Soil Erosion and Pollutant Erosion by the River Erft

Markus Kaspari, Michael Mittelstaedt

Inspired by a visit to the environment exhibition Envitec in Düsseldorf, we studied the water quality of the river Erft in 1986. Our investigation area extended from the spring of the Kuhbach creek, which joins the river Erft at its source, to the village Kirspenich. Except for the river Eschweilerbach all tributaries of the river Erft in this area are small creeks. The area is about 120 km2 in size with a population of about 14,000. Except for few exceptions all villages and hamlets have sewers throughout and there are no major industrial estates. There is grazing land and cropland as many villagers earn part of their income from agriculture. However, it is not intensive farming as full-time farmers have become rare. The structure of the investigation area is important for identifying sources of pollutants in the river Erft.

We used three approaches to determine the water quality: We determined the levels of certain pollutants using water analysis kits, based on biological indicators we determined the general water quality and we measured the amount of suspended substances using physical methods.

The chemical tests included oxygen, nitrate, nitrite, phosphate, ammonia and the pH-value. Nitrate, phosphate and ammonia from fertilisers or feces can end up in the ground water and in rivers. We identified six locations for taking measurements: the Kuhbach spring, before Bad Münstereifel, after Bad Münstereifel, in the village Iversheim, before the village Arloff and after the village Kirspenich. The oxygen deficit was relatively small in all measurements (averaging 1.6 mg/l), however, it did rise slowly from the spring to Kirspenich. Ammonia and phosphate were below 0.5 mg/l in all measurements, i.e. substantially below the respective 1.0 mg/l limits. Also nitrate was significantly below the limit of 11.3 mg/l with variations between 2.5 and 6 mg/l. No significant amounts of nitrite were found (up to 0.1 mg/l) and the pH-value varied between 7.5 and 8.5, i.e. the Erft river is slightly alkaline. Biological water quality indicators are organisms the presence of which indicates the water quality. Biological water quality indicators in Schönau, after Bad Münstereifel and after Kirspenich, mostly indicate a water quality class of 2 on a scale of 1-4, where 1 is best. Overall, this indicates a moderate level of pollution of the river Erft. We did not find evidence of any continuous water quality degradation from the spring to Kirspenich.

Measurements of the suspended load of the river Erft in Bad Münstereifel and Kirspenich allowed us to estimate the soil erosion in our investigation area. We conducted these measurements on days with visibly cloudy water and used average values that we had determined in advance for days with clear water. Based on a complicated calculation that takes precipitation, the size of the investigation area and currents into account, we estimate a level of soil erosion of about 30 mm per 1000 years.

Our results regarding water quality and soil erosion suggest that most pollutants in the river Erft originate in the soil. They end up in the soil due to agricultural use of the land. Even though the level of pollution of the river Erft is not alarming, care must be taken to ensure that the habitat Erft is preserved. Targeted fertilisation, a complete sewage system, no new industry and no further river straightening are some measures that would protect the river Erft.

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