Clay mineral distribution in surface sediments of the South China Sea and its significance for in sediment sources and transport

Clay minerals of surface sediments in the South China Sea （SCS） are analyzed with X-ray diffraction, and their transport is explored with a grain size trend analysis （GSTA） model. Results show that clay mineral types in various sedimentary environments have different sediment sources and transport routes. Sediments in the northern SCS （north of 20°N） between the southwest of Taiwan Island and the outer mouth of the Pearl River have high contents of illite and chlorite, which are derived mainly from sediments on Taiwan Island and/or the Yangtze River. Sediments from the Pearl River are characterized by high kaolinite and low smectite content, and most are distributed in the area between the mouth of the Pearl River and northeast of Hainan Island and transported vertically from the continental shelf to the slope. Characterized by high illite content, sediments from Kalimantan Island are transported toward the Nansha Trough. Sediments from Luzon Island are related with volcanic materials, and are transported westwards according to smectite distribution. On the Sunda Shelf, sediments from the Mekong River are transported southeast in the north while sediments from the Indonesian islands are transported northward in the south. Ascertaining surface sediment sources and their transport routes will not only improve understanding of modem transportation and depositional processes, but also aid paleoenvironmental and paleoclimatic analysis of the SCS.

Characteristics of Clay Minerals in the Northern South China Sea and Its Implications for Evolution of East Asian Monsoon since Miocene

Clay mineral assemblages, crystallinity, chemistry, and micromorphology of clay particles in sediments from ODP Site 1146 in the northern South China Sea （SCS） were analyzed, and used to trace sediment sources and obtain proxy records of the past changes in the East Asian monsoon climate since the Miocene, based on a multi-approach, including X-ray diffraction （XRD） and scanning electron microscopy combined with energy dispersive X-ray spectrometry （SEM-EDS）. Clay minerals consist mainly of illite and smectite, with associated chlorite and kaolinite. The illite at ODP Site 1146 has very well-to-well crystallinity, and smectite has moderate-to-poor crystallinity. In SEM the smectite particles at ODP Site 1146 often appear cauliflower-like, a typical micromorphology of volcanic smecites. The smectite at ODP Site 1146 is relatively rich in Si element, but poor in Fe, very similar to the smectite from the West Philippine Sea. In contrast, the chemical composition of illite at ODP Site 1146 has no obvious differences from those of the Loess plateau, Yellow River, Yangtze River, and Pearl River. A further study on sediment source indicates that smectite originates mainly from Luzon, kaolinite from the Pearl River, and illite and chlorite from the Pearl River, Taiwan and/or the Yangtze River. The clay mineral assemblages at ODP Site 1146 were not only controlled by continental eathering regimes surrounding the SCS, but also by the changing strength of the transport processes. The ratios of （illite＋chlorite）/smectite at ODP Site 1146 were adopted as proxies for the East Asian monsoon evolution. Relatively higher ratios reflect strongly intensified winter monsoon relative to summer monsoon, in contrast, lower ratios indicate a strengthened summer monsoon relative to winter monsoon. The consistent variation of this clay proxy from those of Loess plateau, eolian deposition in the North Pacific, planktonic, benthic foraminifera, and black carbon in the SCS since 20 Ma shows that three profound shifts of the East Asian winter monsoon intensity, and aridity in the Asian inland and the intensity of winter monsoon relative to summer monsoon, occurred at about 15 Ma, 8 Ma, and the younger at about 3 Ma. The phased uplift of the Himalaya-Tibetan plateau may have played a significant role in strengthening the Asian monsoon at 15 Ma, 8 Ma, and 3 Ma.

Effects of different mechanical direct seeding methods on grain yield and lodging resistance of early indica rice in South China

Direct seeding of rice has become a main planting method due to the low labor input and high economic benefit in South China.Dry direct seeding(DDS)has been widely used for single-season rice planting establishment.However,few studies have examined the performance of early-season indica rice under mechanical dry direct seeding.A two-year field experiment was conducted with two indica rice cultivars(i.e.,Zhongjiazao 17 and Zhuliangyou 819)to study lodging characteristics and grain yield formation under DDS,flooded direct seeding(FDS)and wet direct seeding(WDS)patterns.The results showed that the annual grain yield in DDS was higher by 14.42–26.34%for cultivar ZLY819 and 6.64–24.58%for cultivar ZJZ17 than in WDS and FDS,respectively,and these increases were mainly attributed to the improvement of the panicles.The DDS pattern significantly increased the seedling emergence rate of early indica rice cultivars,and increased total dry weight and crop growth rate.Meanwhile,shorter basal internodes,better stem diameter and stem wall thickness and lower lodging index were found in DDS in contrast to FDS and WDS.In particular,DDS improved the stem lodging resistance.Our results suggested that the appropriate direct seeding method was beneficial for improving the grain yield and lodging resistance of early indica rice.

The distribution characteristics of clay minerals in the northern South China Sea

The clay minearals are composed of illite, chlorite, kaolinite, montmorillonite and mixed-layer minerals in the submarine sediments of the northern South China Sea. Three types of clay mineral zone can be recognized on the basis of the distributive regularity of clay minerals, submarine relief, hydrodynamic conditions and depositional characteristics in this region. Apart from the northern mainland source, kaolinites carried from the Philippines volcanic arc in the east and Malaysia in the south are also assumed to be one of the sources of the clay minerals in the deep sea. The increase of chlorites to the abyssal direction in the west of 116° E might be associated with the residual chlorites carried from the ancient Zhujiang River during the glacial period and the conversion of kaolinite into chlorite submarine volcanoes appear to be one of the sources of the increment of montmorillonite and chlorite around the Huangyan Island. From the distribution pattern of clay minerals in the whole area, it is known that the types of clay mineral assemblage in the study area are mainly controlled by climate and rock types of the source are-

New Algorithm of Clay CEC for Soils in Tropical and Subtropical Regions of South China

Clay CEC is one of identification indexes of the LAC-ferric horizon which is the diagnostic horizon of ferrosols in Chinese Soil Taxonomy, and it is defined as soil CEC × 1000/clay content, rather than the measured CEC of the extracted clays;however, such a calculation method would definitely lead to an overestimation of clay CEC because it doesn’t remove the contribution to soil CEC from other soil parameters. In this study, the physiochemical data of the subhorizons from 82 soil series in the tropical and subtropical regions in south China were used, clay CEC was calculated according to the current formula and measured after clays being extracted, the measured and calculated clay CEC were compared, the influencing factors were analyzed for their difference, and the new algorithms were established for clay CEC. The results showed that the measured clay CEC was 21.86% - 99.53% with a mean of 66.88% of the calculated one (significantly lower at p < 0.01), and their difference was significantly correlated with the contents of clays, sand and OM, and mainly decided by the contents of clays and Fe2O3 (the contribution was 52.51% and 25.36%, respectively). By comparison of established regression models of clay CEC with other soil parameters, two new algorithms were recommended for clay CEC as follows: 1) Clay CEC = 10.32 − 0.14pH − 0.05OM − 0.11Fe2O3 + 0.01Silt − 0.01Clay + 1.17CECsoil, R2 = 0.705, P < 0.01;2) Clay CEC = −3.40 + 0.01Sand + 0.02Silt + 1.05CECsoil, R2 = 0.589, P < 0.01).

Plant Ideotype at Heading for Super High-Yielding Rice in Double-Cropping System in South China

The newly released super high-yielding hybrid rice combinations, Yueza 122, Fengyou 428, Peiza 67, and the super high-yielding conventional cultivars, Guangchao 3 and Shengtai 1, were grown in both early and late seasons. The morphological characters of each population were investigated at the heading stage, and the data were analyzed by using ANOVY and other statistic methods. The plant ideal morphological characters at the heading stage were established as follows： 1 ） for the early-season cropping, 90-105 cm plant height; 11-12 tillers per plant; 35-40 em length and 2.1-2.2 cm width of flag leaf; 46-50 cm length and 1.8-2.1 cm width of the second leaf from the top （L2）; 59-64 cm length and 1.4-1.9 cm width of the third leaf from the top （L3）; 7°-14°, 18° and 200-33° for the ideal leaf angles of the flag leaf, L2 and L3, respectively; 2） for the late-season cropping, 90-100 cm plant height; 9-15 tillers per plant; 30-41 cm length and 1.8-2.0 cm width of flag leaf; 53-61 cm length and 1.3-1.8 cm width of L2; 52-58 cm length and 1.2-1.5 cm width of L3; 9°-19°, 15°-37° and 16°-49° for the ideal leaf angles of the flag leaf, L2 and L3, respectively. The main physiological characteristics of these varieties were also analyzed.

Undrained shear strength evaluation for hydrate-bearing sediment overlying strata in the Shenhu area, northern South China Sea

The undrained shear strength of shallow strata is a critical parameter for safety design in deep-water operations.In situ piezocone penetration tests(CPTU) and laboratory experiments are performed at Site W18-19 in the Shenhu area, northern South China Sea, where China's first marine hydrate exploitation operation is due to be located. The validation of the undrained shear strength prediction model based on CPTU parameters. Different laboratory tests, including pocket penetrometer, torvane, miniature vane and unconsolidated undrained triaxial tests, are employed to solve empirical cone coefficients by statistical and mathematical methods. Finally, an optimized model is proposed to describe the longitudinal distribution of undrained shear strength in calcareous clay strata in the Shenhu area. Research results reveal that average empirical cone coefficients based on total cone resistance, effective resistance, and excess-pore pressure are 13.8, 4.2 and 14.4, respectively. The undrained shear strength prediction model shows a good fit with the laboratory results only within specific intervals based on their compaction degree and gas-bearing conditions. The optimized prediction model in piecewise function format can be used to describe the longitudinal distribution of the undrained shear strength for calcareous clay within all depth intervals from the mud-line to the upper boundary of hydrate-bearing sediments(HBS). The optimized prediction result indicates that the effective cone resistance model is suitable for very soft to firm calcareous clays,the excess-pore pressure model can depict the undrained shear strength for firm to very stiff but gas-free clays,while the total cone resistance model is advantageous for evaluating the undrained shear strength for very stiff and gassy clays. The optimized model in piecewise function format can considerably improve the adaptability of empirical models for calcareous clay in the Shenhu area. These results are significant for safety evaluations of proposed hydrate exploitation projects.

Paleoenvironmental records from the northern South China Sea since the Last Glacial Maximum

Core ZHS-176 contains the paleoenvironmental records from the northern South China Sea （NSCS） since the Last Glacial Maximum （LGM）. A coupled approach based on clay mineral assemblages, planktonic foraminiferal oxygen and carbon isotopes, and calcium carbonate content is used to trace the sources of the fine-grained sediment and to investigate the paleoenviornmental evolution in this area. Clay mineral assemblages are dominated by illite （average about 39%） and chlorite （about 27%）, which comes mainly from Taiwan and the East China Sea. Kaolinite, which accounts for about 13%, comes mainly from the Zhujiang （Pearl） River, and Luzon Island is the main source for smectite （about 21%）. The planktonic foraminiferal oxygen isotopic oscillations during the last glacial period are coeval with climate variations recorded in the Greenland ice core and Western Pacific sediment. These variations include the LGM, Heinrich event 1, Bφlling-Allerφd （B/A）, and Younger Dryas. For the Holocene, three periods of strong precipitation （S1-S3） and three periods of weak precipitation （W1-W3） are identified. The oxygen isotopic record exhibits corre-lation with climate records from distant regions, including the high-latitude Northern Hemisphere, providing evidence for global tele-connection among regional climate. A brief, negative planktonic foraminiferal carbon isotopic excursion during B/A reflects increased methane released from marine gas hydrate due to the rapid warming of the water. By comparing calcium carbonate content curves of the core ZHS-176 with these of other five boreholes lying above the lysocline, a remarkable low calcium carbonate event is found during the early Holocene in NSCS.

Groundwater Flow Simulation and its Application in Groundwater Resource Evaluation in the North China Plain,China

The purpose of this study is to establish a 3D groundwater flow modelling for evaluating groundwater resources of the North China Plain. First, the North China Plain was divided into three aquifers vertically through a characterization of hydrogeological conditions. Groundwater model software GMS was used for modeling to divide the area of simulation into a regular network of 164 rows and 148 lines. This model was verified through fitting of the observed and the simulated groundwater flow fields at deep and shallow layers and comparison between the observed and simulated hydrographs at 64 typical observation wells. Furthermore, water budget analysis was also performed during the simulation period （2002-2003）. Results of the established groundwater flow model showed that the average annual groundwater recharge of the North China Plain during 1991 to 2003 was 256.68x10s m3/yr with safe yield of groundwater resources up to 213.49x10s m3/yr, in which safe yield of shallow groundwater and that of deep groundwater was up to 191.65x10s m3/yr and 22.64x10s m~/yr respectively. Finally, this model was integrated with proposal for groundwater withdrawal in the study area after commencement of water supply by South-North Water Transfer Project, aiming to predict the changing trend of groundwater regime. As indicated by prediction results, South-North Water Transfer Project, which is favorable for effective control of expansion and intensification of existing depression cone, would play a positive role in alleviation of short supply of groundwater in the North China Plain as well as maintenance and protection of groundwater.

Research on Integrated Planning Method of Offshore Oil and Gas Exploration and Development

Under the requirement of high-quality development, the research method of integrated model planning for offshore oil and gas exploration and development suitable for the western South China Sea is put forward. Based on the new round of resource evaluation and exploration and development research in the western South China Sea, the in-depth research on underground oil and gas resources, surface development facilities, external factors and economic indexes are carried out to clarify the industrial layout of oil and gas development. The potential and prospect of oil and gas exploration and development were implemented, and the main external factors and corresponding measures affecting the planning were clarified in this paper. The economic evaluation model suitable for the region is established based on the analysis of internal rate of return, comprehensive barrel oil cost, critical price, financial net present value and other important indicators, and a set of planning and research methods suitable for the integration of exploration and development in the western South China Sea is finally formed. This method has been applied to the replacement reserve study of Weizhou X and Weizhou Y oil fields. It is found that the planned reserves and production are consistent with the actual ones, and good practical results have been achieved.

Clay mineral records of East Asian monsoon evolution during late Quaternary in the southern South China Sea

High-resolution clay mineral records combined with oxygen isotopic stratigraphy over the past 190 ka during late Quaternary from core MD01-2393 off the Mekong River in the southern South China Sea are reported to reconstruct a history of East Asian monsoon evolution.The dominating clay mineral components indicate a strong glacial-interglacial cyclicity, with high glacial illite, chlorite, and kaolinite contents and high interglacial smectites content. The provenance analysis indicates the direct input of clay minerals via the Mekong River drainage basin.Illite and chlorite derived mainly from the upper reach of the Mekong River, where physical erosion of meta-sedimentary rocks is dominant. Kaolinite derived mainly from active erosion of inhered clays from reworked sediments in the middle reaches. Smectites originated mainly through bisiallitic soils in the middle to lower reaches of the Mekong River. The smectites/(illite+chlorite)and smectites/kaolinite ratios are determined as mineralogical indicators of East Asian monsoon variations. Relatively high ratios occur during interglacials and indicate strengthened summer-monsoon rainfall and weakened winter-monsoon winds; relatively lower ratios happened in glacials, indicating intensified winter monsoon and weakened summer monsoon. The evolution of the summer and winter monsoons provides an almost linear response to the summer insolation of the Northern Hemisphere, implying an astronomical forcing of the East Asian monsoon evolution.

Late Quaternary clay minerals off Middle Vietnam in the western South China Sea: Implications for source analysis and East Asian monsoon evolution

High-resolution clay mineral records combined with oxygen isotopic stratigraphy over the past 450 ka during late Quaternary from Core MD05-2901 off Middle Vietnam in the western South China Sea are re-ported to reconstruct a history of East Asian monsoon evolution. Variations in Illite, chlorite, and kaolinite contents indicate a strong glacial-interglacial cyclicity, while changes in smectite content present a higher frequency cyclicity. The provenance analysis indicates a mixture of individual clay minerals from various sources surrounding the South China Sea. Smectite derived mainly from the Sunda shelf and its major source area of the Indonesian islands. Illite and chlorite originated mainly from the Mekong and Red rivers. Kaolinite was provided mainly by the Pearl River. Spectral analysis of the kaolin-ite/(illite+chlorite) ratio displays a strong eccentricity period of 100 ka, implying the ice sheet-forced win-ter monsoon evolution; whereas higher frequency changes in the smectite content show an ice sheet-forced obliquity period of 41 ka, and precession periods of 23 and 19 ka and a semi-precession period of 13 ka as well, implying the tropical-forced summer monsoon evolution. The winter monsoon evolution is generally in coherence with the glacial-interglacial cyclicity, with intensified winter monsoon winds during glacials and weakened winter monsoon winds during interglacials; whereas the summer monsoon evolution provides an almost linear response to the summer insolation of low latitude in the Northern Hemisphere, with strengthened summer monsoon during higher insolation and weakened summer monsoon during lower insolation. The result suggests that the high-latitude ice sheet and low-latitude tropical factor could drive the late Quaternary evolution of East Asian winter and summer monsoons, respectively, implying their diplex and self-contained forcing mechanism.

RCEP背景下中日韩股票市场的联动性与风险溢出衍变

在RCEP实施推进的背景下,从区域经济一体化引致金融一体化的视角切入对比了RCEP推进的不同阶段中日韩三国股票市场的联动情况和风险溢出情况。结果表明,三国股票市场的收益波动具有显著的杠杆效应,危机爆发时期股市间的联动性会显著提升;股市间的一体化程度正在加深,韩国是风险输入国,中国和日本是风险输出国。为了维护金融稳定,除了进一步加强宏观审慎监管,各国应协同合作,构建区域统一、协调的风险防范机制。

Clay mineral assemblages of the oceanic red beds in the northern South China Sea and their responses to the Middle Miocene Climate Transition

The Middle Miocene Climate Transition(MMCT,~14 Ma)is the largest cooling event in the Cenozoic“Coolhouse”,which significantly impacts the global chemical weathering pattern.In this paper,the responses of the MMCT global cooling event in the deep South China Sea were studied by clay mineral assemblages analysis of the oceanic red beds(ORB)at International Ocean Discovery Program(IODP)Expedition 368 Site U1502.The results show that the clay mineral assemblages of the ORB at Site U1502 are mainly composed of smectite(56–88%),illite(7–29%),and kaolinite(6–20%),without chlorite.The contents of these clay minerals and illite crystallinity show a four-stage variation pattern during early-middle Miocene(22.8–10.8 Ma).Smectite decreased from average 81%during 22.8–16.2 Ma and 16.2–14.4 Ma to average 67%during 13.8–10.8 Ma,with a rapid decrease of~14%during 14.4–13.8 Ma.On the contrary,illite and kaolinite increased rapidly by~8%and~6%,respectively,during 14.4–13.8 Ma.Illite crystallinity increased from average 0.18°Δ2θduring 22.8–16.2 Ma to average 0.19°Δ2θduring 16.2–14.4 Ma,and then decreased rapidly by~0.02°Δ2θduring 14.4–13.8 Ma.The provenance analysis of clay minerals shows that illite and kaolinite mainly originated from South China landmass due to physical erosion,while smectite mainly came from the Luzon arc as the product of chemical weathering.Therefore,smectite/illite ratio and illite crystallinity are used as proxies of chemical weathering intensity in the early-middle Miocene.High values of the ratio and the crystallinity represent the enhanced chemical weathering,whereas low values indicate the weakened chemical weathering or the strengthened physical erosion process.The smectite/illite ratio and illite crystallinity both decreased rapidly during 14.4–13.8 Ma,indicating the chemical weathering in the surrounding area of the South China Sea weakened rapidly,which we believe is the result of the MMCT event forcing.In addition,their values increased slightly during 16.2–14.4 Ma,which is in response to the relatively enhanced chemical weathering during the Middle Miocene Climate Optimum(MMCO).The variation pattern of clay mineral assemblages of the early-middle Miocene ORB in the South China Sea and its rapid transformation during the MMCT reveal that the Cenozoic cooling played a specific role in controlling the chemical weathering of the Earth’s surface.

施氮水平对华南优质稻产量和食味的影响及适宜施用量探讨

优质稻生产面临的一个主要挑战是如何在不影响稻米品质前提下提高稻谷产量。本研究以4个广东丝苗米优质常规稻品种及优质杂交稻品种泰丰优208为供试材料,于2021年早、晚两季在广州同一田块上开展不同施氮量(N0,0 kg/hm^(2);N1,90 kg/hm^(2);N2,135 kg/hm^(2);N3,180 kg/hm^(2))效果试验。结果表明,华南优质稻产量受品种、季节、施氮水平、品种×施氮水平互作效应和季节×品种×施氮水平互作效应等5种因子影响,但米饭食味值仅受品种和施氮水平影响。早季同一施氮水平下品种间稻谷产量有显著差异,但品种间食味值差异不显著;晚季除N0处理外,其他处理品种间稻谷产量有显著差异;食味值仅N3处理品种间存在显著差异。施氮量与稻谷产量呈极显著正相关,早、晚季的相关系数分别为0.977和0.950;施氮量与食味值则呈极显著负相关,早、晚季的相关系数分别为-0.972和-0.956。根据试验结果,提出了各参试品种既高产又食味优良的适宜施氮量。

Quaternary clay mineralogy in the northern South China Sea (ODP Site 1146) —— Implications for oceanic current transport and East Asian monsoon evolution

Measurement of clay mineralogy at ODP Site 1146 in the northern South China Sea (SCS) indicates that illite, chlorite, and kaolinite contents increased during glacials and smectite content increased during interglacials. The smectite/(illite+chlorite) ratio and the smectite abundance were determined as mineralogical indicators for the East Asian monsoon evolution. At a 10 ka timescale, prevailing southeasterly surface oceanic currents during interglacials transported more smectite from the south and east areas to the north, showing a strengthened summer monsoon circulation, whereas dominated counter-clockwise surface currents during glacials carried more illite and chlorite from Taiwan as well as from the Yangtze River via the Luzon Strait to the northern SCS, indicating a strongly intensified winter monsoon. Based on a 100 ka timescale, a linear correlation between the smectite/(illite+chlorite) ratio and the sedimentation rate reflects that the winter monsoon has prevailed in the northern SCS in the intervals 2000—1200 ka and 400—0 ka and the summer monsoon did the same in the interval 1200—400 ka. The evolution of the summer monsoon provides an almost linear response to the summer insolation of Northern Hemisphere, implying an astronomical forcing of the East Asian monsoon evolution.

Effects of ultraviolet radiation B (UV-B) on photosynthesis of natural phytoplankton assemblages in a marine bay in Southern China

Solar ultraviolet radiation B (UVB) is known to have inhibitive effects on phytoplankton photosynthesis. UVB light decreases rapidly with increasing depth in the water column and exerts different degrees of UVB inhibitive effects on phytoplankton photosynthesis. In this study, the objectives were to quantify effects of UVB on phytoplankton photosynthesis and quantum yield, and to examine UVB effects on phytoplankton photosynthesis when light varies. The insitu experiments were conducted in Da Ya Bay, which is a semienclosed area in the subtropical South China. The results showed a significant reduction of photosynthetic rates and quantum yield in the presence of UVB. Maximum photosynthetic rates (Pmax) and maximum quantum yield (Φmax) were 11%-22% and 17%-49% less under solar radiation with UVB than without UVB. A simplified model was developed to describe the UVB biologically effective fluence rate (E*inh) as an exponential decay function of depth. Light-shift experiments, in which water samples from the surface and at depth of 4 m were divided into several subsamples, and each subsamples were then incubated at different depths with and without UVB in the water column, showed that phytoplankton from the deeper water (4 m) had more inhibitive rates by UVB than that from the surface when exposed to the same light condition.

华南双季稻低碳高产栽培技术研究进展

分析了华南双季稻田CH4和N2O排放量,从低碳品种筛选、节水减排灌溉、化肥减量增效等方面介绍了华南双季稻低碳高产关键技术及其集成应用情况。综述了华南双季稻低碳高产栽培技术研究的主要进展、存在问题和今后工作重点。华南双季稻低碳高产栽培技术节水节肥、减排控污、增产增收,实现了低碳与高产的协调,应用前景好。目前,该技术主要存在可用品种少、种植模式单一、推广难度大等问题;今后,在加大政策支持的同时,亟需加强品种筛选、模式集成、基础理论等方面的研究,以确保国家粮食安全,实现碳达峰碳中和的目标。

华南区稻田耕地质量空间分布与产能提升潜力

为了明确华南区稻田耕地质量空间分布及其提升潜力,为实现华南区水稻高产稳产提供科学依据,本研究基于2017年农业农村部耕地质量监测保护中心在华南区开展的耕地质量区域汇总评价数据,分析华南区稻田耕地质量空间分布情况及其与产能对应关系,并利用随机森林模型明确影响产能提升的主要限制因子。华南区稻田耕地质量等级呈现“中间高,四周低”的空间分布规律;利用半方差函数拟合结果表明,华南区稻田耕地质量等级呈中度空间相关性(R2=0.95),以广东(3.82)最高,海南(5.32)最低。华南区耕地质量评价指标中,土壤养分指标空间分布差异较大,土壤全氮和缓效钾含量空间分布呈强烈的空间相关性,分别呈现“西高东低”和“北高南低”空间分布规律;土壤有机质、有效磷、速效钾含量呈中度空间分布相关性,分别呈现由西向东、由东向西、由北向南不断降低的空间分布趋势;土壤pH整体呈弱酸性(5.40)。土壤物理性状、立地条件、土壤管理情况及土壤健康状况以东部较好,西部较差。华南区稻田耕地质量等级与单产整体呈显著正相关性(R2=0.9140),水稻产量随耕地质量等级提升呈先迅速增加后趋于平缓趋势;华南区稻田耕地质量等级与水稻产量可持续指数呈显著正相关(R^(2)=0.9333)。随机森林模型的重要性分析结果表明,土壤有效磷含量、灌溉能力和土壤有机质含量是影响华南区水稻产量的最关键因素。情景模拟表明,若华南区稻田耕地质量等级分别提升0.5、1.0、1.5个等级,则水稻将增产14.93%、22.39%、29.86%,相当于节约耕地面积31.77万hm^(2)、56.35万hm^(2)、75.95万hm^(2)。华南区稻田耕地质量和产能仍有较大提升潜力,通过提升耕地质量来提升产能对保障粮食安全、促进农业绿色生产具有重大意义。

南海北部刺鲳最大可持续产量的评估

根据2008—2020年渔港渔业生产抽样调查数据,开展了南海北部刺鲳(Psenopsis anomala)资源的评估,并采用剩余产量模型对12个单位捕捞努力量渔获量(CPUE)数据进行分析。统计结果表明,南海北部的刺鲳捕捞方式主要为拖网和刺网,分别占其产量组成的40.52%和53.14%。平衡Schaefer模型计算的最大可持续产量(MSY)为47402.96 t,平衡Fox模型计算的MSY为36739.93 t,非平衡Schaefer模型计算的MSY为29198.74 t。双拖400 kW以上、单拖100~200 kW、刺网50 kW以下等作业方式与功率段的捕捞努力量投入过度,其他的则未发生过度捕捞,资源利用总体处于安全水平。综合推断总可捕量可设定为2.8×104~3.2×104 t。