Land-use change and its ecological responses: a pilot study of typical agro-pastoral region in the Heihe River,northwest China

Although rapid land-use change has taken place in many arid and semi-arid regions of northwestern China, relatively less attention has been paid to studying the characteristics of land use change, as well as the ecological responses of land use change in these regions, especially in fragile agro-pastoral regions. This paper analyzes the land use change and its ecological responses during 1985–2005 based on the landscape metrics change and transition matrix of land use types by the combined use of satellite remote sensing and geographical information systems in Shandan County, a typical agro-pastoral region in the middle and upper reaches of Heihe River, northwest China. The results indicate significant changes in land use have occurred and the landscape has become more continuous, clumped and more homogeneous within the examined area. Land use change was mainly characterized by remarkable expansion of barred land and water area, slight increase of cropland and urbanized land, and evident shrinkage of grassland and woodland. The study also demonstrates that the land cover suffered severe degeneration and the ecological environment tended to deteriorate over the study period, mainly as follows: grassland degradation, land desertification and ecosystem services decline.     

Physiological responses of transplants of the freshwater angiosperm Vallisneria americana along a salinity gradient in the Caloosahatchee Estuary (Southwestern Florida)

Fluctuations in freshwater input may affect the physiology and survival of submerged aquatic vegetation (SAV) occurring in oligoaline to mesohaline estuarine regions. Controls on the distribution of the freshwater angiosperm Vallisneria americana, were investigated by transplanting ramets. Pots (3.8-1) containing ramets were distributed among four sites (upstream site [least saline], donor site, near downstream site, and far downstream site [most saline]) in the Caloosahatchee Estuary (Southwest Florida) during wet (May–August) and dry (October–February) seasons. During 2–4 mo of each season, physiological indicators were monitored, including photosynthesis, glutamine synthetase activity, and protein content in shoots, and carbohydrates and total nitrogen and carbon in shoot and subterranean tissues. Where the physical environment (light or salinity) was suboptimal, all physiological indices, except photosynthetic rate, showed similar stress responses, which ranged from a slow decline to a rapid drop in physiological function. Levels of soluble carbohydrates decreased in response to unfavorable conditions more rapidly than did insoluble carbohydrates. Shoot protein of V. americana declined prior to transplant death, suggesting that measuring protein content may provide a rapid assessment of physiological health. V. americana transplants at the low-salinity upstream site died during both wet and dry season experiments, likely in response to light limitation and/or partial burial by sediments. At the far downstream site, death occurred within 2–4 wk, and was attributable to elevated salinities (>ca. 15‰). Comparison of physiological responses with salinity and light regimes at the donor and near downstream sites suggest that light may ameliorate salinity stress. This study demonstrates that V. americana, nominally classed as a freshwater macrophyte, is capable of a remarkable degree of halotolerance.     

Loss of nutrients from catchments and their ecological impacts in the Peel-Harvey estuarine system,Western Australia

Rivers draining coastal-plain soils with a low phosphorus-binding capacity load nutrients into the estuarine system in winter. Phosphorus is largely trapped by diatom blooms and recycled via the sediments to support growth, during the warmer months, of blue-green algae in Harvey Estuary or macroalgae in Peel Inlet. The magnitude of blue-green algae (Nodularia) blooms is related to the amount of river water entering in winter; blooms collapse as salinities rise toward that of the ocean. For macroalgae the relationship between light and nutrient availability is of critical importance. Control measures are concerned with reducing phosphorus loads from catchments and increasing water exchange with the ocean through the proposed construction of a new channel.     

Groundwater-level response to land-use change and the implications for salinity management in the West Moorabool River catchment, Victoria, Australia

The connection between the removal of native vegetation, rising water tables and increasing stream salinity has been established for many catchments across Australia. However, the West Moorabool River in south west Victoria is an example of a catchment where there has been little discernable effect on groundwater levels following land clearing. Over the past 150 years, a significant portion of the catchment has been cleared of dense forest for agricultural development. Historic standing water-level records from 1870–1871 and 1881 are compared with contemporary measurements (1970s to 2007) recorded in the government bore databases. The data show that the earliest recorded groundwater levels are well within the seasonal range of values observed today. By integrating geology and hydrogeology with historical observations of groundwater levels, climate data and land use, the contemporary field observations of stream salinity are linked to the changed water use and shift in rainfall. In contrast to the normally accepted axiom, reafforestation as a management strategy to mitigate the rising salinity in the West Moorabool River catchment would seem inappropriate.     

Impact of climate change on waterlogging and salinity distributions in Huai Khamrian subwatershed, NE Thailand

Regional climate models project significant changes in temperature and rainfall over the Greater Mekong Subregion over the twenty-first century. The potential impacts of climate change on areas affected by waterlogging and shallow saline groundwater in Northeast Thailand was investigated using the variable density groundwater model SEAWAT supported with recharge estimates derived from the hydrologic model HELP3. The focal area is the 154 km² Huai Kamrian subwatershed. Changes in groundwater salinity and waterlogging areas at the middle and end of this century were predicted using the calibrated model. These predictions used the dynamically downscaled PRECIS regional climate change scenarios generated by ECHAM4 GCM A2 and B2 scenarios. Recharge rates are predicted to increase as a result of the higher intensity of rainfall. Shallow watertable areas are projected to increase by approximately 23 % from existing conditions during the middle of the century and up to 25 % by the end of this century. Although the precise rate and timing of climate change impacts are uncertain, all of the scenarios clearly point towards an extension in the area of waterlogging and area affected by shallow saline groundwater areas. Given that areas affected by shallow saline watertables are predicted to expand for both climate change scenarios as well as for the base case, it is concluded that climate change will have a significant impact on the area affected by salinity and waterlogging areas for both climate change scenarios. Evaluation of management options that explore the adaptation to saline environments and to means to reduce salt affected areas are required.     

Spatial variability in fluvial style and likely responses to sea‐level change,Herbert River,Queensland

In broad terms, fluvial systems can be considered as comprising two basic geomorphologic features, a channel and its floodplain (overbank), each of which may accumulate sediment or undergo erosion. The sedimentary relationships between channels and floodplains, the resultant sedimentary architecture and the form of the dependent landscape may all be considered in terms of the relative rates of channel and floodplain aggradation and/or erosion. Using this approach, the Herbert River in north Queensland can be divided into seven ‘fluvial fields’. By considering the likely migration directions of field boundaries in the lower floodplain we conclude that, contrary to many sequence‐stratigraphic models, lowering sea‐level would drive a general aggradation of the system on the Great Barrier Reef shelf, whereas a sea‐level rise would cause further incision of the modern coastal plain.     

Holocene fluctuations of Lake Ngami,Middle Kalahari: chronology and responses to climatic change

Lake Ngami, a 3000 km² basin at the distal end of the Okavango Delta, Botswana, has a complex suite of shorelines ranging from the lake sump at 919 m asl up to 945 m asl, linked to topographic thresholds and inflows, current and fossil, in the Okavango system. The lake has been ephemeral throughout the 20th century and completely dry since 1982, yet held a substantial body of water up to a level of 930 m asl when visited by European travellers in the mid-nineteenth century. The historical decline in the lake has been well documented and used as evidence for regional desiccation, but the Holocene record, based on archaeological studies and radiocarbon dating of inorganic carbonates, is more speculative.A study of a 30 km² diatomite at the eastern end of the basin indicates that a substantial freshwater lake at a level of at least 932 m asl was present throughout the Holocene, linked to a now abandoned inflow of the Kunyere River. A programme of 18 luminescence age determinations of the peripheral Dautsa and Magotlwanen shoreline sequences suggests that they are old features that have been constructed on a lacustrine substrate dating back to 90–100 ka or earlier, and have been modified by Holocene fluctuations in lake level and subsequent aeolian reworking. The water level peaked at 936 m asl between 4 and 3 ka, returned to 934 m at 2.8–2 ka, ponding water into the Phatane Gap, and fell rapidly thereafter to 932 m and thence to historical levels. The 936 m level can be correlated with increased throughflow in the Okavango Delta, hence increased rainfall in the catchment. The subsequent decline can be attributed to episodic closure and rerouting of Okavango distributaries, in particular the Thaoghe, perhaps aided by anthropogenic activities. As such the desiccation of the lake is not indicative of regional climatic change.     

Physiological acclimation strategies of riparian plants to environment change in the delta of the Tarim River,China

The occurrence and development of riparian forests, which were mainly dominated by mesophytes species related closely with surface water. Since there was no water discharged to the lower reaches of Tarim River in the past three decade years, the riparian forests degrade severely. The groundwater table, the saline content of the groundwater, as well as the content of free proline, soluble sugars, plant endogenous hormones (abscisic acid (ABA), and cytokinins (CTK)) of the leaves and relative rates of sap flow of the Populus euphratica Oliv. (arbor species), Tamarix ramosissima Ldb. (bush species), and Apocynum venetum L. (herb species) were monitored and analyzed at the lower reaches of the Tarim River in the study area where five positions on a transect were fixed at 100 m intervals along a sampling direction from riverbank to the sand dunes before and after water release. The physiological responses and acclimation strategies of three species to variations in water and salinity stress were discussed. It was found that A. venetum population recovered to groundwater table ranging from −1.73 to −3.56 m, and when exposed to saline content of the groundwater ranging from 36.59 to 93.48 m mol/L; P. euphratica appeared to be more sensitive to the elevation of groundwater table than the A. venetum and T. ramosissima at groundwater table ranging from −5.08 to −5.80 m, and when exposed to saline content of the groundwater ranging from 42.17 to 49.55 m mol/L. T. ramosissima tended to be the best candidate species for reclamation in this hyper-arid area because it responded to groundwater table ranging from −1.73 to −7.05 m, and when exposed to saline content of the groundwater ranging from 36.59 to 93.48 m mol/L. These results explained the distribution patterns of desert vegetation in the lower reaches of the Tarim River. Understanding the relationships among ecological factors variables, physiological response and acclimation strategies of plant individuals could provide guidance to sustainable management, reclamation and development of this and similar regions.     

黄河内蒙古段头道拐断面冰期水流特征及其对气候变化与人类活动的响应

利用最新冰凌观测数据,分析了1960年以来黄河内蒙古段头道拐断面冰期流量特点及其影响因素.结果表明：头道拐断面小流量持续时间的年际变化具有明显的阶段性特征,1960-1967年、1968-1985年和1986-2010年小流量平均持续天数分别为68 d、17 d和37 d.气候变化和人类活动是影响小流量过程的主要因素,气候变化通过影响冰盖厚度和冰花堆积来影响封冻河段流量过程;河道冲淤演变则是冰期流量过程和槽蓄水增量长期变化的重要原因;刘家峡水库调度直接影响着内蒙古河段的流量过程. 最近10 a来,凌汛期气温变化剧烈,上游来水有所减少,河道淤积更加严重,河道工程增多是黄河头道拐断面小流量持续天数延长的主要原因.     

Nebkha development and its relationship to environmental change in the Alaxa Plateau,China

Extensive nebkha areas develop mainly under the control of aeolian processes, and their sediments record information on regional environmental changes during different periods. Such areas have developed on the dry riverbeds and deserted arable lands of China’s Alaxa Plateau, Taklimakan, and Kumutage deserts. In this paper, we studied nebkhas that had developed in the Heicheng–Juyan region to determine their CaCO₃ contents, particle size distributions, and creation dates. Extensive human activities have occurred in this region since at least in the late Tang Dynasty (618–907 ad). Although historical records show that most of the region’s rivers dried up around 1372, surface water persisted in some areas until the early Qing Dynasty (1644–1911 ad). After the 1600s, extensive nebkhas began to develop due to drying of the region’s rivers. The early stages of nebkha development were controlled by both the sediment supply and the regional wind regime, whereas late stages were controlled primarily by variations in wind activity. In the Alaxa Plateau, it took about 100 years for arable lands and riverbeds to evolve into gobi deserts, and during this time, several phases occurred with different levels of wind activity. The land degradation processes in this region are mainly controlled by surface water resources, and the impact of human activities such as reclamation on land degradation appear to have been overestimated in previous studies.     

Effect of salinity on osmoregulation and survival of a rhizocephalan parasite,Loxothylacus panopaei,and its crab host,Rhithropanopeus harrisii

The rhizocephalanLoxothylacus panopaei parasitizes the estuarine crabRhithropanopeus harrisii. Parasitized crabs are abundant during summers when salinities increase to around 15‰ in the crab–s habitat and scarce when salinities are lower. The two hypotheses that were proposed to explain this pattern were (1) that the parasite interferes with crab osmoregulation causing the host to die in low salinity water and (2) that salinity tolerance of the parasite larvae controls the incidence of parasitism. The first hypothesis was shown to be incorrect because (1) osmoregulation of infected crabs was, not altered by the parasite and (2) crab mortality did not increase in low salinity water down to 1‰. Unparasitized and parasitized crabs and the parasite itself were hypersomotic at low salinities (below 27‰ for the crabs). The parasite became slightly hyperosmotic at high salinities while the crabs were slightly hypoosmotic. The second hypothesis appears correct, becauseL. panopaei larvae survived poorly in salinities below 10‰ but well in salinities from 10 to 15‰. ThusR. harrisii, have a reproductive refuge at salinities below 10‰, because parasite larvae cannot survive and infect the mud crab at these low salinities.     

城市化过程中都市农业景观变化及其生态安全评价——以西安市为例

快速城市化过程中都市农业景观变化及其生态安全研究是城市化区域生态安全和可持续发展研究的重要课题.构建都市农业景观生态安全评价指标与方法,探讨城市化对都市农业景观生态安全的影响具有重要的科学意义.以西安市为例,应用GIS和RS技术方法,结合"压力-状态-响应"(PSR)模型建立了都市农业景观生态安全综合评价指标体系,通过提取1999、2006和2013年的农业景观类型信息,定量分析了都市农业景观变化特征、动态评价了都市农业景观生态安全过程.结果表明:1999-2013年西安市农业景观结构变化剧烈,景观斑块数量增加、平均斑块面积减小,聚集度变差,景观趋于复杂化、破碎化,耕地、林地面积显著减少,园地面积增加.城市化的快速发展导致都市农业生态安全压力指数由0.43上升为0.59,生态安全状态指数由0.73降至0.28,生态安全响应指数则由0.26上升为0.77,生态系统服务价值下降;城市化过程带来的景观压力指数上升以及景观状态指数下降,使得都市农业景观生态安全综合指数由0.56先下降为0.4,后上升到0.48.城市化过程中的都市农业景观生态安全评价可以为都市农业可持续发展、土地可持续利用管理和科学决策提供依据.     

祁连山东段童子坝河阶地对气候变化与新构造运动的响应*

通过对祁连山东段童子坝河各级阶地的年代和变形程度进行测定,得到了河流阶地的形成年代和过程,推算出民乐—大马营逆断裂的活动强度和速率,并分析了阶地形成和气候变化之间的关系。童子坝河5级阶地(年龄分别为16.70±1.81 cal,ka BP、 10 092.5±27.5 cal a BP、8127.5±72.5 cal a BP、2900±60 cal a BP、282.5±17.5 cal a BP)均形成于气候由冷转暖的阶段,属于气候成因阶地。基于断裂两侧阶地面的平面几何形态并结合上、下盘阶地横剖面同级阶地的高差,得到T4、T3、T2和T1阶地在民乐—大马营断裂处的垂直位错分别为10.6±3.1,m、5.0±2.6 m、2.0±1.9 m和1.9±1.3 m,推算出全新世以来民乐—大马营断裂的垂直滑动速率为1.05±0.31 mm/a,水平缩短速率为1.02±0.60 mm/a。     

The influence of upwelling and short-term changes in concentrations of nutrients in the water column on fluxes across the surface of a salt marsh

Oceanic upwelling results in the intermittent intrusion of cold ocean water enriched in nitrate, and to a lesser extent soluble reactive phosphorus (SRP), into the Kariega Estuary (South Africa). Laboratory measocosm experiments were conducted to determine the effects of such changes on fluxes of dissolved nutrients across the surface of a salt marsh within the estuary. When replicate mesocosms of the tidal creek and salt marsh were inundated with nonupwelled water (at 25°C and nitrate concentrations of 4.5 μmoll^?1), nitrate fluxes in both regions were small, and the tidal creek exhibited net uptake (negative value) of nitrate from the water column (?85 μmol m^?2 tide^?1), and the marsh, net release (positive values; 113 μmol m^?2 tide^?1). When the mesocosms were inundated with upwelled water, at 16°C and with nitrate concentrations of 24.2 μmol l^?1, both regions exhibited large net uptakes of nitrate (?514 μmol m^?2 tide^?1 and ?226 μmol m^?2 tide^?1 for the tidal creek and salt marsh, respectively). In contrast to nitrate, the fluxes of nitrite, ammonium, and SRP were not significantly different under upwelling and nonupwelling conditions, probably because initial concentrations in the two water types were similar. To determine the extent to which the nitrate uptakes were caused by decreased water temperatures or increased concentrations of nitrate, experiments were conducted in which mesocosms were inundated with water with a range of nitrate concentrations (1.8–25 μmol l^?1), at two temperatures representative of summer upwelling (16°C) and nonupwelling conditions (25°C). In both regions, the net fluxes of nitrate were positively correlated with initial concentrations of nitrate in the water column. For any given concentration, the fluxes at 16°C fell within the range of values at 25°C, indicating that the shifts in fluxes caused by upwelling occurred in response to increased concentrations in the water column and not reduced temperatures.     

浙江玄武岩风化壳红土磁性特征及其对成土过程的响应

以位于浙江磐安县的玄武岩风化壳红土（XZ剖面）为研究对象,对其进行系统环境磁学分析,结合常量元素、漫反射光谱、有机质等分析手段,研究玄武岩风化壳红土的磁性特征,并探讨磁性特征与风化成土过程之间的关系。结果表明：在风化成土初期,玄武岩风化壳红土磁性较强,具有较高的磁化率（χ）和饱和等温剩磁（SIRM）,磁性矿物主要为原生多畴（MD）颗粒亚铁磁性矿物（磁铁矿、钛磁铁矿）,磁性特征继承了母岩特性;随着风化成土作用的增强,土壤中的原生亚铁磁性矿物逐渐转化为次生不完全反铁磁性矿物（赤铁矿、针铁矿等）,导致土壤磁性降低,但细颗粒磁性矿物逐渐增加;强风化成土阶段,原生亚铁磁性矿物进一步减少,反铁磁性矿物仍表现出一定高值,同时大量成土成因的细颗粒次生强磁性矿物（SP颗粒磁铁矿、磁赤铁矿）逐渐生成,导致土壤χ持续升高。本研究显示玄武岩风化壳红土的磁学特征与风化成土过程具有紧密的关系,磁性参数χ_fd%可作为亚热带地区玄武岩风化壳红土成土过程和成土强度的指示指标。

     

黄河流域生态系统服务价值变化评估及生态地质调查建议

黄河流域是中国重要的生态屏障,生态系统服务功能十分重要。基于ArcGIS、Google Earth Engine等平台,以黄河流经市域生成流域范围,对2000—2015年间黄河流域生态系统服务价值的变化进行评估,揭示生态系统服务功能的强弱及生态系统的稳定性状况,提出生态地质调查工作建议,为黄河流域国土空间优化、生态环境保护和高质量发展提供重要依据。评估结果表明,黄河流域生态系统服务以水文调节、气候调节、土壤保持调节服务为主,空间分布上呈"南高北低、上下游低、中游高"的空间特征。15年间,黄河流域生态系统总服务价值增长了33.4%,呈现"上游玉树-阿坝一带山区明显减少、中游黄土高原区显著增加、下游轻微降低"的空间格局特点,但总体上生态环境与经济发展处于低度协调状态,下游生态系统服务供给与需求之间存在空间不匹配问题。建议动态评估流域生态系统承载能力,聚焦关键过程、关键区域、关键要素,部署生态地质调查工作,提升生态系统服务价值,优化流域国土空间结构。     

吉林省季节冻土冻结深度变化及对气候的响应

为了掌握季节冻土冻结深度的变化对气候的响应,利用1961-2015年吉林省46个气象站的逐日平均气温、地表温度、积雪深度、冻土冻结深度等数据,采用线性倾向估计、突变分析等方法,研究了吉林省季节冻土冻结深度的时空演变规律及其与气温、积雪的关系。结果表明：吉林省季节冻土最大冻结深度呈由西向东逐渐减小的空间分布特征,绝大多数站最大冻结深度呈减小趋势。基本上在10月开始冻结,次年3月达到最深,6月完全融化。西部冻土冻结深度变幅较大,其次是中部,东部最小。1961-2015年季节冻土最大冻结深度以-5.8 cm·（10a）^-1的速率显著减小（P<0.01）。最大冻结深度基本上呈逐年代减小的趋势,从20世纪90年代开始,最大冻结深度明显减小。最大冻结深度在1987年发生了突变,突变后平均最大冻结深度比突变前平均最大冻结深度减小了22.2 cm。通过分析气温和积雪深度对冻结深度的影响,认为冻土冻结深度对气温变化较为敏感,绝大多数站最大冻结深度与平均气温呈负相关关系。在年际变化上,气温的上升是最大冻结深度减小的主要原因。在季节冻土稳定冻结期,积雪深度超过10 cm,保温作用逐渐变强;当积雪深度达到20 cm时,保温作用显著,冻土冻结深度变浅。     

珠穆朗玛峰自然保护区湖泊动态及对区域气候变化的响应

利用Landsat卫星影像,采用面向对象分类方法提取珠穆朗玛峰自然保护区湖泊信息,分析了湖泊动态及对区域气候变化的响应关系。结果表明：（1）2015年保护区湖泊总面积为489.07 km²,构造湖、河成湖、冰川湖分别占总面积的77.3%、2.6%、20.1%。（2）1975-2015年,保护区内各类湖泊面积变化速率不同,冰川湖最大（1.05 km²·a^-1）,构造湖次之（-0.85 km²·a^-1）,河成湖最稳定（0.013 km²·a^-1）;保护区南坡冰川湖面积变化速率（0.53 km²·a^-1）略大于北坡（0.52 km²·a^-1）。（3）北坡构造湖、河成湖对区域气候的响应呈阶段性变化规律,1975-2000年珠峰地区气候呈暖湿化趋势,2000年构造湖、河成湖面积达到峰值,两类总计增加22.8 km²;2000-2015年转变为显著的暖干气候,构造湖、河成湖面积均呈减少趋势,总共减少57.16 km²。随着区域气候的变暖,冰川湖总面积不断扩大,近40年间冰川湖面积累计增加43.06 km²。（4）灰色关联度分析显示,年极端低温对构造湖面积变化影响最显著,年均气温对冰川湖起主导作用,年均相对湿度对河成湖影响最大。较其他气候因子而言,降水量对各类湖泊面积变化的影响均最小。     

Wind erosion of saline playa sediments and its ecological effects in Ebinur Lake,Xinjiang, China

In many arid and semiarid areas, dry lake beds (saline playa) represent a tremendous source of unconsolidated salt-rich sediments that are available for aeolian transport. Severe salt-dust storms caused by the erosion of such landforms have become very harmful natural phenomena. In this study, sample analysis and field erosion monitoring of Ebinur Lake was conducted to investigate the salt content, chemical composition, and wind erosion intensity of surface salt-rich sediments. The effects of salt-dust rising from the playa on the growth and physiological health of plants were also evaluated in this study through a leaf dustfall test. The results indicate that water-soluble salts assemble densely on the dry lake bed surface. At a depth of 0–2 cm, the highest salt contents can exceed 40%, with sulfate and chloride being the main anions present and Na⁺, Ca²⁺, and Mg²⁺ being the primary cations. The annual wind erosion rate ranged from 0.48 to 5.6 cm in the northwest portion of the lake and from 0.24 to 0.96 cm in the southeast portion. Salt-dust storms caused by wind erosion of saline playa sediments seriously influenced the normal absorption of minerals by plant leaves. Under the influence of salt-dust storms, plant leaves absorb more Na⁺, but far less K⁺.