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Shallow lakes and ponds undergo frequent temporary thermal stratification. How this affects greenhouse gas (GHG) emissions is moot, with both increased and reduced GHG emissions hypothesised. Here, weekly estimation of GHG emissions were combined with high-resolution temperature and oxygen profiles of an 11 hectare shallow lake to investigate how thermal stratification shapes GHG emissions. There were three main stratification periods with profound anoxia in the bottom waters occurring quickly upon isolation from the atmosphere. Average diffusive emission of methane (CH4) and nitrous oxide (N2O) were larger and more variable in stratified phase, whereas carbon dioxide (CO2) was on average lower. CH4 ebullition was an order of magnitude greater in the stratified phase. In addition, there was a large efflux of CH4 and CO2 when the lake mixed after periods of extended (circa 14 days) thermal stratification. These two turnover events were estimated to have released the majority of the CH4 emitted between May and September. These results highlight the role of turnover emissions resulting from temporary thermal stratification and also the need high frequency measurements of GHG emission in order to accurately characterise emissions from these temporarily stratifying lakes.

Yapısal karmaşa ve bulanıklık (türbidite), balıkların habitat seçiminde önemli roller oynayabilmektedir. Kızılgöz balığı (Rutilus rutilus) ve tatlısu levreği (Perca fluviatilis) Avrupa’nın kuzey ılıman göllerinin baskın (dominant) türleridir. Bu türlerin görece önemi, genel olarak trofik seviyeye ve habitat karmaşıklığına bağlıdır. Kızılgöz ve tatlısu levreğinin, su berraklığı ve makrofit yayılımı sürekli değişen Væng gölü ile bulanık Søbygård gölündeki dağılımları 15 yıllık bir dönem boyunca çalışılmıştır. Örnekleme, her yıl aynı program takip edilerek, göllerin çeşitli kısımlarından, farklı göz açıklıklarına sahip galsama ağları kullanılarak gerçekleştirilmiştir. Türler, Væng gölünün bulanık olduğu dönemde, Søbygård gölünde ise tüm çalışma sürecinde, göllerin tüm kısımlarında ve tüm habitatlarda eşit dağılmışlardır. Væng gölünün berrak döneminde ise kızılgöz ve tatlısu levreğinin dağılımları eşit değildir. Türlerin bolluğu, makrofit yayılımı ve yoğunluğu ile negatif korelasyon gösterirken, bu ilişkinin kuvvetinin türlere ve balık boylarına göre farklı olduğu ortaya konulmuştur. Sonuç olarak, çalışılan iki gölde, kızılgöz ve tatlısu levreğinin dağılımında, suyun berraklığı ve makrofit yoğunluğunun anahtar belirleyici faktörler olduğu bulunmuş, bu durumun diğer benzer kuzey-ılıman sığ göllerde de gözlenebileceği öngörülmüştür., Roach (Rutilus rutilus) and perch (Perca fluviatilis) are dominant species in northern-temperate lakes of Europe, their relative importance depending on trophic state and habitat complexity. We studied the habitat distribution of roach and perch over a 15-year period in two Danish lakes, Lake Væng, undergoing major changes in water clarity and macrophyte coverage, and the permanent turbid Lake Søbygård. We used multi-mesh sized gill nets in 5-6 different sections of the lakes following the same program in all years. Both species were evenly distributed in the sections and among habitats, in Lake Væng during the turbid period and in Lake Søbygård during the whole study period. During the clear-water period in Lake Væng, however, the distribution of roach and perch was uneven and the density negatively correlated with macrophyte coverage and density, but the strength of the relationship differed between the two species and between small (≤ 8 cm for roach and

I dette projekt er der udviklet værktøjer, som standardiserer og delvis automatiserer arbejdsgangene til opsætning af sø-specifikke dynamiske, procesbaserede modeller. Modellerne er i projektet opsat og tilpasset fem forskellige danske søer (Ravnsø, Bryrup Langsø, Søholm Sø, Arreskov Sø og Hinge Sø). Modellernes evne til at simulere tilstanden i disse søer sammenlignes med erfaringer fra andre dynamiske model- studier og også med den empiriske modeltilgang, der anvendes i den nuværende vandområdeplanlægning. Når de dynamiske. procesbaserede modeller sammenlignes med andre forskningsbaserede modelstudier, er resultaterne for de fem danske søer særdeles gode og ofte bedre end resultaterne fra andre sammenlignelige studier. Resultaterne viser desuden, at usikkerheden, med enkelte undtagelser, generelt reduceres, når de dynamiske, procesbaserede modellers evne til at beskrive den aktuelle tilstand sammenlignes med simple empiriske modeller. Projektet illustrerer og redegør for, at der er potentiale for i højere grad at anvende disse dynamiske, procesbaserede modeller i forvaltningen af søer i Danmark.

Sørestaurering er et af virkemidlerne til at opnå en tilstrækkelig god økologisk kvaliteti de danske søer, der er omfattet af de nuværende vandområdeplaner. I dennerapport gennemgås de forskellige metoder til restaurering af søer. Deresanvendelighed vurderes, og der gives en vejledning i, hvilke forhold der skalundersøges forud for, under og efter en restaurering. Metoderne omfatter kemiskfældning med aluminium eller Phoslock, sedimentfjernelse, iltning og opfiskning affredfisk. Derudover omtales også en række andre metoder, og betydningen afklimaforandringer for gennemførelsen af fremtidige sørestaureringer vurderes.

Rapporten er et katalog over virkemidler, som kan målrettes til de områder, hvorbåde risikoen for fosfortab er stor, og hvor vandmiljøet er fosforfølsomt. Virkemidlernekan anvendes i en målrettet fosforindsats i de kommende vandområdeplaner 2021-2027. Kataloget indeholder samtidig forslag til afværgeforanstaltninger modfosfortab i den nationale vådområdeindsats.

Trophic niche divergence is considered to be a major process by which species coexistence is facilitated. When studying niche segregation in lake ecosystems, we tend to view the niche on a one-dimensional pelagic-littoral axis. In reality, however, the niche use may be more complex and individual fidelity to a niche may be variable both between and within populations. In order to study this complexity, relative simple systems with few species are needed. In this paper, we study how competitor presence affects the resource use of brown trout (Salmo trutta) in 11 species-poor Faroese lakes by comparing relative abundance, stable isotope ratios and diet in multiple habitats. In the presence of three-spined sticklebacks (Gasterosteus aculeatus), a higher proportion of the trout population was found in the pelagic habitat, and trout in general relied on a more pelagic diet base as compared to trout living in allopatry or in sympatry with Arctic charr (Salvelinus alpinus). Diet analyses revealed, however, that niche-segregation may be more complex than described on a one-dimensional pelagic-littoral axis. Trout from both littoral and offshore benthic habitats had in the presence of sticklebacks a less benthic diet as compared to trout living in allopatry or in sympatry with charr. Furthermore, we found individual habitat specialization between littoral/benthic and pelagic trout in deep lakes. Hence, our findings indicate that for trout populations interspecific competition can drive shifts in both habitat and niche use, but at the same time they illustrate the complexity of the ecological niche in freshwater ecosystems

Submerged macrophytes play a key role in north temperate shallow lakes by stabilizing clear-water conditions. Eutrophication has resulted in macrophyte loss and shifts to turbid conditions in many lakes. Considerable efforts have been devoted to shallow lake restoration in many countries, but long-term success depends on a stable recovery of submerged macrophytes. However, recovery patterns vary widely and remain to be fully understood. We hypothesize that reduced external nutrient loading leads to an intermediate recovery state with clear spring and turbid summer conditions similar to the pattern described for eutrophication. In contrast, lake internal restoration measures can result in transient clear-water conditions both in spring and summer and reversals to turbid conditions. Furthermore, we hypothesize that these contrasting restoration measures result in different macrophyte species composition, with added implications for seasonal dynamics due to differences in plant traits. To test these hypotheses, we analyzed data on water quality and submerged macrophytes from 49 north temperate shallow lakes that were in a turbid state and subjected to restoration measures. To study the dynamics of macrophytes during nutrient load reduction, we adapted the ecosystem model PCLake. Our survey and model simulations revealed the existence of an intermediate recovery state upon reduced external nutrient loading, characterized by spring clear-water phases and turbid summers, whereas internal lake restoration measures often resulted in clear-water conditions in spring and summer with returns to turbid conditions after some years. External and internal lake restoration measures resulted in different macrophyte communities. The intermediate recovery state following reduced nutrient loading is characterized by a few macrophyte species (mainly pondweeds) that can resist wave action allowing survival in shallow areas, germinate early in spring, have energy-rich vegetative propagules facilitating rapid initial growth and that can complete their life cycle by early summer. Later in the growing season these plants are, according to our simulations, outcompeted by periphyton, leading to late-summer phytoplankton blooms. Internal lake restoration measures often coincide with a rapid but transient colonization by hornworts, waterweeds or charophytes. Stable clear-water conditions and a diverse macrophyte flora only occurred decades after external nutrient load reduction or when measures were combined.

The likelihood of an ecological system to undergo undesired regime shifts is expected to increase as climate change effects unfold. To understand how regional climate settings can affect resilience, i.e., the ability of an ecosystem to tolerate disturbances without changing its original structure and processes, we used a synchronized mesocosm experiment (representative of shallow lakes) along a latitudinal gradient. We manipulated nutrient concentrations and water levels in a synchronized mesocosm experiment in different climate zones across Europe involving Sweden, Estonia, Germany, the Czech Republic, Turkey and Greece. We assessed attributes of zooplankton communities that might contribute to resilience under different ecological configurations. We assessed four indicator of relative ecological resilience (cross-scale, within-scale structures, aggregation length and gap size) of zooplankton communities, inferred from discontinuity analysis. Similar resilience attributes were found across experimental treatments and countries, except Greece, which experienced severe drought conditions during the experiment. These conditions apparently led to a lower relative resilience in the Greek mesocosms. Our results indicate that zooplankton community resilience in shallow lakes is marginally affected by water level and the studied nutrient range unless extreme drought occurs. In practice, this means that drought mitigation could be especially challenging in semi-arid countries in the future.

Space-for-time substitution studies (SFTS, e.g. latitudinal gradient analyses) are often used to unravel climate effects on lake biota, and have shown a reduction in size, changes in diet and more frequent reproduction of fish in warmer climates, with cascading effects such as lower zooplankton and higher phytoplankton biomasses. SFTS results from continental lakes are, however, potentially confounded by biogeographical and evolutionary differences leading to often higher species richness in warm lakes. To somehow reduce these confounding effects, we studied species-poor lakes located in two remote island groups with contrasting climates but similar seasonality: The Faroe Islands (cold; 6.5±2.8°C) and the Azores (warm; 17.3±2.9°C). We analysed community and food web structure using a stable isotopes approach investigating fish, macro-invertebrates, and zooplankton in 20 lakes. We found a smaller mean body size of fish in the Azorean lakes even if standardised by maximum length of the fish species present, suggesting a higher predation pressure on zooplankton and consequently higher phytoplankton abundance at the same nutrient levels. A triangular shape of the food web, with wider carbon range for basal organisms and for the whole food web appeared in the colder lakes. In contrast to previous works, though, Layman metrics of the fish food web were similar between the two climatic regions despite differences in basal organisms. Our results from insular systems showed a reduced fish body size structure in the warmer region and suggest that temperature differences may drive the changes in fish size structure.

Lithium-ion batterier er strømkilden, der har revolutioneret vores transportable elektronik. Familien af ion-batterier er imidlertid større end som så og har meget, meget mere at byde på.

Moss kommune, i samarbeid med vannområdet Morsa, Østfold fylkeskommune og EU-prosjektet REFRESH, arrangerte den 21. og 22. oktober 2013 en workshop om Vansjø. I denne rapporten oppsummeres både foredrag og gruppearbeid fra workshop’en. Den kanskje viktigste meldingen er at Vansjø ikke er friskmeldt, og at klimaendringer antakelig kan forverre tilstanden i innsjøen. Dette medfører at det fortsatt må være et omfattende fokus på miljøtiltak i nedbørfeltet.