Evaluating preprocessing methods of digital elevation models for hydrological modelling

With the introduction of high‐resolution digital elevation models, it is possible to use digital terrain analysis to extract small streams. In order to map streams correctly, it is necessary to remove errors and artificial sinks in the digital elevation models. This step is known as preprocessing and will allow water to move across a digital landscape. However, new challenges are introduced with increasing resolution because the effect of anthropogenic artefacts such as road embankments and bridges increases with increased resolution. These are problematic during the preprocessing step because they are elevated above the surrounding landscape and act as artificial dams. The aims of this study were to evaluate the effect of different preprocessing methods such as breaching and filling on digital elevation models with different resolutions (2, 4, 8, and 16 m) and to evaluate which preprocessing methods most accurately route water across road impoundments at actual culvert locations. A unique dataset with over 30,000 field‐mapped road culverts was used to assess the accuracy of stream networks derived from digital elevation models using different preprocessing methods. Our results showed that the accuracy of stream networks increases with increasing resolution. Breaching created the most accurate stream networks on all resolutions, whereas filling was the least accurate. Burning streams from the topographic map across roads from the topographic map increased the accuracy for all methods and resolutions. In addition, the impact in terms of change in area and absolute volume between original and preprocessed digital elevation models was smaller for breaching than for filling. With the appropriate methods, it is possible to extract accurate stream networks from high‐resolution digital elevation models with extensive road networks, thus providing forest managers with stream networks that can be used when planning operations in wet areas or areas near streams to prevent rutting, sediment transport, and mercury export.     

Development of a Default Vapor Intrusion Attenuation Factor for Industrial Buildings

An investigation at a major industrial facility in the Midwestern United States provides insights regarding the amount of attenuation of sub-surface vapors occurring at industrial buildings. The buildings at the facility were ranked in terms of vapor intrusion potential and testing began in October 2016 and is ongoing. Results have been evaluated for data collected at 718 unique locations across 77 buildings. A total of 1646 sample pairs (sub-slab and indoor air) have been collected and analyzed for 65 analytes, resulting in a total of 106,990 data pairs. As many as 49 sample pairs were collected within a given building during a single sampling event and up to 11 rounds of seasonal testing have been performed at selected buildings. Seasonal variability in sub-slab soil-gas concentrations was found to be negligible. Data analysis was performed to look for data trends across the entire data set and identify inter-building comparisons. This data evaluation focused on individual volatile organic compounds (e.g., tetrachloroethylene, trichloroethylene) present in the sub-slab soil gas at concentrations exceeding 1000 μg/m³. A total of 157 building-specific attenuation coefficients (α) were evaluated. This evaluation demonstrated that large industrial buildings have a much greater attenuation than that assumed for single-family residential buildings. All attenuation coefficient values were lower than 0.03, which is the standard regulatory default for non-residential buildings. The median value was 9.3E-05 and the 95% upper confidence limit was 2.7E-04. There is some evidence of lower attenuation under wintertime conditions. The data suggests that the default attenuation factor of 0.03 over-predicts indoor air impacts at this industrial facility by at least two orders of magnitude.     

Soil seed flora, germination and regeneration pattern of woody species in an Acacia woodland of the Rift Valley in Ethiopia

The objectives of this study were to determine the composition, density and spatial distribution of the soil seed bank of woody species, as well as their regeneration pattern in two different land use systems, controlled (ranch) and open grazing, in an Acacia woodland of the Rift Valley in Ethiopia. We also compared the species composition of the soil seed bank and the above-ground vegetation to find out if differences exist in the soil seed bank and advance regeneration between the two land use systems. The germination requirements of seeds of the woody species were also investigated under laboratory conditions. Acacia senegal, Acacia seyal, Acacia tortilis, Dichrostacys cinerea and Balanites aegyptiaca were encountered in the above-ground vegetation in both systems. Seeds of only A. tortilis (90±32 seeds m⁻²) from the ranch, and A. senegal (5±3 seeds m⁻²) and A. tortilis (72±34 seeds m⁻²) from the open system were found in the soil seed bank along transects with patchy horizontal pattern. The two systems were not significantly different in density of soil seed banks of A. senegal andA. tortilis . Jaccard's similarity index showed that only a few woody species were common in the soil seed flora and above ground vegetation. However, all of the species accumulated seeds (58±43–331±130 seeds m⁻²) in/on the soil under the canopy. Very large numbers of seeds of A. tortilis (19382±9722 seeds m⁻²) and D. cinerea (1278±494 seeds m⁻²) were also found in barns. Most of the seeds recovered from the soil samples (60–80%) were found in the litter layer. Acid and mechanical scarification improved legume germination (36–99% and 60–99%, respectively) over boiling water (0–48%). Treatment means differed significantly for all the legumes (p<0·001) but not for Balanites. Height and diameter class distribution of regeneration of A. tortilis and D. cinerea in both systems and A. senegal in the open system had a negative exponential correlation (r_s=−0·5, −0·25 and −0·86, respectively). A. seyal and B. aegyptiaca showed poor regeneration. Horizontal distribution of advance regeneration of all the species was patchy. Advance regeneration of A. seyal, A. tortilis and B. aegyptiaca were not significantly different, while that of A. senegal and D. cinerea were significantly different between the two systems. Poor representation of species in the soil seed bank along transects and in the different height and diameter classes may be attributed to the low density of mature trees as well as the mode and strategy of seed dispersal. Ungulate and wind dispersed species (e.g. A. senegal, A. tortilis and D. cinerea) were highly favoured. Patchiness in the distribution of seeds and advance regeneration was also a result of endozoochory. Dispersal of non-ungulate dispersed seeds (A. senegal, A. seyal and B. aegyptiaca) was restricted to the canopy zone. Piles of seeds ofA. tortilis and D. cinerea that were found in barns were a result of consumption of their pods by cattle. High concentration of seeds in the litter layer may be due to low soil disturbance and larger size of seeds. The height and diameter class distribution of A. senegal (in the open system), A. tortilis and D. cinerea also indicated that the species have good regeneration. Results from the germination tests indicated that seeds of the legumes require pre-sowing treatments to give a rapid, uniform and improved germination. Intervention through artificial regeneration should be employed to improve the density and regeneration capacity of those species with hampered regeneration at both systems.     

The Rainstorm and Flash Flood at Mount Fulufjället In August 1997: The Meteorological and Hydrological Situation

The flood at Mount Fulufjället, 30-31 August 1997 was caused by the most furious rainstorm ever documented in Sweden. Private measurements on the mountain show not less than 276 mm over 24 hours, and the distribution of severe damage suggests even higher amounts in other parts of the mountain. The precipitation was connected to a front attacking a high pressure that had been dominating the weather in Sweden for several weeks, but orographic lifting on the east-facing slopes of the mountain may partly have caused the extreme intensity. In River Fulan, one of the upper branches of River Dalälven, the discharge peaked at a diurnal mean value of 233 m 3/s;, the highest since measurements began in 1913. At the stream Tangån and the new common outlet of the streams Stora and Lilla Göljån, both locations with a normal discharge of only around 1 m 3/s, instantaneous values of approximately 300 m 3/s have been estimated, corresponding to values close to the normal discharge at the mouth of River Dalälven on the coast of the Sea of Bothnia.     

大陆裂谷中断层的演化：北贝加尔盆地西南端构造地貌证据

北贝加尔盆地西南端位于贝加尔盆地中部,包括Olkhon岛及其邻区,文中研究了这个区域的构造地貌格架。北贝加尔盆地西南端的构造地貌类型是由走滑构造末端的一系列雁列构造、裂谷断层及次级断层的末端复合构造控制。朝着海的方向Olkhon地区次级断层包括4个连续的末端复合构造Primorsky断层带,Buguldeika-Chernorud地堑—MaloyeMore裂谷盆地—Ushkaniy断层带,Tazheran高原—Olkhon岛鞍部和淹没的Akademichesky山脊,Olkhon断层带。这个末端构造被横向断层切为几段,其活动时间在南西最年轻,向北东逐渐加大,同时断层垂直断距从数十米增至2000余米,且断层带变得更为宽阔,也更为复杂。Pri-morsky断层带向北东从西南端简单的线性断层崖,变为断层围限的断块系统,再变为上升和沉降(盆地)块体系统,并最终汇入一个盆地之中;沿着这个方向裂谷边界断层则突然地复合于盆地构造中。这种构造地貌类型记录了断层演化的时间和空间关系,即从属于递进的沉降和加宽直至最终发育为盆地。因此其趋势是发育完好的湖盆、陆地构造直至被水淹没。陆地构造淹没趋势及没有断层围限块体的盆内构造组合可能是与犁式断层旋转相关的陆内裂谷的共同特点,并具一般裂谷的打开机制。     

Toxic effects of decomposing red algae on littoral organisms

Large masses of filamentous red algae of the genera Polysiphonia, Rhodomela, and Ceramium are regularly washed up on beaches of the central Baltic Sea. As the algal masses start to decay, red coloured effluents leak into the water, and this tinge may be traced several hundred meters off shore. In this study, possible toxic effects of these effluents were tested on littoral organisms from different trophic levels. Effects on fertilisation, germination and juvenile survival of the brown seaweed Fucus vesiculosus were investigated, and mortality tests were performed on the crustaceans Artemia salina and Idotea baltica, as well as on larvae and adults of the fish Pomatoschistus microps. Fucus vesiculosus was the most sensitive species of the tested organisms to the red algal extract. The survival of F. vesiculosus recruits was reduced with 50% (LC50) when exposed to a concentration corresponding to 1.7 g l⁻¹ dw red algae. The lethal concentration for I. baltica, A. salina and P. microps were approximately ten times higher. The toxicity to A. salina was reduced if the algal extract was left to decompose during two weeks but the decline in toxicity was not affected by different light or temperature conditions. This study indicates that the filamentous red algae in the central Baltic Sea may produce and release compounds with negative effects on the littoral ecosystem. The effects may be particularly serious for the key species F. vesiculosus, which reproduce in autumn when filamentous red algal blooms are most severe.     

Summer Moisture Variability in East Central Sweden Since the Mid-Eighteenth Century Recorded in Tree Rings

To make predictions of future climate it is necessary to understand the past climate—temperature as well as precipitation. While a wealth of temperature proxies exist from northern latitudes, there is still a lack of information about past precipitation variability. Here we present a 300‐year‐long tree‐ring width chronology from xeric‐site Scots pines (Pinus sylvestris L.) in Tyresta National Park, east central Sweden. Tree‐ring widths were compared to the long observed temperature and precipitation records from Stockholm during 1786–2000. Analyses of the climate/growth relationship showed that, in general, May–June precipitation had a dominating influence on pine growth. However, during dry periods, negative responses to June–July temperature were stronger, especially evident in the late nineteenth century. Periods of below‐average growth were associated with dry conditions in May–June, but occasionally periods of wet and cool summers also produced narrow rings. Periods of above‐average growth were linked to wet, but sporadically also cool and dry, early summers. The years between 1815 and 1833 appear to be particularly dry in the 300‐year context. Since growth anomalies are found in other Swedish drought‐sensitive tree‐ring chronologies during this period, it is likely that this dry period had a regional extent. This is the first tree‐ring chronology from southern Sweden that provides multi‐century information of past summer drought and moisture variability with high resolution and the study will add important information regarding past climate variability in southern Sweden.     

Comparison of the behaviour of rare earth elements in surface waters,overburden groundwaters and bedrock groundwaters in two granitoidic settings,Eastern Sweden

This work, which was done within the Swedish nuclear waste management program, was carried out in order to increase the understanding of the mobility and fate of rare earth elements (REEs) in natural boreal waters in granitoidic terrain. Two areas were studied, Forsmark and Simpevarp, one of which will be selected as a site for spent nuclear fuel. The highest REE concentrations were found in the overburden groundwaters, in Simpevarp in particular (median ∑REE 52 μg/L), but also in Forsmark (median ∑REE 6.7 μg/L). The fractionation patterns in these waters were characterised by light REE (LREE) enrichment and negative Ce and Eu anomalies. In contrast, the surface waters had relatively low REE concentrations. They were characterised either by an increase in relative concentrations throughout the lanthanide series (Forsmark which has a carbonate-rich till) or flat patterns (Simpevarp with carbonate-poor till), and had negative Ce and Eu anomalies. In the bedrock groundwaters, the concentrations and fractionation patterns of REEs were entirely different from those in the overburden groundwaters. The median La concentrations were low (just above 0.1 μg/L in both areas), only in a few samples were the concentrations of several REEs (and in a couple of rare cases all REEs) above the detection limit, and there was an increase in the relative concentrations throughout the lanthanide series. In contrast to these large spatial variations, the temporal trends were characterised by small (or non existent) variations in REE-fractionation patterns but rather large variations in concentrations. The Visual MINTEQ speciation calculations predicted that all REEs in all waters were closely associated with dissolved organic matter, and not with carbonate. In the hydrochemical data for the overburden groundwater in particular, there was however a strong indication of association with inorganic colloids, which were not included in the speciation model. Overall the results showed that within a typical boreal granitoidic setting, overburden groundwaters are enriched in REEs, organic complexes are much more important than carbonate complexes, there is little evidence of significant mixing of REEs between different water types (surface, overburden, bedrock) and spatial variations are more extensive than temporal ones.     

Meteorological impacts on the water quality in the Pajuluoma acid sulphate area,W. Finland

Water samples (n = 354) from a small catchment (7.4 km²) covered by acid sulphate soils (pH < 4) were collected during all seasons and all types of hydrological conditions in 1990–2001. The electric conductivity (EC) and pH, i.e. the key indicators of acid sulphate soil impact in the current setting, were determined. Representative daily runoff and precipitation data was available for the whole study period. The 10th and 90th percentiles for EC and pH were 29–140 mS/m and 3.8–4.6, respectively. While the water quality varied remarkably from year to year, and even within seasons, some regularity was found. The water quality was generally worst in late autumn (water temperature < 5 °C) and in spring. Of all seasons the variations were clearly smallest in spring, indicating that most representative samples can be obtained in this season. There were significant correlations between autumn, early winter and spring water quality within hydrological years. Thus acid and metal surges in spring are somewhat predictable. At base flow conditions (runoff about 1 L/s km² or less), the water quality was relatively good in all seasons. Above base flow conditions, the impact of acid sulphate soils tended to slightly increase with increasing runoff and precipitation, especially in early summer, but not in late summer. No significant signs of dilution during flood conditions (up to 100 L/s km²) were found and neither were there any correlations to rising or falling limbs. The severity of individual summer droughts, which in theory should increase the oxidation of S and acidity in the soils, had little or no impact on the water quality in subsequent autumn and spring. On the other hand, there was a remarkable long-term increase in EC and a corresponding decrease in pH (starting in 1995) after a suite of several very dry summers. After that the water quality did not improve even if the dry summers were followed by some wet summers. This indicates that the temporary pool of readily leachable acidity in the soils is fairly large. Moreover, it indicates that the potential shift towards more extreme global weather conditions (with more severe dry spells) may have significant impacts on the water quality in midwestern Finland, a region that is heavily affected by acidity and metals from acid sulphate soils.