Late Holocene changes in the humic state of a boreal lake and their associations with organic matter transport and climate dynamics

An important factor in the ontogeny of boreal lakes is the development of their humic state through terrigenous input of organic matter (carbon) that affects strongly the functioning and structure of these ecosystems. The long-term dynamics and role of humic substances for these systems in relation to climate are not clear. In this study, a boreal lake from southern Finland was investigated using paleolimnological methods, including diatom, chironomid and geochemical analyses, for Late Holocene changes in the humic state. The aim was to examine the relationship between sediment biogeochemistry and climate variation. Consistent trends were found in diatom-inferred total lake-water organic carbon (TOC) and in the ratio of humic/oligohumic chironomids. Sediment geochemistry provided further evidence for the limnological development of the lake and related long-term climate trends in the region. The results indicated three distinct phases with differing humic state; the beginning of the record at ca. 4,500 cal year BP was characterized by extremely humic conditions coinciding with warm and dry climatic conditions, a meso-oligohumic period between ca. 3,000–500 cal year BP with increasing allochthonous organic matter transport and cooler and wetter climate, and recent period with polyhumic (TOC >10 mg L^?1) lake status and warming climate. This study shows that instead of straightforward linear development, boreal lakes evolve through dynamic humic stages related to climate and lake-catchment coupling processes. As the changes in the humic state are ultimately climate-driven, the ongoing climate change probably has a major influence on boreal lakes through direct and indirect effects on organic carbon transport, utilization and accumulation.     

Historical changes in the aquatic environment and input of polycyclic aromatic hydrocarbons over 1000 years in Lake Kitaura,Japan

We examined the vertical distributions of total organic carbon (TOC), total nitrogen (TN), total sulfur (TS), and 21 polycyclic aromatic hydrocarbons (PAHs) in a 100-cm-long sediment core collected from Lake Kitaura, a small and shallow eutrophic freshwater lake in central Japan, to elucidate changes in its aquatic environment and the input of PAHs with respect to human activity over the last 1000 years. Using a cross-plot of TOC and TS, the aquatic environment of this lake was well classified into four stages: a marine–brackish water period (≤1321 AD), a brackish–freshwater period (1394–1646 AD), a freshwater period (1726–1958 AD), and a eutrophication period (≥1971 AD). During the current eutrophication period, both TOC and TN have increased dramatically and TOC/TN (which is a useful indicator for distinguishing between aquatic and terrestrial plant sources) has decreased because algal production has markedly increased recently due to eutrophication. The vertical distributions of PAHs (which have derived primarily from combustion over the last 1000 years) showed increases in layers corresponding to periods of volcanic activity in the 18th century, as well as dramatic increases from 1971 to the present. Thus, both the aquatic environment and the input of PAHs in Lake Kitaura have been strongly affected by recent human activity. On the other hand, among all of the PAHs, only perylene—which is known to be of biological origin—was consistently formed via first-order kinetics over the period covered by the core. Its formation was barely influenced by fluctuations in the input of the precursor of perylene or how reductive the environment in the bottom water was.     

The Dry Holocene Megathermal in Inner Mongolia

The paleoclimate since 14 kyr BP (¹⁴C age) was reconstructed based on a 16.22-m-long sediment core collected from Lake Yanhaizi, a saline lake located near the northern limit of the East Asian summer monsoon in Inner Mongolia. Coarse sediments were deposited there during a shrinkage phase of the lake when sand dunes reactivated. These sediments have low organic carbon contents but high maturity indices, indicating that they were deposited in an arid environment. By contrast, based on high organic contents and low maturity indices, fine sediments were deposited during periods of high lake stand in a humid environment. It was in general dry between 8.0 and 4.3 kyr BP. The above dry and wet phases are consistent with those recovered from the arid-semiarid transition zone elsewhere, but are unlike the widely perceived humid Holocene Megathermal reported in east China and the newly reconstructed record in the alpine Retreat Lake in Taiwan. The discrepancy may be due to a relative insensitivity to humidity changes in these two areas since they have both been under the total influence of the summer monsoon. On the other hand, much enhanced evaporation over higher monsoon precipitation at Lake Yanhaizi reduces the effective humidity in the warm climate near the northern boundary of the summer monsoon. This also accounts for the fact the high-temperature Holocene Megathermal, as revealed in the Okinawa Trough and the northern South China Sea, is correlated to the dry phases at Lake Yanhaizi. Conversely, the 4-2-kyr BP coldest period in the Holocene corresponds to a wet phase at Lake Yanhaizi.     

滇中阳宗海流域过去1200年以来的环境变化

根据滇中阳宗海78 cm沉积岩芯的花粉/炭屑分析,重建了阳宗海流域过去1200年的植被演替、气候变化和森林火灾史。岩芯年代框架的建立基于底部一个植物残体的AMS14C测年和上部的210Pb测年。结果表明:1)阳宗海流域过去1200年的植被变化经历了4个阶段:暖干期(780—1630 AD)的植被以松栎混交林为主,草本植物少;凉湿期(1630—1860 AD)的植被仍以松栎混交林为主,但比重有所减少并存在明显波动,草本植物显著增加;冷干期(1860—1950 AD)和随后的暖干期(1950 AD之后)受人类活动干扰强烈,人类活动可能已成为影响植被的主导性因素。2) 1200年以来,阳宗海流域气候变化存在明显的暖期(780—1630 AD)和冷期(1630—1950 AD),分别对应了中世纪暖期和小冰期,且水热条件配置呈现暖干-冷湿的模式,与滇西天才湖、洱海和青藏高原东部等邻近区域较为同步。整个暖期气温波动不大,仅在最暖的12世纪中期到15世纪中期温度表现出较大的波动,小冰期存在两个气候波动阶段,分别是1630—1860 AD凉湿期和1860—1950 AD的冷干期。阳宗海流域气候变化的主...     

Investigating Changes in Land Use Cover and Associated Environmental Parameters in Taihu Lake in Recent Decades Using Remote Sensing and Geochemistry

Humans have had a significant impact on the terrestrial pedosphere through activities such as agriculture and urbanization. The effects of human activities on land use and the related environmental changes were investigated through point and areal studies surrounding Meiliang Bay, which is an open area of extreme eutrophication in Taihu Lake, China. This study used remote sensing and environmental-tracer profiles [total nitrogen (TN), total phosphorus (TP), total organic carbon (TOC), grain size, and geochemical parameters] to determine the causes of changes in land use and the associated environmental parameters. The results of LUCCs (Land use/cover changes) indicate that over the past three decades, total farmland decreased by 862.49 km², with an annual decrement rate of 28.75 km²/year, and total urbanized land increased by 859.71 km², with an annual growth rate of 28.66 km²/year. The geochemical results indicate that the trophic state of Taihu Lake was persistently intensifying and that the TN, TP, and TOC concentrations increased twofold, threefold, and twofold, respectively, from 1949 to 2010. The sources of TN, TP, and TOC were highly similar after 1975. However, before 1974, TN and TP originated from different sources than TOC. The grassland and woodland around the lake retain nutrients and sand from the land of study area. The increase in urbanized land and tertiary industries significantly increased the sediment concentrations of TN, TP, and TOC after 1980.     

Lake Sediment Records on Climate Change and Human Activities in the Xingyun Lake Catchment,SW China

Sediments from Xinyun Lake in central Yunnan, southwest China, provide a record of environmental history since the Holocene. With the application of multi-proxy indicators (total organic carbon (TOC), total nitrogen (TN), δ¹³C and δ¹⁵N isotopes, C/N ratio, grain size, magnetic susceptibility (MS) and CaCO₃ content), as well as accelerator mass spectrometry (AMS) ¹⁴C datings, four major climatic stages during the Holocene have been identified in Xingyun′s catchment. A marked increase in lacustrine palaeoproductivity occurred from 11.06 to 9.98 cal. ka BP, which likely resulted from an enhanced Asian southwest monsoon and warm-humid climate. Between 9.98 and 5.93 cal. ka BP, a gradually increased lake level might have reached the optimum water depth, causing a marked decline in coverage by aquatic plants and lake productivity of the lake. This was caused by strong Asian southwest monsoon, and coincided with the global Holocene Optimum. During the period of 5.60–1.35 cal. ka BP, it resulted in a warm and dry climate at this stage, which is comparable to the aridification of India during the mid- and late Holocene. The intensifying human activity and land-use in the lake catchment since the early Tang Dynasty (∼1.35 cal. ka BP) were associated with the ancient Dian culture within Xingyun’s catchment. The extensive deforestation and development of agriculture in the lake catchment caused heavy soil loss. Our study clearly shows that long-term human activities and land-use change have strongly impacted the evolution of the lake environment and therefore modulated the sediment records of the regional climate in central Yunnan for more than one thousand years.     

太湖沉积物微生物生物量及其与碳、氮、磷的相关性

对太湖沉积物中微生物生物量碳(MBc)、氮(MBN)、磷(MBp),以及沉积物总有机碳(TOC)、总氮(TN)、总磷(TP)进行测定并进行相关性分析,揭示太湖沉积物微生物对太湖沉积物营养盐的响应及反馈特征.结果表明:沉积物微生物生物量(MB)在湖体沿岸地区大于湖心区,平均值为184.66 mg·kg-1,MBc在西部沿岸区以及竺山湾和梅梁湾区域较高,平均值为127.57 mg·kg-1;MBN在梅梁湾、贡湖部分区域以及靠近梅梁湾和贡湖的湖心区域和东部沿岸区较高,平均值为19.25 mg·kg-1;MBp在东部沿岸区及其附近的湖心区最高,平均值为19.09 mg·kg-1;沉积物TOC高值区(≥2.30 g· kg-1)主要集中在竺山湾、西部沿岸区、梅梁湾、贡湖地区,平均值为1.59 g·kg-1;沉积物TN高值区(≥0.30g· kg-1)主要集中在贡湖、梅梁湾、竺山湾部分地区以及西部沿岸区,平均值为0.21 g·kg-1;沉积物TP高值区(≥1.20g·kg-1)主要集中在东部沿岸区以及湖心部分区域,平均值为0.55 g·kg-1;太湖沉积物TOC/TN在7～19,平均值为8.97,表明太湖沉积物中的有机质具有明显的双重来源,其中陆源有机质主要集中在西部沿岸区;太湖沉积物MB与沉积物TOC和TN呈显著正相关,与沉积物TP相关性不显著;沉积物MBc/MBN与沉积物TOC/TN显著相关.太湖沉积物微生物主要受沉积物TOC、TN影响,且沉积物TOC/TN的变化显著影响微生物群落结构.     

Paleoenvironmental changes in northwest Mongolia during the last 27?kyr inferred from organic components in the Lake Hovsgol sediment core record

We studied organic components in the X106 sediment core (length 130.3 cm, water depth 236 m, 50°53′01″N, 100°21′22″E) from Lake Hovsgol to elucidate the biological production, source of organic components, and paleoenvironmental and paleolimnological changes during the last 27 kyr in northwest Mongolia. Total organic carbon (TOC) contents (0.20–0.70%) in the core of the last glacial period increased dramatically and attained 3.16–5.85% in the postglacial period (Holocene), together with the increase of the contribution of terrestrial organic matter. Biological production (both terrestrial and aquatic production) based on the TOC contents in the Holocene was 14 times higher than that in the last glacial period. The B?lling-Aller?d warm period and Younger Dryas cool period were both observed at depths of 55–50 cm (ca. 15–13 cal kyr BP) and 50–45 cm (ca. 13–11 cal kyr BP), respectively. We propose here a terrestrial/aquatic index (TAI) for organic matter in lake sediments. The TAI values suggest that terrestrial organic matter in the bottom of the core was less than 10%, increased to 48% in the B?lling-Aller?d warm period, decreased abruptly to 20% in the Younger Dryas cool period, and again increased to 30–40% in the Holocene. Normal-C₃₁ alkane (a biomarker of herbaceous land plants) and n-C₁₈ alkanoic acid (marker of plankton) decreased from the last glacial period to the Holocene, whereas n-C₂₃ alkane and n-C₂₂ alkanoic acid (a marker of higher vascular plants) increased from the last glacial period to the Holocene. Scarce herbaceous plant vegetation, such as Artemisia spp. of the lake basin in the last glacial period, changed into an abundance of higher woody plant vegetation (e.g., Pinus spp., Betula spp. and/or Larix spp.) in the Holocene. Stanol/sterol ratios suggest that relatively high oxygen tension of the lake bottom in ca. 27–22 cal kyr BP decreased from this age to the present, though benthic organisms are still abundant.     

The effect of a shift from macrophyte to phytoplankton dominance on phosphorus forms and burial in the sediments of a shallow hard-water lake

In shallow lakes, increasing phosphorus (P) loading has often been accompanied by a shift from a clear-water, macrophyte-dominated state to a turbid state featuring phytoplankton dominance. The effect of a regime shift on P burial and P fractions in lake sediments, however, is poorly understood. We used sediment cores from a eutrophic hard-water lake (Lake Gollinsee, Germany) that had undergone a regime shift (in approximately 1917) to investigate the effect on the accumulation rate of P and on changes in P forms. The cores were dated using Hg contents and radioisotopes (²¹⁰Pb, ¹³⁷Cs, and ²⁴¹Am). A combination of total organic carbon to total nitrogen ratios (TOC:TN), δ¹³TOC values, X-ray fluorescence calcium (Ca) counts, and sediment colour clearly distinguished sediment layers that were deposited during periods of macrophyte or phytoplankton dominance. The accumulation rate of total P (TP) in the sediments was 1.8 times higher after the regime shift and was associated with changes in the distribution of P fractions. The proportions of loosely-(NH₄Cl-extracted TP) and Ca-(HCl-extracted TP) bound P decreased significantly, whilst the proportions of biogenic P (NaOH-extracted NRP) and aluminium-bound P (NaOH-extracted SRP) increased significantly. A higher dry mass deposition rate, reduced burial of stable Ca-P complexes, and increased contents and proportions of the mobile iron-bound (BD-extracted TP) and biogenic P fractions in the near-surface sediment layers are assumed to have enhanced the internal cycling of P and hence to have helped to maintain a state of phytoplankton dominance.

     

惠州西湖底泥中氮磷特征的初步研究

惠州西湖为典型的亚热带城市浅水湖泊.为了调查该湖泊底泥性质了解底泥对水质的影响.2004年8月在惠州西湖5个子湖(南湖、丰湖、平湖、菱湖和鳄湖)采集了6个底泥柱样,对其含水率、烧失量(LOI)、总氮(TN)、总磷(TP)、藻类可利用性磷(AAP)和粒度的垂向特征进行了初步研究.结果表明,各子湖中南湖内源负荷最大,底泥中的LOI、TN、TP和AAP含量高于其他湖区数倍以上,表层值较高,表明曾遭受过严重的污染,而其它湖区的垂向变化不明显.底泥成分以粘土、粉砂为主,水体混浊度高可能与底泥粒径较小以及鱼类和游船活动的强扰动性有关.     

Severe drought in the early Holocene (10,000–6800 BP) interpreted from lake sediment cores, southwestern Alberta, Canada

Six lake sediment vibracores from the foothills and mountain valleys of southwestern Alberta were analysed on the basis of AMS radiocarbon dates, tephrochronology and sediment geochemistry. From these results, the magnitude, timing and duration of the early Holocene warm period are presented. At about 10,000 BP, immediately following the Younger Dryas cold period, climate warmed dramatically, precipitation decreased and surface evaporation increased. Previous research has identified this warm interval, but new results have improved resolution of regional scale effects, specific timing and severity. Sedimentation changed from extra-basinal clastic to intra-basinal organic between 10,000 and 9400 BP. Changes in subalpine lakes from sand/silt deposition to biogenic carbonate precipitation suggest decreases in suspended sediment load caused by complete ablation of glacial sediment sources. Peat which formed in lakes of less than 4 m (present depth) indicates climate-induced lake level lowering in the foothills. Water depth and stratigraphic position of the peat suggest that regional water table levels decreased by up to 6.5 m. At Cartwright Lake, an erosional unconformity 6.5 m below the modern lake surface indicates the lake had completely dried out either during or immediately after Mazama tephra time (6800 BP).     

乌梁素海沉积物中有机质和全氮含量分布特征

针对乌梁素海富营养化日趋严重和湿地面积逐渐萎缩,系统地研究了其生态环境地球化学效应.结果表明,乌梁素海表层沉积物中的全氮含量存在明显的经向和纬向分异特征;沉积物中全氮养分含量与有机质含量显著相关(r＞0.93);沉积物中C/N的平均值介于12.07～19.95之间,表明有机质主要来源于湖中水生植物,水体富营养化具有显著的内源性.TN和有机质在不同粒级表层沉积物中的粒度效应明显,且TN和有机质在IV粒级的含量分别为I粒级的3.1～7.6倍和2.5～8.0倍.     

宁波沿海平原Z02孔第四纪地层及古环境演变

宁波沿海平原第四纪沉积物属于海陆交互沉积,记录了良好的古气候变化信息,是研究古气候冷暖变化、沉积物沉积特征的良好载体.对位于宁波沿海平原东南部的Z02孔进行14C和古地磁测年,根据钻孔岩性、孢粉组合、有孔类和介形类组合、粒度等环境替代指标特征,确定了 Z02孔第四纪地层划分,揭示了研究区第四纪以来的古环境演变信息.结果...     

Changing patterns of organic carbon and nitrogen accretion on the middle Ebro floodplain (NE Spain)

Sediment profiles from four sites of the middle Ebro River (NE Spain) were examined to describe total organic carbon (TOC) and total nitrogen (TN) accretion patterns during the last century. Such patterns were related to the potential of floodplain substrates to act as C and N sinks. Two oxbow lakes with different hydroperiods and two patches of riparian forest at different successional stages were selected to represent permanently and intermittently flooded habitats, respectively. Total organic carbon (TOC) and total nitrogen (TN) stocks were estimated, whereas Cs-137 dating and aerial photographs were used to determine historical accretion rates. Our results indicate that TOC and TN accretion patterns have been modified during the last century as a result of human impact on natural river processes at both basin and site scales. Since 1963, sediment deposition at the study sites has diminished, regardless of their hydrological connectivity, indicating a reduction in the potential of the middle Ebro floodplains to act as TOC and TN sinks. Although TOC and TN concentrations are markedly higher in recent sediments, accretion rates between 1927 and 1963 still exceed those of recent years. Despite such recent human-induced changes at basin and habitat scale, the middle Ebro floodplains presented relatively high TOC and TN accretion rates, a fact that should be considered in future basin management plans. Based on those results, suggestions to maximize TOC and TN accretion through ecological restoration are provided. Specific actions include the rehabilitation of fine-grained (<2 mm) sediment delivery, land reclamation or dyke reconfiguration.     

Environmental changes in Lake Taihu during the past century as recorded in sediment cores

The Lake Taihu drainage basin is an economically developed area with some of the highest population densities in China. The lake has deteriorated due to ecological destruction and eutrophication. Three short sediment cores from eastern, northeastern and southwestern Lake Taihu were collected. Total organic carbon (TOC), total nitrogen (TN), pigments, elements and particle size were analyzed for the purpose of understanding past trophic status and pollution levels. Sedimentation rates were based on ¹³⁷Cs or ²¹⁰Pb methods. Results indicated that sediment particle size became coarser since the 1920s, and the lake was contaminated by heavy metals, such as Cu and Zn, since the 1970s. A remarkable increase in eutrophication since the 1980s due to increased loading of untreated effluents from industry, agriculture and urbanization is reflected by total organic carbon, total nitrogen and pigments in the studied cores. However the onset times of eutrophication in different parts of Lake Taihu were not synchronous.     

Ecosystem responses to increased precipitation and permafrost decay in subarctic Sweden inferred from peat and lake sediments

Recent accelerated decay of discontinuous permafrost at the Stordalen Mire in northern Sweden has been attributed to increased temperature and snow depth, and has caused expansion of wet minerotrophic areas leading to significant changes in carbon cycling in the mire. In order to track these changes through time and evaluate potential forcing mechanisms, this paper analyses a peat succession and a lake sediment sequence from within the mire, providing a record for the last 100 years, and compares these with monitored climate and active layer thickness data. The peat core was analysed for testate amoebae to reconstruct changes in peatland surface moisture conditions and water table fluctuations. The lake sediment core was analysed by near infrared spectroscopy to infer changes in the total organic carbon (TOC) concentration of the lake‐water, and changes in δ¹³C and C, N and δ¹⁵N to track changes in the dissolved inorganic carbon (DIC) pool and the influence of diagenetic effects on sediment organic matter, respectively. Results showed that major shifts towards increased peat surface moisture and TOC concentration of the lake‐water occurred around 1980, one to two decades earlier than a temperature driven increase in active layer thickness. Comparison with monitored temperature and precipitation from a nearby climate station indicates that this change in peat surface moisture is related to June–September (JJAS) precipitation and that the increase in lake‐water TOC concentration reflects an increase in total annual precipitation. A significant depletion in ¹³C of sediment organic matter in the early 1980s probably reflects the effect of a single or a few consecutive years with anomalously high summer precipitation, resulting in elevated DIC content of the lake water, predominantly originating from increased export and subsequent respiration of organic carbon from the mire. Based on these results, it was not possible to link proxy data obtained on peat and lake‐sediment records directly to permafrost decay. Instead our data indicate that increased precipitation and anomalously high rainfall during summers had a significant impact on the mire and the adjacent lake ecosystem. We therefore propose that effects of increased precipitation should be considered when evaluating potential forcing mechanisms of recent changes in carbon cycling in the subarctic.     

宁夏东部风沙区固定沙丘土壤性质小尺度空间变异特征

随着流动沙丘的不断固定,不同地形部位的土壤机械组成、有机碳(SOC)和全氮(TN)含量的变化存在差异。为了探明固定沙丘的土壤机械组成与土壤养分空间变异特征,本研究以宁夏黄沙古渡固定沙丘为对象,分析了固定沙丘不同部位、不同土层的风沙土机械组成、SOC和TN特征。结果表明: 各土层土壤机械组成均以中沙和细沙为主。SOC和TN有明显的表聚作用,SOC和TN含量最大值分别为5.781和0.412 g·kg^-1,分布在丘间地,脊线和背风坡含量最少。随着土层深度的增加,背风坡和迎风坡的SOC含量逐渐减少,丘间地的SOC含量先减少后增加。SOC和TN在小尺度上均表现出明显的空间异质性;SOC和TN与粉沙和极细沙含量呈显著正相关,与中沙和粗沙含量呈显著负相关。土壤机械组成对SOC和TN含量有明显影响,而且SOC和TN含量随着细颗粒含量的增加而增加,表明土壤细颗粒对有机质的吸附和积累起着重要作用。     

Eutrophication,recovery and temperature in Lake Mjøsa: detecting trends with monitoring data and sediment records

1. How climate warming may interact with other pressures on aquatic ecosystems is an important issue for research and management. We combined lake monitoring data with a palaeolimnological study to explore the combined effects of eutrophication and subsequent oligotrophication with a long‐term temperature increase in epilimnetic waters. Our goals were (i) to evaluate how well sediment‐based reconstructions reflect the instrumental observations, (ii) to use the palaeo‐record to characterise a reference state for the lake and (iii) to explore whether data from the sediment record can aid in separating the effects of nutrient load and temperature in a large and deep lake. 2. Lake Mjøsa is a large and deep lake in south‐eastern Norway. Eutrophication symptoms peaked in the 1970s, which led to extensive measures to reduce the phosphorus load. A monitoring programme has run continuously from 1972. Monitoring has documented a marked decrease in phosphorus load and algal biomass and also revealed an increase in epilimnetic temperature and extended summer stratification. 3. Records of algal pigments and diatoms were extracted from sediment cores taken from 236 m depth. The pigment record documented dramatic changes in lake production consistent with the monitoring record. The diatom record reflected well the eutrophication history of the lake and also demonstrated that the assemblage of the recent recovery stage differs from that of the pre‐eutrophication period. 4. Ordination of diatom assemblages over time constrained by proxies for nutrient load and temperature indicated that the diatom assemblage correlated with both factors, which together accounted for 60% of the variation in diatom composition. No interaction was detected between these factors. The results suggest that the diatom assemblage has responded to varying nutrient loads as well as to changes in temperature and/or factors that correlate with temperature. 5. Reconstructions of algal biomass and total phosphorus content mirrored known changes through the monitoring period, although the absolute phosphorus estimates were too high relative to the instrumental record. The sediment record from Lake Mjøsa provides a baseline for lake production in terms of algal pigments and organic contents, and for the diatom assemblage composition in a pristine stage.     

Unraveling the effects of water–sediment conditions and spatial patterns on Unionida assemblages in seasonally connected floodplain lakes

Floodplain lakes are good metacommunity systems to study the environmental and spatial processes structuring local assemblages. They are more connected during high-water periods and are more isolated during low-water periods. We evaluated the effects of lake spatial patterning and water and sediment conditions on Unionida species assemblages. Moran Eigenvector Maps were used to generate spatial variables representing spatial patterns at different scales. We sampled 35 lakes from the Pantanal floodplain, Brazil. To understand the effects of environmental and spatial variables, we performed Redundancy Analyses and variation partitioning to separate environmental and spatial pattern effects. Environmental variables explained almost twice the variation in the Pantanal mussel assemblages than did spatial variables. Unionida species presence was driven mainly by variations in sediment coarse sand and silt contents. The weak spatial patterns observed may be related to increased connectivity between lakes during floods, which facilitates mussel host fish dispersal. Mussel abundances were driven mainly by organic matter availability, but varied between species. Changes in lake connectivity can affect the regional sediment dynamics and affect mussel assemblages.

     

汕头南澳养殖区表层沉积物中生源要素的分布及其污染评价

于2010年9月采集南澳海域鱼类养殖区、贝类养殖区、大型藻类栽培区和对照区4个功能区表层沉积物样品,分析沉积物中生物硅(BSi)、总有机碳(TOC)、总氮(TN)和总磷(TP)4种生源要素的含量。结果表明,南澳海域生源要素含量与国内外养殖区相比属于中等水平。鱼类养殖区TOC、TN、TP的含量最高,而BSi的最高含量出现在藻类栽培区(平均含量为0.30%)。鱼类养殖区BSi、TOC、TN和TP的平均含量分别为0.24%、0.89%、0.13%和0.097%。根据沉积物中TOC/TN比值分析,发现鱼类养殖区的TOC主要来源于水生,贝类、藻类和对照区TOC则主要来源于陆源。生源要素污染评价表明,4个功能区的TN均属于Ⅱ类污染,鱼类和贝类养殖区的TP属于Ⅱ类轻度污染。