Zoology 315: Limnology Nitrogen & phosphorus Abby Popp July 3rd, 2006 INTRO 1. Nutrients defined: Macronutrients: Micronutrients: Biogeochemistry: cycling of biologically important elements between living (biotic) and non-living (abiotic) components of an ecosystem 2. Studying nutrient dynamics Approach #1: BudgetsApproach #2: Cycles Pools: Fluxes: 3. Types of nutrient cycles atmospheric: geologic: combination: 4. Nutrient limitation Liebig’s Law of the Minimum The limiting nutrient is the nutrient whose ratio of supply to demand is… Redfield Ratio If N:P > 20 If N:P < 10Thought Question #0  A given part of a lake has concentrations of nutrients as follows:  42,400 mg/m3 Carbon  2,400 mg/m3 Nitrogen  300 mg/m3 Phosphorus  Given the Redfield ratio of 106 C : 16 N : 1 P, which of these nutrients is the limiting one? NITROGEN 1. Forms of nitrogen in aquatic systems Organic N Inorganic N Gaseous forms…N comes mainly from air, but sometimes… 2. Transformations of nitrogen Biotic uptake Mineralization Fixation Nitrification (needs O2) Denitrification (needs anoxia)Pretend you’re an N2 molecule…. N inputs to lakes N losses from lakes Nitrogen & oxygen O2 presence/absence has major effect on N cycle O2 present: O2 absent:Thought Question #1  Which process in the N-cycle needs oxygen? What does this process do?  Which process happens when there is no oxygen?  What form of nitrogen is most easily consumed by plants? Draw the expected profiles for NH4 and NO3 in an oligotrophic and eutrophic lake. Impacts of nitrate in the water supplyThought Question #2:  What are options for reducing the amount of nitrate in surface waters? o What two processes decrease the amount of nitrate? o How could you facilitate those processes? (don’t be afraid to be creative!) PHOSPHORUS 1a. Sources of Phosphorus Geologic cycle: Anthropogenic:1b. Forms of Phosphorus Total P: all P in the sample Inorganic P: Organic P: 2. Phosphorus transformations Biotic uptake (assimilation): Mineralization: Precipitation/dissolution Sorption/desorption Phosphate(PO43-) -3 charge means it’s very reactive Example: Fe3+ + PO43- →FePO4 If no O2 is present in the hypolimnion…P cycling in the epilimnion: P cycling in the hypolimnion: P cycling in the whole lake:“Typical” P profiles 3. Phosphorus in lakes & rivers Excess P in lakes: What to do about it? Reduce P within the lake Reduce P entering the