【作者】 杨学芬；

【导师】 熊邦喜；

【作者基本信息】 华中农业大学 ， 水产养殖， 2010， 博士

【摘要】 水体富营养化问题是全球关注的环境问题之一。随着城市化的发展,承担着容纳城市生活污水任务的城区湖泊水质迅速恶化。南湖是湖北省武汉市中心城区第二大湖泊。近年来,随着武汉市城市化的推进,南湖周边地区居住人口数量猛增,大量经过一定程度处理或未经处理的生活污水排入南湖,导致南湖水体富营养化。本文以南湖为研究对象,对南湖水体、沉积物和间隙水中的氮磷营养盐动态,表层沉积物磷的释放,降雨和地表径流氮磷的输入状况,沉积物中有机质,沉积物中重金属的污染状况等进行研究。主要研究结果如下：1.水体中TN的平均浓度为12.66 mg/L,采样期间随着时间推移呈上升趋势。DIN中,NO3--N的平均浓度为1.076 mg/L,NH4+-N为0.832 mg/L,NO2--N为0.238 mg/L；DIN的季节变化上,NH4+-N的最高值、NO3--N和NO2--N的最低值均出现在8月。水体TP和PO43--P的平均浓度分别为0.240 mg/L和0.033 mg/L。TP和PO43--P均在11月浓度最高,但TP浓度的最低值出现在2月,PO43--P则是8月最低。2.沉积物中,TN的平均浓度为3.3922 mg/g(DW),季节变化趋势与湖水TN一致；垂直变化上,在0-25 cm深度范围内,TN浓度随深度增加逐渐降低。NH4+-N的平均浓度为0.0882 mg/g(DW),占总DIN的70%-96%；季节变化和垂直分布趋势与TN一致。NO3--N的浓度则很低。沉积物中TP的平均浓度为1.005mg/g(DW).季节变化上,4月～11月呈上升的趋势,11月～2月趋于稳定；垂直分布则随沉积深度增加逐渐降低。柱状沉积物中的不同形态磷以无机磷为主,占TP的61.4%-77.1%。沉积物中活性磷的浓度很高,但活性磷随沉积深度增加显著降低。此外,对沉积物不同形态磷和间隙水PO43--p的相关性分析结果表明,沉积物主要以活性磷和自生钙磷的释放来供给水体磷。3.间隙水中,NH4+-N的平均浓度为11.59 mg/L,占总DIN的90%以上；采样期间随着时间推移呈明显上升趋势；垂直分布上,最大值出现在5-15 cm。NO3--N和NO2--N的平均浓度分别为0.212 mg/L和0.025 mg/L；NO3--N的最大值出现在5-10 cm；NO2--N则随深度增加而降低。间隙水PO43--P的平均浓度为0.209 mg/L,11月时浓度最高,2月最低；垂直分布规律与沉积物TP一致。4.水体、沉积物和间隙水中氮磷水平分布的规律是,靠近南湖最大的点污染源的点Ⅳ,各测定指标的浓度最高且季节变化和垂直梯度最显著；周围没有较大点污染源的点Ⅲ和点Ⅴ,各指标的浓度相对较低且季节变化和垂直梯度较小。5.南湖表层沉积物中磷的释放量随pH变化呈“U”形曲线变化,即在中性(pH=7.1)磷释放量最小(0.017 mg/L),而pH=4.6时磷的释放量最大(0.073 mg/L)。在酸性条件下,pH的改变对磷的释放量的影响更显著。不同pH条件下磷的饱和度也有差异,在pH=4.6时磷的饱和度最大,为0.696 mg/L,中性条件下磷的饱和度最小,为0.412 mg/L。好氧和厌氧条件均能造成磷的释放,但是释放量和释放速率有显著差异。厌氧条件下的释放量和释放速率是好氧条件下的近10倍。6.南湖沉积物含水率的平均浓度为72.4%。季节变化不大,垂直分布呈显著的随沉积深度增加而降低的变化趋势。沉积物LOI的平均浓度为10.20%。季节变化上,LOI的最大值出现在11月,2月的浓度稍降,但2月的表层和次表层间浓度差异最小。垂直分布与含水率的分布一致,即随着沉积深度的增加,LOI显著下降。沉积物中TN、TP、LOI两两间均呈极显著相关,反映了南湖沉积物中氮、磷和有机质的同步积累趋势。在0-15 cm的沉积层,各测次间LOI的浓度差异较大；而在15～25cm的沉积层,各测次间的浓度差异不大,表明南湖沉积物中有机质的分解矿化主要发生在0-15 cm的沉积层,较深沉积层的分解矿化较弱,有机质处于相对稳定的状态。7.丘陵植被地表径流中TN、TP的浓度均高于降雨和城市地表径流。降雨、城市地表径流和丘陵植被地表径流中的DIN以NH4+-N为主,其次是N03--N；降雨中的NH4+-N浓度远大于径流中的浓度。溶解态PO43--p的浓度,城市地表和丘陵植被地表径流的浓度均低于降雨的浓度。2005年4月至2006年3月间,降雨和径流中的各形态氮、磷浓度,除NH4+-N呈逐渐递减的趋势,其余指标均呈波动性变化,且没有明显的季节性差异。8.南湖柱状沉积物中各种重金属的平均浓度(mg/kg, DW)分别为Cd:0.155, Cu:47.0, Cr:147.8, Mn:1026.5, Pb:55.7, Zn:132.1。水平分布上,重金属的最大值出现在点Ⅳ和点Ⅰ,且平均浓度也高于其他的点；垂直分布,最大值出现在表层或次表层,随沉积深度的增加而降低。而且,在各种重金属之间以及重金属与有机质之间存在显著的正相关,表明外源污染对沉积物中重金属的负荷具有重要影响。应用地质累积指数Igeo值对重金属污染状况进行评价,结果表明,重金属的污染主要是Cr和Cd,其中Cr的最高浓度为231.9(mg/kg,DW),Cd为0.348(mg/kg, DW)。但是重金属的污染程度较轻。更多还原

【Abstract】 The lake eutrophication is one of the most serious environment problems with social-economic development and pollutants discharge increment. Urban, shallow lakes are generally exposed to anthropogenic activities and particularly vulnerable to human interference that cause enhanced primary productivity and can rapidly be transferred into a state of highly eutrophication.Lake Nanhu is a shallow, polymictic lake located in Wuhan city, the middle reach of the Yangtze River. Its open water area has a surface area of 4.0 km2 and the water depth ranges from 1.85 m to 2.50 m. Many universities, hospitals, and residential areas located around the lake. In recent decades, with the intensification of human activities and the rapid development of economy, there were drastic changes in the lake environment, in which the lake eutrophication is most serious. The nitrogen and phosphorus dynamics in water column, sediment, interstitial water, rainfall, runoff, the phosphorus release from sediment and heavy metal pollution in sediment in Lake Nanhu were investigated from April,2005 to February,2006. The main results were as follows:1. The average of TN in water column was 12.66 mg/L. TN concentrations were increaseing during the sampling time. The dominant form of DIN in waters was NO3--N. The average concentrations of NO3--N, NH4+-N and N02--N were 1.076 mg/L,0.832 mg/L and 0.238 mg/L, respectively. The maximum of NH4+-N, and the minimum of NO3--N and NO2--N appeared all in August. And the averages of total phosphorus (TP) and orthophosphate were 0.240 mg/L and 0.033 mg/L, respectively. The maximum of TP and orthophosphate in water column occurred in November, and the lowest concentrations of TP and orthophosphate in February and August, respectively.2. The mean of TN in sediments was 3.3922 mg/g (DW). The seasonal variation of TN in sediments was the same as the TN in waters; and it decreased with the sediment depth in 0-25 cm layer. The average of NH4+-N in sediments was 0.0882 mg/g (DW) and the proportion to DIN ranged from 70% to 96%. The concentration of NH4+-N had the same trend as the TN in sediments in seasonal variation and vertical distribution. The concentration of NO3--N in sediments was very low. The average of NH4+-N in interstitial water was 11.59 mg/L and with a percentage of higher than 90% in DIN. The concentration of NH4+-N in interstitial water increased with sampling time; and vertically the maximum was in 5～15 cm layers. The averages of NO3--N and NO2--N in interstitial water were 0.212 mg/L and 0.025 mg/L, respectively; vertically, the maximum of NO3--N was in 5～10 cm layers and NO2--N decreases with the sediment depth. The nitrogen concentration was the highest and had the most significantly gradient at the siteⅣ. But it was the reverse at the site III. The results of correlation analysis showed that TN in sediments was an important source for the lake and the nitrogen diffuses mainly by NH4+-N. The average of TP in sediment was 1.005 mg/g (DW), and that of orthophosphate in interstitial water 0.209 mg/L. Seasonally, the concentration of TP in sediment increased from April to November, and then became stable; the concentration of orthophosphate in interstitial water reached the maximum in November and the minimum in February. Vertically, the concentration of TP in sediment decreased with sediment depth, and orthophosphate in interstitial water had the same pattern. Horizontally, the maximum concentration of phosphorus in sediment and interstitial water occurred at the siteⅣ. The dominant form of phosphorus fractionation in sediment was inorganic phosphorus (IP) and the proportions to the total extracted phosphorus ranged from 61.4% to 77.1%. The concentration of bio-available phosphorus (BA-P) in sediment was very high, but it decreased significantly with sediment depth. The high BA-P concentration in surface sediment suggested that there was a strong potential phosphorus release from sediments to the overlying water. According to the significant correlation between phosphorus fractionation in sediment and orthophosphate in interstitial water, the main source of TP released from sediments should be BA-P and ACa-P.3. As to the horizontal distributions of different forms of nitrogen and phosphorus in water, sediment and interstitial water, the maximum was at the site IV and the minimum was at the site III and V.4. The pH value and dissolved oxygen (DO) were the important factor affecting the release of phosphorus from these sediments. A simulated study was made for the influence of different pH value and DO on the concentration of orthophosphate in overlaying water. Under acid and alkaline conditions it favored the phosphorus release. The P release concentration was higher under acid than under alkaline condition; the maximal and the minimum release concentrations were in the pH values of 4.6 and 7.1, respectively in the experiment pH range. Both anaerobic and aeration condition could make P release from the sediments. But the release concentration and the release rate in anaerobic condition were about 10 times higher than the aeration condition.5. The average of the moisture concentration was 72.4% in sediment. There was a slight variation among months. The concentration decreased significantly with the sediment depth. The average of LOI was 10.20%. The maximum of LOI was in November. There were significant correlations among TN, TP and LOI. This meant that there were same sediment trend about N, P and organic matters. According to the present results, the dissolved nutrients in sediment and in interstitial water decreased with the sediment depth in the sediment cores in the sampling period. And the concentrations of the dissolved nutrients had a sharp gradient in 0-15 cm layer, then decreased slightly in 15～25 cm layer. This indicated that the regeneration depth was almost the same in these two cores, i.e., deeper to 25 cm. In the top 0-15 cm layer, the regeneration was actively, and then decreased with the sediment depth.6. The concentration of TN and TP in foothill vegetation runoff was higher than in rainfall and urban runoff. The main form of DIN was NH4+-N, then NO3--N. The NH4+-N concentration in rainfall was significant higher than in runoff. The concentration of soluble PO43--P was higher in rainfall than in either foothill vegetation runoff or urban runoff. During sampling period, the different forms of nitrogen and phosphorus in rainfall and runoff had a fluctuant variation (except NH4+-N in rainfall, which decreased in annual variation).7. The averages (mg/kg, DW) of Cd, Cu, Cr, Mn, Pb and Zn were 0.155,47.0,147.8, 1 026.5,55.7, and 132.1, respectively. Horizontally, the heavy metal concentrations at the siteⅣandⅠwere relatively higher. The heavy metal concentrations decreased with the sediment depth from surface to bottom and the concentrations in surface sediments were significantly higher than the deeper ones. The results suggested that there was a higher concentration of the heavy metals at the siteⅣandⅠ. According to Igeo values, the major heavy metal pollutions in Lake Nanhu were Cr and Cd and the highest concentrations (mg/kg, DW) of Cr and Cd were 231.9 and 0.348, respectively. But the pollution status of heavy metals in Lake Nanhu was generally light. The present results revealed that municipal sewage discharge and rainfall runoff had significant cause of heavy metal pollution in Lake Nanhu and it is necessary to control the pollutions from these "point-sources" input.更多还原