The Burrum River estuary: identifying reference sites for Australian sub-tropical estuarine systems using paleolimnological methods

There is a pressing need to obtain historical information on estuaries so that levels of natural variability and ecosystem thresholds can be identified. Once these factors are known, estuaries that exhibit high conservation value and minimal impact from anthropogenic activity can be acknowledged and protected. In order to understand and quantify the level of change that may have occurred due to human impact, near pristine estuaries that have the potential to act as reference sites need to be identified. However, this is often difficult due to a lack of documented knowledge of estuary variability. This paper retrospectively assesses environmental conditions in the Burrum River, a sub-tropical east Australian estuary on the coast of Queensland, using diatom and stable isotope analyses. These techniques were combined with AMS ¹⁴C dating methods to determine if this system has undergone any natural or anthropogenically induced change. Diatom assemblages have shown very little variation over the past 5,000 years, indicating minimal changes to water quality. Upper and lower limits for δ¹³C and δ¹⁵N stable isotope results also infer that the sources of carbon and nitrogen to the Burrum River estuary have remained constant over this time period. Carbon inputs have been dominated by marine autotrophic production, whilst nitrogen inputs are indicative of terrestrial sources. Hence, the Burrum River has not been altered by anthropogenic activities and is a suitable reference site for benchmarking impacted sub-tropical estuaries. This paper demonstrates that paleolimnological techniques can be applied successfully to identify estuaries that are suitable as reference sites.     

Temporal and spatial changes of suspended sediment concentration and resuspension in the Yangtze River estuary

A detailed analysis of suspended sediment concentration (SSC) variations over a year period is presented using the data from 8 stations in the Yangtze River estuary and its adjacent waters, together with a discussion of the hydrodynamic regimes of the estuary. Spatially, the SSC from Xuliujing downwards to Hangzhou Bay increases almost constantly, and the suspended sediment in the inner estuary shows higher concentration in summer than in winter, while in the outer estuary it shows higher concentration in winter than in summer, and the magnitude is greater in the outer estuary than in the inner estuary, greater in the Hangzhou Bay than in the Yangtze River estuary. The sediments discharged by the Yangtze River into the sea are resuspended by marine dynamics included tidal currents and wind waves. Temporally, the SSC shows a pronounced neap-spring tidal cycle and seasonal variations. Furthermore, through the analysis of dynamic mechanism, it is concluded that wave and tidal current are two predominant factors of sediment resuspension and control the distribution and changes of SSC, in which tidal currents control neap-spring tidal cycles, and wind waves control seasonal variations. The ratio between river discharge and marine dynamics controls spatial distribution of SSC.     

长江口水域悬沙浓度时空变化与泥沙再悬浮

A detailed analysis of suspended sediment concentration (SSC) variations over a year period is presented using the data from 8 stations in the Yangtze River estuary and its adjacent waters, together with a discussion of the hydrodynamic regimes of the estuary. Spatially, the SSC from Xuliujing downwards to Hangzhou Bay increases almost constantly, and the suspended sediment in the inner estuary shows higher concentration in summer than in winter, while in the outer estuary it shows higher concentration in winter than in summer, and the magnitude is greater in the outer estuary than in the inner estuary, greater in the Hangzhou Bay than in the Yangtze River estuary. The sediments discharged by the Yangtze River into the sea are resuspended by marine dynamics included tidal currents and wind waves. Temporally, the SSC shows a pronounced neap-spring tidal cycle and seasonal variations. Furthermore, through the analysis of dynamic mechanism, it is concluded that wave and tidal current are two predominant factors of sediment resuspension and control the distribution and changes of SSC, in which tidal currents control neap-spring tidal cycles, and wind waves control seasonal variations. The ratio between river discharge and marine dynamics controls soatial distribution of SSC.     

近期长江北支口门圆陀角附近潮滩地貌动态变化

圆陀角位于长江北支岸线与江苏海岸线的交会处,独特的互花米草潮滩、淤泥质光滩环境和复杂的河海沉积动力,决定了潮滩地貌对海洋环境变化的响应具有敏感性。由于大规模的围垦,圆陀角附近过去40年来海岸线向东推进了6km。根据2006年以来多次的野外调查和室内粒度与钻孔岩芯的¹³⁷Cs分析, 2006年以来圆陀角附近潮滩淤积明显加强,由¹³⁷Cs时标估算的互花米草滩多年平均沉积速率为2.3cm/a, 2006~2008年观测到的互花米草滩淤积速率>4cm/a,粉砂淤泥质光滩的淤积速率更高;圆陀角风景区内互花米草滩前缘陡坎在风暴潮影响下侵蚀后退,并因粉砂淤泥质光滩的快速淤长而消亡,圆陀角附近潮滩地貌动态是对人类围垦活动、风暴潮与潮汐海洋动力的综合响应,互花米草与光滩快速淤积是近期圆陀角附近潮滩地貌演化的主要特点。     

Natural and anthropogenic aquatic environmental changes reconstructed by paleolimnological analyses in Lake Kitaura,central Japan

In order to assess the recent anthropogenic environmental changes in Lake Kitaura, central Japan, changes during the past few centuries were reconstructed from results of radiometric and tephrochlonological age determination, magnetic susceptibility measurements, total organic carbon analyses, total nitrogen analyses and fossil diatom analyses on a sediment core from the lake. A total of six major and sub-zones are recognized according to the diatom fossil assemblages, and we discuss aquatic environmental change in Lake Kitaura mainly based on these diatom assemblage change. Zone Ia and Zone Ib (older than AD 1707) are marine to brackish. In Zone IIa (AD␣1707–AD 1836), most of the brackish diatoms disappeared, and were replaced by freshwater species indicating a decrease in salinity. We interpret the salinity decrease in Zone I–IIa as a sea-level fall during the Little Ice Age. The salinity of the lake decreased to near freshwater conditions in Zone IIb (AD 1836–AD 1970), which could arise from alteration in River Tone or development of a sandspit in the mouth of River Tone in addition to sea-level change. In Zone IIIa (AD 1970–AD 1987), the diatom assemblage indicates a freshwater environment, and sedimentation rates increase rapidly. These changes reflect sedimentary environment change and an ecosystem transition due to the construction of the tide gate. In Zone IIIb (AD 1987–AD 2002), the diatom flux (valves cm⁻² y⁻¹) increased and species composition changed. The changes in Zone IIIb show a good agreement with limnological monitoring data gathered from the lake. These paleolimnological data suggest that the recent human-induced changes of the aquatic environment of the lake after the 1970s exceed rates during the period concerned in this study.     

沉积强度及氮养分改变对闽江河口短叶茳芏残体短期分解与养分释放的影响

互花米草入侵过程中较强的促淤作用可导致湿地沉积环境和养分状况发生明显变化.2017年4月,选择闽江河口鳝鱼滩西北部受互花米草入侵影响的短叶茳芏湿地为研究对象,基于野外原位沉积及养分改变模拟试验,设置无沉积强度(S0,0 cm·a-1)、当前沉积强度(S5,5 cm·a-1,氮养分水平为沉积物自然氮背景值)以及当前沉积强...     

Holocene lake-level changes and their reflection in the paleolimnological records of two lakes in northern Estonia

Sediment cores from two neighbouring lakes (Viitna Linajärv and Viitna Pikkjärv) in northern Estonia were studied to determine lake-level fluctuations during the Holocene and their impact on biogeochemical cycling. Organic matter and pollen records dated by radiocarbon and radiolead indicated a water level rise in both lakes during the early Holocene (c. 10 000–8000 BP). A regression followed around 7500 BP and several transgressions occurred during the latter half of the Holocene, c. 6500 and 3000 BP. Human impact during the last centuries has caused short-term lake-level fluctuations and accelerated sediment accumulation in the lakes. The differences in water depth led to variations in sediment formation. During 10 000–8000 BP (Preboreal and Boreal chronozones) mineral-rich sediments with coloured interlayers deposited in L. Linajärv. These sediments indicate intensive erosion from the catchment and oxygen-rich lake, which favoured precipitation of iron oxides and carbonates. Fluctuations in water depth, leaching of nutrients from catchment soils and climatic changes increased the trophy of L. Linajärv around 6000 BP. The subsequent accumulation of gyttja, the absence of CaCO₃ and the decrease in both the C/N ratio and phosphorus content in the sediments also indicate anoxic conditions in the hypolimnion. The similarity in the development of L. Linajärv and L. Pikkjärv and their proximity made it possible to discern the impact of water depths changes on biogeochemical cycling in lakes.     

Subsidence, sedimentation and sea-level changes in the Eromanga Basin, Australia

Abstract The Jurassic-Cretaceous subsidence history of the Eromanga Basin, a large intracratonic sedimentary basin in central eastern Australia, has been examined using standard backstripping techniques, allowing for porosity reduction by compaction and cementation. Interpretation of the results suggests that during the Jurassic the basin was subsiding in a manner consistent with the exponentially decreasing form predicted by simple thermally based tectonic models. By the Early Cretaceous, the rate of subsidence was considerably higher than that expected from such models and nearly half of the total sediment thickness was deposited over the final 20 Myr of the basin's 95 Myr Mesozoic depositional history. The Early Cretaceous also marks the first marine incursion into the basin, consistent with global sea-level curves. Subsequently, however, the sediments alternate between marine and non-marine, with up to 1200 m of fluvial sediments being deposited, and this was followed by a depositional hiatus of about 50 Myr in the Late Cretaceous. This occurred at a time when global sea-level was rising to its peak. A model is presented which is consistent with the rapid increase in tectonic subsidence rate and the transgressive-regressive nature of the sediments. The model incorporates a sediment influx which is greater than that predicted by the thermally based tectonic models implied by the Jurassic subsidence history. The excess sedimentation results in the basin region attaining an elevation which exceeds that of the contemporary sea-level, and thereby giving the appearance of a regression. The present day elevation of the region predicted by the model is about 100–200 m above that observed. This discrepancy may arise because the primary tectonic subsidence is better represented by a linear function of time rather than an exponentially decreasing form.     

Contrasting the effects of climatic, nutrient, and oxygen dynamics on subfossil chironomid assemblages: a paleolimnological experiment from eutrophic High Arctic ponds

Nutrients from the waste products of large seabird colonies can enter freshwater ecosystems, markedly altering water quality and biotic assemblages, especially in nutrient-poor regions like the Canadian High Arctic. Here, we investigate the influence of nutrient-rich seabird wastes on freshwater larval chironomid assemblages from two distinct seabird colonies. The study sites include four ponds dominated by northern fulmars (Fulmarus glacialis) at Cape Vera, Devon Island, as well as one pond near a large group of common eider ducks (Somateria mollissima borealis) on Tern Island (unofficial name) near Cornwallis Island, Nunavut. The rare combination of nutrient-enriched and well-oxygenated waters allowed us to contrast the effects of nutrients, oxygen, and temperature on chironomid community structure in shallow Arctic ponds using sediment cores. Despite highly elevated nutrient levels, the subfossil assemblages were dominated by cold stenotherms typical of oligotrophic waters. Although nutrient inputs appear to have increased chironomid head capsule numbers due to enhanced food availability, the fertilization had little direct effect on assemblage composition, at least at the taxonomic level achievable based on fossil material. The presence of low abundances of eutrophic/anoxic taxa, such as Chironomus plumosus-type, suggests that biogeographic barriers to dispersal are not influencing the assemblages. These data demonstrate that, in the presence of high concentrations of dissolved oxygen, nutrient enrichment had little direct effect on chironomid community composition in shallow Arctic ponds.     

Hydroclimatological changes in the Bagmati River Basin, Nepal

Study on hydroclimatological changes in the mountainous river basins has attracted great interest in recent years. Changes in temperature, precipitation and river discharge pattern could be considered as indicators of hydroclimatological changes of the river basins. In this study, the temperatures （maximum and minimum）, precipitation, and discharge data from 1980 to 2009 were used to detect the hydroclimatological changes in the Bagmati River Basin, Nepal. Simple linear regression and Mann-Kendall test statistic were used to examine the significant trend of temperature, precipitation, and discharge. Increasing trend of temperature was found in all seasons, although the change rate was different in different seasons for both minimum and maximum temperatures. However, stronger warming trend was found in maximum temperature in comparison to the minimum in the whole basin. Both precipitation and discharge trend were increasing in the pre-monsoon season, but decreasing in the post-monsoon season. The significant trend of precipitation could not be observed in winter, although discharge trend was decreasing. Furthermore, the intensity of peak discharge was increasing, though there was not an obvious change in the intensity of maximum precipitation events. It is expected that all these changes have effects on agriculture, hydropower plant, and natural biodiversity in the mountainous river basin of Nepal.     

Quantifying the effects of hydrological changes on long-term water quality trends in temperate reservoirs: insights from a multi-scale,paleolimnological study

Declining water quality in reservoirs is of growing concern in many regions, yet there is still little understanding of long-term water quality trends in these systems. Across the landscape, reservoirs have diverse origins, functions, and operational strategies. In temperate environments, winter water-level drawdown is a common operational practice in reservoirs but the long-term impacts of this hydrological modification has not been extensively studied. We paired a comparative, pre-dam-to-contemporary study (i.e. a top–bottom design) of 12 reservoirs with a detailed paleolimnological study of a focal lake to generate quantitative insights into the relative effect of hydrological changes vs. landscape and climatic drivers on water quality. The focal reservoir, Grand Lac Saint-François, is of relatively similar morphometry, geography, and limnology to our other sites, and has experienced annual winter water-level drawdown of?~?5 m since it was dammed approximately 100 years ago. Based on our top–bottom analysis, we did not find strong correlations between long-term changes in water quality (i.e. diatom-inferred TP estimates) and winter water-level drawdown amplitudes. Instead, reservoir morphometry and watershed characteristics (i.e. geography, maximum depth, and cropland areas) appeared to be stronger drivers of trends across the region. From the detailed paleolimnological analysis, we found that sedimentary pigments and DI-TP concentrations significantly increased over the last century based on Mann–Kendall trend analyses. Breakpoint analyses showed that changes in biological-proxy trends, as well as the sedimentology (i.e. lithology and accumulations rates), coincided with dam construction and the onset of water level regulation. However, given the high variability in metrics and the extent of water level monitoring records, we were unable to quantitatively associate the impacts of drawdown with water quality trends at Grand Lac Saint-François. Conversely, we did find that watershed nutrient surpluses from livestock farming, and warming temperatures were significant explanatory variables of water quality metrics.     

Assessing changes in extreme precipitation over Xinjiang using regional climate model of PRECIS

In this paper, an analysis, with the simulation of PRECIS(Providing Regional Climate for Impact Studies), was made for future precipitation extremes, under SRES(Special Report on Emission Scenarios) A2 and B2 in IPCC(Intergovernmental Panel on Climate Change) AR4. The precipitation extremes were calculated and analyzed by ETCCDI(Climate Change Detection and Indices). The results show that:(1) In Present Scenario(1961–1900), PRECIS could capture the spatial pattern of precipitation in Xinjiang.(2) The simulated annual precipitation and seasonal precipitation in Xinjiang had a significantly positive trend and its variability had been deeply impacted by terrain. There was a strong association between increasing trend and the extreme precipitation's increase in frequency and intensity during 1961–2008. Under SRES A2 and B2, extreme precipitation indicated an increasing tendency at the end of the 21 st century. The extreme summer precipitation increased prominently in a year.(3) PRECIS's simulation under SRES A2 and B2 indicated increased frequency of heavy precipitation events and also enhancement in their intensity towards the end of the 21 st century. Both A2 and B2 scenarios show similar patterns of projected changes in precipitation extremes towards the end of the 21 st century. However, the magnitude of changes in B2 scenario was on the lower side. In case of extreme precipitation, variation between models can exceed both internal variability and variability of different SRES.     

黄渭洛三河汇流区湿地景观变化

流域经济快速发展使得黄河、渭河及北洛河三河汇流区湿地景观变化显著。应用GIS/RS技术与景观格局分析软件FRAGSTATS,对1989、1996、2000年5月黄渭洛三河汇流区湿地景观的演变过程进行计算和分析,探讨了湿地景观格局特征的变化趋势以及湿地景观演化的驱动力因素,主要结论为:①水文因素和人文因素是汇流区景观变化的主要驱动力;②草地、盐碱地和裸地的面积在增加,而耕地和水域的面积在减少;③土地盐碱化形势依旧严峻,分别有1.38 km2的耕地、0.54 km2的草地和0.47 km2的水域演化为盐碱地;④景观指标表明湿地景观多样性和均匀性逐年升高。     

黄河口不同粒度泥沙沉积与扩散分析

本文采集和收集大量黄河三角洲沉积物剖面和钻孔泥沙粒度资料以及黄河口来沙粒度组成数据,定量研究了黄河口泥沙的沉积与扩散特征.结果 显示黄河口来沙以粉砂为主,黏土次之,砂最少,年均中值粒径无长期变化趋势.黄河三角洲平原相泥沙与来沙的黏土、粉砂和砂含量无显著差异;前缘相泥沙比来沙的黏土含量较低,砂含量较高;前三角洲相泥沙比来...     

Phytoplankton dynamics in Lake Biwa during the 20th century: complex responses to climate variation and changes in nutrient status

We examined algal remains and fossil pigments in ²¹⁰Pb-dated sediment cores from Lake Biwa to explore historical changes in the phytoplankton community of the lake over the past 100 years and to identify environmental factors that caused those changes. Fluxes of fossil pigments and algal remains were very low before the 1960s, but increased through the 1960s and 1970s, indicating that the lake had eutrophied in the 20 years since 1960. After 1980, however, fluxes of all fossil pigments and algal remains decreased or stabilized. Redundancy analysis with meteorological and limnological variables explained more than 70% of the variation of these fluxes and showed that the decrease in fluxes of most algal taxa that occurred in the 1980s was related to changes in meteorological variables such as wind velocity, rather than changes in the lake’s trophic state. Sedimentary records of algal remains also revealed that Aulacoseira nipponica, an endemic diatom species that grows in winter, decreased dramatically after 1980, while Fragilaria crotonensis, a cosmopolitan spring diatom species, became dominant. Replacement of one dominant diatom species by another could not be explained simply by changes in the lake trophic state, but was reasonably strongly related with an increase in winter water temperature. These results suggest that the phytoplankton community in Lake Biwa was influenced by changes in local environmental conditions (nutrient loading) through the 1960s and 1970s, but more so by regional (meteorological) and global (climate warming) factors since 1980.     

Chaoborus (Diptera: Chaoboridae) mandibles—paleolimnological indicators of the historical status of fish populations in acid-sensitive lakes

Paleolimnological analyses of Chaoborus mandibles were used to assess the status of fish populations over the previous 150 to 300 years in five lakes from the Adirondack region of New York State. Windfall Pond (pH 6.5) has not acidified and currently has viable fish populations. Big Moose Lake (pH 5.0) has acidified in recent years, and the number of fish populations declined from 14 in the 1930's to seven in the early 1980's. The occurrence of only migratory Chaoborus (subgenus Sayomyia) in the cores indicated the long term presence of fish populations in Windfall Pond and Big Moose Lake. Brooktrout Lake (pH 5.0), Deep Lake (pH 4.7) and Upper Wallface Pond (pH 4.8) have all acidified in recent years, and all three are currently fishless. Chaoborus (Sayomyia) was present throughout the Brooktrout Lake core, but the entirely limnetic species, C. americanus, appeared in the topmost interval in the core. The appearance of C. americanus in the top of the core indicated a recent elimination of fish from Brooktrout Lake, probably during the 1970's. Elimination of fish by the 1940's was inferred for Deep Lake because C. americanus appeared above the 1930 level and replaced C. trivittatus as the dominant. Dominance of C. americanus throughout the Upper Wallface Pond core indicated that planktivorous fish were never present. These results strongly suggest that stratigraphic analyses of Chaoborus mandibles provide a useful assessment of the general status of historical fish populations in Adirondack lakes. The technique should be useful in other regions, as well as for applications other than those concerning lake acidification.This is the eleventh of a series of papers to be published by this journal which is a contribution of the Paleoecological Investigation of Recent Lake Acidification (PIRLA) project. Drs. D.F. Charles and D.R. Whitehead are guest editors for this series.     

闽江河口湿地互花米草钾元素分布、积累与季节动态

选取闽江河口湿地入侵植物互花米草（Spartina alterniflora）为研究对象,测定其各个构件生物量和钾元素含量季节变化,结果表明：互花米草地上部分各个构件钾元素含量从春季到冬季逐渐减少,除夏季外,其余季节绿茎和绿叶钾元素含量显著高于立枯部分（P〈0．05）,花仅出现在秋冬季节,且在秋季钾元素含量达到峰值（8...     

挠力河流域河流径流量对气候变化的敏感性分析

流域径流量对气候变化的敏感性分析是理解气候变化对流域水资源影响的重要手段。本文利用非更新式人工神经网络(ANN)模型,以年平均降雨、年最低气温和最高气温为输入参数,年平均径流量为输出变量,构建了三江平原挠力河流域的径流量预测ANN模型;并根据IPCC第四次报告的气候变化模式,设定了9种不同的气候变化情景,利用构建的ANN模型分析了流域径流量对气候变化的敏感性。结果表明:构建的人工神经网络模型能够较好的模拟径流量,可用于气候变化的敏感性分析;挠力河流域上游径流量对气候变化的敏感性要大于中游区域的,降水变化对径流量的影响大于气温对其产生的影响。     

闽江口潮汐盐沼湿地土壤碳氮磷的空间变化

以闽江口区最大的鳝鱼滩潮汐盐沼湿地为研究对象,选择远、近潮沟区2个不同潮水水淹地段设置样线,采集3种优势植物芦苇(Phragmites australis)、咸草(Cyperus malac-censisvar.bervifolius)和藨草(Scirpus triqueter)下18个土壤剖面分层样品,分析土壤中DOC、TN和TP等含量和储量的空间分布规律及土壤物理特征对其的影响。结果表明:远、近潮沟区3种植物下土壤表层(0~10 cm)TN浓度范围为0.24~1.91g kg-1,TP为0.21~1.34 g kg-1,DOC为13.68~93.73 mg kg-1,无论是近潮沟区还是远潮沟区,芦苇和咸草下土壤DOC、TN和TP含量十分接近,且均大于藨草下土壤DOC、TN含量,藨草下土壤TN和TP含量和储量在近潮沟区均明显大于远潮沟区,而芦苇和咸草下土壤TN和TP含量在远、近潮沟区差距不大;土壤DOC、TN和TP含量与土壤粒径、容重和含水量呈显著相关,盐度对土壤中NH4+-N和NO3--N含量影响显著,与NH4+-N为正相关关系,与NO3--N为负相关关系。     

Assessing trends and seasonal changes in elephant poaching risk at the small area level using spatio-temporal Bayesian modeling

Knowledge about changes in wildlife poaching risk at fine spatial scale can provide essential background intelligence for law enforcement and crime prevention. We assessed interannual trends and seasonal changes in elephant poaching risk for Kenya’s Greater Tsavo ecosystem for 2002 to 2012 using spatio-temporal Bayesian modeling. Poaching data were obtained from the Kenya Wildlife Service’s database on elephant mortality. The novelty of our paper is (1) combining space and time when defining poaching risk for elephant; (2) the inclusion of environmental risk factors to improve the accuracy of the spatio-temporal Bayesian model; and (3) the separate analysis of dry and wet seasons to understand season-dependent poaching patterns. Although Tsavo’s overall poaching level increased over time, the risk of poaching differed significantly across space. Three of the 34 spatial units had a consistently high poaching risk regardless of whether models included environmental risk factors. Adding risk factors enhanced the model’s predictive power. We found that highest poaching risk areas differed between the wet and dry season. The findings improve our understanding of elephant poaching and highlight high risk areas within Tsavo where action to reduce elephant poaching is required.