水环境条件对三峡库区消落带狗牙根氮磷养分淹水浸泡释放的影响

Impacts of Environmental Conditions on the Soaking Release of Nitrogen and Phosphorus from Cynodon dactylon(Linn.) Pers.in the Water-level Fluctuation Zone of the Three Gorges Reservoir Region

三峡库区消落带会经历周期性的淹水-出露循环过程,消落带在出露期大量植物生长,淹水期植物体淹没腐解并释放氮磷养分,可能加剧三峡水库水环境压力.狗牙根[Cynodon dactylon(Linn.)Pers.]是三峡库区分布最广泛的优势植物之一.针对三峡水库水环境条件(温度、p H和光照)变化对狗牙根淹水条件下矿化分解及养分释放过程的影响进行了研究.结果表明,狗牙根淹水后,植物残体矿化分解,干重下降,全氮和全磷含量减少.狗牙根浸泡200 d后,25℃和15℃时总氮(TN)释放量分别为(2.66±0.29)g·kg^(-1)和(3.76±0.04)g·kg^(-1),总磷(TP)释放量分别为(0.79±0.03)g·kg^(-1)和(1.40±0.02)g·kg^(-1);上覆水p H为5.0、7.0、9.0时,TN释放量分别为(3.76±0.08)、(2.66±0.29)、(2.55±0.12)g·kg^(-1),TP的释放量分别为(1.53±0.04)、(0.79±0.03)、(1.70±0.07)g·kg^(-1);避光时上覆水TN和TP的释放量为(3.87±0.14)g·kg^(-1)和(1.78±0.08)g·kg^(-1).氮的释放以颗粒态氮(PN)为主,占80%以上,而颗粒态磷(PP)占比在50%左右.随三峡水环境条件变化,如温度降低,狗牙根的氮磷浸泡释放量增大;而酸、碱性水体较中性条件有利于氮磷释放;避光时狗牙根的氮磷释放得到促进.研究结果表明三峡水库冬季蓄水或污水排放导致的水环境变化将进一步促进消落带植物淹水分解及养分释放,从而可能加剧三峡库区水体富营养化.

The flooding-drying cycles in the water-level fluctuation zone（WLFZ） of the Three Gorges Reservoir（TGR） result in an abundance of plants that are submerged and decomposed to release nutrients.This has the potential to lead to water quality deterioration of the TGR.Cynodon dactylon（Linn.） Pers.,one of the typical plants in the WLFZ,was collected and inundated in the laboratory under different conditions under temperatures of 15℃ and 25℃,a p H 5.0 to 9.0,and under light and dark conditions,respectively,to measure the decomposition rate and nitrogen and phosphorus release mechanisms.The dry weight lost with the contents of nitrogen and phosphorus was found to decrease after Cynodon dactylon（Linn.） Pers.was soaked for decomposition.The amount released of total nitrogen（TN） and total phosphorus（TP） at 25℃ for 200-days inundation was（2.66 ± 0.29） g· or（3.76 ± 0.04） g·kg^-1,respectively and at 15℃ was（0.79 ± 0.03） g·kg^-1 or（1.40 ± 0.02） g·kg^-1,respectively.When the p H of the water submerging the grass was 5.0,7.0 and 9.0,the amount of TN released was（3.76 ± 0.08） g·kg^-1,（2.66 ± 0.29） g·kg^-1,and（2.55 ± 0.12）g·kg^-1,respectively while the amount of TP released was（1.53 ± 0.04） g·kg^-1,（0.79 ± 0.03） g·kg^-1,and（1.70 ± 0.07）g·kg^-1,respectively.The TN and TP released was（3.87 ± 0.14） g·kg^-1 and（1.78 ± 0.08） g·kg^-1 under dark condition.The lower the temperature,the higher the amount of TN and TP will be released for inundation from Cynodon dactylon（Linn.） Pers.When the overlying water is acidic or alkaline,more TN and TP is released.Dark conditions are beneficial to nitrogen and phosphorus release into the overlying water.Thus,the water environment changes in each flooding season in winter.Sewage discharge will also accelerate the nutrients released from soaked plants through their decomposition in the WLFZ,and then will aggravate the deterioration of water quality in TGR.