SUMMARY1. 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 cha...

Isotope turnover in muscle of ectotherms depends primarily on growth rather than on metabolic replacement. Ectotherms, such as fish, have a discontinuous pattern of growth over the year, so the isotopic signature of muscle (delta13C and delta15N) may only reflect food consumed during periods of growth. In contrast, the liver is a regulatory tissue, with a continuous protein turnover. Therefore, the isotopic composition of liver should respond year round to changes in the isotopic signature of food sources. Therefore, we predicted that (1) Whitefish in Lake Geneva would have larger seasonal variation in the isotopic variation of the liver compared to that of the muscle tissue, and (2) the isotope composition of fish muscle would reflect a long-term image of the isotope composition of the food consumed only throughout the growth period. To test these expectations, we compared the isotope compositions of Whitefish muscle, liver and food in a 20-month study. We found that the seasonal amplitude of isotope variation was two to three times higher in liver compared to muscle tissue. During the autumn and winter, when growth was limited, only the isotopic signature of liver responded to changes in the isotope composition of the food sources. The delta13C and delta15N of muscle tissue only reflected the food consumed during the spring and summer growth period.

10.1007/s10750-012-1182-1Contact CEH NORA team at noraceh@ceh.ac.ukThe NERC and CEH trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. form, nor will it be during the first three months after its submission to Hydrobiologia."Corresponding author: Erik Jeppesen (ej@dmu.dk)We dedicate this paper to the late Prof. Jürgen Benndorf, a true pioneer and mentor in lake and reservoir management oriented research, who inspired a number of us to initiate longterm comprehensive experimental ecological studies on lakes and reservoirs. AbstractFish play a key role in the trophic dynamics of lakes. With climate warming, complex changes in fish assemblage structure may be expected owing to direct effects of temperature and indirect effects operating through eutrophication, water level changes, stratification and salinisation. We reviewed published and new long-term (10-100 years) fish data series from 24 European lakes (area: 0.04-5648 km 2 ; mean depth: 1-177m; a north-south gradient from 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 4 Sweden to Spain). Along with an annual temperature increase of about 0.15-0.3 °C per decade profound changes have occurred in either fish assemblage composition, body size and/or age structure during recent decades and a shift towards higher dominance of eurythermal species.These shifts have occurred despite a reduction in nutrient loading in many of the lakes that should have benefited the larger-sized individuals and the fish species typically inhabiting cold-water, low-nutrient lakes. The cold-stenothermic Arctic charr has been particularly affected and its abundance has decreased in the majority of the lakes where its presence was recorded. The harvest of cool-stenothermal trout has decreased substantially in two southern lakes. Vendace, whitefish and smelt show a different response depending on lake depth and latitude. Perch has apparently been stimulated in the north, with stronger year classes in warm years, but its abundance has declined in the southern Lake Maggiore, Italy. Where introduced, roach seems to take advantage of the higher temperature after years of low population densities. Eurythermal species such as common bream, pike-perch and/or shad are apparently on the increase in several of the lakes. The response of fish to the warming has been surprisingly strong and fast in recent decades, making them ideal sentinels for detecting and documenting climate-induced modifications of freshwater ecosystems.

The scales of whitefish Coregonus lavaretus were used in place of dorsal muscle, which necessitates killing the fish, to study food webs from the δ13C and δ15N isotopic ratios in the organic fraction. As scales are composed of both organic and calcified fractions, a protocol for scale decalcification was first devised. The δ13C and δ15N values of the decalcified scales were then shown to be closely correlated to those of the dorsal muscle, demonstrating that scales could be used in place of muscle to study food webs. Changes in the δ13C of whitefish were determined from a scale collection that extended over the period during which the trophic state of Lake Geneva was recovering.

The contributions presented at the European Inland Fisheries Advisory Commission Symposium on The Effects of Fisheries Management Practises on Freshwater Ecosystems in 2002 are reviewed. The principal mechanisms of inland fisheries management concentrate on four categories: fish stock enhancement (stocking and introductions); rehabilitation and habitat manipulation for fisheries purposes, including biomanipulation; fisheries regulations; and conservation and protection of fish and fisheries. The negative and beneficial impacts of these activities are summarised and options for improving the outputs of fisheries management practices to accrue wider benefits to society are discussed. Wider stakeholder participation and a shift from traditional fisheries towards ecosystem-based management approaches are the main mechanism proposed. This calls for new management tools to cater for legitimate human demand for water abstraction, hydropower generation and effluent disposal, as well as alternative commercial use of water bodies such as bathing, boating and tourism, in addition to fisheries exploitation and conservation needs.biomanipulation, fish conservation, fish stock enhancement, fishery rehabilitation, inland fisheries management.