Jens Peder Jensen's research while affiliated with Marine Environmental Research Institute and other places

Publications (39)

Article
Lake restoration in Denmark has involved the use of several different restoration techniques, all aiming to improve lake water quality and establishing clear-water conditions. The most frequently used method, now used in more than 20 lakes, is the reduction of zooplanktivorous and benthivorous fish (especially roach (Rutilus rutilus) and bream (Abr...
Article
Shallow lakes respond to nutrient loading reductions. Major findings in a recent multi-lake comparison of data from lakes with long time series revealed: that a new state of equilibrium was typically reached for phosphorus (P) after 10–15 years and for nitrogen (N) after <5–10 years; that the in-lake Total N:Total P and inorganic N:P ratios increas...
Chapter
Shallow lakes respond to nutrient loading reductions. Major findings in a recent multi-lake comparison of data from lakes with long time series revealed: that a new state of equilibrium was typically reached for phosphorus (P) after 10–15 years and for nitrogen (N) after <5–10 years; that the in-lake Total N:Total P and inorganic N:P ratios increas...
Article
Based on monthly mass balances on 7-8 yr of data from 16 shallow (mean depth: 1-10 m), eutrophic, unstratified, or only temporarily stratified Danish lakes, we developed a simple empirical model relating the seasonal variation in lake total phosphorus (TP) concentrations to external loading, accumulated phosphorus in the sediment, hydraulic retenti...
Article
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...
Article
Summary1. Concentrations of phosphorus, nitrogen and silica and alkalinity were monitored in eight shallow and four deep Danish lakes for 13 years following a phosphorus loading reduction. The aim was to elucidate the seasonal changes in nutrient concentrations during recovery. Samples were taken biweekly during summer and monthly during winter.2....
Article
Summary1. For 13 years the response of the plankton and fish community to a decline in external phosphorus loading was studied in eight lakes with a mean depth <5 m. We conducted chi-square analyses of sign of slope (positive or negative) of bimonthly averages of plankton variables for the eight lakes versus time. For fish, we compared results from...
Article
1The European Water Framework Directive (WFD) requires that all European waterbodies are assigned to one of five ecological classes, based primarily on biological indicators, and that minimum good ecological quality is obtained by 2015. However, the directive provides only general guidance regarding indicator definitions and determination of bounda...
Article
To investigate the importance of lake size, we analysed the chemical and biological characteristics of nearly 800 Danish lakes ranging from 0.01 to 4200 ha. Most of the lakes were shallow (median depth = 1.5 m) and eutrophic (lake water mean total phosphorus = 0.26 mg P l–1 and mean chlorophyll-a = 60 g l–1). Phosphorus and nitrogen concentrations...
Article
1. The effect of total nitrogen (TN) and phosphorus (TP) loading on trophic structure and water clarity was studied during summer in 24 field enclosures fixed in, and kept open to, the sediment in a shallow lake. The experiment involved a control treatment and five treatments to which nutrients were added: (i) high phosphorus, (ii) moderate nitroge...
Article
1. It is well accepted that fish, if abundant, can have a major impact on the zooplankton community structure during summer, which, particularly in eutrophic lakes, may cascade to phytoplankton and ultimately influence water clarity. Fish predation affects mean size of cladocerans and the zooplankton grazing pressure on phytoplankton. Little is, ho...
Article
The sediment plays an important role in the overall nutrient dynamics of shallow lakes. In lakes where the external loading has been reduced, internal phosphorus loading may prevent improvements in lake water quality. At high internal loading, particularly summer concentrations rise, and phosphorus retention can be negative during most of the summe...
Article
During the last two decades the nutrient loading to Danish lakes has been reduced with the aim to improve water quality. However, because of internal P-loading and biological resistance, the expected improvement has been delayed. Therefore, to reduce the duration of the recovery period and to accelerate recolonisation of submerged macrophytes, seve...
Article
Full-text available
In order to disentangle the causes of variations in water chemistry among European shallow lakes, we performed standardised sampling programs in 86 lakes along a latitudinal gradient from southern Spain to northern Sweden. Lakes with an area of 0.1 to 27 000 ha and mean depth of 0.4–5.6 m located in low to high altitudes were investigated within th...
Article
Water managers often debate whether resuspension of sediment with high organic matter and water content accumulated during eutrophication delays improvement of water clarity after reduction of external nutrient loading. Using data from 15 shallow (mean depth <5 m) eutrophic lakes surveyed during 8-12 yr, we show that the reduction in phytoplankton...
Article
Using empirical data from 466 temperate to arctic lakes covering a total phosphorus (TP) gradient of 2-1036 mg L-1, we describe how the relative contributions of resource supply, and predator control change along a nutrient gradient. We argue that (a) predator control on large-bodied zooplankton is unimodally related to TP and is highest in the mos...
Article
Climatic warming and regime shifts in lake food webs—some comments In a recent issue of Limnology and Oceanography, Schef-fer et al. (2001) argued that ''the probability of clear water phases increases with increasing lake water temperature in shallow lakes and that small decreases in temperature may create a shift to a turbid state and an increase...
Article
To elucidate the possibilities of using zooplankton remains in the surface sediment to describe present-days community structure and population dynamics of zooplankton, fish abundance and temperature, we compared contemporary data sampled in the pelagial during summer with the sediment record from the upper 1 cm of the sediment in 135 lakes coverin...
Chapter
Many lakes world-wide suffer from eutrophication as a result of high external nutrient inputs from domestic sewage, industry and agricultural activities. Increased demands for water by a growing and developing human population as well as enhanced global warming may escalate the eutrophication on a global scale in the next century. Yet, in some coun...
Article
1. The European Water Framework Directive requires the determination of ecological status in European fresh and saline waters. This is to be through the establishment of a typology of surface water bodies, the determination of reference (high status) conditions in each element (ecotype) of the typology and of lower grades of status (good, moderate,...
Article
SUMMARY 1. Seasonal phosphorus variability may be considerable in eutrophic lakes and patterns are influenced by internal, as well as external, nutrient loading. The strong seasonality of planktonic diatoms, with main growth periods in the spring and also in the autumn in meso- to eutrophic lakes, means that the measure of total phosphorus (TP) tha...
Article
To investigate how phosphorus concentrations and retention were affected during recovery after reduced external phosphorus loading, phosphorus concentrations and loading were seasonally monitored for 11 years in 15 shallow eutrophic Danish lakes. Hydraulic loading, inlets, and lake water were sampled monthly during the winter (October-April) and bi...
Article
The response of the biological community to total phosphorus loading reductions was studied by sampling fortnightly during the summer for 11 years in 18 lakes with significant in-lake total phosphorus reductions, as well as in five reference lakes. Fish manipulation was conducted in four of the total phosphorus-reduced lakes during the study period...
Article
The zooplankton community structure in lakes is highly influenced by size-selective predation by fish, with small zooplankton species dominating at high predation pressure. Remains of cladocerans are preserved in the sediment and may be used to trace historical changes in fish predation. We determined how contemporary data on planktivorous fish wer...
Article
The field of lake palaeoecology has undergone significant changes. Powerful quantitative techniques have been developed to investigate anthropogenic impacts on lakes. Inclusion of zooplankton and benthic chydorid cladocerans has provided previously unavailable information on the historical development of planktivorous fish populations, submerged ma...
Article
Full-text available
In the autumn of 1995, coordinated national lake surveys were conducted in the Nordic countries, including Russian Kola. The 11 metals (Pb, Cd, As, Zn, Cu, Ni, Co, Fe, Mn, Cr, V) investigated in nearly 3000 lakes have generally low concentrations and distinct geographical patterns. Direct and indirect influence of long-range transported air polluti...
Article
1. Using data from 71, mainly shallow (an average mean depth of 3 m), Danish lakes with contrasting total phosphorus concentrations (summer mean 0.02–1.0 mg P L−l), we describe how species richness, biodiversity and trophic structure change along a total phosphorus (TP) gradient divided into five TP classes (class 1–5: <0.05, 0.05–0.1, 0.1–0.2, 0.2...
Article
Nitrate [Ca(NO3)2] was added to the hypolimnion of eutrophic Lake Lyng (10 ha, maximum depth 7.6 m), Denmark, over a 2-year period to study the impact on sediment phosphorus release and to evaluate the potential of hypolimnetic nitrate dosing as a lake restoration method. Dissolved (1995) or granulated (1996) nitrate was added 10 to 11 times at a d...
Article
High phosphorus concentrations due to internal loading from the sediment with a strongly negative impact on lake water quality, is often seen in shallow lakes after a reduction of external loading. To analyse the nature of internal loading we studied 1. the seasonal phosphorus concentrations of 265 Danish shallow, mainly eutrophic lakes; 2. seasona...
Article
Within a certain nutrient level shallow lakes may alternate between two states, a clearwater and a turbid state. To obtain more information on the characteristics of these two states, we compared seasonal variations in trophic structure and physico-chemical variables of two clear and two turbid lakes studied during seven or eight years. The clearwa...
Article
The effects of major reductions in organic matter, total phosphorus (TP), and total nitrogen (TN) loading on the chemical environment, trophic structure, and dynamics of the hypertrophic, shallow Lake Søbygård were followed for 18 years. After the reduction in organic matter loading in 1976, the lake initially shifted from a summer clear-water stat...
Chapter
Evidence from both empirical studies (Canfield et al., 1984; Jeppesen et al., 1990; Faafeng and Mjelde, this volume, Chapter 27) and numerous experimental field studies (see e.g., Gulati et al., 1990; van Donk et al., 1990; Mortensen et al., 1994) indicates that in freshwater lakes extensive growth of submerged macrophytes may lead to clearwater co...
Article
Based on data from 233 Danish lakes, enclosure experiments, full-scaleexperiments and published empirical models we present evidence that top-downcontrol is more important in shallow lakes than in deep lakes, excepting lakeswith a high abundance of submerged macrophytes. The evidence in support is: (1)That at a given epilimnion total phosphorus con...
Article
1. As quantitative information on historical changes in fish community structure is difficult to obtain directly from fish remains in lake sediments, transfer function for planktivorous fish abundance has been developed based on zooplankton remains in surface sediment (upper 1 cm). The transfer function was derived using weighted average regression...
Article
The impact of fish-mediated changes on the structure and grazing of zooplankton on phytoplankton and bacterioplankton was studied in Lake Søbygaard during the period 1984–92 by means of in vitro grazing experiments (14C-labelled phytoplankton, 3H-labelled bacterioplankton) and model predictions. Measured zooplankton clearance rates ranged from 0–25...
Article
A detailed mass balance on nitrogen was carried out in shallow and hypertrophic Lake Søbygård during 4.5 years before through 2.5 years after a 36 % reduction in nitrogen loading. Annual mean loss rate of nitrogen was 159–229 mg N m−2 d−1 before the loading reduction and 125 mg N m−2 d−1 after. In spite of a short hydraulic retention time (18–27 da...

Citations

... In particular, it may be the absence of a sufficiently long-term view of systems characterised by inter-annual variability that makes it difficult to define an ecosystem state as stable or transient. Long-term studies of shallow lakes have tended to show gradual rather than step-changes in ecological conditions in response to reductions in nutrient concentration 15,35,36 . Although it has been suggested that regime shifts may occur slowly for some ecosystems 37 , regime shifts in shallow lakes have been characterised as catastrophic and occurring over short time scales 7 . ...
... Limnological information was extracted from an existing database established by local authorities as part of the Danish aquatic monitoring programme NOVANA (Persson et al., 1991;Jeppesen et al., 2006b). We analysed lakes that were sampled by both electrofishing along the shore and gillnetting at different depth strata (Kronvang et al., 1993;Søndergaard et al., 2005;Jeppesen et al., 2006aJeppesen et al., ) between 1989Jeppesen et al., and 2003. ...
... Shallow lakes are generally accepted as the best example of an ecosystem occupying alternative equilibria 14,[18][19][20] . Here, in place of a predictable, deterministic relationship between nutrients and phytoplankton biomass (chlorophyll-a), there exist two alternative equilibria, each state being reinforced by a suite of positive feedback mechanisms 9 . ...
... In this intermediate range of nutrient loads, an increase in emergent macrophyte richness and abundance due to lower levels of competitive exclusion overcompensates for the decrease in submerged macrophyte richness and abundance due to elevated water turbidity [67][68][69]. Jeppesen et al. [70] placed this intermediate range of nutrient loads between 50 and 150 μg/L TP for northern temperate lakes, while Romo et al. [71] suggested 50 μg/L TP as a critical threshold for Mediterranean lakes to avoid the shift to a turbid-water phase and preserve macrophyte dominance. ...
... With climate warming and the development of urbanization, industry, agriculture, and tourism in the region, many lakes have been facing many ecological degradation, including salinization, eutrophication, and macrophyte degradation . Some studies have shown different ecological response patterns to changes in trophic status for freshwater and brackish lakes (Hansson et al. 1990;Jeppesen et al. 1997;Amsinck et al. 2003). During the past century, the ecological shifts of many brackish and freshwater shallow temperate lakes due to an increase in nutrient loading have been studied (Moss 1994). ...
... The increased sedimentation rates of Ceriodaphnia sp. ephippia after~2005 probably reflects the preference of this genus for the littoral (Jeppesen et al. 2003). Littoral areas were subjected to reworking and resuspension during dredging, which artificially increased the sedimentation rates of Ceriodaphnia sp. ...
... There is some evidence that even a small increase in temperature may create a shift in turbid shallow lakes to a clear-water phase (Scheffer et al. 2001). Contrary to this view, Jeppesen et al. (2003) presented data showing that probability of a shift to the clear-water state in nutrient-rich lakes decreases with higher temperature. Studies of long-term effects of changing anthropogenic pressure on phytoplankton and macrophyte dynamics can provide useful information on the degree of environmental impairment and extrinsic and intrinsic factors stabilizing the alternative states of lake ecosystems. ...
... temporal resolution; more complex models can simulate shorter-term variations within lakes (Jensen et al. 2006;Andersen et al. 2020), but the sediment record cannot provide the necessary information. Consequently, long-term (> > annual) underlying trends can be studied, but as clearly demonstrated by Ginn et al. (2012), subannual lake-water TP variations are not reflected in sediment composition. ...
... This inference is supported by the high availability of phytoplankton, a food resource for zooplankton, which would not be a limiting resource. Zooplankton densities were suggested to be lower at both low and high macrophyte biomass, since the refuge function is counteracted by the high predation pressure within this vegetation (Jeppesen et al. 1998;Hargeby et al. 2005;Blindow et al. 2014). In Kakel Huincul lake higher macrophyte abundance started to develop ca. ...
... In general, the most important sources of anthropogenic N and P loads are the urban-, industrial-and agricultural runoffs, the direct inflow of untreated sewage, and the atmospheric deposition (Carpenter et al. 1998;Tang and Xie 2000;Jeppesen et al. 2003;Camarero and Catalan 2012). Moreover, the recent adverse shift in the P balance of the global fish production -caused by the intensifying use of fertilizers and modern feeds with high nutrient contents -is now also seriously threatening natural aquatic ecosystems (Huang et al. 2020). ...