SUMMARY Lagoons and limans of Kamchatka being transitional zones (ecotones) between marine and terrestrial ecosystems are the places of adaptation of juvenile salmon fish (smolt) migrating from the rivers to the sea and re-adaptation of the adult salmon returning to the rivers for spawning. As far as the salmon fishery is the basics of Kamchatka economy, the study on hydrobiological processes of anthropogenic origin taking place in lagoons and limans becomes one of the leading problems of sustainable nature management in the region.

Lagoon formation on Kamchatka has its own particularities, which are well demonstrated using the example of western Kamchatka. The western coast of Kamchatka is a relatively straight line bulging out slightly into the Sea of Okhotsk. The currently observed orientation of the coastline is the result of the last major rebuilding of the coast, which occurred in the middle of the Holocene. These rebuilding processes did not end then, and are reflected today in the erosion which is observed along the entire western coastline of Kamchatka. The main prerequisites for coastal erosion are the modern rise in global sea level, the creation of equilibrium profiles on the underwater continental slope, and the cutting-off of river estuaries from the sea. This last phenomenon brings about a deficit in detrital material and, at the same time, frees up wave energy for the erosion of the shore. Tidal currents, which can reach 2m/second, also play a significant role in the formation of the coastal zone.

As a result of the activity of these natural processes, practically all of western Kamchatka is made up of the lagoon-estuary type of coastline, where numerous interlaced lagoons stretch for tens of kilometers. Increasingly active and intensive anthropogenic influence on the hydrochemical regime, as reflected in the sharp increase in the concentration of such pollutants as heavy metals, detergents and especially oil products, is observed in all of these water bodies. This process of pollution (deterioration would be a better word) is accentuated by the fact that lagoons serve as a sharply defined geochemical barrier between the terrestrial and oceanic environments, and thus possess their own particular geochemical nature. This is seen in the form of geochemical barriers at the zone of contact between fresh water from rivers and salt water of the lagoons themselves, and in the contact zone between these waters and oceanic waters.

Geochemical studies of Kamchatka lagoons showed that maximum concentrations of pollutants are noted in the contact zone, i.e. the zone of active mixing and interaction between sea and fresh waters. Heavy metals and detergents, very stable and having a tendency to accumulate, are concentrated not only in the waters of the lagoons, but also in their sediments, thus worsening the lagoons’ oxygen regimes.

Lagoons surrounded by fishery plants and settlements are polluted by oil products and waste waters most intensively. For instance, according to drilling data from the near-shore sediments of Icha estuary, layers from 2.8–4.5 m are saturated by oil products. Moreover, the polluted layer is located lower than the surface of the estuary, and therefore oil products are actively filtrated to the water layer and then accumulate in the bottom sediments. Low temperatures reduce the speed with which oil products break down, thus causing their conservation.

Nevertheless, the lagoons of Kamchatka as a whole are only in the initial stages of pollution. The sharp decrease in fish processing activity along the coast in the past several years, which has brought about the closing of many such factories, has significantly slowed the pollution process. Nonetheless, the ill-advised destruction of connecting bars dividing the lagoons from the sea continues with no less intensity than in the past.

There is quite a different situation in Avacha Bay, one of the largest, most beautiful and convenient harbors in the world. In its geomorphological structure, and in the particularities of sediment accumulation, it is quite similar to a typical lagoon. The Bay has been seriously damaged by intensive anthropogenic pollution, and is now in a critical condition. The main criteria of the ecological crisis are as follows: an abrupt increase in the process of silt accumulation (up to 20 cm per year in the estuarine part of the Bay), active accumulation of oil products in the bottom sediments, and, most importantly, a considerable decrease in the productivity and reproductive success of hydrobionts. This process of biota degradation in the Bay may become irreversible.

Avacha Bay is an orb-shaped, closed water body, whose main axis is oriented from SE-NW. It is connected with the ocean (with Avacha Inlet) by a relatively narrow channel. The Bay’s shoreline is extremely windy and is cut by numerous smaller bays — Tarya, Rakovaya, Babya, Petropavlovskaya, Seroglaska, Moxovaya and others.

The Bay is essentially isolated from the ocean’s turbulence. Because of this, wave action year round is limited to what local winds can stir up. The most commonly encountered waves are those up to 0.25 m in height, with a primarily western heading. Only rarely, when the wind blows strongly from the NW, can waves in the Bay reach 2m. This happens most often in the winter.

Fluctuation in water level in the Bay and the outflow of water from its boundaries is accomplished via tidal flow and weak longshore currents. Tides as a rule are of an irregular daily character, with a maximum amplitude of 1.5 m.

In this way, anthropogenic pollution is made possible by a whole host of factors. First of all, the closed nature of the Bay as a whole and its isolation from the ocean’s turbulence impedes active ocean-bay water exchange. Second of all, two large rivers, the Avacha and the Paratunka, as well as plenty of small ones flow into the Bay. They carry large quantities of tractional material (sands and aleuro-pelites) and suspended load. Thirdly, on the shoreline and within the watershed of the Bay is found a large human population (approximately 350,000), with its ports and docks, its ship repair yards, fish processing and other industries. Finally, the temperature regime of the Bay itself, with its clearly defined yearly maximum (13 C in August) and minimum (-1 C in January-February) and yearly ice-over of the near-coastal zone and the smaller bays for 4–5 months each year, doesn’t allow the dissipation and break-down of pollutants.

The presence within the Bay of numerous inlets also contributes to the Bay’s pollution in that the Bay’s longshore current can cover only a small part of the Bay itself, and simply isn’t capable of carrying out the sedimentary materials deposited in these quite isolated water bodies. Intensive modern settling of the Bay’s floor increases the process of sediment accumulation.

As a result of all of these processes, upper bottom sediments in Avacha Bay are represented by silts, sands, gravel, pebbles, stones and sometimes also by bedrock. Black silt covers about 45% of the entire bottom area of the Bay, and is found mainly in deeper, central parts of the Bay and its smaller inlets (Moxovaya, Bogatyrovka, etc.), in water deeper than 22–23 m. Near the city’s coast, this silt rises to a depth of 14–21 m, which is most likely connected with intensive anthropogenic influence. Brown silt (more than 25% of the Bay’s area) engirdles the entire Bay in a band of uneven width at depths of 5–20 m. This silt is most dominant in the southern part of the Bay, and near its mouth, where it is found at depths to 23 m, which it would seem is the result of the ocean’s influence. Brown silt is least abundant along the city’s shore.

Sand deposits lie in the estuarine regions of the Bay, as well as near its mouth. These regions are approximately equal in area and together cover around 60 square km. Large grained, clean sand is also found on the shoals of the Seroglaska, Rakovaya, Zavoyko and Turpanka Bays.

Shoal areas are dominated by gravel, pebbles and clastic layers (Bogatyrovka Bay, Cape Signalny, the upper littoral area of Turpanka Bay). Large grained clastic material is most often found near the slopes of actively eroding cliffs, such as at CapeKazak, or the candle rocks in Agatovaya or Seroglaska Bays.

Overall, the size of the loose sedimentary layers in the Bay is insignificant, ranging from 3m in the near-shore zone to 10m, and in some cases to 20m, in the Bay’s central areas.

As a result of the low level of water exchange with the ocean, and the high level of water outflow into the Bay from human sources, the rate of sedimentation in the Bay has risen sharply. In some areas of the Bay (for instance, Mokhovaya Bay) silt sedimentation occurs at a rate of 10-20 cm per year, and because of the spilling of oil and factory run-off into the water, bottom sediments to a depth of 3-5m are saturated by oil products.

It is clearly seen that these unfavorable conditions are one of the main causes of the lowering of biomass productivity amongst the Bay’s hydrobionts. In part, observations over the past several years of its benthic fauna have shown a sharp decrease in algae species diversity, mainly in the disappearance (up to 60%) of red, brown (to 50%) and green (to 25%). We suppose the sterilizing effect of toxic materials in the bottom sediments to be the principal cause of red algae loss in the Bay. The differing susceptibilities of various groups of algae to pollution brings about serious changes in the structure of phytocenoses and the establishment of a new equilibrium between algae and the rest of the Bay’s biocomponents.

In this way the unfavorable geochemical regime which has arisen in Kamchatka lagoons as a result of anthropogenic pollution becomes one of the main causes of the lowering of biomass productivity of the lagoons themselves and of the rivers that flow into them. Since modern lagoons cover most of the western coast of Kamchatka, as well as the coast of the Karaginsky-Olyutorsky Bay — some of the world’s richest fishing grounds — the problem of their pollution has not only scientific meaning, but also an important socio-economic one as well.