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Chennai modeling phosphorus transport via surface runoff
 

Chennai modeling phosphorus transport via surface runoff

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Modeling Phosphorus Transport via Surface Runoff in Songkhla Lake Basin, Thailand

Modeling Phosphorus Transport via Surface Runoff in Songkhla Lake Basin, Thailand

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    Chennai modeling phosphorus transport via surface runoff Chennai modeling phosphorus transport via surface runoff Presentation Transcript

    • Modeling Phosphorus Transport via Surface Runoff in Songkhla Lake Basin, Thailand Kitipan Kitbamroong G.Padmanabhan Penjai Sompongchaiyakul
    • Songkhla Lake Basin
    • A Lake In Distress Current and Future State
      • Macrophyte blooms lasting for several months have been observed in the middle of the lake.
      • Increasing use of agricultural chemicals in the catchments and consequent loads of phosphorus discharging into the lake over the coming decades is of concern.
      • Could devastate the health and local economy of some 1.5 million people living in this region.
      • Major economic activities in the basin and the lake include rubber plantation, paddy rice farming, fruit tree orchards, fishery, aquaculture and husbandry.
      • A healthy lake is critical to the local economy.
    • Research Objective
      • The comprehensive goal of this research is to model the non-point source loading of phosphorus to the Songkhla Lake from the surrounding drainage area and to develop a decision support system to assist water quality management of the lake.
      • Focus of this presentation is the modeling part.
    • Model Framework Model Input Mgt Tools SFA Pre-Processing Post-Processing GIS
    • Model Development
      • Model Selection Criteria
        • Can the model handle predominantly agricultural land use?
        • Do we have the required input data available?
        • Does the model have GIS interface?
        • Selected Model
        • Annualized Agricultural Non-Point Source Pollution Model (AnnAGNPS)
    • Model Development
      • AnnAGNPS is a cell-based spatially distributed model designed to track non point source pollutant transport via surface runoff in agricultural watersheds.
      • It is capable of tracking sediments and nutrients such as phosphates and nitrates.
    • Input Preparation
      • The study used data for the year 2004.
      • The data was assembled into a GIS database. Topographic data used is in the Digital Elevation Model (DEM) format with 30mx30m resolution.
      • Crop, fertilizer and management data on field, schedule and operation were collected from field survey and from farmers, fertilizer resellers, cooperatives, and farmers.
      • The phosphorus data available for transport was estimated using Substance Flux Analysis (SFA).
      • Non-crop data was obtained from field surveys and literature reviews.
    • Model Calibration
      • The AnnAGNPS model was calibrated for surface runoff by varying the CN parameter for the cells.
      • The sediment yield estimation was improved by varying the cropping factor (C) in the USLE and the hydrologic shape factor.
      • The other soil erosion coefficient such as soil erodibility factor (K), practice factor (P), surface condition constant, and soil texture for a particular cell or subcell were assigned according to the field observation or analyses based on the observed data or suitably taken from the literature.
    • Scenarios modeled Scenario No. Description Strategy 1 Change in fertilizer usage
      • Change in fertilizer application rate by
      • +10%
      • + 50%
      • -10%
      • - 50%
      2 Types of fertilizer applied (N-P-K) Replacement of 8-24-24 and 13-13-21 by 15-15-15 3 Change in type of crops Replacement of horticultural crops by rubber crop
    • Results
      • One third of the phosphorus contribution occurred from U-Tapao and Eastern Coast Sub Basin 4 sub-watershed, followed by Klong Pa Payom & Thanae, Phru Poh & Rattaphum sub-watershed, with approximately equal relative contributions of 15% each respectively
      • The amount of P was not excessively high. However, P transport was of concern because Chlorophyll a was found to be high in the upper and middle of the Songkhla Lake.
    • Results
    • Results
      • High fertilizer application rate could be found in horticultural crops to achieve high yield. Low fertilizer application rate could be found in field crops, rubber and palm plantations
      • A potentially favorable scenario for phosphorus loading reduction appears to be the one of adopting rubber cultivation instead of horticultural crops.
      F A B C D E Point 2004 load P (mg/kg dry soil) Scenarios 1.1 1.2 1.3 1.4 2 3 A 24.43 28.52 37.61 21.26 15.65 15.03 14.43 B 76.05 102.1 124.92 60.31 36.96 31.69 27.17 C 122.02 156.26 195.99 100.09 65.97 58.96 52.69 D 62.81 70.39 94.98 55.96 42.82 42.3 41.79 E 44.35 58.44 72.21 35.65 22.52 19.64 17.12 F 316.22 439.52 528.26 244.15 140.5 116.5 96.64 Annual Loading (tons/year) 14,195 18,796 23,164 11,372 7,129 6,245 5,491
    • Conclusions
      • Modeling was accomplished by delineating the basin into 8 major sub-watersheds. Paucity of data is a major problem particularly for applying data-intensive distributed parameter models. Efforts to build a good data base for the models need to be continued.
      • U-Tapao and Eastern Coast Sub Basin 4 sub-watershed contributed one third of the phosphorous loading to the lake. Resources could be proportionately allocated to those sub-watersheds for phosphorus loading reduction programs.
      • The scenario results for phosphorus reduction from this study indicates a potentially favorable scenario of adopting rubber cultivation instead of horticultural crops.
    • Acknowledgements
      • The authors acknowledge
      • - The National Research Center for Environmental and Hazardous Waste Management, Chulalongkorn University, Bangkok, Thailand for sponsoring this research
      • - The Department of Civil Engineering, Faculty of Environmental Management, Prince of Songkhla University, Songkhla, Thailand for providing laboratory facilities
      • - The Department of Civil Engineering, North Dakota State University, USA for hosting the first author as a visiting scholar during the early stages of the study.