Quality of Surface Waters (Chemistry) 2001
The temperature is an important quantum affecting all natural events in bodies of water. Biological, chemical and physical events in the water are temperature-dependent e.g. reduction and production processes, likewise adsorption and solubility for gaseous, liquid and solid substances. This also applies to interactions between water and underground or floating substances and sediments, as well as between the water and the atmosphere. The viability and life activity of water organisms are tied to certain temperature limits or optimums, as are the occurrences of species or organisms and various adapted fish populations in Central European river regions.
The representation of the thermal power stations in the map as well as its influence on the temperatures of bodies of water must be taken into account in the assessment.
The temperature distribution map shows clearly that there has been a decline in the immission of heat into the Berlin bodies of water within the last few years, primarily in the area of the mouth of the Spree and in the Havel. The critical threshold of 28°C was not exceeded, and the maximums, or 95th percentiles, lie in the area of 25°C. Temperatures above 28°C were still being measured sporadically at the end of the ‘90s.
The reduction in heat pollution from Berlin power stations into bodies of water since 1993 has amounted to approx. 13 million GJ, and is due primarily to the connection of the Berlin power supply system to the Western European integrated grid system. Sinking power procurement costs caused by the liberalization of the electric-power market and the resulting reduced production of the Berlin power stations has led to the closure or partial closure of power stations. This has to some extent also occurred in connection with modernization for increased efficiency.
Present heat pollution amount to approx. 10 million GJ.
Oxygen Content (02.01.1)
The oxygen content of the water is the result of oxygen-infusion and consumption processes. Oxygen enters the water from the atmosphere, with oxygen intake depending primarily on the size of the water surface, the water temperature, the saturation deficit, the water turbulence and the movement of the air. Oxygen is also released by the photosynthesis of aquatic plants, which may result in oxygen super-saturation.
Oxygen is used up by the natural decomposition of organic material in the water by microorganisms as well as by the breathing of animals and plants. This can lead to oxygen deficiency in the bodies of water. The critical value below which sensitive species of fish can be damaged is 4 mg/l.
The readings from both the values from the measurement stations and from sampling indicate only a partial improvement in the oxygen content of the Berlin bodies of water. The bodies of water into which mixed-water overflows take place are still critical. In the mixed-water sewage system, rain water and polluted water are collected in a sewage pipe and moved by pumping stations to the sewage-treatment plants. This sewage system exists throughout inner-city Berlin (cf. Map 02.09).
At heavy rainfalls, the intake capacity of the mixed-sewage system is insufficient, and a mixture of rainwater and untreated waste water spills over into the Spree and Havel. This can lead to oxygen deficits because of oxygen-consumption processes. Particularly extreme events may even trigger fish kills in some watercourse segments (especially in the Landwehr Canal and the Neukölln Shipping Canal).
To considerably reduce the amounts of overflow in the future, additional underground storage spaces are to be activated or newly created in the context of a comprehensive redevelopment program.
The critical situations in the Tegel Creek is due to the aftereffects of sewage farms, or to agriculture.
TOC (02.01.10) and AOX (02.01.7)
The total organic load in surface bodies of water was investigated with the aid of the conduction parameter TOC (total organic carbon). The total of “adsorbable organically-bound halogens” is represented by the AOX determination.
For the determination of the combined AOX parameter, the halogens (AOI, AOCl, AOBr) in a variety of substances with quite different qualities are ascertained. Thus, the parameter serves less for the eco-toxicological assessment of bodies of water than for the monitoring of the success of measures for the reduction of the entry of “adsorbable organically-bound halogens”.
Fundamentally, neither measurement quantum allows any conclusion to be drawn on the composition and origin of the organic load. However, in major urban areas like Berlin, increased AOX values can principally be ascribed to anthropogenic immissions from municipal sewage plants. TOC entries can be of either anthropogenic or natural origin, e.g. due to the entry of humic substances from the catchment area, which to some extent limits the ability of the parameter to provide significant ecological statements. The assessment scale for the two measurement quanta is the 90th percentile.
With the application of this strict standard, the target quantum of Quality Class II for TOC is already exceeded for all main and subsidiary streams, both in the tributaries flowing into Berlin and in their stream courses flowing through the city.
Measurements for AOX are not available for all stream-course segments of the surface bodies of water in Berlin. Nevertheless it can be deduced that slightly increased AOX values occur only in segments immediately exposed to sewage-treatment plant immissions (Neuenhagen Mill Stream, Wuhle, Teltow Canal, Nordgraben), where target values are only slightly exceeded (Quality Classes II to III).
Ammonium Nitrogen (02.01.3), Nitrite Nitrogen (02.01.5), Nitrate Nitrogen (02.01.4)
Nitrogen appears in the water both in molecular form as nitrogen (N2) and in inorganic and organic compounds. When organically bound, it is primarily fixed in vegetable and animal material (biomass). Inorganically bound nitrogen occurs primarily as ammonium (NH4) and nitrates (NO3). In the water, soil and air as well as in technical facilities (e.g. sewage-treatment plants), bio-chemical (microbial) and physio-chemical transformation of nitrogen compounds take place (oxidation and reduction reactions). A unique feature of nitrogen infusion is nitrogen-fixing, a bio-chemical metabolic activity of bacteria and blue-green algae (cyanobacteria), which can introduce molecular gaseous nitrogen from the atmosphere into the metabolic process.
In Berlin, immission via sewage-treatment plants is the main source of this pollution. The rain drainage systems sporadically cause critical ammonium immissions.
In higher concentrations, ammonium can be a considerable burden on the oxygen balance, since the microbial oxidation (nitrification) of 1 mg of ammonium nitrogen to nitrate consumes approx. 4.5 mg of oxygen. However, his process is strongly temperature-dependent. Considerable transformation levels occur only during the warm season. At times, oxygen consumption due to nitrification processes considerably exceeds that caused by the decomposition of carbon compounds. Ammonium may become toxicologically significant if the pH value is moved into the alkaline range, and ammonia, which is toxic to fish, is released in waters with high ammonium contents.
Nitrite nitrogen occurs as an intermediate stage in the microbial oxidation of ammonium to nitrate (nitrification). Nitrite is of relatively minor eco-toxicological significance. At increased chloride concentrations and at the same pH value, nitrite toxicity is reduced.
While the LAWA quality targets (Quality Class II) are met for NH4-N in the Spree, Dahme and Havel upstream from Berlin, the targets are exceeded wherever bodies of water are exposed to the immission of municipal sewage-treatment plants and mixed-water or rainwater immissions.
The upgrading of the nitrification capacity of the sewage-treatment plants of the Berlin waterworks since reunification has led to a significant relief of the bodies of water in the city, with quality leaps of three or four classes. Many stream-course segments have even jumped into Quality Class II.
The values for the Wuhle and parts for the suburban Spree no longer reflect the current situation, since the closure of the Falkenberg sewage-treatment plant in the spring of 2003 has removed a significant pollution source.
The major pollution of the Teltow Canal could also be reduced considerably with the closure of the Marienfelde sewage-treatment plant (Teltow Canal, 1998) and the upgrading of the Wassmansdorf plant.
The Neuenhagen Mill Stream is still very highly polluted. There is need for action here at the Münchehofe sewage-treatment plant.
The City Spree (from Köpenick up its mouth into the Havel) consistently maintains Quality Classes II or III, and thus fails to achieve the LAWA target, as do the Lower Havel, the Teltow Canal and the inner-city canals, which are affected by mixed-water immission.
In 2001, sewage-treatment plant influenced segments of Neuenhagen Creek, the Wuhle and of three sections of the Teltow Canal exceeded the LAWA targets for nitrite nitrogen (90th percentile) (see above remark).
The nitrate values of the Berlin bodies of water are non-critical throughout.
In the Berlin bodies of water the natural chloride content is less than 60 mg/l. Anthropogenic increases in chloride concentrations are due to domestic and industrial waste water as well as road salt from winter road clearance. The chloride concentration typically undergoes a fluctuation over the course of a year due to the summertime drop in Spree water flow and the resulting higher concentration in the city. At chloride values above 200 mg/l, problems for the drinking water supply may occur.
The chloride values of the Berlin bodies of water do not constitute any problem for the ecology of the bodies of water.
Anthropogenic impairment in the Berlin area is considered to begin at about 120 mg/l. Thus, Quality Class II (< 100 mg/l) cannot be the target quantum for our region. The significance of the sulfate parameter in the Spree-Havel area involves not so much its eco-toxicological relevance as its significance for the drinking water supply. The drinking water limit value is 240 mg/l (especially for the protection of the kidneys of babies from an excessive salt intake). The streams flowing into Berlin show concentrations of between 150 and 180 mg/l. In the future, an increase in the sulfate inflow from the Lusatian mining regions is to be expected.
The following immissions into the bodies of water are of relevance in the Spree area:
- Immission of drainage water from strip-mines;
- Direct immission from post-strip-mining lakes used for water storage;
- Indirect immission via the ground water from strip-mined areas;
- Immission from active mining;
- Atmospheric sulfur immission (burning of fossil fuels);
- Diffuse and direct entries (sewage-treatment plant discharge, wash-outs, agriculture).
From the point of view of the ecology of bodies of water, increased sulfate concentrations may have a eutrophication-promoting effect. Sulfates may lead to the mobilization of phosphorus trapped in the sediment.
Overall Phosphorus (02.01.6)
Phosphorus is a nutrient element which can cause mass algae development in surface bodies of water under certain conditions (for a more detailed explanation, see Map 02.03). Pollution-free spring creeks show overall phosphorus concentrations of < 1 to 10 µg/l P; the upper reaches of stream courses with no anthropogenic immissions in catchment areas with deciduous forest lands have 20-50 µg/l P. The geogenic background concentrations for the lower Spree and the Havel are in the area of 60 to 90 µg/l P.
Due to the extensive use of phosphate-free detergents and especially, too, the progressive phosphate elimination in sewage treatment, phosphate immissions via municipal sewage-treatment plants dropped considerably especially during the period between 1990 and 1995. Immissions via farmland has also has declined.
Phosphorus pollution of Berlin’s bodies of water for the time period 1995-1997 was as follows:
Inflow to Berlin 188 t/a
Total, sewage plants 109 t/a
Mixed-water and sewage systems 38 t/a
Total inflow and immissions 336 t/a
Total, outflow 283 t/a
For inflows to Berlin, diffuse entries predominate, with approx. 60 %. The groundwater provides the predominant inflow path, accounting for 50 % (diffuse entry: 100 %).
For overall phosphorus, the mean value for the corresponding years is used as the basis. This shows increased P pollution of Berlin bodies of water of approximately at a factor of 2 or 3 above the background values.
Tegel Lake constitutes an exception. The inflow to the main basin of the Tegel Lake passes through a P-elimination facility, which reduces nutrient entry into the lake by approx. 20 t/a.