Example 2. Indicators of the Ecological Status of Agroecosystems and Pesticides' Dynamics

Nonpoint source loading of agricultural chemicals and sediments from agroecosystems is a measure of the efficiency of the agroecosystem with respect to resources an inputs, and a measure of the potential for contamination of surrounding areas. Nonpoint source loading include agricultural chemicals, animal wastes, eroded soils and genetically engineered organisms.

Nonpoint pollution is characterized by highly variable loading, with rainfall and other environmental characteristics dominating the timing and magnitude of chemical transport. Chemicals are exported from their site of application to nearby streams and lakes by runoff and subsurface flow, leaching to ground water drift from aerial and ground application equipment, chemical dust transport and volatilization. Irrigation practices are known to enhance leaching of chemicals from soil, including applied chemicals, naturally occurring salts, selenium and other trace elements. Irrigation from contaminated water sources can introduce organic chemicals, salts, and nitrates to agroecosystems. Many of these chemicals are subsequently transported to surface water. Chemicals application in irrigation water (chemigation) raises similar concerns. (Meyer et al., 1992).

After careful consideration of the scientific, social, economic and environmental issues concerning agroecosystems and ecosystem health (Schaffer et al., 1988; Rapport, 1989), three assessment endpoints were identified that summarize the essence of the issues (Fig. 19). The assessment endpoints will be used to focus the interpretation of indicator data; they are

quantifiable expression of environmental value that do not change over time, even when specific issuers do change. The assessment endpoints are sustainability, contamination of natural resources, and the quality of agricultural landscapes.

Contamination of natural resources refers to alteration in the quality of air, water and soil by anthropogenically generated stressors that are inputs to or outputs from agroecosystems. Contamination of natural resources may, in turn, impact the structure or function of one or more agroecoystem component, from the biochemical to the ecosystem level. Contaminants can be found in the air, soil, water and biota of agroecoystems and may include air pollutants, agricultural chemicals, animal and municipal wastes, water pollutants and genetically-altered organisms.

Sustainability refers to the capacity of a particular agroecosystm to maintain a level of commodity production that provides food and fiber for basic human needs and an econon~ically viable livelihood for farmers, without jeopardizing the structural and functional components of the ecosystem.

Quality of the agricultural landscape refers to the various ways in which the landscape matrix is modified or used over time for agricultural and non-agricultural purposes. Agricultural land use patterns modify the landscape in which they are developed and influence ecological processes. A vital characteristic of landscape modification is the extent to which the surrounding landscape can support populations of non crop vegetation and wildlife.

We discuss here the problem of agroecosystem contamination, and the next paragraph is devoted to the issues of agroecosystem sustainability and quality of agricultural landscape.

Assessing the spatial and temporal trends in the distribution and concentration of contaminants in agroecosystems is a complex undertaking because of existence of thousands of contaminant sources, spatial and temporal variability of source strengths, multi-media distribution of contaminants, and transformation reactions resulting in products different from the parent contaminants. Connel and Miller (1984) state that the objectives of environmental monitoring can be realized by focusing on two aspects:

monitoring contaminants in different compartments of the environment , and monitoring the effects of contaminants on biota (Fig. 20). The physical and chemical monitoring of air, water and soil can provide information regarding the spatial and temporal trends of the contaminants, but monitoring of the ambient environment does not address issues pertaining to the bioavailability and fate of a contaminant, nor their potential for biological effects. Given these complexities, it is necessary to monitor both the abiotic and biotic component of ecosystem.

Based on the concepts of response functions method and resistance index as well as in case of radionuclides, the model of pesticides dynamics in the elementary ecosystem has been elaborated (Malkina-Pykh and Pykh, 1992).

As it has the structure similar to 9 0 ~ r model, we will not give its detailed description, but pay special attention to simulation results.

Fig. 21-23 demonstrate pesticides dynamics in each unit of elementary ecosystems of various geographical zones.

Pesticides of the 3rd class persistence were chosen as an example (atrazin, etc.) It was applied annually to soils of various types in the amount of 3.3 k g h a before the sowing of potato's leaving 30 years.

The rate of self-purification of soils is increasing from north to south, and the rate of self-purification of surface water is increasing from south to north.

Also the period of stabilization of pesticides accumulation level is decreasing from north to south. The levels of stabilization of pesticides accumulation in soils are as follows: in middle taiga ^- 109,O mglkg, in southern taiga ^- 980; in forest steppe - 580; in steppe - 440; in subtropical 33,O and in desert zone 27.0 (Fig. 21).

The rate of pesticides decomposition in plants, as well as in soils is increasing from north to south and the level of stabilization of pollutant's concentration are equal 0,72 mglkg in the middle-taiga up to 0,025 mglkg in the desert (Fig.

22).

The period, when the level of accumulation is stabilizing, is decreasing from more than 30 years in the middle taiga to 5 years in desert (Fig. 23)

The period, when the level of accumulation is stabilizing, is decreasing from more than 30 years in the middle taiga to 5 years in the desert.

As well as in case of radioactive contamination it is possible to calculate the resistance index of each unit of ecosystems towards the flow of pesticides contamination.

13. Example 3. Soil Organic Matter Dynamics and the Indicator of