blooms

38. Phosphorus – Lake budget

39. Nutrients – phosphorus cycle • Major pools and sources of P in lakes • “Natural” inputs are mostly associated with particles • Wastewater is mostly dissolved phosphate • P is rapidly removed from solution by algal-bacterial uptake or by adsorption to sediments

40. Phosphorus cycling – major sources • Sewage • Dissolved • Tributaries and deposition • Particulate • Erosion • Particulate • Sediments • Particulate and dissolved

41. Phosphorus cycling – internal recycling • Rapid PO4-3 recycling • Bacterial uptake • Algal uptake • Adsorption to particles • Detritus mineralization • Zooplankton excretion • Fish excretion

42. Modified from Horne and Goldman, 1994. Limnology. McGraw Hill. Phosphorus cycle – major transformations • The whole phosphorus cycle

43. Nitrogen – basic properties • Nitrogen is relatively scarce in some watersheds and therefore can be a limiting nutrient in aquatic systems • Essential nutrient (e.g., amino acids, nucleic acids, proteins, chlorophyll) • Differences from phosphorus • Not geological in origin • Unlike phosphorus, there are many oxidation states

44. Nitrogen – biologically available forms • N2 – major source, but usable by only a few species • Blue green algae (cyanobacteria) and anaerobic bacteria • Nitrate (NO3-) and ammonium (NH4+) – major forms of “combined” nitrogen for plant uptake • Also called dissolved inorganic nitrogen (DIN) • Total nitrogen (TN) – includes: • DIN + dissolved organic nitrogen (DON) + particulate nitrogen

45. Nitrogen – general properties • Essential for plant growth • Not typically limiting but can be in: • Highly enriched lakes • Pristine, unproductive lakes located in watersheds with nitrogen-poor soils • Estuaries, open ocean • Lots of input from the atmosphere • Combustion NO2, fertilizer dust

46. Nitrogen – general properties • Mobile – in the form of nitrate (soluble), it goes wherever water flows • Ammonium (NH4+) adsorbs to soil particles • Blue green algae can fix nitrogen (N2) from the atmosphere • Nitrogen has many redox states and is involved in many bacterial transformations

47. Nitrogen – sources • Atmospheric deposition • Wet and dry deposition (NO3- and NH4+) • Combustion gases (power plants, vehicle exhaust, acid rain), dust, fertilizers • Streams and groundwater (mostly NO3-) • Sewage and feedlots (NO3- and NH4+) • Agricultural runoff (NO3- and NH4+) • Regeneration from aquatic sediments and the hypoliminion (NH4+)

48. Nitrogen - toxicity • Methemoglobinemia – “blue baby” syndrome • > 10 mg/L NO3--N or > 1 mg/L NO2--N in well water • Usually related to agricultural contamination of groundwater • NO3- – possible cause of stomach/colon cancer • Un-ionized NH4+ can be toxic to coldwater fish • NH4OH and NH3 at high pH • N2O and NOx – contribute to smog, haze, ozone layer depletion, acid rain

49. Nitrogen – many oxidation states • Unlike P there are many oxidation states • Organisms have evolved to make use of these oxidation-reduction states for energy metabolism and biosynthesis

50. Nitrogen – bacterial transformations • Decomposition • Nitrification • Denitrification • Nitrogen fixation