Littoral Zone Of Lake Research Articles

Spatiotemporal Variability in Lake‐Atmosphere Net CO2 Exchange in the Littoral Zone of an Oligotrophic Lake

AbstractLakes may function as either sinks or sources of CO2. Their response to climate change is uncertain, as we lack continuous data of lake CO2 efflux and its drivers. This is especially true in the littoral zone of lakes, which can be very dynamic from the continuous injection and remobilization of terrestrial nutrients. This study used high‐frequency measurements of CO2 exchange during the ice‐free season by prototype low‐power floating forced diffusion autochambers. We quantified the net surface flux of CO2 across a transect of the littoral zone of a small deep oligotrophic lake in eastern Nova Scotia, Canada, and examined potential drivers. The littoral zone was a net source for CO2, on average emitting 0.171 ± 0.023 μmol CO2 · m−2 · s−1, but we did observe significant temporal variation across diel and seasonal periods, as well as with distance from shore. While no pelagic environmental driver appeared to explain this variability in CO2 exchange, our study suggests that factors that vary on a fine spatial scale within the littoral zone may effectively regulate CO2 exchange. If environmental drivers of pelagic CO2 exchange are unrelated to CO2 exchange in the littoral zone, this may have large implications for current mechanistic understandings of lake carbon dynamics and for upscalings of fluxes. This work shows the spatial and temporal variability of littoral CO2 efflux, as well as the utility of low‐power forced diffusion automated chambers for observing lake‐atmosphere net CO2 exchange.

Optimum water depth ranges of dominant submersed macrophytes in a natural freshwater lake.

Macrophytes show a zonal distribution along the lake littoral zone because of their specific preferred water depths while the optimum growth water depths of dominant submersed macrophytes in natural lakes are not well known. We studied the seasonal biomass and frequency patterns of dominant and companion submersed macrophytes along the water depth gradient in Lake Erhai in 2013. The results showed that the species richness and community biomass showed hump-back shaped patterns along the water depth gradient both in polydominant and monodominant communities. Biomass percentage of Potamogenton maackianus showed a hump-back pattern while biomass percentages of Ceratophyllum demersum and Vallisneria natans appeared U-shaped patterns across the water depth gradient in polydominant communities whereas biomass percentage of V. natans increased with the water depth in monodominant communities. Dominant species demonstrated a broader distribution range of water depth than companion species. Frequency and biomass of companion species declined drastically with the water depth whereas those of dominant species showed non-linear patterns across the water depth gradient. Namely, along the water depth gradient, biomass of P. maackianus and V. natans showed hump-back patterns and biomasses of C. demersum displayed a U-shaped pattern in the polydominant communities but biomass of V. natans demonstrated a hump-back pattern in the monodominant communities; frequency of P. maackianus showed a hump-back pattern and C. demersum and V. natans maintained high frequencies in the two types of communities. We can speculate that in Lake Erhai the optimum growth water depths of P. maackianus and C. demersum in the polydominant communities are 2.5–4.5 m and 1–2 m or 5–6 m, respectively and that of V. natans is 3–5 m in the polydominant communities and 2.5–5 m in the monodominant communities. This is the first report that the optimum water depth ranges in the horizontal direction of three dominant submersed macrophytes in a natural freshwater lake were determined.

A glimpse into the littoral nutrient dynamics of a lake system connected to the sea

In South Africa more than 80% of estuaries are small, dynamic and predominantly linear systems. Nutrient characteristics in these systems are mostly influenced by external catchment processes, except during extended periods of closure. However, a small percentage of the country’s estuaries (< 3%) comprise larger estuarine lakes mostly evolved from drowned river valleys. The physical properties of these systems suggest relatively low flushing rates, and the potentially stronger influence of in-situ processes on nutrient characteristics. This study investigates dissolved inorganic nutrient dynamics in the littoral zones of these estuarine lake systems, and potential influencing factors, using the Wilderness Lake System as a case study. Comparison of inter-annual and seasonal trends in dissolved inorganic nutrients (NOx-N, NH4-N and PO4-P) in river inflow and in the three lakes confirmed that external catchment fluxes are most likely not the sole, or even the dominant drivers of average long-term or seasonal dissolved inorganic nutrient patterns in the lake littoral zones. Relatively low NOx:NH4 ratios (mostly less than 1) in the lakes (especially in Eilandvlei and Langvlei) indicated a stronger influence of in-situ processes, such as bacteriological remineralisation, similar to observations in other lake type systems with low flushing rates. Low NO3:NH4 ratios are known to stimulate cyanobacteria, having the metabolic ability to potentially produce microcystins. Therefore, incremental dissolved inorganic nutrient and organic matter enrichment may cause these systems to tip into eutrophic, possibly toxic, aquatic states that will be difficult, if not impossible, to reverse given their weak flushing mechanisms. The findings from this study highlight the importance of appropriate water resource management, both in the catchments and within the floodplains of estuarine lake systems.

普者黑岩溶湖泊湿地湖滨带景观格局演变对水质的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 普者黑岩溶湖泊湿地湖滨带景观格局演变对水质的影响 DOI: 10.5846/stxb201703130419 作者: 作者单位: 西南林业大学国家高原湿地研究中心;西南林业大学环境科学与工程学院,西南林业大学环境科学与工程学院;西南林业大学农村污水处理研究所,西南林业大学环境科学与工程学院,西南林业大学环境科学与工程学院;西南林业大学农村污水处理研究所,西南林业大学林学院,西南林业大学环境科学与工程学院;西南林业大学农村污水处理研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（31760245，31560237，31460195） The effects of landscape pattern evolution in Puzhehei karst lake wetland littoral zone on water quality Author: Affiliation: National Plateau Wetlands Reasearch Center, Southwest Forestry University;College of Environmental Science and Engineering, Southwest Forestry University,College of Environmental Science and Engineering, Southwest Forestry University;Research Institute of Rural Sewage Treatment, Southwest Forestry University,,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要: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。 Abstract:The lake littoral zone, an important transitional area between land and lake, is an integral part of a healthy lake ecosystem. The evolution of landscape patterns in the lake littoral zone will have an important effect on wetland water quality. Therefore, studying the key littoral zone landscape factors that affect karst wetland water quality changes is of great importance in understanding the process and the underlying mechanism regarding how landscape patterns effect karst wetland water quality. Using Puzhehei karst lake wetland as the study area, and obtaining Landsat remote sensing images and the collected water quality monitoring data from 2005, 2007, 2009, and 2011, we studied the influence of landscape pattern indices on Puzhehei karst lake wetland littoral zone water quality through delineating the buffer zones and using correlation and redundancy analysis. The results showed that the littoral zone landscape patterns were quite different in various buffer zones. The effects of water quality on land use type and landscape pattern indices in the low flow period was greater than that in the high flow period; the landscape patterns had different effects on the water quality of karst lake wetlands at different buffer zones. Individual landscape indices better revealed the influence of landscape pattern evolution on water quality in the Puzhehei karst lake wetland, accompanied by increased buffer zone distances. Among them, Contagion Index, Patch Cohesion Index, and Shannon's Evenness Index values had a substantial influence on water quality, and Area-weighted Mean Patch Fractal Dimension exhibited a significantly negative correlation with water quality parameters. The effects of other landscape indices on water quality were not significant. Among them, the effects of Edge Density and Aggregation Index values on water quality gradually weakened accompanied by the increased buffer region distances. Largest Patch Index values were closely correlated with water quality when the buffer distance was less than 300m. Beyond this, the effect of Shannon's Diversity Index on water quality was uncertain. Additionally, most water quality parameters showed a good correlation with land use type area, and the proportion of wetland area was the main index to characterize the water environment quality of the karst lake wetland. 参考文献 相似文献 引证文献

Ecological impacts of winter water level drawdowns on lake littoral zones: a review

Freshwater littoral zones harbor diverse ecological communities and serve numerous ecosystem functions that are controlled, in part, by natural water level fluctuations. However, human alteration of lake hydrologic regimes beyond natural fluctuations threaten littoral zone ecological integrity. One type of hydrologic alteration in lakes is winter water level drawdowns, which are frequently employed for hydropower, flood control, and macrophyte control, among other purposes. Here, we synthesize the abiotic and biotic responses to annual and novel winter water level drawdowns in littoral zones of lakes and reservoirs. The dewatering, freezing, and increased erosion of exposed lakebeds drive changes in the littoral zone. Shoreline-specific physicochemical conditions such as littoral slope and shoreline exposure further induce modifications. Loss of fine sediment decreases nutrient availability over time, but desiccation may promote a temporary nutrient pulse upon re-inundation. Annual winter drawdowns can decrease taxonomic richness of macrophytes and benthic invertebrates and shift assemblage composition to favor taxa with r-selected life history strategies and with functional traits resistant to direct and indirect drawdown effects. Fish assemblages, though less directly affected by winter drawdowns (except where there is critically low dissolved oxygen), experience negative effects via indirect pathways like decreased food resources and spawning habitat. We identify eight general research gaps to guide future research that could improve our understanding about the complex effects of winter drawdowns on littoral zone ecology.

Biomass loss and nutrient release from decomposing aquatic macrophytes: effects of detrital mixing

Aquatic plant decomposition is typically studied on species held separately, whereas diverse plant communities are usually found in lake littoral zones and decomposition occurs as mixtures of multiple species. Here, we examined whether detrital mixing affects the rate of aquatic macrophyte decomposition. Specifically, we measured decomposition rates of detritus from four species (Myriophyllum heterophyllum, Ceratophyllum demersum, Typha × glauca, and Potamogeton robinsii) in single, double, triple, and quadruple species mixtures held over two summer months in a mesotrophic lake in southern Ontario, Canada. We measured detrital mass loss after different time periods for all combinations. There were limited effects of mixing on decomposition rates with inhibitory effects observed in only two of the eleven multi-species mixtures. Decomposition rates of single and mixed species detritus varied with initial C:N and C:P ratios with faster rates seen for more nutrient-rich detritus. Overall, there was no effect of detrital species richness on macrophyte decomposition rates other than smaller differences among the averages of more species-rich mixtures. Our results were inconsistent with interactive effects of mixing on decomposition rates of multiple aquatic plant taxa. Instead, we found decomposition rates of mixed species communities were largely predicted by biomass composition and single-species decomposition estimates. There were also no apparent effects of species mixing on N- or P-specific fluxes or the ratio of these fluxes that resulted during decomposition during our experiment. Our results indicate that future changes in aquatic plant biodiversity may affect rates of decomposition in these ecosystems, but these should be largely predictable based on changes in plant communities and their biomass-weighted stoichiometry.

Overlapping trophic niches among co‐occurring amphipods from a cryptic species complex

Abstract Ecological differences among species are usually associated with phenotypic differences that enable species to lessen interspecific competition. Many cryptic species co‐occur in communities, thus raising the question of their ecological equivalency. In the case of freshwater amphipods from the Hyalella azteca cryptic species complex, both ecological differences and overlaps have been reported among species that co‐occur in lakes. Since lakes are heterogeneous habitats that vary in space and time, it is possible that species minimise interspecific competition by occupying different trophic niches. We tested the hypothesis that amphipod species from the H. azteca complex co‐occur by feeding on different food resources in the littoral zone of boreal lakes. We compared the stable isotopes ratios (δ13C and δ15N) of amphipods from different species, and reconstructed their diets using mixing models. We showed that H. azteca amphipods from different species had isotopic compositions and habitat uses that greatly overlapped. Differences in isotopic composition often occurred, but they were also observed for amphipods of the same species sampled at different depths. This suggests that H. azteca amphipods fed mainly on resources that were available at the site where they occurred rather than distributed according to the occurrence of a specific resource. The overlap in diets suggests that H. azteca amphipods had overlapping trophic niches. Therefore, niche partitioning for food resources was not a process explaining the co‐occurrence of these species within these lakes. Competition for food resources was not likely an important mechanism to explain H. azteca species assemblages in communities. Each H. azteca species apparently fed on food items that were abundant in the littoral zone of lakes, meaning that competition for food might be avoided most of the time. If food scarcity ever happens, the period of scarcity is probably too short to allow the exclusion of one amphipod species by competitive exclusion because of the low differences in fitness between the species, allowing Hyalella cryptic species to co‐occur during the open‐water season. Neutral mechanisms and ecological drift might also influence assemblage dynamics.

Impacts of the cryptic macroalgal invader, Nitellopsis obtusa, on macrophyte communities

AbstractEarly detection of aquatic invasive species, such as Nitellopsis obtusa, is often critical to reduce their long-term negative effects. This macroalga resembles native taxa and can invade deep locations in littoral zones of lakes in North America. Studies in which effects of Nitellopsis on macrophyte communities were quantified are rare. We surveyed 4 lakes in central New York where Nitellopsis is present to document whether macrophyte communities are negatively affected by this invasive macroalgae and to test whether Nitellopsis was found more frequently in deeper- than in shallow-water habitats. We found lower macrophyte species richness when Nitellopsis was abundant. This pattern was consistent at 3 water depths (shallow [>1 m], intermediate [1–2 m], and deep [>2 m]). Macrophyte biomasses (total, including native and other nonnative species, and only native species) were significantly lower in quadrats with greater abundance of Nitellopsis. Nitellopsis biomass exceeded the combined biomass of ma...

Bridging between litterbags and whole-ecosystem experiments: a new approach for studying lake sediments

<p>Nearshore sediments have a major influence over the functioning of aquatic ecosystems, but predicting their response to future environmental change has proven difficult. Previous manipulative experiments have faced challenges controlling environmental conditions, replicating sediment mixing dynamics, and extrapolating across spatial scales. Here we describe a new approach to manipulate lake sediments that overcomes previous concerns about reproducibility and environment controls, whilst also bridging the gap between smaller microcosm or litterbag experiments and whole-ecosystem manipulations. Our approach involves submerging moderate-sized (~15 L) artificial substrates that have been standardised to mimic natural sediments within the littoral zones of lakes. We show that this approach can accurately mirror the absolute dissolved organic carbon concentrations and pH of pore water, and to a lesser degree inorganic carbon concentrations, from natural lake sediments with similar organic matter profiles. On a relative basis, all measured variables had similar temporal dynamics between artificial and adjacent natural sediments. Late-summer zooplankton biomass also did not differ between natural and artificial sediments. By offering a more realistic way to manipulate freshwater sediments than previously possible, our approach can improve predictions of lake ecosystems in a changing world.<br /><br /><img src="/public/site/images/ttaccini/88x31.png" alt="" /> <br />This work is licensed under a <a href="https://creativecommons.org/licenses/by/4.0/" target="_blank">Creative Commons Attribution 4.0 International</a>.</p>

A rare Uroglena bloom in Beaver Lake, Arkansas, spring 2015

ABSTRACTGreen WR, Hufhines B. 2017. A rare Uroglena bloom in Beaver Lake, Arkansas, spring 2015. Lake Reserve Manage. 33:8–13.A combination of factors triggered a Uroglena volvox bloom and taste and odor event in Beaver Lake, a water-supply reservoir in northwest Arkansas, in late April 2015. Factors contributing to the bloom included increased rainfall and runoff containing increased concentrations of dissolved organic carbon, followed by a stable pool, low nutrient concentrations, and an expansion of lake surface area and littoral zone. This was the first time U. volvox was identified in Beaver Lake and the first time it was recognized as a source of taste and odor. Routine water quality samples happened to be collected by the US Geological Survey and the Beaver Water District throughout the reservoir during the bloom. Higher than normal rainfall in March 2015 increased the pool elevation in Beaver Lake by 2.3 m (by early April), increased the surface area by 10%, and increased the littoral zone by 1214 ha; these conditions persisted for 38 days, resulting from flood water being retained behind the dam. Monitoring programs that cover a wide range of reservoir features, including dissolved organic carbon, zooplankton, and phytoplankton, are valuable in explaining unusual events such as this Uroglena bloom.

Water level changes affect carbon turnover and microbial community composition in lake sediments.

Due to climate change, many lakes in Europe will be subject to higher variability of hydrological characteristics in their littoral zones. These different hydrological regimes might affect the use of allochthonous and autochthonous carbon sources. We used sandy sediment microcosms to examine the effects of different hydrological regimes (wet, desiccating, and wet-desiccation cycles) on carbon turnover. 13C-labelled particulate organic carbon was used to trace and estimate carbon uptake into bacterial biomass (via phospholipid fatty acids) and respiration. Microbial community changes were monitored by combining DNA- and RNA-based real-time PCR quantification and terminal restriction fragment length polymorphism (T-RFLP) analysis of 16S rRNA. The shifting hydrological regimes in the sediment primarily caused two linked microbial effects: changes in the use of available organic carbon and community composition changes. Drying sediments yielded the highest CO2 emission rates, whereas hydrological shifts increased the uptake of allochthonous organic carbon for respiration. T-RFLP patterns demonstrated that only the most extreme hydrological changes induced a significant shift in the active and total bacterial communities. As current scenarios of climate change predict an increase of drought events, frequent variations of the hydrological regimes of many lake littoral zones in central Europe are anticipated. Based on the results of our study, this phenomenon may increase the intensity and amplitude in rates of allochthonous organic carbon uptake and CO2 emissions.

Diatom communities and vegetation of springs in the south-western Alps

Abstract Springs are unique but understudied habitats. Diatom communities have received some attention but have remained largely unknown in the south-western Alps. We therefore studied the springs of the south-western extreme of the Alpine mountain range. We analysed epilithic and epiphytic assemblages in 48 springs of different ecomorphological types, located on contrasting lithological substrata (carbonate/siliceous). Moreover, phytosociological relevés were carried out for carbonate springs. The diatom flora consisted of 223 taxa. Most (198) of the taxa were included in the Red List, and 12.5% belonged to threatened categories. Characteristic spring taxa (crenophiles) were present. The ecological preferences of crenophilous diatom species described in the eastern Alps were confirmed. Diatom species characteristic of the lake-littoral zone were found in pool springs. We observed no significant differences in species richness and diversity between epilithic and epiphytic assemblages, but some species showed a preference for bryophytes, and five occurred in the epibryon only. As regards moisture conditions, 15% of the taxa occurred on wet or temporarily dry sites, and 4% lived mostly outside water bodies. The main environmental factors influencing diatom assemblages were pH, conductivity, altitude, and shading. The carbonate-substratum crenic vegetation was composed of a mixture of vascular plants and bryophytes, which find their ecological optimum in springs. Bryophyte cover was dominant, with the most abundant taxa belonging to the genus Palustriella. The vegetation corresponded to the Cratoneuretum commutati association.

A test of sampling methods for fishes in the littoral zone of Lake Vänern, Sweden

Shallow, vegetated habitats play an important role as spawning and nursery areas for several species of fish. Such habitats are often laborious to monitor with conventional sampling methods. We evaluated two quantitative methods for sampling of young fishes in shallow habitats; point abundance with electrofishing and low-impact pressure wave sampling using small underwater detonations. The study was conducted in the littoral zone of an archipelago area in Lake Vänern, Sweden. Both methods rendered quantitative estimates on the most common fish species. However, underwater detonations yielded more species and lower variation among samples. These differences are likely due to the larger sample area of detonations. Species distribution and juvenile fish density estimates and size-structure were compared with results from multi-mesh gill nets. The dominant fish species in the gill net program were recorded with both active methods although the relative composition differed, mainly as a consequence of differences in species and size selectivity. Detonations provided additional, small-bodied, species that were not recorded in the gill net program. Quantitative methods can provide relevant information for identifying essential fish habitats, understanding ecosystem dynamics and providing a baseline for assessing long-term changes (e.g. due to climate change or new water level regimes) in Lake Vänern.

Seismically-triggered organic-rich layers in recent sediments from Göllüköy Lake (North Anatolian Fault, Turkey)

Multi-proxy analyses on the sedimentary sequence of Göllüköy Lake, which is located on the eastern North Anatolian Fault (NAF), reveals a complete and high-resolution paleoseismic record for the last 650 years. Six sedimentary events are detected in a 3.1 m-long piston core. They form distinct organic-rich intercalations within the background sedimentation, which are characterized by strong anomalies on the loss-on-ignition (LOI550) and total organic carbon (TOC) profiles, as well as by lighter colours on the X-ray radiographic images. Itrax micro-XRF core scanner data are also used to contribute to the detection and characterization of the event deposits. After the detection of the sedimentary events, their temporal correlation with the earthquakes in the historical seismicity catalogue of the NAF is tested. The youngest event is dated to 1940s by using 210Pb and 137Cs profiles in sediment, which coincides with the 1939 earthquake (Ms = 7.7) on the NAF. The ages of the older five events are determined based on radiocarbon dating and regional time–stratigraphic correlation. Radiocarbon dating on the bulk sediment samples does not provide reliable results due to hard-water effect. On the other hand, dating on charcoals, Ephippia of Daphnia and phragmite remains significantly improves the results and implies a mean sedimentation rate of 0.28 cm/yr. Based on this preliminary sedimentation rate, we show that organic matter content variations through our record correlate with the varve-based δ18O record of Nar Lake, which is located 350 km southwest of Göllüköy Lake. Accordingly, high-precipitation/low-evaporation climatic episodes detected in Nar Lake are represented by higher organic matter content in Göllüköy sediments. Fine-tuning the Göllüköy LOI550 record to the Nar δ18O record reveals that the ages of the sedimentary events in Göllüköy match with well-known historical earthquakes that occurred around the lake. Finally, the origin of the organic-rich intercalations is discussed based on macroscopic observations and organic geochemistry. The events are attributed to reworked organic matter eroded from the lake's littoral zone by seismically-induced water oscillations (seiche), and their subsequent deposition at the middle parts of the lake. These seismically-induced events are atypical compared to the classic earthquake-triggered sedimentary processes in lacustrine environments, which are shortly reviewed in order to emphasize the unusual Göllüköy Lake record.

Is coarse woody debris in lakes a refuge or a trap for benthic invertebrates exposed to fish predation?

Summary Coarse woody debris (CWD) in the littoral zone of lakes constitutes a preferred habitat for macroinvertebrates and fish. CWD differs in the surface complexity depending on its decay status. Therefore, CWD may provide distinct types of shelters and thus modify the structure of the macroinvertebrate community as well as its susceptibility to fish predation. We ran an enclosure experiment in a lake littoral zone to test the effect of surface complexity of CWD on the interactions between the predator, Eurasian perch (Perca fluviatilis) and its potential macroinvertebrate prey. We deployed 10 enclosures containing fresh wood with a smooth surface and 10 enclosures containing decayed wood with a more complex, rough surface and allowed colonisation by macroinvertebrates. Five enclosures of each type were then stocked by perch and exposed to fish predation. The abundance and biomass of macroinvertebrates were significantly higher on decayed wood with greater surface complexity than on fresh wood; however, the type of CWD did not strongly influence the taxonomic composition and diversity of invertebrates. The direct effect of perch predation on the macroinvertebrate community was weak. Perch reduced only the abundance of adult Dikerogammarus villosus, while other potential prey, such as chironomids, was more abundant in the presence of the fish. The impact of perch consumption of these larvae was probably obscured by interspecific interactions among chironomids and D. villosus, which were impaired in the fish enclosures. We found no clear evidence that the influence of perch on macroinvertebrates was mediated by the complexity of the wood surface. However, fish diet analysis showed that on decayed wood, perch preferentially consumed chironomids, and consumption of D. villosus was much lower, while on fresh wood, the preferential consumption of chironomids decreased with increasing consumption of gammarids. This suggests that such differences in fish diet could be an effect of complex interactions between wood microstructure, prey density and its ability to find refuge in CWD. The effect of CWD microstructure on predator–prey interactions was visible with respect to interspecific relationships between chironomids and gammarids, which on more complex decayed wood were moderated in the absence of perch.

Quantifying ecological responses to amplified water level fluctuations in standing waters: an experimental approach

Summary Global freshwater demand is increasing dramatically, with water withdrawal rates more than tripling in the last five decades. Consequently, alteration of water level regimes, particularly in the form of amplified water level fluctuations (WLF), is rapidly becoming one of the major disturbances of aquatic ecosystems globally. However, even though the impacts of WLF are likely to be strongest in littoral zones, little is known about their effects on the structure and functioning of littoral assemblages in standing water systems. We established an experiment in large outdoor pond mesocosms to examine the effects of WLF on littoral assemblages and explore the potential for development of ecological indicators of WLF. Water level fluctuations reduced benthic algal biomass and the density and taxonomic distinctness of benthic invertebrate assemblages. Both the taxonomic and trophic structure of benthic assemblages were altered significantly in ponds with WLF and homogenized along the depth gradient. Synthesis and applications. Our results indicate that water level fluctuations (WLF) can reduce considerably the productivity and biological diversity of lake littoral zones. Given that the problem is likely to be exacerbated by predicted increases in climatic variability and enhanced demand for water and hydropower, our findings have important implications for the conservation and management of global aquatic biodiversity. We identified several specific ways that WLF modify littoral assemblages along the depth gradient. This ability to identify separate pressures is an important requirement of robust ecological assessment tools. This study confers potential for development of ecological indicators of WLF in standing waters, provides indication of sampling strategies to be employed and demonstrates the need to mitigate the most extreme water withdrawals.

Is there light after depth? Distribution of periphyton chlorophyll and productivity in lake littoral zones

Periphyton and phytoplankton contribute to the base of lake food webs, and both groups of microalgae are influenced by resources and physical forcing. Spatial variation in light availability interacts with the physical dynamics of the water column to create predictable depth gradients in resources and disturbance that may differentially affect periphyton vs phytoplankton. We characterized the depth distribution of chlorophyll and productivity of periphyton on sediments (epipelon) and phytoplankton in the euphotic zones of 13 oligomesotrophic lakes that span a large size gradient (0.017–32,600 km2). Epipelic chlorophyll usually increased with depth in the epilimnion. Light was the primary driver of the consistent within-lake patterns in periphyton productivity across this lake-size gradient. In 5 lakes, epipelic periphyton exhibited a unimodal distribution of productivity with depth in the photic zone, but no evidence of photoinhibition was found for periphyton. Rather, patterns in sediment N and P and observed changes in biofilm structure were consistent with determination of epipelic biomass by disturbance at depths ≤1 m in the smaller lakes and by light limitation at depths >1 m. Further quantification of the effects of disturbance on epipelon is needed. Nonetheless, our data demonstrate that the perceived high spatial variability in periphyton biomass and productivity is not an impediment to development of robust models of whole-lake primary production that include both phytoplankton and periphyton.

Susceptibility of native perca (Percichthys trucha) and exotic rainbow trout (Oncorhynchus mykiss) to high temperature in Patagonia: different physiological traits and distinctive responses

The aim of this work was to explore for the existence of a physiological basis for the apparent exclusion of salmonid fish from the littoral zone of lakes in Patagonia in response to increasing water temperature, to the benefit of the native perca (Perc- ichthys trucha). We conducted experiments on the thermal preferences of juvenile perca and rainbow trout collected in three sites of Northern Patagonia. We characterized the relationship between preferred and acclimation temperature (PT, AT) for perca and trout and analyzed between-sites variations in PTs. Both species responded with increasing PT to higher AT, but with differences in overall PT for perca from different sites (lower PTs for fish from cooler lake). In general, rainbow trout displayed lower PT and a narrower range of PT than perca. Our results provide the first comparative view of PTs of one important native fish and the main sport fish species of Patagonia. Native perca may be better equipped to cope with warmer waters than exotic rainbow trout, in agreement with their geographic distribution. Also, perca may have an advantage at the local level, particularly in littoral areas of lakes, through the alleviation of predation by and trophic competition with trout.

Parasites of zooplankton and periphyton assemblages in the littoral zone of lakes in Drawa National Park, Poland

Studies on parasitism in zooplankton and periphyton assemblages were carried out on samples of water collected from Lakes Płociczno and Płociowe in the Drawa National Park in 2008-2011. Occurrence of the fungal mycobiotal and protozoan parasites of invertebrates was recorded in both lakes. Parasitism of <em>Chydorus </em>sp. (Cladocera) by <em>Saprolegnia </em>sp. occurred on 0.8% of individuals of the host population, of <em>Brachionus calyciflorus </em>(Rotifera) by <em>Microsporidium </em>sp. on 1.2% of the host population, and of Nematoda members by <em>Pythium </em>sp. on 5% of the host population. Parasites were recorded only in springtime.

Millennial stocks and fluxes of large woody debris in lakes of the North American taiga

Summary Large woody debris (LWD) is an important cross‐boundary subsidy that enhances the productivity of lake ecosystems and the stability of aquatic food webs. LWD may also be an important carbon sink because LWD pieces are preserved for centuries in the littoral zone of lakes and rivers. However, a long‐term analysis of LWD stocks and fluxes in lakes, coupled with the reconstruction of past disturbances at the site level, has never been attempted. Large woody debris was sampled in five lakes of the Quebec taiga. Actual LWD stocks were described and residence time of the LWD pieces was established using tree‐ring and radiocarbon dating. LWD losses by decomposition and burial and other factors influencing LWD residence time were investigated using linear regressions. Impacts of wildfires on LWD fluxes during the last 1400 years were reconstructed separately for the five lakes using piecewise regression models. Fire years at each site were identified from the recruitment dates of charred LWD pieces. Large woody debris volume ranged between 0.92 and 1.57 m3 per 100 m of shoreline, and extrapolating these results to the landscape scale, it was concluded that LWD littoral carbon pools represent a minimal portion of boreal carbon storage. Large woody debris residence time in boreal lakes was confirmed to be very long. Tree‐ring dates of 1571 LWD pieces, mainly black spruce (Picea mariana (Mill.) BSP.), spanned the last 1400 years, while LWD specimens of older floating chronologies were preserved from decomposition for up to five millennia. The most influential variables explaining the variation in LWD residence time were the degree of burial and the distance from the shore. Large woody debris recruitment rates averaged 5.8 pieces per century per 100 m of shoreline. Fourteen wildfires were the primary cause for changes in the rates of tree establishment in the riparian forests and of LWD recruitment in the lakes. Synthesis. Interactions between terrestrial and aquatic ecosystems in northern boreal regions are strongly influenced by wildfires whose effects can last for centuries due to the slow large woody debris decay rate. Actual LWD stocks and carbon pools are a legacy of the past fire history.