Estuaries are generally considered to be important sources of atmospheric CO2. However, the differences between estuaries, and inadequate observations of partial pressure of CO2 in estuarine water (pCO2water) hamper global estuarine CO2 budgeting. In this study, the longitudinal distribution of CO2 in the waters of Modaomen (MSE) and Lingdingyang (LSE), two sub-estuaries of the Pearl River Estuary (PRE), and its influencing mechanism are studied. The change in the distribution of pCO2water along the distance from the upstream estuary to the ocean between LSE and MSE was significantly different. pCO2water at the LSE ranges from 238 to 7267 µatm, whereas the MSE ranges from 406 to 3078 µatm. Stronger microbial respiration and relatively long water retention times were the main influences that led to higher pCO2water at LSE than at MSE. Seasonally, the increase of soil CO2 into the water in the upstream basin caused by precipitation is the potential influencing factor that the water pCO2water in the flood season is higher than in the dry season. PRE was a net source of atmospheric CO2 with an average annual water–air flux of 41.2 ± 33.3 mmol m−2 day−1. Our results suggest that the differences in longitudinal gradients of pCO2water between estuaries in the same region and the effects of different gas transport velocity models on CO2 emission estimates need to be considered in estuarine CO2 emission budgeting.

在过去30 a间深圳市的土地利用经历了从剧烈变化到近于饱和的过程.文章基于1988—2015年10期深圳市土地覆盖/利用数据,结合形态学空间格局分析(morphological spatial pattern analysis,MSPA)和图论模型定量分析了深圳生态用地的景观连通性.结果表明,生态用地中耕地在深圳城市化不同阶段均为城市用地扩张的主要土地来源,2005年后林地作为城市土地来源的比例显著提升.景观连通性方面,1988—2015年间深圳市生态用地等效连通面积(equivalent connected area,ECA)减少了1175.4 km2,网络连接度(degree of network connectivity,DOC)降低了43.51％.自深圳2005年划定基本生态控制线以来,城市生境退化趋势明显放缓,但生态用地ECA依然以每年11.9 km2的速度被逐渐侵蚀.斑块重要性分析表明,阳台山和塘朗山等区域是目前维持深圳市现有景观连通性的关键枢纽节点,需加大保护力度.

地球表层元素硅（Si）的生物地球化学循环影响全球初级生产力和全球碳循环进而影响地球环境变化。土壤生物硅（BSi）因其易溶解而成为岩石圈-土壤圈-生物圈-水圈等圈层之间Si迁移-转化的枢纽。采集海南岛西南部的热带季雨林、经济林（橡胶林、桉树林、芒果林）和农作物（香蕉、甘蔗）土壤样品。采用热碱消化连续提取法萃取BSi;运用相关分析和主成分分析法识别土壤BSi含量变化的主要驱动因素。结果表明：研究区不同植物群落土壤BSi含量从大到小依次为：香蕉地（（2.38±0.72）mg/g）＞热带季雨林（（1.86±1.34） mg/g）＞橡胶林（（1.42±0.81） mg/g）＞桉树林（（1.22±0.28） mg/g）＞芒果林（（0.98±0.71） mg/g）＞甘蔗地（（0.62±0.74） mg/g）;研究区土壤BSi含量存在随群落变化的季节变化：森林群落土壤BSi含量干季大于湿季，农业草本群落（香蕉和甘蔗）土壤BSi含量则出现湿季大于干季的特征。研究区土壤BSi含量变化主要受生物因素（总氮和碳/氮（C/N））和非生物因素（化学风化程度）耦合驱动。在全球尺度上，海南岛西南部土壤BSi含量（1.43 mg/g）低于热带雨林土壤BSi含量（2.5 mg/g）,揭示水热同期的季风气候区山地土壤较活跃的微生物活动和较强的降雨、径流侵蚀作用，均有利于土壤BSi发生迁移-转换，最终以溶解态硅的形式随地表径流注入南海，在一定程度上保持南海生态系统的营养成分结构，确保南海生态系统良性循环。

于2012年7月和2013年1月定点采集新丰江水库表层水样,测定水样的理化及生物学参数,计算水体中二氧化碳分压(p(CO2))大小并分析其时空变化,探讨新丰江水库p(CO2)的影响因素及其CO2源/汇机制.结果表明:丰水期p(CO2)变化范围为16～3545 μatm,均值为999 μatm,从水库上游到坝前p(CO2)逐渐升高;枯水期p(CO2)变化范围为399～1355μatm,均值为756 μatm,从水库上游到坝前p(CO2)呈下降趋势.丰水期p(CO2)受温度影响较小,与营养盐(NO3-、DSi)浓度呈正相关,与叶绿素a(Chl.a)、溶解有机碳(DOC)浓度呈负相关,与溶解无机碳(DIC)浓度没有明显相关性;枯水期p(CO2)受温度影响也较小,受碳酸盐体系的影响,与NO3-、DSi、Chl.a、DIC浓度呈正相关,与DOC浓度没有明显相关性.新丰江水库相对于大气来说是一个通量值偏低的CO2源.

The seasonal and spatial characterization of dissolved CO2 and its control mechanism in the Modaomen Estuary of the Pearl River (China) were determined by the four underway surveys in April, July, October 2013 and January 2014, respectively. The partial pressure of carbon dioxide (pCO(2) ) was various among different seasons, which may be attributed to the variational runoff among wet and dry seasons. The pCO(2) is wet season (April and July) was greatly higher than that of dry season (October and January). The runoff may be regarded as the mainly source of CO2 in the estuary, while the contribution of in situ biologic respiration in the estuary may be limited. The outgassing fluxes of CO2 in the Modaomen Estuary were approximately 30.80 mol C m(-2) yr(-1). Approximately 2% dissolved inorganic carbon (DIC) in the runoff was emitted into atmosphere during transportation processes in the estuary. The runoff was the key factor for the seasonal variation of CO2 outgassing fluxes in the Modaomen Estuary.

The continent ocean transfer of dissolved silica (DSi, formed as Sio(2)) via rivers constitutes an important part of the global silica cycle. The uptake of terrestrial vegetation and riverine phytoplankton are the key process controlling DSi migration within the drainage basin. Anthropogenic activities (including land use change and damming) have been altering DSi export by changing biological uptakes in the basin. A significant artificial lake effect of damming was exhibited on the spatial variations of chlorophyll-a (Chl.a) and DSi, which caused 15.39% of riverine DSi to be detained in the reservoir region of Changhuajiang River basin, Hainan Island, China. The biological uptake of terrestrial vegetation was behindhand responsible for seasonal fluctuations of DSi. The DSi uptake yields ranged from 19.44 t/km(2)/yr to 86.76 t/km(2)/yr during the different terrestrial vegetation types in the basin, in turn, tropical rainforest > crops > artificial economic forests > grassland. The try calculating of the DSi yield released by the silicates weathering was carried out taking biological processes in the basin into account. Taking into the plants uptake within the basin consideration, the corrected DSi yield from the silicates weathering was 18.6 t/km(2)/yr. Accordingly, the silicates weathering rate was up to 41.55 t/km(2)/yr, which was 1.36 times higher than that (30.39 t/km(2)/yr) without consideration of the biological uptake, and close to the fastest weathering rate of the granite basin (Puerto Rico) in the earth surface. Of the DSi released by the silicates weathering, 28.56% was absorbed by terrestrial vegetation, and 31.43% was consumed by riverine phytoplankton, and the rest was drainaged into the South China Sea. (C) 2016 Published by Elsevier Ltd.

The focal area of this study is the Pearl River Estuary (PRE).In this study,the surface par-tial pressure of carbon dioxide (pCO2 ),temperature,salinity and dissolved oxygen (DO)were deter-mined by underway measurement system during four field surveys,and their seasonal and spatial varia-tions were shown.Significant seasonal variations of pCO2 was observed in the upstream region of PRE, pCO2 in summer was the lowest at the same salinity,medium in spring and fall,the highest in winter, which indicated that the weathering-derived dissolved inorganic carbon was diluted in wet season and sea water was more close to upstream region in dry season.High pCO2 and low DO occurred in the upstream region during four seasons,and pCO2 and DO showed a strong negative linear correlation,and aerobic respiration was the most important factor in modulating high pCO2 .Especially,the maximum ofpCO2 was 71 7.2 Pa and the minimum of DO was 41 .4 μmol /L when salinity was 0.1 9‰ in spring.Pearl River runoff discharged an amount of nutrients into nearshore waters and promoted primary production in broad region in spring and summer.Phytoplankton photosynthesis produced oxygen into sea water and removed carbon dioxide from sea water.The lowest pCO2 ,1 6.5 Pa and the highest DO,41 8.8 μmol /L existed in the western of Hong Kong where salinity ranged from 1 5‰ to 25‰ in summer.

To evaluate the carbon sink capacity caused by rock chemical weathering processes and its controlling factors in the tropical monsoon region, the hydrochemistry of the granite-hosted Changhuajiang River (CHJR) basin in Hainan Island, China, were systematically investigated by collecting water samples from the river mouth to headwater in the dry season and the wet season, respectively. The results show that Na+, Ca2+ and HCO3 − are dominant in the chemical runoff of the CHJR. The spatial and temporal variations of major ions imply the influence of the multi-sources. The concentrations of Ca2+, Mg2+, HCO3 − and DSi, mainly sourcing from rock (silicates and carbonates) weathering, are lower in the wet season than those in the dry season. However, the concentrations of K+, Cl−, SO4 2−and NO3 −, mainly sourcing from the atmospheric precipitation and human activities, are significantly controlled by the monsoon rainfall and hydrological stage in the CHJR basin. The contributions of the silicates chemical weathering, human activities, atmospheric input, evaporites dissolution and carbonates chemical weathering to the chemical runoff are 82.62, 9.05, 5.24, 2.05 and 1.05 % in the CHJR, respectively. The chemical weathering rates of silicates, carbonates and evaporites are 16.25, 0.40 and 0.62 t km−2 year−1, respectively. Chemical weathering rates in global granite-hosted basins significantly correlate with temperatures (P < 0.01) and rapidly increase when temperatures are up to 24 °C. There are two kinds of relationship between chemical weathering rates and runoff depths: logarithmic pattern (temperatures <10 °C) and linear pattern (temperatures >10 °C). On a regional scale, we find that the chemical weathering rates in the southern China appear a weak positive correlation with normalized differential vegetation indexes (NDVI), which need to be confirmed by enough data. The flux of atmospheric CO2 consumption from rock weathering in the CHJR basin is 2.71 × 105 mol km−2 year−1 by the discharge water of 2014, with being close to that (2.9 × 105 mol km−2 year−1) in the other tropical basins and far from that (5.06 × 105 mol km−2 year−1) calculated by the averaged discharge water of over years in the CHJR. The silicates weathering intensity lies at the moderate phase, implying that the weathering processes are still developing in global tropical granite basins. Hence, how the atmospheric CO2 consumption from rock weathering will change with increasing the atmospheric CO2 level and dam construction altering water cycle in the tropical monsoon area is expected to be deserved.

根据2014年1月实测的海南岛昌化江径流化学组成,运用物质平衡法和相关分析法估算化学径流组成的来源和控制因素,探讨流域化学风化产物HCO3-和溶解性硅(DSi)的输出及生态环境意义.结果表明昌化江流域水体呈中偏弱碱性,化学径流组成阴离子以HCO3-为主,阳离子以Ca2+、Na+为主.其中,77.30％的离子源于流域内硅酸盐岩的化学风化,1.38％的离子来源于碳酸盐岩风化,大气沉降对化学径流的贡献为5.45％,人类活动对干、支流化学径流的贡献分别为15.90％与21.04％,差异显著(P＜0.01).地貌条件、岩性及径流深度是影响流域化学径流组成的关键因素.昌化江流域干季输入南海的HCO3-和DSi量分别为2.12×108 mol、1.38×108 mol,是南海海洋生态系统初级生产力的主要物质来源之一,在南海生态系统物质循环预算中不可忽视.

Within the drainage basin, information about natural processes and human activities can be recorded in the chemical composition of riverine water. The analysis of the Guijiang River, the first level tributary of the Xijiang River, demonstrated that the chemical composition of water in the Guijiang River was mainly influenced by the chemical weathering of carbonate rocks within the drainage basin, in which CO2 was the main erosion medium, and that the weathering of carbonate rock by H2SO4 had a remarkable impact on the water chemical composition in the Guijiang River. Precipitation, human activities, the weathering of carbonate rocks and silicate rocks accounted for 2.7%, 6.3%, 72.8% and 18.2% of the total dissolved load, respectively. The stable isotopic compositions of dissolved inorganic carbon (delta13C(DIC)) indicated that DIC in the Guijiang River had been assimilated by the phytoplankton in photosynthesis. The primary production of phytoplankton contributed to 22.3%-30.9% of particulate organic carbon (POC) in the Guijiang River, which implies that phytoplankton can transform DIC into POC by photosynthesis, and parts of POC will sink into the bottom of the river in transit, which leads into the formation of burial organic carbon.

河口区是联系大气圈、岩石圈、水圈和生物圈的重要枢纽.厘清河口区碳的行为机理,特别是二氧化碳(CO2)在水—气界面的交换过程,有助于提高对近海碳源汇格局的认识.通过总结河口CO2水—气交换的国内外最新进展,得出如下结论:①不同河口水体二氧化碳分压(pCO2)空间分布存在一般模式,但pCO2具体季节变化存在差异;②全球河口区面积虽小,但其CO2的水—气释放通量高达0.25 ×1015～0.50× 1015g C/a,约有1/3的河流碳经过河口过程被释放到大气中;③有机质的呼吸降解、外源CO2的横向传递、水体内部矿物沉淀以及水流的紊动构成了河口水体CO2向大气释放的主要驱动过程.目前,气体传输速率k和全球河口面积估算的不确定性依旧很大,已有的河口样本还不能充分代表不同类型的河口系统来支撑全球河口CO2水—气界面交换通量的精确估算.