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Оглавление
Предисловие
Анализ взаимодействия биосферы и геосферы планеты, проявляющегося в биогеохимических процессах почвенного покрова, особенно в условиях растущего влияния хозяйственной деятельности человека на природу, – важнейшая проблема современности. В условиях глобальных и локальных климатических колебаний для понимания современного состояния и прогнозирования направленности процессов развития природно-ландшафтных систем в будущем необходимо знание реакции ландшафтов и их компонентов на подобные изменения в прошлом. В современный период в связи с накоплением большого фактологического материала происходит формирование новых научных разделов и направлений в рамках и на стыке многих наук. В частности, в почвоведении за последние годы сформировались такие направления, как мелиоративное, лесное, археологическое, функционально-экологическое почвоведение и другие. Обобщающей основой этих новых направлений является теория и методология почвоведения. В то же время каждый из разделов при общности исходных теоретических позиций имеет специфику объекта и предмета исследований, из которых вытекает и специфичность методологических подходов к получению и интерпретации эмпирических материалов. В почвах и седиментах существует группа объектов – микробиоморфы, которые хорошо известны (Тюрин, 1937; Усов, 1943; Полынов, 1944; Скрынникова, 1944; Вильямс, 1949; Пономарева, Сотникова, 1972; Добровольский, Шоба, 1978; Рубилина, 1983; Роде, 1984; Гельцер и др., 1985; Ковда, 1985; Штина, 1987; Добровольский, 1999 и др.), однако их информационная роль детально не исследована. Вместе с тем в общей системе научных знаний важен каждый элемент, в том числе микробиоморфы, которые дают новые данные для понимания процессов генезиса и географии природных и антропогенных систем и их взаимосвязи. В работе обосновывается выделение самостоятельного направления в общем блоке морфогенетического (микроморфологического) исследования почв и седиментов – микробиоморфологии. Объектом исследования является микробиоморфный комплекс (МБК), имеющий биогенную природу и характерную морфологию. Показано, что данный комплекс отражает специфику генезиса и эволюции природных и антропогенных ландшафтных систем. Разработка диагностики подобных объектов – актуальная проблема эволюционной географии. Основным методом исследования является сравнительно-географический, заключающийся в изучении микробиоморфных комплексов в различных географических условиях с последующим их сопоставлением. Целью данной работы является показ широких информационных и практических возможностей микробиоморфных комплексов для решения проблемных вопросов почвоведения, географии, археологии и других областей знаний. Объектом исследования явились микробиоморфные комплексы, выделенные из современных и погребенных, разновозрастных культурных слоев поселений и седиментов различных ландшафтных систем и природных зон европейской территории России. Отдельные данные получены по сопредельным территориям Северного Кавказа и Западной Сибири; равнинам Венгрии, Германии, Сирии, Таджикистана, Туркмении, Узбекистана, Украины; предгорьям, межгорным котловинам и горным регионам Абхазии, Австрии, Казахстана, Словении, США. Проведено комплексное исследование этапов становления и развития культурных слоев Москвы и Санкт-Петербурга. Изучено более 250 разрезов, проведено около 3500 микробиоморфных исследований, включающих качественную и количественную оценку отдельных микробиоморф с последующим анализом микробиоморфных комплексов и микробиоморфных профилей в целом. В работе впервые: [–] Разработано и теоретически обосновано выделение самостоятельного направления научных исследований – микробиоморфологии, показано его место в общей системе морфогенетического исследования почв и седиментов. [–] Детально изучена самостоятельная группа включений и новообразований биогенной природы – микробиоморфы, образующие устойчивые микробиоморфные комплексы в почвах и седиментах. [–] Показаны процессы и механизмы, формирующие микробиоморфные комплексы и микробиоморфные профили в почвенно-ландшафтных системах. [–] Выявлены диагностические характеристики микробиоморфных комплексов и микробиоморфных профилей в почвах основных природных зон европейской территории России и интразональных ландшафтах. [–] Определены скорость и специфика процессов формирования и замещения микробиоморфных комплексов, высокая сохранность которых позволяет фиксировать кратковременные этапы развития почв и ландшафтов даже спустя длительные промежутки времени. [–] Описаны диагностически значимые особенности антропогенно измененных микробиоморфных комплексов и микробиоморфных профилей вне зависимости от ландшафтно-географических и хронологических интервалов. [–] Продемонстрирована высокая информационная значимость микробиоморфологии при проведении палеоклиматических и исторических реконструкций, решении ряда спорных и дискуссионных проблем почвоведения. [–] На основе данных микробиоморфологии проведен целый ряд палеоландшафтных реконструкций, выявлен широкий ареал антропогенно нарушенных почв в прошлом. [–] В научный лексикон вводятся следующие термины: микробиоморфы – микроскопические остатки растений и животных, обладающие специфической морфологией; микробиоморфные комплексы – совокупность микробиоморф в образце; микробиоморфные профили – последовательная вертикальная смена микробиоморфных комплексов в почве или седименте. Микробиоморфный метод применяется при проведении археологических работ с культурными слоями поселений и погребальными комплексами курганов, дольменов, грунтовых могильников. Большой вклад в создании данной монографии внесла Н.А.Караваева, чьи конструктивные и доброжелательные советы и рекомендации позволили привести многолетний фактический материал в предлагаемую читателям научно-литературную форму. Сами исследования начинались на факультете почвоведения МГУ им.М.В.Ломоносова под внимательным руководством Г.В.Добровольского и С.А.Шобы. При обсуждении результатов работы постоянную помощь конструктивными советами оказывали В.П.Чичагов, Н.И.Белоусова, О.А.Чичагова. Накопление информационно значимого материала, создание обширной базы данных стало возможным благодаря помощи многих научных сотрудников ИГ РАН, МГУ им.Ломоносова и других институтов нашей страны и за рубежом, любезно предоставивших свои образцы для микробиоморфных исследований. Автор выражает глубокую благодарность Е.А.Агафоновой, А.Л.Александровскому, Н.А.Березиной, М.А.Бронниковой, М.П.Гласко, С.В.Горячкину, Р.Г.Грачевой, А.Е.Додонову, Э.П.Зазовской, Б.А.Ильичеву, Л.О.Карпачевскому, И.В.Ковде, Н.Н.Матинян, В.В.Мурашовой, А.Н.Русакову, С.Н.Седову, А.С.Семиколенных, С.А.Сычевой, В.О.Таргульяну, И.В.Туровой, О.В.Фишкис, О.С.Хохловой, M.Andrich, A.Barchi, C.Chang, F.Hiebert, B.Terhorst. Автор считает своим долгом выразить искреннюю признательность безвременно ушедшим Ф.И.Козловскому и Н.Ф.Глазовскому за доброжелательную поддержку на различных этапах исследований. Особую благодарность хотелось бы выразить своим близким – А.В.Гольеву и И.В.Забоевой за поддержку, всемерную помощь и терпение. Исследовательская работа по отдельным разделам монографии осуществлялась при поддержке грантов РФФИ: 06-05-64559, 06-05-65203, 06-06-80517; РГНФ: 06-01-00242а, а также Slovenian Ministry of Education, Science and Sports, projects no. Z6-4074-0618-03, J6-6348-0648-04 and J6-3075. В работе представлены основные результаты, полученные за последние 15 лет. Значительная часть описаний исследованных образцов опубликована в монографиях, сборниках и журналах, и поэтому в книгу включены только полученные выводы, но в отдельных случаях приводятся и сами описания, они в тексте даны более мелким шрифтом. Основу исследования составляет соотношение качественного и количественного распределения микробиоморф. Часть из них (например, растительный детрит и кутикулярные слепки) сложно количественно сосчитать, поскольку они очень хрупкие и могут дробиться даже под действием покровного стекла при приготовлении препарата. Поэтому для общей сравнительной характеристики микробиоморфного комплекса используется полуколичественный анализ – содержание отдельных компонентов приводится по группам, которые в таблицах показаны крестиками: +++ – много (более 100 единиц в исследованном объеме); ++ – средне (50–100 единиц); + – мало (5–50 единиц); Ед. – единично (1–4 единицы). В работе все таблицы полуколичественной характеристики содержания и распределения микробиоморф имеют единую систему обозначений: Дт – детрит (включает в себя древесный и травянистый виды детрита, при описании образца тип детрита указывается отдельно); Кс – кутикулярные слепки; Фт – фитолиты; Пс – пыльцевые зерна и споры; Дв – диатомовые водоросли; Сг – спикулы губок; Уг – частицы древесного угля, Ра –раковинные амебы. Введение
Одним из основных разделов исследования почв и седиментов различного генезиса является морфологический, изучающий морфоны разного масштаба – от субмикроскопических глинистых частиц до горизонтов, профилей и даже фрагментов почвенного покрова (Розанов, 1983). Однако при этом из поля зрения исследователей выпадает существенная часть включений и новообразований биогенного происхождения (биоморф), как правило, рассеянная в почвенной или иной вмещающей их массе. На рис. представлено место биоморф в общей системе морфогенетического анализа (Розанов, 1983). Биогенные включения и новообразования представлены в почвах очень широко, от крупных и сложносоставных форм, таких как кротовины, сурчины (включения части одного горизонта в массу другого), до микроскопических остатков биоты. По размерам биоморфы распадаются на две большие группы – макробиоморфы и микробиоморфы (рис.). В первую группу входят те формы, которые хорошо различимы при работе в поле и учитываются уже на самых начальных стадиях описания разреза. Это кротовины, червоходы, остатки корней и т.п. Они изучены достаточно хорошо в работах В.А.Ковды (1985), Б.Г.Розанова (1983), Е.В.Пономаренко (1999). Однако в их трудах недостаточно внимания уделялось второй группе (микробиоморфам), которая имеет микроскопические размеры, обладает морфологической самостоятельностью и устойчивостью, требует специальных лабораторных методов выделения (мацерации). Микробиоморфы – обязательный компонент природных и антропогенных систем. Они являются индикаторами особенностей функционирования почв и ландшафтов в целом. При этом они не влияют на функционирование вмещающей их среды, инертны по отношению к почвенным и другим растворам. Предлагаемая работа посвящена исследованию информационных возможностей именно этой группы биоморф. Микробиоморфы очень разнообразны. Однако по составу их можно разделить на две большие группы: органические новообразования и включения и минеральные (кремнеземистые). Каждая из микробиоморф связана с определенными типами ландшафта и несет свою информационную нагрузку, свидетельствующую об отдельных этапах его развития. Наиболее интересна информация, получаемая при комплексном изучении всех микробиоморф. Одновременный учет количественных и качественных характеристик всех присутствующих в образце частных микробиоморф дает новую информацию, которую в ряде случаев невозможно получить при использовании традиционных методов. Поэтому основу микробиоморфологии составляет изучение не отдельных частных микробиоморф, а их совокупный анализ, т.е. анализ микробиоморфного комплекса, который и выступает основным объектом изучения микробиоморфологии. Изучение микробиоморфных комплексов позволяет получать дополнительную информацию для выработки новых или подтверждения имеющихся гипотез в дискуссионных вопросах почвоведения и эволюционной географии. Summary
Microbiomorphic analysis as tool for natural and anthropogenic landscape investigation Morphological analysis is one of the main methods of studying soil. It can be performed at different scales from microscopic clay particles to soil horizons, profiles, and even fragments of the soil cover. It seems that this analysis covers all the possible features and properties of soil and even fragments of the soil cover. Although it includes most of the possible features and properties of soil, there is a large group of soil components that has hitherto escaped the attention of researchers and remains beyond the scope of traditional soil morphology. At best, these components are mentioned only briefly in reports, yet they can solve various pedogenetic problems. They include a range of microscopic materials of biogenic origin that are scattered through the soil mass and require special methods for their separation. Biomorphic analysis is the study of the macro- and micro-remains of organisms (biomorphs) in the context of the conditions of their origin. Biomorphic analysis can indicate modern and past conditions of pedogenesis and reveal evolutionary trends in individual soils and pedosediments or more widely in the whole soil cover. This is done mainly through the reconstruction of past vegetation conditions. Biomorphs include various types of biogenic inclusions in soil. The diversity of biomorphs is very great-from large and complex forms such as krotovmas and marmot burrows, which often result from mass transfer of soil material from one horizon to another, to the microscopic remains of biota that entered the soil mass by illuviation or pedoturbation processes. In this paper, my discussion is restricted to the two main microscopic groups of biomorphs represented by siliceous and organic remains. Microbiomorphs can be divided into inclusions and neoformations. However, some may be neoformations in one horizon and inclusions in another. For example, diatoms and sponge spicules inherited from the parent material are inclusions, but those formed in the soil horizons are neoformations. Each of the microbiomorphs is characteristically associated with certain types of landscape and can provide information on landscape evolution. They therefore provide objective and reliable information on the conditions of soil formation and landscape development. Mineral microbiomorphs Phytoliths are microscopic grains of opal that form in plants by intracellular precipitation of silica. The morphology of phytoliths resembles that of host plant cells. As they are consequently characteristic of species or other groups, they can be used to investigate the evolution of the plant cover (Rovner, 1986). Phytoliths are 20–100 \mu m in size and can easily be studied under the microscope (Piperno, 1988). They are useful in paleopedological studies because of their resistance to weathering and to physical damage during transportation. They enter the soil through leaf fall and accumulate in the topsoil. Penetration into deeper horizons results from disturbance by soil fauna, which is conditioned by physico-chemical soil properties, or from burial beneath new sediment. In alluvial soils, phytoliths may migrate laterally by water flow. However, they can be modified or even destroyed by some biochemical processes, so their preservation is often better in lower soil horizons, and buried soils may contain large numbers of phytoliths.Almost all phytolith features can be used for diagnostic purposes. Unlike pollen grains, phytoliths are not transported by the wind, so they characterise vegetation, which is or was strictly confined to the place of study. Phytolith analysis can indicate the number and sequence of vegetation changes and whether the soil was subject to erosion or deposition of new sediment. Every vegetation stage during soil development forms its own phytolith profile (Golyeva, 1997b). Human impacts such as grazing, tillage or tree felling can also exert a considerable influence upon the distribution of phytoliths with depth, so that new phytolith profiles are superimposed on those of earlier vegetational phases. Grazing is accompanied by a sharp increase in the amount and diversity of phytoliths from aboveground parts of plants and by the predominance of small phytoliths. These anthropogenically modified phytolith profiles are often well preserved in buried soils. Ploughing and arable cultivation can also result in a reduction in total phytolith contents, and may be indicated by the appearance of a few Gramineae phytoliths atypical of the local climate. Also, if arable fields are abandoned and overgrown by woodland or meadow, new plant phytoliths may dominate the upper part of the phytolith profile. Diatoms are also composed of opaline silica (Battarbee, 1986), and are found in the upper horizons of soils subjected to temporary accumulations of surface water, which can result from a high groundwater table, a slowly permeable subsurface horizon or melting of ground ice. The species composition of diatom assemblages in soils can indicate the extent of soil hydromorphism. It is possible to distinguish between soils with periodical water flooding, submerged soils and alluvial deposits. Sponges are composed of spicules that are also siliceous. In soils, most sponges are freshwater types, and so indicate soils subject to flooding, such as alluvial soils. Sponge spicules have a rounded cylindrical form with tubular central channel, which serves as the main diagnostic feature and distinguishes them from some forms of phytoliths. Their abundance in a soil sample may indicate the duration and intensity of floods. Silicified cuticle casts are deposited as films on the outer walls of epidermal cells of the green parts of plants–leaves and young stems (Kerp, 1991; Palmer, 1976). Silica absorbed by the roots forms not only phytoliths but also accumulates in a separate layer between the cuticle and the walls of the epidermis, forming a siliceous cast of the surface of the epidermal cells. As the walls of epidermal cells have rather sinuous outlines, the patterns of which are often specific for different families of plants (Grosse-Brauckmann, 1986), the cuticle casts can be used to identify the source families of plants living on the soil. Entering the soil through leaf fall, cuticle casts are usually preserved for some time, but only in the uppermost soil horizons. Even here they may not be preserved for very long periods, as they are very thin and subject to dissolution or comminution. However, if the soil is rapidly buried by a thick layer of sediment, the cuticle casts can be preserved as evidence for the surface character of the buried horizon. Testate amoebae often possess siliceous shells and may occur in acid peaty soils (Corbet, 1973). However, they are limited to the uppermost horizons, and are often poorly preserved. Organic microbiomorphs Pollen and spores occur in the surface horizons of almost all soils (Dimbleby, 1957). However, the preservation in aerated soils is much poorer than in anaerobic (e.g. peaty) soils because of their greater microbiological and biochemical activity (Havinga, 1974). The pollen of some plant families may be completely destroyed in soil because of selective processes of decomposition (Havinga, 1985), or may be displaced by earthworms (Walch et al., 1970). Consequently, many soil pollen spectra are incomplete representations of the contemporary vegetation, and results from soils should be verified where possible by a comparative studies of pollen from adjacent peatlands. Nevertheless, the degree of preservation in some soils is sufficient to draw definite and unambiguous genetic conclusions (Dimbleby, 1985; Il'ichev and Golyeva, 1997).The occurrence and distribution of pollen in a soil profile may be of great interest in pedogenetic studies, even if preservation is too poor for species identification. Some pollen may migrate downwards through fissures and root channels, but the amounts are usually small, so the presence of a pollen peak well below the surface usually indicates the presence of a buried surface horizon. Human impacts on soils such as grazing and tillage can lead to considerable modification of the pollen spectrum. Deformed, crushed, broken and flattened grains predominate in the soil of disturbed sites, and disturbance can decrease the total amount of pollen. Pollen and spores can generally be identified at generic and sometimes even at specific level. Phytolith analysis sometimes offers this opportunity as well, and often for groups (e.g. different species of cereals) that cannot be identified at the same level from their pollen. More often phytoliths only provide data for general characterisation of the plant community. Most dicotyledonous plants produce few or no silica forms. However, when they are found, phytoliths are better indicators of the exact locality and horizon of the source plant, because they have a much smaller migration capacity than pollen grains. Pollen analysis therefore provides a general description of the vegetation over a fairly large area, whereas phytoliths allow one to trace the evolution of vegetation over a restricted area or to study the spatial variability of the plant cover over a restricted time interval (Kurmann, 1985). Used together, the two methods enable us to make better judgments on the evolution of the vegetation of a site and its surrounding landscape, the role of human influences on the environment, the duration of land cultivation, etc. (Rovner, 1988). Charcoal and wood remains are often found in buried soils and horizons modified by human activities. The presence of coarse charcoal fragments at depth is good evidence for a buried soil. However, most charcoal in soil samples occurs in very small particles and cannot be identified to specific or generic level. Its presence usually indicates natural fires, but in garden or other cultivated soils it can result from incorporation of ash as a fertiliser or of burnt stubble. An especially high content of fine charcoal and unburnt woody remains is typical of urban soils and cultural layers. Layers enriched in coarse charcoal fragments and buried beneath alluvial or colluvial sediment indicate the following sequence of events: (1) a strong fire that exposed the soil surface, (2) acceleration of erosion, and (3) deposition of sediment in valleys, depressions or at the bottom of slopes. Plant detritus is usually microscopic, and is mainly found in surface soil horizons, though small amounts may occur in lower horizons as well. In soil, it is composed of the remains of skeletal tissues that originally protected a plant from rupture. These tissues are relatively resistant to decomposition, and their morphology can often be used for identification at generic or even specific level. It can be divided into tree and herbaceous detritus. Tree detritus occurs in forest soils and can often be identified at specific level. It is also typical of urban cultural layers, especially those corresponding to periods of timber construction. Changes in the species composition of tree detritus within the vertical column of a cultural layer may indicate changes in the predominant species of local forests, because the species used in construction are usually local. The presence of a detritus maximum in deeper horizons may indicate a buried soil. Analysis of plant detritus is especially informative with respect to cultural layers and can reveal spatial and temporal changes in the economic activities of human society. Multiplemicro biomorphic analysis The most interesting results are often gained from multiple microbiomorphic analyses because different types of microbiomorph can reveal different aspects of environmental or soil development. Their information capacity is different, and results for different microbiomorphs are often complementary. Methods of microbiomorphic analysis The main method involves the consecutive study of the different types of biomorph under a microscope. Fifty-gram samples are treated with a 30% solution of hydrogen peroxide, and then separated from quartz and other mineral grains by flotation in a heavy liquid, usually a mixed cadmium iodide and potassium iodide solution with a specific gravity of 2.3. After centrifugation, the floating siliceous and organic microbiomorphs are collected and washed several times with distilled water, then immersed in oils (usually glycerine) for study with an optical microscope at magnifications ranging from 200x to 900x. The entire complex of biomorphs is identified and counted. Quantitative assessment allows comparisons of their distribution through and between soil profiles. Examples of work in which microbiomorphic analyses have been used Different parts of the Russian Plain were studied. We used microbiomorphic method for analysing modern and buried soils, cultural layers. We expected it to establish use of this method for paleoenvironment reconstruction in several examples. 1. Surface soils and palaeosols buried under archaeological monuments of different ages have been studied within the Chechen depression of the Northern Caucasus (Russia) in order to determine soil evolution and environmental changes during the second half of the Holocene period (Khokhlova et al, 2001). The key sites in our study are located on both banks of the Sunzha River, 5 km to southeast of Nazran city, the modern capital of the Ingush Republic. Geomorphologically, this territory belongs to the eastern part of the Osetin plain and the western part of the Sunzha alluvial plain within the Chechen depression. There are four erosional and depositional river terraces. The climate of the study site is typical of the semi-arid steppe zone: mean annual temperature is 8.4o and mean annual precipitation about 600mm. The wind regime is determined by orography. The depression is protected from strong southerly, easterly, and northerly winds by the high mountain ranges of the Northern Caucasus. Microbiomorphic analysis indicates that, during the Late Atlantic period, the vegetation of the Chechen depression was dominated by steppic associations. Later, these were replaced by forest and meadow with some elements of the steppe flora being retained. The proportion of steppic elements (including cereal crops) increased because of anthropogenic disturbance of the vegetation. A long period (ca. 4000 yr) of cultivation is indicated for the Chechen depression. The chronosequenee consists of palaeosols buried under archaeological monuments dated to > 5000. 3800–4000 and 1600–1700 BP and modern surface soils. The results of microbiomorphic analysis indicate the following vegetation development in this region. In the Middle Holocene (> 5000 yrBP) the soils of the depression developed under a steppe vegetation with some meadow grasses, while the soils of surrounding mountains developed under a forest cover. By the period 3800–4000 BP the plant cover had changed. Soils not subject to ploughing developed in conditions of alternating forest and meadow vegetation. As there are clear indications of agricultural use of some soils about 4000 years ago, human-induced impacts on the vegetation must have been considerable, with conversion of forest lands to croplands and pastures. Pedogenesis in the last half of the Holocene was accompanied by synchronous accumulation of loess-like material. The Holocene soils of the depression have developed by a "synlithogenic" model of soil formation. Alternating periods of active sedimentation and pedogenesis on a stable land surface occurred in the Late Pleistocene. The studied Holocene soils probably represent one (the present) pedogenic stage in a sequence pedogenic and lithogenic events that affected this region during the Late Quaternary The microbiomorphic analysis has also confirmed hypothesis on accumulation of allochthonous material. Colluvial sediments have accumulated periodically on the surfaces of both modern surface soils and buried palaeosols. They occur at both key sites, suggesting that sediment accumulation was widespread in the Chechen depression during the second half of the Holocene. 2. A complex biocoenosis has been analyzed in vertisol area with gilgai microrelief within the steppe zone of Southern part of European Russia (Stavropol region) (Kovda et al., 1998). The gilgai landscape is located in the southwestern part of the Stavropol' upland and represents a typical example of landscapes that occur sporadically in the steppe zone of Central Ciscaucasia. A wide zone with distinct microrelief occurs on the slope at the absolute height 470 m above sea level. The microrelief is represented by alternating rounded elevations and depressions with amplitude up to 30–50 cm. Elevations and depressions are combined through a microslope. Saddles connected either a pair of depressions, or a pair of elevations are another, more rare, element of microrelief. The area of depressions covers about 10% of the territory, while mounds and microslopes occupy about 45% of the territory each. Soils are formed on eluvial-deluvial marine clays. The territory is located in continental climate: temperature of January and July are 4.1 to 5.1\gc and 21\gc, respectively. The annual precipitation is about 500 mm, the coefficient of humidity is 0.8–0.85. The soil cover is represented by three-members gilgai complex, which consist of vertic chernozem on mounds, typic vertisols on microslopes, and meadow-bog vertic soils in depressions. The total amount of microbiomorphs, including phytoliths and diatoms, decreased regularly along the soil profile. Phytoliths occurred to a depth of 70 cm on the mound, 105 cm on the microslope, and 80 cm in the depression. The amount of microbiomorphs in soil horizons underwent significant changes with respect to their position in the microrelief. For example, in soil of the mound, microbiomorphs were represented by phytoliths only, while diatoms were absent. The amount of phytoliths was low: from 12 in the upper horizon to 1 below 40 cm. In the microslope soil, the amount of silica microbiomorphs was markedly higher but decreased rather sharply: from 207–210 in the upper horizons to 9 in the lower horizons, with the second peak (14) at a depth of 70–105 cm. The highest (for the entire gilgai) amount of phytoliths and diatoms (290–462) was recorded in the upper 20 cm of the soil profile. Their amount decreased downwards to 27, with the second peak of phytoliths (50) at a depth of 40–65 cm. The diatom shells occurred to a depth of 40 cm. Since in the A12 horizons, fragments of diatom shells predominated, rather than whole shells, it means that they were introduced in this horizon from the above. Phytoliths include forest, meadow, steppe, dry-steppe, and water plants. Phytoliths of the stems of dicotyledonous herbs and a group of non-identified forms of the local flora phytoliths were most abundant in all soil profiles. As a whole, the diversity of phytoliths was the highest in the soil of depressions and the lowest in the mounds. Most forms of various phytoliths were absent in the mound soil. Nevertheless, the phytoliths of forest grasses were presented, although singly, even in the soil of the mound. The percentage of forest grasses phytoliths from their total number increases in all soils of the complex at a depth of about 15–40 cm. In addition, the second peak of the phytoliths of forest grasses was observed in the depression (65–80 cm). Large phytoliths are rather abundant in the depression suggesting the presence of large plants, for example,. Microbiomorph analysis has shown that the entire profile of soil of the mound and, especially, the upper horizons, contain very few phytoliths, which is not typical for the upper soil horizons (Golyeva, 1995). Such an amount of phytoliths could serve as an evidence of rare, inhibited plant cover on the mounds. However, taking into account the results of botanical analysis, this suggests superficial erosion of soil materials, including phytoliths. This also explains an elevated amount of phytoliths in the upper horizons of the microslope and depression soils, since the soil materials are brought to these microrelief elements. Absolute maximum of phytoliths and their diversity were recorded in the upper horizons of the depression soil, which is related to erosive accumulation. As was indicated above, the highest diversity of phytoliths in the depression is observed against the background of plant cover relatively poor in species diversity. A sharply reduced diversity of phytoliths was recorded at a depth of 15 cm in the microslope soil and 40 cm in the depression soil. Thus, the lateral superficial migration and accumulation of phytoliths appears to be most distinct above these depths. Distribution of phytoliths in the mound soil is rather complicated and reflects not only erosive processes, but also mechanical deformations of the soil. Intrusions of underlying materials (horizons AC1 and AC2), well discernible in the soil profile by a lighter color, are relatively younger than more ancient humus horizons, in which they penetrate. Hence, the extrusion materials contains less phytoliths than the older humus horizon at the same depth. Thus, the central, younger, part of soil profile on the mound contains less phytoliths than adjoining lateral humus horizons. Processes of vertical migration. Phytoliths are usually distributed in the soil profile to a depth of 30–50 cm. The most characteristic size of phytoliths is 5–20\dsso \mu m (Drees et al., 1989) and, therefore, they have a limited ability for intraprofile migration. In the gilgai clayey soils, the depth of penetration of phytoliths markedly exceeded the usual depth (to 70–105 cm). This appears to be accounted for by specificity of vertisols, since they are strongly cracked during summer drying. Cracks are filled with material from upper horizons as well as, with water during rains. Thus, phytoliths may penetrate in deep horizons by mechanical and water migration. Consequently, the depth of penetration of phytoliths reflects simultaneously the depth of moistening and intensity of cracking. Specifically, it was proposed to use the amount and depth of penetration of biogenic opal as a index of mixing of the soil material of vertisols (Boettinger, 1994). According to field observations, a marked cracking pattern was noted in soils on mounds and microslope to a depth of 150 cm and in depressions, to 60–75 cm. Below 90–100 cm, the width of cracks did not exceed 0.5 cm in the mound and 1 cm in the microslope. Hence, the presence of cracks alone is not sufficient for penetration of phytoliths deeper down. Taking into account the data on seasonal oscillation of humidity in the gilgai complex (Kovda et al., 1995), one could note that the depth of penetration of phytoliths more or less coincides with the strong and middle amplitudes of seasonal oscillation. Thus, soil moistening is an essential conditions of phytolith migration. Microbiomorphology has a high information content for analysis of the current and paleolandscape environment, as well for diagnostics of some soil processes. Such type of analysis clearly demonstrates the scale of surface matter transfer from the mounds to depressions. In such a case, determination of the rate of erosion and its comparison with the rate of the inverse process, gradual bulging of mounds, becomes a very important. Comparison of these rates will allow to establish the common trend of microrelief development. Vertisols are characterized by deep penetration of phytoliths in the soil: up to 70–105 cm in the investigated soils. Similar depths (90–115 cm) were also recorded for vertisols of Australia (Boettinger, 1994). However, we believe that the depth of phytoliths distribution is due not only to their migration down the profile. Vertical mixing of materials through filling of cracks proposed for vertisols is, according to our data, insufficiently intensive: phytoliths do not penetrate to the ends of cracks. Comparison of the profile distribution of phytoliths in different soils of the microcomplex shows the most gradual change of their amount in the mound soil and this could be due to migration along the cracks. The phytoliths content in the soils of microslope and depression is sharply (four- to nine times) reduced, as compared to the surface horizons. Moreover, comparative analysis of the qualitative composition of phytoliths along the soil profile shows unequal reduction of individual groups with the depth. Specifically, phytoliths of the xerophytic and hydrophytic flora and diatoms disappear, while the proportion of forest species increases. This suggests, above all, a qualitative difference of the current flora from the past flora of the previous periods. It is essential that the amount of diatoms is sharply reduced from 43 to 1 upon transition from horizon A12 to horizon A13. Under pronounced microbiomorphs migration a more gradual decreasing in their amount could have been expected. Hence, the phytolith complex of deep horizons reflects the initial composition of plants of a territory before or at the early stages of gilgai formation, rather than is due to migration. In this case, a deeper penetration of phytoliths in vertisols is due to lateral redeposition of the soil mass and burial of the initial surface at a certain depth. 3. Microbiomorph analysis was utilized to study soils buried under early nomad burial mounds (kurgans) in the Orenburg region (southern Russia) (Golyeva, Khokhlova, 2003). The earliest of the studied kurgans (VI–V centuries B.C.) were constructed in an undisturbed meadow-steppe. During VI–V centuries B.C., the study region had a rather rich floristic variety, as it was covered with grassland that included the plants from both meadow-steppe and dry steppe ecosystems. The diverse phytolith assemblages indicate that some phytoliths were introduced to the soil with animal excrements. Kurgan construction significantly disturbed the topsoil at only one locale. In sum, we did not find evidence for any significant and widespread disturbance of the soils buried under the kurgans of this period. A dramatic change occurred during the subsequent early Sarmatian period. The subsequent group (IV–II centuries B.C.) was built on a highly disturbed, eroded landsurface that was largely devoid of vegetation and topsail. Stable low phytolith quantities in the samples of the upper horizons of soils buried under kurgans of this period are not typical for the topsoil of natural profiles formed in mature ecosystems. These phytolith concentrations are usually found at a depth of more than 5 cm below the buried soil surface. We conclude that the soil had already lost the upper part of its humus horizon (5 cm or more) prior to Sarmatian period kurgan construction. The reasons for this loss could be anthropogenic or natural. Possible anthropogenic agents include the disturbance of the ground surface during the course of kurgan construction as a part of the burial ritual and human-induced erosion due to overgrazing. Possible natural reasons include accelerated erosion as a result of a shift in the climate regime to drier conditions and the subsequent impoverishment of plant cover. Both processes may have led to the loss of vegetation and of the upper soil layer prior to kurgan building. After a prolonged break, kurgans again were built in II–III centuries A.D., on a surface where the vegetation and soil cover had partly recovered from human occupation. In late Sarmatian times, the vegetation around Pokrovka returned to a relatively undisturbed plant cover dominated by meadow-steppe associations with a few dry steppe species present. Erosion processes were weak or nearly absent. The contemporary plant cover is somewhat similar to that of VI–V centuries B.C. and II–III centuries A.D. However, various aspects of the human impact of recent decades, such as cultivation, fertilization, and the planting of tree strips can be detected. Summarizing these results we conclude that some buried soils show the signs of plant cover and surface stability while others exhibit the indicators of degradation. The paleovegetation and soils buried under the early Sarmatian kurgans suffered the most severe disturbance, which is reflected in the microbiomorph assemblages of modern soils. The results of research clearly demonstrate anthropogenic soil disturbance before or during the course of kurgan construction. The grade of disturbance varies in the different historical epochs and reflects the intensity of anthropogenic impact on ecosystems and landscapes. When buried soils under kurgans are used for paleoclimatic studies, it should be taken into account that anthropogenic soil transformation can modify various parameters such as the thickness of the topsail horizon and thus the depth to carbonate and salt horizons. These changes may not be detected by a morphological study or through the analysis of physical and chemical properties (humus content, etc.), whereas the microbiomorph method may identify them. These changes documented on the basis of morphological and analytical data could be misinterpreted as indicators of climatic change whereas microbiomorph analysis allows researchers to avoid this mistake. Thus soils under kurgans, if they were human modified, can give incorrect information about the natural environmental conditions of a given historical period. Earlier, a number of researchers hypothesized large-scale anthropogenic soil and vegetation changes in the Eurasian steppe during the second half of the Holocene, relying on palynological, paleofauna and archaeological data (Dinesman, 1976; Ivanov and Vasilyev, 1995: Nikolaev, 1997). Microbiomorph analysis allows us to evaluate the intensity and grade of the upper soil horizon transformation at the moment of kurgan building. This method should be included in the complex investigation of soils buried under archaeological constructions. Microbiomorph analysis suggests that the rituals accompanying mound construction and burial ceremonies may be more complicated than previously supposed and may have changed through time. Sponge spicules and phytoliths indicate that Early Sarmatian people brought lacustrine or alluvial deposits to the site for kurgan construction. Conclusions Microbiomorphic analysis can provide specific information on the origin and evolution of soils, which is otherwise difficult or impossible to obtain. The evidence from different microbiomorph types is often complementary, and the integrated results of multiple microbiomorphic analyses can provide a clear picture of the sequence of events in the development of a soil. They allow one: Determine the parent material, especially of hydromorphic soils. Identify past erosional and depositional events and estimate the thickness of resulting deposits. Determine the composition of past local and regional plant communities. Identify buried soils. Assess anthropogenic impacts on soils, even where there are no evident morphological traces of these impacts. Об авторе
Доктор географических наук, старший научный сотрудник лаборатории географии и эволюции почв Института географии РАН, специалист в области палеопочвоведения, археологического почвоведения, микробиоморфных исследований. Автор более 130 научных публикаций в отечественных и зарубежных изданиях, учебных пособий, соавтор 4 монографий. Автор лекционных курсов по фитолитному и микробиоморфному анализам. Является членом Российского научного общества почвоведов и Международного научного общества по фитолитным исследованиям. |
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