"Nature quality" in brooks, ditches and pools
In the last 50 years, the intensification of agriculture has led to a dramatic decline in the "nature quality" (this term is explained in the Technical note) of streams, ditches and pools.
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Trends
Pools, brooks and ditches are a characteristic component of the Dutch landscape. In 2000, however, their "nature quality" in terms of their macrofauna and aquatic plants, was half what it had been in 1950. This was true for all water types and all regions.
The most important reason for the decline in "nature quality" is the intensification of agriculture in the second half of the 20th century. Nutrients applied to farmland have ended up in surface water via runoff or leaching, causing water quality to deteriorate. Furthermore, in order to be able to regulate the water levels in the agricultural area, many stream courses have been straightened, dams and weirs have been constructed and the banks of ditches and pools have been steepened. The result is that the gradual transitions from land to water so important as a habitat for many plants and animals, have disappeared.
Technical note
"Nature quality" is the literal translation of a Dutch concept for indicating the status of a number of species typical of a certain habitat. It is obtained as follows: first, using the statistics on the numbers or density of each of these species, an index value for each species relative to 1950 is calculated. The index values of all the characteristic aquatic plants or macrofaunal species are then averaged.
The macrofauna are the invertebrates that are visible with the naked eye, such as mosquito larvae, water beetles, water spiders and dragonfly larvae. The "nature quality" of the macrofauna in pools has not been calculated.
References
- Brink, B.J.E. ten, A. van Hinsberg, M. de Heer, D.C.J. van der Hoek, B. de Knegt, O.M. Knol, W. Ligtvoet, R. Rosenboom en M.J.S.M. Reijnen (2002). Technisch ontwerp Natuurwaarde en toepassing in Natuurverkenning 2. RIVM rapport 408657007. Bilthoven.
