The content of heavy metals in the habitat of birds, Zeya-Bureya plain

. From 2019 to 2021, the content of heavy metals in the components of the aquatic ecosystem, which is the habitat of birds on the territory of the Zeya-Bureya plain, was studied (water, sediments, macrophytes, bird feathers). High levels of iron and manganese were found in the water of small rivers. Due to heavy rains and floods, heavy metals were washed out of the surface layers of soil in agricultural fields into rivers. High concentrations of copper and lead were found in the bottom sediments of small rivers. Agricultural pollution of aquatic ecosystems affected the accumulation of lead and manganese in macrophytes. Bird feathers contained the highest amounts of iron, zinc, copper, and manganese, and the lowest amounts of cobalt and cadmium. The feathers of protected bird species such as Swan Goose, Red-crowned Crane, Hooded Crane and Daurian white-naped Crane contained lead 13.5 -38.2 mg/kg, cadmium 0.17 - 0.51 mg/kg. The elements in the feathers of birds were of exogenous origin. Birds are bioindicators of anthropogenic pollution. Researches in this direction are necessary for an estimation of ecological risk of environment and acceptance of measures on its protection.


Introduction
The transformation of the natural landscapes of the Zeya-Bureya Plain occurred as a result of the development of agriculture in the area, the construction of roads and the social infrastructure of villages located along the banks of small rivers.The number of animals and plants has decreased, and their biodiversity has decreased.The use of chemicals in agriculture poses a threat of organic pollutants and heavy metals entering the environment and negatively affecting living organisms.The accumulation of toxic elements such as lead and cadmium in the environment has a negative impact on birds, contributes to disease and death of chicks [1].In order to preserve natural landscapes with intensive agriculture in the vast areas of the Zeya-Bureya plain, it is necessary to make decisions on nature conservation, to use scientifically sound technologies in agriculture.
The purpose of this work was to study the content of heavy metals in the environment and in the feathers of birds inhabiting the territory of the Zeya-Bureya plain.

Objects and methods of research
Objects for study are water, bottom sediments of small rivers and lakes, macrophytes, bird feathers.
Areas of study are small rivers -Dim, Arguzikha, Gilchin, a Bol'shoy Alim (Manga)left tributaries of the Amur river and the Belaya River is a left tributary of the Zeya River.Small rivers have ceased to be full-flowing and navigable since reservoirs were built on them more than forty years ago.At present, the reclamation systems are in need of repair.The riverbanks are swampy.In the lower reaches of the rivers at the confluence of small rivers into the Amur are wetlands, which are home to about 300 species of birds, including rare and endangered species under protection -the red-crowned crane, the Oriental stork, the hooded crane and the Daurian white-naped crane.
Water sampling in small rivers was carried out from 2019 to 2021 in different seasons of the year: in the period after the opening of the ice (may), during the peak of vegetation (June-August) and autumn cooling of waters (September).
Bottom sediment sampling was carried out in the summer of 2019 at a distance of 0.2-1 m from the river Bank at a depth of 0.2 m.Bottom sediments were transported in opaque plastic bags, stored in a refrigerator before analysis.Macrophytes were selected in summer, washed with deionized water, and dried in a drying Cabinet at a temperature of 60 °C to an air-dry state.Sample preparation was carried out on the complex «Temos-Express TE-1», based on the destruction of interfering organic substances by thermal action together with oxidants (HNO3, H2O2).Heavy metals in river waters, aquatic plants, bottom sediments, bird feathers were determined by atomic absorption method using the Quant-Z.ETA spectrometer.Hydrochemical indicators were performed in accordance with the regulatory documentation.

The content of heavy metals in water of small rivers
The acid-base properties of water in a river determine the form in which a metal is found.In an acidic environment, metals are in ionic form and become bioavailable.In spring, the pH value of water in the rivers of the Zeya-Bureya Plain was normal and was 6.8 to 8.4.In autumn, the pH value in the Arguzikha River was 9.3, and in the Manga River it was 9.0.Increase of water pH value in small rivers, which was observed in summer and autumn, is connected with high bioproductivity of phytoplankton.Water conductivity was low in spring from 39 μS/cm in the Dim River to 120 μS/cm in the Arguzikha River, in summer specific conductivity increased from 179 μS/cm in the Dim River to 300 μS/cm in the Gilchin, Manga and Arguzikha Rivers.Water in small rivers of the Zeya-Bureya Plain is characterized by low mineralization [2,3].Low values of water hardness and mineralization affect the mobility of heavy metals and contribute to an increase in bioaccumulation [4].The content of cadmium in the water of small rivers during the research period did not exceed the norm.The high concentration of heavy metals in water was observed during the disastrous flood in the Amur River basin in the summer of 2013 and 2021.During the flood in 2021, very high levels of heavy metals were detected in the Zavitaya River: Cu 19,66-65,66 µg/L, Zn 17.85-25.65µg/L, Cd 0.35-0.85µg/L, Pb 7,57-29,89 µg/L [5].Maximum concentrations of heavy metals were observed in the lower reaches of small rivers.Due to heavy rains and floods, heavy metals were washed out of the surface layers of soil in agricultural fields and into rivers.The high iron content in the streams of the Amur basin is due to the presence of iron-containing minerals in the soils and rocks of the taiga territories (Table 1).
Floods are the cause of contamination of reservoirs and small rivers with heavy metals, organic substances that enter the water from the surface layers of soils [6].

Heavy metal Content in bottom sediments of small rivers
The final link in the cycle of technogenic elements in the landscape is the bottom sediments of reservoirs.Accumulation of pollutants in bottom sediments may cause secondary contamination of reservoirs [7].A high concentration of copper was found in the bottom sediments of the small Manga and Gilchin rivers (Table 2).Copper compounds and zinc enter into the composition of fungicides and other means of chemicalization of agriculture.
The content of lead and copper in the bottom sediments of small rivers is much higher than in the bottom sediments of the Muravyovka Reserve lakes, which are taken as background values.[3].

Heavy metal Content in macrophytes of small rivers
Macrophytes extract heavy metals from bottom sediments and water [8].Aquatic plants participate in the process of self-purification of small rivers, enrich the water with oxygen during photosynthesis.Macrophytes are successfully used for monitoring and indication of anthropogenic pollution [9,10], for phytoremediation [11,12].It was important to determine the amount of heavy metals in aquatic plants in order to study the habitats of aquatic and semi-aquatic birds.Birds feed on seeds, rhizomes and other parts of aquatic plants.Birds nest in reed beds.A high concentration of lead and manganese in aquatic plants was found (Table 3), which depends on the content of these elements in water and bottom sediments [3].High content of lead in is dangerous for plants because it causes disturbances in the process of photosynthesis.Manganese causes chlorosis of plants [8].In [13] the accumulation of pollutants in plants of wetlands subjected to technogenic pollution was analyzed and heavy metal pollution was found for two plants Phragmites australis and Typha orientalis, respectively: lead 7. 16 mg/kg and 7.05 mg/kg, cadmium 0.59 mg/kg and 0.53 mg/kg, copper 17.6 mg/kg and 12.6 mg/kg, zinc 81.5 mg/kg and 58.9 mg/kg.The content of lead and cadmium in macrophytes increases with anthropogenic pollution.

Heavy metal Content in fish
Fish can contain high concentrations of heavy metals that accumulate in various tissues and organs [14].Perccottus glenii, Rutilus rutilus lacustris, Cobitis faenia live in the rivers and reservoirs of the Zeya-Bureya plain.The content of zinc, copper and lead in fish was within the normal range, arsenic from 2.09±0.73mg/kg to 3.17±1.11mg/kg, mercury from 0.25±0.09mg/kg to 0.34±0.12mg/kg.High concentrations of toxic elements in the muscle tissue of fish pose a threat to those who eat it.Fish is a food base for cranes, storks and other birds.

Heavy metal Content in bird feathers
Birds are bio-indicators of anthropogenic environmental pollution [15].Birds respond to changes in the environment, they can accumulate pollutants from the atmosphere, soil and water.The accumulation of microplastics [16], agricultural chemicals [17], heavy metals and other pollutants [2,3] in various tissues and organs of birds has been studied.Accumulation of heavy metals has been studied in blood, liver and muscles, bones of birds [18], in egg shells, and in feathers of birds [2,3,19,20].Different bird species, differing in lifestyle and type of diet, are studied, but the most important are studies on the determination of heavy metals in the habitat of endangered wetland birds [2, 3, 19 -22].In the feathers of birds Muravyevsky and Amur reserve in the largest quantities were present iron, manganese, copper and zinc, in the least, cobalt and cadmium.The ratio of elements that has developed during the evolution of the biosphere is due to the biological role of elements and geochemical conditions of the environment.High lead content was detected in bird feathers (table 4, 5).The presence of heavy metals in the feathers of birds living in the wetlands of the Amur and Muravyevsky nature reserves indicated exogenous contamination.

Conclusions
Due to heavy rains and floods, heavy metals leached from surface soil layers of agricultural fields and entered the rivers.In the Gilchin and Arguzikha rivers, mosaic contamination of water and bottom sediments with heavy metals and accumulation of lead and manganese in macrophytes were observed during spring and summer.The elements detected in the feathers of birds were of exogenous origin.The results obtained by studying heavy metal pollution of habitats of rare and endangered birds are of great importance for taking conservation measures.Conservation measures should be aimed at preserving the habitats and nesting grounds of water and near-water birds.Solutions for effective land use and science-based farming system in agriculture should be elaborated.

Table 1 .
Heavy metal concentration in the waters of small rivers of the Zeya-Bureya plain, μg/L

Table 2 .
The level of heavy metals in bottom sediments of small rivers of the Zeya-Bureya plain,

Table 3 .
The level of heavy metals in aquatic plants of small rivers of the Zeya-Bureya plain, mg/kg

Table 4 .
Heavy metal content in bird feathers in the Muravyevsky reserve, mg/kg

Table 5 .
Heavy metal content in bird feathers in the Amur nature reserve, mg/kg