Carl C. Hoffmann

• PhD
• Senior Researcher at Aarhus University

The potential and limitations of the Borehole Nuclear Magnetic Resonance (BNMR) technique as an in situ measurement for peatland soil characterization was tested in 163 boreholes at four selected peatlands in Denmark. The BNMR data effectively differentiated various geological units in peatland environments due to their distinct NMR responses. More...

Nitrogen (N) and phosphorus (P) losses to surface and coastal waters are still critically high across Europe and globally. Measures to mitigate and reduce these losses are being implemented both at the cultivated land surface and at the edge-of-fields. Woodchip bioreactors represent a new alternative in Denmark for treating agricultural drainage wa...

The world is currently facing a biodiversity and climate crisis which are globally interlinked. Nature-based solutions (NBS), defined as “actions to protect, sustainably manage, and restore natural and modified ecosystems that address societal challenges effectively and adaptively, simultaneously benefiting people and nature” is part of the solutio...

Nitrogen (N) and phosphorus (P) losses to surface and coastal waters are still critically high across Europe and globally. Measures to mitigate and reduce these losses are presently implemented both at the cultivated land surface and at the edge-of-fields. Woodchip bioreactors represent a novel alternative for treating agricultural drainage water,...

Floodplain wetlands in agricultural river basins provide critical ecosystem services such as nutrient retention, flood mitigation, carbon sequestration and ecological habitats and are a key component of a nature‐based solution approach to restoration. In the context of the global challenge to reducing impact increasingly intensive food production o...

Dette faglige notat giver et overblik over fjernelsen af næringsstoffer i en ny mæt-tet randzone, der blev etableret i forbindelse med projektet ”Innovationsplat-form for virkemidler til begrænsning af drænvand” for overvågningsåret 2021. Det skal bemærkes, at resultaterne er foreløbige, således at de nuværende kon-klusioner skal yderligere underby...

Rivers of Europe, Second Edition, presents the latest update on the only primary source of complete and comparative baseline data on the biological and hydrological characteristics of more than 180 of the highest profile rivers in Europe. With even more full-color photographs and maps, the book includes conservation information on current patterns...

Some of the main rivers of the Central European Highlands and Plains flow into the Baltic and North Seas, including the rivers Weser, Elbe, and Oder, drain the ecoregion of the central European highlands and plains. In addition to these rivers, this chapter describes some smaller but peculiar rivers such as the Em (Sweden), Skjern (Denmark), Spree...

For more than two decades, wetland restoration has been successfully applied in Denmark as a tool to protect watercourses from elevated nutrient inputs from agriculture, but little is known about how the flora and fauna respond to restoration. The main objective of this study was therefore to: (1) examine plant community characteristics in 10 wetla...

Woodchip bioreactors are increasingly used as tools to mitigate nitrogen (N) pollution from agricultural drainage water. They consist of a basin filled with woodchip material through which N contaminated drainage water can flow. During the water transport through the filter matrix, oxygen is rapidly depleted and denitrification removes a fraction o...

Natural wetlands used to cover a significant part of the landscape, but these ecosystems have declined by >50% worldwide, and even more in Denmark and Sweden. However, since the 1980s, various policies have been implemented to restore and create wetlands. This study provides a comprehensive historical overview of policies used to stimulate the crea...

The purpose of this catalogue is to give a description of the effects and costs of 20 measures used on areas and 12 measures used as drain measures. The measures are to be used in the targeted regulation for the next River Basin Management Plans for 2021-2027

Diffusive losses of nitrogen and phosphorus from agricultural areas have detrimental effects on freshwater and marine ecosystems. Mitigation measures treating drainage water before it enters streams hold a high potential for reducing nitrogen and phosphorus losses from agricultural areas. To achieve a better understanding of the opportunities and c...

Nutrient losses from agricultural areas constitute a major cause for the degradation of aquatic ecosystems worldwide. In this paper, we use the intensively cultivated country of Denmark as an example to synthesise and discuss results, experiences and challenges for an optimised implementation of nutrient transport mitigation measures targeting agri...

Ponds are increasingly recognized as significant sources of greenhouse gases (GHGs) emitted to the atmosphere. Concomitant with increasing urbanization, more urban ponds are created, many with the aim of buffering peak runoff and improving water quality in downstream waterbodies. However, the impact of urban ponds on GHG emissions is poorly elucida...

Wetland buffer zones (WBZs) are riparian areas that form a transition between terrestrial and aquatic environments and are well-known to remove agricultural water pollutants such as nitrogen (N) and phosphorus (P). This review attempts to merge and compare data on the nutrient load, nutrient loss and nutrient removal and/or retention from multiple...

Large-scale re-establishment of wetland buffer zones (WBZ) along rivers is regarded as an effective measure in order to reduce non-point source nitrogen (N) and phosphorus (P) pollution in agricultural catchments. We estimated efficiency and costs of a hypothetical establishment of WBZs along all watercourses in an agricultural landscape of the low...

Subsurface flow wetlands with a woodchip‐based biofilter are known to act as effective measures in mitigating site‐specific nutrient losses in agricultural drainage. To optimize operation, the combined effect of water temperature, hydraulic residence time (HRT), and filter design is fundamental. This 2‐yr study evaluated a combination of three flow...

Subsurface flow constructed wetlands with wood chips (SSF-CWs) have proven to effectively reduce the loss of nitrogen (N) from agricultural fields to surface water, however in some cases production of negative side effects such as methane and phosphate occur. We examined if these side effects can be avoided by decreasing the hydraulic retention tim...

Wetland restoration is considered an effective mitigation method for decreasing nitrogen (N) losses from agricultural land. However, when former cropland becomes rewetted, there is a risk that phosphorus (P) accumulated in soils will be released downstream. Here, we evaluate N and P retention in eight restored wetlands in Denmark monitored for 1 ye...

Integrated buffer zones (IBZs) have recently been introduced in the Northwestern Europe temperate zone to improve delivery of ecosystem services compared with the services associated with long‐established vegetated buffer zones. A common feature of all the studied IBZ sites is that tile drainage, which previously discharged directly into the stream...

Integrated buffer zones (IBZs) represent a novel form of edge-of-field technology in Northwest Europe. Contrary to the common riparian buffer strips, IBZs collect tile drainage water from agricultural fields by combining a ditch-like pond (POND), where soil particles can settle, and a flow-through filter bed (FILTERBED) planted with Alnus glutinosa...

The hydrology of riparian areas changes rapidly these years because of climate change‐mediated alterations in precipitation patterns. In this study, we used a large‐scale in situ experimental approach to explore effects of drought and flooding on plant taxonomic diversity and functional trait composition in riparian areas in temperate Europe. We fo...

Drained riparian wetlands have been rewetted and restored in recent decades to remove nutrients, increase biodiversity, and mitigate soil carbon dioxide (CO2) emissions. Yet, few studies have documented the long-term effects of rewetting on complete greenhouse gas (GHG) balances including emissions of CO2, methane (CH4), and nitrous oxide (N2O). He...

Biogeochemical processes in subsurface flow constructed wetlands are influenced by flow direction, degree of saturation and influent loading position. This study presents a simulation tool, which aims to predict the performance of the unit and improve the design. The model was developed using the HYDRUS program, calibrated and verified on previousl...

Shallow lakes are a key component of the global carbon cycle. It is, therefore, important to know how shallow lake ecosystems will respond to the current climate change. Global warming affects not only average temperatures, but also the frequency of heat waves (HW). The impact of extreme events on ecosystems processes, particularly greenhouse gas (...

In many parts of the world, the magnitude and frequency of cold-season precipitation are expected to increase in the near future. This will result in an increased magnitude and duration of winter and spring flooding by rain-fed streams and rivers. Such climate-driven increases in flooding are likely to affect riparian plant communities, but future...

Mitigation of agricultural nitrogen (N) loss via tile drains using woodchip-based subsurface constructed wetlands seems promising. However, the stochastic nature of drainage discharge and consequent temporal variations in hydraulic loading rates may result in the emission of the greenhouse gases (GHG) nitrous oxide (N2O) and methane (CH4) with pote...

Background Eutrophication of aquatic environments is a major environmental problem in large parts of the world. In Europe, EU legislation (the Water Framework Directive and the Marine Strategy Framework Directive), international conventions (OSPAR, HELCOM) and national environmental objectives emphasize the need to reduce the input of nutrients to...

Unregulated and event‐driven agricultural tile drainage discharge poses several challenges that potentially limit the nitrate (NO 3 ) removal performance of woodchip‐based wetlands constructed to intercept subsurface tile drain flows. Laboratory column tests were conducted to evaluate the biogeochemical response of mixed reactive media (woodchips–s...

Documentation of the effects of different mitigation measures adopted at different scales to reduce phosphorus (P) loadings to surface waters is needed to help catchment managers select the best management practices. Water quality monitoring data from the outlets of two paired catchments (the River Odense catchment versus a neighbouring control cat...

Nitrate is typically removed from aquaculture effluents using heterotrophic denitrification reactors. Heterotrophic denitrification reactors, however, require a constant input of readily available organic carbon (C) sources which limits their application in many aquaculture systems for practical and/or economic reasons.

ABSTRACTLand-based total nitrogen (N) loadings to Danish coastal waters have been markedly reduced since2000. This has been achieved by general measures reducing discharges from all point sources and Nleaching from farmed land supplemented with more local and targeted mitigation measures such asrestoration of wetlands to increase the catchment-spec...

In recent years a large focus has been dedicated to exploring different mitigation options that can assist in reducing nitrogen (N) emission from fields to streams, lakes and coastal areas. One of the mitigation measures that have been implemented in Denmark is restoration of wetlands, with a total of 7,121 ha restored in 2010. Furthermore, in an e...

Wetland restoration projects often focus on mitigating losses of nutrients (nitrogen and phosphorus) towards downstream aquatic recipients and, so far, there is no clear guidance on how to restore environmental conditions to improve biodiversity values in the restored areas. However, to provide such guidance, it is necessary to obtain a better unde...

Generally, wet ponds are constructed only to reduce the hydraulic load of downstream receiving water bodies. Often most particulate matter will be retained, whereas dissolved nutrients mostly will be unaffected by the pond due to short retention times. A suite of lab-experiments have demonstrated that crushed concrete has high affinity for dissolve...

Background Eutrophication of aquatic environments is a major environmental problem in large parts of the world. In Europe, EU legislation (the Water Framework Directive and the Marine Strategy Framework Directive), international conventions (OSPAR, HELCOM) and national environmental objectives emphasize the need to reduce the input of plant nutrien...

Stream restoration often aims at mitigating nutrient pollution in aquatic ecosystems. However, despite recent research efforts, effects of restoration practices on in-stream nitrogen removal remain unclear. In this study, denitrification rates as well as factors controlling denitrification in unrestored and restored sections of two Danish streams (...

River restoration projects that allow temporary inundations of the floodplain are important for increasing the water storage potential of the landscape which can decrease flood risk to vulnerable downstream urban areas. During inundation, coarse and fine fluvial sediments are deposited on the floodplain leading to reduced organic matter and nutrien...

This study presents the first annual estimates of net ecosystem exchange (NEE) of CO2 and net ecosystem carbon balances (NECB) of contrasting Danish agricultural peatlands. Studies were done at eight sites representing permanent grasslands (PG) and rotational (RT) arable soils cropped to barley, potato or forage grasses in three geo-regional settin...

Re-established riparian wetlands used to mitigate nitrogen (N) loss from agricultural soils to surface water may lose phosphorus (P) from the top soils that often have received fertilizers. This could lead to eutrophication of lakes and estuaries. For a 2-year period we established mass balances of N and P in two restored riparian wetlands of ∼0.6...

Background and Aims Drained peatlands are considered to be insignificant CH4 sources, but the effect of drainage on CH4 dynamics has not been extensively studied. We investigated seasonal dynamics of CH4 in two fen peat soils and one bog peat soil under permanent grassland in Denmark. Methods Soil CH4 concentrations were measured several times thro...

To avoid eutrophication of receiving waters, effective methods to remove P in urban and agricultural runoff are needed. Crushed concrete may be an effective filter material to remove dissolved and particulate P. Five types of crushed concrete were tested in the laboratory to evaluate the retention capacity of dissolved P. All types removed P very e...

The use of organic soils by agriculture involves drainage and tillage, and the resulting increase in C and N turnover can significantly affect their greenhouse gas balance. This study estimated annual fluxes of CH4 and N2O, and ecosystem respiration (Reco), from eight organic soils managed by agriculture. The sites were located in three regions rep...

The use of organic soils by agriculture involves drainage and tillage, and the resulting increase in C and N turnover can significantly affect their greenhouse gas balance. This study estimated annual fluxes of CH4 and N2O, and ecosystem respiration (Reco), from eight organic soils managed by agriculture. The sites were located in three regions rep...

During the last 15–20years, re-establishment of freshwater riparian wetlands and remeandering of streams and rivers have been used as a tool to mitigate nutrient load in downstream recipients in Denmark. The results obtained on monitoring four different streams and wetland restoration projects are compared with respect to hydrology, i.e. flow patte...

1. Running waters, including associated riparian areas, are embraced by international legal frameworks outlining targets for the preservation, protection and improvement of the quality of the environment. Interactions between stream and river processes and riparian habitats have not received much attention in the management of stream ecosystems, an...

Climate change might have profound effects on the nitrogen (N) dynamics in the cultivated landscape as well as on N transport in streams and the eutrophication of lakes. N loading from land to streams is expected to increase in North European temperate lakes due to higher winter rainfall and changes in cropping patterns. Scenario (IPCC, A2) analyse...

River floodplains and riparian areas are often considered efficient traps for sediment and sediment-associated nutrients such as nitrogen (N) and phosphorus (P). However, few studies have focused on the fate of sediment-bound N and P after deposition on floodplains. In this study, the leaching of N and P from sediment deposited on a Danish-restored...

A field-scale pulse-injection experiment with the herbicide Isoproturon was conducted in a Danish riparian wetland. A non-reactive tracer (bromide) experiment was also carried out to characterize the physical transport system. Groundwater flow and reactive transport modelling was used to simulate flow paths, residence times, as well as bromide and...

Ground water and surface water interactions are of fundamental importance for the biogeochemical processes governing phosphorus (P) dynamics in riparian buffers. The four most important conceptual hydrological pathways for P losses from and P retention in riparian buffers are reviewed in this paper: (i) The diffuse flow path with ground water flow...

Restoration of river systems allowing the transformation of former drained and dry riparian areas into riparian wetlands will increase the overbank storage of sediment and sediment-associated phosphorus (P). Wetland restoration is therefore a cost-effective mitigation measure to reduce the sediment and nutrient transport to river systems. The studi...

An important step in the implementation of the Water Framework Directive is to define and characterize the natural status, designated as the reference condition (RC). Here we present the results of a type-specific screening for reference stream sites in Denmark using two different approaches. First, we performed a screening applying physicochemical...

Denitrification as a sink of dissolved nitrous oxide (N[sub 2]O) was investigated in a freshwater riparian fen. In a 15-m transect extending from the hillslope and into the fen the groundwater concentrations of nitrate (NO[sub 3][sup [minus]]) declined from 1.8 mM NO[sub 3][sup [minus]] to less than 0.01 mM NO[sub 3][sup [minus]], dissolved oxygen...

A national programme for the restoration of freshwater wetlands in Denmark was initiated in 1998. The purpose was to reduce nitrogen load to down-stream recipients and to enhance nature values in restored areas. In August 2005, 3060 ha of land was restored and 3769 ha of land approved for restoration. A monitoring programme for surveying the effect...

Water exchange, flow patterns and deposition of sediment and phosphorus were measured in cross-sections of a naturally functioning floodplain during one winter and in three restored floodplains following remeandering of formerly straightened and channelized rivers. Sediment and phosphorus depositional processes were studied, deploying artificial gr...

Groundwater flow and nutrient transport were studied in a riparian meadow during a three-year period. The meadow is situated along a first order stream in the River Gjern catchment area, Jutland, Denmark. Field data included measurements of hydraulic head, hydraulic conductivity and soil characteristics. Groundwater sampled from piezometers was ana...

The Mike 11–TRANS modelling system was applied to the lowland Gjern river basin in Denmark to assess climate-change impacts on hydrology and nitrogen retention processes in watercourses, lakes and riparian wetlands. Nutrient losses from land to surface waters were assessed using statistical models incorporating the effect of changed hydrology. Clim...

In this paper we show the quantitative and relative importance of phosphorus (P) losses from agricultural areas within European river basins and demonstrate the importance of P pathways, linking agricultural source areas to surface water at different scales. Agricultural P losses are increasingly important for the P concentration in most European r...

Fiftysix studies showing how buffer zones, constructed wetlands and restoration of streems, lakes and wetlands can minimize diffuse pollution fram catchments. Conf. proc. with several authors from the Nordic countries. Each presentation is from 2-4 pages.

The concentration and loss of two herbicides (bentazone and MCPA), two fungicides (fenpropimorph and propiconazole) and two insecticides (dimethoate and pirimicarb) were measured in tile drainage water from a 2,813 m2 experimental grass field from May to August 2001. Three different pesticides were applied to the field and subsequently a rainfall o...

Introductory work on implementation of the EU Water Framework Directive has outlined criteria for classification of the physical-chemical status of groundwater and surface water bodies, recognizing that the quantitative and qualitative status of ground water may have an impact on the quantitative, qualitative and ecological status of surface waters...

This chapter provides an overview of the present state of nitrogen pollution in European streams, rivers, and lakes. The main focus of this chapter is on diffuse sources of nitrogen. Concern about elevated nitrogen concentrations and loading to groundwater and surface water in Europe has prompted the introduction of many reduction strategies at int...

Denitrification rates in the range of 359 to 599 mmol N m-2 d-1 were found in the waterlogged soil of a minerotrophic fen. Three different methods were used to estimate denitrification rates. The fen revealed a zone of enhanced denitrification and within this zone the spatial variation of denitrification rates was elucidated using two different app...

In Denmark, as in many other European countries, the diffuse losses of nitrogen (N) and phosphorus (P) from the rural landscape are the major causes of surface water eutrophication and groundwater pollution. The export of total N and total P from the Gjern river basin amounted to 18.2 kg ha−1 and 0.63 kg P ha−1 during June 1994 to May 1995. Diffuse...

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...

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. Groundwate...

Water exchange, sediment budget and net sedimentation were measured on a lowland river floodplain during a winter period. The study area is inundated from a ditch at low water stages and flooded at higher stages in the river. Return period of overbank flooding is 0.5 years which is three times as often as in natural lowland rivers. Therefore, the s...

A riparian fen-meadow ecosystem in the River Gjern catchment area (114 km 2 ) was studied intensively during a four year period. Land use in the catchment is mainly agriculture, 77.4%, while forests occupy 13.9%, towns and paved areas 4.6%, and meadows and wetlands 4.4%. Soil types are sandy loams, 61.2%, loam, 34.8% and loamy sand 4.0%. The River...