| Abstract | SUMMARY
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 lg L)1 before loading reduction), subtropical to
temperate (latitude: 28-65), and lowland to upland (altitude: 0-481 m). Shallow northtemperate
lakes were most abundant.
2. Reduction of external total phosphorus (TP) loading resulted in lower in-lake TP
concentration, lower chlorophyll a (chl a) concentration and higher Secchi depth in most
lakes. Internal loading delayed the recovery, but in most lakes a new equilibrium for TP was reached after 10-15 years, which was only marginally influenced by the hydraulic
retention time of the lakes. With decreasing TP concentration, the concentration of soluble
reactive phosphorus (SRP) also declined substantially.
3. Decreases (if any) in total nitrogen (TN) loading were lower than for TP in most lakes. As
a result, the TN : TP ratio in lake water increased in 80% of the lakes. In lakes where the
TN loading was reduced, the annual mean in-lake TN concentration responded rapidly.
Concentrations largely followed predictions derived from an empirical model developed
earlier for Danish lakes, which includes external TN loading, hydraulic retention time and
mean depth as explanatory variables.
4. Phytoplankton clearly responded to reduced nutrient loading, mainly reflecting
declining TP concentrations. Declines in phytoplankton biomass were accompanied by
shifts in community structure. In deep lakes, chrysophytes and dinophytes assumed
greater importance at the expense of cyanobacteria. Diatoms, cryptophytes and chrysophytes
became more dominant in shallow lakes, while no significant change was seen for
cyanobacteria.
5. The observed declines in phytoplankton biomass and chl a may have been further
augmented by enhanced zooplankton grazing, as indicated by increases in the zooplankton
: phytoplankton biomass ratio and declines in the chl a : TP ratio at a summer mean TP
concentration of <100-150 lg L)1. This effect was strongest in shallow lakes. This implies
potentially higher rates of zooplankton grazing and may be ascribed to the observed large
changes in fish community structure and biomass with decreasing TP contribution. In 82%
of the lakes for which data on fish are available, fish biomass declined with TP. The
percentage of piscivores increased in 80%of those lakes and often a shift occurred towards
dominance by fish species characteristic of less eutrophic waters.
6. Data on macrophytes were available only for a small subsample of lakes. In several of
those lakes, abundance, coverage, plant volume inhabited or depth distribution of
submerged macrophytes increased during oligotrophication, but in others no changes
were observed despite greater water clarity.
7. Recovery of lakes after nutrient loading reduction may be confounded by concomitant
environmental changes such as global warming. However, effects of global change
are likely to run counter to reductions in nutrient loading rather than reinforcing
re-oligotrophication. |
| Authors | ERIK JEPPESEN, 1 , 2 MARTIN SØNDERGAARD,1 JENS PEDER JENSEN,1 KARL E. HAVENS,3 ORLANE ANNEVILLE,4 LAURENCE CARVALHO,5 MICHAEL F. COVENEY,6 RAINER DENEKE,7 MARTIN T. DOKULIL, 8 BOB FOY,9 DANIEL GERDEAUX,4 STEPHANIE E. HAMPTON,10 SABINE HILT,11 KU¨ LLI KANGUR,12 JAN KO¨ HLER,11 EDDY H.H.R. LAMMENS,13 TORBEN L. LAURIDSEN,1 MARINA MANCA,14 MARI´A R. MIRACLE,15 BRIAN MOSS,16 PEETER NO~ GES,17 GUNNAR PERSSON,17 GEOFF PHILLIPS,18 ROB PORTIELJE,13 SUSANA ROMO,15 CLAIRE L. SCHELSKE,19 DIETMAR STRAILE,20 ISTVAN TATRAI,21 EVA WILLE´ N17 AND MONIKA WINDER10 |
| Text | 52862 2005 10.1111/j.1365 2427.2005.01415.x ISI Web of Science WOS 000231860600013 fish macrophytes nutrient oligotrophication plankton Lake responses to reduced nutrient loading an analysis of contemporary data from 35 European and North American long term studies ERIK JEPPESEN, 1 , 2 MARTIN SØNDERGAARD,1 JENS PEDER JENSEN,1 KARL E. HAVENS,3 ORLANE ANNEVILLE,4 LAURENCE CARVALHO,5 MICHAEL F. COVENEY,6 RAINER DENEKE,7 MARTIN T. DOKULIL, 8 BOB FOY,9 DANIEL GERDEAUX,4 STEPHANIE E. HAMPTON,10 SABINE HILT,11 KU¨ LLI KANGUR,12 JAN KO¨ HLER,11 EDDY H.H.R. LAMMENS,13 TORBEN L. LAURIDSEN,1 MARINA MANCA,14 MARI´A R. MIRACLE,15 BRIAN MOSS,16 PEETER NO GES,17 GUNNAR PERSSON,17 GEOFF PHILLIPS,18 ROB PORTIELJE,13 SUSANA ROMO,15 CLAIRE L. SCHELSKE,19 DIETMAR STRAILE,20 ISTVAN TATRAI,21 EVA WILLE´ N17 AND MONIKA WINDER10 Department of Freshwater Ecology, National Environmental Research Institute, Silkeborg, Denmark 2Department of Plant Biology, University of Aarhus, Aarhus, Denmark 3Department of Fisheries and Aquatic Sciences, University of Florida, FL, U.S.A. 4INRA, Centre Alpin de Recherche sur les Re´seaux Trophiques des Ecosyste`mes Limniques, Station d Hydrobiologie Lacustre, Universite´ de Savoie, Cedex, France 5Centre for Ecology and Hydrology, Edinburgh, Bush Estate, Penicuik, Scotland 6Water Resources Department/Environmental Sciences Division, St Johns River Water Management District, Palatka, FL, U.S.A. 7Brandenburg University of Technology BTUC , Research Station Bad Saarow, Bad Saarow, Germany 8Institute for Limnology, Mondsee, Austria 9Agricultural and Environmental Science Division, Newforge Lane, Belfast, U.K. 10University of Washington, School of Aquatic and Fishery Sciences, Seattle, WA, U.S.A. 11Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany 12Vo rtsja¨rv Limnological Station, Institute of Zoology and Botany, Estonian Agricultural University, Estonia 13RIZA, Lelystad, The Netherlands 14CNR, Pallanza, Italy 15A ´ rea de Ecolog ´a, Facultad de Biolog ´a, Ed. Investigacio´n, Campus Burjasot, Valencia, Spain 16School of Biological Sciences, Derby Building, University of Liverpool, Liverpool, U.K. 17Department of Environmental Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden 18Environment Agency, National Ecology Technical Team, Reading, U.K. 19Department of Geological Sciences, Land Use and Environmental Change Institute, University of Florida, Gainesville, FL, U.S.A. 20Limnologisches Institut, Fachbereich Biologie, Universita¨t Konstanz, Konstanz, Germany 21Limnological Research Institute, Hungarian Academy of Sciences, Tihany, Klebelsberg, Hungary SUMMARY 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 lg L 1 before loading reduction , subtropical to temperate latitude 28 65 , and lowland to upland altitude 0 481 m . Shallow northtemperate lakes were most abundant. 2. Reduction of external total phosphorus TP loading resulted in lower in lake TP concentration, lower chlorophyll a chl a concentration and higher Secchi depth in most lakes. Internal loading delayed the recovery, but in most lakes a new equilibrium for TP was reached after 10 15 years, which was only marginally influenced by the hydraulic retention time of the lakes. With decreasing TP concentration, the concentration of soluble reactive phosphorus SRP also declined substantially. 3. Decreases if any in total nitrogen TN loading were lower than for TP in most lakes. As a result, the TN TP ratio in lake water increased in 80% of the lakes. In lakes where the TN loading was reduced, the annual mean in lake TN concentration responded rapidly. Concentrations largely followed predictions derived from an empirical model developed earlier for Danish lakes, which includes external TN loading, hydraulic retention time and mean depth as explanatory variables. 4. Phytoplankton clearly responded to reduced nutrient loading, mainly reflecting declining TP concentrations. Declines in phytoplankton biomass were accompanied by shifts in community structure. In deep lakes, chrysophytes and dinophytes assumed greater importance at the expense of cyanobacteria. Diatoms, cryptophytes and chrysophytes became more dominant in shallow lakes, while no significant change was seen for cyanobacteria. 5. The observed declines in phytoplankton biomass and chl a may have been further augmented by enhanced zooplankton grazing, as indicated by increases in the zooplankton phytoplankton biomass ratio and declines in the chl a TP ratio at a summer mean TP concentration of <100 150 lg L 1. This effect was strongest in shallow lakes. This implies potentially higher rates of zooplankton grazing and may be ascribed to the observed large changes in fish community structure and biomass with decreasing TP contribution. In 82% of the lakes for which data on fish are available, fish biomass declined with TP. The percentage of piscivores increased in 80%of those lakes and often a shift occurred towards dominance by fish species characteristic of less eutrophic waters. 6. Data on macrophytes were available only for a small subsample of lakes. In several of those lakes, abundance, coverage, plant volume inhabited or depth distribution of submerged macrophytes increased during oligotrophication, but in others no changes were observed despite greater water clarity. 7. Recovery of lakes after nutrient loading reduction may be confounded by concomitant environmental changes such as global warming. However, effects of global change are likely to run counter to reductions in nutrient loading rather than reinforcing re oligotrophication. 50 Lake responses to reduced nutrient loading an analysis JEPPESEN_ETAL_2005.pdf Articolo in rivista Blackwell Scientific Publications. 0046 5070 Freshwater biology Print Freshwater biology Print Freshw. biol. Print marinamarcella.manca MANCA MARINA MARCELLA TA.P04.016.004 Ecologia teorica e applicata degli ecosistemi acquatici |
