Macrophyte diversity of lakes in the Pannon Ecoregion (Hungary)

We examined the distribution of submerged and emergent macrophyte species and the entire macrophyte community within and between five lake types (highland reservoirs, alkali lakes, large shallow lakes, small to medium sized shallow lakes, marshes) in the Pannon Ecoregion, Hungary. The lowest submerged, emergent and total species richness was found in alkali lakes. The highest submerged macrophyte richness was in small to medium sized lakes, while the highest emergent macrophyte species richness was in reservoirs, small to medium sized lakes, and marshes. The values of within-lake type beta diversity were generally lower than the values of alpha diversity, especially for submerged macrophytes, indicating between site homogeneity in species composition within the lake types. Emergent macrophyte communities contributed the most to within and between lake type diversity and total (gamma) diversity. Canonical correspondence analyses showed that the main environmental variables which influenced the distribution of submerged macrophytes were conductivity, Secchi transparency and water nitrogen contents. For emergent macrophytes conductivity, lake width, altitude and water depth proved to be the most influential variables. Our results contribute to the knowledge of large-scale distribution of macrophytes in the Pannon Ecoregion and to the identification of conservation value of lakes using macrophytes. The results support the importance of small lakes and artificial lakes in the conservation of macrophyte diversity compared to large and natural lakes in the Pannon Ecoregion.     

2000-2013年青藏高原湖泊面积MODIS遥感监测分析

青藏高原上分布着大量的高原内陆湖泊群,该区域湖泊面积与区域及全球气候变化之间存在较强的耦合关系,遥感监测湖泊的分布和面积变化趋势,对分析区域自然生态环境具有重要意义。本研究将MOD09A1（地表反射率8天合成数据）进行逐月合成,提出了一种综合多种水体指数的青藏高原地区湖泊提取方法,并通过活动窗口、DEM和时间序列去噪等方法,消除山体阴影、冰雪等因素的干扰。最后,提取和合成了2000-2013年青藏高原逐年和逐月的湖泊范围,并选取色林错和卓乃湖2个典型湖泊与人工解译Landsat系列影像进行验证分析,其线性拟合度分别为0.99和0.97,从时空变化趋势上分析了青藏高原湖泊面积动态变化。结果表明：（1）2000-2013年,青藏高原地区湖泊范围整体上呈较显著的扩张趋势,湖泊总面积增加速率约为490.98 km² a^-1（R²约为0.96）;（2）1-12月份湖泊面积逐月变化率均大于0,表明青藏高原湖泊面积呈整体扩张,而非季节性扩张。除2-4月份外,其他月份增加速率均在400 km² a^-1以上（R²>0.79）,表现为稳定且持续扩张趋势。     

Mediated spatio-temporal patterns of macroinvertebrate assemblage associated with key environmental factors in the Qinghai Lake area,China

The Qinghai Lake area is one of key regions in the Qinghai–Tibet Plateau for supporting a highly specific array of biodiversity. However, little is known about the composition and spatio-temporal patterns of benthic assemblages across this region. Herein, we examined how the community structure and community–environment relationships of macroinvertebrates varied over three consecutive years (2012–2014) across its three distinct water types of the saline main-body (MB) and sub-lakes (SSLs) and the freshwater bodies (FWBs). These waters harbored a poor benthic fauna, with identification of 30 taxa (6 in MB, 6 in SSLs and 23 in FWBs). There were distinct differences of assemblage composition among three water bodies, whereas weak (inter-year) or insignificant (seasons) differences at temporal scales. The CCA models indicated that there were highly naturally-driven environmental-assemblage relationships through time, with constant environmental factors of salinity, water depth and nutrients being the key environmental factors affecting macroinvertebrate variations. The currently overall benthic community composition and structure remains quite stable through years, indicating their suffering less from human activities. These results provide implications for projecting comprehensive benthic biomonitoring and conservation planning for those fragile and under-investigated lakes in the Qinghai–Tibet Plateau.     

Spatial distribution and ecology of the Recent Ostracoda from Tangra Yumco and adjacent waters on the southern Tibetan Plateau: A key to palaeoenvironmental reconstruction

We elucidate the ecology of Recent Ostracoda from a deep brackish lake, Tangra Yumco (30°45′—31°22′N and 86°23′—86°49′E, 4595 m a.s.l.) and adjacent waters on the southern Tibetan Plateau. Ostracod associations (living and empty valves) in sixty-six sediment samples collected from diverse aquatic habitats (lakes, estuary-like water and lagoon-like water waters, rivers, ponds and springs) were quantitatively assessed.Eleven Recent Ostracoda were found (nine living and two as empty valves only). Cluster analysis established two significant (p < 0.05) habitat specific associations; (i) Leucocytherella sinensis, Limnocythere inopinata, Leucocythere? dorsotuberosa, Fabaeformiscandona gyirongensis and Candona xizangensis are lacustrine fauna. (ii) Tonnacypris gyirongensis, Candona candida, Ilyocypris sp., Heterocypris incongruens and Heterocypris salina are temporary water species.Ostracod distribution and abundance are significantly (p < 0.05) correlated to physico-chemical variables. The first two axes of a canonical correspondence analysis (CCA) explain 30.9% of the variation in the species abundance data. Conductivity and habitat types are the most influential ecological factors explaining the presence and abundance of ostracods. Spearman correlation analysis reveals that: (i) Two species, L.? dorsotuberosa (r = 0.25) and L. inopinata (r = 0.36) have a significant positive correlation with conductivity while one species, T. gyirongensis (r = −0.68) displays a significant negative correlation with conductivity. Limnocythere inopinata correlates significantly positive (r = 0.37) with alkalinity. Fabaeformiscandona gyirongensis correlates significantly positive (r = 0.28) with water depth.Key indicator living assemblages are: (i) L. sinensis dominates Ca-depleted brackish waters although ubiquitously distributed; (ii) L.? dorsotuberosa dwells in fresh to brackish waters; (iii) L. inopinata predominates in mesohaline to polyhaline waters; (iv) F. gyirongensis inhabits exclusively brackish-lacustrine deeper waters; (v) C. candida populates freshwaters; (vi) T. gyirongensis and Ilyocypris sp. are restricted to shallow temporary waters; (vii) H. incongruens occurs in ponds.Water depth indicators are F. gyirongensis and L.? dorsotuberosa, useful in ostracod assemblages for palaeo-water depth reconstruction.Our results expand the knowledge of the ecological significance of Recent Tibetan Ostracoda ecology. This is a new insight on habitat chacteristics of both living assemblages and sub-Recent associations of ostracods in mountain aquatic ecosystems. The new modern ostracod dataset can be used for the quantitative reconstruction of past environmental variables (e.g., conductivity) and types of water environment. The key indicator ostracods are relevant in palaeolimnological and climate research on the Tibetan Plateau.     

湖北省湖泊现状与变化遥感研究

湖北省是长江流域重要的湖泊分布区,由于河(江)湖关系自然演变和人类活动的双重影响,湖泊数量和湖泊面积变化都较大。本文利用时相为1975、2000、2007、2017年的卫星遥感影像作为基本信息源,借助GIS技术,调查研究了湖北省湖泊现状及变化情况。结果表明,2017年,湖北省域大、小天然湖泊共计808个(其中大于100km2的湖泊有4个),湖泊总面积(平水位)2776.96km2,湖泊面积总量大,数量多,但空间分布极度不匀;1975-2017年的40余年间,湖泊总面积共减少了129.88km2,年平均减少量为3.09km2;湖泊变化阶段性特征突出,前30余年湖泊面积消减,数量减少,后10年面积增加,数量增加,反映出近10年来湖泊湿地生态环境总体趋于良性演化。     

An overview of late Holocene climate and environmental change inferred from Arctic lake sediment

The 14 papers in this Special Issue of the Journal of Paleolimnology report new records of Holocene climate and environmental change from Arctic lakes, with emphasis on the last 2000 years. The study sites span the high latitudes of North America and extend into northwestern Europe. The studies rely on multiple proxy indicators to reconstruct past climate, including: varve thicknesses, chironomid, diatom, and pollen assemblages, biogenic-silica and organic-matter content, oxygen-isotope ratios in diatoms, and the frequency of lake-ice-rafted aggregates. These proxies primarily document changes in past summer temperatures, the main control on physical and biological processes in lakes at high latitudes. The records will be integrated into a larger network of paleoclimate sites to investigate the spatial and temporal variability of climate change and to compare the paleoclimate inferences with the output of general circulation models. This is the Introduction to a series of fourteen papers published as a special issue dedicated to reconstructing late Holocene climate change from Arctic lake sediments. The special issue is a contribution to the International Polar Year and was edited by Darrell Kaufman.     

LAKE-ICE BLISTERS, TERRA NOVA BAY AREA, NORTHERN VICTORIA LAND, ANTARCTICA

Ice blisters, typically 0.2–0.8 m high and 5–20 m long, develop annually on perennially frozen lakes in Northern Victoria Land. They are believed to be caused by hydrostatic pressures generated through progressive freezing of solute-rich water beneath the lake-ice cover during winter. Lake-ice blisters in the study area differfrom icing blisters described from the northern hemisphere. The latter are caused by hydraulic pressures and are found at locations such as river beds or spring sites on sloping terrain. The Antarctic lake-ice blisters reflect the occurrence of dry-based perennially frozen lakes with high salt contents in an extremely cold and arid environment.     

Diatoms reveal complex spatial and temporal patterns of recent limnological change in West Greenland

Diatoms in sediment cores were analysed across a range of stratigraphic resolutions along a transect of 23 lakes spanning the ice-free margin of the west coast of Greenland (~67°N), to explore spatial and temporal patterns of recent (last ~150 years) environmental change in the region. These records display heterogeneous lake development trajectories over the last several centuries. Estimates of species composition turnover (beta-diversity) since 1850 AD are among the lowest for lakes in the Arctic, and are comparable to “unimpacted” reference lakes from temperate regions. Most of the change that occurred in West Greenland lakes pre-dates potential industrial anthropogenic effects, while post-1850 change is well within the natural range of variability for these systems. Nonetheless, a spatial pattern in core “top–bottom” changes is apparent across the transect: lakes in the arid interior of the region, adjacent to the ice sheet, and those with higher pH, register greater change than those in the more maritime climate of the coast. This suggests that climate plays an indirect role in the recent development of these lakes, and that recent anthropogenic forcing has not yet exceeded major ecological thresholds in this region.     

Substrate influence and temporal changes on periphytic biomass accrual and metabolism in a tropical humic lagoon

We performed a field experiment in a tropical humic coastal lagoon to evaluate periphyton biomass accrual and metabolism on three different substrates (1) plastic ribbons, (2) green and (3) senescent leaves of the emergent macrophyte Typha domingensis) over 30 days. The contribution of autotrophic biomass decreased as total biomass increased over the time. Mean periphytic ash free dry weight ranged from 0.8 to 5.6 mg cm⁻², but periphyton chlorophyll a concentrations presented shorter amplitudes, which oscillated from 0.12 to 0.44 μg cm⁻² throughout the experiment. Periphyton metabolism was overall heterotrophic on all substrates, especially on senescent leaves. Our data show that substrate type influenced both biomass accrual and periphyton net productivity and respiration rates throughout periphyton development and highlighted the dominance of heterotrophic metabolism. The periphyton respiration may be subsidized by both water- and substrate-derived allochthonous energy pathways, shedding light on the role of periphytic assemblages to the carbon cycling, as a source of CO₂ to the system.     

Effects of fish manipulation on the plankton community in small hypertrophic lakes from the Pampa Plain (Argentina)

Trophic cascade hypotheses predict that fish will affect the structure and biomass of pelagic plankton communities. In order to investigate trophic cascade effects from fish down to phytoplankton, whole-lake studies were performed in five hypertrophic (mean total phosphorus (TP) concentrations higher than 1000 mg m⁻³) shallow lakes located in the Pampa Plain. The main climatic characteristic of this region is the alternation between periods of drought and flood, with corresponding changes of lake depth and conductivity of lake water. All lakes were studied from April to December 2000. Samples were taken of their physical and chemical characteristics and biotic communities, focusing on the zooplankton community. Fish were manipulated in four lakes (Capurro, Longinotti, Vedia 1, Vedia 2), while the fifth (Lake Vedia 3) was left undisturbed as a reference system. High abundance of planktivorous minnows (Jenynsia multidentata and Cheirodon interruptus) dominated the fish community in the reference lake. In the manipulated lakes, fish stocks were largely reduced in late autumn (May). During winter, Capurro, Longinotti and Vedia 1 were stocked with a visual planktivore, the pampean silverside (Odontesthes bonariensis, Atherinidae). Fish stocking was 24, 33 and 19 kg ha⁻¹, respectively. In contrast, no fish were stocked in Lake Vedia 2. Following fish removal, large Daphnia appeared in these lakes and grazed intensively on the phytoplankton. In contrast, no Daphnia were found in the reference lake (Vedia 3). The stocking of O. bonariensis in lakes Capurro, Longinotti and Vedia 1 led to a decrease in the percentage of large cladocerans and a rise in the phytoplankton biomass:TP ratio. Moreover, the lakes mentioned were stocked with different quantities of silversides over different periods of time. These differences were reflected temporarily in the plankton dynamics, affecting mainly larger sized zooplankton. Nevertheless, the presence of Daphnia was short lived in the lake where fish had been removed and no O. bonariensis were stocked. Competition for resources and recruitment of remaining fish probably caused a collapse in the zooplankton biomass. Our results support the idea that fish predation on zooplankton and its effect on phytoplankton is very intense in small pampean lakes. Fish removal was short lived, however. This could be because in small pampean lakes fish recolonization is favored, and minnows are highly prolific. Moreover, if manipulation of the trophic structure of lakes is undertaken in the pampean region, high nutrient loading from the watershed, climate and hydrology should also be taken into account.