Anthropogenic impact on the shelf
First of all, we need to note the extreme diversity and mosaic nature of anthropogenic impact on the hydrosphere. It includes such multifactorial phenomena as changes in temperature regime and radioactive background, discharges of toxic effluents and inflow of nutrients, irretrievable water consumption and damage of water organisms during seismic surveys, landing of commercial species and their cultivation, destruction of the shoreline and construction of drilling rigs.
Underestimation of the striking complexity of anthropogenic impact on the water ecosystems and the use of a single-factorial approach to analyze their state, focusing on some single aspect of human activity, generally lead to a distorted picture of the consequences of such activity. Simultaneous impacts of several factors can cause synergetic effects when the consequences can exceed the mere sum of the effects caused by each factor separately. Such situations are quite possible, for example, when radioactive, chemical, and thermal impacts are combined.
Another important circumstance is that many kinds of economic activities are rather difficult to differentiate based on their effects in the marine and freshwater systems. Many pure inland activities can lead to the ecological changes in the marine environment. Examples include dam construction, removal of river water for irrigation, cutting of forests, use of chemicals in agriculture, atmospheric emissions from factories and automobiles, sewage discharges into lakes and rivers, and many other impacts that take place hundreds and thousands of kilometers away from the seashore. Sooner or later, these activities affect the ecology of estuaries, bays, coastal waters, and sometimes of entire seas. The situations that developed, for example, in the Aral and Caspian Seas, the Sea of Asov, the Baltic and Black Seas clearly show that dividing the ecological problems and environmental protection programs into marine and freshwater ones is artificial and inept. From a broader perspective, we may state that effective protection of the water environment is impossible without protection of the inland ecosystems and vice versa.
Anthropogenic impact on the water environment should be defined as a cumulative manifestation of all kinds of human activity which causes obvious and/or hidden disturbances in the natural structure and functions of water biotic communities, anomalies in their habitats, changes in the hydrology and geomorphology of water bodies, diminishing their fisheries and recreational value, and other negative effects of ecological, economic, or socioeconomic nature. This definition is based on the concept of a multifactorial nature of anthropogenic impact on the hydrosphere. This impact cumulatively results in structural and functional responses of the water ecosystems and biota.
The concept of anthropogenic impact is extremely important for analyzing the ecology of coastal and shelf zone. For centuries this zone has been the center of various human activities. These include urbanization, construction of seaports and harbors, development of natural resources (including oil production and fishing), marine aquaculture, shipping, recreation, and many others. Various activities that are in progress in the narrow area on both sides of the shoreline provide 50% and more of the gross national product of many countries. All of these activities affect (usually directly and hazardously) the shelf ecology. At present, the anthropogenic disturbances of the shelf zone are found on a global scale. In many areas, they have reached critical limits. This is the prize for the unjustifiably rapid economic growth and shortsighted environmental policy (or rather for its absence).
At least two reasons allow us to consider pollution as the main, most widespread, and most dangerous factor of anthropogenic impact on the hydrosphere. First, pollution accompanies most kinds of human activities, including offshore oil and gas production and marine oil transportation. Second, in contrast with land ecosystems, in the water environment, pollutants quickly spread over large distances from the sources of pollution. In the freshwater and inland ecosystems, the effects of pollution are obvious. They literally appear right in front of our eyes. In contrast, the World Ocean has a large inertia of response to all forms of external impact. It requires a long hidden (latent) period to manifest the evidence of non-obvious consequences of this impact. The danger of the situation is complicated by the fact that when it happens, it will be too late to do anything.
Pollutant input into the marine environment
Among all the diversity of human activities and sources of pollution, we can distinguish three main ways that pollutants enter the marine environment:
- direct discharge of effluents and solid wastes into the seas and oceans (industrial discharge, municipal waste discharge, coastal sewage, and others);
- land runoff into the coastal zone, mainly with rivers;
- atmospheric fallout of pollutants transferred by the air mass onto the seas' surface.
Certainly, the relative contribution of each of these channels into the combined pollution input into the sea will be different for different substances and in different situations. Quantitative estimates of these processes are difficult because of the lack of reliable data and the extreme complexity of the natural processes, especially at the sea-land and sea-atmosphere boundaries.
For a number of pollutants (metals, nitrates, phosphates, oil and some other hydrocarbons), this task is even more complicated. They are distributed in the marine environment in the background of natural biogeochemical cycles of the same substances. There are numerous examples when extremely high concentrations of oil and gas hydrocarbons, heavy metals, radionuclides, nutrients, and suspended substances are not connected with human activity at all. It can happen as a result of such natural processes as volcanic activity; oil and gas seepage on the bottom; splits and breaks of the earth's crust; algae blooms; mud flows; river floodings; and many others. These phenomena should be taken into consideration in order to get the objective assessment of anthropogenic impact and its consequences in the hydrosphere.
Recognizing these complications explains why many earlier conclusions about the levels, flows, and balance of many substances in the hydrosphere are currently under revision. Developing new approaches and more precise analytical methods to determine trace amounts of contaminants allowed to get more reliable estimates of the contribution of different channels into the total contamination of the marine environment. The data show that land-based and atmospheric sources account for about two-thirds of the total input of contaminants into the marine environment, constituting 44% and 33%, respectively. The main pollution press undoubtedly falls on the shelf zones and especially on the coastal areas [Windom, 1992].
Sources, composition, and degree of hazards of pollution components
We need to mention the extreme diversity of marine pollution components, variety of their sources, scales of distribution, and degree of hazards. These pollutants can be classified in different ways, depending on their composition, toxicity, persistence, sources, volumes, and so on.
In order to analyze large-scale pollution and its global effects, it is common to distinguish a group of the most widespread pollutants. These include chlorinated hydrocarbons, heavy metals, nutrients, oil hydrocarbons, surface-active substances, and artificial radionuclides. These substances form the so-called background contamination that exists at present in any place in the hydrosphere.
Depending on the type of impact on the water organisms, communities, and ecosystems, the pollutants can be grouped in the following order of increasing hazard:
- substances causing mechanical impacts (suspensions, films, solid wastes) that damage the respiratory organs, digestive system, and receptive ability;
- substances provoking eutrophic effects (e.g., mineral compounds of nitrogen and phosphorus, and organic substances) that cause mass rapid growth of phytoplankton and disturbances of the balance, structure, and functions of the water ecosystems;
- substances with saprogenic properties (sewage with a high content of easily decomposing organic matter) that cause oxygen deficiency followed by mass mortality of water organisms, and appearance of specific microphlora;
- substances causing toxic effects (e.g., heavy metals, chlorinated hydrocarbons, dioxins, and furans) that damage the physiological processes and functions of reproduction, feeding, and respiration;
- substances with mutagenic properties (e.g., benzo(a)pyrene and other polycyclic aromatic compounds, biphenyls, radionuclides) that cause carcinogenic, mutagenic, and teratogenic effects.
Some of these pollutants (especially chlorinated hydrocarbons) cause toxic and mutagenic effects. Others (decomposing organic substances) lead to eutrophic and saprogenic effects. Oil and oil products are a group of pollutants that have complex and diverse composition and various impacts on living organisms - from physical and physicochemical damage to carcinogenic effects.
To estimate the hazard of different pollutants, we should take into account not only their hazardous properties but other factors, too. These include the volumes of their input into the environment, the ways and scale of their distribution, the patterns of their behavior in the water ecosystems, their ability to accumulate in living organisms, the stability of their composition, and other properties.
Global and regional aspects
At present, the signs and consequences of human activity can be found everywhere on the Earth. One of the typical features of marine pollution is global spreading of a number of contaminants. Numerous data undoubtedly indicate the existence of a large-scale (global) field of background contamination of the hydrosphere.
Another important feature of marine pollution is the existence of increased pollution levels in the enclosed seas and coastal waters as compared with the open ocean.
Contamination levels also increase during the transition from the southern parts of all oceans to the north, where the main industrial centers and main pollution sources are concentrated. Besides the general pattern of distribution of pollution sources, there are two other factors explaining the relative stability of the global pollutant distribution in the World Ocean. Those are the relative confinement of large-scale water circulation within the limits of each hemisphere and the predominance of the zonal transport (that is, moving along the geographic parallels) of the traces in the atmosphere.
Another distinctive and repeatedly registered feature of the general picture of contaminants distribution in the marine environment is their localization at the water-atmosphere and water-bottom sediment boundaries. Practically everywhere and for all trace components (primarily for oil hydrocarbons), their concentrations are considerably (usually hundreds and thousands of times) higher in the surface microlayer of water and in the upper layer of bottom sediments. These boundaries provide the biotopes for the communities of hyponeuston and benthos, respectively.
The existence of elevated levels of contaminants in the zones of high bioproductivity is extremely ecologically alarming. These zones include the water layer up to 100 m from the water surface (photic layer) and boundaries of natural environments (water-atmosphere and water-bottom sediment, as previously mentioned) as well as enclosed seas, estuaries, coastal and shelf waters. In particular, in shelf and coastal zones, which take only 10% of the World Ocean surface and less than 3% of its volume, the most intense processes of bioproduction, including the self-reproduction of the main living resources of the sea, take place. The main press of anthropogenic impact is also concentrated here.
It is significant that at the regional and local levels, the intensity of anthropogenic press on the marine environment generally increases. The number and diversity of pollution components is growing as well. The contaminants with global distribution are combined here with hundreds and thousands of ingredients of local and regional distribution. Most of these substances are wastes and discharges from different local industries and activities. Often they are not included in the sphere of chemical-analytical control and monitoring. We usually get to know about their existence in the water environment from various signs of environmental trouble. These include the decline of abundance and various pathologies among fish and other organisms, poisoning or diseases among people, degradation of coastal ecosystems, fouled beaches, unusual algae blooms, and so forth.
Different marine regions are subjected to various and specific impact factors. The combination of these factors under specific conditions ultimately defines the ecological situation in a given area. In particular, we want to stress the alarming features of the ecological situation in many Russian marine areas. The pollution levels here very often exceed the maximum permissible limits. This fact was one of the reasons why during the United Nations Conference on Environment and Development in 1992, Russia was rated as one of the most polluted countries of the world [Rybalski, Zaslavski, 1993].