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营养盐是水生生态系统中生物生长所必需的重要营养元素和化学物质,也是生态系统食物链的基础[1]。氮、磷作为水体环境中主要营养盐,被认为是影响水生态环境富营养化程度的关键性因子[2]。过量的氮、磷输入导致农村沟渠水体富营养化程度日益加重,加快藻类的生长和异常繁殖,进而破坏沟渠水体生态系统及其功能[3]。沟渠中氮、磷等营养盐在底泥和上覆水间存在着一定的动态平衡。当沟渠生态系统环境发生变化时,底泥会通过扩散、对流、底泥再悬浮等作用向上覆水体释放氮磷污染物,造成“二次污染”[4]。大量研究表明:营养盐在底泥-上覆水间的动态迁移转化主要受溶解氧[5]、pH[6]、温度[7]、氧化还原电位[8]、盐度[9]、扰动和微生物[10]等因素影响,其中以pH的影响最为显著。张茜[11]对溶解氧、pH、温度的正交实验发现:影响水库沉积物中总磷、总氮释放量的环境因子中,显著性从大到小依次为pH、温度、溶解氧;JENSEN等[12]发现:丹麦大部分湖泊中,强碱促进溶解性活性磷的释放;李家兵等[13]研究表明:偏酸性条件会抑制河口湿地沉积物中氮的硝化和反硝化活性,但不直接影响氮的矿化作用。目前学者多关注于河流、湖泊、城市内河、河口湿地和水库中的底泥研究,对山地农村沟渠底泥-水界面氮磷营养盐的迁移释放报道较少。云贵高原山地农村沟渠地形条件特殊,流域边界明显,是下游河流、湖泊富营养化治理的重点区域;沟渠污水来源差异大,主要包括厨余垃圾、畜禽粪便浸出水和生活污水等,沟中氮磷营养盐沉降和累积明显[14],同时由于水深较浅、流动性差、分布密度大和流域来水量少,农村沟渠水环境污染日益严重[15-16]。本研究以云贵高原滇池流域典型高原山地农村沟渠底泥为对象,采用室内模拟静态培养实验法探析不同pH条件下沟渠底泥-水界面氮磷营养盐动态迁移释放特征,为进一步提高农村生态环境质量,保护高原湖泊、河流和建设美丽乡村提供科学依据。
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研究区昆明市官渡区小康郎小村(25°06′~25°07′ N,102°53′~102°54′ E )位于滇池东北岸,属于滇池流域宝象河子流域。于2019年夏季对研究区沟渠进行现场采样。利用彼得森采泥器采集表层(0~15 cm)底泥样品20 kg,风干,捡出杂物,研磨后过100目不锈钢筛,分别采用酸溶-钼锑抗比色法和凯氏定氮法测定底泥总磷(TP)和总氮(TN)质量分数。采用四步连续提取法测定钙结合态磷(Ca-P)、铁铝结合态磷(Fe/Al-P),采用重铬酸钾法测定有机质(OM)。利用水质采样器(BC-9600)采集底层原位水15 L,24 h内测定上覆水中TN、TP、溶解性总磷(DTP)、铵态氮(
${\rm{NH}}_4^{+} $ -N)质量浓度,具体参照文献[17]方法进行。营养盐基本理化指标如表1所示。利用哈希HQ30D便携式多参数水质分析仪测定上覆水、底泥溶解氧(DO)、氧化还原电位(ORP)、pH等理化指标。表 1 沟渠营养盐基本理化指标
Table 1. Basic physical and chemical indexes of nutrients in ditch
指标 底泥 上覆水 TN/(mg·kg−1) TP/(mg·kg−1) ${{\rm{NH}}_4^{+} }$-N/(mg·L−1) DTP/(mg·L−1) TP/(mg·L−1) TN/(mg·L−1) 最大值 5 618.12 1 854.21 81.64 0.19 0.23 113.12 最小值 4 875.08 1 548.23 56.34 0.11 0.19 69.12 平均值 5 016.60 1 760.22 72.29 0.15 0.20 97.22 -
农村沟渠pH通常为6.5~8.5[4],但也有局部农村地区沟渠pH大于10.5[4, 15-16]。设置灭菌和未灭菌2个处理,4个pH梯度[酸性(pH 5.5),中性(pH 7.5),弱碱性(pH 9.5),强碱性(pH 11.5)],重复3次。以2 L有机玻璃容器作为静态模拟释放反应器,其中灭菌组为棕色瓶,上覆水高温灭菌处理(121 ℃,30 min),底泥三氯甲烷灭菌处理(1 L底泥与500 mL三氯甲烷均匀混合,浸泡24 h后过滤)[8],橡胶塞塞紧瓶口并用凡士林密封,避光放置。以1 mol·L−1氢氧化钠和1 mol·L−1盐酸调节上覆水pH,处理持续30 d;隔5 d测定上覆水物理指标(pH、DO、Eh),分别采集底泥和水样,测定氮磷含量。每次采样后补充等量的沟渠原位水至玻璃容器原始刻度处,以pH 7.5作为各组对照。
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根据上覆水体总氮和溶解性总磷质量浓度随时间的变化,可计算出沉积物的营养盐氮磷释放通量。其计算公式为[18-19]:
$$r = {{\left[ {V \left( {C_n - C_0} \right) + \sum\limits_{i = 1}^n {V_i \left( {C_{i - 1} - C_{\rm{a}}} \right)} } \right]}\Big/{A t}}\text{。}$$ 其中r为释放通量(mg·m−2·d−1);V为上覆水体积(L),Cn为第n次取样水中营养盐质量浓度(mg·L−1),C0为上覆水初始营养盐质量浓度(mg·L−1),Vi为每次采集水样的体积(L),Ca为添加沟渠原水中营养盐质量浓度(mg·L−1),Ci−1为第i−1次采样时水中营养盐的质量浓度(mg·L−1),A为沉积物表面积(m2),t为释放时间(d)。
采用Excel预处理数据,Origin 2019制图,Canoco 5.0进行冗余分析,用SPSS 21.0进行统计分析。
Effects of pH on the dynamic migration of nutrient salts in the sediment of ditches in mountain rural areas
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摘要:
目的 酸碱度是影响沟渠底泥营养盐迁移释放的关键性因子。探究不同pH条件下山地农村沟渠底泥营养盐释放迁移的动态变化,为农村生态环境治理提供理论依据。 方法 采集滇池流域典型山地农村沟渠底泥,通过室内模拟实验测定未灭菌与灭菌处理下不同pH (5.5、7.5、9.5、11.5)条件的底泥、上覆水中营养盐含量,估算底泥-水界面营养盐释放通量。 结果 底泥中总氮质量分数随着pH升高而减少,未灭菌组强碱性(pH 11.5)和酸性(pH 5.5)条件下总氮释放通量分别是对照(pH 7.5)的8和4倍,灭菌组均为对照的2倍。上覆水中溶解性总磷质量浓度和释放通量随pH升高而增加,未灭菌组强碱性(pH 11.5)和弱碱性(pH 9.5)条件下溶解性总磷释放通量分别是对照的12和4倍,灭菌组分别是对照的30和15倍;未灭菌组溶解性总磷释放通量高于灭菌组。冗余分析表明:酸性条件促进底泥中钙结合态磷(Ca-P)的释放,碱性(pH≥9.5)条件促进总氮、总磷和铁铝结合态磷(Fe/Al-P)的释放,中性(pH 7.5)条件对底泥中氮/磷释放影响较小。 结论 碱性(pH≥9.5)和酸性显著促进山地农村沟渠底泥中氮磷营养盐释放,中性条件下释放量最小。底泥灭菌处理降低了不同pH下的微生物活性,阻碍山地农村沟渠底泥中氮磷向上覆水体迁移释放。图6表1参36 Abstract:Objective As pH is a key factor affecting the migration and release of nutrients in the ditch sediment, this study, with an investigation of the dynamic changes of nutrient release and migration in the bottom mud of mountainous rural ditches under different pH conditions, is aimed to provide a theoretical basis for rural ecological environment management. Method With the bottom mud of typical mountainous rural ditches in the Dianchi Lake Basin collected, indoor simulation experiments were conducted to determine the nutrient salt content of the bottom mud and the overlying water under different pH (pH 5.5, 7.5, 9.5, 11.5) conditions under non-sterilized and sterilized treatments after which the nutrient release flux at the sediment-water interface was estimated. Result The mass fraction of total nitrogen (TN) in the bottom sludge decreased with the increase of pH. The total nitrogen release flux under the strong alkaline (pH 11.5) and acidic (pH 5.5) conditions of the non-sterilized group was 8 and 4 times of the control (pH 7.5), and its release flux in the sterilization group was 2 times of that in the control. The mass concentration and release flux of soluble total phosphorus (DTP) in the overlying water increased with the increase of pH. The release of DTP under the conditions of strong alkaline (pH 11.5) and weak alkaline (pH 9.5) in the non-sterilized group was 12 and 4 times of that in the control, respectively, and its release flux in the sterilized group was 30 and 15 times of that in the control while the non-sterilized group had higher DTP release flux than the sterilized group. RDA shows that acidic conditions promote the release of calcium-bound phosphorus (Ca-P) in sediments, and alkaline (pH≥9.5) conditions promote the release of total nitrogen, total phosphorus and iron-aluminum-bound phosphorus (Fe/Al-P). Neutral (pH 7.5) conditions have little effect on the release of nitrogen or phosphorus in the sediments. Conclusion Alkalinity (pH≥9.5) and acidity significantly promote the release of nitrogen and phosphorus nutrients in the bottom mud of mountain rural ditches, and the release amount is the smallest under neutral conditions. Also, the sterilization of the bottom sludge reduces the microbial activity at different pH levels, and prevents the migration and release of nitrogen and phosphorus in the bottom sludge of mountain and rural ditches to the overlying water. [Ch, 6 fig. 1 tab. 36 ref.] -
Key words:
- pH /
- mountain rural ditches /
- sediment /
- nutrients /
- dynamic migration
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表 1 沟渠营养盐基本理化指标
Table 1. Basic physical and chemical indexes of nutrients in ditch
指标 底泥 上覆水 TN/(mg·kg−1) TP/(mg·kg−1) ${{\rm{NH}}_4^{+} }$-N/(mg·L−1) DTP/(mg·L−1) TP/(mg·L−1) TN/(mg·L−1) 最大值 5 618.12 1 854.21 81.64 0.19 0.23 113.12 最小值 4 875.08 1 548.23 56.34 0.11 0.19 69.12 平均值 5 016.60 1 760.22 72.29 0.15 0.20 97.22 -
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