Morten Lauge Pedersen

From Natural to Degraded Rivers and Back Again: A Test of Restoration Ecology Theory and Practice

Extensive degradation of ecosystems, combined with the increasing demands placed on the goods and services they provide, is a major driver of biodiversity loss on a global scale. In particular, the severe degradation of large rivers, their catchments, floodplains and lower estuarine reaches has been ongoing for many centuries, and the consequences are evident across Europe. River restoration is a relatively recent tool that has been brought to bear in attempts to reverse the effects of habitat simplification and ecosystem degradation, with a surge of projects undertaken in the 1990s in Europe and elsewhere, mainly North America. Here, we focus on restoration of the physical properties (e.g. substrate composition, bank and bed structure) of river ecosystems to ascertain what has, and what has not, been learned over the last 20 years. First, we focus on three common types of restoration measures—riparian buffer management, instream mesohabitat enhancement and the removal of weirs and small dams—to provide a structured overview of the literature. We distinguish between abiotic effects of restoration (e.g. increasing habitat diversity) and biological recovery (e.g. responses of algae, macrophytes, macroinvertebrates and fishes). We then addressed four major questions: (i) Which organisms show clear recovery after restoration? (ii) Is there evidence for qualitative linkages between restoration and recovery? (iii) What is the timescale of recovery? and (iv) What are the reasons, if restoration fails? Overall, riparian buffer zones reduced fine sediment entry, and nutrient and pesticide inflows, and positive effects on stream organisms were evident. Buffer width and length were key: 5–30 m width and > 1 km length were most effective. The introduction of large woody debris, boulders and gravel were the most commonly used restoration measures, but the potential positive effects of such local habitat enhancement schemes were often likely to be swamped by larger-scale geomorphological and physico-chemical effects. Studies demonstrating long-term biological recovery due to habitat enhancement were notable by their absence. In contrast, weir removal can have clear beneficial effects, although biological recovery might lag behind for several years, as huge amounts of fine sediment may have accumulated upstream of the former barrier. Three Danish restoration schemes are provided as focal case studies to supplement the literature review and largely supported our findings. While the large-scale re-meandering and re-establishment of water levels at River Skjern resulted in significant recovery of riverine biota, habitat enhancement schemes at smaller-scales in other rivers were largely ineffective and failed to show long-term recovery. The general lack of knowledge derived from integrated, well-designed and long-term restoration schemes is striking, and we present a conceptual framework to help address this problem. The framework was applied to the three restoration types included in our study and highlights recurrent cause–effect chains, that is, commonly observed relationships of restoration measures (cause) and their effects on abiotic and biotic conditions (effect). Such conceptual models can provide useful new tools for devising more effective river restoration, and for identifying avenues for future research in restoration ecology in general.

Influence of disturbance on habitats and biological communities in lowland streams

We studied 68 small lowland streams in Denmark of which the majority were affected by physical and chemical stress or a combination of both. Using DCA analyses, we analysed macrophyte and macroinvertebrate communities along a combined disturbance gradient. Both macrophytes and macroinvertebrate communities responded to the combined pressure gradient. We used a rigorous classification of the 68 sites, into 5 disturbance groups, with respect to physical and chemical disturbance and studied the effects of disturbance on physical habitat structure and density and diversity of macrophytes, macroinvertebrates and fish. Physical habitat structure in the disturbed streams was similar, except for variations in width which was lowest, and coverage of mud, which was highest in heavily disturbed streams. Macrophyte communities were impacted by disturbance. Average species richness and diversity were significantly lower in disturbed streams (8.6 and 2.8) than in relatively undisturbed streams (15.3 and 5.6). The total number of Ephemeroptera, Plecoptera and Trichoptera taxa (EPT) was significantly lower in disturbed streams (4.1) compared to streams experiencing intermediate disturbance (6.0-7.6) and undisturbed streams (7.0). Taxa associated with stable substrata, such as Leuctra sp. and Baetis sp., were reduced in abundance by approximately 50% on disturbed sites. Density of trout (Salmo trutta L.) was markedly lower in disturbed streams (14 per 100 m 2 ) than in undisturbed streams (55-204 per 100 m 2 ). The results indicate that disturbance cascades through the stream ecosystem, primarily meditated by changes in macrophyte communities that are essential providers of habitat in unshaded lowland streams in which other structural elements, as coarse inorganic substrates and woody debris, are scarce. The analyses also show that the community variable responses to the combined stressors are not linear, which is an important issue implementing the ecological classification in the Water Framework Directive.

Effects of channelisation, riparian structure and catchment area on physical habitats in small lowland streams.

Rivers and streams form a longitudinal network in which physical conditions and biological processes change through the river system. Geomorphology, topography, geology and hydraulic conditions change from site to site within the river system, thereby creating a complex network of reaches that are dominated by a hierarchy of physical processes. The complexity is further enhanced by local human alteration of the physical structure, natural processes and alteration of the riparian areas. The aim of the study was to analyse variations in land use and riparian characteristics along small Danish streams and to determine the effect of channelisation on physical habitats. Physical stream characteristics were measured in 149 stream small and medium sized Danish streams (catchment area: 0.1 to 67.2 km 2 ). The measured physical parameters included discharge, stream slope, width, depth, current velocity, substrata and coverage of macrophytes. Riparian land use, valley form and information on channelisation and channel dredging were also collected. Small headwater streams were either dominated by forests or semi-natural land use. In contrast, the riparian areas of the streams in the larger streams were dominated by agricultural or semi-natural / meadow land use. The results suggest that a combination of within-system variations in geomorphological, hydrological and geological conditions as well as human alterations of the natural environment in small Danish catchments facilitate discontinuous changes to the stream bed substrata and in-stream habitats. The physical habitats and substratum characteristics of the channelised streams were significantly different from the structure in natural streams unaffected by physical modifications. Riparian land use and valley form potentially influence the degree of channelisation, i.e. a confined and steep valley (V-shaped) is less likely to be used for agricultural production compared to a broad valley. The results are useful to water managers, who seek to identify natural and impacted physical conditions in large river systems.

Restoration of the Rivers Brede, Cole and Skerne: a joint Danish and British EU‐LIFE demonstration project, IV—implications for nitrate and iron transformation

1. The possible effects on the hydrological and biogeochemical processes in the River Brede valley were studied from August 1994 to August 1996 based on measurements in piezometers installed along four transects across the river valley and two river monitoring stations located immediately upstream and downstream of the restored reach. 2. Groundwater discharge to the river varied considerably both along the restored river reach and from bankside to bankside. Comparison of the water balance derived from two river monitoring stations and the groundwater balance for the restored part of the river valley, based on Darcys equation, indicated that a deep-lying regional aquifer probably discharges to the river in the restored area. 3. The nitrate balance for the floodplain revealed that 92 kg NO3-N ha−1 year−1 was removed during passage through the river valley, probably as a result of pyrite oxidation. In contrast, iron leaked from the floodplain to the river at the rate of 400 kg Fe ha−1 year−1. 4. A prolonged dry period, starting four months after completion of the restoration work and lasting for the remainder of the study period, makes it difficult to conclude whether the results obtained are reflective of river and floodplain restoration. Nitrate concentration measurements at the two river monitoring stations revealed no overall significant changes when comparing a pre-restoration period with two similar post-restoration periods. However, comparison of nitrate losses from an upstream control catchment and the restored reach catchment indicated enhanced removal of nitrate along the restored river reach during a three month period of flooding immediately following completion of restoration work (January to March 1995).

Rivers of the Central European Highlands and Plains

The ecoregion of the central European highlands and plains is drained by some of the main rivers that flow into the Baltic and North Seas, including the Weser, Elbe, and Oder Rivers. In addition to these rivers, this chapter describes some smaller but peculiar rivers, such as the Em (Sweden), Skjern (Denmark), Spree (Germany) and Drawa (Poland) rivers. The Weser River exhibits a balanced longitudinal sequence of geomorphologically distinctive river sections typical of the Central European Highlands and Plains. The Weser and its tributaries provide important ecological services to society, including drinking water, sewage removal, water for irrigation, cooling water for power plants and industrial facilities, hydropower, habitat for organisms, and recreation and tourism. With a length of 1094 km, the 8th order River Elbe (Czech: Labe) is the third longest river in central Europe (after the Danube and Rhine). The Elbe is often seen as a river still possessing a natural river bed with active flood-plains. The Oder (Polish and Czech: Odra) is the sixth largest river flowing into to the Baltic Sea, with an annual discharge volume of 17.3 km. Being 854 km long, the Oder is the second longest river in Poland (after the Vistula). It has been used early for navigation both in north-south and east-west directions, as it has been connected early with the Elbe catchment via two canals.

Re-Meandering of Lowland Streams: Will Disobeying the Laws of Geomorphology Have Ecological Consequences?

We evaluated the restoration of physical habitats and its influence on macroinvertebrate community structure in 18 Danish lowland streams comprising six restored streams, six streams with little physical alteration and six channelized streams. We hypothesized that physical habitats and macroinvertebrate communities of restored streams would resemble those of natural streams, while those of the channelized streams would differ from both restored and near-natural streams. Physical habitats were surveyed for substrate composition, depth, width and current velocity. Macroinvertebrates were sampled along 100 m reaches in each stream, in edge habitats and in riffle/run habitats located in the center of the stream. Restoration significantly altered the physical conditions and affected the interactions between stream habitat heterogeneity and macroinvertebrate diversity. The substrate in the restored streams was dominated by pebble, whereas the substrate in the channelized and natural streams was dominated by sand. In the natural streams a relationship was identified between slope and pebble/gravel coverage, indicating a coupling of energy and substrate characteristics. Such a relationship did not occur in the channelized or in the restored streams where placement of large amounts of pebble/gravel distorted the natural relationship. The analyses revealed, a direct link between substrate heterogeneity and macroinvertebrate diversity in the natural streams. A similar relationship was not found in either the channelized or the restored streams, which we attribute to a de-coupling of the natural relationship between benthic community diversity and physical habitat diversity. Our study results suggest that restoration schemes should aim at restoring the natural physical structural complexity in the streams and at the same time enhance the possibility of re-generating the natural geomorphological processes sustaining the habitats in streams and rivers. Documentation of restoration efforts should be intensified with continuous monitoring of geomorphological and ecological changes including surveys of reference river systems.

From Natural to Degraded Rivers and Back Again

Extensive degradation of ecosystems, combined with the increasing demands placed on the goods and services they provide, is a major driver of biodiversity loss on a global scale. In particular, the severe degradation of large rivers, their catchments, floodplains and lower estuarine reaches has been ongoing for many centuries, and the consequences are evident across Europe. River restoration is a relatively recent tool that has been brought to bear in attempts to reverse the effects of habitat simplification and ecosystem degradation, with a surge of projects undertaken in the 1990s in Europe and elsewhere, mainly North America. Here, we focus on restoration of the physical properties (e.g. substrate composition, bank and bed structure) of river ecosystems to ascertain what has, and what has not, been learned over the last 20 years. First, we focus on three common types of restoration measures—riparian buffer management, instream mesohabitat enhancement and the removal of weirs and small dams—to provide a structured overview of the literature. We distinguish between abiotic effects of restoration (e.g. increasing habitat diversity) and biological recovery (e.g. responses of algae, macrophytes, macroinvertebrates and fishes). We then addressed four major questions: (i) Which organisms show clear recovery after restoration? (ii) Is there evidence for qualitative linkages between restoration and recovery? (iii) What is the timescale of recovery? and (iv) What are the reasons, if restoration fails? Overall, riparian buffer zones reduced fine sediment entry, and nutrient and pesticide inflows, and positive effects on stream organisms were evident. Buffer width and length were key: 5–30 m width and > 1 km length were most effective. The introduction of large woody debris, boulders and gravel were the most commonly used restoration measures, but the potential positive effects of such local habitat enhancement schemes were often likely to be swamped by larger-scale geomorphological and physico-chemical effects. Studies demonstrating long-term biological recovery due to habitat enhancement were notable by their absence. In contrast, weir removal can have clear beneficial effects, although biological recovery might lag behind for several years, as huge amounts of fine sediment may have accumulated upstream of the former barrier. Three Danish restoration schemes are provided as focal case studies to supplement the literature review and largely supported our findings. While the large-scale re-meandering and re-establishment of water levels at River Skjern resulted in significant recovery of riverine biota, habitat enhancement schemes at smaller-scales in other rivers were largely ineffective and failed to show long-term recovery. The general lack of knowledge derived from integrated, well-designed and long-term restoration schemes is striking, and we present a conceptual framework to help address this problem. The framework was applied to the three restoration types included in our study and highlights recurrent cause–effect chains, that is, commonly observed relationships of restoration measures (cause) and their effects on abiotic and biotic conditions (effect). Such conceptual models can provide useful new tools for devising more effective river restoration, and for identifying avenues for future research in restoration ecology in general.

Chapter Three - From Natural to Degraded Rivers and Back Again: A Test of Restoration Ecology Theory and Practice

Extensive degradation of ecosystems, combined with the increasing demands placed on the goods and services they provide, is a major driver of biodiversity loss on a global scale. In particular, the severe degradation of large rivers, their catchments, floodplains and lower estuarine reaches has been ongoing for many centuries, and the consequences are evident across Europe. River restoration is a relatively recent tool that has been brought to bear in attempts to reverse the effects of habitat simplification and ecosystem degradation, with a surge of projects undertaken in the 1990s in Europe and elsewhere, mainly North America. Here, we focus on restoration of the physical properties (e.g. substrate composition, bank and bed structure) of river ecosystems to ascertain what has, and what has not, been learned over the last 20 years. First, we focus on three common types of restoration measures—riparian buffer management, instream mesohabitat enhancement and the removal of weirs and small dams—to provide a structured overview of the literature. We distinguish between abiotic effects of restoration (e.g. increasing habitat diversity) and biological recovery (e.g. responses of algae, macrophytes, macroinvertebrates and fishes). We then addressed four major questions: (i) Which organisms show clear recovery after restoration? (ii) Is there evidence for qualitative linkages between restoration and recovery? (iii) What is the timescale of recovery? and (iv) What are the reasons, if restoration fails? Overall, riparian buffer zones reduced fine sediment entry, and nutrient and pesticide inflows, and positive effects on stream organisms were evident. Buffer width and length were key: 5–30 m width and > 1 km length were most effective. The introduction of large woody debris, boulders and gravel were the most commonly used restoration measures, but the potential positive effects of such local habitat enhancement schemes were often likely to be swamped by larger-scale geomorphological and physico-chemical effects. Studies demonstrating long-term biological recovery due to habitat enhancement were notable by their absence. In contrast, weir removal can have clear beneficial effects, although biological recovery might lag behind for several years, as huge amounts of fine sediment may have accumulated upstream of the former barrier. Three Danish restoration schemes are provided as focal case studies to supplement the literature review and largely supported our findings. While the large-scale re-meandering and re-establishment of water levels at River Skjern resulted in significant recovery of riverine biota, habitat enhancement schemes at smaller-scales in other rivers were largely ineffective and failed to show long-term recovery. The general lack of knowledge derived from integrated, well-designed and long-term restoration schemes is striking, and we present a conceptual framework to help address this problem. The framework was applied to the three restoration types included in our study and highlights recurrent cause–effect chains, that is, commonly observed relationships of restoration measures (cause) and their effects on abiotic and biotic conditions (effect). Such conceptual models can provide useful new tools for devising more effective river restoration, and for identifying avenues for future research in restoration ecology in general.

A Marine Spatial Planning framework for the optimal siting of Marine Renewable Energy Installations: two Danish case studies.

ABSTRACT Azzellino A., Kofoed J.P., Lanfredi C., Margheritini L., Pedersen M., 2013. A Marine Spatial Planning framework for the optimal siting of Marine Renewable Energy Installations: two Danish case studies. In this analysis two Danish case studies are investigated using a spatial planning approach. The first case study concerns the area on the west coast of Denmark that has been elected as test site by the Danish Wave Energy Center (DanWEC), a foundation constituted by local authorities, Aalborg University supported by the national wave energy industry. The second case study attains the Danish portion of the western Baltic sea, where many offshore windfarms are already installed and many projects are in construction or in the planning stage. The environmental background for the two areas is considered through set of multiple indicators (e.g. sea bottom topography and characteristics, marine biodiversity, presence of vulnerable species). Environmental indicators are aggregated into environmental impact indexes that constitute the basis for evaluating the site suitability for Marine Renewable Energy Installations (MREIs). Concurrenlty, areas of potential conflicts between the interests of MREI developers and commercial, recreational users are identified. Multivariate analysis techniques allow to disentangle the different components of the environmental vulnerability of the two areas and suggest sound criteria for the optimal siting of these infrastructures. The two case studies, concerning respectively a regional and local scale, offer good examples about how spatial planning has the potential to guide the transition from the single sector management toward the integrated management of sea uses.

Invertebrates in stormwater wet detention ponds — Sediment accumulation and bioaccumulation of heavy metals have no effect on biodiversity and community structure

The invertebrate diversity in nine stormwater wet detention ponds (SWDP) was compared with the diversity in eleven small shallow lakes in the western part of Denmark. The SWDPs and lakes were chosen to reflect as large a gradient of pollutant loads and urbanization as possible. The invertebrates as well as the bottom sediments of the ponds and shallow lakes were analyzed for copper, iron, zinc, cadmium, chromium, lead, aluminum, nickel, arsenic and the potentially limiting nutrient, phosphorus. The Principal Component Analysis showed that invertebrates in SWDPs and lakes differed with respect to bioaccumulation of these elements, as did the sediments, albeit to a lesser degree. However, the Detrended Correspondence Analysis and the TWINSPAN showed that the invertebrate populations of the ponds and lakes could not be distinguished, with the possible exception of highway ponds presenting a distinct sub-group of wet detention ponds. The SWDPs and shallow lakes studied seemed to constitute aquatic ecosystems of similar taxon richness and composition as did the 11 small and shallow lakes. This indicates that SWDPs, originally constructed for treatment and flood protection purposes, become aquatic environments which play a local role for biodiversity similar to that of natural small and shallow lakes.