White Sea watershed hydrology and anthropogenic impact 2 page

2. River catchment within the Republic of Karelia

Total watershed of the 717,700 230 189 41 1950-1998 White Sea basin

Note: Information about basin mouth stations of the White Sea rivers are presented in Table 2.1. The total river runoff relevant to non-investigated parts of their watersheds (below the basin mouth and interfluves) is presented in accordance with the available annual mean runoff maps.

* Data are given on the basis of maps of mean annual water inflow.

Figure 2.5. (a) Interannual and (b) seasonal variations of the freshwater inflow to the White Sea. 1 - river water inflow; 2 - atmospheric precipitaton contribution.

values. A significant variation in the seasonal runoff temporal distribution has been found and thought to be the cause of alterations to the hydrological and hydro- chemical regimes of rivers and their estuaries.

2.3 VARIABILITY IN THE HYDROLOGICAL AND CHEMICAL REGIMES OF RIVER SYSTEMS

Earlier, it was emphasized that variations in the water and heat balance character- istics caused by climate change and various anthropogenic impacts first lead to

Sec. 2.3]

changes in the regional hydrology and eventually result in alterations to the ecologi- cal state of the river systems. In addition, bottom deepening, navigation condition improvements, sand and gravel excavation, and timber rafting lead to changes in the moisture storage capacity of the river bed, the water surface slope, current speeds, and the violation of the relationship between the water consumption and level and the appearance of uncontrolled deformations in the zone of influence of quarrying. In conditions of dynamic equilibrium, the river flow in a river course with a mobile stream bed is characterized by a stability of the basic indicators of the hydrological and stream bed regimes. At the same time, the characteristics of liquid and solid runoff and basic morphometric indicators remain unchanged for a long time. This makes it possible, on the basis of acknowledged methods, to forecast the development of the river course process for the future, and to take the forecast

data into account when planning the future economic activity in the river basin.

In the case of the interference of civil engineering activities with the natural course of stream bed processes, the flow responds to artificial changes in its river bed. Its reaction reveals itself at various levels of the water flow-river course system and, depending on the extent of impact, can have different spatial- temporal expressions. As a rule, during the initial period, these processes are more intensive along relatively short stretches of the river course. Further on, the intensity of changes slows down, however, the impact per se broadens both upstream and downstream of the point where the civil engineering activities took place. In such cases, one may speak about alterations to the river bed stability.

The response of the water flow to artificial changes in the river course is always directed toward enhancing its stability. However, such interactions only occur in a

water flow-river course system within certain limits, depending on the extent of civil engineering interference, and they persist until the flow remains capable of adjusting the characteristics of its course by itself.

In determining the extent of a permissible impact upon the river course process for planned civil engineering constructions and activities, one must take into account that on the navigable rivers of the Barents Sea the impact of anthropogenic activity has already taken place on both the catchment and in the river courses. Therefore, in planning future exploitation of these waterways for the purpose of economic activity, one must take account of their present-day state. The admissible extent of the impact should be determined as a function of the nature of the water body in question and the actual status of the natural environmental setting (Gladkov, 1994; Grishanin, 1997).

At present, there are no reliable estimates of long-term variations of the water and river course regimes as affected by global impacts. However, with knowledge of generally regular features of interactions between the water flow and river course with increased water content in rivers, one may expect some enhancement in rates of the river course processes as well as a transition of the river course network into a new state with changed hydraulic-morphological characteristics.

In light of the anticipated variations in atmospheric heat balance elements and runoff rates, the ice cover and thermal regimes of rivers will also be subjected to certain alterations. The Russian Hydrometeorological Centre (Ginzburg and

Soldatova, 1999) conducted an analysis, of a number of anomalies occurring with the onset of floating ice and spring ice movement on the Pechora and Severnaya Dvina Rivers, revealing the presence of a tendency towards a milder ice regime. This manifests itself as an earlier ice-breaking and a later freezing of rivers. However, the absolute values of the tendency are small and only constitute 2 to 5 days per one hundred years. Such a tendency is 3 to 4 times weaker than the similar ones for rivers of more southern regions in the European part of Russia. It has been established that the sign and magnitude of the revealed tendencies are dependent on the trends of the monthly mean air temperature in the specific area. On the basis of various scenarios of global climate warming, it has been established that during the current decade (1996-2005), the onset of the appearance of ice on the rivers of the White Sea basin may happen somewhat later (by 2-6 days), and conversely, the onset of the ice break- up apparently occurs earlier (by 1-3 days).

The ecological state of riverine estuaries in the White Sea is strongly influenced by anthropogenic factors that manifest themselves firstly in a change of their state at the transition from oligotrophic ecosystems to mesotrophic ones, and sometimes even to eutrophic ecosystems. These changes take place under conditions of severe climate, ample cases of areas of deeply freezing rocks, a low potential of self- purification and low restoration capability of natural waters, and finally, low biodiversity. This in total determines the high vulnerability of the ecosystems under consideration, including their high sensitivity to all kinds of natural and man-made impacts.

Natural factors include, first of all, the atmospheric precipitation, water and sediment runoff, thermal-ice and river course regimes, and solar radiation.

The main anthropogenically-induced factors are: (1) physical impacts such as river runoff regulation by HEPS, thermal effects, navigation improvement activities, quarry works, and onshore hydrotechnical construction works; and (2) chemical contamination due to sewage and gas emissions from industrial enterprises.

The principal intra-system factors involve redox reactions and production- decomposition processes, and the transformation of pollutants. The role of these factors for the dynamics of the state of the river systems can be different, depending on the actual environmental conditions and specific nature of the economic activity. The dynamics of the regional hydrochemical regime can be evaluated on the basis of the relevant long-term (1965-1999) hydrochemical data from permanent observation stations composing the Governmental Observation Network (GON) of the former USSR, and at present, the Russian Federation. GON was and is intended for monitoring the quality of surface waters. Observation stations are located in 16 rivers, including the Severnaya Dvina, Onega, Ponoy, Niva and Mezen. These rivers constitute the basic inflow of river water to the White Sea

(Yearbooks of .. ., 1981-2000).

The locations of the observation are presented in Figure 2.6. The main hydro- logical characteristics collected at the rivers lowest stations are shown in Table 2.4 (for all stations of hydrochemical observations, the corresponding data on the hydrometeorological regime are available) (Resources of Surface Waters .. ., 1963, 1965; Ivanov, 1998).

Figure 2.6. Location of the hydrochemical observation stations in the rivers of the White Sea basin performed under the GON.

2.4 MAIN FEATURES OF POLLUTANT TRANSPORT VIA RIVER RUNOFF

Analyses of long-term data from GON have revealed some general tendencies in spatial-temporal variations of the hydrochemical regime in river estuaries entering the White Sea. Differences in water level and nature of anthropogenic forcing on the rivers of the region affect the regime of basic parameters of water quality. The most salient features of interannual and seasonal variability have been registered for nutrients and pollutants of major priority.

2.4.1 Mineral forms of nitrogen and phosphorus

For the estuaries, fairly significant differences are observed in the ranges of concen- tration variations of mineral forms of nitrogen and phosphorus in water (Table 2.5).

Table 2.4. Basic hydrometeorological variables from the GON (rivers lowest stations) within the White Sea Basin.

From Ivanov (1998).

Mezen 78,000 Malonisogorskaya 186 56,400 13.3-28.5 28.0

village

b.l. = below the level of measurement sensitivity.

The broadest concentration variation ranges are as follows: the Niva River - ammonia nitrogen (below level of detection (b.l.)-3.19 mg l-1); the Ponoy River - nitrite nitrogen (b.l.-0.070 mg l-1); the Varzuga River - nitrate nitrogen (b.l.-0.12 mg l-1); and the Mezen River - phosphate phosphorus (b.l.-0.263 mg l-1). On the whole, regarding the concentrations in water of nitrogen and phosphorus-containing chemicals, the regime of nutrients in these rivers is fairly similar to that in mesotrophic water bodies, with a tendency to periodic accumula- tions in water of mineral forms of nitrogen and phosphorus up to concentrations exceeding the maximum ecologically permissible concentrations (MEPC) adopted for mesotrophic water bodies by a factor of 3-70 in the case of maximum values in a multi-year variation series, and by a factor of 2-10 in the case of maximum values

within the modal interval.

A characteristic feature of nutrient variations in these rivers is a tendency towards increased interannual and seasonable variability of concentrations of nitrogen and phosphorus-containing compounds with the enhancement of anthro- pogenic loads (Figures 2.7 and 2.8). The characteristic features inherent in the seasonal dynamics of nutrients in natural conditions have been altered for most rivers under investigation due to periodic variations in anthropogenic forcing.

Figure 2.7. Interannual variability in the concentrations (mg l-1) of mineral forms of nitrogen and phosphorus in the Niva and Sosnovka Rivers encompassed by the White Sea. (a) Ammonia nitrogen; (b) nitrate nitrogen; (c) nitrite nitrogen; (d) phosphate phosphorus.

Figure 2.8. Seasonal variability of concentrations (mg l-1) of mineral forms of nitrogen and phosphorus in the Niva and Onega Rivers encompassed by the White Sea. (a) Ammonia nitrogen; (b) nitrate nitrogen; (c) nitrite nitrogen; (d) phosphate phosphorus.

2.4.2 Pollutants

Anthropogenic forcing is manifested mainly in both considerable interannual varia- bility of concentrations of numerous pollutants reaching the estuaries, as well as in considerable broadening of the range of pollutant concentration variations. The broadest range of concentration (in mg l-1) variations is documented for the following rivers (Table 2.6):

• Ponoy River: nickel compounds (b.l.-0.073).

• Varzuga and KerettRivers: easily oxidizable organic matter (EOOC) (0.02- 8.52).

• Niva River: phenols (b.l.-0.380), oil products (b.l.-6.90), and SAS (b.l.-0.940).

• Onega River: copper compounds (b.l.-0.061).

• Severnaya Dvina River: zinc compounds (b.l.-0.248).

A comparative evaluation of the level of pollution in estuaries by the level of excess of MEPC makes it possible to conclude that the critical indices of pollution are:

• Phenols whose concentrations in water sometimes reached 380 MEPC in the mouth of the Niva River and 63 MEPC in the mouth of the Ponoy River.

• Hydrocarbons of oil origin whose maximum concentration was sometimes 138 MEPC in the Niva River mouth and 35-46 MEPC in the mouths of the Chaloma, Varzuga, Onega, and Zolotitsa Rivers.

• Copper compounds, whose concentrations sometimes exceeded MEPC by a factor of 61 in the Onega River mouth and by a factor of 9 in the Mezen River mouth.

For the estuary zone of the Severnaya Dvina River, the critical indices of pollution were lignosulphonates (MEPC = 1.0 mg l-1) whose concentrations in water were in most cases 10-34 mg l-1, with the total range of their long-term content variation being 1.0-212 mg l-1. Cases of an accumulation of methanol in water (MEPC = 0.10 mg l-1) in the concentration range 10.0-33.0 mg l-1are also frequent (Yearbooks of .. ., 2000).

The tendency of accumulation of organic and inorganic pollutants in aquatic environments leads first of all to alterations of the oxygenic regime of the river ecosystems. In estuary zones these alterations reveal themselves in a considerable broadening of the range of dissolved oxygen concentration (up to 2.20-17.8 mg l-1), with a tendency of increasing cases of anoxia. This is very strongly pronounced at the lowest stations in the Niva and Severnaya Dvina Rivers (Table 2.5). Inhomogeneous in terms of duration and levels, anthropogenic forcing is evident in the concentra- tions of numerous pollutants (Figure 2.9).

The observed high variability in the hydrochemical regime of the rivers at their outlets and a significant enhancement of the anthropogenically-altered back- ground for the entire group of most abundant pollutants warrants, under current

Table 2.6. Prevailing pollutants identified at the lowest stations on the rivers flowing into the White Sea basin.

Range of concentrations variations (mg l-1)

EOOC - easily oxidizable organic compounds; b.l. = below the level of detectability; SAS = surface-active substances.

Date: 2016-03-03; view: 484