System-Specific Complex Interactions Shape Soil Organic Carbon Distribution in Coastal Salt Marshes.

Coastal wetlands provide many critical ecosystem services including carbon storage. Soil organic carbon (SOC) is the most important component of carbon stock in coastal salt marshes. However, there are large uncertainties when estimating SOC stock in coastal salt marshes at large spatial scales. So far, information on the spatial heterogeneity of SOC distribution and determinants remains limited. Moreover, the role of complex ecological interactions in shaping SOC distribution is poorly understood. Here, we report detailed field surveys on plant, soil and crab burrowing activities in two inter-tidal salt marsh sites with similar habitat conditions in Eastern China. Our between-site comparison revealed slight differences in SOC storage and a similar vertical SOC distribution pattern across soil depths of 0-60 cm. Between the two study sites, we found substantially different effects of biotic and abiotic factors on SOC distribution. Complex interactions involving indirect effects between soil, plants and macrobenthos (crabs) may influence SOC distribution at a landscape scale. Marked differences in the SOC determinants between the study sites indicate that the underlying driving mechanisms of SOC distribution are strongly system-specific. Future work taking into account complex interactions and spatial heterogeneity is needed for better estimating of blue carbon stock and dynamics.

[A multi-scale study on the formation mechanism and main controlling factors of urban thermal field based on urban big data.] / åŸºäºŽåŸŽå¸‚å¤§æ•°æ®çš„çƒ­åœºæ ¼å±€å½¢æˆæœºåˆ¶åŠä¸»å¯¼å› ç´ çš„å¤šå°ºåº¦ç ”ç©¶.

The composition and structure of urban landscape and human activity intensity are key factors shaping urban thermal fields, whereas the relative importance of influencing factors for urban thermal distribution remains unclear. We carried out a case study in Yixing City. Land surface temperature (LST), ecological infrastructure (including vegetation and water cover), building volume and point of interest data were extracted from the RS interpretation, field mapping and programming technique. Using Pearson correlation analysis, univariete regression analysis, multiple regression analysis and relative weight analysis, we quantitatively analyzed the relationships between urban land surface temperature to ecological infrastructure, building volume, POI density at multiple scales (500, 1000, 2000 m) as well as their relative importance. The results showed that ecological infrastructure had a significant cooling effect, and the building volume and POI density were positively correlated with LST. Among the influence factors of urban heat field, ecological infrastructure had the highest relative weight (21.3%-43.8%), followed by building volume (20.7%-22.6%) and POI density (13.7%-21.7%). Our results would help to understand the relative importance of factors driving urban thermal field and offer important reference for taking mitigation measures to alleviate urban heat island effect.

[Effects of aquatic plants during their decay and decomposition on water quality].

Taking 6 aquatic plant species as test objects, a 64-day decomposition experiment was conducted to study the temporal variation patterns of nutrient concentration in water body during the process of the aquatic plant decomposition. There existed greater differences in the decomposition rates between the 6 species. Floating-leaved plants had the highest decomposition rate, followed by submerged plants, and emerged plants. The effects of the aquatic plant species during their decomposition on water quality differed, which was related to the plant biomass density. During the decomposition of Phragmites australis, water body had the lowest concentrations of chemical oxygen demand, total nitrogen, and total phosphorus. In the late decomposition period of Zizania latifolia, the concentrations of water body chemical oxygen demand and total nitrogen increased, resulting in the deterioration of water quality. In the decomposition processes of Nymphoides peltatum and Nelumbo nucifera, the concentrations of water body chemical oxygen demand and total nitrogen were higher than those during the decomposition of other test plants. In contrast, during the decomposition of Potamogeton crispus and Myriophyllum verticillatum, water body had the highest concentrations of ammonium, nitrate, and total phosphorus. For a given plant species, the main water quality indices had the similar variation trends under different biomass densities. It was suggested that the existence of moderate plant residues could effectively promote the nitrogen and phosphorus cycles in water body, reduce its nitrate concentration to some extent, and decrease the water body nitrogen load.

[Spatial distribution patterns of soil organic carbon under Elacagnus angustifolia--Achnatherum splendens community in an arid area of Northwest China].

An investigation was conducted to study the relationships of soil organic carbon (SOC) content with root biomass and soil moisture content as well as the accumulation mechanisms of SOC under the Elacagnus angustifolia-Achnatherum splenden community in Ningxia Hui Autonomous Region of Northwest China. The results showed that the SOC content decreased gradually with increasing soil depth, and changed gently in both horizontal and vertical directions. The correlations of the SOC content and its affecting factors varied with soil depth. In 0-30 cm layer, the SOC content was significantly negatively correlated with soil moisture content; in 60-150 cm layer, the SOC content was significantly positively correlated with soil moisture content and root biomass. Partial regression analysis indicated that the root biomass density in 0-30 cm soil layer contributed significantly to the variance of SOC content. In 60-150 cm layer, the SOC content was mainly affected by root system and soil moisture content; in 30-60 cm layer, no significant correlations were observed between the SOC content and the root biomass and soil moisture content. There was an obvious difference in the accumulation mechanism of SOC in different soil layers and at different locations of E. angustifolia--A. splendens community.

[Effects of riparian ecological restoration engineering with offshore wave-elimination weir on restoration area's water quality].

Riparian ecological restoration engineering with offshore wave-elimination weir is an engineering measure with piled wave-elimination weir some meters away from the shore. This measure can dissipate waves, promote sediment deposition, and create an artificial semi-closed bay to restore vegetation in a riparian area which has hard dam and destroyed vegetation. Three habitat gradient zones, i. e., emerged vegetation zone, submerged vegetation zone, and open water area, can be formed after this engineering. In June 2010-May 2011, a field investigation was conducted on the water quality in the three zones in an ecological restoration area of Gonghu Bay, Taihu Lake. The water body inside the weir generally had lower concentrations of nitrite and nitrate but higher concentrations of ammonium and total nitrogen than the water body outside the weir. The water phosphorus concentration inside the weir was lower than that outside the weir in autumn and winter, while an opposite trend was observed in spring and summer. The coefficients of variation of the water body' s nitrite and orthophosphate concentration inside the weir decreased, and the annual maximum values of the water nitrite, nitrate, and orthophosphate concentrations inside the weir were lower than those outside the weir. On the contrary, the coefficients of variation of the water body's ammonium and total nitrogen concentrations inside the weir increased, and the annual maximum values of the water ammonium and total nitrogen concentrations inside the weir were higher than those outside the weir. To some extent, the restoration engineering could exacerbate the deterioration of the water quality indices such as ammonium and total nitrogen in the restoration area by the end of growth season

[Changes of characteristic scale of Nanjing urban landscape].

Based on 3 scenes of Landsat TM image taken in 1988, 1998 and 2006, the changes of the structural characteristics of Nanjing central urban area were studied with one-dimensional wavelet analysis. The results showed that it was necessary to select an optimal sampling width when using wavelet analysis to detect the characteristic scales of landscape transects. Too narrow transects could cause lack of stabilization, while too wide ones could cause loss of some minor characteristic scales. From the TM images (30 m resolution) of Nanjing urban area, the optimal sampling width was identified as four pixels. The results from one-dimensional wavelet transform indicated that the landscape of Nanjing central urban area had four relatively stable characteristic scale domains in 1988, 1998 and 2006, corresponding to functional clumps, small blocks, middle-sized blocks, and large blocks, respectively. From 1988 to 2006, the scales of large blocks were nearly unchanged, while the other three domains all changed significantly with a similar trend. Moreover, the variations among the characteristic scales within each scale domain declined from 1988 to 2006, indicating that the landscape structure of Nanjing central urban area tended to be more stable and accordant. The scale domains showed synchronous changes as well.