White Sea watershed hydrology and anthropogenic impact 4 page

The results of the analyses of long-term data from GON for 16 rivers of the White Sea basin indicate that the occurred long-time anthropogenic impact has already disturbed their natural hydrochemical regime and led to the establishment of a higher anthropogenically-altered background in terms of ammonia nitrogen, EOOC, phenols, oil hydrocarbons, and copper and zinc compounds. The highest contemporary background concentrations related to ammonia nitrogen proved to be in the estuaries of the rivers under investigation of the Republic of Karelia and the Archangelsk Oblast. Regarding EOOC, these are the estuaries of the Severnaya Dvina, Mezen, Keret, Pongoma, and Niukhcha Rivers. For phenols these are the estuaries of the Murmansk region rivers, and with regard to oil hydrocarbons and zinc compounds, these are the estuaries of the Archangel region rivers (Table 2.12).

Table 2.12. Anthropogenically-altered natural background for the major pollutants in river outlets of the White Sea basin.

Modal interval* (mg l-1)

* Natural background - modal interval of the variation series of concentration values from a long-term (1980-1999) observations under GON; b.l. = below the level of detectability; EOOC - easily oxidizable organic compounds; BOD = biological oxygen demand.

The tendency towards accumulation of organic and inorganic pollutants in the aquatic environment results in the disturbance of the seasonal dynamics of nutrients and the concentration of dissolved oxygen. A tendency toward recurring situations of oxygen deficit/anoxia in the aquatic environment is observed, which is especially typical of the estuaries of the Niva and Severnaya Dvina Rivers.

The fact that water samples with high concentrations of nitrite nitrogen (exceeding MEPC by a factor of 10-70) and ammonia nitrogen (exceeding MEPC by a factor of 18-60) are frequently found indicates a potential danger of toxic impact upon the White Sea biocenoses.

Analyses of the GON hydrobiological data has revealed that, due to anthro- pogenic forcing on the ecosystems of the rivers of the Barents Sea region, two basic intra-system processes become accelerated:

• Anthropogenic eutrophication due to the input of a considerable amount of nitrogen and phosphorus-containing nutrients and EOOC.

• Ecological regress of individual communities of water organisms, sometimes leading to their destruction, caused by pollutants (often toxic) periodically accumulated in the aquatic environment in concentrations exceeding MEPC by tens and hundreds of times, and the disturbance of the oxygen regime even in subsurface layers of the waterways.

Anthropogenic eutrophication manifests itself, above all, in a long-term succes- sion of phytoplankton communities, in which the following changes have been observed to develop:

• Broadening of the range of mass species.

• Replacement of low-productive oligotrophic species by highly productive eutrophic ones in the group of diatomic species.

• In the group of diatomic species, periodically predominant position of the Fragillaria crotonensis algae, which can actively vegetate not only in oligotrophic conditions, but also under pressure of anthropogenic eutrophication.

• Massive development during the summer-autumn period of blue-green algae.

• Aphanizomenon fios-aquae, usually present in phytoplankton, but also some species of the class of Anabaena, Oscillatoria and Microcyctis.

The toxic effect of anthropogenic nature, causing an element of ecological regress of individual communities, reveals itself most apparently in the development of:

• Phytoplanktonic communities, for which not only a decrease in total number, but also a disturbance of structural organization is characteristic because o:- saprobic species from the classes Steppanodiscus and Syndra have been occupying a predominant position.

• Zoobenthic communities, whose natural modifications were accompanied not so much by a low level of growth (when their number did not exceed 0.30 thousand

52 White Sea watershed hydrology and anthropogenic impact [Ch. 2

per square meter) as by an active development of the group of oligokhets taking the leading position (with a relative number of 60-100%).

The results of analyses of contemporary tendencies in long-term (multi-year) variability of the hydrological and ecological conditions in the rivers of the White Sea basin, make it possible to draw a conclusion that the controlling factors of the changes, apart from the income of pollutants from transboundary transport and technogenic impacts of human activity (chemical, oil-and-gas production, pulp- and-paper, mining and coal industries, ferrous and non-ferrous metallurgy, electric power engineering, and agriculture), are the growing rate of the intra-system processes, such as anthropogenic eutrophication and ecological regress, which drive the estuary systems to a new trophic state (Bryzgalo and Ivanov, 2000).

Detailed study of the variability of the contents and quantitative composition of the river runoff chemical substances brought to the coastal regions of the White Sea has shown that anomalously high runoff is periodically possible for the Ponoy, Niva, Onega, Severnaya Dvina, and Mezen Rivers with regard to ammonia nitrogen and oil hydrocarbons, and for the Sosnovka, Chapoma, Varzuga, Umba, Niva, Onega, Severnaya Dvina, Mudyuga, and Zolotitsa Rivers with regard to EOOC.

It has been noted that the basic specific feature of the runoff chemical composi- tion is an obvious predominance of ammonia nitrogen over nitrate nitrogen, as well as the violation of the relationship between the seasonal distribution of water runoff and the nutrients runoff.

A comparative assessment of the intensity of matter washout from watersheds (the chemical runoff module) has revealed that a consequence of anthropogenic impact is a qualitatively and quantitatively enhanced inter-system inhomogeneity of the constituent composition of river inflow to the White Sea. It should be noted that a further increase of the runoff of pollutants will result in a greater contamination of bottom sediments in the halocline zone, and hence, in the bio- logical accumulation of pollutants in brackish water species of planktonic and benthic communities.

Date: 2016-03-03; view: 685