Nutrient Cycling in an Aquatic Ecosystem

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1 Nutrient Cycling in an Aquatic Ecosystem 2.1 Productivity 2.2 Oxygen 2.3 Salinity 2.4 Carbon 2.5 Nitrogen 2.6 Phosphorous 2.7 Iron 2.8 Sulphur 2.9 Silica

2 2.3 Salinity of Inland Waters The salinity of freshwaters is best expressed as the sum of the ionic composition of the eight major cations and anions in mass or milliequivalents per liter. Salinity is the correct chemical term for the ionic composition of fresh waters. It is best expressed in mg/l or meq/l. Salinity is governed by ionic contributions via leaching from rock and soil and runoff of the drainage basin, atmosphere precipitation and deposition, and the balance between evaporation and precipitation. The concentrations of major ions of many surface waters of the world tend to exist in the proportions of: Calcium is greater than Magnesium is greater or equals to Sodium is greater than Potassium and Carbonate is less than Bicarbonate is greater than Sulphate is greater than Chloride.

3 Salinity of Inland Waters 1. The total salinity of inland waters is usually dominated by four major cations (Ca ++, Mg ++, Na +, and K +) and four major anions (HCO 3 -, CO 3 --, SO 4 --, and Cl - ). 2. The salinity of surface waters has a world average concentration of about 120 mg/l, but varies among continents and with the lithology of the land masses.

4 Salinity of Inland Waters The three major mechanisms controlling the salinity of world surface water are rock dominance, atmospheric precipitation, and the evaporation-precipitation process. Waters of the rock dominated end of a spectrum are rich in calcium and bicarbonate ions. The chemical composition of lowsalinity waters, dominated by Sodium and Chloride, is influenced by dissolved salts derived from atmospheric precipitation derived from the ocean. The third factor is evaporation and fractional crystallisation with subsequent sedimentation of mineral salts.

5 Salinity of Inland Waters Concentrations of the cations Magnesium, Sodium, and Potassium and the major anion Chloride are relatively conservative, and undergo only minor spatial and temporal fluctuations within a lake from biotic utilization or biotically mediated environmental changes. Calcium, inorganic carbon, and sulphate are dynamic, and concentrations of these ions are strongly influenced by microbial metabolism. - The proportional concentrations of major cations and the ratios of monovalent:divalent cations can influence the metabolism of many organisms, especially certain algae and macrophytes, as much as absolute concentrations can. - Factors that influence the availability of some cations disproportionately to others can indirectly affect seasonal population succession and productivity.

6 Salinity of Inland Waters The relatively low salinity of freshwaters has greatly influenced the distribution of biota and their long evolutionary history of physiological adaptations for osmotic and ionic regulation in an extremely hypotonic environment. Although some groups of bacteria and algae are relatively homoiosmotic and can tolerate only a narrow range of salinity, most of the lower flora and fauna are euryhaline, ie., adaptable to a wide range of salinity. Most higher freshwater animals originated from the sea or from land, and adapted to freshwater secondarily. In comparison to marine forms, nearly all of these organisms have reduced osmotic pressures of body fluids and have developed efficient mechanisms for active uptake of ions and renal mechanisms for ion retention.

7 2.4 Carbon in Freshwaters Most carbon of freshwaters occurs as equilibrium products of carbonic acid. A smaller amount of carbon occurs in organic compounds as dissolved and particulate detrital carbon, and a small fraction occurs as carbon of living biota.

8 2.4 Carbon in Freshwaters The distribution of CO 2 and ph in surface waters varies both seasonally and vertically in lakes in relation to loading from allochthonous sources, physical solutions, and with biotic inputs and consumption. Unproductive lakes exhibit an orthograde ΣCO2 curve. In productive waters, an inverse ΣCO2 is found. In hard water ΣCO2 is greatly modified by biologically induced decalcification of the epilimnion.

9 2.5 The Nitrogen Cycle in Water Nitrogen, along with carbon, hydrogen, and phosphorous, is one of the major constituents of cellular protoplasm of organisms. Nitrogen is a major nutrient that affects the productivity of fresh waters. Sources of nitrogen include; a) Precipitation falling directly onto the lake surface b) Nitrogen fixation both in the water and the sediments, and c) Inputs from surface and groundwater drainage. Losses of nitrogen occur by; a) Effluent outflow from the basin b) Reduction of NO 3 to N 2 by bacterial denitrification with subsequent return of N 2 to the atmosphere, and c) Permanent sedimentation loss of inorganic and organic nitrogen-containing compounds to the sediments. The Nitrogen Cycle consists of a balance between nitrogen inputs to and losses of nitrogen from an aquatic ecosystem.

10 Nitrogen Cycle Nitrogen in Atmosphere = 79% Problem is getting N into a form that plants can use. Most N in soil used for Agriculture or Sources of N = OM = 37%, Manure = 19%, Fixed by soil organisms = 19%, Rainfall = 8%, Fertilizer = 13%, Sewage = 4%.

11 Nitrogen Cycle Essential to building proteins 4 Major processes: 1. Fixation convert N 2 to NH 3 & NO 3-2. Mineralization (ammonification) Conversion of dead organic material to energy and NH 3 3. Nitrification Process where NH 3 yields NO 3 -& NO 2 and Energy 4. Denitrification Nitrates (NO 3 ) reduced to gaseous Nitrogen (N 2 )

12 Bacterial Processing of Nitrogen

13 1. Nitrogen Fixation- Conversion of N2 into NH3 or R-NH2 A. Non-Biological Fixation -Air Pollution - nitric acid - rainfall additions from electrical discharge (lightning) 2-5 lbs.../acre/year N > NO3-

14 1. Nitrogen Fixation Conversion of N2 into NH3 or R-NH2 B. Biological Fixation 1. Non-Symbiotic (independent organism) - Azotobacter - aerobic & Clostridium - anaerobic about 5-50 lbs.../acre/year 2. Symbiotic - mutually beneficial for host organism and bacteria - complex plant - bacteria interaction

15 2. Ammonification A. Ammonification is the conversion of organic N (RNH2) into inorganic ammonia (NH3) R-NH2 ---> NH3 + H+ ----> NH4 + heterotrophic organ. (ammonium)

16 3. Nitrification 2 - step process 1. 2NH4+ + 3O2 ---> 2NO2- + 4H+ + 2H20 + E Nitrosomonas 2. 2NO2- + O2 --> 2NO3- + Nitrobacter Process is acid causing due to release of 4 H+

17 3. Fates of Nitrate *Immobilization ---> Plant uptake of NO3- *NO3- is not held by soil particles and is easily leached - when ppm NO3 -is > 10 ppm the water is considered to be contaminated * Denitrification - stimulated by anaerobic conditions.

18 4. Denitrification Involves conversion of NO3- to N2 gas C6H12O6 + 4NO3- --> 6CO2 + 6H2O + 2N2(gas) + NO + NO2 Bacteria = anaerobic Through nitrification and denitrification % of the applied N is lost. Nitrification inhibitors can be applied like N- Serve. This chemical inhibits the growth of nitrosomonas and nitrobacter.

19 Depth-Time Distribution of Nitrogen in Lakes The distribution of nitrogen in a lake can change rapidly. As lakes become more productive, concentrations of NO 3 -N and NH 4 -N in the trophogenic zone can be severely reduced and depleted by photosynthetic assimilation. In anaerobic hypolimnion, NO 3 -N is rapidly denitrified to N 2, which is either fixed or lost to the atmosphere. NH 4 -N concentrations accumulate from decomposition of organic matter and release of NH 4 -N from sediments under anaerobic conditions.

20 Bioremediation-Probiotics Fuel Additives Demulsifiesr Polymers Chemicals Cats HOME

21 Nitrate in drinking water supplies Nitrate has been detected in surface- and ground-water supplies in various parts. Low levels of nitrate can be found in most of the surface waters. In a recent survey of water wells, a large percentage contained excessive nitrate concentrations.

22 Drinking Water In cases where the concentration of nitratenitrogen exceeds the maximum contaminant level of 10 mg/l, as set forth by the U.S. EPA - water suppliers are required to issue a nitrate alert to users. The health of infants, the elderly and others, and certain livestock may be affected by the ingestion of high levels of nitrate.

23 Conclusion Increased loading of inorganic nitrogen to rivers and lakes frequently results from agricultural activities, sewage, and atmospheric pollution In unproductive lakes, phosphorous availability is often the principal limiting nutrient for plant growth. In productive lakes, nitrogen becomes more important as a growth-limiting nutrient.