Jan Köhler

Leibniz-Institute of Freshwater Ecology and Inland Fisheries | IGB · Department of Ecosystem Research

Understanding controls on primary productivity is essential for describing ecosystems and their responses to environmental change. In lakes, pelagic gross primary productivity (GPP) is strongly controlled by inputs of nutrients and dissolved organic matter. Although past studies have developed process models of this nutrient‐color paradigm (NCP), b...

Dense beds of water plants can be perceived as nuisance, but this perception, however, may not be similar for different user categories, and this may affect their willingness-to-pay (WTP) for plant removal. A questionnaire survey was used to test this for residents and visitors and find underlying socio-cultural or economic drivers. We studied five...

Dense beds of aquatic plants are often perceived as nuisance and therefore mechanically removed, often at substantial cost. Such removal, however, may affect a range of ecosystem functions and consequently also the ecosystem services that benefit society. We studied five cases: River Otra (Norway), River Spree (Germany), Lake Kemnade (Germany), Lak...

Mass developments of macrophytes occur frequently worldwide and are often considered a nuisance when interfering with human activities. It is crucial to understand the drivers of this perception if we are to develop effective management strategies for ecosystems with macrophyte mass developments. Using a comprehensive survey spanning five sites wit...

Mass development of macrophytes is an increasing problem in many aquatic systems worldwide. Dense mats of macrophytes can negatively affect activities like boating, fishing or hydropower production and one of the management measures often applied is mechanical removal. In this study, we analyzed the effect of mechanical macrophyte removal on phytop...

Mass development of macrophytes in freshwater ecosystems is today considered a worldwide problem and substantial resources are spent on macrophyte removal each year. By removing the dominant primary producer, however, this management practice radically changes the ecosystem overnight. Here, we studied short-term effects of the removal of a mass dev...

There is a need to determine and quantify global change induced phenological asynchrony because of possible loss of biodiversity and implications for the food web. Phenological asynchrony in freshwater lakes can be studied retrospectively by analysing historical data, and prospectively by scenario analysis based on historical data. Models allowing...

• Terrestrial loads of dissolved organic carbon (DOC) have increased in recent years in many north temperate lakes, leading to widespread brownification. This process can profoundly alter the relative strength of planktonic and benthic primary production in lakes due to changes in light and nutrient availability. While most existing in situ studies...

“Research for the Future of our Freshwaters“ is IGB’s guiding principle. This involves giving objective and evidence-based information and advice to policymakers, authorities, associations, industry, educational institutions and the public. Within the institute’s publication series called IGB Outlines, which includes the IGB Policy Brief, IGB disse...

Nuttall’s waterweed (Elodea nuttallii) is the most abundant invasive aquatic plant species in several European countries. Elodea populations often follow a boom-bust cycle, but the causes and consequences of this dynamics are yet unknown. We hypothesize that both boom and bust periods can be affected by dreissenid mussel invasions. While mutual fac...

Dissolved organic carbon (DOC) concentrations in many freshwater ecosystems of the northern hemisphere have increased in recent decades due to additional terrestrial inputs. This phenomenon, known as brownification, can strongly alter the physical, chemical, and biological traits of aquatic ecosystems. Extreme rainfall can also cause sudden brownif...

Induced bank filtration (IBF) is a water abstraction technology using different natural infiltration systems for groundwater recharge, such as river banks and lake shores. It is a cost-effective pre-treatment method for drinking water production used in many regions worldwide, predominantly in urban areas. Until now, research concerning IBF has alm...

Delayed fluorescence (DF) is a characteristic feature of light-excited plant cells caused by the back-reaction of electrons through the electron transport chain. Targeting the response of light-adapted green algae to diurnal light changes, the present study presents novel results of DF measurements in the absence of an artificial excitation light s...

Resource distribution heterogeneity offers niche opportunities for species with different functional traits to develop and potentially coexist. Available light (photosynthetically active radiation or PAR) for suspended algae (phytoplankton) may fluctuate greatly over time and space. Species‐specific light acquisition traits capture important aspect...

The effectiveness of controlling nitrogen (N) to manage lake eutrophication is debated. Long‐term, whole‐lake case studies are required to determine whether diazotrophic cyanobacteria can fix sufficient N to offset a reduction of N‐inputs. We document the recovery of shallow, productive Lake Müggelsee (Germany) over 37 yr (sampling interval 1–2 wee...

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...

Kettle holes are often abundant within agriculturally used moraine landscapes. They are highly enriched with nutrients and considered hotspots of carbon turnover. However, data on their primary productivity remain rare. We analysed two kettle holes typical to Germany with common aquatic plant communities during one year. We hypothesised that gross...

Phytoplankton growth depends not only on mean intensity but also on the dynamics of the light supply. In surface mixed layers, phytoplankton may rapidly move between strong light and almost darkness. The nonlinear light-dependency of growth may differ between constant and fluctuating light because of the different frequency distribution of light an...

The sum of benthic autotrophic and bacterial production often exceeds the sum of pelagic autotrophic and bacterial production, and hence may contribute substantially to whole‐lake carbon fluxes, especially in shallow lakes. Furthermore, both benthic and pelagic autotrophic and bacterial production are highly edible and of sufficient nutritional qua...

The diel (24-h) oxygen (O2) curves approach has become a popular method for analyzing gross primary production (GPP) and ecosystem respiration (ER) rates in aquatic systems. Despite the simplicity of this approach, there remain aspects of the calculation and interpretation of diel O2 curves which may skew results, with potentially large implication...

The Taihu (Tai lake) region is one of the most economically prospering areas of China. Due to its location within this district of high anthropogenic activities, Taihu represents a drastic example of water pollution with nutrients (nitrogen, phosphate), organic contaminants and heavy metals. High nutrient levels combined with very shallow water cre...

Forecasting models for Anabaena, Aphanizomenon and Microcystis have been developed for the hypertrophic phase from 1979 to 1990 and the eutrophic phase from 1997 to 2012 of the polymictic Lake Müggelsee by means of the hybrid evolutionary algorithm HEA. Comparisons of limnological parameters of the two phases revealed not only a distinct seasonal e...

Evaluating ecological responses to restoration is important for assessing the success of river restorations. We evaluated the response of species richness and diversity of aquatic macrophyte (hydrophyte, instream aquatic plant) growth forms and strategies (Grime’s CSR strategies; C competitive, S stress tolerant, R ruderal) in 10 small- and 10 larg...

Ecosystems are generally linked via fluxes of nutrients and energy across their boundaries. For example, freshwater ecosystems in temperate regions may receive significant inputs of terrestrially derived carbon via autumnal leaf litter. This terrestrial particulate organic carbon (POC) is hypothesized to subsidize animal production in lakes, but di...

Stickstofflimitation in Binnengewässern - Ist Stickstoffreduktion ökologisch sinnvoll und wirtschaftlich vertretbar? Abschlussbericht NITROLIMIT Phase II

Restoration of river hydromorphology often has limited detected effects on river biota. One frequently discussed reason is that the restored river length is insufficient to allow populations to develop and give the room for geomorphological processes to occur. We investigated ten pairs of restored river sections of which one was a large project inv...

Dissolved organic nitrogen ( DON ) compounds dominate the nitrogen pool of many lakes, but their importance as nitrogen sources for freshwater phytoplankton is not fully understood. Previous growth experiments demonstrated the availability of urea and amino acids but often at unnaturally high concentrations. The importance of complex DON compounds...

The applicability of algorithms for estimation of phycocyanin (PC) concentration based on light spectral reflectance heavily depends on the specific absorption of the pigment. But the determination of PC-specific absorption coefficient is not a straightforward task, as PC optical activity is overlapped by absorption of chlorophylls. The aim of our...

Food-web effects of winterkill are difficult to predict as the enhanced mortality of planktivorous fish may be counterbalanced by an even higher mortality of piscivores. We hypothesised that a winterkill in a clear and a turbid shallow lake would equalise their fish community composition, but seasonal plankton successions would differ between lakes...

In lakes, trophic change and climate change shift the relationship between nutrients and physical factors, like temperature and photoperiod, and interactions between these factors should affect the growth of phytoplankton species differently. We therefore determined the relationship between P-limited specific growth rates and P-quota (biovolume bas...

This study examines a natural, rapid, fivefold increase in dissolved organic carbon (DOC) concentrations in a temperate shallow lake, describing the processes by which increased DOC resulted in anoxic conditions and altered existing carbon cycling pathways. High precipitation for two consecutive years led to rising water levels and the flooding of...

Food-web effects of winterkill are difficult to predict as the enhanced mortality of planktivorous fish may be counterbalanced by an even higher mortality of piscivores. We hypothesised that a winterkill in a clear and a turbid shallow lake would equalise their fish community composition, but seasonal plankton successions would differ between lakes...

To identify the seasonal pattern of nitrogen (N) and phosphorus (P) limitation of phytoplankton in four different lakes, biweekly experiments were conducted from the end of March to September 2011. Lake water samples were enriched with N, P or both nutrients and incubated under two different light intensities. Chlorophyll a fluorescence (Chla) was...

Lake ecosystems are strongly linked to their terrestrial surroundings by material and energy fluxes across ecosystem boundaries. However, the contribution of terrestrial particulate organic carbon (tPOC) from annual leaf fall to lake food webs has not yet been adequately traced and quantified. In this study, we conducted whole-lake experiments to t...

Ecological regime shifts and carbon cycling in aquatic systems have both been subject to increasing attention in recent years, yet the direct connection between these topics has remained poorly understood. A four-fold increase in sedimentation rates was observed within the past 50 years in a shallow eutrophic lake with no surface in-or outflows. Th...

1. Regime shifts are commonly associated with the loss of submerged macrophytes in shallow lakes; yet, the effects of this on whole-lake primary productivity remain poorly understood. This study compares the annual gross primary production (GPP) of two shallow, eutrophic lakes with different plant community structures but similar nutrient concentra...

Diatoms often dominate temperate lakes and rivers in spring, when increasing temperature and daylength coincide with decreasing silicate concentrations. Since interactions between these factors may be important, we cultivated Stephanodiscus minutulus and Nitzschia acicularis (freshwater diatoms) under silicon limitation at different temperatures an...

During eutrophication, submerged macrophytes in temperate E uropean shallow lakes are thought to undergo a sequence from seasonally ‘stable’ conditions characterised by high water clarity in spring and summer, through ‘crashing’ conditions where the water is clear in spring but dominated by phytoplankton in late summer, to ‘turbid’ conditions with...

We measured specific growth rates of Stephanodiscus minutulus, Nitzschia acicularis (diatoms), and Limnothrix redekei (cyanobacterium) under fluctuating and constant light in semi-continuous culture at 10°C, 15°C, and 20°C and under photoperiods of 6 h d−1 and 12 h d−1. Fluctuating light regimes simulated regular vertical mixing in lakes with a rat...

Regime shifts between clear and turbid water states are commonly found in shallow lakes. These shifts are attributed to a positive feedback between water clarity and submerged macrophytes (underwater plants). Altering the retention time of the water may influence these interactions and thus potentially reduce the probability of alternative stable s...

Long-term changes of freshwater ecosystems are mainly caused by immissions from drainage basin and atmosphere (nutrients, acid substances, etc.) and by changing climatic conditions. Freshwater ecosystems often react in non-linear ways to these external forces. Beyond a certain threshold, gradual shifts may cause catastrophic switches to another sta...

Growth of aquatic vegetation is often controlled by light supply, which is potentially decreased by bank vegetation, water turbidity and epiphytic biofilm. To understand the relative importance of these shading factors and the interactions between them we analysed the seasonal course of macrophyte biomass, shading by bank vegetation, turbidity of t...

1. Although macrophytes play a key role in the structure and functioning of lowland rivers, most of the basic plant, hydrodynamic and sediment-water interactions have only been described qualitatively. We therefore studied quantitatively, the seasonal dynamics of matter deposition and mobilisation inside and outside (free path) a representative pat...

The effects of the recent warming trend in many northern temperate lakes on the species composition of spring phytoplankton remain poorly understood, especially because a recent change in nutrients has complicated efforts, and previous studies have defined spring according to the calendar. We analysed data from 1979 to 2004 from Lake Müggelsee (Ber...

Global climate change alters the relationship between temperature and light in aquatic ecosystems, which is expected to affect the success of different phytoplankton species. To examine this, the interactions between temperature, photoperiod and light exposure (LE) (integral daily light supply) on specific growth rates were analysed for Limnothrix...

For a century eutrophication has been the most serious environmental threat to lakes in the densely populated or agricultural areas of Europe. During the last decades, however, major efforts have been used to reduce the external nutrient loading, not least from point sources. Despite these comprehensive efforts, lake eutrophication remains a major...

Aquatic plants increase hydraulic resistance, modify transport and mixing processes. To assess quantitatively the impact of vegetation on these processes field tracer studies were performed on the Müggelspree river. Analysis of obtained data indicated that in early spring, when vegetation is absent and water discharges are relatively high, the volu...

This study was designed to quantify and model the effects of macrophytes on phosphorus retention in a lowland river. The seasonal course of phosphorus retention was calculated from the measured difference in TP between beginning and end of a 30-km river course and the estimated lateral P input. The coverage of submersed macrophytes was mapped and c...

1. Phytoplankton carbon assimilation and losses (exudation, dark carbon losses) as well as oxygen release and dark community respiration were measured regularly for 2 years at four stations along the lower Spree (Germany). Carbon balance of river phytoplankton was estimated using measured assimilation, metabolic losses and variations in algal carbo...

1. This synthesis examines 35 long-term (5–35 years, mean: 16 years) lake re-oligotrophication studies. It covers lakes ranging from shallow (mean depth <5 m and/or polymictic) to deep (mean depth up to 177 m), oligotrophic to hypertrophic (summer mean total phosphorus concentration from 7.5 to 3500 ug L-1 before loading reduction), subtropical to...

1. The responses of nutrient concentrations, plankton, macrophytes and macrozoobenthos to a reduction in external nutrient loading and to contemporary climatic change were studied in the shallow, moderately flushed Lake Müggelsee (Berlin, Germany). Weekly to biweekly data from 1979 to 2003 were compared with less frequently collected historical dat...

The formation, particle size distribution, structure and retention of aggregates were studied in a river-lake system of the lowland River Spree and factors influencing these processes were evaluated. Samples were taken from the inflow and outflow of a flushed lake, as well as along the adjacent flowing reach of the River Spree, between April 2001 a...

We studied chlorophyll a (chl. a), biovolume and species composition of benthic algae and phytoplankton in the eutrophic lower River Spree in 1996. The chl. a concentration was estimated as 3.5 (2.7–4.5) µg/cm2 for epipsammon, 9.4 (7.4–11.9) µg/cm2 for epipelon and 6.7 (5.7–7.8) µg/cm2 for the epilithon (median and 95% C. L.). The mean total biomas...

Photogrammetrical methods were combined with field studies to map macrophytes in a medium-sized river, which has not been practised prior to our studies.In August 2001, aerial photos were made at a 15 km long section of the Lower River Spree. In the same time, we described the spatial distribution of submersed macrophytes along two 50 m long river...

Growth of phytoplankton depends on light supply and thus on mixing depth. Rates of sedimentation and of contact with benthic filter-feeders should decline with rising water level. Therefore, discharge-dependent water depth should predispose the fate of phytoplankton transported down a river. Growth and loss of phytoplankton have been studied at dif...

Carbon assimilation is usually measured at fairly constant light intensities. Under natural condi- tions, however, planktonic algae are moved through the water column and experience light of fluc- tuating intensity and spectral composition. They may cope with strong UV for a short residence in the upper water layer. In order to estimate the effects...

Biomass and structure of phytoplankton of a flushed, shallow lake were compared between a decade with hypertrophic conditions (1980-1990) and a period with 40-50 % reduced external nutrient load (1991-1997). Nutrient concentrations in the inflow declined less than loads because of reduced discharge. At the same time, the phytoplankton biovolume dec...

Phytoplankton dynamics in Lake Mggelsee, a eutrophic and polymictic lake in Berlin, and in the inflowing lowland River Spree have been comprehensively investigated during the last two decades. Zooplankton dynamics, nutrient supply, light climate, duration of ice cover and of summer stratification have also been regularly measured to help to explain...

The shallow (mean depth 4.9 m), polymictic and eutrophic lake Müggelsee was highly loaded with phosphorus (6 gP m-2a-1) and nitrogen (170 gN m-2a-1) by the river Spree up to the end of the 1980s. Annual load declined by 40–50% during the last years (1991–97). Phosphorus retention fluctuated strongly during the seasonal cycle between −200 and +100 k...

The shallow (mean depth 4.9 m), polymictic and eutrophic lake Mggelsee was highly loaded with phosphorus (6 gP m-2a-1) and nitrogen (170 gN m-2a-1) by the river Spree up to the end of the 1980s. Annual load declined by 40–50% during the last years (1991–97). Phosphorus retention fluctuated strongly during the seasonal cycle between –200 and +100 kg...

The present study demonstrates, that fluorescence measurements can be successfully used for continuous environmental monitoring. The technique may be useful to determine the development of chlorophyll-a concentrations and photochemical efficiency with time in a dynamic system. The development of chlorophyll-a concentrations with time, as determine...

The development of the main phytoplankton taxa was studied in a water parcel flowing along a 28-km stretch of the lower Spree as well as in simultaneously incubated dialysis chambers. The chambers were continuously moved through the water column in order to provide the enclosed algae with light of the same mean intensity and of comparable frequency...

In situ measurement of the growth rates of planktonic populations can be improved by using dialysis chambers (‘cage cultures’) to avoid shifts in the chemical environment during incubation. Vertical mixing and small-scale turbulence affect the growth of planktonic populations, there fore natural mixing conditions should be simulated as closely as p...

The influences of imports of nutrients and planktonic algae from the River Spree on the dynamics of phytoplankton were examined in the shallow, eutrophic Mggelsee, which has a retention time of only 42 days. Phytoplankton biomass and nutrient concentrations were measured in both the lake and its inflow from 1980–1990. On a long-term average, mean b...

The River Spree (Germany) flows through an impoundment and several shallow lakes in its middle and lower course. In this river-lake system, the seasonal and longitudinal dynamics of dominant phytoplankton populations were studied in relation to retention time of water, mixing conditions and nutrient supply from 1988-92. Some phytoplankton species p...

The seasonal and longitudinal dynamics of dominant phytoplankton populations were observed in the lower Spree (Germany), a lowland river draining several lakes. Centric diatoms and cyanobacteria were the chief components of the total phytoplankton biomass of 16 mg−1 at the end of the river course (average March-October, 1988–89). The cyanobacteria...

Biomass and community structure of phytoplankton have been analysed in the eutrophic, shallow, polymictic Müggelsee and in the inflowing Spree since 1980. In both lake and river, mean biomass and vitality of phytoplankton were similar. A regular annual succession of planktonic algae was found in both the river and the lake. The same species were fo...

Zooplankton-eating fish had been completely eliminated by stocking with predacious fish in 1981 and consecutive years in a small Experimental water (flooded quarry, surface area 0.044 ha, mean depth 7 m). The short-term response of the plankton community to this food-web manipulation was reported by Benndorf et al. (1984). The present paper analyse...