Quality of macroinvertebrate in fresh surface water, 1991-2010

Poor to moderate ecological quality in most surface waters

The quality of macro invertebrate is poor or moderate is most surface waters. This was calculated based on the method of the Water Framework Directive (WFD) to quantify the quality based on the presence of macroinvertebrate species. With this method, a quality between 0.8 and 1.0 refers to the natural situation with an undisturbed fresh water (good ecological quality) or the maximum quality for artificial surface waters, such as ditches and canals (the maximum ecological potential).
Macroinvertebrates are small invertebrate animals that are visible to the naked eye and live in surface waters (insects, snails, etc.). The macroinvertebrate present at each monitoring site were compared with the reference for natural water bodies, or with the maximum achievable quality for artificial water bodies. Only a few of the water bodies had a good ecological quality; these were found along the border with Germany, in springs in the Veluwe, the Wieden and Weerribben, in brackish waters in Zeeland and along the Vecht in Overijssel. There were only a few water bodies with a poor ecological quality, due to the water quality improvements made between 1980 and 1990.

Little change in almost 20 years

There was a slight improvement in ecological quality between 1990 and 2010, of three to five percent on average in streams, ditches and canals. No improvement in the quality of macroinvertebrates was seen in the monitoring period in lakes. The ecological quality has remained stable in all water body types in recent years.
Ecological quality is mainly determined by eutrophication of the surface water and management of the surface water. Eutrophication occurs as a result of high nitrogen and phosphorus levels, management of water levels, construction of banks and canalizing streams determine whether different habitats are available. In the case of streams, the extent of meander or canalisation determines the opportunities for macroinvertebrates. In the case of canals, ditches and lakes, the layout of the banks and the water level have an important effect on ecological quality. Lakes are increasingly often given hard stone banks to protect them from erosion, which denies macrofauna a suitable habitat. The introduction of fish can also negatively impact the ecological quality. For example, much fewer macrofauna species were found, and at lower densities, in pools in which the pumpkinseed sunfish had been introduced.

Improvements slow

Improvements to the ecological quality of water are taking place very slowly. After 1990, the eutrophication of most surface waters decreased. However, improvements to ecological quality were minimal in the monitoring period; much less than improvements in water quality. The recovery of ecological quality is taking place so slowly because many macrofauna species have disappeared at the local level, or have even become extinct in the Netherlands. The long recovery time is also due to the fact that many sediments have become so nutrient-rich that the water is clouded by sludge and humus. Aquatic plants are therefore unable to grow, and the macrofauna do not have a suitable habitat. Often, unnaturally-high fish stocks can also hinder further recovery of the ecology. The high fish populations may be due to the nutrient-richness of the water during the previous decades, or to the introduction of too many fish.