Carl Christian Hoffmann

Phosphorus retention in riparian buffers: review of their efficiency.

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 through the riparian aquifer, (ii) the overland flow path across the riparian buffer with water coming from adjacent agricultural fields, (iii) irrigation of the riparian buffer with tile drainage water from agricultural fields where disconnected tile drains irrigate the riparian buffer, and (iv) inundation of the riparian buffer (floodplain) with river water during short or longer periods. We have examined how the different flow paths in the riparian buffer influence P retention mechanisms theoretically and from empirical evidence. The different hydrological flow paths determine where and how water-borne P compounds meet and interact with iron and aluminum oxides or other minerals in the geochemical cycling of P in the complex and dynamic environment that constitutes a riparian buffer. The main physical process in the riparian buffer-sedimentation-is active along several flow paths and may account for P retention rates of up to 128 kg P ha(-1) yr(-1), while plant uptake may temporarily immobilize up to 15 kg P ha(-1) yr(-1). Retention of dissolved P in riparian buffers is not as pronounced as retention of particulate P and is often below 0.5 kg P ha(-1) yr(-1). Several studies show significant release of dissolved P (i.e., up to 8 kg P ha(-1) yr(-1)).

Climate change effects on nitrogen loading from cultivated catchments in Europe: implications for nitrogen retention, ecological state of lakes and adaptation

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) analyses using a number of models of various complexity for Danish streams and lakes suggest an increase in runoff and N transport on an annual basis (higher during winter and typically lower during summer) in streams, a slight increase in N concentrations in streams despite higher losses in riparian wetlands, higher absolute retention of N in lakes (but not as percentage of loading), but only minor changes in lake water concentrations. However, when taking into account also a predicted higher temperature there is a risk of higher frequency and abundance of potentially toxic cyanobacteria in lakes and they may stay longer during the season. Somewhat higher risk of loss of submerged macrophytes at increased N and phosphorus (P) loading and a shift to dominance of small-sized fish preying upon the key grazers on phytoplankton may also enhance the risk of lake shifts from clear to turbid in a warmer North European temperate climate. However, it must be emphasised that the prediction of N transport and thus effects is uncertain as the prediction of regional precipitation and changes in land-use is uncertain. By contrast, N loading is expected to decline in warm temperate and arid climates. However, in warm arid lakes much higher N concentrations are currently observed despite reduced external loading. This is due to increased evapotranspiration leading to higher nutrient concentrations in the remaining water, but may also reflect a low-oxygen induced reduction of nitrification. Therefore, the critical N as well as P loading for good ecological state in lakes likely has to be lower in a future warmer climate in both north temperate and Mediterranean lakes. To obtain this objective, adaptation measures are required. In both climate zones the obvious methods are to change agricultural practices for reducing the loss of nutrients to surface waters, to improve sewage treatment and to reduce the storm-water nutrient runoff. In north temperate zones adaptations may also include re-establishment of artificial and natural wetlands, introduction of riparian buffer zones and re-meandering of channelised streams, which may all have a large impact on, not least, the N loading of lakes. In the arid zone, also restrictions on human use of water are urgently needed, not least on the quantity of water used for irrigation purposes.

Retention of nutrients in river basins

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 losses of N and P from agricultural areas were the main nutrient source in the river basin contributing 76% and 51%, respectively, of the total export.Investigations of nutrient cycling in the Gjern river basin have revealed the importance of permanent nutrient sinks (denitrification and overbank sedimentation) and temporary nutrient storage in watercourses. Temporary retention of N and P in the watercourses thus amounted to 7.2–16.1 g N m−2 yr−1 and 3.7–8.3 g P m−2 yr−1 during low-flow periods. Deposition of P on temporarily flooded riparian areas amounted from 0.16 to 6.50 g P m−2 during single irrigation and overbank flood events, whereas denitrification of nitrate amounted on average to 7.96 kg N yr−1 per running metre watercourse in a minerotrophic fen and 1.53 kg N yr−1 per linear metre watercourse in a wet meadow. On average, annual retention of N and P in 18 Danish shallow lakes amounted to 32.5 g N m−2 yr−1 and 0.30 g P m−2 yr−1, respectively, during the period 1989–1995.The results indicate that permanent nutrient sinks and temporary nutrient storage in river systems represent an important component of river basin nutrient budgets. Model estimates of the natural retention potential of the Gjern river basin revealed an increase from 38.8 to 81.4 tonnes yr−1 and that P-retention increased from −0.80 to 0.90 tonnes yr−1 following restoration of the water courses, riparian areas and a shallow lake. Catchment management measures such as nature restoration at the river basin scale can thus help to combat diffuse nutrient pollution.

Sediment deposition and net phosphorus retention in a hydraulically restored lowland river floodplain in Denmark: combining field and laboratory experiments.

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 studied floodplain of the River Odense was restored in 2003 by remeandering the river channel along a 6-km reach. The restoration project involved 78 ha of riparian areas that were transformed from mainly arable land to extensive grassland and wetlands. The aim of the study was to quantify and model sediment and particulate P deposition on restored river floodplains. The present study suggests that during a 47-day flooding period, the river floodplain is able to retain 914.8% of the sediment and 1.13.7% of the particulate P transported in the river. Incubation experiments further showed that a maximum of 1125% of the deposited phosphorus can be released as dissolved inorganic phosphorus following deposition. The results from the best deposition model (R2 ≤ 0.42 for sediment and R2 ≤ 0.44 for particulate P) show that work should be done to further improve the performance of these models.

Crushed Concrete as a Phosphate Binding Material: A Potential New Management Tool

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 effectively (5.1-19.6 g P kg(-1) concrete), while the possible release of bound P varied between 0.4 and 4.6%. The retention rate was positively related to a decreasing concrete grain size due to an increasing surface area for binding. The P retention was also related to a marked increase in pH (up to pH 12), and the highest retention was observed when pH was high. Under these circumstances, column experiments showed outlet P concentrations <0.0075 mg P L(-1). Furthermore, experiments revealed that release of heavy metals is of no importance for the treated water. We demonstrate that crushed concrete can be an effective tool to remove P in urban and agricultural runoff as filter material in sedimentation/infiltration ponds provided that pH in the treated water is neutralized or the water is diluted before outlet to avoid undesired effects caused by the high pH.

Nitrogen Transport and Fate in European Streams, Rivers, Lakes, and Wetlands

Publisher Summary 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 international, national, and local levels. Measures to reduce point source discharges of nitrogen focus on tertiary treatment of urban wastewater as well as various key industries have been implemented in most countries within the EU. Today, a high proportion of the total anthropogenic nitrogen loading to the aquatic environment consists of nitrogen loading from agriculture. However, reducing the nitrogen input from agriculture is difficult for both technical and political reasons. Measures may be introduced/implemented at the source to reduce the large nitrogen surplus. Another approach may be to introduce transport measures to reduce the level of nitrogen before it reaches surface and thus increase the nitrogen-removal potential along the routes followed by nitrogen from soil to water.

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).

Modelling Nutrient Retention by a Reedswamp and Wet Meadow in Denmark

Simulation modelling is suggested as a management tool for investigating the usefulness of wet meadows and other wetlands in Denmark for the protection of surface and ground waters from nutrient inflows from agricultural lands. Field studies are currently measuring many physical, chemical, and biological aspects of a reedswamp adjacent to a lake and a wet meadow which is between a stream and agricultural upland. A modelling effort is being incorporated into these research projects to assist in the design of experimental measurements and to determine the efficiency of using wetland systems as buffer zones between agriculture and aquatic systems.

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.

Successful reduction of diffuse nitrogen emissions at catchment scale: example from the pilot River Odense, Denmark

Land-based total nitrogen (N) loadings to Danish coastal waters have been markedly reduced since 2000. This has been achieved by general measures reducing discharges from all point sources and N leaching from farmed land supplemented with more local and targeted mitigation measures such as restoration of wetlands to increase the catchment-specific N retention. In the catchment of River Odense, restoration of wetlands has been extensive. Thus, in the major gauged catchment (485 km(2)) eleven wetlands (860 ha) have been restored since 2000. A comparison of data on N concentrations and loss from a gauging station in the River Odense with data from a control catchment (772 km(2)), in which a significantly less intensive wetland restoration programme has been undertaken, showed an excess downward trend in N, amounting to 124 t N yr(-1), which can be ascribed to the intensive wetland restoration programme carried out in the River Odense catchment. In total, the N load in the River Odense has been reduced by 377 t N yr(-1) (39%) since 2000. The observed downward trend is supported by monitoring data from two wetlands restored in 2001 and 2004 in the River Odense catchment.