Soil - land use - surface water relationship

Surface waters can be considered as an extremely small part of a bigger water body (groundwater within the catchment area). The headwater reaches are usually cleaner and more influenced by soil characteristics than the lowland sections (potamon). Beside physical and chemical reactions in the "water body", biological influences gain increasingly more importance for the type and composition of organic and inorganic matter. In the potamon,  macrophytes, phytoplankton and anthropogenic pollution change the water quality significantly. Consequently, it is not very similar to the neighboring (cleaner) groundwater.

Besides water, sediments are also transported down the river. They originate from erosion caused by agriculture, from storm water run-off in the cities and from river bank erosion. They also have a strong influence on the ecological state of a river.

Examples of studies:

(1.) The first example shows that the rule outlined above is not always true in case of smaller rivers. In the Ukrainian capital Kiev, the river sources are already influenced by anthropogenic activities (agriculture, garden, cattle, etc.) . Later, biological activities, self purification, sedimentation in reservoirs (fish ponds) and, sometimes (!), dilution with cleaner drainage water improve the water quality.

The first figure shows the catchment areas of three city rivers delineated with the ArcView SWAT program. These are the rivers (from left to the right): Nivka, Siretz, Libid, Darnitza. The source area of the r. Darnitza is divided into 2 subbasins. The big river in the middle of Kiev is the Dnepr with the reservoir in the North.

Fig. 1 Kiev City River basin delineation

The second picture shows the storm water run-off canalisation system connected to the river Siretz (scan from the "Ecological Atlas of Kiev"). During rainy weather and snow melt the Siretz becomes heavily polluted.

Fig. 2 Rain water canalisation connected to the r. Siretz in Kiev (flowing from South-West to North-East)

In times of dry weather, water looks quite clean and clear and electrical conductivity  decreases.

Figure 3 shows monitoring results of the electrical conductivity (EC) measured in two of the small streams in Kiev, river Nivka (N) and river Siretz (C). EC was chosen because it often indicates pollution and is strongly correlated to nitrate, sulphate and a few other ions.

Fig. 3: Regular changes of electr. conductivity (medians 1997- 2000) between source (0 km) and mouth of river Nivka  and Siretz

(2.) The second example concerns the water quality of village wells north and south of Kiev. In spite of local anthropogenic influences, the concentration of organic compounds in the north (sandy soils) was always higher than in the south where we find dense soils with bigger buffer capacity and higher carbonate content. Here, water only slowly infiltrates into deeper layers and is filtered more effectively. Fig. 4 shows results of repeated samplings; not all results are visible because of the map scale!
 

(3.) The impact of land use on rivers is shown in fig. 5.  The electrical conductivity (depending on ion concentration) north-west of Kiev (area of sandy soils but more forests) is always lower than in the South-east  where agriculture dominates (and in Kiev itself). The pollution with organic matter is rather low but not shown here  because it is influenced by other factors (e.g. plankton) as well.

  Fig. 5: Different electr. conductivity (EC) in small rivers north-west of  Kiev and in the southern regions   (no significant point pollution sources)

(4) In the area west and north-west of the Kiev reservoir (distances up to some hundred km), soils are usually sandy and with low buffer capacity. In lowlands are bogs and marshes or have been there in former times. Ground water in those areas has a smaller el. conductivity (EC), but is rich in humic matter compared to ground water south of Kiev. The main tributary from the Northwest is the Pripjat river. Its water contains humic acids reducing photosynthetic activity.

During springtime, many river valleys are flooded and huge landscapes are under water. The water results from thawing snow on-site and after the thaw in the upstream hills. In early summer, these waters are still connected to rivers but then they evaporate, infiltrate into the soil, shrink and get more and more isolated. In these waters, micro-organisms develop forming the main food source for primary consumers. Among them, Culex mosquito larvae appear to be most significant.

The Dnepr itself flows from the Northeast (Russia) into the reservoir. It is charged with nutrients enhancing seasonal phytoplankton development.  Differences between the west and east side of the reservoir decrease when water flows to the south and becomes more and more mixed. The differences shown in fig. 6 appear to be not very big on the map but they are significant.

Fig. 6: Different contents of organic matter (humic acids) between the west and east side of the Kiev reservoir (mean values of several years' observation)

Another type of water that is strongly influenced by soil characteristics are artificial sand and gravel pits in and around Kiev; they must be considered as "groundwater windows". They are strongly influenced by the inflowing groundwater that was in contact with the upstream aquifer  (1).  As the organic load has different origins it must be analysed more in detail using various methods of geographical and simple physico-chemical analyses (as explained in 2, 3 and the Dnepr report). Organic matter, like humic acids, which are released from the underground,  must be taken into account, when assessing anthropogenic influences.

Conclusion

The page demonstrates that the natural soil quality in the river basin influences the surface water quality beside point and other non-point sources of pollution. This can have an effect on the inorganic and organic water chemistry in general and on eutrophication that must be considered as one of the main problems of water quality (in northern Ukraine) today. This underlines the necessity to include many more aspects into water resources management and to analyse the role of soil types, land use, vegetation cover etc. with corresponding simulation models as the above mentioned SWAT model. (An earlier study with the focus on landuse impacts was about the Ob in Siberia).

Literature:

1.  Arbeitsgruppe Baggerseen der Dt. Ges. f. Limnologie  (1996): Untersuchung, Ueberwachung und Bewertung von Baggerseen - Empfehlungen und Entscheidungshilfen  der DGL. - Mitt., ISBN 3-9802188-7-2, 125 p.

2.  HOFFMANN, M. (1986): Untersuchungen  zur oekochemischen Bewertung organischer Stoffe im Grundwasser. - Vom  Wasser, Bd. 65, 6 p.

3.. HOFFMANN, M., and GALAGAN, A. (1999): Hydrochemical Investigations on the Occurrence of  Toxicological  Relevant Matter in Rivers and Drinking Water (in Russian). - Chemistry and Technology of Water, 2, p.154 - 166);

Original title: Хоффманн, М. и  Галаган, А. (1999): Гидрохимические исследования пространственного распределения загрязнения рек, подземных вод и питьевой воды - Химия и технология воды, 2, ст. 154 - 166