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NUTRIENT DYNAMICS IN LENTIC ECOSYSTEMS:
A COMBINED THERETICAL AND PRACTICAL APPROACH
Yallappa Pulyagol1,2, Durga Madhab Mahapatra1 and Ramachandra T.V1
1 Energy and Wetlands Research Group, CES, IISc Bangalore2 Industrial Pollution Control, Department of Chemical Engineering, NITK Surathkal
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INTRODUCTION
• In shallow lakes, water quality, nutrient concentrations, biochemical
transformations and aquatic biota may have complex relationships due to
– flow pattern and residence time for lakes with inlets and outlets
– frequent mixing of water column and resuspension of unconsolidated sediments
– substantial internal loading of nutrients from sediment to water column
– lack of stable long-term thermal stratification
• Disposal of untreated or partially treated sewage affects the ecological health and biotic-abiotic complex fragile interactions in the lake ecosystem by nutrient stress and altered physico-chemical properties of water
– Carbon (250-1000 mgL-1 COD, 110-400 mgL-1 BOD), nitrogen (20-85mgL-1) and phosphorus (4-15mgL-1)
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• Nutrient resources constitute the main factor for prokaryote community composition
• Nutrient use efficiency depends on temperature and light availability
• Organic matter governs N and P balance in lakes
• Forms and concentrations of nutrients are the cause and consequences of existing conditions affecting biochemical transformations
• The lakes polluted by continuous inflow of sewage are under nutrient stress; NH3+NH4
+ 12-50 mgL-1 with no or very less NO2- and NO3
-
– microbial degradation of OM also contributes to DON and ammonia
• Organic P (1-5 mgL-1) and inorganic P (3-10 mgL-1) is the total P in the sewage which if let to lakes causes high P concentration in the system
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• Mineralization• Immobalization• Nitrification • Denitrification • Ammonia oxidation
– hydrogen dependent denitrification OM where aerobic bacteria use oxygen from nitrate in anaerobic conditions and produce N2
– ANNAMOX (anaerobic ammonia oxidation): a process first discovered in wastewater in which ammonia and NO2
- can react directly to form N2
– NO2- dependent ammonia oxidation denitrification
– OLLAND (oxygen-limited autotrophic nitrification-denitrification): a two step process in which NO2
- formed in first step is used to oxidize ammonia to form N2
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Objectives
• Water quality assessment
• Quantification of forms of N and P
• To apply theoretical concepts for nitrification rates
• To justify importance of further research
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MATERIALS AND METHODS
Study area-Varthur Lake
Location Catchment(sq.km)
Total area(m2)
Maximum depth(m)
Mean depth(m)
Residence time(days)
Bagalore South talukBangalore districtKarnataka
1.8 1,478,000 2.0 1.5 4.74
Site Site name GPS (Deg.)
Lat Long
S1S2S3S4S5
SiddapurRamagondanahalliNorth outletSouth outletKodi
12.9472112.9508312.9527812.9498012.94509
77.7353377.7422677.7444977.7468677.74351
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• Sampling
– Water samples were collected at a depth of 10-30cm below the water surface in the morning hours from five sampling sites S1, S2, S3, S4 and S5 during August, September and October of 2010 in a clean 500mL polyethylene bottles, transported to laboratory within 8 hours and stored in refrigerator
• Analysis
– Onsite
• DO, free CO2
• pH, EC, water temperature, TDS(T) and salinity were measured using EXTECH pH/Conductivity meter
• ORP using ORP testr meter
• Turbidity using turbidity meter
– Lab measurements
• total and soluble COD, BOD, alkalinity, Ca and total hardness, chlorides, phosphates, ammonia, nitrates, sodium and potassium by standard methods (APHA, 20th Edition-1988; NEERI, 1988)
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• Free ammonia and ionized ammonia concentration was obtained using Emerson’s
(1975) equations
Incubation experiment
4 different experimental setups with 3 replicates of 500ml water samples in a 500ml polyethylene bottle were incubated for 1,2,3 and 4days at room temperature
Bottle cap was kept just open to ensure no light is available for algal photosynthesis and nutrient uptake
Increase in nitrate concentration was determined after every 24hrs incubation and first order kinetics was applied to get nitrification rate constant
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RESULTS AND DISCUSSION
• Water quality
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Incubation results
• Overall reaction of nitrification can be expressed as the conversion of ammonia and nitrite to nitrate and thus
– increase in nitrate concentration gives the best measure of nitrification process
irrespective of inhibition and limiting steps
• Assuming very less or no accumulation of N in nitrite form and any form of N getting converted to nitrate as net process we can represent the
process by first order kinetics
Solution of [5] is
Where
No= initial concentration of nitrate, K=nitrification rate constant
t = residence or incubation time
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Plot of ln (N/No) V/s incubation time t gives a straight line with slope K
Nitrification constant K=0.172 d-1
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• Taking average pH 7.8 and temperature 27.8ºC
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Highest ammonia concentration was found in S1 site near inlet and decreasing gradation towards outlets
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CONCLUSION
• Nitrification rate in Varthur lake is higher than fresh-water lakes butcompared to high ammonia concentration it is very less and the differencein ammonia concentration from inlet to outlet is 14.5 mg/L but there is notmuch increase in nitrate concentrationThis shows possibility of otherpathways of N transformations (Marcel et al., 2005)
• Combined theoretical and practical approach gives rate of the process butneeds further detailed study of each process to validate results
• Further research on processes– (a) hydrogen dependent denitrification with organic matter; (b) ANNAMOX;
(c) NO2- dependent ammonia oxidation denitrification; (d) OLLAND; (e)effect of ammonia on steps of nitrification process; (f) accumulation of N in theform of nitrite; (g) N and P uptake by phytoplankton and plants is necessary tounderstand N and P dynamics in the lake
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