Odense Fjord River Basin
Landscape and soil types
The Odense Fjord River Basin is about 1046 km2 and encompasses approx. 1 100 km of open watercourse and 2 600 lakes and ponds (>100m2). The last Glacial Period, 11 500-100 000 years ago, is the prime creator the landscape known on the Island of Fyn today. Moraine planes covered by moraine clay are predominant.
The water created melt water valleys flowing away from the ice. An example is the Odense river valley, which was formed by a melt water river that had largely the same overall course as today’s river. Clay soil types are slightly dominant and encompass approx. 51% of the basin while sandy soil types cover approx. 49%. The moraine soils of Fyn are particular well suited to cultivation of agricultural crops. Agriculture has therefore left clear traces in the landscape. Deep ploughing, liming and the suchlike have thus rendered the surface soils more homogeneous.
Land use, population and wastewater
Just as elsewhere in Denmark, land use in OdenseRiver Basin is dominated by agricultural exploitation. Farmland thus accounts for 68% of the basin. Of the remainder, approx. 16% is accounted for by urban areas, 10% by woodland, and 6% by natural/semi natural areas (meadows, bogs/fens/swamp forests, dry grasslands, lakes and wetlands, which are protected by Section 3 of the Protection of Nature Act). The corresponding figures for farmland, woodland and natural/semi natural areas for Denmark as a whole are 62%, 11% and just over 9%, respectively.
The population of OdenseRiver Basin numbers approx. 246 000, of which approx. 182 000 inhabit Odense, which is Denmark's third largest city.
Approx. 90% of the population in the basin discharge their wastewater to a municipal wastewater treatment plant. The remaining 10% of the population live outside the towns in areas without access to sewerage. There are a total of 6 900
residential buildings in these sparsely built-up areas outside the sewerage system catchments.
Due to increasing industrialization and the spread of flushing toilets, poorly treated wastewater from towns, dairies, abattoirs etc. started to be discharged into the water bodies of Fyn at the beginning of the 20th century. In the 1950s, the agricultural sector also started to cause serious pollution of the aquatic environment by discharging silage juice, liquid manure and manure seepage.
Many of the dairies and abattoirs were closed down due to centralization, and serious efforts were initiated to treat urban wastewater. Main measures, however, was not made until the 1980s and early 1990s, when treatment of urban and industrial wastewater was considerably improved, and unlawful discharges of silage juice etc. by the agricultural sector were stopped.
In 2000, there were approx. 1 870 registered farms in OdenseRiver Basin, of which approx. 960 were livestock farms. Livestock production in the basin amounts to approx. 60 000 livestock units (LU) (1999–2002), consisting of 59% pigs, 37% cattle and 4% other livestock.
Livestock density averages 0.9 LU/ha farmland, corresponding to the national average, but varies to some extent within the individual catchments that comprise OdenseRiver Basin. Overall, livestock production in the basin has increased in recent years. This masks a production decrease in dairy farming and a marked increase in pig farming. Based on the applications for permission to increase herd size submitted to FynCounty (EIA screening) it is concluded that livestock production will continue to increase in the coming years. Thus in the period from 2000 to mid 2003, permits have been granted to increase livestock production in the basin by 17%.
The dominant crop type in OdenseRiver Basin is cereals (2/3 winter cereals), while only 10% is accounted for by grass/green fodder. The concentration of market gardens in the basin is relatively high, occupying approx. 3% of the farmland.
Historical development – Artificial drainage and land reclamation in Odense River Basin
Over the past 50–100 years, artificial drainage has been established on an estimated 55% of the cultivated land in OdenseRiver Basin. The aim has been to ensure rapid drainage of the arable land and to optimize the possibilities for cultivation.
In addition, bogs/fens/swamp forests, meadows, watercourses and shallow lakes and areas of the fjord have undergone major physical changes or have been erased from the map due to reclamation of the land for cultivation. Thus 72% of the major areas of meadow and bog/fen/swamp forest have disappeared from OdenseRiver Basin over the past 100 years. Much of this has been turned into farmland through regulation of watercourses and regular watercourse maintenance. Moreover, many watercourses and ditches have been piped, and many watercourses have been straightened.
A corresponding significant reduction has taken place in the number of minor lakes and ponds. All in all, decades of land reclamation and drainage of wetlands and farmland have considerably reduced the natural self-cleansing ability of OdenseRiver Basin. Specific knowledge of currently drained farmland in OdenseRiver Basin is lacking. This knowledge is important for determining the pressure placed on the environment by the individual agricultural areas, and is necessary for future prioritization of environmental initiatives in the agricultural areas.
Historical development – farming in Fyn County
Danish agriculture has undergone considerable structural development since the 1950s. Among other things, holding structure has become more specialized, and livestock herds have become concentrated. Since the 1950s, the number of holdings in FynCounty has decreased by 75%, and their average size has increased by 250%. Diversified farming with mixed livestock and crop production has increasingly been replaced by specialized cattle or pig holdings or exclusively crop holdings.
Crop distribution in the agriculture of the 1950s reflected the diversified holding structure, with mixed livestock and crop production. At that time, up to half of the farmland was cultivated with grass, green fodder and root crops, while the other half was cultivated with cereal crops, primarily spring cereals.
Among other things, agricultural development has entailed a more than 50% reduction of grass, green fodder and root crops in the area since the 1950s, while the area of cereals has increased. At present approximately 18% of farmland is cultivated with grass, green fodder and root crops, while more than 60% is under cereals. The reduction in the area under grass, green fodder and root crops to the benefit of cereal crops has increased leaching of nitrogen due to the fact that the long growing season for grass and green fodder crops renders them better able to retain the nitrogen than cereals. Since the 1980s, the proportion of the land under winter cereals has increased at the expense of spring cereals.
From the 1950s to the end of the 1980s livestock herd declined in size by 35% due to a decrease in the cattle herd. Since the end of the 1980s, the size of the herd has begun to increase again. The increase is attributable to an increase in the pig herd, while the cattle herd continues to decrease in size.
Due to the great specialization the livestock herd – in contrast to previously – is much more unevenly distributed between the individual holdings. The pig herd in particular has become concentrated in holdings with very large herds. The livestock herd and hence manure and the application of it have thus become concentrated on a far smaller area than previously. Due to new legal requirements pertaining to utilization of manure, however, it is once again being applied to a greater area in recent years.
Prior to the 1950s, manure was the chief source of nutrient input to the crops. From the 1950s onwards, the use of commercial fertilizer became increasingly widespread. Consumption of commercial fertilizer increased steadily up through the 1960s and 1970s, leading to a marked increase in total nitrogen input to the crops of nearly 86% over the period 1950 to 1980. Total nitrogen input remained high during the 1980s. Approx. 63% of the total nitrogen input was accounted for by commercial fertilizer, and this alone was sufficient to meet crop nitrogen requirements. This reflects the fact that the fertilizer value of manure was considerably underestimated at that time.
Nitrogen consumption began to fall from 1992-93. Among other reasons, consumption of commercial nitrogen fertilizer fell as a result of a number of legal measures aimed at reducing pressure on the environment from agriculture, e.g. requirements on improved utilization of the nitrogen content of manure. Consumption of commercial fertilizer continued to decrease up through the 1990s until the present day. In all, total consumption of commercial nitrogen fertilizer has decreased by approx. 20% since its peak in the 1980s.
The increasing consumption of commercial fertilizer up through the 1960s and 1970s also entailed an increase in phosphorus input to the crops, which increased by 20% from the mid 1950s to the mid 1970s. Input of phosphorus far exceeded the amount of phosphorus removed with the crops, resulting in phosphorus accumulation in the soil. From the beginning of the 1980s, the total input of phosphorus began to decrease due to a fall in consumption of commercial phosphorus fertilizer, but input continued to exceed removal with the crops. From mid 1980s to the present day, total phosphorus input to the crops in FynCounty has decreased by 28%. The major source of phosphorus input to crops today is manure, accounting for approx. 72%. The amount of phosphorus in the applied manure roughly corresponds to the average amount removed with the crops. As the livestock herd is now concentrated on fewer holdings with very large herds, application of the manure is concentrated on a far smaller area of farmland than previously. As a consequence, land fertilized with manure is particularly subject to over fertilization with phosphorus. Continued over fertilization with phosphorus will increase phosphorus loading of the aquatic environment from agricultural land.