Oceanography Lecture 16

Transcription

1 Only those that intend the absurd, achieve the impossible Escher Oceanography Lecture 16 a. Dissolved gases b. The chemistry of Life and Biogeochemical Cycles c. Nutrient cycles d. The carbonate system and the Carbon cycle e. Coastal hypoxia Dissolved gases in water Take a break, Grab a soda Let s assume we have a clear bottle of soda You pop the lid! gas escapes! (pressure) You shake it! more gas escapes! (mixing) You warm it up! even more gas escapes! (temperature) Does it stop?!when final gas content of soda is at equilibrium with temperature and pressure Dissolved gases in water Take a break, Grab a soda The total amount of gas that can be dissolved eventually reaches an equilibrium concentration which is proportional to: - Atmospheric concentration of gas in atmosphere - Temperature, - Pressure, - Salinity of water. The amount of gas usually " as: P " T # S #

2 Density structure of the Ocean Oxygen in the Ocean CO 2 (gas) + H 2 O + Energy $ H 12 C 6 O 6 (sugar) + O 2 (gas) Photosynthesis possible only in photic zone (0-200 m) Oxygen minimum (utilization) at pycnocline O 2 Minimum Dissolved gases in the Ocean CO 2 (gas) + H 2 O + Energy $ H 12 C 6 O 6 (sugar) + O 2 (gas) Photosynthesis only in possible in photic zone (0-200 m) Oxygen limitation (utilization) at pycnocline O 2 Minimum Dissolved gases in the Ocean Temperature is the most important controlling factor! The most abundant gases in the atmosphere: - N 2 (78%) - O 2 (21%) - Argon (0.9%) - CO 2 (0.03%) The most abundant gases in the Oceans: - CO 2 (94.3%). Much more soluble! - N 2 (3.4%) - O 2 (2%) - Argon (0.3%) Difference due to the reactivity of CO 2 is seawater leading to the various carbonate and bicarbonate equilibria CO 2 (gas) + H 2 O $ H 2 CO 3 $ H + + HCO 3 - $ H + + CO 3

3 Dissolved gases in the Ocean Dissolved gases in the Ocean Argon and the other noble gases (He, Ne, Kr, and Ra) and Nitrogen are essentially unreactive in the Oceans: Conservative gases In contrast, CO 2 and O 2 concentrations are altered by many biological and chemical processes in the sea. Non-conservative gases Photosynthesis/Respiration: CO 2 (gas) + H 2 O + Energy % H 12 C 6 O 6 (sugar) + O 2 (gas) H 12 C 6 O 6 (sugar) + O 2 (gas) % CO 2 (gas) + H 2 O + Energy CO 2 (gas) + H 2 O + Energy $ H 12 C 6 O 6 (sugar) + O 2 (gas) Photosynthesis only possible in photic zone (0-200 m) Oxygen limitation (utilization) at pycnocline O 2 Minimum Defining the Ecosystem Biology is not the sole subject of ecosystem studies! The flow of energy and materials (i.e. water, chemicals) into and out of biological communities defines the main theme of ecosystem studies Defining the Ocean Ecosystem There exists an inseparable relationship between the flow of energy and the flow of nutrient elements (i.e. N, P, K, Ca, etc)

4 Biogeochemical Cycles Chemical Elements (the Periodic Table) and those essential for life A simple thing, really " Of the 103 elements in the Periodic Table, only 24 are required by organisms " Macronutrients: Required in large amount ( Big Six : C, N, P, S, O, H) " Micronutrients: small or moderate amount Required elt Toxic elt Required for some life forms Chemical Elements - Essential for life Carbon " Carbon forms three-dimensional molecules of large size and complexity in organic (carbon-containing) compounds that form large molecules (amino acids, sugars, enzymes, DNA), and other chemicals vital to life on Earth. Chemistry of Life Element Symbol Representative Use Major Components >100,000 of every M atoms Carbon C All organic molecules Oxygen O Almost all organic molecules Hydrogen H All organic molecules Nitrogen N Proteins, Nucleic acids Macronutrients 1,000 < per M atoms <100,000 Phosphorus P Nucleic acids, teeth/bones/shell Sulfur S Proteins, cell division Calcium Ca Shell, bone, coral, teeth Silicon Si Hard parts Sodium Na Body fluids, osmotic regulation Magnesium Mg Osmotic regulation, chlorophyll Chlorine Cl ATP formation, nerve discharge Potassium K Nerve discharge, osmotic balance Iodine I Thyroid hormone Micronutrients < 1,000 of every M atoms Iron Fe Electron transport, N assimilation Copper Cu Electron transport Zinc Zn Nucleic acid replication

5 Chemical Elements - Essential for life Nitrogen " Nitrogen (along with carbon) is the essential element that allows formation of amino acids (! proteins) and DNA. Proteins contain up to 16% N Chemical Elements - Essential for life Phosphorus " Phosphorus is the energy element occurring in compounds called ATP and ADP important for energy transfer processes and DNA. Chemical Elements - Essential for life Carbon:Nitrogen:Phosphorus Ratios " Organisms actively concentrate certain elements essential for life:! Algae concentrate Iron (Fe) 100,000 times vs. its concentration in the Ocean Most organisms keep a rather constant chemical composition! Algae and plankton C:N:P ratio of 106:16:1 (Redfield Ratio)! Soil microbes maintain a relatively constant proportion of nutrients in their biomass (and at higher levels than the OM they decompose) Chemical Elements - Essential for life Availability of some elements (particularly N & P) is often limited and the supply of these elements may control the rate (or type) of primary production in ocean ecosystems. External sources of nutrients are varied and depend of nutrient! Annual circulation dominates most inputs of limiting elements (N, P, K)

6 Biogeochemical cycles in the Ocean The carbonate system and the Carbon cycle CO 2 (gas) dissolves readily in water and forms carbonic acid (H 2 CO 3 ). However, at ph of natural waters, carbonic acid equilibrates as bicarbonate (HCO 3- : 80%) CO 2 (gas) + H 2 O $ H 2 CO 3 $ H + + HCO 3 - $ H + + CO 3 CO 2 (gas) + H 2 O + Nutrients (N,P) + Energy $ OM + O 2 (gas) The carbonate system and the Carbon cycle The carbonate system and the Carbon cycle Ca + + CO 3 $ CaCO 3 (solid) Formation of CaCO 3 skeleton parts by micro-organisms as hard part:! foraminifers, coccolithophorids, pteropods to precipitate CaCO 3. CO 2 (gas) + H 2 O $ H 2 CO 3 $ H + + HCO 3 - $ H + + CO 3 + Ca 2+ $ CaCO 3

7 The carbonate system and the Carbon cycle Ca + + CO 3 $ CaCO 3 (solid) Ocean surface waters are nearly everywhere supersaturated with respect to calcium carbonate. However, no spontaneous precipitation occurs! (inhibition from Mg 2+ in solution)!intervention of marine organisms (foraminifers, coccolithophorids, pteropods) to precipitate CaCO 3. - CaCO 3 dissolves readily with decreasing temperature and increasing pressure. Also, - Calcite and Aragonite have the same formula but different crystalline structure. Aragonite is less stable. The carbonate system and the Carbon cycle As organic matter (OM) rains to the sea floor, it is mostly degraded (>90% regeneration!)! production of CO 2! increased formation of acid! increased dissolution of carbonates! CO 2 (gas) + H 2 O $ H 2 CO 3 $ H + + HCO 3 - $ H + + CO 3 $ CaCO 3 Where should you find carbonate sedimentation? Where should you not find it? The carbonate system and the Carbon cycle Where should you find carbonate sedimentation? Where should you not find it? The carbonate system and the Carbon cycle Carbonate Compensation Depth (CCD): the depth at which all carbonates have dissolved! The CCD is shallower for Aragonite that for calcite CO 2 (gas) + H 2 O $ H 2 CO 3 $ H + + HCO 3 - $ H + + CO 3 $ CaCO 3 CO 2 (gas) + H 2 O $ H 2 CO 3 $ H + + HCO 3 - $ H + + CO 3 $ CaCO 3

8 The Carbon cycle Different timescales Most C in carbonate rocks (85%) Second largest reservoir in soil and sediment OM (15%) Dissolved C in Oceans (0.08%) Fossil fuels (0.02%) Additional less significant reservoirs (Atmosphere, Biosphere, etc) General equilibrium: 75%! Biogeochemical cycles in the Ocean CO 2 (gas) + H 2 O + Nutrients (N,P) + Energy $ OM + O 2 (gas) Dissolved (trace) nutrients in the Ocean The silicon cycle Phosphorus Nitrogen Silicon behaves like a nutrient! Minor element! essential for formation of frustules! undersaturated in the Oceans! Micro-organisms (diatoms, radiolaria) can still use it!! More soluble in cold waters.! No Compensation Depth: Slow dissolution despite undersaturation!! General equilibrium: 10%! CO 2 (gas) + H 2 O + Nutrients (N,P) + Energy $ OM + O 2 (gas) Where should you find silicate sedimentation? Where should you not find it?

9 Distribution of Ocean Sediments Hardness and detergents The hard and soft appellation of waters reflect the fact that doubly charged Ca 2+ and Mg 2+ ions can precipitate detergents (molecules with long hydrocarbon chains and polar head groups) Detergents are excellent cleanser because of their ability to act as emulsifying agents (an emulsifier is capable of dispersing one liquid into another immiscible liquid). Disadvantages: As salts of weak acids, they are converted by mineral acids into free fatty acids: CH 3 (CH 2 ) 16 CO 2 - Na + + HCl! CH 3 (CH 2 ) 16 CO 2 H + Na + + Cl - Soaps form insoluble salts in hard water, such as water containing magnesium, calcium, or iron: 2 CH 3 (CH 2 ) 16 CO 2 - Na + + Mg 2+! [CH 3 (CH 2 ) 16 CO 2 ] 2 Mg Na + Where should you find silicate sedimentation? Where should you not find it? Hardness and detergents Addition of chelating agents ( (builder)) can bind with cations through multiple bonds. Particularly effective chelating agents: The first is a limiting nutrient, the other two biodegrade slowly (T dependent) and mobilize toxic chemical! Phosphorus Control Measures A U.S. Case Study Nitrilotriactetic acid (NTA) Sodium Tripolyphosphate (STP) EDTA Source: USGS 1999 As more States passed detergent-bans legislation, the industry was faced with maintaining duplicate inventories of detergent around the Nation and ultimately decided (cost effective) to phase out phosphorus use in domestic detergents Phosphates are still permitted in dishwashing detergents and industrial cleaning agents.

10 Phosphorus Control Measures A U.S. Case Study Phosphorus Control Measures A U.S. Case Study Source: USGS 1999 As more States passed detergent-bans legislation, the industry was faced with maintaining duplicate inventories of detergent around the Nation and ultimately decided (cost effective) to phase out phosphorus use in domestic detergents Phosphates are still permitted in dishwashing detergents and industrial cleaning agents. Source: USGS 1999 Only about 15% of municipal waste-water treatment plants (~40% of total municipal waste-water discharge) were required to monitor phosphorus Only 7% have phosphorus limitations ( mg/l) through tertiary treatment! Phosphorus Control Measures: A U.S. Case Study Non-Point Sources of Phosphorus Phosphorus from manure and commercial fertilizers Phosphate ban reduced annual loads to Lake Erie (&86%) and Chesapeake Bay (&( 55%) Temporal trend in declining phosphorus levels in surface waters (except Southeast). However, at least one third of all hydrological units studied showed more than 1/2 of total phosphorus concentrations exceeding the EPA recommended limit in flowing waters (0.1 mg/l)

11 Coastal Hypoxia Nutrient over-enrichment from anthropogenic sources is one of the major stresses impacting coastal ecosystems. Generally, excess nutrients lead to eutrophic conditions and increased algal production which in turn increases the availability of organic carbon within the aquatic ecosystem. Gulf Coast Hypoxia Nitrogen is the most significant nutrient controlling algal growth in coastal waters, while phosphorus is the most significant nutrient in fresh water Both the near-coastal hydrodynamics that generate water column stratification and the nutrients that fuel primary productivity contribute to the formation of hypoxic zones. Human activities on land can add excess nutrients to coastal areas or compromise the ability of ecosystems to remove nutrients either from the landscape or from the waterways themselves. (source: USGC) Coastal Hypoxia Gulf of Mexico: a large area of the Louisiana continental shelf with seasonallydepleted oxygen levels (< 2mg/l). Most aquatic species cannot survive at such low oxygen levels. The oxygen depletion (hypoxia) begins in late spring, reaches a maximum in midsummer, and disappears in the fall. After the Mississippi River flood of 1993, the spatial extent of this zone more than doubled in size, to over 18,000 km 2, and has remained about that size each year through midsummer The hypoxic zone forms in the middle of the most important commercial and recreational fisheries in the coterminous United States and could threaten the economy of this region of the Gulf. Coastal Hypoxia Estimated areal extent of bottom water hypoxia from mid-summer cruise in the period km (source: Louisiana Universities marine Consortium)

12 10 6 metric tons/year Gulf Coast Hypoxia Long-term record of drainage basin changes: a) annual amount of fertilizer application Gulf Coast Hypoxia Nitrogen yields from the Mississippi River Drainage Basin About 56% of the nitrate transported to the Gulf enters the Mississippi River above the Ohio River. The Ohio basin subsequently adds another 34% of the nitrate load of acres b) area artificially drained Gulf Coast Hypoxia On average, 61% of the nitrogen load is nitrate; 24% is dissolved organic nitrogen. The most significant nutrient trend has been nitrate loads, which have almost tripled from 0.33 million metric tons per year during to 0.95 million metric tons per year during That s it folks Streamflow Organic N Nitrate