J. P. Jensen's research while affiliated with Marine Environmental Research Institute and other places

Publications (15)

Article
Major efforts have been made world-wide to improve the ecological quality of shallow lakes by reducing external nutrient loading. These have often resulted in lower in-lake total phosphorus (TP) and decreased chlorophyll a levels in surface water, reduced phytoplankton biomass and higher Secchi depth. Internal loading delays recovery, but in north...
Chapter
Major efforts have been made worldwide to improve the ecological quality of shallow lakes by reducing external nutrient loading. These have often resulted in lower in-lake total phosphorus (TP) and decreased chlorophyll a levels in surface water, reduced phytoplankton biomass and higher Secchi depth. Internal loading delays recovery, but in north t...
Article
Abstract –  The horizontal distribution of fish in lakes varies with species, age, predation risk, vegetation coverage and water clarity. Although sporadic data are available for specific lakes, little is known about how habitat distribution generally changes along a gradient in nutrients and clarity. Here we analyse littoral and pelagic fish catch...
Article
To study how changes in biomass of cyprinids (mainly roach, Rutilus rutilus L., and bream, Abramis brama L.) affect nitrogen retention in shallow lakes, we conducted mass balances of total nitrogen for 6-11 years in four eutrophic lakes in which the fish biomass changed markedly, either from natural causes or due to manipulation. The decline in cyp...
Article
Full-text available
Phytoplankton dominance (as biomass) by heterocystous cyanobacteria, nonheterocystous cyanobacteria, and chlorophytes was studied along a trophic gradient (0.011-2.2 mg P.L(-1)) by analyzing regularly collected semiquantitative data from 178 shallow Danish lakes (mean depth <3 m) and quantitative data from 32 lakes. Heterocystous cyanobacteria were...
Article
The effects of nutrients on the biological structure of brackish and freshwater lakes were compared. Quantitative analysis of late summer fish, zooplankton, mysid and macrophyte populations was undertaken in 20–36 shallow brackish lakes of various trophic states and the findings compared with a similar analysis of shallow freshwater lakes based on...
Article
The effects of fish stock reduction have been studied in 3 Dutch lakes (Lake Zwemlust, Lake Bleiswijkse Zoom and Lake Noorddiep) and 1 Danish lake (Lake Væng) during 4–5 years. A general response is described. The fish stock reduction led in general to a low fish stock, low chlorophyll-a, high Secchi-disc transparency and high abundance of macrophy...
Chapter
The effects of nutrients on the biological structure of brackish and freshwater lakes were compared. Quantitative analysis of late summer fish, zooplankton, mysid and macrophyte populations was undertaken in 20–36 shallow brackish lakes of various trophic states and the findings compared with a similar analysis of shallow freshwater lakes based on...
Article
In order to evaluate short-term and long-term effects of fish manipulation in shallow, eutrophic lakes, empirical studies on relationships between lake water concentration of total phosphorus (P) and the occurrence of phytoplankton, submerged macrophytes and fish in Danish lakes are combined with results from three whole-lake fish manipulation expe...
Article
The use of fish manipulation as a tool for lake restoration in eutrophic lakes has been investigated since 1986 in three shallow, eutrophic Danish lakes. The lakes differ with respect to nutrient loading and nutrient levels (130–1000 µg P l−1, 1–6 mg N l−1). A 50% removal of planktivorous fish in the less eutrophic cyanobacteria-diatom dominated La...

Citations

... Combined reductions in both N by ∼50% and P by ∼56% from load inputs resulted in significant declines in nutrient concentrations, primary production and phytoplankton biomass and increased deep water macroalgae cover in Danish coastal area (Riemann et al., 2016). The decline in phytoplankton resulting from nutrient load reduction has distinctly impacted zooplankton abundance, community composition, zooplankton:phytoplankton abundance ratio, and individual size, via cascading trophic interactions (Hardy et al., 1986;Jeppesen et al., 2007;Chen et al., 2012). The longterm variation in zooplankton assemblages is an effective and comprehensive indicator to reflect and assess the recovery and health of coastal ecosystems in response to eutrophication management, such as nutrient load reduction. ...
... In such lakes, bottom sediments in particular can be the main source of phosphorus, instead of acting as a trap for phosphorus [28,29]. The intensity and duration of the process of phosphorus release from bottom sediments to the overlying waters has a significant impact on the concentration of this element in lake water and, consequently, on water quality [30]. The process of phosphorus release from bottom sediments plays a significant role in lake eutrophication [29]. ...
... In zoete wateren is dit een belangrijke parameter voor de vestiging en groei van waterplanten. Over het belang van doorzicht in brakke wateren bestaat onduidelijkheid: aan de ene kant suggereert de wetenschappelijke literatuur dat ondergedoken waterplanten in brakke wateren onder aanmerkelijk troebelere condities kan groeien (in vergelijking met zoete wateren; zie Jeppesen et al., 1994;Moss et al., 1994). Aan de andere kant zijn kenmerkende brakwatersoorten (zoals Ruppia en kranswieren (Chara) sterk gevoelig voor eutrofiëring (Verhoeven et al., 1978a(Verhoeven et al., ,b, 1979 ...
... Danish scientists confirmed the presence of a systematic correlation between transparency and macrophyte abundance in large lakes. For example, Jensen et al., (1991) and Jeppesen (1990) showed that a large number of shallow lakes with a well-developed vegetation cover have higher transparency than lakes without dense vegetation. However, this result is based on an assessment of the presence and absence of (dense) vegetation and can have several alternative explanations: ...
... The empirical model was developed on the basis of different existing nutrient retention models. It associates mean long-term nutrient concentration in water bodies with nutrient inputs, total loss rate to the atmosphere, flushing rate, and sediment (Kirchner and Dillon, 1975;Vollenweider, 1975;Jeppesen et al., 1998;Brett and Benjamin, 2008). The phosphorus retention rate could be expressed as follows: ...
... In productive ecosystems, where the level of nutrients is relatively high, external loading of terrestrial organic matter with their nutrients may further accelerate eutrophication, leading to absolute dominance by cyanobacteria or chlorophytes (Jensen et al. 1994;Lürling et al. 2018). This, in turn, may lower the food quality due to a decreasing EPA content of seston (Persson et al. 2007;Taipale et al. 2018), resulting in the observed negative effect of terrestrial organic matter on zooplankton (Carpenter et al. 2005;Pace et al. 2007;Mehner et al. 2016;Taipale et al. 2016). ...
... Morphometric and chemical data for the five lakes are outlined inTable 1 and described in detail in Landkildehus et al. (2002) and Jensen et al. (2002). All study lakes are generally nutrient-poor, but varied considerably as to lake area and depth. ...
... For fresh waters, the ratio of 13 C to its lighter isotope 12 C is used to distinguish benthic carbon sources, which tend to have an enriched isotope ratio relative to limnetic, terrestrial, or profundal carbon sources (Vander Zanden and Rasmussen, 1999;Jeppesen et al., 2002). The ratio of 15 N to its lighter isotope 14 N reflects trophic position (Fry, 2006). ...
... Water clarity can also affect fish habitat distribution (Blaber and Blaber 1980;Skov et al. 2002;Jacobsen et al. 2004;Jeppesen et al. 2006;Pekcan-Hekim et al. 2010;Nurminen et al. 2010). High turbidity can reduce the predation risk and thereby enhance the foraging activity of the prey fish (Gregory and Northcote 1993). ...
... Submerged macrophytes play critical roles in many key ecological processes of lake ecosystems, such as water purification and environmental heterogeneity, and further provide extensive habitats and food resources for algae, benthic organisms, and fish (Timms and Moss, 1984;Carpenter and Lodge, 1986;Dvořák, 1996). However, the ecological functions of submerged macrophytes are affected by their areal distribution and community structure (Dale, 1986;Jeppesen et al., 1990;Schriver et al., 1995). ...