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Nutrients and Water Quality Eutrophication - too many nutrients • Adding nutrients to a water system can upset the balance • Similar to adding BOD • River or lake systems are in a delicate balance • Adding excess nutrients causes the wrong things to grow drake.marin.k12.ca.us Law of the barrel Sera 17 Limiting Nutrients • Nitrogen and phosphorus are generally the two most limiting nutrients in water systems • Both macronutrients for plant growth – This includes plants on the farm as well as plants in the stream • Adding excess causes excess growth including algae • What effects would this have on system? N is responsible • For lush green color • Too much N can cause excess growth – Plants do not have sufficient structural integrity to support growth – Lodging • N deficiency = yellow leaves – ‘Chlorosis’ 1 Nitrogen basics • In atmosphere N2 gas (77% of atmosphere) • Where does soil N come from? Fertilizers • Organic • Inorganic – Manures – Anhydrous ammonia – Composts – Ammonium nitrate – Biosolids – Urea How does it go from atmosphere to soil? • Lightning N2 NO3 • Bacterial associations One Example N forms • In soils 3 forms – Organic N ( in plant and animal tissue) N cycle Organic N N2 gas – Mineral N • NO3• NH4+ • Transformations in the form of N are explained using the N cycle Organic N NO3 , NH4 Mineral N Soil microbes Or water microbes 2 All transformations of N in soil are microbially mediated • Eating is the first step • This is what happens when microbes eat SOM, they need N to use the C • Mineral N to organic N – Immobilization • Organic N to NH4+ or NO3 – Mineralization Energy, respiration reactions • NH4 + to NO3 - - nitrosimonas, nitrobacter – Nitrification • NO3- to gaseous N – Denitrification • Denitrification – Occurs in anaerobic environments – Wetlands, soil microsites Phosphorous Wetlands or water without O2 • When water is still and O2 is depleted, the microbes will need an electron acceptor (remember eating) • Primary function of wetlands • Very important plant nutrient • Plants contain .2 % P • Used in many functions including ATP, seed germination, photosynthesis, all growth and metabolism • P deficiency = purple leaves P deficiency Sources of P • TSP – Triple super phosphate – Phosphate mines in ID and FLA • Organic amendments – Biosolids, manures – Not all P is equally available 3 SERA 17 Tendency to over fertilize with P • Relatively immobile in soils • Assure that you have sufficient amount • Very high soil P • So when soil erodes off of the field, the river or stream gets all that P laden sediment USGS Sediment - primary source of P Irrigation USGS Irrigation Irrigation 4 Irrigation Irrigation Irrigation Irrigation 5