Metal pollution natural inputs

As a result of their geographical circumstances and these various historical developments, many estuaries appear to be among the most heavily loaded ecosystems in the world in terms of the amount of nitrogen and phosphorus received per unit area (Fig. 5). Even the farm fields of the American corn belt do not receive the fertilization common to many estuaries, and the nutrient inputs to natural terrestrial systems and fresh waters appear to be orders of magnitude lower. There are fewer data available on the inputs of metals and other pollutants to estuaries, but the evidence at hand suggests that the delivery of heavy metals to estuaries may equal or exceed that deposited from the atmosphere on heavily industrialized urban areas and exceed that deposited on rural terrestrial ecosystems by orders of magnitude (Fig. 6). 

A differentiation between natural and anthropogenic heavy metal loads into the Baltic is not possible because metals are also natural components of the earth s crust. Taking into consideration that the HELCOM database is stiU incomplete, a general reduction of the total metal load was calculated for Hg ( 74%), Pb (< 66%), Cd ( 62%), and Zn ( 9%) between 1990 and 1995. For Cu, an increase of 13% was estimated. With the addition of the trace metal input data from the fourth pollution load compilation, the situation changed drastically. Compared to 1995 (HELCOM, 1998), the total heavy metal loads increased by a factor of -3 for Cd, 4 for Pb, and 9 for Hg in 2000 (HELCOM, 2004,2005), while for Cu (0.7) and Zn (0.8) a decrease of the river loads was estimated. The heavy metal export into the North Sea is of circumstantial relevance in relation to the total metal load entering the Baltic Sea (Dippner and Pohl, 2004). 

Alterations in trace metal concentrations in the marine environment due to man s activities are difficult to establish, since natural levels are often poorly known, or when known show variations. At present, measurement of concentration gradients (both vertical and horizontal) from known pollution sources is the primary method to assess trace metal contamination of the marine environment. High trace metal inputs into estuarine or coastal areas from industrial effluents as well as from river run-off have been measured. Without knowledge of the make-up of these source materials, distinguishing between a natural and an anthropogenic origin for increased metal concentrations is an insoluble problem. 

Ions added to sea water by natural processes exceed man s input, with few exceptions. Harbor and estuarine waters, however, are sites potentially capable of sustaining significant increases in many metal ion concentrations due to pollution. The effect of non-essential ions on living systems will be to select against those individuals in a population which are incapable of handling the stress caused by the increased concentration perturbation. If the conditions persist, the - usually — toxic metal ion will be passed upwards in the food chain at higher concentrations than before. Toleration by individuals of this increased dose will vary the effects on man will probably range from uncomfortable to hazardous. 

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