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421.
Wetland ecosystems are profoundly affected by altered nutrient and sediment loads received from anthropogenic activity in
their surrounding watersheds. Our objective was to compare a gradient of agricultural and urban land cover history during
the period from 1949 to 1997, with plant and soil nutrient concentrations in, and sediment deposition to, riparian wetlands
in a rapidly urbanizing landscape. We observed that recent agricultural land cover was associated with increases in Nitrogen
(N) and Phosphorus (P) concentrations in a native wetland plant species. Conversely, recent urban land cover appeared to alter
receiving wetland environmental conditions by increasing the relative availability of P versus N, as reflected in an invasive,
but not a native, plant species. In addition, increases in surface soil Fe content suggests recent inputs of terrestrial sediments
associated specifically with increasing urban land cover. The observed correlation between urban land cover and riparian wetland
plant tissue and surface soil nutrient concentrations and sediment deposition, suggest that urbanization specifically enhances
the suitability of riparian wetland habitats for the invasive species Japanese stiltgrass [Microstegium vimenium (Trinius) A. Camus]. 相似文献
422.
By the method of P fractionation, we examined sedimentary P fractions in Lake Dianchi before and during cyanobacterial blooms,
namely in April 2004 and August 2004, respectively. In this study, the whole lake is divided into four areas to discuss P
fractions in sediment and the relationship between them and water quality or the nutrient status. The results show that where
the water body was much more eutrophic (higher levels of total phosphorus, total nitrogen, chlorophyll and trophic status
index) in Lake Dianchi, there can be more potentially available phosphorus (BD–P and NaOH–P) and less no available phosphorus
(HCl–P and residual P) in the corresponding sediments. Statistical analysis and statistical plots are used to compare the
distribution of every P fraction during cyanobacterial blooms with that before cyanobacterial blooms, and the results indicate
that the different P fractions had the different mobility. HCl–P and residual P were relatively stable, while NaOH–P, BD–P
and NH4Cl–P were more mobile. BD–P can intensively be released from sediment to water and consequently promote cyanobacterial
blooms, and at the same time the NaOH–P concentration increased in sediment, which can result from that BD–P released can
be partly immobilized to NaOH–P. During cyanobacterial blooms BD–P can be as a source, but NaOH–P as a sink. Besides, total
phosphorus in sediment had no significant differences between two samplings. 相似文献
423.
424.
The dwindling global reserves of extractable phosphorus (P) and its growing demand to produce the required food for a burgeoning global population (the global P crisis) necessitate the sustainable use of this crucial resource. To advert the crisis requires informed policy decisions which can only be obtained by a better understanding of the nature and magnitude of P flow through different systems at different geographical scales. Through a systematic and in-depth review of twenty one recent substance flow analyses of P, we have assessed the key P inflows, outflows, stocks, internal flows, and recycling flows at the city, regional, and country scales. The assessment has revealed, the main inflow and outflow of P at the city scale occurs through food and wastewater respectively, while the main stock of P occurs in landfill. At the regional scale, mineral ore is the main P inflow and chemical P fertilizer is the main outflow particularly in the regions that have P fertilizer production sector. In contrast, either chemical P fertilizer or animal feed is the key inflow and either food and agricultural products or soil losses (erosion, runoff, and/or leaching) is the major outflow especially in the regions without P fertilizer production sector. At the country scale, the key P inflow occurs either through mineral ore or chemical P fertilizer and the key outflow takes place either as food and agricultural products, waste (both solid and liquid), or soil losses (erosion, runoff, and/or leaching). The main stock of P both at the regional and country scales occurs in the soil of the agricultural production sector. As identified in this assessment, the key unproductive outflows and stocks at different geographical scales indicate that there is a potential scope to improve P management through the increased P recovery and recycling, and by the utilization of available soil P stocks. In many of the studies at all the geographical scales, P recycling flow has been found to be less than 20% of the total inflow, and even in some studies at the country scale, P recycling has been found to be entirely absent, which is a clear indication of poor P management. This study has also identified, there is a clear knowledge gap in relation to understanding the P flow over multiple years at the regional scale. The information about the key flows and stocks at different geographical scales as we identified can be utilized to make better P policy and management decisions for a city, region, or country. The information can also be used to guide future research that aims to analyze P flow at the city, regional, and country scales. 相似文献
425.
Research on biofuel production pathways from algae continues because among other potential advantages they avoid key consequential effects of terrestrial oil crops, such as competition for cropland. However, the economics, energetic balance, and climate change emissions from algal biofuels pathways do not always show great potential, due in part to high fertilizer demand. Nutrient recycling from algal biomass residue is likely to be essential for reducing the environmental impacts and cost associated with algae-derived fuels. After a review of available technologies, anaerobic digestion (AD) and hydrothermal liquefaction (HTL) were selected and compared on their nutrient recycling and energy recovery potential for lipid-extracted algal biomass using the microalgae strain Scenedesmus dimorphus. For 1 kg (dry weight) of algae cultivated in an open raceway pond, 40.7 g N and 3.8 g P can be recycled through AD, while 26.0 g N and 6.8 g P can be recycled through HTL. In terms of energy production, 2.49 MJ heat and 2.61 MJ electricity are generated from AD biogas combustion to meet production system demands, while 3.30 MJ heat and 0.95 MJ electricity from HTL products are generated and used within the production system.Assuming recycled nutrient products from AD or HTL technologies displace demand for synthetic fertilizers, and energy products displace natural gas and electricity, the life cycle greenhouse gas reduction achieved by adding AD to the simulated algal oil production system is between 622 and 808 g carbon dioxide equivalent (CO2e)/kg biomass depending on substitution assumptions, while the life cycle GHG reduction achieved by HTL is between 513 and 535 g CO2e/kg biomass depending on substitution assumptions. Based on the effectiveness of nutrient recycling and energy recovery, as well as technology maturity, AD appears to perform better than HTL as a nutrient and energy recycling technology in algae oil production systems. 相似文献