Water quality in a shallow eutrophic lake is unaffected by extensive thinning of planktivorous and benthivorous fish species.

Ambitious to fulfill the European Water Framework Directive obligations, the European governments support projects to rehabilitate lakes with poor water quality. However, most lake restorations having relied on biomanipulation by fish thinning have failed to improve or even maintain water quality. Previous attempts removed all target fish species simultaneously, thus making it impossible to assess the specific impact of each feeding group on water chemistry.

Methane and carbon dioxide fluxes at high spatiotemporal resolution from a small temperate lake.

Lakes are hotspots for CH and CO effluxes, but their magnitude and underlying drivers are still uncertain due to high spatiotemporal variation within and between lakes. We measured CH and CO fluxes at high temporal (hourly) and spatial resolution (approx. 13 m) using 24 automatic floating chambers equipped with continuously recording sensors that enabled the determination of diffusive and ebullitive gas fluxes.

Predicting water quality from geospatial lake, catchment, and buffer zone characteristics in temperate lowland lakes.

Lakes provide essential ecosystem services and strongly influence landscape nutrient and carbon cycling. Therefore, monitoring water quality is essential for the management of element transport, biodiversity, and public goods in lakes. We investigated the ability of machine learning models to predict eight important water quality variables (alkalinity, pH, total phosphorus, total nitrogen, chlorophyll a, Secchi depth, color, and pCO) using monitoring data from 924 to 1054 lakes.

Physiological Adaptation and Plant Distribution along a Steep Hydrological Gradient.

Plant species often separate strongly along steep environmental gradients. Our objective was to study how coupling between plant physiology and environmental conditions shapes vegetation characteristics along a distinct hydrological gradient. We therefore investigated species photosynthesis in air and under water within a limited area from dry-as-dust to complete submergence in a nutrient-poor limestone habitat on Öland's Alvar, Sweden.

Removal of chromophoric dissolved organic matter under combined photochemical and microbial degradation as a response to different irradiation intensities.

Throughout the freshwater continuum, Dissolved Organic Carbon (DOC) and the colored fraction, Chromophoric Dissolved Organic Material (CDOM), are continuously being added, removed, and transformed, resulting in changes in the chromophoricity and lability of organic matter over time. We examined, experimentally, the effect of increasing irradiation-intensities on the combined photochemical and microbial degradation of CDOM and DOC. This was done by using a simulated mixed water column: aged water from a humic lake was exposed to four irradiation-intensities - representing winter, early and late spring, and summer conditions (0.

Wind drives fast changes of light climate in a large, shallow re-established lake.

With ever greater frequency, wetlands and shallow lakes that had been diverted for agriculture are being re-established to reduce nutrient loss and greenhouse gas emission, as well as to increase biodiversity. Here, we investigate drivers of water column light attenuation (K) at multiple time scales and locations in Lake Fil, Denmark, during the first five years after its re-establishment in 2012. We found that K was generally high (overall mean: 3.

Century-long records reveal shifting challenges to seagrass recovery.

Global losses over the 20th century placed seagrass ecosystems among the most threatened ecosystems in the world, with eutrophication, and associated deterioration of the submarine light environment identified as the main driver. Growing appreciation of the ecological and societal benefits of healthy seagrass meadows has stimulated efforts to protect and restore them, largely focused on reducing nutrient input to coastal waters. Here we analyze a unique data set spanning 135 years on eelgrass (Zostera marina), the dominant seagrass of the northern hemisphere.

Large pools and fluxes of carbon, calcium and phosphorus in dense charophyte stands in ponds.

Bicarbonate and calcium set bounds on photosynthesis and degradation processes in calcareous freshwaters. Charophytic algae use bicarbonate in photosynthesis, and direct variable proportions to assimilate organic carbon and to precipitate calcium carbonate on their surfaces. To evaluate pools of organic carbon (C), carbonate carbon (C), and phosphorus (P) in dense charophyte vegetation, we studied apical and basal tissue and carbonate surface precipitates, as well as underlying sediments in ten calcareous ponds.

From drought to flood: Sudden carbon inflow causes whole-lake anoxia and massive fish kill in a large shallow lake.

Fish kills are a recurring phenomenon in hypereutrophic lakes. The effects of a sudden injection of anoxic bottom water into surface waters are well known, as well as the degradation of phytoplankton blooms and the release of phytoplankton toxins. However, in this study we report on a new, climate-related cause of fish kills in a shallow lake.

Catchment properties and the photosynthetic trait composition of freshwater plant communities.

Unlike in land plants, photosynthesis in many aquatic plants relies on bicarbonate in addition to carbon dioxide (CO) to compensate for the low diffusivity and potential depletion of CO in water. Concentrations of bicarbonate and CO vary greatly with catchment geology. In this study, we investigate whether there is a link between these concentrations and the frequency of freshwater plants possessing the bicarbonate use trait.

More is less: net gain in species richness, but biotic homogenization over 140 years.

While biodiversity loss continues globally, assessments of regional and local change over time have been equivocal. Here, we assess changes in plant species richness and beta diversity over 140 years at the level of regions within a country. Using 19th-century flora censuses for 14 Danish regions as a baseline, we overcome previous criticisms concerning short time series and neglect of completely altered habitats.

Shallow plant-dominated lakes - extreme environmental variability, carbon cycling and ecological species challenges.

Background: Submerged plants composed of charophytes (green algae) and angiosperms develop dense vegetation in small, shallow lakes and in littoral zones of large lakes. Many small, oligotrophic plant species have declined due to drainage and fertilization of lakes, while some tall, eutrophic species have increased. Although plant distribution has been thoroughly studied, the physiochemical dynamics and biological challenges in plant-dominated lakes have been grossly understudied, even though they may offer the key to species persistence.

Sexual conflict and intrasexual polymorphism promote assortative mating and halt population differentiation.

Sexual conflict is thought to be an important evolutionary force in driving phenotypic diversification, population divergence, and speciation. However, empirical evidence is inconsistent with the generality that sexual conflict enhances population divergence. Here, we demonstrate an alternative evolutionary outcome in which sexual conflict plays a conservative role in maintaining male and female polymorphisms locally, rather than promoting population divergence.

Carbon limitation of lake productivity.

Phytoplankton productivity in lakes controls the rate of synthesis of organic matter that drives energy flow through the food webs and regulates the transparency and oxygen conditions in the water. Limitation of phytoplankton productivity and biomass by nutrients and light availability is an established paradigm for lake ecosystems, whereas invasion of atmospheric CO has been assumed to cover the high demands of dissolved inorganic carbon (DIC) during intense organic productivity. We challenge this paradigm, and show up to a 5-fold stimulation of phytoplankton productivity and biomass in outdoor mesocosms enriched with DIC, compared to mesocosms with lower DIC concentrations.

The Dangers of Being a Small, Oligotrophic and Light Demanding Freshwater Plant across a Spatial and Historical Eutrophication Gradient in Southern Scandinavia.

European freshwater habitats have experienced a severe loss of plant diversity, regionally and locally, over the last century or more. One important and well-established driver of change is eutrophication, which has increased with rising population density and agricultural intensification. However, reduced disturbance of lake margins may have played an additional key role.

Extreme diel dissolved oxygen and carbon cycles in shallow vegetated lakes.

A common perception in limnology is that shallow lakes are homogeneously mixed owing to their small water volume. However, this perception is largely gained by downscaling knowledge from large lakes to their smaller counterparts. Here we show that shallow vegetated lakes (less than 0.

Profound afternoon depression of ecosystem production and nighttime decline of respiration in a macrophyte-rich, shallow lake.

Small, shallow lakes with dense growth of submerged macrophytes are extremely abundant worldwide, but have remained grossly understudied although open water oxygen measurements should be suitable to determine diel fluctuations and test drivers of ecosystem metabolism during the day. We measured the temporal and spatial variability of environmental conditions as well as net ecosystem production (NEP) and respiration (R) in a small, shallow Swedish lake with dense charophyte stands by collecting data from oxygen-, pH-, temperature- and light-sensors across horizontal and vertical gradients during different periods between April and June in 3 years. We found reproducible diel oxygen patterns and daily metabolic rates.

Time-restricted flight ability influences dispersal and colonization rates in a group of freshwater beetles.

Variation in the ability to fly or not is a key mechanism for differences in local species occurrences. It is increasingly acknowledged that physiological or behavioral mechanisms rather than morphological differences may drive flight abilities. However, our knowledge on the seasonal variability and stressors creating nonmorphological differences in flight abilities and how it scales to local and regional occurrences is very limited particularly for small, short-lived species such as insects.

Ecophysiology of gelatinous Nostoc colonies: unprecedented slow growth and survival in resource-poor and harsh environments.

Background: The cyanobacterial genus Nostoc includes several species forming centimetre-large gelatinous colonies in nutrient-poor freshwaters and harsh semi-terrestrial environments with extended drought or freezing. These Nostoc species have filaments with normal photosynthetic cells and N2-fixing heterocysts embedded in an extensive gelatinous matrix of polysaccharides and many other organic substances providing biological and environmental protection. Large colony size imposes constraints on the use of external resources and the gelatinous matrix represents extra costs and reduced growth rates.

Underwater photosynthesis of submerged plants - recent advances and methods.

We describe the general background and the recent advances in research on underwater photosynthesis of leaf segments, whole communities, and plant dominated aquatic ecosystems and present contemporary methods tailor made to quantify photosynthesis and carbon fixation under water. The majority of studies of aquatic photosynthesis have been carried out with detached leaves or thalli and this selectiveness influences the perception of the regulation of aquatic photosynthesis. We thus recommend assessing the influence of inorganic carbon and temperature on natural aquatic communities of variable density in addition to studying detached leaves in the scenarios of rising CO2 and temperature.

Moss cushions facilitate water and nutrient supply for plant species on bare limestone pavements.

Dense moss cushions of different size are distributed across the bare limestone pavements on Øland, SE Sweden. Increasing cushion size is predicted to physically protect and improve performance and colonization by vascular plants. Therefore, we tested water balance, phosphorus supply, and species richness, and evaluated duration of plant activity during desiccation as a function of ground area, for a large collection of moss cushions.

Tolerance of the widespread cyanobacterium Nostoc commune to extreme temperature variations (-269 to 105°C), pH and salt stress.

Nostoc commune is a widespread colonial cyanobacterium living on bare soils that alternate between frost and thaw, drought and inundation and very low and high temperatures. We collected N. commune from alternating wet and dry limestone pavements in Sweden and tested its photosynthesis and respiration at 20°C after exposure to variations in temperature (-269 to 105°C), pH (2-10) and NaCl (0.

High sensitivity of Lobelia dortmanna to sediment oxygen depletion following organic enrichment.

• Lobelia dortmanna thrives in oligotrophic, softwater lakes thanks to O(2) and CO(2) exchange across roots and uptake of sediment nutrients. We hypothesize that low gas permeability of leaves constrains Lobelia to pristine habitats because plants go anoxic in the dark if O(2) vanishes from sediments. • We added organic matter to sediments and followed O(2) dynamics in plants and sediments using microelectrodes.

Outstanding Lobelia dortmanna in iron armor.

Lobelia dortmanna leads a group of small, highly-valued rosette species that grow on coarse, nutrient-poor soils in temperate soft-water lakes. They acquire most CO(2) for photosynthesis by root uptake and efficient gas transport in large air channels to the leaves. Lobelia is the only species that releases virtually all photosynthetic oxygen from the roots and generates profound day-night changes in oxygen and CO(2) in the sediment pore-water.