Martin Søndergaard

Aarhus University | AU · Department of Ecoscience

In lakes where phosphorus (P) supply is dominated by external loads, long-term mean lake-water total phosphorus (TP) concentrations can be successfully reconstructed from sediment P profiles and dating using the Sediment-Inferred lake-water Total Phosphorous (SI-TP) mass balance model. However, it has not yet been shown that the model is applicable...

Aquatic macrophytes are generally recognized to influence fish–prey interactions. We assessed how fish consume particular foods, and how their foraging efficiency, trophic niche breadth, and niche overlap respond to gradients of macrophyte density and diversity. We sampled fish and macrophytes in 30 stands distributed over a 13.7 km stretch of the...

Zooplankton grazing at similar nutrient levels is generally regarded as lower in brackish than in freshwater lakes, but experimental evidence of this is lacking. Accordingly, we conducted short-term zooplankton grazing experiments in bottles with water from 12 Danish brackish lakes covering a large gradient in salinity (0.3–17.4‰) and nutrient conc...

Temporary summer stratification is probably a common, but easily overlooked phenomenon in many shallow lakes, because short-term temperature stratification and mixing events are not easily discovered by routine samplings. We used two years of high frequency measurements and monitoring of 5-m deep and hypereutrophic Lake Ormstrup, Denmark to study t...

We investigated the ability of the process-based, 1-dimensional hydrodynamic-ecosystem lake model GOTM-WET to reproduce the fluctuating dynamics and shifts between turbid and clear water states following restoration in temperate, shallow Lake Arreskov, Denmark. The lake model was calibrated on a comprehensive 12-year dataset with a multiple single-...

In lakes where phosphorus (P) supply is dominated by external loads, long-term mean lake water TP concentrations can be successfully reconstructed from sediment P profiles and dating using the SI-TP (Sediment Inferred lake water Total Phosphorus) mass balance model. However, it has not yet been shown that the model is applicable at lakes with high...

In lakes where phosphorus (P) supply is dominated by external loads, long-term mean lake water TP concentrations can be successfully reconstructed from sediment P profiles and dating using the SI-TP (Sediment Inferred lake water Total Phosphorus) mass balance model. However, it has not yet been shown that the model is applicable at lakes with high...

Characteristics of bottom sediments in lake mesocosms 11 years after starting the experiment were studied in order to determine the effects of nutrient loading, temperature increase and vegetation type on concentration and vertical distribution of phosphorus (P) forms. The experimental setup consisted of 24 outdoor flow-through mesocosms with two n...

Fish larvae play an important structuring role for their prey and show ontogenetic shifts in diet. Changes in diet differ between species and habitats and may also be affected by turbidity (eutrophication). We investigated the diet (stomach content) and the food selection (ratio of ingested prey and prey availability) of roach and perch larvae in a...

Increased urea is one of the common nitrogen forms polluting coastal waters and affecting nutrient dynamics. To investigate the effects of urea on sediment phosphorus (P) release, we carried out a 2-month mesocosm experiment with six targeted loadings of urea (0-0.6 mg N L − 1 d − 1). Results showed that: i) urea was rapidly transformed into ammoni...

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 Vaeng, undergoing major changes in water clarity and mac...

Cross-latitude studies on lakes have a potential to predict how global warming may cause major changes in phytoplankton biomass and composition, e.g., the development of favourable conditions for cyanobacteria dominance. However, results from these studies may be influenced by biogeographical factors, and the conclusions may, therefore, not hold wh...

Copepods are important contributors to the zooplankton community in lakes. Being ‘‘sandwiched’’ between predators and resources, they are sensitive to changes in the environment. It has been proposed that the proportion of calanoids of total copepod abundance or biomass could be a valuable indicator of eutrophication. We investigated relationships...

The effectiveness of controlling nitrogen (N) to manage eutrophication of aquatic ecosystems remains debated. To understand the mechanisms behind phytoplankton growth in shallow lakes (resource and grazing effects) under contrasting N loading scenarios, we conducted a 70-days mesocosm experiment in summer. The mesocosms contain natural plankton com...

We analysed long-term monitoring data on submerged macrophytes and water chemistry from 666 Danish lakes > 1 hectare and mean depth < 3 m, encompassing a total of 1447 lake years. Our aim was to describe how plant cover (COV), plant volume inhabited (PVI) and species richness related to physical and chemical and environmental variables. Boosted reg...

A mesocosm experiment was conducted in a temperate eutrophic lake with the hypotheses: 1) the addition of a labile form of DOC would trigger a more pronounced response in phytoplankton biomass and composition compared with a non-labile form; 2) DOC addition would increase phytoplankton biomass by co-inserting organic nutrients for phytoplankton gro...

Human-induced changes in external nutrient loading affect the phytoplankton community and abundance directly by changing the amount of nutrients available, but also indirectly through changes in the zooplankton (that is, grazer) community structure, mediated in part by changes in the fish community structure and biomass. Such shifts affect the spec...

Disentangling the effects of climate change on nature is one of the main challenges facing ecologists nowadays. Warmer climates forces strong effects on lake biota for fish, leading to a reduction in size, changes in diet, more frequent reproduction, and stronger cascading effects. Space-for-time substitution studies (SFTS) are often used to unrave...

The global surface temperature has increased by about 0.74°C over the past 100 years, and the frequency of extreme weather has increased as well. We used the state-of-the-art complex, dynamic, mechanistic model GOTM-FABM-PCLake to quantify the impacts of extreme summer warming on a summer-stratified temperate Danish lake. Simulated values of all ca...

Shallow lakes, the most numerous waterbodies on Earth, are susceptible to climate warming and nutrient enrichment whose effects on the microbial functional potentials are not yet fully understood, however. Here, we applied a microarray-based technology termed GeoChip 5.0 to investigate microbial functional genes at the beginning of April in shallow...

Seasonal and annual dynamics of the zooplankton community in lakes are affected by changes in abiotic drivers, trophic interactions (e.g., changes in phytoplankton and fish communities and abundances) and habitat characteristics (e.g. macrophyte abundance and composition). However, little is known about the temporal responses of the zooplankton com...

Phosphorus (P) release from sediment is a key process affecting the effectiveness of eutrophication mitigation. We hypothesized that high nitrate (NO3⁻) input may have dual effect on sediment P release: reduce the sediment P release by improving the oxidation of sediment or promote P release by stimulating the growth of phytoplankton and increase t...

Global changes (e.g., warming and population growth) affect nutrient loadings and temperatures , but global warming also results in more frequent extreme events, such as heat waves. Using data from the world's longest-running shallow lake experimental mesocosm facility, we studied the effects of different levels of nutrient loadings combined with v...

Phytoplankton usually responds directly and fast to environmental fluctuations, making them useful indicators of lake ecosystem changes caused by various stressors. Here, we examined the phytoplankton community composition before, during, and after a simulated 1-month heat wave in a mesocosm facility in Silkeborg, Denmark. The experiment was conduc...

Shallow lakes are globally the most numerous water bodies and are sensitive to external perturbations, including eutrophication and climate change, which threaten their functioning. Extreme events, such as heat waves (HWs), are expected to become more frequent with global warming. To elucidate the effects of nutrients, warming, and HWs on zooplankt...

Submerged macrophytes are of key importance for the structure and functioning of shallow lakes and can be decisive for maintaining them in a clear water state. The ongoing climate change affects the macrophytes through changes in temperature and precipitation, causing variations in nutrient load, water level and light availability. To investigate h...

World-wide, reducing the external nutrient loading to lakes has been the primary priority of lake management in the restoration of eutrophic lakes over the past decades, and as expected this has resulted in an increase in the local environmental heterogeneity, and thus biotic heterogeneity, within lakes. However, little is known about how the regio...

In the EU Water Framework Directive, lakes are classified into different types primarily on the basis of morphological and chemical characteristics. Lake type definition is not trivial because the different lake types may require different nutrient loading reduction targets to achieve the goal of at least "good" ecological status. Using data from 7...

This Special Issue of Inland Waters (featuring 2 Special Sections spread across 2 issues) celebrates the contribution of Brian Moss to the science and management of freshwater ecosystems. Brian passed away in 2016, and since then much has been written about his life and achievements (Carvalho and Johnes 2016, Irvine and Barker 2016, Jeppesen and Jo...

During the past century, many brackish shallow lakes worldwide have become eutrophic. How the zooplankton have responded to this development is not well elucidated. Here, we analysed the decadal changes (from 1999-2000 to 2017-2018) in zooplankton biomass, body mass, and potential top-down control on phytoplankton during summer in 4 Danish shallow...

In recent years, considerable efforts have been made to restore turbid, phytoplankton‐dominated shallow lakes to a clear‐water state with high coverage of submerged macrophytes. Various dynamic lake models with simplified physical representations of vertical gradients, such as PCLake, have been used to predict external nutrient load thresholds for...

Internal loading or release of phosphorus (P) from lake sediments can be an important factor determining lake water quality in both deep and shallow lakes. In deep lakes, anoxic conditions increase the accumulation of phosphate in the hypolimnion during stratification, which eventually may reach the epilimnion during mixing. In shallow and mixed la...

Lake Søbygaard (Denmark) is a shallow and highly eutrophic lake that was subjected to very high levels of external phosphorus (P) loading from a nearby town until 1982. Since then, the lake has suffered from an internal loading of P, which during the first 10–15 years after external load reduction, led to summer total P (TP) concentrations being th...

Rapid climate changes may potentially have strong impacts on the ecosystem structure and nutrient dynamics of lakes as well as implications for water quality. We used a space-for-time approach to elucidate such possible effects by comparing data from 1656 shallow lakes (mean depth <3 m) in north temperate Denmark (DK) and subtropical Florida (FL)....

Climate extremes, which are steadily increasing in frequency, can have detrimental consequences for lake ecosystems. We used a state-of-the-art, one-dimensional, hydrodynamic-ecosystem model [General Ocean Turbulence Model (GOTM)-framework for aquatic biogeochemical models (FABM)-PCLake] to determine the influence of extreme climate events on a tem...

1. Breeding waterbird communities have suffered globally from the effects of anthropogenic changes in water quality (especially nutrient enrichment) in recent decades, but few studies have demonstrated the positive effects of restorative actions. 2. Annual breeding waterbird surveys in the period 1977-2005 at two restored southern Danish lake basi...

Canfield DE, Jr., Bachmann RW, Hoyer MV, Johansson LS, Søndergaard M, and Jeppesen E. 2018. To measure chlorophyl or phytoplankton biovolume: an aquatic conundrum with implications for the management of lakes. Lake Res Manage. 00:00–00. The log10-transformed relationship between measured phytoplankton biovolumes and chlorophyll concentrations, surr...

Common pochard Aythya ferina are rapidly declining globally, partly due to water quality change at breeding habitats. Lake restoration at two southern Danish lakes (external nutrient loading reduction, bream Abramis brama and roach Rutilus rutilus removal and stocking of pike Esox lucius) improved water clarity and submerged macrophyte cover. Nesti...

We studied community-environment relationships of lake macrophytes at two metacommunity scales using data from 16 regions across the world. More specifically, we examined (a) whether the lake macrophyte communities respond similar to key local environmental factors, major climate variables and lake spatial locations in each of the regions (i.e., wi...

Important drivers of gross primary production (GPP) and ecosystem respiration (ER) in lakes are temperature, nutrients, and light availability, which are predicted to be affected by climate change. Little is known about how these three factors jointly influence shallow lakes metabolism and metabolic status as net heterotrophic or autotrophic. We co...

The European Water Framework Directive has been adopted by Member States to assess and manage the ecological integrity of surface waters. Specific challenges include harmonizing diverse assessment systems across Europe, linking ecological assessment to restoration measures and reaching a common view on ‘good’ ecological status. In this study, nine...

The articel "Synergy between nutrients and warming enhances methane ebullition from experimental lakes" was published in Nature Climate Change 6 months ago.

In aquatic ecosystems, ammonium is one of the dominant substances in the effluent discharge from wastewater treatment plants and its impact has been widely explored as it is thought, in its toxic form (NH3), to cause stress on organisms. Little is, however, known about its potential effect on the release of phosphorus (P) from the sediment. In a tw...

Blooms of cyanobacteria are a current threat to global water security that is expected to increase in the future because of increasing nutrient enrichment, increasing temperature and extreme precipitation in combination with prolonged drought. However, the responses to multiple stressors, such as those above, are often complex and there is contradi...

We analysed changes in the abundance, biomass and cell size of the microbial food web community (bacteria, heterotrophic nanoflagellates, ciliates) at contrasting nutrient concentrations and temperatures during a simulated heat wave. We used 24 mesocosms mimicking shallow lakes in which two nutrient levels (unenriched and enriched by adding nitroge...

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 submer...

Link to read only version of the paper "http://rdcu.be/FhSR". Lakes and ponds are important natural sources of the potent greenhouse gas methane (CH4), with small shallow waters identified as particular hotspots1,2. Ebullition (bubbles) of CH4 makes up a large proportion of total CH4 flux3,4. However, difficulty measuring such episodic events5 ma...

Nature Ecology & Evolution - online Abstract There is a pressing need to apply stability and resilience theory to environmental management to restore degraded ecosystems effectively and to mitigate the effects of impending environmental change. Lakes represent excellent model case studies in this respect and have been used widely to demonstrate th...

Lakes in Greenland are species-poor ecosystems and many are fishless. We studied the structuring role of fish in lakes in high- and low-Arctic Greenland. Major differences were observed in the trophic structure of the 87 lakes studied. Pelagic zooplankton biomass was on average 3–4-fold higher in the fishless lakes and dominated by large-bodied tax...

Mining of gravel and sand for construction purposes is big business and gravel pit lakes have become increasingly common all over the world. In Denmark, hundreds of gravel pit lakes have been created during the past decades. We investigated the chemical and biological status of 33-52 gravel pit lakes and compared the results with data from similar-...

Summary 1. Carbon (C) and nitrogen (N) stable isotope composition (15N:14N, d15N and 13C:12C, d13C) have been widely used to elucidate changes in aquatic ecosystem dynamics created by eutrophication and climate warming, often, however, without accounting for seasonal variation. 2. Here, we aim to determine the factors controlling the stable isotope...

We used data on nutrients, chlorophyll a (Chla) and submerged macrophyte cover from up to 817 Danish lakes to elucidate seasonal variations in nitrogen (N) and phosphorus (P) concentrations and to study the impact of N or its role in combination with P. In both deep and shallow lakes, we found marked seasonality in the ratio between total N and tot...

The ongoing global climate change involves not only increased temperatures but may also produce more frequent extreme events, such as severe rainfall that could trigger a pulse of nutrients to lakes. In shallow lakes, this may affect primary producers through a number of direct and indirect mechanisms. We conducted a six-month mesocosm experiment t...

Lentic ecosystems act as sentinels of climate change, and evidence exists that their sensitivity to warming varies along a latitudinal gradient. We assessed the effects of nutrient and water level variability on zooplankton community composition, taxonomic diversity and size structure in different climate zones by running a standardised controlled...

1. Shallow lakes may play an important role for the nitrogen (N) balance in drainage basins by processing, transferring and retaining N inputs. An increase in the frequency of storm-induced short-term N pulses and increased water temperatures are both likely outcomes of climate change, potentially affecting the N processing in lakes. 2. An experime...

Nye danske søer-design af optimal miljøtilstand og biodiversitet Danmark er internationalt førende ved at have skabt omkring 50 nye søer større end 10 ha. Med få undtagelser kender vi imidlertid ikke deres naturkvalitet. Med optimalt fysisk design og forvaltning kan nye søer sikre overlevelse af kritisk truede eller sjaeldne arter. Derfor har fersk...

Shallow lakes are a key component of the global carbon cycle. It is, therefore, important to know how shallow lake ecosystems will respond to the current climate change. Global warming affects not only average temperatures, but also the frequency of heat waves (HW). The impact of extreme events on ecosystems processes, particularly greenhouse gas (...