Water Level Manipulation Research Articles

A sedimentary DNA perspective about the influence of environmental and food‐web changes on the microbial eukaryotic community of Lake Biwa

Abstract The impacts of environmental change on Lake Biwa have been explored for decades, with water monitoring and palaeolimnological studies revealing how environmental forcing, including climate warming, eutrophication, water level manipulation and human manipulation of fish populations, has influenced the food web of Lake Biwa. However, these studies have rarely accounted for microbial food‐web components. This knowledge gap is mostly due to the lack of time series spanning more than a couple of decades, coupled with the high taxonomical expertise required to identify organisms belonging to very diverse groups. The use of a sedimentary DNA approach allows for the reconstruction of past changes in the diversity, composition and structure of the microbial eukaryotic community of aquatic systems. The application of 18S metabarcoding has been proven successful to describe the response of unicellular eukaryotes (protists) and aquatic fungi in lake ecosystems, encompassing a large taxonomic and functional diversity such as phototrophs, heterotrophs and mixotrophs. We applied 18S metabarcoding to 31 sediment core samples from Lake Biwa, spanning the past 100 years and explored the response of microbial eukaryotic communities to changes in multiple environmental stressors, including nutrient levels, lake water level, climate, as well as fish and zooplankton biomass for the period 1973–2010. We found that the manipulation of the water level and changes in fish community composition were the primary factors impacting (indirectly) the structure of the lake microbial eukaryotic community with minor, but significant, effects of climate warming and phosphorus levels. Co‐occurrence network analysis highlighted the potential food web impacts on the microbial eukaryotic community, suggesting that organisms from this compartment were impacted by both bottom‐up and top‐down processes.

Native macrophyte community response to water-level manipulation for an invasive species

Disturbance regimes related to water level fluctuation play an important role in the structuring of aquatic macrophyte communities. In managed systems, winter water level drawdowns have shown promise in controlling populations of nuisance macrophytes, however, drawdowns may have unintended negative consequences on erosion, fauna, and non-target plant species. The Chippewa Flowage, located in Sawyer County, WI, has implemented targeted winter water level drawdowns with the goal of reducing nuisance levels of Myriophyllum spicatum. To evaluate the effects of water level drawdowns on Myriophyllum spicatum and the native macrophyte community, we conducted repeated full lake surveys of aquatic macrophytes at 2018 points under drawdown and normal water level management in 2005/06, 2015, and 2017. We supplemented these efforts with downscaled surveys in 2007, 2010, and 2016. Surveys revealed a statistically significant decline in both Myriophyllum spicatum occurrence and abundance, and average macrophyte abundance during active drawdown management. Kernel distributions of change in point-specific c-value between the two time periods showed a significant increase under drawdown conditions, and a decrease under normal management (D = 0.41, P ≤0.0001). Drawdown management appeared to successfully control Myriophyllum spicatum abundance and allowed for improvements in the floristic quality of the macrophyte community but resulted in reduced macrophyte abundance overall.

Air–plant interaction and air–soil exchange of polycyclic aromatic hydrocarbons in a large human-influenced reservoir in southwest China

The Three Gorges Reservoir (TGR) is totally manmade, strongly influenced by anthropogenic activity, and lies on the upper reaches of Yangtze River. The periodic storage and discharge of water from the Three Gorges Dam could have altered the original air-plant/soil interactions of contaminants in TGR. Herein, paired atmospheric gas–particle, air–plant, and air–soil samples were collected to investigate the air–plant interaction and air–soil exchange of 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs). The air–plant interaction based on McLachlan's framework to our datasets suggests that PAHs were absorbed via gaseous deposition that was restricted by the plant–gas dynamic equilibrium. The equilibrium indicates a dynamic balance between the gaseous phase and plant surface in PAH absorption. The main limiting factor influencing the PAH uptake was the plant species rather than the atmospheric PAH concentration. The air–soil exchange of PAHs exhibited a net volatilization flux of 16.71 ng/m2/d from the soil to the air based on annual average. There was more volatilization and less deposition in summer and more deposition and less volatilization in autumn and winter. The soil serves as a secondary source of atmospheric PAHs. As the first attempt on probing the multi-interface geochemical process of PAHs, this study highlights the influence of manual water level manipulation from the TGD and environmental factors (such as temperature, humidity, and soil properties) on the regional fate of PAHs in the TGR.

A Multi-Sensor Approach to Characterize Winter Water-Level Drawdown Patterns in Lakes

Artificial manipulation of lake water levels through practices like winter water-level drawdown (WD) is prevalent across many regions, but the spatiotemporal patterns are not well documented due to limited in situ monitoring. Multi-sensor satellite remote sensing provides an opportunity to map and analyze drawdown frequency and metrics (timing, magnitude, duration) at broad scales. This study developed a cloud computing framework to process time series of synthetic aperture radar (Sentinel 1-SAR) and optical sensor (Landsat 8, Sentinel 2) data to characterize WD in 166 lakes across Massachusetts, USA, during 2016–2021. Comparisons with in situ logger data showed that the Sentinel 1-derived surface water area captured relative water-level fluctuations indicative of WD. A machine learning approach classified lakes as WD versus non-WD based on seasonal water-level fluctuations derived from Sentinel 1-SAR data. The framework mapped WD lakes statewide, revealing prevalence throughout Massachusetts with interannual variability. Results showed WDs occurred in over 75% of lakes during the study period, with high interannual variability in the number of lakes conducting WD. Mean WD magnitude was highest in the wettest year (2018) but % lake area exposure did not show any association with precipitation and varied between 8% to 12% over the 5-year period. WD start date was later and duration was longer in wet years, indicating climate mediation of WD implementation driven by management decisions. The data and tools developed provide an objective information resource to evaluate ecological impacts and guide management of this prevalent but understudied phenomenon. Overall, the results and interactive web tool developed as part of this study provide new hydrologic intelligence to inform water management and policies related to WD practices.

Water Level Fluctuation Rather than Eutrophication Induced the Extinction of Submerged Plants in Guizhou’s Caohai Lake: Implications for Lake Management

The intensifying global decline in submerged aquatic lake plants is commonly attributed to lake eutrophication, while other drivers such as water levels are seldom considered. This study focused on the sudden extinction of the submerged plants in Caohai Lake, Guizhou, and employed long-term data and a whole-lake water level manipulation experiment to explore the impacts of nutrients and water level changes on the decline in submerged plants. The results indicated that over the past 40 years, the total nitrogen and ammonia nitrogen in the water did not change significantly, while the total phosphorus showed a significant decreasing trend. In recent years, however, the water level rose. The biomass of submerged plants continuously increased until a sudden large-scale extinction occurred in 2021; chlorophyll a also significantly increased. It is speculated that the large-scale extinction of the submerged plants was caused by water level fluctuations rather than eutrophication. After the restoration of the natural hydrological regime of low water levels in winter and spring and high levels in summer and autumn, the submerged plants gradually recovered, with the biomass increasing to 922.6 g/m2 in 2023. The structural equation modeling indicated that the water depth and bottom light availability were the main drivers for the changes in the submerged plants. However, in lake protection and management, more attention is often paid to controlling nutrients, while other influencing factors are neglected. These findings confirm the importance of water levels in the decline in and restoration of submerged plants in shallow lakes, suggesting a focus on water level management in lake protection and aquatic vegetation restoration.

Unraveling environmental influences on the spatial and temporal dynamics of cyanobacterial blooms in Lake Erhai during its early stage of eutrophication

ABSTRACT Lake Erhai, a lake in the early stage of eutrophication, has been threatened by algal blooms (particularly the overproliferation of blue-green algae), which can have an impact on drinking water safety and the lake’s ecosystem. Understanding the governing factors of cyanobacterial blooms is critical for taking timely and effective action during this key eutrophication-transition period. However, long-term records of cyanobacterial bloom and its key dominating factors remain unclear. It is, therefore, essential to understand the bloom dynamics and the driving forces before any control strategies can be determined. We investigated the cyanobacterial phycocyanin concentration variability based on satellite observations from 2003 to 2019, by using the empirical orthogonal function analysis. We observed a decrease in the coverage of the dominant mode of variability in phycocyanin magnitudes compared to the period 2003 to 2011, with variations primarily occurring in the northern bays. The largest variability was identified to be predominant in July, and an apparent timing shift in variability was observed in December 2016 and 2017. The 95% quantile regression model indicated a distinct upper boundary response in cyanobacteria proliferation to the joint Total Nitrogen (TN) and Total Phosphorus (TP) concentrations, which occurred in summer from 2003 to 2011. An apparent response of cyanobacterial bloom to TP was observed during the winters from 2016 to 2019. Additionally, water level and TN: TP ratio played a central role in summer from 2003 to 2011, while from 2016 to 2019, TN: TP ratio was found to dominate in the summer months. In winter, air temperature turned out to be a significant modulating factor compared to water level. Our results suggest that implementing a phosphorus reduction strategy, while controlling TN: TP ratio and suitable water level manipulation, should be considered to ensure the sustainability of Lake Erhai, especially under a consistent global warming scenario.

Suchozemští plži přírodní rezervace Plané loučky a přírodních památek Častava, Hvězda a Kurfürstovo rameno v CHKO Litovelské Pomoraví [Terrestrial gastropods of Plané loučky Nature Reserve and Častava, Hvězda, and Kurfürstovo rameno Nature Monuments in Litovelské Pomoraví PLA

In 2022, four small-scale protected areas (SPA) within Litovelské Pomoraví Protected Landscape Area were surveyed for terrestrial molluscs. All localities are floodplain forest fragments with oxbow lakes, pools and marshes in the Morava river catchment. The most species-rich SPA was Hvězda Natural Monument (NM), with 38 species recorded. The threatened species Cochlicopa nitens (Endangered), known from this area from previous surveys, was not recorded despite high sampling effort. This sensitive hygrophilous species disappeared probably due to droughts occurring in earlier years. However, other sensitive hygrophilous species such as Euconulus alderi (Nearly Threatened) and Vertigo antivertigo were recorded. The latter was also found in Plané loučky Nature Reserve (NR; 27 spp. in total) and Častava NM (19 spp. in total). Relatively common floodplain forest species Perforatella bidentata was recorded in Plané loučky NR and Hvězda NM; however, it was absent in Častava NM and Kurfürstovo rameno NM (20 spp. in total). The partial absence of this species and the complete absence of substantially declining floodplain species Pseudotrichia rubiginosa (Nearly Threatened) and other sensitive taxa indicate habitat degradation caused mainly by stream regulations and water level decrease and manipulation. The presence of invasive plant species known to decrease terrestrial mollusc species diversity and abundance are of the essence as well. Highly invasive species Arion vulgaris was the most abundant species in all of the surveyed SPAs, except for Hvězda NM, where it was present in lower numbers. Over some twenty years, this species spread from anthropogenic areas to natural habitats to become one of the most prominent features of floodplain biocoenoses in Litovelské Pomoraví and elsewhere. To improve the habitat conservation status, it is important to maintain favourable water level in streams and water bodies adjacent to SPAs, especially during the critical periods of summer droughts. Furthermore, it is advised to focus the management on neophyte extirpation.

Landscape elements affect public perception of nature-based solutions managed by smart systems

Smart technologies promise innovative approaches to manage nature-based solutions (NBS) for more effective regulating functions under climate change. However, smart systems may also affect people’s experiences of NBS by introducing noticeable changes in urban landscapes. This study investigated public perception of “smart” retention ponds that had changing water level as controlled by smart systems and varied in the following microscale landscape elements determined by planning and design choices: land use context, basin slope, and surrounding plants. Using visualizations that showed pond landscape design alternatives at typical, low (draining water), and high (retaining water) water levels, we surveyed residents in three American cities for their perceptions of smart ponds (n = 974). Our results suggest that water level manipulation by smart systems negatively affects perceptions of stormwater ponds; both low and high water were perceived as significantly less attractive, neat, and safe than the typical water level condition. Furthermore, these effects of water level were moderated by other design elements. Perceptions of high water level were more positive for ponds in greenspace than in residential or commercial contexts. Perceptions of low water level were more positive for ponds in residential contexts than in greenspace or commercial contexts, as well as for ponds surrounded by woody or unmaintained plants than those surrounded by mown turf edge. In both high and low water conditions, ponds with steep slopes were perceived more positively than those with shallow slopes. These findings can support successful planning, design, and management of smart NBS.

Complex effects of acidification, habitat properties and fish stock on littoral macroinvertebrate assemblages in montane standing waters

Littoral macroinvertebrates in acidified waterbodies are affected by the interaction of acidification and local environmental conditions. Understanding the interplay of these factors in the structuring of communities is essential for interpreting responses to and/or recovery from acidification. Here, we analyse the species composition and richness of littoral macroinvertebrates in a range of acidified montane standing waters in relation to water chemistry, littoral characteristics and fish stock. The main species composition gradients were related to pH and conductivity; however, considerable variation along these gradients was associated with local habitat characteristics (changing water levels and littoral structure) and concentration of ionic aluminium and dissolved organic carbon. Although fish stock effects were confounded by correlated acidity, we observed a significant decline in abundance of macroinvertebrates vulnerable to fish predation at sites with fish stock. Overall, littoral macroinvertebrates of acidic waterbodies were diverse due to the heterogeneity of local habitat properties, despite they were dominated by acid-tolerant species. Acidic humic sites with dense, heterogeneous littoral vegetation were species-rich, hosting numerous habitat specialists and rare species, while chronically acidified lakes with high aluminium concentrations and sparse littoral vegetation had species-poor assemblages, characteristic of strong acid-stress. Water level manipulation resulted in serious assemblage impoverishment, overriding the effects of more favourable water chemistry. This study shows that the littoral fauna of acidic waterbodies is structured by complex effects induced by local factors in addition to acidity, resulting in acid-stressed assemblages with relatively high variability, emphasising a need to analyse local habitat factors when evaluating the impact of acidification on macroinvertebrates.

Comparison of eddy covariance CO<sub>2</sub> and CH<sub>4</sub> fluxes from mined and recently rewetted sections in a northwestern German cutover bog

Abstract. With respect to their role in the global carbon cycle, natural peatlands are characterized by their ability to sequester atmospheric carbon. This trait is strongly connected to the water regime of these ecosystems. Large parts of the soil profile in natural peatlands are water saturated, leading to anoxic conditions and to a diminished decomposition of plant litter. In functioning peatlands, the rate of carbon fixation by plant photosynthesis is larger than the decomposition rate of dead organic material. Over time, the amount of carbon that remains in the soil and is not converted back to carbon dioxide grows. Land use of peatlands often goes along with water level manipulations and thereby with alterations of carbon flux dynamics. In this study, carbon dioxide (CO2) and methane (CH4) flux measurements from a bog site in northwestern Germany that has been heavily degraded by peat mining are presented. Two contrasting types of management have been implemented at the site: (1) drainage during ongoing peat harvesting on one half of the central bog area and (2) rewetting on the other half that had been taken out of use shortly before measurements commenced. The presented 2-year data set was collected with an eddy covariance (EC) system set up on a central railroad dam that divides the two halves of the (former) peat harvesting area. We used footprint analysis to split the obtained CO2 and CH4 flux time series into data characterizing the gas exchange dynamics of both contrasting land use types individually. The time series gaps resulting from data division were filled using the response of artificial neural networks (ANNs) to environmental variables, footprint variability, and fuzzy transformations of seasonal and diurnal cyclicity. We used the gap-filled gas flux time series from 2 consecutive years to evaluate the impact of rewetting on the annual vertical carbon balances of the cutover bog. Rewetting had a considerable effect on the annual carbon fluxes and led to increased CH4 and decreased CO2 release. The larger relative difference between cumulative CO2 fluxes from the rewetted (13±6 mol m−2 a−1) and drained (22±7 mol m−2 a−1) section occurred in the second observed year when rewetting apparently reduced CO2 emissions by 40 %. The absolute difference in annual CH4 flux sums was more similar between both years, while the relative difference of CH4 release between the rewetted (0.83±0.15 mol m−2 a−1) and drained (0.45±0.11 mol m−2 a−1) section was larger in the first observed year, indicating a maximum increase in annual CH4 release of 84 % caused by rewetting at this particular site during the study period.

Effects of water impoundment and water-level manipulation on the bioaccumulation pattern, trophic transfer and health risk of heavy metals in the food web of Three Gorges Reservoir (China)

The Three Gorges Reservoir (TGR) of China, the largest hydropower project over the world, has attracted much attention to the water impoundment and water-level manipulation. In this study, we evaluated potential effects of water impoundment and seasonal water-level manipulation on the bioaccumulation, trophic transfer and health risk of HMs (Cu, Fe, Zn, Hg, Cd and Pb) in food web components (seston, aquatic invertebrate and fish) in TGR. Our results show that, after the impoundment for eight years (2003–2010), all of the six metal concentrations in aquatic biota fell within the criteria of safety quality guidelines. The concentrations of Cu, Fe, Zn and Hg in fish and aquatic invertebrates were higher than those before impoundment, whereas Cd and Pb were lower than those before impoundment. Nonetheless, Hg, Cd and Pb in aquatic consumers underwent an increasing trend during the entire impoundment, implying potential reservoir effect in the future. Only the concentrations of Hg, Cd and Pb in aquatic consumers exhibited a declining trend towards the dam, showing consistent with the background level at the three reaches. Seasonal variations in HM concentrations of fish and aquatic invertebrates were ascribed to the water-level manipulation associated with reservoir management. Our findings show that Hg or Cd biomagnified through aquatic food web during different hydrological periods, whereas Pb, Cu, Fe and Zn exhibited weak biomagnification power. Overall, Hg, Cd and Pb showed a higher risk than that of Cu, Fe and Zn.

Navigating the ancient Tigris – insights into water management in an early state

This paper offers the first detailed investigation of water management in pre-classical antiquity based on primary sources. The importance of water management for ancient societies can hardly be overstated, as many of the earliest civilizations emerged in large river valleys (Nile, Euphrates and Tigris, Indus, Yellow and Yangtze river). More importantly many of those early civilizations occupied the reach of the river, which was located in the arid/semi-arid zone, by which rivers vital sources of water, in particular for irrigation. Many studies on ancient water management have focused on irrigation, often failing to recognize the full extent to which rivers were managed and utilized. The water management scheme of late 3rd millennium Southern Mesopotamia, described in this paper, was designed to not only serve irrigation, but equally navigation and flood control. It combined the manipulation of water levels with the diligent observation and maneuvering of water masses of the ancient Tigris, by which the otherwise conflicting demands of irrigation, navigation and flood control could be reconciled. The written sources used in this study allowed to describe this water control system in great detail and is a testimony to remarkable ancient hydraulic engineering as early as the 3rd Millennium BC.

Evidence for lasting alterations to aquatic food webs with short-duration reservoir draining

Large dams and their respective reservoirs provide renewable energy and water security, but also can profoundly alter riverine ecosystems. Here, we present evidence of changing aquatic food web structure in the seasons following short-duration, extreme manipulation of water levels in a reservoir (i.e., draining of the reservoir to the original riverbed during fall to assist outmigration of juvenile Chinook Salmon). We find unintended and lagged consequences of transitioning from a lake to a river, even temporarily, that resulted in trophic shifts away from piscivory and towards feeding at lower trophic levels for two common piscivorous fishes in reservoirs. Using natural abundances of nitrogen stable isotopes, we observed lower trophic level of feeding for invasive Largemouth Bass (Micropterus salmoides) and native Rainbow Trout (Oncorhynchus mykiss) during the summers following reservoir refilling than in nearby reference reservoirs that were not temporarily drained during fall. Declines in trophic levels of aquatic top predators have been rarely documented outside of controlled laboratory conditions. While useful for assisting outmigration of juvenile salmonids, the temporary draining of a reservoir to riverbed can also result in novel shifts in foodweb dynamics including reduced piscivory. As large dams continue to be operated and constructed worldwide, increased understanding of the community and ecosystem-level effects of reservoir management will be critical to evaluating trade-offs between human water needs, conservation of high value species, and ecosystem services impacted by river fragmentation.

Assessing rehabilitation of managed mangrove ecosystems using high resolution remote sensing

Mangroves are valuable ecosystems for coastal protection, carbon sequestration and storage, and they provide habitat, refuge and rearing areas for many important marine species. To control mosquito outbreaks in coastal regions, mangroves were often impounded and managed using a variety of techniques that ranged from the application of insecticides to water level manipulation. Since continuous impounding had been shown to have negative effects on mangrove vegetation, other techniques have been used to manage hydrology in impoundments. A recent technique is called rotational impoundment management (RIM) and it involves flooding impoundments in summer and spring, the reproductive season of the mosquitos. In this study, we assessed the effects of 5 years of RIM management on mangrove vegetation in an impoundment on the east coast of Florida. We compared mangrove vegetation in the RIM impoundment with an adjacent impoundment that was not managed. We created a map of leaf area index (LAI) to assess vegetation productivity and its change in the two impoundments. We classified color-infrared aerial photographs from 2008 to 2010 and a WorldView-2 satellite image from 2014 to measure the extent of mangrove vegetation types and temporal changes in the two impoundments. We found a 38% increase in cover of dense mangrove vegetation after five years for the RIM-impounded area. Classification accuracy was around 80% for all imagery. The increased growth of plants and cover of dense mangroves in the RIM impoundment was corroborated by observed leaf area index values. Overall, the study demonstrates that vegetation in the RIM impoundment is becoming denser and in the near future will probably become similar to an impoundment that is open to tidal exchange or mangrove dominated areas that are not impounded.

Sora (Porzana carolina) autumn migration habitat use.

Palustrine wetland management across the USA is often conducted under a moist soil management framework aimed at providing energetic resources for non-breeding waterfowl. Moist soil management techniques typically include seasonal water-level manipulations and mechanical soil disturbance to create conditions conducive to germination and growth of early successional, seed-producing wetland plants. The assumption is that providing stopover and wintering habitat for non-breeding waterfowl will also accommodate life-history needs of a broader suite of migratory waterbirds including shorebirds, wading birds and marsh birds. Although studies of wetlands provide some evidence to support this assumption for shorebirds and wading birds, there is less information on how other marshbirds respond. Sora (Porzana carolina) are a species of migratory rail that depend on wetlands year round as they migrate across North America. It is a species for which the consequences of wetland management decisions directed towards non-breeding waterfowl are unknown. We conducted nocturnal surveys on 10 public properties in Missouri, USA during autumn migration during 2012–2016 to examine sora habitat use in wetland impoundments managed to enhance the production of moist soil vegetation. We found a positive relationship with sora presence and mean water depth and annual moist soil vegetation; sora used, on average, deeper water than was available across surveyed impoundments and used locations with a higher percentage of annual moist soil vegetation than was available. We found a negative relationship with sora use and upland vegetation, woody vegetation and open water. We found sora using deeper water than have previously been reported for autumn migration, and that moist soil management techniques used on Missouri's intensively managed public wetland areas may be compatible with sora autumn migration stopover habitat requirements.

Multispecies benefits of wetland conservation for marsh birds, frogs, and species at risk

Wetlands conserved using water level manipulation, cattle exclusion, naturalization of uplands, and other techniques under the North American Waterfowl Management Plan (“conservation project wetlands”) are important for ducks, geese, and swans (“waterfowl”). However, the assumption that conservation actions for waterfowl also benefit other wildlife is rarely quantified. We modeled detection and occupancy of species at sites within 42 conservation project wetlands compared to sites within 52 similar nearby unmanaged wetlands throughout southern Ontario, Canada, and small portions of the adjacent U.S., using citizen science data collected by Bird Studies Canada's Great Lakes Marsh Monitoring Program, including 2 waterfowl and 13 non-waterfowl marsh-breeding bird species (n = 413 sites) and 7 marsh-breeding frog species (n = 191 sites). Occupancy was significantly greater at conservation project sites compared to unmanaged sites in 7 of 15 (47%) bird species and 3 of 7 (43%) frog species, with occupancy being higher by a difference of 0.12–0.38 across species. Notably, occupancy of priority conservation concern or at-risk Black Tern (Chlidonias niger), Common Gallinule (Gallinula galeata), Least Bittern (Ixobrychus exilis), Sora (Porzana carolina), and Western Chorus Frog (Pseudacris triseriata) was significantly higher at conservation project sites compared to unmanaged sites. The results demonstrate the utility of citizen science to inform wetland conservation, and suggest that actions under the North American Waterfowl Management Plan are effective for conserving non-waterfowl species.

The Impact of Experimental Temperature and Water Level Manipulation on Carbon Dioxide Release in a Poor Fen in Northern Poland

Peatlands are ecosystems for which carbon budget relies strongly on the meteorological and hydrological conditions. Here, using a manipulative field experiment, we measured ecosystem respiration (RECO) over two years (2013–2014) in a poor fen in Poland to estimate the carbon emission in a changing climate. The experiment consisted of warming (open-top chambers - OTC) and water table manipulation. The application of OTC increased the mean values of daily maximum air temperature by approx. 1.1–1.8 °C. Warming or the increased water table depth separately resulted in an increase in ecosystem respiration by approx. 0.1 μmol CO2 m−2 s−1 and 0.3 μmol CO2 m−2 s−1, respectively. However, our results show also the additive nature of warming and water table drawdown impact on daily RECO during the studied years (2013–0.80 μmol CO2 m−2 s−1 and 2014–1.16 μmol CO2 m−2 s−1). With the natural dry period event which occurred in 2014, the seasonal RECO increased by approx. 0.2 μmol CO2 m−2 s−1 as compared to the previous year. Projected global warming will therefore significantly enhance C loss from poor fens in this region of Europe.

Copepod assemblage structure (Crustacea: Copepoda) along a longitudinal environmental gradient in a tropical river-floodplain system, Brazil

Abstract Aim: In this study, we analyzed the structure of the copepod community along a longitudinal axis of the last undammed stretch of the Upper Paraná River floodplain, downstream of Porto Primavera reservoir. We hypothesized that (i) copepod assemblage would show an increase in the abundance of organisms, species richness and specific diversity with the distance from the Porto Primavera reservoir, due to the arrival of species from adjacent lakes and tributaries; (ii) copepod abundance and species richness would be higher in tributaries and adjacent lakes located at the floodplain, which show higher environmental heterogeneity and function as a species source; and (iii) spatial patterns of copepod assemblage structure are related to the environmental gradient, since copepods show a rapid response to the variation of environmental conditions. Method Sampling was performed quarterly from August 2013 to July 2014, at the subsurface of the pelagic region. Sampling sites were located along the Paraná River, in seven of its tributaries, and in eight lakes located in its floodplain. Results We identified 29 species belonging to two families: Cyclopidae (21 species) and Diaptomidae (eight species). On contrary of our first hypothesis, ANOVA results showed a significant decrease in copepod abundance in the downstream direction. Similarly, the tributaries showed higher values of ecological attributes in the upstream stretch. RDA results showed that in axis 1, the Paraná River and the lakes were positively correlated with conductivity, pH, temperature and suspended organic matter, characterized by the most abundant copepod species. The tributaries, on the other hand, were negatively correlated with turbidity, total nitrogen, total phosphorus and depth. Axis 2 showed a positive correlation of the Paraná River with conductivity and suspended organic matter, and a higher abundance of Argyrodiaptomus azevedoi, Notodiaptomus iheringi, N. henseni, N. cearensis and N. cf. spinuliferus. On the other hand, the lakes were positively correlated with temperature and pH and also with a higher abundance of Thermocyclops minutus and T. decipiens. Conclusion We highlight the importance of the maintenance of the ecological integrity of the Upper Paraná River floodplain, especially of its tributaries, in order to support the high biodiversity registered in the last undammed stretch. Furthermore, we highlight the importance of manipulation of water levels in reservoirs located upstream of this stretch, a necessary condition to maintain the hydrological connectivity between floodplain habitats and the main river.

Effects of Management Practices and Environmental Factors on Largemouth Bass Abundance in Illinois Inland Lakes

An understanding of the relative importance of natural factors and management practices affecting largemouth bass (Micropterus salmoides) abundance is key for enhanced angling. Standardized fish surveys, management practices, and environmental data were available from 42 man-made, inland lakes between 1960 and 1991. Management practices tested were largemouth bass stocking, lake rehabilitation, water level manipulation, aquatic vegetation controls, small fish removal, and changes in length limits of harvestable fish. Environmental factors not controlled by management were spring water influx, growing and cooling degree days, and snow depth. Lake rehabilitation (complete drainage and reflooding), changes in length limits, and aquatic vegetation controls were the only significant factors affecting largemouth bass abundance. The largest effects were due to lake rehabilitation, which increased next-year young largemouth bass numbers by 566% on average, and more restrictive limits on harvestable size, with an increase of up to 440% in adult numbers.

How to mitigate cyanobacterial blooms and cyanotoxin production in eutrophic water reservoirs?

Cyanobacterial blooms and cyanotoxin production were studied for 2 years in four hydrologically modified lakes with nutrient-rich waters. We hypothesized that frequency of flushing may considerably influence cyanobacterial blooms. Abundance, biomass and diversity of cyanobacteria as well as cyanotoxins’ variability and concentrations (by HPLC–PDA; -FLD) were determined. In two larger lakes, into which nutrient-rich water was supplied once a year, lower cyanobacterial species diversity, higher biomass of Microcystis spp., Aphanizomenon spp., Dolichospermum spp. and higher microcystin (MC) concentrations were found. In the other lakes, with several irregular water-level manipulations per year (alternating outputs and inputs), higher diversity, lower biomass of cyanobacteria and MC concentrations were observed. MC-LF, -LR and -RR produced by Microcystis spp. predominated in the more stable lakes, whereas in the lakes with frequent water manipulations different species of Oscillatoriales developed and MC-LA, -LY, -LW and -WR were also important. RDA analysis revealed that the frequency of water manipulations was the most significant variable for composition of cyanobacterial communities. The study highlights that a higher frequency of water-level manipulations, which increased flushing rate, was beneficial to nutrient-rich water reservoirs.