Acid waters in upland Wales: causes, effects and remedies

Although situated on the western seaboard of the UK, and hence in the path of predominantly maritime air masses arriving directly from the Atlantic, Wales receives acidic deposition when winds are from the east. In conjunction with the highly base-poor rocks and soils found in the region, significant acidification of surface waters has occurred. Extensive afforestation in the Welsh uplands in the last 40 years has exacerbated acidification effects by elevating the loading of acidic anions received by catchments, thus increasing the concentrations of aluminium in watercourses. In considering possible remedial strategies, results of liming investigations from the Llyn Brianne Project in mid-Wales are presented. These studies have mainly involved liming small streams by a variety of catchment liming techniques. The most effective catchment treatments were those where finely ground CaCO3 was applied to the hydrological source areas at rates of up to 25 tonnes ha(-1). Possible drawbacks with such liming are discussed, although it is emphasized that liming is likely to be a component of any remedial strategy in the next 30 years until emissions reductions greater than those proposed in the forthcoming EC Directive are implemented.     

中国露天生物质燃烧的温室气体排放及秸秆禁燃政策的协同减排效应

露天生物质燃烧是温室气体(CO₂、CH₄、N₂O)的重要排放源之一,这些排放可影响本地、区域和全球的大气化学和气候变化,并带来一系列生态环境问题,进而对人类及其他生物的生存环境产生影响.本研究采用卫星火点排放清单(FINN),对2010—2019年中国露天生物质燃烧温室气体排放进行研究,并分析秸秆禁燃政策对温室气体排放的影响,对后续秸秆禁燃政策的制定具有重要参考价值.结果表明,我国2010—2019年平均年温室气体排放量为1.53×10⁸t(将CH₄和N₂O的温室效应换算为同等效应的CO₂当量单位),总体呈波动性下降趋势.温室气体排放量最大的植被类型是森林(7.43×10⁷t)和农作物(3.19×10⁷t),分别占总排放量的48.7%和20.9%.从月分布来看,露天生物质燃烧排放的温室气体集中在2—6月,3月是高峰值.从空间分布上看,排放主要集中在华南、西南和华东地区,占总排放量的72.9%...     

Environmental contaminants in nonviable eggs of the endangered Mississippi sandhill crane (Grus canadensis pulla)

Our objectives were to determine if concentrations of environmental pollutants and microbial contamination in nonviable eggs of the endangered Mississippi sandhill crane (Grus canadensis pulla) contributed to egg failure. Six eggs collected in 1990 and four in 1991 contained only background levels of organochlorine pesticides and polychlorinated biphenyls (PCBs), and tests for microbial contamination were all negative. Two eggs contained late dead embryos, but neither revealed obvious abnormalities. Three eggs contained potentially harmful concentrations (23, 39, 146 pg/g, wet mass) of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), based on 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TCDD-EQ) for combined compounds. Because of the scarcity of material suitable for laboratory examination and the endangered status of the crane, we recommend that nonviable eggs continue to be monitored for toxic pollutants.     

Spatial patterns concentrations in upland Wales in relation to catchment forest cover and forest age

Data on nitrate nitrogen were collected weekly during 1984 from 136 sites on streams in upland Wales. Mean nitrate concentrations in summer (0.02 to 1.5 mg litre(-1)) were significantly lower (P<0.001) than in winter (0.02 to 1.26 mg litre(-1)), particularly at sites with mature conifers (>30 years old). Mean concentrations increased significantly with the average age of conifers on each catchment (P<0.001), and with increasing areal cover by trees over 30 years old (P<0.001). Nitrate concentrations increased significantly with stream total hardness (P<0.001), possibly reflecting nitrogen mineralisation in soils of higher base status. Concentrations also increased with stream chloride (P<0.001), which is predominantly atmospherically derived, implying that increased nitrate occurred where general atmospheric inputs of solutes were increased. After accounting for variation in hardness, residual nitrate concentrations still increased with the average age of the conifers (P<0.001), and with catchment cover by mature trees (P<0.001). We infer that some additional nitrate under older conifers is thus independent of catchment sources associated with increasing hardness. Two possibilities are increased inputs and decreased retention of nitrogen within the ecosystem of maturing conifer forest. Residual nitrate after accounting for variations in chloride also increased significantly with conifer age (P<0.01) and cover (P<0.01), a pattern implying that some sources of nitrate may also be independent of increased sea-salt deposition. We allude to the possibility that additional nitrogen deposition adds to nitrogen throughputs from maturing forests, and we discuss the potential ecological role of additional nitrogen in runoff.     

The effect of sampling frequency on chemical parameters in acid-sensitive streams

We assessed the effects of different simulated sampling regimes (weekly, fortnightly, monthly and bimonthly) on parameters describing the water chemistry of 72 streams in acid-sensitive areas of Wales. For pH, sulphate, total hardness and aluminium, reduced sampling frequency had no discernible or systematic effect on the apparent annual mean chemistry relative to the values derived from weekly data. Standard deviations and coefficients of variation were either unaffected, or were reduced. However, sampling frequency had a moderate effect on mean pH when the data were separated into seasons: winter mean pH increased on average by 0.13 units and summer means decreased on average by 0.12 units, when using bimonthly data relative to weekly. Extreme values were detected less effectively at lower sampling frequencies, significantly altering the intercept and/or the slope of the strong relationships between the means and minimum pH or maximum Al. These effects almost certainly reflect the exclusion of extreme events (summer drought and winter floods) from low sample frequencies and reveal limitations in the use of mean values from periodic sampling programmes for summarising some aspects of site chemistry. Nevertheless, previously established relationships between mean stream chemistry, land use and stream biology were still strong at all sampling frequencies. Clear recommendations about the needs to fully parameterise episodic fluctuations depend on unanswered questions about: (i) whether biota respond to mean or episodic chemical conditions and (ii) whether baseflow chemistry, episodic fluctuations, or some combination of these, will best reflect trends in acidification.     

Multiple-year water balance of soil covers in a semiarid setting

Surface covers are used to isolate contaminants in hazardous and low-level radioactive sites for time frames ranging from hundreds of years to millennia or more. In the absence of data for such durations, the long-term performance of surface barriers can only be represented with short-term tests or inferred from analogs and modeling. This paper provides evidence of field performance of soil covers for periods up to 17 yr. The results of lysimeter studies from a semiarid site in Washington State show that a cover design known as the Hanford Barrier, which consists of 1.5 m of silt loam above a sand-gravel capillary break, can nearly eliminate drainage. The results were similar if plants were present or not, demonstrating the robustness of the design. Furthermore, reducing the silt loam thickness to 1.0 m (as might occur via erosion), with or without plants, did not lead to drainage. When irrigated to mimic 3x average precipitation conditions, the vegetated Hanford Barrier continued to prevent drainage. Overall, the results showed no loss in performance during the 17 yr of testing. Only when plants were eliminated completely from the 3x precipitation test did drainage occur (rates ranged from 6 to 16 mm yr(-1)). In a separate test, replacing the top 0.2 m of silt loam with dune sand and reducing the plant cover did not lead immediately to the onset of drainage, but soil matric heads within the silt loam noticeably increased. This observation suggests that dune sand migration onto a surface cover has the potential to reduce a cover's ability to minimize deep drainage.     

Whole blood is the sample matrix of choice for monitoring systemic triclocarban levels

The antibacterial triclocarban (TCC) concentrates in the cellular fraction of blood. Consequently, plasma levels are at least two-fold lower than the TCC amount present in blood. Utilizing whole blood sampling, a low but significant absorption of TCC from soap during showering is demonstrated for a small group of human subjects.     

The use of inert carriers in regulatory biodegradation tests of low density poorly water-soluble substances

Many poorly water-soluble compounds fail regulatory ready biodegradation tests as the method of test material preparation limits the bioavailability of the chemical. The recognised method for delivery of poorly soluble materials into biodegradability tests consists of coating test material inside the test vessel or onto inert substrates (i.e., glass cover slide, boiling beads, filter paper, or Teflon stir bar) that are placed inside the vessels. Volatile solvents are often used to augment this process. Although these substrates work fairly well for delivering many poorly soluble materials into biodegradability tests, they have not been effective in keeping low density, poorly water-soluble substances in the test medium. Soon after medium is added to the test vessels, these chemicals break loose from the substrates and float on the surface where they have limited contact with micro-organisms in the test medium. Hence, there is a reduced potential for measuring substantial biodegradability in the test. This paper describes the work undertaken to establish a standard method of adding low density, poorly water-soluble substances into test vessels of biodegradability studies to ensure these materials remain in contact with micro-organisms in the test medium. The substances are prepared for testing by adsorption onto silica gel followed by dispersion into the culture medium. This method of delivery may provide greater intra- and inter-laboratory consistency in biodegradability test results for low density, poorly water-soluble substances and it may more closely mimic the probable transport and fate of these substances in the environment.