Guojiang Wan

The spatial distribution and emission of nitrous oxide (N2O) in a large eutrophic lake in eastern China: anthropogenic effects.

The emission of N(2)O from China is globally significant, but relatively few direct observations have been made in many of the fresh water environments most likely to be important sites of N(2)O production. In this paper, N(2)O saturations were examined in the ecologically heterogeneous, eutrophied, Lake Taihu, as well as in surrounding rivers in eastern China. The emissions of N(2)O were estimated and compared with those from other landscapes within the Lake Taihu drainage basin. We found that anthropogenically-enhanced inorganic N inputs act as a limited primary control on the spatial distribution of N(2)O saturations in heavily eutrophied parts of the lake only and that overall, lake N(2)O production and emission are not raised as significantly as expected due to high N inputs. In comparison, the heavily eutrophied river network is an important fraction of the local N(2)O budget, and when considered together with emissions of N(2)O from the lake, constitute a major (10-50% depending on season) fraction of total N(2)O emissions from the Lake Taihu drainage basin.

Dissolved Organic Matter in Natural Waters

Organic matter (OM) in water is composed of two major fractions: dissolved and non-dissolved, defined on the basis of the isolation technique using filters (0.1–0.7 μm). Dissolved organic matter (DOM) is the fraction of organic substances that passes the filter, while particulate organic matter (POM) remains on the filter (Danielsson 1982; Kennedy et al. 1974; Liu et al. 2007; Mostofa et al. 2009a). DOM is generally originated from three major sources: (i) allochthonous Dissolved Organic Matter in Natural Waters

A comparison on the accumulation characteristics of 7Be and 137Cs in lake sediments and surface soils in western Yunnan and central Guizhou, China

Abstract The uplifting of the Himalayas has resulted in the development of a three-tiered landform in Southern China, the Yunnan–Guizhou Plateau is the middle tier of this landform on the eastern slope of the Himalayas. Lake Hongfeng and Lake Baihua in central Guizhou are about 1000 km away from Lake Erhai in western Yunnan. Sediment cores were collected from Lakes Erhai and Lugu in west Yunnan and Lakes Hongfeng and Baihua in central Guizhou, along with 28 surface soil cores from the watersheds of these lakes. The accumulation characteristics of 7xxxx Be and 137yyyy Cs show that: (1) 137 Cs activities in the soil cores of central Guizhou were higher than that in the western Yunnan. The activities and maximum penetrative depth of 7 Be were similar for the two regions. The activity ratio of 7 Be/ 137 Cs in surface soil reached 100–1000 in western Yunnan, but only 10–100 for central Guizhou region. (2) 7 Be inventories in soil cores at most sampling sites of central Guizhou were low, reflecting severe soil erosion. 7 Be inventories in the soil cores of Lake Lugu watershed in summer–autumn were higher than that in Lake Hongfeng/Baihua watershed and also higher than that in Lake Erhai watershed. This could be related to high 7 Be precipitation in summer and altitude. (3) 7 Be inventories in sediment cores of Lake Erhai, Lake Lugu and Lake Baihua were 237±73, 322±19 and 783±44 Bq m −2 , respectively. Based on activity values that were corrected to deposition, prior to 1986, 137 Cs inventories in these lakes were 519±26, 937±13 and 3704±56 Bq m −2 , respectively. (4) Modeling indicated that 7 Be and 137 Cs accumulations in Lake Hongfeng and Lake Baihua were dominated by watershed erosion, and controlled by the retention factor in Lake Erhai and Lake Lugu, but the 137 Cs inventory ratios obtained in the sediment core and from direct atmospheric fallout were similar, and the ratios were smaller for 7 Be. (5) 7 Be inventories from direct atmospheric fallout in Lake Erhai, Lake Lugu and Lake Baihua were 0.07±0.02, 0.29±0.02 and 0.08±0.01 Bq m −2 , respectively. Prior to 1986, 137 Cs inventories were 0.11±0.01, 0.22±0.01 and 0.37±0.01 Bq m −2 , respectively, showing that 137 Cs deposition has a regional difference. This phenomenon may reflect that uplift of the Himalayas has a screening effect on the fallout of globally distributed atmospheric pollutants in western Yunnan, China.

Sediment particle size distribution and its environmental significance in Lake Erhai, Yunnan Province

A closed or semi-closed plateau lake, whose sediment records can provide us with plenty of fine and high resolution information, is a sensitive indicator of climatic and environmental changes. During the reconstruction of various short-time-scale climatic and environmental changes, the geochemical records in plateau-lake sediments are superior to other natural files. Based on fine dissection of the vertical profile of sediment particle sizes, this paper reveals the quasi-periodical changes of sediment particle sizes, which indicates the quasi-periodical fluctuations of the regional climate. A synthetic analysis of multiple indexes shows that sediment particle size is a more sensitive and more effective index of climatic and environmental changes than other geochemical indexes. High content of >20µm sediment particles and low content of 2–10µm sediment particles indicate a warm-dry climate and conversely a cold-humid climate, and their ratio can be used as an effective index of climatic changes. The basic climate succession in the region of Lake Erhai is characterized as being alternatively warm-dry and cold-humid and it has been developing into a warm-dry climate as a whole. There exist at least 2 time-scale quasi-periodical fluctuations of the regional climate in Lake Erhai. At present, the region of Lake Erhai is at the end of the warm-dry period and at the beginning of a cold-humid period, so the temperature will go down and the water level will rise.

Dynamics of CO2 in a karst catchment in the southwestern plateau, China

Inland waters, including rivers and lakes, are increasingly recognized as playing significant roles in the transport, mineralization and burial of organic carbon exported from land. However, in many areas, dissolved inorganic carbon (DIC) dominates the carbon export from catchments. Owing to different production processes and turnover times of organic versus inorganic carbon, CO2 emitted from rivers and lakes may have different impacts on global carbon cycling depending on its origin. Here, pCO2 and dissolved oxygen concentrations were determined, and the ratios of excess CO2 to O2 depletion (ΔCO2/ΔO2) were compared in spring water, river water and lake water in a carbonate catchment located in the southwestern plateau region of China. Results show that groundwater CO2 evasion, at 2.0xa0gxa0Cxa0m−2year−1, is insignificant in terms of terrestrial carbon loss compared with soil CO2 emission. In the rivers, calcite precipitation due to oversaturation is an important mechanism for CO2 production in some seasons. In the lake, HCO3− contributed approximately 75xa0% of the total carbon supply to organic matter production and calcite deposition during seasons favoring photosynthesis. The seasons which had high ΔCO2/ΔO2 are the main periods of CO2 emission from the lake, and the extra CO2 may be produced from HCO3− titration by H+. Thus, lake CO2 evasion was controlled primarily by pH, not respiration. The spring, river, and lake waters mainly process DIC exported from the catchment, of which HCO3− is primarily derived from carbonate weathering by soil CO2 that, with extraordinarily high ΔCO2/ΔO2, may originate from sources including organic matter decomposition, root respiration (autotrophic), and acid dissolution. Therefore, freshwater CO2 emission is a return pathway of catchment soil CO2 to the atmosphere more than that of net primary production and net ecosystem production.

Atmospheric pollutants transport tracks revealed from 131I, 137Cs, and 134Cs leaked from Fukushima accident and 7Be and 210Pb observed at Guiyang of China

A massive earthquake measuring 9.0 on the Richter scale that occurred on March 11, 2011, on Honshu Island, Japan, caused radioactivity leakage from the Fukushima Nuclear Power Plant, which led to the leakage of artificial nuclides (131I, 137Cs, and 134Cs) and their global transportation by atmospheric circulation. This paper reports a systematic comparative observation on radioactive concentrations of natural nuclides (7Be and 210Pb) and artificial nuclides (131I, 137Cs, and 134Cs) at the surface level, measured in weekly continuous aerosol sampling at Mount Guanfeng, Guiyang, China, from March 17, 2011 to April 28, 2011. During this period, the variations in the nuclide concentrations associated with their transport paths were analyzed with 315 hour back-trajectories of air mass initialized 500 m above the surface level at Guiyang. The results show that the pollutants of nuclear leakage from the Fukushima accident were transported to the Guiyang region of China via two significant pathways. In the first pathway the first wave of nuclear pollutants were transported from west to east in air masses at higher altitudes via global atmospheric circulation. The nuclear pollutants encircled the Earth almost once and after about 10 days to two weeks, between March 24 and March 31, 2011, intruded Guiyang from the northwestern region of China. In the second pathway, the nuclear pollutants from the Fukushima region arrived at Guiyang between April 7 and April 14, 2011, via air masses at lower altitudes that moved southwards because of the squeezing of the northeast Asian weather system and then by the influence, in succession, of the northeastern and southeastern air currents in the low-latitude region. The first transport pathway for atmospheric pollutants is on a global scale and based on air masses at higher altitudes, and the second transport pathway is on an eastern Asia regional scale and based on the air masses at lower altitude.

Microbiological denitrification and denitrifying activity ofParacoccus Denitrificans

With rapidly industrial and agricultural development, more and more fertilizers, chemicals and heavy ions will be discharged into lakes and rivers, which would cause lake eutrophication and quality deterioration in drinking water sources. Therefore, denitrification is essential for controlling the amounts of nitrogen. During the transformation process from nitrate to the end products-nitrogen and several intermediates [e.g. nitrite (NO2−), nitrous oxide (N2O) and nitric oxide (NO)] may be accumulated, which have more toxic influences on the environment. In this study, the denitrification effect ofParacoccus Denitrificans was examined on the changes between oxic and anoxic conditions at varying pH. At pH= 7.5, denitrification proceeded well after 3 switches from oxic to anoxic conditions and vice versa. Production of N2 was constant and the amounts of NO2−, N2O and NO were extremely low. However, at pH= 6.8, denitrification activity was inhibited and there were large amounts of the intermediates. The denitrifying bacteria decreased violently in dry weight and were washed out.