中国七大流域人为净磷输入及河流入海磷通量研究

磷(P)是生物生长发育不可缺少的营养元素，但过量的磷输入会造成水体富营养化等问题，进而威胁生物体的生命活动。长江、黄河、珠江、松花江、辽河、海河、淮河是中国境内主要的七条外流河，流域总面积达451.19×10~4 km~2，占全国陆地总面积的47%，流域总人口为11.03×10~8，占全国总人口的79%，且处于我国经济发达地区。流域内人类活动会导致大量磷素从陆地环境进入河流，并由河流携带流向邻近海域，进而影响近海区域生态环境质量。本论文研究了中国七大流域的人为净磷输入量(Net Anthropogenic Phosphorus Inputs，NAPI)，包括肥料磷输入(P_(fert))和食品、饲料及非食品磷输入(P_(im&nf))以及相应河流的总磷(TP)通量，同时，探究了河流TP通量与流域人为净磷输入、河流径流量及流域内湖泊面积占比之间的关系，建立了相应的响应模型，旨在为中国河流磷污染控制提供依据。珠江流域、松花江流域和辽河流域1999-2018年期间的人为净磷输入总体呈增长趋势，其中，辽河流域人为净磷输入增长幅度较大;长江流域、黄河流域、海河流域和淮河流域的人为净磷输入呈现先增加后降低的趋势。七大流域1999-2018年的平均人为净磷输入在空间上呈现明显的不均匀分布，人口密度大、社会经济发展快的流域，人为净磷输入值更高。其中，淮河流域人为净磷输入最高，达到了3988.28 kg P km~(-2)yr~(-1)，这是由于该流域经济活动和农业生产活动强度均较大造成的。人为净磷输入最低值出现在松花江流域，仅为327.17 kg P km~(-2) yr~(-1)。人为净磷输入各项磷源输入的不同贡献情况主要归因于各流域不同的土地利用类型。人为净磷输入各营养成分的相对转化量可为流域磷输入控制提供依据，其中，肥料磷到作物磷的转化率和作物磷到畜禽产品磷的转化效率均较低，分别为13%和16%，因此，可通过提高肥料利用效率、调整畜禽养殖饲料的营养成分比例、改进饲养方法等措施减少磷输入。基于人为净磷输入与人口、牲畜和作物之间的相关关系，建立了基于人口总量、牲畜数量和作物产量的人为净磷输入模型(R~2=0.86)，大大简化了模型的计算过程，有利于模型的推广应用。长江、黄河、珠江、松花江和海河1999-2018年的TP通量总体上呈增加趋势，辽河和淮河的TP通量增加趋势不明显。1999-2018年，中国七条主要河流的入海TP通量合计为年均98.31×10~3 t P yr~(-1)，其中长江的TP通量最高(71.13×10~3 t P yr~(-1))，占七条河流TP通量之和的72.36%，海河的TP通量最低，仅为0.14×10~3 t P yr~(-1)。总磷通量与径流量、牲畜数量、人口总量和磷肥施用量相关性较强。研究建立了TP通量与人为净磷输入、河流径流量及流域内湖泊面积占比之间的定量关系(R~2=0.82)，该模型可以很好地描述河流TP通量的影响因素。本研究结果可为河流磷污染的有效管理与控制提供更多的依据和多角度的治理思路。

Phosphorus (P) is an essential nutrient for the growth and development of organisms, but excessive phosphorus input can cause problems such as water eutrophication, thereby threatening the life activities of organisms. The Yangtze River, Yellow River, Pearl River, Songhua River, Liao River, Hai River and Huai River are the seven major outflow rivers in China, with a total basin area of 451.19 × 10⁴ km², accounting for 47% of China’s total land area, and a total basin population of 11.03 × 10⁸, accounting for 79% of China’s total population, and they are located in China’s economically developed regions. Human activities in the basins will cause a large amount of phosphorus to enter rivers from terrestrial environments, and be carried by rivers to adjacent sea areas, thereby affecting the ecological environment quality of offshore areas. This paper studied the Net Anthropogenic Phosphorus Inputs (NAPI) of China’s seven major river basins, including fertilizer phosphorus input (P_fert) and food, feed and non-food phosphorus input (P_im&nf), as well as the total phosphorus (TP) flux of the corresponding rivers. Meanwhile, it explored the relationship between river TP flux and basin-scale NAPI, river runoff and the proportion of lake area in the basin, and established a corresponding response model, aiming to provide a basis for phosphorus pollution control in Chinese rivers. The NAPI of the Pearl River, Songhua River and Liao River basins showed an overall increasing trend from 1999 to 2018, among which the Liao River basin had a relatively large increase in NAPI. The NAPI of the Yangtze River, Yellow River, Hai River and Huai River basins showed a trend of first increasing and then decreasing. The average NAPI of the seven major river basins from 1999 to 2018 showed obvious uneven spatial distribution: basins with high population density and rapid socio-economic development had higher NAPI values. Among them, the Huai River basin had the highest NAPI, reaching 3988.28 kg P km⁻² yr⁻¹, which was caused by the high intensity of economic and agricultural activities in this basin. The lowest NAPI value appeared in the Songhua River basin, which was only 327.17 kg P km⁻² yr⁻¹. The different contributions of various phosphorus sources to NAPI are mainly attributed to the distinct land use types of each basin. The relative conversion amounts of different nutrient components in NAPI can provide a basis for basin phosphorus input control. Among them, the conversion efficiency of fertilizer phosphorus to crop phosphorus and crop phosphorus to livestock and poultry product phosphorus are relatively low, at 13% and 16% respectively. Therefore, phosphorus input can be reduced by measures such as improving fertilizer use efficiency, adjusting the nutrient composition ratio of livestock and poultry feed, and improving breeding methods. Based on the correlations between NAPI and population, livestock quantity and crop yield, this study established an NAPI model based on total population, livestock quantity and crop yield (R²=0.86), which greatly simplifies the model’s calculation process and facilitates its popularization and application. The TP fluxes of the Yangtze River, Yellow River, Pearl River, Songhua River and Hai River from 1999 to 2018 showed an overall increasing trend, while the increasing trends of TP fluxes in the Liao River and Huai River basins were not obvious. From 1999 to 2018, the total annual offshore TP flux of China’s seven major rivers averaged 98.31 × 10³ t P yr⁻¹. Among them, the Yangtze River had the highest TP flux (71.13 × 10³ t P yr⁻¹), accounting for 72.36% of the total TP flux of the seven rivers, while the Hai River had the lowest TP flux, which was only 0.14 × 10³ t P yr⁻¹. TP flux had strong correlations with runoff, livestock quantity, total population and phosphorus fertilizer application rate. This study established a quantitative relationship between TP flux and NAPI, river runoff and the proportion of lake area in the basin (R²=0.82), which can well describe the influencing factors of river TP flux. The results of this study can provide more basis and multi-angle governance ideas for the effective management and control of river phosphorus pollution.