BIOL 203 Lecture 05: Movement of Elements in Ecosystems PDF

Lecture 05 Movement of elements in ecosystems BIOL 203 October 4th, 2024 1 Learning objectives 1. Describe how the hydrologic cycle moves many elements through ecosystems 2. Explain why the carbon cycle is closely tied to the movement of energy 3. I...

Lecture 05 Movement of elements in ecosystems BIOL 203 October 4th, 2024 1 Learning objectives 1. Describe how the hydrologic cycle moves many elements through ecosystems 2. Explain why the carbon cycle is closely tied to the movement of energy 3. Illustrate the ways in which nitrogen cycles through ecosystems in many different forms 2 Learning objectives 4. Describe how the phosphorus cycle moves between land and water 5. Explain why most nutrients are generated from organic matter in the soil in terrestrial ecosystems 6. Illustrate why most nutrients are generated from organic matter in the sediments in aquatic ecosystems 3 A dead zone at the mouth of the Mississippi river In summer, large amounts of nutrients deposited at mouth of Mississippi Drainage from 41% of USA Combined with warmer temperatures, leads to algal bloom 4 A dead zone at the mouth of the Mississippi river As algae die, broken down by decomposers, results in large use of O2 Oxygen becomes so low it cannot support life, creates a dead zone Can be >22,000 km2 5 Global dead zones 1910: 5 DZ 1980s: 87 DZ Present: >500 DZ Due to agriculture, climate change 6  The hydrologic cycle moves Key concept many elements through ecosystems 7 The hydrologic cycle moves many elements through ecosystems The movement of water through ecosystems and the atmosphere Driven by evaporation, transpiration, and precipitation Key distributor of elements 8 The hydrologic cycle moves many elements through ecosystems When precipitation falls in terrestrial ecosystems, three possibly pathways: Run-off Groundwater Absorbed by plants 9 The hydrologic cycle moves many elements through ecosystems In terrestrial systems, precipitation exceeds evaporation (gains water) Excess precipitation is transported via runoff/groundwater into aquatic systems In aquatic systems, evaporation exceeds precipitation (loses water) Evaporated water is transported through atmosphere to fall on terrestrial environments No net loss/gain through entire biosphere 10  Human impacts on the hydrologic cycle Changes in one part of water cycle will influence other parts Developed areas tend to have more impervious surfaces, more run-off and soil erosion Events such as logging/fires can have significant impacts E.g.) 2021 flooding in BC Gillett et al., 2022 11 Concept check What are three pathways that water can take when precipitation falls on terrestrial ecosystems? How does tree removal affect the hydrologic cycle? 12  The carbon cycle Key concept is closely tied to the movement of energy 13 The carbon cycle is closely tied to the movement of energy Movement of carbon largely follows the same paths as the movement of energy Reservoirs include hydrosphere, atmosphere, biosphere, lithosphere Six types of transformations 14 Photosynthesis and respiration Photosynthesis pulls carbon from atmosphere to make sugars Respiration releases carbon to atmosphere (CO2, CH4) 15 Exchange CO2 can be exchanged between aquatic ecosystems and the atmosphere Movement in both directions, little net transfer over time Some dissolved CO2 used for photosynthesis, some ends of as CaCO3, becomes ocean sediment 16 Burial and sedimentation Burial and sedimentation can lock of carbon millions of years Carbon moves very slowly through these pools Eventually becomes fossil fuels 17 Extraction and combustion Extraction pulls fossil fuels from deep soils/sediments Combustion release organic carbon into atmosphere as CO2 18 Human impact on the carbon cycle We can measure historical CO2 levels using bubbles in ice cores Current concentration of CO2 is 35% higher than peak over past 400k years Extraction/combustion 19 Concept check What are some ways that carbon is pulled from the atmosphere? Ways it is added to the atmosphere? 20  Nitrogen cycles through Key concept ecosystems in many different forms 21 Nitrogen cycles through ecosystems in many different forms Nitrogen (N) is an important component of amino acids and nucleic acids; prevalent in atmosphere Reservoirs include hydrosphere, atmosphere, biosphere, lithosphere Five major transformation 22 Nitrogen fixation Nitrogen fixation = process of converting atmospheric nitrogen into forms usable by producers N2 → NH3 Usually converted to ammonium (NH4+) or nitrate (NO3-) Cyanobacteria and some bacteria can carry out biotic fixation 23 Nitrogen fixation Abiotic processes can also produce NO3- Lightning converts N2 into NO3- in the atmosphere (high energy) Wildfires/fossil fuels produce NO3- during combustion; released to atmosphere Falls to ground with precipitation 24 Nitrification Nitrification is a process where ammonium is converted into nitrite and then nitrate NH4+ → NO2- → NO3- Carried out by prokaryotes; requires oxygen Nitrosomonas/Nitrosococcus (NO2-) Nitrobacter/Nitrococcus (NO3-) 25 Assimilation and mineralization Producers incorporate NH4+/NO3- into their tissues (assimilation) Consumers can further assimilate during ingestion or excrete as waste Waste broken down into ammonia/inorganic compounds (mineralization) 26 Denitrification NO3- highly water soluble, leach out of soils, settle in anaerobic sediments Under these conditions, converts back into nitrites, then nitric oxide (Pseudomonas denitrificans) NO3- → NO2- → NO 27 Denitrification Additional reactions produce nitrogen gas NO → N2O → N2 Denitrification 28 Human impacts on nitrogen cycle Human activities have nearly doubled nitrogen inputs to terrestrial ecosystems (fertilizers, nitrogen-fixing crops, combustion of fossil fuels) Can affect ecosystems E.g.) Productivity and species richness 29 Concept check What are three processes that cause nitrogen fixation? Why/how does human production of nitrogen fertilizers alter plant species richness? 30  Phosphorus Key concept cycles between land and water 31 Phosphorus cycles between land and water Phosphorus is critical for building scales/bones, nucleic acids, ATP Commonly a limiting nutrient in both aquatic/terrestrial ecosystems Reservoirs include hydrosphere, biosphere, and lithosphere (limited atmosphere) 32 Phosphorus cycles between land and water Phosphorus does not have gas phase; limited cycling in atmosphere (dust) Rarely changes chemical form; usually exists as phosphate (PO43-) Plants uptake phosphate; animals eliminate via urine 33 Sedimentation, geological forces, and weathering Phosphate rocks (e.g., Ca(H2PO4)2) major source of phosphate Ca(H2PO4)2 precipitates out of ocean water, forms sedimentary rock Geologic forces expose rocks, weathering releases phosphate 34 Phosphorus cycles between land and water In terrestrial ecosystems, PO43- strongly binds soil or is taken up by plants Excess PO43- removed via runoff, leaching (enters groundwater) Soil erosion releases PO43- Carried to aquatic systems 35 Phosphorus cycles between land and water In aquatic ecosystems, PO43- taken up by producers Well-oxygenated waters causes PO43- to bind with Ca/Fe; precipitates, becomes sediment Slowly converted back into calcium phosphate rocks 36 Human impacts on phosphorus cycle Eutrophication = increase in productivity of aquatic ecosystems Cultural eutrophication = eutrophication caused by human activities 37 Concept check What are the two paths dissolved phosphates can take in aquatic environments? 38  In terrestrial ecosystems, Key concept most nutrients are generated from organic matter in the soil 39 In terrestrial ecosystems, most nutrients are generated from organic matter in the soil Terrestrial ecosystems constantly losing nutrients via leaching (groundwater dissolving nutrients, moving further down into soil), runoff Must balance inputs with losses For some (N, C), can get from atmosphere; others come from bedrock beneath soil (P) Weathering = physical/chemical alteration of rock material near Earth’s surface 40 Determining rate of weathering can be difficult Bedrock exists far below surface of the soil Solution: measure nutrients that enter via precipitation and the nutrients that leave by leaching If in equilibrium, difference between nutrients entering/nutrients leaving should equal weathering 41 Determining rate of weathering can be difficult Commonly measure nutrient inputs/outputs from a watershed = area of land that drains into a single stream/river Rate of weathering estimated by measuring net movement of Ca2+, K+, Na+, Mg2+ 42 Rates of weathering vary geographically Affected by regional temperature, precipitation, and soil conditions (e.g., acidic soils increase rate of weathering) E.g.) Watersheds in Quebec 43 The breakdown of organic matter Weathering is very slow, so primary production largely relies on rapid recycling of nutrients by breaking down organic matter In forests, break down occurs in four ways: 1. Soluble materials leach out of dead organic matter 2. Large detritivores consume dead organic matter 3. Fungi break down woody components/leaves 4. Bacteria decompose everything 44 Soluble materials leach out of organic matter Leaching removes 10-30% of soluble substances from organic matter Includes most organic salts, sugars, amino acids Left behind are complex carbohydrates (e.g., cellulose) and large organic compounds (e.g., lignin, proteins) Broken down by fungi/bacteria 45 Large detritovores consume organic matter Includes millipedes, earthworms, etc. Consume 30-45% of energy in leaf litter; much lower fraction in wood Break down organic matter via direct consumption, maceration into small pieces of detritus (increases surface- to-volume ratio) 46 Bacteria/fungi convert organic matter into inorganic nutrients Fungi can penetrate tissues of leaves/wood via hyphae, Reaches areas that bacteria/large detritovores cannot get to 47 Rates of decomposition are affected by several factors Temperature, pH, moisture, chemical composition (e.g., lignin) Fastest in the tropics; slower at northern latitudes Proportion of dead plant matter is ~20% biomass in temperature coniferous forests; 5% in temperate hardwood; 1-2% in tropical rainforests 48 Concept check What factors influence the rate at which organic matter is broken down? 49  In aquatic ecosystems, most nutrients Key Concept are generated from organic matter in sediments 50 In aquatic ecosystems, most nutrients are generated from organic matter in the sediments Most cycling of elements takes place in an aqueous medium, so processes are similar between terrestrial/aquatic systems, but the location differs In terrestrial systems, nutrients generated close to location where they are taken up by producers In aquatic systems, nutrients are generated from sediments; often far below where dominant producers located 51 In aquatic ecosystems, most nutrients are generated from organic matter in the sediments Decomposition also differs Terrestrial = aerobic is most common Aquatic = sediments deep under water, anaerobic most common Considerably slower 52 In streams and small, forested wetlands, decomposition process similar to terrestrial ecosystems Allochthonous inputs (dead leaves) fall into water; settle on bottom Leaching followed by maceration followed by decomposition by bacteria/fungi Affected by temperature and chemical composition of leaves 53 In rivers/lakes/oceans, organic matters accumulates in deep sediments Most nutrients come from sediments (benthos), slowly return to productive surface waters Explains differences in productivity between ecosystems (e.g., oceans lowest; wetlands highest) Stratification also reduces the availability of nutrients to surface waters 54 Concept check Why is ocean upwelling an important process in regenerating nutrients in deep ocean waters? Why is decomposition typically anaerobic in the deep waters of lakes and oceans? 55 Next class Evolutionary ecology (Chapter 6) Lab: Plant-pollinator interactions – Data Visualization and Analysis Bring your laptop + data 56