80. Lake clarity TW: sources of nitrogen 1.kw1: 提出one theory-frommatter on the lake bottom by convection theory: from where and the process of convection 2.kw2: active-bottom hydrothermal vents& heat & springs—support theory a: vents account for high concentrations b: heatàwater convect c: thermal springs 3.kw3 (CS): evidence of hydrothermal vents& 结论(deep water)—support theory evidence: a: higher temperature and salinity gradients b: prolific bacteria whose water temperature c: brine pool more concentrated CS: from deep watersà85% nitrogen 推测:from sewage insignificant 总结:论点-论据(support)-论据(support)&CS
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