Geogenically Acidified Mining Lakes — Living Conditions and Possibilities of Restoration

Pyrite and marcasite oxidation in the consequence of lignite surface mining creates lakes with pH as low as 2 to 3, buffered by high contents of iron and aluminium. Living conditions in this extreme habitat for plants and animals are described as well as the characteristics of the pioneer settlement. The utilization of these fish-free lakes is very limited. As possibilities for a water quality improvement special recultivation methods of overburden, chemical neutralization and biological ecotechnologies are recommended.     

Degraded Softwater Lakes: Possibilities for Restoration

In the Netherlands, the characteristic flora of shallow softwater lakes has declined rapidly as a consequence of eutrophication, alkalization and acidification. The sediment of most lakes has become nutrient rich and anaerobic. We expected that, if a vital seed bank was still present, restoration of the original water quality and sediment conditions would lead to the return of softwater macrophytes. The restoration of 15 degraded, shallow, softwater lakes in the Netherlands was monitored from 1983 to 1998. In eutrophied as well as in acidified lakes, removal of accumulated organic matter from the sediment and shores was followed by rapid recolonization of softwater macrophytes present in the seedbank. After isolation from alkaline water and subsequent mud removal, this recovery was also observed in alkalized lakes. Further development of softwater vegetation correlated strongly with the water quality. When renewed eutrophication was successfully prevented, softwater macrophytes could expand. However, in acidified lakes, Juncus bulbosus and Sphagnum species became dominant after restoration. Liming of an acidified lake was followed by re‐acidification within 3 years. Recolonization by softwater macrophytes was inhibited by high turbidity of the water column and spreading of large helophytes on the shore. As an alternative, controlled inlet of alkaline, nutrient‐poor groundwater was studied in a few lakes. The pH of those lakes increased, the carbon and nitrogen availability decreased and softwater macrophytes returned. Successful restoration has contributed considerably to maintaining biodiversity in softwater lakes in the Netherlands.     

The Potential for Restoration of Acid-Damaged Lake Trout Lakes

This review of long-term monitoring and experimental manipulation studies from Ontario, Canada, offers encouraging evidence that lake trout ( Salvelinus namaycush ) populations can be restored to acidified lakes once the problem of acid deposition is solved in North America. Predicting the rate of chemical and biological recovery remains difficult, because there are several limnological attributes (dissolved organic carbon, flushing rate) and biological attributes (acid sensitivity, species longevity, fish community composition) of lake trout ecosystems that can either enhance or delay the recovery process. Some options for managing recovering lakes are also reviewed, including increased pollution controls, liming, hatchery stocking, and harvest controls.     

Setting Attainable Goals of Stream Habitat Restoration from a Macroinvertebrate View

Many efforts have been undertaken to reduce the impairment of stream ecosystems by wastewaters and other pollution, leading to a remarkable improvement of the water quality in most parts of Central Europe. Actually, the most severe disturbance to stream systems in Central Europe is the structural degradation of stream morphology. Restoration practices increasing the structural heterogeneity of formerly degraded stream sections are necessary to create new habitats at different scales that could provide habitat for a diverse invertebrate community. Increasing biodiversity of aquatic invertebrates strengthens the ecological integrity of streams and is therefore a desirable goal in stream restoration. Nevertheless, recent studies focusing on the effect of structural restoration of stream sections often displayed results that did not really met the preset goal of increasing invertebrate diversity. This might be due to sometimes severe disturbance caused by the restoration practice itself, impairing the established invertebrate community in the restored stream section. Additionally, the potential for immigration of new species into the restored stream section is often limited. Therefore, several important prerequisites must be accounted for in the planning of restoration practices to improve structurally degraded stream sections, when the goal of restoration is increasing invertebrate diversity.     

Phytoplankton periodicity of the Waitaki Lakes,New Zealand

The Waitaki River system in the South Island of New Zealand includes three large glacially-formed headwater lakes, Tekapo, Pukaki and Ohau, which drain into the manmade Lake Benmore. Phytoplankton periodicity was followed from December 1975 to January 1980 as part of a study investigating possible changes in these lakes as a consequence of hydroelectric development. The phytoplankton was highly dominated by diatoms, e.g., Diatoma elongatum, Cyclotella stelligera, Asterionella formosa, and Synedra acus, but in lakes Ohau and Benmore populations of green algae occasionally developed. In all four lakes seasonal phytoplankton periodicity was observed with maximum biomass in spring and summer. In Lake Tekapo, the first lake in the chain, maximum biomass did not exceed 300 mg m^–3, but in the very turbid Lake Pukaki the maximum summer biomass ranged between 300 and 800 mg m^–3. In Lake Ohau, the least turbid lake, maximum biomass was around 1 000 mg m^–3. In the newly created Lake Benmore periodicity was less evident and summer maxima reached over 1 500 mg m^–3. The phytoplankton periodicity in these lakes is greatly influenced by seasonal patterns of turbidity from inflowing glacial silt.     

Defining the Limits of Restoration: The Need for Realistic Goals

The search for a universal statement of goals for ecological restoration continues to generate discussion and controversy. I discuss the diverse roots of restoration ecology, and show how the complex lineages within the field have led to diverse, and divergent, sets of goals. I then review the three major themes that currently are used to develop statements of goals: restoration of species, restoration of whole ecosystems or landscapes, and the restoration of ecosystem services, and point out both the advantages and the limitations and problems associated with each category. Finally, I suggest that restoration ecology would be better served by recognizing that the diversity of conditions requiring restoration demands much flexibility in goal setting, and that restorationists should seek to develop guidelines for defining the sets of conditions under which different kinds of goals are appropriate. I further suggest that goals would be more easily and more appropriately set if restorationists would set forth at the outset the true scope and limitations of what is possible in a given project. Key words: goal‐setting, wetlands, conservation biology, ecosystem management, ecosystem services, landscape management.     

Setting Effective and Realistic Restoration Goals: Key Directions for Research

Restoration ecology has made significant advances in the past few decades and stands to make significant contributions both to the practical repair of damaged ecosystems and the development of broader ecological ideas. I highlighted four main areas where progress in research can assist with this. First, we need to enhance the translation of recent advances in our understanding of ecosystem and landscape dynamics into the conceptual and practical frameworks for restoration. Second, we need to promote the development of an ability to correctly diagnose ecosystem damage, identify restoration thresholds, and develop corrective methodologies that aim to overcome such thresholds. This involves understanding which system characteristics are important in determining ecosystem recovery in a range of ecosystem types, and to what extent restoration measures need to overcome threshold and hysteresis effects. A third key requirement is to determine what realistic goals for restoration are based on the ecological realities of today and how these will change in the future, given ongoing changes in climate and land use. Finally, there is a need for a synthetic approach which draws together the ecological and social aspects of the issues surrounding restoration and the setting of restoration goals.     

Phytoplankton and Primary Production of Lakes in the Matamek Watershed,Quebec

The productivity of three Shield lakes on Quebec's North Shore was found to be comparable with that of the most oligotrophic lakes known. Factors contributing to this condition may be that the moderately sized lakes of this study are deep relative to their surface areas, highly stained by humic substances, of very low conductivity, and contain little dissolved CO₂. Standing crops of phytoplankton are very low, never exceeding 600 mg/m³. Chrysophyceae are dominant over all other classes of algae in both biomass and numbers, comprising approximately 50% of the fresh weight throughout the season. The abundance of micro-flagellates implies a large surface area to volume ratio and the ability to move are an advantage in a nutrient poor environment. Much of the phytoplankton present may grow heterotrophically and energy additions from the terrestrial environment may be extremely important to the productivity of northern lakes when photosynthetic production is not significant.     

Stretch Goals and Backcasting: Approaches for Overcoming Barriers to Large-Scale Ecological Restoration

The destruction and transformation of ecosystems by humans threatens biodiversity, ecosystem function, and vital ecosystem services. Ecological repair of ecosystems will be a major challenge over the next century and beyond. Restoration efforts to date have frequently been ad hoc, and site or situation specific. Although such small‐scale efforts are vitally important, without large‐scale visions and coordination, it is unlikely that large functioning ecosystems will ever be constructed by chance through the cumulative effects of small‐scale projects. Although the problems of human‐induced environmental degradation and the need for a solution are widely recognized, these issues have rarely been addressed on a sufficiently large‐scale basis. There are numerous barriers that prevent large‐scale ecological restoration projects from being proposed, initiated, or carried through. Common barriers include the “shifting baseline syndrome,” the scale and complexity of restoration, the long‐term and open‐ended nature of restoration, funding challenges, and preemptive constraint of vision. Two potentially useful approaches that could help overcome these barriers are stretch goals and backcasting. Stretch goals are ambitious long‐term goals used to inspire creativity and innovation to achieve outcomes that currently seem impossible. Backcasting is a technique where a desired end point is visualized, and then a pathway to that end point is worked out retrospectively. A case study from the Scottish Highlands is used to illustrate how stretch goals and backcasting could facilitate large‐scale restoration. The combination of these approaches offers ways to evaluate and shape options for the future of ecosystems, rather than accepting that future ecosystems are victims of past and present political realities.     

Germination Requirement of Vallisneria natans Seeds: Implications for Restoration in Chinese Lakes

Due to eutrophication submerged macrophytes have disappeared from many Chinese lakes. This is unfortunate as submerged macrophytes are important to improve water quality, and its re-establishment is therefore desirable. For this purpose a potential method to use is re-seeding, this being particularly attractive due to the high seed productivity of V. natans. We conducted laboratory studies to investigate the effects of five environmental variables (temperature, substratum, oxygen, light availability, and burial depth) on the seed germination of V. natans. Our results showed that a wide temperature range (25–35 °C) was favorable for germination; that seeds germinated well under both gravel and silt; that anaerobic condition proved to accelerate seed germination although the final germination percentage did not rise; and that light and burial acted as limiting factors. These results suggest that V. natans is a potential candidate for successful restoration of vegetation in lakes recovering from eutrophication.     

Nitrogen and Phosphorus Limitation of Phytoplankton Growth in New Zealand Lakes: Implications for Eutrophication Control

We examine macronutrient limitation in New Zealand (NZ) lakes where, contrary to the phosphorus (P) only control paradigm, nitrogen (N) control is widely adopted to alleviate eutrophication. A review of published results of nutrient enrichment experiments showed that N more frequently limited lake productivity than P; however, stoichiometric analysis of a sample of 121 NZ lakes indicates that the majority (52.9%) of lakes have a mean ratio of total nitrogen (TN) to total phosphorus (TP) (by mass) indicative of potential P-limitation (>15:1), whereas only 14.0% of lakes have mean TN:TP indicative of potential N-limitation (<7:1). Comparison of TN, TP, and chlorophyll a data between 121 NZ lakes and 689 lakes in 15 European Union (EU) countries suggests that at the national scale, N has a greater role in determining lake productivity in NZ than in the EU. TN:TP is significantly lower in NZ lakes across all trophic states, a difference that is driven primarily by significantly lower in-lake TN concentrations at low trophic states and significantly higher TP concentrations at higher trophic states. The form of the TN:TP relationship differs between NZ and the EU countries, suggesting that lake nutrient sources and/or loss mechanisms differ between the two regions. Dual control of N and P should be the status quo for lacustrine eutrophication control in New Zealand and more effort is needed to reduce P inputs.     

Rising CO2 Levels Will Intensify Phytoplankton Blooms in Eutrophic and Hypertrophic Lakes

Harmful algal blooms threaten the water quality of many eutrophic and hypertrophic lakes and cause severe ecological and economic damage worldwide. Dense blooms often deplete the dissolved CO₂ concentration and raise pH. Yet, quantitative prediction of the feedbacks between phytoplankton growth, CO₂ drawdown and the inorganic carbon chemistry of aquatic ecosystems has received surprisingly little attention. Here, we develop a mathematical model to predict dynamic changes in dissolved inorganic carbon (DIC), pH and alkalinity during phytoplankton bloom development. We tested the model in chemostat experiments with the freshwater cyanobacterium Microcystis aeruginosa at different CO₂ levels. The experiments showed that dense blooms sequestered large amounts of atmospheric CO₂, not only by their own biomass production but also by inducing a high pH and alkalinity that enhanced the capacity for DIC storage in the system. We used the model to explore how phytoplankton blooms of eutrophic waters will respond to rising CO₂ levels. The model predicts that (1) dense phytoplankton blooms in low- and moderately alkaline waters can deplete the dissolved CO₂ concentration to limiting levels and raise the pH over a relatively wide range of atmospheric CO₂ conditions, (2) rising atmospheric CO₂ levels will enhance phytoplankton blooms in low- and moderately alkaline waters with high nutrient loads, and (3) above some threshold, rising atmospheric CO₂ will alleviate phytoplankton blooms from carbon limitation, resulting in less intense CO₂ depletion and a lesser increase in pH. Sensitivity analysis indicated that the model predictions were qualitatively robust. Quantitatively, the predictions were sensitive to variation in lake depth, DIC input and CO₂ gas transfer across the air-water interface, but relatively robust to variation in the carbon uptake mechanisms of phytoplankton. In total, these findings warn that rising CO₂ levels may result in a marked intensification of phytoplankton blooms in eutrophic and hypertrophic waters.     

Field and Laboratory Studies on Nile Phytoplankton in Egypt. II. Phytoplankton

Variations in chlorophyll a concentration and in qualitative and quantitative counts of Nile phytoplankton were followed at Assiut from September 1980 to September 1982. Chlorophyll a concentrations usually correlated well with phytoplankton density. The total phytoplankton exhibited higher counts in spring and summer than in autumn and winter. While diatoms exhibited the highest counts, green algae contributed more genera to the phytoplankton community.     

Laurentian Great Lakes Phytoplankton and Their Water Quality Characteristics,Including a Diatom-Based Model for Paleoreconstruction of Phosphorus

Recent shifts in water quality and food web characteristics driven by anthropogenic impacts on the Laurentian Great Lakes warranted an examination of pelagic primary producers as tracers of environmental change. The distributions of the 263 common phytoplankton taxa were related to water quality variables to determine taxon-specific responses that may be useful in indicator models. A detailed checklist of taxa and their environmental optima are provided. Multivariate analyses indicated a strong relationship between total phosphorus (TP) and patterns in the diatom assemblages across the Great Lakes. Of the 118 common diatom taxa, 90 (76%) had a directional response along the TP gradient. We further evaluated a diatom-based transfer function for TP based on the weighted-average abundance of taxa, assuming unimodal distributions along the TP gradient. The r² between observed and inferred TP in the training dataset was 0.79. Substantial spatial and environmental autocorrelation within the training set of samples justified the need for further model validation. A randomization procedure indicated that the actual transfer function consistently performed better than functions based on reshuffled environmental data. Further, TP was minimally confounded by other environmental variables, as indicated by the relatively large amount of unique variance in the diatoms explained by TP. We demonstrated the effectiveness of the transfer function by hindcasting TP concentrations using fossil diatom assemblages in a Lake Superior sediment core. Passive, multivariate analysis of the fossil samples against the training set indicated that phosphorus was a strong determinant of historical diatom assemblages, verifying that the transfer function was suited to reconstruct past TP in Lake Superior. Collectively, these results showed that phytoplankton coefficients for water quality can be robust indicators of Great Lakes pelagic condition. The diatom-based transfer function can be used in lake management when retrospective data are needed for tracking long-term degradation, remediation and trajectories.     

Consequences of Fish Kills for Long-Term Trophic Structure in Shallow Lakes: Implications for Theory and Restoration

Fish kills are a common occurrence in shallow, eutrophic lakes, but their ecological consequences, especially in the long term, are poorly understood. We studied the decadal-scale response of two UK shallow lakes to fish kills using a palaeolimnological approach. Eutrophic and turbid Barningham Lake experienced two fish kills in the early 1950s and late 1970s with fish recovering after both events, whereas less eutrophic, macrophyte-dominated Wolterton Lake experienced one kill event in the early 1970s from which fish failed to recover. Our palaeo-data show fish-driven trophic cascade effects across all trophic levels (covering benthic and pelagic species) in both lakes regardless of pre-kill macrophyte coverage and trophic status. In turbid Barningham Lake, similar to long-term studies of biomanipulations in other eutrophic lakes, effects at the macrophyte level are shown to be temporary after the first kill (c. 20 years) and non-existent after the second kill. In plant-dominated Wolterton Lake, permanent fish disappearance failed to halt a long-term pattern of macrophyte community change (for example, loss of charophytes and over-wintering macrophyte species) symptomatic of eutrophication. Important implications for theory and restoration ecology arise from our study. Firstly, our data support ideas of slow eutrophication-driven change in shallow lakes where perturbations are not necessary prerequisites for macrophyte loss. Secondly, the study emphasises a key need for lake managers to reduce external nutrient loading if sustainable and long-term lake restoration is to be achieved. Our research highlights the enormous potential of multi-indicator palaeolimnology and alludes to an important need to consider potential fish kill signatures when interpreting results.     

The Saline Lakes of Saskatchewan IV. Primary Production by Phytoplankton in Selected Saline Ecosystems

Primary production by phytoplankton, efficiency of photosynthesis, and chlorophyll-a concentrations were determined for seven saline lakes that varied widely in ionic concentration and composition. The investigations were done during the summer months of 1972 and 1973. Productivity ranged from 0.001 to 11.135 g C m⁻³ day⁻¹ and 0.053 to 7.968 g C m⁻² day⁻¹. Highest productivities were measured in two lakes that supported blooms of Aphanizomenon flos-aquae and Nodularia spumigena, respectively. Species of Cyanophyceae, Bacillariophyceae and Chlorophyceae dominated the phytoplankton of the study lakes. Active chlorophyll-a ranged from 0.01 to 116 mg m⁻³. Integral photosynthetic efficiency estimates were <1% except during phytoplankton blooms when they were considerably higher. The overall range of 0.03 to 3.8% is concordant with estimates for other lacustrine ecosystems. The extinction of light caused by photo-synthetic processes, or in situ efficiency, was <1% in the trophogenic zone for most lakes but, it was considerably higher during blooms. In situ efficiencies invariably increased with depth in ail lakes.     

Toxicity Studies with the Blue-Green Alga Oscillatoria Agardhii from two Eutrophic Norwegian Lakes

Extracts of the blue-green alga Oscillatoria agardhii were tested for acute toxicity on laboratory mice and rats. Material originating from lake Gjersjøen proved to be toxic to the animals, samples from the nearby lake Årungen did not. Clinical symptoms culminated in the development of a fatal shock due to decrease in circulating blood volume. Pathological examination revealed heavy pooling of blood in the liver and severe damage to the organ. Blood analyses also indicated liver damage. Effects were the same with extracts from a laboratory clone culture as from a natural water bloom, but the toxin content was higher in the bloom material. Toxicity was not affected by heat, acid or alkali treatment.     

Critical Load Concept to Set Restoration Goals for Liming Acidif ied Nor wegian Waters

The concept of critical load is now widely used in the management of acidified waters. In southern Norway, acidification due to long-range transported air pollutants is one of the most serious environmental problems, affecting an area of 80,000 km². To preserve and restore biodiversity, Norwegian authorities have chosen liming as a temporary mitigation measure. Critical load estimates were used to estimate the material and financial needs for this large-scale program. In 1995, more than 2000 localities ranging from small lakes to large salmon rivers were limed. Liming costs in 1996 were $18 million (U.S.). Critical load estimates also formed the basis for international negotiations on sulfur emission reductions, resulting in the second sulfur protocol for Europe and North America in 1994. The critical load estimates indicated that acidified areas in Norway would be reduced to 35,000 km² after the year 2010, after the commitments of the sulfur protocols are met. By that time, estimated liming costs would be reduced by almost 40%. Lime treatment of River Tovdalselva, with a catchment area of 1885 km², is probably the largest integrated liming project in the world. In 1990 the critical load was exceeded in 98% of the Tovdalselva catchment. After the year 2010 the exceeded area may be reduced to 44% and the liming cost by two-thirds.