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White Sea watershed hydrology and anthropogenic impact 3 page- Represents an absence of data.
Figure 2.9. Interannual variability of the concentrations of pollutants in the Niva, Severnaya Dvina, and Mezen Rivers encompassed by the White Sea. (a) Phenols; (b) oil hydrocarbons; (c) copper compounds; (d) EOOC; (e) lignin sulphate.
conditions of anthropogenic forcing, an urgent necessity to studying the variability of the content and chemical composition of dissolved chemical substances admixed to the White Sea. These data are indispensable for evaluation of the effect of river runoff upon the nature and level of seawater pollution. Numerical assessment and analysis of the variability of river chemical discharge has been made for those components which exhibited substantial differences in the hydrochemical regime at the outlets of the investigated rivers, and of which a high recurrence rate (over 30%) of cases of exceeding MEPC is characteristic. An estimation of the interannual runoff variability was accomplished for the period 1980-1999 for the following chemicals: mineral forms of nitrogen, phosphate and total phosphorus, EOOC, phenols, oil products, synthetic surface-active sub- stances (SSAS), copper, zinc, nickel, chromium and iron compounds, silicic acid, suspended matter, sulphates, chlorides, and the sum of ions. For nitrogen and phosphorus compounds, their seasonal variability in river runoff was studied in detail. A quantitative estimation of the amount of dissolved matter in the runoff was performed by multiplying concentration values by water runoff volumes for a certain time period employing the method offered at the Hydrometeorological Institute (Organization and Functioning .. ., 1999). Time series of at least 8-10 years of observations with a sampling frequency of 6-12 times per year were considered reliable enough for evaluating natural and anthro- pogenic variability patterns in the chemical river runoff. Calculations of chemical substances in the river runoff were undertaken for all rivers under investigation. For a comparative inter-system evaluation of the water and chemical runoffs, a runoff module was introduced (i.e., the relationship between the mean annual runoff and the watershed area surface (tons km2year-1)) (Bryzgalo and Ivanov, 2000). All results of observations of hydrochemical indices have been provided with the data on water runoff published in the State Water Cadastre (Resources of Surface Waters .. ., 1963, 1965; Ivanov, 1998). The results of calculations have revealed first and foremost a very high varia- bility in the chemical composition of runoff for every river system under investiga- tion. Anomalously high amounts of chemical substances in the river runoff were periodically observed in the watershed areas within the Murmansk region (Table 2.7):
• All investigated river mouths (suspended matter, sulphates, and silicon: tens of thousands of tons year-1). • Varzuga, Umba, and Niva Rivers (EOOC up to 10-17 thousand tons year-1; ammonia nitrogen and nitrite nitrogen: up to 2.5 thousand tons year-1; oil hydrocarbons up to 1.5-6.2 thousand tons year-1).
From the watershed areas within the Republic of Karelia, the inflow of chemical substances to the White Sea proved to be very high, periodically (Table 2.8):
• Keret River (suspended matter, the sum of ions, EOOC, and silicon 1.8-16.9 thousand tons year-1).
Table 2.7. Ranges in mean annual amounts of chemical substances in river runoff for the catchment within the Murmansk region (tons year-1).
River (for location of observation stations, see Figure 2.6)
EOOC - easily oxidizable organic compounds; b.l. = below the level of detectability; SAS = surface-active substances.
Table 2.8. Ranges in mean annual amounts (tons year-1) of chemical substances in the river runoff in the Republic of Karelia.
EOOC - easily oxidizable organic compounds; b.l. = below the level of detectability; SAS = surface-active substances.
• Kem River (suspended matter, sulphates, silicon compounds, and EOOC: 23.0- 42.8 thousand tons year-1). • Niukhcha River (the sum of ions: 15.0-35.0 thousand tons year-1).
From the river watershed areas within the Archangelsk region, the highest runoff of chemical substances has been observed for some specific years (Table 2.9):
• Ammonia nitrogen, nitrate nitrogen, and oil hydrocarbons for the Onega, Severnaya Dvina, and Mezen Rivers: 2.0-14.0 thousand tons year-1. • EOOC and silicon compounds for the Severnaya Dvina and Mezen Rivers: 85.0-335.0 thousand tons year-1. • Suspended matter and sulphates for the Severnaya Dvina River: 2.5 x 103thousand tons year-1and 6.2 x 103thousand tons year-1, respectively). Also revealed was a tendency of broadening of range of mean annual runoff when anthropogenic loading is enhanced due to high temporal variability of the concentrations of numerous pollutants in the river water. The higher the anthropo- genic impact, the more considerable becomes the interannual variability of chemical substances in the river runoff (Figure 2.10). Another distinguishing feature of the river runoff chemical composition is the obvious predominance of ammonia nitrogen over nitrate nitrogen at the outlets of the rivers: Ponoy (the ratio is 3 : 1), Niva (5 : 1), and Severnaya Dvina and Mezen (2 : 1). This may be accounted for by not so much the specific features of the watershed as the disturbance of the equilibrium between the intra-system processes of ammonification and nitrification toward the enhancement of the processes of mineralization of great amounts of organic matter of anthropogenic origin in conditions of anoxia. Indeed, the minimum detectable values of dissolved oxygen were reduced to 2.20 mg l-1(Table 2.5). A third distinguishing feature of the river runoff chemical composition is a considerable seasonal variability in the amounts of nutrients (Table 2.10). The broad range of variations of mineral forms of nitrogen and phosphorus in the mean monthly runoff is due to the following factors:
• Specific features of the aquatic regime phases. • Seasonal dynamics of the chemical concentrations. • Alterations to the rate and directions of intra-aquatic processes of mineraliza- tion of organic substances.
Anthropogenic pressure often disturbs the natural seasonal regularity. Figure 2.11 reveals a lack of interdependence between seasonal distribution of water runoff and amounts of ammonia nitrogen and nitrite nitrogen in the river runoff (for the Niva, Zolotitsa, Onega, and Severnaya Dvina Rivers). Because absolute values of the chemical runoff are determined mainly by the water runoff volumes, which are very different for different rivers, the latter are unsuitable for defining the role of the anthropogenic factor in the formation of
Table 2.9. Ranges in mean annual amounts (tons year-1) of chemical substances in river runoff in the Archangelsk region.
EOOC - easily oxidizable organic compounds; b.l. = below the level of detectability; SSAS = synthetic surface-active substances.
(b)
(c)
Figure 2.10. Interannual variability in mean annual amounts (thousand of tons year-1) of the most abundant pollutants in the river runoff: 1 - Severnaya Dvina; 2 - Onega; 3 - Mezen. (a) Oil hydrocarbons; (b) copper compounds; (c) ammonia nitrogen.
the quantitative and qualitative composition of the chemical runoff and its spatial (intra-system) inhomogeneity. For this purpose the module of the mean annual runoff of chemical substances is most useful (tons km-2year-1) (Bryzgalo and Ivanov, 2000).
Table 2.10. Seasonable variability of nitrogen and phosphorus-containing compounds in the river outlets into the White Sea.
Multi-year mean seasonable variation ranges of
n.d. = no available data; b.l. = below the level of detectability; * = data on total phosphorus are presented.
Figure 2.11. Seasonal variations of the water and chemical runoff as assessed by averaging the relevant multi-year data. (a) Niva River, (b) Onega River, (c) Severnaya Dvina River, (d) Zolotitsa River.
The results of calculations of the runoff module for the most abundant pollutants make it possible to conclude that the most intensive inflow of chemical substances with river water takes place, according to Table 2.11, as follows: • Ammonia nitrogen, with the runoffs of the Kem, Zolotitsa, and Mudyuga Rivers: 0.041-0.067 tons km-2year-1. • Nitrate nitrogen, with the runoffs of the Sosnovka, Varzuga, and Severnaya Dvina Rivers: 0.049 tons km-2year-1. • Silicon, with the runoffs of the Ponoy, Sosnovka, Chapoma, Mudyuga, and Mezen Rivers: 1.00-1.40 tons km-2year-1. • EOOC, with the runoffs of the Severnaya Dvina, Mudyuga, Zolotitsa, and Mezen Rivers: 0.72-1.06 tons km-2year-1. • Oil hydrocarbons, with the runoffs of the Mudyuga and Zolotitsa Rivers: 0.10-0.27 tons km-2year-1. The runoffs of the Severnaya Dvina, Onega, and Mudyuga Rivers bring a substantial amount of suspended matter (10.4-14.6 tons km-2year-1) and sulphates (6.88-7.09 tons km-2 year-1) to the coastal regions of the White Sea.
2.5 ANTHROPOGENIC IMPACTS ON ESTUARIES
The necessity for separate consideration of estuary regions of large rivers as inde- pendent aquatic elements within the White Sea basin system is due to the fact that, unlike the remaining part of the hydrologic network of the river basin, their regime is largely governed by marine factors, such as: background sea level, dynamics, thermohaline structure and chemical composition of sea waters, and the presence of brackish forms of biocenoses. This makes it possible to single out a separate kind of aquatic ecosystem: the so-called estuarine ecosystem. The estuarine ecosystem is located mostly in brackish waters, where a number of complex transformations of properties of river discharge (encompassing fluxes of heat, suspended matter, and chemical compounds) take place. The estuarine ecosystem is thus located at the mixing zone of freshwater and seawater, with an unavoidable salinity gradient (always longitudinal and sometimes, additionally, transverse). The estuary zones of such large rivers as the Severnaya Dvina, Onega, Mezen, Kem, and Kovda extend from the river outlet to the delta bar, and are mainly influenced by fresh river water. Estuarine ecosystems, although occupying rather small aquatic areas in the zones of interaction between rivers and seas, are presently considered to be independent ecosystem elements, in the same way as surface, freshwater, and marine ecosystems. In hydrology and geomorphology, only one of the types of the estuary region of a river or its part bears the name of the estuary: viz. the tidal funnel-like river mouth. The other types of estuary region of a river are the delta and the estuary-delta. The analysis of the criteria used for determining the location of the abutments of river estuary zones and estuary ecosystems shows that there is only one such criterion in common, namely, the degree of water mineralization expressed as water salinity.
Table 2.11. Spatial variability of the runoff module of most abundant pollutants: coastal zone of the White Sea (Bryzgalo and Ivanov, 2002). The calculations have been performed for the period 1980-1992.
Runoff module of most abundant pollutants (tons km2year-1)
Compounds
Ponoy 0.017 0.013 0.006 0 1.00 0.30 0.025 0.002 4 0.001 4 0.000 9 0.002 3 0.001 0 1.06 1.50
EOOC - easily oxidizable organic compounds; BOD = biological oxygen demand; SSAS = synthetic surface-active substances.
As a result of multi-factor analysis of hydrological-morphological, hydro- chemical, and hydrobiological characteristics of natural estuary complexes, a conclusion has been drawn that Arctic estuary ecosystems occupy areas of estuary regions where river and marine waters are mixed with a resultant salinity of 0.5- 260. They retain their location in the region during a period that exceeds the duration of the acclimatization of living bottom organisms (2-3 weeks); they are characterized by the presence of specific brackish water forms (Ivanov and Khlebovich, 1996). Since the estuary zones of Arctic rivers are usually strongly influenced by river water, the estuary ecosystem, as a rule, extends toward the marine boundaries of the estuarine zone; often it also encompasses the near- estuary sea areas which are actually outside their hydrological-morphological boundaries (Ivanov, 1987). The main external factors determining the occurring changes in river mouth zones (natural complexes) are: river runoff (water runoff, heat and ice flows, shore wash, chemical and biogenic substances), and at the coastline, water dynamics and thermohaline conditions. The state and formation of river mouth areas here is subject to great change due to human economic activity in the river watershed area and within the estuary zone proper. Among the estuary zones of the White Sea, the most important for the economy and ecology are the Severnaya Dvina, Onega, Ponoy, Niva, Kovda, Kem, and Mezen River mouth regions. The general hydrological characteristics of these regions have been thoroughly discussed in the literature (Georgievsky et al., 1995; Zalogin and Radionov, 1969; Polonsky et al., 1992; Mikhailov, 1997). However, no predictions have been offered concerning the potential changes in the estuary zones of the above-mentioned rivers under the influence of global change. Since the recent decade a stable increase in river runoff has been observed. Its intra-annual redistribution has also exhibited pronounced changes. Since this tendency is confirmed by global climate change scenarios, some variations in the halocline position and its intra-annual location may be expected in the river mouth zones of the rivers within the White Sea Basin. The average halocline location in river mouths is anticipated to progressively shift toward the sea, while its seasonal variability will subside. The extent of penetration of both seawater and brackish water biocenosis habitats into rivers will displace accordingly. Date: 2016-03-03; view: 483
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Rivers (for location of observation stations, see Figure 2.6)
(a)
Nitrogen
Ammonia Phosphorus EOOS, Mineral Suspended River nitrogen Nitrite phosphate Silicon BOD oils Phenol SSAS Copper Zinc Nickel Sulphates matter
Mezen 0.035 0.013 0.008 0 1.09 0.94 0.045 0.001 3 0.003 7 0.001 2 0.007 4 0.001 6 3.19 4.73