Lecture 8: Biogeochemical cycles PDF

Lecture 8: Biogeochemical cycles Dr. Mansoor Hamed AlJahdhami [email protected]  Review question ❑ Formation and contribution of HNO3 to the acid precipitation involves ____________. A. water cycle B. carbon cycle C. nitrogen cycle...

Lecture 8: Biogeochemical cycles Dr. Mansoor Hamed AlJahdhami [email protected]  Review question ❑ Formation and contribution of HNO3 to the acid precipitation involves ____________. A. water cycle B. carbon cycle C. nitrogen cycle D. sulfur cycle E. two of the above 2  Reading materials CHAPTER 2 Environmental Systems: Matter, Energy and Life 2.6 Biogeochemical cycles and life processes 📄 Pages: 41 ‒ 48 3  Learning outcomes Describe the importance of P and S cycles for the ecosystems Understand how human activities can interfere with P and S and their consequences 4  The phosphorus cycle Phosphorous (P) Essential nutrient for plants and animals ❑ For what? Not very common in the biosphere Found in soil and rock ❑ Sedimentary rocks (primary sinks). In which chemical species? ✔ Released slowly by the action of weathering and acid rain Does not enter the atmosphere ❑ Why? 5 The phosphorus cycle 6  The phosphorus cycle Phosphorous (P) P in Sedimentary rocks → soil → producers → consumers ❑ P is found in form of phosphate ion (PO43–) or hydrogen phosphate (HPO42–) ❑ P is slowly releasing from terrestrial rocks by weathering and action of acid rain ❑ Producer organisms take in inorganic P (in what form?) → incorporated into organic molecules → eventually pass them to consumers P in producers and consumers → environment 7 The phosphorus cycle 8 The phosphorus cycle 9  Human interference with the phosphorus cycle – Anthropogenic activities can alter P-cycle How? P is mined in large quantities to make detergent and inorganic fertilizers 🢂 excess P Clear-cutting of tropical habitats for agriculture 🢂 less amount of available P Runoff from feedlots, fertilizers and discharge of municipal sewage plants to rivers and oceans 🢂 excess P 10 ❑ What are the consequences?  Human interference with the phosphorus cycle – Anthropogenic activities can alter P-cycle Excess P in water bodies 🢂 stimulate explosive growth of algae and blue-green photosynthetic bacteria (cyanobacteria) 🢂 ? 🢂 kill other aquatic organisms Mechanisms? © 2013 Regents of the University of Michigan 11  Algal blooms in Omani water Red tide as an example Different causes? 12 Algal blooms in Omani water 13 Algal blooms in Omani water 14 Human interference with the phosphorus cycle – Anthropogenic activities can alter P-cycle 15  The sulfur cycle Sulfur (S) S is a minor but essential component of proteins S compounds are determinant of acidity of precipitation, surface water and soil S particles and tiny air droplets may act as critical regulator of global climate. How? 16  The sulfur cycle Aerosol particles that evolve from biogenic-derived DMS emissions play a role in the global radiation balance © Atmospheric Chemistry Group 17 The sulfur cycle 18  The sulfur cycle S is commonly found in underground deposits or near natural hot springs or volcanoes S assumes many oxidation states –1, – 2, 0, +1, +2, +3, +4, +5, +6 S in lithosphere: 13th most abundant element in Earth’s crust High S content in sedimentary rocks (e.g. iron disulfide‒FeS2, calcium sulfate‒CaSO4 …etc.) 19 S mobilized by slow weathering of rock material 🢂 runoff  The sulfur cycle S in hydrosphere: Main storage form in oceans is dissolved sulfate Dimethyl sulfide (DMS, (CH3)2S): most volatile S compound from seawater ❑ Produced by algal (phytoplankton) and bacterial decay Rivers transport about 110 million tons of S per year to oceans ❑ S compounds: 2nd most abundant in rivers ❑ High fluctuations in S concentrations with seasons 20  The sulfur cycle S in soil and biosphere: SO42‒: dominant form in soil which enters biosphere through plant uptake 🢂 food chains Main sources: ❑ Atmospheric deposition ❑ Weathering of rocks ❑ Decay of organic matter ❑ Anthropogenic fertilizers, pesticides and irrigation water From biosphere to soil through decomposition (SO42‒ form) Anaerobic decomposition releases hydrogen sulfide (H2S) 21  The sulfur cycle S in atmosphere: Carbonyl sulfide (COS): most abundant but inert ❑ Produced by decomposition processes ❑ Sinks: stratospheric photolysis + tropospheric photochemical reactions Carbon disulfide (CS2): more reactive than COS ❑ Sink: photochemical reactions ❑ Small contribution from fossil fuel combustion Dimethyl sulfide ((CH3)2S): ❑ Much greater concentrations than COS and CS2 22 ❑ Rapidly oxidized to SO 🢂 acid rain deposition  The sulfur cycle S in atmosphere: Hydrogen sulfide (H2S): released by anaerobic decay ❑ Mainly produced during anaerobic decay ❑ Highly reactive and removed by reaction with OH– and COS Sulfur dioxide (SO2): ❑ Mainly from burning of fossil fuels ❑ Acid rain deposition Sulfate aerosols (SO42‒): mainly from sea spray ❑ Mainly from sea spray 23 ❑ Annually, 3.3 million tons from anthropogenic sources Human interference with the sulfur cycle – Anthropogenic activities can alter S-cycle 24  Human interference with the sulfur cycle – Anthropogenic activities can alter S-cycle Release large quantities of S mainly through burning of fossil fuels Anthropogenic S emissions exceed natural emissions. Then what? ❑ Acid rain (due to what?) is serious problem in many areas ❑ SO2 and SO42– aerosols cause human health problems, damage buildings and vegetation and reduce visibility ❑ SO2 and SO42– aerosols absorb UV radiation and create cloud cover 🢂 cools cities and may be offsetting greenhouse effect of rising [CO2] 25  Human interference with the sulfur cycle – Anthropogenic activities can alter S-cycle The Great London Smog in 1952 Sulfur dioxide affects both people and plants 26  The sulfur cycle Cools cities and may be offsetting greenhouse effect of rising [CO2] © Atmospheric Chemistry Group 27 Questions? 28