Papers by Martin Søndergaard
Routledge eBooks, May 18, 2017
Ecological studies, 1998
Evidence from both empirical studies (Canfield et al., 1984; Jeppesen et al., 1990; Faafeng and M... more 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 conditions, even at high nutrient concentrations. Several factors seem to be involved, including both increased Zooplankton grazer control and nutrient constraint on phytoplankton, alterations in the physical environment that result in less wind-induced and fish-induced resuspension, and possibly also allelophatic effects (Jeppesen et al., 1990; Moss, 1990; Scheffer et al., 1993). A cross-analysis of survey data from 35 Danish brackish lakes revealed a significant decrease in Secchi depth with increasing concentrations of total phosphorus (TP); in contrast to freshwater lakes, however, transparency was independent of whether submerged macrophytes were present at high density (Jeppesen et al., 1994). Similarly, Moss (1994) found that nutrient-rich brackish lakes with extensive growth of submerged macrophytes tend to be in a turbid state. By using both empirical data and field experiments conducted in several brackish and freshwater shallow Danish lakes, we examine here how differences in top-down control may influence the turbidity of freshwater and brackish lakes in the macrophyte state.
Journal of Plankton Research, 1996
The impact of fish-mediated changes on the structure and grazing of zooplankton on phytoplankton ... more The impact of fish-mediated changes on the structure and grazing of zooplankton on phytoplankton and bacterioplankton was studied in Lake S0bygaard during the period 1984-92 by means of in vitro grazing experiments (14 C-labelled phytoplankton, 3 H-labelled bacterioplankton) and model predictions. Measured zooplankton clearance rates ranged from 0-25 ml I' 1 h" 1 on phytoplankton to 0-33 ml H h" 1 on bacterioplankton. The highest rates were found during the summer when Daphnia jpp. were dominant. As the phytoplankton biomass was substantially greater than that of bacterioplankton throughout the study period, ingestion of phytoplankton was 26-fold greater than that of bacterioplankton. Multiple regression analysis of the experimental data revealed that Daphnia spp., Bosmina longirostru and Cyclops vidnus, which were the dominant zooplankton, all contributed significantly to the variation in ingestion of phytoplankton, while only Daphnia spp. contributed significantly to that of bacterioplankton. Using estimated mean values for clearance and ingestion rates for different zooplankters, we calculated zooplankton grazing on phytoplankton and bacterioplankton on the basis of monitoring data of lake plankton obtained during a 9 year study period. Summer mean grazing ranged from 2 to 4% of phytoplankton production and 2% of bacterioplankton production to maxima of 53 and 88%, respectively. The grazing percentage decreased with increasing density of planktrvorous fish caught in August each year using gill nets and shoreline electrofishing.The changes along a gradient of planktivorous fish abundance seemed highest for bacterioplankton. Accordingly, the percentage contribution of bacterioplankton to the total ingestion of the two carbon sources decreased from a summer mean value of 8% in ZJap/tnia-dominated communities at lower fish density to 0.7-1.1% at high fish density, when cyclopoid copepods or Bosmina and rotifers dominated. Likewise, the percentage of phytoplankton production channelled through the bacteria varied, it being highest (5-8%) at high fish densities. It is argued that the negative impact of zooplankton grazing on bacterioplankton in shallow lakes is highest at intermediate phosphorus levels, under which conditions Daphnia dominate the zooplankton community.
Water Research, Nov 1, 2018
High ammonium loading can increase alkaline phosphatase activity and promote sediment phosphorus ... more High ammonium loading can increase alkaline phosphatase activity and promote sediment phosphorus release: a two-month mesocosm experiment,
Inland Waters, Jul 10, 2023
Encyclopedia of earth sciences, 2012
Adrian Shine investigator since 1973 Location of sightings and assessment In considering the loca... more Adrian Shine investigator since 1973 Location of sightings and assessment In considering the location of the "sightings" in Loch Ness, the following places seem to have been the most rewarding (see Figure 1
Elsevier eBooks, 2009
continued to recover from acidification (Keller et al., 2001a). Lead concentrations, lead isotope... more continued to recover from acidification (Keller et al., 2001a). Lead concentrations, lead isotopes, and spheroidal carbonaceous fly ash particles results were used in an isotope mixing model to quantify lead accumulation in an acidified lake in Sweden (Bindler et al., 2001). Recent trends and status of the effects of sulphur emissions from the Sudbury, Ontario metal smelting industry on lakes in Ontario, Canada was documented indicating a strong inverse relationship with distance to about 45 km being most pronounced in lakes within about 20 km (Keller et al., 2001b). Water quality effects of the management of Lac de Guiers (Guiers Lake) and use of its waters was reported with special emphasis on salinity and eutrophication (Cogels et al., 2001) whereas water quality of Lake Tohopekaliga, Florida and the effects of point-source removal were presented by Williams (2001). Movements of a hydrothermal plume with vertical and horizontal length scales of about 18 and 300 m, respectively were documented (Colomer et al., 2001). Another study quantifying the flux of hydrothermal fluids by use of helium isotopes indicated a subsurface helium source in Mono Lake (Clark and Hudson, 2001). Studies on spatial and temporal variability in water temperatures in the littoral zone of a multibasin lake suggested that the observed variability in water temperature would result in differences in the productivity of different portions of the littoral zone (Finlay et al., 2001). An assessment of the impact of Mingoa Stream on the bacteriological water quality of Municipal Lake of Yaoundé found that the stream contributed to the high levels of bacterial numbers in the lake (Jugnia and Sime-Ngando, 2001). Studies on the microbial cycling of dissolved free amino acids and protein in mesotrophic Lake Constance, Germany were conducted examining their release by phytoplankton and various heterotrophic organisms and incorporation by heterotrophic bacterioplankton (Rosenstock and Simon, 2001). Water quality, land use and aquatic macrophyte information from 62 coastal and inland wetlands in the Great Lakes basin concluded that species richness and community structure of macrophytes were a function of geographic location and water quality (Lougheed et al., 2001). Physical and chemical changes in water quality and phytoplankton community were collected from an artificial lake for seven years and the results showed that the relationship between water quality variables and phytoplankton community structure changed substantially (Kalin et al., 2001). Results on water chemistry, algae and trophic status of an
Freshwater Biology, Apr 10, 2015
1. Excess loading of phosphorus (P) and nitrogen (N) triggers a shift in the trophic structure of... more 1. Excess loading of phosphorus (P) and nitrogen (N) triggers a shift in the trophic structure of shallow lakes from a clear-water, macrophyte-dominated state to an algal-dominated turbid state. However, the role of N in the shift is debated, and experimental evidence is, with a few exceptions, based on short-term studies (days to a few months). 2. We studied the effect of N loading on macrophytes (dominated by Potamogeton lucens and Cabomba caroliniana), periphyton, filamentous algae and phytoplankton in mesocosms over 10 months (starting in October) in subtropical China (Wuhan). There were three N treatments: controls (CN) without nitrogen addition (mean TN = 1.9 mg L À1), low nitrogen (LN) addition (mean TN = 3.5 mg L À1) and high nitrogen (HN) addition (mean TN = 5.5 mg L À1). Total phosphorus (TP) concentration in the water column remained moderate (0.05-0.07 mg L À1) during the experiment in all treatments. 3. Macrophyte abundance declined in the LN and HN treatments in the first 6 months, but not in controls, followed by a partial recovery in the LN treatments. They disappeared completely in the HN treatments the following summer. Periphyton (biofilm on plastic) and phytoplankton biomass remained unaffected during the first 6 months but increased over the summer by two or three times, compared with controls, in low and high nitrogen treatments, respectively. By contrast, the abundance of filamentous algae increased over winter but declined during the summer with no obvious relationship to the N treatments. There was no difference in the TN or nitrate concentrations or soluble protein, soluble sugar and Chl-a content of P. lucens leaves and stems with increasing N load. 4. Macrophyte populations are partially resilient to abrupt increases in N loading at moderate TP concentrations, but, after prolonged exposure, a complete collapse occurs. Our results further indicate that macrophyte loss is exacerbated by shading by filamentous algae during the winter, and by phytoplankton and periphyton in the summer, while there was no indication of direct N toxicity.
Hydrobiologia, Apr 5, 2012
ABSTRACT Nutrient availability, in particular of phos-phorus (P), is a key factor for the structu... more ABSTRACT Nutrient availability, in particular of phos-phorus (P), is a key factor for the structure and functioning of shallow lakes, and not least the sediment plays an important role by acting as both a nutrient source and sink. We used 21 years of monthly mass balance and lake water data from six shallow (mean depth = 1.2–2.7 m) and fast flushed (mean hydraulic retention time = 0.6–2.6 months) eutrophic Danish lakes (mean summer P concentrations ranging from 0.09 to 0.61 mg/l) to investigate long-term trends in yearly and seasonal patterns of P retention. To one of the lakes, the external P input was reduced by 70% in the early 1990s, whereas none of the other lakes have experienced major changes in external P loading for more than 20 years. All lakes showed a distinct seasonal pattern with high P concentrations and typically negative P retention during summer (up to -300% of the external loading from May to August). During winter, P retention was overall positive (up to 50% of the external loading from December to April). Internal P loading from the sediment delayed lake recovery by approximately 10 years in the lake with the most recently reduced external loading, but in all the lakes net release of P from the sediment occurred during summer. P release in the six lakes has not abated during the past decade, indicating that the sediment of eutrophic and turbid shallow lakes remains a net source of P during summer. The seasonal variations in P retention became more pronounced with increasing P levels, and retention decreased with increasing temperature, but increased if clear water conditions were established.
Limnology and Oceanography, May 1, 2003
Water, Nov 4, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Hydrobiologia, Sep 7, 2015
The role of nitrogen (N) in the shift from a macrophyte-dominated state to a phytoplankton-domina... more The role of nitrogen (N) in the shift from a macrophyte-dominated state to a phytoplankton-dominated one at high N concentrations in shallow lakes is still debated. To elucidate possible toxic and ecological effects of high N on macrophyte growth, we conducted a short-term (40 day) study of a eutrophication-tolerant macrophyte, Vallisneria spinulosa (Hydrocharitaceae), incubated in pots in a mesocosm system subjected to different N concentrations (1, 3, and 5 mg l-1). Plant leaf and root length as well as growth rate decreased significantly with increased N concentrations, but most N-and P-related physiological parameters, including the soluble protein content, nitrate reductase activity, acid phosphatase activity, and tissue N and P contents, did not differ significantly among the N treatments. Only the alkaline phosphatase activity differed, being lower at high nitrogen loading, likely due to P limitation. Epiphyton and phytoplankton biomasses increased significantly with increasing N loading. Our results including a large number of physiological tests of the macrophytes, therefore, provide supporting evidence that the loss of submerged macrophytes, like V. spinulosa, seen at high N loading in shallow lakes, can be attributed to competition with phytoplankton and epiphyton rather than to toxic effects.
Marine Ecology Progress Series, 2003
The 3-spined stickleback Gasterosteus aculeatus often dominates fish communities in eutrophic, br... more The 3-spined stickleback Gasterosteus aculeatus often dominates fish communities in eutrophic, brackish, north-temperate lakes where it is thought to contribute significantly to the low zooplankton biomass and low grazing pressure on phytoplankton. To elucidate its effect on zooplankton community structure and phytoplankton biomass (chl a), we conducted a 5.5 mo enclosure experiment with sticklebacks at different densities in high nutrient concentrations and a salinity of 2 psu. Increasing fish density (0 to 10.2 sticklebacks m-2) led to substantial changes in the zooplankton community structure, an increase in phytoplankton chl a, and a reduction in water clarity. At densities below 4 to 6 sticklebacks m-2 , large-bodied cladocerans dominated the zooplankton biomass, the zooplankton:phytoplankton biomass ratio was high (>1), and chl a was accordingly low (< 20 µg l-1). At higher stickleback densities, large cladocerans disappeared and the abundance of small cladocerans was low. Instead, cyclopoid copepods and rotifers dominated, the zooplankton:phytoplankton biomass ratio was well below 0.5, and chl a exceeded 200 µg l-1 in late summer. The fish density level for a shift from a clear to a turbid state is low compared to the densities observed in several eutrophic, brackish lagoons. We conclude that fish have a strong impact on water clarity in shallow, eutrophic, brackish lakes with low salinity, which may explain the usually low zooplankton:phytoplankton biomass ratio and the turbid state of such aquatic environments. However, our results also indicate that once the density level declines to below 4 to 6 sticklebacks m-2 , a shift to a clear state is likely to occur.
Water Research, Apr 1, 2021
Phosphorus (P) release from sediment is a key process affecting the effectiveness of eutrophicati... more 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 the decomposition rates and oxygen consumption at the sediment water interface. To test the effect of different NO3- concentrations, we conducted a three-month experiment in 15 cement tanks (1 m3), with five targeted concentrations of NO3-: control, 2 mg L-1, 5 mg L-1, 10 mg L-1, and 15 mg L-1. The results showed that: i) when NO3- was maintained at high levels: NO3-≥5-7 mg L-1 (range of median values), there was no effect of NO3- on net P release from the sediment, likely because the positive effects of NO3- (increasing oxidation) was counteracted by a promotion of phytoplankton growth. ii) after NO3- addition was terminated NO3- dropped sharply to a low level (NO3-≤0.4 mg L-1), followed by a minor P release in the low N treatments but a significant P release in the high N treatments, which likely reflect that the inhibition effect of NO3- on P release decreased, while the promotion effects at high NO3- concentrations continued. The results thus supported our hypotheses of a dual effect on sediment P release and suggest dose-dependent effect of NO3- loading on stimulating P release from the sediment, being clear at high NO3- exceeding 5-7 mg L-1.
40, Dec 1, 2013
Moss kommune, i samarbeid med vannområdet Morsa, Østfold fylkeskommune og EU-prosjektet REFRESH, ... more 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 vaere et omfattende fokus på miljøtiltak i nedbørfeltet.
Marine Pollution Bulletin, 2022
Increased urea is one of the common nitrogen forms polluting coastal waters and affecting nutrien... more 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 ammonium and then nitrate (NO3-). ii) When nitrogen occurred as urea or ammonium, minor P release was observed. iii) After urea were mostly converted to NO3-, P release became clearer. iv) NO3- had a dual effect by promoting P release through decreasing sediment pH and increasing alkaline phosphatase activity or by inhibiting P release through improving sediment oxidation. v) The overall effects of urea on P release depended on the ultimate NO3- concentrations, being prominent when NO3- ≥ 11 mg N L-1. Our findings are of relevance when determining nitrogen reduction targets needed for combating eutrophication.
Shallow lakes and ponds undergo frequent temporary thermal stratification. How this affects green... more 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
Water
The water quality of lakes is highly dependent on external phosphorus (P) loading. The vast exter... more The water quality of lakes is highly dependent on external phosphorus (P) loading. The vast external loadings from sewage and other wastewater discharge that European lakes have historically received have been dramatically reduced today by improved wastewater treatment. Gaining knowledge of the catchment characteristics that influence external P-loading should enable predictions of the achievable water quality of lakes. In this study, we tested this proposition. Data from 90 new Danish lakes show no apparent relationship between the mean summer P-concentration and the size or land use of the catchments. The external P-loading and resulting annual P-concentration were further investigated on a representative subset of 12 of the new lakes, using six methods. Three of the methods used empirical estimates of P-transport from catchments, based on the national average P-transport, runoff-dependent P-transport, and crop-dependent P-transport, and the other three methods used different empi...
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Papers by Martin Søndergaard