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Effects of Invasive Non-Native Species on the Native Biodiversity in the River Rhine 261
Basel, the number of stonefly species declined from 13 to four between 1910
and 1990, and those of mayflies from 19 to 13 (Küry 1994).
The decline of the freshwater fauna in the river Rhine is linked to extensive
habitat deterioration caused by channelisation and flow regulation by weirs,
stream fragmentation, organic pollution from land-use activities, toxic contaminants
from municipal and industrial sources, and interactions with an
increasing number of non-native species (Streit 1992; Baur and Ringeis 2002;
Van der Velde et al. 2002; Nehring 2003). Since the industrial revolution and
the construction of sewage systems, domestic and industrial pollution have
led to a gradual deterioration in water quality, and this from the second half of
the 19th century to the end of the 1960s. Water quality was very poor during
the period 1950–1970, with low oxygen levels, serious eutrophication, high
chemical and organic pollution loads, salination caused by French potassium
mines and mining water from brown coal mines in Germany, and thermal
pollution (Rhine river water temperature has risen by approximately 2 °C
above its natural value; Admiraal et al. 1993).
Faunal diversity in the river Rhine was lowest in the late 1960s,when levels of
toxicants were highest and oxygen levels extremely low (Kinzelbach 1972; Streit
1992). During the period 1970–1986, waste water treatment plants were constructed
along the river,resulting in improvements of water quality including an
increase in oxygen levels and a reduction of some heavy metals and organic pesticides.
Also, faunal diversity began to recover (Admiraal et al. 1993). Driven
partly by the toxic spill following the Sandoz accident (see below), ministers
from riparian countries decided in 1986 to establish the Rhine Action Programme.One
of its aims is the restoration of the river ecosystem.
Haas et al. (2002) described three successional phases in the development
of benthic communities in the German section of the Rhine, following the
extreme toxic and organic contamination which the river has known in earlier
times.
1. From 1970 to 1986, the aquatic community was species-poor and still in an
early recovery. Because of the remaining organic pollution, only sewageresistant
taxa such as the leech Erpobdella octoculata, the isopod Asellus
aquaticus, the snail Radix ovata, sponges, chironomids and oligochaetes
occurred. The non-native zebra mussel Dreissena polymorpha started to
colonise hard substrates. However, the major Sandoz industrial accident
near Basel in 1986, when runoff from water used in firefighting carried
nearly 30 t of toxic chemicals (insecticides, fungicides and herbicides) into
the Rhine, caused serious damage to the flora and fauna over hundreds of
kilometres, resetting the recovery process. In 1987, benthic faunal densities
were still close to zero (Den Hartog et al. 1992).Yet, D. polymorpha was able
to quickly recolonise the Rhine following the Sandoz spill because of the
immigration of pelagic larvae from unaffected sites.
2. In 1987 and 1988, the non-native amphipod Corophium curvispinum
(=Chelicorophium curvispinum), and the Asiatic clams Corbicula fluminea