Optimizing the removal of small fish passage barriers

Removing small artificial barriers that hinder upstream migrations of fish is a major problem in riparian habitat restoration. Because of budgetary limitations, it is necessary to prioritize barrier removal and repair decisions. These have usually been based on scoring and ranking procedures, which, although simple to use, can be very inefficient in terms of increasing the amount of accessible instream habitat. We develop a novel decision-making approach, based on integer programming techniques, which optimizes repair and removal decisions. Results show based on real datasets of barrier culverts located in Washington State that scoring and ranking is over 25% below the optimum on average and a full 100% below in the worst case, producing no net habitat gain whatsoever. This is compared to a dynamic programming method that was able to find optimal solutions in less than a second, even for problems with up to several hundred variables, and a heuristic method, which found solutions with less than a 1% average optimality gap in even less time.     

SI-traceable certification of Cu, Cr, Cd and Pb in sediment and fly ash candidate reference materials

Many fields in environmental analytical chemistry deal with very low limits and thresholds as set by governmental legislations or transnational regulations. The need for the accuracy, comparability and traceability of analytical measurements in environmental analytical chemistry has significantly increased and total uncertainties are even asked for by accreditation bodies of environmental laboratories. This paper addresses achieving these goals to guarantee accuracy, quality control, quality assurance or validation of a method by means of certified reference materials. The assessment of analytical results in certified reference materials must be as accurate as possible and every single step has to be fully evaluated. This paper presents the SI-traceable certification of Cu, Cr, Cd and Pb contents in geological and environmentally relevant matrices (three sediments and one fly ash sample). Certification was achieved using isotope dilution (ID) ICPMS as a primary method of measurement. In order to reduce significantly the number of analytical steps and intermediate samples a multiple spiking approach was developed. The full methodology is documented and total uncertainty budgets are calculated for all certified values. A non-element specific sample digestion process was optimised. All wet chemical digestion methods examined resulted in a more or less pronounced amount of precipitate. It is demonstrated that these precipitates originate mainly from secondary formation of fluorides (essentially CaF2) and that their formation takes place after isotopic equilibration. The contribution to the total uncertainty of the final values resulting from the formation of such precipitates was in general < 0.1% for all investigated elements. Other sources of uncertainty scrutinised included the moisture content determination, procedural blank determination, cross-contamination from the different spike materials, correction for spectral interferences, instrumental background and deadtime effects, as well as the use of either certified values or IUPAC data in the IDMS equation. The average elemental content in the sediment samples was 30-130 micrograms g-1 for Pb, 0.5-3 micrograms g-1 for Cd and 50-70 micrograms g-1 for Cu. Cr was measured in one sample and was about 60 micrograms g-1. The concentrations in the fly ash sample were up to 2 orders of magnitude higher. Expanded uncertainty for the investigated elements was about 3% (coverae factor k = 2) except for Cr, (measured by high resolution ICPMS), for which the expanded uncertainty was about 7% (k = 2).     

Spatial properties of nutrient concentrations in the Baltic Sea

Using existing monitoring data, the present study attempts to characterize spatial patterns of surface water nutrients in the Baltic Sea. The analysis was made for two different spatial scales, differences between and within sub-basins.Non-parametric methods were chosen to reduce problems with the distributional properties of the data. By dividing the data into four seasons care was taken as to seasonality. To avoid bias due to different laboratory analysis, only data from Nordic countries were used, whose results did not apparently depart from each other. Bias due to different sampling frequency was another problem. This was reduced by using only the last observation in each season for every station and year.The results suggested differences in the nutrient concentrations between basins. The two northernmost basins (Bothnian Bay and Bothnian Sea) had lower phosphate concentrations and higher silicate concentrations compared to the rest of the Sea. Bothnian Bay and the Gulf of Finland had higher nitrate concentrations.The concentration structure within basins was studied using transects in both latitudinal and longitudinal direction. A gradient for phosphate and nitrate was found in the Gulf of Finland, with lower concentrations at the mouth. The Bothnian Sea showed lower concentrations in the middle of the basin compared to the coasts. The highest concentrations of phosphate were found close to the Finnish coast and for silicate the highest concentrations were located near the Swedish coast. It was not possible to study variation in the west-east direction within the Baltic proper, due to data shortage. For the transects in the north-south direction no differences were detected for nitrate and silicate. Phosphate gave one significant result during autumn for the transect in the eastern part of the Baltic proper.This study revealed several problems associated with the data available. Uneven sampling in space and time put severe constraints on the study. A better design of the monitoring program is suggested, where spatial properties are considered explicitly. Revision of the program in this direction is needed for reasonable calculation of total amounts and concentrations representative for a basin.     

Migration of pollutants in groundwater: I. reduction of numerical dispersion by conformal mapping

The partial differential equations governing the migration of adsorbable pollutants undergoing 2-dimensional flow in saturated aquifers are presented. The analytical solution of these equations is rarely possible, and the use of mesh or grid techniques for numerical integration leads to so-called numerical dispersion, excessive dispersion which is an artifact associated with the numerical method. We discuss here the use of conformal mapping techniques to develop coordinate systems in which numerical dispersion transverse to the direction of flow is eliminated. Some simple illustrations are presented.     

Declines in organochlorines in eggs of red-breasted mergansers from Lake Michigan, 1977–1978 versus 1990

From 1977–1978 to 1990, concentrations of polychlorinated biphenyls (PCBs) and most organochlorine pesticides declined in eggs of red-breasted mergansers (Mergus serrator) nesting on islands in northwestern Lake Michigan. Total PCBs decreased 60% (from 21 ppm in 1977–1978 to 8.5 ppm in 1990) and p,p-DDE decreased 66% (from 6.5 to 2.2 ppm). Dieldrin decreased only 16% (from 0.82 to 0.69 ppm). In 1990, 79.1% of incubated eggs hatched, which was not significantly different from the 83.5% that hatched in 1977–1978.The U.S. Government right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged.     

安大略基拉尼公园及实验湖泊区浮游生物群落对酸化的响应及其恢复过程

人们普遍推测控制SO2排放可以促进加拿大、美国和欧洲的酸化淡水湖泊的恢复.本文研究了1998～2000年间靠近安大略省基拉尼公园的22个湖泊(pH值范围4.5～7.7)的浮游生物群落变化,将结果与安大略省西北的实验湖泊区(ELA)人工酸化(pH值从6.7降至4.5)又恢复(pH升至6.0)的南302号湖的数据进行了对比,以评价酸化后的恢复效果.根据历史记录,基拉尼地区数个湖泊的pH值由先前酸化的5.0～5.5反弹到6.0.浮游生物量与pH不相关,但其物种的丰富度与pH值间呈显著相关.将所得到的物种多样性数据与历史数据加以组合,可观察到其中6个湖泊中的恢复轨迹.相关分析表明:pH值得到提高后,其中几个湖泊的浮游生物群落开始向中性环境中的典型群落转化.     

让我们积极应对气候变化

气候确实在发生变化。以往人们随意地认为这与温室效应气体排放量的增加有关，现在这种观点已得到充分证实。自1991年以来．已出现了自有记录以来全球气温最高的十个年份．而在上个世纪，温度上升7约0.6摄氏度。在同一期间内，全球的海平面上升了约20厘米．部分原因是陆地上冰层融化．海洋自身发生热膨胀。许多山峰上的冰盖正在消失．最近几十年来，夏秋季节北冰洋的冰层厚