Accounting for littoral primary production by periphyton shifts a highly humic boreal lake towards net autotrophy

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Size spectra and abundance of planktonic ciliates within various habitats in a macrophyte-dominated lake (Eastern Poland)

Body size, community structure, abundance and biomass of ciliates were compared in various stands of macrophytes in a macrophyte-abundant shallow lake in Eastern Poland. Samples were collected in belts of Phragmites, Typha, Ceratophyllum, Elodea, Stratiotes and Chara. Additionally, protozooplankton was collected from the open water zone surrounding the vegetation belts. Differences in numbers of ciliate taxa between micro-sites were statistically significant. The highest numbers were found in Chara and Ceratophyllum stands, lower numbers in Stratiotes and Elodea stands and the lowest in the open water, Phragmites and Typha areas. Ciliate biomass was, like density, significantly higher in submerged macrophytes than in emergent macrophytes and open water zones. Based on differences in macrophyte structure, two groups of habitats with similar patterns of size-related ciliate distribution were distinguished. The first group consisted of two vegetated zones of sparse stem structure (Phragmites and Typha) and the open water zone, the second group comprised submerged macrophyte species, which were more dense and complex. Generally, the abundance of ciliates correlated positively with total suspension solid (TSS) and total organic carbon (TOC) concentrations. In the Chara and Ceratophyllum stands, relations between ciliate numbers, TSS and TOC were stronger.     

Rapid changes in fish community structure and habitat distribution following the precipitation of lake phosphorus with aluminium

1. Fish community structure and habitat distribution of the abundant species roach, perch and ruffe were studied in Lake Nordborg (Denmark) before (August 2006) and after (August 2007) aluminium treatment to reduce internal phosphorus loading. 2. Rapid changes in fish community structure, abundance and habitat distribution occurred following a decline in in‐lake phosphorus concentrations from 280 to 37 μg P L^?1 and an increase in Secchi depth transparency from 1.1 to 1.9 m (August). The proportion of perch in overnight gill net catches increased, whilst roach decreased, and the average weight of all key species increased. 3. The habitat distribution of perch and roach changed from a high proportion in the upper pelagic and littoral zones in 2006, towards enhanced proportions in the deeper pelagic and profundal zone in 2007. The abundance of large‐bodied zooplankton increased and the abundance of benthic invertebrates decreased in the same period, suggesting that the habitat shift was not induced by food limitation. 4. Ruffe shifted from the littoral and upper profundal zones towards the deep profundal zone, likely reflecting an increased predation risk in the littoral zone and better oxygen conditions in the deep profundal. 5. Our results indicate that enhanced risk of predation in the upper pelagic and the littoral zones and perhaps improved oxygen concentrations in the deeper profundal zone at decreasing turbidity are responsible for the observed habitat shift. The results indicate that fish respond rapidly to changes in nutrient state, both in terms of community structure and habitat use.     

Movement of plankton through lake-stream systems

1. River plankton are often assumed to come from upstream lakes, but the factors controlling the movement of plankton between lakes and rivers into outflow streams are unclear. We tested the possibility that the physical structure of the littoral zone near the lake outlet (depth, presence of macrophytes) and diurnal differences in plankton composition at the lake surface influence the movement of plankton from the lake into the stream and determine their persistence downstream. 2. Zooplankton and phytoplankton biomass, community composition and mean body size were compared between two deep lakes without macrophytes at the lake edge and two shallow lakes with macrophytes at the lake edge. Samples were collected day and night on three dates, in the lake centre, in the littoral zone adjacent to the lake outlet, at the outlet and at two sites downstream in Algonquin Park, Ontario, Canada. 3. The morphology of lake edges clearly affects the movement of lake zooplankton into outlet streams. Outlets draining deeper littoral zones had higher zooplankton biomass than shallow littoral outlets (P < 0.0001), but these differences disappeared within 50 m downstream of the lake. There was no difference in mean zooplankton body size among lake outlets or between littoral and outlet samples. However, shallow littoral zones were dominated by cyclopoid copepods and deeper littoral zones were dominated by Bosmina longirostris. In contrast, phytoplankton biomass entering the outlet was similar to that found within the lake and did not vary with lake outlet morphology. These effects were consistent across several sampling weeks and were not affected by surface zooplankton biomass changes associated with diurnal vertical migration in the lake centre. 4. A comparison with published river zooplankton data suggests that zooplankton are rapidly eliminated from shallow outlet streams (≤1 m deep) but persist in most deeper outlet rivers (≥2 m deep). Because the depth of an outlet river determines downstream zooplankton community development, the contribution of lakes to river plankton communities may be influenced by the location of each lake within the drainage basin. These findings suggest that lake and outflow physical structure influences connection strength between spatially successive habitats.     

Restoring lakes by using artificial plant beds: habitat selection of zooplankton in a clear and a turbid shallow lake

1. Return of large‐bodied zooplankton populations is of key importance for creating a shift from a turbid to a clear‐water state in shallow lakes after a nutrient loading reduction. In temperate lakes, recovery is promoted by submerged macrophytes which function as a daytime refuge for large zooplankton. However, recovery of macrophytes is often delayed and use of artificial plant beds (APB) has been suggested as a tool to enhance zooplankton refuges, thereby reinforcing the shift to a clear‐water state and, eventually, colonisation of natural plants. 2. To further evaluate the potential of APB in lake restoration, we followed the day–night habitat choices of zooplankton throughout summer in a clear and a turbid lake. Observations were made in the pelagic and littoral zones and in APB in the littoral representing three different plant densities (coverage 0%, 40% and 80%). 3. In the clear lake, the zooplankton (primarily Daphnia) were mainly found in the pelagic area in spring, but from mid‐May they were particularly abundant in the APB and almost exclusively so in mid‐June and July, where they appeared in extremely high densities during day (up to 2600 ind. L⁻¹). During night Daphnia densities were overall more equally distributed between the five habitats. Ceriodaphnia was proportionally more abundant in the APB during most of the season. Cyclopoids were more abundant in the high APB during day but were equally distributed between the five habitats during night. 4. In the turbid lake, however, no clear aggregation was observed in the APB for either of the pelagic genera (Daphnia and Bosmina). This may reflect a higher refuge effect in the open water due to the higher turbidity, reduced ability to orient to plant beds and a significantly higher fish density (mainly of roach, Rutilus rutilus, and perch, Perca fluviatilis) in the plant beds than in the clear lake. Chydorus was found in much higher proportions among the plants, while cyclopoids, particularly the pelagic Cyclops vicinus, dominated in the pelagic during day and in the pelagic and high density plants during night. 5. Our results suggest that water clarity is decisive for the habitat choice of large‐bodied zooplankton and that introduction of APB as a restoration measure to enhance zooplankton survival is only a useful tool when water clarity increases following loading reduction. Our results indicate that dense APB will be the most efficient.     

普者黑岩溶湖泊湿地湖滨带景观格局演变对水质的影响

湖滨带作为湖泊与陆地之间的过渡带,是健康湖泊生态系统的重要组成部分。湖滨带景观格局的演变会对湿地水质产生重要影响,因此探究影响岩溶湿地水质变化的湖滨带关键景观因子,对深入了解景观格局对岩溶湿地水质的影响过程与机制具有重要意义。选择普者黑岩溶湖泊湿地为研究对象,以2005、2007、2009、2011年共4年的Landsat遥感影像及水质监测数据为基础,通过划定湖泊湿地湖滨带缓冲区域,运用秩相关分析和冗余分析研究湖滨带景观格局对普者黑岩溶湖泊湿地水质的影响。结果表明,湖滨带不同缓冲区内景观结构类型比例差异较大;枯水期水质与土地利用类型和景观格局指数的影响大于丰水期;景观格局在不同缓冲区尺度对岩溶湿地的水质具有不同的效应;随着监测点缓冲距离的增加,个别景观指数可较好的揭示湖滨带景观格局演变对岩溶湿地水质的影响,其中,蔓延度指数(CONTAG)、斑块结合度指数(COHSION)、均匀度指数(SHEI)对水质参数的影响较大,边界密度(ED)、聚集度(AI)对水质参数的影响随缓冲距离的增加逐渐减弱,其他景观指数对水质影响差异并不明显,最大斑块指数(LPI)在缓冲距离≤300m的区域内与水质的关系较密切,面积加权平均斑块分维数(AWMPFD)与水质参数有显著负相关性,多样性指数(SHDI)对水质的影响具有不确定性;另外,大部分水质参数与土地利用面积比例有较好的相关性,且湿地面积比例是表征岩溶湖泊湿地水环境质量的主要指标。     

Distribution of Gammarus lacustris Sars (Amphipoda, Gammaridae) in Lake Shira (Khakasia, Siberia) and laboratory study of its growth characteristics

Spatial distribution of Gammarus lacustris in Lake Shira and growth of young specimens that feed on lake biota were studied. The amphipods have been shown to inhabit the littoral, sublittoral and the upper aphytal zones of the lake on stony-sandy soil and silted sand. The young and adult individuals stay apart. The young live in submerged or semi-submerged vegetation in the littoral, the adults in the sublittoral and upper aphytal zones. Maximum density of amphipods was encountered in the areas influenced by human activity.The feeding experiments revealed that the lake plankton is a more important food source for G. lacustris than any other food species. The specific growth rate measured was 0.039 d^–1, with a length increment 0.095 mm d^–1.     

咸海湖泊退缩对岸边土壤真菌和植物内生真菌的影响研究

[目的]研究咸海岸边不同暴露时期土壤带的土壤真菌和植物内生真菌群落构成及其对湖泊干涸的响应.[方法]从咸海湖岸远端(土壤带的暴露时间最长)到湖岸近端(土壤带的暴露时间最短)的不同土壤带采集土壤样品,对其进行地球化学和矿物学分析.同时也采集各土壤带的土壤样品和优势植物,通过ITS基因高通量测序方法分析土壤真菌和植物内生真...     

Are zooplankton food resources poor in the vegetated littoral zone of shallow lakes?

1. The distribution of zooplankton in shallow lakes is negatively related to macrophyte density. However, the abundance of their food along density gradients of macrophytes is unknown. A common but untested assumption is that food quantity and quality for pelagic zooplankton is poor in the littoral zone owing to the deleterious influence of macrophytes on phytoplankton. 2. We tested this assumption with a combination of a field survey and laboratory experiments. We collected seston samples from the littoral and pelagic zones of four shallow temperate lakes and related food quantity (phytoplankton biovolume) and quality to macrophyte abundance (per cent volume infested). Seston food quality was assessed in three ways: N/C and P/C ratios, polyunsaturated fatty acid content and phytoplankton community composition. In the laboratory, we measured the growth and reproduction of Daphnia pulicaria on diets consisting of seston from the littoral and pelagic zones in one lake. 3. In our four study lakes, food quantity was not significantly influenced by macrophyte abundance, and food quality was generally high. Laboratory experiments showed increased juvenile growth, but no significant change in D. pulicaria reproduction, when feeding on littoral resources compared to pelagic resources. 4. Our results suggest that there is no nutritional cost to pelagic zooplankton inhabiting the littoral zone. Therefore, it is likely that other factors (e.g. predation, abiotic factors) are involved in determining zooplankton habitat use.     

Palaeolimnology as a tool to inform shallow lake management: an example from Upton Great Broad,Norfolk, UK

This palaeolimnological study investigates recent changes in the biological structure of an English shallow lake (Upton Great Broad, Norfolk). By focusing on the historical occurrence of submerged macrophytes, particularly the rare UK species, Najas marina L. (Holly-leaved Naiad), we address a management question that frequently arises for shallow lakes, namely whether to undertake sediment removal to increase water depth and/or restore conservation value. Macro-remains of aquatic macrophytes and molluscs were analysed in two littoral sediment cores and combined with other historical ecological data covering the last 100 years. Before around 1900, the lake had Chara meadows (including at least three species) and an associated species-rich community of Mollusca. Between around 1900–1970 a period of high angiosperm diversity is suggested with a reduction of Characeae and the development of patches of water-lily (particularly Nymphaea alba L.) and fen swamp in the open water. Then, after around 1970, our data indicate a rapid shift towards Najas-dominance coupled with a decrease in the seasonal length of the plant-covered period. The expansion of Najas was clearly associated with, and may even be dependent upon, a highly unusual fluid, green sediment formation that developed at the site from around the same time. Thus, despite the loss of an earlier more diverse vegetation and associated fauna, we suggest that best practice conservation may be allow natural site development and not to undertake active management such as sediment removal which might threaten the status of Najas. Our conclusion could only have been arrived at through the long-term ecological perspective that a palaeolimnological approach provides.     

The diet and growth of roach (Rutilus rutilus (L.)) in Lake Vesijärvi and possible changes in the course of biomanipulation

Previous studies have suggested that the roach Rutilus rutilus (L.) stock of Lake Vesijärvi is one of the main factors delaying the recovery of the lake after sewage diversion. This study is concerned with the documentation of the diet of roach in the lake. In total, 531 roach were examined. Both in the pelagial and in the littoral the roach had mixed diets in May and in September—October. The importance of zooplankton decreased and the importance of benthos and plants increased with increasing size of roach. In July, in the pelagic zone all sizes of roach fed exclusively on zooplankton (Bosmina spp.), while in the littoral zooplankton had the highest volume proportions only in the smallest (<130 mm) roach. The frequent use of plant food and slow growth rate of large roach indicate a low availability of animal prey. As the fish densities decrease due to the mass removal taking place in the lake, the percentage of plant food in the diets of roach will probably decrease and the growth of roach will increase. Additionally, the tendency of the roach to migrate into the pelagic zone in early summer may be reduced, which would decrease their predation on the zooplankton.     

Hydrologic and anthropogenic influences on aquatic macrophyte development in a large,shallow lake in China

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Fish community structure response to major habitat changes within the littoral zone of an estuarine coastal lake

Synopsis The littoral environment and fish fauna of Swartvlei, an estuarine lake, was monitored for four years during which major habitat changes occurred. Initially (1979) the zone was dominated by the submerged macrophytes Potamogeton pectinatus, Chara globularis and Lamprothamnium papulosum. This plant community was replaced by filamentous algal mats during 1980 and with the disappearance of these mats in 1981 the littoral zone was transformed into a sandy habitat. There was a highly significant decline in the numbers of fishes in the littoral zone between the macrophyte and sand phases but no significant decrease in fish biomass between the two phases. Analysis of gill net catches revealed an increase in the CPUE of the family Mugilidae between the macrophyte and sand phases but a decline in the CPUE of vegetation associated species such as Monodactylus falciformis and Rhabdosargus holubi over the same period. The increase in mullet stocks during the sand phase was attributed to epipsammic micro-algal production and the input of allochthonous detritus during the 1981 floods. The three fish species diversity indices used in this study showed minor fluctuations between the habitat phases and these variations were related to changes in the equitability of distribution between the individual species within each habitat type. The numbers of fish species recorded during the macrophyte, algal mat and sand phases varied by less than 20%. The resilience of estuarine fishes to major alterations in their environment was illustrated by the fact that all fish species recorded at the beginning of 1979 were present at the end of 1982, despite major habitat and food resource changes.     

Seasonal dynamics,typhoons and the regulation of lake metabolism in a subtropical humic lake

1. We used high‐frequency in situ dissolved oxygen measurements to investigate the seasonal variability and factors regulating metabolism in a subtropical alpine lake in Taiwan between May 2004 and October 2005, specifically exploring how the typhoon season (from June or July to October) affects lake metabolism. 2. Gross primary production (GPP) and ecosystem respiration (R) both peaked in early summer and mid‐autumn but dropped during the typhoon season and winter. Yuan‐Yang Lake is a net heterotrophic ecosystem (annual mean net ecosystem production ?39.6 μmole O₂ m^?3). 3. Compared to the summer peaks, seasonal averages of GPP and R decreased by approximately 50% and 25%, respectively, during the typhoon season. Ecosystem respiration was more resistant to external disturbances than GPP and showed strong daily variation during typhoon seasons. 4. Changes in the quality and quantity of dissolved organic carbon controlled the temporal dynamics and metabolic regulation. External disturbances (typhoons) caused increased allochthony, increasing DOC and water colour and influencing lake metabolism. 5. Seasonal winter mixing and typhoon‐induced water mixing in summer and autumn play a key role in determining the extent to which the lake is a seasonal carbon sink or source to the atmosphere.     

Remote sensing evidence for the episodic transport of phosphorus from the littoral zone of a thermally stratified lake

• 1 Esthwaite Water in Cumbria is a small, thermally stratified lake fringed with beds of reed in the shallow littoral. In this study, we used a combination of in situ measurements and airborne remote sensing to investigate some of the physical processes influencing the transport of water and nutrients from the littoral zone.
• 2 The analysis of water samples collected from the reed beds, the littoral zone and the open water showed that significantly higher concentrations of dissolved reactive phosphorus (DRP) were frequently recorded in the reed beds in early summer.
• 3 Experiments with surface and near‐surface free‐running drogues demonstrated that the movement of water from the littoral zone was strongly influenced by the development of a secondary thermocline. When there was no secondary stratification, the surface currents generated by light winds seldom exceeded 2 cm s^‐1. When a secondary thermocline was present, surface current speeds of 5–10 cm s^‐1 were recorded even when the wind speed was less than 200 cm s^‐1.
• 4 A series of thermal surveys using a Daedalus Airborne Thematic Mapper (ATM) demonstrated that plumes of warm water frequently developed in the littoral zone when the weather was calm. Some of these plumes covered several hundred square metres and persisted for several hours. Others were only a few metres in width and acted as episodic ‘pumps’ that appeared and dispersed in less than an hour.

     

Carbon,phosphorus and nitrogen budgets of the littoral Equisetum belt in an oligotrophic lake

Stores and flows of carbon, phosphorus and nitrogen in a littoral Equisetum stand were studied in 1978–1980 in the oligotrophic, mesohumic lake Pääjärvi, southern Finland. The major carbon and nutrient stores were sediment and Equisetum. The seasonal cycle of the macrophyte vegetation had a profound influence on the whole littoral ecosystem. In spring, when only dead remains of Equisetum were present above ground, there were few differences in nutrient, chlorophyll a and zooplankton concentrations between the littoral and the open lake; phytoplankton and epiphytes were the major producers.In early June, when new shoots of Equisetum reached the water surface, water exchange between the littoral and the open lake started to diminish, and the characteristic features of a closed macrophyte zone gradually developed: by August the P, Chl a and zooplankton concentrations in the littoral were 5–10 times those in the open lake. From late June until autumn Equisetum was overwhelmingly dominant both in biomass and in production.The measured total primary production and respiration values indicated a high rate of internal cycling of carbon and nutrients. The daily P requirements of plant growth exceeded the total P stored in the water by a factor of 2–4, and also exceeded the release of nutrients in excretion. High N:P ratios in the water (total 10–64, inorganic 18–171) suggested that P was probably always the limiting nutrient.The P content of the annual production of Equisetum in Pääjärvi was 2.3% of the mean annual P load, and 5.3% of the mean total P storage in the water volume of the lake.     

Deep-water aquatic plant communities in an oligotrophic lake: physiological responses to variable light

1. Oligotrophic Lake Waikaremoana, New Zealand, is used for hydroelectric power generation and the lake levels are manipulated within an operating range of 3 m. There was concern that rapidly changing water levels adversely affected the littoral zone by decreasing light availability in two ways: local turbidity caused by shoreline erosion at low water levels; and decreased light penetration to the deep littoral zone caused by high water levels in summer. 2. The littoral zone was dominated by native aquatic plants with vascular species to 6 m and a characean meadow below this to 16 m. The biomass and heights of the communities in the depth zone 0–6 m were reduced at a site exposed to wave action relative to those at a sheltered site. However, the community structure below 6 m was similar at exposed and sheltered sites. The lower boundary of the littoral zone was sharply delimited at 16 m and this bottom boundary remained constant throughout the year despite large seasonal changes in solar radiation and the 3 m variation in lake level. 3. There was evidence that the deep-water community consisting of Chara corallina had adapted physiologically to low-light conditions. Net light saturated photosynthesis (CO₂ exchange) per unit chlorophyll a (Chl a) was reduced to 1.7 μg C (μg Chl a)^?1 h^?1 at the lower boundary, half of that recorded at 5 m. The concentration of Chi a per gram of biomass (dry weight), was considerably greater at the lower boundary than higher in the profile [c. 7 mg Chl a (g dry wt)^?1 at 16 m vs. 4 mg Chl a (g dry wt)^?1 at 5 m]. Chl b also increased with depth and there was no change in the ratio of Chl a and Chl b with increasing depth. The saturation light intensity (I_k) of the community at the lower boundary was only 78 μmol photons m^?2 s^?1. Photosynthetic parameters (I_k and α) as well as the Chl a content remained relatively constant throughout the seasonal and short-term changes in radiation. 4. The photosynthetic characteristics of the littoral community were therefore not greatly affected by the lake level change caused by the present hydroelectric operations. However, the sharpness of the lower boundary and its extreme shade characteristics imply that the deep-water community would be sensitive to any further changes in underwater light availability.     

Recovery of plankton from hurricane impacts in a large shallow lake

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Spatial patterns and population dynamics of plant-associated microcrustacea (Cladocera) in an English shallow lake (Little Mere, Cheshire)

Little Mere (Cheshire) is a small (2.7 ha) and shallow (average depth 0.7 m) fertile lake in Cheshire, UK. Nymphaeids cover almost 40 % of its entire surface during the growing season (April to October) and practically all the rest is covered by a mixed community of submerged plants. The lake was intensively sampled for plant-associated Cladocera and zooplankters from April 1998-April 2000. Samples were collected at five sites across the lake, three of them located within lily beds, the other two over submerged plant beds of mixed composition. Specific sampling techniques were developed for floating lily leaves, petioles, submerged plants and water. Significant horizontal differences were identified for most cladoceran species, both open-water and plant-associated, for chydorid periphyton scrapers and for filter-feeders. Daphnia hyalina (L.) and Ceriodaphnia sp were significantly more abundant in lily beds than in more open water in both growing seasons, suggesting lily beds are an effective refuge against fish predation. Size-structure and egg-ratio data support this contention. Egg-ratio models were examined for Daphnia hyalina and Simocephalus vetulus (O.F. Müller), a plant-associated cladoceran. The fertility of S. vetulus in lily beds was generally high throughout growing seasons. The construction of egg-ratio models for this species was hampered by their generally very patchy distributions.