Characterization of biochar produced from sewage sludge and its potential use as a substrate and plant growth improver.

Biochar is a product rich in carbon produced by pyrolysis of different kinds of biomass and it modifies the physical, chemical, and biological properties of soil. In this study, biochar, produced at different pyrolysis temperatures (590 °C, 665 °C, and 765 °C), was physico-chemically characterized. It was explored whether biochar made from sewage sludge can become an alternative solution for future water and phosphorus management in agricultural production. A pot experiment was conducted using Chinese cabbage (Brassica rapa subsp. pekinensis) to investigate the effect of applying different biochars to the substrate, taking into account different growth parameters and the biochemical composition of the plants, as well as the physico-chemical properties of the substrate. According to the results, pyrolysis temperature influences the content of elements in biochar and their availability to plants, with total phosphorus contents in biochar ranging from 4.6% to 4.9%. In addition, applying biochar to the substrate significantly increases the volumetric water content up to 4.5 fold more compared to the control, which indicates a promising application in drought stress conditions and, at the same time, is a source of nutrients and can help to reduce the amount of mineral fertilizer application.

Land-use and climate controls on aquatic carbon cycling and phototrophs in karst lakes of southwest China.

Land-use and climate changes have been repeatedly identified as important factors affecting terrestrial carbon budgets, however little is known about how deforestation and catchment development affect aquatic systems in carbonate-rich regions. Multi-proxy analyses of 210Pb-dated sediment cores from two hard-water lakes with different land-use histories were applied for assessing carbon cycling and limnological changes in response to land-use changes over the past century in southwest China. Logging of primary forests in the catchment of Lugu Lake, starting in the 1950s, led to a significant increase of catchment erosion, as well as a consistent decline in inferred lake-water total organic carbon (TOC) levels and sediment carbonate accumulation. This process of recent deforestation may significantly reduce the role of lake systems to act as carbon sinks through hampering of both the soil organic carbon flux and the dissolution of catchment carbonate. The decline in lake-water TOC in Lugu Lake further increased algal production (i.e. tracked through sediment trends in chlorophyll a and its main diagenetic products) and changes in diatom composition. In comparison, there was little variation of sediment carbonate content in Chenghai Lake, which has a long history of catchment deforestation, while both primary production and lake-water TOC increased following cultural eutrophication during the last three decades. Furthermore, regional warming was associated with an increase in small-sized diatoms in both deep lakes, likely due to enhanced thermal stability. This study highlights the significant role of vegetation cover and land use in driving aquatic carbon cycling and phototrophs, revealing that deforestation can strongly reduce both inorganic and organic carbon export to lakes and thus aquatic carbon storage in karst landscapes.

Recent atmospheric metal deposition in peatlands of northeast China: A review.

China is one of the fastest-growing economies of the late 20th and early 21st centuries, and heavy metal emissions have increased in parallel with rapid industrialization and urbanization. Over the last decade, several studies of geochemical records from peat have reconstructed changes in atmospheric metal pollution in China. We review the peat records that detail the history of atmospheric metal pollution over the last two centuries in NE China. The ecological risk (ER) of accumulated metals and their potential eco-toxicological effects, through threshold and probable effect concentrations (TEC and PEC), are also evaluated. Peat records of metals show an increase of pollution loads in the environment over the pre-industrial level during the past two centuries, with an unprecedented increase in China over the last 60 years. There is generally good agreement between geochemical peat records from NE China and others records elsewhere in China. However, some discrepancies are observed especially with Hg records from lake sediments. These discrepancies could be explained by several factors, including post-depositional processes or uncertainties arising from dating methods. The ecological risk of heavy metals is found to be relatively weak in the remote and high-altitude environment in NE China. Although, most metals are under the TEC, Pb concentrations usually surpass it and are getting close to the PEC which indicates increasing ecological risks. Some areas of improvement have been highlighted such as the need for more long-term studies on atmospheric metals and a greater number of Pb isotopes records to better capture the long history of human activity and the spatial variability in metal deposition of the region.

The importance of catchment vegetation for alkalinity, phosphorus burial and macrophytes as revealed by a recent paleolimnological study in a soft water lake.

The land use within a catchment may markedly affect the environmental conditions in a lake and the storage capability of its sediments. This study investigated how changes in the dominant catchment vegetation (from local stands of deciduous trees over extensive heathland with some agriculture to mainly coniferous forest) occurring during the last ca. 200years were reflected in the sediments of a soft water lake and how these changes influenced the lake ecosystem. Pollen, macrofossils, metals, different phosphorus (P) forms, organic matter, carbon and nitrogen contents were determined in short sediment cores. This novel combination of proxies revealed that 1) the reduction of deciduous trees in the watershed seemingly reduced the calcium (Ca) supply to the lake and thereby its buffering capacity. This development was accompanied by decreased abundances of Ca-dependent species and subsequent increases in acidophilic species. 2) The sedimentary contents of organic matter, non-reactive P and humic-bound P were evidently higher in sediments deposited during the time when deciduous trees were abundant, which is probably linked to a stabilising effect by Ca. 3) An erosion event clearly reduced the amounts of macrofossils of isoetid species and characeans, indicating a reduction in their maximum distribution depth because of lower water transparency. Overall, the results of our paleolimnological study are of importance within lake management by convincingly showing how land use changes may (irreversibly) affect environmental conditions and species composition in soft water lakes and the storage of organic matter and P in their sediments.