Communities physical processes interconnect to form ecosystems Ecosystems

Communities + physical processes interconnect to form ecosystems Ecosystems are connected by: 1. energy flow between trophic levels; energy also released as heat energy into environment • Autotrophs = 10 producers – Primary productivity = amount of C fixed in an ecosystem by: CO 2 + H 20 + light --> (C 6 H 1206) + O 2 • Heterotrophs – Consumers: herbivores, omnivores, carnivores – Decomposers 2. Nutrient and water cycling (Biogeochemical cycling) 1. water, 2. carbon, 3. nitrogen, 4. phosphorus Humans have impacts on ecosystems

Energy flow (also refer to Fig. 20. 3 & 20. 7) • Only ~10 % transfers between levels. • Loss due to: Metabolism and waste

Bio. Geo. Chemical cycles = Nutrients cycle btwn biotic & abiotic forms Definitions of: Reservoirs and fluxes, mineralization, fixation/assimilation Flux rate dependent on ? Major Biogeochemical cycles: Atmospheric cycles = carbon and nitrogen; Sedimentary = phosphorus; Hydrologic 9 9

Carbon • Reservoirs = ? • Transformations?

Nitrogen - why is N impt? - what is symbiotic N fixation? - cause and results of excess N? N 2 Nitrogen fixation Dead organisms Rhizobium Decomposition Fungi, bacteria, inverts Plants Organic matter Mineralization Assimilation Denitrification Anaerobic bacteria Fungi, bacteria NH 4+ NO 2 - NO 3 - ammonium nitrite nitrate Industrial inputs: Fertilizer, atmospheric deposition

Phosphorus Pools? Transformations? Cause and consequences of excess P in aquatic systems

–PO 4 - is difficult to acquire – 80 % of plants have mycorrhizal symbionts to help (fungi); other benefits (+H 20) offset cost

• Biotic factors increase nutrient retention – how? • Excessive disturbance decreases retention – why?

Human Impact 1 • Reduced biodiversity, habitat loss, habitat fragmentation

Human Impact 2 • Pollution: air, water, land • Reduction in ozone layer

Human Impact 3 - Excess N & P

Human Impact 4 - Accelerated release of CO 2