Frank Landkildehus

Biomanipulation as a Restoration Tool to Combat Eutrophication: Recent Advances and Future Challenges

Eutrophication resulting from high nutrient loading has been the paramount environmental problem for lakes world-wide for the past four decades. Efforts are being made in many parts of the world to reduce external nutrient loading via improved wastewater treatment or diversion of nutrient-rich inflows. However, even after a reduction of the external phosphorus loading, the effects obtained may be unsatisfactory. This may reflect an insufficient reduction in the external nutrient loading to effectively limit phytoplankton growth. However, the lack of success may also be due to chemical or biological within-lake inertia preventing or delaying improvements. To overcome the resilience and thereby reinforce recovery, a number of physico-chemical and biological restoration methods have been developed. n nIn this chapter, we describe recent developments of biological restoration methods related to eutrophication, their short-term and long-term effects, and discuss the possibility of using combined physico-chemical and biological methods to improve the long-term stability of restoration and to reduce restoration costs. As comprehensive reviews of the effect of fish manipulation in cold temperate lakes are numerous, for these waterbodies, we highlight recent results, including effects on biodiversity and metabolism, and present new approaches of biomanipulation. Our particular focus is, however, directed at biomanipulation in warm lakes and on combined treatments which are far less well described in the literature.

Reconstructing the historical changes in Daphnia mean size and planktivorous fish abundance in lakes from the size of Daphnia ephippia in the sediment

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 were related to the size of Daphnia ephippia (dorsal length) in the surface sediment (0-1 cm) of 52 mainly shallow lakes with contrasting densities of fish and nutrients (TP: 0.002-0.60 mg P l-1). Density of fish expressed as catch per unit effort, in terms of numbers in multiple mesh-sized gill nets (CPUEn), decreased significantly with increasing mean size of ephippia. The relationship was improved by adding TP as an independent variable, now explaining 90% of the variation in CPUEn on the full data set covering lakes in Denmark, Greenland and New Zealand, and 78% if only data on Danish lakes were used. CPUE by weight of planktivorous fish and mean weight of Daphnia in the pelagial during summer were also related to ephippial size. By including contemporary data on established relationships between the sizes of egg-bearing female Daphnia and ephippia, we inferred changes in the CPUEn, mean size of ephippia-bearing Daphnia and summer mean body weight of Daphnia from ephippial size in four lakes during the past 1-2 centuries. In a hypertrophic lake subject to periodic fish kills, Daphnia mean body weight was high and CPUEn was low compared with those in two eutrophic lakes, while CPUEn was low and Daphnia body weight was high in the least eutrophic, clearwater lake. Estimated CPUEn and Daphnia mean weight in the surface sediment of these four lakes corresponded well with contemporary data. Only small changes in ephippial size with time were observed in the clearwater lake and in one of the lakes that had suffered early eutrophication, while major changes occurred in the two other lakes that had been subjected to a major increase in nutrient input or fish kills. We conclude that Daphnia ephippia preserved in the surface sediments of lakes may be a useful and efficient method to quantify the present-day abundance of planktivorous fish and Daphnia mean size. The method is particularly valid in surveys aimed to give a general picture of the fish stock and the ecological state in a set of lakes in a region rather than a precise estimate for a single lake. Though some evidence is provided, more work is needed to evaluate whether the equations are valid for hind-casting in down-core palaeoecological studies.

Fish and crustaceans in northeast Greenland lakes with special emphasis on interactions between Arctic charr (Salvelinus alpinus), Lepidurus arcticus and benthic chydorids

We studied the trophic structure in the pelagial and crustacean remains in the surface 1 cm of the sediment of 13 shallow, high arctic lakes in northeast Greenland (74° N). Seven lakes were fishless, while the remaining six hosted a dwarf form of Arctic charr (Salvelinus alpinus). In fishless lakes, Daphnia pulex was abundant, while no daphnids were found in the pelagial of lakes with fish. In fish lakes, the zooplankton community was dominated numerically by cyclopoid copepods and rotifers. Both lake sampling and analysis of remains in the top 1 cm of the sediment indicated that the phyllopod, Lepidurus arcticus, occurred in all fishless lakes, but was either absent or present in low densities from lakes with fish. Adult Lepidurus are mainly predators and forage in the top layer of the sediment. An analysis of surface sediment revealed low abundance of the benthic chydorids Alona sp. and Macrothrix sp. in lakes with Lepidurus, while they were abundant in lakes with fish. The low abundance in fishless lakes could not be explained by damage of crustacean remains caused by Lepidurus feeding in the sediment, because remains of the more soft-shelled, pelagic-living Daphnia were abundant in the sediment of these lakes. No significant differences between lakes with and without fish were found in chlorophyll a, total phosphorus, total nitrogen, conductivity or temperature, suggesting that the observed link between Lepidurus arcticus and the benthic crustacean community is causal. Consequently, remains of crustaceans in high arctic lake sediments may be useful for detecting the impact of past climate change on top-down control by fish. Not only remains of pelagic species, but also of Lepidurus and some benthic chydorids, may be used to detect changes in fish abundance and predation pressure in the past.

Reconstructing the salinity and environment of the Limfjord and Vejlerne Nature Reserve, Denmark, using a diatom model for brackish lakes and fjords

Diatoms in surface sediments from a data set of 27 brackish lakes and nine fjords in Jutland, Denmark (range 0.2 x96 31 g·Lx961 total dissolved solids (TDS)), were analysed using multivariate methods to determine response to measured parameters (depth, total phosphorus (TP), total nitrogen (TN), TN/TP, salinity, water body type). Water body type, salinity, depth and TP together explained 25.3% of the variation in the diatom data and were all independently significant predictors. A diatomx96salinity model (r2jack = 0.887, root mean square error of prediction = 0.246 log salinity, g·Lx961) was developed from the 36 sample training set and applied to fossil diatom assemblages in three sediment cores from the east Vejlerne wetland, Denmark, a nature reserve created after the damming of an embayment of the polyhaline Limfjord (~26 g·Lx961 TDS) in the late 19th century. The diatomx96inferred salinity reconstructions reflect the known salinity history of the Limfjord and the freshwaterx96subsaline Vejlerne lakes, and appear s...

Interactions between piscivores, zooplanktivores and zooplankton in submerged macrophytes: preliminary observations from enclosure and pond experiments

The effects of piscivores upon zooplanktivore behaviour anddistribution and the impact of zooplanktivores on the abundance anddistribution of zooplankton are well documented. However, thepotential indirect effect of piscivores reducing the predationpressure upon grazing zooplankton through behavioural changes ofzooplanktivores has received little attention, even though this maybe an important mechanism in enhancing the stability of submergedmacrophytes in shallow lakes. Preliminary observations from anunreplicated large-scale field enclosure experiment and areplicated pond experiment suggest that this mechanism is plausiblewith the set of piscivores (pike Esox lucius and perch Perca fluviatilis) and the zooplanktivores (0+ roach Rutilusrutilus and perch) common in temperate Europe. The presence ofpiscivores typically changed the habitat use and the activity levelof zooplanktivores and the presence of zooplanktivores typicallychanged the habitat selection of cladoceran zooplankton. In thecase of piscivore/zooplanktivore interactions, the risk ofpredation was enough to generate clear responses even where thelosses to predation were low. However, only in the enclosureexperiment was an indirect impact of the presence of piscivores,enabling Daphnia spp. to utilise open water in the presenceof a high density of zooplanktivorous fish observed. Whether themagnitude and direction of the effect of piscivores is sufficientto benefit zooplankton may depend on the functional group (capableof foraging within structured habitats) of the predator (bothpiscivore and zooplanktivore), absolute and relative densities ofpredator and prey and predator dietary choice.

Landlocked Arctic charr (Salvelinus alpinus) population structure and lake morphometry in Greenland - is there a connection?

Abstract Landlocked Arctic charr (Salvelinus alpinus) populations in sub-Arctic and Arctic Greenland lakes were sampled with multi-mesh-sized survey gillnets. The study covered a range of small shallow lakes (0.01u2009km2, maximum depth <3.3u2009m) to large deep lakes (43u2009km2, maximum depth >200u2009m). Arctic charr were found in one to three different forms in lakes with maximum depths >3u2009m. A dwarf form occurred in all lakes inhabited by Arctic charr and was the only form in lakes with maximum depths <8u2009m. In deeper lakes with maximum depths >20u2009m and a surface area <0.5u2009km2, larger charr were found, although in low numbers, the length-frequency distribution being unimodal with a tail towards large sizes. In lakes with a maximum depth >20u2009m, large-sized charr were more abundant, and the length-frequency distribution of the population was bimodal, with a first mode around 10–12u2009cm and a second mode around 26–37u2009cm. In a single large and deep lake, a distinct medium-sized pelagic zooplankton-eating charr form occurred. Maximum size of individual charr was significantly positively correlated with lake maximum depth and volume, and the mean size of large-sized charr was significantly positively correlated with lake volume. Our study indicates that the charr population structure became more complex with increasing lake size. Moreover, the population structure seemed to be influenced by lake-water transparency and the presence or absence of three-spined stickleback (Gasterosteus aculeatus).

Focused groundwater discharge of phosphorus to a eutrophic seepage lake (Lake Væng, Denmark): implications for lake ecological state and restoration

A study on Lake Væng in Denmark demonstrates a high potential for loading of phosphorous via groundwater to seepage lakes. Groundwater discharges are displayed as an important source of phosphorous to a lake due to: (1) high concentrations in the aquifer just below the lake, and (2) the main flow paths through the aquifer–lakebed interface either being overland flow through a seepage face, or focused in zones with very high discharge rates. In-lake springs have measured discharge of up to 7.45xa0m3 per m2 of lakebed per day. These findings were based on seepage meter measurements at 18 locations, stable isotope (δ18O) analyses, temperature profiles and mapping of ice cover distribution. Groundwater–lake interaction was modelled with a 2D conceptual flow model (MODFLOW) with hydrogeology interpreted from catchment multi electrode profiling, on-lake ground-penetrating radar, well logging and borehole data. Discharge was found to be much focused and opposite to expected increase away from the shoreline. The average total phosphorus concentration in discharging groundwater sampled just beneath the lakebed was 0.162xa0mg TP/l and thereby well over freshwater ecological thresholds (0.043–0.612, median = 0.117xa0mg TP/l). The study illustrates a direct link between groundwater and lake chemistry.RésuméUne étude sur le lac Væng au Danemark montre un haut potentiel de décharge de phosphore par la nappe dans des lacs d’émergence. Les décharges d’eau sont présentées comme une étant une importante source de phosphore dans un lac en raison: i) de hautes concentrations dans l’aquifère juste en dessous du lac, et ii) des principaux chenaux découlement à travers l’interface aquifère-fond du lac qui sont soit un écoulement en nappe à travers une surface d’exfiltration soit focalisés dans des zones à très haut taux de débit de débordement. Les sources sous lacustres ont un débit de débordement de jusqu’à to 7.45xa0m3 par m2 de lit de lac pa rjour. Ces découvertes sont basées sur les mesures de débordement en 18 emplacements, analyses d’isotope stable (δ18O), profils de température et cartographie de la distribution de la couverture de glace. L’interaction nappe-lac a été modélisée avec un modèle conceptuel d’écoulement 2D (MODFLOW), l’hydrogéologie interprétée avec saisie de profils multi électrodes, données radar pénétrant le fond du lac et forage carottage. On a trouvé une décharge très localisée et opposée à l’augmentation attendue à l’écart de la ligne de rivage. La concentration moyenne totale en phosphate dans l’eau de décharge de la nappe échantillonnée juste sous le fond du lac est 0.162xa0mg TP/l et par là bien au dessus des seuils écologiques de l’eau douce (0.043–0.612, médiane = 0.117xa0mg TP/l). L’étude illustre un lien direct entre la chimie de l’eau souterraine et celle du lac.ResumenUn estudio del lago Væng en Dinamarca demostró un alto potencial de la carga de fósforo a través del agua subterránea a los lagos de filtración. La descarga de agua subterránea son presentados como una fuente importante de fósforo hacia un lago debido a: i) altas concentraciones en el acuífero justamente debajo del lago, y ii) las trayectorias principales de flujo a través de la interfase acuífero–lecho del lago, tanto siendo el flujo superficial a través de la fase de filtración como el concentrado en zonas con muy altas tasas de descarga. En los manantiales dentro del lago se han medido descargas de hasta 7.45xa0m3 por m2 de lecho del lago por día. Estos hallazgos estuvieron basados en mediciones de filtración en 18 sitios, análisis de isótopos estables (δ18O), perfiles de temperatura y mapeo de distribución de la cubierta de hielo. La interacción agua subterránea–lago fue modelada con un modelo de flujo conceptual 2 D (MODFLOW) con la hidrogeología interpretada a partir de perfilajes multi electrodos en la cuenca, de georradar en el lago, de perfilajes de pozos y datos de las perforaciones. Se encontró que la descarga estaba muy concentrada y era opuesta al incremento esperado de la distancia de la línea de costa. La concentración de fósforo promedio total en la descarga de agua subterránea muestreada justamente por debajo del lecho del lago fue 0.162xa0mg TP/l y por lo tanto por encima de los umbrales ecológicos del agua dulce (0.043–0.612, mediana = 0.117xa0mg TP/l). El estudio ilustra una conexión directa entre la química del agua subterránea y del lago.摘要对丹麦Væng湖的研究展示了通过地下水排泄到渗水湖使磷增加的潜在风险。地下水的排泄 是湖中磷含量增加的重要来源, 这是因为 : 1) 湖下面的含水层中磷含量很高, 2) 通过含水层-湖底的界面的主要水流通道不是通过渗水面的地面水流就是集中在排泄率很高的地带。湖中的泉测得的排泄量为每天湖床每平米7.45m3。这些发现基于18个点的渗水测量、稳定同位素(δ18O)分析、温度轮廓及冰层分布图。采用2D概念流模型(MODFLOW)、流域多电极剖面湖上探地雷达、测井和钻孔资料对地下水 –湖相互作用进行了模拟。发现排泄更加集中, 并与远离海岸线的预期的增加相反。从湖底之下采取的排泄水中的平均总磷含量为0.162xa0mg TP/l, 因此, 大大超过淡水生态阀值(0.043–0.612, 中间值 = 0.117xa0mg TP/l)。研究描述了地下水化学成分和湖中化学曾芬之间的直接联系。ResumoUm estudo feito no lago Væng, na Dinamarca, revela um elevado potencial para a descarga de fósforo através da água subterrânea em lagos drenantes. As descargas de água subterrânea são interpretadas como fontes importantes de fósforo para o lago devido às: i) elevadas concentrações no aquífero imediatamente debaixo do lago e ii) linhas de fluxo através da interface aquífero-leito do lago, quer seja por meio de descarga subaérea através de uma superfície de drenagem, quer seja descarga localizada em zonas com elevada taxa de descarga. As nascentes dentro do lago apresentam descargas medidas que podem ir até 7.45xa0m3 por m2 de leito do lago por dia. Estes resultados são baseados em medições feitas com medidor de infiltração em 18 locais, análises de isótopos estáveis (δ18O), perfis de temperatura e mapeamento da distribuição da cobertura de gelo. A interação água subterrânea-lago foi simulada com o modelo concetual de fluxo 2D (MODFLOW), com hidrogeologia interpretada a partir de perfis multi-elétrodos da bacia hidrográfica, radar de penetração do solo no lago, e dados de diagrafias de furos e sondagens. Descobriu-se que a descarga é muito localizada e, contrariamente ao esperado, aumenta com a distância à margem. A concentração média de fósforo total na água subterrânea de descarga, amostrada imediatamente abaixo do leito do lago, foi de 0.162xa0mg TP/L, visivelmente acima dos limiares definidos para o estado ecológico da água doce (0.043–0.612, mediana = 0.117xa0mg TP/L). Este estudo revela uma ligação direta entre a água subterrânea e a composição química do lago.

Lake Flora and Fauna in Relation to Ice-Melt, Water Temperature and Chemistry at Zackenberg

Publisher Summary The ecology of arctic lakes is strongly influenced by climate-generated variations in snow coverage and the duration of the ice-free period, which, in turn, affect the physical and chemical conditions of the lakes. The physical and chemical conditions in arctic lakes leave a very short growing season for aquatic organisms, and the role of climate is, therefore, very important. The nutrient concentrations are low in the arctic lakes because of the inflowing water that primarily originates from runoff of melting ice and snow. The melted water transports silt, inorganic and organic particles, as well as the atmospheric deposition of substances into the lakes. Most lakes have low average summer temperatures, low nutrient availability, and, with it, low primary production. This implies that species richness is limited and biomass is often relatively low compared to lakes in temperate regions. Therefore, interactions among organisms are less complex than elsewhere. Plants and animals are active before the ice melts. The increased influx of light in April–May means that sufficient light can penetrate the snow and ice layer, thereby initiating plant photosynthesis and a consequent phytoplankton biomass increase. This shows that light and not water temperature is the limiting factor for primary production prior to ice-out. Despite the low abundance of arctic charr, it has a strong regulating impact on the composition and density of the zooplankton community and the abundance of the arctic tadpole shrimp, Lepidurus arcticus , which likely regulates the density of benthic cladocerans.

Eutrophication effects on greenhouse gas fluxes from shallow‐lake mesocosms override those of climate warming

Fresh waters make a disproportionately large contribution to greenhouse gas (GHG) emissions, with shallow lakes being particular hot spots. Given their global prevalence, how GHG fluxes from shallow lakes are altered by climate change may have profound implications for the global carbon cycle. Empirical evidence for the temperature dependence of the processes controlling GHG production in natural systems is largely based on the correlation between seasonal temperature variation and seasonal change in GHG fluxes. However, ecosystem-level GHG fluxes could be influenced by factors, which while varying seasonally with temperature are actually either indirectly related (e.g. primary producer biomass) or largely unrelated to temperature, for instance nutrient loading. Here, we present results from the longest running shallow-lake mesocosm experiment which demonstrate that nutrient concentrations override temperature as a control of both the total and individual GHG flux. Furthermore, testing for temperature treatment effects at low and high nutrient levels separately showed only one, rather weak, positive effect of temperature (CH4 flux at high nutrients). In contrast, at low nutrients, the CO2 efflux was lower in the elevated temperature treatments, with no significant effect on CH4 or N2 O fluxes. Further analysis identified possible indirect effects of temperature treatment. For example, at low nutrient levels, increased macrophyte abundance was associated with significantly reduced fluxes of both CH4 and CO2 for both total annual flux and monthly observation data. As macrophyte abundance was positively related to temperature treatment, this suggests the possibility of indirect temperature effects, via macrophyte abundance, on CH4 and CO2 flux. These findings indicate that fluxes of GHGs from shallow lakes may be controlled more by factors indirectly related to temperature, in this case nutrient concentration and the abundance of primary producers. Thus, at ecosystem scale, response to climate change may not follow predictions based on the temperature dependence of metabolic processes.

Horizontal distribution of cladocerans in arctic Greenland lakes – impact of macrophytes and fish

Submerged macrophytes may play an important role as a refuge for zooplankton against predators. However, a recent study suggests that their importance depends on the trophic state of the lake. We studied the impact of fish and macrophytes on the horizontal distribution of pelagic cladocerans in 56 oligotrophic arctic Greenland lakes. In north-east and western Greenland, zooplankton was sampled in the near-shore (littoral) and central (pelagial) part of all lakes and fish were sampled with multiple mesh-sized gill nets. Macrophytes were visually estimated in the littoral. In north-east Greenland, 5 taxa of cladocerans were found, while 14 taxa were recorded in western Greenland. Daphnia pulex occurred only in fishless lakes in both northeast and western Greenland and avoided the near-shore areas in the shallow and deep lakes. Bosmina spp. and Holopedium gibberum were evenly distributed between the littoral and the pelagial in the deep and shallow fishless lakes. However, their near-shore density was lowest in the presence of fish. Macrophyte-related and benthic cladocerans concentrated either in the littoral or were evenly distributed between the littoral and the pelagial, irrespective of depth and fish presence or absence. Macrophytes had no impact on the horizontal distribution of pelagic cladocerans. Thus, it is concluded that horizontal heterogeneity of Bosmina spp. and Holopedium gibberum might be affected by the presence of fish.