Inter-lake movements of the Lesser Flamingo Phoeniconaias minor and their conservation in the saline lakes of Kenya

Maina, J.G. 2000. Inter-lake movements of the Lesser Flamingo Phoeniconaias minor and their conservation in the saline lakes of Kenya. Ostrich 71 (1 & 2): 126.

The Lesser Flamingo Phoeniconaias minor is the only algivore in the saline lakes of Kenya occurring in spectacular assemblages that form the tourism base. The flamingos show unpredictable, spontaneous, “nomadic” movements between the saline lakes whose precipitating ecological factors were not well established. Food, conductivity, breeding, predation and fresh water availability were regarded as the primary factors in spite of their global coverage in explaining animal movements. Evidence is emerging that food, especially algal species composition, density, and lake levels are the primary driving factors for these inter-lake movements, with other factors being consequences of these. Algal species composition and lake levels are subject to limnological processes in the lakes, climatic conditions and human activities in the catchment of the saline lakes. Environmental degradation is now a critical factor influencing the limnology of these fragile ecosystems with far ranging consequences on lake levels, algal species composition and succession. These changes determine flamingo utilization patterns within and between the lakes. This calls for a review of the conservation status and management of the saline lakes, home to a few but highly specialised species.     

Limnological contrasts and anomalies in two adjacent saline lakes

Differences in physical, chemical, and biological conditions in two small (<20 ha) saline lakes less than 1 km apart in south-central British Columbia are examined. Although the lake basins are morphometrically similar, differences in their watershed geology and topography in large part may be responsible for the more saline lake showing severe and anomalous meromictic features while the less saline lake exhibits normal dimictic characteristics. Bacterial and phytoplankton population densities and production profiles of the lakes are compared along with some aspects of their zooplankton populations.     

Saline systems of the Great Plains of western Canada: an overview of the limnogeology and paleolimnology

In much of the northern Great Plains, saline and hypersaline lacustrine brines are the only surface waters present. As a group, the lakes of this region are unique: there is no other area in the world that can match the concentration and diversity of saline lake environments exhibited in the prairie region of Canada and northern United States. The immense number of individual salt lakes and saline wetlands in this region of North America is staggering. Estimates vary from about one million to greater than 10 million, with densities in some areas being as high as 120 lakes/km². Despite over a century of scientific investigation of these salt lakes, we have only in the last twenty years advanced far enough to appreciate the wide spectrum of lake types, water chemistries, and limnological processes that are operating in the modern settings. Hydrochemical data are available for about 800 of the lake brines in the region. Composition, textural, and geochemical information on the modern bottom sediments has been collected for just over 150 of these lakes. Characterization of the biological and ecological features of these lakes is based on even fewer investigations, and the stratigraphic records of only twenty basins have been examined. The lake waters show a considerable range in ionic composition and concentration. Early investigators, concentrating on the most saline brines, emphasized a strong predominance of Na⁺ and SO₄ ^-2 in the lakes. It is now realized, however, that not only is there a complete spectrum of salinities from less than 1 ppt TDS to nearly 400 ppt, but also virtually every water chemistry type is represented in lakes of the region. With such a vast array of compositions, it is difficult to generalize. Nonetheless, the paucity of Cl-rich lakes makes the northern Great Plains basins somewhat unusual compared with salt lakes in many other areas of the world (e.g., Australia, western United States). Compilations of the lake water chemistries show distinct spatial trends and regional variations controlled by groundwater input, climate, and geomorphology. Short-term temporal variations in the brine composition, which can have significant effects on the composition of the modern sediments, have also been well documented in several individual basins. From a sedimentological and mineralogical perspective, the wide range of water chemistries exhibited by the lakes leads to an unusually large diversity of modern sediment composition. Over 40 species of endogenic precipitates and authigenic minerals have been identified in the lacustrine sediments. The most common non-detrital components of the modern sediments include: calcium and calcium-magnesium carbonates (magnesian calcite, aragonite, dolomite), and sodium, magnesium, and sodium-magnesium sulfates (mirabilite, thenardite, bloedite, epsomite). Many of the basins whose brines have very high Mg/Ca ratios also have hydromagnesite, magnesite, and nesquehonite. Unlike salt lakes in many other areas of the world, halite, gypsum, and calcite are relatively rare endogenic precipitates in the Great Plains lakes. The detrital fraction of the lacustrine sediments is normally dominated by clay minerals, carbonate minerals, quartz, and feldspars. Sediment accumulation in these salt lakes is controlled and modified by a wide variety of physical, chemical, and biological processes. Although the details of these modern sedimentary processes can be exceedingly complex and difficult to discuss in isolation, in broad terms, the processes operating in the salt lakes of the Great Plains are ultimately controlled by three basic factors or conditions of the basin: (a) basin morphology; (b) basin hydrology; and (c) water salinity and composition. Combinations of these parameters interact to control nearly all aspects of modern sedimentation in these salt lakes and give rise to four 'end member' types of modern saline lacustrine settings in the Great Plains: (a) clastics-dominated playas; (b) salt-dominated playas; (c) deep water, non-stratified lakes; and (d) deep water, "permanently" stratified lakes.     

The plankton community of a young, eutrophic, Antarctic saline lake

A shallow, saline lake (Rookery Lake) close to the sea and surrounded by a penguin rookery was investigated during the austral spring and summer of 1996/1997. The proximity to the sea means that the lake is likely to have been formed recently during isostatic uplift. Inputs of carbon and nutrients from the penguin rookery have rendered Rookery Lake eutrophic compared with other brackish and saline lakes in the Vestfold Hills. Chlorophyll a concentration, bacterioplankton, heterotrophic nanoflagellate and phototrophic nanoflagellate abundances were all significantly higher than in other non-enriched lakes. The high productivity created seasonal anoxia during winter and spring below ice cover. The ciliate community resembled the marine community, and was dissimilar to that seen in older saline lakes within the Vestfold Hills. Thus Rookery Lake provides valuable evidence of the impact of natural eutrophication on an Antarctic lake, as well as of the evolution of the typical microbial community which dominates the older lakes of the Vestfold Hills. Accepted: 2 May 1999     

MARINE‐DERIVED DINOFLAGELLATES IN ANTARCTIC SALINE LAKES: COMMUNITY COMPOSITION AND ANNUAL DYNAMICS1*[link]

The saline lakes of the Vestfold Hills in Antarctica offer a remarkable natural laboratory where the adaptation of planktonic protists to a range of evolving physiochemical conditions can be investigated. This study illustrates how an ancestral marine community has undergone radical simplification leaving a small number of well‐adapted species. Our objective was to investigate the species composition and annual dynamics of dinoflagellate communities in three saline Antarctic lakes. We observed that dinoflagellates occur year‐round despite extremely low PAR during the southern winter, which suggests significant mixotrophic or heterotrophic activity. Only a small number of dominant dinoflagellate species were found in each lake, in contrast to the species‐rich Southern Ocean from which the lake communities are believed to be derived. We verified that the lake species were representatives of the marine polar dinoflagellate community, and not freshwater species. Polarella glacialis Montresor, Procaccini et Stoecker, a bipolar marine species, was for the first time described in a lake habitat and was an important phototrophic component in the higher salinity lakes. In the brackish lakes, we found a new sibling species to the brackish‐water species Scrippsiella hangoei (J. Schiller) J. Larsen, previously observed only in the Baltic Sea.     

A comparison of zooplankton communities in saline lakewater with variable anion composition

Although salinity and aquatic biodiversity are inversely related in lake water, the relationship between types of salts and zooplankton communities is poorly understood. In this study, zooplankton species were related to environmental variables from 12 lakes: three saline lakes with water where the dominant anions were SO₄ and CO₃, four saline lakes with Cl-dominated water, and five dilute, subsaline (0.5–3 gl^?1 total dissolved solids) lakes of variable anion composition. Although this study comprised only 12 lakes, distinct differences in zooplankton communities were observed among the two groups of chemically defined saline lakes. Canonical correspondence analysis identified total alkalinity, sulphate, chloride, calcium, sodium, potassium, and total phosphorus as all contributing to the first two ordination axes (λ₁ = 0.97 and λ₂ = 0.62, P<0.05). The rotifer Brachionus plicatilis and the harpactacoid copepod Cletocamptus sp. prevailed lakes with Cl-dominated water. In contrast, the calanoid copepods Leptodiaptomus sicilis and Diaptomus nevadensis were dominant in the SO₄/CO₃-dominated lake water with elevated potassium (79–128 mg l^?1) and total phosphorus concentrations (1322-2915 μg l^?1). The contrasting zooplankton species distribution among these two saline lake types is likely explained by variable selective pressure on zooplankton and their predators from differing physiological tolerances to salt stress and specific ions. While inland saline lakes with Cl as the dominant anion are relatively rare in Canada and SO₄/CO₃ are the common features, our study provided an opportunity to compare zooplankton communities across the two groups of lakes.     

Phosphorus limitation in some tropical African lakes

Two of three Kenyan lakes studied between November 1979 and October 1980 have very short ³³PO₄ turnover times, indicating a high phosphorus (P) demand throughout the year. The P turnover time in Lakes Oloidien and Sonachi is as rapid as in the most P deficient temperate zone lakes. The third lake, Lake Naivasha, has a lower overall P demand and a wide seasonal range, with lowest demand between November 1979 and February 1980 when a P deficiency was unlikely. On an annual basis the Lake Naivasha status is, however, not statistically different from that recorded during the summer in Lake Memphremagog, a generally P-limited temperate zone lake. Lake Naivasha and Lake Oloidien fit well to the line of best fit for the Dillon-Rigler relationship relating total phosphorus (TP) and chlorophyll a derived in temperate zone lakes. Thus, temperate zone models predicting aspects of lake behaviour on the basis of TP may also be applicable to these two tropical lakes. Saline lake Sonachi had not only a short P turnover time but also responded dramatically to the fertilization of enclosures with P. However, it does not fit the TP-chla or the total nitrogen-chla plots from the temperate zone. This suggests that, in this saline lake at least, much of the TP is unavailable to the algae, with some of it in a particulate form that is readily extracted with boiling water. The epilimnetic N:P ratios also characterize lakes Oloidien and Sonachi lakes as highly P deficient and lake Naivasha as more moderately P limited. A single set of measurements in Winam Gulf (Lake Victoria) also showed a rapid P turnover time and thus P limitation, but as in lake Sonachi much of the TP was in a non-algal particulate form. Occasional measurements in three other hypertrophic and saline lakes suggest them to be primarily light limited on the basis of their very high photosynthetic cover. These findings support the hypothesis of a primary P limitation for those lakes not light limited, and contradicts literature suggestions that nitrogen is the primary limiting element in tropical lakes.     

Reconstruction of historical productivity using visible-near-infrared (VNIR) reflectance properties from boreal and saline lake sediments

Chlorophylls preserved in lake sediments have been used as a proxy to infer past trophic status. Recently, it has been demonstrated that visible-near-infrared (VNIR) reflectance spectroscopy can provide a rapid and non-destructive estimation of fossil chlorophylls from alpine lake sediments. The present study explores, (a) the applicability of VNIR reflectance spectroscopy to reconstructing historical productivity from boreal and saline lakes, and (b) the ability of an inference model combining all lake types to reconstruct historical chlorophyll concentrations from lake sediments. Results revealed that regardless of the lake type, a common sediment spectral feature of a reflectance trough centered near 675 nm, was observed. Additionally, the amplitude of reflectance in the VNIR region differs within and among lakes depending on their trophic states. The inferred concentration of total chlorophylls and derivatives from sediment spectral properties reflected a recent nutrient enrichment in most of the study lakes. Predicted chlorophyll concentration, when plotted against high-pressure liquid chromatography (HPLC) measured concentration combining all lake types, was found to be statically significant (r ² = 0.80, P < 0.01). Collectively, results from this study indicate that regardless of the lake type, a common chlorophyll absorption feature near 675 nm can be detected, which is associated with contrasting limnological settings and, therefore, can be used as a viable tool to reconstruct paleoproductivity. A similar approach can be implemented for rapid and non-destructive detection of historical lake water quality in a wide range of lake sediments.     

Trace fossils and rhizoliths as a tool for sedimentological and palaeoenvironmental analysis of ancient continental evaporite successions

Recognition of evaporite formations from continental Tertiary basins of Spain provides evidence that trace fossils (including rhizoliths) can be abundant in some saline lake systems and their study helps in palaeoenvironmental interpretation of ancient continental evaporite sequences. Six main types of trace fossils have been distinguished and include: (1) networks of small rhizoliths; (2) large rhizoliths; (3) tangle-patterned small burrows; (4) isolated large burrows; (5) L-shaped traces; and (6) vertebrate tracks. Rhizoliths were related to both marginal areas of hypersaline lakes and lakes of moderately high saline waters. In these settings, pedoturbation resulted from colonization by grasses and bushes of distinct lake subenvironments. The activity of burrowing invertebrate faunas was especially intense in lakes of moderately concentrated brines from which gypsum was the main evaporite mineral deposited. A specific gypsum lithofacies (‘bioturbated gypsum deposits') forming thick, massive beds has a widespread occurrence in many of the basins. Tangle-patterned small burrows and minor isolated large burrows constitute the typical trace fossil types within the gypsum. The traces are interpreted as having been caused by burrowing insect larvae, probably chironomids, coleopterans and annelids. The behaviour of these organisms in recent lake environments yields information about the salinity range of lake waters from which gypsum precipitated. Concentration values averaging 100–150 g/l may be thus deduced though some organisms involved in the formation of the traces can tolerate higher salinities. The combined analysis of lithofacies and trace fossils from the lacustrine evaporite sequences contributes to the study of distinct saline lake subenvironments as well as changes in the sedimentary evolution of the lake systems. Consequently, trace fossils can provide valuable insight for palaeoenvironmental analysis of at least some evaporite formations that accumulated in continental settings.     

Associations of zooplankton in six crater lakes in Arizona, Mexico and New Mexico

Zooplankton associations in six crater lakes have been compared by means of indices of similarity and diversity, and by k -dominance curves. The lakes covered a wide range of salinities and vegetational characteristics.
The total number of species identified were: Protozoa, 34; Rotifera, 48; Gastrotricha, 7; Crustacea, 24; and Chaoborus larvae, 2; giving an overall total of 115. The numbers of zooplankton species in each lake varied from 68, in a richly vegetated fresh crater lake in Arizona, to one in a highly saline lake in New Mexico.
Testate rhizopods and gastrotrichs were not found in the more saline lakes. A comparison of the rotifer associations with those of crater lakes in other parts of the world shows that there is a general tendency for a reduction in the total number of species when the conductivity rises above 400 μS cm⁻¹ 20°C, and when the conductivity reaches 10,000 μS cm⁻¹ 20°C the number of rotifer species is usually reduced to two. The two species found at high salinities show some variation in different parts of the world, but generally include species of Brachionus and Hexarthra.
There is a general tendency for the number of rotifer species in a crater lake to increase with increasing vegetation, at least up to the stage where there is a dense, zoned vegetation, and before a complete mosaic of vegetation covers the lake.     

Ephemeral saline lakes on the Canadian prairies: their classification and management for emergent macrophyte growth

At two ephemeral saline lakes in Saskatchewan, changes in the physical and chemical features of water and sediments at various basin positions were monitored during a wet-dry cycle in 1978 and 1979. Water salinity fluctuated widely in response to changes in water volume and mass of solute in the water. When basins were dry, the soluble salt content of sediments 0–10 cm deep was higher than sediments 50–60 cm deep and sediments in the lake centre were more saline than at the shoreline. Upon reflooding, there was a large immediate decrease in sediment salinity at the 0–10 cm depth, such that this layer was less saline than sediments 50–60 cm deep. Sediments in the lake centre remained more saline than at the shoreline.Classification of lake salinity is necessary to assess the potential of a lake for emergent production. The large variances in ephemeral lake salinity due to water volume changes indicate that classification should be based upon the water volume-salinity cycle of these lakes rather than the salinity of any single water or sediment sample. Water management efforts to lower salinities, to improve these wetlands for emergent growth, should be aimed at reducing the salinity regime of the littoral zone. Flushing, dilution and drying and reflooding techniques are discussed as methods to decrease salinity.     

Microbiology of Lonar Lake and other soda lakes

Soda lakes are saline and alkaline ecosystems that are believed to have existed throughout the geological record of Earth. They are widely distributed across the globe, but are highly abundant in terrestrial biomes such as deserts and steppes and in geologically interesting regions such as the East African Rift valley. The unusual geochemistry of these lakes supports the growth of an impressive array of microorganisms that are of ecological and economic importance. Haloalkaliphilic Bacteria and Archaea belonging to all major trophic groups have been described from many soda lakes, including lakes with exceptionally high levels of heavy metals. Lonar Lake is a soda lake that is centered at an unusual meteorite impact structure in the Deccan basalts in India and its key physicochemical and microbiological characteristics are highlighted in this article. The occurrence of diverse functional groups of microbes, such as methanogens, methanotrophs, phototrophs, denitrifiers, sulfur oxidizers, sulfate reducers and syntrophs in soda lakes, suggests that these habitats harbor complex microbial food webs that (a) interconnect various biological cycles via redox coupling and (b) impact on the production and consumption of greenhouse gases. Soda lake microorganisms harbor several biotechnologically relevant enzymes and biomolecules (for example, cellulases, amylases, ectoine) and there is the need to augment bioprospecting efforts in soda lake environments with new integrated approaches. Importantly, some saline and alkaline lake ecosystems around the world need to be protected from anthropogenic pressures that threaten their long-term existence.     

High Genetic Diversity and Novelty in Eukaryotic Plankton Assemblages Inhabiting Saline Lakes in the Qaidam Basin

Saline lakes are intriguing ecosystems harboring extremely productive microbial communities in spite of their extreme environmental conditions. We performed a comprehensive analysis of the genetic diversity (18S rRNA gene) of the planktonic microbial eukaryotes (nano- and picoeukaryotes) in six different inland saline lakes located in the Qaidam Basin. The novelty level are high, with about 11.23% of the whole dataset showing <90% identity to any previously reported sequence in GenBank. At least 4 operational taxonomic units (OTUs) in mesosaline lakes, while up to eighteen OTUs in hypersaline lakes show very low CCM and CEM scores, indicating that these sequences are highly distantly related to any existing sequence. Most of the 18S rRNA gene sequence reads obtained in investigated mesosaline lakes is closely related to Holozoa group (48.13%), whereas Stramenopiles (26.65%) and Alveolates (10.84%) are the next most common groups. Hypersaline lakes in the Qaidam Basin are also dominated by Holozoa group, accounting for 26.65% of the total number of sequence reads. Notably, Chlorophyta group are only found in high abundance in Lake Gasikule (28.00%), whereas less represented in other hypersaline lakes such as Gahai (0.50%) and Xiaochaidan (1.15%). Further analysis show that the compositions of planktonic eukaryotic assemblages are also most variable between different sampling sites in the same lake. Out of the parameters, four show significant correlation to this CCA: altitude, calcium, sodium and potassium concentrations. Overall, this study shows important gaps in the current knowledge about planktonic microbial eukaryotes inhabiting Qaidam Basin (hyper) saline water bodies. The identified diversity and novelty patterns among eukaryotic plankton assemblages in saline lake are of great importance for understanding and interpreting their ecology and evolution.     

西藏达则错盐湖沉积背景与有机沉积结构

以西藏拟溞(Daphniopsis tibetana Sars)为优势浮游动物物种的低盐度盐湖是西藏湖泊的一个重要类型,以达则错为代表,分析了其沉积背景及沉积物组成。结果如下:(1)湖泊敞水区无机沉积以内生化学沉积为主,可代表深水盐湖无机沉积物的自然沉积过程。(2)达则错盐湖浮游植物以蓝藻、硅藻、裸藻、绿藻为主,总生物量11.35 mg/L;浮游动物生物量为4.92 mg/L,其中西藏拟溞占 82.30%;浮游植物残体受盐梯度影响在盐梯度层之上聚集,而浮游动物残体及粪粒(Fecal pellets)因外表有碳酸盐附着可穿过盐梯度层沉积湖底,生物残体与浮游动物代谢产物构成了沉积有机物的物质基础。(3)表层沉积物平均含水量为66.70%,粒径0.004-0.02 mm范围内的颗粒物含量最大,占20.42%,其次为<0.004 mm的粘土,占4.53%。(4)表层沉积物总有机碳(TOC)平均含量为27.99 mg/g(干重),其中颗粒有机碳(POC)约为18.11 mg/g,占TOC的64.70%;在POC中,西藏拟溞粪粒贡献最大,约占POC的60.48%,占TOC的39.06%,占沉积物总量的1.12%,其次为西藏拟溞残体,占POC的38.85%。分析结果表明盐湖因其独特的水化学和生物学特征具有较强的沉积能力,以化学沉积为主的无机沉积及以西藏拟溞粪粒和残肢碎屑为主的有机沉积构成了该类型盐湖颗粒物沉降及沉积的主要过程。     

Biological observations on the crater lakes of Jebel Marra, Sudan

Two lakes lie in a caldera at the top of Jebel Marra. One is shallow and highly saline, with a dense bloom of planktonic blue-green algae and a zooplankton consisting entirely of rotifers. The other is over 100 metres deep, is less saline, with a sparse phytoplankton of diatoms, and the dominant zooplankter is Eucyclops gibsoni. The marginal fauna of the deep lake includes a number of widespread insects, but is unusual in that it includes an aquatic glowworm (Family Lampyridae).
In the shallow lake there is a superabundance of oxygen in the upper two metres, but no oxygen below six metres, except when strong winds mix the lake so that there is then about 40% saturation throughout the water column. In the deep lake it was found that after strong winds there was only about 12% saturation in the top 30 metres of water. The restricted fauna of these lakes appears to be a result of the combined effects of isolation, salinity and a variable oxygen regime.     

The Saline Lakes of Saskatchewan II. Locale,Hydrography and other Physical Aspects

The geology and physiography, climate, soils and vegetation of the saline lakes region of southern Saskatchewan are briefly reviewed. The location and morphometry of 60 saline lakes was determined. Some of them are large (307 km²) but mean depths do not exceed 10 m and many are very shallow. Light penetration varied considerably from very turbid shallow lakes to Redberry Lake where the 1% light level was below 16.5 m. Light extinction coefficients for the entire water column of deeper lakes (7) varied from 0.256 to 2.558. Shallow lakes failed to stratify thermally but a dozen deeper lakes stratified for at least several months. Higher salinity tends to prolong stratification. Thermal stratification augmented chemical stratification in two meromictic lakes. Maximum temperature up to 30 °C in very saline shallow waters was recorded while temperatures as low as-3 °C occurred under the ice. Freezing was delayed and thawing accelerated in more saline lakes. Annual heat budgets varied from 3350 to 13,900 g cal cm-² in seven lakes. Oxygen concentration was reduced below thermoclines and was virtually absent below the ice in very shallow lakes and, at times, in a very productive lake.     

Zooplankton Seasonal Abundance of South AmericanSaline Shallow Lakes

The central provinces of Argentina are characterized by the presence of a high number of shallow lakes, located in endorheic basins, many of which have elevated salinities as well as eutrophic or hypereutrophic condition. The zooplankton of four saline shallow lakes of the province of La Pampa was studied on a monthly basis during a 2‐year period to determine its temporal and spatial variation. The surface of these shallow lakes (<2.5 m depth) varied between 56.8 and 215.9 ha, and some have from 8.4 to 20.8 g · l^–1. The more saline lakes have “clear” water and the less saline lakes “turbid” water. Fishes, Jenynsia multidentata , were present in only two lakes during the last two months of the studied period. The zooplankton was composed of 17 taxa of Rotifera, 5 taxa of Cladocera and 4 taxa of Copepoda. The low diversity and the faunistic composition are characteristic of saline environments. Although the studied lakes share 38% of the species, the faunistic similarity was higher between the two least saline lakes. The lowest diversity was found in the two most saline lakes. All four shallow lakes were characterized by their very high zooplankton density, especially in the least saline lakes (<80000 ind · l^–1). The abundance is significantly correlated with the water transparency but not with salinity. The zooplankton temporal variation was characterized by the alternation of macro‐ and microzooplankton, probably regulated by competition and intrazooplanktonic predation. In each lake, the spatial abundance distribution of the macro‐ and microzooplankton was homogeneous. It was related to the shallow depht of the lakes and their polymictic condition. The Scheffer model on alternative states in shallow lakes acknowledges that it cannot be applied to saline lakes because Daphnia , the main responsible for the clear water state, is not tolerant to high salinity. Our study shows that the most saline lakes, where the halophylic Daphnia menucoensis is abundant, have also the most clear waters. Another difference that we found with regards to the mentioned model is that, in turbid lakes, it could not have had a top‐down control on macrozooplankton exerted by fishes because in these lakes fishes were practically absent. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

1987—2016年武汉城市湖泊时空演变及其生态服务价值响应

城市湖泊面积萎缩、水体污染及流域生态系统功能退化已成为影响城市生存与发展的重要环境问题,明确城市湖泊时空演变特征及其生态系统服务价值响应能强化人类对城市湖泊的保护认知,对维护湖泊及流域生态系统稳定、确保城市湖泊资源可持续利用有着重要意义。选取武汉市现主城区1987、1996、2007和2016年遥感影像,提取湖泊及流域水面信息,探讨武汉城市湖泊时空演变特征及其驱动力;并结合不同时期社会经济、自然环境等实际,进行湖泊水域生态功能服务价值定量估算,探讨其对人类活动及湖泊时空演变的响应规律。主要结果如下:(1)29年间,武汉主城区湖泊水域面积共缩减82 km²,减少了56.9%;越靠近城市建成区,湖泊面积缩减越明显;湖泊面积越小,填占现象越严重;湖泊水系由1987年纵横交错的网络格局发展为2016年相互分散的独立斑块。(2)农业生产和城市建设是造成湖泊面积减少的主要原因,相关保护政策及条例的实施是湖泊面积增加的驱动因素,城市不同发展时期主要的驱动因素各异。(3)1987—2016年,武汉主城区湖泊水域生态系统服务价值由20.95亿元减少到6.78亿元,共减少了67.64...     

Do Patterns of Bacterial Diversity along Salinity Gradients Differ from Those Observed for Macroorganisms?

It is widely accepted that biodiversity is lower in more extreme environments. In this study, we sought to determine whether this trend, well documented for macroorganisms, also holds at the microbial level for bacteria. We used denaturing gradient gel electrophoresis (DGGE) with phylum-specific primers to quantify the taxon richness (i.e., the DGGE band numbers) of the bacterioplankton communities of 32 pristine Tibetan lakes that represent a broad salinity range (freshwater to hypersaline). For the lakes investigated, salinity was found to be the environmental variable with the strongest influence on the bacterial community composition. We found that the bacterial taxon richness in freshwater habitats increased with increasing salinity up to a value of 1‰. In saline systems (systems with >1‰ salinity), the expected decrease of taxon richness along a gradient of further increasing salinity was not observed. These patterns were consistently observed for two sets of samples taken in two different years. A comparison of 16S rRNA gene clone libraries revealed that the bacterial community of the lake with the highest salinity was characterized by a higher recent accelerated diversification than the community of a freshwater lake, whereas the phylogenetic diversity in the hypersaline lake was lower than that in the freshwater lake. These results suggest that different evolutionary forces may act on bacterial populations in freshwater and hypersaline lakes on the Tibetan Plateau, potentially resulting in different community structures and diversity patterns.     

Diversity of Chironomidae (Diptera) along a salinity gradient in lakes of the endorheic Great Lakes region of western Mongolia

Hydrobiologia - The Great Lakes region of western Mongolia includes a diversity of lake ecosystems, from alpine freshwater to lowland, saline lakes, which increasingly face environmental threats...