洞庭湖生态功能保护的原则和任务

根据洞庭湖的实际情况,在大量实地调查研究的基础上,首先从洞庭湖的主导和辅助生态功能两个方面确定了其在长江中游的生态功能地位,并根据其战略定位,提出了湖区生态功能保护应遵循的调蓄洪水为主、生态保护优先、保护与恢复并举等基本原则,最后基于这些原则和当前所存在的实际问题提出了洞庭湖生态功能保护所面临的若干任务。     

Evaluating the trophic status of a shallow polluted lake,lake Ioannina,Greece

Lake Ioannina in western Greece is a shallow lake, charged by springs as well as untreated discharges of the nearby urban area. Physicochemical and biological parameters have been evaluated verifying the deterioration of the lake aquatic environment. The water quality and the trophic status of the lake are greatly altered during the last ten years while the total phosphorus critical loading is already at a dangerous state.     

A 200-year perspective on alternative stable state theory and lake management from a biomanipulated shallow lake

Multiple stressors to a shallow lake ecosystem have the ability to control the relative stability of alternative states (clear, macrophyte-dominated or turbid, algal-dominated). As a consequence, the use of remedial biomanipulations to induce trophic cascades and shift a turbid lake to a clear state is often only a temporary solution. Here we show the instability of short-term manipulations in the shallow Lake Christina (Minnesota, USA) is governed by the long-term state following a regime shift in the lake. During the modern, managed period of the lake, three top-down manipulations (fish kills) were undertaken inducing temporary (5-10 years) unstable clear-water states. Paleoecological remains of diatoms, along with proxies of primary production (total chlorophyll a and total organic carbon accumulation rate) and trophic state (total P) from sediment records clearly show a single regime shift in the lake during the early 1950s; following this shift, the functioning of the lake ecosystem is dominated by a persistent turbid state. We find that multiple stressors contributed to the regime shift. First, the lake began to eutrophy (from agricultural land use and/or increased waterfowl populations), leading to a dramatic increase in primary production. Soon after, the construction of a dam in 1936 effectively doubled the depth of the lake, compounded by increases in regional humidity; this resulted in an increase in planktivorous and benthivorous fish reducing phytoplankton grazers. These factors further conspired to increase the stability of a turbid regime during the modern managed period, such that switches to a clear-water state were inherently unstable and the lake consistently returned to a turbid state. We conclude that while top-down manipulations have had measurable impacts on the lake state, they have not been effective in providing a return to an ecosystem similar to the stable historical period. Our work offers an example of a well-studied ecosystem forced by multiple stressors into a new long-term managed period, where manipulated clear-water states are temporary, managed features.     

Periodically driven circulation near the shore of a lake

Solutions are found for a linear model of the circulation near the shore of a lake that is subject to two diurnal forcing mechanisms. The first is the day/night heating/cooling induced horizontal pressure gradient. The second is an unsteady surface stress modelling a sea breeze/gully wind pattern. The two forcing mechanisms can oppose or reinforce each other depending on their relative phase. The interplay of different dynamic balances at different times and locations in the domain lead to complex circulation patterns especially during the period of flow reversal.     

A mesoscale vortex in a small stratified lake

A mesoscale vortex structure in the small stratified Lake Stechlin has been revealed by field experiments with satellite-tracked quasi-lagrangian drifters. The vortex with a radius of about 200 m drifted at 300 m/day along the western bight of the lake with nearly constant rotation speed of 3 cpd. Analysis of kinematical properties of the vortex motion demonstrates solid body character of rotation. Extrapolation of the vortex drift trajectory over the period preceding the observations combined with data on local winds and seiche dynamics has allowed tracing the vortex fate from its generation point. The normal modes analysis of the internal seiching in the lake reveals the vortex generation mechanism to be the interaction of certain seiche modes with local bottom topography and suggests generation of the mesoscale vortices to be the a regular feature of the lake circulation. Analysis of vorticity suggests additional energy supply to rotational flow, possibly from inverse cascading of small-scale turbulent motions—a feature typical for quasi-2D turbulence. The vortices can play an important role in the energy transport from basin-scale motions to small-scale boundary mixing. They can also contribute significantly to the horizontal heterogeneity of phyto- and zooplankton distribution as well as to the transport of dissolved matter such as nutrients between littoral and profundal areas. The topographically generated traveling vortices represent an analog of the synoptic eddies in the Ocean and in the Atmosphere, whereas their role in the lake hydrodynamics is practically unknown.     

Unusual characteristics in a Meromictic lake in Greece

The studied lake, a meromictic shallow lagoon, in Peloponissos, presents unusual physical and chemical features which derive mainly from its mineral springs, and the sea water that invades into the lake. The form of vegetation and the abundant organic matter of the mud together with the sulfate salts of the water create conditions which are responsible for the production of gases such as H₂S and CH₄. Vertical profiles of temperature, salinity and oxygen show that a large area of the lake is well stratified, at least periodically and no marked mixing occurs, between the upper less saline water and the lower saline water. In the halocline the vertical gradient of salinity is large. Mesothermic and poikilothermic conditions were also observed, whereas large temperature differences were recorded in water column.     

Structure and resilience of the social network in an insect colony as a function of colony size

Social interactions are critical to the organization of worker activities in insect colonies and their consequent ecological success. The structure of this interaction network is therefore crucial to our understanding of colony organization and functioning. In this paper, I study the properties of the interaction network in the colonies of the social wasp Ropalidia marginata. I find that the network is characterized by a uniform connectivity among individuals with increasing heterogeneity as colonies become larger. Important network parameters are found to be correlated with colony size and I investigate how this is reflected in the organization of work in colonies of different sizes. Finally, I test the resilience of these interaction networks by experimental removal of individuals from the colony and discuss the structural properties of the network that are related to resilience in a social network. This contribution is part of the special issue “Social Networks: new perspectives” (Guest Editors: J. Krause, D. Lusseau, and R. James).     

Identification of a dynamic lake model by the group method of data handling: An application to lake ontario

A revised algorithm of the group method of data handling (GMDH) is used to model and identify water quality dynamics in Lake Ontario. The state variables in the model are corrected chlorophyll a, volume-averaged over the top 20 m, and soluble reactive phosphorus in three layers, 0–20 m, 20–40 m and from 40 m to bottom. Inputs are the average quarterly temperatures for each layer and the total phosphorus loadings. Two kinds of model are developed: recursive and iterative; they are used to simulate long-term predictions for three different hypothetical rates of phosphorus loading. Results show that GMDH can be usefully employed to develop lake models with a very low expense of manpower and computer time. This exercise compares well with other large-scale modelling efforts of Lake Ontario, even if necessarily more limited in scope.     

Structure and function of the locomotory system of the Scyphomedusa Cyanea capillata

The structure and function of the locomotory system of the jellyfish Cyanea capillata L. were studied by dissection, histology, photography and cinematography. The swimming muscle consists of a highly-folded subeptithelial-stratum of striated fibrils arranged on larger mesogleal folds. A proximal coronal muscle divided into 16 fields is anchored to the umbrella proper along the radial septa separating the fields. Sixteen distal couples of radial muscles are anchored to peripheral mesogleal buttresses. On the lower surface of the umbrellar mesoglea is a series of 16 deep radial grooves confluent with a coronal groove. These grooves (joints) are anchored to the exumbrellar surface of the umbrella by rows of large branching mesogleal fibers. During contraction, the muscles cause a folding of the umbrella around the system of joints. Sequences of swimming and turning were analyzed, and it was concluded that this swimming mechanism is much less refined than the hydrozoan mechanism.     

Evaluation and application of a three-dimensional water quality model in a shallow lake with complex morphometry

Fundamental hydrodynamic and ecological processes of a lake or reservoir could be adequately depicted by one-dimensional (1D) numerical simulation models. Whereas, lakes with significant horizontal water quality and hydrodynamic gradients due to their complex morphometry, inflow or water level fluctuations require a three-dimensional (3D) hydrodynamics and ecological analyses to accurately simulate their temporal and spatial dynamics. In this study, we applied a 3D hydrodynamic model (ELCOM) coupled with an ecological model (CAEDYM) to simulate water quality parameters in three bays of the morphologically complex Lake Minnetonka. A considerable effort was made in setting up the model and a systematic parameterization approach was adopted to estimate the value of parameters based on their published values. Model calibration covered the entire length of the simulation periods from March 29 to October 20, 2000. Sensitivity analysis identified the top parameters with the largest contributions to the sensitivity of model results. The model was next verified with the same setup and parameter values for the period of April 25 to October 10, 2005 against field data. Spatial and temporal dynamics were well simulated and model output results of water temperature (T), dissolved oxygen (DO), total phosphorus (TP) and one group of algae (Cyanobacteria) represented as chlorophyll a (Chla) compared well with an extensive field data in the bays. The results show that the use of the model along with an accurate bathymetry, a systematic calibration and corroboration (verification) process will help to analyze the hydrodynamics and geochemical processes of the morphologically complex Lake Minnetonka. An example of an ecological application of the model for Lake Minnetonka is presented by examining the effect of spatial heterogeneity on coolwater fish habitat analysis in 3D and under a scenario where horizontal spatial heterogeneity was eliminated (1D). Both analyses captured seasonal fish habitat changes and the total seasonal averages differed moderately. However, the 1D analysis did not capture local and short duration variabilities and missed suitable fish habitat variations of as much as 20%. The experiment highlighted the need for a 3D analysis in depicting ecological hot spots such as unsuitable fish habitats in Lake Minnetonka.     

Structure and function of the third maxillipeds of the banana prawn Penaeus merguiensis

The functions of the third maxilliped of Penaeus merguiensis de Man are described. It has a 6-segmented endopodite which is used in feeding, grooming and possible pheromone reception. In feeding, large pieces of food are gripped by the stout spines on inner borders of the ischia which hold them to the mouth so that particles can be torn off and ingested. All the distal segments have long setae used in grooming chelate pereiopods and the antennules. In mature males there is a tuft of about 300 slender setae at the end of the propus, but its function remains obscure.     

Structure and function of the chelate pereiopods of the banana prawn Penaeus merguiensis

Penaeus merguiensis de Man systematically searches the substratum and removes small particles of food from it using the small chelae of the first three pairs of pereiopods. One or more chelae are used to transfer food particles to the mouth. The propus and dactylus of these limbs bear numerous setae arranged in discrete groups along the length of the segments. The tip of each seta is elaborately sculptured and has a large sub-terminal pore. It is probable that these are chemosensory organs responsible for discriminating edible from non-edible material. Proximal to almost every setal group is a much-branched seta (rarely two) which probably measures the depth to which the chela has been inserted into the substratum. At the articulation of the propus and carpus of the first pereiopod are three groups of differently sculptured setae, whose function is to clean the other chelate pereiopods. An elaborate system of pegs and a ridge on the apposable fringes of the chelae might be a mechano-receptive device with a particle size discriminating function. The ridges merge into opposable terminal denticulate pads whose function is to grasp food and other particles, which may be quite small (10 to 20 m upwards).     

Seasonal succession and diversity of phytoplankton in a eutrophic lagoon (Liman lake)

The seasonal succession, composition and diversity of phytoplankton in a eutrophic lagoon (Liman lake) were studied between January 2002 and November 2003. Samples were collected from surface water and deeper (1 m depth) at stations and species diversity (Shannon-Weaver, H) and evenness were calculated. Shannon Diversty was similar at Station 1 and Station 2. Minimum and maximum diversity values (0.101 and 0.765 bits. mm3) were recorded in June and July 2003 at Station 2. Cluster analysis and NMDS (Non metric multidimensial scaling) were applied to the phytoplankton community. The lagoon exhibits high conductivity (7211-10757 microScm(-1)), mean temperature of 17.7 degrees C, varying concentrations of dissolved oxygen (3.3-8.4 mg l(-1)). Light, temperature, rainfall, turbidity and salinity were expected to be the main factors affecting the seasonal succession. The seasonal succession of phytoplankton were similar at surface water and 1 m depth. A total of 130 taxa belonging to Bacillariophyta, Chlorophyta, Euglenophyta, Cyanophyta, Dinophyta, Xantophyta, Chrysophyta and Cryptophyta divisions were identified. Pseudanabaena limnetica, Kirchneriella obesa, Kirchneriella lunaris, Ankistrodesmus falcatus and Ankistrodesmus spiralis were highly represented.     

Tracking the metal distribution in the tropical Valencia lake catchment: Soil, rivers and lake

In tropical areas, the relations between soil, rivers, and lakes are poorly understood as regard to the physicochemical transformation that occurs when solid materials are transferred among them. In order to ascertain the natural dynamics of Na, K, Mg, Ca, Al, Fe, Mn, Pb, Zn, Cu, Ni, Cr, and Co, as well as the perturbations by human activity, soils and sediments from a tropical catchment were studied. To accomplish the above mentioned objective, the Valencia Lake catchment was subdivided into three systems, i.e. soils, rivers and lakes. Original data and those previously published by Mogolló;n and Bifano (1994), and Mogolló;n et al. (1995, 1996) were used to establish the numerical relation between the average concentration in the three systems. The percentage labile fraction and metal distribution in different particle size fractions were studied in selected samples. A total of 410 samples was analysed.Lithology and topography are the main factors that differentiate the physicochemical characteristics of soils and sediments. Processes coupled with solid material transport from the upland to lowland area cause the increase of the HNO₃ (1M) extractable metal concentration, and of the percentage labile fraction, metal redistribution towards fine particle fraction. In spite of the tropical climate, the pedogenesis of exposed sediments and the transport along the river courses, have very low influence. Most of the transformations seem to occur during the soils – river transfer of materials. The carbonate precipitation in the lake causes further increase of metal concentration and the percentage labile fraction. The pollutant input increases metal concentration, the percentage labile fraction and the trend of accumulation toward fine particles.     

Role of water hyacinth in the health of a tropical urban lake

The paper assesses health of the tropical urban Robertson Lake, Jabalpur which receives domestic sewage from neighboring human inhabitation and is infested with water hyacinth. Peak density of this macrophyte was 12.5 t dw ha(-1). The water-column was anaerobic (0.6 to 1.9 mg O2 L(-1)), neutral in pH, and enriched with inorganic carbon (23.5 to 37.1 mg L(-1)), NH4-N (0.48 to 2.96 mg L(-1)), and organic nitrogen and phosphorus. Density of heterotrophic bacteria was high (6.8 to 15x10(5) cfu ml(-1)) along with that of total coliforms and fecal bacteria. Species diversity of phytoplankton and submerged macrophytes was very low. Growing stands of water hyacinth could store up to 613 g C m(-2), 23.5 g N m(-2) and 5.5 g P m(-2) and released them during decomposition. The release of nutrients was 3-4 times faster than the uptake. Water hyacinth stabilized water quality and provided substantial support to bacterial density, which in turn contributed significantly to its growth and nutrient dynamics. Turnover of water hyacinth was only 70-80%, adding approximately 175 t humus in the lake. The results denote poor health of the lake, characterized by low species diversity, fast shallowing, dominance of detritus food--webs, and the water unsuitable for human consumption.     

Relative salinity tolerance of warm season turfgrass species

Fresh water, coupled with soil salinization in many areas has resulted in an increased need forscreening of salt tolerant turf grasses. Relative salinity tolerance of eightwarm season turfgrass species were examined in this study in sand culture. Grasses were grown in a glasshouse, irrigated with either distilled water or saline sea water adjusted to 24, 48 or 72 dSm-1. Salt tolerances of the grasses were assessed on the basis of their shoot and root growth, leaf firing and turf quality. Regression analysis indicated that Zoysiajaponica (Japanese lawn grass) (JG), Stenotaphrum secundatum (St. Augustine) (SA), Cynodon dactylon (satiri) (BS), Zoysia teneuifolia (Korean grass) (KG), Digitaria didactyla (Serangoon grass) (SG), Cynodon dactylon (Tifdwarf) (TD), Paspalum notatum (Bahia grass) (BG) and Axonopus compressus(Pearl blue) (PB) suffered a 50% shoot growth reduction at 36.0, 31.8, 30.9, 28.4, 26.4, 25.7, 20.0 and 18.6 dSm1 of salinity, respectively and a root growth reduction at44.9, 43.7, 33.4, 31.0, 29.5 27.5, 21.5 and 21.4 dSm- of salinity, respectively. Leaf firing and turf quality of the selected species, as a whole, were also found to be affected harmoniously with the change in root and shoot growth. On the basis of the experimental results the selected species were ranked for salinity tolerance as JG>SA>BS>KG>SG >TD>BG>PB.     

Integrated model projections of climate change impacts on a North American lake

Climate change is likely to impact terrestrial and aquatic ecosystems via numerous physical and biological mechanisms. This study outlines a framework for projecting potential impacts of climate change on lakes using linked environmental models. Impacts of climate drivers on catchment hydrology and thermal balance in Onondaga Lake (New York State) are simulated using mechanistic models HSPF and UFILS4. Outputs from these models are fed into a lake ecosystem model, developed in AQUATOX. Watershed simulations project increases in the magnitude of peak flows and consequent increases in catchment nutrient export as the magnitude of extreme precipitation events increases. This occurs concurrently with a decrease in annual stream discharge as a result of increased evapotranspiration. Simulated lake water temperatures increase by as much as 5 °C during the 2040-2069 time period, accompanied by a prolonging of the duration of summer stratification. Projected changes include shifts in the timing of nutrient cycling between lake sediments and water column. Plankton taxa projected to thrive under climate change include green algae and Bosmina longirostris. Responses for species at higher trophic levels are mixed. Benthic macroinvertebrates may either prosper (zebra mussels) or decline (chironomids), while fish (e.g., gizzard shad) exhibit high seasonal variability without any clear trend.     

Shift in nutrient and plankton community in eutrophic lake following introduction of a freshwater bivalve

The impact of the freshwater bivalve Corbicula leana on plankton community dynamics was examined during a cyanobacterial bloom period. Nutrient and chlorophyll concentrations, primary productivity, and phytoplankton and zooplankton communities in the experimental enclosures were measured at 2-3 day intervals. The introduction of mussels reduced net primary productivity and phytoplankton and chlorophyll. Chlorophyll decreased immediately following addition of 100 mussels and then increased over time. After 600 mussels were added, chlorophyll decreased continuously from 87to 25 microg l(-1), approaching that in the mussel-free enclosure. Simultaneously, water transparency increased and concentrations of suspended solids and total phosphorus decreased. Mussel addition caused short-term increases in nutrient concentrations, especially following high-density treatment: phytoplankton density decreased, while cell density in the mussel-free enclosure increased. Zooplankton densities in the two enclosures were similar; however, carbon biomass in the mussel enclosure increased, associated with an increase in large zooplankton. The trophic relationship between phytoplankton and zooplankton was positive in the mussel-free enclosure and negative in the mussel-treatment enclosure, possibly reflecting effects of mussels on both consumer and resource control in the plankton community. Thus, filter feeding by Corbicula affects nutrient recycling and plankton community structure in a freshwater ecosystem through direct feeding and competition for food resources.